Excess processing of oxidative damaged bases causes hypersensitivity to oxidative stress and low dose rate irradiation

Abstract

Ionizing radiations such as X-ray and γ-ray can directly or indirectly produce clustered or multiple damages in DNA. Previous studies have reported that overexpression of DNA glycosylases in Escherichia coli (E. coli) and human lymphoblast cells caused increased sensitivity to γ-ray and X-ray irradiation. However, the effects and the mechanisms of other radiation, such as low dose rate radiation, heavy-ion beams, or hydrogen peroxide (H₂O₂), are still poorly understood. In the present study, we constructed a stable HeLaS3 cell line overexpressing human 8-oxoguanine DNA N-glycosylase 1 (hOGG1) protein. We determined the survival of HeLaS3 and HeLaS3/hOGG1 cells exposed to UV, heavy-ion beams, γ-rays, and H₂O₂. The results showed that HeLaS3 cells overexpressing hOGG1 were more sensitive to γ-rays, OH^•, and H₂O₂, but not to UV or heavy-ion beams, than control HeLaS3. We further determined the levels of 8-oxoG foci and of chromosomal double-strand breaks (DSBs) by detecting γ-H2AX foci formation in DNA. The results demonstrated that both γ-rays and H₂O₂ induced 8-oxoguanine (8-oxoG) foci formation in HeLaS3 cells. hOGG1-overexpressing cells had increased amounts of γ-H2AX foci and decreased amounts of 8-oxoG foci compared with HeLaS3 control cells. These results suggest that excess hOGG1 removes the oxidatively damaged 8-oxoG in DNA more efficiently and therefore generates more DSBs. Micronucleus formation also supported this conclusion. Low dose-rate γ-ray effects were also investigated. We first found that overexpression of hOGG1 also caused increased sensitivity to low dose rate γ-ray irradiation. The rate of micronucleus formation supported the notion that low dose rate irradiation increased genome instability.

Keywords::

• hOGG1
• 8-oxoG
• reactive oxygen species
• clustered damage
• low dose rate radiation
• micronuclei

Acknowledgments

We thank Dr. Elizabeth Nakajima and Ms. Ako Matsui for critically reading the manuscript and thank Ms. Ako Matsui for assistance with the heavy-ion beams and low dose rate radiation experiments. This study was supported by the Research Project with Heavy Ions at NIRS-HIMAC (12J-393). This work was supported in part by Grants- in-Aid for Scientific Research (#24510071) from the Ministry of Education, Culture, Sports, Science and Technology of Japan. This work was performed at the Joint Usage/Research Center (Radiation Biology Center), Kyoto University.

Declaration of interest

The authors report no declarations of interest. The authors alone are responsible for the content and writing of the paper.