CFTR in a lipid raft-TNFR1 complex modulates gap junctional intercellular communication and IL-8 secretion.

Mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) cause a chronic inflammatory response in the lung of patients with Cystic Fibrosis (CF). We have showed that TNF-alpha signaling through the Src family tyrosine kinases (SFKs) was defective as determined by an inability of TNF-alpha to regulate gap junctional communication (GJIC) in CF cells. Here, we sought to elucidate the mechanisms linking TNF-alpha signaling to the functions of CFTR at the molecular level. In a MDCKI epithelial cell model expressing wild-type (WtCFTR) or mutant CFTR lacking its PDZ-interacting motif (CFTR-DeltaTRL), TNF-alpha increased the amount of WtCFTR but not CFTR-DeltaTRL in detergent-resistant membrane microdomains (DRMs). This recruitment was modulated by SFK activity and associated with DRM localization of TNFR1 and c-Src. Activation of TNFR1 signaling also decreased GJIC and markedly stimulated IL-8 production in WtCFTR cells. In contrast, the absence of CFTR in DRMs was associated with abnormal TNFR1 signaling as revealed by no recruitment of TNFR1 and c-Src to lipid rafts in CFTR-DeltaTRL cells and loss of regulation of GJIC and IL-8 secretion. These results suggest that localization of CFTR in lipid rafts in association with c-Src and TNFR1 provides a responsive signaling complex to regulate GJIC and cytokine signaling.