Melanoma cells resistant to inhibition of growth by melanocyte stimulating hormone

Melanocyte stimulating hormone (MSH) enhances melanization but inhibits proliferation of Cloudman S91 melanoma cells in culture. We have isolated variants of these cells that can grow in the presence of MSH. The conclusions we have reached from analyses of these cells are the following: (1) Basal tyrosinase activity (monophenol monooxygenase; monophenol, dihydroxyphenylalanine:oxygen oxidoreductase, EC 1.14.18.1), i.e., the activity that is present in the absence of added MSH, is related through a common biochemical pathway to MSH-mediated control of growth. (2) MSH-inducible tyrosinase activity does not appear to be related to MSH control of growth. (3) The morphological changes that occur following the addition of MSH or cAMP are related to controls of growth and not to those of melanization.