CFTR and tight junctions in cultured bronchial epithelial cells

Airway epithelial salt and water transport takes place through paracellular and transcellular pathways. This transport depends critically on the epithelial sodium channel (ENaC) and the cystic fibrosis transmembrane conductance regulator (CFTR), operating in concert with the paracellular pathway through the tight junctions (TJ). Normal (16HBE14o-), cystic fibrosis (CFBE41o-), and corrected CFBE41o- (CFBE41o-pCep4 overexpressing wtCFTR) airway epithelial cell lines were cultured under isotonic conditions. Transepithelial electrical resistance (TEER) was measured as indicator of the tightness of the cultures. Morphology was investigated by immunofluorescence and paracellular permeability by lanthanum nitrate or [14C] mannitol as permeability markers. The CFTR-defective cell line CFBE41o- developed higher TEER than its corrected counterpart CFBE41o-pCep4. Addition of a specific inhibitor of CFTR (CFTR(inh)-172) to 16HBE14o- and CFBE41o-pCep4 cells resulted in a time-dependent increase in TEER, whereas stimulation of CFTR by IBMX and forskolin caused a decrease. Permeability to lanthanum and [14C] mannitol was lower in CFBE41o- and in 16HBE14o- cells exposed to CFTR(inh)-172, compared to untreated 16HBE14o- and CFBE41o-pCep4 cells, respectively. 16HBE14o- cells exposed to IBMX and forskolin showed higher permeability to lanthanum but lower permeability to [14C] mannitol compared to control. Immunofluorescence revealed a disorganization of F-actin and alpha-tubulin in 16HBE14o- cells and CFBE41o- pCep4 exposed to CFTR(inh)-172 and in CFBE41o- cells. Changes in F-actin and alpha-tubulin in 16HBE14o- cells exposed to IBMX and forskolin were also seen. These results suggest the possibility of an interaction between CFTR and the TJ protein complex, probably via the cytoskeleton.