Leung-Pineda Van, Ryan Christine E, Piwnica-Worms Helen
Department of Cell Biology and Physiology & Howard Hughes Medical Institute, Washington University School of Medicine, Box 8228, 660 South Euclid Ave., St. Louis, MO 63110, USA.
Mol Cell Biol. 2006 Oct;26(20):7529-38. doi: 10.1128/MCB.00447-06. Epub 2006 Aug 5.
In higher eukaryotic organisms, the checkpoint kinase 1 (Chk1) contributes essential functions to both cell cycle and checkpoint control. Chk1 executes these functions, in part, by targeting the Cdc25A protein phosphatase for ubiquitin-mediated proteolysis. In response to genotoxic stress, Chk1 is phosphorylated on serines 317 (S317) and 345 (S345) by the ataxia-telangiectasia-related (ATR) protein kinase. Phosphorylation of Chk1 on these C-terminal serine residues is used as an indicator of Chk1 activation in vivo. Here, we report that inhibition of Chk1 kinase activity paradoxically leads to the accumulation of S317- and S345-phosphorylated Chk1 in vivo and that ATR catalyzes Chk1 phosphorylation under these conditions. We demonstrate that Chk1 phosphorylation by ATR is antagonized by protein phosphatase 2A (PP2A). Importantly, dephosphorylation of Chk1 by PP2A is regulated, in part, by the kinase activity of Chk1. We propose that the ATR-Chk1-PP2A regulatory circuit functions to keep Chk1 in a low-activity state during an unperturbed cell division cycle but at the same time keeps Chk1 primed to respond rapidly in the event that cells encounter genotoxic stress.
在高等真核生物中，关卡激酶1（Chk1）对细胞周期和关卡控制都起着至关重要的作用。Chk1部分通过将细胞周期蛋白依赖性激酶25A（Cdc25A）蛋白磷酸酶作为泛素介导的蛋白水解作用的靶点来执行这些功能。响应基因毒性应激，Chk1在丝氨酸317（S317）和345（S345）位点被共济失调毛细血管扩张症相关（ATR）蛋白激酶磷酸化。Chk1在这些C末端丝氨酸残基上的磷酸化被用作体内Chk1激活的指标。在此，我们报告Chk1激酶活性的抑制在体内反常地导致S317和S345磷酸化的Chk1积累，并且在这些条件下ATR催化Chk1磷酸化。我们证明ATR介导的Chk1磷酸化被蛋白磷酸酶2A（PP2A）拮抗。重要的是，PP2A对Chk1的去磷酸化部分受Chk1激酶活性的调节。我们提出ATR-Chk1-PP2A调节回路的作用是在未受干扰的细胞分裂周期中将Chk1保持在低活性状态，但同时使Chk1在细胞遇到基因毒性应激时能够迅速做出反应。
