Roles of BRCA1, BRCA2 in Homologous Recombination

描述（由申请人提供）：BRCA 1或BRCA 2的功能丧失导致基因组不稳定和乳腺癌易感性，尽管乳腺癌中从杂合突变种系到纯合失活的精确机制尚不清楚。BRCA1和BRCA2在较小程度上参与了各种各样的细胞过程，但这两种蛋白质共有的特性是参与同源重组（HR）。HR可用于DNA双链断裂（DSB）的无错修复或用于停滞或受损DNA复制叉的重新启动。如果无错误的HR是有缺陷的，则易错的同源和非同源修复变得更加普遍，这可能导致基因组不稳定。因此，明确BRCA 1和BRCA 2在HR中的作用可能是理解BRCA突变携带者癌症易感表型的关键。 这项研究有两个主要目的，这与BRCA1在细胞对DNA损伤的反应中起着近端和广泛的作用有关，它将损伤的传感和信号传导与效应成分联系起来。(1)我们将测试的假设，BRCA1控制的DSB修复的几个途径，而BRCA2，这是位于下游的BRCA1，只促进过程中的无错误的HR.Thus，它是预测，在BRCA1缺陷的细胞中观察到的错误倾向的修复表型是不同的，也许更严重，比没有BRCA2的细胞。我们将使用新的基于质粒的检测系统研究DNA序列和染色体水平上的易错修复的结果。(2)BRCA 1与（i）细胞周期检查点调节因子Chk 2（与复制叉相关的hMus 81蛋白连接）以及（ii）由Mrel 1、Rad50和NBS 1（MRN）蛋白组成的DNA损伤处理和信号传导复合物相互作用。我们将测试BRCA1的双重模型，其中BRCA1与Chk2一起促进同源介导的修复和复制重启，同时抑制MRN复合物固有的易错修复活性。这些实验可能支持最近的流行病学证据，将Chk2和BRCA蛋白置于共同的乳腺癌预防途径中。 本研究的主要目的是确定BRCA1和BRCA2在同源介导的DSB修复中的作用。最终，通过引起遗传不稳定性促进致癌作用的HR缺陷也可能为这种情况下出现的癌症提供新的治疗靶点。

DESCRIPTION (provided by applicant): Loss of function of either BRCA1 or BRCA2 results in genomic instability and breast cancer predisposition, although the precise mechanism from a heterozygous mutant germline to homozygous inactivation in breast cancers is unknown. BRCA1 and to a lesser extent BRCA2 have been implicated in a wide variety of cellular processes, but a property shared by both proteins is an involvement in homologous recombination (HR). HR can be utilized for the error-free repair of DNA double-strand breaks (DSBs) or for the restart of stalled or damaged DNA replication forks. If error-free HR is defective, error-prone homologous and non-homologous repair becomes more prevalent, which may result in genomic instability. Thus, defining the roles of BRCA1 and BRCA2 in HR may be the key to understanding the cancer-prone phenotype of BRCA mutation carriers. This study has two main aims, which are related to the view that BRCA1 plays a proximal and extensive role in the cellular response to DNA damage, where it links sensing and signaling of damage to effector components. (1) We will test the hypothesis that BRCA1 controls several pathways of DSB repair, while BRCA2, which is located downstream of BRCA1, only promotes the process of error-free HR. Thus, it is predicted that the error-prone repair phenotype observed in BRCAl-deficient cells is different, and perhaps more severe, than in cells without BRCA2. We will study the outcome of error-prone repair on both the DNA sequence and the chromosomal level using novel plasmid-based assay systems. (2) BRCA1 interacts with (i) the cell-cycle checkpoint regulator Chk2, which is connected to the replication-fork-associated hMus81 protein, and with (ii) the DNA damage processing and signaling complex comprised of the Mrel 1, Rad50, and NBS1 (MRN) proteins. We will test a dual model ofBRCA1, in which BRCA1 in conjunction with Chk2 promotes homologymediated repair and replication restart, while at the same time inhibits the error-prone repair activity that is inherent to the MRN complex. These experiments may support the recent epidemiological evidence that places Chk2 and the BRCA proteins in a common breast cancer-preventing pathway. The primary goal of this study is to define the roles of BRCA1 and BRCA2 in homology-mediated DSB repair. Ultimately, the defects in HR that promote carcinogenesis by causing genetic instability may also offer a novel therapeutic target against the cancers that arise in this setting.