The number of receptors for beta-melanocyte stimulating hormone in Cloudman melanoma cells is increased by dibutyryl adenosine 3':5'-cyclic monophosphate or cholera toxin.

Cultured Cloudman melanoma cells exposed either to dibutyryl 3':5'-cyclic AMP and theophylline or to cholera toxin bind significantly more 125I-labeled beta-melanocyte stimulating hormone (MSH) and fluorescein-labeled MSH than untreated cells. MSH binds to melanoma cells in the G2 phase of the cell cycle. The stimulation of MSH binding by dibutyryl cyclic AMP results from an increase in the number of MSH receptors per G2 cell and, to a lesser extent, from an increase in the number of G2 cells. The affinity of the receptors for MSH is not influenced by dibutyryl cyclic AMP.