Mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene cause cystic fibrosis (CF). The most common mutation, ΔF508, 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 ΔF508 CFTR (ΔFRD) restores the biogenesis of mature ΔF508 CFTR protein. In addition, ΔFRD elicited a cAMP-stimulated anion conductance response in primary human bronchial epithelial (HBE) cells isolated from homozygous ΔF508 CF patients. A protein transduction domain (PTD) could efficiently transduce (∼90%) airway epithelial cells. When fused to a PTD, direct addition of the ΔFRD peptide conferred a dose-dependent, cAMP-stimulated anion efflux to ΔF508 HBE cells. Hsp70 and Hsp90 associated equally with WT and ΔF508 CFTR, whereas nearly twice as much of the Hsp90 cochaperone, Aha1, associated with ΔF508 CFTR. Expression of ΔFRD produced a dose-dependent removal of Aha1 from ΔF508 CFTR that correlated with its functional rescue. These findings indicate that disruption of the excessive association of the cochaperone, Aha1, with ΔF508 CFTR is associated with the correction of its maturation, trafficking and regulated anion channel activity in human airway epithelial cells. Thus, PTD-mediated ΔFRD fragment delivery may provide a therapy for CF. - Sun, F., Mi, Z., Condliffe, S. B., Bertrand, C. A., Gong, X., Lu, X., Zhang, R., Latoche, J. D., Pilewski, J. M., Robbins, P. D., Frizzell, R. A. Chaperone displacement from mutant cystic fibrosis transmembrane conductance regulator restores its function in human airway epithelia.