Roles of non-homologous end joining repair for DNA double strand breaks induced by X-rays under oxic and hypoxic conditions

Abstract

We have previously reported that the oxygen effect for induction of DNA-DSB was bigger (∼ 6) than that for cell killing level. The large oxygen effects for DNA-DSB decreased to the cell killing level (∼ 3) by DNA repair in a short time. The mechanism of oxygen effect decreased by DNA repair was further examined and here reported. Two chinese hamster cell lines, i.e., wild-type CHO and a Ku80 mutant CHO (xrs6) cells were exposed to 200 kVp X-rays at ice temperature under oxic or hypoxic conditions. Static-field gel electrophoresis (SFGE) was used to determine radiation-induced DSB. Oxygen enhancement ratio (OER) of DSB for CHO cells after X-ray irradiation was 6.3 without repair, and decreased to 3.4 when a repair time of 15 minutes was observed. However, the decrease of OER value was not observed for wild-type CHO cells pretreated with 20 µM wortmannin for 1 hour or xrs6 cells.
We conclude that the radiation-induced DSB by the NHEJ repair system under oxic condition is more efficiently repaired than that under hypoxic condition.