title: Cell surface targeting of VPAC1 receptors: evidence for implication of a quality control system and the proteasome.
abstract: Like for most transmembrane proteins, translation of G protein-coupled receptors (GPCRs) mRNA takes place at the endoplasmic reticulum (ER) where they are synthesized, folded and assembled. The molecular mechanisms involved in the transport process of GPCRs from ER to the plasma membrane are poorly investigated. Here we studied the mechanisms involved in glycosylation-dependent cell surface expression and quality control of the receptor for Vasoactive Intestinal Polypeptide (VIP) VPAC1, a member of the B family of GPCRs. Using biochemical and pharmacological techniques and fluorescence microscopy, we have shown that only a fraction of newly synthesized VPAC1 attains properly conformation that allows their cell surface targeting. Misfolded or immature VPAC1 are taken in charge by co- and post-translational quality control that involves: 1) calnexin-dependent folding strictly through a glycan-dependent mechanism, 2) BiP-dependant folding, 3) translocation to the cytoplasm and proteasome-dependent degradation of improper proteins, and 4) post-ER quality control check points. Our data suggest that VPAC1 expression/trafficking pathways are under the control of complex and precise molecular mechanisms to ensure that only proper VPAC1 reaches the cell surface.
authors.affiliation: Laboratory of Biological Chemistry and Nutrition, School of Medicine, Université Libre de Bruxelles, 808 route de Lennik CP611, B-1070 Brussels, Belgium. ilanger@ulb.ac.be
authors.forename: Ingrid
authors.initials: I
authors.lastname: Langer
authors.forename: Karelle
authors.initials: K
authors.lastname: Leroy
authors.forename: Nathalie
authors.initials: N
authors.lastname: Gaspard
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Brion
authors.forename: Patrick
authors.initials: P
authors.lastname: Robberecht
mesh_terms: D000818:Animals; D016466:CHO Cells; D002462:Cell Membrane / Q000378:metabolism*; D006224:Cricetinae; D003412:Cricetulus; D018832:Molecular Chaperones / Q000378:metabolism; D009154:Mutation; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D021381:Protein Transport; D051238:Receptors, Vasoactive Intestinal Polypeptide, Type I / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D013696:Temperature; D025801:Ubiquitin / Q000378:metabolism
chemical_list: D018832:Molecular Chaperones; D051238:Receptors, Vasoactive Intestinal Polypeptide, Type I; D025801:Ubiquitin; D046988:Proteasome Endopeptidase Complex