BLM-mediated Homologous Recombination Regulation and Tumor Suppression

描述（由申请人提供）：布卢姆综合征（BS）是一种常染色体隐性遗传病，其特征为身材矮小、阳光敏感、对感染和呼吸道疾病的易感性增加以及对广谱癌症的强烈倾向。平均死亡年龄为27岁，最常见的原因是癌症。在细胞水平上，BS表现出高度升高的姐妹染色单体交换、同源重组和异位重组水平，表明同源重组（HR）失调。已经提出，异常HR事件导致BS中基因组的一般不稳定，表现为染色体畸变和重排，包括断裂、四边形和易位。BLM是由BS中突变的基因编码的蛋白质，是RecQ解旋酶家族的成员。BLM具有解开DNA底物的能力，包括类似于HR中间体的那些，并且它与拓扑异构酶III α（一种IA型拓扑异构酶）一起工作，以溶解双霍利迪连接（DHJ），从而产生非交换重组体。BLM还与新的多肽BLAP 75结合并结合hRad 51重组酶。重要的是，我们的初步研究发现BLAP 75对BLM-Topo III α介导的反应具有显著的刺激作用。该研究项目包括三个特定目标下的分子研究，致力于破译BLM-Topo III alpha-BLAP 75（BTB）复合物在HR中间体加工，定义HR途径选择和调节hRad 51活性方面的生物学意义。具体来说，我们将（1）描述BLM，拓扑III α，和BLAP 75在BTB复合物中的功能作用，需要HR调节，（2）定义BLAP 75介导的配体相互作用对BTB复合物功能的贡献，和（3）测试关于BLM-hRad 51相互作用的功能意义的假设。我们的研究结果将揭示BLM依赖的HR控制机制，并将为BS患者的基因组不稳定性和癌症易感性提供解释。

DESCRIPTION (provided by applicant): Bloom's syndrome (BS), an autosomal recessive disorder, is characterized by short stature, sunlight sensitivity, an increased susceptibility to infections and respiratory illness, and a strong disposition to a wide spectrum of cancers. The mean age of death is 27 years and the cause is most frequently cancer-related. At the cellular level, BS exhibits highly elevated levels of sister chromatid exchanges, interhomologue recombination, and ectopic recombination, indicative of homologous recombination (HR) deregulation. It has been proposed that abnormal HR events lead to the general destabilization of the genome in BS, manifested as chromosome aberrations and rearrangements including breaks, quadriradials, and translocations. BLM, the protein encoded by the gene mutated in BS, is a member of the RecQ helicase family. BLM has the ability to unwind DNA substrates including those that resemble HR intermediates, and it works in conjunction with Topo III alpha, a type IA topoisomerase, to dissolve the double Holliday junction (DHJ) to yield non-crossover recombinants. BLM also associates with a novel polypeptide BLAP75 and binds the hRad51 recombinase. Importantly, our preliminary studies have found a dramatic stimulatory effect of BLAP75 on the reactions mediated by BLM-Topo III alpha. This research project comprising molecular studies under three specific aims strives to decipher the biological significance of the BLM-Topo III alpha-BLAP75 (BTB) complex with regard to the processing of HR intermediates, defining HR pathway choice, and regulating the activity of hRad51. Specifically, we will (1) delineate the functional roles of BLM, Topo III alpha, and BLAP75 in the BTB complex needed for HR modulation, (2) define the contributions of BLAP75-mediated ligand interactions to BTB complex functions, and (3) test hypotheses concerning the functional significance of the BLM-hRad51 interaction. The results from our research endeavors will shed mechanistic light on BLM-dependent control mechanisms of HR and will provide an explanation for the genome instability and cancer susceptibility in BS patients.