Cardamonin Inhibits the Nuclear Translocation and DNA Binding of RelA in the Tumor Necrosis Factor-α-Induced NF-κB Signaling Pathway in Human Lung Adenocarcinoma A549 Cells

Tumor necrosis factor α (TNF-α) activates the nuclear factor κB (NF-κB) signaling pathway, which promotes the expression of NF-κB-responsive genes, including intercellular adhesion molecule 1 (ICAM-1). We previously reported that cardamonin, a chalcone-type flavonoid, inhibited TNF-α-induced ICAM-1 expression in human lung adenocarcinoma A549 cells. However, the mechanisms by which cardamonin inhibits the TNF-α-induced NF-κB signaling pathway have yet to be elucidated. Therefore, we herein investigated the effects of cardamonin on TNF-α-induced gene expression and the NF-κB-dependent signaling pathway. Cardamonin reduced TNF-α-induced ICAM-1 mRNA expression and NF-κB reporter activity. It did not affect the inhibitor of NF-κB α (IκBα) degradation, but prevented RelA nuclear translocation and binding to the ICAM-1 promoter. Consistent with this result, three other chalcone derivatives (4'-hydroxychalcone, isoliquiritigenin, and xanthohumol) did not affect the degradation of IκBα, but inhibited nuclear RelA translocation. Cardamonin exhibited the same inhibitory profiles in human breast cancer MCF-7 cells and human fibrosarcoma HT-1080 cells. Cysteine 38 (C38) of RelA was not a primary target site of cardamonin because cardamonin inhibited the nuclear translocation of the RelA C38S mutant. An <i>in silico</i> molecular docking analysis confirmed that cardamonin was not positioned close enough to RelA C38 to mediate covalent binding, and also that cardamonin interacted with RelA at different sites. Mutations in these interaction sites abrogated the nuclear translocation of RelA in response to a TNF-α stimulation. The present results demonstrate that cardamonin inhibited the nuclear translocation of RelA and its DNA binding in the NF-κB signaling pathway in response to a TNF-α stimulation.