Bai Gongshi, Smolka Marcus B, Schimenti John C
Department of Biomedical Sciences, Cornell University, Ithaca, New York, United States of America.
Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York, United States of America.
PLoS Genet. 2016 Jan 14;12(1):e1005787. doi: 10.1371/journal.pgen.1005787. eCollection 2016 Jan.
Circumstances that compromise efficient DNA replication, such as disruptions to replication fork progression, cause a state known as DNA replication stress (RS). Whereas normally proliferating cells experience low levels of RS, excessive RS from intrinsic or extrinsic sources can trigger cell cycle arrest and senescence. Here, we report that a key driver of RS-induced senescence is active downregulation of the Minichromosome Maintenance 2-7 (MCM2-7) factors that are essential for replication origin licensing and which constitute the replicative helicase core. Proliferating cells produce high levels of MCM2-7 that enable formation of dormant origins that can be activated in response to acute, experimentally-induced RS. However, little is known about how physiological RS levels impact MCM2-7 regulation. We found that chronic exposure of primary mouse embryonic fibroblasts (MEFs) to either genetically-encoded or environmentally-induced RS triggered gradual MCM2-7 repression, followed by inhibition of replication and senescence that could be accelerated by MCM hemizygosity. The MCM2-7 reduction in response to RS is TRP53-dependent, and involves a group of Trp53-dependent miRNAs, including the miR-34 family, that repress MCM expression in replication-stressed cells before they undergo terminal cell cycle arrest. miR-34 ablation partially rescued MCM2-7 downregulation and genomic instability in mice with endogenous RS. Together, these data demonstrate that active MCM2-7 repression is a physiologically important mechanism for RS-induced cell cycle arrest and genome maintenance on an organismal level.
损害高效DNA复制的情况，如复制叉进展受阻，会导致一种称为DNA复制应激（RS）的状态。正常增殖细胞经历的RS水平较低，而来自内在或外在来源的过度RS会触发细胞周期停滞和衰老。在这里，我们报告RS诱导衰老的一个关键驱动因素是微小染色体维持蛋白2 - 7（MCM2 - 7）因子的活性下调，这些因子对于复制起点许可至关重要，并且构成复制解旋酶核心。增殖细胞产生高水平的MCM2 - 7，这使得能够形成休眠起点，可在急性实验诱导的RS反应中被激活。然而，关于生理RS水平如何影响MCM2 - 7调节知之甚少。我们发现，原代小鼠胚胎成纤维细胞（MEF）长期暴露于基因编码或环境诱导的RS会触发MCM2 - 7的逐渐抑制，随后复制受到抑制并出现衰老，MCM半合子状态可加速这种情况。RS反应中MCM2 - 7的减少是TRP53依赖性的，并且涉及一组TRP53依赖性的微小RNA，包括miR - 34家族，它们在复制应激细胞进入终末细胞周期停滞之前抑制MCM表达。miR - 34缺失部分挽救了内源性RS小鼠中MCM2 - 7的下调和基因组不稳定。总之，这些数据表明，活跃的MCM2 - 7抑制是RS诱导细胞周期停滞和生物体水平基因组维持的一种生理上重要的机制。
