Department of Biology, McMaster University, Hamilton, Ontario L8S 4K1, Canada.
Genome Stability Laboratory, CHU de Québec Research Center, HDQ Pavilion, Oncology Division, 9 McMahon, Québec City, QC G1R 3S3, Canada.
Nucleic Acids Res. 2019 Nov 18;47(20):10678-10692. doi: 10.1093/nar/gkz784.
CSB, a member of the SWI2/SNF2 superfamily, has been implicated in evicting histones to promote the DSB pathway choice towards homologous recombination (HR) repair. However, how CSB promotes HR repair remains poorly characterized. Here we demonstrate that CSB interacts with both MRE11/RAD50/NBS1 (MRN) and BRCA1 in a cell cycle regulated manner, with the former requiring its WHD and occurring predominantly in early S phase. CSB interacts with the BRCT domain of BRCA1 and this interaction is regulated by CDK-dependent phosphorylation of CSB on S1276. The CSB-BRCA1 interaction, which peaks in late S/G2 phase, is responsible for mediating the interaction of CSB with the BRCA1-C complex consisting of BRCA1, MRN and CtIP. While dispensable for histone eviction at DSBs, CSB phosphorylation on S1276 is necessary to promote efficient MRN- and CtIP-mediated DNA end resection, thereby restricting NHEJ and enforcing the DSB repair pathway choice to HR. CSB phosphorylation on S1276 is also necessary to support cell survival in response to DNA damage-inducing agents. These results altogether suggest that CSB interacts with BRCA1 to promote DNA end resection for HR repair and that although prerequisite, CSB-mediated histone eviction alone is insufficient to promote the pathway choice towards HR.
CSB 是 SWI2/SNF2 超级家族的成员，它被牵连到将组蛋白驱逐出去，以促进 DSB 通路选择向同源重组（HR）修复。然而，CSB 如何促进 HR 修复仍然知之甚少。在这里，我们证明 CSB 以细胞周期调控的方式与 MRE11/RAD50/NBS1（MRN）和 BRCA1 相互作用，前者需要其 WHD 并主要发生在早期 S 期。CSB 与 BRCA1 的 BRCT 结构域相互作用，这种相互作用受 CSB 在 S1276 上的 CDK 依赖性磷酸化调节。CSB-BRCA1 相互作用在晚期 S/G2 期达到峰值，负责介导 CSB 与 BRCA1-C 复合物（由 BRCA1、MRN 和 CtIP 组成）的相互作用。虽然 CSB 在 DSB 处的组蛋白驱逐作用并不必需，但 CSB 在 S1276 上的磷酸化对于促进有效的 MRN 和 CtIP 介导的 DNA 末端切除是必要的，从而限制 NHEJ 并强制 DSB 修复途径选择 HR。CSB 在 S1276 上的磷酸化对于应对 DNA 损伤诱导剂的细胞存活也是必要的。这些结果表明，CSB 与 BRCA1 相互作用以促进 HR 修复的 DNA 末端切除，并且尽管是必需的，但 CSB 介导的组蛋白驱逐本身不足以促进 HR 修复途径的选择。
