Stimulation of Tyrosinase Activity and Melanin Formation of Cultured Melanoma Cells by Serum Deprivation Alone or in Combination with Dibutyryl Cyclic AMP and Theophylline
2014
Leising, H. B. | Schachtschabel, D. O.
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 [¹⁴C] 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 (Bu₂cAMP, 5×10⁻⁴ᴍ) 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 Bu₂cAMP 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 Bu₂cAMP and theophylline was prevented by cycloheximide (or actinomycin D), de novo protein synthesis seems to be required for these stimulatory effects.
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