title: Small heat-shock proteins select deltaF508-CFTR for endoplasmic reticulum-associated degradation.
abstract: Secreted proteins that fail to achieve their native conformations, such as cystic fibrosis transmembrane conductance regulator (CFTR) and particularly the DeltaF508-CFTR variant can be selected for endoplasmic reticulum (ER)-associated degradation (ERAD) by molecular chaperones. Because the message corresponding to HSP26, which encodes a small heat-shock protein (sHsp) in yeast was up-regulated in response to CFTR expression, we examined the impact of sHsps on ERAD. First, we observed that CFTR was completely stabilized in cells lacking two partially redundant sHsps, Hsp26p and Hsp42p. Interestingly, the ERAD of a soluble and a related integral membrane protein were unaffected in yeast deleted for the genes encoding these sHsps, and CFTR polyubiquitination was also unaltered, suggesting that Hsp26p/Hsp42p are not essential for polyubiquitination. Next, we discovered that DeltaF508-CFTR degradation was enhanced when a mammalian sHsp, alphaA-crystallin, was overexpressed in human embryonic kidney 293 cells, but wild-type CFTR biogenesis was unchanged. Because alphaA-crystallin interacted preferentially with DeltaF508-CFTR and because purified alphaA-crystallin suppressed the aggregation of the first nucleotide-binding domain of CFTR, we suggest that sHsps maintain the solubility of DeltaF508-CFTR during the ERAD of this polypeptide.
authors.affiliation: Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA 15260, USA.
authors.forename: Annette
authors.initials: A
authors.lastname: Ahner
authors.forename: Kunio
authors.initials: K
authors.lastname: Nakatsukasa
authors.forename: Hui
authors.initials: H
authors.lastname: Zhang
authors.forename: Raymond A
authors.initials: RA
authors.lastname: Frizzell
authors.forename: Jeffrey L
authors.initials: JL
authors.lastname: Brodsky
mesh_terms: D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000737:chemistry / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D017353:Gene Deletion; D015870:Gene Expression; D015966:Gene Expression Regulation, Fungal; D050888:Heat-Shock Proteins, Small / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D025821:Polyubiquitin / Q000378:metabolism; D011485:Protein Binding; D011499:Protein Processing, Post-Translational; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D038202:alpha-Crystallin A Chain / Q000235:genetics
chemical_list: D050888:Heat-Shock Proteins, Small; D012333:RNA, Messenger; D038202:alpha-Crystallin A Chain; C093349:cystic fibrosis transmembrane conductance regulator delta F508; D025821:Polyubiquitin; D019005:Cystic Fibrosis Transmembrane Conductance Regulator