Institute of Molecular Cancer Research, University of Zurich, Winterthurerstrasse 190, 8057, Zurich, Switzerland.
Department of Molecular Mechanisms of Disease, University of Zurich, Winterthurerstrasse 190, 8057, Zurich, Switzerland.
Nat Commun. 2020 Jul 15;11(1):3531. doi: 10.1038/s41467-020-17324-z.
Homologous recombination (HR) factors were recently implicated in DNA replication fork remodeling and protection. While maintaining genome stability, HR-mediated fork remodeling promotes cancer chemoresistance, by as-yet elusive mechanisms. Five HR cofactors - the RAD51 paralogs RAD51B, RAD51C, RAD51D, XRCC2 and XRCC3 - recently emerged as crucial tumor suppressors. Albeit extensively characterized in DNA repair, their role in replication has not been addressed systematically. Here, we identify all RAD51 paralogs while screening for modulators of RAD51 recombinase upon replication stress. Single-molecule analysis of fork progression and architecture in isogenic cellular systems shows that the BCDX2 subcomplex restrains fork progression upon stress, promoting fork reversal. Accordingly, BCDX2 primes unscheduled degradation of reversed forks in BRCA2-defective cells, boosting genomic instability. Conversely, the CX3 subcomplex is dispensable for fork reversal, but mediates efficient restart of reversed forks. We propose that RAD51 paralogs sequentially orchestrate clinically relevant transactions at replication forks, cooperatively promoting fork remodeling and restart.
同源重组 (HR) 因子最近被牵涉到 DNA 复制叉重塑和保护中。虽然维持基因组稳定性，但 HR 介导的叉重塑通过迄今仍难以捉摸的机制促进癌症的化疗耐药性。五个 HR 辅助因子 - RAD51 蛋白家族的 RAD51B、RAD51C、RAD51D、XRCC2 和 XRCC3 - 最近被认为是关键的肿瘤抑制因子。尽管在 DNA 修复中得到了广泛的研究，但它们在复制中的作用尚未得到系统的研究。在这里，我们在复制应激时筛选 RAD51 重组酶的调节剂，鉴定了所有的 RAD51 同源蛋白。在同基因细胞系统中对叉进展和结构的单分子分析表明，BCDX2 亚基复合物在应激时会抑制叉的进展，促进叉的反转。因此，BCDX2 在 BRCA2 缺陷细胞中引发非计划的反转叉降解，从而增强基因组不稳定性。相反，CX3 亚基对于叉反转不是必需的，但介导反转叉的有效重新启动。我们提出，RAD51 同源蛋白序列地协调复制叉上的临床相关反应，协同促进叉重塑和重新启动。
