MELANOTROPIC ACTIVITY OF GAMMA-MSH PEPTIDES IN MELANOMA-CELLS

We studied the pigmentary activity of the peptides gamma(1), and gamma(2) and gamma(3) melanocyte stimulating hormone (MSH), which differ in the structure of their C-termini, using hamster and mouse melanoma cell lines responsive to beta-MSH by increasing tyrosinase activity. Gamma(1)-MSH alone or in combination with beta-MSH had no effect on either cell line. Gamma(2)-MSH alone was biologically inactive but potentiated beta-MSH stimulation of tyrosinase activity. Gamma(3)-MSH at high concentration (10-mu-M) induced tyrosinase activity and dendrite formation in the hamster melanoma line. When added together with beta-MSH, gamma(3)-MSH partially inhibited the tyrosinase activity response to beta-MSH. Thus, gamma-MSH peptides have low intrisic melanotropic activity in mammalian melanoma cells; the specific pigmentary responses appear to be affected by the structure of the C-terminal portion.