Correlation Between Dose of Ultraviolet B Irradiation and Apoptotic Phase of HaCaT Cells

Objective To elucidate the correlation between the dose of ultraviolet B (UVB) irradiation and apoptotic phase of keratinocytes (HaCaT cells). Methods Cultured immortalized human ker-atinocyte cell line, HaCaT cells, was irradiated with ultraviolet B (UVB) in doses of 20, 40, 60, 80, 100 and 120 mJ/cm2. Cellular viability, cell cycles and apoptosis were simultaneously detected at 2, 12, 24, 48 and 72 h after irradiation. The caspase-mediated apoptosis was detected by FITC-labelled VAD-FMK, which could irreversibly bind to activated caspases. FITC-Annexin V and PI double staining detected cell membrane-mediated apoptosis. Cell nucleus-mediated apoptosis was detected by DNA ladder electrophoresis. Results Cell cycle analysis revealed that UVB treated HaCaT cells were blocked predominantly in G2/M phase in a dose-dependent manner. Treatment with UVB decreased the viability of HaCaT cells in dose- and time-dependent manners. The rates of apoptosis were increased with increasing dose and prolongation of time after UVB irradiation. The apoptosis of UVB-treated HaCaT presented in an obvious time-dependent manner, in which caspase- and cell membrane-mediated apoptosis was predominantly in early phase and cell nucleus-mediated apoptosis predominantly in late phase. Conclusions The apoptosis of UVB treated HaCaT cells appears in dose- and time-dependent manners, which warrants further detection with multiple parameters and at different phases.