Alpha-MSH and other melanogenic activators mediate opposite effects on tyrosinase and dopachrome tautomerase in B16/F10 mouse melanoma cells.

alpha-MSH was found to decrease the recently characterized dopachrome tautomerase activity in cultures of B16/F10 mouse melanoma cells. Other stimulating agents of melanogenesis, like dibutyryl cyclic AMP, 3-isobutyl-1-methylxanthine, theophylline, retinol, and retinoic acid, caused the same effect. The grade of inhibition depended on the nature of the agent and the time of exposure. In all cases, both melanin production and tyrosinase activity were activated by these treatments, although the grade of tyrosine hydroxylase and dopa oxidase stimulation was different. Moreover, no correlation among the intensities of dopachrome tautomerase inhibition and tyrosinase activation by the tested agents could be obtained. The significance of these results in the regulation of mammalian melanogenesis is discussed.