Wnt inhibitory factor (WIF)-1 promotes melanogenesis in normal human melanocytes

Summary Wnt signaling plays a role in the differentiation as well as the development of melanocytes. Using a microarray analysis, hyperpigmentary skin of melasma expressed high levels of Wnt inhibitory factor‐1 (WIF‐1) compared with perilesional normal skin. In this study, the expression and functional roles of WIF‐1 on melanocytes were investigated. WIF‐1 was expressed both in the melanocytes of normal human skin and in cultured melanocytes. The upregulation of WIF‐1 on cultured normal human melanocytes significantly induced expressions of MITF and tyrosinase, which were associated with increased melanin content and tyrosinase activity. Consistent with the stimulatory effect of WIF‐1, WIF‐1 siRNA reduced melanogenesis in the cells. Moreover, WIF‐1 increases pigmentation in melanocytes co‐cultured with WIF‐1‐overexpressed fibroblasts and of organ‐cultured human skin. These findings suggest that melanocytes express WIF‐1 constitutively in vivo and in vitro and that WIF‐1 promotes melanogenesis in normal human melanocytes.