Abstract: To study the mechanism of low-doses of ultraviolet B (UVB, 280—315 nm) on human immortalized cells (HaCaT cells) apoptosis, proliferation and Bad pathway, chose the most suitable 5 mJ/cm² intensity of UVB from 3,5 and 7 mJ/cm² to irradiate the HaCaT cells for 18, 36 and 72 hours, then, collected the cells for the detection of apoptosis and proliferation; The total protein in HaCaT cells was extracted from the irradiated cell for western blot to detect the expression of AKT, Bad and the Bad-p136. The results showed that the apoptotic effects of 5 mJ/cm² intensity irradiation on HaCaT cells have no distinguish difference among different time point. But the proliferation rate after 72 hours irradiation on HaCaT cells was significant higher than control group. Immunoblotting experiments confirmed the expression levels of AKT and Bad-p136 were significant increasing compared to normal expression of Bad protein after UVB irradiation. Therefore, a long time UVB radiation of 5 mJ/cm² may promote cell proliferation signaling pathway by Bad, which may be a potential risk factor for the development of skin tumors.

Key words: cell apoptosis, cell proliferation, ultraviolet UVB