Inhibition of NFκB-Mediated Interleukin-1β-Stimulated Prostaglandin E₂ Formation by the Marine Natural Product Hymenialdisine

Abstract

Exposure of human rheumatoid synovial fibroblasts (RSF) to interleukin 1β (IL-1β) results in the coordinate up-regulation of 85-kDa phospholipase A₂ (PLA₂) and mitogen-inducible cyclooxygenase (COX II) and subsequent biosynthesis of prostaglandin E₂ (PGE₂). We have recently demonstrated, through the use of oligonucleotide decoys and antisense, the participation of the proinflammatory transcription factor, nuclear factor κB (NFκB), in the regulation of the prostanoid-metabolizing enzymes. Hymenialdisine, a marine natural product has recently been characterized as an inhibitor of NFκB activation and exposure of IL-1-stimulated RSF-inhibited PGE₂ production in a concentration-dependent manner (IC₅₀ ∼1 μM). Alternatively, both an analog, aldisine, and the protein kinase C inhibitor, RO 32–0432, were without affect. Direct action of hymenialdisine on IL-1-induced NFκB activation was demonstrated by a significant reduction (∼80%) in NFκB binding to the classical κB consensus motif (as assessed by electrophoretic mobility shift assay) and inhibition of stimulated p65 migration from the cytosol of treated cells (as assessed by Western analysis). Consistent with the role of NFκB in the transcriptional regulation of COX II and 85-kDa PLA₂, hymenialdisine-treated RSF did not transcribe the respective mRNAs in response to IL-1. This led to reductions in their respective protein levels and subsequent reductions in the ability to produce PGE₂. Specificity of action is suggested as IL-1-stimulated interleukin-8 (IL-8) production, which is known to be an NFκB-regulated event, was also inhibited by hymenialdisine, whereas IL-1-induced production of vascular endothelial growth factor, a non-NFκB-regulated gene, was not affected by exposure to hymenialdisine. Taken together, hymenialdisine inhibits IL-1-stimulated-RSF PGE₂ formation acting predominately through modulation of NFκB activation and offers an interesting novel tool to evaluate the role of NFκB in inflammatory disease.