BRCA1/2 help maintain genomic integrity by stabilizing stalled forks. Here, we identify the E3 ligase RFWD3 as an essential modulator of stalled fork stability in BRCA2-deficient cells and show that codepletion of RFWD3 rescues fork degradation, collapse, and cell sensitivity upon replication stress. Stalled forks in BRCA2-deficient cells accumulate phosphorylated and ubiquitinated replication protein A (ubq-pRPA), the latter of which is mediated by RFWD3. Generation of this intermediate requires SMARCAL1, suggesting that it depends on stalled fork reversal. We show that in BRCA2-deficient cells, rescuing fork degradation might not be sufficient to ensure fork repair. Depleting MRE11 in BRCA2-deficient cells does block fork degradation, but it does not prevent fork collapse and cell sensitivity in the presence of replication stress. No such ubq-pRPA intermediate is formed in BRCA1-deficient cells, and our results suggest that BRCA1 may function upstream of BRCA2 in the stalled fork repair pathway. Collectively, our data uncover a novel mechanism by which RFWD3 destabilizes forks in BRCA2-deficient cells.

译文

:BRCA1 / 2通过稳定停滞的叉子来帮助维持基因组完整性。在这里,我们将E3连接酶RFWD3确定为BRCA2缺陷细胞失速叉稳定性的重要调节剂,并表明RFWD3的编码缺失可在复制压力下挽救叉的降解,塌陷和细胞敏感性。 BRCA2缺陷细胞中的叉子停滞,积累了磷酸化和泛素化的复制蛋白A(ubq-pRPA),后者是由RFWD3介导的。生成此中间体需要SMARCAL1,这表明它取决于停滞的货叉反转。我们显示,在BRCA2缺失的细胞中,抢救货叉降解可能不足以确保货叉修复。在缺乏BRCA2的细胞中消耗MRE11确实可以阻止前叉降解,但是在存在复制压力的情况下,它不能防止前叉塌陷和细胞敏感性。在缺乏BRCA1的细胞中没有这种ubq-pRPA中间体形成,我们的结果表明BRCA1可能在停滞的叉子修复途径中的BRCA2上游起作用。总体而言,我们的数据揭示了RFWD3破坏BRCA2缺陷细胞中叉子的稳定性的新机制。

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