Suppression of the NF-κB signalling pathway by ergolide, sesquiterpene lactone, in HeLa cells

We have previously reported that ergolide, a sesquiterpene lactone isolated from Inula britannica, suppresses inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) expression by inhibiting nuclear factor-κB (NF-κB) in RAW 264.7 macrophages. In this study, we show that ergolide suppresses the DNA binding activity of NF-κB and nuclear translocation of NF-κB p65 subunit, leading to the inhibition of NF-κB-dependent gene transcription in 12-O-tetradecanoylphorbol 13-acetate (TPA)-stimulated HeLa cells. We also show that ergolide decreases the degradation and phosphorylation of IκB, an inhibitory protein of NF-κB, and this effect is accompanied by a simultaneous reduction of IκB kinase (IKK) activity. However, ergolide does not inhibit in-vitro IKK activity directly, suggesting the possible involvement of upstream IKK kinases in the regulation of NF-κB activation. Furthermore, ergolide-mediated protein kinase Cα (PKCα) inhibition is involved in reduction of NF-κB inhibition, as demonstrated by the observation that dominant negative PKCα, but not p44/42 MAPK and p38 MAPK, inhibits TPA-stimulated reporter gene expression. Taken together, our results suggest that ergolide suppresses NF-κB activation through the inhibition of PKCα-IKK activity, providing insight for PKCα as a molecular target for anti-inflammatory drugs.