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, Delta F508, 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 Delta F508 CFTR (Delta FRD) restores the biogenesis of mature Delta F508 CFTR protein. In addition, Delta FRD elicited a cAMP-stimulated anion conductance response in primary human bronchial epithelial (HBE) cells isolated from homozygous Delta F508 CF patients. A protein transduction domain (PTD) could efficiently transduce (similar to 90%) airway epithelial cells. When fused to a PTD, direct addition of the Delta FRD peptide conferred a dose-dependent, cAMP-stimulated anion efflux to Delta F508 HBE cells. Hsp70 and Hsp90 associated equally with WT and Delta F508 CFTR, whereas nearly twice as much of the Hsp90 cochaperone, Aha1, associated with Delta F508 CFTR. Expression of Delta FRD produced a dose-dependent removal of Aha1 from Delta F508 CFTR that correlated with its functional rescue. These findings indicate that disruption of the excessive association of the cochaperone, Aha1, with Delta F508 CFTR is associated with the correction of its maturation, trafficking and regulated anion channel activity in human airway epithelial cells. Thus, PTD-mediated Delta FRD fragment delivery may provide a therapy for CF.