Withaferin A inhibits NF-kappaB activation by targeting cysteine 179 in IKKβ

The transcription factor NF-kappa B is one of the main players involved in inflammatory responses during which NF-kappa B becomes rapidly activated. However to maintain homeostasis, this NF-kappa B activation profile is only transient. Nevertheless deregulation of NF-kappa B activity is often observed and can lead to chronic inflammatory diseases as well as cancer. Therefore various research projects focus on the development of therapeutics that target the NF-kappa B activation pathway. One such compound is Withaferin A from the Ayurvedic plant Withania somnifera. Several reports already described the NF-kappa B inhibiting, anti-inflammatory capacity of WA, either in vitro as well as in vivo. However the underlying molecular mechanism remains largely unknown. In this paper we demonstrate a direct interaction of WA with the IKK-complex, more specifically with IKK beta, a kinase which is indispensable for the nuclear translocation of NF-kappa B. Hereby WA directly inhibits IKK catalytic activity. By mutation of Cys179 in IKK beta we could demonstrate loss of interaction between IKK beta and WA indicating that WA exerts its anti-inflammatory effects by targeting the crucial Cys179 residue located in the catalytic site of IKK beta. Upon docking of WA to a IKK beta homology structure model, WA was found to fit nicely into the groove of IKK beta where it can form hydrogen bond to stabilize its interaction with Cys179. (C) 2014 Elsevier Inc. All rights reserved.