Fig. 1

APE1 initiates DSBs generation at an early phase following IR exposure. a–b APE1 affected temporal formation of DSBs following IR Exposure. NC and shAPE1 cells were treated with 10 Gy IR (treatment for IR was used throughout the study unless stated otherwise) and allowed to recover for various time from 1 to 64 h in HeLa a and SiHa b cell line. The γ-H2AX and cleaved-PARP level were assayed by immunoblotting. c–d The endonuclease capacity of APE1 involved in DSBs formation at early phase following IR exposure. HeLa c or SiHa d WT cells were pre-incubated for 6 h with E3330 (10 μM) or Inhibitor III (2.5 μM) prior to IR treatment and allowed to recover for 1 h. e Inducible HeLa APE1^shRNA cells were stably transfected with the expression vector encoding wildtype APE1 (WT) or redox activity mutant of APE1 (C65S), respectively. APE1 levels in both cells pre- and post 14-day induction by doxycycline (Dox) were measured by immunoblotting. f The γ-H2AX was independent on the redox activity of APE1 at early phase post-damage. HeLa WT-APE1 and HeLa C65S-APE1cells were treated with IR then allowed to recover for 0.5 h or 1 h. g–h SSB and DSB level of HeLa NC and shAPE1 cell line was evaluated using alkaline and neutral Comet assay, respectively. Cells were treated with IR and allowed to recover for 1 h, followed by comet assays. Tail moment values were calculated for > 100 cells and plotted via a distribution dot plot. The data were presented as the mean ± SEM from three independent experiments. The p-values were determined using an unpaired Student’s t-test (****p < 0.0001)