Exposure of human rheumatoid synovial fibroblasts (RSF) to interleukin 1beta (IL-1beta) 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 kappaB (NFkappaB), in the regulation of the prostanoid-metabolizing enzymes. Hymenialdisine, a marine natural product has recently been characterized as an inhibitor of NFkappaB activation and exposure of IL-1-stimulated RSF-inhibited PGE2 production in a concentration-dependent manner (IC50 approximately 1 microM). 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 NFkappaB activation was demonstrated by a significant reduction (approximately 80%) in NFkappaB binding to the classical kappaB 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 NFkappaB 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 NFkappaB-regulated event, was also inhibited by hymenialdisine, whereas IL-1-induced production of vascular endothelial growth factor, a non-NFkappaB-regulated gene, was not affected by exposure to hymenialdisine. Taken together, hymenialdisine inhibits IL-1-stimulated-RSF PGE2 formation acting predominately through modulation of NFkappaB activation and offers an interesting novel tool to evaluate the role of NFkappaB in inflammatory disease.