Regulation of Homologous Recombination in Human Cells

描述（由申请人提供）：同源重组（HR）是通过修复双链断裂和修复受损复制叉来维持细胞基因组完整性的重要机制。RAD 51重组酶催化HR途径中的中心步骤，通过同源依赖性链侵入形成接合分子。BLM解旋酶是Bloom综合征（BS）中突变的基因，调节RAD 51。BLM可以促进RAD 51功能，例如通过产生用于RAD 51结合的底物，或者它可以通过解旋RAD 51催化的产物来抑制RAD 51功能，这防止了毒性重组中间体的积累。因此，通过其调节的RAD 51，BLM有亲和反重组功能在HR。我们已经表明，BLM是由小泛素相关的修饰剂（SUMO）和BLM SUMO化调节BLM的功能停滞复制叉，刺激HR修复。此外，RAD 51是SUMO结合的，并且BLM SUMO化在体外刺激BLM与RAD 51的相互作用。我们的研究结果支持了一个模型，其中BLM SUMO化控制BLM的抗重组功能和促重组功能之间的转换。为了验证这一假设，我们有四个具体的目标：（1）表征BLM SUMO化在稳定复制叉中的作用;（2）表征RAD 51 SUMO结合在复制叉稳定性和HR修复中的作用;（3）分析BLM SUMO化对BLM生化活性和RAD 51功能的影响;以及（4）分析BLM SUMO化和RAD 51 SUMO结合对基因组完整性的影响。我们的研究将阐明在受损复制叉处调节HR的分子机制，为BLM和RAD 51在HR修复中的动态功能提供见解，并深入了解SUMO通路如何调节这些功能。由于HR修复机制在癌细胞中经常失调，我们的工作将有助于更好地了解癌症中的基因组不稳定性，并有助于在癌症治疗中利用这种不稳定性。

DESCRIPTION (provided by applicant): Homologous recombination (HR) is an essential mechanism that maintains genomic integrity in cells by repairing double-strand breaks and repairing damaged replication forks. The RAD51 recombinase catalyzes the central step in the HR pathway, forming joint molecules through homology-dependent strand invasion. The BLM helicase, which is the gene mutated in Bloom's syndrome (BS), regulates RAD51. BLM can promote RAD51 function, for example by generating substrate for RAD51 binding, or it can inhibit RAD51 function by unwinding the products of RAD51 catalysis, which prevents the accumulation of toxic recombination intermediates. Thus, through its regulation of RAD51, BLM has both pro- and anti-recombinogenic functions in HR. We have shown that BLM is modified by small ubiquitin-related modifiers (SUMOs) and that BLM SUMOylation regulates BLM's functions at stalled replication forks, stimulating HR repair. In addition, RAD51 is SUMO-binding, and BLM SUMOylation stimulates BLM's interaction with RAD51 in vitro. Our findings support a model in which BLM SUMOylation controls a switch between BLM's anti- recombinogenic and pro-recombinogenic functions. To test this hypothesis, we have four specific aims: (1) characterization of the role of BLM SUMOylation in stabilization of replication forks; (2) characterization of the role of RAD51 SUMO binding in replication fork stability and HR repair; (3) analysis of the effects of BLM SUMOylation on BLM's biochemical activities and RAD51 function; and (4) analysis of the effects of BLM SUMOylation and RAD51 SUMO binding in genomic integrity. Our studies will elucidate the molecular mechanisms that regulate HR at damaged replication forks, providing insights into the dynamic functions of BLM and RAD51 in HR repair and leading to a deeper understanding of how these functions are regulated by the SUMO pathway. Because HR repair mechanisms are often dysregulated in cancer cells, our work will lead to a better understanding of genomic instability in cancer and will facilitate the exploitation of this instability in cancer treatments.