α-Melanocyte stimulating hormone-induced pigmentation is blocked by depletion of protein kinase C

Abstract

We have explored the role of protein kinase C (PKC) in pigmentation induced by α-melanocyte stimulating hormone (α-MSH). Using the well- studied S91 Cloudman mouse melanoma model system in which 10-7 M α-MSH is known to produce a time-dependent increase in pigmentation, we found an increase in the activity of tyrosinase, the key enzyme in pigmentation, between Days 2 and 6 accompanied by an increase in mRNA and protein levels of tyrosinase, as well as an increase in the level of specifically the β isoform of PKC. When S91 cells were treated with phorbol dihutyrate, 95% of PKC activity was lost within 48 h and the α-MSH-induced melanogenesis was completely blocked, as was the induction of tyrosinase mRNA and protein. Serially passaged S91 cells no longer capable of responding to α-MSH had an undetectable level of PKC-β, although the tyrosinase protein level was identical to that of α-MSH-responsive cells. Furthermore, in these S91 cells α-MSH also did not increase the level of tyrosinase mRNA. Thus, induction of murine melanogenesis by α-MSH involves up-regulation of tyrosinase mRNA and protein mediated in part by the PKC-dependent pathway, associated with an up- regulation of the β isoform previously demonstrated to specifically activate tyrosinase in human melanocytes.