Expression of melanocyte stimulating hormone receptors correlates with mammalian pigmentation, and can be modulated by interferons

The relationship between melanogenesis and the expression of melanocyte stimulating hormone (MSH) receptors on the surface of melanocytes was examined using sublines generated from the melanotic JB/MS melanoma. JB/MS cells were propagated in long term culture to allow for phenotypic drift in their characteristics of differentiation, and then were cloned; the cloned cells ranged from well differentiated and pigmented to undifferentiated and amelanotic. Spontaneous and MSH-induced melanogenesis in these different lines was measured and correlated with the number of MSH receptors expressed. After 6 months of in vitro culture, the ability of the cells to respond to MSH was significantly reduced, as were the number of MSH receptors expressed; the cells had reduced pigmentation and were relatively undifferentiated histologically. Subsequently, clonally-derived pigmented cells were found to have numbers of surface MSH receptors (approximately 60,000 per cell) and levels of melanogenic activity similar to the original JB/MS cell line. However, an amelanotic clone had an even more dramatically reduced level of pigmentation which correlated with a further decrease in the expression of MSH receptors (less than 1,000 per cell) and the production of a potent melanogenic inhibitor. We also examined the responses of these various sublines to alpha, beta, and gamma-interferons and found significant heterogeneity in their abilities to respond to these cytokines. This study clearly shows that there is a direct correlation between melanogenesis and the expression of MSH receptors on the surface of melanocytes, and that melanogenic inhibitors may be critically involved in the regulation of mammalian pigmentation.