Kan Qiuming, Jinno Shigeki, Yamamoto Hanako, Kobayashi Kohei, Okayama Hiroto
Department of Biochemistry and Molecular Biology, Graduate School and Faculty of Medicine, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
Proc Natl Acad Sci U S A. 2008 Mar 25;105(12):4757-62. doi: 10.1073/pnas.0706392105. Epub 2008 Mar 20.
When cells progressing in mid-S phase are damaged with a base-modifying chemical, they arrest in S phase long after the CHK1 checkpoint signal fades out, partly because of p53-mediated long-lasting induction of the cyclin-dependent kinase inhibitor p21(WAF1/CIP1). We have recently found that enforced expression of Cdc6, the assembler of prereplicative complexes, markedly advances recovery from the prolonged S-phase arrest and reactivation of Cdk2 despite the presence of a high level of induced p21. Here, we report that Cdc6 protein can activate p21-associated Cdk2 in an ATP-dependent manner in vitro. Consistently, Cdc6 mutated for ATPase or a putative cyclin binding motif is no longer able to activate the Cdk2 in vitro or promote reinitiation of S-phase progression and reactivation of Cdk2 in vivo. These results reveal the never anticipated function of Cdc6 and redefine its role in the control of S-phase progression in mammalian cells.
当处于S期中期的细胞被一种碱基修饰化学物质损伤时，它们会在CHK1检查点信号消失很久之后仍停滞在S期，部分原因是p53介导的细胞周期蛋白依赖性激酶抑制剂p21（WAF1/CIP1）的长期诱导。我们最近发现，尽管存在高水平诱导的p21，但预复制复合物组装因子Cdc6的强制表达能显著加速从延长的S期停滞中恢复以及Cdk2的重新激活。在此，我们报告Cdc6蛋白在体外能以ATP依赖的方式激活与p21相关的Cdk2。一致的是，因ATP酶或假定的细胞周期蛋白结合基序发生突变的Cdc6在体外不再能够激活Cdk2，也无法促进体内S期进程的重新启动和Cdk2的重新激活。这些结果揭示了Cdc6未曾预料到的功能，并重新定义了其在哺乳动物细胞S期进程控制中的作用。
