Cell cycle-dependent and ATM-independent expression of human Chk1 kinase
Cell cycle-dependent and ATM-independent expression of human Chk1 kinase
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DOI：
10.1038/sj.onc.1202706
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发表时间：
1999-06-24
期刊：
影响因子：
8
通讯作者：
Nakanishi, M
中科院分区：
文献类型：
--
作者：
Kaneko, Y;Watanabe, N;Nakanishi, M
当DNA受损或DNA复制受阻时，检查点基因会导致细胞周期停滞。尽管最近报道了Chk 1的人类同源物（hChk 1）通过CaS 25 A、B和C的磷酸化参与DNA损伤检查点，但尚不知道hChk 1在细胞周期的哪个（哪些）阶段起作用以及hChk 1如何响应于DNA损伤而引起细胞周期停滞。在本研究中，我们证明，在正常的人成纤维细胞（MJ 90），hChk 1是在RNA和蛋白质水平的细胞周期的S至M期特异性表达，它是本地化的细胞核在这个时候。通过Cdc 25 C的磷酸化测定的hChk 1活性在细胞周期的S至M期容易检测到，并且由UV或电离辐射诱导的DNA损伤不增强hChk 1的表达或其活性。此外，hChk 1在来源于缺乏功能性AT突变（ATM）基因产物的共济失调毛细血管扩张（AT）患者的成纤维细胞中以活性形式存在于S至M期，表明hChk 1表达不依赖于功能性ATM。结合丝氨酸216上Cdc 25 C磷酸化在S至M期增加的发现，提示在细胞周期的这一特定阶段，甚至在没有DNA损伤的情况下，hChk 1磷酸化丝氨酸216上的Cdc 25 C，这被认为是G2/M检查点的先决条件。因此，hChk 1可能在保持Cdc 25 C准备响应DNA损伤的磷酸化其丝氨酸残基在216在S到M期期间发挥重要作用。
Checkpoint genes cause cell cycle arrest when DNA is damaged or DNA replication is blocked. Although a human homolog of Chk1 (hChk1) has recently been reported to be involved in the DNA damage checkpoint through phosphorylation of CaS25A, B, and C, it is not known at which phase(s) of the cell cycle hChk1 functions and how hChk1 causes cell cycle arrest in response to DNA damage. In the present study, we demonstrate that in normal human fibroblasts (MJ90), hChk1 is expressed specifically at the S to M phase of the cell cycle at both the RNA and protein levels and that it is localized to the nucleus at this time. hChk1 activity, as determined by phosphorylation of Cdc25C, is readily detected at the S to M phase of the cell cycle, and DNA damage induced by UV or ionizing radiation does not enhance the expression of hChk1 or its activity. Furthermore, hChk1 exists in an active form at the S to M phase in fibroblasts derived from patients with ataxia telangiectasia (AT) which lack the functional AT mutated (ATM) gene product, suggesting that hChk1 expression is independent of functional ATM, Taken together with the findings that phosphorylation of Cdc25C on serine 216 is increased at the S to M phase, it is suggested that at this particular phase of the cell cycle, even in the absence of DNA damage, hChk1 phosphorylates Cdc25C on serine 216, which is considered to be a prerequisite for the G2/M checkpoint. Thus, hChk1 may play an important role in keeping Cdc25C prepared for responding to DNA damage by phosphorylating its serine residue at 216 during the S to M phase.