title: Heterodimerization with beta2-adrenergic receptors promotes surface expression and functional activity of alpha1D-adrenergic receptors.
abstract: The alpha1D-adrenergic receptor (alpha1D-AR) is a G protein-coupled receptor (GPCR) that is poorly trafficked to the cell surface and largely nonfunctional when heterologously expressed by itself in a variety of cell types. We screened a library of approximately 30 other group I GPCRs in a quantitative luminometer assay for the ability to promote alpha1D-AR cell surface expression. Strikingly, these screens revealed only two receptors capable of inducing robust increases in the amount of alpha1D-AR at the cell surface: alpha1B-AR and beta2-AR. Confocal imaging confirmed that coexpression with beta2-AR resulted in translocation of alpha1D-AR from intracellular sites to the plasma membrane. Additionally, coimmunoprecipitation studies demonstrated that alpha1D-AR and beta2-AR specifically interact to form heterodimers when coexpressed in HEK-293 cells. Ligand binding studies revealed an increase in total alpha1D-AR binding sites upon coexpression with beta2-AR, but no apparent effect on the pharmacological properties of the receptors. In functional studies, coexpression with beta2-AR significantly enhanced the coupling of alpha1D-AR to norepinephrine-stimulated Ca2+ mobilization. Heterodimerization of beta2-AR with alpha1D-AR also conferred the ability of alpha1D-AR to cointernalize upon beta2-AR agonist stimulation, revealing a novel mechanism by which these different adrenergic receptor subtypes may regulate each other's activity. These findings demonstrate that the selective association of alpha1D-AR with other receptors is crucial for receptor surface expression and function and also shed light on a novel mechanism of cross talk between alpha1- and beta2-ARs that is mediated through heterodimerization and cross-internalization.
authors.affiliation: Department of Pharmacology, Emory University School of Medicine, 5113 Rollins Research Center, 1510 Clifton Rd., Atlanta, GA 30322, USA.
authors.forename: Michelle A
authors.initials: MA
authors.lastname: Uberti
authors.forename: Chris
authors.initials: C
authors.lastname: Hague
authors.forename: Heide
authors.initials: H
authors.lastname: Oller
authors.forename: Kenneth P
authors.initials: KP
authors.lastname: Minneman
authors.forename: Randy A
authors.initials: RA
authors.lastname: Hall
mesh_terms: D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000420:Albuterol / Q000494:pharmacology; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D006801:Humans; D047468:Immunoprecipitation; D018613:Microscopy, Confocal; D010957:Plasmids / Q000235:genetics; D011869:Radioligand Assay; D018340:Receptors, Adrenergic, alpha-1 / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D018343:Receptors, Adrenergic, beta-2 / Q000235:genetics / Q000502:physiology*; D011956:Receptors, Cell Surface / Q000378:metabolism*; D043562:Receptors, G-Protein-Coupled / Q000378:metabolism
chemical_list: C547719:ADRA1D protein, human; D000318:Adrenergic beta-Agonists; D018340:Receptors, Adrenergic, alpha-1; D018343:Receptors, Adrenergic, beta-2; D011956:Receptors, Cell Surface; D043562:Receptors, G-Protein-Coupled; D000420:Albuterol; D002118:Calcium