MGRN1 does not inhibit adenylyl cyclase activation by forskolin or a constitutively active Gs protein. A, cAMP levels in HEK293T cells expressing MC1R alone (empty bars) or with (+)S (filled bars), following stimulation with forskolin (10−5 m, 30 min). B, cAMP levels in HEK cells expressing a constitutively active Gαs mutant (Gs*) alone or in combination with (+)S MGRN1. Error bars represent S.D., n = 5.