Global proteomic approach unmasks involvement of keratins 8 and 18 in the delivery of cystic fibrosis transmembrane conductance regulator (CFTR)/ΔF508‐CFTR to the plasma membrane

Cystic fibrosis (CF) is a genetic disease caused by mutations in the CF gene ( cftr ). Physiologically, CF is characterized by an abnormal chloride secretion in epithelia due to a dysfunction of a mutated cystic fibrosis transmembrane conductance regulator (CFTR). CFTR is a cAMP‐dependent chloride channel whose most frequent mutation, ΔF508, leads to an aberrantly folded protein which causes a dysfunction of the channel. However, a growing number of reports suggest that modifier genes and environmental factors are involved in the physiology of CF. To identify proteins whose expression depends on wild‐type WT‐CFTR or ΔF508‐CFTR, we chose a global proteomic approach based on the use of two‐dimensional gel electrophoresis (2‐DE) and mass spectrometry. The experiments were carried out with HeLa cells stably transfected with WT‐CFTR (pTCFWT) or ΔF508‐CFTR (pTCFΔF508). These experiments unmasked keratin 8 (K8) and 18 (K18) which were differentially expressed in pTCFWT vs. pTCFΔF508. An immunoblot of K18 confirmed the 2‐DE results. Intracellular localization experiments of WT‐CFTR, ΔF508‐CFTR, K8, and K18 suggest that the expression of these proteins are linked, and that the concentrations of K8 and K18 and/or their distribution may be involved in the traffic of WT‐CFTR/ΔF508‐CFTR. A functional assay for CFTR revealed that specifically lowering K18 expression or changing its distribution leads to the delivery of functional ΔF508‐CFTR to the plasma membrane. This work suggests a novel function of K18 in CF.