Lemaçon Delphine, Jackson Jessica, Quinet Annabel, Brickner Joshua R, Li Shan, Yazinski Stephanie, You Zhongsheng, Ira Grzegorz, Zou Lee, Mosammaparast Nima, Vindigni Alessandro
Edward A. Doisy Department of Biochemistry and Molecular Biology, Saint Louis University School of Medicine, St Louis, MO, 63104, USA.
Department of Pathology and Immunology, Division of Laboratory and Genomic Medicine, Washington University School of Medicine, St Louis, MO, 63110, USA.
Nat Commun. 2017 Oct 16;8(1):860. doi: 10.1038/s41467-017-01180-5.
The breast cancer susceptibility proteins BRCA1 and BRCA2 have emerged as key stabilizing factors for the maintenance of replication fork integrity following replication stress. In their absence, stalled replication forks are extensively degraded by the MRE11 nuclease, leading to chemotherapeutic sensitivity. Here we report that BRCA proteins prevent nucleolytic degradation by protecting replication forks that have undergone fork reversal upon drug treatment. The unprotected regressed arms of reversed forks are the entry point for MRE11 in BRCA-deficient cells. The CtIP protein initiates MRE11-dependent degradation, which is extended by the EXO1 nuclease. Next, we show that the initial limited resection of the regressed arms establishes the substrate for MUS81 in BRCA2-deficient cells. In turn, MUS81 cleavage of regressed forks with a ssDNA tail promotes POLD3-dependent fork rescue. We propose that targeting this pathway may represent a new strategy to modulate BRCA2-deficient cancer cell response to chemotherapeutics that cause fork degradation.BRCA proteins have emerged as key stabilizing factors for the maintenance of replication forks following replication stress. Here the authors describe how reversed replication forks are degraded in the absence of BRCA2, and a MUS81 and POLD3-dependent mechanism of rescue following the withdrawal of genotoxic agent.
乳腺癌易感蛋白BRCA1和BRCA2已成为复制应激后维持复制叉完整性的关键稳定因子。在它们缺失的情况下，停滞的复制叉会被MRE11核酸酶广泛降解，从而导致化疗敏感性。在此我们报告，BRCA蛋白通过保护药物处理后发生叉反转的复制叉来防止核酸酶降解。在BRCA缺陷细胞中，反转叉未受保护的回归臂是MRE11的切入点。CtIP蛋白启动MRE11依赖性降解，EXO1核酸酶会进一步延长这种降解。接下来，我们表明回归臂最初的有限切除为BRCA2缺陷细胞中的MUS81建立了底物。反过来，MUS81对带有单链DNA尾巴的回归叉的切割促进了POLD3依赖性的叉拯救。我们提出，靶向这一途径可能代表一种新策略，用于调节BRCA2缺陷癌细胞对导致叉降解的化疗药物的反应。BRCA蛋白已成为复制应激后维持复制叉的关键稳定因子。在此，作者描述了在缺乏BRCA2的情况下反转复制叉是如何被降解的，以及在去除基因毒性剂后一种依赖MUS81和POLD3的拯救机制。
