Coatomer Protein I Modulates CFTR (Cystic Fibrosis Transmembrane Conductance Regulator) Folding Maturation

Cystic fibrosis results from mutations in the ABC transporter cystic fibrosis transmembrane conductance regulator (CFTR). In this study, we examined whether the coatomer protein I (COPI) cellular trafficking machinery operates in the maturation of CFTR polypeptide into a functional chloride channel. We employed the mutant temperature‐sensitive cell line ldlF to inhibit COPI function and then examine whether CFTR polypeptide biosynthesized from a transfected gene developed into a cAMP regulated chloride channel. When COPI was inactivated by an elevated temperature pulse, CFTR polypeptide was detected on the cell surface by immunofluorescent microscopy and cell surface biotinylation. However, electrophysiological measurements indicated an absence of cAMP stimulated chloride efflux. In contrast, expression of CFTR at the same elevated temperature pulse in a COPI rescued cell line (ldlF(ldlF)), which harbors an introduced wild‐type ε‐COP gene in addition to the mutant ε‐COP gene, revealed restoration of cAMP stimulated channel activity. These experimental observations therefore imply that generation of the folded‐functional conformation of CFTR requires COPI activity.