Cystic fibrosis (CF) is a fatal, autosomal, recessive genetic disease that is characterized by profound lung inflammation. The inflammatory process is believed to be caused by massive overproduction of the proinflammatory protein IL-8, and the high levels of IL-8 in the CF lung are therefore believed to be the central mechanism behind CF lung pathophysiology. We show here that digitoxin, at sub nM concentrations, can suppress hypersecretion of IL-8 from cultured CF lung epithelial cells. Certain other cardiac glycosides are also active but with much less potency. The specific mechanism of digitoxin action is to block phosphorylation of the inhibitor of NF-B (I B␣). I B␣ phosphorylation is a required step in the activation of the NF-B signaling pathway and the subsequent expression of IL-8. Digitoxin also has effects on global gene expression in CF cells. Of the informative genes expressed by the CF epithelial cell line IB-3, 58 are significantly (P < 0.05) affected by gene therapy with wild-type (CFTR CF transmembrane conductance regulator). Of these 58 genes, 36 (62%) are similarly affected by digitoxin and related active analogues. We interpret this result to suggest that digitoxin can also partially mimic the genomic consequences of gene therapy with CF transmembrane conductance regulator. We therefore suggest that digitoxin, with its lengthy history of human use, deserves consideration as a candidate drug for suppressing IL-8-dependent lung inflammation in CF.

GLME had a beneficial effect on the clinical signs of dogs presumptively diagnosed with mild-to-moderate DJD. Long-term therapy may be required before improvement is apparent.

Background/Aims: Chronic lung infection in cystic fibrosis leads to an inflammatory response that persists because of the chronic presence of bacteria and ultimately leads to a catastrophic failure of lung function. Methods: We use a combination of biochemistry, cell and molecular biology to study the interaction of TRADD, a key adaptor molecule in TNFα signaling, with CFTR in the regulation of NFκB. Results: We show that Wt CFTR binds to and colocalizes with TRADD. TRADD is a key signaling intermediate connecting TNFα with activation of NFκB. By contrast, ΔF508 CFTR does not bind to TRADD. NF-κB activation is higher in CFBE expressing ΔF508 CFTR than in cells expressing Wt CFTR. However, this differential effect is abolished when TRADD levels are knocked down. Transfecting Wt CFTR into CFBE cells reduces NF-κB activity. However the reduction is abolished by the CFTR chloride transport inhibitor-172. Consistently, transfecting in the correctly trafficked CFTR conduction mutants G551D or S341A also fail to reduce NFκB activity. Thus CFTR must be functional if it is to regulate NF-κB activity. We also found that TNFα produced a greater increase in NF-κB activity in CFBE cells than in the same cell when Wt CFTR-corrected. Consistently, the effect is also abolished when TRADD is knocked down by shRNA. Thus, Wt CFTR control of TRADD modulates the physiological activation of NF-κB by TNFα. Based on studies with proteosomal and lysosomal inhibitors, the mechanism by which Wt CFTR, but not ΔF508 CFTR, suppresses TRADD is by lysosomal degradation. Conclusion: We have uncovered a novel mechanism whereby Wt CFTR regulates TNFα signaling by enhancing TRADD degradation. Thus by reducing the levels of TRADD, Wt CFTR suppresses downstream proinflammatory NFκB signaling. By contrast, suppression of NF-κB activation fails in CF cells expressing ΔF508 CFTR.