Withaferin A strongly elicits IκB kinase β hyperphosphorylation concomitant with potent inhibition of its kinase activity

Abstract

The transcription factor NFκB plays a critical role in normal and pathophysiological immune responses. Therefore, NFκB and the signaling pathways that regulate its activation have become a major focus of drug development programs. Withania somnifera (WS) is a medicinal plant that is widely used in Palestine for the treatment of various inflammatory disorders. In this study we show that the leave extract of WS, as well as its major constituent withaferin A (WA), potently inhibits NFκB activation by preventing the tumor necrosis factor-induced activation of IκB kinase β via a thioalkylation-sensitive redox mechanism, whereas other WS-derived steroidal lactones, such as withanolide A and 12-deoxywithastramonolide, are far less effective. To our knowledge, this is the first communication of IκB kinase β inhibition by a plant-derived inhibitor, coinciding with MEK1/ ERK-dependent Ser-181 hyperphosphorylation. This prevents IκB phosphorylation and degradation, which subsequently blocks NFκB translocation, NFκB/DNA binding, and gene transcription. Taken together, our results indicate that pure WA or WA-enriched WS extracts can be considered as a novel class of NFκB inhibitors, which hold promise as novel anti-inflammatory agents for treatment of various inflammatory disorders and/or cancer. © 2007 by The American Society for Biochemistry and Molecular Biology, Inc.