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Interactions between insulin and the cyclic AMP system of Cloudman S91 mouse melanoma cells

Insulin inhibits the proliferation of wild‐type Cloudman S91 mouse melanoma cells. The effects, which are mediated through specific, high‐affinity receptors for insulin, appear to involve interactions with the cAMP system. Our evidence is as follows: (1) Cloudman cells have a cAMP requirement for proliferation and pigmentation. Exposure of cells to insulin results in a lowering of intracellular cAMP levels and inhibition of both cell division and pigment formation. (2) The effects of insulin are reversed by agents which raise cAMP levels, or by the cAMP analogue dibutyryl cAMP. (3) A mutant cell line with a temperature‐dependent requirement for cAMP is most sensitive to the growth inhibitory effects of insulin when its requirements for cAMP are maximal. (4) Mutants selected only for alterations in their response to Insulin frequently have concomitant alterations in their cAMP systems. (5) The melanotropin‐responsive adenylate cyclase system is stimulated following prolonged exposure of cells in culture to insulin. Although we do not know the mechanism(s) for the interactions between the insulin and the cAMP system, our initial findings suggest that protein phosphorylation/dephosphorylation reactions are involved.