LRRC19, a novel member of the leucine-rich repeat protein family, activates NF-κB and induces expression of proinflammatory cytokines

We have identified a new functional transmembrane receptor, LRRC19 (leucine-rich repeat containing 19), that belongs to the LRR protein family. LRRC19’s central core has four analogous LRR repeating modules in a juxtaposed array and a casein kinase (CK2) phosphorylation site in the cytoplasmic domain. LRRC19 mRNA was found in the kidney, spleen and intestine of adult mice using both RT-PCR and in situ hybridization. LRRC19 does not contain a cytoplasmic Toll/IL-1 receptor (TIR) domain but was able to activate NF-κB and induce production of proinflammatory cytokines. LRRC19 shares a close evolutionary relationship with multiple Toll-like receptors (TLRs), especially TLR3. Importantly, the TLR3 ligand, as well as other TLR ligands, significantly promoted the expression of proinflammatory cytokines and the activation of NF-κB by LRRC19. Thus, LRRC19 may play an important role in inducing innate immune responses in certain tissues such as the kidney.     

Ectopic expression of OX1R in ulcerative colitis mediates anti-inflammatory effect of orexin-A

Orexins (orexin-A and orexin-B) are hypothalamic peptides that are produced by the same precursor and are involved in sleep/wake control, which is mediated by two G protein-coupled receptor subtypes, OX1R and OX2R. Ulcerative colitis (UC) is an inflammatory bowel disease, (IBD) which is characterized by long-lasting inflammation and ulcers that affect the colon and rectum mucosa and is known to be a significant risk factor for colon cancer development. Based on our recent studies showing that OX1R is aberrantly expressed in colon cancer, we wondered whether orexin-A could play a role in UC. Immunohistochemistry studies revealed that OX1R is highly expressed in the affected colonic epithelium of most UC patients, but not in the non-affected colonic mucosa. Injection of exogenous orexin-A specifically improved the inflammatory symptoms in the two colitis murine models. Conversely, injection of inactive orexin-A analog, OxB7–28 or OX1R specific antagonist SB-408124 did not have anti-inflammatory effect. Moreover, treatment with orexin-A in DSS-colitis induced OX1R^?/? knockout mice did not have any protective effect. The orexin-A anti-inflammatory effect was due to the decreased expression of pro-inflammatory cytokines in immune cells and specifically in T-cells isolated from colonic mucosa. Moreover, orexin-A inhibited canonical NFκB activation in an immune cell line and in intestinal epithelial cell line. These results suggest that orexin-A might represent a promising alternative to current UC therapies.     

Differential effects of proinflammatory cytokines on cell death and ER stress in insulin-secreting INS1E cells and the involvement of nitric oxide

Proinflammatory cytokines produced by immune cells destroy pancreatic beta cells in type 1 diabetes. The aim of this study was to investigate the cytokine network and its effects in insulin-secreting cells. INS1E cells were exposed to different combinations of proinflammatory cytokines. Cytokine toxicity was estimated by MTT assay and caspase activation measurements. The NFκB-iNOS pathway was analyzed by a SEAP reporter gene assay, Western-blotting and nitrite measurements. Gene expression analyses of ER stress markers, Chop and Bip, were performed by real-time RT-PCR. Cytokines tested in this study, namely IL-1β, TNFα and IFNγ, had deleterious effects on beta cell viability. The most potent toxicity exhibited IL-1β and its combinations with other cytokines. The toxic effects of IL-1β towards cell viability, caspase activation and iNOS activity were dependent on nitric oxide and abolished by an iNOS blocker. IL-1β was the strongest inducer of the NFκB activation. An iNOS blocker inhibited IL-1β-mediated NFκB activation in the first, initial phase of cytokine action, but did not affect significantly NFκB activation after prolonged incubation. Interestingly iNOS protein expression was induced predominantly by IL-1β and decreased in the presence of an iNOS blocker in the case of a short time exposure. The changes in the expression of ER stress markers were also almost exclusively dependent on the IL-1β presence and counteracted by iNOS blockade. Thus cytokine-induced beta cell death is primarily IL-1β mediated with a NO-independent enhancement by TNFα and IFNγ. The deleterious effects on cell viability and function are crucially dependent on IL-1β-induced nitric oxide formation.     

Rotenone Could Activate Microglia Through NFκB Associated Pathway

Parkinson’s disease (PD) is a common neurodegenerative disease, and its etiology remains obscure. Increasing evidence has suggested an important role for environmental factors such as exposure to pesticides in increasing the risk of developing PD and inflammation is the early incident during the process of PD. In this study, we measure the pro-inflammatory cytokines by enzyme-linked immunosorbnent assay and RT-PCR methods; analyze the reactive oxygen species by DCFH-DA; detected nuclear factor κB (NFκB) translocation by western blot and immunofluorescence methods; and analyze the phosphorylation of mitogen-activated protein (MAP) kinase and protein level of Nurr1 by western blot. Results showed that rotenone could induce tumor neurosis factor α (TNFα) and interleukin 1β (IL-1β) release from BV-2 cells, enhance TNFα and IL-1β mRNA levels in substantia nigra lesioned by rotenone; also, rotenone could increase the phosphorylation of inhibitor of κB (IκB), extracellular regulated protein kinase , c-Jun N-terminal kinase, p38 MAP kinases and promote p65 subunit of NFκB translocation to nuclear; at the same time, rotenone could decrease the protein level of Nurr1 in nuclear. So, rotenone exerted toxicity through activating microglia, and its mechanism might be associated with NFκB signal pathway.     

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.     

Development of atopic dermatitis-like skin lesions in STAT6-deficient NC/Nga mice

Atopic dermatitis (AD) is a pruritic inflammatory skin disease characterized by elevation of plasma levels of total IgE, infiltration of mast cells and eosinophils, and the expression of cytokines by Th2 T cells. However, the role of Th2 cells in the pathogenesis of AD is not fully understood. In this study we examined the NC/Nga (NC) mouse model of AD and established STAT6-deficient (SATA6(-/-)) NC mice to investigate the relevance of IL-4-mediated immune responses. Surprisingly, these mice elicited AD-like skin lesions at equivalent frequency and time of onset compared with normal NC littermates. Histological features of the lesion in STAT6(-/-) NC mice fulfilled the criteria for the pathogenesis of AD, although these mice fail to produce IgE and Th2 cytokines. The lymph nodes proximal to the regions of skin that developed lesions exhibited massive enlargement elicited by the accumulation of activated IFN-gamma-secreting T cells. Moreover, caspase I, IL-18, IL-12, and IFN-gamma are found to be highly expressed at the skin lesion, occurring simultaneously with elevation of eotaxin 2 and CCR3 expression. Therefore, the Th2-mediated immune response is not necessary for the development of AD-like skin disease in NC mice. The skin microenvironment that favored IFN-gamma production tightly correlates with the skin disease in NC mice through the infiltration of eosinophils.     

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.     

NF‐κB regulates a cassette of immune/inflammatory genes in human pregnant myometrium at term

The onset of human labour resembles inflammation with increased synthesis of prostaglandins and cytokines. There is evidence from rodent models for an important role for nuclear factor‐κB (NF‐κB) activity in myometrium which both up‐regulates contraction‐associated proteins and antagonizes the relaxatory effects of progesterone. Here we show that in the human, although there are no differences in expression of NF‐κB p65, or IκB‐α between upper‐ or lower‐segment myometrium or before or after labour, there is nuclear localization of serine‐256‐phospho‐p65 and serine‐536‐phospho‐p65 in both upper‐ and lower‐segment myometrium both before and after the onset of labour at term. This shows that NF‐κB is active in both upper and lower segment prior to the onset of labour at term. To identify the range of genes regulated by NF‐κB we overexpressed p65 in myocytes in culture. This led to NF‐κB activation identical to that seen following interleukin (IL)‐1β stimulation, including phosphorylation and nuclear translocation of p65 and p50. cDNA microarray analysis showed that NF‐κB increased expression of 38 genes principally related to immunity and inflammation. IL‐1β stimulation also resulted in an increase in the expression of the same genes. Transfection with siRNA against p65 abolished the response to IL‐1β proving a central role for NF‐κB. We conclude that NF‐κB is active in myocytes in both the upper and lower segment of the uterus prior to the onset of labour at term and principally regulates a group of immune/inflammation associated genes, demonstrating that myocytes can act as immune as well as contractile cells.     

Requirement of Rab21 in LPS-induced TLR4 signaling and pro-inflammatory responses in macrophages and monocytes

Lipopolysaccharide (LPS) induces macrophage/monocyte activation and pro-inflammatory cytokines production by activating Toll-like receptor 4 (TLR-4) signaling. Rab GTPase 21 (Rab21) is a member of the Rab GTPase subfamily. In the present study, we show that LPS induced TLR4 and Rab21 association and endosomal translocation in murine bone marrow–derived macrophages (BMDMs) and primary human peripheral blood mononuclear cells (PBMCs). In BMDMs, shRNA-mediated stable knockdown of Rab21 inhibited LPS-induced expression and production of pro-inflammatory cytokines (IL-1β, IL-6 and TNF-α). Conversely, forced overexpression of Rab21 by an adenovirus construct potentiated LPS-induced IL-1β, IL-6 and TNF-α production in BMDMs. Further studies show that LPS-induced TLR4 endosomal traffic and downstream c-Jun and NFκB (nuclear factor-kappa B) activation were significantly inhibited by Rab21 shRNA, but intensified with Rab21 overexpression in BMDMs. Finally, in the primary human PBMCs, siRNA-induced knockdown of Rab21 significantly inhibited LPS-induced IL-1β, IL-6 and TNF-α production. Taken together, we suggest that Rab21 regulates LPS-induced pro-inflammatory responses by promoting TLR4 endosomal traffic and downstream signaling activation.     

Opisthorchis viverrini excretory/secretory products induce toll-like receptor 4 upregulation and production of interleukin 6 and 8 in cholangiocyte

Biliary tract infection with the Group I carcinogenic liver fluke Opisthorchis viverrini is associated with severe inflammation leading to cholangiocarcinoma--a major biliary cancer in Southeast Asia. However, mechanism(s) by which the liver fluke induces host mucosal immune/inflammatory responses is unclear. In the present study we address whether a normal immortalized human cholangiocyte cell line (H69 cells) recognizes and responds to O. viverrini excretory/secretory products (OVES). Expression of multiple TLRs, activation of NF-κB, and expression of pro-inflammatory cytokines were monitored in the presence and absence of OVES. Our results showed that OVES induced increased cholangiocyte TLR4 mRNA expression, induced IκB-α degradation in a MyD88-dependent manner, and activated NF-κB nuclear translocation. Moreover, OVES induced expression and secretion of the strong chemoattractant chemokine interleukin 8 (IL-8) and pro-inflammatory cytokine IL-6. These results demonstrate that secreted/excreted products of O. viverrini are recognized by human cholangiocytes and initiate innate mucosal immunity/inflammatory cascades, a primary event in the pathogenesis of opisthorchiasis and cholangiocarcinoma.     

P2X7 receptor positively regulates MyD88-dependent NF-κB activation

Recent studies have demonstrated that P2X7 plays a critical role in the immune system. Here, our results showed that P2X7 activated a NF-κB - but not an IFN-β-dependent luciferase reporter gene in HEK293T cells. P2X7 was involved in the LPS- and ATP-induced NF-κB activation but did not significantly impact the response to Zymosan in RAW264.7 cells. The activation of NF-κB and IFN-β induced by myeloid differentiation primary-response protein 88 (MyD88) was enhanced by P2X7 co-expression. The siRNA silencing MyD88 almost abolished the NF-κB activation induced by P2X7, and co-immunoprecipitation showed that P2X7 interacted with MyD88. The amino acids in the C-terminus, especially the LPS-binding region of P2X7, were critical for the cellular localization and immune function of P2X7. P2X7ΔC (190 amino acids deleted in the C-terminus) and P2X7 G586A variants localized throughout the cytoplasma with a little aggregation, which differs from the cell membrane localization of wild type P2X7. Both of them could not localize to Golgi or endoplasmic reticulum. P2X7ΔC and P2X7 G586A had impaired proteolytic cleavage of caspase-1 into the functional p20 subunit, which can activate pro-inflammatory cytokines such as IL-1β. P2X7 G586A also showed a slight interaction with MyD88 in our co-immunoprecipitation experiment. This interaction might result in the attenuated activation of NF-κB and IFN-β induced by MyD88.     

Smac mimetic compounds potentiate interleukin-1beta-mediated cell death

Smac mimetic compounds (SMCs) potentiate TNFα-mediated cancer cell death by targeting the inhibitor of apoptosis (IAP) proteins. In addition to TNFα, the tumor microenvironment is exposed to a number of pro-inflammatory cytokines, including IL-1β. Here, we investigated the potential impact of IL-1β on SMC-mediated death of cancer cells. Synergy was seen in a subset of a diverse panel of 21 cancer cell lines to the combination of SMC and IL-1β treatment, which required IL-1β-induced activation of the NF-κB pathway. Elevated NF-κB activity resulted in the production of TNFα, which led to apoptosis dependent on caspase-8 and RIP1. In addition, concurrent silencing of cIAP1, cIAP2, and X-linked IAP by siRNA was most effective for triggering IL-1β-mediated cell death. Importantly, SMC-resistant cells that produced TNFα in response to IL-1β treatment were converted to an SMC-sensitive phenotype by c-FLIP knockdown. Reciprocally, ectopic expression of c-FLIP blocked cell death caused by combined SMC and IL-1β treatment in sensitive cancer cells. Together, our study indicates that a positive feed-forward loop by pro-inflammatory cytokines can be exploited by SMCs to induce apoptosis in cancer cells.     

Essential role for IKKβ in production of type 1 interferons by plasmacytoid dendritic cells

Plasmacytoid dendritic cells (pDCs) are characterized by their ability to produce high levels of type 1 interferons in response to ligands that activate TLR7 and TLR9, but the signaling pathways required for IFN production are incompletely understood. Here we exploit the human pDC cell line Gen2.2 and improved pharmacological inhibitors of protein kinases to address this issue. We demonstrate that ligands that activate TLR7 and TLR9 require the TAK1-IKKβ signaling pathway to induce the production of IFNβ via a pathway that is independent of the degradation of IκBα. We also show that IKKβ activity, as well as the subsequent IFNβ-stimulated activation of the JAK-STAT1/2 signaling pathway, are essential for the production of IFNα by TLR9 ligands. We further show that TLR7 ligands CL097 and R848 fail to produce significant amounts of IFNα because the activation of IKKβ is not sustained for a sufficient length of time. The TLR7/9-stimulated production of type 1 IFNs is inhibited by much lower concentrations of IKKβ inhibitors than those needed to suppress the production of NFκB-dependent proinflammatory cytokines, such as IL-6, suggesting that drugs that inhibit IKKβ may have a potential for the treatment of forms of lupus that are driven by self-RNA and self-DNA-induced activation of TLR7 and TLR9, respectively.     

Eupatilin inhibits lipopolysaccharide-induced expression of inflammatory mediators in macrophages

AimsEupatilin (5,7-dihydroxy-3,4,6-trimethoxyflavone) is a pharmacologically active ingredients in Stillen^TM, a drug for the gastric mucosal ulcers. Eupatilin has been known to possess anti-peptic, anti-cancer, and anti-allergy activity. In this report, we defined the effect of eupatilin on the endotoxin-induced inflammation in lipopolysaccharide (LPS)-stimulated macrophages.Main methodsMouse J774A.1 cell line and mouse peritoneal macrophages were used. Gene expression and production of inflammatory mediators were determined by real-time PCR and Western blot.Key findingsEupatilin dose-dependently suppressed LPS-induced expression of inducible nitric oxide synthase (iNOS) and production of nitric oxide (NO). Eupatilin decreased LPS-induced expression of inflammatory mediators and pro-inflammatory cytokines such as cyclooxygenase-2, monocyte chemoattractant protein-1, tumor necrosis factor-α, interleukin (IL)-1β and IL-6. In addition, this suppression of inflammatory mediators was nuclear factor (NF)-κB dependent.SignificanceOur findings imply that eupatilin suppresses inflammatory responses by the inhibition of NF-κB signaling pathway, and downstream inflammatory mediators in endotoxin-stimulated macrophages.