Chaperone-Independent Peripheral Quality Control of CFTR by RFFL E3 Ligase

Dev Cell. 2018 Mar 26;44(6):694-708.e7. doi: 10.1016/j.devcel.2018.02.001. Epub 2018 Mar 1.


The peripheral protein quality control (QC) system removes non-native membrane proteins, including ΔF508-CFTR, the most common CFTR mutant in cystic fibrosis (CF), from the plasma membrane (PM) for lysosomal degradation by ubiquitination. It remains unclear how unfolded membrane proteins are recognized and targeted for ubiquitination and how they are removed from the apical PM. Using comprehensive siRNA screens, we identified RFFL, an E3 ubiquitin (Ub) ligase that directly and selectively recognizes unfolded ΔF508-CFTR through its disordered regions. RFFL retrieves the unfolded CFTR from the PM for lysosomal degradation by chaperone-independent K63-linked poly-ubiquitination. RFFL ablation enhanced the functional expression of cell-surface ΔF508-CFTR in the presence of folding corrector molecules, and this effect was further improved by inhibiting the Hsc70-dependent ubiquitination machinery. We propose that multiple peripheral QC mechanisms evolved to dispose of non-native PM proteins and to preserve cellular proteostasis, even at the cost of eliminating partially functional polypeptides.

Keywords: CFTR; cystic fibrosis; endosome; protein quality control; ubiquitination.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cell Membrane / metabolism
  • Cells, Cultured
  • Cystic Fibrosis / genetics
  • Cystic Fibrosis / metabolism*
  • Cystic Fibrosis / pathology
  • Cystic Fibrosis Transmembrane Conductance Regulator / genetics
  • Cystic Fibrosis Transmembrane Conductance Regulator / metabolism*
  • Epithelial Cells / metabolism
  • Gene Knockdown Techniques
  • Humans
  • Lysosomes / metabolism
  • Molecular Chaperones*
  • Mutation
  • Proteolysis
  • RNA, Small Interfering / genetics
  • Ubiquitin / metabolism*
  • Ubiquitin-Protein Ligases / metabolism*
  • Ubiquitination


  • CFTR protein, human
  • Molecular Chaperones
  • RNA, Small Interfering
  • Ubiquitin
  • cystic fibrosis transmembrane conductance regulator delta F508
  • Cystic Fibrosis Transmembrane Conductance Regulator
  • Ubiquitin-Protein Ligases