Bacterial peptidoglycan-induced tnf-alpha transcription is mediated through the transcription factors Egr-1, Elk-1, and NF-kappaB

Polyvalent Bacterial Lysate with Potential Use to Treatment and Control of Recurrent Urinary Tract Infections

Overuse of antimicrobials has greatly contributed to the increase in the emergence of multidrug-resistant bacteria, a situation that hinders the control and treatment of infectious diseases. This is the case with urinary tract infections (UTIs), which represent a substantial percentage of worldwide public health problems, thus the need to look for alternatives for their control and treatment. Previous studies have shown the usefulness of autologous bacterial lysates as an alternative for the treatment and control of UTIs. However, a limitation is the high cost of producing individual immunogens. At the same time, an important aspect of vaccines is their immunogenic amplitude, which is the reason why they must be constituted of diverse antigenic components. In the case of UTIs, the etiology of the disease is associated with different bacteria, and even Escherichia coli, the main causal agent of the disease, is made up of several antigenic variants. In this work, we present results on the study of a bacterial lysate composed of 10 serotypes of Escherichia coli and by Klebsiella pneumoniae, Klebsiella aerogenes, Enterococcus faecalis, Proteus mirabilis, Citrobacter freundii, and Staphylococcus haemolyticus. The safety of the compound was tested on cells in culture and in an animal model, and its immunogenic capacity by analysing in vitro human and murine macrophages (cell line J774 A1). The results show that the polyvalent lysate did not cause damage to the cells in culture or alterations in the animal model used. The immunostimulatory activity assay showed that it activates the secretion of TNF-α and IL-6 in human macrophages and TNF-α in murine cells. The obtained results suggest that the polyvalent lysate evaluated can be an alternative for the treatment and control of chronic urinary tract infections, which will reduce the use of antimicrobials.

elk1/miR-462-731 Feedback Loop Regulates Macrophages Polarization and Phagocytosis in Grass Carp (Ctenopharyngodon idella)

MicroRNA clusters are microRNAs (miRNAs) that are distributed in close proximity on chromosomes. In this study, we report a miRNA cluster identified from grass carp (Ctenopharyngodon idella), miR-462-731, which plays a positive role in host antibacterial immunity. The expression of miR-462-731 was disrupted after infection by Aeromonas hydrophila. Transcription factor ETS transcription factor ELK1 was identified to bind to the promoter of the miR-462-731 cluster and suppress its expression. In addition, miR-731 negatively regulates the expression of elk1, forms an elk1/miR-462-731 double negative feedback loop. In addition, we found that miR-731 directly targets ezrin a (ezra), participates in inducing PI3K/AKT signaling in macrophage, to induce macrophage polarization to the M1 phenotype with stronger phagocytosis. Our results demonstrate a novel elk1/miR-462-731 feedback loop. The data deepen our understanding of the relationship between macrophage polarization and phagocytosis in teleost fish.

Rapid pathogen-specific recruitment of immune effector cells in the skin by secreted toxins

Swift recruitment of phagocytic leucocytes is critical in preventing infection when bacteria breach through the protective layers of the skin. According to canonical models, this occurs via an indirect process that is initiated by contact of bacteria with resident skin cells and which is independent of the pathogenic potential of the invader. Here we describe a more rapid mechanism of leucocyte recruitment to the site of intrusion of the important skin pathogen Staphylococcus aureus that is based on direct recognition of specific bacterial toxins, the phenol-soluble modulins (PSMs), by circulating leucocytes. We used a combination of intravital imaging, ear infection and skin abscess models, and in vitro gene expression studies to demonstrate that this early recruitment was dependent on the transcription factor EGR1 and contributed to the prevention of infection. Our findings refine the classical notion of the non-specific and resident cell-dependent character of the innate immune response to bacterial infection by demonstrating a pathogen-specific high-alert mechanism involving direct recruitment of immune effector cells by secreted bacterial products.

Neurotensin receptor 2 is induced in astrocytes and brain endothelial cells in relation to neuroinflammation following pilocarpine-induced seizures in rats

Neurotensin (NT) acts as a primary neurotransmitter and neuromodulator in the CNS and has been involved in a number of CNS pathologies including epilepsy. NT mediates its central and peripheral effects by interacting with the NTSR1, NTSR2, and Sort1/NTSR3 receptor subtypes. To date, little is known about the precise expression of the NT receptors in brain neural cells and their regulation in pathology. In the present work, we studied the cellular distribution of the NTSR2 protein in the rat hippocampus and questioned whether its expression was modulated in conditions of neuroinflammation using a model of temporal lobe epilepsy induced by pilocarpine. This model is characterized by a rapid and intense inflammatory reaction with reactive gliosis in the hippocampus. We show that NTSR2 protein is expressed in hippocampal astrocytes and its expression increases together with astrocyte reactivity following induction of status epilepticus. NTSR2 immunoreactivity is also increased in astrocytes proximal to blood vessels and their end-feet, and in endothelial cells. Proinflammatory factors such as IL1β and LPS induced NTSR2 mRNA and protein in cultured astroglial cells. Antagonizing NTSR2 with SR142948A decreased NTSR2 expression as well as astroglial reactivity. Together, our results suggest that NTSR2 is implicated in astroglial and gliovascular inflammation and that targeting the NTSR2 receptor may open new avenues in the regulation of neuroinflammation in CNS diseases.

Early Growth Response 1 Deficiency Protects the Host against Pseudomonas aeruginosa Lung Infection

Pseudomonas aeruginosa is an opportunistic pathogen that is a common cause of nosocomial infections. The molecular mechanisms governing immune responses to P. aeruginosa infection remain incompletely defined. Early growth response 1 (Egr-1) is a zinc-finger transcription factor that controls inflammatory responses. Here, we characterized the role of Egr-1 in host defense against P. aeruginosa infection in a mouse model of acute bacterial pneumonia. Egr-1 expression was rapidly and transiently induced in response to P. aeruginosa infection. Egr-1-deficient mice displayed decreased mortality, reduced levels of proinflammatory cytokines (tumor necrosis factor [TNF], interleukin-1β [IL-1β], IL-6, IL-12, and IL-17), and enhanced bacterial clearance from the lung. Egr-1 deficiency caused diminished NF-κB activation in P. aeruginosa-infected macrophages independently of IκBα phosphorylation. A physical interaction between Egr-1 and NF-κB p65 was found in P. aeruginosa-infected macrophages, suggesting that Egr-1 could be required for assembly of heterodimeric transcription factors that direct synthesis of inflammatory mediators. Interestingly, Egr-1 deficiency had no impact on neutrophil recruitment in vivo due to its differential effects on chemokine production, which included diminished accumulation of KC (CXCL1), MIP2 (CXCL2), and IP-10 (CXCL10) and increased accumulation of LIX (CXCL5). Importantly, Egr-1-deficient macrophages and neutrophils displayed significant increases in nitric oxide production and bacterial killing ability that correlated with enhanced bacterial clearance in Egr-1-deficient mice. Together, these findings suggest that Egr-1 plays a detrimental role in host defense against P. aeruginosa acute lung infection by promoting systemic inflammation and negatively regulating the nitric oxide production that normally assists with bacterial clearance.

Intestinal Epithelial Wnt Signaling Mediates Acetylcholine-Triggered Host Defense against Infection

Regulated antimicrobial peptide expression in the intestinal epithelium is key to defense against infection and to microbiota homeostasis. Understanding the mechanisms that regulate such expression is necessary for understanding immune homeostasis and inflammatory disease and for developing safe and effective therapies. We used Caenorhabditis elegans in a preclinical approach to discover mechanisms of antimicrobial gene expression control in the intestinal epithelium. We found an unexpected role for the cholinergic nervous system. Infection-induced acetylcholine release from neurons stimulated muscarinic signaling in the epithelium, driving downstream induction of Wnt expression in the same tissue. Wnt induction activated the epithelial canonical Wnt pathway, resulting in the expression of C-type lectin and lysozyme genes that enhanced host defense. Furthermore, the muscarinic and Wnt pathways are linked by conserved transcription factors. These results reveal a tight connection between the nervous system and the intestinal epithelium, with important implications for host defense, immune homeostasis, and cancer.

Intestinal Microbiome Shifts, Dysbiosis, Inflammation, and Non-alcoholic Fatty Liver Disease

Adverse fluctuations in the distribution of the intestinal microbiome cohort has been associated with the onset of intra- and extra-intestinal inflammatory conditions, like the metabolic syndrome (MetS) and it's hepatic manifestation, non-alcoholic fatty liver disease (NAFLD). The intestinal microbial community of obese compared to lean subjects has been shown to undergo configurational shifts in various genera, including but not limited to increased abundances of Prevotella, Escherichia, Peptoniphilus, and Parabacteroides and decreased levels of Bifidobacteria, Roseburia, and Eubacteria genera. At the phylum level, decreased Bacteroidetes and increased Firmicutes have been reported. The intestinal microbiota therefore presents an important target for designing novel therapeutic modalities that target extra-intestinal inflammatory disorders, such as NAFLD. This review hypothesizes that disruption of the intestinal-mucosal macrophage interface is a key factor in intestinal-liver axis disturbances. Intestinal immune responses implicated in the manifestation, maintenance and progression of NAFLD provide insights into the dialogue between the intestinal microbiome, the epithelia and mucosal immunity. The pro-inflammatory activity and immune imbalances implicated in NAFLD pathophysiology are reported to stem from dysbiosis of the intestinal epithelia which can serve as a source of hepatoxic effects. We posit that the hepatotoxic consequences of intestinal dysbiosis are compounded through intestinal microbiota-mediated inflammation of the local mucosa that encourages mucosal immune dysfunction, thus contributing important plausible insight in NAFLD pathogenesis. The administration of probiotics and prebiotics as a cure-all remedy for all chronic diseases is not advocated, instead, the incorporation of evidence based probiotic/prebiotic formulations as adjunctive modalities may enhance lifestyle modification management strategies for the amelioration of NAFLD.

The cytotoxic type 3 secretion system 1 of Vibrio rewires host gene expression to subvert cell death and activate cell survival pathways

Bacterial effectors potently manipulate host signaling pathways. The marine bacterium Vibrio parahaemolyticus (V. para) delivers effectors into host cells through two type 3 secretion systems (T3SSs). T3SS1 is vital for V. para survival in the environment, whereas T3SS2 causes acute gastroenteritis in human hosts. Although the natural host is undefined, T3SS1 effectors attack highly conserved cellular processes and pathways to orchestrate nonapoptotic cell death. To understand how the concerted action of T3SS1 effectors globally affects host cell signaling, we compared gene expression changes over time in primary fibroblasts infected with V. para that have a functional T3SS1 (T3SS1⁺) to those in cells infected with V. para lacking T3SS1 (T3SS1^-). Overall, the host transcriptional response to both T3SS1⁺ and T3SS1^-V. para was rapid, robust, and temporally dynamic. T3SS1 rewired host gene expression by specifically altering the expression of 398 genes. Although T3SS1 effectors targeted host cells at the posttranslational level to cause cytotoxicity, V. para T3SS1 also precipitated a host transcriptional response that initially activated cell survival and repressed cell death networks. The increased expression of several key prosurvival transcripts mediated by T3SS1 depended on a host signaling pathway that is silenced posttranslationally later in infection. Together, our analysis reveals a complex interplay between the roles of T3SS1 as both a transcriptional and posttranslational manipulator of host cell signaling.

Developmental Control of NRAMP1 (SLC11A1) Expression in Professional Phagocytes

NRAMP1 (SLC11A1) is a professional phagocyte membrane importer of divalent metals that contributes to iron recycling at homeostasis and to nutritional immunity against infection. Analyses of data generated by several consortia and additional studies were integrated to hypothesize mechanisms restricting NRAMP1 expression to mature phagocytes. Results from various epigenetic and transcriptomic approaches were collected for mesodermal and hematopoietic cell types and compiled for combined analysis with results of genetic studies associating single nucleotide polymorphisms (SNPs) with variations in NRAMP1 expression (eQTLs). Analyses establish that NRAMP1 is part of an autonomous topologically associated domain delimited by ubiquitous CCCTC-binding factor (CTCF) sites. NRAMP1 locus contains five regulatory regions: a predicted super-enhancer (S-E) key to phagocyte-specific expression; the proximal promoter; two intronic areas, including 3' inhibitory elements that restrict expression during development; and a block of upstream sites possibly extending the S-E domain. Also the downstream region adjacent to the 3' CTCF locus boundary may regulate expression during hematopoiesis. Mobilization of the locus 14 predicted transcriptional regulatory elements occurs in three steps, beginning with hematopoiesis; at the onset of myelopoiesis and through myelo-monocytic differentiation. Basal expression level in mature phagocytes is further influenced by genetic variation, tissue environment, and in response to infections that induce various epigenetic memories depending on microorganism nature. Constitutively associated transcription factors (TFs) include CCAAT enhancer binding protein beta (C/EBPb), purine rich DNA binding protein (PU.1), early growth response 2 (EGR2) and signal transducer and activator of transcription 1 (STAT1) while hypoxia-inducible factors (HIFs) and interferon regulatory factor 1 (IRF1) may stimulate iron acquisition in pro-inflammatory conditions. Mouse orthologous locus is generally conserved; chromatin patterns typify a de novo myelo-monocytic gene whose expression is tightly controlled by TFs Pu.1, C/ebps and Irf8; Irf3 and nuclear factor NF-kappa-B p 65 subunit (RelA) regulate expression in inflammatory conditions. Functional differences in the determinants identified at these orthologous loci imply that species-specific mechanisms control gene expression.

The Host Cell Transcription Factor EGR1 Is Induced by Bacteria through the EGFR-ERK1/2 Pathway

The essential first step in bacterial colonization is adhesion to the host epithelial cells. The early host-responses post-bacterial adhesions are still poorly understood. Early growth response 1 (EGR1) is an early response transcriptional regulator that can be rapidly induced by various environmental stimuli. Several bacteria can induce EGR1 expression in host cells, but the involved bacterial characteristics and the underlying molecular mechanisms of this response are largely unknown. Here, we show that EGR1 can be induced in host epithelial cells by different species of bacteria independent of the adherence level, Gram-staining type and pathogenicity. However, bacterial viability and contact with host cells is necessary, indicating that an active interaction between bacteria and the host is important. Furthermore, the strongest response is observed in cells originating from the natural site of the infection, suggesting that the EGR1 induction is cell type specific. Finally, we show that EGFR–ERK1/2 and β1-integrin signaling are the main pathways used for bacteria-mediated EGR1 upregulation. In conclusion, the increase of EGR1 expression in epithelial cells is a common stress induced, cell type specific response upon host-bacteria interaction that is mediated by EGFR–ERK1/2 and β1-integrin signaling.

Macrophages Are Involved in Gut Bacterial Translocation and Reversed by Lactobacillus in Experimental Uremia

BACKGROUND

Uremia causes gut microbiome dysbiosis, which is characterized by a reduction in beneficial bacteria. Intestinal bacterial translocation (BT) contributes to microinflammation in uremia, which is associated with adverse outcomes. Whether macrophages are involved in BT remains unclear.

AIMS

We investigated the involvement of macrophages in BT and microinflammation in uremic rats and whether Lactobacillus LB can influence macrophage activity.

METHODS

Male Sprague-Dawley rats were randomly divided into three groups: sham, uremia, and uremia + probiotic. Macrophages and GFP-labeled tracer bacteria in intestinal and extraintestinal tissues were observed by fluorescence microscopy. The macrophage ultrastructure was examined by transmission electron microscopy. Immunochemistry was used to analyze the expression of cluster of differentiation 11a (CD11a), inducible nitric oxide synthase (iNOS), and intercellular adhesion molecule-1 (ICAM-1). RT-PCR and Western blot were employed to assess the mRNA and protein expression of early growth response gene 1 (EGR1) and toll-like receptor 4 (TLR4).

RESULTS

In uremic rats, the colocalization of GFP-labeled tracer bacteria and macrophages was visible in intestinal and extraintestinal tissues. Compared with the sham group, the uremic macrophages showed fewer cytoplasmic protrusions and pseudopodia. Administration of Lactobacillus LB restored the protrusions and pseudopodia. Compared with the sham group, the uremia group exhibited macrophages with higher staining intensities for CD11a, iNOS, and ICAM-1, and higher mRNA and protein expression of TLR4 and EGR1.

CONCLUSIONS

Intestinal macrophages in the uremic rats are polarized toward a proinflammatory phenotype, resulting in microinflammation. Macrophages with impaired phagocytic function are associated with BT. Lactobacillus LB reduces BT by enhancing macrophage phagocytosis.

Activating transcription factor 3-mediated chemo-intervention with cancer chemokines in a noncanonical pathway under endoplasmic reticulum stress

The cell-protective features of the endoplasmic reticulum (ER) stress response are chronically activated in vigorously growing malignant tumor cells, which provide cellular growth advantages over the adverse microenvironment including chemotherapy. As an intervention with ER stress responses in the intestinal cancer cells, preventive exposure to flavone apigenin potentiated superinduction of a regulatory transcription factor, activating transcription factor 3 (ATF3), which is also known to be an integral player coordinating ER stress response-related gene expression. ATF3 superinduction was due to increased turnover of ATF3 transcript via stabilization with HuR protein in the cancer cells under ER stress. Moreover, enhanced ATF3 caused inhibitory action against ER stress-induced cancer chemokines that are potent mediators determining the survival and metastatic potential of epithelial cancer cells. Although enhanced ATF3 was a negative regulator of the well known proinflammatory transcription factor NF-κB, blocking of NF-κB signaling did not affect ER stress-induced chemokine expression. Instead, immediately expressed transcription factor early growth response protein 1 (EGR-1) was positively involved in cancer chemokine induction by ER stressors. ER stress-induced EGR-1 and subsequent chemokine production were repressed by ATF3. Mechanistically, ATF3 directly interacted with and recruited HDAC1 protein, which led to epigenetic suppression of EGR-1 expression and subsequent chemokine production. Conclusively, superinduced ATF3 attenuated ER stress-induced cancer chemokine expression by epigenetically interfering with induction of EGR-1, a transcriptional modulator crucial to cancer chemokine production. Thus, these results suggest a potent therapeutic intervention of ER stress response-related cancer-favoring events by ATF3.

MPYS/STING-mediated TNF-α, not type I IFN, is essential for the mucosal adjuvant activity of (3'-5')-cyclic-di-guanosine-monophosphate in vivo

The bacterial second messenger (3'-5')-cyclic-di-guanosine-monophosphate (CDG) is a promising mucosal adjuvant candidate that activates balanced Th1/Th2/Th17 responses. We showed previously that CDG activates stimulator of IFN genes (STING)-dependent IFN-I production in vitro. However, it is unknown whether STING or IFN-I is required for the CDG adjuvant activity in vivo. In this study, we show that STING(-/-) mice (Tmem173(<tm1Camb>)) do not produce Ag-specific Abs or Th1/Th2/Th17 cytokines during CDG/Ag immunization. Intranasal administration of CDG did not induce TNF-α, IL-1β, IL-6, IL-12, or MCP-1 production in STING(-/-) mice. Surprisingly, we found that the cytokine and Ab responses were unaltered in CDG/Ag-immunized IFNAR(-/-) mice. Instead, we found that CDG activates STING-dependent, IFN-I-independent TNF-α production in vivo and in vitro. Furthermore, using a TNFR1(-/-) mouse, we demonstrate that TNF-α signaling is critical for CDG-induced Ag-specific Ab and Th1/Th2 cytokine production. This is distinct from STING-mediated DNA adjuvant activity, which requires IFN-I, but not TNF-α, production. Finally, we found that CDG activates STING-dependent, but IRF3 stimulation-independent, NF-κB signaling. Our results established an essential role for STING-mediated TNF-α production in the mucosal adjuvant activity of CDG in vivo and revealed a novel IFN-I stimulation-independent STING-NF-κB-TNF-α pathway.

Peptidoglycan induced expression of peroxisome proliferator-activated receptor γ in mouse peritoneal macrophages: role of ERK and JNK MAP kinases

The peroxisome proliferator-activated receptor (PPAR) γ plays an important role in macrophage inflammatory homeostasis. Here we investigate the cross talk between PPARγ and TLR2 signaling pathway in mouse peritoneal macrophages. Real time RT-PCR and immunoblot analysis revealed that peptidoglycan (PGN) treatment of macrophages leads to biphasic effect on PPARγ expression i.e. an early upregulation and a late suppression. Inhibition of ERK MAP kinase by PD98059 abolished the early and rapid induction of PPARγ, while the inhibition of JNK MAP kinase by SP600125 nullifies the late inhibitory effect on the PPARγ expression in a dose-dependent manner. Furthermore, PPARγ knockdown macrophages showed enhanced NF-κB activity after PGN treatment. PGN treatment also enhances PPARγ interaction with p65 as observed by immunoprecipitation. This interaction may inhibit NF-κB (p65) activity as increased nuclear localization of p65 was observed in PPARγ knockdown macrophages after PGN treatment. PPARγ knockdown also increased the PGN-induced inflammatory cytokines (TNF-α, IL-1β, IL-12p40) production. Thus, our observations suggest that PGN induces PPARγ expression which is regulated by MAPKs activation and this enhanced PPARγ in turn attenuate NF-κB activity probably via enhancing p65 nuclear export. These results provide insight into how these pathways could be modulated in inflammatory diseases.

Phosphodiesterase inhibitors suppress Lactobacillus casei cell-wall-induced NF-κB and MAPK activations and cell proliferation through protein kinase A--or exchange protein activated by cAMP-dependent signal pathway

Specific strains of Lactobacillus have been found to be beneficial in treating some types of diarrhea and vaginosis. However, a high mortality rate results from underlying immunosuppressive conditions in patients with Lactobacillus casei bacteremia. Cyclic AMP (cAMP) is a small second messenger molecule that mediates signal transduction. The onset and progression of inflammatory responses are sensitive to changes in steady-state cAMP levels. L. casei cell wall extract (LCWE) develops arteritis in mice through Toll-like receptor-2 signaling. The purpose of this study was to investigate whether intracellular cAMP affects LCWE-induced pathological signaling. LCWE was shown to induce phosphorylation of the nuclear factor κB (NF-κB) and mitogen-activated protein kinase (MAPK) signaling pathways and cell proliferation in mice fibroblast cells. Theophylline and phosphodiesterase inhibitor increased intracellular cAMP and inhibited LCWE-induced cell proliferation as well as phosphorylation of NF-κB and MAPK. Protein kinase A inhibitor H89 prevented cAMP-induced MAPK inhibition, but not cAMP-induced NF-κB inhibition. An exchange protein activated by cAMP (Epac) agonist inhibited NF-κB activation but not MAPK activation. These results indicate that an increase in intracellular cAMP prevents LCWE induction of pathological signaling pathways dependent on PKA and Epac signaling.

Green tea polyphenol epigallocatechin-3-gallate inhibits TLR2 signaling induced by peptidoglycan through the polyphenol sensing molecule 67-kDa laminin receptor

Here we show the molecular basis for the inhibition of peptidoglycan (PGN)-induced TLR2 signaling by a major green tea polyphenol epigallocatechin-3-gallate (EGCG). Recently, we identified the 67-kDa laminin receptor (67LR) as the cell-surface EGCG receptor. Anti-67LR antibody treatment or silencing of 67LR resulted in abrogation of the inhibitory action of EGCG on PGN-induced production of pro-inflammatory mediators and activation of mitogen-activated protein kinases. Silencing of Toll-interacting protein (Tollip), a negative regulator of TLR signaling impaired the TLR2 signaling inhibitory activity of EGCG, suggesting that TLR2 response could be inhibited by EGCG via 67LR and Tollip.

Divergent responses to peptidoglycans derived from different E. coli serotypes influence inflammatory outcome in trout, Oncorhynchus mykiss, macrophages

Background

Pathogen-associated molecular patterns (PAMPs) are structural components of pathogens such as lipopolysaccharide (LPS) and peptidoglycan (PGN) from bacterial cell walls. PAMP-recognition by the host results in an induction of defence-related genes and often the generation of an inflammatory response. We evaluated both the transcriptomic and inflammatory response in trout (O. mykiss) macrophages in primary cell culture stimulated with DAP-PGN (DAP; meso-diaminopimelic acid, PGN; peptidoglycan) from two strains of Escherichia coli (PGN-K12 and PGN-O111:B4) over time.

Results

Transcript profiling was assessed using function-targeted cDNA microarray hybridisation (n = 36) and results show differential responses to both PGNs that are both time and treatment dependent. Wild type E. coli (K12) generated an increase in transcript number/diversity over time whereas PGN-O111:B4 stimulation resulted in a more specific and intense response. In line with this, Gene Ontology analysis (GO) highlights a specific transcriptomic remodelling for PGN-O111:B4 whereas results obtained for PGN-K12 show a high similarity to a generalised inflammatory priming response where multiple functional classes are related to ribosome biogenesis or cellular metabolism. Prostaglandin release was induced by both PGNs and macrophages were significantly more sensitive to PGN-O111:B4 as suggested from microarray data.

Conclusion

Responses at the level of the transcriptome and the inflammatory outcome (prostaglandin synthesis) highlight the different sensitivity of the macrophage to slight differences (serotype) in peptidoglycan structure. Such divergent responses are likely to involve differential receptor sensitivity to ligands or indeed different receptor types. Such changes in biological response will likely reflect upon pathogenicity of certain serotypes and the development of disease.

Regulation of heme oxygenase-1 gene by peptidoglycan involves the interaction of Elk-1 and C/EBPalpha to increase expression

Heme oxygenase (HO)-1 is a cytoprotective enzyme with anti-inflammatory properties. HO-1 is induced during a systemic inflammatory response, and expression of HO-1 is beneficial during sepsis of a Gram-positive source. Systemic infection from Gram-positive organisms has emerged as an important cause of sepsis, with Staphylococcus aureus as a common etiology. An important mediator of Gram-positive infections is peptidoglycan (PGN), a cell wall component of these organisms. Here, we demonstrate that HO-1 played an important, protective role in vivo, as mice deficient in HO-1 were very sensitive to the lethal effects of PGN derived from S. aureus. PGN induced HO-1 protein and mRNA levels, and this regulation occurred at the level of gene transcription. The PGN-responsive region of the HO-1 promoter (from -117 to -66 bp) contains a functional EBS, and Ets proteins are known to be involved in the regulation of inflammatory responses. We showed previously that Ets factors (activators Ets-2 and Ets-1 and repressor Elk-3) regulate HO-1 expression by Gram-negative endotoxin. However, during exposure to a Gram-positive stimulus in the present study, Elk-1 was a potent activator of HO-1 in conjunction with PGN. The ability of Elk-1 to induce HO-1 promoter activity was independent of direct DNA binding, but rather occurred by interacting with the CCAAT/enhancer-binding protein-alpha (C/EBPalpha), which binds to DNA. Moreover, silencing of C/EBPalpha in macrophages prevented induction of HO-1 promoter activity by either Elk-1 or PGN. These data provide further insight into the regulation and function of HO-1 by a mediator of Gram-positive bacteria.

Apoptosis signal-regulating kinase 1 in peptidoglycan-induced COX-2 expression in macrophages

In this study, we investigated the role of ASK1 in PGN-induced C/EBPbeta activation and COX-2 expression in RAW 264.7 macrophages. The PGN-induced COX-2 expression was attenuated by the DNs of ASK1, JNK1, JNK2, a JNK inhibitor (SP600125), and an AP-1 inhibitor (curcumin). PGN caused ASK1 dephosphorylation time-dependently at Ser967, dissociation from the ASK1-14-3-3 complex, and subsequent ASK1 activation. In addition, PGN activated PP2A and suppression of PP2A by okadaic acid markedly inhibited PGN-induced ASK1 Ser967 dephosphorylation and COX-2 expression. PGN induced the activation of the JNK-AP-1 signaling cascade downstream of ASK1. PGN-increased C/EBPbeta expression and DNA-binding activity were inhibited by the ASK1-JNK-AP-1 signaling blockade. COX-2 promoter luciferase activity induced by PGN was attenuated in cells transfected with the COX-2 reporter construct possessing the C/EBP-binding site mutation. In addition, the ASK1-JNK-AP-1-C/EBPbeta cascade was activated in human peripheral mononuclear cells exposure to PGN. The TLR2 agonist Pam(3)CSK(4) was also shown to induce ASK1 Ser967 dephosphorylation, JNK and c-jun phosphorylation, C/EBPbeta activation, and COX-2 expression in RAW 264.7 macrophages. PGN-induced COX-2 promoter luciferase activity was prevented by selective inhibition of TLR2 and c-Jun in RAW 264.7 macrophages. Our data demonstrate that PGN might activate the TLR2-mediated PP2A-ASK1-JNK-AP-1-C/EBPbeta cascade and subsequent COX-2 expression in RAW 264.7 macrophages.

Transcriptional control of the TNF gene

The cytokine TNF is a critical mediator of immune and inflammatory responses. The TNF gene is an immediate early gene, rapidly transcribed in a variety of cell types following exposure to a broad range of pathogens and signals of inflammation and stress. Regulation of TNF gene expression at the transcriptional level is cell type- and stimulus-specific, involving the recruitment of distinct sets of transcription factors to a compact and modular promoter region. In this review, we describe our current understanding of the mechanisms through which TNF transcription is specifically activated by a variety of extracellular stimuli in multiple cell types, including T cells, B cells, macrophages, mast cells, dendritic cells, and fibroblasts. We discuss the role of nuclear factor of activated T cells and other transcription factors and coactivators in enhanceosome formation, as well as the contradictory evidence for a role for nuclear factor kappaB as a classical activator of the TNF gene. We describe the impact of evolutionarily conserved cis-regulatory DNA motifs in the TNF locus upon TNF gene transcription, in contrast to the neutral effect of single nucleotide polymorphisms. We also assess the regulatory role of chromatin organization, epigenetic modifications, and long-range chromosomal interactions at the TNF locus.

Peptidoglycan enhances IL-6 production in human synovial fibroblasts via TLR2 receptor, focal adhesion kinase, Akt, and AP-1- dependent pathway

Peptidoglycan (PGN), the major component of the cell wall of Gram-positive bacteria, activates the innate immune system of the host and induces the release of cytokines and chemokines. We investigated the signaling pathway involved in IL-6 production stimulated by PGN in rheumatoid arthritis synovial fibroblasts. PGN caused concentration- and time-dependent increases in IL-6 production. PGN-mediated IL-6 production was attenuated by TLR2 small interfering RNA and nucleotide-binding oligomerization domain 2 small interfering RNA. Pretreatment with PI3K inhibitor (Ly294002 and wortmannin), Akt inhibitor, and AP-1 inhibitor (tanshinone IIA) also inhibited the potentiating action of PGN. PGN increased the focal adhesion kinase (FAK), PI3K, and Akt phosphorylation. Stimulation of rheumatoid arthritis synovial fibroblast cells with PGN increased the accumulation of phosphorylated c-Jun in the nucleus, AP-1-luciferase activity, and c-Jun binding to the AP-1 element on the IL-6 promoter. PGN mediated an increase in the accumulation of phosphorylated c-Jun in the nucleus, AP-1-luciferase activity, and c-Jun binding to AP-1 element was inhibited by Ly294002, Akt inhibitor, and FAK mutant. Our results suggest that PGN increased IL-6 production in human synovial fibroblasts via the TLR2 receptor/FAK/PI3K/Akt and AP-1 signaling pathway.

Rho proteins are negative regulators of TLR2, TLR3, and TLR4 signaling in astrocytes

The family of Toll-like receptors (TLRs) expressed by innate immune cells recognizes a spectrum of microbial components as well as molecules released from injured tissues. TLR ligation activates intracellular signaling cascades that culminate in the up-regulation of proinflammatory genes. We have recently demonstrated that the up-regulation of inflammatory cytokines mediated by TLR4 in astrocytes is negatively controlled by the monomeric GTPases of Rho subfamily. The present study was undertaken to examine further the involvement of Rho proteins in the inflammatory response of astrocytes elicited by the ligation of three TLRs that use divergent signaling pathways. Astrocyte cultures established from newborn rat brains were challenged with ligands of TLR2, TLR3, and TLR4. The expression of genes encoding interleukin (IL)-1beta, IL-6, tumor necrosis factor-alpha (TNFalpha), interferon-beta (IFNbeta), and inducible nitric oxide synthase (NOS2) was up-regulated 24 hr after the challenge as determined by real-time RT-PCR. Pretreatment of the cells with toxin B, which specifically inactivates Rho proteins, enhanced the up-regulation of gene expression. The extent of this enhancement was both receptor and gene dependent. The enhancing effect of Rho protein inactivation was also evident at the protein level of IL-6 and NOS2 as revealed by ELISA and immunoblot analyses, respectively. These results suggest that Rho proteins control TLR-mediated up-regulation of inflammatory genes in astrocytes by interfering with multiple events along the signaling pathways.

Peptidoglycan induces cyclooxygenase-2 expression in macrophages by activating the neutral sphingomyelinase-ceramide pathway

The sphingomyelin signal transduction pathway is known to play a role in mediating the action of various cytokines. Herein, we examined the role of neutral sphingomyelinase (nSMase)/ceramide in peptidoglycan (PGN)-induced NF-kappaB activation and cyclooxygenase-2 (COX-2) expression in macrophages. PGN-induced COX-2 expression was attenuated by an nSMase inhibitor (3-O-methyl-sphingomyeline, 3-OMS) and ceramidase, but not by an acidic SMase inhibitor (imipramine). C2-ceramide, bacterial SMase (which mimics cellular SMase activity), and a ceramidase inhibitor (N-oleoyl-ethanolamine) individually had no effect on COX-2 expression; however, they markedly enhanced PGN-induced COX-2 expression. PGN activated nSMase, but not acidic SMase, resulting in increased ceramide generation. PGN-induced nSMase activation and ceramide formation were inhibited by 3-OMS, but not by imipramine. PGN-induced COX-2 expression was inhibited by a p38 MAPK inhibitor (SB 203580) and dominant negative mutants of MAPK kinase (MKK) 3, MKK6, and p38 MAPKalpha. 3-OMS selectively inhibited PGN-induced p38 MAPK and MKK3/6 activation, but not JNK or ERK1/2. C2-ceramide, bacterial SMase, and N-oleoyl-ethanolamine all induced p38 MAPK or MKK3/6 activation. The PGN-mediated increases in kappaB-luciferase activity were also inhibited by 3-OMS and the p38 MAPKalphaDN, but not by imipramine. Furthermore, C2-ceramide caused an increase in kappaB-luciferase activity. Our data demonstrate for the first time that PGN activates the nSMase/ceramide pathway to induce MKK3/6/p38 MAPK activation, which in turn initiates NF-kappaB activation and ultimately induces COX-2 expression in macrophages. The nSMase/ceramide pathway is required but might not be sufficient for COX-2 expression induced by PGN.

Structure, organization and expression of common carp (Cyprinus carpio L.) NKEF-B gene

Natural killer (NK) cell enhancing factor (NKEF) belongs to the newly defined peroxiredoxin (Prx) family. Its functions are to enhance NK cell cytotoxicity and to protect DNA and proteins from oxidative damage. In this study, a partial cDNA sequence of carp NKEF-B was isolated from thymus cDNA library. Subsequently, the full-length cDNA of carp NKEF-B was obtained by means of 3' and 5' RACE, respectively. The full-length cDNA of carp NKEF-B was 1022 bp, consisting of a 73 bp 5'-terminal untranslated region (UTR), a 355 bp 3'-terminal UTR, and a 594 bp open reading frame coding for a protein of 197 amino acids. Carp NKEF-B contained two consensus Val-Cys-Pro (VCP) motifs and three consensus cysteine (Cys-51, Cys-70 and Cys-172) residues. Sequence comparison showed that the deduced amino acid sequence of carp NKEF-B had an overall similarity of 74-96% to that of other species homologues. Phylogenetic analysis revealed that carp NKEF-B forms a cluster with other known teleost NKEF-Bs. Then, by PCR we obtained a 5.1-k long genomic DNA of carp NKEF-B containing six exons and five introns. Real-time RT-PCR results showed that carp NKEF-B gene was predominantly detected in kidney and head kidney under un-infected conditions. Whereas under SVCV-infection condition, the expression of NKEF-B gene was significantly increased in blood cells, gill, intestine and spleen, but maintained in liver, and decreased significantly in kidney and head kidney. Finally, the rNKEF-B was constructed and expressed in Escherichia coli. By using an antibody against carp rNKEF-B, immunohistochemical study further indicated that NKEF-B positive cells are mainly some RBCs and a few epithelial cells in gill and intestine, and that under SVCV-infection condition, these positive cells or positive products in their cytoplasm were mainly increased in gill and spleen sections of carp. The results obtained in the present study will help to understand the function of NKEF-B in teleost innate immunity.

Genomic analysis of Ovis aries (Ovar) MHC class IIa loci

Determining the genomic organization of the Ovis aries (Ovar) major histocompatibility complex class IIa region is essential for future functional studies related to antigen presentation. In this study, a bacterial artificial chromosome (BAC) library of genomic DNA from peripheral blood leukocytes (PBL) of a Rambouillet ram was constructed, and BAC clone consisting of the major histocompatibility complex (MHC) class II DQB2, DQA2, DQB1, DQA1, and DRB1 loci was identified and completely sequenced. The BAC clone consists of 160,889 bp of finished sequence with the loci arranged in the following order: DQB2, DQA2, DQB1, DQA1, and DRB1 with 14.3, 25, 6.6, and 40.9 Kb spanning between the loci, respectively. All five of these loci were transcribed in the animal used to generate the MHC class II BAC clone. Repeat or retrotransposable elements along with MHC class II cis promoter elements consisting of S, X, and Y boxes were identified in the sequence. In addition, 16 non-coding conserved sequences amongst primates, carnivores, and ruminants were identified (p < 0.001). These conserved sequences include binding sites for transcription factors with known roles in immune cells, and they provide a basis for further functional investigation of the genes in this region. This is the first ruminant finished sequence of the DQB2-DRB1 region, and this sequence information will aid in whole genome and transcriptome analyses of MHC class II.

Predicting combinatorial binding of transcription factors to regulatory elements in the human genome by association rule mining

Background

Cis-acting transcriptional regulatory elements in mammalian genomes typically contain specific combinations of binding sites for various transcription factors. Although some cis-regulatory elements have been well studied, the combinations of transcription factors that regulate normal expression levels for the vast majority of the 20,000 genes in the human genome are unknown. We hypothesized that it should be possible to discover transcription factor combinations that regulate gene expression in concert by identifying over-represented combinations of sequence motifs that occur together in the genome. In order to detect combinations of transcription factor binding motifs, we developed a data mining approach based on the use of association rules, which are typically used in market basket analysis. We scored each segment of the genome for the presence or absence of each of 83 transcription factor binding motifs, then used association rule mining algorithms to mine this dataset, thus identifying frequently occurring pairs of distinct motifs within a segment.

Results

Support for most pairs of transcription factor binding motifs was highly correlated across different chromosomes although pair significance varied. Known true positive motif pairs showed higher association rule support, confidence, and significance than background. Our subsets of high-confidence, high-significance mined pairs of transcription factors showed enrichment for co-citation in PubMed abstracts relative to all pairs, and the predicted associations were often readily verifiable in the literature.

Conclusion

Functional elements in the genome where transcription factors bind to regulate expression in a combinatorial manner are more likely to be predicted by identifying statistically and biologically significant combinations of transcription factor binding motifs than by simply scanning the genome for the occurrence of binding sites for a single transcription factor.

Inhibitory effect of 1,8-cineol (eucalyptol) on Egr-1 expression in lipopolysaccharide-stimulated THP-1 cells

AIM

To study the effects of 1,8-cineol (eucalyptol) on the expression of early growth response factor-1 (Egr-1) and NF-kappaB in the human monocyte THP-1 cell line stimulated by lipopolysaccharide (LPS).

METHODS

The THP-1 cells were incubated with serial doses of 1,8-cineol (1, 10, and 100 mg/L, 30 min) before being stimulated with LPS (1 mg/L, 30 min). The localization of Egr-1 in the THP-1 cells was detected by immunofluorescence and a laser scanning confocal microscope. The expression of Egr-1 in the nuclei and whole cell, and NF-kappaB in the nuclei, were measured by Western blot analysis.

RESULTS

When stimulated by LPS, the FITC-labeled Egr-1 was detected mainly in the nuclei. Moreover, the expression of Egr-1 in the whole cell increased markedly compared with the control cells. 1,8-Cineol pretreatment decreased the expression of Egr-1 in both the nuclei and whole cell of the LPS-stimulated THP-1 cells, and this effect was concentration-dependent, but there was no reaction on the expression of NF-kappaB in the nuclei protein in the LPS-stimulated THP-1 cells.

CONCLUSION

In a concentration-dependent manner, 1,8-Cineol reduces LPS-induced Egr-1 expression in nuclei and in whole cell of THP-1 cells, but shows no effect on NF-kappaB expression.

Manipulation of host signalling pathways by anthrax toxins

Infectious microbes face an unwelcoming environment in their mammalian hosts, which have evolved elaborate multicelluar systems for recognition and elimination of invading pathogens. A common strategy used by pathogenic bacteria to establish infection is to secrete protein factors that block intracellular signalling pathways essential for host defence. Some of these proteins also act as toxins, directly causing pathology associated with disease. Bacillus anthracis, the bacterium that causes anthrax, secretes two plasmid-encoded enzymes, LF (lethal factor) and EF (oedema factor), that are delivered into host cells by a third bacterial protein, PA (protective antigen). The two toxins act on a variety of cell types, disabling the immune system and inevitably killing the host. LF is an extraordinarily selective metalloproteinase that site-specifically cleaves MKKs (mitogen-activated protein kinase kinases). Cleavage of MKKs by LF prevents them from activating their downstream MAPK (mitogen-activated protein kinase) substrates by disrupting a critical docking interaction. Blockade of MAPK signalling functionally impairs cells of both the innate and adaptive immune systems and induces cell death in macrophages. EF is an adenylate cyclase that is activated by calmodulin through a non-canonical mechanism. EF causes sustained and potent activation of host cAMP-dependent signalling pathways, which disables phagocytes. Here I review recent progress in elucidating the mechanisms by which LF and EF influence host signalling and thereby contribute to disease.

Peptidoglycan enhances transcriptional expression of CCAAT/enhancer-binding protein delta gene in mouse macrophages

Peptidoglycan-activated gene expression is mediated through various transcription factors including CCAAT/enhancer-binding protein delta (C/EBPdelta). The purpose of the present study is to elucidate the mechanism of PGN-activated C/EBPdelta gene. PGN stimulated C/EBPdelta protein and mRNA expression in mouse macrophages RAW 264.7 cells. Analysis of C/EBPdelta promoter activity by luciferase reporter assay indicated that PGN-induced C/EBPdelta gene activation is partially mediated by the -345 to +24 bp of C/EBPdelta gene promoter. The in vitro protein-DNA binding assay showed that Sp1, c-Rel and c-Jun are the major protein binding to this PGN-response element of C/EBPdelta promoter, and the binding of c-Rel and c-Jun is increased after PGN treatment. All of these binding activities were abolished when Sp1-, NF-kappaB/APRE-, CRE-sites were mutated. Furthermore, analysis of this promoter region by site-directed mutants constructed in luciferase reporter vector indicated that two Sp1-sites, one NF-kappaB/APRE-site and one CRE-site are prominent for PGN-induced gene expression. In addition, when Sp1, c-Rel or c-Jun transcription factors were overexpressed in cells, all of them enhanced C/EBPdelta promoter activity. In summary, we suggest that Sp1, c-Rel and c-Jun transcription factors play important roles in activation of C/EBPdelta gene promoter under the stimulation of PGN. Given the importance of C/EBPdelta in inflammatory disease, these results reveal a clue as a potential therapeutic target for suppression of C/EBPdelta expression under PGN stimulation.

Differential expression of peptidoglycan recognition protein 2 in the skin and liver requires different transcription factors

Human peptidoglycan recognition protein 2 (PGLYRP2) is an N-acetylmuramoyl-L-alanine amidase that hydrolyzes bacterial peptidoglycan and is differentially expressed in the two major organs in the human body, liver and skin. PGLYRP2 has a high constitutive expression in the liver but is not expressed in healthy human skin. PGLYRP2 mRNA is also not expressed in cultured human keratinocytes but is highly induced upon exposure to bacteria. In this study we identified the transcription start site for pglyrp2 and demonstrated that the differential expression of PGLYRP2 in hepatocytes and keratinocytes is regulated by different transcription factors whose binding sequences are located in different regions of the pglyrp2 promoter. Induction of pglyrp2 in keratinocytes is regulated by sequences in the distal region of the promoter and requires transcription factors NF-kappaB and Sp1, whereas constitutive expression of pglyrp2 in a hepatocyte cell line is regulated by sequences in the proximal region of the promoter and requires transcription factors c-Jun and ATF2. Regulation of constitutive and inducible expression of pglyrp2 is important for systemic and local innate immune responses to bacterial infections.

De novo synthesis of early growth response factor-1 is required for the full responsiveness of mast cells to produce TNF and IL-13 by IgE and antigen stimulation

Early growth-response factor 1 (Egr-1) is a zinc-finger transcription factor that plays a regulatory role in the expression of many genes important for inflammation. Whether Egr-1 is involved in IgE-dependent mast-cell activation was investigated. We demonstrated that IgE and antigen (TNP) stimulation induced a rapid expression of Egr-1 mRNA in mouse bone marrow-derived mast cells (BMMCs). As early as 15 to 20 minutes after IgE + TNP stimulation, Egr-1 protein was detectable in the nucleus of BMMCs by immunofluorescence or electrophoretic mobility shift assay. To examine a role for Egr-1 in IgE-dependent cytokine production by mast cells, Egr-1-deficient (Egr-1-/-) BMMCs were developed from the bone marrow cells of Egr-1 knockout mice. Egr-1-/- BMMCs express similar levels of surface c-kit and IgE receptor as compared with those on Egr-1+/+ BMMCs. Importantly, IgE + TNP-induced TNF and IL-13 expression was significantly reduced at both mRNA and protein levels in Egr-1-/- BMMCs as compared with those in Egr-1+/+ BMMCs. Thus, our results suggest that de novo synthesis of Egr-1 represents a novel mechanism in FcepsilonRI signaling and is required for the full responsiveness of IgE-dependent TNF and IL-13 production by mast cells.

GCF2/LRRFIP1 represses tumor necrosis factor alpha expression

Tumor necrosis factor alpha (TNF-alpha) is an important mediator of inflammation, apoptosis, and the development of secondary lymphoid structures. Multiple polymorphic microsatellites have been identified in and around the gene, and there are also multiple single-base pair biallelic polymorphisms in the introns and promoter. The TNF-alpha -308 promoter polymorphism is a G-to-A transition which has been statistically associated with various autoimmune disorders. Some studies have found that it may directly mediate the increased transcription of TNF-alpha in some circumstances. This study characterizes proteins interacting at the polymorphic promoter site. Affinity purification of binding proteins and confirmatory chromatin immunoprecipitation assays were used to identify the proteins. Electrophoretic mobility shift analyses and surface plasmon resonance were used to define binding characteristics. Proteins interacting at this site include GCF2/LRRFIP1 and Ets-1. GCF2/LRRFIP1 appears to act as a repressor and occupies the -308 site in cells that do not make TNF-alpha. Cells competent to produce TNF-alpha have Ets-1 bound to the -308 promoter site. Active transcription is accompanied by NF-kappaB and c-Jun binding to the proximal promoter. Thus, dynamic changes on the TNF-alpha promoter, particularly at the -308 site, accompany the transition from repressed to active transcription. GCF2/LRRFIP1 is the first TNF-alpha repressor identified.

Peptidoglycan recognition protein 2 (N-acetylmuramoyl-L-Ala amidase) is induced in keratinocytes by bacteria through the p38 kinase pathway

Human peptidoglycan recognition protein 2 (PGLYRP2) is an N-acetylmuramoyl-L-alanine amidase that hydrolyzes bacterial peptidoglycan and is constitutively produced in the liver and secreted into the blood. Here we demonstrate that PGLYRP2 was not expressed in healthy human skin and had low expression in the eye. However, upon exposure to gram-positive and gram-negative bacteria or cytokines, PGLYRP2 expression was highly induced in keratinocytes and to a lower level in corneal epithelial cells. Expression of PGLYRP2 was not induced in nonepithelial cells. Exposure of keratinocytes to bacteria induced keratinocyte differentiation and stress response and inhibited activation of signal transduction molecules involved in cell proliferation. Induction of PGLYRP2 expression correlated with expression of differentiation markers (cytokeratins and transglutaminase). Bacteria induced activation of p38 mitogen-activated protein kinase (MAPK) in keratinocytes, which was required for the induction of PGLYRP2 expression, because induction of PGLYRP2 transcription by bacteria was inhibited by SB203580 (a specific inhibitor of p38 MAPK) and by a dominant-negative p38 construct. Induction of PGLYRP2 expression by bacteria (in contrast to expression of human beta-defensin-2) was not mediated by Toll-like receptor 2 or 4. PGLYRP2 may function in the skin and the eyes as an inducible scavenger of proinflammatory peptidoglycan.

Mannose-binding lectin recognizes peptidoglycan via the N-acetyl glucosamine moiety, and inhibits ligand-induced proinflammatory effect and promotes chemokine production by macrophages

Peptidoglycan (PGN) is the major cell wall component (90%, w/w) of Gram-positive bacteria and consists of N-acetylglucosamine (GlcNAc) and N-acetylmuramic acid (MurNAc) disaccharide repeating arrays that are cross-linked by short peptides. We hypothesized that PGN is a ligand for pathogen-associated pattern-recognition proteins. Mannose-binding lectin (MBL) and serum amyloid component P are two carbohydrate-binding innate immune proteins present in the blood. In this study we show that human MBL, but not serum amyloid component P, binds significantly to PGN via its C-type lectin domains, and that the interaction can be more effectively competed by GlcNAc than by MurNAc. Surface plasmon resonance analyses show that native MBL binds immobilized PGN with high avidity. Competition experiments also show that both native MBL and MBL(n/CRD), a 48-kDa recombinant trimeric fragment of MBL containing neck and carbohydrate recognition domains, have higher affinity for GlcNAc than for MurNAc. Protein arrays and ELISA show that PGN increases the secretion of TNF-alpha, IL-8, IL-10, MCP-2, and RANTES from PMA-stimulated human monocytic U937 cells. Interestingly, the presence of MBL together with PGN increases the production of IL-8 and RANTES, but reduces that of TNF-alpha. Our results indicate that Gram-positive bacterial is a biologically relevant ligand for MBL, and that the collectin preferentially binds to the GlcNAc moiety of the PGN via its C-type lectin domains. MBL inhibits PGN-induced production of proinflammatory cytokines while enhancing the production of chemokines by macrophages, which suggests that MBL may down-regulate macrophage-mediated inflammation while enhancing phagocyte recruitment.

Critical role for Ets, AP-1 and GATA-like transcription factors in regulating mouse Toll-like receptor 4 (Tlr4) gene expression

TLR4 (Toll-like receptor 4) is essential for sensing the endotoxin of Gram-negative bacteria. Mutations or deletion of the TLR4 gene in humans or mice have been associated with altered predisposition to or outcome of Gram-negative sepsis. In the present work, we studied the expression and regulation of the Tlr4 gene of mouse. In vivo, TLR4 levels were higher in macrophages compared with B, T or natural killer cells. High basal TLR4 promoter activity was observed in RAW 264.7, J774 and P388D1 macrophages transfected with a TLR4 promoter reporter vector. Analysis of truncated and mutated promoter constructs identified several positive [two Ets (E twenty-six) and one AP-1 (activator protein-1) sites] and negative (a GATA-like site and an octamer site) regulatory elements within 350 bp upstream of the transcriptional start site. The myeloid and B-cell-specific transcription factor PU.1 bound to the proximal Ets site. In contrast, none among PU.1, Ets-1, Ets-2 and Elk-1, but possibly one member of the ESE (epithelium-specific Ets) subfamily of Ets transcription factors, bound to the distal Ets site, which was indispensable for Tlr4 gene transcription. Endotoxin did not affect macrophage TLR4 promoter activity, but it decreased TLR4 steady-state mRNA levels by increasing the turnover of TLR4 transcripts. TLR4 expression was modestly altered by other pro- and anti-inflammatory stimuli, except for PMA plus ionomycin which strongly increased promoter activity and TLR4 mRNA levels. The mouse and human TLR4 genes were highly conserved. Yet, notable differences exist with respect to the elements implicated in gene regulation, which may account for species differences in terms of tissue expression and modulation by microbial and inflammatory stimuli.

Activation of adenosine receptors inhibits tumor necrosis factor-alpha release by decreasing TNF-alpha mRNA stability and p38 activity

Adenosine receptor agonists have anti-inflammatory properties and modulate immune responses partly by inhibiting pro-inflammatory cytokine production by monocytes. We investigated signal transduction mechanisms by which adenosine receptor activation inhibits tumor necrosis factor-alpha (TNF-alpha) production. Phorbol-12-myristate-13-acetate (PMA) and phytohemagglutinin treatment of human pro-monocytic U937 cells increased TNF-alpha protein release. Activation of adenosine receptors up to 1 hr following stimulation with PMA/phytohemagglutinin significantly inhibited TNF-alpha protein release indicating that inhibition of TNF-alpha occurred post-transcriptionally. The adenosine receptor agonist 2-p-(carboxyethyl)phenethylamino-5'-N-ethylcarboxamidoadenosine hydrochloride (CGS 21680) decreased stability and half-life of PMA/phytohemagglutinin-induced TNF-alpha mRNA from 80 to 37 min. p38 signaling pathways control TNF-alpha mRNA stability in macrophages and we confirmed in our cells that p38 was involved in controlling TNF-alpha release post-transcriptionally. Activation of adenosine receptors with CGS 21680 decreased phospho-p38 protein levels. These data suggest that adenosine receptor activation regulates TNF-alpha release post-transcriptionally by decreasing mRNA stability through a mechanism involving inhibition of p38 activity.

Comparison of the chondrosarcoma cell line SW1353 with primary human adult articular chondrocytes with regard to their gene expression profile and reactivity to IL-1beta

OBJECTIVE

In this study, the human chondrosarcoma cell line SW1353 was investigated by gene expression analysis in order to validate it as an in vitro model for primary human (adult articular) chondrocytes (PHCs).

METHODS

PHCs and SW1353 cells were cultured as high density monolayer cultures with and without 1ng/ml interleukin-1beta (IL-1beta). RNA was isolated and assayed using a custom-made oligonucleotide microarray representing 312 chondrocyte-relevant genes. The expression levels of selected genes were confirmed by real-time polymerase chain reaction and the gene expression profiles of the two cell types, both with and without IL-1beta treatment, were compared.

RESULTS

Overall, gene expression profiling showed only very limited similarities between SW1353 cells and PHCs at the transcriptional level. Similarities were predominantly seen with respect to catabolic effects after IL-1beta treatment. In both cell systems matrix metalloproteinase-1 (MMP-1), MMP-3 and MMP-13 were strongly induced by IL-1beta, without significant induction of MMP-2. IL-6 was also found to be up-regulated by IL-1beta in both cellular models. On the other hand, intercellular mediators such as leukemia inhibitory factor (LIF) and bone morphogenetic protein-2 (BMP-2) were not induced by IL-1beta in SW1353 cells, but significantly up-regulated in PHCs. Bioinformatical analysis identified nuclear factor kappa-B (NFkappaB) as a common transcriptional regulator of IL-1beta induced genes in both SW1353 cells and PHCs, whereas other transcription factors were only found to be relevant for individual cell systems.

CONCLUSION

Our data characterize SW1353 cells as a cell line with only a very limited potential to mimic PHCs, though SW1353 cells can be of value to study the induction of protease expression within cells, a phenomenon also seen in chondrocytes.

TNF-alpha expression is transcriptionally regulated by RANK ligand

Tumor necrosis factor (TNF)-alpha is known for its osteoclastogenic and resorptive activities. Induction of osteoclastogenesis by receptor activator of NF-kappaB ligand (RANKL) is accompanied by increased TNF-alpha expression. In the present study we investigated the mechanism by which RANKL induces expression of TNF-alpha in osteoclast precursors. The macrophage-like cell-line, RAW 264.7 was used as a model for osteoclast precursors. To examine if RANKL-mediated increase in TNF-alpha expression involves increased stability of its transcript, RAW264.7 cells were treated with or without RANKL, and then a transcription inhibitor was added. At different time points, TNF-alpha and L32 mRNA levels were examined. TNF-alpha mRNA stability was not altered by RANKL. We next measured directly the transcription rate of TNF-alpha by a run-on assay and found that RANKL increases TNF-alpha transcription rate by 2.9-fold in RAW264.7 cells. We further characterized this transcriptional induction of TNF-alpha by RANKL. Gel shift assays using nuclear extracts derived from RANKL-treated RAW264.7 cells show increased specific NF-kappaB binding activity on the murine TNF-alpha promoter. Gliotoxin, known for its ability to inhibit NF-kappaB activation blocked RANKL-induced TNF-alpha expression. We finally used 1,260 bp of the murine TNF-alpha promoter fused to luciferase, as well as four mutants of this promoter carrying mutations in each of the four NF-kappaB sites to stably transfect RAW 264.7 cells. Reporter activity was increased in response to RANKL in wild type promoter transfected cells, whereas treatment of the mutants' transfected cells did not elicit reporter activity. In conclusion, RANKL induces TNF-alpha expression via a transcriptional mechanism, depending on the NF-kappaB sites in the TNF promoter.

Mercury (II) alters mitochondrial activity of monocytes at sublethal doses via oxidative stress mechanisms

The perennial controversy about the safety of mercury in dental amalgams has adversely affected the availability and the quality of dental care. Chronic Hg(II) blood concentrations above 300 nM are known to alter function of the nervous system and the kidney. However, the effects of blood concentrations of 10 to 75 nM, far more common in the general population, are not clear and mechanisms of any effects are not known. The monocyte is an important potential target of Hg(II) because of its critical role in directing inflammatory and immune responses. In the current study we tested the hypothesis that concentrations of Hg(II) of 10 to 300 nM alter monocyte activity via a redox-dependent mechanism. Mitochondrial activity was used to establish inhibitory concentrations of Hg(II) following 6 to 72 h of exposures to THP1 human monocytic cells. Then subinhibitory concentrations were applied, and total glutathione levels and reactive oxygen species (ROS) were measured. Antioxidants [N-acetyl cysteine, (NAC); Na2SeO3, (Se)] and a pro-oxidant (tert-butylhydroquinone, tBHQ) were used to support the hypothesis that Hg(II) effects were redox-mediated. After 72 h of exposure, 20 microM of Hg(II) inhibited monocytic mitochondrial activity by 50%. NAC mitigated Hg(II)-induced mitochondrial suppression only at concentrations of greater than 10 microM, but Se had few effects on Hg-induced mitochondrial responses. tBHQ significantly enhanced mitochondrial suppression at higher Hg(II) concentrations. Hg(II) concentrations of 75 and 300 nM (0.075 and 0.30 microM, respectively) significantly increased total glutathione levels, and NAC mitigated these increases. Se plus Hg(II) significantly elevated Hg-induced total cellular glutathione levels. Increased ROS levels were not detected in monocytes exposed to mercury. Hg(II) acts in monocytic cells, at least in part, through redox-mediated mechanisms at concentrations below those commonly associated with chronic mercury toxicity, but commonly occurring in the blood of some dental patients.

Helicobacter pylori activates the early growth response 1 protein in gastric epithelial cells

The early growth response 1 (Egr-1) transcription factor is rapidly induced by various stimuli and is implicated in the regulation of cell growth, differentiation, and gene expression. The aim of this study was to examine the effect of Helicobacter pylori on the expression of Egr-1 and Egr-1-regulated genes in gastric epithelial AGS cells. Egr-1 expression was assayed by immunoblotting and electrophoretic mobility shift assays using H. pylori-stimulated AGS cells. Transient transfection experiments with promoter-reporter constructs of CD44, ICAM-1, and CD95L were used for expression studies. H. pylori induced the expression of Egr-1 in gastric epithelial cell lines in a dose-dependent manner, with the rapid kinetics that are typical of this class of transcription factors. Immunohistochemical studies of biopsies revealed that Egr-1 expression is more abundant in H. pylori-positive patients than in uninfected individuals. Reporter-promoter transfection studies indicated that Egr-1 binding is required for the H. pylori-induced transcriptional promoter activity of the CD44, ICAM-1, and CD95L (APO-1/Fas) constructs. The blocking of egr-1 with an antisense sequence prevented H. pylori-induced Egr-1 and CD44 protein expression. The MEK1/2 signaling cascade participates in H. pylori-mediated Egr-1 expression, but the p38 pathway does not. The data indicate that H. pylori induces Egr-1 expression in AGS cells in vitro and that the Egr-1 protein is readily detectable in biopsies from H. pylori-positive subjects. These observations suggest that H. pylori-associated Egr-1 expression may play a role, in part, in H. pylori-induced pathology.

Human mannose-binding lectin and L-ficolin function as specific pattern recognition proteins in the lectin activation pathway of complement

The innate immune response in vertebrates and invertebrates requires the presence of pattern recognition receptors or proteins that recognize microbial cell components including lipopolysaccharide, bacterial peptidoglycan (PGN), and fungal 1,3-beta-D-glucan. We reported previously that PGN and 1,3-beta-D-glucan recognition proteins from insect hemolymph were able to induce the activation of the prophenoloxidase-activating system, one of the major invertebrate innate immune reactions. The goal of this study was to characterize the biochemical properties and effects of the human counterparts of these molecules. Soluble pattern recognition proteins were purified from human serum and identified as human mannose-binding lectin (MBL) and L-ficolin. The use of specific microbial cell component-coupled columns demonstrated that MBL and L-ficolin bind to PGN and 1,3-beta-D-glucan, respectively. Purified MBL and L-ficolin were associated with MBL-associated serine proteases-1 and -2 (MASPs) and small MBL-associated protein as determined by Western blot analysis. Finally, the binding of purified MBL/MASP and L-ficolin/MASP complexes to PGN and 1,3-beta-D-glucan, respectively, resulted in the activation of the lectin-complement pathway. These results indicate that human PGN and 1,3-beta-D-glucan recognition proteins function as complement-activating lectins.

Peptidoglycan Induces Nuclear Factor-κB Activation and Cyclooxygenase-2 Expression via Ras, Raf-1, and ERK in RAW 264.7 Macrophages

In this study, we investigated the signaling pathway involved in cyclooxygenase-2 (COX-2) expression caused by peptidoglycan (PGN), a cell wall component of the Gram-positive bacterium Staphylococcus aureus, in RAW 264.7 macrophages. PGN caused dose- and time-dependent increases in COX-2 expression, which was attenuated by a Ras inhibitor (manumycin A), a Raf-1 inhibitor (GW 5074), and an MEK inhibitor (PD 098059). Treatment of RAW 264.7 macrophages with PGN caused time-dependent activations of Ras, Raf-1, and ERK. The PGN-induced increase in Ras activity was inhibited by manumycin A. Raf-1 phosphorylation at Ser-338 by PGN was inhibited by manumycin A and GW 5074. The PGN-induced increase in ERK activity was inhibited by manumycin A, GW 5074, and PD 098059. Stimulation of cells with PGN activated IkappaB kinase alpha/beta (IKKalpha/beta), IkappaBalpha phosphorylation, IkappaBalpha degradation, and kappaB-luciferase activity. Treatment of macrophages with an NF-kappaB inhibitor (pyrrolidine dithiocarbamate), an IkappaBalpha phosphorylation inhibitor (Bay 117082), and IkappaB protease inhibitors (l-1-tosylamido-2-phenylethyl chloromethyl ketone and calpain inhibitor I) all inhibited PGN-induced COX-2 expression. The PGN-mediated increase in the activities of IKKalpha/beta and kappaB-luciferase were also inhibited by the Ras dominant negative mutant (RasN17), manumycin A, GW 5074, and PD 098059. Further studies revealed that PGN induced the recruitment of p85alpha and Ras to Toll-like receptor 2 in a time-dependent manner. Our data demonstrate for the first time that PGN activates the Ras/Raf-1/ERK pathway, which in turn initiates IKKalpha/beta and NF-kappaB activation, and ultimately induces COX-2 expression in RAW 264.7 macrophages.

Regulation of inflammation

Inflammation is part of the response to infection. It is often considered to be part of the innate response to infection, but it plays a significant role in molding the adaptive response. Conserved pathways that have evolved to contain the infection and mold the ensuing adaptive response can cause deleterious effects when dysregulated. In this review, the various roles of TNFalpha will be discussed. Its pleomorphic effects require complex regulatory strategies. Our work has focused on the role of TNFalpha in autoimmune diseases and the regulation of its expression by transcription factors and chromatin remodeling.