Hsp70 and DNAJA2 limit CFTR levels through degradation.

Patrick Kim Chiaw,Elizabeth Matthes,Renaud Robert,Michael J H Wong,Jason C Young,John W Hanrahan,Christine Hantouche,Alvin Shrier,Jeffrey L Brodsky

doi:10.1371/journal.pone.0220984

Abstract

Cystic Fibrosis is caused by mutations in the CFTR anion channel, many of which cause its misfolding and degradation. CFTR folding depends on the Hsc70 and Hsp70 chaperones and their co-chaperone DNAJA1, but Hsc70/Hsp70 is also involved in CFTR degradation. Here, we address how these opposing functions are balanced. DNAJA2 and DNAJA1 were both important for CFTR folding, however overexpressing DNAJA2 but not DNAJA1 enhanced CFTR degradation at the endoplasmic reticulum by Hsc70/Hsp70 and the E3 ubiquitin ligase CHIP. Excess Hsp70 also promoted CFTR degradation, but this occurred through the lysosomal pathway and required CHIP but not complex formation with HOP and Hsp90. Notably, the Hsp70 inhibitor MKT077 enhanced levels of mature CFTR and the most common disease variant ΔF508-CFTR, by slowing turnover and allowing delayed maturation, respectively. MKT077 also boosted the channel activity of ΔF508-CFTR when combined with the corrector compound VX809. Thus, the Hsp70 system is the major determinant of CFTR degradation, and its modulation can partially relieve the misfolding phenotype.

Highlights

Cystic Fibrosis (CF) is an autosomal recessive genetic disease which results from mutations in the gene encoding the Cystic Fibrosis transmembrane conductance regulator (CFTR, gene ABCC7)
The most prevalent disease mutation is the deletion of phenylalanine 508 (ΔF508-CFTR), which leads to misfolding and retention of the protein in the endoplasmic reticulum (ER) where it is targeted for degradation through the ER associated degradation (ERAD) pathway [3]
Our results outline how the Hsp70 chaperone system is balanced between the folding and degradation of immature and mature CFTR

Summary

Introduction

Cystic Fibrosis (CF) is an autosomal recessive genetic disease which results from mutations in the gene encoding the Cystic Fibrosis transmembrane conductance regulator (CFTR, gene ABCC7). CFTR normally resides at the apical surface of epithelial cells where it mediates the flux of chloride and bicarbonate ions across the membrane [1, 2]. The most prevalent disease mutation is the deletion of phenylalanine 508 (ΔF508-CFTR), which leads to misfolding and retention of the protein in the endoplasmic reticulum (ER) where it is targeted for degradation through the ER associated degradation (ERAD) pathway [3]. CFTR is a member of the ATP-binding cassette (ABC) transporter superfamily which contains 1480 amino acid residues and forms five subdomains; two membrane-spanning domains. Elucidating the molecular mechanisms of CFTR folding and degradation remains a high priority for understanding CF pathogenesis and development of new therapeutics.

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Conclusion