Abstract:

Objective To investigate the intracellular signal transduction pathways involved in the protective effect of nicotinic acid against ultraviolet B （UVB）-induced damage in human skin keratinocytes. Methods Cultured human keratinocyte HaCaT cells were divided into several groups to be treated with nicotinic acid, UVB irradiation, LY294002 （an inhibitor of Akt）, U0126 （an inhibitor of extracellular signal-regulated kinase （ERK）1/2）, SB203580 （an inhibitor of P38） alone or in combination for different durations. Then, Western blot was performed to quantify the phosphorylation levels of the protein kinase B （Akt）/MAPK pathway-associated proteins including Akt, P38, JNK and ERK1/2, MTT assay to evaluate the activity of HaCaT cells, enzyme-linked immunosorbent assay to determine the levels of endothelin-1 （ET-1） and basic fibroblast growth factor （bFGF） in the culture supernatant of HaCaT cells, and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling （TUNEL） to evaluate the apoptosis in HaCaT cells. Results As Western blot showed, phosphorylated Akt, P38, JNK and ERK1/2 were markedly activated within 60 minutes after pretreatment with nicotinic acid and irradiation with UVB （all P < 0.01）, and the activation was more significant for phosphorylated Akt, P38, and ERK1/2 within 2 hours （all P < 0.01）. Nicotinic acid effectively suppressed the UVB-induced cell death and apoptosis in HaCaT cells. The levels of supernatant ET-1 and bFGF were significantly decreased in HaCaT cells treated with the above 3 inhibitors followed by UVB irradiation than in those treated with the inhibitors alone （all P < 0.05）, and nicotinic acid pretreatment only reversed the decrease in supernatant bFGF in HaCaT cells treated with SB203580 followed by UVB irradiation. Conclusion The Akt signaling pathway may play a regulatory role in the protection by nicotinic acid against UVB-induced damage in HaCaT cells.

Key words: AKT