Butein, a tetrahydroxychalcone, inhibits nuclear factor (NF)-κB and NF-κB-regulated gene expression through direct inhibition of IκBα kinase β on cysteine 179 residue

Although butein (3,4,2′,4′-tetrahydroxychalcone) is known to exhibit anti-inflammatory, anti-cancer, and anti-fibrogenic activities, very little is known about its mechanism of action. Because numerous effects modulated by butein can be linked to interference with the NF-κB pathway, we investigated in detail the effect of this chalcone on NF-κB activity. As examined by DNA binding, we found that butein suppressed tumor necrosis factor (TNF)-induced NF-κB activation in a dose- and time-dependent manner; suppressed the NF-κB activation induced by various inflammatory agents and carcinogens; and inhibited the NF-κB reporter activity induced by TNFR1, TRADD, TRAF2, NIK, TAK1/TAB1, and IKK-β. We also found that butein blocked the phosphorylation and degradation of IκBα by inhibiting IκBα kinase (IKK) activation. We found the inactivation of IKK by butein was direct and involved cysteine residue 179. This correlated with the suppression of phosphorylation and the nuclear translocation of p65. In this study, butein also inhibited the expression of the NF-κB-regulated gene products involved in anti-apoptosis (IAP2, Bcl-2, and Bcl-xL), proliferation (cyclin D1 and c-Myc), and invasion (COX-2 and MMP-9). Suppression of these gene products correlated with enhancement of the apoptosis induced by TNF and chemotherapeutic agents; and inhibition of cytokine-induced cellular invasion. Overall, our results indicated that antitumor and anti-inflammatory activities previously assigned to butein may be mediated in part through the direct inhibition of IKK, leading to the suppression of the NF-κB activation pathway.