Three independent mechanisms for arrest in G2 after ionizing radiation
Three independent mechanisms for arrest in G2 after ionizing radiation
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DOI：
10.4161/cc.10.5.14968
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发表时间：
2011-03-01
期刊：
影响因子：
4.3
通讯作者：
Stokke, Trond
中科院分区：
文献类型：
--
作者：
Landsverk, Kirsti Solberg;Patzke, Sebastian;Stokke, Trond
细胞周期检查点确保真核细胞在电离辐射（IR）后不进入有丝分裂。IR后的G（2）-阻滞是多种信号通路激活的结果，其贡献随照射后时间而变化。我们研究了IR诱导的人B淋巴细胞癌细胞系G（2）-阻滞的时间演变，以及负责阻滞的分子机制。在IR（0.5或4戈伊）后0-2小时，在照射时处于G（2）期的细胞经历了短暂的停滞，其阻断了进入有丝分裂。ATM和CHEK 2的激活与这种早期阻滞同时发生，并且与阻滞一样，被ATM抑制剂KU-55933废除。在辐射（4戈伊）时处于G（2）/S/G（1）的细胞的晚期、永久性和ATM非依赖性停滞（IR后>= 6小时）被咖啡因灭活。这种晚期G（2）停滞不能用G（2）/有丝分裂中功能基因的下调来解释（例如，PLK 1，CCNB 1/2），因为下调是短暂的，并不伴随蛋白质水平的降低。然而，4戈伊后CHEK 1的持续磷酸化表明CHEK 1在晚期阻滞中的作用，与CHEK 1耗尽细胞中阻滞的消除一致。TP 53不是晚期G（2）阻滞所必需的，但介导了一个中间阻滞（IR后2-10小时），独立于ATM和CHEK 1。总之，IR诱导的G（2）细胞阻滞在照射后立即由ATM介导，TP 53作为独立和短暂的备份，而CHEK 1是晚期阻滞所必需的。
Cell cycle checkpoints ensure that eukaryotic cells do not enter mitosis after ionizing irradiation (IR). The G(2)-arrest after IR is the result of activation of multiple signalling pathways, the contributions of which vary with time after irradiation. We have studied the time evolution of the IR-induced G(2)-arrest in human B-lymphocyte cancer cell lines, as well as the molecular mechanisms responsible for the arrest. Cells that were in G(2) phase at the time of irradiation experienced a transient arrest that blocked entry into mitosis at 0-2 hours after IR (0.5 or 4 Gy). Activation of ATM and CHEK2 occurred at the same time as this early arrest and was, like the arrest, abrogated by the ATM-inhibitor KU-55933. A late, permanent and ATM-independent arrest (>= 6 hours after IR) of cells that were in G(2)/S/G(1) at the time of irradiation (4 Gy) was inactivated by caffeine. This late G(2)-arrest could not be explained by downregulation of genes with functions in G(2)/mitosis (e.g., PLK1, CCNB1/2), since the downregulation was transient and not accompanied by reduced protein levels. However, the persistent phosphorylation of CHEK1 after 4 Gy suggested a role for CHEK1 in the late arrest, consistent with the abrogation of the arrest in CHEK1-depleted cells. TP 53 was not necessary for the late G(2)-arrest, but mediated an intermediate arrest (2-10 hours after IR) independently of ATM and CHEK1. In conclusion, the IR-induced arrest in G(2) is mediated by ATM immediately after irradiation, with TP 53 for independent and transient back-up, while CHEK1 is necessary for the late arrest.