title: Role of clathrin-mediated endocytosis in agonist-induced down-regulation of the beta2-adrenergic receptor.
abstract: Previous studies have demonstrated that non-visual arrestins function as adaptors in clathrin-mediated endocytosis to promote agonist-induced internalization of the beta2-adrenergic receptor (beta2AR). Here, we characterized the effects of arrestins and other modulators of clathrin-mediated endocytosis on down-regulation of the beta2AR. In COS-1 and HeLa cells, non-visual arrestins promote agonist-induced internalization and down-regulation of the beta2AR, whereas dynamin-K44A, a dominant-negative mutant of dynamin that inhibits clathrin-mediated endocytosis, attenuates beta2AR internalization and down-regulation. In HEK293 cells, dynamin-K44A profoundly inhibits agonist-induced internalization and down-regulation of the beta2AR, suggesting that receptor internalization is critical for down-regulation in these cells. Moreover, a dominant-negative mutant of beta-arrestin, beta-arrestin-(319-418), also inhibits both agonist-induced receptor internalization and down-regulation. Immunofluorescence microscopy analysis reveals that the beta2AR is trafficked to lysosomes in HEK293 cells, where presumably degradation of the receptor occurs. These studies demonstrate that down-regulation of the beta2AR is in part due to trafficking of the beta2AR via the clathrin-coated pit endosomal pathway to lysosomes.
authors.affiliation: Department of Microbiology and Immunology, Kimmel Cancer Institute, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA.
authors.forename: A W
authors.initials: AW
authors.lastname: Gagnon
authors.forename: L
authors.initials: L
authors.lastname: Kallal
authors.forename: J L
authors.initials: JL
authors.lastname: Benovic
mesh_terms: D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000818:Animals; D002460:Cell Line; D002966:Clathrin / Q000502:physiology*; D003034:Coated Pits, Cell-Membrane; D015536:Down-Regulation; D004705:Endocytosis / Q000502:physiology*; D006801:Humans; D008247:Lysosomes / Q000378:metabolism; D018343:Receptors, Adrenergic, beta-2 / Q000187:drug effects* / Q000378:metabolism
chemical_list: D000318:Adrenergic beta-Agonists; D002966:Clathrin; D018343:Receptors, Adrenergic, beta-2