NF-kB activation in cystic fibrosis: The dream of A20

Abstract

Chronic, exaggerated inflammation in response to infection is characteristic for Cystic Fibrosis (CF) lung disease. Novel CF therapeutics overcome the underlying functional defect in the cystic fibrosis transmembrane conductance regulator (CFTR), but inflammatory markers in sputum remain significantly elevated. Therefore, there is still an unmet need to normalise the inflammatory response. Prolonged/heightened inflammation in CF is mediated by NF-kB and a lack of its regulator A20 (TNFAIP3). Recently, Downstream Regulatory Element Antagonist Modulator (DREAM) has been described as a transcriptional repressor of A20. We hypothesized that higher levels of A20 repressing DREAM contribute to the pro-inflammatory phenotype in CF airway cells. We used airway epithelial cells with/without CFTR mutation to determine A20 and DREAM expression (mRNA, nuclear protein, DNA binding). Results: CF epithelial cells show significantly higher DREAM expression (mRNA/protein), which was associated with significantly lowers levels of A20. We found increased nuclear DREAM protein and increased nuclear expression of the transcriptionally repressing DREAM tetramer in CF airway epithelial cells. ChIP assay confirmed increased and persistent binding of DREAM to its DNA binding site in the TNFAIP3 promoter. Knockdown of DREAM in CF airway cells (siRNA) increased lipopolysaccharide-induced A20 expression and reduced interleukin (IL)-8 release, confirming the action of DREAM. In conclusion, high expression of the repressor DREAM inhibits A20 transcription in CF epithelial cells. Our work suggests an important role of the A20-DREAM axis in (innate) inflammation, providing a new molecular target for the development of innovative anti-inflammatory therapies.