Gottifredi V, Karni-Schmidt O, Shieh S S, Prives C
Department of Biological Sciences, Columbia University, New York, New York 10027, USA.
Mol Cell Biol. 2001 Feb;21(4):1066-76. doi: 10.1128/MCB.21.4.1066-1076.2001.
Both fission yeast and mammalian cells require the function of the checkpoint kinase CHK1 for G2 arrest after DNA damage. The tumor suppressor p53, a well-studied stress response factor, has also been shown to play a role in DNA damage G2 arrest, although in a manner that is probably independent of CHK1. p53, however, can be phosphorylated and regulated by both CHK1 as well as another checkpoint kinase, hCds1 (also called CHK2). It was therefore of interest to determine whether reciprocally, p53 affects either CHK1 or CHK2. We found that induction of p53 either by diverse stress signals or ectopically using a tetracycline-regulated promoter causes a marked reduction in CHK1 protein levels. CHK1 downregulation by p53 occurs as a result of reduced CHK1 RNA accumulation, indicating that repression occurs at the level of transcription. Repression of CHK1 by p53 requires p21, since p21 alone is sufficient for this to occur and cells lacking p21 cannot downregulate CHK1. Interestingly, pRB is also required for CHK1 downregulation, suggesting the possible involvement of E2F-dependent transcription in the regulation of CHK1. Our results identify a new repression target of p53 and suggest that p53 and CHK1 play interdependent and complementary roles in regulating both the arrest and resumption of G2 after DNA damage.
裂殖酵母和哺乳动物细胞在DNA损伤后发生G2期阻滞均需要检查点激酶CHK1发挥作用。肿瘤抑制因子p53是一个经过充分研究的应激反应因子，也已被证明在DNA损伤后的G2期阻滞中发挥作用，尽管其作用方式可能独立于CHK1。然而，p53可被CHK1以及另一种检查点激酶hCds1（也称为CHK2）磷酸化并受到调控。因此，确定p53是否会反过来影响CHK1或CHK2就变得很有意义。我们发现，通过多种应激信号诱导p53表达或使用四环素调控启动子异位表达p53，都会导致CHK1蛋白水平显著降低。p53导致CHK1下调是CHK1 RNA积累减少的结果，这表明抑制发生在转录水平。p53对CHK1的抑制作用需要p21，因为单独的p21就足以导致这种情况发生，而缺乏p21的细胞无法下调CHK1。有趣的是，CHK1下调也需要pRB，这表明E2F依赖性转录可能参与了CHK1的调控。我们的研究结果确定了p53的一个新的抑制靶点，并表明p53和CHK1在调节DNA损伤后G2期的阻滞和恢复中发挥着相互依赖和互补的作用。
