Abstract
The protein kinase Chk2 has been implicated in signaling DNA damage to cell cycle checkpoints. In response to ionizing radiation, Chk2 becomes rapidly phosphorylated at threonine 68 by ataxia-telangiectasia mutated (ATM). Here we show that the Thr(68)-phosphorylated form of Chk2 forms distinct nuclear foci in response to ionizing radiation. Only this activated form of Chk2 localizes at sites of DNA strand breaks. The kinase activity of Chk2 and the number of Chk2 foci formed depend on the severity of DNA damage and gradually decline correlating with the predicted value of slowly re-joining double strand breaks. These results suggest that Chk2 is regulated at the sites of DNA strand breaks in response to ionizing radiation.
Highlights
The protein kinase Chk2 has been implicated in signaling DNA damage to cell cycle checkpoints
In response to ionizing radiation, Chk2 becomes rapidly phosphorylated at threonine 68 by ataxia-telangiectasia mutated (ATM)
Phosphorylation and Activation of Chk2 Depend on the Severity of DNA Damage—To investigate the phosphorylation and activation of Chk2, we raised polyclonal anti-phosphoThr68 antibodies against a Chk2 peptide containing T68P (CETVST(PO4)QELYS)
Summary
We show that the Thr68-phosphorylated form of Chk forms distinct nuclear foci in response to ionizing radiation This activated form of Chk localizes at sites of DNA strand breaks. The kinase activity of Chk and the number of Chk foci formed depend on the severity of DNA damage and gradually decline correlating with the predicted value of slowly re-joining double strand breaks. These results suggest that Chk is regulated at the sites of DNA strand breaks in response to ionizing radiation. We show that the Thr68-phosphorylated form of Chk (Chk2T68P) forms distinct nuclear foci in response to ionizing radiation This activated form localizes at sites of DNA strand breaks. Our findings suggest that Chk activity is initiated and regulated at the sites of DNA strand breaks in response to ionizing radiation
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