MODULATION OF MURINE MELANOCYTE FUNCTION IN-VITRO BY AGOUTI SIGNAL PROTEIN

Molecular and biochemical mechanisms that snitch melanocytes between t he production of eumelanin or pheomelanin involve the opposing action of two intercellular signaling molecules, alpha-melanocyte-stimulating hormone (MSH) and agouti signal protein (ASP). In this study, we have characterized the physiological effects of ASP an eumelanogenic melan ocytes in culture. Following exposure of black melan-a murine melanocy tes to purified recombinant ASP in vitro, pigmentation was markedly in hibited and the production of eumelanosomes was decreased significantl y. Melanosomes that were produced became pheomelanosome-like in struct ure, and chemical analysis showed that eumelanin production was signif icantly decreased, Melanocytes treated with ASP also exhibited time- a nd dose-dependent decreases in melanogenic gene expression, including those encoding tyrosinase and tyrosinase-related proteins 1 and 2, Con versely, melanocytes exposed to MSH exhibited an increase in tyrosinas e gene expression and function. Simultaneous addition of ASP and MSH a t approximately equimolar concentrations produced responses similar to those elicited by the hormone alone. These results demonstrate that e umelanogenic melanocytes call be induced in culture by ASP to exhibit features characteristic of pheomelanogenesis in vivo, Our data are con sistent with the hypothesis that the effects of ASP on melanocytes are not mediated solely by inhibition of MSH binding to its receptor, and provide a cell culture model to identify novel factors whose presence is required for pheomelanogenesis.