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Serum removal from the media of serial monolayer cultures of the Harding-Passey melanoma during an incubation period of 3 days resulted in an exponentially declining DNA synthesis rate (measured by the incorporation of [ 14 C] thymidine) and in an inhibition of cell proliferation. Pro­tein synthesis, as measured by the incorporation of radioactive leucine, was less affected than DNA synthesis. Incubation in serum-free culture medium resulted in significant rises of tyrosinase ac­tivity and cellular melanin content. Addition of dibutyryl adenosine 3′ :5′ monophosphate (Bu 2 cAMP, 5×10 -4 ᴍ) and theophylline (5×10 -4  ᴍ) to serum-free cultures caused a further striking increase of tyrosinase activity and melanin formation, while treatment of serum containing cultures with Bu 2 cAMP and theophylline showed only a slight rise in melanogenesis. It is sug­gested that these stimulatory effects are mediated by an increased intracellular cAMP level, since a correlation between the degree of melanogenesis and cellular cAMP content was indicated. Treat­ment of serum-free or serum-containing cultures with the phosphodiesterase inhibitor theophylline (5×10 -4  - 1×10 -3  ᴍ) alone revealed only a slight enhancement (about 20%) of melanogenesis. Because augmentation of melanogenesis by serum-free medium alone or together with Bu 2 cAMP and theophylline was prevented by cycloheximide (or actinomycin D), de novo protein synthesis seems to be required for these stimulatory effects.

zeitschrift für naturforschung c

Stimulation of Tyrosinase Activity and Melanin Formation of Cultured Melanoma Cells by Serum Deprivation Alone or in Combination with Dibutyryl Cyclic AMP and Theophylline