Wild-type p53-induced Phosphatase 1 Dephosphorylates Histone Variant γ-H2AX and Suppresses DNA Double Strand Break Repair*

In response to DNA double strand breaks, the histone variant H2AX at the break site is phosphorylated at serine 139 by DNA damage sensor kinases such as ataxia telangiectasia-mutated, forming γ-H2AX. This phosphorylation event is critical for sustained recruitment of other proteins to repair the break. After repair, restoration of the cell to a prestress state is associated with γ-H2AX dephosphorylation and dissolution of γ-H2AX-associated damage foci. The phosphatases PP2A and PP4 have previously been shown to dephosphorylate γ-H2AX. Here, we demonstrate that the wild-type p53-induced phosphatase 1 (WIP1) also dephosphorylates γ-H2AX at serine 139 in vitro and in vivo. Overexpression of WIP1 reduces formation of γ-H2AX foci in response to ionizing and ultraviolet radiation and blocks recruitment of MDC1 (mediator of DNA damage checkpoint 1) and 53BP1 (p53 binding protein 1) to DNA damage foci. Finally, these inhibitory effects of WIP1 on γ-H2AX are accompanied by WIP1 suppression of DNA double strand break repair. Thus, WIP1 has a homeostatic role in reversing the effects of ataxia telangiectasia-mutated phosphorylation of H2AX.