Mathematical modeling and sensitivity analysis of the integrated TNFα-mediated apoptotic pathway for identifying key regulators

TNFα-mediated apoptosis is one of the complex and tightly regulated cellular processes as it involves the activation of both pro- and anti-apoptotic signaling pathways. Thus, it is important to elucidate the molecular players of this process and their dynamics in order to gain an in-depth understanding of the mechanisms underlying apoptosis. To this end, we proposed an integrated model of TNFα-mediated apoptosis pathway in Type I cells, formulated based on the principles of mass action kinetics. The model includes major apoptotic modules—the extrinsic and intrinsic pathways, the NFκB survival signaling and various regulatory mechanisms. We performed simulations and sensitivity analyses to study the role of NFκB pathway in regulating apoptosis, and identified IAP as one of the more potent regulators of apoptosis.     

Tumor necrosis factor alpha pathways develops liver apoptosis in type 1 diabetes mellitus

We analyzed the contribution of TNF-α intracellular pathway in the development of apoptosis in the liver of streptozotocin-induced diabetic rats. In liver tissue, diabetes promoted a significant increase of TNF-α/TNF-R1, and led to the activation of caspase-8, of nuclear factor kappa B (NFκB), and JNK signaling pathways. The activation of NFκB led to an induction of iNOS and consequent increase in NO production. As a consequence of such changes a significant increase of caspase-3 activity and of apoptotic index were observed in the liver of diabetic animals. Importantly, the treatment in vivo of diabetic rats with etanercept (TNF-α blocking antibody) or aminoguanidine (selective iNOS inhibitor) significantly attenuated the induction of apoptosis by reduction of caspase-3 activity. Overall, we demonstrated that in the diabetes enhances TNF-α in the liver, which may be a fundamental key leading to apoptotic cell death, through activation of caspase-8, NFκB and JNK pathways.     

细胞凋亡相关基因表达谱与大鼠再生肝的细胞凋亡关系

目的在基因转录水平探讨细胞凋亡相关途径对大鼠肝再生的作用。方法采用大鼠2/3部分肝切除(PH)方法,制备再生肝模型,同时设对照手术(假手术)。用查阅网站资料和相关论文等方法获得凋亡相关基因,用大鼠基因230 2.0芯片检测它们在大鼠再生肝中的表达情况,通过比较真、假手术中上述基因的表达差异性确定肝再生相关基因。结果细胞凋亡相关基因中,252个基因与肝再生相关。在肝再生启动(PH后0.5~4h)、G0/G1过渡(PH后4~6h)、细胞增殖(PH后6~66h)、细胞分化和结构功能重建期(PH后72~168h)等4个阶段起始表达的基因数为81、231、55和16,总表达的基因数为161、100、733和192,表明相关基因主要在肝再生启动阶段起始表达,在不同阶段发挥作用。它们共上调795次,下调291次,表明肝再生中大部分基因表达增强。它们的表达模式分为35种,表明肝再生中细胞凋亡相关基因的表达情况多样和复杂。结论15条细胞凋亡途径参与肝再生调控。     

JNK信号通路调控大鼠再生肝8种细胞的增殖和凋亡

目的 从基因转录水平了解JNK信号通路在大鼠再生肝8种细胞中的作用。方法 用密度梯度离心和免疫磁珠等方法分离肝细胞（HC）、胆管上皮细胞（BEC）、卵圆细胞（OC）、肝星形细胞（HSC）、窦内皮细胞（SEC）、库普弗细胞（KC）、陷窝细胞（PC）、树突状细胞（DC）等8种肝脏细胞,用大鼠Genome 230 2.0芯片检测大鼠再生肝8种细胞的基因表达谱,用生物信息学和系统生物学等方法分析基因表达变化预示的JNK信号通路在调控大鼠再生肝8种细胞增殖、凋亡中的作用。用实时荧光定量PCR方法验证了芯片结果的可靠性。结果 JNK信号通路涉及240个基因和42条途径,其中,225个基因与大鼠肝再生相关。基因协同作用分析显示,在大鼠肝再生启动阶段,JNK信号通路启动HC和KC增殖,促进OC凋亡,启动部分PC和SEC增殖和促进部分PC和SEC凋亡;在进展阶段,JNK信号通路促进HC、BEC、KC和DC增殖,促进部分PC增殖、部分PC凋亡。在终止阶段,JNK信号通路促进HC、OC和PC凋亡,促进部分KC增殖、部分KC凋亡。结论 大鼠肝再生中JNK信号通路的42条途径和225个基因参与调控大鼠再生肝8种细胞的增殖和凋亡。     

Potential autocrine regulation of interleukin-33/ST2 signaling of dendritic cells in allergic inflammation

This study identified a novel phenomenon that dendritic cells (DCs) produced interleukin (IL)-33 via Toll-like receptor (TLR)-mediated innate pathway. Mouse bone marrow–derived DCs were treated with or without microbial pathogens or recombinant murine IL-33. IL-33 mRNA and protein were found to be expressed by DCs and largely induced by several microbial pathogens, highly by lipopolysaccharide (LPS) and flagellin. Using two mouse models of topical challenge by LPS and flagellin and experimental allergic conjunctivitis, IL-33-producing DCs were observed in ocular mucosal surface and the draining cervical lymph nodes in vivo. The increased expression levels of myeloid differentiation primary-response protein 88 (MyD88), nuclear factor (NF)-κB1, NF-κB2, and RelA accompanied by NF-κB p65 nuclear translocation were observed in DCs exposed to flagellin. IL-33 induction by flagellin was significantly blocked by TLR5 antibody or NF-κB inhibitor quinazoline and diminished in DCs from MyD88 knockout mice. IL-33 stimulated the expression of DC maturation markers, CD40 and CD80, and proallergic cytokines and chemokines, OX40L, IL-4, IL-5, IL-13, CCL17 (C-C motif chemokine ligand 17), TNF-α (tumor necrosis factor-α), and IL-1β. This stimulatory effect of IL-33 in DCs was significantly blocked by ST2 antibody or soluble ST2. Our findings demonstrate that DCs produce IL-33 via TLR/NF-κB signaling pathways, suggesting a molecular mechanism by which local allergic inflammatory response may be amplified by DC-produced IL-33 through potential autocrine regulation.     

Nuclear factor kappa B signaling initiates early differentiation of neural stem cells

Inflammatory mediators, many of which activate the signaling of nuclear factor kappa B (NFκB), have received increasing attention in the field of neurogenesis. NFκB signaling regulates neurite outgrowth and neural plasticity as well as the proliferation/apoptosis and terminal differentiation of neural stem cells (NSCs). Early neurogenesis from NSCs produces identical progeny through symmetric division and committed daughter cells through asymmetric division. Here, we show that NFκB signaling is required for NSC initial differentiation. The canonical IKKβ/IκBα/p65 pathway is activated during the initial stages of neural differentiation induced by treatment with TNFα or withdrawal of epidermal growth factor/basic fibroblast growth factor. NSC-specific inhibition of NFκB in transgenic mice causes an accumulation of Nestin(+) /Sox2(+) /glial fibrillary acidic protein(+) NSCs. Inhibition of NFκB signaling in vitro blocks differentiation and asymmetric division and maintains NSCs in an undifferentiated state. The induction of initial differentiation and asymmetry by NFκB signaling occurs through the inhibition of C/EBPβ expression. Our data reveal a novel function of NFκB signaling in early neurogenesis and provide insight into the molecular mechanisms underlying neurodevelopmental disorders and neurodegenerative diseases.     

LETM1 is a potential cancer stem-like cell marker and predicts poor prognosis in colorectal adenocarcinoma

The leucine zipper-EF-hand containing transmembrane protein 1 (LETM1) is highly expressed in many human malignancies and is correlated with poor prognosis. However, LETM1 has rarely been explored as a cancer stem-like cell marker for the prognostic evaluation of colorectal adenocarcinoma (CRA). Herein, we assessed the expression of LETM1 and its relationship with cancer stemness genes, cell cycle markers, PI3K/Akt/NFκB signaling pathway genes, and HIF1α in 102 paraffin-embedded CRA tissue samples using immunohistochemistry (IHC). Additionally, we further confirmed the correlation between LETM1 and cancer stemness genes in CRA cell lines using immunofluorescence (IF) imaging and Western blotting. LETM1 expression was remarkably upregulated in human fetal sagittal sections and CRA tissues. The expression of LETM1 in CRA tissue was correlated with clinical stage, lymph node metastasis, distant metastasis, and microvessel density. LETM1 expression was significantly associated with lower overall survival and disease-free survival. Moreover, the expression of LETM1 positively correlated with SOX9, LSD1, CD44, CD133, LGR5, SOX2, and HIF1α. IF revealed that LETM1 co-localized with CD44, SOX9, and LGR5 in HCT116. Moreover, LETM1 expression was also strongly linked to the expression of cell cycle regulators (cyclinD1, CDK4, p27) and PI3K/Akt/NFκB pathway genes (pPI3K-p85, pAkt-Ser473, pAkt-Thr308, pNFκB-p65). LETM1 may therefore be a cancer stem-like cell marker and an indicator of poor prognosis in patients with CRA.     

The isoprenoid end product N6-isopentenyladenosine reduces inflammatory response through the inhibition of the NFκB and STAT3 pathways in cystic fibrosis cells

Objective

N6-isopentenyladenosine (iPA) is an intermediate of the mevalonate pathway that exhibits various anti-cancer effects. However, studies on its anti-inflammatory activity are scarce and underlying molecular mechanisms are unknown. Therefore, we aimed to investigate the ability of iPA to exert anti-inflammatory effects in the human cystic fibrosis (CF) cell model of exacerbated inflammation.

Materials and methods

TNFα-stimulated CF cells CuFi-1 and its normal counterpart NuLi-1 were pre-treated with increasing concentrations of iPA and cell viability and proliferation were assessed by MTT and BrdU assays. The effect of iPA on IL-8 and RANTES secretion was determined by ELISA, and the activation and expression of signaling molecules and selenoproteins were studied by Western blot. To assess the direct effect of iPA on NFκB activity, luciferase assay was performed on TNFα-stimulated HEK293/T cells transfected with a NFκB reporter plasmid.

Results

We demonstrated for the first time that iPA prevents IL-8 and RANTES release in TNFα-stimulated CF cells and this effect is mediated by increasing the expression of the direct NFκB inhibitor IκBα and decreasing the levels of STAT3. Consistent with this, we showed that iPA inhibited TNFα-mediated NFκB activation in HEK/293T cells. Finally, we also found that iPA improved the levels of glutathione peroxidase 1 and thioredoxin reductase 1 only in CF cells suggesting its ability to maintain sufficient expression of these anti-oxidant selenoproteins.

Conclusions

Our findings indicate that iPA can exert anti-inflammatory activity especially in the cases of excessive inflammatory response as in CF.

     

Anti-citrullinated Protein Antibodies Activated ERK1/2 and JNK Mitogen-activated Protein Kinases via Binding to Surface-expressed Citrullinated GRP78 on Mononuclear Cells

In a previous study, we found that anti-citrullinated protein antibodies (ACPAs) enhance nuclear factor (NF)-κB activity and tumor necrosis factor (TNF)-α production by normal human peripheral blood mononuclear cells (PBMCs) and U937 cells via binding to surface-expressed citrullinated glucose-regulated protein 78 (cit-GRP78). However, the downstream signaling pathways remain unclear after binding. In the present study, we firstly measured the effects of different kinase inhibitors on ACPA-mediated TNF-α production from normal PBMCs and monocytes. Then, the native and phosphorylated mitogen-activated protein kinases (MAPKs) were detected in ACPA-activated U937 cells by Western blotting. We also explored the role of the phosphoinositide 3-kinase (PI3K)-Akt pathway in activating IκB kinase alpha (IKK-α) in ACPA-stimulated U937 cells. Finally, we measured the amount of cit-GRP78 from PBMC membrane extracts in RA patients and controls. We found that MAPK and Akt inhibitors, but not PI3K inhibitor, remarkably suppressed ACPA-mediated TNF-α production. Interestingly, ACPAs selectively activated extracellular signal-regulated kinase 1/2 (ERK1/2) and c-jun N-terminal kinase (JNK), but not p38 MAPK, in U937 cells. This activation was suppressed by cit-GRP78, but not GRP78. The JNK activation further enhanced the phosphorylation of Akt and IKK-α. The expression of cit-GRP78 on cell membrane was higher in RA than normal PBMCs. Taken together; these results suggest that through binding to surface, over-expressed cit-GRP78 on RA PBMCs, ACPAs selectively activate ERK1/2 and JNK signaling pathways to enhance IKK-α phosphorylation, which leads to the activation of NF-κB and the production of TNF-α .     

The involvement of β-actin in the signaling of transmembrane TNF-α-mediated cytotoxicity

Actin cytoskeleton has been shown to play a regulating role in several signaling pathways, and disruption of actin filament has been reported to increase sTNF-α-induced cell death. However, whether actin is involved in tmTNF-α-mediated cytotoxicity remains unclear. Here, we demonstrated that pretreatment of HL-60 with CytD or LatA to depolymerize actin significantly suppressed tmTNF-α-mediated apoptosis. Interestingly, tmTNF-α increased the actin immunoprecipitated by anti-TNFR2 but not anti-TNFR1 antibody, and disruption of the actin filament totally blocked this effect. In addition, TNFR1 knockdown by siRNA did not affect tmTNF-α-mediated cytotoxicity and the inhibitory effect of CytD, suggesting that the involvement of actin in the tmTNF-α-induced apoptosis is linked to the TNFR2 pathway. Our results revealed further that tmTNF-α signaled the inhibition of IκB degradation and NF-κB activity by recruiting RIP1 to and uncoupling TRAF2 from the TNFR2 complex. Nevertheless, CytD totally reversed the tmTNF-α signaling and activated NF-κB by recruiting TRAF2 to and dissociating RIP1 from the TNFR2 complex. Furthermore, tmTNF-α led to activation of caspase-8 by dissociation of cFLIP from TNFR2 and inhibition of the cFLIP expression. Activated caspase-8 cleft RIP1 to suppress NF-κB activity and also mediated tmTNF-α-induced apoptosis. However, CytD blocked the tmTNF-α-induced uncoupling of cFLIP from TNFR2 and prevented caspase-8 activation and the resulting cleavage of RIP1, converting the signaling for tmTNF-α-mediated apoptosis into one for activating NF-κB to survive. These results suggest that the actin cytoskeleton functions in transmitting signals via TNFR2 to mediate tmTNF-α-induced apoptosis.     

Nonstructural protein 1α subunit-based inhibition of NF-κB activation and suppression of interferon-β production by porcine reproductive and respiratory syndrome virus

Induction of type I interferon (IFN-α/β) is an early antiviral response of the host, and porcine reproductive and respiratory syndrome virus (PRRSV) has been reported to downregulate the IFN response during infection in cells and pigs. We report that the PRRSV nonstructural protein 1α (Nsp1α) subunit of Nsp1 is a nuclear-cytoplasmic protein distributed to the nucleus and contains a strong suppressive activity for IFN-β production that is mediated through the retinoic acid-inducible gene I (RIG-I) signaling pathway. Nsp1α suppressed the activation of nuclear factor (NF)-κB when stimulated with dsRNA or tumor necrosis factor (TNF)-α, and NF-κB suppression was RIG-I-dependent. The suppression of NF-κB activation was associated with the poor production of IFN-β during PRRSV infection. The C-terminal 14 amino acids of the Nsp1α subunit were critical in maintaining immunosuppressive activity of Nsp1α for both IFN-β and NF-κB, suggesting that the newly identified zinc finger configuration comprising of Met180 may be crucial for inhibitory activities. Nsp1α inhibited IκB phosphorylation and as a consequence NF-κB translocation to the nucleus was blocked, leading to the inhibition of NF-κB stimulated gene expression. Our results suggest that PRRSV Nsp1α is a multifunctional nuclear protein participating in the modulation of the host IFN system.     

Phosphatidylserine inhibits NFκB and p38 MAPK activation in human monocyte derived dendritic cells

Phosphatidylserine (PS) is an anionic phospholipid restricted to the inner surface of the plasma membrane. PS translocates to the cell surface during early apoptosis where it serves as a marker for rapid uptake by phagocytes. PS is also thought to regulate immune responses. Dendritic cells (DC) are the most potent antigen presenting cells. Previous studies demonstrated that PS inhibits the expression of MHC and co-stimulatory molecules, the secretion of IL-12p70, and the ability to activate T cells by human monocyte derived DCs. However, the cell signaling mechanisms by which PS regulated DCs are not well described. In the current study we tested the effects of PS on signal transduction pathways thought to regulate human myeloid DC maturation and IL-12p70 production. We showed that PS inhibited the activation of nuclear factor-κB (NFκB) in response to LPS by preventing IκBα phosphorylation and degradation. PS also increased the total IκBα levels in immature DCs and inhibited p38 mitogen activated protein kinase (MAPK) phosphorylation and activation. The findings suggest a possible mechanism for regulating the immunostimulatory function of DCs by PS.     

Sjögren's syndrome autoantibodies provoke changes in gene expression profiles of inflammatory cytokines triggering a pathway involving TACE/NF-κB

We explore the association of the inflammatory gene expression profile observed in the chronic inflammatory autoimmune disorder Sj?gren's syndrome (SS) with changes in TNF-α converting enzyme (TACE), tumor necrosis factor (TNF)-α and nuclear factor (NF)-κB levels showing that pathways that include TNF-α signaling converge on NF-κB contributing to exacerbate the diseases. The treatment of human salivary gland epithelial cells (SGECs) with SS anti-Ro/SSA autoantibodies (Abs) result in a progressive increase in NF-κB-DNA binding, that includes a marked enhancement in NF-κB subunit p65 protein-DNA binding. A human cytokine multi-analyte array demonstrated that the NF-κB proinflammatory target genes, increased by anti-Ro/SSA Abs treatment, includes CXC chemokines (CXCL1, CXCL6 and CXCL9), CC chemokines (CCL2, CCL13 and CCL20), interleukins (IL-1α, IL-1β, IL-1F8, IL-6, IL-8, IL-9, IL-13, IL-17 and IL-22) and their receptors (IL-1RN, IL-10Rα, IL-13Rα, CCR1, CCR2, CCR3, CCR4 and CXCR1). Blockade of TACE through the use of the specific inhibitor TAPI-1 regulates proinflammatory cytokines production in SGEC treated with anti-Ro/SSA Abs inhibiting NF-κB nuclear translocation and activation. To further investigate the role of NF-κB on anti-Ro/SSA Abs-determined proinflammatory gene expression, we used the inhibitory protein IκB-α dominant negative super-repressor as inhibitor of NF-κB-DNA binding, demonstrating that transfection with dominant-negative IκB-α in anti-Ro/SSA-treated SGEC determined a marked reduction of proinflammatory cytokines gene expression. Although further studies are needed to clarify the mechanisms underlying SS, our results demonstrate that SS Abs exert their pathogenic effects via triggering the TACE/TNF-α/NF-κB axis.     

ERK controls epithelial cell death receptor signalling and cellular FLICE-like inhibitory protein (c-FLIP) in ulcerative colitis

Intestinal epithelial cell (IEC) death signalling through the Fas receptor is impaired in active ulcerative colitis (UC). This is possibly due to the activation of cytoprotective pathways resulting in limitation of the tissue injury secondary to inflammation. We hypothesized that inflammatory signalling like the nuclear factor (NF)-κB or mitogen activated protein kinase (MAPK) pathways could be involved in (a) the modification of Fas mediated apoptosis responses and (b) the regulation of the Fas receptor inhibitor cellular FLICE-like inhibitory protein (c-FLIP). Phospho-ERK was upregulated in IECs in active UC as well as IECs exposed to pro-inflammatory cytokines in vitro. Similarly, the short form of c-FLIP (c-FLIP_S) was found to be upregulated in IECs from patients with active UC. c-FLIP_S was the main splice variant found in both HT-29 cells and primary human IECs. Both splice variants were induced by TNF-α, IL-1β and IFN-γ, while IL-10 induced c-FLIP_L expression; TNF-α also induced c-FLIP_S in primary IECs. Inhibition of NF-κB, JNK and p38 pathways did not affect c-FLIP expression, whereas ERK inhibition by MEK1 RNA silencing and pharmacologic inhibitors decreased c-FLIP_S expression. Similarly, ERK – but not NF-κB – inhibited Fas ligand and TNF-α-mediated apoptosis responses in both cell line experiments and primary IECs. The present study identifies the MEK-ERK pathway as a major regulator of apoptosis in IECs during flares of UC and an inducer of c-FLIP_S. The results explain the resistance to receptor mediated epithelial apoptosis in active UC. Oncogenic c-FLIP could promote propagation of DNA-damaged IECs and contribute to cancer development in UC.     

Subversion of human intestinal mucosa innate immunity by a Crohn's disease-associated E. coli

Adherent-invasive Escherichia coli (AIEC), associated with Crohn's disease, are likely candidate contributory factors in the disease. However, signaling pathways involved in human intestinal mucosa innate host response to AIEC remain unknown. Here we use a 3D model of human intestinal mucosa explant culture to explore the effects of the AIEC strain LF82 on two innate immunity platforms, i.e., the inflammasome through evaluation of caspase-1 status, and NFκB signaling. We showed that LF82 bacteria enter and survive within a few intestinal epithelial cells and macrophages, without altering the mucosa overall architecture. Although 4-h infection with a Salmonella strain caused crypt disorganization, caspase-1 activation, and mature IL-18 production, LF82 bacteria were unable to activate caspase-1 and induce IL-18 production. In parallel, LF82 bacteria activated NFκB signaling in epithelial cells through IκBα phosphorylation, NFκBp65 nuclear translocation, and TNFα secretion. In addition, NFκB activation was crucial for the maintenance of epithelial homeostasis upon LF82 infection. In conclusion, here we decipher at the whole-mucosa level the mechanisms of the LF82-induced subversion of innate immunity that, by maintaining host cell integrity, ensure intracellular bacteria survival.