Roles of BRCA1, BRCA2 in Homologous Recombination

描述(申请人提供)：BRCA1或BRCA2的功能丧失导致基因组不稳定和乳腺癌易感性，尽管在乳腺癌中从杂合突变种系到纯合失活的确切机制尚不清楚。BRCA1和BRCA2参与了广泛的细胞过程，但这两个蛋白质的共同特性是参与了同源重组(HR)。HR可用于DNA双链断裂(DSB)的无错误修复，或用于重新启动停滞或损坏的DNA复制叉子。如果没有错误的HR是缺陷的，容易出错的同源和非同源修复变得更加普遍，这可能导致基因组的不稳定。因此，明确BRCA1和BRCA2在HR中的作用可能是了解BRCA突变携带者易患癌症表型的关键。 这项研究有两个主要目的，与BRCA1在细胞对DNA损伤的反应中发挥近端而广泛的作用的观点有关，它将损伤的感知和信号传递与效应器成分联系起来。(1)我们将检验这样的假设，即BRCA1控制着DSB修复的几条途径，而位于BRCA1下游的BRCA2只促进无错误的HR过程。因此，可以预测，在BRCA1缺陷细胞中观察到的容易出错的修复表型与没有BRCA2的细胞中观察到的不同，并且可能更严重。我们将使用新的基于质粒的检测系统来研究DNA序列和染色体水平上容易出错的修复的结果。(2)BRCA1与(1)细胞周期检查点调节因子Chk2以及(2)由MREL 1、Rad50和NBS1(MRN)蛋白组成的DNA损伤处理和信号复合体相互作用。我们将测试BRCA1的双重模型，在该模型中，BRCA1与Chk2联合促进同源介导的修复和复制重新开始，同时抑制MRN复合体固有的容易出错的修复活动。这些实验可能支持最近的流行病学证据，即Chk2和BRCA蛋白存在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，通过导致遗传不稳定而促进癌症发生的HR缺陷也可能提供一个针对在这种情况下发生的癌症的新的治疗靶点。

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.