Identifying Conserved Genetic Networks for Eukaryotic MMR Genes

描述（由申请人提供）：DNA错配修复（MMR）是一种保守的修复途径，对于维持原核生物和真核生物的基因组完整性至关重要。 MMR 一直是深入研究工作的焦点，因为 MMR 基因突变是林奇综合征（HNPCC，遗传性非息肉病性结直肠癌）和很大一部分散发性结直肠癌的根本原因。这些癌症病例大多数是由大肠杆菌 mutS 和 mutL 基因的人类同源物突变引起的。人类 MutS 和 MutL 蛋白形成异二聚体复合物，介导 MMR 的初始步骤，包括识别复制错误引起的错配碱基，并向下游蛋白发出信号以促进错配消除。然而，错配修复复合物还识别因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配，并介导细胞周期停滞和细胞凋亡。由于错配修复缺陷，林奇综合征肿瘤和散发性结直肠癌在短重复序列上表现出增加的不稳定性，称为微卫星不稳定性。此外，这些肿瘤对 DNA 损伤剂表现出耐药性，因此无法对传统化疗产生反应。例如，虽然 5-氟尿嘧啶 (5-FU) 治疗 MMR 丰富的结直肠癌可产生有益的结果，但对于 MMR 缺陷的散发性结直肠癌或林奇综合征癌症却并非如此。更令人担忧的是，使用传统化疗药物治疗癌症患者经常会诱发二次治疗相关的白血病（例如急性髓系白血病/骨髓增生异常综合征），这可能是由于选择具有 MMR 缺陷的造血前体细胞引起的。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物的抵抗力。因此，非常需要开发有效且选择性地针对原发性癌症并防止治疗诱发的继发性癌症形成的新治疗策略。实现这些目标的一个有希望的新方向是利用合成致死性，其中两种非必需因子的同时损失对细胞来说是致命的。 在本申请中，我们建议在两种高度分化的真核生物模型中鉴定与 MMR 相关的核心遗传网络，即裂殖酵母（裂殖酵母；Sp）和出芽酵母（酿酒酵母；Sc）。我们将利用这些信息来预测（和测试）在确定的 MMR 缺陷小鼠和人类癌细胞系中合成的患病或致死相互作用。我们提出的研究不仅将确定 MMR 基因的新相互作用和/或功能，而且有可能为流行的人类癌症综合征确定高效的化疗策略。 公共健康相关性：DNA 错配修复系统 (MMR) 通过纠正因错误复制或环境破坏而导致的错配碱基对，对于维持哺乳动物基因组的完整性至关重要。 MMR 缺陷与很大一部分散发性结直肠癌相关，并且是林奇癌症综合征（也称为 HNPCC：遗传性非息肉病性结直肠癌）的根本原因。我们正在研究关键 MMR 基因发生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必需 MMR 基因的新相互作用和/或功能，而且是确定针对流行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.