Induction of the inflammatory regulator A20 by gibberellic acid in airway epithelial cells

Abstract

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

Connectivity mapping (ssCMap) to predict A20-inducing drugs and their antiinflammatory action in cystic fibrosis

“…Karakoline is a highly toxic plant diterpenoid (32), and the pharmacological effects of preparations of Aconitum roots are attributed to diterpenoid alkaloids (33). The antiinflammatory activity of gibberellin (GA 3 ), also a plant-derived diterpenoid, is mediated through A20 induction (24). We therefore selected ikarugamycin and quercetin for further studies.…”

“…GA 3 induced A20, reduced IL-8 secretion, stabilized cytosolic IkBα, and reduced NF-κB (p65) activation (24). Here we set out to identify additional compounds able to induce A20.…”

Chronic Inflammation in CF Airways - A Persistent Issue for A20

“…Therefore, the apparent lack of A20 described in epithelial cells of patients with CF and asthma [23,40] has important implications for the overall immune responses in these chronic airway diseases. Not surprisingly, A20 has recently been identified as a target enzyme for new anti-inflammatory drugs [41,42].…”

“…Using airway epithelial cells (cell lines and primary cells from control subjects), we have previously shown that pharmacological induction of A20 through the plant diterpenoid gibberellin (GA 3 ) is antiinflammatory [42]. Furthermore, using an advanced bioinformatics approach that established the link between disease-specific gene expression and the gene modification through already licensed drugs, statistically significant connections Map (sscMap) [44] we were able to predict drugs already licenced for the use in humans, which through the process of drug repositioning could be made available to CF patients.…”

“…Primary nasal epithelial cells (PNECs) from healthy volunteers and CF patients (all F508del/F508del) were cultured as described [42]. Control participants did not have any acute airways disease at the time of sampling, or a history of any chronic airways inflammation.…”