@misc{oai:repo.qst.go.jp:00071096,
 author = {Katsube, Takanori and Mori, Masahiko and Tsuji, Hideo and Shiomi, Tadahiro and Onoda, Makoto and 勝部 孝則 and 森 雅彦 and 辻 秀雄 and 塩見 忠博 and 小野田 眞},
 month = {May},
 note = {XRCC4-deficient (XRCC4-/-) cells generated by a gene targeting exhibit a lower survival rate and a higher frequency of chromosomal aberrations than parental HCT116 cells after exposure to ionizing radiation or hydrogen peroxide (H2O2). Since XRCC4 is a key component of the non-homologous end-joining, a predominant repair pathway for DNA double-strand breaks (DSBs), the increase in susceptibility of XRCC4-/- cells to H2O2 might be attributed to the induction of DSBs. Compatibly, a marked increase of 53BP1 foci, a marker of DSBs, was observed at 8 h after H2O2 treatment (100-200 µM, 1 h) in XRCC4-/-, but not in HCT116. DNA damages induced by H2O2, such as single-stranded breaks, might be converted to DSBs through DNA replication process, which was stopped for a while and restarted around 8 h after H2O2 treatment. Unexpectedly, the induction of phosphorylated form of histone H2AX (gammaH2AX) showed a striking difference from that of 53BP1 foci. Immunoreactivity of gammaH2AX, which disperses throughout the nucleus, appeared immediately after H2O2 treatment, followed by a gradual descent as time passed, and then reappeared at 24 h after the treatment. In addition, the induction of gammaH2AX was more clearly detected in HCT116 than XRCC4-/- after H2O2 treatment. These results suggest that H2O2-induced gammaH2AX must not depend on DSBs. To clarify the induction mechanism of gammaH2AX by H2O2, we further analysed kinetics of gammaH2AX induction after H2O2 treatment in HCT116. Analyses of pulse-labeled cells with EdU (5-ethyl-2'-deoxyuridine) revealed that gammaH2AX induction immediately after the treatment was found in both S-phase and non-S-phase cells. However, gammaH2AX reappeared 24 h later only in cells which were at S-phase when exposed to H2O2. gammaH2AX induction was delayed and peaked at 2 h after exposure to H2O2 by a prior treatment with ATM inhibitor (KU-55933), while reappearance of gammaH2AX at 24 h after H2O2 treatment was not prevented by inhibition of ATM. On the other hand, when cells were pretreated with ATR inhibitor (VE-821), gammaH2AX induction immediately after the H2O2 treatment was much disturbed and a higher mortality was observed at 24 h after the treatment. These observations suggest that H2O2-induced gammaH2AX must not depend on DSBs and that ATR might be involved in gammaH2AX induction by H2O2 as a major kinase., The 3rd Asian Congress of Radiation Research},
 title = {gamma-H2AX foci are induced by different manners after exposure to ionizing radiation or H2O2},
 year = {2013}
}