Endotoxin-responsive sequences control cachectin/tumor necrosis factor biosynthesis at the translational level

IkappaBbeta acts to inhibit and activate gene expression during the inflammatory response

The activation of pro-inflammatory gene programs by nuclear factor-kappaB (NF-kappaB) is primarily regulated through cytoplasmic sequestration of NF-kappaB by the inhibitor of kappaB (IkappaB) family of proteins. IkappaBbeta, a major isoform of IkappaB, can sequester NF-kappaB in the cytoplasm, although its biological role remains unclear. Although cells lacking IkappaBbeta have been reported, in vivo studies have been limited and suggested redundancy between IkappaBalpha and IkappaBbeta. Like IkappaBalpha, IkappaBbeta is also inducibly degraded; however, upon stimulation by lipopolysaccharide (LPS), it is degraded slowly and re-synthesized as a hypophosphorylated form that can be detected in the nucleus. The crystal structure of IkappaBbeta bound to p65 suggested this complex might bind DNA. In vitro, hypophosphorylated IkappaBbeta can bind DNA with p65 and c-Rel, and the DNA-bound NF-kappaB:IkappaBbeta complexes are resistant to IkappaBalpha, suggesting hypophosphorylated, nuclear IkappaBbeta may prolong the expression of certain genes. Here we report that in vivo IkappaBbeta serves both to inhibit and facilitate the inflammatory response. IkappaBbeta degradation releases NF-kappaB dimers which upregulate pro-inflammatory target genes such as tumour necrosis factor-alpha (TNF-alpha). Surprisingly, absence of IkappaBbeta results in a dramatic reduction of TNF-alpha in response to LPS even though activation of NF-kappaB is normal. The inhibition of TNF-alpha messenger RNA (mRNA) expression correlates with the absence of nuclear, hypophosphorylated-IkappaBbeta bound to p65:c-Rel heterodimers at a specific kappaB site on the TNF-alpha promoter. Therefore IkappaBbeta acts through p65:c-Rel dimers to maintain prolonged expression of TNF-alpha. As a result, IkappaBbeta(-/-) mice are resistant to LPS-induced septic shock and collagen-induced arthritis. Blocking IkappaBbeta might be a promising new strategy for selectively inhibiting the chronic phase of TNF-alpha production during the inflammatory response.

Fragile X-related protein FXR1 controls post-transcriptional suppression of lipopolysaccharide-induced tumour necrosis factor-alpha production by transforming growth factor-beta1

Tumour necrosis factor-alpha (TNF-alpha) is a key mediator of inflammation in host defence against infection and in autoimmune disease. Its production is controlled post-transcriptionally by multiple RNA-binding proteins that interact with the TNF-alpha AU-rich element and regulate its expression; one of these is Fragile X mental retardation-related protein 1 (FXR1). The anti-inflammatory cytokine transforming growth factor-beta1 (TGF-beta1), which is involved in the homeostatic regulation of TNF-alpha, causes post-transcriptional suppression of lipopolysaccharide (LPS)-induced TNF-alpha production. We report here that this depends on FXR1. Using RAW 264.7 cells and bone marrow-derived macrophages (BMDMphi) stimulated with LPS and TGF-beta1, we show that TGF-beta1 inhibits TNF-alpha protein secretion, whereas TNF-alpha mRNA expression remains unchanged. This response is recapitulated by the 3'-UTR of TNF-alpha, which is known to bind FXR1. TGF-beta1 induces FXR1 with a pattern of expression distinct from that of tristetraprolin, T-cell intracellular antigen 1, or human antigen R. When FXR1 is knocked down, TGF-beta1 is no longer able to inhibit LPS-induced TNF-alpha protein production, and overexpression of FXR1 suppresses LPS-induced TNF-alpha protein production. Targeting the p38 mitogen-activated protein kinase pathway of LPS-treated cells with small molecule inhibitors can induce FXR1 protein and mRNA expression. In summary, TGF-beta1 opposes LPS-induced stabilization of TNF-alpha mRNA and reduces the amount of TNF-alpha protein, through induction of expression of the mRNA-binding protein FXR1.

Inflammation: cytokines and RNA-based regulation

The outcome of an inflammatory response depends upon the coordinated regulation of a variety of both pro-inflammatory and anti-inflammatory cytokines and other proteins. Regulation of these inflammation mediators can occur at multiple levels, including transcription, mRNA translation, post-translational modifications, and mRNA degradation. Post-transcriptional regulation has been shown to play an important role in controlling the expression of these mediators, allowing for normal initiation and resolution of the inflammatory response. Many inflammatory mediators have unstable mRNAs due, in part, to the presence of AU-rich elements in their 3'-untranslated regions. Increasing numbers of RNA-binding proteins have been identified that can bind to these AU-rich elements and then regulate the stability and/or translation of the mRNA. This review summarizes current knowledge about the role of several RNA-binding proteins that act through AU-rich elements to post-transcriptionally regulate the biosynthesis of proteins involved in inflammation.

TRIF signaling stimulates translation of TNF-alpha mRNA via prolonged activation of MK2

The adapter protein TRIF mediates signal transduction through TLR3 and TLR4, inducing production of type I IFNs and inflammatory cytokines. The present study investigates the mechanisms by which TRIF signaling controls TNF-alpha biosynthesis. We provide evidence that, in LPS-stimulated murine dendritic cells, TRIF stimulates TNF-alpha biosynthesis selectively at the posttranscriptional level by promoting mRNA translation. In the absence of functional TRIF, the production of TNF-alpha protein was severely impaired, whereas TNF-alpha mRNA levels and stability, as well as transcriptional activity of the Tnfa gene, were not affected. Similarly, TRIF was required for production of LPS-induced TNF-alpha protein, but not of mRNA, in bone marrow-derived macrophages. In peritoneal macrophages, however, TRIF was also required for normal induction of TNF-alpha mRNA, suggesting cell type-related functions of TRIF. The influence of TRIF on dendritic cell TNF-alpha production was independent of type I IFNs. TRIF was required for prolonged activation of MAPKs in LPS-stimulated dendritic cells but was dispensable for the activation of NF-kappaB. Inhibition of late p38 activity attenuated LPS-stimulated elevation of TNF-alpha protein but not mRNA levels. The p38 effector kinase MK2 was directly activated through the TRIF pathway of TLR4. Importantly, stimulation of Mk2(-/-) cells through TLR3 or TLR4 severely impaired TNF-alpha protein production but did not affect TNF-alpha mRNA induction. Together, these results indicate that the TRIF signaling pathway promotes TNF-alpha mRNA translation through activation of the protein kinase MK2.

Translation control: a multifaceted regulator of inflammatory response

A robust innate immune response is essential to the protection of all vertebrates from infection, but it often comes with the price tag of acute inflammation. If unchecked, a runaway inflammatory response can cause significant tissue damage, resulting in myriad disorders, such as dermatitis, toxic shock, cardiovascular disease, acute pelvic and arthritic inflammatory diseases, and various infections. To prevent such pathologies, cells have evolved mechanisms to rapidly and specifically shut off these beneficial inflammatory activities before they become detrimental. Our review of recent literature, including our own work, reveals that the most dominant and common mechanism is translational silencing, in which specific regulatory proteins or complexes are recruited to cis-acting RNA structures in the untranslated regions of single or multiple mRNAs that code for the inflammatory protein(s). Enhancement of the silencing function may constitute a novel pharmacological approach to prevent immunity-related inflammation.

Reduced transcript stabilization restricts TNF-alpha expression in RAW264.7 macrophages infected with pathogenic mycobacteria: evidence for an involvement of lipomannan

Despite the critical role that TNF-alpha plays in the containment of mycobacterial infection, the mechanisms involved in regulation of its expression by mycobacteria are poorly defined. We addressed this question by studying MAP, which causes a chronic enteritis in ruminants and is linked to human Crohn's disease. We found that in MAP infected macrophages, TNF-alpha gene expression was substantially lower than in macrophages infected with nonpathogenic MS or stimulated with LPS. TNF-alpha transcriptional one could not fully explain the differential TNF-alpha mRNA expression, suggesting that there must be a substantial contribution by post-transcriptional mechanisms.Accordingly, we found reduced TNF-alpha mRNA stability in MAP-infected macrophages. Further comparison of MAP- and MS-infected macrophages revealed that lower TNF-alpha mRNA stability combined with lower mRNA and protein expression in MAP-infected macrophages correlated with lower p38 MAPK phosphorylation. These findings were independent of viability of MAP and MS. We demonstrate that the major mycobacterial cell-wall lipoglycan LM of MAP and MS induced TNF-alpha mRNA transcription,but only the MS-LM induced p38 MAPK-dependent transcript stabilization. Overall, our data suggest that pathogenic mycobacteria cause weak p38 and TNF-alpha mRNA stabilization as a result of their structural cell-wall components such as LM and thereby, restrict TNF-alpha expression in macrophages.

Mesenchymal stem cells respond to TNF but do not produce TNF

Previously, we demonstrated that several TLRs are expressed on cord blood-derived USSC. Stimulation of USSC with TLR agonists resulted in a marked increase of IL-6 and IL-8 production. Interestingly, TNF was undetectable after TLR stimulation, which appeared to be a result of an inactivated TNF promoter in USSC. Here, we elaborate this study by demonstrating that although USSC do not produce TNF, they are susceptible to TNF stimulation, resulting in NF-kappaB translocation and cytokine production. Additionally, we compared different stem cell sources for their ability to produce TNF. Interestingly, we found that the TNF promoter in BM-MSC is inactivated as well. Like USSC, they are able to respond to TNF stimulation, but they are not able to produce TNF, even not after LPS stimulation. This limited cytokine response in combination with the well-studied immunosuppressive properties of MSC makes these cells ideal for immune-suppressive treatment modalities such as graft-versus-host disease.

Pathogen recognition and inflammatory signaling in innate immune defenses

The innate immune system constitutes the first line of defense against invading microbial pathogens and relies on a large family of pattern recognition receptors (PRRs), which detect distinct evolutionarily conserved structures on pathogens, termed pathogen-associated molecular patterns (PAMPs). Among the PRRs, the Toll-like receptors have been studied most extensively. Upon PAMP engagement, PRRs trigger intracellular signaling cascades ultimately culminating in the expression of a variety of proinflammatory molecules, which together orchestrate the early host response to infection, and also is a prerequisite for the subsequent activation and shaping of adaptive immunity. In order to avoid immunopathology, this system is tightly regulated by a number of endogenous molecules that limit the magnitude and duration of the inflammatory response. Moreover, pathogenic microbes have developed sophisticated molecular strategies to subvert host defenses by interfering with molecules involved in inflammatory signaling. This review presents current knowledge on pathogen recognition through different families of PRRs and the increasingly complex signaling pathways responsible for activation of an inflammatory and antimicrobial response. Moreover, medical implications are discussed, including the role of PRRs in primary immunodeficiencies and in the pathogenesis of infectious and autoimmune diseases, as well as the possibilities for translation into clinical and therapeutic applications.

Mitogen-activated protein kinases are involved in tumor necrosis factor alpha production in macrophages infected with Orientia tsutsugamushi

Orientia tsutsugamushi, an obligatory intracellular bacterium, is the causative agent of scrub typhus. Here the role of MAPK in TNF-alpha production in macrophages after infection with O. tsutsugamushi has been investigated. ERK1/2, JNK, and p38 MAPK became phosphorylated in Orientia-stimulated macrophages. Selective inhibitors of MAPK cascades could all significantly reduce Orientia-stimulated TNF-alpha production. Orientia-stimulated TNF-alpha production via p38 and JNK pathways was regulated by a post-transcriptional mechanism, whereas the ERK pathway mainly controlled the transcriptional step of TNF-alpha gene expression during infection. In conclusion, our data indicate that MAPK signaling is required to induce maximal TNF-alpha production in macrophages during Orientia infection.

First molluscan TNF-alpha homologue of the TNF superfamily in disk abalone: molecular characterization and expression analysis

Tumor necrosis factor alpha (TNF-alpha) is considered as a multifunctional immune modulator that plays an important role in the innate and adaptive immune systems in vertebrates. Here, we described the characterization and expression analysis of the first TNF-alpha homologue in mollusk abalone, named as AbTNF-alpha. It has 930-bp full length with a 717-bp open reading frame (ORF), encoding 239 amino acids. The AbTNF-alpha amino acid sequence shows the characteristic TNF family signature, N-terminal transmembrane domain consisting of a hydrophobic amino acid cluster and cell attachment sequence at (155)RGD(157). Phylogenic analysis results showed that AbTNF-alpha is more related to the invertebrate Ciona savignyi TNF superfamily ligand member (CsTL). Quantitative real-time PCR expression results showed that AbTNF-alpha was constitutively expressed in both immune and non-immune tissues in a tissue specific manner. The highest constitutive expression was in the gill tissue with a 1.5-fold compared to hemocytes expression. The AbTNF-alpha mRNA expression in gill tissue was monitored in vivo stimulated by a mixture of pathogenic bacteria (Vibrio alginolyticus, Vibrio parahemolyticus, and Lysteria monocytogenes), viral haemorrhagic septicaemia virus (VHSV) and lipopolysaccharide (LPS). The AbTNF-alpha expression was significantly (p<0.05) induced by bacteria, VHSV and LPS compared to the control animals. Moreover, the highest level expressions of each induction were at 24 h (5.2-fold), 48 h (2.8-fold), and 48 h (3.3-fold) by bacteria mixture, VHSV and LPS, respectively. These results indicate that AbTNF-alpha could respond to pathogenic infection or stimulation and may play an important role in the abalone immune system.

The influence of methylmercury on the nitric oxide production of alveolar macrophages

Mercury is a global pollutant considered to be a persistent bioaccumulative and toxic chemical. Humans may be exposed to organic forms of mercury by either inhalation, oral, or dermal routes. Methylmercury is more toxic to living organisms than the inorganic forms. In this study, we attempted to elucidate the altered functions of alveolar macrophage including nitric oxide production after methylmercury exposure. Treatment of 7 muM methylmercury for 24 h inhibited lipopolysaccharide-induced nitric oxide and nitric oxide synthase production of alveolar macrophages. The addition of H-89 (PKA inhibitor) significantly decreased the methylmercury inhibition of lipopolysaccharide-mediated nitric oxide production. We found the cell had a calcium-dependent adenylate cyclase, and MeHg could inhibit the phosphorylation of extracellular-signal regulated kinase (ERK). Because methylmercury could increase the intracellular calcium ion concentration, it might activate the adenylate cyclase by increasing [Ca(2+)](i). Though the interaction of methylmercury with the immune system has been studied by several investigators, the actual mechanisms underlying these interactions are still poorly understood. We discovered that methylmercury could activate protein kinase A, which in turn would inhibit the activation of Raf-1-ERK and so inhibit the release of nitric oxide.

The stability of mRNA influences the temporal order of the induction of genes encoding inflammatory molecules

The inflammatory response plays out over time in a reproducible and organized way after an initiating stimulus. Here we show that genes activated in cultured mouse fibroblasts in response to the cytokine tumor necrosis factor could be categorized into roughly three groups, each with different induction kinetics. Although differences in transcription were important in determining the grouping of these genes, differences in mRNA stability also exerted a strong influence on the temporal order of gene expression, in some cases overriding that of transcriptional control elements. Transcripts of mRNA expressed early had abundant AU-rich elements in their 3' untranslated regions, whereas those expressed later had fewer. Thus, mRNA stability and transcriptional control, two intrinsic characteristics of genes, control the kinetics of gene expression induced by proinflammatory cytokines.

Induction of hepatitis by JNK-mediated expression of TNF-alpha

The c-Jun NH(2)-terminal kinase (JNK) signaling pathway has been implicated in the development of tumor necrosis factor (TNF)-dependent hepatitis. JNK may play a critical role in hepatocytes during TNF-stimulated cell death in vivo. To test this hypothesis, we examined the phenotype of mice with compound disruption of the Jnk1 and Jnk2 genes. Mice with loss of JNK1/2 expression in hepatocytes exhibited no defects in the development of hepatitis compared with control mice, whereas mice with loss of JNK1/2 in the hematopoietic compartment exhibited a profound defect in hepatitis that was associated with markedly reduced expression of TNF-alpha. These data indicate that JNK is required for TNF-alpha expression but not for TNF-alpha-stimulated death of hepatocytes. Indeed, TNF-alpha induced similar hepatic damage in both mice with hepatocyte-specific JNK1/2 deficiency and control mice. These observations confirm a role for JNK in the development of hepatitis but identify hematopoietic cells as the site of the essential function of JNK.

Characterization of the BPI-like gene from a subtracted cDNA library of large yellow croaker (Pseudosciaena crocea) and induced expression by formalin-inactivated Vibrio alginolyticus and Nocardia seriolae vaccine challenges

One expressed sequence tag (EST 64LF004 clone), which is from the subtracted cDNA library of the head kidney of large yellow croaker (Pseudosciaena crocea) stimulated with peptidoglycan (PG) by suppression subtractive hybridization (SSH) method, was cloned using RACE-PCR. The full length cDNA, which possesses typical structural features of a signal peptide, a conserved LPS binding domain and two bactericidal permeability-increasing (BPI) motifs as in higher vertebrates, was identified as a novel homologue, namely of the large yellow croaker BPI-like molecule (Pc-BPI-L). Phylogenetic analysis showed this Pc-BPI-L of large yellow croaker as the most ancestral branch in bony fish clade. The recombinant Pc-BPI-L protein expressed in the Tn-5B1-4 insect cells was successfully produced and confirmed to have the predicted size of 52 kDa by Western blot analysis. At the message level, Pc-BPI-L mRNA was ubiquitously expressed in all tissues examined. Following formalin-inactivated Vibrio alginolyticus and Nocardia seriolae treatment, Pc-BPI-L message was differentially up-regulated in primary immune organs. These results indicate that Pc-BPI-L might be involved in the immune response to bacterial infection.

G9a and HP1 couple histone and DNA methylation to TNFalpha transcription silencing during endotoxin tolerance

TNFalpha gene expression is silenced in the endotoxin tolerant phenotype that develops in blood leukocytes after the initial activation phase of severe systemic inflammation or sepsis. The silencing phase can be mimicked in vitro by LPS stimulation. We reported that the TNFalpha transcription is disrupted in endotoxin tolerant THP-1 human promonocyte due to changes in transcription factor binding and enrichment with histone H3 dimethylated on lysine 9 (H3K9). Here we show that the TNFalpha promoter is hypermethylated during endotoxin tolerance and that H3K9 methylation and DNA methylation interact to silence TNFalpha expression. Chromatin immunoprecipitation and RNA interference analysis demonstrated that, in tolerant cells, TNFalpha promoter is bound by the H3K9 histone methyltransferase G9a which dimethylates H3K9 and creates a platform for HP1 binding, leading to the recruitment of the DNA methyltransferase Dnmt3a/b and an increase in promoter CpG methylation. Knockdown of HP1 resulted in a decreased Dnmt3a/b binding, sustained G9a binding, and a modest increase in TNFalpha transcription, but had no effect on H3K9 dimethylation. In contrast, G9a knockdown-disrupted promoter silencing and restored TNFalpha transcription in tolerant cells. This correlated with a near loss of H3K9 dimethylation, a significant decrease in HP1 and Dnmt3a/b binding and promoter CpG methylation. Our results demonstrate a central role for G9a in this process and suggest that histone methylation and DNA methylation cooperatively interact via HP1 to silence TNFalpha expression during endotoxin tolerance and may have implication for proinflammatory gene silencing associated with severe systemic inflammation.

Streptococcus pneumoniae stabilizes tumor necrosis factor alpha mRNA through a pathway dependent on p38 MAPK but independent of Toll-like receptors

Background

Streptococcus pneumoniae is a human pathogenic bacteria and a major cause of severe invasive diseases, including pneumonia, bacteremia, and meningitis. Infections with S. pneumoniae evoke a strong inflammatory response, which plays a major role in the pathogenesis of pneumococcal disease.

Results

In this study, we have examined how S. pneumoniae affects expression of the inflammatory cytokine tumor necrosis factor (TNF) α, and the molecular mechanisms involved. Secretion of TNF-α was strongly induced by S. pneumoniae, which was able to stabilize TNF-α mRNA through a mechanism dependent on the viability of the bacteria as well as the adenylate uridylate-rich elements in the 3'untranslated region of TNF-α mRNA. The ability of S. pneumoniae to stabilize TNF-α mRNA was dependent on the mitogen-activated protein kinase (MAPK) p38 whereas inhibition of Toll-like receptor signaling via MyD88 did not affect S. pneumoniae-induced mRNA stabilization. P38 was activated through a pathway involving the upstream kinase transforming growth factor-activated kinase 1 and MAPK kinase 3.

Conclusion

Thus, S. pneumoniae stabilizes TNF-α mRNA through a pathway dependent on p38 but independent of Toll-like receptors. Production of TNF-α may contribute significantly to the inflammatory response raised during pneumococcal infection.

Inhibition of tristetraprolin deadenylation by poly(A) binding protein

Tristetraprolin (TTP) is the prototype for a family of RNA binding proteins that bind the tumor necrosis factor (TNF) messenger RNA AU-rich element (ARE), causing deadenylation of the TNF poly(A) tail, RNA decay, and silencing of TNF protein production. Using mass spectrometry sequencing we identified poly(A) binding proteins-1 and -4 (PABP1 and PABP4) in high abundance and good protein coverage from TTP immunoprecipitates. PABP1 significantly enhanced TNF ARE binding by RNA EMSA and prevented TTP-initiated deadenylation in an in vitro macrophage assay of TNF poly(A) stability. Neomycin inhibited TTP-promoted deadenylation at concentrations shown to inhibit the deadenylases poly(A) ribonuclease and CCR4. Stably transfected RAW264.7 macrophages overexpressing PABP1 do not oversecrete TNF; instead they upregulate TTP protein without increasing TNF protein production. The PABP1 inhibition of deadenylation initiated by TTP does not require the poly(A) binding regions in RRM1 and RRM2, suggesting a more complicated interaction than simple masking of the poly(A) tail from a 3'-exonuclease. Like TTP, PABP1 is a substrate for p38 MAP kinase. Finally, PABP1 stabilizes cotransfected TTP in 293T cells and prevents the decrease in TTP levels seen with p38 MAP kinase inhibition. These findings suggest several levels of functional antagonism between TTP and PABP1 that have implications for regulation of unstable mRNAs like TNF.

TLRs and innate immunity

One of the most fundamental questions in immunology pertains to the recognition of non-self, which for the most part means microbes. How do we initially realize that we have been inoculated with microbes, and how is the immune response ignited? Genetic studies have made important inroads into this question during the past decade, and we now know that in mammals, a relatively small number of receptors operate to detect signature molecules that herald infection. One or more of these signature molecules are displayed by almost all microbes. These receptors and the signals they initiate have been studied in depth by random germline mutagenesis and positional cloning (forward genetics). Herein is a concise description of what has been learned about the Toll-like receptors, which play an essential part in the perception of microbes and shape the complex host responses that occur during infection.

Interleukin-12 and interleukin-27 regulate macrophage control of Mycobacterium tuberculosis

Mycobacterium tuberculosis is an intracellular pathogen that persists within macrophages and remains a considerable global threat to human health. The purpose of this study was to investigate how interleukin (IL)-12 and IL-27 regulate human macrophage interactions with M. tuberculosis. Quantitative measurement of transcripts showed that IL-12 or M. tuberculosis induced IL-27 gene expression in human macrophages. Furthermore, IL-27 receptor subunits were shown by reverse transcription-polymerase chain reaction and flow cytometry to be expressed and present at the cell surface. Neutralization of IL-27 in the presence of IL-12 reduced viable M. tuberculosis recovered from macrophages. Antimycobacterial activity was accompanied by a heightened inflammatory response that included tumor necrosis factor, IL-6, interferon-gamma, and a subset of chemokines. These results implicate IL-12 and IL-27 in regulating human macrophages, and IL-27 derived from macrophages during infection impedes control of M. tuberculosis growth.

Cytokine expression in the colonic mucosa of human immunodeficiency virus-infected individuals before and during 9 months of antiretroviral therapy

High-level human immunodeficiency virus (HIV) replication and the rapid breakdown of the mucosal immune system are the hallmarks of HIV infection in the gut. Cytokine dysregulation may be related to both phenomena. Using real-time PCR we quantified the colonic mucosal mRNA expression of selected proinflammatory and regulatory (gamma interferon [IFN-gamma], tumor necrosis factor alpha [TNF-alpha], and interleukin-2 [IL-2], IL-4, IL-6, and IL-10) and HIV-inhibitory (IL-16, CCL3, and CCL5) cytokines for 10 HIV-infected patients before and during 9 months of highly active antiretroviral therapy (HAART). HIV RNA and T-cell dynamics were measured in the colonic mucosa and the blood. Seven HIV-negative individuals served as controls. The mucosal mRNA expression of TNF-alpha, IFN-gamma, IL-4, IL-6, and IL-10 was significantly higher in HIV-infected patients than in control patients and remained elevated during 9 months of HAART despite the decline in blood and mucosal HIV RNA levels and an increase in the level of CD4(+) T lymphocytes. The mRNA levels of CCL3 and CCL5, both of which were elevated before treatment, returned to nearly normal during therapy. Despite reductions in levels of mucosal HIV RNA and the restoration of mucosal CD4(+) T lymphocytes, antiretroviral therapy failed to restore the normal colonic immunologic environment.

Genome-wide identification and characterization of transcripts translationally regulated by bacterial lipopolysaccharide in macrophage-like J774.1 cells

Although Escherichia coli LPS is known to elicit various proinflammatory responses in macrophages, its effect on the translational states of transcripts has not yet been explored on a genome-wide scale. To address this, we investigated the mRNA profiles in polysomal and free messenger ribonucleoprotein particle (mRNP) fractions of mouse macrophage-like J774.1 cells, using Affymetrix Mouse Genome 430 2.0 GeneChips. Comparison of the mRNA profiles in total cellular, polysomal, and free mRNP fractions enabled us to identify transcripts that were modulated at the translational level by LPS: among 19,791 transcripts, 115 and 418 were up- and downregulated at 1, 2, or 4 h after LPS stimulation (100 ng/ml) in a translation-dependent manner. Interestingly, gene ontology-based analysis suggested that translation-dependent downregulated genes frequently include those encoding proteins in the mitochondrial respiratory chain. In fact, the mRNA levels of some transcripts for complexes I, IV, and V in the mitochondrial respiratory chain were translationally downregulated, eventually contributing to the decline of their protein levels. Moreover, the amount of metabolically labeled cytochrome oxidase subunit Va in complex IV was decreased without any change of its mRNA level in total cellular fraction after LPS stimulation. Consistently, the total amounts and activities of complexes I and IV were attenuated by LPS stimulation, and the attenuation was independent of nitric oxide. These results demonstrated that translational suppression may play a critical role in the LPS-mediated attenuation of mitochondrial oxidative phosphorylation in a nitric oxide-independent manner in J774.1 cells.

IL-1beta-stimulated activation of ERK1/2 and p38alpha MAPK mediates the transcriptional up-regulation of IL-6, IL-8 and GRO-alpha in HeLa cells

Epithelial cells represent the first line of defense against infection. Here we have studied the production of inflammatory mediators induced by IL-1beta in the HeLa epithelial cell line. We found that GRO-alpha, IL-6 and IL-8 were the only three inflammatory mediators elevated out of 36 tested. Specific inhibition of p38alpha MAP kinase or preventing the activation of ERK1/ERK2 partially reduced the production of these substances, while the combined blockade of both pathways almost abolished secretion. The suppression of these signaling pathways mainly reduced transcription of the genes encoding GRO-alpha, IL-6 and IL-8, rather than affecting mRNA stability, translation or secretion. The production of these three inflammatory mediators was shown to account for the ability of the HeLa cell culture medium to stimulate the migration of monocytes/macrophages, suggesting a key role for p38 MAPK and ERK1/ERK2 in orchestrating the epithelial cell response to infection.

Modulation of miR-155 and miR-125b levels following lipopolysaccharide/TNF-alpha stimulation and their possible roles in regulating the response to endotoxin shock

We report here that miR-155 and miR-125b play a role in innate immune response. LPS stimulation of mouse Raw 264.7 macrophages resulted in the up-regulation of miR-155 and down-regulation of miR-125b levels. The same changes also occurred when C57BL/6 mice were i.p. injected with LPS. Furthermore, the levels of miR-155 and miR-125b in Raw 264.7 cells displayed oscillatory changes in response to TNF-alpha. These changes were impaired by pretreating the cells with the proteasome inhibitor MG-132, suggesting that these two microRNAs (miRNAs) may be at least transiently under the direct control of NF-kappaB transcriptional activity. We show that miR-155 most probably directly targets transcript coding for several proteins involved in LPS signaling such as the Fas-associated death domain protein (FADD), IkappaB kinase epsilon (IKKepsilon), and the receptor (TNFR superfamily)-interacting serine-threonine kinase 1 (Ripk1) while enhancing TNF-alpha translation. In contrast, miR-125b targets the 3'-untranslated region of TNF-alpha transcripts; therefore, its down-regulation in response to LPS may be required for proper TNF-alpha production. Finally, Emu-miR-155 transgenic mice produced higher levels of TNF-alpha when exposed to LPS and were hypersensitive to LPS/d-galactosamine-induced septic shock. Altogether, our data suggest that the LPS/TNF-alpha-dependent regulation of miR-155 and miR-125b may be implicated in the response to endotoxin shock, thus offering new targets for drug design.

Tumor necrosis factor antagonist mechanisms of action: a comprehensive review

During the past 30 years, elucidation of the pathogenesis of rheumatoid arthritis, Crohn's disease, psoriasis, psoriatic arthritis and ankylosing spondylitis at the cellular and molecular levels has revealed that these diseases share common mechanisms and are more closely related than was previously recognized. Research on the complex biology of tumor necrosis factor (TNF) has uncovered many mechanisms and pathways by which TNF may be involved in the pathogenesis of these diseases. There are 3 TNF antagonists currently available: adalimumab, a fully human monoclonal antibody; etanercept, a soluble receptor construct; and infliximab, a chimeric monoclonal antibody. Two other TNF antagonists, certolizumab and golimumab, are in clinical development. The remarkable efficacy of TNF antagonists in these diseases places TNF in the center of our understanding of the pathogenesis of many immune-mediated inflammatory diseases. The purpose of this review is to discuss the biology of TNF and related family members in the context of the potential mechanisms of action of TNF antagonists in a variety of immune-mediated inflammatory diseases. Possible mechanistic differences between TNF antagonists are addressed with regard to their efficacy and safety profiles.

Mechanisms of dexamethasone-mediated inhibition of Toll-like receptor signaling induced by Neisseria meningitidis and Streptococcus pneumoniae

Excessive inflammation contributes to the pathogenesis of bacterial meningitis, which remains a serious disease despite treatment with antibiotics. Therefore, anti-inflammatory drugs have important therapeutic potential, and clinical trials have revealed that early treatment with dexamethasone significantly reduces mortality and morbidity from bacterial meningitis. Here we investigate the molecular mechanisms behind the inhibitory effect of dexamethasone upon the inflammatory responses evoked by Neisseria meningitidis and Streptococcus pneumoniae, two of the major causes of bacterial meningitis. The inflammatory cytokine response was dependent on Toll-like receptor signaling and was strongly inhibited by dexamethasone. Activation of the NF-kappaB pathway was targeted at several levels, including inhibition of IkappaB phosphorylation and NF-kappaB DNA-binding activity as well as upregulation of IkappaB alpha synthesis. Our data also revealed that the timing of steroid treatment relative to infection was important for achieving strong inhibition, particularly in response to S. pneumoniae. Altogether, we describe important targets of dexamethasone in the inflammatory responses evoked by N. meningitidis and S. pneumoniae, which may contribute to our understanding of the clinical effect and the importance of timing with respect to corticosteroid treatment during bacterial meningitis.

Chemokine and chemoattractant receptor expression: post-transcriptional regulation

The magnitude and character of the inflammatory process are determined in part via the trafficking of leukocytes into sites of injury and infection, and this process depends on proper control of the expression of genes encoding chemoattractant peptides and their receptors. Although these controls operate at multiple mechanistic levels, recent evidence indicates that post-transcriptional events governing the half-life of select mRNAs are important determinants. Adenine-uridine rich elements (AREs) located within 3' untranslated regions (UTRs) confer constitutive mRNA instability and in some cases, stabilization following stimulation by ligands of the Toll-IL-1 receptor (TIR) family. Although the importance of AREs in determining activity and mRNA half-life is well-recognized, the mechanistic scope and diversity remain poorly understood. Using the mouse KC or CXCL1 gene as a model, we have demonstrated that the abundance of mRNA and protein produced during an inflammatory response depends on multiple mechanistically distinct AREs present in the 3' UTR of the mRNA. The mRNA encoding the receptor for N-terminal formyl-methionine-containing peptides is also unstable and subject to stabilization in response to TIR ligands. These two models can, however, be readily distinguished from one another on the basis of specific stimulus sensitivity and the signaling pathways, through which such stimuli couple to the control of mRNA decay. These models demonstrate the substantial diversity operative in the post-transcriptional regulation of inflammatory gene expression.

Tristetraprolin recruits functional mRNA decay complexes to ARE sequences

AU-rich elements (AREs) in the 3' untranslated region (UTR) of numerous mammalian transcripts function as instability elements that promote rapid mRNA degradation. Tristetraprolin (TTP) is an ARE-binding protein that promotes rapid mRNA decay through mechanisms that are poorly understood. A 31 nucleotide ARE sequences from the TNF-alpha 3' UTR promoted TTP-dependent mRNA decay when it was inserted into the 3' UTR of a beta-globin reporter transcript, indicating that this short sequence was sufficient for TTP function. We used a gel shift assay to identify a TTP-containing complex in cytoplasmic extracts from TTP-transfected HeLa cells that bound specifically to short ARE sequences. This TTP-containing complex also contained the 5'-3' exonuclease Xrn1 and the exosome component PM-scl75 because it was super-shifted with anti-Xrn1 or anti-PMscl75 antibodies. RNA affinity purification verified that these proteins associated specifically with ARE sequences in a TTP-dependent manner. Using a competition binding assay, we found that the TTP-containing complex bound with high affinity to short ARE sequences from GM-CSF, IL-3, TNF-alpha, IL-2, and c-fos, but did not bind to a U-rich sequence from c-myc, a 22 nucleotide poly U sequence or a mutated GM-CSF control sequence. High affinity binding by the TTP-containing complex correlated with TTP-dependent deadenylation and decay of capped, polyadenylated transcripts in a cell-free mRNA decay assay, suggesting that the TTP-containing complex was functional. These data support a model whereby TTP functions to enhance mRNA decay by recruiting components of the cellular mRNA decay machinery to the transcript.

Epigenetic silencing of tumor necrosis factor alpha during endotoxin tolerance

Sustained silencing of potentially autotoxic acute proinflammatory genes like tumor necrosis factor alpha (TNFalpha) occurs in circulating leukocytes following the early phase of severe systemic inflammation. Aspects of this gene reprogramming suggest the involvement of epigenetic processes. We used THP-1 human promonocytes, which mimic gene silencing when rendered endotoxin-tolerant in vitro, to test whether TNFalpha proximal promoter nucleosomes and transcription factors adapt to an activation-specific profile by developing characteristic chromatin-based silencing marks. We found increased TNFalpha mRNA levels in endotoxin-responsive cells that was preceded by dissociation of heterochromatin-binding protein 1alpha, demethylation of nucleosomal histone H3 lysine 9 (H3(Lys(9))), increased phosphorylation of the adjacent serine 10 (H3(Ser(10))), and recruitment of NF-kappaB RelA/p65 to the TNFalpha promoter. In contrast, endotoxin-tolerant cells repressed production of TNFalpha mRNA, retained binding of heterochromatin-binding protein 1alpha, sustained methylation of H3(Lys(9)), reduced phosphorylation of H3(Ser(10)), and showed diminished binding of NF-kappaB RelA/p65 to the TNFalpha promoter. Similar levels of NF-kappaB p50 occurred at the TNFalpha promoter in the basal state, during active transcription, and in the silenced phenotype. RelB, which acts as a repressor of TNFalpha transcription, remained bound to the promoter during silencing. These results support an immunodeficiency paradigm where epigenetic changes at the promoter of acute proinflammatory genes mediate their repression during the late phase of severe systemic inflammation.

Limitation in use of luciferase reporter genes for 3'-untranslated region analysis

Luciferase reporter genes are widely used for the functional characterization of regulatory elements in 3'-untranslated region (3'-UTR). Using a transient expression assay system with pancreatic cell lines, we demonstrated that luciferase reporter gene constructs show not only the elements with special sequences in 3'-UTR that can affect luciferase activity, but also elements containing random sequences that were ligated into the same site. The extent of the decrease in luciferase activity was dependent on the length of the DNA fragments. Our findings strongly suggested a need to re-examine the 3'-UTR characterizations of many eukaryotic genes which have been studied to date with luciferase reporter genes.

Post-induction, Stimulus-specific Regulation of Tumor Necrosis Factor mRNA Expression

The tumor necrosis factor (TNF) gene is activated by multiple extracellular signals in a stimulus- and cell type-specific fashion. Based on the presence of kappaB-like DNA motifs in the region upstream of the TNF gene, some have proposed a direct role for NF-kappaB in lipopolysaccharide (LPS)-induced TNF gene transcription in cells of the monocyte/macrophage lineage. However, we have previously demonstrated a general and critical role for a minimal TNF promoter region bearing only one of the kappaB-like motifs, kappa3, which is bound by nuclear factor of activated T cell proteins in lymphocytes and fibroblasts in response to multiple stimuli and Ets proteins in LPS-stimulated macrophages. Here, in an effort to resolve these contrasting findings, we used a combination of site-directed mutagenesis of the TNF promoter, quantitative DNase I footprinting, and analysis of endogenous TNF mRNA production in response to multiple stimuli under conditions that inhibit NF-kappaB activation (using the proteasome inhibitor lactacystin and using cells lacking either functional NF-kappaB essential modulator, which is the IkappaB kinase regulatory subunit, or the Nemo gene itself). We find that TNF mRNA production in response to ionophore is NF-kappaB-independent, but inhibition of NF-kappaB activation attenuates virus- and LPS-induced TNF mRNA levels after initial induction. We conclude that induction of TNF gene transcription by virus or LPS does not depend upon NF-kappaB binding to the proximal promoter; rather, a stimulus-specific post-induction mechanism involving NF-kappaB, yet to be characterized, is involved in the maintenance of maximal TNF mRNA levels.

Signalling to translation: how signal transduction pathways control the protein synthetic machinery

Recent advances in our understanding of both the regulation of components of the translational machinery and the upstream signalling pathways that modulate them have provided important new insights into the mechanisms by which hormones, growth factors, nutrients and cellular energy status control protein synthesis in mammalian cells. The importance of proper control of mRNA translation is strikingly illustrated by the fact that defects in this process or its control are implicated in a number of disease states, such as cancer, tissue hypertrophy and neurodegeneration. Signalling pathways such as those involving mTOR (mammalian target of rapamycin) and mitogen-activated protein kinases modulate the phosphorylation of translation factors, the activities of the protein kinases that act upon them and the association of RNA-binding proteins with specific mRNAs. These effects contribute both to the overall control of protein synthesis (which is linked to cell growth) and to the modulation of the translation or stability of specific mRNAs. However, important questions remain about both the contributions of individual regulatory events to the control of general protein synthesis and the mechanisms by which the translation of specific mRNAs is controlled.

Monocyte p110alpha phosphatidylinositol 3-kinase regulates phagocytosis, the phagocyte oxidase, and cytokine production

Mononuclear phagocytes are critical modulators and effectors of innate and adaptive immune responses, and PI-3Ks have been shown to be multifunctional monocyte regulators. The PI-3K family includes eight catalytic isoforms, and only limited information is available about how these contribute to fine specificity in monocyte cell regulation. We examined the regulation of phagocytosis, the phagocyte oxidative burst, and LPS-induced cytokine production by human monocytic cells deficient in p110alpha PI-3K. We observed that p110alpha PI-3K was required for phagocytosis of IgG-opsonized and nonopsonized zymosan in differentiated THP-1 cells, and the latter was inhibitable by mannose. In contrast, p110alpha PI-3K was not required for ingestion serum-opsonized zymosan. Taken together, these results suggest that FcgammaR- and mannose receptor-mediated phagocytosis are p110alpha-dependent, whereas CR3-mediated phagocytosis involves a distinct isoform. It is notable that the phagocyte oxidative burst induced in response to PMA or opsonized zymosan was also found to be dependent on p110alpha in THP-1 cells. Furthermore, p110alpha was observed to exert selective and bidirectional effects on the secretion of pivotal cytokines. Incubation of p110alpha-deficient THP-1 cells with LPS showed that p110alpha was required for IL-12p40 and IL-6 production, whereas it negatively regulated the production of TNF-alpha and IL-10. Cells deficient in p110alpha also exhibited enhanced p38 MAPK, JNK, and NF-kappaB phosphorylation. Thus, p110alpha PI-3K appears to uniquely regulate important monocyte functions, where other PI-3K isoforms are uninvolved or unable to fully compensate.

Cloning and characterization of a TNF-like protein of Plecoglossus altivelis (ayu fish)

Ayu TNF cDNA contains an open reading frame of 708bp encoding 235 amino acids. Poly adeniration (A) signal and eight AU-rich sequences were present in 858bp 3' UTR. Southern blot analysis indicated that ayu TNF is single-copy gene. The genomic DNA sequence of ayu TNF, consisting of four exons and three introns, was shown to be conserved well throughout evolution from fish to mammals. The amino acid sequence of ayu TNF was shown to have 32-41% of amino acid identity to other known fish TNF, and about 30% of amino acid identity to mammalian TNFs. A phylogenetic analysis based on the amino acid sequence of TNF indicated that ayu has a distinctive evolutionary path. Also, two residues of cysteine important for the formation of the three-dimensional structure were conserved in ayu TNF. For the functional analysis, ayu TNF was inserted into expression vector pCold/TF, transferred into Chaperone Competent Cells BL21 (pKJE7); this produced soluble mature ayu recombinant TNF. Ayu recombinant TNF was shown to induce respiratory burst activity from ayu kidney. The above results indicate that ayu TNF plays an important role in phylaxis, as it does in mammals.

Post-transcriptional regulation of cytokine genes in fish: A role for conserved AU-rich elements located in the 3′-untranslated region of their mRNAs

The overproduction of cytokines, such us interleukin-1beta (IL-1beta) and tumor necrosis factor alpha (TNFalpha), contributes to the pathological complications observed in many inflammatory diseases caused by bacterial endotoxins. The synthesis of these cytokines is tightly regulated at both transcriptional and post-transcriptional levels. Post-transcriptional regulation of gene expression depends on specific cis-acting sequences and trans-acting factors. Thus, the presence of adenylate- and uridylate-rich (AU-rich) elements (AREs) has been described in the 3'-untranslated regions (UTRs) of many unstable mammalian mRNAs. Although, it represents the most widespread, phylogenetically conserved and efficient determinant of mRNA stability among those so far characterized in mammalian cells, no studies are available on the functional relevance of this sequence in non-mammalian vertebrates. In this contribution, we study the enzymatic activity of various luciferase reporter constructs, containing or lacking the 3'UTR of IL-1beta and TNFalpha from different fish species, and report the finding that bony fish AREs are able to decrease luciferase activity but are less potent than their mammalian counterparts. Surprisingly, the 3'UTR of the IL-1beta from the cartilaginous fish small spotted catshark had the greatest ability to decrease luciferase activity. Lastly, the functional significance of the above was confirmed by measuring the half-life of IL-1beta and TNFalpha mRNAs in gilthead seabream leukocytes by blocking transcription with actinomycin D. Both cytokine mRNAs were unstable with an estimated half-life of about 45 min in control and activated cells.

TUMOUR NECROSIS FACTOR: IMPLICATIONS FOR SURGICAL PATIENTS

Tumour necrosis factor alpha (TNF-alpha) is an inflammatory cytokine primarily produced by macrophages. It is a unique protein with contradictive properties; it has the ability to induce cellular death by apoptosis and oncosis, but can also induce cellular regeneration and growth. Genetic polymorphisms in TNFA have been associated with poor outcome in some surgical patients and this may provide a useful tool to screen for high-risk patients. Manipulating TNF-alpha levels in vivo may influence the progression of several pathological conditions. TNF-alpha has anti-cancer properties and has been used to treat cancer patients. Treatment with anti-TNF-alpha drugs and antibodies has been successful in rheumatoid arthritis and other autoimmune diseases, but disappointing in the management of patients with sepsis. This review article focuses on the biological activities, genetic polymorphism of TNFA and the role of TNF-alpha and anti-TNF-alpha treatments, based on animal experiments and clinical trials.

IL-10-induced TNF-alpha mRNA destabilization is mediated via IL-10 suppression of p38 MAP kinase activation and inhibition of HuR expression

Inflammation plays an essential role in vascular injury and repair. Mononuclear phagocytes are important contributors in these processes, in part, via adhesive interactions and secretion of proinflammatory cytokines. The antiinflammatory cytokine interleukin (IL)-10 suppresses such responses via deactivation of monocytes/macrophages and repression of inflammatory cytokine expression. The mechanisms of IL-10's suppressive action are, however, incompletely characterized. Here, we report that systemic IL-10 treatment after carotid artery denudation in mice blunts inflammatory cell infiltration and arterial tumor necrosis factor (TNF) expression. At the molecular level, in a human monocytic cell line, U937 IL-10 suppressed LPS-induced mRNA expression of a number of inflammatory cytokines, mainly via posttranscriptional mRNA destabilization. Detailed studies on IL-10 regulation of TNF-alpha mRNA expression identified AU-rich elements (ARE) in the 3' untranslated region as a necessary determinant of IL-10-mediated TNF-alpha mRNA destabilization. IL-10 sensitivity to TNF depends on the ability of IL-10 to inhibit the expression and mRNA-stabilizing protein HuR and via IL-10 mediated repression of p38 mitogen-activated protein (MAP) kinase activation. Because IL-10 function and signaling are important components for control of inflammatory responses, these results may provide insights necessary to develop strategies for modulating vascular repair and other accelerated arteriopathies, including transplant vasculopathy and vein graft hyperplasia.

MAPKAP Kinase 2-Deficient Mice Are Resistant to Collagen-Induced Arthritis

TNF-alpha is a pleiotropic cytokine considered a primary mediator of immune regulation and inflammatory response and has been shown to play a central role in rheumatoid arthritis (RA). MAPKAP kinase 2 (MK2) is a serine/threonine kinase that is regulated through direct phosphorylation by p38 MAPK, and has been shown to be an essential component in the inflammatory response that regulates the biosynthesis of TNF-alpha at a posttranscriptional level. The murine model of collagen-induced arthritis (CIA) is an established disease model to study pathogenic mechanisms relevant to RA. In this study, we report that deletion of the MK2 gene in DBA/1LacJ mice confers protection against CIA. Interestingly, the MK2 heterozygous mutants display an intermediate level of protection when compared with homozygous mutant and wild-type littermates. We show that MK2(-/-) and MK2(+/-) mice exhibit decreased disease incidence and severity in the CIA disease model and reduced TNF-alpha and IL-6 serum levels following LPS/d-Gal treatment compared with wild-type mice. Additionally, we show that levels of IL-6 mRNA in paws of mice with CIA correlate with the disease status. These findings suggest that an MK2 inhibitor could be of great therapeutic value to treat inflammatory diseases like RA.

A systematic analysis of disease-associated variants in the 3' regulatory regions of human protein-coding genes II: the importance of mRNA secondary structure in assessing the functionality of 3' UTR variants

In an attempt both to catalogue 3' regulatory region (3' RR)-mediated disease and to improve our understanding of the structure and function of the 3' RR, we have performed a systematic analysis of disease-associated variants in the 3' RRs of human protein-coding genes. We have previously analysed the variants that have occurred in two specific domains/motifs of the 3' untranslated region (3' UTR) as well as in the 3' flanking region. Here we have focused upon 83 known variants within the upstream sequence (USS; between the translational termination codon and the upstream core polyadenylation signal sequence) of the 3' UTR. To place these variants in their proper context, we first performed a comprehensive survey of known cis-regulatory elements within the USS and the mechanisms by which they effect post-transcriptional gene regulation. Although this survey supports the view that RNA regulatory elements function within the context of specific secondary structures, there are no general rules governing how secondary structure might exert its influence. We have therefore addressed this question by systematically evaluating both functional and non-functional (based upon in vitro reporter gene and/or electrophoretic mobility shift assay data) USS variant-containing sequences against known cis-regulatory motifs within the context of predicted RNA secondary structures. This has allowed us not only to establish a reliable and objective means to perform secondary structure prediction but also to identify consistent patterns of secondary structural change that could potentiate the discrimination of functional USS variants from their non-functional counterparts. The resulting rules were then used to infer potential functionality in the case of some of the remaining functionally uncharacterized USS variants, from their predicted secondary structures. This not only led us to identify further patterns of secondary structural change but also several potential novel cis-regulatory motifs within the 3' UTRs studied.

Efficiency of tazobactam/piperacillin in lethal peritonitis is enhanced after preconditioning of rats with O3/O2-pneumoperitoneum

Insufflation of ozonized oxygen into the peritoneum (O3/O2-pneumoperitoneum [O3/O2-PP]) of rats reduced the lethality of peritonitis. We evaluated the prophylactic effect of O3/O2-PP combined with tazobactam/piperacillin (TZP) in polymicrobial lethal peritonitis. Wistar rats were conditioned by daily repeated insufflation of ozone for 5 days, and hematologic parameters were determined. Sepsis was induced by i.p. injection of cecal material derived from donor rats. Simultaneously, TZP was applied at a single dosage of 65 mg/kg or at two dosage schedules of 65 mg/kg each at an interval of 1 h. The conditioning effect of O3/O2-PP on the number of blood cells was measured before inoculation of bacteria. The mRNA levels of proinflammatory cytokine IL-lbeta and TNF-alpha were determined at 4 h post infection in spleen and liver by semiquantitative in situ hybridization analysis. Preconditioning of rats by O3/O2-PP enhanced the number of blood leukocytes and granulocytes and increased the survival rate of septic rats up to 33%. The combination of O3/O2-PP and TZP further enhanced the survival rate up to 93%. This effect was accompanied by a reduced amount of IL-1beta and TNF-alpha mRNA in spleen and liver. In contrast, in non-infected animals the combination of O3/O2-PP and TZP enhanced IL-1beta and TNF-alpha mRNA in the spleen and IL-1beta mRNA in liver when compared with TZP- and sham-treated controls. The preconditioning effect of O3/O2-PP seems to support the biological effectiveness of TZP by altering the immune status before and during the onset of sepsis. The combined therapy could be a simple, preoperative intervention for abdominal surgery to reduce postoperative morbidity and mortality.

Dexamethasone suppresses human interleukin-5 gene promoter

Synthetic glucocorticoid dexamethasone suppressed interleukin-5 gene expression in PER-117 human T cells at the level of transcription. The conserved lymphokine element 0 in the interleukin-5 gene promoter context served as a target for dexamethasone.

AU-rich elements and associated factors: are there unifying principles?

The control of mRNA stability is an important process that allows cells to not only limit, but also rapidly adjust, the expression of regulatory factors whose over expression may be detrimental to the host organism. Sequence elements rich in A and U nucleotides or AU-rich elements (AREs) have been known for many years to target mRNAs for rapid degradation. In this survey, after briefly summarizing the data on the sequence characteristics of AREs, we present an analysis of the known ARE-binding proteins (ARE-BP) with respect to their mRNA targets and the consequences of their binding to the mRNA. In this analysis, both the changes in mRNA stability and the lesser studied effects on translation are considered. This analysis highlights the multitude of mRNAs bound by one ARE-BP and conversely the large number of ARE-BP that associate with any particular ARE-containing mRNA. This situation is discussed with respect to functional redundancies or antagonisms. The potential relationship between mRNA stability and translation is also discussed. Finally, we present several hypotheses that could unify the published data and suggest avenues for future research.

Activation of the adenosine A3 receptor in RAW 264.7 cells inhibits lipopolysaccharide-stimulated tumor necrosis factor-alpha release by reducing calcium-dependent activation of nuclear factor-kappaB and extracellular signal-regulated kinase 1/2

Bacterial lipopolysaccharide (LPS) activates the immune system and promotes inflammation via Toll-like receptor (TLR) 4, which regulates the synthesis and release of tumor necrosis factor (TNF)-alpha and other inflammatory cytokines. Previous studies have shown that the nucleoside adenosine suppresses LPS-stimulated TNF-alpha release in human UB939 macrophages by activating an adenosine A(3) receptor (A(3)AR) subtype on these cells. In this study, we examined the mechanism(s) underlying A(3)AR-dependent inhibition of TNF-alpha release in a mouse (RAW 264.7) cell line. Treatment of RAW 264.7 cells with LPS (3 mug/ml) increased TNF-alpha release, which was reduced in a dose-dependent manner by adenosine analogs N(6)-(3-iodobenzyl)-adenosine-5'-N-methyluronamide (IB-MECA) and R-phenylisopropyladenosine and reversed by selective A(3)AR blockade. The increase in TNF-alpha release was preceded by an increase in intracellular Ca(2+) levels. Inhibition of intracellular Ca(2+) release by IB-MECA, a selective agonist of the A(3)AR, or with BAPTA-AM, an intracellular Ca(2+) chelator, reduced LPS-stimulated TNF-alpha release. Activation of the A(3)AR or inhibition of intracellular Ca(2+) release also reduced LPS-stimulated nuclear factor-kappaB (NF-kappaB) activation and extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation. Similar inhibition by A(3)AR was observed for LPS-stimulated inducible nitric-oxide synthase. These data support the contention that inhibition of LPS-stimulated release of inflammatory molecules, such as TNF-alpha and NO via the A(3)AR, involves suppression of intracellular Ca(2+)signaling, leading to suppression of NF-kappaB and ERK1/2 pathways.

Posttranscriptional mechanisms regulating the inflammatory response

The inflammatory response is a complex physiologic process that requires the coordinate induction of cytokines, chemokines, angiogenic factors, effector-enzymes, and proteases. Although transcriptional activation is required to turn on the inflammatory response, recent studies have revealed that posttranscriptional mechanisms play an important role by determining the rate at which mRNAs encoding inflammatory effector proteins are translated and degraded. Most posttranscriptional control mechanisms function to dampen the expression of pro-inflammatory proteins to ensure that potentially injurious proteins are not overexpressed during an inflammatory response. Here we discuss the factors that regulate the stability and translation of mRNAs encoding pro-inflammatory proteins.

Genetic Analysis of Innate Immunity

The inflammatory response to microbes--and host perception of microbes in general--is largely initiated by a single class of receptors, named for their similarity to the prototypic Toll receptor of Drosophila. The mammalian Toll-like receptors (TLRs) are ultimately responsible for most phenomena associated with infection. This includes both "good" effects of infection (e.g., the induction of lasting specific immunity to an infectious agent) and "bad" effects of infection (systemic inflammation and shock). Although they are essential for host defense, no other endogenous proteins can match their lethal potential. The TLR complexes transduce the toxicity of lipopolysaccharide (LPS), cysteinyl lipopeptides, and many other molecules of microbial origin. The identification of the TLRs as the key conduit to host awareness of microbial infection was a victory for reductionism, proving that the complexity of infectious inflammation as a phenomenon belies the simplicity of its origins. It was achieved by a classical genetic approach, proceeding from phenotype to gene. Further analysis of the signaling pathways activated by the TLRs has depended on both classical and reverse genetic methods. Additional work will ultimately disclose the extent to which sterile inflammatory diseases are mediated by aberrations in these pathways.

Adenosine augments IL-10 production by macrophages through an A2B receptor-mediated posttranscriptional mechanism

Adenosine receptor ligands have anti-inflammatory effects and modulate immune responses by up-regulating IL-10 production by immunostimulated macrophages. The adenosine receptor family comprises G protein-coupled heptahelical transmembrane receptors classified into four types: A1, A2A, A2B, and A3. Our understanding of the signaling mechanisms leading to enhanced IL-10 production following adenosine receptor occupancy on macrophages is limited. In this study, we demonstrate that adenosine receptor occupancy increases IL-10 production by LPS-stimulated macrophages without affecting IL-10 promoter activity and IL-10 mRNA levels, indicating a posttranscriptional mechanism. Transfection experiments with reporter constructs containing sequences corresponding to the AU-rich 3'-untranslated region (UTR) of IL-10 mRNA confirmed that adenosine receptor activation acts by relieving the translational repressive effect of the IL-10 3'-UTR. By contrast, adenosine receptor activation failed to liberate the translational arrest conferred by the 3'-UTR of TNF-alpha mRNA. The IL-10 3'-UTR formed specific complexes with proteins present in cytoplasmic extracts of RAW 264.7 cells. Adenosine enhanced binding of proteins to a region of the IL-10 3'-UTR containing the GUAUUUAUU nonamer. The stimulatory effect of adenosine on IL-10 production was mediated through the A(2B) receptor, because the order of potency of selective agonists was 5'-N-ethylcarboxamidoadenosine (NECA) > N6-(3-iodobenzyl)-adenosine-5'-N-methyluronamide (IB-MECA) > 2-chloro-N6-cyclopentyladenosine (CCPA) = 2-p-(2-carboxyethyl)phenethylamino-5'-N-ethyl-carboxamidoadenosine (CGS-21680). Also, the selective A2B antagonist, alloxazine, prevented the effect of adenosine. Collectively, these studies identify a novel pathway in which activation of a G protein-coupled receptor augments translation of an anti-inflammatory gene.