Chini C C S, Wood J, Chen J
Department of Oncology, Mayo Clinic and Foundation, Rochester, MN 55905, USA.
Oncogene. 2006 Jul 13;25(30):4165-71. doi: 10.1038/sj.onc.1209447. Epub 2006 Feb 27.
Claspin is a Chk1-interacting protein that participates in the DNA replication checkpoint. Expression of Claspin fluctuates in a cell cycle-dependent manner, but the mechanisms involved in the regulation of Claspin protein levels have not been explored. In this study, we show that Claspin expression is downregulated by the proteasome-mediated degradation pathway and that Chk1 is required to maintain Claspin stability. Downregulation of Chk1 expression by siRNA or inhibition of Chk1 activity by UCN01 decreases Claspin levels in cells. Conversely, overexpression of Chk1 increases Claspin levels. These data indicate a role of Chk1 in regulating Claspin stability in the cell. Since Claspin has also been shown to participate in Chk1 activation following DNA damage, we further explored the exact role of Claspin during Chk1 activation following replication stress. We observed that while Rad17 is required for early Chk1 activation after hydroxyurea treatment, Claspin is only required to sustain Chk1 activation. Based on these findings, we propose that Claspin functions at late stages of Chk1 activation following DNA damage. Once Chk1 is activated, it stabilizes Claspin, which in turn helps to maintain Chk1 activation during replication stress. In summary, these data indicate that the interaction between Claspin and Chk1 is complex. These proteins regulate each other and thus ensure the proper cell cycle progression and replication checkpoint control.
Claspin是一种与Chk1相互作用的蛋白质，参与DNA复制检查点。Claspin的表达以细胞周期依赖性方式波动，但调节Claspin蛋白水平的机制尚未得到探索。在本研究中，我们表明Claspin的表达通过蛋白酶体介导的降解途径下调，并且Chk1是维持Claspin稳定性所必需的。通过siRNA下调Chk1表达或用UCN01抑制Chk1活性会降低细胞中Claspin的水平。相反，Chk1的过表达会增加Claspin的水平。这些数据表明Chk1在调节细胞中Claspin稳定性方面的作用。由于Claspin也已被证明在DNA损伤后参与Chk1激活，我们进一步探索了Claspin在复制应激后Chk1激活过程中的具体作用。我们观察到，虽然Rad17是羟基脲处理后早期Chk1激活所必需的，但Claspin仅在维持Chk1激活时才需要。基于这些发现，我们提出Claspin在DNA损伤后Chk1激活的后期发挥作用。一旦Chk1被激活，它会使Claspin稳定，这反过来又有助于在复制应激期间维持Chk1激活。总之，这些数据表明Claspin和Chk1之间的相互作用是复杂的。这些蛋白质相互调节，从而确保细胞周期的正常进展和复制检查点控制。
