Title: Genetic approaches to combating colorectal cancer
Funder: Medical Research Council

Abstract: Objectives: To identify novel common low penetrance colorectal cancer susceptibility loci, including structural sequence variants. To build models to enable profiling of genetic and other risk in the general population for public health benefit. To identify novel rare high penetrance alleles, including structural sequence variants, responsible for colorectal cancer susceptibility. To define gene-environment interactions. To identify modifier alleles of known susceptibility alleles. To define the contribution of known genes predisposing to colorectal cancer in order to target clinical preventative measures including modifiable environmental risk factors. To determine the molecular mechanisms involved in the antitumour effect of aspirin and other NSAIDs to inform translational research in human chemoprevention. Progress: Colorectal Cancer susceptibility We identified 10 new common colorectal cancer susceptibility loci through a genome-wide association (GWA) approach. We used Scottish GWA data to estimate the number of loci that would account for the entire genetic contribution to colorectal cancer and have estimated the number of loci required to provide 80% power to define genetic risk in the population. After fine mapping, we have undertaken molecular studies investigating the causal variants at a number of the associated loci we identified. We continue to refine understanding of the role of defects in DNA mismatch repair genes in colorectal cancer susceptibility and establish gene prevalence and penetrance. This work led to ongoing translational research investigating the potential for primary and secondary prevention, including the first ever RCT. We have established the largest resource of DNA mismatch repair gene mutations and now embarked on a GWA approach to mapping genetic modifiers of Lynch Syndrome, the most colon dominant gene disorder predisposing to colorectal cancer. Chemoprevention We showed that aspirin modulates apoptotic response in colorectal cancer cells by a mechanism that is dependent on NF-kappaB transcription factor activation. We showed that aspirin induces signal-specific I-kappaB degradation and nuclear translocation of p65 in colorectal cancer cells. We engineered cells to constitutively express mutant IkappaB, resistant to phosphorylation and degradation and showed that these cells are resistant to aspirin induced NF-kappaB activation and to apoptosis. We showed that sulindac, sulindac sulfone and indomethacin activate the NF-kappaB pathway in colorectal cancer cells and show that NSAIDs induce nucleolar translocation of the RelA subunit of NF-kappaB. Using RelA deleted for the previously described nucleolar localization signal, we demonstrated that this response is causally involved in the apoptotic effects of these agents. As well as providing new understanding of the molecular determinants of RelA function, these findings also have relevance to the development of novel chemotherapeutic and chemopreventative agents. We have also shown that CDK4 inhibitors induce translocation of RelA/p65 from the cytoplasm to the nucleoplasm and then to the nucleolus. This was accompanied by a repression of NFkappaB-driven transcription and apoptosis of the cancer cells. When cells expressing this mutant protein were treated with the CDK4 inhibitor, RelA translocated from the cytoplasm to the nucleoplasm, but was excluded from the nucleolus. Furthermore, apoptosis induced by CDK4 inhibition RelA dependent. In this work we have further expanded understanding of the molecular mechanisms that regulate programmed cell death induced by disruption of the cyclin D1/CDK4 complex in colorectal cancer. Our in vitro findings have been extended into clinical studies of patients with rectal cancer, showing that the p65 nuclear translocation induced by aspirin results in repression of NF-kappaB driven transcription by induction of repressive complexes.


Research activity codes: 2.1 BIOLOGICAL AND ENDOGENOUS FACTORS;5.1 PHARMACEUTICALS
Health categories: CANCER AND NEOPLASMS