Abstract
When exposed to ionizing radiation (IR), eukaryotic cells activate checkpoint pathways to delay the progression of the cell cycle1,2,3. Defects in the IR-induced S-phase checkpoint cause ‘radioresistant DNA synthesis’, a phenomenon that has been identified in cancer-prone patients suffering from ataxia-telangiectasia, a disease caused by mutations in the ATM gene4,5,6. The Cdc25A phosphatase7 activates the cyclin-dependent kinase 2 (Cdk2) needed for DNA synthesis8,9, but becomes degraded in response to DNA damage10 or stalled replication11. Here we report a functional link between ATM, the checkpoint signalling kinase Chk2/Cds1 (Chk2)12 and Cdc25A, and implicate this mechanism in controlling the S-phase checkpoint. We show that IR-induced destruction of Cdc25A requires both ATM and the Chk2-mediated phosphorylation of Cdc25A on serine 123. An IR-induced loss of Cdc25A protein prevents dephosphorylation of Cdk2 and leads to a transient blockade of DNA replication. We also show that tumour-associated Chk2 alleles13 cannot bind or phosphorylate Cdc25A, and that cells expressing these Chk2 alleles, elevated Cdc25A or a Cdk2 mutant unable to undergo inhibitory phosphorylation (Cdk2AF) fail to inhibit DNA synthesis when irradiated. These results support Chk2 as a candidate tumour suppressor, and identify the ATM–Chk2–Cdc25A–Cdk2 pathway as a genomic integrity checkpoint that prevents radioresistant DNA synthesis.
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Acknowledgements
We thank S. Elledge, G. Evan, S. I. Reed and Y. Shiloh for providing reagents; K. Hansen for advice; and the Danish Cancer Society, the Human Frontier Science Programme, Alfred Benzon's Fund, the European Commission, the Danish Medical Research Council and the Danish Cancer Research Fund for financial support.
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Falck, J., Mailand, N., Syljuåsen, R. et al. The ATM–Chk2–Cdc25A checkpoint pathway guards against radioresistant DNA synthesis. Nature 410, 842–847 (2001). https://doi.org/10.1038/35071124
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DOI: https://doi.org/10.1038/35071124
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