Abstract: OBJECTIVE: To investigate the mechanisms and effect of ultra violet A (UVA) radiation on vitality and apoptosis of human keratinocytes (HaCaT). METHODS: After different doses of UVA irradiation to keratinocytes, MTT and flow cytometric analysis were used to detect cell survival and apoptosis;immunofluorescence and Western blot were used to detect the formation of intracellular γH2AX focus and its protein levels;and atomic force microscopy was used to detect DNA breakage. RESULTS: UVA irradiation inhibited survival of HaCaT cells in a dose-response manner at the range of 5-30 J/cm² (r=0.982,P=0.009). Early apoptotic cell fraction increased significantly at 20^th hour after UVA irradiation,and had an increasing trend at the range of 10-40 J/cm² (r=0.936,P=0.008) with the rising radiation doses. The 30 and 40 J/cm² doses of UVA induced γH2AX foci formation. After different doses of irradiation,γH2AX expression could be observed,moreover,the expression of γH2AX reached the highest level at 5 J/cm² and 10 J/cm² doses. DNA breaks increased significantly over the control group after irradiation,as detected by atomic force microscopy. CONCLUSION: UVA exposure inhibited HaCaT cell survival,promoted its apoptosis and induced DNA chain break,leading to cell death.

Key words: ultra violet A, γH2AX, DNA damage, HaCaT cells