register interest

Professor Xin Lu

Research Area: Cell and Molecular Biology
Technology Exchange: Computational biology, Crystallography, Drug discovery, ES cell / homologous recombination, Immunohistochemistry, In situ hybridisation, In vivo imaging, Microscopy (Confocal), Microscopy (Video), Protein interaction, Transcript profiling and Transgenesis
Scientific Themes: Cancer Biology
Keywords: Cancer, p53 tumour suppressor, Cellular plasticity and Reprogramming
Web Links:
Xin Lu's Group

Xin Lu's Group

Research Areas

The main goal of our research is to identify molecular mechanisms that control cellular plasticity and suppress tumour growth. Cells are able to change their characteristics and cell fate in response to external signals. This ability to change – cellular plasticity – underlies cancer initiation, metastasis and resistance to therapy. We are particularly interested in ‘guardians’ of plasticity in epithelial cells, from which over 80% of human tumours originate. We have a long-standing interest in the tumour suppressor p53 and the ASPP family of proteins (Apoptosis-Stimulating Protein of p53; Ankyrin repeats, SH3 domain and Prolin rich sequence containing proteins), which have several roles including regulation of p53.

Our current areas of interest include: understanding how selective transcription is controls cell fate; identifying regulators of cellular plasticity in upper gastrointestinal cancer initiation and metastasis (particularly oesophageal cancer and gastric cancer); and understanding the influence of infection on cell plasticity and cancer (particularly Helicobacter pylori and Epstein Barr Virus (EBV) infection).

Name Department Institution Country
Robert Goldin Imperial College United Kingdom
Professor Colin R Goding Oxford Ludwig Institute Oxford University, Old Road Campus Research Building United Kingdom
Dr John Christianson Oxford Ludwig Institute Oxford University, Old Road Campus Research Building United Kingdom
Dr Benjamin Schuster-Böckler Oxford Ludwig Institute Oxford University, Old Road Campus Research Building United Kingdom
Professor Benedikt M Kessler Target Discovery Institute Oxford University, NDM Research Building United Kingdom
Professor Stefan Knapp Structural Genomics Consortium Oxford University, NDM Research Building United Kingdom
Professor Christopher Schofield Chemistry Oxford University United Kingdom
Dr Giovanni Blandino Regina Elena Cancer Institute Italy
Professor Gerry Melino University of Leicester United Kingdom
Professor Oren Moshe Weizmann Institute of Science Israel
Professor Christian Siebold Structural Biology Oxford University, Henry Wellcome Building of Genomic Medicine United Kingdom
Chris Ponting University of Oxford United Kingdom
Professor Zoltan Molnar Physiology, Anatomy and Genetics University of Oxford United Kingdom
Dr Francis Szele (RDM) Department of Physiology, Anatomy and Genetics University Oxford United Kingdom
Professor Sir Peter J Ratcliffe FRS Target Discovery Institute Oxford University, NDM Research Building United Kingdom
Professor Olaf Ansorge University of Oxford United Kingdom
Dr Sarah De Val Oxford Ludwig Institute Oxford University, Old Road Campus Research Building United Kingdom
Professor Jens Rittscher Target Discovery Institute Oxford University, NDM Research Building United Kingdom
Professor Skirmantas Kriaucionis Oxford Ludwig Institute Oxford University, Old Road Campus Research Building United Kingdom
Professor E. Yvonne Jones FRS FMedSci Structural Biology Oxford University, Henry Wellcome Building of Genomic Medicine United Kingdom
Mark Middleton Department of Oncology, University of Oxford United Kingdom
Prof Kieran Clarke (RDM) The University of Oxford, DPAG United Kingdom
Professor Carolyn Carr Department of Physiology, Anatomy and Genetics University of Oxford United Kingdom
Prof David JP Ferguson (RDM) Nuffield Division of Clinical Laboratory Sciences Oxford University, John Radcliffe Hospital United Kingdom
Dr Stephan Feller (RDM) Oxford University,
Professor Shankar Srinivas Department of Physiology, Anatomy and Genetics University of Oxford United Kingdom
Jonathan Cebon Ludwig Institute Australia
David Kelsell Blizard Institute United Kingdom
Dr Timothy Mohun (RDM) NIMR United Kingdom
Julian Downward Francis Crick Institute United Kingdom
Annie Cheung University of Hong Kong Hong Kong
Erec Stebbins Rockefeller University United States
Curtis Harris National Cancer Institute United States
Stefan Constantinescu Brussels Belgium
Gigi Lozano MD Anderson United States
Qimin Zhan Beijing China
Yan-Ning Gao Peking Union Medical College & Chinese Academy of Medical Sciences, Beijing China
Yeh T-L, Leissing TM, Abboud MI, Thinnes CC, Atasoylu O, Holt-Martyn JP, Zhang D, Tumber A, Lippl K, Lohans CT et al. 2017. Molecular and cellular mechanisms of HIF prolyl hydroxylase inhibitors in clinical trials Chem. Sci., | Read more

Falletta P, Sanchez-Del-Campo L, Chauhan J, Effern M, Kenyon A, Kershaw CJ, Siddaway R, Lisle R, Freter R, Daniels MJ et al. 2017. Translation reprogramming is an evolutionarily conserved driver of phenotypic plasticity and therapeutic resistance in melanoma. Genes Dev, 31 (1), pp. 18-33. | Show Abstract | Read more

The intratumor microenvironment generates phenotypically distinct but interconvertible malignant cell subpopulations that fuel metastatic spread and therapeutic resistance. Whether different microenvironmental cues impose invasive or therapy-resistant phenotypes via a common mechanism is unknown. In melanoma, low expression of the lineage survival oncogene microphthalmia-associated transcription factor (MITF) correlates with invasion, senescence, and drug resistance. However, how MITF is suppressed in vivo and how MITF-low cells in tumors escape senescence are poorly understood. Here we show that microenvironmental cues, including inflammation-mediated resistance to adoptive T-cell immunotherapy, transcriptionally repress MITF via ATF4 in response to inhibition of translation initiation factor eIF2B. ATF4, a key transcription mediator of the integrated stress response, also activates AXL and suppresses senescence to impose the MITF-low/AXL-high drug-resistant phenotype observed in human tumors. However, unexpectedly, without translation reprogramming an ATF4-high/MITF-low state is insufficient to drive invasion. Importantly, translation reprogramming dramatically enhances tumorigenesis and is linked to a previously unexplained gene expression program associated with anti-PD-1 immunotherapy resistance. Since we show that inhibition of eIF2B also drives neural crest migration and yeast invasiveness, our results suggest that translation reprogramming, an evolutionarily conserved starvation response, has been hijacked by microenvironmental stress signals in melanoma to drive phenotypic plasticity and invasion and determine therapeutic outcome.

Zak J, Vives V, Szumska D, Vernet A, Schneider JE, Miller P, Slee EA, Joss S, Lacassie Y, Chen E et al. 2016. ASPP2 deficiency causes features of 1q41q42 microdeletion syndrome. Cell Death Differ, 23 (12), pp. 1973-1984. | Show Abstract | Read more

Chromosomal abnormalities are implicated in a substantial number of human developmental syndromes, but for many such disorders little is known about the causative genes. The recently described 1q41q42 microdeletion syndrome is characterized by characteristic dysmorphic features, intellectual disability and brain morphological abnormalities, but the precise genetic basis for these abnormalities remains unknown. Here, our detailed analysis of the genetic abnormalities of 1q41q42 microdeletion cases identified TP53BP2, which encodes apoptosis-stimulating protein of p53 2 (ASPP2), as a candidate gene for brain abnormalities. Consistent with this, Trp53bp2-deficient mice show dilation of lateral ventricles resembling the phenotype of 1q41q42 microdeletion patients. Trp53bp2 deficiency causes 100% neonatal lethality in the C57BL/6 background associated with a high incidence of neural tube defects and a range of developmental abnormalities such as congenital heart defects, coloboma, microphthalmia, urogenital and craniofacial abnormalities. Interestingly, abnormalities show a high degree of overlap with 1q41q42 microdeletion-associated abnormalities. These findings identify TP53BP2 as a strong candidate causative gene for central nervous system (CNS) defects in 1q41q42 microdeletion syndrome, and open new avenues for investigation of the mechanisms underlying CNS abnormalities.

Markolovic S, Leissing TM, Chowdhury R, Wilkins SE, Lu X, Schofield CJ. 2016. Structure-function relationships of human JmjC oxygenases-demethylases versus hydroxylases. Curr Opin Struct Biol, 41 pp. 62-72. | Show Abstract | Read more

The Jumonji-C (JmjC) subfamily of 2-oxoglutarate (2OG)-dependent oxygenases are of biomedical interest because of their roles in the regulation of gene expression and protein biosynthesis. Human JmjC 2OG oxygenases catalyze oxidative modifications to give either chemically stable alcohol products, or in the case of N(ɛ)-methyl lysine demethylation, relatively unstable hemiaminals that fragment to give formaldehyde and the demethylated product. Recent work has yielded conflicting reports as to whether some JmjC oxygenases catalyze N-methyl group demethylation or hydroxylation reactions. We review JmjC oxygenase-catalyzed reactions within the context of structural knowledge, highlighting key differences between hydroxylases and demethylases, which have the potential to inform on the possible type(s) of reactions catalyzed by partially characterized or un-characterized JmjC oxygenases in humans and other organisms.

Lu M, Muers MR, Lu X. 2016. Introducing STRaNDs: shuttling transcriptional regulators that are non-DNA binding. Nat Rev Mol Cell Biol, 17 (8), pp. 523-532. | Show Abstract | Read more

Many proteins originally identified as cytoplasmic - including many associated with the cytoskeleton or cell junctions - are increasingly being found in the nucleus, where they have specific functions. Here, we focus on proteins that translocate from the cytoplasm to the nucleus in response to external signals and regulate transcription without binding to DNA directly (for example, through interaction with transcription factors). We propose that proteins with such characteristics are classified as a distinct group of extracellular signalling effectors, and we suggest the term STRaND (shuttling transcriptional regulators and non-DNA binding) to refer to this group. Crucial roles of STRaNDs include linking cell morphology and adhesion with changes in transcriptional programmes in response to signals such as mechanical stresses.

Turnquist C, Horikawa I, Foran E, Major EO, Vojtesek B, Lane DP, Lu X, Harris BT, Harris CC. 2016. p53 isoforms regulate astrocyte-mediated neuroprotection and neurodegeneration. Cell Death Differ, 23 (9), pp. 1515-1528. | Show Abstract | Read more

Bidirectional interactions between astrocytes and neurons have physiological roles in the central nervous system and an altered state or dysfunction of such interactions may be associated with neurodegenerative diseases, such as Alzheimer's disease (AD) and amyotrophic lateral sclerosis (ALS). Astrocytes exert structural, metabolic and functional effects on neurons, which can be either neurotoxic or neuroprotective. Their neurotoxic effect is mediated via the senescence-associated secretory phenotype (SASP) involving pro-inflammatory cytokines (e.g., IL-6), while their neuroprotective effect is attributed to neurotrophic growth factors (e.g., NGF). We here demonstrate that the p53 isoforms Δ133p53 and p53β are expressed in astrocytes and regulate their toxic and protective effects on neurons. Primary human astrocytes undergoing cellular senescence upon serial passaging in vitro showed diminished expression of Δ133p53 and increased p53β, which were attributed to the autophagic degradation and the SRSF3-mediated alternative RNA splicing, respectively. Early-passage astrocytes with Δ133p53 knockdown or p53β overexpression were induced to show SASP and to exert neurotoxicity in co-culture with neurons. Restored expression of Δ133p53 in near-senescent, otherwise neurotoxic astrocytes conferred them with neuroprotective activity through repression of SASP and induction of neurotrophic growth factors. Brain tissues from AD and ALS patients possessed increased numbers of senescent astrocytes and, like senescent astrocytes in vitro, showed decreased Δ133p53 and increased p53β expression, supporting that our in vitro findings recapitulate in vivo pathology of these neurodegenerative diseases. Our finding that Δ133p53 enhances the neuroprotective function of aged and senescent astrocytes suggests that the p53 isoforms and their regulatory mechanisms are potential targets for therapeutic intervention in neurodegenerative diseases.

Verrill C, Cerundolo L, Mckee C, White M, Kartsonaki C, Fryer E, Morris E, Brewster S, Ratnayaka I, Marsden L et al. 2016. Altered expression of epithelial-to-mesenchymal transition proteins in extraprostatic prostate cancer. Oncotarget, 7 (2), pp. 1107-1119. | Show Abstract | Read more

Epithelial to mesenchymal transition (EMT) of cancer cells involves loss of epithelial polarity and adhesiveness, and gain of invasive and migratory mesenchymal behaviours. EMT occurs in prostate cancer (PCa) but it is unknown whether this is in specific areas of primary tumours. We examined whether any of eleven EMT-related proteins have altered expression or subcellular localisation within the extraprostatic extension component of locally advanced PCa compared with other localisations, and whether similar changes may occur in in vitro organotypic PCa cell cultures and in vivo PCa models. Expression profiles of three proteins (E-cadherin, Snail, and α-smooth muscle actin) were significantly different in extraprostatic extension PCa compared with intra-prostatic tumour, and 18/27 cases had an expression change of at least one of these three proteins. Of the three significantly altered EMT proteins in pT3 samples, one showed similar significantly altered expression patterns in in vitro organotypic culture models, and two in in vivo Pten-/- model samples. These results suggest that changes in EMT protein expression can be observed in the extraprostatic extension component of locally invasive PCa. The biology of some of these changes in protein expression may be studied in certain in vitro and in vivo PCa models.

Hu Y, Ge W, Wang X, Sutendra G, Zhao K, Dedeić Z, Slee EA, Baer C, Lu X. 2015. Caspase cleavage of iASPP potentiates its ability to inhibit p53 and NF-κB. Oncotarget, 6 (40), pp. 42478-42490. | Show Abstract | Read more

An intriguing biological question relating to cell signaling is how the inflammatory mediator NF-kB and the tumour suppressor protein p53 can be induced by similar triggers, like DNA damage or infection, yet have seemingly opposing or sometimes cooperative biological functions. For example, the NF-κB subunit RelA/p65 has been shown to inhibit apoptosis, whereas p53 induces apoptosis. One potential explanation may be their co-regulation by common cellular factors: inhibitor of Apoptosis Stimulating p53 Protein (iASPP) is one such common regulator of both RelA/p65 and p53. Here we show that iASPP is a novel substrate of caspases in response to apoptotic stimuli. Caspase cleaves the N-terminal region of iASPP at SSLD294 resulting in a prominent 80kDa fragment of iASPP. This caspase cleavage site is conserved in various species from zebrafish to Homo sapiens. The 80kDa fragment of iASPP translocates from the cytoplasm to the nucleus via the RaDAR nuclear import pathway, independent of p53. The 80kDa iASPP fragment can bind and inhibit p53 or RelA/p65 more efficiently than full-length iASPP. Overall, these data reveal a potential novel regulation of p53 and RelA/p65 activities in response to apoptotic stimuli.

Zak J, Lu X. 2015. Aspp1: A Guardian of Hematopoietic Stem Cell Integrity. Cell Stem Cell, 17 (1), pp. 3-5. | Show Abstract | Read more

Eliminating hematopoietic stem cells (HSCs) with DNA damage is necessary to maintain the homeostasis of HSCs, but the mechanisms underlying this apoptotic elimination are unclear. Now in Cell Stem Cell, Yamashita et al. (2015) show that Aspp1 coordinates with p53 to protect HSC pool integrity, guarding against hematological malignancies.

Notari M, Hu Y, Sutendra G, Dedeić Z, Lu M, Dupays L, Yavari A, Carr CA, Zhong S, Opel A et al. 2015. iASPP, a previously unidentified regulator of desmosomes, prevents arrhythmogenic right ventricular cardiomyopathy (ARVC)-induced sudden death. Proc Natl Acad Sci U S A, 112 (9), pp. E973-E981. | Show Abstract | Read more

Desmosomes are anchoring junctions that exist in cells that endure physical stress such as cardiac myocytes. The importance of desmosomes in maintaining the homeostasis of the myocardium is underscored by frequent mutations of desmosome components found in human patients and animal models. Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a phenotype caused by mutations in desmosomal components in ∼ 50% of patients, however, the causes in the remaining 50% of patients still remain unknown. A deficiency of inhibitor of apoptosis-stimulating protein of p53 (iASPP), an evolutionarily conserved inhibitor of p53, caused by spontaneous mutation recently has been associated with a lethal autosomal recessive cardiomyopathy in Poll Hereford calves and Wa3 mice. However, the molecular mechanisms that mediate this putative function of iASPP are completely unknown. Here, we show that iASPP is expressed at intercalated discs in human and mouse postmitotic cardiomyocytes. iASPP interacts with desmoplakin and desmin in cardiomyocytes to maintain the integrity of desmosomes and intermediate filament networks in vitro and in vivo. iASPP deficiency specifically induces right ventricular dilatation in mouse embryos at embryonic day 16.5. iASPP-deficient mice with exon 8 deletion (Ppp1r13l(Δ8/Δ8)) die of sudden cardiac death, displaying features of ARVC. Intercalated discs in cardiomyocytes from four of six human ARVC cases show reduced or loss of iASPP. ARVC-derived desmoplakin mutants DSP-1-V30M and DSP-1-S299R exhibit weaker binding to iASPP. These data demonstrate that by interacting with desmoplakin and desmin, iASPP is an important regulator of desmosomal function both in vitro and in vivo. This newly identified property of iASPP may provide new molecular insight into the pathogenesis of ARVC.

Wang Y, Bu F, Royer C, Serres S, Larkin JR, Soto MS, Sibson NR, Salter V, Fritzsche F, Turnquist C et al. 2014. ASPP2 controls epithelial plasticity and inhibits metastasis through β-catenin-dependent regulation of ZEB1. Nat Cell Biol, 16 (11), pp. 1092-1104. | Show Abstract | Read more

Epithelial to mesenchymal transition (EMT), and the reverse mesenchymal to epithelial transition (MET), are known examples of epithelial plasticity that are important in kidney development and cancer metastasis. Here we identify ASPP2, a haploinsufficient tumour suppressor, p53 activator and PAR3 binding partner, as a molecular switch of MET and EMT. ASPP2 contributes to MET in mouse kidney in vivo. Mechanistically, ASPP2 induces MET through its PAR3-binding amino-terminus, independently of p53 binding. ASPP2 prevents β-catenin from transactivating ZEB1, directly by forming an ASPP2-β-catenin-E-cadherin ternary complex and indirectly by inhibiting β-catenin's N-terminal phosphorylation to stabilize the β-catenin-E-cadherin complex. ASPP2 limits the pro-invasive property of oncogenic RAS and inhibits tumour metastasis in vivo. Reduced ASPP2 expression results in EMT, and is associated with poor survival in hepatocellular carcinoma and breast cancer patients. Hence, ASPP2 is a key regulator of epithelial plasticity that connects cell polarity to the suppression of WNT signalling, EMT and tumour metastasis.

Lu M, Miller P, Lu X. 2014. Restoring the tumour suppressive function of p53 as a parallel strategy in melanoma therapy FEBS Letters, 588 (16), pp. 2616-2621. | Show Abstract | Read more

The tumour suppressor p53 is a master sensor of stress and it controls the expression of hundreds to thousands of genes with diverse biological functions including cell cycle arrest, apoptosis, and senescence. Consequently p53 is the most mutated gene found in human cancer and p53 mutation rate varies from 5% to 95%. Importantly p53 activity is often inactivated in tumours expressing structurally wild type p53. Thus one of the major challenges in cancer research is to restore the tumour suppressive function of p53. Intensive studies in the past decade have demonstrated that in addition to mutation, p53 activities are largely regulated by cellular factors that control the expression level and/or transcriptional activities of p53. MDM2, MDM4, p14 ARF and the ASPP family of proteins are among the most studied regulators of p53. With increased understanding of the complexity of p53 regulation, various p53 reactivating approaches are being developed. This review will focus on the recent understanding of p53 inactivation in melanoma and the approaches to reactivate p53 in preclinical studies. Recent success in the therapeutic targeting of the BRAFV600E oncogenic protein was accompanied with subsequent relapse caused by acquired drug resistance. Restoration of the tumour suppressive function of p53 presents a parallel cancer therapeutic opportunity alongside BRAFV600E inhibition. Thus targeted therapy and concurrent reactivation of p53 may be a fertile ground to achieve synergistic killing of the 50% of cancer cells that express structurally wild type p53. © 2014 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.

Goding CR, Pei D, Lu X. 2014. Cancer: pathological nuclear reprogramming? Nat Rev Cancer, 14 (8), pp. 568-573. | Show Abstract | Read more

The ability of stem cells to self-renew and generate different lineages during development and organogenesis is a fundamental, tightly controlled, and generally unidirectional process, whereas the 'immortality' of cancer cells could be regarded as pathological self-renewal. The molecular mechanisms that underpin the generation of induced pluripotent stem cells are remarkably similar to those that are deregulated in cancer - so much so that aberrant reprogramming is tumorigenic. The similarities also suggest that mutations in genes implicated in DNA methylation dynamics might represent a hallmark of cancers with a stem cell origin, and they highlight an alternative view of cancer that may be of clinical benefit.

Turnquist C, Wang Y, Severson DT, Zhong S, Sun B, Ma J, Constaninescu SN, Ansorge O, Stolp HB, Molnár Z et al. 2014. STAT1-induced ASPP2 transcription identifies a link between neuroinflammation, cell polarity, and tumor suppression. Proc Natl Acad Sci U S A, 111 (27), pp. 9834-9839. | Show Abstract | Read more

Inflammation and loss of cell polarity play pivotal roles in neurodegeneration and cancer. A central question in both diseases is how the loss of cell polarity is sensed by cell death machinery. Here, we identify apoptosis-stimulating protein of p53 with signature sequences of ankyrin repeat-, SH3 domain-, and proline-rich region-containing protein 2 (ASPP2), a haploinsufficient tumor suppressor, activator of p53, and regulator of cell polarity, as a transcriptional target of signal transducer and activator of transcription 1 (STAT1). LPS induces ASPP2 expression in murine macrophage and microglial cell lines, a human monocyte cell line, and primary human astrocytes in vitro. LPS and IFNs induce ASPP2 transcription through an NF-κB RELA/p65-independent but STAT1-dependent pathway. In an LPS-induced maternal inflammation mouse model, LPS induces nuclear ASPP2 in vivo at the blood-cerebral spinal fluid barrier (the brain's barrier to inflammation), and ASPP2 mediates LPS-induced apoptosis. Consistent with the role of ASPP2 as a gatekeeper to inflammation, ASPP2-deficient brains possess enhanced neuroinflammation. Elevated ASPP2 expression is also observed in mouse models and human neuroinflammatory disease tissue, where ASPP2 was detected in GFAP-expressing reactive astrocytes that coexpress STAT1. Because the ability of ASPP2 to maintain cellular polarity is vital to CNS development, our findings suggest that the identified STAT1/ASPP2 pathway may connect tumor suppression and cell polarity to neuroinflammation.

Gao S, Yang C, Jiang S, Xu XN, Lu X, He YW, Cheung A, Wang H. 2014. Applications of RNA interference high-throughput screening technology in cancer biology and virology. Protein Cell, 5 (11), pp. 805-815. | Show Abstract | Read more

RNA interference (RNAi) is an ancient intra-cellular mechanism that regulates gene expression and cell function. Large-scale gene silencing using RNAi high-throughput screening (HTS) has opened an exciting frontier to systematically study gene function in mammalian cells. This approach enables researchers to identify gene function in a given biological context and will provide considerable novel insight. Here, we review RNAi HTS strategies and applications using case studies in cancer biology and virology.

Lu M, Zak J, Chen S, Sanchez-Pulido L, Severson DT, Endicott J, Ponting CP, Schofield CJ, Lu X. 2014. A code for RanGDP binding in ankyrin repeats defines a nuclear import pathway. Cell, 157 (5), pp. 1130-1145. | Show Abstract | Read more

Regulation of nuclear import is fundamental to eukaryotic biology. The majority of nuclear import pathways are mediated by importin-cargo interactions. Yet not all nuclear proteins interact with importins, necessitating the identification of a general importin-independent nuclear import pathway. Here, we identify a code that determines importin-independent nuclear import of ankyrin repeats (ARs), a structural motif found in over 250 human proteins with diverse functions. AR-containing proteins (ARPs) with a hydrophobic residue at the 13th position of two consecutive ARs bind RanGDP efficiently, and consequently enter the nucleus. This code, experimentally tested in 17 ARPs, predicts the nuclear-cytoplasmic localization of over 150 annotated human ARPs with high accuracy and is acquired by the most common familial melanoma-associated CDKN2A mutation, leading to nuclear accumulation of mutant p16ink4a. The RaDAR (RanGDP/AR) pathway represents a general importin-independent nuclear import pathway and is frequently used by AR-containing transcriptional regulators, especially those regulating NF-κB/p53.

Lu M, Miller P, Lu X. 2014. Restoring the tumour suppressive function of p53 as a parallel strategy in melanoma therapy. FEBS Lett, 588 (16), pp. 2616-2621. | Show Abstract | Read more

The tumour suppressor p53 is a master sensor of stress and it controls the expression of hundreds to thousands of genes with diverse biological functions including cell cycle arrest, apoptosis, and senescence. Consequently p53 is the most mutated gene found in human cancer and p53 mutation rate varies from 5% to 95%. Importantly p53 activity is often inactivated in tumours expressing structurally wild type p53. Thus one of the major challenges in cancer research is to restore the tumour suppressive function of p53. Intensive studies in the past decade have demonstrated that in addition to mutation, p53 activities are largely regulated by cellular factors that control the expression level and/or transcriptional activities of p53. MDM2, MDM4, p14(ARF) and the ASPP family of proteins are among the most studied regulators of p53. With increased understanding of the complexity of p53 regulation, various p53 reactivating approaches are being developed. This review will focus on the recent understanding of p53 inactivation in melanoma and the approaches to reactivate p53 in preclinical studies. Recent success in the therapeutic targeting of the BRAFV600E oncogenic protein was accompanied with subsequent relapse caused by acquired drug resistance. Restoration of the tumour suppressive function of p53 presents a parallel cancer therapeutic opportunity alongside BRAFV600E inhibition. Thus targeted therapy and concurrent reactivation of p53 may be a fertile ground to achieve synergistic killing of the 50% of cancer cells that express structurally wild type p53.

Nešić D, Buti L, Lu X, Stebbins CE. 2014. Structure of the Helicobacter pylori CagA oncoprotein bound to the human tumor suppressor ASPP2. Proc Natl Acad Sci U S A, 111 (4), pp. 1562-1567. | Show Abstract | Read more

The Cytotoxin associated gene A (CagA) protein of Helicobacter pylori is associated with increased virulence and risk of cancer. Recent proteomic studies have demonstrated an association of CagA with the human tumor suppressor Apoptosis-stimulating Protein of p53-2 (ASPP2). We present here a genetic, biochemical, and structural analysis of CagA with ASPP2. Domain delineation of the 120-kDa CagA protein revealed a stable N-terminal subdomain that was used in a yeast two-hybrid screen that identified the proline-rich domain of ASPP2 as a host cellular target. Biochemical experiments confirm this interaction. The cocrystal structure to 2.0-Å resolution of this N-terminal subdomain of CagA with a 7-kDa proline-rich sequence of ASPP2 reveals that this domain of CagA forms a highly specialized three-helix bundle, with large insertions in the loops connecting the helices. These insertions come together to form a deep binding cleft for a highly conserved 20-aa peptide of ASPP2. ASPP2 forms an extended helix in this groove of CagA, burying more than 1,000 Å(2) of surface area. This interaction is disrupted in vitro and in vivo by structure-based, loss-of-contact point mutations of key residues in either CagA or ASPP2. Disruption of CagA and ASPP2 binding alters the function of ASPP2 and leads to the decreased survival of H. pylori-infected cells.

Gao S, Yang C, Jiang S, Xu XN, Lu X, He YW, Cheung A, Wang H. 2014. Applications of RNA interference high-throughput screening technology in cancer biology and virology Protein and Cell, 5 (11), pp. 805-815. | Show Abstract | Read more

© 2014, The Author(s). RNA interference (RNAi) is an ancient intra-cellular mechanism that regulates gene expression and cell function. Large-scale gene silencing using RNAi high-throughput screening (HTS) has opened an exciting frontier to systematically study gene function in mammalian cells. This approach enables researchers to identify gene function in a given biological context and will provide considerable novel insight. Here, we review RNAi HTS strategies and applications using case studies in cancer biology and virology.

Royer C, Koch S, Qin X, Zak J, Buti L, Dudziec E, Zhong S, Ratnayaka I, Srinivas S, Lu X. 2014. ASPP2 links the apical lateral polarity complex to the regulation of YAP activity in epithelial cells. PLoS One, 9 (10), pp. e111384. | Show Abstract | Read more

The Hippo pathway, by tightly controlling the phosphorylation state and activity of the transcription cofactors YAP and TAZ is essential during development and tissue homeostasis whereas its deregulation may lead to cancer. Recent studies have linked the apicobasal polarity machinery in epithelial cells to components of the Hippo pathway and YAP and TAZ themselves. However the molecular mechanism by which the junctional pool of YAP proteins is released and activated in epithelial cells remains unknown. Here we report that the tumour suppressor ASPP2 forms an apical-lateral polarity complex at the level of tight junctions in polarised epithelial cells, acting as a scaffold for protein phosphatase 1 (PP1) and junctional YAP via dedicated binding domains. ASPP2 thereby directly induces the dephosphorylation and activation of junctional YAP. Collectively, this study unearths a novel mechanistic paradigm revealing the critical role of the apical-lateral polarity complex in activating this localised pool of YAP in vitro, in epithelial cells, and in vivo, in the murine colonic epithelium. We propose that this mechanism may commonly control YAP functions in epithelial tissues.

Morris EV, Cerundolo L, Lu M, Verrill C, Fritzsche F, White MJ, Thalmann GN, ten Donkelaar CS, Ratnayaka I, Salter V et al. 2014. Nuclear iASPP may facilitate prostate cancer progression. Cell Death Dis, 5 (10), pp. e1492. | Show Abstract | Read more

One of the major challenges in prostate cancer (PCa) research is the identification of key players that control the progression of primary cancers to invasive and metastatic disease. The majority of metastatic PCa express wild-type p53, whereas loss of p63 expression, a p53 family member, is a common event. Here we identify inhibitor of apoptosis-stimulating protein of p53 (iASPP), a common cellular regulator of p53 and p63, as an important player of PCa progression. Detailed analysis of the prostate epithelium of iASPP transgenic mice, iASPP(Δ8/Δ8) mice, revealed that iASPP deficiency resulted in a reduction in the number of p63 expressing basal epithelial cells compared with that seen in wild-type mice. Nuclear and cytoplasmic iASPP expression was greater in PCa samples compared with benign epithelium. Importantly nuclear iASPP associated with p53 accumulation in vitro and in vivo. A pair of isogenic primary and metastatic PCa cell lines revealed that nuclear iASPP is enriched in the highly metastatic PCa cells. Nuclear iASPP is often detected in PCa cells located at the invasive leading edge in vivo. Increased iASPP expression associated with metastatic disease and PCa-specific death in a clinical cohort with long-term follow-up. These results suggest that iASPP function is required to maintain the expression of p63 in normal basal prostate epithelium, and nuclear iASPP may inactivate p53 function and facilitate PCa progression. Thus iASPP expression may act as a predictive marker of PCa progression.

Cited:

38

Scopus

Goding CR, Pei D, Lu X. 2014. Cancer: Pathological nuclear reprogramming? Nature Reviews Cancer, 14 (8), pp. 568-573. | Show Abstract | Read more

The ability of stem cells to self-renew and generate different lineages during development and organogenesis is a fundamental, tightly controlled, and generally unidirectional process, whereas the 'immortality' of cancer cells could be regarded as pathological self-renewal. The molecular mechanisms that underpin the generation of induced pluripotent stem cells are remarkably similar to those that are deregulated in cancer-so much so that aberrant reprogramming is tumorigenic. The similarities also suggest that mutations in genes implicated in DNA methylation dynamics might represent a hallmark of cancers with a stem cell origin, and they highlight an alternative view of cancer that may be of clinical benefit. © 2014 Macmillan Publishers Limited.

Pagotto A, Caballero OL, Volkmar N, Devalle S, Simpson AJ, Lu X, Christianson JC. 2013. Centrosomal localisation of the cancer/testis (CT) antigens NY-ESO-1 and MAGE-C1 is regulated by proteasome activity in tumour cells. PLoS One, 8 (12), pp. e83212. | Show Abstract | Read more

The Cancer/Testis (CT) antigen family of genes are transcriptionally repressed in most human tissues but are atypically re-expressed in many malignant tumour types. Their restricted expression profile makes CT antigens ideal targets for cancer immunotherapy. As little is known about whether CT antigens may be regulated by post-translational processing, we investigated the mechanisms governing degradation of NY-ESO-1 and MAGE-C1 in selected cancer cell lines. Inhibitors of proteasome-mediated degradation induced the partitioning of NY-ESO-1 and MAGE-C1 into a detergent insoluble fraction. Moreover, this treatment also resulted in increased localisation of NY-ESO-1 and MAGE-C1 at the centrosome. Despite their interaction, relocation of either NY-ESO-1 or MAGE-C1 to the centrosome could occur independently of each other. Using a series of truncated fragments, the regions corresponding to NY-ESO-1(91-150) and MAGE-C1(900-1116) were established as important for controlling both stability and localisation of these CT antigens. Our findings demonstrate that the steady state levels of NY-ESO-1 and MAGE-C1 are regulated by proteasomal degradation and that both behave as aggregation-prone proteins upon accumulation. With proteasome inhibitors being increasingly used as front-line treatment in cancer, these data raise issues about CT antigen processing for antigenic presentation and therefore immunogenicity in cancer patients.

Tordella L, Koch S, Salter V, Pagotto A, Doondeea JB, Feller SM, Ratnayaka I, Zhong S, Goldin RD, Lozano G et al. 2013. ASPP2 suppresses squamous cell carcinoma via RelA/p65-mediated repression of p63. Proc Natl Acad Sci U S A, 110 (44), pp. 17969-17974. | Show Abstract | Read more

Squamous cell carcinoma (SCC) is highly malignant and refractory to therapy. The majority of existing mouse SCC models involve multiple gene mutations. Very few mouse models of spontaneous SCC have been generated by a single gene deletion. Here we report a haploinsufficient SCC mouse model in which exon 3 of the Tp53BP2 gene (a p53 binding protein) was deleted in one allele in a BALB/c genetic background. Tp53BP2 encodes ASPP2 (ankyrin repeats, SH3 domain and protein rich region containing protein 2). Keratinocyte differentiation induces ASPP2 and its expression is inversely correlated with p63 protein in vitro and in vivo. Up-regulation of p63 expression is required for ASPP2(Δexon3/+) BALB/c mice to develop SCC, as heterozygosity of p63 but not p53 prevents them from developing it. Mechanistically, ASPP2 inhibits ΔNp63 expression through its ability to bind IκB and enhance nuclear Rel/A p65, a component of the NF-κB transcription complex, which mediates the repression of p63. Reduced ASPP2 expression associates with tumor metastasis and increased p63 expression in human head and neck SCCs. This study identifies ASPP2 as a tumor suppressor that suppresses SCC via inflammatory signaling through NF-κB-mediated repression of p63.

Mak VC, Lee L, Siu MK, Wong OG, Lu X, Ngan HY, Wong ES, Cheung AN. 2013. Downregulation of ASPP2 in choriocarcinoma contributes to increased migratory potential through Src signaling pathway activation. Carcinogenesis, 34 (9), pp. 2170-2177. | Show Abstract | Read more

Gestational choriocarcinoma is a malignant tumor derived from placental trophoblast and the most aggressive member of gestational trophoblastic disease (GTD). Apoptosis-stimulating protein of p53-2 (ASPP2) is a member of ASPP family that transactivates p53 and thereby functions as a tumor suppressor. In this study, the expression profile of ASPP2 in choriocarcinoma was examined in comparison with normal placentas and hydatidiform moles, the latter being a type of GTD that carries malignant potential. Downregulation of ASPP2 messenger RNA and protein was demonstrated in choriocarcinoma by quantitative PCR and immunohistochemistry. ASPP2-transfected choriocarcinoma cells (JEG-3 and JAR) showed an increase in apoptosis and a decrease in cell migration as detected by TdT-mediated dUTP nick end labeling and wound healing assays, respectively, illustrating the complex action of ASPP2 on cell functions other than programmed cell death. Activated Src is known to be important in tumor progression. Transfection of ASPP2 but not ASPP1, another tumor-suppressive ASPP, was found to be related to subsequent decreased Src-pY416 phosphorylation, suggesting an inactivating effect of ASPP2 on Src. Moreover, this ASPP2-mediated inactivation of Src could be abolished by RNA interference with C-terminal Src kinase (Csk), a kinase that can inhibit Src activation. Our findings suggested that the ability of ASPP2 to attenuate Src activation was specific to ASPP2 in a Csk-dependent manner. Taken together, we demonstrated a loss of tumor-suppressive ASPP2 in choriocarcinoma with effects on cell migration and apoptosis. We also unveiled a possible mechanistic link between ASPP2 and Csk/Src signaling pathway, implicating the multiple cellular functions of ASPP2.

Lu M, Breyssens H, Salter V, Zhong S, Hu Y, Baer C, Ratnayaka I, Sullivan A, Brown NR, Endicott J et al. 2013. Restoring p53 function in human melanoma cells by inhibiting MDM2 and cyclin B1/CDK1-phosphorylated nuclear iASPP. Cancer Cell, 23 (5), pp. 618-633. | Show Abstract | Read more

Nearly 90% of human melanomas contain inactivated wild-type p53, the underlying mechanisms for which are not fully understood. Here, we identify that cyclin B1/CDK1-phosphorylates iASPP, which leads to the inhibition of iASPP dimerization, promotion of iASPP monomer nuclear entry, and exposure of its p53 binding sites, leading to increased p53 inhibition. Nuclear iASPP is enriched in melanoma metastasis and associates with poor patient survival. Most wild-type p53-expressing melanoma cell lines coexpress high levels of phosphorylated nuclear iASPP, MDM2, and cyclin B1. Inhibition of MDM2 and iASPP phosphorylation with small molecules induced p53-dependent apoptosis and growth suppression. Concurrent p53 reactivation and BRAFV600E inhibition achieved additive suppression in vivo, presenting an alternative for melanoma therapy.

Kim H, Claps G, Möller A, Bowtell D, Lu X, Ronai ZA. 2014. Siah2 regulates tight junction integrity and cell polarity through control of ASPP2 stability. Oncogene, 33 (15), pp. 2004-2010. | Show Abstract | Read more

Changes in cell adhesion and polarity are closely associated with epithelial cell transformation and metastatic capacity. The tumor suppressor protein ASPP (Apoptosis-Stimulating Proteins of p53) 2 has been implicated in control of cell adhesion and polarity through its effect on the PAR complex. Here we demonstrate that under hypoxic conditions, the ubiquitin ligase Siah (seven in absentia homolog)2 controls ASPP2 availability, with concomitant effect on epithelial cell polarity. LC-MS/MS analysis identified ASPP2 and ASPP1 as Siah2-interacting proteins. Biochemical analysis confirmed this interaction and mapped degron motifs within ASPP2, which are required for Siah2-mediated ubiquitination and proteasomal-dependent degradation. Inhibition of Siah2 expression increases ASPP2 levels and enhances ASPP2-dependent maintenance of tight junction (TJ) integrity, and polarized architecture in three dimensional (3D) organotypic culture. Conversely, increase of Siah2 expression under hypoxia decreases ASPP2 levels and the formation of apical polarity in 3D culture. In all, our studies demonstrate the role of Siah2 in regulation of TJ integrity and cell polarity under hypoxia, through its regulation of ASPP2 stability.

Terrinoni A, Serra V, Bruno E, Strasser A, Valente E, Flores ER, van Bokhoven H, Lu X, Knight RA, Melino G. 2013. Role of p63 and the Notch pathway in cochlea development and sensorineural deafness. Proc Natl Acad Sci U S A, 110 (18), pp. 7300-7305. | Show Abstract | Read more

The ectodermal dysplasias are a group of inherited autosomal dominant syndromes associated with heterozygous mutations in the Tumor Protein p63 (TRP63) gene. Here we show that, in addition to their epidermal pathology, a proportion of these patients have distinct levels of deafness. Accordingly, p63 null mouse embryos show marked cochlea abnormalities, and the transactivating isoform of p63 (TAp63) protein is normally found in the organ of Corti. TAp63 transactivates hairy and enhancer of split 5 (Hes5) and atonal homolog 1 (Atoh1), components of the Notch pathway, known to be involved in cochlear neuroepithelial development. Strikingly, p63 null mice show morphological defects of the organ of Corti, with supernumerary hair cells, as also reported for Hes5 null mice. This phenotype is related to loss of a differentiation property of TAp63 and not to loss of its proapoptotic function, because cochleas in mice lacking the critical Bcl-2 homology domain (BH-3) inducers of p53- and p63-mediated apoptosis--Puma, Noxa, or both--are normal. Collectively, these data demonstrate that TAp63, acting via the Notch pathway, is crucial for the development of the organ of Corti, providing a molecular explanation for the sensorineural deafness in ectodermal dysplasia patients with TRP63 mutations.

Wang Y, Godin-Heymann N, Dan Wang X, Bergamaschi D, Llanos S, Lu X. 2013. ASPP1 and ASPP2 bind active RAS, potentiate RAS signalling and enhance p53 activity in cancer cells. Cell Death Differ, 20 (4), pp. 525-534. | Show Abstract | Read more

RAS mutations occur frequently in human cancer and activated RAS signalling contributes to tumour development and progression. Apart from its oncogenic effects on cell growth, active RAS has tumour-suppressive functions via its ability to induce cellular senescence and apoptosis. RAS is known to induce p53-dependent cell cycle arrest, yet its effect on p53-dependent apoptosis remains unclear. We report here that apoptosis-stimulating protein of p53 (ASPP) 1 and 2, two activators of p53, preferentially bind active RAS via their N-terminal RAS-association domains (RAD). Additionally, ASPP2 colocalises with and contributes to RAS cellular membrane localisation and potentiates RAS signalling. In cancer cells, ASPP1 and ASPP2 cooperate with oncogenic RAS to enhance the transcription and apoptotic function of p53. Thus, loss of ASPP1 and ASPP2 in human cancer cells may contribute to the full transforming property of RAS oncogene.

Godin-Heymann N, Wang Y, Slee E, Lu X. 2013. Phosphorylation of ASPP2 by RAS/MAPK pathway is critical for its full pro-apoptotic function. PLoS One, 8 (12), pp. e82022. | Show Abstract | Read more

We reported recently that apoptosis-stimulating protein of p53 (ASPP) 2, an activator of p53, co-operates with oncogenic RAS to enhance the transcription and apoptotic function of p53. However, the detailed mechanism remains unknown. Here we show that ASPP2 is a novel substrate of mitogen-activated protein kinase (MAPK). Phosphorylation of ASPP2 by MAPK is required for RAS-induced increased binding to p53 and increased transactivation of pro-apoptotic genes. In contrast, an ASPP2 phosphorylation mutant exhibits reduced p53 binding and fails to enhance transactivation and apoptosis. Thus phosphorylation of ASPP2 by RAS/MAPK pathway provides a novel link between RAS and p53 in regulating apoptosis.

Slee EA, Lu X. 2013. Requirement for phosphorylation of P53 at Ser312 in suppression of chemical carcinogenesis. Sci Rep, 3 (1), pp. 3105. | Show Abstract | Read more

The p53 tumour suppressor is activated in response to a wide variety of genotoxic stresses, frequently via post-translational modification. Using a knock in mouse model with a Ser312 to Ala mutation, we show here that phosphorylation of p53 on Ser312 helps to prevent tumour induction by the alkylating agent MNU, which predominantly caused T cell lymphomas. This is consistent with our previous observation that p53(312A/A) mice are more susceptible to X-ray induced tumourigenesis. Phosphorylation on Ser312 aids p53's interaction with E2F1, and enhances p53-mediated apoptosis. Loss of E2F1 alone does not affect tumour susceptibility to MNU, but its absence partially rescues tumour formation in p53(312A/A) mice, thus reflecting the oncogenic properties of E2F1. Our data confirms the participation of Ser312 phosphorylation in tumour suppression by p53.

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Wang Y, Godin-Heymann N, Dan Wang X, Bergamaschi D, Llanos S, Lu X. 2013. ASPP1 and ASPP2 bind active RAS, potentiate RAS signalling and enhance p53 activity in cancer cells Cell Death and Differentiation, 20 (4), pp. 525-534. | Show Abstract | Read more

RAS mutations occur frequently in human cancer and activated RAS signalling contributes to tumour development and progression. Apart from its oncogenic effects on cell growth, active RAS has tumour-suppressive functions via its ability to induce cellular senescence and apoptosis. RAS is known to induce p53-dependent cell cycle arrest, yet its effect on p53-dependent apoptosis remains unclear. We report here that apoptosis-stimulating protein of p53 (ASPP) 1 and 2, two activators of p53, preferentially bind active RAS via their N-terminal RAS-association domains (RAD). Additionally, ASPP2 colocalises with and contributes to RAS cellular membrane localisation and potentiates RAS signalling. In cancer cells, ASPP1 and ASPP2 cooperate with oncogenic RAS to enhance the transcription and apoptotic function of p53. Thus, loss of ASPP1 and ASPP2 in human cancer cells may contribute to the full transforming property of RAS oncogene. © 2013 Macmillan Publishers Limited All rights reserved.

Wang Y, Wang XD, Lapi E, Sullivan A, Jia W, He YW, Ratnayaka I, Zhong S, Goldin RD, Goemans CG et al. 2012. Autophagic activity dictates the cellular response to oncogenic RAS. Proc Natl Acad Sci U S A, 109 (33), pp. 13325-13330. | Show Abstract | Read more

RAS is frequently mutated in human cancers and has opposing effects on autophagy and tumorigenesis. Identifying determinants of the cellular responses to RAS is therefore vital in cancer research. Here, we show that autophagic activity dictates the cellular response to oncogenic RAS. N-terminal Apoptosis-stimulating of p53 protein 2 (ASPP2) mediates RAS-induced senescence and inhibits autophagy. Oncogenic RAS-expressing ASPP2((Δ3/Δ3)) mouse embryonic fibroblasts that escape senescence express a high level of ATG5/ATG12. Consistent with the notion that autophagy levels control the cellular response to oncogenic RAS, overexpressing ATG5, but not autophagy-deficient ATG5 mutant K130R, bypasses RAS-induced senescence, whereas ATG5 or ATG3 deficiency predisposes to it. Mechanistically, ASPP2 inhibits RAS-induced autophagy by competing with ATG16 to bind ATG5/ATG12 and preventing ATG16/ATG5/ATG12 formation. Hence, ASPP2 modulates oncogenic RAS-induced autophagic activity to dictate the cellular response to RAS: to proliferate or senesce.

Lu X. 2012. ASPP2: Tumor suppression through the control of polarity and proliferation CANCER RESEARCH, 72 (8 Supplement), pp. 1174-1174. | Read more

Lu X. 2012. P53: A Target and a Biomarker of Cancer Therapy? pp. 197-213. | Read more

Galluzzi L, Vitale I, Abrams JM, Alnemri ES, Baehrecke EH, Blagosklonny MV, Dawson TM, Dawson VL, El-Deiry WS, Fulda S et al. 2012. Molecular definitions of cell death subroutines: recommendations of the Nomenclature Committee on Cell Death 2012. Cell Death Differ, 19 (1), pp. 107-120. | Show Abstract | Read more

In 2009, the Nomenclature Committee on Cell Death (NCCD) proposed a set of recommendations for the definition of distinct cell death morphologies and for the appropriate use of cell death-related terminology, including 'apoptosis', 'necrosis' and 'mitotic catastrophe'. In view of the substantial progress in the biochemical and genetic exploration of cell death, time has come to switch from morphological to molecular definitions of cell death modalities. Here we propose a functional classification of cell death subroutines that applies to both in vitro and in vivo settings and includes extrinsic apoptosis, caspase-dependent or -independent intrinsic apoptosis, regulated necrosis, autophagic cell death and mitotic catastrophe. Moreover, we discuss the utility of expressions indicating additional cell death modalities. On the basis of the new, revised NCCD classification, cell death subroutines are defined by a series of precise, measurable biochemical features.

Llanos S, Royer C, Lu M, Bergamaschi D, Lee WH, Lu X. 2011. Inhibitory member of the apoptosis-stimulating proteins of the p53 family (iASPP) interacts with protein phosphatase 1 via a noncanonical binding motif. J Biol Chem, 286 (50), pp. 43039-43044. | Show Abstract | Read more

Although kinase mutations have been identified in various human diseases, much less is known about protein phosphatases. Here, we show that all apoptosis-stimulating proteins of p53 (ASPP) family members can bind protein phosphatase 1 (PP1) via two distinct interacting motifs. ASPP2 interacts with PP1 through an RVXF PP1 binding motif, whereas the inhibitory member of the ASPP family (iASPP) interacts with PP1 via a noncanonical motif (RNYF) that is located within its Src homology 3 domain (SH3). Phe-815 is crucial in mediating iASPP/PP1 interaction, and iASPP(F815A) fails to inhibit the transcriptional and apoptotic function of p53. This study identifies iASPP as a new binding partner of PP1, interacting through a noncanonical PP1 binding motif.

Jiang L, Siu MK, Wong OG, Tam KF, Lu X, Lam EW, Ngan HY, Le XF, Wong ES, Monteiro LJ et al. 2011. iASPP and chemoresistance in ovarian cancers: effects on paclitaxel-mediated mitotic catastrophe. Clin Cancer Res, 17 (21), pp. 6924-6933. | Show Abstract | Read more

PURPOSE: iASPP is a specific regulator of p53-mediated apoptosis. Herein, we provided the first report on the expression profile of iASPP in ovarian epithelial tumor and its effect on paclitaxel chemosensitivity. EXPERIMENTAL DESIGN: Expression and amplification status of iASPP was examined in 203 clinical samples and 17 cell lines using immunohistochemistry, quantitative real-time PCR, and immunoblotting, and correlated with clinicopathologic parameters. Changes in proliferation, mitotic catastrophe, apoptosis, and underlying mechanism in ovarian cancer cells of different p53 status following paclitaxel exposure were also analyzed. RESULTS: The protein and mRNA expression of iASPP was found to be significantly increased in ovarian cancer samples and cell lines. High iASPP expression was significantly associated with clear cell carcinoma subtype (P = 0.003), carboplatin and paclitaxel chemoresistance (P = 0.04), shorter overall (P = 0.003), and disease-free (P = 0.001) survival. Multivariate analysis confirmed iASPP expression as an independent prognostic factor. Increased iASPP mRNA expression was significantly correlated with gene amplification (P = 0.023). iASPP overexpression in ovarian cancer cells conferred resistance to paclitaxel by reducing mitotic catastrophe in a p53-independent manner via activation of separase, whereas knockdown of iASPP enhanced paclitaxel-mediated mitotic catastrophe through inactivating separase. Both securin and cyclin B1/CDK1 complex were involved in regulating separase by iASPP. Conversely, overexpressed iASPP inhibited apoptosis in a p53-dependent mode. CONCLUSIONS: Our data show an association of iASPP overexpression with gene amplification in ovarian cancer and suggest a role of iASPP in poor patient outcome and chemoresistance, through blocking mitotic catastrophe. iASPP should be explored further as a potential prognostic marker and target for chemotherapy.

Notari M, Hu Y, Koch S, Lu M, Ratnayaka I, Zhong S, Baer C, Pagotto A, Goldin R, Salter V et al. 2011. Inhibitor of apoptosis-stimulating protein of p53 (iASPP) prevents senescence and is required for epithelial stratification. Proc Natl Acad Sci U S A, 108 (40), pp. 16645-16650. | Show Abstract | Read more

Inhibitor of apoptosis-stimulating protein of p53 (iASPP) is the most ancient member of the ASPP family of proteins and an evolutionarily conserved inhibitor of p53. iASPP is also a binding partner and negative regulator of p65RelA. Because p65RelA and the p53 family members often have opposite effects in controlling cell fate, it is important to understand the cellular context in which iASPP can regulate their activities. To address this question and to study the biological importance of iASPP in vivo, we generated a transgenic mouse in which iASPP expression is controlled by the Cre/loxP recombination system. We observed that iASPP is able to prevent premature cellular senescence in mouse embryonic fibroblasts. iASPP loss resulted in increased differentiation of primary keratinocytes both in vitro and in vivo. In stratified epithelia, nuclear iASPP often colocalized with p63 in the nuclei of basal keratinocytes. Consistent with this, iASPP bound p63 and inhibited the transcriptional activity of both TAp63α and ΔNp63α in vitro and influenced the expression level of p63-regulated genes such as loricrin and involucrin in vivo. In contrast, under the same conditions, p65RelA was frequently expressed as a cytoplasmic protein in the suprabasal layers of stratified epithelia and rarely colocalized with nuclear iASPP. Thus, iASPP is likely to control epithelial stratification by regulating p63's transcriptional activity, rather than p65RelA's. This study identifies iASPP as an inhibitor of senescence and a key player in controlling epithelial stratification.

Wang X, Ouyang H, Yamamoto Y, Kumar PA, Wei TS, Dagher R, Vincent M, Lu X, Bellizzi AM, Ho KY et al. 2011. Residual embryonic cells as precursors of a Barrett's-like metaplasia. Cell, 145 (7), pp. 1023-1035. | Show Abstract | Read more

Barrett's esophagus is an intestine-like metaplasia and precursor of esophageal adenocarcinoma. Triggered by gastroesophageal reflux disease, the origin of this metaplasia remains unknown. p63-deficient mice, which lack squamous epithelia, may model acid-reflux damage. We show here that p63 null embryos rapidly develop intestine-like metaplasia with gene expression profiles similar to Barrett's metaplasia. We track its source to a unique embryonic epithelium that is normally undermined and replaced by p63-expressing cells. Significantly, we show that a discrete population of these embryonic cells persists in adult mice and humans at the squamocolumnar junction, the source of Barrett's metaplasia. We show that upon programmed damage to the squamous epithelium, these embryonic cells migrate toward adjacent, specialized squamous cells in a process that may recapitulate early Barrett's. Our findings suggest that certain precancerous lesions, such as Barrett's, initiate not from genetic alterations but from competitive interactions between cell lineages driven by opportunity.

Royer C, Lu X. 2011. Epithelial cell polarity: a major gatekeeper against cancer? Cell Death Differ, 18 (9), pp. 1470-1477. | Show Abstract | Read more

The correct establishment and maintenance of cell polarity are crucial for normal cell physiology and tissue homeostasis. Conversely, loss of cell polarity, tissue disorganisation and excessive cell growth are hallmarks of cancer. In this review, we focus on identifying the stages of tumoural development that are affected by the loss or deregulation of epithelial cell polarity. Asymmetric division has recently emerged as a major regulatory mechanism that controls stem cell numbers and differentiation. Links between cell polarity and asymmetric cell division in the context of cancer will be examined. Apical-basal polarity and cell-cell adhesion are tightly interconnected. Hence, how loss of cell polarity in epithelial cells may promote epithelial mesenchymal transition and metastasis will also be discussed. Altogether, we present the argument that loss of epithelial cell polarity may have an important role in both the initiation of tumourigenesis and in later stages of tumour development, favouring the progression of tumours from benign to malignancy.

Slee EA, Lu X. 2011. In the right place at the right time: analysis of p53 serine 312 phosphorylation in vivo. Cell Cycle, 10 (9), pp. 1345-1346. | Read more

Gillotin S, Lu X. 2011. The ASPP proteins complex and cooperate with p300 to modulate the transcriptional activity of p53. FEBS Lett, 585 (12), pp. 1778-1782. | Show Abstract | Read more

Understanding how p53 is able to specifically respond to particular stress signals and regulate many different signalling pathways remains a challenge. Several studies have demonstrated that p53's interactions with different protein partners are essential for it to be able to coordinate specific responses. In particular, the apoptotic pathway is regulated by p53 in cooperation with the Apoptosis Stimulating Proteins of p53 (ASPP) proteins. In this study, we showed that the ASPP proteins are able to bind and cooperate with p300, a well defined co-factor of p53, to selectively regulate p53's transcriptional activity on promoters such as p53-inducible gene 3 but not on p21waf1. This is the first demonstration that the ASPPs can function together with p300 in regulating the transcriptional activity of p53.

Mak VCY, Lee L, Siu MKY, Wong OGW, Lu X, Ngan HYS, Wong E, Cheung ANY. 2011. Downregulation of ASPP2 in choriocarcinoma contributes to increased migratory potential through Src activation CANCER RESEARCH, 71 (8 Supplement), pp. 2107-2107. | Read more

Galluzzi L, Vitale I, Abrams JM, Alnemri ES, Baehrecke EH, Blagosklonny MV, Dawson TM, Dawson VL, El-Deiry WS, Fulda S et al. 2011. Molecular definitions of cell death subroutines: recommendations of the Nomenclature Committee on Cell Death 2012 Cell Death and Differentiation,

Gillotin S, Lu X. 2011. The ASPP proteins complex and cooperate with p300 to modulate the transcriptional activity of p53 FEBS Letters, 585 (12), pp. 1778-1782. | Show Abstract | Read more

Understanding how p53 is able to specifically respond to particular stress signals and regulate many different signalling pathways remains a challenge. Several studies have demonstrated that p53's interactions with different protein partners are essential for it to be able to coordinate specific responses. In particular, the apoptotic pathway is regulated by p53 in cooperation with the Apoptosis Stimulating Proteins of p53 (ASPP) proteins. In this study, we showed that the ASPP proteins are able to bind and cooperate with p300, a well defined co-factor of p53, to selectively regulate p53's transcriptional activity on promoters such as p53-inducible gene 3 but not on p21waf1. This is the first demonstration that the ASPPs can function together with p300 in regulating the transcriptional activity of p53. © 2011 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.

Shi Y, Yang S, Troup S, Lu X, Callaghan S, Park DS, Xing Y, Yang X. 2011. Resveratrol induces apoptosis in breast cancer cells by E2F1-mediated up-regulation of ASPP1. Oncol Rep, 25 (6), pp. 1713-1719. | Show Abstract | Read more

Resveratrol is a natural polyphenolic compound with cancer chemopreventive activity. However, our understanding of the molecular mechanism responsible for resveratrol-induced apoptosis is still very limited. Here, we used MCF-7 and MDA-MB231 breast cancer cells as a model to demonstrate that resveratrol induced the expression of ASPP1, a new member of the ASPP (apoptosis stimulation protein of p53) family, which plays an important role in the regulation of apoptosis. Moreover, resveratrol enhanced apoptosis of MCF-7/ASPP1 cells, accompanied by higher expression of bax and p21. In contrast, siRNA-mediated knockdown of ASPP1 inhibited apoptosis in MB231 cells. Furthermore, we found that higher levels of ASPP1 were associated with adenovirus-mediated overexpression of E2F1 while siRNA-mediated E2F1 knockdown led to down-regulation of ASPP1. In conclusion, our results demonstrate that overexpression of ASPP1 rendered MCF-7 and MDA-MB231 breast cancer cells more sensitive to resveratrol-mediated apoptosis via the E2F pathway, thus suggesting that ASPP1 may represent a novel therapeutic target for resveratrol in human breast cancer.

Mak VCY, Lee L, Siu MKY, Wong OGW, Lu X, Ngan HYS, Wong ESY, Cheung ANY. 2011. Downregulation of ASPP1 in gestational trophoblastic disease: Correlation with hypermethylation, apoptotic activity and clinical outcome Modern Pathology, 24 (4), pp. 522-532. | Show Abstract | Read more

Gestational trophoblastic disease encompasses a spectrum of trophoblastic lesions including true neoplasms such as choriocarcinomas and the potentially malignant hydatidiform moles, which may develop persistent disease requiring chemotherapy. ASPP1, a member of apoptosis-stimulating proteins of p53 (ASPPs), is a proapoptotic protein that can stimulate apoptosis through its interaction with p53. We evaluated the promoter methylation and expression profiles of ASPP1 in different trophoblastic tissues and its in vitro functional effect on two choriocarcinoma cell lines, namely JEG-3 and JAR. Significant downregulation of ASPP1 mRNA and protein levels was demonstrated in hydatidiform moles and choriocarcinomas, when compared with normal placentas by quantitative-PCR and immunohistochemistry. The ASPP1 mRNA level was significantly correlated with its hypermethylation status, evaluated with methylation-specific PCR, in placenta and gestational trophoblastic disease samples (P=0.024). Moreover, lower ASPP1 immunoreactivity was shown in hydatidiform moles that progressed to persistent gestational trophoblastic neoplasms than in those that regressed (P=0.045). A significant correlation was also found between expression of ASPP1 and proliferative indices (assessed by Ki67 and MCM7), apoptotic activity (M30 CytoDeath antibody), p53 and caspase-8 immunoreactivities. An in vitro study showed that ectopic expression of ASPP1 could trigger apoptosis through intrinsic and extrinsic pathways as indicated by an increase in cleaved caspase-9 and Fas ligand protein expression. The latter suggests a hitherto unreported novel link between ASPP1 and the extrinsic pathway of apoptosis. Our findings suggest that downregulation of ASPP1 by hypermethylation may be involved in the pathogenesis and progress of gestational trophoblastic disease, probably through its effect on apoptosis. © 2011 USCAP, Inc. All rights reserved.

Hernández-Acosta NC, Cabrera-Socorro A, Morlans MP, Delgado FJG, Suárez-Solá ML, Sottocornola R, Lu X, González-Gómez M, Meyer G. 2011. Dynamic expression of the p53 family members p63 and p73 in the mouse and human telencephalon during development and in adulthood Brain Research, 1372 pp. 29-40. | Show Abstract | Read more

p63 and p73, family members of the tumor suppressor p53, are critically involved in the life and death of mammalian cells. They display high homology and may act in concert. The p73 gene is relevant for brain development, and p73-deficient mice display important malformations of the telencephalon. In turn, p63 is essential for the development of stratified epithelia and may also play a part in neuronal survival and aging. We show here that p63 and p73 are dynamically expressed in the embryonic and adult mouse and human telencephalon. During embryonic stages, Cajal-Retzius cells derived from the cortical hem co-express p73 and p63. Comparison of the brain phenotypes of p63- and p73- deficient mice shows that only the loss of p73 function leads to the loss of Cajal-Retzius cells, whereas p63 is apparently not essential for brain development and Cajal-Retzius cell formation. In postnatal mice, p53, p63, and p73 are present in cells of the subventricular zone (SVZ) of the lateral ventricle, a site of continued neurogenesis. The neurogenetic niche is reduced in size in p73-deficient mice, and the numbers of young neurons near the ventricular wall, marked with doublecortin, Tbr1 and calretinin, are dramatically decreased, suggesting that p73 is important for SVZ proliferation. In contrast to their restricted expression during brain development, p73 and p63 are widely detected in pyramidal neurons of the adult human cortex and hippocampus at protein and mRNA levels, pointing to a role of both genes in neuronal maintenance in adulthood. © 2010 Elsevier B.V.

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Wang XD, Lapi E, Sullivan A, Ratnayaka I, Goldin R, Hay R, Lu X. 2011. SUMO-modified nuclear cyclin D1 bypasses Ras-induced senescence Cell Death and Differentiation, 18 (2), pp. 304-314. | Show Abstract | Read more

Oncogene-induced senescence represents a key tumor suppressive mechanism. Here, we show that Ras oncogene-induced senescence can be mediated by the recently identified haploinsufficient tumor suppressor apoptosis-stimulating protein of p53 (ASPP) 2 through a novel and p53/p19 Arf /p21 waf1/cip1-independent pathway. ASPP2 suppresses Ras-induced small ubiquitin-like modifier (SUMO)-modified nuclear cyclin D1 and inhibits retinoblastoma protein (Rb) phosphorylation. The lysine residue, K33, of cyclin D1 is a key site for this newly identified regulation. In agreement with the fact that its nuclear localization is required for its oncogenic activity, we show that nuclear cyclin D1 is far more potent than wild-type (WT) cyclin D1 in bypassing Ras-induced senescence. Thus, this study identifies SUMO modification as a positive regulator of nuclear cyclin D1, and reveals a new way by which cell cycle entry and senescence are regulated. © 2011 Macmillan Publishers Limited All rights reserved.

Slee EA, Benassi B, Goldin R, Zhong S, Ratnayaka I, Blandino G, Lu X. 2010. Phosphorylation of Ser312 contributes to tumor suppression by p53 in vivo. Proc Natl Acad Sci U S A, 107 (45), pp. 19479-19484. | Show Abstract | Read more

The tumor suppressor p53 is a master sensor of stress, and posttranslational modifications are key in controlling its stability and transcriptional activities. p53 can be phosphorylated on at least 23 Ser/Thr residues, the majority of which are phosphorylated by stress-related kinases. An exception is Ser315 in human p53 (Ser312 in mouse), which is predominantly phosphorylated by cell cycle-related kinases. To understand the biological importance of Ser312 phosphorylation in vivo, we generated p53Ser312Ala knock-in mice. We show here that, although Ser312 is not essential for mouse life span under normal physiological conditions, Ser312Ala mutation dampens p53's activity during embryonic development. This is evident from its partial rescue of embryonic lethality caused by Mdm4 deletion. In agreement with the notion that Ser312 mutation weakens p53 function, Ser312Ala mice are also more susceptible to tumorigenesis following a sublethal ionizing radiation dose. Importantly, in the cohort studied, Ser312 mutation predisposes mice to develop thymic lymphomas and liver tumors, partly due to p53Ser312Ala's inability to fully induce a set of p53 target genes including p21 and cyclin G1. Thus, we demonstrate that phosphorylation of Ser312 is required for p53 to function fully as a tumor suppressor in vivo.

Caballero OL, Zhao Q, Rimoldi D, Stevenson BJ, Svobodová S, Devalle S, Röhrig UF, Pagotto A, Michielin O, Speiser D et al. 2010. Frequent MAGE mutations in human melanoma. PLoS One, 5 (9), pp. e12773-e12773. | Show Abstract | Read more

BACKGROUND: Cancer/testis (CT) genes are expressed only in the germ line and certain tumors and are most frequently located on the X-chromosome (the CT-X genes). Amongst the best studied CT-X genes are those encoding several MAGE protein families. The function of MAGE proteins is not well understood, but several have been shown to potentially influence the tumorigenic phenotype. METHODOLOGY/PRINCIPAL FINDINGS: We undertook a mutational analysis of coding regions of four CT-X MAGE genes, MAGEA1, MAGEA4, MAGEC1, MAGEC2 and the ubiquitously expressed MAGEE1 in human melanoma samples. We first examined cell lines established from tumors and matching blood samples from 27 melanoma patients. We found that melanoma cell lines from 37% of patients contained at least one mutated MAGE gene. The frequency of mutations in the coding regions of individual MAGE genes varied from 3.7% for MAGEA1 and MAGEA4 to 14.8% for MAGEC2. We also examined 111 fresh melanoma samples collected from 86 patients. In this case, samples from 32% of the patients exhibited mutations in one or more MAGE genes with the frequency of mutations in individual MAGE genes ranging from 6% in MAGEA1 to 16% in MAGEC1. SIGNIFICANCE: These results demonstrate for the first time that the MAGE gene family is frequently mutated in melanoma.

Wang XD, Lapi E, Sullivan A, Ratnayaka I, Goldin R, Hay R, Lu X. 2011. SUMO-modified nuclear cyclin D1 bypasses Ras-induced senescence. Cell Death Differ, 18 (2), pp. 304-314. | Show Abstract | Read more

Oncogene-induced senescence represents a key tumor suppressive mechanism. Here, we show that Ras oncogene-induced senescence can be mediated by the recently identified haploinsufficient tumor suppressor apoptosis-stimulating protein of p53 (ASPP) 2 through a novel and p53/p19(Arf)/p21(waf1/cip1)-independent pathway. ASPP2 suppresses Ras-induced small ubiquitin-like modifier (SUMO)-modified nuclear cyclin D1 and inhibits retinoblastoma protein (Rb) phosphorylation. The lysine residue, K33, of cyclin D1 is a key site for this newly identified regulation. In agreement with the fact that its nuclear localization is required for its oncogenic activity, we show that nuclear cyclin D1 is far more potent than wild-type (WT) cyclin D1 in bypassing Ras-induced senescence. Thus, this study identifies SUMO modification as a positive regulator of nuclear cyclin D1, and reveals a new way by which cell cycle entry and senescence are regulated.

Sottocornola R, Royer C, Vives V, Tordella L, Zhong S, Wang Y, Ratnayaka I, Shipman M, Cheung A, Gaston-Massuet C et al. 2010. ASPP2 binds Par-3 and controls the polarity and proliferation of neural progenitors during CNS development. Dev Cell, 19 (1), pp. 126-137. | Show Abstract | Read more

Cell polarity plays a key role in the development of the central nervous system (CNS). Interestingly, disruption of cell polarity is seen in many cancers. ASPP2 is a haplo-insufficient tumor suppressor and an activator of the p53 family. In this study, we show that ASPP2 controls the polarity and proliferation of neural progenitors in vivo, leading to the formation of neuroblastic rosettes that resemble primitive neuroepithelial tumors. Consistent with its role in cell polarity, ASPP2 influences interkinetic nuclear migration and lamination during CNS development. Mechanistically, ASPP2 maintains the integrity of tight/adherens junctions. ASPP2 binds Par-3 and controls its apical/junctional localization without affecting its expression or Par-3/aPKC lambda binding. The junctional localization of ASPP2 and Par-3 is interdependent, suggesting that they are prime targets for each other. These results identify ASPP2 as a regulator of Par-3, which plays a key role in controlling cell proliferation, polarity, and tissue organization during CNS development.

Lu X. 2010. Tied up in loops: positive and negative autoregulation of p53. Cold Spring Harb Perspect Biol, 2 (5), pp. a000984. | Show Abstract | Read more

The tumor suppressor p53 is a master sensor of stress that controls many biological functions, including implantation, cell-fate decisions, metabolism, and aging. In response to a defined stress signal such as gamma radiation, the response of p53 is heterogeneous in vivo. Like a complex barcode, the ability of p53 to function as a central hub that integrates defined stress signals into decisive cellular responses, in a time- and cell-type dependent manner, is facilitated by the extraordinary complexity of its regulation. Key components of this barcode are the autoregulation loops, which positively or negatively regulate p53's activities. Thus, this article focuses on reviewing our current understanding of how autoregulation loops formed between p53 and how its transcriptional targets regulate the activities of p53 at a variety of levels, through mdm2-dependent and -independent pathways. Knowing that a large number of autoregulation loops exist that influence p53's activity, our future challenge is to elucidate which of these play a central role in regulating p53, under which conditions, in response to what stress, and at which particular stage of our lives. Such knowledge may ultimately lead to the development of more effective anticancer therapeutics.

Gillotin S, Yap D, Lu X. 2010. Mutation at Ser392 specifically sensitizes mutant p53H175 to mdm2-mediated degradation. Cell Cycle, 9 (7), pp. 1390-1398. | Show Abstract | Read more

Mdm2 is one of the main E3 ubiquitin ligases, which targets both wild type and mutant p53 for degradation. The ability of post-translational modifications, such as phosphorylation, to modulate the function and stability of wild type p53 has been extensively studied. However, their ability to modulate the functions and stability of mutant forms of p53 remains poorly documented. Here we show, for the first time, that the stability of mutant p53 can be regulated by phosphorylation. Mutation of serine 392 to alanine shortens the half life of p53H175, and renders p53H175A392 more sensitive to mdm2-mediated degradation than p53H175. This effect of Ser392 phosphorylation specifically affects p53H175, a misfolded mutant, and does not affect p53W248 which maintains a native conformation. Detailed analysis subsequently showed that the reduced stability of p53H175A392 is not due to an increase in mdm2/p300 binding or polyubiquitin chain formation, uncoupling the extent of polyubiquitin chain formation and the stability of mutant p53. This is supported by the observation that Ser392 mutation enhances polyubiquitin chain formation on p53W248, without reducing its stability. These results suggest that the inhibition of phosphorylation at Ser392 of p53, together with the use of an mdm2-enhancing agent such as nutlin, could present a new therapeutic strategy with which to treat tumors expressing mutant p53H175.

Hernández-Acosta NC, Cabrera-Socorro A, Morlans MP, Delgado FJ, Suárez-Solá ML, Sottocornola R, Lu X, González-Gómez M, Meyer G. 2011. Dynamic expression of the p53 family members p63 and p73 in the mouse and human telencephalon during development and in adulthood. Brain Res, 1372 pp. 29-40. | Show Abstract | Read more

p63 and p73, family members of the tumor suppressor p53, are critically involved in the life and death of mammalian cells. They display high homology and may act in concert. The p73 gene is relevant for brain development, and p73-deficient mice display important malformations of the telencephalon. In turn, p63 is essential for the development of stratified epithelia and may also play a part in neuronal survival and aging. We show here that p63 and p73 are dynamically expressed in the embryonic and adult mouse and human telencephalon. During embryonic stages, Cajal-Retzius cells derived from the cortical hem co-express p73 and p63. Comparison of the brain phenotypes of p63- and p73- deficient mice shows that only the loss of p73 function leads to the loss of Cajal-Retzius cells, whereas p63 is apparently not essential for brain development and Cajal-Retzius cell formation. In postnatal mice, p53, p63, and p73 are present in cells of the subventricular zone (SVZ) of the lateral ventricle, a site of continued neurogenesis. The neurogenetic niche is reduced in size in p73-deficient mice, and the numbers of young neurons near the ventricular wall, marked with doublecortin, Tbr1 and calretinin, are dramatically decreased, suggesting that p73 is important for SVZ proliferation. In contrast to their restricted expression during brain development, p73 and p63 are widely detected in pyramidal neurons of the adult human cortex and hippocampus at protein and mRNA levels, pointing to a role of both genes in neuronal maintenance in adulthood.

Mak VC, Lee L, Siu MK, Wong OG, Lu X, Ngan HY, Wong ES, Cheung AN. 2011. Downregulation of ASPP1 in gestational trophoblastic disease: correlation with hypermethylation, apoptotic activity and clinical outcome. Mod Pathol, 24 (4), pp. 522-532. | Show Abstract | Read more

Gestational trophoblastic disease encompasses a spectrum of trophoblastic lesions including true neoplasms such as choriocarcinomas and the potentially malignant hydatidiform moles, which may develop persistent disease requiring chemotherapy. ASPP1, a member of apoptosis-stimulating proteins of p53 (ASPPs), is a proapoptotic protein that can stimulate apoptosis through its interaction with p53. We evaluated the promoter methylation and expression profiles of ASPP1 in different trophoblastic tissues and its in vitro functional effect on two choriocarcinoma cell lines, namely JEG-3 and JAR. Significant downregulation of ASPP1 mRNA and protein levels was demonstrated in hydatidiform moles and choriocarcinomas, when compared with normal placentas by quantitative-PCR and immunohistochemistry. The ASPP1 mRNA level was significantly correlated with its hypermethylation status, evaluated with methylation-specific PCR, in placenta and gestational trophoblastic disease samples (P=0.024). Moreover, lower ASPP1 immunoreactivity was shown in hydatidiform moles that progressed to persistent gestational trophoblastic neoplasms than in those that regressed (P=0.045). A significant correlation was also found between expression of ASPP1 and proliferative indices (assessed by Ki67 and MCM7), apoptotic activity (M30 CytoDeath antibody), p53 and caspase-8 immunoreactivities. An in vitro study showed that ectopic expression of ASPP1 could trigger apoptosis through intrinsic and extrinsic pathways as indicated by an increase in cleaved caspase-9 and Fas ligand protein expression. The latter suggests a hitherto unreported novel link between ASPP1 and the extrinsic pathway of apoptosis. Our findings suggest that downregulation of ASPP1 by hypermethylation may be involved in the pathogenesis and progress of gestational trophoblastic disease, probably through its effect on apoptosis.

Zhao J, Wu G, Bu F, Lu B, Liang A, Cao L, Tong X, Lu X, Wu M, Guo Y. 2010. Epigenetic silence of ankyrin-repeat-containing, SH3-domain-containing, and proline-rich-region- containing protein 1 (ASPP1) and ASPP2 genes promotes tumor growth in hepatitis B virus-positive hepatocellular carcinoma. Hepatology, 51 (1), pp. 142-153. | Show Abstract | Read more

UNLABELLED: The ankyrin-repeat-containing, SH3-domain-containing, and proline-rich-region-containing protein (ASPP) family of proteins regulates apoptosis through interaction with p53 and its family members. This study evaluated the epigenetic regulation of ASPP1 and ASPP2 in hepatitis B virus (HBV)-positive hepatocellular carcinoma (HCC) and explores the effects of down-regulation of ASPP1 and ASPP2 on the development of HCC. HCC cell lines and tissues from HCC patients were used to examine the expression and methylation of ASPP1 and ASPP2. The expression of ASPP1 and ASPP2 was diminished in HCC cells by epigenetic silence owing to hypermethylation of ASPP1 and ASPP2 promoters. Analyses of 51 paired HCC and surrounding nontumor tissues revealed that methylation of ASPP1 and ASPP2 was associated with the decreased expression of ASPP1 and ASPP2 in tumor tissues and the early development of HCC. Moreover, ASPP2 became methylated upon HBV x protein (HBx) expression. The suppressive effects on tumor growth by ASPP1 and ASPP2 were examined with RNA interference-mediated gene silence. Down-regulation of ASPP1 and ASPP2 promoted the growth of HCC cells in soft agar and in nude mice and decreased the sensitivity of HCC cells to apoptotic stimuli. CONCLUSION: ASPP1 and ASPP2 genes are frequently down-regulated by DNA methylation in HBV-positive HCC, which may play important roles in the development of HCC. These findings provide new insight into the molecular mechanisms leading to hepatocarcinogenesis and may have potent therapeutic applications.

Aylon Y, Ofir-Rosenfeld Y, Yabuta N, Lapi E, Nojima H, Lu X, Oren M. 2010. The Lats2 tumor suppressor augments p53-mediated apoptosis by promoting the nuclear proapoptotic function of ASPP1. Genes Dev, 24 (21), pp. 2420-2429. | Show Abstract | Read more

Apoptosis is an important mechanism to eliminate potentially tumorigenic cells. The tumor suppressor p53 plays a pivotal role in this process. Many tumors harbor mutant p53, but others evade its tumor-suppressive effects by altering the expression of proteins that regulate the p53 pathway. ASPP1 (apoptosis-stimulating protein of p53-1) is a key mediator of the nuclear p53 apoptotic response. Under basal conditions, ASPP1 is cytoplasmic. We report that, in response to oncogenic stress, the tumor suppressor Lats2 (large tumor suppressor 2) phosphorylates ASPP1 and drives its translocation into the nucleus. Together, Lats2 and ASPP1 shunt p53 to proapoptotic promoters and promote the death of polyploid cells. These effects are overridden by the Yap1 (Yes-associated protein 1) oncoprotein, which disrupts Lats2-ASPP1 binding and antagonizes the tumor-suppressing function of the Lats2/ASPP1/p53 axis.

Shi H, Tan SJ, Zhong H, Hu W, Levine A, Xiao CJ, Peng Y, Qi XB, Shou WH, Ma RL et al. 2009. Winter temperature and UV are tightly linked to genetic changes in the p53 tumor suppressor pathway in Eastern Asia. Am J Hum Genet, 84 (4), pp. 534-541. | Show Abstract | Read more

The tumor suppressor p53 is a master sensor of stress. Two human-specific polymorphisms, p53 codon 72 and MDM2 SNP309, influence the activities of p53. There is a tight association between cold winter temperature and p53 Arg72 and between low UV intensity and MDM2 SNP309 G/G in a cohort of 4029 individuals across Eastern Asia that suggests causative selection. Moreover, the two polymorphisms are not coselected. Haplotype-based selection analysis further suggests that this is a striking example of two functional polymorphisms being strongly selected for in human populations in response to environmental stresses.

Shi Y, Zhu J, Salomoni P, Tucci P, Lu X. 2009. A Sino-British frontier workshop of cancer biology. Cell Death Differ, 16 (4), pp. 648-650. | Read more

Lapi E, Di Agostino S, Donzelli S, Gal H, Domany E, Rechavi G, Pandolfi PP, Givol D, Strano S, Lu X, Blandino G. 2008. PML, YAP, and p73 are components of a proapoptotic autoregulatory feedback loop. Mol Cell, 32 (6), pp. 803-814. | Show Abstract | Read more

p73 has been identified as a structural and functional homolog of the tumor suppressor p53. The transcriptional coactivator Yes-associated protein (YAP) has been demonstrated to interact with and to enhance p73-dependent apoptosis in response to DNA damage. Here, we show the existence of a proapoptotic autoregulatory feedback loop between p73, YAP, and the promyelocytic leukemia (PML) tumor suppressor gene. We demonstrate that PML is a direct transcriptional target of p73/YAP, and we show that PML transcriptional activation by p73/YAP is under the negative control of the proto-oncogenic Akt/PKB kinase. Importantly, we find that PML and YAP physically interact through their PVPVY and WW domains, respectively, causing PML-mediated sumoylation and stabilization of YAP. Hence, we determine a mechanistic pathway in response to DNA damage that could have relevant implications for the treatment of human cancer.

Hu C, van Dommelen J, van der Heijden R, Spijksma G, Reijmers TH, Wang M, Slee E, Lu X, Xu G, van der Greef J, Hankemeier T. 2008. RPLC-ion-trap-FTMS method for lipid profiling of plasma: method validation and application to p53 mutant mouse model. J Proteome Res, 7 (11), pp. 4982-4991. | Show Abstract | Read more

A reversed-phase liquid chromatography-linear ion trap-Fourier transform ion cyclotron resonance-mass spectrometric method was developed for the profiling of lipids in human and mouse plasma. With the use of a fused-core C 8 column and a binary gradient, more than 160 lipids belonging to eight different classes were detected in a single LC-MS run. The method was fully validated and the analytical characteristics such as linearity ( R (2), 0.994-1.000), limit of detection (0.08-1.28 microg/mL plasma), repeatability (RSD, 2.7-7.9%) and intermediate precision (RSD, 2.7-15.6%) were satisfactory. The method was successfully applied to p53 mutant mice plasma for studying some phenotypic effects of p53 expression.

Murray-Zmijewski F, Slee EA, Lu X. 2008. A complex barcode underlies the heterogeneous response of p53 to stress. Nat Rev Mol Cell Biol, 9 (9), pp. 702-712. | Show Abstract | Read more

The tumour suppressor p53 is activated following stress and initiates a heterogeneous response in a cell-, tissue- and stress-dependent manner. This heterogeneity is reflected in the different physiological outcomes that follow p53 activation. One mechanism that may contribute to this variability is the promoter selectivity of p53 target genes. p53 is at the hub of numerous signalling pathways that are triggered in response to particular stresses, all of which can leave their mark on p53 by way of post-translational modifications and interactions with cofactors. The precise combination of these marks, much like the bars in a barcode, dictates the behaviour of p53 in any given situation.

Wilson MD, Wang D, Wagner R, Breyssens H, Gertsenstein M, Lobe C, Lu X, Nagy A, Burke RD, Koop BF, Howard PL. 2008. ARS2 is a conserved eukaryotic gene essential for early mammalian development. Mol Cell Biol, 28 (5), pp. 1503-1514. | Show Abstract | Read more

Determining the functions of novel genes implicated in cell survival is directly relevant to our understanding of mammalian development and carcinogenesis. ARS2 is an evolutionarily conserved gene that confers arsenite resistance on arsenite-sensitive Chinese hamster ovary cells. Little is known regarding the function of ARS2 in mammals. We report that ARS2 is transcribed throughout embryonic development and is expressed ubiquitously in mouse and human tissues. The mouse ARS2 protein is predominantly localized to the nucleus, and this nuclear localization is ablated in ARS2-null embryos, which in turn die around the time of implantation. After 24 h of culture, ARS2-null blastocysts contained a significantly greater number of apoptotic cells than wild-type or heterozygous blastocysts. By 48 h of in vitro culture, null blastocysts invariably collapsed and failed to proliferate. These data indicate ARS2 is essential for early mammalian development and is likely involved in an essential cellular process. The analysis of data from several independent protein-protein interaction studies in mammals, combined with functional studies of its Arabidopsis ortholog, SERRATE, suggests that this essential process is related to RNA metabolism.

Robinson RA, Lu X, Jones EY, Siebold C. 2008. Biochemical and structural studies of ASPP proteins reveal differential binding to p53, p63, and p73. Structure, 16 (2), pp. 259-268. | Show Abstract | Read more

ASPP1 and ASPP2 are activators of p53-dependent apoptosis, whereas iASPP is an inhibitor of p53. Binding assays showed differential binding for C-terminal domains of iASPP and ASPP2 to the core domains of p53 family members p53, p63, and p73. We also determined a high-resolution crystal structure for the C terminus of iASPP, comprised of four ankyrin repeats and an SH3 domain. The crystal lattice revealed an interaction between eight sequential residues in one iASPP molecule and the p53-binding site of a neighboring molecule. ITC confirmed that a peptide corresponding to the crystallographic interaction shows specific binding to iASPP. The contributions of ankyrin repeat residues, in addition to those of the SH3 domain, generate distinctive architecture at the p53-binding site suitable for inhibition by small molecules. These results suggest that the binding properties of iASPP render it a target for antitumor therapeutics and provide a peptide-based template for compound design.

Hou L, Cai Y, Chen J, Xin HM, Gao X, Lu X, Zhong S, Liu ZJ. 2008. Effect of iASPP RNAi vector transfection on apoptosis of MCF-7 Chinese Journal of Cancer Prevention and Treatment, 15 (21), | Show Abstract

Objective: To observe the effect of the iASPP RNAi vector transfection on the apoptosis of breat cancer cell MCF-7. Methods: The specific siRNA sequence was designed according to the genebank. The sequence was cloned into PGCsilencer™ H1/Neo/GFP. The recombinant plasmid was transfected into MCF-7 by Lipofectamine™ 2000. The iASPP expression was analyzed by RT-PCR and Western blot. The cell apoptosis was detected by FCM. Results: The iASPP expression in MCF-7 cell lines was descended from 40% to 50% after the RNAi transfection. The expression of p53 protein increased from 0.37 to 0.64, and the apoptosis rate increased from 17.8% and 16.2% to 53.5% and 51.3%. Conclusion: The inhibition of endogenous iASPP may resume the apoptosis activity of p53 in MCF-7.

Liu ZJ, Cai Y, Hou L, Gao X, Xin HM, Lu X, Zhong S, Gu SZ, Chen J. 2008. Effect of RNA interference of iASPP on the apoptosis in MCF-7 breast cancer cells. Cancer Invest, 26 (9), pp. 878-882. | Show Abstract | Read more

ASPP family is proved to be apoptotic specific regulators of p53. Among them, iASPP acts as an inhibitor of p53. To investigate the effect of the iASPP RNAi on the apoptosis of breast cancer cell MCF-7, we transfected the recombinant plasmid PGCsilencer H1/Neo/GFP/RNAi into MCF-7. The iASPP expression was analyzed by RT-PCR and Western blot. The cell apoptosis was detected by FCM. The results show that the expression of iASPP is descended and the apoptosis rate is increased after transfection. Therefore, we conclude that inhibition of expression of iASPP may resume the ability of p53 to induce apoptosis in MCF-7 cells.

Dufour JF, Huber O, Kozma SC, Lu X, Toftgård R. 2007. Tumour suppressors in liver carcinogenesis. J Hepatol, 47 (6), pp. 860-867. | Show Abstract | Read more

The circuitous cell signalling pathways of hepatocytes comprise several factors that operate to downgrade or even interrupt the transmission of a given signal. These down-regulating influences are essential to keep cell proliferation and cell survival in check and if impaired, can alter a delicate balance in favour of cell proliferation. Each signalling pathway that has been implicated in carcinogenesis is influenced by both oncogenic factors that promote tumour growth when activated as well as tumour suppressor proteins that have to be impaired to favour tumour growth. This summary of the Tumour Suppressors in Liver Carcinogenesis Symposium held at the 2007 EASL Annual Meeting discusses four pathways with pre-eminent tumour suppressor activity, each involved in hepatocarcinogenesis: p53, mTOR, beta-catenin and hedgehog.

Mantovani F, Tocco F, Girardini J, Smith P, Gasco M, Lu X, Crook T, Del Sal G. 2007. The prolyl isomerase Pin1 orchestrates p53 acetylation and dissociation from the apoptosis inhibitor iASPP. Nat Struct Mol Biol, 14 (10), pp. 912-920. | Show Abstract | Read more

The tumor-suppressor function of p53 relies on its transcriptional activity, which is modulated by post-translational modifications and interactions with regulatory proteins. The prolyl isomerase Pin1 has a central role in transducing phosphorylation of p53 into conformational changes that affect p53 stability and function. We found that Pin1 is required for efficient loading of p53 on target promoters upon stress. In addition, Pin1 is recruited to chromatin by p53 and stimulates binding of the p300 acetyltransferase and consequent p53 acetylation. Accordingly, tumor-associated mutations at Pin1-binding residues within the p53 proline-rich domain hamper acetylation of p53 by p300. After phosphorylation of p53 at Ser46 triggered by cytotoxic stimuli, Pin1 also mediates p53's dissociation from the apoptosis inhibitor iASPP, promoting cell death. In tumors bearing wild-type p53, expression of Pin1 and iASPP are inversely correlated, supporting the clinical relevance of these interactions.

Liu ZJ, Xin HM, Chen J, Lu X, Zhong S, Gu SZ, Wang G, Liu L, Cai Y, Hou L. 2007. A new strategy to resume the apoptosis activity of p53 in leukemia cell lines retaining wild-type p53. Leuk Res, 31 (8), pp. 1156-1158. | Read more

Bell HS, Dufes C, O'Prey J, Crighton D, Bergamaschi D, Lu X, Schätzlein AG, Vousden KH, Ryan KM. 2007. A p53-derived apoptotic peptide derepresses p73 to cause tumor regression in vivo. J Clin Invest, 117 (4), pp. 1008-1018. | Show Abstract | Read more

The tumor suppressor p53 is a potent inducer of tumor cell death, and strategies exist to exploit p53 for therapeutic gain. However, because about half of human cancers contain mutant p53, application of these strategies is restricted. p53 family members, in particular p73, are in many ways functional paralogs of p53, but are rarely mutated in cancer. Methods for specific activation of p73, however, remain to be elucidated. We describe here a minimal p53-derived apoptotic peptide that induced death in multiple cell types regardless of p53 status. While unable to activate gene expression directly, this peptide retained the capacity to bind iASPP - a common negative regulator of p53 family members. Concordantly, in p53-null cells, this peptide derepressed p73, causing p73-mediated gene activation and death. Moreover, systemic nanoparticle delivery of a transgene expressing this peptide caused tumor regression in vivo via p73. This study therefore heralds what we believe to be the first strategy to directly and selectively activate p73 therapeutically and may lead to the development of broadly applicable agents for the treatment of malignant disease.

Gubser C, Bergamaschi D, Hollinshead M, Lu X, van Kuppeveld FJ, Smith GL. 2007. A new inhibitor of apoptosis from vaccinia virus and eukaryotes. PLoS Pathog, 3 (2), pp. e17. | Show Abstract | Read more

A new apoptosis inhibitor is described from vaccinia virus, camelpox virus, and eukaryotic cells. The inhibitor is a hydrophobic, multiple transmembrane protein that is resident in the Golgi and is named GAAP (Golgi anti-apoptotic protein). Stable expression of both viral GAAP (v-GAAP) and human GAAP (h-GAAP), which is expressed in all human tissues tested, inhibited apoptosis induced by intrinsic and extrinsic apoptotic stimuli. Conversely, knockout of h-GAAP by siRNA induced cell death by apoptosis. v-GAAP and h-GAAP display overlapping functions as shown by the ability of v-GAAP to complement for the loss of h-GAAP. Lastly, deletion of the v-GAAP gene from vaccinia virus did not affect virus replication in cell culture, but affected virus virulence in a murine infection model. This study identifies a new regulator of cell death that is highly conserved in evolution from plants to insects, amphibians, mammals, and poxviruses.

Sullivan A, Lu X. 2007. ASPP: a new family of oncogenes and tumour suppressor genes. Br J Cancer, 96 (2), pp. 196-200. | Show Abstract | Read more

The apoptosis stimulating proteins of p53 (ASPP) family consists of three members, ASPP1, ASPP2 and iASPP. They bind to proteins that are key players in controlling apoptosis (p53, Bcl-2 and RelA/p65) and cell growth (APCL, PP1). So far, the best-known function of the ASPP family members is their ability to regulate the apoptotic function of p53 and its family members, p63 and p73. Biochemical and genetic evidence has shown that ASPP1 and ASPP2 activate, whereas iASPP inhibits, the apoptotic but not the cell-cycle arrest function of p53. The p53 tumour suppressor gene, one of the most frequently mutated genes in human cancer, is capable of suppressing tumour growth through its ability to induce apoptosis or cell-cycle arrest. Thus, the ASPP family of proteins helps to determine how cells choose to die and may therefore be a novel target for cancer therapy.

Liu ZJ, Xin HM, Chen J, Lu X, Zhong S, Gu SZ, Wang G, Liu L, Cai Y, Hou L. 2007. A new strategy to resume the apoptosis activity of p53 in leukemia cell lines retaining wild-type p53 Leukemia Research, 31 (8), pp. 1164-1166. | Read more

Bergamaschi D, Samuels Y, Sullivan A, Zvelebil M, Breyssens H, Bisso A, Del Sal G, Syed N, Smith P, Gasco M et al. 2006. iASPP preferentially binds p53 proline-rich region and modulates apoptotic function of codon 72-polymorphic p53. Nat Genet, 38 (10), pp. 1133-1141. | Show Abstract | Read more

iASPP is one of the most evolutionarily conserved inhibitors of p53, whereas ASPP1 and ASPP2 are activators of p53. We show here that, in addition to the DNA-binding domain, the ASPP family members also bind to the proline-rich region of p53, which contains the most common p53 polymorphism at codon 72. Furthermore, the ASPP family members, particularly iASPP, bind to and regulate the activity of p53Pro72 more efficiently than that of p53Arg72. Hence, escape from negative regulation by iASPP is a newly identified mechanism by which p53Arg72 activates apoptosis more efficiently than p53Pro72.

Vives V, Slee EA, Lu X. 2006. ASPP2: a gene that controls life and death in vivo. Cell Cycle, 5 (19), pp. 2187-2190. | Show Abstract | Read more

The fundamental role of apoptosis in tumor prevention and the important role of p53 in this process are now universally recognized. Recently, several families of p53-binding proteins have been shown to influence p53's decision to direct the cells either into the apoptotic pathway or in cell cycle arrest. Among them, the ASPP family specifically regulate p53-dependent apoptosis. Its member ASPP2 was discovered more than 10 years ago as a binding partner of p53 and its role as a positive regulator of p53 mediated apoptosis has been clearly established in vitro. However, its physiological importance in vivo has just emerged through the generation and characterisation of the ASPP2-deficient mice. We now know that ASPP2 is a haploinsufficient tumor suppressor and an important activator of p53 during mouse development and tumor suppression in vivo. ASPP2 might be a novel target for future cancer therapy.

Braithwaite AW, Del Sal G, Lu X. 2006. Some p53-binding proteins that can function as arbiters of life and death. Cell Death Differ, 13 (6), pp. 984-993. | Show Abstract | Read more

Four sets of p53-binding proteins are discussed in this review. These are the E2F family, the ASPP family, Y-box-binding protein YB1, and the prolyl isomerase Pin1. Each appears to play a role in the decision by p53 to induce an arrest of cell proliferation or apoptosis and they may also be independent markers of cancer. Their activities appear to be linked with the cell cycle and they may also interact with each other. In this review, the properties of each protein class are discussed as well as how they affect p53 functions. A model is proposed as to how their activities might be coordinated.

Thornton JK, Dalgleish C, Venables JP, Sergeant KA, Ehrmann IE, Lu X, Saunders PT, Elliott DJ. 2006. The tumour-suppressor protein ASPP1 is nuclear in human germ cells and can modulate ratios of CD44 exon V5 spliced isoforms in vivo. Oncogene, 25 (22), pp. 3104-3112. | Show Abstract | Read more

The ASPP1 (Apoptosis Stimulating Protein of p53) protein is an important tumour-suppressor. We have detected a novel protein interaction between the human ASPP1 (hASPP1) protein and the predominantly nuclear adaptor protein SAM68. In the human testis, full-length endogenous hASPP1 protein is located in the nucleus like SAM68, predominantly within meiotic and postmeiotic cells. Mouse ASPP1 (mASPP1) protein is mainly expressed in the brain and testis. The interaction with nuclear SAM68 is likely to be restricted to human germ cells, since endogenous mASPP1 protein is exclusively cytoplasmic. The C-terminal region of hASPP1 efficiently targeted a fused GFP molecule to the nucleus, whereas the N-terminus of hASPP1 targeted GFP to the cytoplasm. In the context of the full-length molecule this cytoplasmic targeting sequence is dominant in HEK293 and Saos-2 cells, since full-length hASPP1-GFP is almost exclusively cytoplasmic. Despite its predominantly cytoplasmic location, we show that ASPP1-GFP expression in HEK293 cells can regulate the ratio of alternative spliced isoforms derived from a pre-mRNA regulated downstream of cytoplasmic signalling pathways, and our data suggest that ASPP1 may operate in this case downstream or parallel to RAS signalling pathways.

Vives V, Su J, Zhong S, Ratnayaka I, Slee E, Goldin R, Lu X. 2006. ASPP2 is a haploinsufficient tumor suppressor that cooperates with p53 to suppress tumor growth. Genes Dev, 20 (10), pp. 1262-1267. | Show Abstract | Read more

ASPP2 stimulates the apoptotic function of the p53 family in vivo. We show here that ASPP2-/- pups died before weaning. This postnatal lethality was significantly enhanced in p53+/- background and both deletions are synthetic lethal. ASPP2+/- mice developed spontaneous tumors. The tumor onset was accelerated by gamma-irradiation or in p53+/- background. Tumors derived from ASPP2+/- mice retained wild-type ASPP2 allele even though some of them lost p53. These provide the first genetic evidence that ASPP2 is a haploinsufficient tumor suppressor that shares overlapping function(s) with p53 in mouse development and tumor suppression.

Trigiante G, Lu X. 2006. ASPP [corrected] and cancer. Nat Rev Cancer, 6 (3), pp. 217-226. | Show Abstract | Read more

One of the most frequently mutated genes in human cancers, tumour suppressor p53 (TP53), can induce cell-cycle arrest and apoptosis. The apoptotic function of p53 is tightly linked to its tumour-suppression function and the efficacy of many cancer therapies depends on this. The identification of a new family of proteins, known as ASPPs (ankyrin-repeat-, SH3-domain- and proline-rich-region-containing proteins), has led to the discovery of a novel mechanism that selectively regulates the apoptotic function, but not the cell-cycle-arrest function, of p53, and gives an insight into how p53 responds to different stress signals. ASPPs might be new molecular targets for cancer therapy.

Liu ZJ, Lu X, Zhong S. 2005. ASPP--Apoptotic specific regulator of p53. Biochim Biophys Acta, 1756 (1), pp. 77-80. | Show Abstract | Read more

The p53 protein is one of the best-known tumor suppressors. The recently identified ASPP family (apoptosis-stimulating protein of p53) can interfere with the working of p53. Three members of ASPP family are proved to be apoptotic specific regulators of p53. The discovery of ASPP family may answer such questions as "how cells choose to die". Understanding the ASPP status in human cancer will allow us to develop better strategies to treat cancer.

Fogal V, Hsieh JK, Royer C, Zhong S, Lu X. 2005. Cell cycle-dependent nuclear retention of p53 by E2F1 requires phosphorylation of p53 at Ser315. EMBO J, 24 (15), pp. 2768-2782. | Show Abstract | Read more

We show here that the cell cycle-dependent DNA-binding and transcriptional activity of p53 correlates with E2F expression in human primary fibroblasts. E2F1 binds and stimulates DNA-binding, transactivation and apoptotic functions of p53 but not p63 and p73. E2F1 binds residues 347-370 of p53 and enhances nuclear retention of Ser315 phosphorylated p53. This regulation of p53 by E2F1 is cell cycle dependent, as the cellular distribution of Ser315 phosphorylated p53 is associated with the periodic expression of E2F and cyclin A throughout the cell cycle. This is the first demonstration that the activities of p53 are regulated during the cell cycle by E2F/p53 interactions and that phosphorylation of p53 at Ser315 is required for this regulation.

Bergamaschi D, Samuels Y, Zhong S, Lu X. 2005. Mdm2 and mdmX prevent ASPP1 and ASPP2 from stimulating p53 without targeting p53 for degradation. Oncogene, 24 (23), pp. 3836-3841. | Show Abstract | Read more

Using various mutants of p53 and mdm2, we demonstrate here that both the DNA binding and transactivation function of p53 are required for ASPP1 and ASPP2 to stimulate the apoptotic functions of p53. Mdm2 and mdmx prevent ASPP1 and ASPP2 from stimulating the apoptotic function of p53 by binding and inhibiting the transcriptional activity of p53. Importantly, mdm2 and mdmx can prevent the stimulatory effects of ASPP1 and ASPP2 without targeting p53 for degradation. These data provide a novel mechanism by which mdm2 and mdmx act as potent inhibitors of p53.

Zhang W, Bergamaschi D, Jin B, Lu X. 2005. Posttranslational modifications of p27kip1 determine its binding specificity to different cyclins and cyclin-dependent kinases in vivo. Blood, 105 (9), pp. 3691-3698. | Show Abstract | Read more

Using 2-dimensional gel electrophoresis (2D-gel) analysis, we show here that cell-cycle entry is associated with a significant increase in p27(kip1) phosphorylation in human primary B cells. A similar pattern of increase in p27(kip1) phosphorylation was also seen in 2 fast-growing tumor cell lines, Burkitt lymphoma cell line BL40 and breast carcinoma cell line Cal51, where inactive p27(kip1) is expressed at high levels. Detailed analysis revealed for the first time that different cyclins and cyclin-dependent kinases (cdk's) interact with distinct posttranslationally modified isoforms of p27(kip1) in vivo. Cyclin E but not cyclin A selectively interacts with phosphorylated p27(kip1) isoforms, while cyclin D1 and D2 favor unphosphorylated p27(kip1) isoforms in vivo. Interestingly, cyclin D3 and cdk4 selectively interact with phosphorylated p27(kip1) in BL40 cells. Among all D-type cyclin/cdk4 and cdk6 complexes, cyclin D3/cdk4 is most active in sequestering the inhibitory activity of p27(kip1) in vitro in a cyclinE/cdk2 kinase assay. This novel feature of the binding specificity of p27(kip1) to cyclins and cdk's in vivo is interpreted in the context of overexpression of cyclin D3 in the presence of high levels of p27(kip1) in human B-cell lymphomas with adverse clinical outcome.

Fogal V, Kartasheva NN, Trigiante G, Llanos S, Yap D, Vousden KH, Lu X. 2005. ASPP1 and ASPP2 are new transcriptional targets of E2F. Cell Death Differ, 12 (4), pp. 369-376. | Show Abstract | Read more

The E2F family of transcription factors regulates the expression of a number of genes whose products are involved in cell cycle control, DNA replication and apoptosis. We show here that E2F-1 binds in vivo the promoters of ASPP1 and ASPP2 genes, two activators of p53-mediated apoptosis, E2F-1, E2F-2 and E2F-3 all activate the isolated ASPP1 and ASPP2 promoters. Overexpression or deregulation of E2F-1 increased the expression levels of ASPP1 and ASPP2 mRNA and proteins. The identification of ASPP1 and ASPP2 genes as transcriptional targets of E2F provides another mechanism by which E2F cooperates with p53 to induce apoptosis.

Liu ZJ, Lu X, Zhang Y, Zhong S, Gu SZ, Zhang XB, Yang X, Xin HM. 2005. Downregulated mRNA expression of ASPP and the hypermethylation of the 5'-untranslated region in cancer cell lines retaining wild-type p53. FEBS Lett, 579 (7), pp. 1587-1590. | Show Abstract | Read more

The p53 protein is one of the best-known tumour suppressors. Recently discovered ASPP1 and ASPP2 are specific activators of p53. To understand, if apoptosis-stimulating protein of p53 (ASPP) inactivation offers a selective advantage to tumors that have wild-type p53, we measured the mRNA expression of ASPP1 and ASPP2 in tumor cell lines retaining wide-type p53. In addition, the CpG island methylation status of ASPP1 gene and ASPP2 gene in the 5'-untranslated region was also investigated in order to understand the possible cause of abnormal expression of ASPP1 and ASPP2 in the tumor cell lines retaining wide-type p53. The data showed that mRNA expression of ASPP1 and ASPP2 is downregulated and CpG island tested is hypermethylated. These results indicated that ASPP CpG island aberrant methylation could be one molecular and genetic alteration in wild-type p53 tumours.

Lu X. 2005. p53: a heavily dictated dictator of life and death. Curr Opin Genet Dev, 15 (1), pp. 27-33. | Show Abstract | Read more

In 2003, a p53-expressing adenovirus was approved as a cancer therapy drug in China. Consequently, there has been a surge in the need to understand the regulation of wild type p53 function in vivo. The majority of the progress made during the past two years has focused on the cellular factors and post-translational modifications that regulate the expression levels and activities of p53 in response to stress signals.

Slee EA, Gillotin S, Bergamaschi D, Royer C, Llanos S, Ali S, Jin B, Trigiante G, Lu X. 2004. The N-terminus of a novel isoform of human iASPP is required for its cytoplasmic localization. Oncogene, 23 (56), pp. 9007-9016. | Show Abstract | Read more

ASPP1 and ASPP2 are both proteins that interact with p53 and enhance its ability to induce apoptosis by selectively elevating the expression of proapoptotic p53-responsive genes. iASPP(RAI) is a third member of the family that is the most conserved inhibitor of p53-mediated apoptosis. Here, we have described iASPP, a longer form of iASPP(RAI), which at 828 amino acids is more than twice the size of iASPP(RAI). Using two antibodies that recognize both iASPP and iASPP(RAI), we report that this longer form of iASPP is the predominant form of the molecule expressed in cells. Like iASPP(RAI), iASPP also binds to p53 and inhibits apoptosis induced by p53 overexpression. However, whereas iASPP(RAI) is predominantly nuclear, the N-terminus of iASPP is entirely cytoplasmic, and the longer iASPP is located in both the cytoplasm and the nucleus. The effect upon subcellular localization of the longer N-terminus of iASPP means that this new, longer form of the molecule may be subject to greater regulation and provides another layer in the control of p53-induced apoptosis.

Yap DB, Hsieh JK, Zhong S, Heath V, Gusterson B, Crook T, Lu X. 2004. Ser392 phosphorylation regulates the oncogenic function of mutant p53. Cancer Res, 64 (14), pp. 4749-4754. | Show Abstract | Read more

Despite the wealth of information on the regulation of wild-type p53 function by phosphorylation, nothing is known about the biological effect of phosphorylation on mutant p53. Here we show that p53H175 is phosphorylated like wild-type p53 in cells of the same background. Ser(392) nonphosphorylatable p53 mutants p53H175A392 and p53W248A392 more potently transformed rat embryo fibroblasts in cooperation with the ras oncogene than p53H175S392 and p53W248S392. p53H175A392 also had an enhanced ability to confer cellular resistance to the cytotoxic effect of cisplatin and UV radiation. This correlated with p53H175A392 being a more potent dominant negative mutant than p53H175 in inhibiting the apoptotic functions of wild-type p53. Moreover, p53H175E392, which mimics the phosphorylated form of p53H175, was less able to confer cellular resistance to DNA-damaging agents. p53H175 and p53W248 are phosphorylated like wild-type p53 in cells of the same background. Ser(392) nonphosphorylated p53 was present in human breast tumors expressing mutant p53 including p53H175. Together, these results demonstrated a novel function of Ser(392) phosphorylation in regulating the oncogenic function of mutant p53.

Sullivan A, Syed N, Gasco M, Bergamaschi D, Trigiante G, Attard M, Hiller L, Farrell PJ, Smith P, Lu X, Crook T. 2004. Polymorphism in wild-type p53 modulates response to chemotherapy in vitro and in vivo. Oncogene, 23 (19), pp. 3328-3337. | Show Abstract | Read more

A single-nucleotide polymorphism (SNP) in exon 4 results in expression of either arginine (72R) or proline (72P) at codon 72 of p53. We demonstrate that the in vitro response of cells exposed to anticancer agents is strongly influenced by this SNP in wild-type p53. In inducible systems and in cells expressing the endogenous protein, expression of 72P wild-type p53 results in a predominant G1 arrest, with only a minor apoptosis, at drug concentrations causing extensive apoptosis in cells expressing the 72R wild-type variant. The superior apoptosis-inducing activity of the 72R form correlates with more efficient induction of specific apoptosis-associated genes, and is maximal in the presence of serine 46 (S46). In vivo, the outcome of chemo-radiotherapy of squamous carcinomas is more favourable in cancers retaining a wild-type 72R allele, such cases having higher response rates and longer survival than those with wild-type 72P. Together, these results reveal that this SNP is an important determinant of response to anticancer agents in cells expressing wild-type p53. Analysis of complete p53 genotype (mutation and SNP) merits detailed investigation as a simple means for prediction of treatment response and survival in clinical oncology.

Slee EA, O'Connor DJ, Lu X. 2004. To die or not to die: how does p53 decide? Oncogene, 23 (16), pp. 2809-2818. | Show Abstract | Read more

p53 is frequently mutated in cancer and as a result is one of the most intensely studied tumour suppressors. Analysis of the primitive forms of p53 found in Caenorhabditis elegans and Drosophila, alongside studies using transgenic mouse models, indicate that the induction of apoptosis is both the most conserved function of p53 and vital for tumour suppression. p53-mediated apoptosis occurs through a combination of mechanisms which include pathways that are both dependent and independent of alterations in gene expression. In response to genotoxic insult, these pathways probably act together, thereby amplifying the apoptotic signal. However, the picture is complicated because the p53 activity is determined by stress type and individual cellular characteristics. The numerous p53 responsive genes that have been identified also provide further means of controlling the actions of p53. The recent discoveries of proteins that interact with p53 and specifically regulate the ability of p53 to trigger apoptosis have provided further mechanistic insights into the role of p53 in inducing cell death. Understanding the molecular basis of the proapoptotic action of p53 can assist in our quest to reintroduce or reactivate p53 in human tumours.

Bergamaschi D, Samuels Y, Jin B, Duraisingham S, Crook T, Lu X. 2004. ASPP1 and ASPP2: common activators of p53 family members. Mol Cell Biol, 24 (3), pp. 1341-1350. | Show Abstract | Read more

We recently showed that ASPP1 and ASPP2 stimulate the apoptotic function of p53. We show here that ASPP1 and ASPP2 also induce apoptosis independently of p53. By binding to p63 and p73 in vitro and in vivo, ASPP1 and ASPP2 stimulate the transactivation function of p63 and p73 on the promoters of Bax, PIG3, and PUMA but not mdm2 or p21(WAF-1/CIP1). The expression of ASPP1 and ASPP2 also enhances the apoptotic function of p63 and p73 by selectively inducing the expression of endogenous p53 target genes, such as PIG3 and PUMA, but not mdm2 or p21(WAF-1/CIP1). Removal of endogenous p63 or p73 with RNA interference demonstrated that (16) the p53-independent apoptotic function of ASPP1 and ASPP2 is mediated mainly by p63 and p73. Hence, ASPP1 and ASPP2 are the first two identified common activators of all p53 family members. All these results suggest that ASPP1 and ASPP2 could suppress tumor growth even in tumors expressing mutant p53.

Melino G, Lu X, Gasco M, Crook T, Knight RA. 2003. Functional regulation of p73 and p63: development and cancer. Trends Biochem Sci, 28 (12), pp. 663-670. | Show Abstract | Read more

The transcription factor and tumour suppressor p53 and its two homologues p63 and p73 form a family of proteins. p63 and p73 show much greater molecular complexity than p53 because they are expressed both as multiple alternatively spliced C-terminal isoforms, and as N-terminally deleted, dominant-negative proteins that show reciprocal functional regulation. In addition, several other factors, such as post-translational modifications and specific and common family regulatory proteins, result overall in subtle modulation of their biological effects. Although all p53, p63 and p73 family members are regulators of the cell cycle and apoptosis, the developmental abnormalities of p73- and p63-null mice do not show enhanced tumour susceptibility of p53 knockouts, suggesting that complex regulatory processes modulate the functional effects of this family of proteins.

Renton A, Llanos S, Lu X. 2003. Hypoxia induces p53 through a pathway distinct from most DNA-damaging and stress-inducing agents. Carcinogenesis, 24 (7), pp. 1177-1182. | Show Abstract | Read more

The p53 tumour suppressor gene is a transcription factor that can induce cell cycle arrest and apoptosis. In response to various stress-inducing signals, p53 level increases and this is accompanied with increased activities of p53. Interestingly, the methylxanthine caffeine can abrogate the p53 accumulation induced by certain DNA-damaging agents by an unknown mechanism. In an effort to understand how different signals induce p53, human tumour cell lines were treated with combinations of various stress-inducing agents and caffeine. Caffeine inhibited the accumulation of p53 induced by leptomycin B (LMB), an inhibitor of CRM1, but not N-acetyl-leu-leu-norleucinal, a proteasome inhibitor. Furthermore, caffeine also inhibited the accumulation of p53 by a variety of stress-inducing agents in vivo, such as 5-fluorouracil, doxorubicin, mitomycin C, camptothecin and roscovitine. However, caffeine failed to affect the accumulation of p53 in hypoxia (HYP)-treated cells. These results suggested that HYP must use a distinct pathway from most DNA-damaging and stress-inducing agents to induce p53.

Slee EA, Lu X. 2003. The ASPP family: deciding between life and death after DNA damage. Toxicol Lett, 139 (2-3), pp. 81-87. | Show Abstract | Read more

It is well established that p53 is a primary target for mutation in human cancer. p53 carries out the important task of ensuring that damaged DNA is not passed on during cell division, a duty that it performs by either inhibiting the cell cycle or inducing apoptosis. However, it is unclear how this decision is made. The recent identification of the ASPP family of proteins, which act to direct the cell away from cell cycle arrest and towards death following p53 upregulation, may explain how this dilemma is resolved. Furthermore, the observation that ASPP2 is in fact the full length form of the previously identified 53BP2/Bbp protein has clarified the ambiguous data that has been generated in relation to this molecule. The further characterisation of these proteins will enable us to gain further insights into the response of the cell to DNA damage and the progression of the cell towards malignancy.

Bergamaschi D, Gasco M, Hiller L, Sullivan A, Syed N, Trigiante G, Yulug I, Merlano M, Numico G, Comino A et al. 2003. p53 polymorphism influences response in cancer chemotherapy via modulation of p73-dependent apoptosis. Cancer Cell, 3 (4), pp. 387-402. | Show Abstract | Read more

Intact p73 function is shown to be an important determinant of cellular sensitivity to anticancer agents. Inhibition of p73 function by dominant-negative proteins or by mutant p53 abrogates apoptosis and cytotoxicity induced by these agents. A polymorphism encoding either arginine (72R) or proline (72P) at codon 72 of p53 influences inhibition of p73 by a range of p53 mutants identified in squamous cancers. Clinical response following cisplatin-based chemo-radiotherapy for advanced head and neck cancer is influenced by this polymorphism, cancers expressing 72R mutants having lower response rates than those expressing 72P mutants. Polymorphism in p53 may influence individual responsiveness to cancer therapy.

Bergamaschi D, Samuels Y, O'Neil NJ, Trigiante G, Crook T, Hsieh JK, O'Connor DJ, Zhong S, Campargue I, Tomlinson ML et al. 2003. iASPP oncoprotein is a key inhibitor of p53 conserved from worm to human. Nat Genet, 33 (2), pp. 162-167. | Show Abstract | Read more

We have previously shown that ASPP1 and ASPP2 are specific activators of p53; one mechanism by which wild-type p53 is tolerated in human breast carcinomas is through loss of ASPP activity. We have further shown that 53BP2, which corresponds to a C-terminal fragment of ASPP2, acts as a dominant negative inhibitor of p53 (ref. 1). Hence, an inhibitory form of ASPP resembling 53BP2 could allow cells to bypass the tumor-suppressor functions of p53 and the ASPP proteins. Here, we characterize such a protein, iASPP (inhibitory member of the ASPP family), encoded by PPP1R13L in humans and ape-1 in Caenorhabditis elegans. iASPP is an evolutionarily conserved inhibitor of p53; inhibition of iASPP by RNA-mediated interference or antisense RNA in C. elegans or human cells, respectively, induces p53-dependent apoptosis. Moreover, iASPP is an oncoprotein that cooperates with Ras, E1A and E7, but not mutant p53, to transform cells in vitro. Increased expression of iASPP also confers resistance to ultraviolet radiation and to cisplatin-induced apoptosis. iASPP expression is upregulated in human breast carcinomas expressing wild-type p53 and normal levels of ASPP. Inhibition of iASPP could provide an important new strategy for treating tumors expressing wild-type p53.

Vousden KH, Lu X. 2002. Live or let die: the cell's response to p53. Nat Rev Cancer, 2 (8), pp. 594-604. | Read more

Hsieh JK, Yap D, O'Connor DJ, Fogal V, Fallis L, Chan F, Zhong S, Lu X. 2002. Novel function of the cyclin A binding site of E2F in regulating p53-induced apoptosis in response to DNA damage. Mol Cell Biol, 22 (1), pp. 78-93. | Show Abstract | Read more

We demonstrate here that the E2F1 induced by DNA damage can bind to and promote the apoptotic function of p53 via the cyclin A binding site of E2F1. This function of E2F1 does not require its DP-1 binding, DNA binding, or transcriptional activity and is independent of mdm2. All the cyclin A binding E2F family members can interact and cooperate with p53 to induce apoptosis. This suggests a novel role for E2F in regulating apoptosis in response to DNA damage. Cyclin A, but not cyclin E, prevents E2F1 from interacting and cooperating with p53 to induce apoptosis. However, in response to DNA damage, cyclin A levels decrease, with a concomitant increase in E2F1-p53 complex formation. These results suggest that the binding of E2F1 to p53 can specifically stimulate the apoptotic function of p53 in response to DNA damage.

Zhao J, Wang H, Wei LX, Habib N, Lu X, Wu MC, Guo YJ. 2001. The cytotoxic effect of E1B55kDa-mutant adenovirus on human hepatocellular carcinoma cell lines CANCER GENE THERAPY, 8 (11), pp. 924-924.

Samuels-Lev Y, O'Connor DJ, Bergamaschi D, Trigiante G, Hsieh JK, Zhong S, Campargue I, Naumovski L, Crook T, Lu X. 2001. ASPP proteins specifically stimulate the apoptotic function of p53. Mol Cell, 8 (4), pp. 781-794. | Show Abstract | Read more

We identified a family of proteins termed ASPP. ASPP1 is a protein homologous to 53BP2, the C-terminal half of ASPP2. ASPP proteins interact with p53 and specifically enhance p53-induced apoptosis but not cell cycle arrest. Inhibition of endogenous ASPP function suppresses the apoptotic function of endogenous p53 in response to apoptotic stimuli. ASPP enhance the DNA binding and transactivation function of p53 on the promoters of proapoptotic genes in vivo. Two tumor-derived p53 mutants with reduced apoptotic function were defective in cooperating with ASPP in apoptosis induction. The expression of ASPP is frequently downregulated in human breast carcinomas expressing wild-type p53 but not mutant p53. Therefore, ASPP regulate the tumor suppression function of p53 in vivo.

Zhao J, Wang H, Wei L, Habib NA, Lu X, Wu M, Guo Y. 2001. The cytotoxic effect of E1B 55-kDa mutant adenovirus on human hepatocellular carcinoma cell lines. Cancer Gene Ther, 8 (5), pp. 333-341. | Show Abstract | Read more

It has been suggested the E1B 55 kDa mutant adenovirus dl1520 can selectively kill p53-deficient human tumor cells. In this study, we examined the cytotoxic effect of dl1520 on nine human hepatocellular carcinoma (HCC) cell lines with different p53 genetic and functional status. The results showed that HCC cell lines with deleted or mutant p53 gene and reduced p53 transcriptional activities were more susceptible to dl1520-induced cytolysis. Hep3B (p53-null) and HepG2 (p53-wt) cells were arrested at G2/M phase when cytolysis occurred. Cyclin-dependent kinase inhibitor (CDKI) p21(Waf-1/Cip-1) was downregulated 24 hours after dl1520 infection in HepG2 cells and increased when cytolysis occurred. No p21 expression was detected in Hep3B cells. DNA fragmentation was found in both Hep3B and HepG2 cells after dl1520 infection. Bax expression increased in dl1520-infected HepG2 cells but not in Hep3B cells. Notably, three Bax-like proteins, molecular mass around 40 to 80 kDa, accumulated 48 hours after adenovirus infection in Hep3B cells but not in HepG2 cells. These results suggest that the susceptibility of HCC cells to dl1520-induced cytolysis is related to both p53 genotype and functional status, and is mediated by both cell cycle disturbance and apoptosis.

Yap DB, Hsieh JK, Lu X. 2000. Mdm2 inhibits the apoptotic function of p53 mainly by targeting it for degradation. J Biol Chem, 275 (47), pp. 37296-37302. | Show Abstract | Read more

The ability of Mdm2 to inhibit the activities of a C-terminal truncated p53 mutant, p53-Delta30, which can bind Mdm2 but is resistant to Mdm2-mediated protein degradation was investigated. The inhibitory function of an Mdm2 mutant, Mdm2-Delta(222-437), which can bind p53 but is defective in targeting p53 for degradation was also studied. We have demonstrated that targeting p53 for degradation is the most effective way for Mdm2 to inhibit the apoptotic function of p53. However, we have also shown that Mdm2 can inhibit the transactivation function of p53 without targeting it for degradation, although Mdm2 releases the transrepression ability of p53 mainly by targeting it for degradation. The ability of Mdm2 to inhibit the apoptotic function of p53 was linked to its ability to inhibit the transrepression but not the transactivation function of p53. Furthermore, we have demonstrated that the transrepression function of p53 was specific to p53-induced apoptosis and was not simply a result of cell death.

Lopez CD, Ao Y, Rohde LH, Perez TD, O'Connor DJ, Lu X, Ford JM, Naumovski L. 2000. Proapoptotic p53-interacting protein 53BP2 is induced by UV irradiation but suppressed by p53. Mol Cell Biol, 20 (21), pp. 8018-8025. | Show Abstract | Read more

p53 is an important mediator of the cellular stress response with roles in cell cycle control, DNA repair, and apoptosis. 53BP2, a p53-interacting protein, enhances p53 transactivation, impedes cell cycle progression, and promotes apoptosis through unknown mechanisms. We now demonstrate that endogenous 53BP2 levels increase following UV irradiation induced DNA damage in a p53-independent manner. In contrast, we found that the presence of a wild-type (but not mutant) p53 gene suppressed 53BP2 steady-state levels in cell lines with defined p53 genotypes. Likewise, expression of a tetracycline-regulated wild-type p53 cDNA in p53-null fibroblasts caused a reduction in 53BP2 protein levels. However, 53BP2 levels were not reduced if the tetracycline-regulated p53 cDNA was expressed after UV damage in these cells. This suggests that UV damage activates cellular factors that can relieve the p53-mediated suppression of 53BP2 protein. To address the physiologic significance of 53BP2 induction, we utilized stable cell lines with a ponasterone A-regulated 53BP2 cDNA. Conditional expression of 53BP2 cDNA lowered the apoptotic threshold and decreased clonogenic survival following UV irradiation. Conversely, attenuation of endogenous 53BP2 induction with an antisense oligonucleotide resulted in enhanced clonogenic survival following UV irradiation. These results demonstrate that 53BP2 is a DNA damage-inducible protein that promotes DNA damage-induced apoptosis. Furthermore, 53BP2 expression is highly regulated and involves both p53-dependent and p53-independent mechanisms. Our data provide new insight into 53BP2 function and open new avenues for investigation into the cellular response to genotoxic stress.

O'Connor DJ, Lu X. 2000. Stress signals induce transcriptionally inactive E2F-1 independently of p53 and Rb. Oncogene, 19 (20), pp. 2369-2376. | Show Abstract | Read more

One of the common features of cellular response to stress is cell cycle arrest or apoptosis. E2F is one of the key factors which controls cell cycle progression. Overexpression of E2F-1 can also induce apoptosis. In order to understand the role of E2F-1 in cellular response to stress, we studied the E2F-1 response in various cell lines to different types of stress signals including UV irradiation, cisplatin, etoposide and hypoxia. We showed here that the expression level of E2F-1 can be up regulated by the treatment of DNA damage agents as well as hypoxia. The kinetics of E2F-1 increase was dependent on the types of inducer and was similar to that of p53. However, stress signals can induce E2F-1 expression independently of p53 and Rb. Furthermore, the induced E2F-1 was transcriptionally inactive. All these results suggested that E2F-1 may play a very important role in cellular response to stress and this novel role of E2F-1 is independent of its transactivation function.

Yap DB, Hsieh JK, Chan FS, Lu X. 1999. mdm2: a bridge over the two tumour suppressors, p53 and Rb. Oncogene, 18 (53), pp. 7681-7689. | Show Abstract | Read more

The inactivation of the p53 and Rb pathways would account for the majority of human tumours. There are many levels of cross talk between p53 and Rb that have been identified. However, the identification of the mdm2-Rb interaction established a closer link between the two most well studied tumour suppressors, p53 and Rb. Recent studies of the novel trimeric complex Rb-mdm2-p53 provided us with a functional insight of how the two tumour suppressors can act together in regulating p53 induced apoptosis. Beginning with the properties of the Rb-mdm2-p53 trimeric complex, we shall review the propounding evidence suggesting that the apoptotic function of p53 is linked to its transrepression function. The uncoupling of the apoptotic function and transactivation function of p53 will also be discussed.

Barnouin K, Fredersdorf S, Eddaoudi A, Mittnacht S, Pan LX, Du MQ, Lu X. 1999. Antiproliferative function of p27kip1 is frequently inhibited in highly malignant Burkitt's lymphoma cells. Oncogene, 18 (46), pp. 6388-6397. | Show Abstract | Read more

Lack of detectable expression of p27kip1 cyclin dependent kinase inhibitor has previously been correlated with high degree of malignancy in human breast, colorectal, gastric and small cell lung carcinomas. Here we demonstrate that an inverse correlation between p27kip1 expression and tumour malignancy also exists in most types of human B cell lymphomas examined. A clear exception was Burkitt's lymphoma (BL), a highly malignant tumour which often expresses high levels of p27kip1. Analysis of p27kip1 derived from Burkitt's lymphoma cell lines expressing high levels of p27kip1, BL40 and BL41, in a cyclin E/cdk2 kinase inhibition assay demonstrated that p27kip1 is not permanently inactivated since heat treatment can restore the inhibitory activity of p27kip1. However, p27kip1 expressed in these two cell lines is largely sequestered in inactive complexes and we have no evidence that c-myc or Epstein-Barr virus are responsible for the sequestration of p27kip1 in these two cell lines although c-myc and EBV are two oncogenic agents often associated with Burkitt's lymphomas. Interestingly, we observed that high level p27kip1 expression often correlated with cyclin D3 overexpression both in vivo and in BL cell lines. The majority of p27kip1 in BL40 cells was complexed with cyclin D3 indicating that overexpressed cyclin D3 may at least be part of the sequestering activity for the inhibitory function of p27kip1. Furthermore, cyclinD3/cdk4 complex could sequester p27kip1 in a cyclin E/cdk2 kinase assay in vitro. Finally, we show that cyclin D3 transfected into an inducible p27kip1 cell line could overcome the G1 arrest mediated by p27kip1. These results argue that in addition to down-regulation of p27kip1 expression, some tumour cells can sequester and tolerate the antiproliferative function of p27kip1. They also suggest a novel role for the overexpression of D-type cyclins as one pathway allowing tumour cells to overcome the antiproliferative function of p27kip1.

Erdamar S, Yang G, Harper JW, Lu X, Kattan MW, Thompson TC, Wheeler TM. 1999. Levels of expression of p27KIP1 protein in human prostate and prostate cancer: an immunohistochemical analysis. Mod Pathol, 12 (8), pp. 751-755. | Show Abstract

p27KIP1 is a member of the CIP/KIP family of cyclin-dependent kinase inhibitory proteins that negatively regulate cell proliferation. Recent studies reported decreased p27 expression in breast and colon carcinomas and found that the loss of p27 is associated with a poor prognosis. We report here the results of our immunohistochemical analysis of p27 in human prostate cancer. Formalin-fixed, paraffin-embedded, whole-mount sections of prostate cancer from 73 selected patients treated by radical retropubic prostatectomy were obtained from the Department of Pathology, The Methodist Hospital, Houston, Texas. Ten histologically normal and nine high-grade prostatic intraepithelia neoplasia foci were selected from these whole-mount sections, and nine cases of transplant donor prostates were chosen as controls. Also, 10 prostate cancer metastatic lymph nodes were used to compare with the primary cancer group. Sections were immunostained with a monoclonal antibody against p27 protein using the avidin-biotin complex immunohistochemical method. Immunoactivity was evaluated without knowledge of follow-up and recorded as the p27 labeling index (LI) (defined as the percentage of p27-positive cells among epithelia of the same category). The p27 (LI) in normal prostatic epithelia was 86.4+/-3.5% (the mean +/- the standard error of the mean). In contrast, the p27 immunoreactivity was significantly lower in cancers (LI: 43.5 +/-3.7%, P < .001) and in the high-grade prostatic intraepithelial neoplasia group (LI: 59.3 +/- 3.2%, P < .05). Expression of p27 in the metastatic lymph node group was significantly lower than in the other groups, including the prostate cancer cases and the cases of high-grade intraepithelial neoplasia (LI, 7.0%; P = .05). There was no association of the mean p27 LI with progression after radical prostatectomy. Nonrecurrent cases, with a mean follow-up time of greater than 5 years (n = 45), equalled 41.9%; recurrent cases, with a mean follow-up time of 18.3 months (n = 28), equalled 40.0%. The mean p27 LI was not associated with pathologic stage. Organ-confined specimens (n = 21) equalled 34.2%; cases of extraprostatic extension (n = 24) equalled 46.5%; and samples showing seminal vesicle involvement (n = 14) equalled 47.6%. In 14 cases with lymph node metastases, the mean p27 LI was 48.1% in the primary cancer (P = .2322). There was no association of the mean p27 LI with the Gleason score (P = .4747) nor with the clinical stage (P = .9914).

Fallis LH, Richards E, O'Connor DJ, Zhong S, Hsieh JK, Packham G, Lu X. 1999. The biological response of MCF7 breast cancer cells to proteosome inhibition or gamma-radiation is unrelated to the level of p53 induction. Apoptosis, 4 (2), pp. 99-107. | Show Abstract | Read more

The p53 tumour suppressor is stabilised following exposure to genotoxic agents, such as gamma-radiation. Cell responses to p53 stabilisation include induction of apoptosis and/or cell cycle arrest. Several studies have suggested that gamma-radiation stabilises p53 by blocking ubiquitin mediated proteolysis. Here we have compared the biological activities of p53 stabilized following exposure to gamma-radiation or treatment with the proteosome inhibitor N-acetyl-leucinyl-leucinyl-norleucinal (ALLN) in MCF7 cells with wild type p53. Stabilisation of p53 by ALLN was reversible and was not blocked by caffeine. Although ALLN was a more effective p53 stabilising agent than gamma-radiation, ALLN was not as effective at inducing cell cycle arrest/apoptosis as gamma-radiation. Although p53 stabilised by ALLN and gamma-radiation were both able to bind DNA and activate transcription, ALLN did not increase expression of BAX, which is involved in p53-induced apoptosis. Therefore, p53 stabilised by different agents is not always biologically active to the same extent and additional alterations triggered by gamma-radiation may enable p53 to activate a subset of critical target genes, such as BAX, which are required for p53 responses.

Ellis M, Chew YP, Fallis L, Freddersdorf S, Boshoff C, Weiss RA, Lu X, Mittnacht S. 1999. Degradation of p27(Kip) cdk inhibitor triggered by Kaposi's sarcoma virus cyclin-cdk6 complex. EMBO J, 18 (3), pp. 644-653. | Show Abstract | Read more

The Kaposi's sarcoma-associated human herpesvirus 8 (KSHV/HHV8) encodes a protein similar to cellular cyclins. This cyclin is most closely related to cellular D-type cyclins, but biochemically it behaves atypically in various respects. Complexes formed between the viral cyclin and the cyclin-dependent kinase subunit, cdk6, can phosphorylate a wider range of substrates and are resistant to cdk inhibitory proteins. We show here that the KSHV-cyclin-cdk6 complex phosphorylates p27(Kip) on a C-terminal threonine that is implicated in destabilization of this cdk inhibitor. Expression of the viral cyclin in tissue culture cells overcomes a cell cycle block by p27(Kip). However, full cell-cycle transit of these cells appears to depend on C-terminal phosphorylation of p27(Kip) and seems to involve transactivation of other cellular cyclin-dependent kinases. A p27(Kip)-phosphorylating cdk6 complex exists in cell lines derived from primary effusion lymphoma and in Kaposi's sarcoma, this indicating that virally induced p27(Kip) degradation may occur in KSHV-associated tumours.

Hsieh JK, Chan FS, O'Connor DJ, Mittnacht S, Zhong S, Lu X. 1999. RB regulates the stability and the apoptotic function of p53 via MDM2. Mol Cell, 3 (2), pp. 181-193. | Show Abstract | Read more

The binding of RB to MDM2 is shown to be essential for RB to overcome both the antiapoptotic function of MDM2 and the MDM2-dependent degradation of p53. The RB-MDM2 interaction does not prevent MDM2 from inhibiting p53-dependent transcription, but the RB-MDM2 complex still binds to p53. Since RB specifically rescues the apoptotic function but not the transcriptional activity of p53 from negative regulation by MDM2, transactivation by wild-type p53 is not required for the apoptotic function of p53. However, an RB-MDM2-p53 trimeric complex is active in p53-mediated transrepression. These data link directly the function of two tumor suppressor proteins and demonstrate a novel role of RB in regulating the apoptotic function of p53.

Gillett CE, Smith P, Peters G, Lu X, Barnes DM. 1999. Cyclin-dependent kinase inhibitor p27Kip1 expression and interaction with other cell cycle-associated proteins in mammary carcinoma. J Pathol, 187 (2), pp. 200-206. | Show Abstract | Read more

p27, cyclin D1, and retinoblastoma (Rb) protein have been demonstrated using immunohistochemistry in 189 cases of primary breast carcinoma with long-term follow-up. There was a statistically significant association between the expression of p27 and both cyclin D1 and the retinoblastoma gene product (pRb), corresponding to their close interactions in regulating the G1/S transition in the cell cycle. Low levels of p27 were seen in high-grade, rapidly proliferating, oestrogen receptor-negative tumours. In univariate analysis, low p27 expression was associated with a reduced relapse-free and overall survival. In multivariate analysis, p27 was not an independent predictor of survival when either histological grade or proliferative activity (S-phase fraction) was included in the model. When the combined expression of p27 and cyclin D1 was related to survival, patients with high levels of p27, regardless of their cyclin D1 status, did well, whilst those with low p27 had a poor outcome. The only exception, in the latter group, was patients with tumours expressing high levels of cyclin D1, who did as well as the high p27 group. We have shown that in clinical material p27 expression is associated with proliferative activity and while univariate analysis shows it to be a significant indicator of prognosis, this significance is lost in multivariate analysis when traditional prognostic factors are included in the model. The interest in p27 expression in mammary carcinoma lies in its behaviour when examined in combination with other G1 cell cycle regulators.

Dahia PL, Aguiar RC, Honegger J, Fahlbush R, Jordan S, Lowe DG, Lu X, Clayton RN, Besser GM, Grossman AB. 1998. Mutation and expression analysis of the p27/kip1 gene in corticotrophin-secreting tumours. Oncogene, 16 (1), pp. 69-76. | Show Abstract | Read more

The molecular mechanisms leading to Cushing's disease are unclear. Inhibitors of cyclin-cyclin dependent kinase (CDK) complexes are regulators of the cell cycle and may function as tumour suppressor genes, many of which have been involved in the pathogenesis of several human malignancies. A member of this family, the p27/kip1 gene, maps to chromosome 12p13 and encodes an inhibitor of several cyclin-CDK complexes; these control the progression of the cell cycle from G1 to S-phase. Complete lack of p27/kip1 function, as occurs in the p27/kip1 'knockout' mouse, produces a complex phenotype associated with the development of pituitary tumours, specifically those of the intermediate lobe corticotrophs. We therefore investigated whether structural and functional abnormalities of the p27/kip1 gene and loss at the chromosome 12p13 region were present in human corticotrophin (ACTH)-secreting pituitary tumours. We studied 21 pituitary tumours, of which 20 were ACTH-secreting (two of these had biochemical and histological features of 'intermediate-lobe' tumours and one was malignant) while the remaining tumour was a prolactinoma; three ectopic secretors of ACTH (two bronchial and one thymic carcinoid); and a non-secretory thymic carcinoid. The whole coding region of the p27/ kip1 gene was screened for mutations by PCR-SSCP analysis and/or direct sequencing, while tumour mRNA expression was analysed by means of a semi-quantitative duplex PCR. Three polymorphic microsatellite markers of the 12p13 region were used to assess loss of heterozygosity (LOH) in 12 samples. Finally, tumour p27/kip1 protein expression was assessed by immunohistochemistry using a monoclonal antibody in 12 samples suitable for analysis. No sequence abnormalities were found in any of the samples other than a previously-described polymorphism. No LOH was observed in the tumours analysed. p27/kip1 mRNA expression was similar in tumour samples in comparison with normal pituitaries. Seven of the eight corticotroph tumours analysed by immunohistochemistry stained positive for p27/kip1, including the intermediate lobe. The only malignant pituitary tumour in the original series showed an absence of staining for p27/kip1. In addition, the three carcinoid tumours studied were negative on immunohistochemistry. Of a further three malignant pituitary tumours assessed, two (including a prolactinoma) were essentially negative, while the third was moderately positive. We conclude that mutations of the p27/kip1 gene, deletions of the 12p13 area or changes in expression, are not a general feature of corticotroph tumours, even those with intermediate lobe characteristics. However, other mechanisms of p27/kip1 inactivation, such as an abnormality at the post-translational level, may be related to more aggressive histological subtypes of ACTH-secreting and possibly other pituitary tumours.

Hsieh JK, Fredersdorf S, Kouzarides T, Martin K, Lu X. 1997. E2F1-induced apoptosis requires DNA binding but not transactivation and is inhibited by the retinoblastoma protein through direct interaction. Genes Dev, 11 (14), pp. 1840-1852. | Show Abstract | Read more

E2F1 overexpression has been shown to induce apoptosis in cooperation with p53. Using Saos-2 cells, which are null for p53 and lack functional Rb, we have demonstrated that E2F1 overexpression can also induce apoptosis in the absence of p53 and retinoblastoma protein (Rb). E2F1-induced apoptosis can be specifically inhibited by Rb but not mdm2, which is known for its ability to inhibit p53-induced apoptosis. Through the study of the apoptotic function of a set of E2F1 mutants, it was clear that the transactivation and the apoptotic function of E2F1 are uncoupled. The transactivation-defective E2F1 mutants E2F1(1-374), E2F1(390-1)DF(delta mdm2), and E2F1(406-415)(delta Rb) can induce apoptosis as effectively as wild-type E2F1. In contrast to E2F1 transactivation, the DNA-binding activity of E2F1 was proven to be essential for its apoptotic function, as the DNA-binding-defective mutants E2F1(132) and E2F1(132)(1-374) failed to induce apoptosis. Therefore Rb may inhibit E2F1-induced apoptosis by mechanisms other than the suppression of the transactivation of E2F1. This hypothesis was supported by our observation that although Rb overexpression can specifically repress the apoptosis induced by wild-type E2F1 and a Rb-binding-competent E2F1 mutant E2F1(390-1)DF(delta mdm2), it failed to inhibit the apoptosis induced by mutants E2F1(1-374) and E2F1(delta 406-415)(delta Rb), which are defective or reduced in Rb binding and transactivation. All of these points argue for a novel function for E2F1 and Rb in controlling apoptosis. The results also indicate that transcriptional repression rather than the transactivation function of E2F1 may be involved in its apoptotic function. The results presented here may provide us some physiological implication of the repression function of the Rb-E2F1 complex.

Fredersdorf S, Burns J, Milne AM, Packham G, Fallis L, Gillett CE, Royds JA, Peston D, Hall PA, Hanby AM et al. 1997. High level expression of p27(kip1) and cyclin D1 in some human breast cancer cells: inverse correlation between the expression of p27(kip1) and degree of malignancy in human breast and colorectal cancers. Proc Natl Acad Sci U S A, 94 (12), pp. 6380-6385. | Show Abstract | Read more

The expression of cyclin-dependent kinase inhibitor p27(kip1) in human tumors and normal tissues was investigated using a panel of novel anti-p27(kip1) mAbs. An inverse correlation between expression of p27(kip1) and cell proliferation was generally observed after analyzing its expression in 25 different normal human tissues. In some highly proliferative human breast cancer cells, however, high level p27(kip1) expression was seen, indicating the existence of a mechanism by which some growing tumor cells may tolerate this inhibitor of cell cycle progression. Detailed studies demonstrated a correlation between the high level expression of p27(kip1) and cyclin D1 in human breast cancer cells. There was also an inverse correlation between the expression of p27(kip1) and the degree of tumor malignancy in human breast and colorectal cancers, indicating that p27(kip1) may be a useful prognostic marker in these cancers.

Hsieh JK, Fredersdorf S, Lu X. 1997. E2F1 induced apoptosis requires DNA binding but not transcriptional activity and is inhibited by RB EUROPEAN JOURNAL OF CELL BIOLOGY, 72 pp. 86-86.

Royds JA, Stewart R, Silcocks PS, Shorthouse AJ, Santini A, Fredersdorf S, Lu X. 1997. p27(kip1) localisation is an independent prognostic marker for colorectal cancer. JOURNAL OF PATHOLOGY, 182 pp. A9-A9.

Lu X, Burbidge SA, Griffin S, Smith HM. 1996. Discordance between accumulated p53 protein level and its transcriptional activity in response to u.v. radiation. Oncogene, 13 (2), pp. 413-418. | Show Abstract

In response to DNA damage, the transcriptional activity of p53 rises. This has been thought to be due to an increase in the level of p53 protein. By comparing the p53 protein level and its ability to transactivate target genes Waf1/Cip1 and mdm2 in both T22 and NIH3T3 cells irradiated with u.v., a discordance between the p53 protein level and its transcriptional activity was observed. When the cells were irradiated with 10 J/m2 of u.v., there was a substantial increase in expression of Waf1/ Cip1 and mdm2. However, little increase in Waf1/Cip1 and mdm2 expression was observed in T22 and NIH3T3 cells 8 or 9 h after exposure to 50 J/m2 of u.v., although the p53 protein level accumulated to its highest level under these conditions. Interestingly, a significant increase in Waf1/Cip1 expression was seen 24 h after irradiation in NIH3T3 cells, indicating that the inhibition of p53 transcriptional activity is reversible. Discordance between the transcriptional activity of p53 and its protein level was further studied using a cell line expressing the p53 reporter plasmid RGC delta fosLacZ. Using double immunofluorescence staining, the coexpression of p53 and beta-galactosidase from the reporter plasmid in the same cells was investigated. The observed lack of correlation between the elevated p53 and beta-galactosidase and expression in u.v. irradiated cells strongly indicates that the ability of p53 to transactivate its target genes is not simply correlated to its protein level. The results indicate that the transcriptional activity of p53 may be negatively regulated.

Fredersdorf S, Milne AW, Hall PA, Lu X. 1996. Characterization of a panel of novel anti-p21Waf1/Cip1 monoclonal antibodies and immunochemical analysis of p21Waf1/Cip1 expression in normal human tissues. Am J Pathol, 148 (3), pp. 825-835. | Show Abstract

As a universal inhibitor of cyclin-dependent kinases and one of the target genes of the tumor suppresser p53, p21Waf1/Cip1 can act as a tumor suppresser through its ability to control cell cycle progression. To study the function of p21Waf1/Cip1 protein and to investigate its tissue distribution, a panel of anti-p21Waf1/Cip1 monoclonal antibodies was generated. These anti-p21Waf1/Cip1 monoclonal antibodies were initially raised against a GST-p21Waf1/Cip1 fusion protein produced in bacteria. Detailed characterization of the antibodies showed that they can specifically detect p21Waf1/Cip1 by immunoblotting, immunoprecipitation, and immunostaining. The specific induction of p21Waf1/Cip1 expression in response to gamma-radiation in cells containing p53 was also detected by these antibodies. The ability to detect p21Waf1/Cip1 expression in conventionally fixed tissue sections allowed us to investigate the distribution of p21Waf1/Cip1 in 23 different types of normal human tissues, and p21Waf1/Cip1 expression was found in most tissues. A close inverse relationship between p21Waf1/Cip1 expression and proliferation was seen in some tissues, including gastrointestinal tract. However, such association is not universal. In tissues such as lung, kidney, thyroid, pancreatic ducts and acini, and liver, despite the fact that most of the cells are quiescent, expression of p21Waf1/Cip1 was detected only in occasional epithelial cells. All these suggest that the expression of p21Waf1/Cip1 varies among different human tissues. Finally, epitope mapping of the anti-p21Waf1/Cip1 antibodies using a peptide library covering the entire p21Waf1/Cip1 protein sequence indicates that two of the antibodies recognize a region of p21Waf1/Cip1 close to that bound by proliferating cell nuclear antigen. These two monoclonal antibodies will therefore be additionally useful in further understanding the functions of p21Waf1/Cip1 both in vitro and in vivo.

Rowan S, Ludwig RL, Haupt Y, Bates S, Lu X, Oren M, Vousden KH. 1996. Specific loss of apoptotic but not cell-cycle arrest function in a human tumor derived p53 mutant. EMBO J, 15 (4), pp. 827-838. | Show Abstract

The p53 tumor-suppressor gene product is frequently inactivated in malignancies by point mutation. Although most tumor-derived p53 mutants show loss of sequence specific transcriptional activation, some mutants have been identified which retain this activity. One such mutant, p53175P, is defective for the suppression of transformation in rodent cells, despite retaining the ability to suppress the growth of p53-null human cells. We now demonstrate that p53175P can induce a cell-cycle arrest in appropriate cell types but shows loss of apoptotic function. Our results therefore support a direct role of p53 transcriptional activation in mediating a cell-cycle arrest and demonstrate that such activity is not sufficient for the full apoptotic response. These data suggest that either p53 can induce apoptosis through a transcriptionally independent mechanism, a function lost by p53175P, or that this mutant has specifically lost the ability to activate genes which contribute to cell death, despite activation of genes responsible for the G1 arrest. This dissociation of the cell-cycle arrest and apoptotic activities of p53 indicates that inactivation of p53 apoptotic function without concomitant loss of growth inhibition can suffice to relieve p53-dependent tumor-suppression in vivo and thereby contribute to tumor development.

O'Connor DJ, Lam EW, Griffin S, Zhong S, Leighton LC, Burbidge SA, Lu X. 1995. Physical and functional interactions between p53 and cell cycle co-operating transcription factors, E2F1 and DP1. EMBO J, 14 (24), pp. 6184-6192. | Show Abstract

One way in which wild-type p53 is able to regulate cell cycle progression is thought to be via the induction of its downstream target gene Waf1/CIP1, thus indirectly regulating the transcriptional activity of E2F. The E2F transcription factors are known to be key effectors of the cell cycle. We report here that there is a physical and functional interaction between p53 and two of the components of the E2F transcription factors, E2F1 and DP1. The expression of wild-type p53 can inhibit the transcriptional activity of E2F, and the expression of both E2F1 and DP1 can also downregulate p53-dependent transcription. The transcriptional activity of p53 is known to be inhibited by the direct binding of mdm2, but we demonstrate here that both E2F1 and DP1 can inhibit p53 transcriptional activity independently of mdm2. Detailed studies of protein-protein interactions have provided evidence that E2F1 and its co-operating factor DP1 can complex with p53 both in vitro and in vivo.

Fuchs B, O'Connor D, Fallis L, Scheidtmann KH, Lu X. 1995. p53 phosphorylation mutants retain transcription activity. Oncogene, 10 (4), pp. 789-793. | Show Abstract

To investigate the effect of phosphorylation on the transcription activity of p53, ten phosphorylation mutants were constructed covering all the identified phosphorylation sites of rat p53. These included mutants of two casein kinase I sites (Ser6 and Ser9), two DNA-PK sites (Ser15 and Ser39), a p34cdc2 site (Ser313), the adjacent Ser312 and a casein kinase II site (Ser390). Two double phosphorylation mutants (Ser4, 6 and Ser15, 390) and one triple phosphorylation mutant (Ser4, 6 and 15) were also constructed. The transcription activity of all the p53 phosphorylation mutants was tested by transfection into two different types of cells, Saos-2 cells and p53(-/-) fibroblasts derived from p53 knock out mice, which both lack endogenouse p53. Surprisingly, all the p53 phosphorylation mutants retain transcription activity and the seven mutants tested can also suppress cell growth.

Lane DP, Midgley CA, Hupp TR, Lu X, Vojtesek B, Picksley SM. 1995. On the regulation of the p53 tumour suppressor, and its role in the cellular response to DNA damage. Philos Trans R Soc Lond B Biol Sci, 347 (1319), pp. 83-87. | Show Abstract | Read more

The p53 gene is required for the normal apoptotic response of mammalian cells to DNA damage caused by ionizing radiation and DNA damaging drugs. DNA damage results in the accumulation of biologically active p53. This response is potentially lethal and is therefore highly regulated. By using both biochemical and cell biological approaches a number of discrete control pathways have been identified. These include analysis of cellular and viral proteins that bind to p53 to inactivate its function, the discovery of cells with defects in the p53 activation pathway and the analysis of an allosteric regulation of p53 function controlled by phosphorylation.

Ralton JE, Lu X, Hutcheson AM, Quinlan RA. 1994. Identification of two N-terminal non-alpha-helical domain motifs important in the assembly of glial fibrillary acidic protein. J Cell Sci, 107 ( Pt 7) pp. 1935-1948. | Show Abstract

The non-alpha-helical N-terminal domain of intermediate filament proteins plays a key role in filament assembly. Previous studies have identified a nonapeptide motif, SSYRRIFGG, in the non-alpha-helical N-terminal domain of vimentin that is required for assembly. This motif is also found in desmin, peripherin and the type IV intermediate filament proteins. GFAP is the only type III intermediate filament protein in which this motif is not readily identified. This study has identified two motifs in the non-alpha-helical N-terminal domain of mouse GFAP that play important roles in GFAP assembly. One motif is located at the very N terminus and has the consensus sequence, MERRRITS-ARRSY. It has some characteristics in common with the vimentin nonapeptide motif, SSYRRIFGG, including its location in the non-alpha-helical N-terminal domain and a concentration of arginine residues. Unlike the vimentin motif in which even conserved sequence changes affect filament assembly, the GFAP consensus sequence, MERRRITS-ARRSY, can be replaced by a completely unrelated sequence; namely, the heptapeptide, MVRANKR, derived from the lambda cII protein. When fused to GFAP sequences with sequential deletions of the N-terminal domain, the lambda cII heptapeptide was used to help identify a second motif, termed the RP-box, which is located just upstream of the GFAP alpha-helical rod domain. This RP-box affected the efficiency of filament assembly as well as protein-protein interactions in the filament, as shown by sedimentation assays and electron microscopy. These results are supported by previous data, which showed that the dramatic reorganization of GFAP within cells was due to phosphorylation-dephosphorylation of a site located in this RP-box. The results in this study suggest the RP-box motif to be a key modulator in the mechanism of GFAP assembly, and support a role for this motif in both the nucleation and elongation phases of filament assembly. The RP-box motif in GFAP has the consensus sequence, RLSL-RM-PP. Sequences similar to the GFAP RP-box motif are also to be found in vimentin, desmin and peripherin. Like GFAP, these include phosphorylation and proteolysis sites and are adjacent to the start of the central alpha-helical rod domain, suggesting that this motif of general importance to type III intermediate filament protein assembly.

Lu X, Lane DP. 1993. Differential induction of transcriptionally active p53 following UV or ionizing radiation: defects in chromosome instability syndromes? Cell, 75 (4), pp. 765-778. | Show Abstract | Read more

Accumulation of p53 protein was seen in the nuclei of mammalian cells following DNA damage caused by ultraviolet radiation (UV), X-ray, or a restriction enzyme. Promoters containing p53-binding sites show a dramatic transcriptional response to DNA damage. The p53 response to X-ray is rapid, reaching a peak at 2 hr after radiation, but is very transitory and reduced in magnitude compared with that seen in response to UV. We find no substantive defect in the p53 response of cells from ataxia telangiectasia or xeroderma pigmentosum complementation group A patients. In contrast, 2 out of 11 primary cultures from Bloom's patients showed a complete absence of p53 accumulation following UV irradiation or SV40 infection and a grossly delayed and aberrant response following X-ray.

Lu X, Quinlan RA, Steel JB, Lane EB. 1993. Network incorporation of intermediate filament molecules differs between preexisting and newly assembling filaments. Exp Cell Res, 208 (1), pp. 218-225. | Show Abstract | Read more

When studying the way in which intermediate filaments assemble in vivo, it is important to distinguish between the incorporation of intermediate filament proteins into an existing intermediate filament network and the ability to form a new network within cells. To distinguish between these alternatives, we have made a hybrid construct consisting of the rod and tail domains of murine glial fibrillary acidic protein (GFAP) coupled to the head domain of bovine keratin 19, called K19GFAP. The assembly characteristics of K19GFAP were analyzed in vitro and in vivo. Replacement of the head domain with the bovine K19 sequence did not prevent the incorporation of K19GFAP into the existing network of vimentin intermediate filaments in NIH 3T3 cells but it was incompatible with de novo formation of filament networks in the epithelial cell line MCF-7, which lacks an endogenous vimentin network. By in vitro assembly studies, it was confirmed that K19GFAP was unable to assemble into typical intermediate filaments. We also investigated the ability of an appropriate type II keratin partner to rescue K19GFAP from incorporation into a vimentin network and initiate de novo filament assembly, using the fibroblast cell line KF-K8(3), an NIH 3T3 fibroblast cell line expressing a single human keratin, K8. The results confirm the importance of the coiled coil interactions in determining the fate of intermediate filament proteins. The results also emphasize that filament networks can not only tolerate but also incorporate assembly-deficient intermediate filament protein subunits.

Lu X, Park SH, Thompson TC, Lane DP. 1992. Ras-induced hyperplasia occurs with mutation of p53, but activated ras and myc together can induce carcinoma without p53 mutation. Cell, 70 (1), pp. 153-161. | Show Abstract | Read more

Using a reconstituted mouse prostate organ, the effects on endogenous p53 expression of the ras oncogene or of the ras + myc oncogenes were investigated. In this system the ras gene alone causes mild hyperplasia, but the combination of ras and myc leads to the formation of carcinomas. Surprisingly, while p53 mutations were found in cells derived from the reconstituted organs containing ras alone, no such mutations were found in the ras + myc-transformed cells. Their growth, unlike that of the cells containing ras alone, was not inhibited by transfection with plasmids encoding wild-type human p53. We suggest that expression of both activated ras and myc genes bypasses the need for p53 mutation by neutralizing the tumor suppressor activity of normal p53.

Zak J, Vives V, Szumska D, Vernet A, Schneider JE, Miller P, Slee EA, Joss S, Lacassie Y, Chen E et al. 2016. ASPP2 deficiency causes features of 1q41q42 microdeletion syndrome. Cell Death Differ, 23 (12), pp. 1973-1984. | Show Abstract | Read more

Chromosomal abnormalities are implicated in a substantial number of human developmental syndromes, but for many such disorders little is known about the causative genes. The recently described 1q41q42 microdeletion syndrome is characterized by characteristic dysmorphic features, intellectual disability and brain morphological abnormalities, but the precise genetic basis for these abnormalities remains unknown. Here, our detailed analysis of the genetic abnormalities of 1q41q42 microdeletion cases identified TP53BP2, which encodes apoptosis-stimulating protein of p53 2 (ASPP2), as a candidate gene for brain abnormalities. Consistent with this, Trp53bp2-deficient mice show dilation of lateral ventricles resembling the phenotype of 1q41q42 microdeletion patients. Trp53bp2 deficiency causes 100% neonatal lethality in the C57BL/6 background associated with a high incidence of neural tube defects and a range of developmental abnormalities such as congenital heart defects, coloboma, microphthalmia, urogenital and craniofacial abnormalities. Interestingly, abnormalities show a high degree of overlap with 1q41q42 microdeletion-associated abnormalities. These findings identify TP53BP2 as a strong candidate causative gene for central nervous system (CNS) defects in 1q41q42 microdeletion syndrome, and open new avenues for investigation of the mechanisms underlying CNS abnormalities.

Lu M, Muers MR, Lu X. 2016. Introducing STRaNDs: shuttling transcriptional regulators that are non-DNA binding. Nat Rev Mol Cell Biol, 17 (8), pp. 523-532. | Show Abstract | Read more

Many proteins originally identified as cytoplasmic - including many associated with the cytoskeleton or cell junctions - are increasingly being found in the nucleus, where they have specific functions. Here, we focus on proteins that translocate from the cytoplasm to the nucleus in response to external signals and regulate transcription without binding to DNA directly (for example, through interaction with transcription factors). We propose that proteins with such characteristics are classified as a distinct group of extracellular signalling effectors, and we suggest the term STRaND (shuttling transcriptional regulators and non-DNA binding) to refer to this group. Crucial roles of STRaNDs include linking cell morphology and adhesion with changes in transcriptional programmes in response to signals such as mechanical stresses.

Hu Y, Ge W, Wang X, Sutendra G, Zhao K, Dedeić Z, Slee EA, Baer C, Lu X. 2015. Caspase cleavage of iASPP potentiates its ability to inhibit p53 and NF-κB. Oncotarget, 6 (40), pp. 42478-42490. | Show Abstract | Read more

An intriguing biological question relating to cell signaling is how the inflammatory mediator NF-kB and the tumour suppressor protein p53 can be induced by similar triggers, like DNA damage or infection, yet have seemingly opposing or sometimes cooperative biological functions. For example, the NF-κB subunit RelA/p65 has been shown to inhibit apoptosis, whereas p53 induces apoptosis. One potential explanation may be their co-regulation by common cellular factors: inhibitor of Apoptosis Stimulating p53 Protein (iASPP) is one such common regulator of both RelA/p65 and p53. Here we show that iASPP is a novel substrate of caspases in response to apoptotic stimuli. Caspase cleaves the N-terminal region of iASPP at SSLD294 resulting in a prominent 80kDa fragment of iASPP. This caspase cleavage site is conserved in various species from zebrafish to Homo sapiens. The 80kDa fragment of iASPP translocates from the cytoplasm to the nucleus via the RaDAR nuclear import pathway, independent of p53. The 80kDa iASPP fragment can bind and inhibit p53 or RelA/p65 more efficiently than full-length iASPP. Overall, these data reveal a potential novel regulation of p53 and RelA/p65 activities in response to apoptotic stimuli.

Zak J, Lu X. 2015. Aspp1: A Guardian of Hematopoietic Stem Cell Integrity. Cell Stem Cell, 17 (1), pp. 3-5. | Show Abstract | Read more

Eliminating hematopoietic stem cells (HSCs) with DNA damage is necessary to maintain the homeostasis of HSCs, but the mechanisms underlying this apoptotic elimination are unclear. Now in Cell Stem Cell, Yamashita et al. (2015) show that Aspp1 coordinates with p53 to protect HSC pool integrity, guarding against hematological malignancies.

Notari M, Hu Y, Sutendra G, Dedeić Z, Lu M, Dupays L, Yavari A, Carr CA, Zhong S, Opel A et al. 2015. iASPP, a previously unidentified regulator of desmosomes, prevents arrhythmogenic right ventricular cardiomyopathy (ARVC)-induced sudden death. Proc Natl Acad Sci U S A, 112 (9), pp. E973-E981. | Show Abstract | Read more

Desmosomes are anchoring junctions that exist in cells that endure physical stress such as cardiac myocytes. The importance of desmosomes in maintaining the homeostasis of the myocardium is underscored by frequent mutations of desmosome components found in human patients and animal models. Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a phenotype caused by mutations in desmosomal components in ∼ 50% of patients, however, the causes in the remaining 50% of patients still remain unknown. A deficiency of inhibitor of apoptosis-stimulating protein of p53 (iASPP), an evolutionarily conserved inhibitor of p53, caused by spontaneous mutation recently has been associated with a lethal autosomal recessive cardiomyopathy in Poll Hereford calves and Wa3 mice. However, the molecular mechanisms that mediate this putative function of iASPP are completely unknown. Here, we show that iASPP is expressed at intercalated discs in human and mouse postmitotic cardiomyocytes. iASPP interacts with desmoplakin and desmin in cardiomyocytes to maintain the integrity of desmosomes and intermediate filament networks in vitro and in vivo. iASPP deficiency specifically induces right ventricular dilatation in mouse embryos at embryonic day 16.5. iASPP-deficient mice with exon 8 deletion (Ppp1r13l(Δ8/Δ8)) die of sudden cardiac death, displaying features of ARVC. Intercalated discs in cardiomyocytes from four of six human ARVC cases show reduced or loss of iASPP. ARVC-derived desmoplakin mutants DSP-1-V30M and DSP-1-S299R exhibit weaker binding to iASPP. These data demonstrate that by interacting with desmoplakin and desmin, iASPP is an important regulator of desmosomal function both in vitro and in vivo. This newly identified property of iASPP may provide new molecular insight into the pathogenesis of ARVC.

Wang Y, Bu F, Royer C, Serres S, Larkin JR, Soto MS, Sibson NR, Salter V, Fritzsche F, Turnquist C et al. 2014. ASPP2 controls epithelial plasticity and inhibits metastasis through β-catenin-dependent regulation of ZEB1. Nat Cell Biol, 16 (11), pp. 1092-1104. | Show Abstract | Read more

Epithelial to mesenchymal transition (EMT), and the reverse mesenchymal to epithelial transition (MET), are known examples of epithelial plasticity that are important in kidney development and cancer metastasis. Here we identify ASPP2, a haploinsufficient tumour suppressor, p53 activator and PAR3 binding partner, as a molecular switch of MET and EMT. ASPP2 contributes to MET in mouse kidney in vivo. Mechanistically, ASPP2 induces MET through its PAR3-binding amino-terminus, independently of p53 binding. ASPP2 prevents β-catenin from transactivating ZEB1, directly by forming an ASPP2-β-catenin-E-cadherin ternary complex and indirectly by inhibiting β-catenin's N-terminal phosphorylation to stabilize the β-catenin-E-cadherin complex. ASPP2 limits the pro-invasive property of oncogenic RAS and inhibits tumour metastasis in vivo. Reduced ASPP2 expression results in EMT, and is associated with poor survival in hepatocellular carcinoma and breast cancer patients. Hence, ASPP2 is a key regulator of epithelial plasticity that connects cell polarity to the suppression of WNT signalling, EMT and tumour metastasis.

Lu M, Miller P, Lu X. 2014. Restoring the tumour suppressive function of p53 as a parallel strategy in melanoma therapy FEBS Letters, 588 (16), pp. 2616-2621. | Show Abstract | Read more

The tumour suppressor p53 is a master sensor of stress and it controls the expression of hundreds to thousands of genes with diverse biological functions including cell cycle arrest, apoptosis, and senescence. Consequently p53 is the most mutated gene found in human cancer and p53 mutation rate varies from 5% to 95%. Importantly p53 activity is often inactivated in tumours expressing structurally wild type p53. Thus one of the major challenges in cancer research is to restore the tumour suppressive function of p53. Intensive studies in the past decade have demonstrated that in addition to mutation, p53 activities are largely regulated by cellular factors that control the expression level and/or transcriptional activities of p53. MDM2, MDM4, p14 ARF and the ASPP family of proteins are among the most studied regulators of p53. With increased understanding of the complexity of p53 regulation, various p53 reactivating approaches are being developed. This review will focus on the recent understanding of p53 inactivation in melanoma and the approaches to reactivate p53 in preclinical studies. Recent success in the therapeutic targeting of the BRAFV600E oncogenic protein was accompanied with subsequent relapse caused by acquired drug resistance. Restoration of the tumour suppressive function of p53 presents a parallel cancer therapeutic opportunity alongside BRAFV600E inhibition. Thus targeted therapy and concurrent reactivation of p53 may be a fertile ground to achieve synergistic killing of the 50% of cancer cells that express structurally wild type p53. © 2014 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.

Goding CR, Pei D, Lu X. 2014. Cancer: pathological nuclear reprogramming? Nat Rev Cancer, 14 (8), pp. 568-573. | Show Abstract | Read more

The ability of stem cells to self-renew and generate different lineages during development and organogenesis is a fundamental, tightly controlled, and generally unidirectional process, whereas the 'immortality' of cancer cells could be regarded as pathological self-renewal. The molecular mechanisms that underpin the generation of induced pluripotent stem cells are remarkably similar to those that are deregulated in cancer - so much so that aberrant reprogramming is tumorigenic. The similarities also suggest that mutations in genes implicated in DNA methylation dynamics might represent a hallmark of cancers with a stem cell origin, and they highlight an alternative view of cancer that may be of clinical benefit.

Turnquist C, Wang Y, Severson DT, Zhong S, Sun B, Ma J, Constaninescu SN, Ansorge O, Stolp HB, Molnár Z et al. 2014. STAT1-induced ASPP2 transcription identifies a link between neuroinflammation, cell polarity, and tumor suppression. Proc Natl Acad Sci U S A, 111 (27), pp. 9834-9839. | Show Abstract | Read more

Inflammation and loss of cell polarity play pivotal roles in neurodegeneration and cancer. A central question in both diseases is how the loss of cell polarity is sensed by cell death machinery. Here, we identify apoptosis-stimulating protein of p53 with signature sequences of ankyrin repeat-, SH3 domain-, and proline-rich region-containing protein 2 (ASPP2), a haploinsufficient tumor suppressor, activator of p53, and regulator of cell polarity, as a transcriptional target of signal transducer and activator of transcription 1 (STAT1). LPS induces ASPP2 expression in murine macrophage and microglial cell lines, a human monocyte cell line, and primary human astrocytes in vitro. LPS and IFNs induce ASPP2 transcription through an NF-κB RELA/p65-independent but STAT1-dependent pathway. In an LPS-induced maternal inflammation mouse model, LPS induces nuclear ASPP2 in vivo at the blood-cerebral spinal fluid barrier (the brain's barrier to inflammation), and ASPP2 mediates LPS-induced apoptosis. Consistent with the role of ASPP2 as a gatekeeper to inflammation, ASPP2-deficient brains possess enhanced neuroinflammation. Elevated ASPP2 expression is also observed in mouse models and human neuroinflammatory disease tissue, where ASPP2 was detected in GFAP-expressing reactive astrocytes that coexpress STAT1. Because the ability of ASPP2 to maintain cellular polarity is vital to CNS development, our findings suggest that the identified STAT1/ASPP2 pathway may connect tumor suppression and cell polarity to neuroinflammation.

Lu M, Zak J, Chen S, Sanchez-Pulido L, Severson DT, Endicott J, Ponting CP, Schofield CJ, Lu X. 2014. A code for RanGDP binding in ankyrin repeats defines a nuclear import pathway. Cell, 157 (5), pp. 1130-1145. | Show Abstract | Read more

Regulation of nuclear import is fundamental to eukaryotic biology. The majority of nuclear import pathways are mediated by importin-cargo interactions. Yet not all nuclear proteins interact with importins, necessitating the identification of a general importin-independent nuclear import pathway. Here, we identify a code that determines importin-independent nuclear import of ankyrin repeats (ARs), a structural motif found in over 250 human proteins with diverse functions. AR-containing proteins (ARPs) with a hydrophobic residue at the 13th position of two consecutive ARs bind RanGDP efficiently, and consequently enter the nucleus. This code, experimentally tested in 17 ARPs, predicts the nuclear-cytoplasmic localization of over 150 annotated human ARPs with high accuracy and is acquired by the most common familial melanoma-associated CDKN2A mutation, leading to nuclear accumulation of mutant p16ink4a. The RaDAR (RanGDP/AR) pathway represents a general importin-independent nuclear import pathway and is frequently used by AR-containing transcriptional regulators, especially those regulating NF-κB/p53.

Lu M, Miller P, Lu X. 2014. Restoring the tumour suppressive function of p53 as a parallel strategy in melanoma therapy. FEBS Lett, 588 (16), pp. 2616-2621. | Show Abstract | Read more

The tumour suppressor p53 is a master sensor of stress and it controls the expression of hundreds to thousands of genes with diverse biological functions including cell cycle arrest, apoptosis, and senescence. Consequently p53 is the most mutated gene found in human cancer and p53 mutation rate varies from 5% to 95%. Importantly p53 activity is often inactivated in tumours expressing structurally wild type p53. Thus one of the major challenges in cancer research is to restore the tumour suppressive function of p53. Intensive studies in the past decade have demonstrated that in addition to mutation, p53 activities are largely regulated by cellular factors that control the expression level and/or transcriptional activities of p53. MDM2, MDM4, p14(ARF) and the ASPP family of proteins are among the most studied regulators of p53. With increased understanding of the complexity of p53 regulation, various p53 reactivating approaches are being developed. This review will focus on the recent understanding of p53 inactivation in melanoma and the approaches to reactivate p53 in preclinical studies. Recent success in the therapeutic targeting of the BRAFV600E oncogenic protein was accompanied with subsequent relapse caused by acquired drug resistance. Restoration of the tumour suppressive function of p53 presents a parallel cancer therapeutic opportunity alongside BRAFV600E inhibition. Thus targeted therapy and concurrent reactivation of p53 may be a fertile ground to achieve synergistic killing of the 50% of cancer cells that express structurally wild type p53.

Nešić D, Buti L, Lu X, Stebbins CE. 2014. Structure of the Helicobacter pylori CagA oncoprotein bound to the human tumor suppressor ASPP2. Proc Natl Acad Sci U S A, 111 (4), pp. 1562-1567. | Show Abstract | Read more

The Cytotoxin associated gene A (CagA) protein of Helicobacter pylori is associated with increased virulence and risk of cancer. Recent proteomic studies have demonstrated an association of CagA with the human tumor suppressor Apoptosis-stimulating Protein of p53-2 (ASPP2). We present here a genetic, biochemical, and structural analysis of CagA with ASPP2. Domain delineation of the 120-kDa CagA protein revealed a stable N-terminal subdomain that was used in a yeast two-hybrid screen that identified the proline-rich domain of ASPP2 as a host cellular target. Biochemical experiments confirm this interaction. The cocrystal structure to 2.0-Å resolution of this N-terminal subdomain of CagA with a 7-kDa proline-rich sequence of ASPP2 reveals that this domain of CagA forms a highly specialized three-helix bundle, with large insertions in the loops connecting the helices. These insertions come together to form a deep binding cleft for a highly conserved 20-aa peptide of ASPP2. ASPP2 forms an extended helix in this groove of CagA, burying more than 1,000 Å(2) of surface area. This interaction is disrupted in vitro and in vivo by structure-based, loss-of-contact point mutations of key residues in either CagA or ASPP2. Disruption of CagA and ASPP2 binding alters the function of ASPP2 and leads to the decreased survival of H. pylori-infected cells.

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