Feijoo C, Hall-Jackson C, Wu R, Jenkins D, Leitch J, Gilbert D M, Smythe C
Division of Cell Signaling, School of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, United Kingdom.
J Cell Biol. 2001 Sep 3;154(5):913-23. doi: 10.1083/jcb.200104099.
Checkpoints maintain order and fidelity in the cell cycle by blocking late-occurring events when earlier events are improperly executed. Here we describe evidence for the participation of Chk1 in an intra-S phase checkpoint in mammalian cells. We show that both Chk1 and Chk2 are phosphorylated and activated in a caffeine-sensitive signaling pathway during S phase, but only in response to replication blocks, not during normal S phase progression. Replication block-induced activation of Chk1 and Chk2 occurs normally in ataxia telangiectasia (AT) cells, which are deficient in the S phase response to ionizing radiation (IR). Resumption of synthesis after removal of replication blocks correlates with the inactivation of Chk1 but not Chk2. Using a selective small molecule inhibitor, cells lacking Chk1 function show a progressive change in the global pattern of replication origin firing in the absence of any DNA replication. Thus, Chk1 is apparently necessary for an intra-S phase checkpoint, ensuring that activation of late replication origins is blocked and arrested replication fork integrity is maintained when DNA synthesis is inhibited.
细胞周期检查点通过在早期事件执行不当的情况下阻止后期事件的发生来维持细胞周期的秩序和保真度。在此，我们描述了Chk1参与哺乳动物细胞S期内检查点的证据。我们发现，在S期，Chk1和Chk2均在一条对咖啡因敏感的信号通路中被磷酸化并激活，但这仅发生在对复制阻滞作出反应时，而非在正常的S期进程中。复制阻滞诱导的Chk1和Chk2激活在共济失调毛细血管扩张症（AT）细胞中正常发生，这些细胞在对电离辐射（IR）的S期反应中存在缺陷。去除复制阻滞后合成的恢复与Chk1的失活相关，但与Chk2无关。使用一种选择性小分子抑制剂，缺乏Chk1功能的细胞在没有任何DNA复制的情况下，复制起点激活的全局模式会发生渐进性变化。因此，Chk1显然是S期内检查点所必需的，可确保当DNA合成受到抑制时，后期复制起点的激活被阻断，并且停滞的复制叉完整性得以维持。
