Chaperone displacement from mutant cystic fibrosis transmembrane conductance regulator restores its function in human airway epithelia.

Mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene cause cystic fibrosis (CF). The most common mutation, DeltaF508, omits the phenylalanine residue at position 508 in the first nucleotide binding domain (NBD1) of CFTR. The mutant protein is retained in the endoplasmic reticulum and degraded by the ubiquitin-proteasome system. We demonstrate that expression of NBD1 plus the regulatory domain (RD) of DeltaF508 CFTR (DeltaFRD) restores the biogenesis of mature DeltaF508 CFTR protein. In addition, DeltaFRD elicited a cAMP-stimulated anion conductance response in primary human bronchial epithelial (HBE) cells isolated from homozygous DeltaF508 CF patients. A protein transduction domain (PTD) could efficiently transduce (approximately 90%) airway epithelial cells. When fused to a PTD, direct addition of the DeltaFRD peptide conferred a dose-dependent, cAMP-stimulated anion efflux to DeltaF508 HBE cells. Hsp70 and Hsp90 associated equally with WT and DeltaF508 CFTR, whereas nearly twice as much of the Hsp90 cochaperone, Aha1, associated with DeltaF508 CFTR. Expression of DeltaFRD produced a dose-dependent removal of Aha1 from DeltaF508 CFTR that correlated with its functional rescue. These findings indicate that disruption of the excessive association of the cochaperone, Aha1, with DeltaF508 CFTR is associated with the correction of its maturation, trafficking and regulated anion channel activity in human airway epithelial cells. Thus, PTD-mediated DeltaFRD fragment delivery may provide a therapy for CF.