Eriocalyxin B selectively inhibits NF-κB activity by targeting multiple steps of the NF-κB activation pathway

Abstract

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NF-κB has been recognized to play a critical role in cell survival and inflammatory processes since its discovery in 1986. It has become a target for intense drug development for the treatment of cancer, inflammatory and autoimmune diseases. Recent progress in the development of NF-κB inhibitors has largely focused on blocking its nuclear translocation. However, compounds such as non-steroidal anti-inflammatory drugs were reported to show nonspecific inhibition. We previously reported the novel action of diterpenoids isolated from Isodon rubescens on the DNA-binding activity of NF-κB. Here we describe a highly selective and potent NF-κB inhibitor, eriocalyxin B isolated from Isodon eriocalyx (an anti-inflammatory remedy), that targets multiple sites of the NF-κB activation pathway in a concentration-dependent manner. Our data showed that eriocalyxin B selectively inhibited both TNFα- and LPS- induced NF-κB activity while it had no significant effect on several other pathways, including PKA, PKC, ERK1/2, p38 and SAPK/JNK, at relevant concentrations (≤ IC₇₅). High concentrations of eriocalyxin B (> IC₇₅) suppressed IKK kinase activity which led to the inhibition of IκB-α phosphorylation, degradation and subsequent NF-κB nuclear translocation. Chromatin immunoprecipitation assays showed for the first time that the drug interfered with the DNA-binding activity of NF-κB to its response DNA sequence in the nucleus at low concentrations (≤ IC₇₅). Electrophoretic mobility shift assays suggest that eriocalyxin B interacted with both p65 and p50 subunits at a site other than the DNA-binding site of NF-κB. In addition, the DNA-binding activity of NF-κB was found to be more susceptible to the action of the drug compared with that of CREB or AP-1. This could account for the selectivity of the compound. The current study reveals the unique properties of this potent and highly selective NF-κB inhibitor which could be used for the treatment of a variety of NF-κB associated diseases. (Yung-Chi Cheng is a Fellow of the National foundation for Cancer Research.)