Roles of Chromatin Modification in BRCA1 Dependent DNA Repair

联系PD/PI：Greenberg，Roger A. 总结 DNA修复执行是癌症病因学和对治疗反应的最重要决定因素之一; 要求深入了解其分子机制和改变时存在的脆弱性。 癌细胞经常在其竞争性DNA修复的相对利用（重新布线）方面发生变化 这对癌症基因组进化和靶向治疗的临床反应有着深远的影响。 剂.突出的例子存在于遗传性乳腺癌和卵巢癌综合征和不同的光谱 通过同源重组维持端粒长度的癌症。胚系BRCA 1和BRCA 2 基因突变导致乳腺癌和卵巢癌的高发病率。这两种蛋白质都是典型的， Rad 51依赖性同源重组，从而解释了对聚（ADP）核糖的敏感性增加 聚合酶抑制剂（PARPi）由BRCA无效肿瘤表现。不幸的是，不到一半的BRCA突变体 癌症最初对PARPi有反应，而耐药性总是出现在那些有反应的癌症中。DNA修复如何发生 因此，在BRCA功能障碍的背景下，这是一个至关重要的问题。一些线索表明 影响这个过程的因素。也就是说，令人信服的遗传证据表明，特定的超激活 染色质指导的DNA修复机制强烈影响基因组完整性、癌症病因和反应 到BRCA突变细胞的治疗。为了了解这种现象的生物化学基础，我的实验室 开发的方法，以确定全谱的组合核小体修饰，介导 识别受损的染色质并指导利用特定的DNA修复机制。值得注意的是， 这些改变也是人们所知甚少的端粒替代性延长（ALT）现象的基础， 端粒是端粒维持的进化保守形式，发生在近15%的人类癌症中。我们有 最近表明，ALT依赖于BRCA-Rad 51独立同源重组， 高阶染色质结构的变化，以响应双链 DNA断裂。这是通过我们开发的方法学来同步激活ALT和 在ALT端粒中，以真实的时间可视化包含同源重组的每个主要步骤。有趣的是， 我们观察到ALT和BRCA突变细胞中重叠的遗传脆弱性，这表明ALT和BRCA突变细胞中的共性。 在每个场景中随之而来的修复过程。我们的首要目标是描绘分子事件 同源重组的典型和替代机制所必需的，这种机制出现在以下情况中： (1)BRCA突变细胞中的治疗抗性，和（2）ALT期间。这些目标将在 平行的，同样重要的。我们的研究将为理解癌症带来根本性的进步 基因组完整性控制，并阐明新的战略，以针对潜在的脆弱性，在广泛的 恶性肿瘤。 !

Contact PD/PI: Greenberg, Roger A. Summary DNA repair execution is among the most important determinants of cancer etiology and response to therapy; mandating intimate knowledge of its molecular mechanisms and the vulnerabilities that present when it is altered. Cancer cells frequently harbor changes in their relative utilization (rewiring) of competing DNA repair mechanisms, and this has a profound influence on cancer genome evolution and clinical response to targeted agents. Prominent examples reside in hereditary breast and ovarian cancer syndrome and in a different spectrum of cancers that maintain telomere length through homologous recombination. Germline BRCA1 and BRCA2 gene mutations confer high penetrance breast and ovarian cancer. Both proteins are required for canonical, Rad51 dependent homologous recombination, thus accounting for the increased sensitivity to poly(ADP)ribose polymerase inhibitors (PARPi) exhibited by BRCA null tumors. Unfortunately, less than half of BRCA mutant cancers initially respond to PARPi and resistance invariably emerges in those that do. How DNA repair occurs in the context of BRCA dysfunction is therefore a question of central importance. Some clues exist as to the factors that influence this process. Namely, compelling genetic evidence indicates that hyperactivation of specific chromatin directed DNA repair mechanisms strongly influences genome integrity, cancer etiology, and response to therapy in BRCA mutant cells. To understand the biochemical basis for this phenomenon, my laboratory has developed approaches to identify the full spectrum of combinatorial nucleosome modifications that mediate recognition of damaged chromatin and directs utilization of specific DNA repair mechanisms. Notably, chromatin alterations also underlie the poorly understood phenomenon of alternative telomere lengthening (ALT), an evolutionarily conserved form of telomere maintenance that occurs in nearly 15% of human cancers. We have recently shown that ALT relies on BRCA-Rad51 independent homologous recombination and enacts dramatic changes in higher order chromatin structure to synthesize long telomere tracts in response to double-stranded DNA breaks. This was made possible by our development of methodologies to synchronously activate ALT and visualize every major step encompassing homologous recombination in real time at ALT telomeres. Interestingly, we observe overlapping genetic vulnerabilities in ALT and BRCA mutant cells, suggesting commonality in the repair processes that ensue in each scenario. Our overarching goals are to delineate molecular events necessary for canonical and alternative mechanisms of homologous recombination that arises in the setting of (1) therapeutic resistance in BRCA mutant cells, and (2) during ALT. These objectives will be performed in parallel and with equal emphasis. Our studies will yield fundamental advances to the understanding cancer genome integrity control and clarify new strategies to target underlying vulnerabilities in a broad range of malignancies. !