Abstract
Exposure of macrophages to lipopolysaccharide (LPS) induces release of tumor necrosis factor-α (TNF-α), which is initially synthesized as a 26-kDa pro-TNF-α followed by proteolytic processing to a 17-kDa secreted form. In this study, justicidin A, an arylnaphthalide lignan isolated from Justicia procumbens, was found to inhibit LPS-stimulated TNF-α release from RAW 264.7 macrophages in a concentration- and time-dependent manner, and the underlying mechanism was investigated. In the presence of justicidin A, challenge with LPS increased the steady-state level of the 26-kDa membrane-bound form of TNF-α protein, whereas justicidin A had little effect on the expression of TNF-α mRNA and on the synthesis of pro-TNF-α protein. Results of the pulse-chase experiment, revealed that the conversion of pro-TNF-α to mature TNF-α was inhibited by justicidin A. Moreover, justicidin A suppressed the transport of TNF-α to cell surface as analyzed by flow cytometry. The immunofluorescence analysis demonstrated that large amounts of LPS-induced TNF-α accumulated primarily within Golgi complex. These results indicate that justicidin A inhibits TNF-α release at the step of transport of pro-TNF-α to cell surface, and this leads to the accumulation of TNF-α in Golgi complex in RAW 264.7 macrophages.
- Received August 25, 2003.
- Accepted January 26, 2004.
- The American Society for Pharmacology and Experimental Therapeutics
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