GSK3β inhibition promotes melanogenesis in mouse B16 melanoma cells and normal human melanocytes

Glycogen synthase kinase 3 beta (GSK beta) is implicated in many biological events, including embryonic development, cell differentiation, apoptosis, and the insulin response. GSK3 beta also plays a key role in the Wnt/beta-catenin pathway. The master regulator of the pigmentation microphthalmia-associated transcription factor (MITF) is a target for the Wnt pathway, however, to date, the regulatory role of GSK3 beta in the control of melanogenesis has not been elucidated. In this study, we evaluated the effect of inhibiting GSK3 beta activity on the regulation of melanocyte differentiation. Exposure of the murine melanoma cell line B16 and normal human melanocytes to GSK3 beta specific inhibitors (SB216763, SB415286, BIO, and LiCl) resulted in a dose-dependent accumulation of beta-catenin. This is associated with the induction of melanocyte differentiation-associated markers such as melanin synthesis, tyrosinase activity, and expression of tyrosinase and the microphthalmia-associated transcription factor. Attenuation of GSK3 beta activity has an inhibitory effect on cell growth, and this was accompanied by morphological changes. Moreover, treatment of B16 cells with a siRNA targeted against beta-catenin completely abolished the promelanogenic effect of GSK3 beta inhibition, however, the overexpression of a constitutively active mutant form of beta-catenin (pCS2 beta-cat-mut) only slightly increased the degree of pigmentation. These results demonstrated that GSK3 beta is implicated in the regulation of melanogenesis and that pharmacological inhibition of its activity could increase melanin synthesis through mechanisms probably not restricted to Wnt/beta-catenin pathway activation. (C) 2008 Elsevier Inc. All rights reserved.