[Melanocyte-stimulating hormone induces growth of human malignant melanoma amelanotic cells with a change in cAMP, phosphatidylinositols, and inositol phosphate concentration].

The melanocyte-stimulating hormone (alpha-MSH) used at 10(-6)-5 x 10(-8) M concentrations inhibited the growth of amelanotic cells of human malignant melanoma BRO and influenced cell morphology without any effect on melanization or tyrosinase activity. Inhibition of tumour cell growth was accompanied by marked elevation of intracellular cAMP levels but not that of cGMP. Dibutyryl-cAMP and the cAMP-dependent protein kinase A inhibitor also inhibited the cell growth. alpha-MSH increased mono-, di- and 1.4.5-myoinositol triphosphate concentrations and influenced the activities of phosphatidylinositol kinase and phosphatidylinositol-4-phosphate kinase determining phosphatidylinositol-4-phosphate kinase and phosphatidylinositol-4.5-diphosphate levels. Myoinositol phosphate concentrations changed on a second scale and levelled off by the 3rd-5th min, whereas that of cAMP increased drastically by the 30th min.