title: Endocytosis of ligand-human parathyroid hormone receptor 1 complexes is protein kinase C-dependent and involves beta-arrestin2. Real-time monitoring by fluorescence microscopy.
abstract: Endocytosis and intracellular trafficking of the human parathyroid hormone receptor subtype 1 (hPTH1-Rc) and its ligands was monitored independently by real-time fluorescence microscopy in stably transfected HEK-293 cells. Complexes of fluorescence-labeled parathyroid hormone (PTH)-(1-34) agonist bound to the hPTH1-Rc internalized rapidly at 37 degrees C via clathrin-coated vesicles, whereas fluorescent PTH-(7-34) antagonist-hPTH1Rc complexes did not. A functional C terminus epitope-tagged receptor (C-Tag-hPTH1-Rc) was immunolocalized to the cell membrane and, to a lesser extent, the cytoplasm. PTH and PTH-related protein agonists stimulated C-Tag-hPTH1-Rc internalization. Relocalization to the cell membrane occurred 1 h after removal of the ligand. Endocytosis of fluorescent PTH agonist-hPTH1-Rc complexes was blocked by the protein kinase C (PKC) inhibitor staurosporine but not by the specific protein kinase A inhibitor N-(2-(methylamino)ethyl)-5-isoquinoline-sulfonamide. Fluorescent PTH antagonist-hPTH1-Rc complexes were rapidly internalized after PKC activation by phorbol 12-myristate 13-acetate or thrombin, but not after stimulation of the cAMP/protein kinase A pathway by forskolin. In cells co-expressing the hPTH1-Rc and a green fluorescent protein-beta-arrestin2 fusion protein (beta-Arr2-GFP), PTH agonists stimulated beta-Arr2-GFP mobilization to the cell membrane. Subsequently, fluorescent PTH-(1-34)-hPTH1Rc complexes and beta-Arr2-GFP co-localized intracellularly. In conclusion, agonist-activated hPTH1-Rc internalization involves beta-arrestin mobilization and targeting to clathrin-coated vesicles. Our results also indicate that receptor occupancy, rather than receptor-mediated signaling, is necessary, although not sufficient, for endocytosis of the hPTH1-Rc. Activation of PKC, however, is absolutely required.
authors.affiliation: Division of Bone and Mineral Metabolism, Harvard-Thorndike Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts 02215, USA.
authors.forename: S L
authors.initials: SL
authors.lastname: Ferrari
authors.forename: V
authors.initials: V
authors.lastname: Behar
authors.forename: M
authors.initials: M
authors.lastname: Chorev
authors.forename: M
authors.initials: M
authors.lastname: Rosenblatt
authors.forename: A
authors.initials: A
authors.lastname: Bisello
mesh_terms: D019390:Arrestins / Q000378:metabolism*; D002460:Cell Line; D002966:Clathrin / Q000378:metabolism; D004705:Endocytosis; D005456:Fluorescent Dyes; D049452:Green Fluorescent Proteins; D006801:Humans; D008024:Ligands; D008164:Luminescent Proteins / Q000378:metabolism; D008856:Microscopy, Fluorescence; D011493:Protein Kinase C / Q000378:metabolism*; D018016:Receptors, Parathyroid Hormone / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D000071560:beta-Arrestin 2; D000071557:beta-Arrestins
chemical_list: C000605254:ARRB2 protein, human; D019390:Arrestins; D002966:Clathrin; D005456:Fluorescent Dyes; D008024:Ligands; D008164:Luminescent Proteins; D018016:Receptors, Parathyroid Hormone; D011993:Recombinant Fusion Proteins; D000071560:beta-Arrestin 2; D000071557:beta-Arrestins; D049452:Green Fluorescent Proteins; D011493:Protein Kinase C