Departments of Oncology and Experimental Medicine, Lady Davis Institute and Segal Cancer Centre, Jewish General Hospital, McGill University, 3755 Chemin Côte-Ste-Catherine, Montréal, Quebec H3T 1E2, Canada.
Department of Microbiology and Immunology, McGill University, 3775 University Street, Montréal, Quebec H3A 2B4, Canada.
Sci Adv. 2017 May 24;3(5):e1601898. doi: 10.1126/sciadv.1601898. eCollection 2017 May.
The repair of DNA double-strand breaks (DSBs) is mediated via two major pathways, nonhomologous end joining (NHEJ) and homologous recombination (HR) repair. DSB repair is vital for cell survival, genome stability, and tumor suppression. In contrast to NHEJ, HR relies on extensive homology and templated DNA synthesis to restore the sequence surrounding the break site. We report a new role for the multifunctional protein CCCTC-binding factor (CTCF) in facilitating HR-mediated DSB repair. CTCF is recruited to DSB through its zinc finger domain independently of poly(ADP-ribose) polymers, known as PARylation, catalyzed by poly(ADP-ribose) polymerase 1 (PARP-1). CTCF ensures proper DSB repair kinetics in response to γ-irradiation, and the loss of CTCF compromises HR-mediated repair. Consistent with its role in HR, loss of CTCF results in hypersensitivity to DNA damage, inducing agents and inhibitors of PARP. Mechanistically, CTCF acts downstream of BRCA1 in the HR pathway and associates with BRCA2 in a PARylation-dependent manner, enhancing BRCA2 recruitment to DSB. In contrast, CTCF does not influence the recruitment of the NHEJ protein 53BP1 or LIGIV to DSB. Together, our findings establish for the first time that CTCF is an important regulator of the HR pathway.
DNA 双链断裂 (DSB) 的修复是通过两条主要途径介导的，非同源末端连接 (NHEJ) 和同源重组 (HR) 修复。DSB 修复对于细胞存活、基因组稳定性和肿瘤抑制至关重要。与 NHEJ 不同，HR 依赖于广泛的同源性和模板 DNA 合成来恢复断裂位点周围的序列。我们报告了多功能蛋白 CCCTC 结合因子 (CTCF) 在促进 HR 介导的 DSB 修复中的新作用。CTCF 通过其锌指结构域被募集到 DSB，而不依赖于多聚 (ADP-核糖) 聚合物，即 PARylation，由多聚 (ADP-核糖) 聚合酶 1 (PARP-1) 催化。CTCF 确保了对 γ-辐照的适当 DSB 修复动力学，而 CTCF 的缺失会损害 HR 介导的修复。与它在 HR 中的作用一致，CTCF 的缺失会导致对 DNA 损伤诱导剂和 PARP 抑制剂的敏感性增加。从机制上讲，CTCF 在 HR 途径中 BRCA1 的下游起作用，并以 PARylation 依赖的方式与 BRCA2 结合，增强 BRCA2 向 DSB 的募集。相比之下，CTCF 不影响 NHEJ 蛋白 53BP1 或 LIGIV 向 DSB 的募集。总之，我们的研究结果首次确立了 CTCF 是 HR 途径的重要调节因子。
