Identification of a Novel Blocker of IκBα Kinase That Enhances Cellular Apoptosis and Inhibits Cellular Invasion through Suppression of NF-κB-Regulated Gene Products

Abstract

1′-Acetoxychavicol acetate (ACA), extracted from rhizomes of the commonly used ethno-medicinal plant Languas galanga, has been found to suppress chemical- and virus-induced tumor initiation and promotion through a poorly understood mechanism. Because several genes that regulate cellular proliferation, carcinogenesis, metastasis, and survival are regulated by activation of the transcription factor NF-κB, we postulated that ACA might mediate its activity through modulation of NF-κB activation. For this report, we investigated the effect of ACA on NF-κB and NF-κB-regulated gene expression activated by various carcinogens. We found that ACA suppressed NF-κB activation induced by a wide variety of inflammatory and carcinogenic agents, including TNF, IL-1β, PMA, LPS, H2O2, doxorubicin, and cigarette smoke condensate. Suppression was not cell type specific, because both inducible and constitutive NF-κB activations were blocked by ACA. ACA did not interfere with the binding of NF-κB to the DNA, but, rather, inhibited IκBα kinase activation, IκBα phosphorylation, IκBα degradation, p65 phosphorylation, and subsequent p65 nuclear translocation. ACA also inhibited NF-κB-dependent reporter gene expression activated by TNF, TNFR1, TNFR-associated death domain protein, TNFR-associated factor-2, and IκBα kinase, but not that activated by p65. Consequently, ACA suppressed the expression of TNF-induced NF-κB-regulated proliferative (e.g., cyclin D1 and c-Myc), antiapoptotic (survivin, inhibitor of apoptosis protein-1 (IAP1), IAP2, X-chromosome-linked IAP, Bcl-2, Bcl-xL, Bfl-1/A1, and FLIP), and metastatic (cyclooxygenase-2, ICAM-1, vascular endothelial growth factor, and matrix metalloprotease-9) gene products. ACA also enhanced the apoptosis induced by TNF and chemotherapeutic agents and suppressed invasion. Overall, our results indicate that ACA inhibits activation of NF-κB and NF-κB-regulated gene expression, which may explain the ability of ACA to enhance apoptosis and inhibit invasion.