Roles of Chromatin Modification in BRCA1 Dependent DNA Repair

联系PD/PI：Greenberg，Roger A. 摘要 DNA修复的执行是癌症病因和治疗反应的最重要的决定因素之一； 要求对其分子机制和当其改变时出现的脆弱性有深入的了解。 癌细胞经常在其竞争DNA修复的相对利用(重新连接)方面发生变化 机制，这对肿瘤基因组的进化和临床靶向反应有着深刻的影响 探员们。突出的例子存在于遗传性乳腺癌和卵巢癌综合征中，并且具有不同的谱系 通过同源重组保持端粒长度的癌症。种系BRCA1和BRCA2 基因突变会导致高外显性乳腺癌和卵巢癌。这两种蛋白质都是规范所必需的， RAD51依赖的同源重组，从而解释了对聚(ADP)核糖的敏感性增加 BRCA缺失型肿瘤表现为聚合酶抑制物(PARPI)。不幸的是，只有不到一半的BRCA突变体 癌症最初对PARPI有反应，耐药总是出现在那些对PARPI有反应的人身上。DNA修复是如何发生的 因此，在BRCA的背景下，功能障碍是一个至关重要的问题。有一些线索是关于 影响这一过程的因素。也就是说，令人信服的遗传证据表明，特定的 染色质引导的DNA修复机制强烈影响基因组完整性、癌症病因和反应 在BRCA突变细胞中进行治疗。为了了解这种现象的生化基础，我的实验室已经 已开发的鉴定组合核小体修饰全谱的方法 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，染色质 改变也是鲜为人知的替代端粒延长(ALT)现象的基础，一种 在进化上保守的端粒维持形式，出现在近15%的人类癌症中。我们有 最近发现，ALT依赖于BRCA-RAD51独立的同源重组，并产生戏剧性的 高阶染色质结构的变化以合成长端粒束对双链的响应 DNA断裂。这是因为我们开发了同步激活ALT和ALT的方法 可视化每一个主要步骤，包括在ALT端粒上实时同源重组。有趣的是， 我们在ALT和BRCA突变细胞中观察到重叠的遗传脆弱性，表明在 修复每个场景中的后续流程。我们的首要目标是描绘分子事件 对于同源重组的规范和替代机制来说是必要的 (1)BRCA突变细胞的抗药性；(2)在ALT过程中。这些目标将在 并行不悖，同等重视。我们的研究将为理解癌症带来根本性的进展 基因组完整性控制和阐明针对广泛的潜在脆弱性的新战略 恶性肿瘤。 好了！

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. !