title: Trafficking of beta2-adrenergic receptors: insulin and beta-agonists regulate internalization by distinct cytoskeletal pathways.
abstract: Insulin and beta-adrenergic agonists stimulate a rapid phosphorylation and sequestration of the beta2-adrenergic receptors (beta2ARs). Although the expectation was that a common pathway would be involved in the trafficking of the beta2AR in response to either hormone, studies reported herein show the existence of unique cytoskeletal requirements for internalization/recycling of G-protein-coupled receptors, such as the beta2AR. Treatment of human epidermoid carcinoma A431 cells with nocodazole, which binds tubulin monomer in vivo and catalyzes the depolymerization of microtubules, effectively blocks beta-adrenergic agonist-induced, but not insulin-induced, sequestration of beta2ARs. Treatment with latrunculin-A, an agent that sequesters actin monomer and leads to loss of actin filaments, had no effect on the ability of beta-adrenergic agonists to stimulate internalization of beta2ARs, but blocked the ability of insulin to stimulate counterregulation of beta2ARs via internalization. Although nocodazole had no effect on insulin-stimulated sequestration of beta2ARs, the recycling of the internalized receptors to the cell membrane was sensitive to depolymerization of microtubules by this agent. Latrunculin-A, by contrast, blocks the recycling of beta2ARs internalized in response to beta-agonist, while attenuating recycling of receptors internalized in response to insulin stimulation. These data show the existence of unique cytoskeletal requirements for G-protein-coupled-receptor trafficking in response to agonist compared with a counterregulatory hormone, and for sequestration versus recycling of the receptors to the cell membrane.
authors.affiliation: Department of Pharmacology, Diabetes & Metabolic Diseases Research Center-HSC, State University of New York at Stony Brook, Stony Brook, NY 11794-8651, USA.
authors.forename: Elena
authors.initials: E
authors.lastname: Shumay
authors.forename: Shai
authors.initials: S
authors.lastname: Gavi
authors.forename: Hsien-yu
authors.initials: HY
authors.lastname: Wang
authors.forename: Craig C
authors.initials: CC
authors.lastname: Malbon
mesh_terms: D000318:Adrenergic beta-Agonists / Q000378:metabolism / Q000494:pharmacology*; D000818:Animals; D016466:CHO Cells; D002294:Carcinoma, Squamous Cell / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism; D045744:Cell Line, Tumor; D006224:Cricetinae; D003599:Cytoskeleton / Q000187:drug effects / Q000378:metabolism*; D049452:Green Fluorescent Proteins; D006801:Humans; D007328:Insulin / Q000378:metabolism / Q000494:pharmacology*; D007545:Isoproterenol / Q000378:metabolism / Q000494:pharmacology; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D018613:Microscopy, Confocal; D017239:Paclitaxel / Q000494:pharmacology; D010766:Phosphorylation; D021381:Protein Transport / Q000502:physiology; D018343:Receptors, Adrenergic, beta-2 / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*
chemical_list: D000318:Adrenergic beta-Agonists; D002352:Carrier Proteins; D007328:Insulin; D008164:Luminescent Proteins; D018343:Receptors, Adrenergic, beta-2; D049452:Green Fluorescent Proteins; D007545:Isoproterenol; D017239:Paclitaxel