Abstract: Objective To elucidate the correlation between the dose of ultraviolet B (UVB) irradiation and apoptotic phase of keratinocytes (HaCaT cells).Methods Cultured immortalized human keratinocyte 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 timedependent 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 timedependent manners,which warrants further detection with multiple parameters and at different phases.

Key words: Utraviolet rays, Keratinocytes, Cells,cultured, Apoptosis