Regulation of Tyrosinase Synthesis and its Processing in the Hair Follicular Melanocytes of the Mouse During Eumelanogenesis and Phaeomelanogenesis

Abstract

Tyrosinase synthesis and its posttranslational processing was compared in hair follicular melanocytes of C3H-HeAvy mice during eumelanogenesis and phaeomelanogenesis. Tyrosinase activity was increased during eumelanogenesis and this was paralleled by an increase in tyrosinase synthesis, as measured by the incorporation of [35S]methionine. Although tyrosinase activity was lower during phaeomelanogenesis there was no change in tyrosinase synthesis. alpha-Melanocyte stimulating hormone (alpha-MSH) increased tyrosinase activity and its synthesis during eumelanogenesis but not during phaeomelanogenesis. Bromo-adenosine 3,5-cyclic monophosphate sodium salt (8-bromo-cAMP) was similarly effective during eumelanogenesis, but unlike alpha-MSH stimulated tyrosinase synthesis during phaeomelanogenesis. This suggests that during phaeomelanogenesis the melanocytes may fail to express MSH receptors. This cannot account for the lower tyrosinase activity, however, for alpha-MSH acts predominantly at the level of tyrosinase synthesis and this was similar during eumelanin and phaeomelanin production. The reduced tyrosinase activity is, therefore, presumably due to some posttranslational change. Accordingly, less tyrosinase was associated with the melanosomal fraction during phaeomelanogenesis than during eumelanogenesis. Glycosylation of tyrosinase, as measured by the incorporation of [3H]glucosamine was also reduced during phaeomelanogenesis. Although 8-bromo-cAMP increased glycosylation of tyrosinase in both eumelanin and phaeomelanin producing melanocytes, it failed to alter the subcellular distribution of the enzyme. It would appear that, although glycosylation of tyrosinase is lower during phaeomelanogenesis, the reduced tyrosinase expression is the result of decreased uptake of tyrosinase by the melanosome.