Background and Purpose NF‐κB‐driven inflammation is negatively regulated by the zinc finger protein A20. Gibberellic acid (GA3) is a plant‐derived diterpenoid with documented anti‐inflammatory activity, which is reported to induce A20‐like zinc finger proteins in plants. Here, we sought to investigate the anti‐inflammatory effect of GA3 in airway epithelial cells and determine if the anti‐inflammatory action relates to A20 induction. Experimental Approach Primary nasal epithelial cells and a human bronchial epithelial cell line (16HBE14o‐) were used. Cells were pre‐incubated with GA3, stimulated with Pseudomonas aeruginosa LPS; IL‐6 and IL‐8 release, A20, NF‐κB and IκBα expression were then evaluated. To determine if any observed anti‐inflammatory effect occurred via an A20‐dependent mechanism, A20 was silenced using siRNA. Key Results Cells pre‐incubated with GA3 had significantly increased levels of A20 mRNA (4 h) and protein (24 h), resulting in a significant reduction in IL‐6 and IL‐8 release. This effect was mediated via reduced IκBα degradation and reduced NF‐κB (p65) expression. Furthermore, the anti‐inflammatory action of GA3 was abolished in A20‐silenced cells. Conclusions and Implications We showed that A20 induction by GA3 attenuates inflammation in airway epithelial cells, at least in part through its effect on NF‐κB and IκBα. GA3 or gibberellin‐derived derivatives could potentially be developed into anti‐inflammatory drugs for the treatment of chronic inflammatory diseases associated with A20 dysfunction. Linked Articles This article is part of a themed section on Inflammation: maladies, models, mechanisms and molecules. To view the other articles in this section visit 10.1111/bph.2016.173.issue-4

Prevotella spp. are frequently identified in Cystic Fibrosis sputum. This study examined whether infection with Prevotella nigrescens, a frequently identified member of this species, contributes to inflammation in CF bronchial epithelial cells through activation of TLR-and NF-κB signalling pathways. CFBE41o-cells were infected with either P.nigrescens or Pseudomonas aeruginosa and incubated under anaerobic conditions for 4 hours. P.nigrescens activated TLR2 signalling but not TLR4 signalling while P.aeruginosa activated TLR4 signalling with a lesser effect on TLR2. P.aeruginosa induced significant IκBα phosphorylation 10 minutes post infection with a return to control levels by 30 minutes post infection. A significant induction in nuclear p65 DNA binding was observed at 2 hours post infection. In contrast, infection with P.nigrescens induced phosphorylation of IκBα 120 minutes post infection, with significant induction in nuclear p65 DNA binding at 4 hours post infection only. Cytokine gene and protein responses were lower for P.nigrescens compared to P.aeruginosa. This study demonstrates the ability of a clinical P.nigrescens isolate to provoke a delayed NF-κB(p65) driven response through induction in TLR2 signalling and activation of sustained levels of IKKα.

Cystic Fibrosis (CF), caused by mutations affecting the CFTR gene, is characterised by viscid secretions in multiple organ systems. CF airways contain thick mucus, creating a gradient of hypoxia, which promotes the establishment of polymicrobial infection. Such inflammation predisposes to further infection, a self-perpetuating cycle in mediated by NF-κB. Anaerobic Gram-negative Prevotella spp. are found in sputum from healthy volunteers and CF patients and in CF lungs correlate with reduced levels of inflammation. Prevotella histicola (P. histicola) can suppress murine lung inflammation, however, no studies have examined the role of P. histicola in modulating infection and inflammation in the CF airways. We investigated innate immune signalling and NF-kB activation in CF epithelial cells CFBE41o-in response to clinical stains of P. histicola and Pseudomonas aeruginosa (P. aeruginosa). Toll-Like Receptor (TLR) expressing HEK-293 cells and siRNA assays for TLRs and IKKα were used to confirm signalling pathways. We show that P. histicola infection activated the alternative NF-kB signalling pathway in CF bronchial epithelial cells inducing HIF-1α protein. TLR5 signalling was responsible for the induction of the alternative NF-kB pathway through phosphorylation of IKKα. The induction of transcription factor HIF-1α was inversely associated with the induction of the alternative NF-kB pathway and knockdown of IKKα partially restored canonical NF-kB activation in response to P. histicola. This study demonstrates that different bacterial species in the respiratory microbiome can contribute differently to inflammation, either by activating inflammatory cascades (P. aeruginosa) or by muting the inflammatory response by modulating similar or related pathways (P. histicola). Further work is required to assess the complex interactions of the lung microbiome in response to mixed bacterial infections and their effects in people with CF.