Narrow‐band ultraviolet‐B stimulates proliferation and migration of cultured melanocytes

Abstract: Narrow‐band ultraviolet‐B (UVB) radiation is an effective treatment for vitiligo vulgaris. However, the mechanisms of narrow‐band UVB in inducing repigmentation of vitiligo lesions are not thoroughly clarified. The purpose of our study was to investigate the effects of narrow‐band UVB irradiation on melanocyte proliferation and migration in vitro . Our results showed that the cell counts as well as [3H]thymidine uptake of melanocytes were significantly enhanced by narrow‐band UVB‐irradiated keratinocyte supernatants. In these supernatants, a significant increase in basic fibroblast growth factor (bFGF) and in endothelin‐1 (ET‐1) release was observed. bFGF is a natural mitogen for melanocytes, whereas ET‐1 can stimulate DNA synthesis in melanocytes. This stimulatory effect of melanocyte proliferation by supernatants derived from narrow‐band UVB‐irradiated keratinocytes was significantly reduced by a selective endothelin‐B (ET‐B) receptor antagonist (BQ788), suggesting an essential role of ET‐1 on melanocyte proliferation. Our results of time‐lapse microphotography revealed a stimulatory effect of narrow‐band UVB irradiation on melanocyte migration. Focal adhesion kinase (FAK) plays a pivotal role in cell migration. Phosphorylated FAK (p125 FAK ) expression on melanocyte was enhanced by narrow‐band UVB irradiation. In this study, narrow‐band UVB irradiation stimulated a significant increase in matrix metalloproteinase‐2 (MMP‐2) activity in melanocyte supernatants. Narrow‐band UVB‐irradiation‐induced migration of melanocytes was significantly annihilated by the addition of p125 FAK inhibitor (herbimycin‐A) or MMP‐2 inhibitor (GM6001). These results suggest that p125 FAK and MMP‐2 activity play important roles in narrow‐band UVB‐induced migration of melanocytes. Our results provide a theoretical basis for the effectiveness of narrow‐band UVB irradiation in treating vitiligo.