DNA mismatch repair and cancer in murine models

描述(申请人提供)：DNA错配修复(MMR)系统对于维持哺乳动物基因组的完整性是必不可少的，它通过去除错误复制引起的错误结合的核苷酸，并在暴露于遗传毒性药物后介导DNA损伤反应。哺乳动物MMR基因的突变会导致自发突变率增加，并极易患癌症。真核MMR是一个复杂的系统，需要多个MutS和MutL蛋白相互作用才能启动修复反应。在错配识别之后，下游事件被激活，导致错误结合或受损的核苷酸被切除，并发出DNA损伤诱导细胞周期停滞和凋亡的信号。我们的研究计划集中于阐明哺乳动物MMR中单个MutS同源基因(MSH)的功能，并评估它们对抑制癌症的重要性。在过去的资助期间，我们发现损害Msh2-MSH6复合体(称为MutS1)的ATPase活性的突变会导致DNA修复缺陷，但不会损害复合体的DNA损伤反应功能，从而使我们能够有效地分离这两个功能。我们的研究进一步证明，MutS1的DNA损伤信号在该过程的初始阶段对于抑制肿瘤的发生具有重要意义。此外，我们还证明了MMR错义突变比完全丧失功能突变导致的癌症表型异质性更多。基于这些结果，我们假设MutS1的DNA修复和DNA损伤信号都有助于抑制MMR依赖的肿瘤发生和组织特异性。在这个持续的应用中，我们计划通过分析MutS1对氧化DNA损伤修复的贡献来研究这一假说，并评估这种修复对MutS1突变小鼠肿瘤抑制的意义。我们还将利用新的条件Msh2突变小鼠模型来研究MutS1的DNA修复和损伤反应功能在肠道肿瘤发生和化疗中的意义。最后，我们建议建立一个体内系统来分析MMR复合体的形成，并识别与MutS1相互作用并参与错配切除和小鼠组织DNA损伤反应的新蛋白。公共卫生相关性：DNA错配修复系统(MMR)对于维持哺乳动物基因组的完整性至关重要，MMR的缺陷是导致人类癌症综合征、遗传性非息肉病、结直肠癌(HNPCC)和大量散发性癌症的原因。我们正在研究具有关键MMR基因突变的小鼠品系，以确定对DNA修复功能、体内突变表型和MMR抑制肿瘤形成的能力的影响。我们的研究将更好地了解这一重要的基因组维持系统的生物学功能，以及防止哺乳动物肿瘤形成的分子机制。

DESCRIPTION (provided by applicant): The DNA mismatch repair (MMR) system is essential for maintaining the integrity of mammalian genomes by removing misincorporated nucleotides that result from erroneous replication and by mediating a DNA damage response after exposure to genotoxic agents. Mutations in mammalian MMR genes result in increased spontaneous mutation rates and strong predisposition to cancer. Eukaryotic MMR is a complex system that requires the interaction of several MutS and MutL proteins for the initiation of the repair reaction. Subsequent to mismatch recognition, downstream events are activated that lead to the excision of misincorporated or damaged nucleotides and the signaling of DNA damage-induced cell cycle arrest and apoptosis. Our research program focuses on elucidating the functions of the individual MutS homologs (Msh) in mammalian MMR and on assessing their importance for the suppression of cancer. In the past funding period, we found that mutations impairing the ATPase activity of the Msh2-Msh6 complex (termed MutS1) cause DNA repair deficiency but do not impair the DNA damage response function of the complex, allowing us to effectively separate these two functions. Our studies further demonstrated that DNA damage signaling by MutS1 is important for the suppression of tumorigenesis in the initial stages of the process. In addition, we demonstrated that MMR missense mutations could result in more heterogeneous cancer phenotypes than those caused by complete loss of function mutations. Based on these results, we hypothesize that both DNA repair and DNA damage signaling by MutS1 contribute to the suppression and tissue specificity of MMR-dependent tumorigenesis. In this continuing application, we plan to investigate this hypothesis by analyzing the contribution of MutS1 to the repair of oxidative DNA damage and assessing the significance of this repair for tumor suppression in MutS1 mutant mice. We will also utilize novel conditional Msh2 mutant mouse models to study the significance of the DNA repair and damage response functions of MutS1 for intestinal tumorigenesis and chemotherapeutic treatment. Finally, we propose to establish an in vivo system to analyze MMR complex formation and identify novel proteins that interact with MutS1 and participate in mismatch excision and DNA damage response in mouse tissues. PUBLIC HEALTH RELEVANCE: The DNA mismatch repair system (MMR) is essential for maintaining the integrity of mammalian genomes and defects in MMR are the cause of the cancer syndrome hereditary nonpolyposis colorectal cancer (HNPCC) and a significant number of sporadic cancers in humans. We are studying mouse lines with mutations in key MMR genes to determine the impact on DNA repair functions, in vivo mutator phenotypes and the ability of MMR to suppress tumor formation. Our studies will provide a better understanding of the biological functions of this important genome maintenance system and of the molecular mechanisms that prevent tumor formation in mammals.