Department of Toxicogenetics; Leiden University Medical Center; Leiden, The Netherlands.
Cell Cycle. 2013 Sep 15;12(18):3070-82. doi: 10.4161/cc.26033. Epub 2013 Aug 20.
The cellular response to ionizing radiation (IR)-induced DNA double-strand breaks (DSBs) in native chromatin requires a tight coordination between the activities of DNA repair machineries and factors that modulate chromatin structure. SMARCA5 is an ATPase of the SNF2 family of chromatin remodeling factors that has recently been implicated in the DSB response. It forms distinct chromatin remodeling complexes with several non-canonical subunits, including the remodeling and spacing factor 1 (RSF1) protein. Despite the fact that RSF1 is often overexpressed in tumors and linked to tumorigenesis and genome instability, its role in the DSB response remains largely unclear. Here we show that RSF1 accumulates at DSB sites and protects human cells against IR-induced DSBs by promoting repair of these lesions through homologous recombination (HR) and non-homologous end-joining (NHEJ). Although SMARCA5 regulates the RNF168-dependent ubiquitin response that targets BRCA1 to DSBs, we found RSF1 to be dispensable for this process. Conversely, we found that RSF1 facilitates the assembly of centromere proteins CENP-S and CENP-X at sites of DNA damage, while SMARCA5 was not required for these events. Mechanistically, we uncovered that CENP-S and CENP-X, upon their incorporation by RSF1, promote assembly of the NHEJ factor XRCC4 at damaged chromatin. In contrast, CENP-S and CENP-X were dispensable for HR, suggesting that RSF1 regulates HR independently of these centromere proteins. Our findings reveal distinct functions of RSF1 in the 2 major pathways of DSB repair and explain how RSF1, through the loading of centromere proteins and XRCC4 at DSBs, promotes repair by non-homologous end-joining.
细胞对电离辐射（IR）诱导的天然染色质中 DNA 双链断裂（DSBs）的反应需要 DNA 修复机制和调节染色质结构的因子之间的紧密协调。SMARCA5 是 SNF2 家族的染色质重塑因子中的 ATP 酶，它最近被牵连到 DSB 反应中。它与几个非典型亚基形成不同的染色质重塑复合物，包括重塑和间隔因子 1（RSF1）蛋白。尽管 RSF1 通常在肿瘤中过度表达，并与肿瘤发生和基因组不稳定性有关，但它在 DSB 反应中的作用在很大程度上仍不清楚。在这里，我们表明 RSF1 积累在 DSB 位点，并通过促进同源重组（HR）和非同源末端连接（NHEJ）修复这些损伤来保护人类细胞免受 IR 诱导的 DSBs 的影响。尽管 SMARCA5 调节 RNF168 依赖性泛素反应，该反应将 BRCA1 靶向 DSBs，但我们发现 RSF1 对于该过程是可有可无的。相反，我们发现 RSF1 促进着丝粒蛋白 CENP-S 和 CENP-X 在 DNA 损伤部位的组装，而 SMARCA5 对于这些事件并不必需。从机制上讲，我们发现 CENP-S 和 CENP-X 在被 RSF1 整合后，促进了 NHEJ 因子 XRCC4 在受损染色质上的组装。相比之下，CENP-S 和 CENP-X 对于 HR 是可有可无的，这表明 RSF1 独立于这些着丝粒蛋白调控 HR。我们的研究结果揭示了 RSF1 在 DSB 修复的两种主要途径中的不同功能，并解释了 RSF1 如何通过将着丝粒蛋白和 XRCC4 加载到 DSB 上，促进非同源末端连接修复。
