title: The N-terminal region of the dopamine D2 receptor, a rhodopsin-like GPCR, regulates correct integration into the plasma membrane and endocytic routes.
abstract: OBJECTIVE
  Functional roles of the N-terminal region of rhodopsin-like GPCR family remain unclear. Using dopamine D(2)  and D(3)  receptors as a model system, we probed the roles of the N-terminal region in the signalling, intracellular trafficking of receptor proteins, and explored the critical factors that determine the functionality of the N-terminal region.
  
  
  METHODS
  The N-terminal region of the D(2)  receptor was gradually shortened or switched with that of the D(3)  receptor or a non-specific sequence (FLAG), or potential N-terminal glycosylation sites were mutated. Effects of these manipulations on surface expression, internalization, post-endocytic behaviours and signalling were determined.
  
  
  RESULTS
  Shortening the N-terminal region of the D(2)  receptor enhanced receptor internalization and impaired surface expression and signalling; ligand binding, desensitization and down-regulation were not affected but their association with a particular microdomain, caveolae, was disrupted. Replacement of critical residues within the N-terminal region with the FLAG epitope failed to restore surface expression but partially restored the altered internalization and signalling. When the N-terminal regions were switched between D(2)  and D(3)  receptors, cell surface expression pattern of each receptor was switched. Mutations of potential N-terminal glycosylation sites inhibited surface expression but enhanced internalization of D(2)  receptors.
  
  
  CONCLUSIONS
  Shortening of N-terminus or mutation of glycosylation sites located within the N-terminus enhanced receptor internalization but impaired the surface expression of D(2)  receptors. The N-terminal region of the D(2)  receptor, in a sequence-specific manner, controls the receptor's conformation and integration into the plasma membrane, which determine its subcellular localization, intracellular trafficking and signalling properties.
authors: Department of Pharmacology, College of Pharmacy, Research Institute of Drug Development, Chonnam National University, Gwang-Ju, 500-757 Korea.
authors: D I
authors: DI
authors: Cho
authors: C
authors: C
authors: Min
authors: K S
authors: KS
authors: Jung
authors: S Y
authors: SY
authors: Cheong
authors: M
authors: M
authors: Zheng
authors: S J
authors: SJ
authors: Cheong
authors: M H
authors: MH
authors: Oak
authors: J H
authors: JH
authors: Cheong
authors: B K
authors: BK
authors: Lee
authors: K M
authors: KM
authors: Kim
mesh_terms: D000595:Amino Acid Sequence; D019390:Arrestins / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism; D004705:Endocytosis / Q000502:physiology; D054769:G-Protein-Coupled Receptor Kinase 2 / Q000378:metabolism; D006031:Glycosylation; D057809:HEK293 Cells; D006801:Humans; D008969:Molecular Sequence Data; D011487:Protein Conformation; D021381:Protein Transport / Q000502:physiology; D017448:Receptors, Dopamine D2 / Q000737:chemistry* / Q000378:metabolism*; D050637:Receptors, Dopamine D3 / Q000737:chemistry / Q000378:metabolism; D000071557:beta-Arrestins
chemical_list: D019390:Arrestins; D017448:Receptors, Dopamine D2; D050637:Receptors, Dopamine D3; D000071557:beta-Arrestins; D000242:Cyclic AMP; C496567:GRK2 protein, human; D054769:G-Protein-Coupled Receptor Kinase 2