A Role for the Distal Carboxyl Tails in Generating the Novel Pharmacology and G Protein Activation Profile of μ and δ Opioid Receptor Hetero-oligomers

• Published in: The Journal of biological chemistry Vol. 280; no. 46; pp. 38478 - 38488
• Main Authors: Fan, Theresa, Varghese, George, Nguyen, Tuan, Tse, Roderick, O'Dowd, Brian F., George, Susan R.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 18.11.2005
• Subjects: Adenylyl Cyclases - metabolism; Analgesics, Opioid - pharmacology; Animals; Cell Membrane - metabolism; Chlorocebus aethiops; CHO Cells; Cloning, Molecular; COS Cells; Cricetinae; Disease Models, Animal; DNA, Complementary - metabolism; Dose-Response Relationship, Drug; Enkephalin, Ala-MePhe-Gly- - pharmacology; Enkephalin, D-Penicillamine (2,5)- - pharmacology; Gene Deletion; GTP-Binding Proteins - chemistry; Guanine - chemistry; Guanosine 5'-O-(3-Thiotriphosphate) - metabolism; Immunoblotting; Immunohistochemistry; Immunoprecipitation; Ligands; Microscopy, Fluorescence; Oligopeptides - chemistry; Pertussis Toxin - pharmacology; Protein Binding; Protein Biosynthesis; Protein Structure, Tertiary; Rats; Receptors, Opioid, delta - chemistry; Receptors, Opioid, mu - chemistry; Signal Transduction; Time Factors; Transfection
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M505644200

Opioid receptor pharmacology in vivo has predicted a greater number of receptor subtypes than explained by the profiles of the three cloned opioid receptors, and the functional dependence of the receptors on each other shown in gene-deleted animal models remains unexplained. One mechanism for such findings is the generation of novel signaling complexes by receptor hetero-oligomerization, which we previously showed results in significantly different pharmacology for μ and δ receptor hetero-oligomers compared with the individual receptors. In the present study, we show that deltorphin-II is a fully functional agonist of the μ-δ heteromer, which induced desensitization and inhibited adenylyl cyclase through a pertussis toxin-insensitive G protein. Activation of the μ-δ receptor heteromer resulted in preferential activation of Gαz, illustrated by incorporation of GTPγ35S, whereas activation of the individually expressed μ and δ receptors preferentially activated Gαi. The unique pharmacology of the μ-δ heteromer was dependent on the reciprocal involvement of the distal carboxyl tails of both receptors, so that truncation of the distal μ receptor carboxyl tail modified the δ-selective ligand-binding pocket, and truncation of the δ receptor distal carboxyl tail modified the μ-selective binding pocket. The distal carboxyl tails of both receptors also had a significant role in receptor interaction, as evidenced by the reduced ability to co-immunoprecipitate when the carboxyl tails were truncated. The interaction between μ and δ receptors occurred constitutively when the receptors were co-expressed, but did not occur when receptor expression was temporally separated, indicating that the hetero-oligomers were generated by a co-translational mechanism.