STABLE EXPRESSION OF THE HUMAN MSH RECEPTOR IN A MOUSE MELANOMA CELL-LINE

Stable expression of the MSH receptor in a homologous system is import ant for the study of the function and mechanism of signalling of this receptor. This is the first report on the stable expression of the hum an alpha-MSH receptor in the mouse melanoma G4F clone which lacks an e ndogenous MSH receptor. Several stable transfectant cell lines were ob tained all of which express the human MSH receptor in high numbers. Hu man MSH receptor mRNA expression was detected by Northern blot analysi s. Competition binding experiments showed that the MSH receptors expre ssed in these cells have the same affinity for [Nle(4),D-Phe(7)]-alpha -MSH as the MSH receptors of the human HBL melanoma cell line. Several of the transfectant cell lines produced melanin constitutively, some of them secreting melanin into the medium whereas other clones did not secrete melanin. MSH and cholera toxin did not or only marginally inc rease melanogenesis in these clones, and forskolin had an opposite eff ect. These results suggest that the human MSH receptor may be constitu tively active in these transfected mouse melanoma cells.