Anti-inflammatory action of Gibberellin in lung epithelial cells is mediated by modification of NF-κB related kinase expression

Airway inflammation is driven by activation of the transcription factor NF-kB. NF-kB signalling is negatively regulated by the zinc finger protein A20. In Cystic Fibrosis A20 expression / function is significantly reduced and the lack of A20 is associated with reduced lung function (Kelly et al. 2012, 2013). The plant diterpene gibberellin (GA 3 ) has anti-inflammatory properties by induction of A20 and reduction of the NF-κB subunit p65, but A20 itself is NF-κB induced. The pro- and anti-inflammatory effects of NF-κB may be mediated by different activation (phosphorylation) of p65 facilitated by IKKα/β, Glycogen Synthase Kinase 3β (GSK3β) and Tank Binding Kinase 1 (TBK1). We hypothesised that the anti-inflammatory action of GA 3 is mediated by the p65 phosphorylating kinases. Our results with bronchial epithelial cell lines show significantly increased expression of IKKα/β and GSK3β in CF epithelial cells. GA alone induces IKKα/β and TBK1 (8, 4h). Importantly, in CF cells, GA 3 reduces the LPS-induced expression of IKKα/β and GSK3β (8h after LPS). GSK3β is a key regulator of inflammation, phosphorylating p65 on Ser536 and Ser468. In non-activated cells, GSK3β is constitutively active, giving rise to p65 Ser468 phosphorylation, which is associated with negative control of NF-kB. Using A20 induction by Hepatocyte Growth Factor, the 9anti-inflammatory 9 arm of NF-κB has been described to be mediated by inactivation of GSK3β and suppression of p65 Ser468 phosphorylation (Gong et al. 2008). Further work will investigate the effect of GA 3 on p65 phosphorylation and on stimulated epithelial cells from patients with chronic airway disease such as CF and asthma.