title: Cell signaling and trafficking of human melanocortin receptors in real time using two-photon fluorescence and confocal laser microscopy: differentiation of agonists and antagonists.
abstract: Melanocortin hormones and neurotransmitters regulate a vast array of physiologic processes by interacting with five G-protein-coupled melanocortin receptor types. In the present study, we have systematically studied the regulation of individual human melanocortin receptor wild subtypes using a synthetic rhodamine-labeled human melanotropin agonist and antagonist, arrestins fused to green fluorescent protein in conjunction with two-photon fluorescence laser scanning microscopy and confocal microscopy. Stimulation of the melanocortin receptors by its cognate agonist triggered rapid arrestin recruitment and receptor internalization for all four human melanocortin receptors examined. Antagonists-bound melanocortin receptors, on the other hand, did not recruit beta-arrestins, and remained in the cell membrane even after long-term (30 min) treatment. Agonist-mediated internalization of all melanocortin receptor subtypes was sensitive to inhibitors of clathrin-dependent endocytosis, but not to caveolae inhibitors. In summary, agonist-mediated internalization of all subtypes of melanocortin receptors are dependent upon beta-arrestin-mediated clathrin-coated pits, whereas, beta-arrestin-2 conjugated green fluorescence protein (beta-arrestin-2-GFP) recruitment is not dependent on protein kinase A activation. Real time two-photon fluorescence laser scanning microscopy is a most powerful tool to study the dynamic processes in living cells and tissues, without inflicting significant and often lethal damage to the specimen.
authors.affiliation: Department of Chemistry, University of Arizona, Tucson, AZ 85721, USA.
authors.forename: Minying
authors.initials: M
authors.lastname: Cai
authors.forename: Eva V
authors.initials: EV
authors.lastname: Varga
authors.forename: Magda
authors.initials: M
authors.lastname: Stankova
authors.forename: Alexander
authors.initials: A
authors.lastname: Mayorov
authors.forename: Joseph W
authors.initials: JW
authors.lastname: Perry
authors.forename: Henry I
authors.initials: HI
authors.lastname: Yamamura
authors.forename: Dev
authors.initials: D
authors.lastname: Trivedi
authors.forename: Victor J
authors.initials: VJ
authors.lastname: Hruby
mesh_terms: D019390:Arrestins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D001667:Binding, Competitive; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D021941:Caveolae / Q000378:metabolism; D002460:Cell Line; D022163:Clathrin-Coated Vesicles / Q000378:metabolism; D005576:Colforsin / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D007546:Isoquinolines / Q000494:pharmacology; D007700:Kinetics; D009074:Melanocyte-Stimulating Hormones / Q000494:pharmacology; D018613:Microscopy, Confocal / Q000379:methods*; D036641:Microscopy, Fluorescence, Multiphoton / Q000379:methods*; D008958:Models, Molecular; D010456:Peptides, Cyclic / Q000494:pharmacology; D044101:Receptors, Melanocortin / Q000819:agonists / Q000037:antagonists & inhibitors / Q000502:physiology*; D012235:Rhodamines / Q000737:chemistry; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D013449:Sulfonamides / Q000494:pharmacology; D014162:Transfection; D000521:alpha-MSH / Q000031:analogs & derivatives / Q000494:pharmacology; D000071560:beta-Arrestin 2; D000071557:beta-Arrestins
chemical_list: C000605254:ARRB2 protein, human; D019390:Arrestins; D007546:Isoquinolines; D010456:Peptides, Cyclic; D044101:Receptors, Melanocortin; D012235:Rhodamines; D013449:Sulfonamides; D000071560:beta-Arrestin 2; D000071557:beta-Arrestins; C079282:melanotan-II; D049452:Green Fluorescent Proteins; C103272:SHU 9119; D005576:Colforsin; D000521:alpha-MSH; D009074:Melanocyte-Stimulating Hormones; D017868:Cyclic AMP-Dependent Protein Kinases; C063509:N-(2-(4-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide