The anti-inflammatory sesquiterpene lactone helenalin inhibits the transcription factor NF-κB by directly targeting p65

The sesquiterpene lactone helenalin is a potent antiinflammatory drug whose molecular mechanism of action remains unclear despite numerous investigations. We have previously shown that helenalin and other sesquiterpene lactones selectively inhibit activation of the transcription factor NF-kappa B, a central mediator of the human immune response. These drugs must target a central step in NF-kappa B pathway, since they inhibit NF-kappa B induction by four different stimuli. It has previously been reported that sesquiterpene lactones exert their effect by inhibiting degradation of I kappa B, the inhibitory subunit of NF-kappa B. These data contradicted our report that I kappa B is not detectable in helenalin-treated, ocadaic acid-stimulated cells. Here we use confocal laser scanning microscopy to demonstrate the presence of I kappa B-released, nuclear NF-kappa B in helenalin-treated, tumor necrosis factor-alpha stimulated cells. These data show that neither I kappa B degradation nor NF-kappa B nuclear translocation are inhibited by helenalin. Rather, we provide evidence that helenalin selectively alkylates the p65 subunit of NF-kappa B. This sesquiterpene lactone is the first anti-inflammatory agent shown to exert its effect by directly modifying NF-kappa B.