Mismatch Repair Functions Affected During Tumorigenesis

描述（由申请人提供）：结肠癌是影响男性和女性的第三大常见癌症，也是癌症死亡的第二大原因。导致结直肠癌的最常见疾病是遗传性非息肉性结肠癌（HNPCC），它源于DNA错配修复（MMR）基因的突变。此外，在10-30%的散发性结直肠癌、子宫内膜癌和其他癌症中也检测到MMR缺陷。这一建议将解决为什么MMR通路缺陷导致肿瘤发生的广泛问题。MMR系统纠正由DNA聚合酶错误、异源序列之间的重组或内源性和外源性诱变剂引起的错配或损伤的DNA。因此，MMR功能的丧失导致突变率升高（突变表型）。然而，MMR系统也是激活细胞周期检查点和响应DNA损伤的细胞凋亡所必需的。我们假设这种依赖于mmr的检查点/凋亡反应在肿瘤保护中起着重要作用，因为它的破坏会使基因组不稳定性增加的细胞不受控制地生长。基于这一假设的预测是，肿瘤中含有破坏损伤修复和检查点/凋亡反应功能的MMR基因突变。我们将通过确定癌症相关的MMR基因hMSH2和hMSH6错义突变是否影响DNA修复和检查点/凋亡反应来验证这一预测。

DESCRIPTION (provided by applicant): 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.