title: Signaling by dopamine regulates D2 receptors trafficking at the membrane.
abstract: sGi2 is a spliced variant of the GTP-binding protein G(alpha i2). By difference with G(alpha i2), which is mainly present at the plasma membrane, sGi2 is localized in intracellular compartments. The splicing event generates a novel C-terminal region in sGi2, which is necessary for its intracellular localization. The role of sGi2 is presently unknown, although its intracellular localization might underlie a possible role in the regulation of trafficking of 7TM receptors. Here, we show that sGi2 complexes with dopamine D2 receptors (D2R) in striatal neurons. The sGi2-D2R complex is readily observed in immunoprecipitation studies using specific antibodies for both proteins on mouse striatal extracts, which identify D2-specific bands of >80 KDa suggesting sGi2 interactions with D2R dimers. Importantly, the sGi2-D2R complex in the absence of receptor stimulation is mostly found in intracellular perinuclear areas in primary neuronal cultures. Treatment of neurons with quinpirole, a D2-specific agonist, results into diffusion of D2R and sGi2 staining throughout the cell and into neurites and membranes. This suggests that dopamine could regulate availability of D2 receptors at the cell surface. The formation of sGi2-D2R complex is mediated through the interaction of sGi2 with the third intracellular loop of D2Rs. As functional consequence of the D2R-sGi2 interaction, we observed a reduction of D2 binding sites at the plasma membrane, when the two proteins are co-expressed in transfected cells. Altogether these studies identify sGi2 as a D2R interacting protein involved in the regulation of D2R at the membrane through a dopamine mediated mechanism.
authors.affiliation: Department of Microbiology & Molecular Genetics, University of California Irvine, Irvine, California 92697, USA.
authors.forename: Emanuele
authors.initials: E
authors.lastname: Tirotta
authors.forename: Valerie
authors.initials: V
authors.lastname: Fontaine
authors.forename: Roberto
authors.initials: R
authors.lastname: Picetti
authors.forename: Monica
authors.initials: M
authors.lastname: Lombardi
authors.forename: Tarek A
authors.initials: TA
authors.lastname: Samad
authors.forename: Mustafa
authors.initials: M
authors.lastname: Oulad-Abdelghani
authors.forename: Robert
authors.initials: R
authors.lastname: Edwards
authors.forename: Emiliana
authors.initials: E
authors.lastname: Borrelli
mesh_terms: D000818:Animals; D019556:COS Cells; D002451:Cell Compartmentation; D002462:Cell Membrane / Q000187:drug effects* / Q000378:metabolism*; D002522:Chlorocebus aethiops; D004298:Dopamine / Q000494:pharmacology*; D051960:GTP-Binding Protein alpha Subunit, Gi2 / Q000378:metabolism; D051379:Mice; D017072:Neostriatum / Q000166:cytology; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D011485:Protein Binding / Q000187:drug effects; D020033:Protein Isoforms / Q000378:metabolism; D017433:Protein Structure, Secondary; D021381:Protein Transport / Q000187:drug effects; D017448:Receptors, Dopamine D2 / Q000819:agonists / Q000737:chemistry / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects*; D014162:Transfection
chemical_list: D020033:Protein Isoforms; D017448:Receptors, Dopamine D2; D051960:GTP-Binding Protein alpha Subunit, Gi2; D004298:Dopamine