Hu Yiduo, Lu Xincheng, Zhou Guangjin, Barnes Ellen L, Luo Guangbin
Department of Genetics, Case Comprehensive Cancer Center, University Hospitals of Cleveland and Case Western Reserve University, Cleveland, OH 44106, USA.
Mol Biol Cell. 2009 Jan;20(1):114-23. doi: 10.1091/mbc.e08-06-0565. Epub 2008 Nov 5.
Disruption of replication can lead to loss of genome integrity and increase of cancer susceptibility in mammals. Thus, a replication impediment constitutes a formidable challenge to these organisms. Recent studies indicate that homologous recombination (HR) plays an important role in suppressing genome instability and promoting cell survival after exposure to various replication inhibitors, including a topoisomerase I inhibitor, camptothecin (CPT). Here, we report that the deletion of RecQ helicase Recql5 in mouse ES cells and embryonic fibroblast (MEF) cells resulted in a significant increase in CPT sensitivity and a profound reduction in DNA replication after the treatment with CPT, but not other DNA-damaging agents. This CPT-induced cell death is replication dependent and occurs primarily after the cells had exited the first cell cycle after CPT treatment. Furthermore, we show that Recql5 functions nonredundantly with Rad51, a key factor for HR to protect mouse ES cells from CPT-induced cytotoxicity. These new findings strongly suggest that Recql5 plays an important role in maintaining active DNA replication to prevent the collapse of replication forks and the accumulation of DSBs in order to preserve genome integrity and to prevent cell death after replication stress as a result of topoisomerase I poisoning.
复制过程的破坏可导致哺乳动物基因组完整性丧失及癌症易感性增加。因此，复制障碍对这些生物体构成了巨大挑战。近期研究表明，同源重组（HR）在抑制基因组不稳定以及促进细胞在暴露于包括拓扑异构酶I抑制剂喜树碱（CPT）在内的各种复制抑制剂后存活方面发挥着重要作用。在此，我们报告，在小鼠胚胎干细胞和胚胎成纤维细胞（MEF）中缺失RecQ解旋酶Recql5，导致在用CPT处理后CPT敏感性显著增加且DNA复制大幅减少，但在用其他DNA损伤剂处理后并非如此。这种CPT诱导的细胞死亡是复制依赖性的，主要发生在细胞在CPT处理后退出第一个细胞周期之后。此外，我们表明Recql5与Rad51功能非冗余，Rad51是HR的关键因子，可保护小鼠胚胎干细胞免受CPT诱导的细胞毒性。这些新发现强烈表明，Recql5在维持活跃的DNA复制以防止复制叉崩溃和双链断裂积累方面发挥重要作用，从而保持基因组完整性并防止拓扑异构酶I中毒导致复制应激后细胞死亡。
