BRCA1 and its cofactor in chemotherapy-associated cardiotoxicity

 描述（由申请人提供）：随着早期癌症诊断和化疗疗效的提高，阿霉素诱导的心脏毒性已日益成为癌症幸存者发病率和死亡率的重要原因。例如，长期儿童癌症幸存者的心脏死亡率估计比预期高出8倍以上。减少治疗相关的心脏毒性的一个主要挑战是缺乏关于可以减轻多柔比星对心肌的不良影响的分子参与者和途径的知识。多柔比星通过形成三元Top2-多柔比星-DNA复合物靶向拓扑异构酶II（Top2），其可导致DNA断裂并最终触发细胞凋亡。哺乳动物有两个Top2编码基因，Top2α β和Top2β。Top2α在分裂的癌细胞中过表达，很可能是阿霉素抗肿瘤活性的主要靶点。相反，Top2β在有丝分裂后的心肌细胞中表达，并通过与代谢相关基因的启动子相关介导阿霉素的心脏毒性作用。由于心肌细胞对能量产生有很高的需求，特别是在应激条件下，这增加了对能量代谢相关基因表达重要的转录因子可能减轻阿霉素诱导的Top2β介导的心脏毒性的可能性。 BRCA 1辅因子（COBRA 1）是PI实验室发现的BRCA 1相互作用蛋白。它是负延伸因子（NELF）的一部分，通过RNA聚合酶II（Pol II）暂停调节转录。我们的初步工作表明，COBRA 1在心肌细胞中起着重要的作用，维持能量代谢相关基因的转录。重要的是，心肌细胞特异性COBRA 1或BRCA 1缺失加剧了阿霉素诱导的心脏毒性。考虑到BRCA 1和COBRA 1之间的物理相互作用，我们假设这两种蛋白质通过（1）维持能量代谢相关基因的转录和（2）优先在这些基因的启动子处抵消Top2β介导的遗传毒性应激来联合减轻阿霉素诱导的心脏毒性。我们的应用在概念上是新颖的，因为它探索了以前未被重视的能量代谢相关的转录和阿霉素诱导的心脏毒性之间的联系。此外，我们提出的工作挑战了BRCA 1的流行DNA修复中心范式，并试图阐明BRCA 1/COBRA 1和Pol II在有丝分裂后组织背景下暂停之间有趣的功能联系。通过整合不同的尖端技术和调整历史上独立的研究领域，这个跨学科的研究团队致力于提供深入了解临床重要但机制上未充分探索的化学毒性和长期癌症生存问题。

 DESCRIPTION (provided by applicant): With earlier-stage cancer diagnosis and improved efficacy of chemotherapy, doxorubicin-induced cardiotoxicity has increasingly become a significa nt cause of morbidity and mortality among cancer survivors. For example, the cardiac mortality of long-term pediatric cancer survivors is estimated to be more than eight times higher than expected. A major challenge in reducing therapy-associated cardiotoxicity is the paucity of knowledge about the molecular players and pathways that can mitigate the undesired effects of doxorubicin on myocardium. Doxorubicin targets topoisomerase II (Top2) by forming a ternary Top2-doxorubicin-DNA complex, which can lead to DNA breaks and ultimately trigger apoptosis. Mammals have two Top2-encoding genes, Top2αand Top2β. Top2α is overexpressed in dividing cancer cells and most likely serve as a primary target of the antitumor activity of doxorubicin. In contrast, Top2β is expressed in postmitotic cardiomyocytes and mediates the cardiotoxic effect of doxorubicin through its association with promoters of metabolism-related genes. As cardiomyocytes have a high demand for energy production, especially under stressed conditions, it raises the possibility that transcription factors important for energy metabolism-related gene expression may alleviate doxorubicin-induced, Top2β-mediated cardiotoxicity. Cofactor of BRCA1 (COBRA1) is a BRCA1-interacting protein discovered in the PI's lab. It is part of the negative elongation factor (NELF) that regulates transcription through RNA polymerase II (Pol II) pausing. Our preliminary work indicates that COBRA1 in cardiomyocytes plays an important role in sustaining transcription of energy metabolism-related genes. Importantly, cardiomyocyte-specific deletion of COBRA1 or BRCA1 exacerbates doxorubicin-induced cardiotoxicity. Given the physical interaction between BRCA1 and COBRA1, we hypothesize that these two proteins jointly mitigate doxorubicin-induced cardiotoxicity by (1) sustaining transcription of energy metabolism-related genes and (2) counteracting Top2β-mediated genotoxic stress preferentially at the promoters of these genes. Our application is conceptually novel because it explores a previously unappreciated connection between energy metabolism-related transcription and doxorubicin-induced cardiotoxicity. In addition, our proposed work challenges the prevailing DNA repair- centric paradigm for BRCA1 and seeks to elucidate an intriguing functional link between BRCA1/COBRA1 and Pol II pausing in a postmitotic tissue context. By integrating different cutting-edge technologies and aligning historically separate research areas, this trans-disciplinary research team strives to provide insights into a clinically important yet mechanistically under-explored problem in chemo-toxicity and long-term cancer survivorship.