Institute of Molecular Cancer Research, University of Zurich, Zurich, Switzerland.
Nat Struct Mol Biol. 2012 Mar 4;19(4):417-23. doi: 10.1038/nsmb.2258.
Topoisomerase I (Top1) releases torsional stress during DNA replication and transcription and is inhibited by camptothecin and camptothecin-derived cancer chemotherapeutics. Top1 inhibitor cytotoxicity is frequently linked to double-strand break (DSB) formation as a result of Top1 being trapped on a nicked DNA intermediate in replicating cells. Here we use yeast, mammalian cell lines and Xenopus laevis egg extracts to show that Top1 poisons rapidly induce replication-fork slowing and reversal, which can be uncoupled from DSB formation at sublethal inhibitor doses. Poly(ADP-ribose) polymerase activity, but not single-stranded break repair in general, is required for effective fork reversal and limits DSB formation. These data identify fork reversal as a means to prevent chromosome breakage upon exogenous replication stress and implicate proteins involved in fork reversal or restart as factors modulating the cytotoxicity of replication stress-inducing chemotherapeutics.
拓扑异构酶 I（Top1）在 DNA 复制和转录过程中释放扭转应力，并被喜树碱和喜树碱衍生的癌症化疗药物抑制。Top1 抑制剂的细胞毒性通常与双链断裂（DSB）的形成有关，因为 Top1 被捕获在复制细胞中带有缺口的 DNA 中间体上。在这里，我们使用酵母、哺乳动物细胞系和非洲爪蟾卵提取物表明，Top1 毒物会迅速诱导复制叉减速和反转，这可以在亚致死抑制剂剂量下与 DSB 形成解耦。多聚（ADP-核糖）聚合酶活性，但不是一般的单链断裂修复，对于有效叉反转和限制 DSB 形成是必需的。这些数据表明叉反转是防止外源复制应激引起染色体断裂的一种手段，并暗示参与叉反转或重新启动的蛋白质是调节复制应激诱导化疗药物细胞毒性的因素。
