The lipopolysaccharide-binding protein is a secretory class 1 acute-phase protein whose gene is transcriptionally activated by APRF/STAT/3 and other cytokine-inducible nuclear proteins

Lipopolysaccharide binding protein binds to triacylated and diacylated lipopeptides and mediates innate immune responses

LPS binding protein (LBP) is an acute-phase protein synthesized predominantly in the liver of the mammalian host. It was first described to bind LPS of Gram-negative bacteria and transfer it via a CD14-enhanced mechanism to a receptor complex including TLR-4 and MD-2, initiating a signal transduction cascade leading to the release of proinflammatory cytokines. In recent studies, we found that LBP also mediates cytokine induction caused by compounds derived from Gram-positive bacteria, including lipoteichoic acid and peptidoglycan fragments. Lipoproteins and lipopeptides have repeatedly been shown to act as potent cytokine inducers, interacting with TLR-2, in synergy with TLR-1 or -6. In this study, we show that these compounds also interact with LBP and CD14. We used triacylated lipopeptides, corresponding to lipoproteins of Borrelia burgdorferi, mycobacteria, and Escherichia coli, as well as diacylated lipopeptides, corresponding to, e.g., 2-kDa macrophage activating lipopeptide of Mycoplasma spp. Activation of Chinese hamster ovary cells transfected with TLR-2 by both lipopeptides was enhanced by cotransfection of CD14. Responsiveness of human mononuclear cells to these compounds was greatly enhanced in the presence of human LBP. Binding of lipopeptides to LBP as well as competitive inhibition of this interaction by LPS was demonstrated in a microplate assay. Furthermore, we were able to show that LBP transfers lipopeptides to CD14 on human monocytes using FACS analysis. These results support that LBP is a pattern recognition receptor transferring a variety of bacterial ligands including the two major types of lipopeptides to CD14 present in different receptor complexes.

CD14 is an acute-phase protein

The origin of soluble CD14 (sCD14) in the circulation is uncertain. To examine whether CD14 could be an acute-phase protein (APP), the levels of sCD14, IL-6, and C-reactive protein were determined by ELISA in serum and synovial fluid (SF) of patients with various arthropathies, and the regulation of CD14 synthesis was examined in liver cells. In patients with crystal-mediated or immunologically mediated arthritis (rheumatoid arthritis), serum levels of sCD14 were higher than or similar to those found in infection-mediated arthritis (reactive arthritis), precluding a relation with bacteria exposure. Levels of sCD14 were similar in SF and serum, and did not correlate with the number of SF leukocytes, excluding an important source from leukocyte membrane-bound CD14, by protease-mediated shedding. In contrast, serum levels of sCD14 in patients correlated with those of C-reactive protein, a classical APP, and IL-6, a cytokine known to regulate the synthesis of APP in the liver. Serum levels of sCD14 also correlated with disease activity in rheumatoid arthritis and reactive arthritis patients. IL-6 stimulated the production of CD14 by HepG2 hepatoma cells. By real-time PCR, the inducibility of CD14 by IL-6 was also observed at the mRNA level both in HepG2 cells and human primary hepatocytes. These in vitro results were confirmed by in vivo studies in IL-6(-/-) mice injected with turpentine, an experimental model of acute-phase response. Liver levels of CD14 mRNA increased in IL-6(+/+), but not in IL-6(-/-) mice. These results indicate that sCD14 can be considered as a type 2 APP.

Association of the -159 C --> T polymorphism in the CD14 promoter with variations in serum lipoproteins in healthy subjects

The CD14-159 C --> T polymorphism, a single nucleotide polymorphism (SNP) at position -159 in the promoter region of the gene encoding the pattern recognition receptor CD14, has been associated with elevated plasma concentrations of soluble CD14, lowered serum immunoglobulin E, increased risk for myocardial infarction, and decreased risk for allergy and asthma. In the present study, the CD14-159 C --> T polymorphism has been investigated in order to determine its frequency and association with proinflammatory variables and lipid profile traits of 117 volunteers. The frequency of the CD14 promoter genotype as determined by polymerase chain reaction amplification-restriction fragment length polymorphism analysis was 35.0% (CC), 44.4% (CT), and 20.5% (TT), and the T allele frequency was 42.7%. Compared with the other genotypes, notably CC homozygotes, TT homozygotes were associated with lower total cholesterol, low-density lipoprotein cholesterol and apolipoprotein B-100 (P < 0.01) concentrations in serum. However, no association was found between the investigated SNP and inflammatory mediators such as fibrinogen, interleukin-6, tumor necrosis factor-alpha, tissue factor, C-reactive protein, plasminogen activator inhibitor-1, leukotriene B4, or thromboxane B2. In conclusion, the CD14-159 C --> T polymorphism may be an important genetic trait, related to the ability of CD14 to bind and transport lipids, such as cholesterol.

Tissue lipopolysaccharide-binding protein expression in rats after thermal injury: potential role of TNF-alpha

Recent studies have suggested that levels of lipopolysaccharide-binding protein (LBP) might play a harmful role by up-regulating the host's sensitivity to endotoxin. Our previous studies demonstrated that local endotoxin could up-regulate LBP expression after acute insults, however, the definite molecular mechanisms downstream of endotoxin action remain unclear. This study investigates whether tumor necrosis factor (TNF-alpha) might be responsible for the LBP formation during endogenous endotoxemia postburn. Wistar rats were anesthetized, and a 35% TBSA full-thickness burn was created. Animals were randomly divided into normal control, thermal injury and anti-TNF-alpha mAb treatment group. A significant elevation of plasma endotoxin concentration was observed after acute insults. TNF-alpha levels in plasma also rapidly increased after thermal injury. Meanwhile, LBP mRNA expression markedly increased in liver, lungs, kidneys and intestine postburn. There was no detectable TNF-alpha in the plasma of anti-TNF-alpha mAb treated animals. Treatment with anti-TNF-alpha mAb also resulted in significantly lower concentrations of LBP mRNA in local tissues. Additionally, several organ function parameter levels in plasma significantly decreased in treatment group. These results demonstrated that an increase of plasma TNF-alpha levels caused by burns might be associated with a marked elevation of tissue LBP mRNA expression, which could contribute to the development of multiple organ damage.

Hepatic expression of multiple acute phase proteins and down-regulation of nuclear receptors after acute endotoxin exposure

Acute systemic lipopolysaccharide (endotoxin, LPS) exposure, which can lead to septic shock, enhances the hepatic expression of inflammatory and acute-phase proteins (APPs). To better understand how LPS aggravates damage, changes in hepatic gene expression after a single LPS dose was screened by using microarrays for 1176 rat genes. We detected more than 20 new potential LPS-induced APPs. Following acute LPS challenge, significant up-regulation of the steady-state mRNA levels of several important early transcription factors, such as c-jun and STAT3, and cytokine-associated genes, was observed. In contrast, RT-PCR analysis revealed marked down-regulation of the nuclear receptors RXRalpha, PXR, FXR, LXR, PPARalpha and CAR. Also genes encoding lipolytic, antioxidant as well as drug- and alcohol-metabolizing enzymes were down-regulated. These data suggest that acute LPS treatment induces important early transcription factors and co-ordinately down-regulates nuclear receptors, and that this results in altered expression of a large number of downstream genes.

Cloning and analyses of a BPI/LBP cDNA of the Atlantic cod (Gadus morhua L.)

Using the differential screening technique, a cDNA related to the mammalian family of lipid transfer/lipopolysaccharide-binding proteins was cloned from the Atlantic cod (Gadus morhua L.). The gene is an ortholog of a recently identified gene of rainbow trout (Oncorhynchus mykiss). Phylogenetic analyses suggest that teleost BPI/LBP are modern descendants of the ancestor of mammalian bactericidal/permeability-increasing protein (BPI) and lipopolysaccharide-binding protein (LBP), and a gene of the urochordate Ciona intestinalis is related to this gene family. Molecular modeling suggests that the structure of cod BPI/LBP is similar to mammalian BPI and LBP, while its highly basic character is similar to BPI. Cod BPI/LBP is constitutively expressed in head-kidney (HK) leukocytes. After intraperitoneal injection of bacterin high levels of cod BPI/LBP mRNA were detected also in peripheral blood cells and spleen, while moderate to low levels of transcript were found in heart, liver, gills, skin, brain, and intestine. We conclude that the patterns of charge and expression of cod BPI/LBP are more similar to mammalian BPI than to mammalian LBP.

Activation of the STAT pathway in acute lung injury

Acute lung injury (ALI) is a devastating clinical problem with a mortality as high as 60%. It is now appreciated that ALI represents a cytokine excess state that involves the microvasculature of multiple organs. The signal transducers and activators of transcription (STAT) family of transcription factors activate critical mediators of cytokine responses, but there is limited knowledge about their role in mediating ALI. In the present study, we demonstrate that the STAT transcription factors are activated rapidly in the lungs after intraperitoneal and intranasal LPS administration in mice. We also demonstrated that LPS activates both the STAT kinases, Src and JAK, in the lung with kinetics that are consistent with STAT activation. LPS treatment resulted in STAT3 activation throughout the resident lung cells, as well as in the recruited inflammatory cells. Whereas direct LPS treatment did not lead to STAT activation in cultured epithelial or endothelial cells, IL-6 activated STAT3 in both of these cell types. Furthermore, IL-6 was induced by LPS in serum and in the lung with kinetics consistent with STAT3 activation, suggesting that IL-6 may be one mechanism of STAT activation by LPS. In addition, STAT activation required reactive oxygen species, as the overexpression of catalase in mice prevented LPS-mediated STAT activation in the lung. STATs may be a common pathway for mediating ALI, regardless of the inciting factor, as STAT activation also occurred in both a gastric acid aspiration and acute pancreatitis model of ALI. Finally, STATs are activated in the lung long before signs of ALI are present, suggesting that the STAT transcription factors may play a role in initiating the inflammatory response seen in the lung.

Lipopolysaccharide binding protein is an essential component of the innate immune response to Escherichia coli peritonitis in mice

Lipopolysaccharide (LPS) binding protein (LBP) is an acute-phase protein that enhances the responsiveness of immune cells to LPS by virtue of its capacity to transfer LPS to CD14. To determine the role of LBP in the innate immune response to peritonitis, LBP gene-deficient (LBP(-/-)) and normal wild-type mice were intraperitoneally infected with Escherichia coli, the most common causative pathogen of this disease. LBP was detected at low concentrations in peritoneal fluid of healthy wild-type mice, and the local LBP levels increased rapidly upon induction of peritonitis. LBP(-/-) mice were highly susceptible to E. coli peritonitis, as indicated by accelerated mortality, earlier bacterial dissemination to the blood, impaired bacterial clearance in the peritoneal cavity, and more severe remote organ damage. LBP(-/-) mice displayed diminished early tumor necrosis factor alpha, interleukin-6, cytokine-induced neutrophil chemoattractant, and macrophage inflammatory protein 2 production and attenuated recruitment of polymorphonuclear leukocytes to the site of infection, indicating that acute inflammation was promoted by LBP. Locally produced LBP is an essential component of an effective innate immune response to E. coli peritonitis.

Involution of the mouse mammary gland is associated with an immune cascade and an acute-phase response, involving LBP, CD14 and STAT3

Introduction

Involution of the mammary gland is a complex process of controlled apoptosis and tissue remodelling. The aim of the project was to identify genes that are specifically involved in this process.

Methods

We used Affymetrix oligonucleotide microarrays to perform a detailed transcript analysis on the mechanism of controlled involution after withdrawal of the pups at day seven of lactation. Some of the results were confirmed by semi-quantitative reverse transcriptase polymerase chain reaction, Western blotting or immunohistochemistry.

Results

We identified 145 genes that were specifically upregulated during the first 4 days of involution; of these, 49 encoded immunoglobulin genes. A further 12 genes, including those encoding the signal transducer and activator of transcription 3 (STAT3), the lipopolysaccharide receptor (CD14) and lipopolysaccharide-binding protein (LBP), were involved in the acute-phase response, demonstrating that the expression of acute-phase response genes can occur in the mammary gland itself and not only in the liver. Expression of LBP and CD14 was upregulated, at both the RNA and protein level, immediately after pup withdrawal; CD14 was strongly expressed in the luminal epithelial cells. Other genes identified suggested neutrophil activation early in involution, followed by macrophage activation late in the process. Immunohistochemistry and histological staining confirmed the infiltration of the involuting mammary tissue with neutrophils, plasma cells, macrophages and eosinophils.

Conclusion

Oligonucleotide microarrays are a useful tool for identifying genes that are involved in the complex developmental process of mammary gland involution. The genes identified are consistent with an immune cascade, with an early acute-phase response that occurs in the mammary gland itself and resembles a wound healing process.

Significance of lipopolysaccharide-binding protein (an acute phase protein) in monitoring critically ill patients

Introduction

The present study was conducted to assess the value of serum concentration of lipopolysaccharide-binding protein (LBP) in patients with systemic inflammatory response syndrome (SIRS), sepsis and septic shock with respect to its ability to differentiate between infectious and noninfectious etiologies in SIRS and to predict prognosis.

Methods

This prospective cohort study was conducted in a multidisciplinary intensive care unit. Sixty-eight patients, admitted consecutively to the intensive care unit and who met criteria for SIRS, sepsis or septic shock were included. Serum LBP was measured using an immunochemiluminiscence assay.

Results

Serum levels of LBP were significantly increased in patients with SIRS (n = 40; median 30.6 μg/ml, range 9.2–79.5 μg/ml), sepsis (n = 19; median 37.1 μg/ml, range 11.8–76.2 μg/ml) and septic shock (n = 9; median 59.7 μg/ml, range 31.1–105 μg/ml), as compared with levels in the healthy volunteers (5.1 ± 2.2 μg/ml; P < 0.0001). Serum LBP at study entry was statistically significantly lower in patients with SIRS than in those with septic shock (P < 0.014); no statistically significant difference existed between patients with SIRS and those with sepsis (P = 0.61). Specificity and sensitivity of an LBP concentration of 29.8 μg/ml to distinguish between infectious and noninfectious etiologies for SIRS were 50% and 74.2%, respectively. There was no statistically significant difference in LBP concentration between survivors and nonsurvivors in both groups of patients. Furthermore, in septic patients the LBP response appeared to exhibit a decreased magnitude.

Conclusion

LBP is a nonspecific marker of the acute phase response and cannot be used as a diagnostic tool for differentiating between infectious and noninfectious etiologies of SIRS.

Endotoxemia and hepatic injury in a rodent model of hindlimb unloading

Hindlimb unloading (HU) is known to induce physiological alterations in various organ systems that mimic some responses observed after exposure to microgravity. In the present study, the effects of up to 4 wk of HU on the liver were assessed in male Wistar rats and two mouse strains: endotoxin-sensitive C57BL/6 mice and endotoxin-resistant C3H/HEJ mice. Plasma levels of endotoxin, a known stimulator of hepatic injury, were measured in portal and systemic blood samples. Endotoxin was elevated by approximately 50% in portal blood samples of mice and rats but was not detectable in systemic blood. This low-grade portal endotoxemia was associated with hepatic injury in rats and C57BL/6 mice as indicated by inflammation and elevated serum transaminase activities. Blood levels of the cytokine TNF-alpha were increased by approximately 50% in C57BL/6 mice; no significant elevation of this cytokine was detected in rats. Messenger RNA levels of the acute-phase proteins serum amyloid A, haptoglobin, and lipopolysaccharide binding protein were significantly enhanced after 3 wk of HU in endotoxin-sensitive rodents. In contrast, no histological changes or significant increases in serum enzyme activity were detected after HU in C3H/HEJ mice despite portal endotoxin levels of 222 +/- 83.4 pg/ml. At the 3-wk time point, expression of acute-phase proteins was not elevated in C3H/HEJ mice; however, expression after 4 wk of HU was similar to endotoxin-sensitive rodents. In conclusion, these findings indicate that HU induced mild portal endotoxemia, which contributed to the observed hepatic injury in endotoxin-sensitive rodents.

Signaling role of hemocytes in Drosophila JAK/STAT-dependent response to septic injury

To characterize the features of JAK/STAT signaling in Drosophila immune response, we have identified totA as a gene that is regulated by the JAK/STAT pathway in response to septic injury. We show that septic injury triggers the hemocyte-specific expression of upd3, a gene encoding a novel Upd-like cytokine that is necessary for the JAK/STAT-dependent activation of totA in the Drosophila counterpart of the mammalian liver, the fat body. In addition, we demonstrate that totA activation also requires the NF-KB-like Relish pathway, indicating that fat body cells integrate the activity of NF-KB and JAK/STAT signaling pathways upon immune response. This study reveals that, in addition to the pattern recognition receptor-mediated NF-KB-dependent immune response, Drosophila undergoes a complex systemic response that is mediated by the production of cytokines in blood cells, a process that is similar to the acute phase response in mammals.

Receptors, mediators, and mechanisms involved in bacterial sepsis and septic shock

Bacterial sepsis and septic shock result from the overproduction of inflammatory mediators as a consequence of the interaction of the immune system with bacteria and bacterial wall constituents in the body. Bacterial cell wall constituents such as lipopolysaccharide, peptidoglycans, and lipoteichoic acid are particularly responsible for the deleterious effects of bacteria. These constituents interact in the body with a large number of proteins and receptors, and this interaction determines the eventual inflammatory effect of the compounds. Within the circulation bacterial constituents interact with proteins such as plasma lipoproteins and lipopolysaccharide binding protein. The interaction of the bacterial constituents with receptors on the surface of mononuclear cells is mainly responsible for the induction of proinflammatory mediators by the bacterial constituents. The role of individual receptors such as the toll-like receptors and CD14 in the induction of proinflammatory cytokines and adhesion molecules is discussed in detail. In addition, the roles of a number of other receptors that bind bacterial compounds such as scavenger receptors and their modulating role in inflammation are described. Finally, the therapies for the treatment of bacterial sepsis and septic shock are discussed in relation to the action of the aforementioned receptors and proteins.

Pentoxifyllin attenuates the systemic inflammatory response induced during isolated limb perfusion with recombinant human tumor necrosis factor-alpha and melphalan

BACKGROUND

Isolated limb perfusion (ILP) with recombinant human tumor necrosis factor-alpha (rhTNF-alpha) and melphalan harbors the risk of septic shock-like syndrome. Pentoxifyllin (PTX) produced a beneficial effect on cytokine response and survival in animal experiments of septic shock, and we were interested to explore its effect during TNF-ILP in humans.

METHODS

Eighteen consecutive patients underwent TNF-ILP and received PTX (30 mg/kg/day), whereas another 13 consecutive patients did not. PTX was given systemically after the limb extracorporeal circulation was started. Cardiac index, systemic vascular resistance (SVR), and pulmonary vascular resistance were recorded via a Swan-Ganz catheter. Blood levels of TNF-alpha, interleukin-6, procalcitonin, and lipopolysaccharide-binding protein were determined before, during, and after ILP.

RESULTS

After reperfusion, systemic levels of TNF-alpha were significantly less increased in the PTX group (peak, 2.8 vs. 1.3 ng/mL; P <.05), as were interleukin-6 values (peak, 68 vs. 22 pg/mL; P <.02) and lipopolysaccharide-binding protein plasma levels (peak, 215 vs. 105 micro g/mL; P <.03). Differences in cardiac index, SVR, and mean arterial blood pressure were not significantly different. Norepinephrine or dobutamine to maintain SVR was less required in the PTX group.

CONCLUSIONS

PTX attenuates systemic cytokine production and influences components of the systemic inflammatory response after TNF-ILP. PTX may play a beneficial role in the management of septic shock-like syndrome, particularly in patients with leakage from the ILP circuit.

Overexpressed nuclear factor-kappaB can participate in endogenous C-reactive protein induction, and enhances the effects of C/EBPbeta and signal transducer and activator of transcription-3

C-reactive protein (CRP), the prototypical human acute phase protein, is produced primarily by hepatocytes. Its expression is modestly induced by interleukin (IL)-6 in Hep3B cells while IL-1, which alone has no effect, synergistically enhances the effects of IL-6. In previous studies of the proximal CRP promoter, we found that signal transducer and activator of transcription-3 (STAT3) and C/EBPbeta -mediated IL-6-induced transcription and that Rel p50 acted synergistically with C/EBPbeta, in the absence of p65, to enhance CRP transcription. Neither a requirement nor a binding site for the classic nuclear factor (NF)-kappaB heterodimer p50/p65 were found. The current studies were undertaken to determine whether similar novel transcription factor interactions might regulate the endogenous CRP gene. Transiently overexpressed p50 or p65 induced CRP mRNA accumulation in Hep3B cells. The heterodimer p50/p65 was markedly more effective than p50 or p65 homodimers. Co-overexpression of p50 or p65 with C/EBPbeta or STAT3 synergistically enhanced CRP expression. Maximal expression was observed with overexpression of all four transcription factors; comparable effects were observed with IL-1beta treatment of cells overexpressing STAT3 + C/EBPbeta. Data from the Human Genome Project revealed 13 potential kappaB sites in the first 4000 bases of the CRP promoter, only one of which, centred at -2652, bound nuclear p50/p65 heterodimer activated by IL-1beta. Our findings indicate that classical NF-kappaB activation can participate in endogenous CRP induction, and that activated NF-kappaB may synergistically enhance the effects of C/EBPbeta and STAT3. They raise the possibility, not as yet established, that NF-kappaB activation may be responsible for the synergistic effect of IL-1beta on IL-6-induced CRP expression.

Lipopolysaccharide-binding protein and lipopolysaccharide receptor CD14 gene expression after thermal injury and its potential mechanism(s)

BACKGROUND

We hypothesized that lipopolysaccharide-binding protein (LBP) and lipopolysaccharide receptor CD14 would present a pair of key molecules in pathophysiologic alterations induced by low concentrations of endotoxin after trauma. The aim of this study was to investigate the relationship between endotoxin translocation and tissue LBP/CD14 messenger ribonucleic acid (mRNA) expression after burn injury, and to define the potential role of LBP/CD14 in mediating inflammatory mediator induction, as well as the pathogenesis of organ damage.

METHODS

Wistar rats were subjected to a 35% full-thickness scald injury, and tissue samples from liver, kidneys, lungs, and intestine were collected to measure LBP/CD14 and tumor necrosis factor-alpha (TNF-alpha) mRNA expression. Peritoneal macrophages were harvested by peritoneal lavage to determine CD14 mRNA expression.

RESULTS

It was found that endotoxin levels in liver, spleen, and lung increased markedly after thermal injury, with the highest level in liver. Both tissue LBP and CD14 mRNA expression increased markedly after burns, peaking at 12 hours, and then decreasing gradually. At 48 hours, LBP gene expression had a tendency to the baseline level, whereas CD14 mRNA expression increased again. Likewise, CD14 mRNA levels were up-regulated markedly in peritoneal macrophages. Conversely, gene expression of TNF-alpha in tissues elevated markedly after acute insults. There were positive correlations between lipopolysaccharide levels and LBP/CD14 mRNA as well as TNF-alpha mRNA expression in tissues. Similar results were also obtained between CD14, TNF-alpha mRNA expression in liver tissue and liver function parameters, and between pulmonary TNF-alpha mRNA and myeloperoxidase activities (p < 0.01).

CONCLUSION

Thermal injury per se can markedly up-regulate both LBP and CD14 gene expression in various organs. Excessive LBP and CD14 mRNA expression might be associated with enhanced synthesis and release of TNF-alpha stimulated by endotoxin translocation after major burns.

Signalling mechanisms involved in the induction of inducible nitric oxide synthase by Lactobacillus rhamnosus GG, endotoxin, and lipoteichoic acid

BACKGROUND AND AIMS

Probiotic Lactobacillus rhamnosus GG (Lactobacillus GG) has been found beneficial in the treatment of viral and antibiotic-associated diarrhea. Recently, it has also been shown to induce nitric oxide (NO) production, and have some other immunostimulatory effects. The aim of the present study was to investigate the mechanisms involved in the induction of inducible nitric oxide synthase (iNOS) and NO production by Lactobacillus GG.

METHODS AND RESULTS

iNOS expression and NO production induced by Lactobacillus GG, lipopolysaccharide (LPS), and lipoteichoic acid (LTA) was abrogated by NOS inhibitors L-NMMA and 1400W, by a protein synthesis inhibitor cycloheximide, by a tyrosine kinase inhibitor genistein and by a NF-kappaB inhibitor pyrrolidinedithiocarbamate (PDTC) in J774 macrophages. Polymyxin B inhibited NO production induced by LPS, but did not inhibit Lactobacillus GG induced NO production. p42/44 MAP-kinase inhibitor PD98059, dexamethasone and cyclosporine A inhibited partially iNOS protein expression and NO formation in Lactobacillus GG, LPS and LTA treated cells. Ro 31-8220 (protein kinase C inhibitor) and SB203580 (p38 MAP-kinase inhibitor) had only a minor effect on NO production.

CONCLUSIONS

Lactobacillus GG induced NO production through iNOS pathway and the mechanisms mediating that process were very similar with those involved in LPS and LTA induced NO synthesis.

Endotoxin and its binding proteins in chronic liver disease: the effect of transjugular intrahepatic portosystemic shunting

BACKGROUND

Gut-derived endotoxin is insufficiently cleared by the diseased liver, and thus, is elevated in plasma of patients with chronic liver disease (CLD). Endotoxin action might be modified by binding to soluble CD14 (sCD14) and lipopolysaccharide-binding protein (LBP), both of which have not yet been sufficiently studied in CLD.

METHODS

Endotoxin, sCD14 and LBP have been determined in peripheral blood of 72 patients and 39 control subjects, and in portal and hepatic venous blood of 12 patients during transjugular intrahepatic portosystemic shunt (TIPS) implantation.

RESULTS

Peripheral endotoxin (average 3-fold increased compared to controls), LBP, and sCD14 plasma levels were elevated in chronic liver disease irrespective of Child stage m, preserve/absence of cirrhosis or aetiology. LBP, and sCD14. Furthermore, endotoxin levels in the portal vein (38.1 +/- 6.1 pg/ml) were only slightly elevated compared to the hepatic vein (29.2 +/- 4.4 pg/ml), and peripheral endotoxin levels did not increase after TIPS.

CONCLUSIONS

Decreased hepatocellular function rather than hepatic blood shunting might be responsible for endotoxemia. The elevation in LBP and sCD14 levels may be a consequence of endotoxemia.

The role of lipopolysaccharide binding protein in resistance to Salmonella infections in mice

Polymorphonuclear leukocytes (PMN) and LPS-binding protein (LBP) are both components of the innate immune system. LBP is a plasma protein that binds to lipid A and enhances the biological activity of LPS 100- to 1000-fold. Recently it was reported that LBP-deficient mice are more susceptible to Salmonella typhimurium infection. Here we report that LBP KO mice are more susceptible to Salmonella peritonitis, but not to oral or i.v. infection. LBP knockout (KO) mice responded normally to i.p. injections of Staphylococcus aureus and casein, but not to i.p. injection of S. typhimurium or Salmonella LPS. Mice with a mutation in Toll-like receptor 4 (C3H/HeJ) have a similar defect in PMN chemotaxis. In normal mice S. typhimurium stimulated production of the CXC chemokines macrophage inflammatory protein-2 and cytokine-induced neutrophil chemoattractant, but levels of cytokine-induced neutrophil chemoattractant and macrophage inflammatory protein-2 were greatly reduced in the LBP KO mice. LBP KO mice pretreated with casein to attract PMN in an LBP-independent manner were more resistant to Salmonella infection, but neutropenic mice were not protected by casein. Splenic TNF-alpha mRNA levels were also lower in LBP KO than in control mice infected with Salmonella. Since TNF-alpha can activate PMN, LBP KO mice may have both fewer and less active PMN in the first few hours after Salmonella are injected, making LBP KO mice more susceptible. This work confirms the importance of PMN in resistance to Salmonella infections and shows that this is facilitated by LBP.

High concentrations of lipopolysaccharide-binding protein in serum of patients with severe sepsis or septic shock inhibit the lipopolysaccharide response in human monocytes

Lipopolysaccharide-binding protein (LBP), an acute-phase protein recognizing lipopolysaccharide (LPS), catalyzes in low concentrations its transfer to the cellular LPS receptor consisting of CD14 and Toll-like receptor-4. It has recently been shown that high concentrations of recombinant LBP can protect mice in a peritonitis model from the lethal effects of LPS. To determine whether in humans the acute-phase rise of LBP concentrations can inhibit LPS binding to monocytes and induction of proinflammatory cytokines, LBP concentrations were analyzed in 63 patients meeting the American College of Chest Physicians/Society of Critical Care Medicine criteria of severe sepsis or septic shock and the ability of these sera to modulate LPS effects in vitro was assessed employing different assays. Transfer of fluorescein isothiocyanate-labeled LPS to human monocytes was assessed by a fluorescence-activated cell sorter-based method, and activation of monocytes was investigated by measuring LPS-induced tumor necrosis factor-alpha secretion in the presence of the sera. Anti-LBP antibodies and recombinant human LBP were instrumental for depletion and reconstitution of acute-phase sera and subsequent assessment of their modulating effects on LPS activity. Sera of patients with severe sepsis/septic shock exhibited a diminished LPS transfer activity and LPS-induced tumor necrosis factor-alpha secretion as compared with sera from healthy controls. LBP depletion of sepsis sera and addition of rhLBP resulting in concentrations found in severe sepsis confirmed that LBP was the major serum component responsible for the observed effects. In summary, the inhibition of LPS effects by high concentrations of LBP in acute-phase serum, as described here, may represent a novel defense mechanism of the host in severe sepsis and during bacterial infections.

Cytokine modulation of liver annexin 1 expression during experimental endotoxemia

Annexin 1 (ANXA1) is a calcium-binding protein endowed with anti-inflammatory properties. Using an extra-hepatic system, we showed that interleukin (IL)-6 regulates ANXA1 expression at the transcriptional level. The purpose of this study was to determine whether ANXA1 synthesis was modulated by IL-6 during experimental inflammation. We have compared liver ANXA1 expression during systemic and localized inflammatory reaction, using lipopolysaccharide (LPS) and turpentine. LPS treatment strongly induced ANXA1 expression in the liver of wild-type (WT) animals (+600%) whereas a modest increase (+60%) was measured in IL-6 knockout (KO) animals. Turpentine treatment did not affect the expression of ANXA1 in either animal type. LPS enhanced serum corticosteroid levels equally in WT and IL-6 KO mice, whereas higher tumor necrosis factor (TNF)-alpha and IL-1beta levels were released in IL-6 KO animals. Injection of mouse recombinant IL-6 to IL-6 KO animals before LPS or TNF-alpha challenge, replenished ANXA1 liver synthesis to that of WT animals. Exogenous ANXA1 but not ANXA5, administered to IL-6 KO mice before LPS challenge inhibited TNF-alpha release. We propose that ANXA1 acts as a novel acute phase protein, which is controlled in the liver by TNF-alpha and IL-6, and which may contribute to the resolution of systemic endotoxemia through a negative feedback on TNF-alpha release.

Interleukin-6 is a major effector molecule of short-term G-CSF treatment inducing bone metabolism and an acute-phase response

OBJECTIVE

The biological steps leading to hematopoietic progenitor cell (HPC) mobilization from the bone marrow to the peripheral blood compartment during G-CSF treatment are still poorly defined. In this study, we investigated G-CSF-mediated secretion of cytokines as potential mediators.

MATERIALS AND METHODS

Plasma and urine samples from G-CSF-mobilized donors for HPC transplantation were collected before and during mobilization therapy. Interleukin-6 (IL-6), alkaline phosphatase (ALP), bone-specific ALP (bone ALP), C-reactive protein (CRP), lipopolysaccharide binding protein (LPB), CD34+ cells and urinary deoxypyridinoline (DPD) concentrations were measured and statistically correlated.

RESULTS

IL-6 was highly elevated at days 4 and 5 of G-CSF treatment. G-CSF administration led to elevation of IL-6 parallel to the appearance of CD34+ cells in the peripheral blood. Major metabolic changes such as high bone ALP plasma concentration and urinary excretion of deoxypyridinoline (DPD), indicating stimulation of bone metabolism, were observed. Elevated concentrations of CRP and LPB indicated an acute-phase response. Furthermore, CRP concentrations correlated significantly with the percentage of mobilized CD34+ cells.

CONCLUSION

Based on these findings, we propose IL-6 as a major physiological effector molecule of G-CSF treatment that induces bone metabolism and an acute-phase reaction along with mobilization of CD34+ cells in the peripheral blood. IL-6 may be responsible for osteopenia observed during short- and long-term G-CSF treatment. These observations may also have implications for G-CSF treatment of patients with plasmocytoma.

DNA binding specificity of different STAT proteins. Comparison of in vitro specificity with natural target sites

STAT transcription factors are expressed in many cell types and bind to similar sequences. However, different STAT gene knock-outs show very distinct phenotypes. To determine whether differences between the binding specificities of STAT proteins account for these effects, we compared the sequences bound by STAT1, STAT5A, STAT5B, and STAT6. One sequence set was selected from random oligonucleotides by recombinant STAT1, STAT5A, or STAT6. For another set including many weak binding sites, we quantified the relative affinities to STAT1, STAT5A, STAT5B, and STAT6. We compared the results to the binding sites in natural STAT target genes identified by others. The experiments confirmed the similar specificity of different STAT proteins. Detailed analysis indicated that STAT5A specificity is more similar to that of STAT6 than that of STAT1, as expected from the evolutionary relationships. The preference of STAT6 for sites in which the half-palindromes (TTC) are separated by four nucleotides (N(4)) was confirmed, but analysis of weak binding sites showed that STAT6 binds fairly well to N(3) sites. As previously reported, STAT1 and STAT5 prefer N(3) sites; however, STAT5A, but not STAT1, weakly binds N(4) sites. None of the STATs bound to half-palindromes. There were no specificity differences between STAT5A and STAT5B.

Role of NAD(P)H oxidase in angiotensin II-induced JAK/STAT signaling and cytokine induction

Inflammatory processes involve both synthesis of inflammatory cytokines, such as interleukin-6 (IL-6), and the activation of their distinct signaling pathways, eg, the janus kinases (JAKs) and signal transducers and activators of transcription (STAT). Superoxide (O(2)(-)) anions activate this signaling cascade, and the vasoconstrictor angiotensin II (Ang II) enhances the formation of O(2)(-) anions via the NAD(P)H oxidase system in rat aortic smooth muscle cells. Ang II activates the JAK/STAT cascade via its type 1 (AT(1)) receptor and induces synthesis and release of IL-6. Therefore, we investigated the role of O(2)(-) anions generated by the NAD(P)H oxidase system on the Ang II activation of the JAK/STAT cascade and its impact on IL-6 synthesis. Ang II stimulation of rat aortic smooth muscle cells induced a rapid increase in O(2)(-) anions determined by laser fluoroscopy, which can be abolished by DPI, a flavoprotein inhibitor. Ang II-induced phosphorylation of JAK2, STAT1alpha/ss, STAT3, and IL-6-synthesis can be abolished by DPI, as determined by immunoprecipitations and Northern blot analysis. Electroporation of neutralizing antisera targeted against p47(phox), a NAD(P)H oxidase subunit, abolished Ang II-induced JAK/STAT activation and IL-6 synthesis. Inhibition of JAK2 by its inhibitor AG490 (10 micromol/L) blocked not only JAK2 activation but also IL-6 synthesis. These results suggest that stimulation of the JAK/STAT cascade by Ang II requires O(2)(-) anions generated by the NAD(P)H oxidase system, and O(2)(-) anion-dependent activation of the JAK/STAT cascade seems to be additionally involved in Ang II-induced IL-6 synthesis. Thus, Ang II-induced inflammatory effects seem to require O(2)(-) anions generated by the NAD(P)H oxidase system.

The Rel family member P50 mediates cytokine-induced C-reactive protein expression by a novel mechanism

Transcription of C-reactive protein (CRP) in Hep 3B cells is induced by IL-6, acting through C/EBP isoforms and STAT3. IL-1beta, which alone has no effect, greatly enhances IL-6-induced transcription by unknown mechanisms. Because IL-1beta activates the NF-kappaB system, we explored the effects of overexpressed Rel family members on CRP expression. Unexpectedly, transactivation assays in transiently transfected Hep 3B cells showed p50 overexpression to markedly induce CRP transcription, acting in a region 3' to -86. In the presence of overexpressed p50, IL-1beta induced a 3-fold increase in CRP expression, and responses to IL-6 and to IL-6 plus IL-1beta were 4-fold greater than seen in cells without p50 overexpression. In contrast, overexpressed p65 abolished CRP induction by p50 and by cytokines. EMSA studies demonstrated that recombinant p50 bound to a nonconsensus kappaB site overlapping the proximal C/EBP binding site on the CRP promoter. Mutation of a polypyrimidine tract in the p50-binding site inhibited the transactivating effect of cytokines. P50- but not p65-containing dimers were found in nuclei of Hep 3B cells 18 h after stimulation with IL-1beta, when C/EBPbeta is greatly activated, in the presence or absence of IL-6. These findings suggest that IL-1beta induces nuclear translocation of p50-containing dimers and that p50 interacts with C/EBPbeta activated by both IL-6 and IL-1beta to induce CRP expression.

Novel protective effects of stem cell factor in a murine model of acute septic peritonitis. Dependence on MCP-1

Mast cells participate in the host response during sepsis and have been shown to have a protective effect in a murine model of acute septic peritonitis and multi-organ failure initiated by cecal ligation and puncture (CLP). Stem cell factor (SCF) is a hematopoietic cytokine important in mast cell proliferation and activation. In the present study, we examined the protective effects of a single intraperitoneal injection of SCF given 2 hours before CLP surgery in mice. Four days after the CLP surgery, SCF pretreatment significantly improved mouse survival from 29 to 56% and mast cells were absolutely required for this effect. Immunoneutralization studies revealed that the SCF-stimulated release of monocyte chemoattractant protein-1 (MCP-1) into the septic peritoneal cavity contributed to the protective effect of SCF in this model. One potential cellular source of MCP-1 was the SCF-activated mast cell. In addition, SCF pretreatment significantly augmented circulating levels of SCF and the immunomodulatory cytokine interleukin-10 in septic mice, in part because the SCF pretreatment seemed to promote the release of both mediators from the liver. Additional hepatic effects of SCF treatment included an accelerated expression of hepatic levels of signal transducer and activator of transcription-3 (STAT-3) in CLP mice pretreated with SCF. Taken together, the findings from the present study demonstrate that the intraperitoneal delivery of SCF has a major protective effect in a murine model of CLP.

Involvement of lipopolysaccharide binding protein, CD14, and Toll-like receptors in the initiation of innate immune responses by Treponema glycolipids

Culture supernatants from Treponema maltophilum associated with periodontitis in humans and Treponema brennaborense found in a bovine cattle disease accompanied with cachexia caused a dose-dependent TNF-alpha synthesis in human monocytes increasing with culture time. This activity could be reduced significantly by blocking the CD14-part of the LPS receptor using the My 4 mAb and by polymyxin B. In the murine macrophage cell line RAW 264.7, Treponema culture supernatants induced TNF-alpha secretion in a LPS binding protein (LBP)-dependent fashion. To enrich for active compounds, supernatants were extracted with butanol, while whole cells were extracted using a phenol/water method resulting in recovery of material exhibiting a similar activity profile. An LPS-LBP binding competition assay revealed an interaction of the treponeme phenol/water extracts with LBP, while precipitation studies implied an affinity to polymyxin B and endotoxin neutralizing protein. Macrophages obtained from C3H/HeJ mice carrying a Toll-like receptor (TLR)-4 mutation were stimulated with treponeme extracts for NO release to assess the role of TLRs in cell activation. Furthermore, NF-kappaB translocation in TLR-2-negative Chinese hamster ovary (CHO) cells was studied. We found that phenol/water-extracts of the two strains use TLRs differently with T. brennaborense-stimulating cells in a TLR-4-dependent fashion, while T. maltophilum-mediated activation apparently involved TLR-2. These results indicate the presence of a novel class of glycolipids in Treponema initiating inflammatory responses involving LBP, CD14, and TLRs.

Production of the acute-phase protein lipopolysaccharide-binding protein by respiratory type II epithelial cells: implications for local defense to bacterial endotoxins

This study demonstrates for the first time that respiratory epithelial cells are able to produce the acute phase protein lipopolysaccharide (LPS)-binding protein (LBP), which is known to play a central role in the defense to bacterial endotoxins (or LPS). Indications for local presence of LBP in human lung was obtained via reverse transcriptase/polymerase chain reaction that showed LBP messenger RNA (mRNA) expression. Therefore, LBP production by the human lung epithelial cell line A549, a human adenocarcinoma with features of type II pneumocytes, was studied. These cells produced LBP in response to interleukin (IL)-1beta, IL-6, and tumor necrosis factor- alpha, a response that was strongly enhanced by dexamethasone. In addition, LBP mRNA was detected in A549 cells, in increasing amounts as a result of stimulation. The pattern of cytokine-induced LBP production in A549 cells was similar to the pattern in the human liver epithelial cell line HuH-7. Moreover, the molecular weight of A549-derived LBP was approximately 60 kD, which is similar to HuH-7-derived LBP. Biologic activity of LBP produced by A549 cells was evaluated on the basis of its ability to interact with LPS. Further indications that type II alveolar epithelial cells are able to produce LBP were obtained from the observations that the murine lung type II epithelial cell line C10 produced murine LBP, and that isolated human primary type II pneumocytes expressed LBP mRNA, which was enhanced after stimulation of cells. The local production of this endotoxin binding protein by lung epithelial cells might contribute to a highly specific response at the site of exposure to bacteria and bacterial endotoxins.

CD14-independent activation of cardiomyocyte signal transduction by bacterial endotoxin

In the heart, lipopolysaccharide (LPS) induces the production of proinflammatory cytokines that cause myocardial dysfunction; however, the signaling pathways involved in cardiomyocyte responses are poorly understood. We studied LPS-induced signaling by treating cardiomyocyte cultures with 0.01-10 microgram/ml LPS for 0-24 h in the presence or absence of 2.5% serum. Cytosolic and nuclear proteins were analyzed for expression and activation of protein kinases. Members of the extracellular signal-regulated kinase (ERK) and signal transducer and activators of transcription (STAT) protein families were uniformly expressed and specifically phosphorylated in response to LPS. Activation was biphasic; peaking at 5-10 min and 24 h after treatment. Inhibitor experiments provided evidence that ERK proteins may regulate STAT activity. Serum did not augment endotoxin-induced phosphorylation. Although cardiomyocytes expressed low levels of CD14 and LPS-binding protein, specific enzymatic removal of glycosyl phosphatidylinositol-linked receptors or incubation with an anti-CD14 antibody had no effect on kinase activation. Treatment of cells with an excess of detoxified LPS attenuated endotoxin-induced signaling. In addition, endotoxin stimulated specific binding of nuclear factors to AP-1, nuclear factor-kappaB (NF-kappaB), STAT1 (SIE, sis-inducible element), and STAT3 consensus-binding sequences. Finally, inhibition of ERK phosphorylation reduced, and NF-kappaB nuclear translocation prevented, tumor necrosis factor-alpha production. Our results indicate that LPS-induced activation of signal transduction in cardiomyocytes occurs by a CD14-independent mechanism.

Kupffer cell inactivation alleviates ethanol-induced steatosis and CYP2E1 induction but not inflammatory responses in rat liver

BACKGROUND/AIMS

Gadolinium chloride inactivates Kupffer cells and alleviates alcohol-induced liver lesions. We investigated the mechanism of gadolinium chloride protection after oral ethanol feeding.

METHODS

Rats were maintained ethanol-intoxicated for 6 weeks by feeding ethanol in a low-carbohydrate/high-fat liquid diet. Macrophages were inactivated by intravenous administrations of gadolinium chloride. At termination, liver samples and cell lysates obtained from the periportal and perivenous region were analyzed for histopathology, mRNA expression of endotoxin-associated parameters and cytokines and for enzymes involved in oxidative stress.

RESULTS

Ethanol treatment alone caused marked microvesicular/macrovacuolar steatosis and focal inflammation. Gadolinium significantly alleviated pathology, by reducing steatosis but not inflammation. Gadolinium treatment eliminated ED2 immunopositive Kupffer cells, which were larger and more frequent periportally. Ethanol significantly increased the mRNA expression of the endotoxin (LPS) receptor CD14 and the LPS binding protein LBP, but not that of the pro-inflammatory cytokines TNF-alpha and IL-1beta. The mRNA of CD14 was found to be expressed preferentially in the perivenous region, but gadolinium treatment had no significant effect on the expression or the distribution. However, gadolinium significantly moderated the ethanol induction of CYP2E1 and this effect correlated to the degree of steatosis. Ethanol increased glutathione transferase and reduced glutathione peroxidase activity, but these changes persisted after gadolinium treatment.

CONCLUSIONS

Our results suggest that gadolinium chloride reduces symptoms of ALD mainly by counteracting steatosis, and that CD14-positive Kupffer cell populations are not involved in gadolinium protection. The strong correlation between pathology and CYP2E1 induction might suggest a steatopathogenic role for this enzyme.

Binding of IL-4 to the IL-13Ralpha(1)/IL-4Ralpha receptor complex leads to STAT3 phosphorylation but not to its nuclear translocation

Interleukin-4 (IL-4) is a pleiotropic cytokine, which acts on both hematopoietic and non-hematopoietic cells, through different types of receptor complexes. In this study, we report that in human B cells, IL-4 caused rapid phosphorylation of Janus kinase (JAK) 1 and JAK3 tyrosine kinases. In keratinocytes, the hematopoietic-specific receptor common gamma(c) chain is not expressed and the IL-13 receptor alpha(1) (IL-13Ralpha(1)) participates in IL-4 signal transduction. In keratinocytes, IL-4 induced JAK1 and JAK2 phosphorylation but, unlike in immune cells, IL-4 did not involve JAK3 activation for its signaling. In both cell types, IL-4 induced phosphorylation and DNA binding activation of the signal transducer and activator of transcription (STAT) 6 protein. Furthermore, IL-4 stimulation of keratinocytes also induced tyrosine phosphorylation of STAT3 which was found to bind to the phosphorylated IL-13Ralpha(1). STAT3 however did not significantly translocate to the nucleus, nor did it bind with high affinity to target DNA sequences.

Human herpesvirus 8 interleukin-6 (vIL-6) signals through gp130 but has structural and receptor-binding properties distinct from those of human IL-6

Human herpesvirus 8 (HHV-8) has been associated with classical, endemic (African), and AIDS-related Kaposi's sarcoma (KS), body cavity-based primary effusion lymphomas, and multicentric Castleman's disease (MCD). HHV-8 encodes a functional homologue of interleukin-6 (IL-6), a cytokine that promotes the growth of KS and myeloma cells and is found at elevated levels in MCD lesions and patient sera. We have previously reported that the viral IL-6 (vIL-6) gene product can support the growth of the IL-6-dependent murine hybridoma cell line, B9, and that the gp80 (IL-6 receptor [IL-6R]) component of the IL-6 receptor-signal transducer (gp180) complex plays a role in mediating this activity. However, it has been shown by others that vIL-6 can function in human cells independently of IL-6R. Here we have extended our functional studies of vIL-6 by identifying transcription factors and pathways used in human Hep3B cells, investigating the utilization of gp130 and IL-6R by vIL-6, and undertaking mutational analyses of vIL-6 and gp130. The data presented here establish that vIL-6, in common with its endogenous counterparts, can mediate signal transduction through gp130 and activate multiple transcription factors, map residues within the vIL-6 protein that are and are not important for vIL-6 signalling, and identify a gp130 mutant that is nonfunctional with respect to vIL-6 signalling in the absence of IL-6R but that retains the ability to mediate vIL-6 and human IL-6 (hIL-6) signal transduction when IL-6R is coexpressed. The data presented demonstrate functional and mechanistic similarities between vIL-6 and endogenous IL-6 proteins but also highlight differences in the structural and receptor-binding properties of vIL-6 relative to its human counterpart.

Cellular physiology of STAT3: Where's the cytoplasmic monomer?

In the standard model of cytokine-induced signal transducer and activator of transcription (STAT) protein family signaling to the cell nucleus, it is assumed that STAT3 is recruited to the cytoplasmic side of the cell surface receptor complex from within a cytosolic monomer pool. By using Superose-6 gel-filtration chromatography, we have discovered that there is little monomeric STAT3 (91 kDa) in the cytosol of liver cells (human hepatoma Hep3B cell line and rat liver). The bulk of STAT3 (and STAT1, STAT5a, and -b) was present in the cytosol as high molecular mass complexes in two broad distributions in the size range 200-400 kDa ("statosome I") and 1-2 MDa ("statosome II"). Upon treatment of Hep3B cells with interleukin-6 (IL-6) for 30 min (i) cytosolic tyrosine-phosphorylated STAT3 was found to be in complexes of size ranging from 200-400 kDa to 1-2 MDa; (ii) a small pool of monomeric STAT3 and tyrosine-phosphorylated STAT3 eluting at 80-100 kDa was observed, and (iii) most of the cytoplasmic DNA-binding competent STAT3 (the so-called SIF-A "homodimer") co-eluted with catalase at 230 kDa. In order to identify the protein components of the 200-400-kDa statosome I cytosolic complexes, we used the novel technique of antibody-subtracted differential protein display using anti-STAT3 antibody. Eight polypeptides in the size range from 20 to 114 kDa co-shifted with STAT3; three of these (p60, p20a, and p20b) were co-shifted in an IL-6-dependent manner. In-gel tryptic fragmentation and mass spectroscopy identified the major IL-6-dependent STAT3-co-shifted p60 protein as the chaperone GRP58/ER-60/ERp57. Taken together, these data (i) emphasize the absence of a detectable STAT3 monomer pool in the cytosol of cytokine-free liver cells as posited by the standard model, and (ii) suggest an alternative model for STAT signaling in which STAT3 proteins function in the cytoplasm as heteromeric complexes with accessory scaffolding proteins, including the chaperone GRP58.

Lipopolysaccharide Binding Protein and Serum Amyloid A Secretion by Human Intestinal Epithelial Cells During the Acute Phase Response

The acute phase proteins LPS binding protein (LBP) and serum amyloid A (SAA) are produced by the liver and are present in the circulation. Both proteins have been shown to participate in the immune response to endotoxins. The intestinal mucosa forms a large surface that is continuously exposed to these microbial products. By secretion of antimicrobial and immunomodulating agents, the intestinal epithelium contributes to the defense against bacteria and their products. The aim of this study was to explore the influence of the inflammatory mediators TNF-α, IL-6, and IL-1β on the release of LBP and SAA by intestinal epithelial cells (IEC). In addition, the induction of LBP and SAA release by cell lines of intestinal epithelial cells and hepatic cells was compared. The data obtained show that in addition to liver cells, IEC also expressed LBP mRNA and released bioactive LBP and SAA upon stimulation. Regulation of LBP and SAA release by IEC and hepatocytes was typical for class 1 acute phase proteins, although differences in regulation between the cell types were observed. Endotoxin did not induce LBP and SAA release. Glucocorticoids were demonstrated to strongly enhance the cytokine-induced release of LBP and SAA by IEC, corresponding to hepatocytes. The data from this study, which imply that human IEC can produce LBP and SAA, suggest a role for these proteins in the local defense mechanism of the gut to endotoxin. Furthermore, the results demonstrate that tissues other than the liver are involved in the acute phase response.

A novel acute-phase marker: lipopolysaccharide binding protein (LBP)

Acute phase proteins are extremely helpful markers for indicating a disturbance of the homeostasis within the organism and for monitoring the course of a disease. Despite the availability of several serum acute phase markers, a better and more specific prediction of sepsis and related disorders, such as systemic inflammatory response syndrome (SIRS) is still needed, as these diseases still have a high mortality rate and have to be detected early and with high specificity. Here a novel acute-phase protein is introduced, that has certain biological functions in host defense and that may be a useful addition for the diagnosis and monitoring of sepsis. Lipopolysaccharide (LPS or endotoxin), binding protein (LBP) is a class 1 acute-phase protein with the ability to bind and transfer bacterial LPS. Changes in serum levels of LBP have profound effects on the host's ability to react to endotoxin stimulation and to defend itself against sepsis. Results obtained from in vitro studies and from an animal model are reviewed here and a perspective on ongoing clinical studies is given. There is evidence that LBP, along with other LPS-recognizing molecules, is an important parameter for monitoring the acute phase and the ability of the host to react to LPS-challenge.

The three-dimensional structure of human bactericidal/permeability-increasing protein: implications for understanding protein-lipopolysaccharide interactions

Gram-negative bacterial infections are often complicated by the inflammatory properties of lipopolysaccharides (LPS) on or released from the bacterial outer membrane. When present in the mammalian bloodstream, LPS can trigger a series of pathological changes, sometimes resulting in septic shock. Two related mammalian proteins, bactericidal/permeability-increasing protein (BPI) and lipopolysaccharide-binding protein (LBP), are known to affect the LPS-induced inflammatory response and are, therefore, of clinical interest. The recently determined three-dimensional structure of human BPI provides information on the overall protein fold, domain organization, and conserved regions of these two proteins. In addition, the discovery of two apolar lipid binding pockets in BPI indicates a possible site of interaction with LPS. The BPI structure is a powerful tool for the design of site-directed mutants, peptide mimetics/inhibitors, and BPI/LBP chimeras. These studies should help further define the functions of BPI and LBP, and their mechanism of interaction with LPS.

Lipopolysaccharide stimulates HepG2 human hepatoma cells in the presence of lipopolysaccharide-binding protein via CD14

Lipopolysaccharide (LPS)-binding protein (LBP), an opsonin for activation of macrophages by bacterial LPS, is synthesized in hepatocytes and is known to be an acute phase protein. Recently, cytokine-induced production of LBP was reported to increase 10-fold in hepatocytes isolated from LPS-treated rats, compared with those from normal rats. However, the mechanism by which the LPS treatment enhances the effect of cytokines remains to be clarified. In the present study, we examined whether LPS alone or an LPS/LBP complex directly stimulates the hepatocytes, leading to acceleration of the cytokine-induced LBP production. HepG2 cells (a human hepatoma cell line) were shown to express CD14, a glycosylphosphatidylinositol-anchored LPS receptor, by both RT/PCR and flow cytometric analyses. An LPS/LBP complex was an effective stimulator for LBP and CD14 production in HepG2 cells, but stimulation of the cells with either LPS or LBP alone did not significantly accelerate the production of these proteins. The findings were confirmed by semiquantitative RT/PCR analysis of mRNA levels of LBP and CD14 in HepG2 cells after stimulation with LPS alone and an LPS/LBP complex. In addition, two monoclonal antibodies (mAbs) to CD14 (3C10 and MEM-18) inhibited LPS/LBP-induced cellular responses of HepG2 cells. Furthermore, prestimulation of HepG2 cells with LPS/LBP augmented cytokine-induced production and gene expression of LBP and CD14. All these findings suggest that an LPS/LBP complex, but not free LPS, stimulates HepG2 cells via CD14 leading to increased basal and cytokine-induced LBP and CD14 production.

Signal transducer and activator of transcription-1 and heat shock factor-1 interact and activate the transcription of the Hsp-70 and Hsp-90beta gene promoters

We have previously demonstrated that interleukin-6 (IL-6) increases the levels of the heat shock protein 90 (Hsp-90) and activates the Hsp-90beta promoter via the IL-6-activated transcription factors NF-IL6 and signal transducer and activator of transcription-3 (STAT-3). Here, we show that interferon-gamma (IFN-gamma) treatment increases the levels of Hsp-70 and Hsp-90 and also enhances the activity of the Hsp-70 and Hsp-90beta promoters with these effects being dependent on activation of the STAT-1 transcription factor by IFN-gamma. These effects were not seen in a STAT-1-deficient cell line, indicating that IFN-gamma modulates Hsp induction via a STAT-1-dependent pathway. The effect of IFN-gamma/STAT-1 was mediated via a short region of the Hsp-70/Hsp-90 promoters, which also mediates the effects of NF-IL6 and STAT-3 and can bind STAT-1. This region also contains a binding site for the stress-activated transcription factor HSF-1. We show that STAT-1 and HSF-1 interact with one another via a protein-protein interaction and produce a strong activation of transcription, which is in contrast to our previous finding that STAT-3 and HSF-1 antagonize one another. To our knowledge this is the first report of HSF-1 interacting directly via a protein-protein interaction with another transcription factor. Such protein-protein interactions and the binding of a number of different stress and cytokine-activated transcription factors to a short region of the Hsp-90 and Hsp-70 gene promoters are likely to play a very important role in Hsp gene activation by non-stressful stimuli and the integration of these responses with the stress response of these genes.

Characterization of nuclear protein binding (AP-1, GR, and STAT) in the genetically obese (fa/fa) Zucker rat

There is evidence to suggest that obese populations have an increased susceptibility to various pathologic disorders. Both AP-1 and STAT nuclear binding proteins have been suggested to play a role in certain obesity-related diseases. The objective of our studies reported herein was to compare constitutive binding activity of nuclear proteins (AP-1, GR, and STAT), that may be relevant to obesity-related diseases in the obese (fa/fa) Zucker rat to lean (Fa/?) littermates. AP-1, GR, and STAT liver nuclear protein binding activity was analyzed using the electrophoretic mobility shift assay (EMSA). EMSA analysis of liver nuclear protein from obese and lean Zucker rats revealed high constitutive AP-1 binding activity in the obese animals. AP-1 binding activity in the obese rats was not further elevated by treatment with phenobarbital, a known inducer of AP-1 binding activity. No differences were observed in GR binding to a consensus GRE between obese and lean animals; however, STAT binding activity to a consensus GAS element was lower in liver tissue from obese Zucker rats. Our findings presented herein suggest that the fa/fa Zucker rat may be a suitable obese rodent model for studying the roles AP-1 and STAT may play in the pathologies of these diseases.

Interleukin-6-type cytokine signalling through the gp130/Jak/STAT pathway

The family of cytokines signalling through the common receptor subunit gp130 comprises interleukin (IL)-6, IL-11, leukaemia inhibitory factor, oncostatin M, ciliary neurotrophic factor and cardiotrophin-1. These so-called IL-6-type cytokines play an important role in the regulation of complex cellular processes such as gene activation, proliferation and differentiation. The current knowledge on the signal-transduction mechanisms of these cytokines from the plasma membrane to the nucleus is reviewed. In particular, we focus on the assembly of receptor complexes after ligand binding, the activation of receptor-associated kinases of the Janus family, and the recruitment and phosphorylation of transcription factors of the STAT family, which dimerize, translocate to the nucleus, and bind to enhancer elements of respective target genes leading to transcriptional activation. The important players in the signalling pathway, namely the cytokines and the receptor components, the Janus kinases Jak1, Jak2 and Tyk2, the signal transducers and activators of transcription STAT1 and STAT3 and the tyrosine phosphatase SHP2 [SH2 (Src homology 2) domain-containing tyrosine phosphatase] are introduced and their structural/functional properties are discussed. Furthermore, we review various mechanisms involved in the termination of the IL-6-type cytokine signalling, namely the action of tyrosine phosphatases, proteasome, Jak kinase inhibitors SOCS (suppressor of cytokine signalling), protein inhibitors of activated STATs (PIAS), and internalization of the cytokine receptors via gp130. Although all IL-6-type cytokines signal through the gp130/Jak/STAT pathway, the comparison of their physiological properties shows that they elicit not only similar, but also distinct, biological responses. This is reflected in the different phenotypes of IL-6-type-cytokine knock-out animals.

Lipopolysaccharide and its analog antagonists display differential serum factor dependencies for induction of cytokine genes in murine macrophages

Monocytes/macrophages play a central role in mediating the effects of lipopolysaccharide (LPS) derived from gram-negative bacteria by the production of proinflammatory mediators. Recently, it was shown that the expression of cytokine genes for tumor necrosis factor alpha (TNF-alpha), interleukin-1beta (IL-1beta), and interferon-inducible protein-10 (IP-10) by murine macrophages in response to low concentrations of LPS is entirely CD14 dependent. In this report, we show that murine macrophages respond to low concentrations of LPS ( Collapse

Key Words Collapse

MESH Headings

• Acute-Phase Proteins
• Animals
• Carrier Proteins/pharmacology
• Chemokine CXCL10
• Chemokines, CXC/biosynthesis
• Culture Media, Serum-Free
• Cytokines/biosynthesis
• Disaccharides/pharmacology
• Dose-Response Relationship, Drug
• Escherichia coli
• Female
• Gene Expression Regulation
• Interleukin-1/biosynthesis
• Lipid A/analogs & derivatives
• Lipid A/pharmacology
• Lipopolysaccharide Receptors/genetics
• Lipopolysaccharide Receptors/pharmacology
• Lipopolysaccharides/antagonists & inhibitors
• Lipopolysaccharides/immunology
• Macrophages/immunology
• Male
• Membrane Glycoproteins
• Mice
• Mice, Inbred C3H
• Mice, Knockout
• Monosaccharides/pharmacology
• Tumor Necrosis Factor-alpha/biosynthesis

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Grants

• R37 AI018797 NIAID NIH HHS
• AI 18797 NIAID NIH HHS
• GM 50870 NIGMS NIH HHS
• R01 GM050870 NIGMS NIH HHS
• R01 AI018797 NIAID NIH HHS
• R56 AI018797 NIAID NIH HHS

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Affiliation(s)

P Y Perera Department of Microbiology and Immunology, Uniformed Services University of the Health Sciences, Bethesda, Maryland 20814-4799, USA
N Qureshi
W J Christ
P Stütz
S N Vogel

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LPS-binding protein protects mice from septic shock caused by LPS or gram-negative bacteria

LPS-binding protein (LBP) recognizes bacterial LPS and transfers it to CD14, thereby enhancing host cell stimulation, eventually resulting in pathogenic states such as septic shock. Recently, LBP also was shown to detoxify LPS by transferring LPS into HDL particles in vitro. Thus, the predominant in vivo function of LBP has remained unclear. To investigate the biological activity of acute phase concentrations of recombinant murine LBP, high concentrations of LBP were investigated in vitro and in vivo. Although addition of low concentrations of LBP to a murine macrophage cell line enhanced LPS-induced TNF-alpha synthesis, acute phase concentrations of LBP blocked this effect in comparison to low-dose LBP. When injected into mice intraperitoneally, LBP inhibited LPS-mediated cytokine release and prevented hepatic failure resulting in a significantly decreased mortality rate in LPS-challenged and D-galactosamine-sensitized mice, as well as in a murine model of bacteremia. These results complement a recent study revealing LBP-deficient mice to be dramatically more susceptible to an intraperitoneal Salmonella infection as compared with normal mice. We conclude that acute phase LBP has a protective effect against LPS and bacterial infection and may represent a physiologic defense mechanism against infection. Despite the limitations of any murine sepsis model, the results shown may imply that LBP could have beneficial effects during gram-negative peritonitis in humans.

Interleukin-6-specific activation of the C/EBPdelta gene in hepatocytes is mediated by Stat3 and Sp1

C/EBPdelta (CCAAT/enhancer binding protein delta) has been implicated as a regulator of acute-phase response (APR) genes in hepatocytes. Its expression increases dramatically in liver during the APR and can be induced in hepatic cell lines by interleukin-6 (IL-6), an acute-phase mediator that activates transcription of many APR genes. Here we have investigated the mechanism by which C/EBPdelta expression is regulated by IL-6 in hepatoma cells. C/EBPdelta promoter sequences to -125 bp are sufficient for IL-6 inducibility of a reporter gene and include an APR element (APRE) that is essential for IL-6 responsiveness. DNA binding experiments and transactivation assays demonstrate that Stat3, but not Stat1, interacts with this APRE. Two Sp1 sites, one of which is adjacent to the APRE, are required for IL-6 induction and transactivation by Stat3. Thus, Stat3 and Sp1 function cooperatively to activate the C/EBPdelta promoter. Replacement of the APRE with Stat binding elements (SBEs) from the ICAM-1 or C/EBPbeta promoter, both of which recognize both Stat1 and Stat3, confers responsiveness to gamma interferon, a cytokine that selectively activates Stat1. Sequence comparisons suggest that the distinct Stat binding specificities of the C/EBPdelta and C/EBPbeta SBEs are determined primarily by a single base pair difference. Our findings indicate that the cytokine specificity of C/EBPdelta gene expression is governed by the APRE sequence.

Cutting Edge: The Induction of Acute Phase Proteins by Lipopolysaccharide Uses a Novel Pathway That Is CD14-Independent

LPS (endotoxin) and proinflammatory cytokines (IL-6, IL-1, and TNF-α) are potent inducers of acute phase proteins (APP). Since LPS induces high levels of these cytokines after its interaction with CD14, a protein expressed on the surface of monocytes and neutrophils, it has been assumed that CD14 mediates the LPS induction of APP expression. To test this hypothesis, CD14-deficient and control mice were injected with low doses of LPS, and the expression of several APP that are normally up-regulated by LPS was measured. CD14-deficient mice showed no alteration in the induction of APP, including serum amyloid A, LPS-binding protein, fibrinogen, or ceruloplasmin; in contrast, C3H/HeJ mice, which carry a mutation in the Lps gene, do not up-regulate the expression of these proteins. These studies show that the up-regulation of APP by LPS utilizes a non-CD14 receptor and requires a functional Lps gene.

Lipopolysaccharide and pneumococcal cell wall components activate the mitogen activated protein kinases (MAPK) erk-1, erk-2, and p38 in astrocytes

Cell wall compounds of gram-positive bacteria are capable of inducing the biosynthesis of proinflammatory cytokines in CNS cells in a similar way as lipopolysaccharide (LPS) of gram-negative bacteria does. Astrocytes, which lack the CD14 LPS receptor, have also been shown to respond to LPS-stimulation by increased cytokine synthesis. However, almost nothing is known about signaling steps involved in this process. We have therefore examined signaling events in primary cultures of rat astrocytes and the human astrocytoma cell line U373MG, brought about by LPS and pneumococcal cell walls (PCW). Of particular interest to us was the tyrosine phosphorylation patterns and activation states of three members of the mitogen activated protein kinase (MAPK) family, i.e., extracellular signal-regulated protein kinase (erk)-1, erk-2, and the recently identified p38. We show that LPS and PCW initiate tyrosine phosphorylation and activation of erk-1, erk-2, and p38 in a dose-dependent fashion. Inhibitors of tyrosine phosphorylation were able to alleviate this effect and also blocked cytokine production of astrocytes. Both, LPS- and PCW-induced responses of astrocytic cells required the presence of soluble CD14 (sCD14) present in serum. Unraveling the signaling steps induced by bacterial compounds in cells of the CNS may potentially help to elucidate the pathomechanisms of meningitis and central nervous complications of sepsis and may offer options for novel treatment strategies.

The nuclear factor interleukin-6 (NF-IL6) and signal transducer and activator of transcription-3 (STAT-3) signalling pathways co-operate to mediate the activation of the hsp90beta gene by interleukin-6 but have opposite effects on its inducibility by heat shock

The levels of the 90 kDa heat-shock protein (hsp90) and the activity of the hsp90beta gene promoter are increased in response to treatment by interleukin (IL)-6. The hsp90beta gene promoter contains binding sites for the transcription factors nuclear factor IL-6 (NF-IL6) and signal transducer and activator of transcription 3 (STAT-3), which are activated respectively by the mitogen-activated-protein-kinase and Jak-kinase pathways following IL-6 treatment. Both these factors can activate the hsp90 promoter and have a strong synergistic effect on its activity, which appears to be critical for IL-6-mediated activation of the promoter. Interestingly, the two factors interact differently with the heat-shock factor (HSF) and a heat-shock stress. Thus STAT-3 reduces the stimulatory effect of heat shock whereas NF-IL6 enhances it. When applied together, heat shock and IL-6 produce only weak activation of the hsp90 promoter compared with either stimulus alone, indicating that the inhibitory effect of STAT-3 on HSF predominates under these conditions. In contrast, IL-1, which activates only the NF-IL6 pathway, synergizes with heat shock to produce strong activation of hsp90. These effects are discussed in terms of the multiple stimuli that may regulate the hsp90 promoter in unstressed cells and their interaction with its stress-mediated activation.