Fisetin inhibits TNF-α/NF-κB-induced IL-8 expression by targeting PKCδ in human airway epithelial cells.

Fisetin (3,7,3',4'-tetrahydroxyflavone), a natural flavonoid, is a therapeutic agent for respiratory inflammatory diseases such as chronic obstructive pulmonary disease (COPD). However, detailed molecular mechanisms regarding the target protein of fisetin remain unknown. Fisetin significantly reduces tumour necrosis factor alpha (TNF-α)-induced interleukin (IL)-8 levels by inhibiting both nuclear factor kappa B (NF-κB) transcriptional activity and the phosphorylation of its upstream effectors. We show that fisetin prevents interactions between protein kinase C (PKC)δ and TNF receptor-associated factor 2 (TRAF2), thereby inhibiting the inhibitor of kappa B kinase (IKK)/NF-κB downstream signalling cascade. Furthermore, we found that fisetin directly binds to PKCδ in vitro. Our findings provide evidence that fisetin inhibits the TNF-α-activated IKK/NF-κB cascade by targeting PKCδ, thereby mediating inflammatory diseases such as COPD. These data suggest that fisetin is a good therapeutic drug for the treatment of inflammatory lung diseases, such as COPD, by inhibiting the TNF-α/NF-κB signalling pathway.