Differences in activation of G2/M checkpoint in keratinocytes after genotoxic stress induced by hydrogen peroxide and ultraviolet a radiation

Abstract

Long-wave ultraviolet radiation (UVA) may cause extensive DNA damage via reactive oxygen species (ROS). In this study we examined whether UVA- and H₂O₂-mediated DNA damage have equivalent effects on the induction of G2/M phase checkpoint and cell cycle progression in a transformed keratinocyte cell line HaCaT. By employing single cell gel electrophoresis (comet assay) we determined the equipotent doses of UVA and H₂O₂ with respect to the induction of alkali-labile sites (an indicator of oxidative DNA decay). However, in contrast to H₂O₂ which caused a pronounced G2/M cell cycle arrest 24h after treatment, UVA irradiation did not affect cell cycle progression. Increasing UVA doses up to 150 kJ/m² did not affect cell cycle and proliferation whereas increasing H₂O₂ concentrations caused a cell cycle block or cell death. Cytometric analysis revealed that G2/M cell cycle arrest took place beyond the cyclin B1 restriction point. We conclude that the DNA damage induced by UVA is easily repaired and does not perturb cell growth, whereas the H₂O₂-induced damage leads ultimately to cell cycle arrest or cell death.

Keywords:

• Ultraviolet radiation
• hydrogen peroxide
• keratinocytes
• DNA damage
• cell cycle