Abstract
Nuclear factor-κB (NF-κB) has been recognized to play a critical role in cell survival and inflammatory processes. It has become a target for intense drug development for the treatment of cancer, inflammatory, and autoimmune diseases. Here, we describe a potent NF-κB inhibitor, eriocalyxin B (Eri-B), an ent-kauranoid isolated from Isodon eriocalyx, an anti-inflammatory remedy. The presence of two α,β-unsaturated ketones give this compound the uniqueness among the ent-kauranoids tested. Eri-B inhibited the NF-κB transcriptional activity but not that of cAMP response element-binding protein. It suppressed the transcription of NF-κB downstream gene products including cyclooxygenase-2 and inducible nitric-oxide synthase induced by tumor necrosis factor-α or lipopolysaccharide in macrophages and hepatocarcinoma cells. Chromatin immunoprecipitation assay indicated that Eri-B selectively blocked the binding between NF-κB and the response elements in vivo without affecting the nuclear translocation of the transcription factor. Down-regulation of the endogenous p65 protein sensitized the cells toward the action of the compound. Furthermore, in vitro binding assays suggested that Eri-B reversibly interfered with the binding of p65 and p50 subunits to the DNA in a noncompetitive manner. In summary, this study reveals the novel action of a potent NF-κB inhibitor that could be potentially used for the treatment of a variety of NF-κB-associated diseases. Modification of the structure of this class of compounds becomes the key to the control of the behavior of the compound against different cellular signaling pathways.
Footnotes
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Y.-C.C. is a Fellow of the National Foundation for Cancer Research. Part of this work was supported by the Natural Science Foundation of Yunnan Province (2004C0008Z).
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ABBREVIATIONS: NF-κB, nuclear factor-κB; TNF-α, tumor necrosis factor-α; LPS, lipopolysaccharide; PMA, phorbol-12-myristate-13-acetate; FSK, forskolin; IKK, IκB kinase; PCR, polymerase chain reaction; COX-2, cyclooxygenase-2; iNOS, inducible nitric-oxide synthase; ChIP, chromatin immunoprecipitation; EMSA, electrophoretic mobility shift assay; CRE, cAMP response element; MAPK, mitogen-activated protein kinase; ERK1/2, extracellular signal-regulated kinase 1 and 2; Dox, doxycycline; PKC, protein kinase C; NP-40, Nonidet P-40; PAGE, polyacrylamide gel electrophoresis; shRNA, short hairpin RNA; Eri-B, eriocalyxin B; DTT, dithiothreitol; CREB, cAMP response element-binding protein; PS-341, bortezomib.
- Received June 30, 2006.
- Accepted August 29, 2006.
- The American Society for Pharmacology and Experimental Therapeutics
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