Tumor necrosis factor α (TNF-α) induces the activation of transcription factor nuclear factor κB (NF-κB), which upregulates a variety of genes, including the gene encoding intercellular adhesion molecule-1 (ICAM-1). Allantopyrone A, a recently identified α-pyrone metabolite from an endophytic fungus, was found to inhibit the TNF-α-induced expression of ICAM-1 in human lung carcinoma A549 cells. Allantopyrone A also inhibited the TNF-α-induced luciferase expression of an NF-κB-responsive reporter. In the NF-κB signaling pathway, allantopyrone A inhibited the nuclear translocation of NF-κB subunits as well as the phosphorylation and subsequent degradation of the inhibitor of NF-κB (IκB) α proteins. By contrast, allantopyrone A did not directly affect the catalytic activity of active IκB kinase β. These findings indicate that allantopyrone A inhibits the NF-κB signaling pathway at a step upstream of IκBα phosphorylation.

Inflammatory cytokines, such as interleukin-1α (IL-1α) and tumor necrosis factor-α (TNF-α), induce the intracellular signaling pathway leading to the activation of nuclear factor κB (NF-κB). A series of eudesmane-type sesquiterpene lactones possessing an α-methylene γ-lactone group and/or an α-bromo ketone group were synthesized and evaluated for their inhibitory effects on the NF-κB-dependent gene expression and signaling pathway. Our present study reveals that eudesmane-type α-methylene γ-lactones and α-bromo ketones inhibit multiple steps in the NF-κB signaling pathway induced by IL-1α and TNF-α.

Pro-inflammatory cytokines, such as tumor necrosis factor (TNF)-α and interleukin-1α (IL-1α), trigger the activation of the transcription factor nuclear factor-κB, a molecule that induces the expression of a variety of genes, including intercellular adhesion molecule-1 (ICAM-1). Here, we report that mycotrienin II, a member of the triene-ansamycin group, inhibited the cell-surface ICAM-1 expression induced by TNF-α more strongly than that induced by IL-1α in human lung carcinoma A549 cells. Mycotrienin II was found to inhibit protein synthesis in intact living cells, as well as in cell-free translation systems. Among translation inhibitors tested, acetoxycycloheximide and anisomycin, but neither puromycin nor emetine, inhibited the TNF-α-induced ICAM-1 expression at lower concentrations than the IL-1α-induced ICAM-1 expression. Several compounds of the triene-ansamycin group (that is, mycotrienin I, trienomycin A, trierixin, quinotrierixin and quinotrierixin HQ) also inhibited ICAM-1 expression, as well as cell-free translation in a manner similar to mycotrienin II. These results indicate that mycotrienin II is a direct inhibitor of translation, thereby inhibiting ICAM-1 expression induced by pro-inflammatory cytokines.

The transcription factor nuclear factor κB (NF-κB) induces the expression of various inflammatory genes. In the common NF-κB signaling pathway, peperomin E and 2,6-didehydropeperomin B inhibited IκB degradation upon stimulation with TNF-α or interleukin-1. Consistent with these results, peperomin E and 2,6-didehydropeperomin B blocked the TNF-α-induced activation of IκB kinase, while they had no direct effect on the IκB kinase activity. Our present results clearly demonstrate that peperomins inhibit the NF-κB signaling pathway by blocking IκB kinase activation.Peperomin E (3) and 2,6-didehydropeperomin B (4) were found to inhibit the induction of cell-surface intercellular adhesion molecule-1 upon stimulation with tumor necrosis factor-α and interleukin-1.

Pro-inflammatory cytokines, such as tumor necrosis factor-α and interleukin-1, trigger the signal transduction pathway leading to the activation of the transcription factor, nuclear factor-κB (NF-κB). NF-κB induces a large number of target genes involved in many biological processes, such as inflammation, immunity, cell survival, cell death and carcinogenesis. As therapeutic agents for inflammatory diseases and cancer, as well as bioprobes for the characterization of intracellular biological response and cell function, a large number of natural and synthetic small molecules have been identified to inhibit the activation of the NF-κB signaling pathway. This review focuses on recent progress in the identification and biological properties of small molecules targeting the NF-κB signaling pathway induced by pro-inflammatory cytokines.

The 16-membered macrolide FD-891 exerts cytotoxicity toward several cancer cell lines. In this study, we showed that FD-891 induces apoptosis in various human cancer cell lines. Human leukemia Jurkat cells were highly sensitive to FD-891, exhibiting caspase activation and mitochondrial release of cytochrome c into the cytosol at early time points after exposure to FD-891. By contrast, Jurkat cells deficient in caspase-8 were resistant to FD-891-induced apoptosis and manifested little induction of cytochrome c release as well as caspase-9 processing. Consistent with these results, the overexpression of the Bcl-2 family member Bcl-xL or the caspase-8 modulator c-FLIPL markedly prevented FD-891-induced apoptosis. These results clearly demonstrate that FD-891 triggers caspase-8-dependent mitochondrial release of cytochrome c and subsequent apoptosis in Jurkat cells.

The linear pentadecapeptide gramicidin A forms an ion channel in the lipid bilayer to selectively transport monovalent cations. Nevertheless, we have surprisingly found that gramicidin A directly inhibits mammalian Na+/K+-ATPase. Gramicidin A inhibited ATP hydrolysis by Na+/K+-ATPase from porcine cerebral cortex at the IC50 value of 8.1 μM, while gramicidin S was approximately fivefold less active. The synthetic gramicidin A analog lacking N-terminal formylation and C-terminal ethanolamine exhibited a weaker inhibitory effect on the ATP-hydrolyzing activity of Na+/K+-ATPase than gramicidin A, indicating that these end modifications are necessary for gramicidin A to inhibit Na+/K+-ATPase activity. Moreover, Lineweaver–Burk analysis showed that gramicidin A exhibits a mixed type of inhibition. In addition to the most well-studied ionophore activity, our present study has disclosed a novel biological function of gramicidin A as a direct inhibitor of mammalian Na+/K+-ATPase activity.

•Ursolic acid inhibits cell-surface expression of ICAM-1.•Ursolic acid induces accumulation of high-mannose-type ICAM-1 in ER.•Ursolic acid induces morphological changes of Golgi apparatus.•Ursolic acid inhibits intracellular trafficking of proteins.Ursolic acid (3β-hydroxy-urs-12-en-28-oic acid) is a natural pentacyclic triterpenoid that is present in many plants, including medicinal herbs, and foods. Ursolic acid was initially identified as an inhibitor of the expression of intercellular adhesion molecule-1 (ICAM-1) in response to interleukin-1α (IL-1α). We report here a novel biological activity: ursolic acid inhibits intracellular trafficking of proteins. Ursolic acid markedly inhibited the IL-1α-induced cell-surface ICAM-1 expression in human cancer cell lines and human umbilical vein endothelial cells. By contrast, ursolic acid exerted weak inhibitory effects on the IL-1α-induced ICAM-1 expression at the protein level. Surprisingly, we found that ursolic acid decreased the apparent molecular weight of ICAM-1 and altered the structures of N-linked oligosaccharides bound to ICAM-1. Ursolic acid induced the accumulation of ICAM-1 in the endoplasmic reticulum, which was linked mainly to high-mannose-type glycans. Moreover, in ursolic-acid-treated cells, the Golgi apparatus was fragmented into pieces and distributed over the cells. Thus, our results reveal that ursolic acid inhibits intracellular trafficking of proteins and induces the accumulation of ICAM-1 linked to high-mannose-type glycans in the endoplasmic reticulum.Download high-res image (195KB)Download full-size image

In eukaryotes, many translation inhibitors have been widely used as bioprobes to evaluate the contribution of translation to signaling pathways and cellular functions. Several types of translation inhibitors are also known to trigger the activation of the mitogen-activated protein kinase superfamily in an intracellular mechanism called ribotoxic stress response. This perspective focuses on the biological properties of recently identified translation inhibitors that trigger ribotoxic stress response, particularly glutarimides as well as triene-ansamycins.