title: N-glycans are direct determinants of CFTR folding and stability in secretory and endocytic membrane traffic.
abstract: N-glycosylation, a common cotranslational modification, is thought to be critical for plasma membrane expression of glycoproteins by enhancing protein folding, trafficking, and stability through targeting them to the ER folding cycles via lectin-like chaperones. In this study, we show that N-glycans, specifically core glycans, enhance the productive folding and conformational stability of a polytopic membrane protein, the cystic fibrosis transmembrane conductance regulator (CFTR), independently of lectin-like chaperones. Defective N-glycosylation reduces cell surface expression by impairing both early secretory and endocytic traffic of CFTR. Conformational destabilization of the glycan-deficient CFTR induces ubiquitination, leading to rapid elimination from the cell surface. Ubiquitinated CFTR is directed to lysosomal degradation instead of endocytic recycling in early endosomes mediated by ubiquitin-binding endosomal sorting complex required for transport (ESCRT) adaptors Hrs (hepatocyte growth factor-regulated tyrosine kinase substrate) and TSG101. These results suggest that cotranslational N-glycosylation can exert a chaperone-independent profolding change in the energetic of CFTR in vivo as well as outline a paradigm for the peripheral trafficking defect of membrane proteins with impaired glycosylation.
authors.affiliation: Hospital for Sick Children Research Institute, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Rina
authors.initials: R
authors.lastname: Glozman
authors.forename: Tsukasa
authors.initials: T
authors.lastname: Okiyoneda
authors.forename: Cory M
authors.initials: CM
authors.lastname: Mulvihill
authors.forename: James M
authors.initials: JM
authors.lastname: Rini
authors.forename: Herve
authors.initials: H
authors.lastname: Barriere
authors.forename: Gergely L
authors.initials: GL
authors.lastname: Lukacs
mesh_terms: D000818:Animals; D019556:COS Cells; D002462:Cell Membrane / Q000378:metabolism*; D002522:Chlorocebus aethiops; D006224:Cricetinae; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism; D004705:Endocytosis; D056827:Endosomal Sorting Complexes Required for Transport; D011992:Endosomes / Q000378:metabolism; D006031:Glycosylation; D006801:Humans; D008247:Lysosomes / Q000378:metabolism; D018832:Molecular Chaperones / Q000378:metabolism; D009154:Mutation; D010750:Phosphoproteins / Q000378:metabolism; D011487:Protein Conformation; D017510:Protein Folding; D011499:Protein Processing, Post-Translational; D055550:Protein Stability; D021381:Protein Transport; D013997:Time Factors; D014157:Transcription Factors / Q000378:metabolism; D014162:Transfection; D025801:Ubiquitin / Q000378:metabolism; D000099177:Tsg101 Protein
chemical_list: D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D004268:DNA-Binding Proteins; D056827:Endosomal Sorting Complexes Required for Transport; D018832:Molecular Chaperones; D010750:Phosphoproteins; D014157:Transcription Factors; D025801:Ubiquitin; D000099177:Tsg101 Protein; C096164:hepatocyte growth factor-regulated tyrosine kinase substrate