Colon cancer is the third most common cancer affecting men and women and the second leading cause of cancer death. The most common disease predisposing patients to colorectal cancer is hereditary non-polyposis colon cancer (HNPCC) which stems from mutations in DNA mismatch repair (MMR) genes. In addition, MMR defects are also detected in 10-30% of sporadic colorectal, endometrial and other cancers. This proposal will address the broad question of why defects in the MMR pathway cause tumorigenesis. The MMR system corrects mispaired or damaged DNA resulting from DNA polymerase errors, recombination between heterologous sequences or endogenous and exogenous mutagens. Thus, loss of MMR function results in an elevated mutation rate (mutator phenotype). However, the MMR system is also required for the activation of cell cycle checkpoints and apoptosis in response to DNA damage. We hypothesize that this MMR-dependent checkpoint/apoptosis response plays a significant role in tumor protection as its disruption would allow cells with increased genomic instability to grow unchecked. A prediction based on this hypothesis is that tumors harbor mutations in MMR genes that disrupt damage repair and checkpoint/apoptosis response functions. We will test this prediction by determining whether cancer-associated missense mutations of the MMR genes hMSH2 and hMSH6 affect both DNA repair and checkpoint/apoptosis response. We propose 3 aims to evaluate the functional consequences of cancer- associated missense mutations in hMSH2 and hMSH6. We have previously detailed the effects of seven hMSH2 missense mutations associated with HNPCC on the biochemical functions of the hMSH2-hMSH6 heterodimer.
In Aim 1, we will examine the biochemical effects of cancer-associated missense mutations in hMSH6.
In Aim 2, we will devise an in vitro assay to examine how the hMSH2-hMSH6 heterodimer interacts with other proteins involved in repair and checkpoint/apoptosis signaling and whether cancer-associated missense mutations affect these interactions. Finally, in Aim 3 we will examine the effects of missense mutations in hMSH2 and hMSH6 on DNA repair and checkpoint/apoptosis functions in human cell culture models. Through this thorough integration of biochemical and cell biology approaches we will utilize cancer-causing missense mutations as tools to further understand the molecular mechanism of MMR and how those mechanisms are disrupted during tumorigenesis.Colon cancer is the third most common malignancy in men and women and ranks behind only lung cancer in cancer deaths. Inherited mutations in genes of the mismatch repair pathway cause the disease hereditary non-polyposis colon cancer, while defects in this pathway are also detected in 10-30% of colorectal, endometrial and other cancers in the general population. Understanding at the molecular level why alterations in this pathway promote tumorigenesis will aide the development of more targeted therapeutic, preventive and diagnostic strategies.

National Institute of Health (NIH)
National Cancer Institute (NCI)
Research Project (R01)
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Cancer Genetics Study Section (CG)
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Okano, Paul
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University of Connecticut
Other Basic Sciences
Schools of Medicine
United States
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Thompson, Bryony A; Spurdle, Amanda B; Plazzer, John-Paul et al. (2014) Application of a 5-tiered scheme for standardized classification of 2,360 unique mismatch repair gene variants in the InSiGHT locus-specific database. Nat Genet 46:107-15
Heinen, Christopher D (2014) Translating mismatch repair mechanism into cancer care. Curr Drug Targets 15:53-64
Lin, Bo; Gupta, Dipika; Heinen, Christopher D (2014) Human pluripotent stem cells have a novel mismatch repair-dependent damage response. J Biol Chem 289:24314-24
Mastrocola, Adam S; Kim, Sang Hwa; Trinh, Anthony T et al. (2013) The RNA-binding protein fused in sarcoma (FUS) functions downstream of poly(ADP-ribose) polymerase (PARP) in response to DNA damage. J Biol Chem 288:24731-41
Mohni, Kareem N; Mastrocola, Adam S; Bai, Ping et al. (2011) DNA mismatch repair proteins are required for efficient herpes simplex virus 1 replication. J Virol 85:12241-53
Heinen, Christopher D; Cyr, Jennifer L; Cook, Christopher et al. (2011) Human MSH2 (hMSH2) protein controls ATP processing by hMSH2-hMSH6. J Biol Chem 286:40287-95
Mastrocola, Adam S; Heinen, Christopher D (2010) Nuclear reorganization of DNA mismatch repair proteins in response to DNA damage. DNA Repair (Amst) 9:120-33
Mastrocola, Adam S; Heinen, Christopher D (2010) Lynch syndrome-associated mutations in MSH2 alter DNA repair and checkpoint response functions in vivo. Hum Mutat 31:E1699-708
Heinen, Christopher D (2010) Genotype to phenotype: analyzing the effects of inherited mutations in colorectal cancer families. Mutat Res 693:32-45
Cyr, Jennifer L; Heinen, Christopher D (2008) Hereditary cancer-associated missense mutations in hMSH6 uncouple ATP hydrolysis from DNA mismatch binding. J Biol Chem 283:31641-8