Regulation of the mouse gene encoding TAFI by TNFα: role of NFκB binding site

Thrombin-activable fibrinolysis inhibitor (TAFI) is a plasma pro-carboxypeptidase, encoded by the gene CPB2, with roles in both inhibition of fibrinolysis and inflammation. In mice, plasma TAFI levels and hepatic CPB2 mRNA expression were found to increase within 24h after intra-peritoneal lipopolysaccharide (LPS) injection. On the other hand, plasma TAFI in humans decrease in experimental endotoxemia and sepsis and we have previously demonstrated that CPB2 mRNA abundance in human hepatoma cells is decreased by inflammatory cytokines. Here, we have evaluated the effects of TNFα on mouse CPB2 expression. Treatment of primary mouse hepatocytes or the mouse hepatic cell line FL83B with TNFα for 12-48h resulted in increases in CPB2 mRNA abundance of up to 2-fold; mouse TAFI protein levels secreted from FL83B cells increased 2.7-fold after 48h treatment with TNFα. When FL83B cells were transfected with reporter plasmids containing the mouse CPB2 5'-flanking region, treatment with TNFα for 24 and 48h resulted in a 1.5-fold increased mouse CPB2 promoter activity. Mutation of a putative NFκB site not conserved in the human gene ablated the increased promoter activity observed following TNFα treatment. This site binds NFκB as assessed by gel mobility shift assays, and TNFα treatment increases the translocation of NFκB from the cytoplasm to the nucleus of mouse hepatocytes. These results demonstrate that the unique NFκB site in the mouse CPB2 promoter is functional and mediates the upregulation of mouse CPB2 expression by TNFα via increase in NFκB translocation to the nucleus.     

HSP70 interacts with TRAF2 and differentially regulates TNFα signalling in human colon cancer cells

Members of tumour necrosis factor (TNF) family usually trigger both survival and apoptotic signals in various cell types. Heat shock proteins (HSPs) are conserved proteins implicated in protection of cells from stress stimuli. However, the mechanisms of HSPs in TNFα‐induced signalling pathway have not been fully elucidated. We report here that HSP70 over‐expression in human colon cancer cells can inhibit TNFα‐induced NFκB activation but promote TNFα‐induced activation of c‐Jun N‐terminal kinase (JNK) through interaction with TNF receptor (TNFR)‐associated factor 2 (TRAF2). We provide evidence that HSP70 over‐expression can sequester TRAF2 in detergent‐soluble fractions possibly through interacting with TRAF2, leading to reduced recruitment of receptor‐interacting protein (RIP1) and IκBα kinase (IKK) signalosome to the TNFR1–TRADD complex and inhibited NFκB activation after TNFα stimuli. In addition, we found that HSP70–TRAF2 interaction can promote TNFα‐induced JNK activation. Therefore, our study suggests that HSP70 may differentially regulate TNFα‐induced activation of NFκB and JNK through interaction with TRAF2, contributing to the pro‐apoptotic roles of HSP70 in TNFα‐induced apoptosis of human colon cancer cells.     

p97/VCP promotes Cullin‐RING‐ubiquitin‐ligase/proteasome‐dependent degradation of IκBα and the preceding liberation of RelA from ubiquitinated IκBα

Cullin‐RING‐ubiquitin‐ligase (CRL)‐dependent ubiquitination of the nuclear factor kappa B (NF‐κB) inhibitor IκBα and its subsequent degradation by the proteasome usually precede NF‐κB/RelA nuclear activity. Through removal of the CRL‐activating modification of their cullin subunit with the ubiquitin (Ub)‐like modifier NEDD8, the COP9 signalosome (CSN) opposes CRL Ub‐ligase activity. While RelA phosphorylation was observed to mediate NF‐κB activation independent of Ub‐proteasome‐pathway (UPP)‐dependent turnover of IκBα in some studies, a strict requirement of the p97/VCP ATPase for both, IκBα degradation and NF‐κB activation, was reported in others. In this study, we thus aimed to reconcile the mechanism for tumour necrosis factor (TNF)‐induced NF‐κB activation. We found that inducible phosphorylation of RelA is accomplished in an IKK‐complex‐dependent manner within the NF‐κB/RelA‐IκBα‐complex contemporaneous with the phosphorylation of IκBα, and that RelA phosphorylation is not sufficient to dissociate NF‐κB/RelA from IκBα. Subsequent to CRL‐dependent IκBα ubiquitination functional p97/VCP is essentially required for efficient liberation of (phosphorylated) RelA from IκBα, preceding p97/VCP‐promoted timely and efficient degradation of IκBα as well as simultaneous NF‐κB/RelA nuclear translocation. Collectively, our data add new facets to the knowledge about maintenance of IκBα and RelA expression, likely depending on p97/VCP‐supported scheduled basal NF‐κB activity, and the mechanism of TNF‐induced NF‐κB activation.     

TNF-alpha induced NFκB signaling and p65 (RelA) overexpression repress Cldn5 promoter in mouse brain endothelial cells

Inflammatory cytokine TNFα enhances permeability of brain capillaries constituting blood brain barrier (BBB). In the monoculture endothelial models of BBB TNFα alters tight junction (TJ) structure and protein content. Claudin-5 (Cldn5) is a key TJ protein whose expression in the brain endothelial cells is critical to the function of BBB. TNFα reduces Cldn5 promoter activity and mRNA expression in mouse brain derived endothelial cells but the regulatory elements and signaling mechanism involved are not defined. Here we report that TNFα acts through NFκB signaling and requires a conserved promoter region for the down-regulation of Cldn5 expression. Overexpression of the NFκB subunit p65 (RelA) alone repressed Cldn5 promoter activity in mouse brain endothelial cells. We observed partial loss of Cldn5 protein expression after prolonged TNFα treatment in primary endothelial culture isolated from C56BL/6 mice brain. Taken together, our results confirm and extend previous observations of TNFα induced down-regulation of Cldn5 expression in mouse brain endothelial cells.     

TNFα regulates the localization of CD40 in lipid rafts of glioma cells

Resistance of glioblastoma multiforme (GBM) to TNFα induced apoptosis is attributed to NFκB activation. As TNF-receptor family member CD40 regulates NFκB activation, we investigated the role of CD40 in NFκB activation in GBM. We observed elevated CD40 levels in human glioma samples as compared to the surrounding normal tissue. Treatment with TNFα elevated CD40 levels in glioma cells and inhibition of CD40 signaling failed to abrogate TNFα induced NFκΒ activity. While TNFα increased the interaction between TRAF2/6, IκBα, IKKα/β in the CD40 signalosome, the level of CD40 in the signalosome remained unaffected upon TNFα treatment. Interestingly, TNFα decreased the spatial localization of CD40 and increased TRAF2/6 co-localization with lipid raft marker Caveolin. As localization of CD40 signalosome in lipid raft is crucial for NFκB activation, TNFα mediated decreased clustering of CD40 in lipid rafts could have possibly contributed to its non-involvement in NFκB activation.     

TNFα increases hypothalamic PTP1B activity via the NFκB pathway in rat hypothalamic organotypic cultures

In obesity, levels of tumor necrosis-factor α (TNFα) are well known to be elevated in adipose tissues or serum, and a high-fat diet (HFD) reportedly increases TNFα expression in the hypothalamus. The expression levels of hypothalamic protein tyrosine phosphatase 1B (PTP1B), a negative regulator of leptin and insulin signaling, are also elevated by HFD, and several lines of evidence support a relationship between TNFα and PTP1B. It remains unclear however how TNFα acts locally in the hypothalamus to regulate hypothalamic PTP1B expression and activity. In this study, we examined whether TNFα can regulate PTP1B expression and activity using rat hypothalamic organotypic cultures. Incubation of cultures with TNFα resulted in increases in mRNA expression, protein levels and activity of PTP1B in a dose- and time-dependent manner, respectively compared with controls. TNFα-induced PTP1B protein levels were not influenced by co-incubation with the sodium channel blocker tetrodotoxin, indicating that the action of TNFα is independent of action potentials. TNFα also increased phosphorylation of p65, a subunit of nuclear factor-κB (NFκB), in a dose- and time-dependent manner. While incubation with inhibitors of NFκB did not affect basal levels of either p65 phosphorylation or PTP1B expression, it markedly suppressed both TNFα-induced p65 phosphorylation and PTP1B expression to almost basal levels. These data suggest that TNFα acts on the hypothalamus to increase hypothalamic PTP1B expression and activity via the NFκB pathway, and that TNFα-mediated induction of NFκB in the hypothalamus may cause leptin and insulin resistance in the hypothalamus by increasing hypothalamic PTP1B activity.     

Time-course of hypothalamic-pituitary-adrenal axis activity and inflammation in juvenile rat brain after cranial irradiation

Recent studies reported that exposure of juvenile rats to cranial irradiation affects hypothalamic-pituitary-adrenal (HPA) axis stability, leading to its activation along with radiation-induced inflammation. In the present study, we hypothesized whether inflammatory reaction in the CNS could be a mediator of HPA axis response to cranial irradiation (CI). Therefore, we analyzed time-course changes of serum corticosterone level, as well IL-1β and TNF-α level in the serum and hypothalamus of juvenile rats after CI. Protein and gene expression of the glucocorticoid receptor (GR) and nuclear factor kappaB (NFκB) were examined in the hippocampus within 24?h postirradiation interval. Cranial irradiation led to rapid induction of both GR and NFκB mRNA and protein in the hippocampus at 1?h. The increment in NFκB protein persisted for 2?h, therefore NFκB/GR protein ratio was turned in favor of NFκB. Central inflammation was characterized by increased IL-1β in the hypothalamus, with maximum levels at 2 and 4?h after irradiation, while both IL-1β and TNF-α were undetectable in the serum. Enhanced hypothalamic IL-1β probably induced the relocation of hippocampal NFκB to the nucleus and decreased NFκB mRNA at 6?h, indicating promotion of inflammation in the key tissue for HPA axis regulation. Concomitant increase of corticosterone level and enhanced GR nuclear translocation in the hippocampus at 6?h might represent a compensatory mechanism for observed inflammation. Our results indicate that acute radiation response is characterized by increased central inflammation and concomitant HPA axis activation, most likely having a role in protection of the organism from overwhelming inflammatory reaction.     

Cytokine induction of tumor necrosis factor receptor 2 is mediated by STAT3 in colon cancer cells

The IL-6/STAT3 and TNFα/NFκB pathways are emerging as critical mediators of inflammation-associated colon cancer. TNF receptor (TNFR) 2 expression is increased in inflammatory bowel diseases, the azoxymethane/dextran sodium sulfate (AOM/DSS) model of colitis-associated cancer, and by combined interleukin (IL) 6 and TNFα. The molecular mechanisms that regulate TNFR2 remain undefined. This study used colon cancer cell lines to test the hypothesis that IL-6 and TNFα induce TNFR2 via STAT3 and/or NFκB. Basal and IL-6 + TNFα-induced TNFR2 were decreased by pharmacologic STAT3 inhibition. NFκB inhibition had little effect on IL-6 + TNFα-induced TNFR2, but did inhibit induction of endogenous IL-6 and TNFR2 in cells treated with TNFα alone. Chromatin immunoprecipitation (ChIP) revealed cooperative effects of IL-6 + TNFα to induce STAT3 binding to a -1,578 STAT response element in the TNFR2 promoter but no effect on NFκB binding to consensus sites. Constitutively active STAT3 was sufficient to induce TNFR2 expression. Overexpression of SOCS3, a cytokine-inducible STAT3 inhibitor, which reduces tumorigenesis in preclinical models of colitis-associated cancer, decreased cytokine-induced TNFR2 expression and STAT3 binding to the -1,578 STAT response element. SOCS3 overexpression also decreased proliferation of colon cancer cells and dramatically decreased anchorage-independent growth of colon cancer cells, even cells overexpressing TNFR2. Collectively, these studies show that IL-6- and TNFα-induced TNFR2 expression in colon cancer cells is mediated primarily by STAT3 and provide evidence that TNFR2 may contribute to the tumor-promoting roles of STAT3.     

The TGFβ1 pathway is required for NFκB dependent gene expression in mouse keratinocytes

The transforming growth factor-beta 1 (TGFβ1) and NFκB pathways are important regulators of epidermal homeostasis, inflammatory responses and carcinogenesis. Previous studies have shown extensive crosstalk between these pathways that is cell type and context dependent, but this has not been well-characterized in epidermal keratinocytes. Here we show that in primary mouse keratinocytes, TGFβ1 induces NFκB-luciferase reporter activity that is dependent on both NFκB and Smad3. TGFβ1-induced NFκB-luciferase activity was blocked by the IκB inhibitor parthenolide, the IκB super-repressor, a dominant negative TGFβ1-activated kinase 1 (TAK1) and genetic deletion of NFκB1. Coexpression of NFκB p50 or p65 subunits enhanced NFκB-luciferase activity. Similarly, inhibition of the TGFβ1 type I receptor with SB431542 or genetic deletion of Smad3 blocked TGFβ1 induction of NFκB-luciferase. TGFβ1 rapidly induced IKK phosphorylation but did not cause a detectable decrease in cytoplasmic IκB levels or nuclear translocation of NFκB subunits, although EMSA showed rapid NFκB nuclear binding activity that could be blocked by SB431542 treatment. TNFα, a well characterized NFκB target gene was also induced by TGFβ1 and this was blocked in NFκB+/− and −/− keratinocytes and by the IκB super-repressor. To test the effects of the TGFβ1 pathway on a biologically relevant activator of NFκB, we exposed mice and primary keratinocytes in culture to UVB irradiation. In primary keratinocytes UVB caused a detectable increase in levels of Smad2 phosphorylation that was dependent on ALK5, but no significant increase in SBE-dependent gene expression. Inhibition of TGFβ1 signaling in primary keratinocytes with SB431542 or genetic deletion of Tgfb1 or Smad3 suppressed UVB induction of TNFα message. Similarly, UVB induction of TNFα mRNA was blocked in skin of Tgfb1+/− mice. These studies demonstrate that intact TGFβ1 signaling is required for NFκB-dependent gene expression in mouse keratinocytes and skin and suggest that a convergence of these pathways in the nucleus rather than the cytoplasm may be critical for regulation of inflammatory pathways in skin by TGFβ1.     

FAK activation is required for TNF‐α‐induced IL‐6 production in myoblasts

Tumor necrosis factor‐α (TNF‐α) is a pleiotropic cytokine produced by activated macrophages. IL‐6 is a multifunctional cytokine that plays a central role in both innate and acquired immune responses. We investigated the signaling pathway involved in IL‐6 production stimulated by TNF‐α in cultured myoblasts. TNF‐α caused concentration‐dependent increases in IL‐6 production. TNF‐α‐mediated IL‐6 production was attenuated by focal adhesion kinase (FAK) mutant and siRNA. Pretreatment with phosphatidylinositol 3‐kinase inhibitor (PI3K; Ly294002 and wortmannin), Akt inhibitor, NF‐κB inhibitor (pyrrolidine dithiocarbamate, PDTC), and IκB protease inhibitor (L ‐1‐tosylamido‐2‐phenyl phenylethyl chloromethyl ketone, TPCK) also inhibited the potentiating action of TNF‐α. TNF‐α increased the FAK, PI3K, and Akt phosphorylation. Stimulation of myoblasts with TNF‐α activated IκB kinase α/β (IKKα/β), IκBα phosphorylation, p65 phosphorylation, and κB‐luciferase activity. TNF‐α mediated an increase of κB‐luciferase activity which was inhibited by Ly294002, wortmannin, Akt inhibitor, PDTC and TPCK or FAK, PI3K, and Akt mutant. Our results suggest that TNF‐α increased IL‐6 production in myoblasts via the FAK/PI3K/Akt and NF‐κB signaling pathway. J. Cell. Physiol. 223: 389–396, 2010. © 2010 Wiley‐Liss, Inc.     

Trans‐repression of NFκB pathway mediated by PPARγ improves vascular endothelium insulin resistance

Previous study has shown that thiazolidinediones (TZDs) improved endothelium insulin resistance (IR) induced by high glucose concentration (HG)/hyperglycaemia through a PPARγ‐dependent‐NFκB trans‐repression mechanism. However, it is unclear, whether changes in PPARγ expression affect the endothelium IR and what the underlying mechanism is. In the present study, we aimed to address this issue. HG‐treated human umbilical vascular endothelial cells (HUVEC) were transfected by either PPARγ‐overexpressing (Ad‐PPARγ) or PPARγ‐shRNA‐containing (Ad‐PPARγ‐shRNA) adenoviral vectors. Likewise, the rats fed by high‐fat diet (HFD) were infected by intravenous administration of Ad‐PPARγ or Ad‐PPARγ‐shRNA. The levels of nitric oxide (NO), endothelin‐1 (ET‐1) and cytokines (TNFα, IL‐6, sICAM‐1 and sVCAM‐1) and the expression levels of PPARγ, eNOS, AKT, p‐AKT, IKKα/β and p‐IKKα/β and IκBα were examined; and the interaction between PPARγ and NFκB‐P65 as well as vascular function were evaluated. Our present results showed that overexpression of PPARγ notably increased the levels of NO, eNOS, p‐AKT and IκBα as well as the interaction of PPARγ and NFκB‐P65, and decreased the levels of ET‐1, p‐IKKα/β, TNFα, IL‐6, sICAM‐1 and sVCAM‐1. In contrast, down‐expression of PPARγ displayed the opposite effects. The results demonstrate that the overexpression of PPARγ improves while the down‐expression worsens the endothelium IR via a PPARγ‐mediated NFκB trans‐repression dependent manner. The findings suggest PPARγ is a potential therapeutic target for diabetic vascular complications.