Effect of testosterone on imidazole-induced tyrosinase expression in B16 melanoma cell culture.

To assess the effect of androgens on tyrosinase activity in B16/C3 melanoma cell cultures, proliferating cultures were treated with testosterone (50 nM) or one of several other androgenic analogues and metabolites. None of these compounds influenced basal enzyme activity. Imidazole (10 mM), however, is a potent inducer of tyrosinase in this cell line. Testosterone blocked induction of tyrosinase by imidazole almost completely. This effect was dose dependent, being maximal at 10 nM and half-maximal at approximately 3 nM, and was rapid, occurring within 15 min. When cultures treated with both imidazole and testosterone were shifted to medium containing only imidazole, enzyme activity approximated that seen in cultures never receiving testosterone within 10 h of the shift. The other steroids tested failed to influence imidazole induction of the enzyme. This action of testosterone could not be demonstrated in broken cell preparations. Results of studies involving inhibitors of protein and RNA synthesis, as well as those quantitating mRNA hybridizable to a synthesized 20-base pair deoxyoligonucleotide tyrosinase probe, suggest that testosterone is blocking imidazole induction at a pretranslational level.