Most hydrogen peroxide-induced histone H2AX phosphorylation is mediated by ATR and is not dependent on DNA double-strand breaks

The nuclear foci of phosphorylated histone H2AX (H2AX) are frequently used as a marker for DNA double-strand breaks (DSBs) following ionizing radiation (IR). However, recent studies reported that H2AX foci do not necessarily correlate with DSBs under other conditions. We showed that H2AX foci induced by oxidative stress in hydrogen peroxide (H2O2)-treated cells displayed several different features from those induced by IR. The magnitude of H2AX induction was heterogeneous among H2O2-treated cells. Some cells expressed small discrete H2AX foci, whereas others expressed a gross H2AX signal that was distributed throughout the nucleus. Oxidative stress-induced H2AX was eliminated in DSB repair-deficient mutant cells as efficiently as in wild-type cells and was not necessarily accompanied by phosphorylated ataxia telangiectasia mutated (ATM) or 53BP1 foci. Analyses using specific inhibitors showed that ATM- and Rad3-related (ATR), rather than ATM, was the prominent kinase mediating the oxidative stress response. These results suggest that a major fraction of H2AX induced by oxidative stress is not associated with DSBs. Single-stranded DNA arisen from stalled replication forks can cause the ATR-mediated induction of H2AX. However, oxidative stress appeared to induce H2AX in both S- and non-S-phase cells. These results suggest that there may be another pathway leading to the ATR-mediated induction of H2AX in non-S-phase cells without DSBs.
Source: Journal of Biochemistry - Category: Biochemistry Authors: Tags: Regular Papers Source Type: research