Responses of the 27-kDa heat shock protein to UVB irradiation in human epidermal melanocytes

Solar ultraviolet radiation (UVR) is a major environmental hazard for the skin, and UVB (280-320nm) has been proposed to be a main factor for melanoma development. In response to sunlight exposure, the skin has adapted a number of innate resistance mechanisms. Among them is the small heat shock protein of 27kDa (HSP27) known to play a role in the protection of cells from variety of environmental insults including UV irradiation. In this study, we demonstrated that UVB irradiation of cultured normal epidermal melanocytes initiates changes in HSP27 phosphorylation and localization. In unstressed melanocytes, HSP27 was present as the non-phosphorylated isoform. UVB irradiation with a physiological dose (7-25mJ/cm²) resulted in the formation of a mono-phosphorylated isoform and sometimes a bi-phosphorylated isoform. The UVB-induced HSP27 phosphorylation was inhibited when melanocytes were treated with the antioxidant N-acetyl cysteine or inhibitor of p38 MAP kinase prior to UVB exposure, suggesting that UVB induced HSP27 phosphorylation through reactive oxygen species/p38 MAP kinase pathway. In response to UBV irradiation, HSP27 in melanocytes translocated from the cytoplasm to the nucleus. The HSP27 responses may provide some protective role against UVB-induced cell damage in the skin.