hMLHI-hMRE11 interplay in DNA mismatch repair

描述(申请人提供)：细胞监测遗传信息的完整性从亲代细胞传递到后代是通过一个蛋白质网络进行的，该网络主要参与细胞周期调节、DNA复制、DNA修复和染色体分离。这个网络中的任何蛋白质因子的缺陷都会导致细胞不同程度的遗传不稳定，因此，容易患上癌症。DNA错配修复系统是DNA错配修复系统之一，它通过监测和纠正DNA重组和DNA合成过程中发生的错配核苷酸，在维持基因组稳定性方面发挥着至关重要的作用。MMR基因的突变会导致更高的突变率，增加微卫星的不稳定性。包括MutS和MutL同源物在内的几个MMR基因的胚系突变与人类遗传性非息肉病性结直肠癌(HNPCC)的发病有关，其中hMLH1和hMSH2基因突变是HNPCC的主要贡献者。我们最近的工作揭示了在体外和体内hMLH1和hMRE11之间的直接物理联系。人hMRE11是多功能蛋白质复合体(hRAD50-hMRE11-NBS1)的重要核酸酶，它促进DNA双链断裂的修复，在DNA损伤反应的信号转导、减数分裂重组和端粒维持中发挥作用。HMRE11基因突变导致罕见的“类AT”(ATLD)疾病的发生。已知hMRE11相关复合体具有动态的时空细胞分布，在DNA损伤部位形成DNA损伤诱导灶。因此，本研究计划的长期目标是阐明MMR涉及的分子机制、MMR蛋白与hMRE11相关蛋白复合体之间的功能联系，以及破坏这些蛋白因子之间相互作用的突变的生物学效应。我们建议通过一种强有力的系统方法来解决这些重要问题，该方法包括以下具体目标：(1)检验hMRE11代表DNA错配修复途径功能成分的假设；(2)确定hMLH1结合是否刺激hMRE11的核酸酶活性以及hMRE11核酸酶活性在MMR过程中的功能作用；(3)检验hMLH1 HNPCC错义突变不同地影响hMLHI-hMRE11和hMLHI-hPMS2异源复合体的形成，从而破坏hMLH1-hMRE11复合体是hMLH1 HNPCC突变致病效应的另一种机制。拟议的研究结果将有助于深入了解MMR和hMRE11相关复合体共同作用以维持遗传稳定性的分子机制，并提供对人类疾病(如癌症)中hMLH1和/或hMRE11缺陷的更好理解。

DESCRIPTION (provided by applicant): Cellular surveillance for the integrity of genetic information passed from parental cells to subsequent generations is carried out by a network of proteins primarily involved in cell-cycle regulation, DNA replication, DNA repair, and chromosome segregation. Defects of any protein factor in this network render cells to genetic instability to different extents, and therefore, predispose to cancer. One of the involved pathways is the DNA mismatch repair (MMR) system that has a crucial role in maintaining genome stability by monitoring and correcting mismatched nucleotides occurred during DNA recombination and DNA synthesis. Mutations in MMR genes can cause higher mutation rates and increase microsatellite instability. Germline mutations in several MMR genes, including MutS and MutL homologues, contribute to the pathogenesis of hereditary nonpolyposis colorectal cancer (HNPCC) in humans, with mutations in hMLH1 and hMSH2 genes representing major contributors to HNPCC. Our recent work has revealed a direct physical link between hMLH1 and hMRE11 both in vitro and in vivo. Human hMRE11 represents an essential nuclease of the multifunctional protein complex (hRAD50-hMRE11-NBS1) that promotes repair of DNA double-strand breaks and plays a role in the signaling of DNA damage response as well as in meiotic recombination and telomere maintenance. Mutations in hMRE11 contribute to the development of the rare "AT-like" (ATLD) disorder. It is known that hMRE11-associated complex displays dynamic spatial and temporal cellular distribution and form DNA-damage induced foci at the sites of DNA damage. Therefore, the long-term goal of this research program is to elucidate the molecular mechanisms involved in MMR and the functional links between MMR proteins and the hMRE11-associated protein complex, as well as the biological effects of mutations that disrupt the interplay among these protein factors. We propose to address these important issues through a vigorous systematic approach that includes the following specific aims: (1) to test the hypothesis that hMRE11 represents a functional component of the DNA mismatch repair pathway; (2) to determine whether hMLH1 binding stimulates nuclease activities of hMRE11 and the functional roles of hMRE11 nuclease activities in the process of MMR; (3) to test the hypothesis that hMLH1 HNPCC missense mutations differentially affect the formation of hMLHI-hMRE11 and hMLHI-hPMS2 heterocomplexes, and therefore disruption of hMLH1-hMRE11 complex represents an alternative mechanism underlying the pathogenic effects of hMLH1 HNPCC mutations. The results of the proposed studies will provide insight into the molecular mechanisms by which MMR and the hMREll-associated complex act together to maintain genetic stability, as well as to provide a better understanding of hMLH1 and/or hMRE11 deficiencies in human diseases such as cancer.