Identifying Conserved Genetic Networks for Eukaryotic MMR Genes

描述(申请人提供)：DNA错配修复(MMR)是一种保守的修复途径，对维持原核生物和真核生物基因组的完整性是必不可少的。MMR一直是密集研究的焦点，因为MMR基因突变是Lynch综合征(HNPCC，遗传性非息肉病性结直肠癌)和相当大比例的散发性结直肠癌的根本原因。这些癌症病例中的大多数是由人类E.Coli MutS和MutL基因的同源物突变引起的。人类MutS和MutL蛋白形成异二聚体复合体，介导MMR的初始步骤，包括识别复制错误引起的错配碱基(S)，以及向下游蛋白质发出信号以促进错配消除。然而，MMR复合体也识别由于暴露于环境基因毒素或化疗药物治疗而导致的受损碱基错对，并介导细胞周期停滞和细胞凋亡。由于MMR缺陷，Lynch综合征肿瘤和散发性结直肠癌在短重复序列上表现出更高的不稳定性，称为微卫星不稳定性。此外，这些肿瘤对DNA损伤剂表现出抗药性，因此对常规化疗没有反应。例如，虽然5-氟尿嘧啶(5-FU)对MMR熟练的结直肠癌的治疗结果是有益的，但对于MMR缺乏的散发性结直肠癌或林奇综合征癌症却不是这样。更令人关注的是，用传统化疗药物治疗癌症患者经常会导致与二次治疗相关的白血病(如急性髓系白血病/骨髓增生异常综合征)，这可能是由于选择了具有MMR缺陷的造血祖细胞造成的。随着这些细胞的增殖，它们会积累更多的突变，并增加对抗癌药的耐药性。因此，开发有效和选择性地针对原发癌并防止治疗诱导的继发性癌症形成的新的治疗策略将是非常可取的。实现这些目标的一个有希望的新方向是利用合成致命性，在这种情况下，同时失去两个否则不必要的因素对细胞来说是致命的。在这个应用中，我们建议在两个高度分化的真核生物模型中识别与MMR相关的核心遗传网络，即分裂酵母(Schizosaccharmyces pombe；Sp)和发芽酵母(Saccharmyces cerevisiae；SC)酵母。我们将利用这些信息来预测(和测试)已确定的MMR缺陷小鼠和人类癌细胞系中的合成、病态或致命性相互作用。我们提出的研究不仅将确定MMR基因的新的相互作用和/或功能，而且还有可能确定针对普遍存在的人类癌症综合征的高效化疗策略。 与公共卫生相关：DNA错配修复系统(MMR)通过纠正错误复制或环境破坏导致的错配碱基对，对于维持哺乳动物基因组的完整性至关重要。MMR缺陷与相当大比例的散发性结直肠癌有关，也是Lynch癌综合征(也称为HNPCC：遗传性非息肉病性结直肠癌)的根本原因。我们正在研究具有关键MMR基因突变的酵母和哺乳动物细胞系，以确定MMR的关键保守遗传网络。我们研究的目标不仅是确定基本MMR基因的新的相互作用和/或功能，而且还确定针对普遍存在的人类癌症综合征的高效化疗策略。

DESCRIPTION (provided by applicant): DNA mismatch repair (MMR) is a conserved repair pathway and is essential for maintaining genomic integrity in prokaryotes and eukaryotes. MMR has been the focus of intensive research efforts because mutations in MMR genes are the underlying cause of Lynch syndrome (HNPCC, hereditary nonpolyposis colorectal cancer) and a significant proportion of sporadic colorectal cancers. The majority of these cancer cases are caused by mutations in the human homologs of the E. Coli mutS and mutL genes. The human MutS and MutL proteins form heterodimeric complexes that mediate the initial steps of MMR, including the recognition of mismatched base(s) arising from errors in replication, and signaling downstream proteins to facilitate mismatch removal. However, MMR complexes also recognize damaged-base mispairs resulting from exposure to environmental genotoxins or treatment with chemotherapeutic agents and mediate cell cycle arrest and apoptosis. As a consequence of their defective MMR, Lynch syndrome tumors and sporadic colorectal cancers display increased instability at short repeat sequences, termed microsatellite instability. In addition, these tumors display resistance to DNA damaging agents, and thus fail to respond to conventional chemotherapy. For example, while the 5-Fluorouracil (5-FU) treatment of MMR-proficient colorectal cancers results in a beneficial outcome, the same is not the case with MMR-deficient sporadic colorectal or Lynch syndrome cancers. Of additional concern, the treatment of cancer patients with conventional chemotherapeutic agents frequently induces secondary therapy-related leukemias (e.g. Acute Myeloid Leukemia / Myelodysplastic Syndrome), which may be caused by selection for hematopoietic precursor cells with MMR-defects. As these cells proliferate they accumulate further mutations and increased resistance to anticancer agents. Thus the development of novel therapeutic strategies that efficiently and selectively target primary cancers and prevent the formation of therapy-induced secondary cancers would be highly desirable. A promising new direction to achieve these goals is the harnessing of synthetic lethality, where the simultaneous loss of two otherwise non- essential factors is fatal for cells. In this application we propose to identify the core genetic networks related to MMR in two highly divergent model eukaryotes, the fission (Schizosaccharomyces pombe; Sp) and budding (Saccharomyces cerevisiae; Sc) yeasts. We will utilize this information to predict (and test) synthetic sick or lethal interactions in defined MMR- deficient mouse and human cancer cell lines. Our proposed studies will not only identify novel interactions and/or functions of the MMR genes, but also have the potential to identify highly effective chemotherapeutic strategies for a prevalent human cancer syndrome. PUBLIC HEALTH RELEVANCE: The DNA mismatch repair system (MMR) is essential for maintaining the integrity of mammalian genomes by correcting mismatched base pairs that result from erroneous replication or environmental damage. Defects in MMR are associated with a significant proportion of sporadic colorectal cancer, and are the underlying cause of the Lynch cancer syndrome (also known as HNPCC: hereditary nonpolyposis colorectal cancer). We are studying yeast and mammalian cell lines with mutations in key MMR genes to identify key conserved genetic networks for MMR. The goal of our studies is not only to determine novel interactions and/or functions of essential MMR genes, but also to identify highly effective chemotherapeutic strategies for a prevalent human cancer syndrome.