title: Derlin-1 promotes the efficient degradation of the cystic fibrosis transmembrane conductance regulator (CFTR) and CFTR folding mutants.
abstract: A complex involving Derlin-1 and p97 mediates the retrotranslocation and endoplasmic reticulum (ER)-associated degradation of misfolded proteins in yeast and is used by certain viruses to promote host cell protein degradation (Romisch, K. (2005) Annu. Rev. Cell Dev. Biol. 21, 435-456; Lilley, B. N., and Ploegh, H. L. (2004) Nature 429, 834-840; Ye, Y., Shibata, Y., Yun, C., Ron, D., and Rapoport, T. A. (2004) Nature 429, 841-847). We asked whether the components of this pathway are involved in the endoplasmic reticulum-associated degradation of the mammalian integral membrane protein, the cystic fibrosis transmembrane conductance regulator (CFTR), a substrate for the ubiquitin-proteasome system. We report that Derlin-1 and p97 formed complexes with CFTR in human airway epithelial cells. Derlin-1 interacted with nonubiquitylated CFTR, whereas p97 associated with ubiquitylated CFTR. Exogenous expression of Derlin-1 led to its co-localization with CFTR in the ER where it reduced wild type (WT) CFTR expression and efficiently degraded the disease-associated CFTR folding mutants, DeltaF508 and G85E (>90%). Consistent with this, Derlin-1 also reduced the amount of WT or DeltaF508 CFTR appearing in detergent-in-soluble aggregates. An approximately 70% knockdown of endogenous Derlin-1 by RNA interference increased the steady-state levels of WT and DeltaF508 CFTR by 10-15-fold, reflecting its significant role in CFTR degradation. Derlin-1 mediated the degradation of N-terminal CFTR fragments corresponding to the first transmembrane domain of CFTR, but CFTR fragments that incorporated additional domains were degraded less efficiently. These findings suggest that Derlin-1 recognizes misfolded, nonubiquitylated CFTR to initiate its dislocation and degradation early in the course of CFTR biogenesis, perhaps by detecting structural instability within the first transmembrane domain.
authors.affiliation: Department of Cell Biology and Physiology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261, USA.
authors.forename: Fei
authors.initials: F
authors.lastname: Sun
authors.forename: Ruilin
authors.initials: R
authors.lastname: Zhang
authors.forename: Xiaoyan
authors.initials: X
authors.lastname: Gong
authors.forename: Xuehui
authors.initials: X
authors.lastname: Geng
authors.forename: Peter F
authors.initials: PF
authors.lastname: Drain
authors.forename: Raymond A
authors.initials: RA
authors.lastname: Frizzell
mesh_terms: D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D003546:Cysteine Endopeptidases / Q000737:chemistry; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000235:genetics* / Q000502:physiology*; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006801:Humans; D008565:Membrane Proteins / Q000502:physiology*; D008861:Microsomes / Q000378:metabolism; D009154:Mutation; D011485:Protein Binding; D011489:Protein Denaturation; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D025801:Ubiquitin / Q000737:chemistry
chemical_list: C505032:CFTR protein, human; C487709:DERL1 protein, human; D008565:Membrane Proteins; D025801:Ubiquitin; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D003546:Cysteine Endopeptidases