Expression of wild-type CFTR suppresses NF-kappaB-driven inflammatory signalling

Mutation of the cystic fibrosis transmembrane-conductance regulator (CFTR) causes cystic fibrosis (CF) but not all CF aspects can easily be explained by deficient ion transport. CF-inflammation provides one example but its pathogenesis remains controversial. Here, we tested the simple but fundamental hypothesis that wild-type CFTR is needed to suppress NF-kappaB activity.

In lung epithelial (H441) and engineered (H57) cell lines; we report that inflammatory markers are significantly suppressed by wild-type CFTR. Transient-transfection of wild-type CFTR into CFTR-naïve H441 cells, dose-dependently down-regulates both basal and Tumour Necrosis Factor-alpha evoked NF-kappaB activity when compared to transfection with empty vector alone (p<0.01, n>5). This effect was also observed in CFTR-naïve H57-HeLa cells which stably express a reporter of NF-kappaB activity, confirming that the CFTR-mediated repression of inflammation was not due to variable reporter gene transfection efficiency. In contrast, H57 cells transfected with a control cyano-fluorescent protein show a significantly elevated basal level of NF-kappaB activity above control. Initial cell seeding density may be a critical factor in mediating the suppressive effects of CFTR on inflammation as only at a certain density (1x10(5) cells/well) did we observe the reduction in NF-kappaB activity. CFTR channel activity may be necessary for this suppression because the CFTR specific inhibitor CFTR(inh172) significantly stimulates NF-kappaB activity by approximately 30% in CFTR expressing 16HBE14o- cells whereas pharmacological elevation of cyclic-AMP depresses activity by approximately 25% below baseline.

These data indicate that CFTR has inherent anti-inflammatory properties. We propose that the hyper-inflammation found in CF may arise as a consequence of disrupted repression of NF-kappaB signalling which is normally mediated by CFTR. Our data therefore concur with in vivo and in vitro data from Vij and colleagues which highlights CFTR as a suppressor of basal inflammation acting through NF-kappaB, a central hub in inflammatory signalling.