Chlorogenic acid inhibits proliferation in human hepatoma cells by suppressing noncanonical NF-κB signaling pathway and triggering mitochondrial apoptosis

Chlorogenic acid (CGA), a phenylpropanoid derived from Eucommia ulmoides Oliver, has been shown to exhibit potent cytotoxic and anti-proliferative activities against several human cancers. However, the effects of CGA on hepatocellular carcinoma (HCC) and the underlying mechanisms have not been intensively studied. In this study, the CGA treatment effects on the viability of human hepatoma cells were investigated by MTT assay. Our data showed that CGA could dose-dependently inhibit the activity of human hepatoma cells Hep-G2 and Huh-7, but did not affect the activity and growth of normal human hepatocyte QSG-7701. The genes and pathways influenced by CGA treatment were explored by RNA sequencing and bioinformatics analysis, which identified 323 differentially expressed genes (DEGs) involved in multiple pharmacological signaling pathways such as MAPK, NF-κB, apoptosis and TGF-β signaling pathways. Further analyses by real-time quantitative PCR, Western blot and flow cytometry revealed that CGA effectually suppressed the noncanonical NF-κB signaling pathway, meanwhile it activated the mitochondrial apoptosis of HCC by upregulation of the BH3-only protein Bcl-2 binding component 3 (BBC3). Our findings demonstrated the potential of CGA in suppressing human hepatoma cells and provided a new insight into the anti-cancer mechanism of CGA.

     

Microtubule-mediated NF-κB activation in the TNF-α signaling pathway

The microtubule cytoskeleton is known to play a role in cell structure and serve as a scaffold for a variety of active molecules in processes as diverse as motility and cell division. The literature on the role of microtubules in signal transduction, however, is marked by inconsistencies. We have investigated a well-studied signaling pathway, TNF-α-induced NF-κB activation, and found a connection between the stability of microtubules and the regulation of NF-κB signaling in C2C12 myotubes. When microtubules are stabilized by paclitaxel (taxol), there is a strong induction of NF-κB even in the absence of TNF-α . Although there was no additive effect of taxol and TNF-α on NF-κB activity suggesting a shared mechanism of activation, taxol strongly induced the NF-κB reporter in the presence of a TNF receptor (TNFR) blocking antibody while TNF-α did not. Both TNF-α and taxol induce the degradation of endogenous IκBα and either taxol or TNF-α induction of NF-κB activity was blocked by inhibitors of NF-κB acting at different sites in the signaling pathway. Both TNF-α and taxol strongly induce known NF-κB chemokine target genes. On the other hand, if microtubules are destabilized by colchicine, then the induction of NF-κB by TNF-α or taxol is greatly reduced. Taken together, we surmise that the activity of microtubules is at the level of the TNFR intracellular domain. This phenomenon may indicate a new level of signaling organization in cell biology, actively created by the state of the cytoskeleton, and has ramifications for therapies where microtubule regulating drugs are used.     

Jolkinolide B inhibits RANKL-induced osteoclastogenesis by suppressing the activation NF-κB and MAPK signaling pathways

Osteoclasts together with osteoblasts play pivotal roles in bone remodeling. The unique function and ability of osteoclasts to resorb bone makes them critical in both normal bone homeostasis and pathologic bone diseases such as osteoporosis and rheumatoid arthritis. Thus, new compounds that may inhibit osteoclastogenesis and osteoclast function may be of great value in the treatment of osteoclast-related diseases. In the present study, we examined the effect of jolkinolide B (JB), isolated from the root of Euphorbia fischeriana Steud on receptor activator of NF-κB ligand (RANKL)-induced osteoclast formation. We found that JB inhibited RANKL-induced osteoclast differentiation from bone marrow macrophages (BMMs) without cytotoxicity. Furthermore, the expression of osteoclastic marker genes, such as tartrate-resistant acid phosphatase (TRAP), cathepsin K (CtsK), and calcitonin receptor (CTR), was significantly inhibited. JB inhibited RANKL-induced activation of NF-κB by suppressing RANKL-mediated IκBα degradation. Moreover, JB inhibited RANKL-induced phosphorylation of mitogen-activated protein kinases (p38, JNK, and ERK). This study thus identifies JB as an inhibitor of osteoclast formation and provides evidence that JB might be an alternative medicine for preventing and treating osteolysis.     

Omentin inhibits TNF-α-induced expression of adhesion molecules in endothelial cells via ERK/NF-κB pathway

In the present study, we investigated whether omentin affected the expression of intracellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) in tumor necrosis factor-α (TNF-α) induced human umbilical vein endothelial cells (HUVECs). Our data showed that omentin decreased TNF-α-induced expression of ICAM-1 and VCAM-1 in HUVECs. In addition, omentin inhibited TNF-α-induced adhesion of THP-1 cells to HUVECs. Further, we found that omentin inhibited TNF-α-activated signal pathway of nuclear factor-κB (NF-κB) by preventing NF-κB inhibitory protein (IκBα) degradation and NF-κB/DNA binding activity. Omentin pretreatment significantly inhibited TNF-α-induced ERK activity and ERK phosphorylation in HUVECs. Pretreatment with PD98059 suppressed TNF-α-induced NF-κB activity. Omentin, NF-kB inhibitor (BAY11-7082) and ERK inhibitor (PD98059) reduced the up-regulation of ICAM-1 and VCAM-1 induced by TNF-α. These results suggest that omentin may inhibit TNF-α-induced expression of adhesion molecules in endothelial cells via blocking ERK/NF-κB pathway.     

ANKRD49 inhibits etoposide-induced intrinsic apoptosis of GC-1 cells by modulating NF-κB signaling

Molecular and Cellular Biochemistry - The osteogenic differentiation of dental follicle cells (DFCs) is inhibited by the onset of cellular senescence, but the cause for this is largely unknown....     

Enterovirus 71 2C protein inhibits TNF-α-mediated activation of NF-κB by suppressing IκB kinase β phosphorylation

Enterovirus 71 (EV71), a single, positive-stranded RNA virus, has been regarded as the most important neurotropic enterovirus after the eradication of the poliovirus. EV71 infection can cause hand, foot, and mouth disease or herpangina. Cytokine storm with elevated levels of proinflammatory and inflammatory cytokines, including TNF-α, has been proposed to explain the pathogenesis of EV71-induced disease. TNF-α-mediated NF-κB signaling pathway plays a key role in inflammatory response. We hypothesized that EV71 might also moderate host inflammation by interfering with this pathway. In this study, we tested this hypothesis and identified EV71 2C protein as an antagonist of TNF-α-mediated activation of NF-κB signaling pathway. Expression of 2C protein significantly reduced TNF-α-mediated NF-κB activation in 293T cells as measured by gene reporter and gel mobility shift assays. Furthermore, overexpression of TNFR-associated factor 2-, MEK kinase 1-, IκB kinase (IKK)α-, or IKKβ-induced NF-κB activation, but not constitutively active mutant of IKKβ (IKKβ SS/EE)-induced NF-κB activation, was inhibited by 2C protein. These data together suggested that the activation of IKKβ is most likely targeted by 2C; this notion was further strengthened by immunoblot detection of IKKβ phosphorylation and IκBα phosphorylation and degradation. Coimmunoprecipitation and colocalization of 2C and IKKβ expressed in mammalian cells provided compelling evidence that 2C interacts with IKKβ. Collectively, our data indicate that EV71 2C protein inhibits IKKβ activation and thus blocks NF-κB activation.     

TRIM22 inhibits the TRAF6-stimulated NF-κB pathway by targeting TAB2 for degradation

Tripartite motif containing 22 (TRIM22), a member of the TRIM/RBCC family, has been reported to activate the nuclear factor-kappa B (NF-κB) pathway in unstimulated macrophage cell lines, but the detailed mechanisms governing this activation remains unclear. We investigated this mechanism in HEK293T cells. We found that overexpression of TRIM22 could activate the NF-κB pathway and conversely, could inhibit the tumor necrosis factor receptor-associated factor 6 (TRAF6)-stimulated NF-κB pathway in HEK293T cells. Further experiments showed that TRIM22 could decrease the self-ubiquitination of TRAF6, and interact with and degrade transforming growth factor-β activated kinase 1 binding protein 2 (TAB2), and that these effects could be partially rescued by a TRIM22 RING domain deletion mutant. Collectively, our data indicate that overexpression of TRIM22 may negatively regulate the TRAF6-stimulated NF-κB pathway by interacting with and degrading TAB2.     

Knockdown of TRAF6 inhibits chondrocytes apoptosis and inflammation by suppressing the NF-κB pathway in lumbar facet joint osteoarthritis

Molecular and Cellular Biochemistry - Tumor necrosis factor receptor-associated factor 6 (TRAF6), a regulator of NF-κB signaling, has been discovered recently to be probably related to...