title: Hsp70 molecular chaperone facilitates endoplasmic reticulum-associated protein degradation of cystic fibrosis transmembrane conductance regulator in yeast.
abstract: Membrane and secretory proteins fold in the endoplasmic reticulum (ER), and misfolded proteins may be retained and targeted for ER-associated protein degradation (ERAD). To elucidate the mechanism by which an integral membrane protein in the ER is degraded, we studied the fate of the cystic fibrosis transmembrane conductance regulator (CFTR) in the yeast Saccharomyces cerevisiae. Our data indicate that CFTR resides in the ER and is stabilized in strains defective for proteasome activity or deleted for the ubiquitin-conjugating enzymes Ubc6p and Ubc7p, thus demonstrating that CFTR is a bona fide ERAD substrate in yeast. We also found that heat shock protein 70 (Hsp70), although not required for the degradation of soluble lumenal ERAD substrates, is required to facilitate CFTR turnover. Conversely, calnexin and binding protein (BiP), which are required for the proteolysis of ER lumenal proteins in both yeast and mammals, are dispensable for the degradation of CFTR, suggesting unique mechanisms for the disposal of at least some soluble and integral membrane ERAD substrates in yeast.
authors.affiliation: Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Zhang
authors.forename: G
authors.initials: G
authors.lastname: Nijbroek
authors.forename: M L
authors.initials: ML
authors.lastname: Sullivan
authors.forename: A A
authors.initials: AA
authors.lastname: McCracken
authors.forename: S C
authors.initials: SC
authors.lastname: Watkins
authors.forename: S
authors.initials: S
authors.lastname: Michaelis
authors.forename: J L
authors.initials: JL
authors.lastname: Brodsky
mesh_terms: D002135:Calcium-Binding Proteins / Q000378:metabolism; D037281:Calnexin; D003546:Cysteine Endopeptidases / Q000378:metabolism; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000737:chemistry / Q000378:metabolism*; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D007425:Intracellular Membranes / Q000378:metabolism; D008856:Microscopy, Fluorescence; D009097:Multienzyme Complexes / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex; D017510:Protein Folding; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D014170:Transformation, Genetic; D014452:Ubiquitins / Q000378:metabolism
chemical_list: D002135:Calcium-Binding Proteins; D018840:HSP70 Heat-Shock Proteins; D009097:Multienzyme Complexes; D014452:Ubiquitins; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D037281:Calnexin; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex