Dr John Christianson
| Research Area: | Cell and Molecular Biology |
|---|---|
| Technology Exchange: | Cell sorting, Microscopy (Confocal) and Protein interaction |
| Keywords: | Ubiquitin-proteasome system (UPS), ER-associated degradation (ERAD), quality control, metastasis, glycoproteins and tumor suppressor |
My lab’s principal focus is on ER-associated degradation (ERAD), a multifaceted process responsible for clearing non-functional and orphan translation products from the early secretory pathway. Ensuring the highest level of fidelity for the transiting protein load is essential, as unabated accumulation or exposure to the extracellular environment of misfolded proteins can negatively impact cellular homeostasis and viability. More than 40 unique proteins have been implicated in ERAD, many as part of transiently forming macromolecular complexes. Yet despite their implied role in ERAD, many of these factors remain poorly characterized. ERAD plays a central role in inherited disorders such as cystic fibrosis and ?1-antitrypsin disease. Many studies have linked ERAD genes to various forms of cancer and recent evidence also suggests a novel role for ERAD in regulating tumor suppressor protein levels.
Our interests lie in characterizing essential components of the ERAD mechanism and indentifying novel substrates of this pathway. We employ proteomic, cell biological, functional genomic and biochemical techniques to identify factors, characterize the complexes they function in, and understand the substrate-specificity with which they operate. We are keenly interested in understanding the role that quality control at the level of the ER plays in the expression of proteins responsible for tumor progression and metastasis. Our long term goals are to explore quality control mechanisms as a novel point of intervention for cancer therapies.
There are no collaborations listed for this principal investigator.
2008. OS-9 and GRP94 deliver mutant alpha1-antitrypsin to the Hrd1-SEL1L ubiquitin ligase complex for ERAD. Nature cell biology, 10 (3), pp. 272-82. Read abstract | View on PubMed
Terminally misfolded or unassembled proteins in the early secretory pathway are degraded by a ubiquitin- and proteasome-dependent process known as ER-associated degradation (ERAD). How substrates of this pathway are recognized within the ER and delivered to the cytoplasmic ubiquitin-conjugating machinery is unknown. We report here that OS-9 and XTP3-B/Erlectin are ER-resident glycoproteins that bind to ERAD substrates and, through the SEL1L adaptor, to the ER-membrane-embedded ubiquitin ligase Hrd1. Both proteins contain conserved mannose 6-phosphate receptor homology (MRH) domains, which are required for interaction with SEL1L, but not with substrate. OS-9 associates with the ER chaperone GRP94 which, together with Hrd1 and SEL1L, is required for the degradation of an ERAD substrate, mutant alpha(1)-antitrypsin. These data suggest that XTP3-B and OS-9 are components of distinct, partially redundant, quality control surveillance pathways that coordinate protein folding with membrane dislocation and ubiquitin conjugation in mammalian cells. Hide abstract
2006. Central pore residues mediate the p97/VCP activity required for ERAD. Molecular cell, 22 (4), pp. 451-62. Read abstract | View on PubMed
The AAA-ATPase p97/VCP facilitates protein dislocation during endoplasmic reticulum-associated degradation (ERAD). To understand how p97/VCP accomplishes dislocation, a series of point mutants was made to disrupt distinguishing structural features of its central pore. Mutants were evaluated in vitro for ATPase activity in the presence and absence of synaptotagmin I (SytI) and in vivo for ability to process the ERAD substrate TCRalpha. Synaptotagmin induces a 4-fold increase in the ATPase activity of wild-type p97/VCP (p97/VCP(wt)), but not in mutants that showed an ERAD impairment. Mass spectrometry of crosslinked synaptotagmin . p97/VCP revealed interactions near Trp551 and Phe552. Additionally, His317, Arg586, and Arg599 were found to be essential for substrate interaction and ERAD. Except His317, which serves as an interaction nexus, these residues all lie on prominent loops within the D2 pore. These data support a model of substrate dislocation facilitated by interactions with p97/VCP's D2 pore. Hide abstract
2005. Increased susceptibility of cytoplasmic over nuclear polyglutamine aggregates to autophagic degradation. Proceedings of the National Academy of Sciences of the United States of America, 102 (37), pp. 13135-40. Read abstract | View on PubMed
CNS neurons are endowed with the ability to recover from cytotoxic insults associated with the accumulation of proteinaceous aggregates in mouse models of polyglutamine disease, but the cellular mechanism underlying this phenomenon is unknown. Here, we show that autophagy is essential for the elimination of aggregated forms of mutant huntingtin and ataxin-1 from the cytoplasmic but not nuclear compartments. Human orthologs of yeast autophagy genes, molecular determinants of autophagic vacuole formation, are recruited to cytoplasmic but not nuclear inclusion bodies in vitro and in vivo. These data indicate that autophagy is a critical component of the cellular clearance of toxic protein aggregates and may help to explain why protein aggregates are more toxic when directed to the nucleus. Hide abstract
2004. Regulation of nicotinic receptor expression by the ubiquitin-proteasome system. The EMBO journal, 23 (21), pp. 4156-65. Read abstract | View on PubMed
Control of ligand-gated ion channel (LGIC) expression is essential for the formation, maintenance and plasticity of synapses. Treatment of mouse myotubes with proteasome inhibitors increased the number of surface nicotinic acetylcholine receptors (AChRs), indicating LGIC expression is regulated by the ubiquitin-proteasome system (UPS). Elevated surface expression resulted from increased AChR delivery to the plasma membrane and not from decreased turnover from the surface. The rise in AChR trafficking was the direct result of increased assembly of subunits in the endoplasmic reticulum (ER). Because proteasome inhibitors also blocked ER-associated degradation (ERAD) of unassembled AChR subunits, the data indicate that the additional AChRs were assembled from subunits normally targeted for ERAD. Our data show that AChR surface expression is regulated by the UPS through ERAD, whose activity determines oligomeric receptor assembly efficiency. Hide abstract
Regulation of ERAD genes in cancer
Endoplasmic reticulum-associated degradation (ERAD) is the constitutive cellular process essential for ensuring fidelity of all secreted and plasma membrane proteins. In response to cellular stress (e.g. oxidative, nutritional, thermal, hypoxic) genes encoding protein quality control components (including ERAD and molecular chaperones) are differentially regulated to deal with an accumulation of unfolded/misfolded proteins that results. Dynamic cellular environments, such as those present in ...
Discovery and characterization of novel ERAD components
Endoplasmic reticulum-associated degradation (ERAD) is the constitutive cellular process essential for ensuring fidelity of all secreted and plasma membrane proteins. An increasing body of evidence suggests that ERAD plays a significant role in the general regulation of steady-state protein levels, both on the cell surface and within the ER. While over 50 unique proteins have already been implicated in ERAD, recent proteomic and functional genomic data from our group has identified a number ...
Isolation and identification of novel ERAD substrates
Endoplasmic reticulum-associated degradation (ERAD) is the constitutive cellular process essential for ensuring fidelity of all secreted and plasma membrane proteins. An increasing body of evidence suggests that ERAD plays a significant role in the general regulation of protein levels, both on the cell surface and within the ER. Yet to date, only a handful of proteins have been established as bona fide ERAD substrates, hardly representative of the diversity of potential targets given that ...
