CB1 receptor-C protein association - Subtype selectivity is determined by distinct intracellular domains

The CB1 cannabinoid receptor in N18TG2 neuroblastoma cells inhibits adenyla te cyclase, and this response can be mimicked by a peptide corresponding to the juxtamembrane C-terminal domain (CB(1)401-417). Guanosine 5'-O-(3-thio )triphosphate binding to G proteins can be stimulated by both peptide CB(1) 401-417 and peptides corresponding to the third intracellular loop [Howlett , A.C., Song, C., Berglund, B.A., Wilken, G.H. & Pigg, J.J. (1998) Mel. Pha rmacol. 53, 504-510; Mukhopadhyay, S., Cowsik, S.M., Welsh, W.J. & Howlett, A.C. (1999) Biochemistry 38, 3447-3455]. In Chaps-solubilized N18TG2 membr anes, the CB1 receptor coimmunoprecipitated with all three Gi subtypes. Per tussis toxin significantly reduced the CB1 receptor-G alpha (i) association and attenuated the CB(1)401-417-induced inhibition of adenylate cyclase. C B(1)401-417 significantly reduced the CB1 receptor association with G alpha (i3), but not with G alpha (i1) or G alpha (i2). In contrast, third intrac ellular loop peptides significantly reduced the CB1 receptor association wi th G alpha (i1) and G alpha (i2), but not G alpha (i3). These interactions are specific for the CB1 receptor because a peptide corresponding to the ju xtamembrane C-terminal domain of the CB2 receptor failed to compete for the association of the CB1 receptor with any of the Gi alpha subtypes, and was not able to activate Gi proteins to inhibit adenylate cyclase. These studi es indicate that different domains of the CB1 receptor direct the interacti on with specific G protein subtypes.