Abstract:

Objective To investigate the effects of NB-UVB on the expression of Gadd45α as well as cell apoptosis and cycle of human HaCaT keratinocytes. Methods Cultured HaCaT cells were exposed to various doses （100, 200, 400 mJ/cm2） of NB-UVB followed by an additional culture of 6, 12 and 24 hours, respectively. Reverse transcription PCR and Western blot were performed to detect the mRNA and protein expression of Gadd45α respectively in HaCaT cells, cell counting kit 8 （CCK8） to measure the proliferation of cells, and flow cytometry to determine the cell cycle distribution of HaCaT cells before and after the exposure to NB-UVB. Results Gadd45α was expressed in HaCaT cells. After exposure to NB-UVB of the three doses, the mRNA and protein levels of Gadd45α increased at 6 hours and 12 hours, but declined at 24 hours, and significant changes were observed in HaCaT cells at the three time points after exposure to NB-UVB of the three doses （all P < 0.05）. The Gadd45α/β-actin mRNA ratio was 1.4360 ± 0.6551, 1.8633 ± 0.0979, 1.9266 ± 0.1724 in HaCaT cells 12 hours after irradiation to NB-UVB of 100, 200 and 400 mJ/cm2, respectively, significantly higher than that in unirradiated cells （0.6000 ± 0.1276, all P < 0.05）. Also, increased Gadd45α/β-actin protein ratio was noted in HaCaT cells 12 hours after irradiation to NB-UVB of 100, 200 and 400 mJ/cm2 compared with unirradiated cells （0.0773 ± 0.0005, 0.1936 ± 0.0015, 0.2373 ± 0.0015 vs. 0.0290 ± 0.0010, all P < 0.05）. NB-UVB inhibited the proliferation of HaCaT cells in a time- and dose-dependent manner. Flow cytometry showed that irradiated HaCaT cells were blocked in G2 phase of the cell cycle, and the percentage of HaCaT cells in G2 phase was 13.53% ± 1.03%, 17.77% ± 2.25%, 30.03% ± 4.29% after exposure to NB-UVB of 100, 200 and 400 mJ/cm2, respectively, compared to 9.24% ± 0.97% in unirradiated cells（all P < 0.05）. Conclusions The expression of Gadd45α is increased in HaCaT cells after exposure to NB-UVB, and Gadd45α may be involved in the NB-UVB-induced suprression of cell proliferation of and cell cycle arrest in HaCaT cells.

Key words: HaCaT