Evidence for increased αMSH receptor binding in the F1 variant of B16 melanoma cells grown in dialyzed fetal calf serum

The specific binding of an αMSH analogue (Ac-[Nle4, D-Phe7] αMSH4–11 NH2) was enhanced in the presence of 10% dialyzed fetal calf serum (FCS) as compared with 10% FCS (nondialyzed) in the F1 variant of B16 melanoma cells. The replenishment of dialyzed serum with adrenocorticotrophic hormone (ACTH) or insulin had no effect on the increased level of αMSH receptor binding in these cells. However, 10 nM αMSH or 1 μM ACTH under identical conditions significantly decreased the level of αMSH binding. Competitive binding studies involving the αMSH analogue revealed that the specificity of the receptor was restricted to the complete molecule of αMSH, our analogue, βMSH and ACTH1–24. ACTH4–10, which contains the amino acid sequence responsible for biological activity, showed a very low affinity for the receptor. Furthermore, we observed an interesting phenomenon unique to dialyzed FCS in that once the cells were grown to confluence and melanin was produced, the cells were no longer viable. However, in McCoy's medium, which is deficient in tyrosine, the cells did not produce melanin and remained viable.