title: Hetero-oligomers of alpha2A-adrenergic and mu-opioid receptors do not lead to transactivation of G-proteins or altered endocytosis profiles.
abstract: Complexes of alpha(2A)-ARs (alpha(2A)-adrenergic receptors) and MORs (mu-opioid receptors), probably hetero-oligomers, were detected by co-immunoisolation after extraction from HEK-293 cells (human embryonic kidney 293 cells). Functional communication between these receptors is revealed by alpha(2A)-AR activation of a pertussis toxin-insensitive G(i)alpha subunit (termed as G(i)1) when fused with the MOR and evaluated in membranes from pertussis toxin-treated cells. However, the alpha(2A)-AR does not require transactivation through MOR, since quantitatively indistinguishable results were observed in cells co-expressing alpha(2A)-AR and a fusion protein of G(i)1 with the first transmembrane span of MOR (myc-MOR-TM1). Functional cross-talk among these alpha(2A)-AR-MOR complexes does not occur for internalization profiles; incubation with adrenaline (epinephrine) leads to endocytosis of alpha(2A)-AR but not MOR, while incubation with DAMGO ([D-Ala,NMe-Phe,Gly-ol]enkephalin) leads to endocytosis of MOR but not alpha(2A)-AR in cells co-expressing both the receptors. Hence, alpha(2A)-AR and MOR hetero-oligomers, although they occur, do not have an obligatory functional influence on one another in the paradigms studied.
authors.affiliation: Department of Pharmacology and Center for Molecular Neuroscience, Vanderbilt University Medical Center, 2200 Pierce Ave., 464A RRB, Nashville, TN 37232-6600, USA.
authors.forename: Y Q
authors.initials: YQ
authors.lastname: Zhang
authors.forename: L E
authors.initials: LE
authors.lastname: Limbird
mesh_terms: D000701:Analgesics, Opioid / Q000494:pharmacology; D015153:Blotting, Western; D002460:Cell Line; D018076:DNA, Complementary / Q000378:metabolism; D004705:Endocytosis; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)- / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000737:chemistry*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D006801:Humans; D047468:Immunoprecipitation; D008856:Microscopy, Fluorescence; D009474:Neurons / Q000378:metabolism; D037342:Pertussis Toxin / Q000737:chemistry; D011485:Protein Binding; D018341:Receptors, Adrenergic, alpha-2 / Q000737:chemistry*; D017450:Receptors, Opioid, mu / Q000737:chemistry*; D011993:Recombinant Fusion Proteins / Q000737:chemistry; D015533:Transcriptional Activation; D014162:Transfection
chemical_list: C547768:ADRA2A protein, human; D000701:Analgesics, Opioid; D018076:DNA, Complementary; D018341:Receptors, Adrenergic, alpha-2; D017450:Receptors, Opioid, mu; D011993:Recombinant Fusion Proteins; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D037342:Pertussis Toxin; D019204:GTP-Binding Proteins