title: Distinct pathways for the trafficking of angiotensin II and adrenergic receptors from the endoplasmic reticulum to the cell surface: Rab1-independent transport of a G protein-coupled receptor.
abstract: The molecular mechanism underlying the transport of G protein-coupled receptors from the endoplasmic reticulum (ER) to the cell surface is poorly understood. This issue was addressed by determining the role of Rab1, a Ras-related small GTPase that coordinates vesicular protein transport in the early secretory pathway, in the subcellular distribution and function of the angiotensin II type 1A receptor (AT1R), beta2-adrenergic receptor (AR), and alpha2B-AR in HEK293T cells. Inhibition of endogenous Rab1 function by transient expression of dominant-negative Rab1 mutants or Rab1 small interfering RNA (siRNA) induced a marked perinuclear accumulation and a significant reduction in cell-surface expression of AT1R and beta2-AR. The accumulated receptors were colocalized with calregulin (an ER marker) and GM130 (a Golgi marker), consistent with Rab1 function in regulating protein transport from the ER to the Golgi. In contrast, dominant-negative Rab1 mutants and siRNA had no effect on the subcellular distribution of alpha2B-AR. Similarly, expression of dominant-negative Rab1 mutants and siRNA depletion of Rab1 significantly attenuated AT1R-mediated inositol phosphate accumulation and ERK1/2 activation and beta2-AR-mediated ERK1/2 activation, but not alpha2B-AR-stimulated ERK1/2 activation. These data indicate that Rab1 GTPase selectively regulates intracellular trafficking and signaling of G protein-coupled receptors and suggest a novel, as yet undefined pathway for movement of G protein-coupled receptors from the ER to the cell surface.
authors.affiliation: Department of Pharmacology and Experimental Therapeutics, Louisiana State University Health Sciences Center, 1901 Perdido Street, New Orleans, LA 70112, USA. gwu@lsuhsc.edu
authors.forename: Guangyu
authors.initials: G
authors.lastname: Wu
authors.forename: Guiqing
authors.initials: G
authors.lastname: Zhao
authors.forename: Youe
authors.initials: Y
authors.lastname: He
mesh_terms: D000818:Animals; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D006056:Golgi Apparatus / Q000378:metabolism; D006801:Humans; D007295:Inositol Phosphates / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D021381:Protein Transport; D051381:Rats; D044140:Receptor, Angiotensin, Type 1 / Q000378:metabolism*; D011941:Receptors, Adrenergic / Q000378:metabolism*; D018341:Receptors, Adrenergic, alpha-2 / Q000378:metabolism; D018343:Receptors, Adrenergic, beta-2 / Q000378:metabolism; D043562:Receptors, G-Protein-Coupled / Q000378:metabolism; D014162:Transfection; D020761:rab1 GTP-Binding Proteins / Q000235:genetics / Q000502:physiology
chemical_list: C547771:ADRA2B protein, human; D007295:Inositol Phosphates; D044140:Receptor, Angiotensin, Type 1; D011941:Receptors, Adrenergic; D018341:Receptors, Adrenergic, alpha-2; D018343:Receptors, Adrenergic, beta-2; D043562:Receptors, G-Protein-Coupled; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D020761:rab1 GTP-Binding Proteins