Review
CFTR: folding, misfolding and correcting the ΔF508 conformational defect

https://doi.org/10.1016/j.molmed.2011.10.003Get rights and content

Cystic fibrosis (CF), the most common lethal genetic disease in the Caucasian population, is caused by loss-of-function mutations of the CF transmembrane conductance regulator (CFTR), a cyclic AMP-regulated plasma membrane chloride channel. The most common mutation, deletion of phenylalanine 508 (ΔF508), impairs CFTR folding and, consequently, its biosynthetic and endocytic processing as well as chloride channel function. Pharmacological treatments may target the ΔF508 CFTR structural defect directly by binding to the mutant protein and/or indirectly by altering cellular protein homeostasis (proteostasis) to promote ΔF508 CFTR plasma membrane targeting and stability. This review discusses recent basic research aimed at elucidating the structural and trafficking defects of ΔF508 CFTR, a prerequisite for the rational design of CF therapy to correct the loss-of-function phenotype.

Section snippets

Cystic fibrosis (CF) and approaches to alleviate the CF clinical phenotype

The cystic fibrosis transmembrane conductance regulator (CFTR) protein is a cyclic AMP (cAMP)-regulated chloride channel expressed in the plasma membrane (PM) of secretory epithelia in the airways, intestine, pancreas, testis and exocrine glands, as well in some non-epithelial cell types. Each CFTR molecule contains two membrane-spanning domains (MSD1 and MSD2), two nucleotide binding domains that participate in ATP binding and hydrolysis (NBD1 and NBD2), and a regulatory domain (R) whose

CFTR domain assembly

In most heterologously expressing cells only 20–40% of newly synthesized CFTR nascent chains attain their native conformation, exit the ER, and undergo complex glycosylation in the Golgi compartment 14, 15. Interestingly, however, the maturation efficiency of CFTR endogenously expressed in two epithelial cell lines was reported to be nearly 100% [16]. Partially folded channels are disposed of by ER-associated degradation (ERAD) via the ubiquitin–proteasome system (UPS) [17]. Although the

Membrane trafficking and functional defects of ΔF508 CFTR

The activity of cellular protein homeostasis networks limits the escape of non-native ΔF508 CFTR from the ER and reduces its metabolic stability at the PM. Modulation of these protein quality control systems by PRs may thus alleviate the ΔF508 CFTR loss-of-function phenotype and be exploited therapeutically [13].

Implications for CF therapy

Correction of defective ΔF508 CFTR folding at the ER by a small molecule is an attractive approach to treat CF because it targets the underlying defect in the appropriate CFTR-expressing cells. In principle, if a PC or PR can modify the ΔF508 CFTR structure to resemble that of WT CFTR, then downstream consequences of defective folding may also be corrected. However, compounds identified thus far have limited efficacy. Because of the complexity of ΔF508 CFTR folding defects discussed above, it

Future perspectives

From the basic science perspective, although there is now a substantial body of data on the biophysics and cellular mechanisms of CFTR folding and ΔF508 CFTR misfolding in vitro, there remain major gaps in our knowledge of how critical components of the quality control machinery recognize the folding defect in tissues. Correctors of ΔF508 CFTR misprocessing have rapidly moved to clinical trials despite even a rudimentary understanding of their mechanism of action. From the translational

Acknowledgments

Work performed in the authors’ laboratories was supported by the Cystic Fibrosis Foundation Therapeutics Inc., Cystic Fibrosis Canada, NIH–NIDDK (National Institutes of Health–National Institute of Diabetes and Digestive and Kidney Diseases), CIHR (Canadian Institute of Health Research) and Canadian Foundation for Innovation. G.L. is holder of a Canada Research Chair. We thank past and present lab members for their invaluable contributions and T. Okiyoneda for careful reading of the manuscript.

Glossary

Complex glycosylated CFTR
N-glycan chain containing fucose, galactose and sialic acid instead of terminal mannose residues, a modification that occurs in Golgi compartments.
Computational screening
virtual screening of compounds by molecular docking computations in which the energetics of compound interaction with a target are calculated using high-resolution crystal structure data for the target.
Core glycosylated CFTR
containing N-glycan chains with terminal mannose residues.
Cysteine (Cys)

References (100)

  • Y. Wang

    Correctors promote maturation of cystic fibrosis transmembrane conductance regulator (CFTR)-processing mutants by binding to the protein

    J. Biol. Chem.

    (2007)
  • B. Kleizen

    Folding of CFTR is predominantly cotranslational

    Mol. Cell

    (2005)
  • A. Khushoo

    Ligand-driven vectorial folding of ribosome-bound human CFTR NBD1

    Mol. Cell

    (2011)
  • H.A. Lewis

    Impact of the deltaF508 mutation in first nucleotide-binding domain of human cystic fibrosis transmembrane conductance regulator on domain folding and structure

    J. Biol. Chem.

    (2005)
  • M. Sharma

    Conformational and temperature-sensitive stability defects of the delta F508 cystic fibrosis transmembrane conductance regulator in post-endoplasmic reticulum compartments

    J. Biol. Chem.

    (2001)
  • P. Bisignano et al.

    Molecular dynamics analysis of the wild type and dF508 mutant structures of the human CFTR-nucleotide binding domain 1

    Biochimie

    (2010)
  • G. Wieczorek et al.

    DeltaF508 mutation increases conformational flexibility of CFTR protein

    J. Cyst. Fibros.

    (2008)
  • L. Cui

    Domain interdependence in the biosynthetic assembly of CFTR

    J. Mol. Biol.

    (2007)
  • T.W. Loo

    Processing mutations disrupt interactions between the nucleotide binding and transmembrane domains of P-glycoprotein and the cystic fibrosis transmembrane conductance regulator (CFTR)

    J. Biol. Chem.

    (2008)
  • L.S. Pissarra

    Solubilizing mutations used to crystallize one CFTR domain attenuate the trafficking and channel defects caused by the major cystic fibrosis mutation

    Chem. Biol.

    (2008)
  • J.L. Brodsky et al.

    Protein folding and quality control in the endoplasmic reticulum: recent lessons from yeast and mammalian cell systems

    Curr. Opin. Cell Biol.

    (2011)
  • J.M. Younger

    Sequential quality-control checkpoints triage misfolded cystic fibrosis transmembrane conductance regulator

    Cell

    (2006)
  • M.J. Henderson

    Ubiquitin C-terminal hydrolase-L1 protects cystic fibrosis transmembrane conductance regulator from early stages of proteasomal degradation

    J. Biol. Chem.

    (2010)
  • H. Caohuy

    Rescue of DeltaF508-CFTR by the SGK1/Nedd4-2 signaling pathway

    J. Biol. Chem.

    (2009)
  • T. Okiyoneda

    Protein quality control at the plasma membrane

    Curr. Opin. Cell Biol.

    (2011)
  • S. Ye

    c-Cbl facilitates endocytosis and lysosomal degradation of cystic fibrosis transmembrane conductance regulator in human airway epithelial cells

    J. Biol. Chem.

    (2010)
  • J.M. Bomberger

    The deubiquitinating enzyme USP10 regulates the post-endocytic sorting of cystic fibrosis transmembrane conductance regulator in airway epithelial cells

    J. Biol. Chem.

    (2009)
  • K.L. Kirk et al.

    A unified view of cystic fibrosis transmembrane conductance regulator (CFTR) gating: combining the allosterism of a ligand-gated channel with the enzymatic activity of an ATP-binding cassette (ABC) transporter

    J. Biol. Chem.

    (2011)
  • M.R. Silvis

    A mutation in the cystic fibrosis transmembrane conductance regulator generates a novel internalization sequence and enhances endocytic rates

    J. Biol. Chem.

    (2003)
  • T. Hegedus

    F508del CFTR with two altered RXR motifs escapes from ER quality control but its channel activity is thermally sensitive

    Biochim. Biophys. Acta

    (2006)
  • H. Yang

    Nanomolar affinity small molecule correctors of defective Delta F508-CFTR chloride channel gating

    J. Biol. Chem.

    (2003)
  • P.L. Zeitlin

    Evidence of CFTR function in cystic fibrosis after systemic administration of 4-phenylbutyrate

    Mol. Ther.

    (2002)
  • X. Wang

    Hsp90 cochaperone Aha1 downregulation rescues misfolding of CFTR in cystic fibrosis

    Cell

    (2006)
  • F. Van Goor

    Rescue of the protein folding defect in cystic fibrosis in vitro by the investigational small molecule, VX-809

    J. Cystic Fibrosis

    (2010)
  • H.M. Sampson

    Identification of a NBD1-binding pharmacological chaperone that corrects the trafficking defect of F508del-CFTR

    Chem. Biol.

    (2011)
  • N. Pedemonte

    Dual activity of aminoarylthiazoles on the trafficking and gating defects of the cystic fibrosis transmembrane conductance regulator chloride channel caused by cystic fibrosis mutations

    J. Biol. Chem.

    (2011)
  • A.D. Mills

    Design and synthesis of a hybrid potentiator-corrector agonist of the cystic fibrosis mutant protein DeltaF508-CFTR

    Bioorg. Med. Chem. Lett.

    (2010)
  • J.R. Riordan

    Assembly of functional CFTR chloride channels

    Annu. Rev. Physiol.

    (2005)
  • J.R. Riordan

    CFTR function and prospects for therapy

    Annu. Rev. Biochem.

    (2008)
  • W. Dalemans

    Altered chloride ion channel kinetics associated with the delta F508 cystic fibrosis mutation

    Nature

    (1991)
  • M.A. Ashlock et al.

    Therapeutics development for cystic fibrosis: a successful model for a multisystem genetic disease

    Annu. Rev. Med.

    (2011)
  • A.W. Cuthbert

    New horizons in the treatment of cystic fibrosis

    Br. J. Pharmacol.

    (2011)
  • Z.W. Cai

    Targeting F508del-CFTR to develop rational new therapies for cystic fibrosis

    Acta Pharmacol. Sin.

    (2011)
  • E.T. Powers

    Biological and chemical approaches to diseases of proteostasis deficiency

    Annu. Rev. Biochem.

    (2009)
  • W.E. Balch

    Emergent properties of proteostasis in managing cystic fibrosis

    Cold Spring Harb. Perspect. Biol.

    (2011)
  • G.L. Lukacs

    Conformational maturation of CFTR but not its mutant counterpart (delta F508) occurs in the endoplasmic reticulum and requires ATP

    EMBO J.

    (1994)
  • A.W. Serohijos

    Phenylalanine-508 mediates a cytoplasmic-membrane domain contact in the CFTR 3D structure crucial to assembly and channel function

    Proc. Natl. Acad. Sci. U.S.A.

    (2008)
  • J.P. Mornon

    Atomic model of human cystic fibrosis transmembrane conductance regulator: membrane-spanning domains and coupling interfaces

    Cell Mol. Life Sci.

    (2008)
  • T.W. Loo

    The V510D suppressor mutation stabilizes DeltaF508-CFTR at the cell surface

    Biochemistry

    (2010)
  • D.E. Grove

    The endoplasmic reticulum-associated Hsp40 DNAJB12 and Hsc70 cooperate to facilitate RMA1 E3-dependent degradation of nascent CFTRDeltaF508

    Mol. Biol. Cell

    (2011)
  • Cited by (298)

    View all citing articles on Scopus
    View full text