TOPICS
Phosphorylated ATM Foci as a Biochemical Marker for DNA Double Strand Breaks

Keiji Suzuki1, Seiji Kodama2 and Masami Watanabe3

1 Division of Radiation Biology, Department of Radiology and Radiation Biology, Course of Life Sciences and Radiation Research, Graduate School of Biomedical Sciences, Nagasaki University, 1-14 Bunkyo-machi, Nagasaki 852-8521, Japan
2 Radiation Biology Laboratory, Radiation Research Center, Frontier Science Innovation Center, Organization for University-Industry-Government Cooperation, Osaka Prefecture University, 1-2 gakuen-machi, Sakai, 599-8570, Japan
3 Laboratory of Radiation, Biology, Kyoto University Research Reactor Institute, Kumatori-cho Sennan-gun, Osaka 590-0494, Japan

AATEX 11(2):101-104, 2005

Abstract
DNA double strand breaks are the most relevant damage related to the detrimental effects of DNA damaging agents. Previous studies have established various biochemical methods to measure DNA double strand breaks in mammalian cells, however, the application of these methods is limited to the experiments using higher doses of DNA damaging agents. Recently, it has been shown that DNA damaging checkpoint pathways are activated by phosphorylation of the checkpoint factors, such as ataxia-telangiectasia mutated (ATM), ATM-Rad3 related (ATR), CHK1/2, and p53 proteins. For example, ATM is activated through its autophosphorylation at serine 1981 (S1981) at the sites of DNA double strand breaks. Because the response is highly amplified, and when visualized with an antibody recognizing phosphorylated ATM at S1981, phosphorylated ATM appears as nuclear foci. Our group has examined the formation of phosphorylated ATM foci in exponentially growing normal human diploid cells exposed to ionizing radiation, and the induction of foci showed a linear dose-relationship with doses ranging from 10 mGy to 1 Gy. The number of phosphorylated ATM foci is well correlated with the estimated number of DNA double strand breaks, providing an unique and sensitive tool for the measure-ment of DNA double strand breaks at the physiological level in situ.

Key words: DNA damage, phosphorylation, ATM

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(AATEX: Altern. Animal Test. EXperiment.: Alternatives to Animal Testing and EXperimentation)