Role of MAPK in the regulation of double-stranded RNA- and encephalomyocarditis virus-induced cyclooxygenase-2 expression by macrophages

Protective effect of β-glucan on Poly(I:C)-induced acute lung injury/inflammation: Therapeutic implications of viral infections in the respiratory system

AIMS

Acute lung inflammation, particularly acute respiratory distress syndrome (ARDS), is caused by a variety of pathogens including bacteria and viruses. β-Glucans have been reported to possess both anti-inflammatory and immunomodulatory properties. The current study evaluated the therapeutic effect of β-glucans on polyinosinic:polycytidylic acid (Poly(I:C)) induced lung inflammation in both hamster and mice models.

MAIN METHODS

Poly(I:C)-induced ALI/inflammation models were developed in hamsters (2.5 mg/kg) and mice (2 mg/kg) by delivering the Poly(I:C) intratracheally, and followed with and without β-glucan administration. After treatment, lung mechanics were assessed and lung tissues were isolated and analyzed for mRNA/protein expression, and histopathological examinations.

KEY FINDINGS

Poly(I:C) administration, caused a significant elevation of inflammatory marker's expression in lung tissues and showed abnormal lung mechanics in mice and hamsters. Interestingly, treatment with β-glucan significantly (p < 0.001) reversed the Poly(I:C)-induced inflammatory events and inflammatory markers expression in both mRNA (IL-6, IL-1β, TNF-α, CCL2 and CCL7) and protein levels (TNF-α, CD68, myeloperoxidase, neutrophil elastase, MUC-5Ac and iNOS). Lung functional assays revealed that β-glucan treatment significantly improved lung mechanics. Histopathological analysis showed that β-glucan treatment significantly attenuated the Poly(I:C) induced inflammatory cell infiltration, injury and goblet cell population in lung tissues. Consistent with these findings, β-glucan treatment markedly reduced the number of neutrophils and macrophages in lung tissues. Our findings further demonstrated that β-glucan could reduce inflammation by suppressing the MAPK pathway.

SIGNIFICANCE

These results suggested that β-glucan may attenuate the pathogenic effects of Poly(I:C)-induced ALI/ARDS via modulating the MAPK pathway, indicating β-glucan as a possible therapeutic agent for the treatment of viral-pulmonary inflammation/injury.

p38 activation and viral infection

Viruses completely rely on the energy and metabolic systems of host cells for life activities. Viral infections usually lead to cytopathic effects and host diseases. To date, there are still no specific clinical vaccines or drugs against most viral infections. Therefore, understanding the molecular and cellular mechanisms of viral infections is of great significance to prevent and treat viral diseases. A variety of viral infections are related to the p38 MAPK signalling pathway, and p38 is an important host factor in virus-infected cells. Here, we introduce the different signalling pathways of p38 activation and then summarise how different viruses induce p38 phosphorylation. Finally, we provide a general summary of the effect of p38 activation on virus replication. Our review provides integrated data on p38 activation and viral infections and describes the potential application of targeting p38 as an antiviral strategy.

MEK/ERK MAP kinase limits poly I:C-induced antiviral gene expression in RAW264.7 macrophages by reducing interferon-beta expression

Toll-like receptor 3 (TLR3) recognizes viral double-stranded RNA (or the synthetic dsRNA analog poly I:C) and induces a signal transduction pathway that results in activation of transcription factors that induce expression of antiviral genes including type I interferon (IFN-I). Secreted IFN-I positively feeds back to amplify antiviral gene expression. In this report, we study the role of MEK/ERK MAP kinase in modulating antiviral gene expression downstream of TLR3. We find MEK/ERK is a negative regulator of antiviral gene expression by limiting expression of IFN-β. However, MEK/ERK does not limit antiviral responses downstream of the type I interferon receptor. These findings provide insights into regulatory mechanisms of antiviral gene expression and reveal potential targets for modulating antiviral immunity.

NSP2 Is Important for Highly Pathogenic Porcine Reproductive and Respiratory Syndrome Virus to Trigger High Fever-Related COX-2-PGE2 Pathway in Pigs

In 2006, atypical porcine reproductive and respiratory syndrome (PRRS) caused by a highly pathogenic PRRSV (HP-PRRSV) strain broke out in China. Atypical PRRS is characterized by extremely high fever and high mortality in pigs of all ages. Prostaglandin E2 (PGE2) derived from arachidonic acid through the activation of the rate-limiting enzyme cyclooxygenase type 1/2 (COX-1/2) plays an important role in fever. Here, we showed that HP-PRRSV infection increased PGE2 production in microglia via COX-2 up-regulation depending on the activation of MEK1-ERK1/2-C/EBPβ signaling pathways. Then, we screened HP-PRRSV proteins and demonstrated that HP-PRRSV nonstructural protein 2 (NSP2) activated MEK1-ERK1/2-C/EBPβ signaling pathways by interacting with 14-3-3ζ to promote COX-2 expression, leading to PGE2 production. Furthermore, we identified that the amino acid residues 500-596 and 658-777 in HP-PRRSV NSP2 were essential to up-regulate COX-2 expression and PGE2 production. Finally, we made mutant HP-PRRS viruses with the deletion of residues 500-596 and/or 658-777, and found out that these viruses had impaired ability to up-regulate COX-2 and PGE2 production in vitro and in vivo. Importantly, pigs infected with the mutant viruses had relieved fever, clinical symptoms, and mortality. These data might help us understand the molecular mechanisms underlying the high fever and provide clues for the development of HP-PRRSV attenuated vaccines.

The protective role of microRNA-21 against coxsackievirus B3 infection through targeting the MAP2K3/P38 MAPK signaling pathway

Background

The P38 mitogen-activated protein kinase (MAPK) pathway plays an essential role in CVB3-induced diseases. We previously demonstrated microRNA-21 has potential inhibitory effect on the MAP2K3 which locates upstream of P38 MAPK and was upregulated in mouse hearts upon CVB3 infection. However, the effect and underlying mechanism of miRNA-21 on CVB3 infection remain unclear.

Methods

We detected continuous changes of cellular miRNA-21 and P38 MAPK proteins expression profiling post CVB3 infection in vitro within 12 h. P38 MAPK signaling was inhibited by the specific inhibitor, small interfering RNA and miRNA-21 mimic in vitro, CVB3 replication, cell apoptosis rate and proliferation were detected. Viral load in the mice heart, cardiomyocyte apoptosis rate and histological of the heart were also detected in the mice model of viral myocarditis pretreated with miRNA-21-lentivirus.

Results

We observed significant upregulation of miRNA-21 expression followed by suppression of the MAP2K3/P38 MAPK signaling in CVB3-infected Hela cells. The inactivation of the MAP2K3/P38 MAPK signaling by P38 MAPK specific inhibitor, small interfering RNA against MAP2K3, or miRNA-21 overexpression significantly inhibited viral progeny release from CVB3-infected cells. Mechanistically, when compared with control miRNA, miRNA-21 showed no effect on capsid protein VP1 expression and viral load within host cells, while significantly reversing CVB3-induced caspase-3 activation and cell apoptosis rate, further promoting proliferation of infected cells, which indicates the inhibitory effect of miRNA-21 on CVB3 progeny release. In the in vivo study, when compared with control miRNA, miRNA-21 pretreatment remarkably inactivated the MAP2K3/P38 MAPK signaling in mice and protected them against CVB3 infection as evidenced by significantly alleviated cell apoptosis rate, reduced viral titers, necrosis in the heart as well as by remarkably prolonged survival time.

Conclusions

miRNA-21 were reverse correlated with P38 MAPK activation post CVB3 infection, miRNA-21 overexpression significantly inhibited viral progeny release and decreased myocytes apoptosis rate in vitro and in vivo, suggesting that miRNA-21 may serve as a potential therapeutic agent against CVB3 infection through targeting the MAP2K3/P38 MAPK signaling.

CCR5 is a required signaling receptor for macrophage expression of inflammatory genes in response to viral double-stranded RNA

Double-stranded (ds) RNA, both synthetic and produced during virus replication, rapidly stimulates MAPK and NF-κB signaling that results in expression of the inflammatory genes inducible nitric oxide synthase, cyclooxygenase 2, and IL-1β by macrophages. Using biochemical and genetic approaches, we have identified the chemokine ligand-binding C-C chemokine receptor type 5 (CCR5) as a cell surface signaling receptor required for macrophage expression of inflammatory genes in response to dsRNA. Activation of macrophages by synthetic dsRNA does not require known dsRNA receptors, as poly(inosinic:cytidylic) acid [poly(I:C)] activates signaling pathways leading to expression of inflammatory genes to similar levels in wild-type and Toll-like receptor 3- or melanoma differentiation antigen 5-deficient macrophages. In contrast, macrophage activation in response to poly(I:C) is attenuated in macrophages isolated from mice lacking CCR5. These findings support a role for CCR5 as a cell surface signaling receptor that participates in activation of inflammatory genes in macrophages in response to the viral dsRNA mimetic poly(inosinic:cytidylic) acid by pathways that are distinct from classical dsRNA receptor-mediated responses.

HEV ORF3 downregulates TLR7 to inhibit the generation of type I interferon via impairment of multiple signaling pathways

Hepatitis E is the most common type of acute hepatitis prevalent worldwide. The open reading frame 3 protein of HEV (HEV ORF3) is proposed to create a favorable environment for viral replication and pathogenesis. However, the mechanisms by which HEV overcomes the effects of host immunity, particularly the role of ORF3, remain to be established. Expression of IFNα and IFNβ in supernatant and cell samples was examined via ELISA and quantitative RT-PCR. The protein levels of specific signaling factors in cells overexpressing HEV ORF3 were examined via western blot. Analyses of cells transfected with vectors expressing ORF3 demonstrated that HEV ORF3 significantly impairs the generation of endogenous type I interferon through downregulating TLR3 and TLR7 as well as their corresponding downstream signaling pathways. Moreover, inhibition of NFκB, JAK/STAT and JNK/MAPK signaling pathways contributed significantly to suppression of increased levels of TLR7. Levels of p-P65, p-STAT1 and p-JNK were markedly impaired in ORF3-expressing cells, even upon treatment with the respective agonists. HEV ORF3 inhibits the production of endogenous type I interferon through downregulation of TLR3 and TLR7. Furthermore, suppression of TLR7 is achieved through impairment of multiple signaling pathways, including NFκB, JAK/STAT and JNK/MAPK.

Inducible GBP5 Mediates the Antiviral Response via Interferon-Related Pathways during Influenza A Virus Infection

Guanylate binding protein (GBP) 5 belongs to the GBP family, which is involved in important cellular processes, including signal transduction, translation, vesicle trafficking, and exocytosis. Structurally, GBPs display a high degree of homology and share highly conserved GTP-binding or hydrolysis domains. GBP5 was reported to be a critical cellular factor in inflammasome assembly. However, little is known about its role in the host antiviral innate immune response. In this study, we found that GBP5 expression was significantly elevated in influenza patients and influenza A virus-infected A549 human lung epithelial cells. The overexpression of GBP5 inhibited virus replication by enhancing the expression of virus-induced interferon (IFN) and IFN-related effectors. Knockdown of GBP5 had the opposite effect. Moreover, GBP5 enhanced endogenous IFN expression by interacting with the NF-κB-essential modulator complex and stimulating NF-κB signaling. Additionally, the expression of proinflammatory factors, such as IL-6, IL-8, tumor necrosis factor-α, cyclooxygenase-2, and inducible nitric oxide synthase, was also activated by GBP5. Taken together, our results reveal that GBP5 inhibited virus replication through the activation of IFN signaling and proinflammatory factors.

Double-stranded RNA upregulates the expression of inflammatory mediators in human aortic valve cells through the TLR3-TRIF-noncanonical NF-κB pathway

Calcific aortic valve disease is a chronic inflammatory condition, and the inflammatory responses of aortic valve interstitial cells (AVICs) play a critical role in the disease progression. Double-stranded RNA (dsRNA) released from damaged or stressed cells is proinflammatory and may contribute to the mechanism of chronic inflammation observed in diseased aortic valves. The objective of this study is to determine the effect of dsRNA on AVIC inflammatory responses and the underlying mechanism. AVICs from normal human aortic valves were stimulated with polyinosinic-polycytidylic acid [poly(I:C)], a mimic of dsRNA. Poly(I:C) increased the production of IL-6, IL-8, monocyte chemoattractant protein-1, and ICAM-1. Poly(I:C) also induced robust activation of ERK1/2 and NF-κB. Knockdown of Toll-like receptor 3 (TLR3) or Toll-IL-1 receptor domain-containing adapter-inducing IFN-β (TRIF) suppressed ERK1/2 and NF-κB p65 phosphorylation and reduced inflammatory mediator production induced by poly(I:C). Inhibition of NF-κB, not ERK1/2, reduced inflammatory mediator production in AVICs exposed to poly(I:C). Interestingly, inhibition of NF-κB by prevention of p50 migration failed to suppress inflammatory mediator production. NF-κB p65 intranuclear translocation induced by the TLR4 agonist was reduced by inhibition of p50 migration; however, poly(I:C)-induced p65 translocation was not, although the p65/p50 heterodimer is present in AVICs. Poly(I:C) upregulates the production of multiple inflammatory mediators through the TLR3-TRIF-NF-κB pathway in human AVICs. The NF-κB activated by dsRNA appears not to be the canonical p65/p50 heterodimers.

Poly(I:C) induces controlled release of IL-36γ from keratinocytes in the absence of cell death

The epithelium is part of an integrated immune system where cytokines, toll-like receptors and their ligands, and extracellular vesicles play a crucial role in initiating an innate immune response. IL-36γ is a pro-inflammatory member of the IL-1 family that is mainly expressed by epithelial cells, but regulation of its expression and release are only beginning to be understood. Previous studies reported that IL-36γ is abundant in recurrent respiratory papillomatosis, a rare but devastating disease caused by human papillomaviruses (HPV) types 6 and 11, in which papillomas recurrently grow in and block the airway. Despite the overexpression of IL-36γ, papilloma tissues show no evidence of inflammation, possibly due to suppression of its release by HPVs. We have used primary human foreskin keratinocytes as a model to study IL-36γ regulation in normal epithelial cells. Low doses of poly(I:C) mediate expression and release of IL-36γ without inducing the cell death reported by those using high doses. PKR, an enzyme required for inflammasome activation, does not contribute to controlled release of IL36γ. The keratinocytes secrete IL-36γ in two forms, soluble and in extracellular vesicles. We conclude that there are two separately regulated pathways for the controlled secretion of IL-36γ from keratinocytes, which could contribute to the modulation of both local and systemic immune responses to viruses and other pathogens.

TREM-1 activation modulates dsRNA induced antiviral immunity with specific enhancement of MAPK signaling and the RLRs and TLRs on macrophages

Triggering receptor expressed on myeloid cells 1(TREM-1) is a newly identified member of the immunoglobulin superfamily and is extensively involved in the regulation of innate immunity. To determine the role of TREM-1 in innate antiviral immunity, we investigated TREM-1 expression and its downstream signaling effect in the murine bone marrow-derived macrophages or RAW264.7 macrophage-like mouse cell line by double-stranded RNA (dsRNA) stimulation. The level of TREM-1 expression was low at the baseline and could up-regulate markedly in dose- and time-dependent manners upon stimulation by dsRNA/poly IC. Inhibitor studies disclosed mitogen-activated protein kinase (MAPK) p38 and PI3K pathways were involved in dsRNA-induced up-regulation of TREM-1. Compared with lipopolysaccharide (LPS), the peak response of poly IC-induced TREM-1 expression is delayed, and cells pretreated with scrambled RNA presented higher expression of TREM-1 upon LPS challenge. After ligation with the agonist antibody, TREM-1 can potentiate type I interferon (IFN) production and antiviral inflammation induced by dsRNA, which is ralated to the enhanced phosphorylation of MAPKs and expression of RLRs and TLRs by TREM-1 ligation. This study is the first to show the regulatory role of TREM-1 in RLRs and TLRs expression, and these findings might enrich the understanding of the up-regulation mechanism and the function of TREM-1.

Poly(I:C) increases the expression of mPGES-1 and COX-2 in rat primary microglia

Background

Microglia recognize pathogen-associated molecular patterns such as double-stranded RNA (dsRNA) present in some viruses. Polyinosinic-polycytidylic acid [poly(I:C)] is a synthetic analog of dsRNA that activates different molecules, such as retinoic acid-inducible gene I, melanoma differentiation-associated gene 5, and toll-like receptor-3 (TLR3). Poly(I:C) increases the expression of different cytokines in various cell types. However, its role in the regulation of the production of inflammatory mediators of the arachidonic acid pathway by microglia is poorly understood.

Methods

In the present study, we evaluated the effect of poly(I:C) on the production of prostaglandin E₂ (PGE₂) and the inducible enzymes cyclooxygenase-2 (COX-2) and microsomal prostaglandin E synthase-1 (mPGES-1) in primary rat microglia. Microglia were stimulated with different concentrations of poly(I:C) (0.1–10 μg/ml), and the protein levels of COX-2 and mPGES-1, as well as the release of PGE₂, were determined by western blot and enzyme immunoassay (EIA), respectively. Values were compared using one-way ANOVA with post hoc Student-Newman-Keuls test.

Results

Poly(I:C) increased the production of PGE₂, as well as mPGES-1 and COX-2 synthesis. To investigate the mechanisms involved in poly(I:C)-induced COX-2 and mPGES-1, we studied the effects of various signal transduction pathway inhibitors. Protein levels of COX-2 and mPGES-1 were reduced by SB203580, SP600125, and SC514 (p38 mitogen-activated protein kinase (MAPK), c-Jun N-terminal kinase (JNK), and IκB kinase (IKK) inhibitors, respectively), as well as by PD98059 and PD0325901 (mitogen-activated protein kinase kinase (MEK) inhibitors). Rapamycin, a mammalian target of rapamycin (mTOR) inhibitor, enhanced the synthesis of COX-2. Inhibition of phosphatidylinositol 3-kinase (PI3K) by LY294002 or dual inhibition of PI3K/mTOR (with NVP-BEZ235) enhanced COX-2 and reduced mPGES-1 immunoreactivity. To confirm the data obtained with the inhibitors, we studied the phosphorylation of the blocked kinases by western blot. Poly(I:C) increased the phosphorylation of p38 MAPK, extracellular signal-regulated kinase (ERK), JNK, protein kinase B (Akt), and IκB.

Conclusions

Taken together, our data demonstrate that poly(I:C) increases the synthesis of enzymes involved in PGE₂ synthesis via activation of different signaling pathways in microglia. Importantly, poly(I:C) activates similar pathways also involved in TLR4 signaling that are important for COX-2 and mPGES-1 synthesis. Thus, these two enzymes and their products might contribute to the neuropathological effects induced in response to dsRNA, whereby the engagement of TLR3 might be involved.

CCR5-Dependent Activation of mTORC1 Regulates Translation of Inducible NO Synthase and COX-2 during Encephalomyocarditis Virus Infection

Encephalomyocarditis virus (EMCV) infection of macrophages results in the expression of a number of inflammatory and antiviral genes, including inducible NO synthase (iNOS) and cyclooxygenase (COX)-2. EMCV-induced macrophage activation has been shown to require the presence of CCR5 and the activation of PI3K-dependent signaling cascades. The purpose of this study was to determine the role of PI3K in regulating the macrophage responses to EMCV. We show that PI3K regulates EMCV-stimulated iNOS and COX-2 expression by two independent mechanisms. In response to EMCV infection, Akt is activated and regulates the translation of iNOS and COX-2 through the mammalian target of rapamycin complex (mTORC)1. The activation of mTORC1 during EMCV infection is CCR5-dependent and appears to function in a manner that promotes the translation of iNOS and COX-2. CCR5-dependent mTORC1 activation functions as an antiviral response, as mTORC1 inhibition increases the expression of EMCV polymerase. PI3K also regulates the transcriptional induction of iNOS and COX-2 in response to EMCV infection by a mechanism that is independent of Akt and mTORC1 regulation. These findings indicate that macrophage expression of the inflammatory genes iNOS and COX-2 occurs via PI3K- and Akt-dependent translational control of mTORC1 and PI3K-dependent, Akt-independent transcriptional control.

Macrophage Expression of Inflammatory Genes in Response to EMCV Infection

The expression and production of type 1 interferon is the classic cellular response to virus infection. In addition to this antiviral response, virus infection also stimulates the production of proinflammatory mediators. In this review, the pathways controlling the induction of inflammatory genes and the roles that these inflammatory mediators contribute to host defense against viral pathogens will be discussed. Specific focus will be on the role of the chemokine receptor CCR5, as a signaling receptor controlling the activation of pathways leading to virus-induced inflammatory gene expression.

Important Role of the IL-32 Inflammatory Network in the Host Response against Viral Infection

The pro-inflammatory cytokine interleukin (IL)-32 has gained much attention recently because of its important role in the inflammatory network. Since the discovery of IL-32 in 2005, our appreciation for its diverse roles continues to grow. Recent studies have discovered the antiviral effects induced by IL-32 and its associated regulatory mechanisms. The interactions between IL-32 and various cytokines including cyclooxygenase 2 (COX-2), inducible nitric oxide synthase (iNOS), interferon (IFN)-λ1, interleukin (IL)-6, and soluble IL-6 receptor have been described. This review aims to integrate these new findings into explicit concepts and raises the intriguing possibility of IL-32 as a therapeutic target.

Toll-like receptor-mediated immune responses are attenuated in the presence of high levels of hepatitis B virus surface antigen

It has been recently shown that Toll-like receptor (TLR) signalling in murine nonparenchymal liver cells (NPCs) is suppressed in the presence of Hepatitis B virus surface antigen (HBsAg). It is not clear, however, whether this is also relevant for the adaptive immune responses and how this effect is mediated. Peripheral blood mononuclear cells (PBMCs) from Hepatitis B virus (HBV) patients and controls were stimulated by TLR ligands in the absence or presence of autologous serum. Interestingly, TLR-mediated cytokine expression (Interleukin-6 and -10) as well as TLR3-induced interferon (IFN) expression in PBMCs of HBV patients was significantly higher than in the healthy volunteers, showing a negative correlation with the levels of HBsAg. In addition, TLR3-mediated IFN-γ production was inhibited in the presence of HBV-containing serum. To mechanistically analyse this observation, murine Kupffer cells (KCs) and sinusoidal endothelial cells (LSECs) were stimulated with TLR3 ligands in the presence or absence of HBsAg. Mixed lymphocyte reactions were performed to study T-cell activation induced by TLR-stimulated NPCs. Gene expression of cytokines and TLR3 was analysed by quantitative rt-PCR, and activation of transcription factors was assessed by Western blot or reporter gene assays. TLR-induced expression of interferon γ, interferon sensitive genes and proinflammatory cytokines in murine KCs and LSECs was efficiently suppressed in the presence of HBsAg, whereas the expression of anti-inflammatory cytokines was enhanced. Activation of NFκB, IRF-3 and MAPKs in these liver cells was potently suppressed by HBsAg. T-cell activation mediated through TLR3-stimulated KCs or LSECs was suppressed by HBsAg which could be reverted by anti-IL-10 antibodies. These findings may, at least in part, explain how HBV evades innate and adaptive immune responses to maintain a persistent infection.

Evidence of MAPK-JNK1/2 activation by hepatitis E virus ORF3 protein in cultured hepatoma cells

Hepatitis E virus (HEV) has recently emerged to cause chronic infection in some immunosuppressed individuals, including extrahepatic manifestations in acute and chronic patients. Mammalian MAPK–JNK1/2 is expressed in hepatocytes, which is known to be involved in anti-apoptotic signaling pathway for the establishment of persistent infection. Though in vitro modulation of cellular MAPK–ERK cascade by HEV-ORF3 protein is suggested to have a role in host pathobiology, activation of the JNK module has not been studied so far. In this report, we have shown for the first time, evidence of MAPK–JNK1/2 activation by HEV-ORF3, using viral replicon as well as expression vector in human hepatoma cells. Phospho-ELISA based relative quantitaion has demonstrated ~54% and ~66% phosphorylation of JNK1/2 in replicon-RNA and ORF3-vector DNA transfected cells, respectively. Our finding however, suggests further molecular studies to validate a role of JNK1/2 in HEV pathogenesis.

Cloning and expression of retinoic acid-induced gene-I and its effect on hepatitis C virus replication

OBJECTIVE

To explore the influence of the retinoic acid indicible gene-I (RIG-I) on hepatitis C virus (HCV) replication and the molecular mechanism of action of RIG-I.

METHODS

We constructed an RIG-I expression vector and co-transfected it into Huh-7 cells along with HCV-replicon RNA. We assayed HCV replication and NS5A protein synthesis via real-time polymerase chain reaction (RT-PCR) and western blotting. Also, we performed an enzyme-linked immunosorbent assay (ELISA) to measure the level of interferon (IFN)-alpha/-beta secretion. Additionally, we examined, via western blotting, the phosphorylation state of p38, Erk1/2, and nuclear factor (NF)-kappaB p65.

RESULTS

Overexpression of RIG-1 in Huh-7 cells co-transfected with an HCV-replicon RNA significantly inhibited HCV replication and NS5A protein synthesis. Co-transfected cells had increased production of IFN-alpha/-beta production and had higher levels of phosphorylated p38, Erk1/2, and NF-kappaB p65.

CONCLUSIONS

RIG-I significantly inhibits HCV replication and NS5A protein synthesis by inducing type I IFN production. The underlying molecular mechanism for this effect appears to be mediated by increased phosphorylation of NF-kappaB p65, p38-mitogen-activated protein kinases (MAPK), and Erk1/2.

Activation of JNK1/2 and p38 MAPK signaling pathways promotes enterovirus 71 infection in immature dendritic cells

Background

c-Jun NH₂-terminal kinase/stress-activated kinase (JNK/SAPK) and the p38 mitogen-activated protein kinase (p38 MAPK) are important components of cellular signal transduction pathways, which have been reported to be involved in viral replication. However, little is known about JNK1/2 and p38 MAPK signaling pathways in enterovirus 71 (EV71)-infected immature dendritic cells (iDCs). Thus, iDCs were induced from peripheral blood mononuclear cells (PBMC) and performed to explore the expressions and phosphorylation of molecules in the two signaling pathways as well as secretions of inflammatory cytokines and interferons during EV71 replication.

Results

We showed that EV71 infection could activate both JNK1/2 and p38 MAPK in iDCs and phosphorylate their downstream transcription factors c-Fos and c-Jun, which further promoted the production of IL-2, IL-6, IL-10, and TNF-α. Moreover, EV71 infection also increased the release of IFN-β and IL-12 p40. Pretreatment of iDCs with SP600125 and SB203580 (20 μM) could severely impair viral replication and its induced phosphorylation of JNK1/2,p38 MAPK, c-Fos and c-Jun. In addition, treatment of EV71-infected iDCs with SP600125 and SB203580 could inhibit secretions of IL-6, IL-10 and TNF-α.

Conclusion

JNK1/2 and p38 MAPK signaling pathways are beneficial to EV71 infection and positively regulate secretions of inflammatory cytokines in iDCs.

Cyclooxygenase-2-prostaglandin E2-eicosanoid receptor inflammatory axis: a key player in Kaposi's sarcoma-associated herpes virus associated malignancies

The role of cyclooxygenase-2 (COX-2), its lipid metabolite prostaglandin E2 (PGE2), and Eicosanoid (EP) receptors (EP; 1-4) underlying the proinflammatory mechanistic aspects of Burkitt's lymphoma, nasopharyngeal carcinoma, cervical cancer, prostate cancer, colon cancer, and Kaposi's sarcoma (KS) is an active area of investigation. The tumorigenic potential of COX-2 and PGE2 through EP receptors forms the mechanistic context underlying the chemotherapeutic potential of nonsteroidal anti-inflammatory drugs (NSAIDs). Although role of the COX-2 is described in several viral associated malignancies, the biological significance of the COX-2/PGE2/EP receptor inflammatory axis is extensively studied only in Kaposi's sarcoma-associated herpes virus (KSHV/HHV-8) associated malignancies such as KS, a multifocal endothelial cell tumor and primary effusion lymphoma (PEL), a B cell-proliferative disorder. The purpose of this review is to summarize the salient findings delineating the molecular mechanisms downstream of COX-2 involving PGE2 secretion and its autocrine and paracrine interactions with EP receptors (EP1-4), COX-2/PGE2/EP receptor signaling regulating KSHV pathogenesis and latency. KSHV infection induces COX-2, PGE2 secretion, and EP receptor activation. The resulting signal cascades modulate the expression of KSHV latency genes (latency associated nuclear antigen-1 [LANA-1] and viral-Fas (TNFRSF6)-associated via death domain like interferon converting enzyme-like- inhibitory protein [vFLIP]). vFLIP was also shown to be crucial for the maintenance of COX-2 activation. The mutually interdependent interactions between viral proteins (LANA-1/vFLIP) and COX-2/PGE2/EP receptors was shown to play key roles in the biological mechanisms involved in KS and PEL pathogenesis such as blockage of apoptosis, cell cycle regulation, transformation, proliferation, angiogenesis, adhesion, invasion, and immune-suppression. Understanding the COX-2/PGE2/EP axis is very important to develop new safer and specific therapeutic modalities for KS and PEL. In addition to COX-2 being a therapeutic target, EP receptors represent ideal targets for pharmacologic agents as PGE2 analogues and their blockers/antagonists possess antineoplastic activity, without the reported gastrointestinal and cardiovascular toxicity observed with few a NSAIDs.

Differential gene expressions of the MAPK signaling pathway in enterovirus 71-infected rhabdomyosarcoma cells

Background

Mitogen-activated protein kinase (MAPK) signaling pathway plays an important role in response to viral infection. The aim of this study was to explore the function and mechanism of MAPK signaling pathway in enterovirus 71 (EV71) infection of human rhabdomyosarcoma (RD) cells.

Methods

Apoptosis of RD cells was observed using annexin V-FITC/PI binding assay under a fluorescence microscope. Cellular RNA was extracted and transcribed to cDNA. The expressions of 56 genes of MAPK signaling pathway in EV71-infected RD cells at 8 h and 20 h after infection were analyzed by PCR array. The levels of IL-2, IL-4, IL-10, and TNF-α in the supernatant of RD cells infected with EV71 at different time points were measured by ELISA.

Results

The viability of RD cells decreased obviously within 48 h after EV71 infection. Compared with the control group, EV71 infection resulted in the significantly enhanced releases of IL-2, IL-4, IL-10 and TNF-α from infected RD cells (p < 0.05). At 8 h after infection, the expressions of c-Jun, c-Fos, IFN-β, MEKK1, MLK3 and NIK genes in EV71-infected RD cells were up-regulated by 2.08–6.12-fold, whereas other 19 genes (e.g. AKT1, AKT2, E2F1, IKK and NF-κB1) exhibited down-regulation. However, at 20 h after infection, those MAPK signaling molecules including MEKK1, ASK1, MLK2, MLK3, NIK, MEK1, MEK2, MEK4, MEK7, ERK1, JNK1 and JNK2 were up-regulated. In addition, the expressions of AKT2, ELK1, c-Jun, c-Fos, NF-κB p65, PI3K and STAT1 were also increased.

Conclusion

EV71 infection induces the differential gene expressions of MAPK signaling pathway such as ERK, JNK and PI3K/AKT in RD cells, which may be associated with the secretions of inflammatory cytokines and host cell apoptosis.

CD11b/CD18 (Mac-1) is a novel surface receptor for extracellular double-stranded RNA to mediate cellular inflammatory responses

During viral infection, extracellular dsRNA is a potent signaling molecule that activates many innate immune cells, including macrophages. TLR3 is a well-known receptor for extracellular dsRNA, and internalization of extracellular dsRNA is required for endosomal TLR3 activation. Preserved inflammatory responses of TLR3-deficient macrophages to extracellular dsRNA strongly support a TLR3-independent mechanism in dsRNA-mediated immune responses. The present study demonstrated that CD11b/CD18 (Mac-1 [macrophage-1 Ag]), a surface integrin receptor, recognized extracellular dsRNA and induced macrophage immune responses. CD11b deficiency reduced inflammatory cytokine induction elicited by polyinosinic:polycytidylic acid (poly I:C; a synthetic dsRNA) in mouse sera and livers, as well as in cultured peritoneal macrophages. dsRNA-binding assay and confocal immunofluorescence showed that Mac-1, especially the CD11b subunit, interacted and colocalized with poly I:C on the surface of macrophages. Further mechanistic studies revealed two distinct signaling events following dsRNA recognition by Mac-1. First, Mac-1 facilitated poly I:C internalization through the activation of PI3K signaling and enhanced TLR3-dependent activation of IRF3 in macrophages. Second, poly I:C induced activation of phagocyte NADPH oxidase in a TLR3-independent, but Mac-1-dependent, manner. Subsequently, phagocyte NADPH oxidase-derived intracellular reactive oxygen species activated MAPK and NF-κB pathways. Our results indicate that extracellular dsRNA activates Mac-1 to enhance TLR3-dependent signaling and to trigger TLR3-independent, but Mac-1-dependent, inflammatory oxidative signaling, identifying a novel mechanistic basis for macrophages to recognize extracellular dsRNA to regulate innate immune responses. This study identifies Mac-1 as a novel surface receptor for extracellular dsRNA and implicates it as a potential therapeutic target for virus-related inflammatory diseases.

RO 90-7501 enhances TLR3 and RLR agonist induced antiviral response

Recognition of virus infection by innate pattern recognition receptors (PRRs), including membrane-associated toll-like receptors (TLR) and cytoplasmic RIG-I-like receptors (RLR), activates cascades of signal transduction pathways leading to production of type I interferons (IFN) and proinflammatory cytokines that orchestrate the elimination of the viruses. Although it has been demonstrated that PRR-mediated innate immunity plays an essential role in defending virus from infection, it also occasionally results in overwhelming production of proinflammatory cytokines that cause severe inflammation, blood vessel leakage and tissue damage. In our efforts to identify small molecules that selectively enhance PRR-mediated antiviral, but not the detrimental inflammatory response, we discovered a compound, RO 90-7501 ('2'-(4-Aminophenyl)-[2,5'-bi-1H-benzimidazol]-5-amine), that significantly promoted both TLR3 and RLR ligand-induced IFN-β gene expression and antiviral response, most likely via selective activation of p38 mitogen-activated protein kinase (MAPK) pathway. Our results thus imply that pharmacological modulation of PRR signal transduction pathways in favor of the induction of a beneficial antiviral response can be a novel therapeutic strategy.

Dysregulated TLR3-dependent signaling and innate immune activation in superoxide-deficient macrophages from nonobese diabetic mice

In type 1 diabetes (T1D), reactive oxygen species (ROS) and proinflammatory cytokines produced by macrophages and other innate immune cells destroy pancreatic β cells while promoting autoreactive T cell maturation. Superoxide-deficient nonobese diabetic mice (NOD.Ncf1(m1J)) are resistant to spontaneous diabetes, revealing the integral role of ROS signaling in T1D. Here, we evaluate the innate immune activation state of bone marrow-derived macrophages (BM-Mϕ) from NOD and NOD.Ncf1(m1J) mice after poly(I:C)-induced Toll-like receptor 3 (TLR3) signaling. We show that ROS synthesis is required for efficient activation of the NF-κB signaling pathway and concomitant expression of TLR3 and the cognate adaptor molecule, TRIF. Poly(I:C)-stimulated NOD.Ncf1(m1J) BM-Mϕ exhibited a 2- and 10-fold decrease in TNF-α and IFN-β proinflammatory cytokine synthesis, respectively, in contrast to NOD BM-Mϕ. Optimal expression of IFN-α/β is not solely dependent on superoxide synthesis, but requires p47(phox) to function in a NOX-independent manner to mediate type I interferon synthesis. Interestingly, MHC-II I-A(g7) expression necessary for CD4 T cell activation is increased 2-fold relative to NOD, implicating a role for superoxide in I-A(g7) downregulation. These findings suggest that defective innate immune-pattern-recognition receptor activation and subsequent decrease in TNF-α and IFN-β proinflammatory cytokine synthesis necessary for autoreactive T cell maturation may contribute to the T1D protection observed in NOD.Ncf1(m1J) mice.

Ccr5 regulates inflammatory gene expression in response to encephalomyocarditis virus infection

Encephalomyocarditis virus (EMCV) is capable of stimulating inflammatory gene expression by macrophages as a result of interactions between EMCV capsid proteins and cell surface receptors. In this study, biochemical and genetic approaches identified a role for Ccr5, a chemokine receptor, in transducing the signals of EMCV infection that result in the expression of inflammatory genes in macrophages. Antibody neutralization and gene knockout strategies were used to show that the presence of Ccr5 is required for EMCV-stimulated mitogen-activated protein (MAP) kinase and nuclear factor-kappa B (NF-κB) activation, and the subsequent expression of the inflammatory gene-inducible nitric oxide synthase (iNOS) and cyclooxygenase 2 (COX-2). Ccr5 appears to participate in the early control of virus replication: EMCV mRNA accumulates to sevenfold higher levels in Ccr5-deficient mice when compared to wild-type controls. These findings support a regulatory role for Ccr5 in the antiviral response to EMCV in which this chemokine receptor participates in regulation of inflammatory gene expression in response to virus infection.

Involvement of mitogen-activated protein kinase activation in cyclooxygenase-2 and transforming growth factor-β production in alveolar macrophage from chronic bronchitis rats

OBJECTIVE

Lipopolysaccharides (LPS) activates several signaling pathways in macrophages including mitogen-activated protein kinases (MAPK). Previous studies have investigated effect of LPS on MAPK activation in macrophage of normal rats. In the current study, we investigated the effect of LPS exposure on activation of MAPK in alveolar macrophage (AM) of chronic bronchitis (CB) rats and researched the corresponding cyclooxygenase-2 (COX-2), prostaglandins-2 (PGE(2)) and transforming growth factor- β (TGF-β) production and their MAPK signal pathways.

METHODS

CB model was established by injection of Bacillus Calmette-Guerin (BCG) and LPS in rats. Special inhibitors of p38, extracellular signal-regulated kinase (ERK) and c-Jun-N-terminal kinases (JNK) MAPK signal pathways were used to determine the effect of MAPK activation on COX-2, PGE(2), TGF-β production in AM of CB rats via RT-PCR, western blotting, radioimmunoassay and ELISA.

KEY FINDINGS

Synthesis of PGE(2) from AM of CB rats was increased and suppressed by either PD98059 or SB203580. SB203580 and PD98059, (inhibitors of ERK and p38 MAPK), could significantly inhibit COX-2 mRNA and protein expression. Moreover, ERK and p38 MAPK had synergistic effect on COX-2 expression. Inhibitor of ERK MAPK signal transduction could inhibit TGF-β expression in AM.

CONCLUSION

These results demonstrated COX-2, PGE(2) and TGF-β productions in AM of CB rats were significantly increased, which might be regulated by the different MAPK signaling pathway.

NFAT and CREB regulate Kaposi's sarcoma-associated herpesvirus-induced cyclooxygenase 2 (COX-2)

COX-2 has been implicated in Kaposi's sarcoma-associated herpesvirus (KSHV) latency and pathogenesis (A. George Paul, N. Sharma-Walia, N. Kerur, C. White, and B. Chandran, Cancer Res. 70:3697-3708, 2010; P. P. Naranatt, H. H. Krishnan, S. R. Svojanovsky, C. Bloomer, S. Mathur, and B. Chandran, Cancer Res. 64:72-84, 2004; N. Sharma-Walia, A. G. Paul, V. Bottero, S. Sadagopan, M. V. Veettil, N. Kerur, and B. Chandran, PLoS Pathog. 6:e1000777, 2010; N. Sharma-Walia, H. Raghu, S. Sadagopan, R. Sivakumar, M. V. Veettil, P. P. Naranatt, M. M. Smith, and B. Chandran, J. Virol. 80:6534-6552, 2006). However, the precise regulatory mechanisms involved in COX-2 induction during KSHV infection have never been explored. Here, we identified cis-acting elements involved in the transcriptional regulation of COX-2 upon KSHV de novo infection. Promoter analysis using human COX-2 promoter deletion and mutation reporter constructs revealed that nuclear factor of activated T cells (NFAT) and the cyclic AMP (cAMP) response element (CRE) modulate KSHV-mediated transcriptional regulation of COX-2. Along with multiple KSHV-induced signaling pathways, infection-induced prostaglandin E(2) (PGE(2)) also augmented COX-2 transcription. Infection of endothelial cells markedly induced COX-2 expression via a cyclosporine A-sensitive, calcineurin/NFAT-dependent pathway. KSHV infection increased intracellular cAMP levels and activated protein kinase A (PKA), which phosphorylated the CRE-binding protein (CREB) at serine 133, which probably led to interaction with CRE in the COX-2 promoter, thereby enhancing COX-2 transcription. PKA selective inhibitor H-89 pretreatment strongly inhibited CREB serine 133, indicating the involvement of a cAMP-PKA-CREB-CRE loop in COX-2 transcriptional regulation. In contrast to phosphatidylinositol 3-kinase and protein kinase C, inhibition of FAK and Src effectively reduced KSHV infection-induced COX-2 transcription and protein levels. Collectively, our study indicates that mediation of COX-2 transcription upon KSHV infection is a paradigm of a complex regulatory milieu involving the interplay of multiple signal cascades and transcription factors. Intervention at each step of COX-2/PGE(2) induction can be used as a potential therapeutic target to treat KSHV-associated neoplasm and control inflammatory sequels of KSHV infection.

Src family kinases participate in the regulation of encephalomyocarditis virus-induced cyclooxygenase-2 expression by macrophages

Src family kinases (SFKs) are non-receptor tyrosine kinases that have been implicated as regulators of the inflammatory response. In this study, the role of SFK activation in the inflammatory response of macrophages to encephalomyocarditis virus (EMCV) infection was examined. Virus infection of macrophages stimulates the expression of cyclooxygenase-2 (COX-2), interleukin (IL)-1β and inducible nitric oxide synthase (iNOS). Inhibition of SFK attenuates EMCV-induced COX-2 expression and prostaglandin E₂ production, iNOS expression and subsequent nitric oxide production, and IL-1β expression. EMCV-induced COX-2 expression requires the activation of nuclear factor-κB and the mitogen-activated protein kinase p38. Consistent with these previous findings, inhibition of SFKs attenuated the phosphorylation of p38 in response to EMCV infection, suggesting that SFKs may act upstream of p38. These findings provide evidence that SFK activation plays an active role in the regulation of inflammatory gene expression by virus-infected macrophages.

Poly(I:C) induces BLyS-expression of airway fibroblasts through phosphatidylinositol 3-kinase

B lymphocyte stimulator (BLyS), B cell activating factor (BAFF), a member of the tumor necrosis factor ligand superfamily has potent co-stimulatory activity on B cells, and BLyS-production in the airway mucosa is of potential importance as it triggers innate and adaptive immune responses. To investigate whether airway fibroblast could express BLyS, we examined BLyS-expression in human nasal airway fibroblasts and compared to its expression in tonsillar and skin fibroblasts as well as the effect of the Toll-like receptor (TLR) ligands on that in human nasal airway fibroblasts. The expression of BLyS by nasal fibroblasts in the presence of polyinocinic-polycytidykic acid (poly(I:C)) was markedly induced, to a level of more than 100 times higher than that observed in the absence of poly(I:C). In order to demonstrate the intracellular pathways involved in poly(I:C)-induced BLyS-expression, we used specific inhibitors of phosphatidylinositol 3-kinase (PI3-kinase), spleen tyrosine kinase (Syk), p38 mitogen-activated protein kinase (p38 MAPK), c-Jun N-terminal kinase (JNK), and extracellular-signal related kinase (ERK)-signaling in these events. Pre-incubation with the PI3-kinase inhibitor LY294002 or Wortmanin reversed the poly(I:C)-induced production and expression of BLyS. Syk kinase inhibitor Piceatannol partially reduced its production and expression. Thus, we were able to show that PI3-kinase signaling is directly involved in poly(I:C)-induced BLyS-expression in nasal airway fibroblasts. These results indicate that human nasal airway fibroblasts strongly induce BLyS-expression and production by poly(I:C) through PI3-K signaling during airway immune responses.

Role of macrophages in the development of pancreatic islet injury in spontaneously diabetic torii rats

Spontaneously diabetic Torii (SDT) rats were established from Sprague-Dawley (SD) rat and are used as an animal model of type 2 diabetes mellitus. In the present study, the mechanism of the development of injury in the pancreas of these rats was examined focusing on the role of monocytes/macrophages. The number of lymphocytes and monocytes in the circulation of SDT rats increased with age, reaching a plateau at around 9 weeks of age and remaining at that level thereafter. The number of leukocytes in SDT rats was almost twice that of wild-type SD rats. Serum IL-18 levels began to increase at 8 weeks of age, forming a prominent peak at 9 weeks of age. In parallel with this, serum levels of NO2/NO3 showed an abrupt rise and decline. Spleen cells prepared from 9-week-old SDT rats expressed high levels of IFN-gamma in response to IL-18, while those from 9-week-old wild-type SD rats did not. Immunohistochemical analysis revealed marked infiltration of CD68+ cells in the islets of SDT rats. Treatment of SDT rats with Cl2MDP-liposomes reduced the number of monocytes as well as levels of NO2/NO3 in the circulation. Consistent with this, the number of infiltrated CD68+ cells in the islets was reduced in SDT rats treated with Cl2MDP-liposomes. These results suggest that macrophages are involved in pancreatic islet injury in SDT rats through excess production of NO induced by IL-18 which increases transitorily at around 9 weeks of age.

Phosphatidylinositol 3-kinase regulates macrophage responses to double-stranded RNA and encephalomyocarditis virus

Virus infection of macrophages stimulates the expression of proinflammatory and antiviral genes interleukin-1 (IL-1), inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2). In this study, we show that phosphatidylinositol 3-kinase (PI3K) is required for the inflammatory response of macrophages to virus infection. When macrophages are infected with encephalomyocarditis virus (EMCV) there is a rapid and transient activation of PI3K and phosphorylation of its downstream target Akt. Inhibitors of PI3K attenuate EMCV- and double-stranded RNA-induced iNOS, COX-2 and IL-1 beta expression in RAW264.7 cells and mouse peritoneal macrophages. The attenuation of inflammatory gene expression in response to PI3K inhibition correlates with the induction of macrophage apoptosis. The morphology of macrophages shifts from activation in response to EMCV infection to apoptosis in the cells treated with PI3K inhibitors and EMCV. These morphological changes are accompanied by the activation of caspase-3. These findings suggest that PI3K plays a central role in the regulation of macrophage responses to EMCV infection. When PI3K is activated, it participates in the regulation of inflammatory gene expression; however, if PI3K is inhibited macrophages are unable to mount an inflammatory antiviral response and die by apoptosis.

Effect of TLR3 and TLR7 activation in uterine NK cells from non-obese diabetic (NOD) mice

Toll-like receptor (TLR)-TLR cross talk is thought to be important in TLR signaling. Herein, we investigated the effect of specific TLR3 and TLR7 agonists, poly (I:C) and R837, individually and in combination, on uterine immune cell function and their subsequent effects on pregnancy outcome. Allogeneic pregnancies in the non-obese diabetic (NOD) mousexC57BL/6 and wild-type BALB/cxC57BL/6 model were used. An additive increase in embryo resorption was observed after induction with both poly (I:C) and R837, and was associated with elevated numbers of both TNF-alpha- and IFN-gamma-producing CD45(+) cells in the uterus. Further examination showed that while cytokine expression was detected in both CD3(+) cells and CD49b(+) cells in BALB/c mice, NOD mouse cells behaved differently. In NOD mice, elevated cytokine expression was attributed to CD3(+) T cells, with no response detected in the CD49b(+) NK cells. The additive effect of combined agonists was partially inhibited by the Jun N-terminal kinase (JNK) mitogen-activated protein kinase (MAPK) inhibitor SP600125 and almost completely abrogated by the extracellular signal-regulated kinase (ERK) MAPK inhibitor PD98059. These results suggest that increased TLR3 and TLR7 signals are transmitted via Th1-type T cells, rather than NK cells, in NOD mice. Furthermore, the ERK MAPK pathway may be critical in TLR3 and TLR7 signaling.

Negative feedback regulation of IL-32 production by iNOS activation in response to dsRNA or influenza virus infection

iNOS plays an important role in mediating inflammation. In this study, we found that iNOS-derived NO was increased 2.4-fold in the serum samples of 101 patients infected with influenza A virus in comparison with samples of 105 healthy individuals. In A549 human lung epithelial cells, infection with influenza A virus or stimulation with poly(I:C)+IFN-gamma resulted in increased mRNA and protein levels of both IL-32 and iNOS, with subsequent release of NO. Over-expression of IL-32 resulted in upregulated iNOS expression with subsequent NO production. Knock down of IL-32 by IL-32-specific siRNA resulted in the inhibition of dsRNA-induced expression of iNOS and NO release, indicating that IL-32 is an upstream regulatory factor of dsRNA-triggered iNOS production. Surprisingly, over-expression of iNOS resulted in the reduction of IL-32 expression, and suppression of iNOS by the selective iNOS inhibitor S-methylisothiourea sulfate stimulated IL-32 expression, indicating that a negative feedback mechanism operates between the iNOS/NO and IL-32 systems. These findings suggest that influenza A virus infection activates IL-32 and iNOS expression by a heretofore unrecognized complex mechanism, in which the two pro-inflammatory factors regulate each other, involving positive and negative feedback regulatory loops.

IL-10-dependent S100A8 gene induction in monocytes/macrophages by double-stranded RNA

The S100 calcium-binding proteins S100A8 and S100A9 are elevated systemically in patients with viral infections. The S100A8-S100A9 complex facilitated viral replication in human CD4(+) T lymphocytes latently infected with HIV-1- and S100A8-induced HIV-1 transcriptional activity. Mechanisms inducing the S100 genes and the potential source of these proteins following viral activation are unknown. In this study, we show that S100A8 was induced in murine macrophages, and S100A8 and S100A9 in human monocytes and macrophages, by polyinosinic:polycytidylic acid, a dsRNA mimetic. Induction was at the transcriptional level and was IL-10 dependent. Similar to LPS-induced S100A8, induction by dsRNA was dependent on p38 and ERK MAPK. Protein kinase R (PKR) mediates antiviral defense and participates in MyD88-dependent/independent signaling triggered by TLR4 or TLR3. Like IL-10, S100 induction by polyinosinic:polycytidylic acid and by LPS was inhibited by the specific PKR inhibitor 2-aminopurine, indicating a novel IL-10, PKR-dependent pathway. Other mediators such as IFN-beta, which synergized with dsRNA, may also be involved. C/EBPbeta bound the defined promoter region in response to dsRNA. S100A8 was expressed in lungs of mice infected with influenza virus and was maximal at day 8 with strong immunoreactivity in epithelial cells lining the airways and in mononuclear cells and declined early in the recovery phase, implying down-regulation by mediator(s) up-regulated during resolution of the infection. IL-10 is implicated in viral persistence. Since S100A8/S100A9 levels are likely to be maintained in conditions where IL-10 is raised, these proteins may contribute to viral persistence in patients infected by some RNA viruses.

Cell Defence and Survival

Central to immune defence mechanisms is the role of transcription factor nuclear factor kappa B (NF-kB). This is a complex biochemical topic with ever more controls revealed. NF-kB determines the production of proinflammatory cytokines and chemokines. Pharmacologists step in with possible means of control. Other systems involved in defence include the cyclooxygenase 2 (Cox-2) enzyme and perioxisome proliferator-activated receptors. Insulin receptor activation needs to be seen in context. The mTOR system directs uptake of nutrients by cells. mTOR is suppressed by rapamycin, whose usage is now quite considerable in the control of transplant rejection.

Melatonin decreases TLR3-mediated inflammatory factor expression via inhibition of NF-kappa B activation in respiratory syncytial virus-infected RAW264.7 macrophages

Double-stranded (ds) RNA has been identified as a ligand for Toll-like receptor 3 (TLR3). Respiratory syncytial virus (RSV), a single-stranded RNA virus and a major respiratory pathogen and pneumovirus in human infants pathogenesis of which relies on early inflammatory and immune events of the host in response to RSV, could be recognized by TLR3 sensing viral dsRNA produced during replication. The downstream signaling pathway from TLR3 leads to activation of IFN regulatory factor (IRF)-3 and/or NF-kappaB and subsequent expression of numerous proinflammatory factors. Melatonin (MT) is an effective regulator of the immune system. To determine the molecular mechanisms responsible for the suppressive effect of MT on RSV infection, we analyzed signaling molecules involved in the TLR3-mediated activation of inflammatory factors in macrophages infected with RSV and the modulatory role of MT on these mediators. We report that RSV infection of RAW264.7 macrophages time-dependently stimulate the rapid activation of TLR3 and NF-kappaB, as well as subsequent NF-kappaB-dependent gene expression such as those encoding TNF-alpha and inducible nitric oxide synthase. Moreover, we demonstrate that MT decreased TLR3-mediated downstream gene expression in RSV-infected macrophages in a dose- and time-dependent manner, and that MT inhibition of NF-kappaB activity seemed to be the key event required to explain the reduction in inflammatory gene expression caused by MT. But MT did not influence TLR3 at either the protein or mRNA level or MyD88 transcription. These results could be related to the beneficial immunoregulatory role of MT in RSV-infected macrophages and address the possible therapeutic potential of this indoleamine in human RSV diseases.

Activation of interleukin-32 pro-inflammatory pathway in response to influenza A virus infection

Background

Interleukin (IL)-32 is a recently described pro-inflammatory cytokine that has been reported to be induced by bacteria treatment in culture cells. Little is known about IL-32 production by exogenous pathogens infection in human individuals.

Methods and Findings

In this study, we found that IL-32 level was increased by 58.2% in the serum samples from a cohort of 108 patients infected by influenza A virus comparing to that of 115 healthy individuals. Another pro-inflammatory factor cyclooxygenase (COX)-2-associated prostaglandin E2 was also upregulated by 2.7-fold. Expression of IL-32 in influenza A virus infected A549 human lung epithelial cells was blocked by either selective COX-2 inhibitor NS398 or Aspirin, a known anti-inflammatory drug, indicating IL-32 was induced through COX-2 in the inflammatory cascade. Interestingly, we found that COX-2-associate PGE₂ production activated by influenza virus infection was significantly suppressed by over-expression of IL-32 but increased by IL-32-specific siRNA, suggesting there was a feedback mechanism between IL-32 and COX-2.

Conclusions

IL-32 is induced by influenza A virus infection via COX-2 in the inflammatory cascade. Our results provide that IL-32 is a potential target for anti-inflammatory medicine screening.

Cyclooxygenase-2/prostaglandin D2/CRTH2 pathway mediates double-stranded RNA-induced enhancement of allergic airway inflammation

Respiratory RNA viruses responsible for the common cold often worsen airway inflammation and bronchial responsiveness, two characteristic features of human asthma. We studied the effects of dsRNA, a nucleotide synthesized during viral replication, on airway inflammation and bronchial hyperresponsiveness in murine models of asthma. Intratracheal instillation of poly I:C, a synthetic dsRNA, increased the airway eosinophilia and enhanced bronchial hyperresponsiveness to methacholine in OVA-sensitized, exposed rats. These changes were associated with induction of cyclooxygenase-2 (COX-2) expression and COX-2-dependent PGD2 synthesis in the lungs, particularly in alveolar macrophages. The direct intratracheal instillation of PGD2 enhanced the eosinophilic inflammation in OVA-exposed animals, whereas pretreatment with a dual antagonist against the PGD2 receptor-(CRTH2) and the thromboxane A2 receptor, but not with a thromboxane A2 receptor-specific antagonist, nearly completely eliminated the dsRNA-induced worsening of airway inflammation and bronchial hyperresponsiveness. CRTH2-deficient mice had the same degree of allergen-induced airway eosinophilia as wild-type mice, but they did not exhibit a dsRNA-induced increase in eosinophil accumulation. Our data demonstrate that COX-2-dependent production of PGD2 followed by eosinophil recruitment into the airways via a CRTH2 receptor are the major pathogenetic factors responsible for the dsRNA-induced enhancement of airway inflammation and responsiveness.

Double-stranded RNA mediates interferon regulatory factor 3 activation and interleukin-6 production by engaging Toll-like receptor 3 in human brain astrocytes

Toll-like receptor 3 (TLR3) participates in the innate immune response by recognizing viral pathogens. In this study, human brain astrocytes were found to constitutively express TLR3, and this expression was increased by interferon-gamma (IFN-gamma) or double-stranded RNA (dsRNA). Treatment employing dsRNA in astrocytes induced IFN regulatory factor 3 (IRF3) phosphorylation, dimer formation and nuclear translocation followed by STAT1 activation. This treatment also activated nuclear factor-kappaB, p38 and c-Jun N-terminal kinase significantly, while activating extracellular signal-regulated kinase to a lesser extent. Treatment with anti-TLR3 antibody inhibited dsRNA-mediated interleukin-6 (IL-6) production. In the presence of mitogen-activated protein kinase inhibitors, astrocytes failed to secrete IL-6 in response to dsRNA treatment. Therefore, dsRNA-induced IL-6 production is dependent on mitogen-activated protein kinases and type I IFN production is dependent on IRF3 in brain astrocytes. These results suggest that brain inflammation, which produces inflammatory cytokines and type I IFNs, may enhance TLR3 expression in astrocytes. Additionally, upregulated TLR3 might modulate inflammatory processes by producing proinflammatory cytokines.

Intracisternal administration of transforming growth factor-β evokes fever through the induction of cyclooxygenase-2 in brain endothelial cells

Transforming growth factor-β (TGF-β), a pleiotropic cytokine, regulates cell proliferation, differentiation, and apoptosis, and plays a key role in development and tissue homeostasis. TGF-β functions as an anti-inflammatory cytokine because it suppresses microglia and B-lymphocyte functions, as well as the production of proinflammatory cytokines. However, we previously demonstrated that the intracisternal administration of TGF-β induces fever like that produced by proinflammatory cytokines. In this study, we investigated the mechanism of TGF-β-induced fever. The intracisternal administration of TGF-β increased body temperature in a dose-dependent manner. Pretreatment with cyclooxygenase-2 (COX-2)-selective inhibitor significantly suppressed TGF-β-induced fever. COX-2 is known as one of the rate-limiting enzymes of the PGE2 synthesis pathway, suggesting that fever induced by TGF-β is COX-2 and PGE2 dependent. TGF-β increased PGE2 levels in cerebrospinal fluid and increased the expression of COX-2 in the brain. Double immunostaining of COX-2 and von Willebrand factor (vWF, an endothelial cell marker) revealed that COX-2-expressing cells were mainly endothelial cells. Although not all COX-2-immunoreactive cells express TGF-β receptor, some COX-2-immunoreactive cells express activin receptor-like kinase-1 (ALK-1, an endothelial cell-specific TGF-β receptor), suggesting that TGF-β directly or indirectly acts on endothelial cells to induce COX-2 expression. These findings suggest a novel function of TGF-β as a proinflammatory cytokine in the central nervous system.

TLR3-dependent induction of nitric oxide synthase in RAW 264.7 macrophage-like cells via a cytosolic phospholipase A2/cyclooxygenase-2 pathway

dsRNA is a by-product of viral replication capable of inducing an inflammatory response when recognized by phagocyte cells. In this study, we identify group IVA cytosolic phospholipase A2 (cPLA2alpha) as an effector of the antiviral response. Treatment of RAW 264.7 murine macrophage-like cells with the dsRNA analog polyinosinic:polycytidylic acid (poly-IC) promotes the release of free arachidonic acid that is subsequently converted into PGE2 by the de novo-synthesized cyclooxygenase-2 (COX-2) enzyme. These processes are blocked by the selective cPLA2alpha inhibitor pyrrophenone, pointing out to cPLA2alpha as the effector involved. In keeping with this observation, the cPLA2alpha phosphorylation state increases after cellular treatment with poly-IC. Inhibition of cPLA2alpha expression and activity by either small interfering RNA (siRNA) or pyrrophenone leads to inhibition of the expression of the inducible NO synthase (iNOS) gene. Moreover, COX-2-derived PGE2 production appears to participate in iNOS expression, because siRNA inhibition of COX-2 also leads to inhibition of iNOS, the latter of which is restored by exogenous addition of PGE2. Finally, cellular depletion of TLR3 by siRNA inhibits COX-2 expression, PGE2 generation, and iNOS induction by poly-IC. Collectively, these findings suggest a model for macrophage activation in response to dsRNA, whereby engagement of TLR3 leads to cPLA2alpha-mediated arachidonic acid mobilization and COX-2-mediated PGE2 production, which cooperate to induce the expression of iNOS.

The Countervailing Actions of Myeloid and Plasmacytoid Dendritic Cells Control Autoimmune Diabetes in the Nonobese Diabetic Mouse

Islet Ag-specific CD4(+) T cells receive antigenic stimulation from MHC class II-expressing APCs. Herein, we delineate the direct in vivo necessity for distinct subsets of macrophages and dendritic cells (DC) in type 1 diabetes mellitus of the NOD mouse by using diphtheria toxin-mediated cell ablation. The ablation of macrophages had no impact on islet Ag presentation or on the induction of insulitis or diabetes in either transfer or spontaneous models. However, the ablation of CD11b(+)CD11c(+) DC led to the loss of T cell activation, insulitis, and diabetes mediated by CD4(+) T cells. When the specific myeloid DC subset was "added-back" to mice lacking total DC, insulitis and diabetes were restored. Interestingly, when NOD mice were allowed to progress to the insulitis phase, the ablation of DC led to accelerated insulitis. This accelerated insulitis was mediated by the loss of plasmacytoid DC (pDC). When pDC were returned to depleted mice, the localized regulation of insulitis was restored. The loss of pDC in the pancreas itself was accompanied by the localized loss of IDO and the acceleration of insulitis. Thus, CD11c(+)CD11b(+) DC and pDC have countervailing actions in NOD diabetes, with myeloid DC providing critical antigenic stimulation to naive CD4(+) T cells and pDC providing regulatory control of CD4(+) T cell function in the target tissue.

Key differences in TLR3/poly I:C signaling and cytokine induction by human primary cells: a phenomenon absent from murine cell systems

TLR3 recognizes double-stranded RNA, a product associated with viral infections. Many details of TLR3-induced mechanisms have emerged from gene-targeted mice or inhibition studies in transformed cell lines. However, the pathways activated in human immune cells or cells from disease tissue are less well understood. We have investigated TLR3-induced mechanisms of human primary cells of the innate immune system, including dendritic cells (DCs), macrophages (MØs), endothelial cells (ECs), and synovial fibroblasts isolated from rheumatoid arthritis joint tissue (RA-SFs). Here, we report that while these cells all express TLR3, they differ substantially in their response to TLR3 stimulation. The key antiviral response chemokine IP-10 was produced by all cell types, while DCs and MØs failed to produce the proinflammatory cytokines TNFalpha and IL-6. Unexpectedly, TNFalpha was found secreted by TLR3-stimulated RA-SF. Furthermore, TLR3 stimulation did not activate NFkappaB, MAPKs, or IRF-3 in DCs and MØs, but was able to do so in ECs and RA-SF. These findings were specific for human cells, thereby revealing a complexity not previously expected. This is the first report of such cell type- and species-specific response for any TLR stimulation and helps to explain important difficulties in correlating murine models of inflammatory diseases and human inflammation.

Expression of IL-27 p28 by Theiler's virus-infected macrophages depends on TLR3 and TLR7 activation of JNK-MAP-kinases

Theiler's murine encephalomyelitis virus (TMEV) causes a demyelinating disease (DD) due to infection of macrophages, stimulation of macrophage Toll-like receptor (TLR)3 and TLR7 pathways, activation of Mitogen-activated protein kinases (MAPK)s, and production of macrophages cytokines. Because expression of IL-27, a macrophage cytokine composed of p28 and EBI3 subunits, has been implicated in DD, we examined IL-27 subunit mRNA expression during TMEV infection of RAW264.7 cells, a macrophage cell line. TMEV infection of RAW264.7 cells did not affect cell viability, resulted in viral RNA replication, as well as p28 and EBI3 expression. Expression of p28 in TMEV-infected RAW264.7 cells depended on TLR3 and TLR7, as well as JNK but not p38 or ERK MAPKs. Since TMEV causes DD in SJL/J but not B10.S mice we determined the difference in expression of IL-27 subunit mRNA in SJL/J compared to B10.S macrophages. SJL/J macrophages expressed significantly more p28 mRNA after TMEV infection and after stimulation with TLR3 and TLR7 agonists compared with B10.S macrophages. Therefore, macrophages expression of IL-27 p28 mRNA in response to TMEV is due to activation of TLR3, TLR7, and JNK MAPKs pathways.

Oxyl radicals, redox-sensitive signalling cascades and antioxidants

Oxidative stress is an increase in the reduction potential or a large decrease in the reducing capacity of the cellular redox couples. A particularly destructive aspect of oxidative stress is the production of reactive oxygen species (ROS), which include free radicals and peroxides. Some of the less reactive of these species can be converted by oxidoreduction reactions with transition metals into more aggressive radical species that can cause extensive cellular damage. In animals, ROS may influence cell proliferation, cell death (either apoptosis or necrosis) and the expression of genes, and may be involved in the activation of several signalling pathways, activating cell signalling cascades, such as those involving mitogen-activated protein kinases. Most of these oxygen-derived species are produced at a low level by normal aerobic metabolism and the damage they cause to cells is constantly repaired. The cellular redox environment is preserved by enzymes and antioxidants that maintain the reduced state through a constant input of metabolic energy. This review summarizes current studies that have been regarding the production of ROS and the general redox-sensitive targets of cell signalling cascades.

2,2',4,4'-Tetrachlorobiphenyl upregulates cyclooxygenase-2 in HL-60 cells via p38 mitogen-activated protein kinase and NF-kappaB

Polychlorinated biphenyls (PCBs) are ubiquitous, persistent environmental contaminants that affect a number of cellular systems, including neutrophils. Among the effects caused by the noncoplanar PCB 2,2',4,4'-tetrachlorobiphenyl (2244-TCB) in granulocytic HL-60 cells are increases in superoxide anion production, activation of phospholipase A(2) with subsequent release of arachidonic acid (AA) and upregulation of the inflammatory gene cyclooxygenase-2 (COX-2). The objective of this study was to determine the signal transduction pathways involved in the upregulation of COX-2 by 2244-TCB. Treatment of HL-60 cells with 2244-TCB led to increased expression of COX-2 mRNA. This increase was prevented by the transcriptional inhibitor actinomycin D in cells pretreated with 2244-TCB for 10 min. The increase in COX-2 mRNA was associated with release of (3)H-AA, phosphorylation of p38 and extracellular signal-regulated kinase (ERK) mitogen-activated protein (MAP) kinases, increased levels of nuclear NF-kappaB and increased superoxide anion production. Bromoenol lactone, an inhibitor of the calcium-independent phospholipase A(2), reduced (3)H-AA release but had no effect on COX-2 mRNA, protein or activity. Pretreatment with SB-202190 or SB-203580, inhibitors of the p38 MAP kinase pathway, prevented the 2244-TCB-mediated induction of COX-2 and phosphorylation of p38 and ERK MAP kinases. These inhibitors did not alter (3)H-AA release. Treatment with PD 98059 or U 0126, inhibitors of the MAP/ERK (MEK) pathway, prevented the 2244-TCB-mediated activation of ERK but had no effect on COX-2 induction or p38 phosphorylation. 2244-TCB treatment did not affect c-Jun N-terminal kinase (JNK) phosphorylation. 2244-TCB exposure increased the amount of nuclear NF-kappaB. This increase was prevented by pretreatment with p38 MAP kinase inhibitors, but not by pretreatment with MEK inhibitors. Pretreatment with inhibitors of NF-kappaB prevented the 2244-TCB-mediated induction of COX-2 mRNA. 2244-TCB-mediated increases in superoxide anion were prevented by the NADPH oxidase inhibitor apocynin or the free radical scavenger 4-hydroxy TEMPO, but neither of these inhibitors affected the 2244-TCB-induced changes in COX-2 mRNA levels or (3)H-AA release. Taken together these data suggest that p38 MAP kinase-dependent activation of NF-kappaB is critical for the 2244-TCB-mediated upregulation of COX-2 mRNA.