Licochalcone A Potently Inhibits Tumor Necrosis Factor ␣- Induced Nuclear Factor-B Activation through the Direct Inhibition of IB Kinase Complex Activation
ABSTRACT Glycyrrhiza inflata has been used as a traditional medicine with anti-inflammatory activity; however, its mechanism has not been fully understood. Licochalcone A is a major and biogenetically characteristic chalcone isolated from G. inflata. Here, we found that licochalcone A strongly inhibited tumor necrosis (TNF)-␣-induced nuclear localization, DNA binding activity, and the transcriptional activity of nuclear factor-B (NF-B). Whereas licochalcone A had no effect on the recruitment of receptor-interacting protein 1 and IB kinase  (IKK) to TNF receptor I by TNF-␣, it significantly inhibited TNF-␣-induced IB kinase complex (IKK) activation and inhibitor of nuclear factor-B degradation. It is interesting that we found that the cysteine residue at position 179 of IKK is essential for licochalcone A-induced IKK inhibition, because licochalcone A failed to affect the kinase activity of the IKK (C179A) mutant. In contrast, a structurally related compound, echinatin, failed to inhibit TNF-␣-induced IKK activation and NF-B activation, suggesting that the 1,1-dimethy-2-propenyl group in licochalcone A is important for the inhibition of NF-B. In addition, TNF-␣-induced expression of inflammatory cytokines CCL2/ monocyte chemotactic protein-1and CXCL1/KC was clearly inhibited by licochalcone A but not echinatin. Taken together, licochalcone A might contribute to the potent anti-inflammatory effect of G. inflata through the inhibition of IKK activation
