Effect of Alpha-MSH on the Tyrosinase Activity and the Rate of Melanin Accumulation of Melanoma Cells in Vitro

A stimulation of the tyrosinase activity was observed when melanoma cells isolated from transplantable mouse melanomas were incubated at 37 degrees C for 6 h in the presence of 1-10 X 10(-6) M alpha-MSH. All strains of mouse melanomas studied (B-16, Cloudman S-91 and Harding-Passey), exhibited similar responses. It was also observed that the intact cellular structure of melanoma cells was not required for the ability to respond to alpha-MSH. The stimulation of the enzymic activity was accompanied by an increase of the rate of incorporation of radioactivity into melanin from L-[U-14C]tyrosine, indicating an enhanced melanogenesis of tumour cells under in vitro conditions.