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To investigate the effect of protein klnase on melanin production via CAMP-dependent pathway, we measured the melanin amount and tyrosinase activity in Bl6 melanoma cells stimul ated by alpha-melanocyte stimulating hormone (MSH), forskolin and 8-Br-Camp MSH, forskolin and 8-Br-Camp significantly increased both melanin production and tyrosinase activity in Bl6 cells. Melanin production and tyrosinase activity by MSH are significantly inhibited by cyclic AMP-dependent protein kinase inhibitor (KT5720) and protein kinase C down-regulation treated with PMA. Bisindolmaleimide (1μM), protein kinase C inhibitor, significantly inhibited melanin production and tyrosinase activity stimulated by MSH, for-skolin and 8-Br-Camp with the following order of potency: MSH>forskolin>8-Br-Camp. Tyrosine kinase inhibitor, genistein and DHC, significantly inhibited both, but the inhibitory effect was more potent in 8-Br-Camp-stimulated Bl6 cells than MSH-stimulated cells. NFkB inhibitor (parthenolide) significantly inhibited melanin production and tyrosinase activity. Neither melanin production nor tyrosinase activity induced by MSH, forskolin and 8-Br-Camp were affected by KN-62 (calm-odulin-dependent protein kinase II inhibitor), PD098059 (mitogen-activated protein kinase inhibitor, MAPKK) and worthmannin (phosphatidylinositol 3-kinase inhibitor). These results suggest that both protein klnase C and tyrosine kinase are involved in melanin production by cyclic AMP-dependent pathway and NFrB pathway may play an important role in cyclic AMP-dependent melanin production in Bl6 melanoma cells.
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