title: Constitutive traffic of melanocortin-4 receptor in Neuro2A cells and immortalized hypothalamic neurons.
abstract: Melanocortin-4 receptor (MC4R) is a G protein-coupled receptor (GPCR) that binds alpha-melanocyte-stimulating hormone (alpha-MSH) and has a central role in the regulation of appetite and energy expenditure. Most GPCRs are endocytosed following binding to the agonist and receptor desensitization. Other GPCRs are internalized and recycled back to the plasma membrane constitutively, in the absence of the agonist. In unstimulated neuroblastoma cells and immortalized hypothalamic neurons, epitopetagged MC4R was localized both at the plasma membrane and in an intracellular compartment. These two pools of receptors were in dynamic equilibrium, with MC4R being rapidly internalized and exocytosed. In the absence of alpha-MSH, a fraction of cell surface MC4R localized together with transferrin receptor and to clathrin-coated pits. Constitutive MC4R internalization was impaired by expression of a dominant negative dynamin mutant. Thus, MC4R is internalized together with transferrin receptor by clathrin-dependent endocytosis. Cell exposure toalpha-MSH reduced the amount of MC4R at the plasma membrane by blocking recycling of a fraction of internalized receptor, rather than by increasing its rate of endocytosis. The data indicate that, in neuronal cells, MC4R recycles constitutively and that alpha-MSH modulates MC4R residency at the plasma membrane by acting at an intracellular sorting step.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock, Arkansas 72205.
authors.forename: Sameer
authors.initials: S
authors.lastname: Mohammad
authors.affiliation: Dipartimento di Morfologia Umana Normale, via Manzoni 16, Universita' di Trieste, I-34138 Trieste, Italy, and the.
authors.forename: Giovanna
authors.initials: G
authors.lastname: Baldini
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock, Arkansas 72205.
authors.forename: Susana
authors.initials: S
authors.lastname: Granell
authors.affiliation: Dipartimento di Morfologia Umana Normale, via Manzoni 16, Universita' di Trieste, I-34138 Trieste, Italy, and the.
authors.forename: Paola
authors.initials: P
authors.lastname: Narducci
authors.affiliation: Dipartimento di Scienze Anatomiche Umane e Fisiopatologia dell'Apparato Locomotore, Sezione di Anatomia, Cell Signalling Laboratory, Universita' di Bologna, via Irnerio 48, I-40126 Bologna, Italy.
authors.forename: Alberto M
authors.initials: AM
authors.lastname: Martelli
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock, Arkansas 72205. Electronic address: gbaldini@uams.edu.
authors.forename: Giulia
authors.initials: G
authors.lastname: Baldini
mesh_terms: D000818:Animals; D001066:Appetite / Q000187:drug effects / Q000235:genetics; D002461:Cell Line, Transformed; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism; D022163:Clathrin-Coated Vesicles / Q000378:metabolism; D004705:Endocytosis / Q000187:drug effects / Q000235:genetics; D004734:Energy Metabolism / Q000187:drug effects / Q000235:genetics; D005089:Exocytosis / Q000187:drug effects / Q000235:genetics; D015870:Gene Expression; D006801:Humans; D007031:Hypothalamus / Q000378:metabolism*; D051379:Mice; D009154:Mutation; D009474:Neurons / Q000378:metabolism*; D021381:Protein Transport / Q000187:drug effects; D044105:Receptor, Melanocortin, Type 4 / Q000819:agonists / Q000235:genetics / Q000378:metabolism*; D011990:Receptors, Transferrin / Q000378:metabolism; D012175:Retinoblastoma / Q000378:metabolism; D000521:alpha-MSH / Q000378:metabolism / Q000494:pharmacology*
chemical_list: D044105:Receptor, Melanocortin, Type 4; D011990:Receptors, Transferrin; D000521:alpha-MSH