The role of adenosine 3',5'-monophosphate in the transformation of Cloudman mouse melanoma cells

Abstract

The role of adenosine 3',5'-monophosphate (cyclic AMP) in the regulation of mouse melanoma cell growth and differentiation was investigated. A variant melanoma (Cloudman S91-F) which displays a greater degree of transformation than the parental cell (Cloudman S91) was isolated. A correlation between cyclic AMP metabolism and transformation was made. Dibutyryl cyclic AMP depressed cell growth and increased pigmentation in both parental and variant cell lines. The parental cell line, however, was more responsive to melanocyte-stimulating hormone (MSH) which was found to affect cell growth and pigmentation by increasing cyclic AMP levels. The more transformed S91-F cell line contained lower levels of cyclic AMP than the parental cell line, and this fact correlated well with the higher degree of growth and lesser degree of pigmentation in the variant. Enzymatic analysis revealed that the hydrolysis of cyclic AMP in both cell lines was similar, while the adenylate cyclase activity of the variant cell line was lower than that of the parental cell line. Lineweaver-Burk plots demonstrated that the Km's for the enzymes in the two cell lines were the same but that the Vmax of the S91-F cell line was significantly less that that of the S91 cell line. Thus, the lesion in the S91-F cell which is responsible for its more transformed characteristics seems to be one which affects adenylate cyclase at the level of the cell membrane.