Prof Ian Tomlinson
|Research Area:||Genetics and Genomics|
|Technology Exchange:||Chromosome mapping, Immunohistochemistry, SNP typing, Transcript profiling and Transgenesis|
|Scientific Themes:||Cancer Biology and Genetics & Genomics|
|Keywords:||Cancer genetics, Population genetics, Colorectal, Renal, Mouse models and Pseudo-hypoxia|
- The identification of genes that predispose to colorectal and other cancers
- Functional genetics of colorectal tumorigenesis, with emphasis on the relative importance of selection and genomic instability.
- Genetic changes and mechanisms of tumorigenesis in renal tumours.
|Dr Jenny Taylor||Wellcome Trust Centre for Human Genetics||Oxford University||UK|
|Prof Chris Holmes||Wellcome Trust Centre for Human Genetics||Oxford University||UK|
|Dr Jean-Baptiste Cazier||Wellcome Trust Centre for Human Genetics||Oxford University||UK|
|Dr Simon Leedham||Wellcome Trust Centre for Human Genetics||Oxford University||UK|
|Prof David Kerr CBE FMedSci FRCP (RDM)||Nuffield Division of Clinical Laboratory Sciences||Oxford University||UK|
|Dr Rachel Midgley (RDM)||Oncology||University of Oxford||United Kingdom|
|Dr Jonathan M Grimes||Structural Biology||Oxford University||UK|
Cancers with chromosomal instability (CIN) are held to be aneuploid/polyploid with multiple large-scale gains/deletions, but the processes underlying CIN are unclear and different types of CIN might exist. We investigated colorectal cancer cell lines using array-comparative genomic hybridization (CGH) for copy number changes and single-copy number polymorphism (SNP) microarrays for allelic loss (LOH). Many array-based CGH changes were not found by LOH because they did not cause true reduction-to-homozygosity. Conversely, many regions of SNP-LOH occurred in the absence of copy number change, comprising an average per cell line of 2 chromosomes with complete LOH; 1-2 terminal regions of LOH (mitotic recombination); and 1 interstitial region of LOH. SNP-LOH detected many novel changes, representing possible locations of uncharacterized tumor suppressor loci. Microsatellite unstable (MSI+) lines infrequently showed gains/deletions or whole-chromosome LOH, but their near-diploid karyotypes concealed mitotic recombination frequencies similar to those of MSI- lines. We analyzed p53 and chromosome 18q (SMAD4) in detail, including mutation screening. Almost all MSI- lines showed LOH and/or deletion of p53 and 18q; some near-triploid lines had acquired three independent changes at these loci. We found consistent results in primary colorectal cancers. Overall, the distributions of mitotic recombination and whole-chromosome LOH in the MSI- cell lines differed significantly from random, with some lines having much higher than expected levels of these changes. Moreover, lines with more LOH changes had significantly fewer copy number changes. These data suggest that CIN is not synonymous with copy number change and some cancers have a specific tendency to whole-chromosome deletion and regain or to mitotic recombination. Hide abstract
The nuclear-encoded Krebs cycle enzymes, fumarate hydratase (FH) and succinate dehydrogenase (SDHB, -C and -D), act as tumour suppressors. Germline mutations in FH predispose individuals to leiomyomas and renal cell cancer (HLRCC), whereas mutations in SDH cause paragangliomas and phaeochromocytomas (HPGL). In this study, we have shown that FH-deficient cells and tumours accumulate fumarate and, to a lesser extent, succinate. SDH-deficient tumours principally accumulate succinate. In situ analyses showed that these tumours also have over-expression of hypoxia-inducible factor 1alpha (HIF1alpha), activation of HIF1alphatargets (such as vascular endothelial growth factor) and high microvessel density. We found no evidence of increased reactive oxygen species in our cells. Our data provide in vivo evidence to support the hypothesis that increased succinate and/or fumarate causes stabilization of HIF1alpha a plausible mechanism, inhibition of HIF prolyl hydroxylases, has previously been suggested by in vitro studies. The basic mechanism of tumorigenesis in HPGL and HLRCC is likely to be pseudo-hypoxic drive, just as it is in von Hippel-Lindau syndrome. Hide abstract
Germ-line mutations in the base-excision-repair gene MYH have been associated with recessive inheritance of multiple colorectal adenomas. Tumors from affected persons displayed excess somatic transversions of a guanine-cytosine pair to a thymine-adenine pair (G:C-->T:A) in the APC gene. Hide abstract
Targeting DNA damage to specific genomic loci to define chromatin regulation of DNA repair
Upon DNA damage detection, large regions of the chromatin surrounding the sites of DNA lesions are modified in programmed molecular events that are crucial for ensuring that the DNA is processed appropriately for the subsequent repair reaction [Chapman & Taylor, 2012]. Imbalances in these processes can lead to deleterious translocation events that drive tumourigenesis in humans, such as those that cause malignancy in patients harbouring mutations in the BRCA1 tumour suppressor gene. To date, ...