(A) PARP inhibition facilitates γH2AX following oxidative stress. The cells were pre-treated with olaparib (1 µM, 1 hour) prior to H2O2 stimulation. 0.1 % DMSO in medium for 1 hour as mock. γH2AX or H2AX was detected using Western blotting and immunostaining assays. The intensity of γH2AX levels were examined by Western blotting normalized by β-actin and averaged. Values are mean ± SD of three assays. P-values were calculated using Student's t-test. **P < 0.01 (left panel). The number of γH2AX foci examined in immunostaining assay was counted by Image J software and graphed by GraphPad Prism 8. 