CYSTEINE DEPRIVATION PROMOTES EUMELANOGENESIS IN HUMAN-MELANOMA CELLS

Melanocytic cells can produce two types of pigment, pheomelanin or eum elanin. We used two types of human melanoma cell lines to explore the regulation of pigmentation by biochemical and enzymatic studies. These two cell Lines were previously designated as either pheomelanotic or of mixed type when cultured in a medium rich in cysteine. We analyzed the effects of L-cysteine depletion on melanin synthesis and the invol vement of the tyrosinase-related proteins in the production of both eu melanin and pheomelanin. Cultures were exposed to L-cysteine concentra tions ranging from 206 to 2.06 mu M, and the following parameters were measured: tyrosine hydroxylase activity, intracellular L-cysteine and glutathione concentrations, eumelanin and pheomelanin formation, and tyrosinase-related protein-1 and -2 mRNA levels, Extracellular L-cyste ine depletion significantly increased tyrosine hydroxylase activity an d promoted both eumelanogenesis and visible pigmentation in both Lines , In contrast, pheomelanogenesis was increased only in the pheomelanot ic cell line, Whereas eumelanogenesis was apparent upon L-cysteine dep letion, tyrosinase-related protein-1 expression was not induced in the pheomelanotic cells, and tyrosinase-related protein-2 expression rema ined unchanged, Thus, tyrosinase-related protein-1 mRNA expression see ms to be concomitant with eumelanogenesis when the L-cysteine concentr ation is high, but does not appear essential for eumelanogenesis at lo w L-cysteine concentrations, The mechanisms governing pheomelanin to e umelanin balance are dependent on L-cysteine, glutathione, and tyrosin ase-related protein-1 expression, but none of these factors alone appe ars to be dominant in directing the synthesis of a particular type of melanin.