title: Agonist occupancy of a single monomeric element is sufficient to cause internalization of the dimeric beta2-adrenoceptor.
abstract: A range of studies have indicated that many rhodopsin-like, family A G protein-coupled receptors, including the beta(2)-adrenoceptor, exist and probably function as dimers. It is less clear if receptors internalize as dimers and if agonist occupancy of only one element of a dimer is sufficient to cause internalization of a receptor dimer into the cell. We have used a chemogenomic approach to demonstrate that this is the case. Following expression of the wild type beta(2)-adrenoceptor, isoprenaline but not 1-(3''4'-dihydroxyphenyl)-3-methyl-1-butanone, which does not have significant affinity for the wild type receptor, caused receptor internalization. By contrast, 1-(3'4'-dihydroxyphenyl)-3-methyl-1-butanone, but not isoprenaline that does not have high affinity for the mutated receptor, caused internalization of Asp(113)Serbeta(2)-adrenoceptor. Following co-expression of wild type and Asp(113)Serbeta(2)-adrenoceptors each of isoprenaline and 1-(3'4'-dihydroxyphenyl)-3-methyl-1-butanone caused the co-internalization of both of these two forms of the receptor. Co-expressed wild type and Asp(113)Serbeta(2)-adrenoceptors were able to be co-immunoprecipitated and 1-(3'4'-dihydroxyphenyl)-3-methyl-1-butanone produced internalization of the wild type receptor that was not prevented by the beta-adrenoceptor antagonist propranolol that binds with high affinity only to the wild type receptor. These results demonstrate that agonist occupancy of either single binding site of the beta(2)-adrenoceptor dimer is sufficient to cause internalization of the dimer and that antagonist occupation of one of the two ligand binding sites is unable to prevent agonist-mediated internalization.
authors.affiliation: Molecular Pharmacology Group, Division of Biochemistry and Molecular Biology, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow G12 8QQ, Scotland, UK.
authors.forename: Nana
authors.initials: N
authors.lastname: Sartania
authors.forename: Shirley
authors.initials: S
authors.lastname: Appelbe
authors.forename: John D
authors.initials: JD
authors.lastname: Pediani
authors.forename: Graeme
authors.initials: G
authors.lastname: Milligan
mesh_terms: D058666:Adrenergic beta-2 Receptor Agonists; D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D002460:Cell Line; D019281:Dimerization; D004318:Doxycycline / Q000494:pharmacology; D004705:Endocytosis / Q000187:drug effects*; D006801:Humans; D007545:Isoproterenol / Q000494:pharmacology; D008562:Membrane Glycoproteins / Q000378:metabolism; D050505:Mutant Proteins / Q000378:metabolism; D011433:Propranolol / Q000494:pharmacology; D014759:Viral Envelope Proteins / Q000378:metabolism
chemical_list: D058666:Adrenergic beta-2 Receptor Agonists; D000318:Adrenergic beta-Agonists; C028391:G protein, vesicular stomatitis virus; D008562:Membrane Glycoproteins; D050505:Mutant Proteins; D014759:Viral Envelope Proteins; D011433:Propranolol; D007545:Isoproterenol; D004318:Doxycycline