title: Small heat shock proteins target mutant cystic fibrosis transmembrane conductance regulator for degradation via a small ubiquitin-like modifier-dependent pathway.
abstract: Small heat shock proteins (sHsps) bind destabilized proteins during cell stress and disease, but their physiological functions are less clear. We evaluated the impact of Hsp27, an sHsp expressed in airway epithelial cells, on the common protein misfolding mutant that is responsible for most cystic fibrosis. F508del cystic fibrosis transmembrane conductance regulator (CFTR), a well-studied protein that is subject to cytosolic quality control, selectively associated with Hsp27, whose overexpression preferentially targeted mutant CFTR to proteasomal degradation. Hsp27 interacted physically with Ubc9, the small ubiquitin-like modifier (SUMO) E2 conjugating enzyme, implying that F508del SUMOylation leads to its sHsp-mediated degradation. Enhancing or disabling the SUMO pathway increased or blocked Hsp27's ability to degrade mutant CFTR. Hsp27 promoted selective SUMOylation of F508del NBD1 in vitro and of full-length F508del CFTR in vivo, which preferred endogenous SUMO-2/3 paralogues that form poly-chains. The SUMO-targeted ubiquitin ligase (STUbL) RNF4 recognizes poly-SUMO chains to facilitate nuclear protein degradation. RNF4 overexpression elicited F508del degradation, whereas Hsp27 knockdown blocked RNF4's impact on mutant CFTR. Similarly, the ability of Hsp27 to degrade F508del CFTR was lost during overexpression of dominant-negative RNF4. These findings link sHsp-mediated F508del CFTR degradation to its SUMOylation and to STUbL-mediated targeting to the ubiquitin-proteasome system and thereby implicate this pathway in the disposal of an integral membrane protein.
authors.affiliation: Department of Cell Biology and Physiology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261, USA.
authors.forename: Annette
authors.initials: A
authors.lastname: Ahner
authors.forename: Xiaoyan
authors.initials: X
authors.lastname: Gong
authors.forename: Bela Z
authors.initials: BZ
authors.lastname: Schmidt
authors.forename: Kathryn W
authors.initials: KW
authors.lastname: Peters
authors.forename: Wael M
authors.initials: WM
authors.lastname: Rabeh
authors.forename: Patrick H
authors.initials: PH
authors.lastname: Thibodeau
authors.forename: Gergely L
authors.initials: GL
authors.lastname: Lukacs
authors.forename: Raymond A
authors.initials: RA
authors.lastname: Frizzell
mesh_terms: D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000235:genetics / Q000378:metabolism*; D015870:Gene Expression; D055785:Gene Knockdown Techniques; D057809:HEK293 Cells; D055551:HSP27 Heat-Shock Proteins / Q000502:physiology*; D006360:Heat-Shock Proteins; D006801:Humans; D018832:Molecular Chaperones; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D059748:Proteolysis; D017384:Sequence Deletion; D058207:Sumoylation; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D044763:Ubiquitin-Conjugating Enzymes / Q000378:metabolism; D000098843:Ubiquitin-Conjugating Enzyme UBC9
chemical_list: C505032:CFTR protein, human; D055551:HSP27 Heat-Shock Proteins; C057725:HSPB1 protein, human; D006360:Heat-Shock Proteins; D018832:Molecular Chaperones; D009687:Nuclear Proteins; C114070:RNF4 protein, human; D014157:Transcription Factors; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D044763:Ubiquitin-Conjugating Enzymes; D046988:Proteasome Endopeptidase Complex; D000098843:Ubiquitin-Conjugating Enzyme UBC9