Activation of the ATM Kinase by Ionizing Radiation and Phosphorylation…

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  • Author Affiliations

    1. C. E. Canman, D.-S. Lim, M. B. Kastan, J. D. Siliciano, The Johns Hopkins School of Medicine, Oncology Center, Baltimore, MD 21205, USA. K. A. Cimprich, Department of Molecular Pharmacology, Stanford University School of Medicine, Stanford, CA 94305, USA. Y. Taya, National Cancer Center Research Institute, Tsukiji 5-chome, Chuo-ku, Tokyo 104, Japan. K. Tamai, Ina Laboratories, MBL Co. Ltd., Ina, Nagano 396, Japan. K. Sakaguchi and E. Appella, Laboratory of Cell Biology, National Institutes of Health, Bethesda, MD 20892, USA.

The p53 tumor suppressor protein is activated and phosphorylated on serine-15 in response to various DNA damaging agents. The gene product mutated in ataxia telangiectasia, ATM, acts upstream of p53 in a signal transduction pathway initiated by ionizing radiation. Immunoprecipitated ATM had intrinsic protein kinase activity and phosphorylated p53 on serine-15 in a manganese-dependent manner. Ionizing radiation, but not ultraviolet radiation, rapidly enhanced this p53-directed kinase activity of endogenous ATM. These observations, along with the fact that phosphorylation of p53 on serine-15 in response to ionizing radiation is reduced in ataxia telangiectasia cells, suggest that ATM is a protein kinase that phosphorylates p53 in vivo.