Developmental Biology Program, Memorial Sloan-Kettering Cancer Center, New York, NY 10065, USA.
Cell. 2011 May 13;145(4):529-42. doi: 10.1016/j.cell.2011.03.041.
Breast cancer suppressor BRCA2 is critical for maintenance of genomic integrity and resistance to agents that damage DNA or collapse replication forks, presumably through homology-directed repair of double-strand breaks (HDR). Using single-molecule DNA fiber analysis, we show here that nascent replication tracts created before fork stalling with hydroxyurea are degraded in the absence of BRCA2 but are stable in wild-type cells. BRCA2 mutational analysis reveals that a conserved C-terminal site involved in stabilizing RAD51 filaments, but not in loading RAD51 onto DNA, is essential for this fork protection but dispensable for HDR. RAD51 filament disruption in wild-type cells phenocopies BRCA2 deficiency. BRCA2 prevents chromosomal aberrations on replication stalling, which are alleviated by inhibition of MRE11, the nuclease responsible for this form of fork instability. Thus, BRCA2 prevents rather than repairs nucleolytic lesions at stalled replication forks to maintain genomic integrity and hence likely suppresses tumorigenesis through this replication-specific function.
乳腺癌抑制因子 BRCA2 对于维持基因组完整性和抵抗破坏 DNA 或使复制叉崩溃的试剂至关重要，这可能是通过同源定向修复双链断裂 (HDR) 实现的。通过单分子 DNA 纤维分析，我们在这里表明，在羟基脲引起的叉停顿之前形成的新生复制片段在没有 BRCA2 的情况下会降解，但在野生型细胞中是稳定的。BRCA2 突变分析表明，一个保守的 C 末端位点参与稳定 RAD51 丝，但不参与将 RAD51 加载到 DNA 上，对于这种叉保护是必需的，但对于 HDR 是可有可无的。野生型细胞中 RAD51 丝的破坏模拟了 BRCA2 的缺失。BRCA2 可以防止复制停顿时的染色体异常，而这种形式的叉不稳定的核酶 MRE11 的抑制可以减轻这些异常。因此，BRCA2 防止而不是修复停滞复制叉上的核酸酶损伤，以维持基因组完整性，因此可能通过这种复制特异性功能抑制肿瘤发生。
