Phosphorylation of p53 Ser-15 through ATM protein kinase and subsequent apoptosis induced by hydrogen peroxide or ionizing radiation

Abstract

Ataxia-telangiectasia (AT) is a highly radiosensitive genetic disorder caused by mutational inactivation of the ATM gene. ATM is activated by DNA double-strand breaks and induces DNA repair and cell cycle arrest. Recently, it has been reported that hydrogen peroxide (H₂O₂) induces ATM activation, and that ATM deficiency sensitizes the cells to H₂O₂. The activation of ATM by H₂O₂ is reported to involve cell surface PDGF receptor in human umbilical vein endothelial cells (HUVECs). In this study, we initially found that ATM is activated by H₂O₂ treatment in human T-cell leukemia cell line MOLT-4, and aimed to assess the role of ATM and p53 in H₂O₂ signaling compared with ionizing radiation signaling. The level of H₂O₂-induced apoptosis in MOLT-4 cells reaches a plateau at 200 µM, which is almost the same level as the apoptosis induced by 5 Gy gamma-ray. We next revealed that H₂O₂-induced apoptosis is specifically mediated by p53 using p53-knockdown MOLT-4 transformants. Furthermore, the apoptosis was highly correlated with the phosphorylation of p53 Ser-15 or ATM autophosphorylation, and less correlated with p53 protein accumulation. Further investigations are needed to determine whether the damaged cell membrane or DNA initiates the signaling.