Lipopolysaccharide-induced cytokine production in human monocytes: role of tyrosine phosphorylation in transmembrane signal transduction

Immune signaling as a node of interaction between systems that sex-specifically develop during puberty and adolescence

Adolescence is pivotal for neural and behavioral development across species. During this period, maturation occurs in several biological systems, the most well-recognized being activation of the hypothalamic-pituitary-gonadal axis marking pubertal onset. Increasing comparative studies of sex differences have enriched our understanding of systems integration during neurodevelopment. In recent years, immune signaling has emerged as a key node of interaction between a variety of biological signaling processes. Herein, we review the age- and sex-specific changes that occur in neural, hypothalamic-pituitary, and microbiome systems during adolescence. We then describe how immune signaling interacts with these systems, and review recent preclinical evidence indicating that immune signaling may play a central role in integrating changes in their typical and atypical development during adolescence. Finally, we discuss the translational relevance of these preclinical studies to human health and wellness.

Role of PI3K in the bone resorption of apical periodontitis

BACKGROUND

Phosphoinositide 3-kinase (PI3K) is located within cells, and is involved in regulating cell survival, proliferation, apoptosis and angiogenesis. The purpose of this study was to investigate the role of PI3K in the process of bone destruction in apical periodontitis, and provide reference data for the treatment of this disease.

METHODS

The relative mRNA expression of PI3K, Acp5 and NFATc1 in the normal human periodontal ligament and in chronic apical periodontitis were analyzed by real-time quantitative polymerase chain reaction (RT-qPCR). A mouse model of apical periodontitis was established by root canal exposure to the oral cavity, and HE staining was used to observe the progress of apical periodontitis. Immunohistochemical staining was used to detect the expression of PI3K and AKT in different stages of apical periodontitis, while enzymatic histochemical staining was used for detection of osteoclasts. An Escherichia coli lipopolysaccharide (LPS)-mediated inflammatory environment was also established at the osteoclast and osteoblast level, and osteoclasts or osteoblasts were treated with the PI3K inhibitor LY294002 to examine the role of PI3K in bone resorption.

RESULTS

The expression of PI3K, Acp5 and NFATc1 genes in chronic apical periodontitis sample groups was significantly increased relative to healthy periodontal ligament tissue (P < 0.05). Mouse apical periodontitis was successfully established and bone resorption peaked between 2 and 3 weeks (P < 0.05). The expression of PI3K and Akt increased with the progression of inflammation, and reached a peak at 14 days (P < 0.05). The gene and protein expression of PI3K, TRAP and NFATc1 in osteoclasts were significantly increased (P < 0.05) in the E. coli LPS-mediated inflammatory microenvironment compared to the normal control group. Meanwhile in osteoblasts, the gene and protein expression of PI3K, BMP-2 and Runx2 were significantly reduced (P < 0.05) in the inflammatory microenvironment. With the addition of LY294002, expressions of bone resorption-related factors (TRAP, NFATc1) and bone formation-related factors (BMP-2, Runx2) significantly decreased (P < 0.05).

CONCLUSIONS

Under the inflammatory environment induced by LPS, PI3K participates in the occurrence and development of chronic apical periodontitis by regulating the proliferation and differentiation of osteoclasts and osteoblasts.

Anti-Inflammatory Functions of Alverine via Targeting Src in the NF-κB Pathway

Alverine, a smooth muscle relaxant, is used to relieve cramps or spasms of the stomach and intestine. Although the effects of alverine on spontaneous and induced contractile activity are well known, its anti-inflammatory activity has not been fully evaluated. In this study, we investigated the anti-inflammatory effects of alverine in vitro and in vivo. The production of nitric oxide (NO) in RAW264.7 cells activated by lipopolysaccharide (LPS) or polyinosinic:polycytidylic acid (poly (I:C)) was reduced by alverine. The mRNA expression of inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), and tumor necrosis factor-α (TNF-α) was also dose-dependently inhibited by treatment with alverine. In reporter gene assays, alverine clearly decreased luciferase activity, mediated by the transcription factor nuclear factor κB (NF-κB) in TIR-domain-containing adapter-inducing interferon-β (TRIF)- or MyD88-overexpressing HEK293 cells. Additionally, phosphorylation of NF-κB subunits and upstream signaling molecules, including p65, p50, AKT, IκBα, and Src was downregulated by 200 μM of alverine in LPS-treated RAW264.7 cells. Using immunoblotting and cellular thermal shift assays (CETSAs), Src was identified as the target of alverine in its anti-inflammatory response. In addition, HCl/EtOH-stimulated gastric ulcers in mice were ameliorated by alverine at doses of 100 and 200 mg/kg. In conclusion, alverine reduced inflammatory responses by targeting Src in the NF-κB pathway, and these findings provide new insights into the development of anti-inflammatory drugs.

Probiotic consumption during puberty mitigates LPS-induced immune responses and protects against stress-induced depression- and anxiety-like behaviors in adulthood in a sex-specific manner

Puberty/adolescence is a significant period of development and a time with a high emergence of psychiatric disorders. During this period, there is increased neuroplasticity and heightened vulnerability to stress and inflammation. The gut microbiome regulates stress and inflammatory responses and can alter brain chemistry and behaviour. However, the role of the gut microbiota during pubertal development remains largely uninvestigated. The current study examined gut manipulation with probiotics during puberty in CD1 mice on lipopolysaccharide (LPS)-induced immune responses and enduring effects on anxiety- and depression-like behaviours and stress-reactivity in adulthood. Probiotics reduced LPS-induced sickness behaviour at 12 h in females and at 48 h following LPS treatment in males. Probiotics also reduced LPS-induced changes in body weight at 48 h post-treatment in females. Probiotic treatment also prevented LPS-induced increases in pro- and anti-inflammatory peripheral cytokines at 8 h following LPS treatment, reduced central cytokine mRNA expression in the hypothalamus, hippocampus and PFC, and prevented LPS-induced changes to in the gut microbiota. A single exposure to LPS during puberty resulted in enduring depression-like behaviour in female mice, and anxiety-like behaviour in male mice in adulthood. However, pubertal exposure to probiotics prevented enduring LPS-induced depression-like behaviour in females and anxiety-like behaviors in males. Moreover, probiotics altered toll-like receptor-4 activity in the paraventricular nucleus of the hypothalamus (PVN) in males in response to a novel stressor in adulthood. Our results suggest that the gut microbiome plays an important role in pubertal neurodevelopment. These findings indicate that exposure to probiotics during puberty mitigates inflammation and decreases stress-induced vulnerabilities to emotional behaviours later in life, in a sex-specific manner.

Role of the Btk-PLCγ2 Signaling Pathway in the Bone Destruction of Apical Periodontitis

Chronic apical periodontitis is characterized by alveolar bone absorption in the apical region and is the result of the participation of various inflammatory mediators. Studies have shown that the Bruton tyrosine kinase- (Btk-) phospholipase Cγ2 (PLCγ2) signaling pathway plays an important role in bone absorption, but it is unknown whether it plays a role in apical periodontitis bone destruction. Therefore, this study verified the role of Btk and PLCγ2 in bone resorption of apical periodontitis by in vivo and in vitro experiments. In the in vivo experiment, a mice model of apical periodontitis was established; apical bone resorption was confirmed by the numbers of osteoclasts and HE staining. Btk, PLCγ2, and nuclear factor of activated T-cells 1 (NFATc-1) were detected by immunohistochemical staining. In the in vitro experiment, lipopolysaccharides (LPS) were used to stimulate osteoclast precursor cell RAW264.7 to establish an inflammatory microenvironment and detect osteoclast differentiation. By silencing Btk, the expression of Btk, PLCγ2, and NFATc-1 was detected by real-time qPCR and Western blot, and osteoclastogenesis was detected by enzyme histochemical staining to further confirm the role of Btk in bone resorption. It was found that the expression of Btk, PLCγ2, and NFATc-1 changed significantly with the progression of inflammation and bone destruction, indicating that Btk and PLCγ2 may be involved in the progression of inflammation in apical periodontitis and bone absorption. In vitro experiments confirmed that the differentiation of osteoclasts and the expression of PLCγ2 and NFATc-1 were significantly inhibited after silencing Btk expression, but osteoclast precursor cells could be differentiated due to the proinflammatory factor lipopolysaccharide. This study demonstrates that Btk and PLCγ2 are key factors involved in the apical inflammatory response and bone destruction.

Large-scale reduction of tyrosine kinase activities in human monocytes stimulated in vitro with N. meningitidis

N. meningitidis induces extensive gene expression changes in human monocytes, suggesting that complex networks of signaling pathways are activated during meningococcal sepsis. These effects are modulated by the anti-inflammatory cytokine interleukin-10 (IL-10). To further study changes in signal transduction suggested by mRNA data, we used kinase substrate arrays to identify composite kinase activities induced by lysates from a primary human monocyte model system. Cell lysates were prepared from monocytes treated with the following experimental conditions: 106 N. meningitidis/mL, 25 ng/mL IL-10, 106 N. meningitidis/mL in combination with 25 ng/mL IL-10, and vehicle. Lysates were subjected to kinase activity profiling with Tyrosine Kinase PamChip® arrays containing 144 kinase peptide substrates. In our experimental model, we were not able to detect a statistically significant large-scale change in ex vivo array peptide phosphorylation by lysates from monocytes treated for 15 minutes. Targets of the IL-10 anti-inflammatory response were not identified. A profound inhibition of array peptide phosphorylation by monocytes treated for 60 minutes was identified, suggesting low activity of a large number of kinases associated with different signaling pathways and immune cell functions, including STAT3 activity, Nf-κB and VEGF signaling, and PTEN signaling activity. The peptide representing ZBTB16, which was reduced in phosphorylation by lysates from all three experimental conditions, was in Ingenuity Pathway Analysis identified to be linked to reduced cytokine release and mRNA levels of tumor necrosis factor (TNF), IL-6, and CXCL10. Further studies should investigate changes in tyrosine kinase-mediated signal transduction in human immune cells, in order to evaluate the potential clinical application of kinome profiling in the study of systemic inflammatory responses to pathogens.

Src family kinase tyrosine phosphorylates Toll-like receptor 4 to dissociate MyD88 and Mal/Tirap, suppressing LPS-induced inflammatory responses

Src family kinases (SFKs) are a family of protein tyrosine kinases containing nine members: Src, Lyn, Fgr, Hck, Lck, Fyn, Blk, Yes, and Ylk. Although SFK activation is a major immediate signaling event in LPS/Toll-like receptor 4 (TLR4) signaling, its precise role has remained elusive due to various contradictory results obtained from a certain SFK member-deficient mice or cells. The observed inconsistencies may be due to the compensation or redundancy by other SFKs upon a SFK deficiency. The chemical rescuing approach was suggested to induce temporal and precise SFK activation in living cells, thereby limiting the chance of cellular adaption to a SFK-deficient condition. Using the rescuing approach, we demonstrate that restoring SFK activity not only induces tyrosine phosphorylation of TLR4, but also inhibits LPS-induced NFκB and JNK1/2 activation and consequently suppresses LPS-induced cytokine production. TLR4 normally recruits TIR domain-containing adaptors in response to LPS, however, temporally restored SFK activation disrupts the LPS-induced association of MyD88 and Mal/Tirap with TLR4. Additionally, using kinase-dead SFK-Lyn (Y397/508F) and constitutively active SFK-Lyn (Y508F), we found that the kinase-dead SFK inhibits TLR4 tyrosine phosphorylation with reduced binding affinity to TLR4, while the kinase-active SFK strongly binds to TLR4 and promotes TLR4 tyrosine phosphorylation, suggesting that SFK kinase activity is required for TLR4 tyrosine phosphorylation and TLR4-SFK interaction. Together, our results demonstrate that SFK activation induces TLR4 tyrosine phosphorylation, consequently dissociating MyD88 and Mal/Tirap from TLR4 and inhibiting LPS-induced inflammatory responses, suggesting a negative feedback loop regulated by SFK-induced tyrosine phosphorylation in TLR4.

Endogenous Nur77 Is a Specific Indicator of Antigen Receptor Signaling in Human T and B Cells

Distinguishing true Ag-stimulated lymphocytes from bystanders activated by the inflammatory milieu has been difficult. Nur77 is an immediate early gene whose expression is rapidly upregulated by TCR signaling in murine T cells and human thymocytes. Nur77-GFP transgenes serve as specific TCR and BCR signaling reporters in murine transgenic models. In this study, we demonstrate that endogenous Nur77 protein expression can serve as a reporter of TCR and BCR specific signaling in human PBMCs. Nur77 protein amounts were assessed by immunofluorescence and flow cytometry in T and B cells isolated from human PBMCs obtained from healthy donors that had been stimulated by their respective Ag receptors. We demonstrate that endogenous Nur77 is a more specific reporter of Ag-specific signaling events than the commonly used CD69 activation marker in both human T and B cells. This is reflective of the disparity in signaling pathways that regulate the expression of Nur77 and CD69. Assessing endogenous Nur77 protein expression has great potential to identify Ag-activated lymphocytes in human disease.

Biological characterization of Pseudomonas aeruginosa endotoxin released by antibiotic treatment in vitro

The supernatants taken from Pseudomonas aeruginosa cultures in human sera or chemically defined M9 medium in the presence of ceftazidime (CAZ) contained high levels of endotoxin, while those of imipenem (IPM) yielded relatively lower levels of endotoxin. The membrane-filtered supernatants were used as a source of endotoxin and the biological activities of the endotoxin were examined in comparison with those of hot-phenol water-extracted LPS. The CAZ-released endotoxin preparation contained large amounts of protein. The protein, however, appeared to lack significant endotoxic activity through the endotoxin-protein component, since the endotoxin did not show any toxic effect in D(+)-galactosamine (GaIN)-sensitized C3H/HeJ mice in vivo or macrophage activation in vitro. The activities of CAZ- and IPM-released endotoxins as assessed by chromogenic Limulus amebocyte coagulation test were fundamentally identical to those of purified P. aeruginosa LPS and Escherichia coli LPS, since their regression lines were parallel. The biological effects of CAZ-released endotoxin, such as lethal toxicity in GaIN-sensitized mice, in vitro induction of TNF and NO production by peritoneal macrophages, and MAP-kinase activation in macrophages of LPS-responsive C3H/He and LPS-low responsive C3H/HeJ mice, were similar to those of the LPS. Macrophage activation by CAZ-released endotoxin as well as LPS was mainly dependent on serum factors and CD14 antigen. Polymyxin B blocked the activity. These findings indicate that the endotoxic activity of CAZ-released endotoxin is due primarily to LPS (lipid A), although such preparations contain a high level of protein released from or produced by the organisms. Finally, the possibility that the treatment of P. aeruginosa infection with some kind of antibiotics may induce endotoxic shock was suggested in a mouse model.

Implication of G i proteins and Src tyrosine kinases in endotoxin-induced signal transduction events and mediator production

Previous studies have suggested that heterotrimeric G proteins and tyrosine kinases may be involved in lipopolysaccharide (LPS) signaling events. Signal transduction pathways activated by LPS were examined in human promonocytic THP-1 cells. We hypothesized that Gi proteins and Src tyrosine kinase differentially affect mitogen-activated protein (MAP) kinases (MAPK) and nuclear factor kappa (NF- B) activation. Post-receptor coupling to G i proteins were examined using pertussis toxin (PTx), which inhibits G i receptor-coupling. The involvement of the Src family of tyrosine kinases was examined using the selective Src tyrosine kinase inhibitor pyrazolopyrimidine-2 (PP2). Pretreatment of THP-1 cells with PTx attenuated LPS-induced activation of c-Jun-N-terminal kinase (JNK) and p38 kinase, and production of tumor necrosis factor-alpha (TNF-) and thromboxane B2 (TxB2). Pretreatment with PP2 inhibited TNF- and TxB2 production, but had no effect on p38 kinase or JNK signaling. Therefore, the G i-coupled signaling pathways and Src tyrosine kinase-coupled signaling pathways are necessary for LPS-induced TNF- and TxB2 production, but differ in their effects on MAPK activation. Neither PTx nor PP2 inhibited LPS-induced activation of interleukin receptor activated kinase (IRAK) or inhibitedtranslocation of NF- B. However, PP2 inhibitedLPS-inducedNF-B transactivation of a luciferase reporter gene construct in a concentration-dependent manner. Thus, LPS induction of Src tyrosine kinases may be essential in downstream NF- B transactivation of genes following DNA binding. PTx had no effect on NF- B activation of the reporter construct. These data suggest upstream divergence in signaling through G i pathways leading to MAPK activation and other signaling events leading to I B degradation and NF- B DNA binding.

Function of CD14 as a peptidoglycan receptor: differences and similarities with LPS

Peptidoglycan (PGN) is a macrophage activator from Gram-positive bacteria. PGN activates cells of hemopoietic origin through CD14 since: (i) PGN-unresponsive CD14-negative cells become PGNresponsive after transfection with CD14 and expression of membrane CD14; (ii) PGN binds to CD14 with high affinity; and (iii) anti-CD14 mAbs inhibit both binding of PGN to CD14 and activation of CD14-positive cells by PGN. However, there are several differences in the function of CD14 as PGN and LPS receptor: (i) the kinetics of binding are different; (ii) the affinity of binding in the absence of LPS-binding protein (LBP) is higher for PGN than LPS; (iii) LBP does not increase the affinity of binding of PGN to CD14 and does not enhance cell activation by PGN (in contrast to LPS); (iv) the regions of CD14 needed for binding and activation are partially similar and partially different for PGN and LPS; (v) sCD14:PGN complexes, in contrast to sCD14:LPS complexes, do not activate CD14-negative cells; (vi) PGN, in contrast to LPS, does not activate CHO cells expressing mCD14; and (vii) PGN and LPS induce differential activation of MAP kinases, but activate similar transcription factors (NF-κB, ATF1/CREB, and AP-1).

Co-operation of TLR4 and raft proteins in LPS-induced pro-inflammatory signaling

Toll-like receptor 4 (TLR4) is activated by lipopolysaccharide (LPS), a component of Gram-negative bacteria to induce production of pro-inflammatory mediators aiming at eradication of the bacteria. Dysregulation of the host responses to LPS can lead to a systemic inflammatory condition named sepsis. In a typical scenario, activation of TLR4 is preceded by binding of LPS to CD14 protein anchored in cholesterol- and sphingolipid-rich microdomains of the plasma membrane called rafts. CD14 then transfers the LPS to the TLR4/MD-2 complex which dimerizes and triggers MyD88- and TRIF-dependent production of pro-inflammatory cytokines and type I interferons. The TRIF-dependent signaling is linked with endocytosis of the activated TLR4, which is controlled by CD14. In addition to CD14, other raft proteins like Lyn tyrosine kinase of the Src family, acid sphingomyelinase, CD44, Hsp70, and CD36 participate in the TLR4 signaling triggered by LPS and non-microbial endogenous ligands. In this review, we summarize the current state of the knowledge on the involvement of rafts in TLR4 signaling, with an emphasis on how the raft proteins regulate the TLR4 signaling pathways. CD14-bearing rafts, and possibly CD36-rich rafts, are believed to be preferred sites of the assembly of a multimolecular complex which mediates the endocytosis of activated TLR4.

Src and fibroblast growth factor 2 independently regulate signaling and gene expression induced by experimental injury to intact articular cartilage

OBJECTIVE

To investigate whether cartilage injury activates protein tyrosine kinases distinct from fibroblast growth factor (FGF)-related signaling, and whether they contribute to injury-induced gene responses.

METHODS

Phosphokinases and protein tyrosine phosphorylation were assayed by Western blotting of cartilage lysates. Immunoprecipitation and Western blotting with 4G10 antibody and immunoprecipitation kinase assay were carried out. Tyrosine-phosphorylated proteins on silver-stained gels of injured cartilage lysates were identified by mass spectrometry. Messenger RNA induction in cartilage explants was assessed by quantitative reverse transcriptase-polymerase chain reaction.

RESULTS

Protein tyrosine phosphorylation occurred within seconds of injury to the surface of intact articular cartilage, as did activation of MAPKs and IKK. Activation did not reoccur upon reinjury of cultured explants. The prominent tyrosine-phosphorylated proteins focal adhesion kinase, paxillin, and cortactin were identified as substrates of Src family kinases. The Src family kinase inhibitor PP2 blocked injury-induced tyrosine phosphorylation. It did not prevent activation of the MAPKs and IKK but differentially inhibited 8 of 10 inflammatory response genes that were induced by injury. In contrast, FGF signaling blockade with PD173074 reduced all MAPK and IKK activation by ∼50% and inhibited a different subset of genes but had no effect on Src-like signaling.

CONCLUSION

Injury to the surface of intact articular cartilage activates Src-like kinases as well as MAPKs and IKK (implying NF-κB activation). FGF-2 contributes to MAPK/IKK activation but not to Src-like signaling, suggesting that the latter is a parallel pathway that also regulates the injury-induced inflammatory gene response.

Tec family kinases in inflammation and disease

Over the last decade, the Tec family of nonreceptor tyrosine kinases (Btk, Tec, Bmx, Itk, and Rlk) have been shown to play a key role in inflammation and bone destruction. Bruton's tyrosine kinase (Btk) has been the most widely studied due to the critical role of this kinase in B-cell development and recent evidence showing that blocking Btk signaling is effective in ameliorating lymphoma progression and experimental arthritis. This review will examine the role of TFK in myeloid cell function and the potential of targeting these kinases as a therapeutic intervention in autoimmune disorders such as rheumatoid arthritis.

Enterobacterial common antigen mutants of Salmonella enterica serovar Typhimurium establish a persistent infection and provide protection against subsequent lethal challenge

Infection with Salmonella spp. is a significant source of disease globally. A substantial proportion of these infections are caused by Salmonella enterica serovar Typhimurium. Here, we characterize the role of the enterobacterial common antigen (ECA), a surface glycolipid ubiquitous among enteric bacteria, in S. Typhimurium pathogenesis. Construction of a defined mutation in the UDP-N-acetylglucosamine-1-phosphate transferase gene, wecA, in two clinically relevant strains of S. Typhimurium, TML and SL1344, resulted in strains that were unable to produce ECA. Loss of ECA did not affect the gross cell surface ultrastructure, production of lipopolysaccharide (LPS), flagella, or motility. However, the wecA mutant strains were attenuated in both oral and intraperitoneal mouse models of infection (P<0.001 for both routes of infection; log rank test), and virulence could be restored by complementation of the wecA gene in trans. Despite the avirulence of the ECA-deficient strains, the wecA mutant strains were able to persistently colonize systemic sites (spleen and liver) at moderate levels for up to 70 days postinfection. Moreover, immunization with the wecA mutant strains provided protection against a subsequent lethal oral or intraperitoneal challenge with wild-type S. Typhimurium. Thus, wecA mutant (ECA-negative) strains of Salmonella may be useful as live attenuated vaccine strains or as vehicles for heterologous antigen expression.

Cellular cholesterol involvement in Src, PKC, and p38/JNK transduction pathways by porins

Biological membranes are described as a mosaic of different domains where interactions between membrane components induce the formation of subdomains with different characteristics and functions. Lipids play an important role in the formation of lipid-enriched microdomains where they dynamically associate to form platforms important for membrane protein sorting and construction of signaling complexes. Cholesterol confined in lipid domains is a crucial component required by microorganisms, directly or indirectly, to enter or exit the intracellular compartment. Cellular activation mediated by superficial bacterial component may be modified by local cholesterol depletion. Therefore, new perspectives for unconventional therapeutic intervention in Gram-negative infections may be envisaged. We tested this hypothesis by using methyl-beta-cyclodextrin (mbetaCD) as a cholesterol-complexing agent to alter the U937 plasma membrane cholesterol content. Our results demonstrate that cholesterol depletion of U937 cells inhibited Salmonella enterica serovar Typhimurium porins-mediated phosphorylation of Src kinase family, protein kinase C (PKC), JNK, and p38, while cholesterol repletion restored the phosphorylation. Lipopolysaccharide (LPS) extracted from the same bacterial strain has been used as a control. Our data demonstrate that the lack of activation of signal transduction pathway observed following cholesterol depletion differently modulates the release of interleukin-6 (IL-6) or tumor necrosis factor-alpha (TNF-alpha), suggesting that Src, associated to lipid domains, may represent an important pathway in Gram-negative-induced cellular signal.

CD14 and toll-like receptors 2 and 4 are required for fibrillar A{beta}-stimulated microglial activation

Microglia are the brain's tissue macrophages and are found in an activated state surrounding beta-amyloid plaques in the Alzheimer's disease brain. Microglia interact with fibrillar beta-amyloid (fAbeta) through an ensemble of surface receptors composed of the alpha(6)beta(1) integrin, CD36, CD47, and the class A scavenger receptor. These receptors act in concert to initiate intracellular signaling cascades and phenotypic activation of these cells. However, it is unclear how engagement of this receptor complex is linked to the induction of an activated microglial phenotype. We report that the response of microglial cells to fibrillar forms of Abeta requires the participation of Toll-like receptors (TLRs) and the coreceptor CD14. The response of microglia to fAbeta is reliant upon CD14, which act together with TLR4 and TLR2 to bind fAbeta and to activate intracellular signaling. We find that cells lacking these receptors could not initiate a Src-Vav-Rac signaling cascade leading to reactive oxygen species production and phagocytosis. The fAbeta-mediated activation of p38 MAPK also required CD14, TLR4, and TLR2. Inhibition of p38 abrogated fAbeta-induced reactive oxygen species production and attenuated the induction of phagocytosis. Microglia lacking CD14, TLR4, and TLR2 showed no induction of phosphorylated IkappaBalpha following fAbeta. These data indicate these innate immune receptors function as members of the microglial fAbeta receptor complex and identify the signaling mechanisms whereby they contribute to microglial activation.

Toll-like receptor signaling in the lysosomal pathways

The lysosomal pathway digests material received by two main routes, phagocytosis and autophagy. Cells use phagocytosis to ingest extracellular particles by invaginations of the plasma membrane. In autophagy, a double membrane structure isolates portions of the cytoplasm to target it for degradation. During infection, phagocytes use both of these cellular functions to restrict microbial replication and at the same time to orchestrate an appropriate response against the invader. Toll-like receptor recognition of a pathogen initiates an innate immune response against the pathogen that includes production of inflammatory cytokines, upregulation of costimulatory molecules to prime an adaptive immune response, and activation of phagocytosis and autophagy. Signaling through this family of receptors also produces a hybrid response in which proteins that participate in autophagy are recruited to phagosomes, resulting in expedited microbial elimination. In this review, we discuss recent views on how Toll-like receptors direct microbes to final destruction by regulating the different pathways that lead to the lysosome.

Zinc signals are essential for lipopolysaccharide-induced signal transduction in monocytes

Cytosolic alterations of calcium ion concentrations are an integral part of signal transduction. Similar functions have been hypothesized for other metal ions, in particular zinc (Zn(2+)), but this still awaits experimental verification. Zn(2+) is important for multiple cellular functions, especially in the immune system. Among other effects, it influences formation and secretion of pro-inflammatory cytokines, including TNF-alpha. Here we demonstrate that these effects are due to a physiological signaling system involving intracellular Zn(2+) signals. An increase of the intracellular zinc ion concentration occurs upon stimulation of human leukocytes with Escherichia coli, LPS, Pam(3)CSK(4), TNF-alpha, or insulin, predominantly in monocytes. Chelating this zinc signal with the membrane permeable zinc-specific chelator TPEN (N,N,N',N'-tetrakis-(2-pyridyl-methyl)ethylenediamine) completely blocks activation of LPS-induced signaling pathways involving p38 MAPK, ERK1/2, and NF-kappaB, and abrogates the release of proinflammatory cytokines, including TNF-alpha. This function of Zn(2+) is not limited to monocytes or even the immune system, but seems to be another generalized signaling system based on intracellular fluctuations of metal ion concentrations, acting parallel to Ca(2+).

The diverse functions of Src family kinases in macrophages

Macrophages are key components of the innate immune response. These cells possess a diverse repertoire of receptors that allow them to respond to a host of external stimuli including cytokines, chemokines, and pathogen-associated molecules. Signals resulting from these stimuli activate a number of macrophage functional responses such as adhesion, migration, phagocytosis, proliferation, survival, cytokine release and production of reactive oxygen and nitrogen species. The cytoplasmic tyrosine kinase Src and its family members (SFKs) have been implicated in many intracellular signaling pathways in macrophages, initiated by a diverse set of receptors ranging from integrins to Toll-like receptors. However, it has been difficult to implicate any given member of the family in any specific pathway. SFKs appear to have overlapping and complementary functions in many pathways. Perhaps the function of these enzymes is to modulate the overall intracellular signaling network in macrophages, rather than operating as exclusive signaling switches for defined pathways. In general, SFKs may function more like rheostats, influencing the amplitude of many pathways.

Bmx tyrosine kinase regulates TLR4-induced IL-6 production in human macrophages independently of p38 MAPK and NFkapp}B activity

Chronic inflammation, as seen in conditions such as rheumatoid arthritis and Crohn disease, is in part driven by discordant production of inflammatory cytokines, such as tumor necrosis factor-alpha and interleukin-6 (IL-6). Tyrosine kinase activity is essential to lipopolysaccharide-induced cytokine production in monocytes, and previous studies by us and others have implicated a role for the Tec kinase Bruton's tyrosine kinase (Btk) in inflammatory cytokine production. Here we show that knockdown of Btk using RNA interference results in decreased tumor necrosis factor-alpha, but not IL-6 production. Further investigations into the signaling mechanisms regulating IL-6 production led to the discovery that the Tec kinase bone marrow tyrosine kinase gene in chromosome X (Bmx) regulates Toll-like receptor-induced IL-6 production. Our data further showed that Bmx-dependent super-induction of IL-6 does not involve nuclear factor-kappaB activity. More detailed investigations of pathways downstream of Bmx signaling revealed that Bmx targets the IL-6 3' untranslated region to increase mRNA stabilization via a novel, thus far undefined, p38 mitogen activated protein kinase-independent pathway. These data have important implications for the design of therapeutics targeted against specific cytokines and their regulators in inflammatory disease.

Chemical inhibition of Src family kinases affects major LPS-activated pathways in primary human macrophages

Understanding the signalling mechanisms controlling inflammatory cytokine production is pivotal to the research of both acute and chronic immune disorders. Tyrosine phosphorylation is one of the earliest events to occur in response to an immune challenge yet the role of specific tyrosine kinases in inflammatory cytokine production has been difficult to ascribe due to conflicting literature. Here we show that the pyrazolo pyrimidine compound PP2, a selective inhibitor of Src family kinases (SFK), can inhibit LPS-induced TNF production as well as a number of other inflammatory cytokines. In addition, we show similar effects of PP2 on cytokine production when induced by other TLRs, (1, 2 and 5-8), indicating that SFK are important common regulators of TLR signalling. PP2 suppressed the activity of both TNF and IL-10 driven reporter genes, suggesting that this activity is mediated at the level of transcription. Interestingly, however, PP2 had no significant effect on the activation of NF-kappaB, or on p42/44 ERK, p46/54 JNK or p38 MAPK phosphorylation. In contrast, PP2 did inhibit AP-1 nuclear accumulation in response to LPS. Taken together, these findings show that the Src kinases are able to control inflammatory cytokine production at the transcriptional level independently of NF-kappaB, and highlight the role of the AP-1 family of transcription factors as downstream mediators of Src kinase action.

Phosphatidyl inositol-3-phosphate kinase mediates CD14 dependent signaling

Lipopolysaccharide (LPS), a component of the cell wall of Gram-negative bacteria, is an important mediator of innate immunity and septic shock, but the exact mechanisms mediating cellular LPS recognition and the subsequent translation to inflammatory gene expression remain incompletely understood. CD14 has been established as a receptor that confers high sensitivity to LPS in cells of the myeloid lineage, probably by presenting LPS to Toll receptors. We use an anti CD14 blocking antibody to define a LPS stimulus that activates only this high affinity component of the LPS receptor and then examine CD14 dependent signaling events that are activated in response to LPS stimulation. We describe a novel LPS activated signaling pathway in human PBMC that leads to cytokine production and is mediated by PI3 kinase through Ras and the MEK/ERK cassette. Moreover, we show the PI3 kinase effectors PKB and PKC(zeta) are also activated by PI3 kinase in a CD14 dependent manner in LPS stimulated human PBMC. Thus, PI3 kinase appears to be an essential component in LPS signal transduction.

CpG-induced tyrosine phosphorylation occurs via a TLR9-independent mechanism and is required for cytokine secretion

Toll-like receptors (TLRs) recognize molecular patterns preferentially expressed by pathogens. In endosomes, TLR9 is activated by unmethylated bacterial DNA, resulting in proinflammatory cytokine secretion via the adaptor protein MyD88. We demonstrate that CpG oligonucleotides activate a TLR9-independent pathway initiated by two Src family kinases, Hck and Lyn, which trigger a tyrosine phosphorylation–mediated signaling cascade. This cascade induces actin cytoskeleton reorganization, resulting in cell spreading, adhesion, and motility. CpG-induced actin polymerization originates at the plasma membrane, rather than in endosomes. Chloroquine, an inhibitor of CpG-triggered cytokine secretion, blocked TLR9/MyD88-dependent cytokine secretion as expected but failed to inhibit CpG-induced Src family kinase activation and its dependent cellular responses. Knock down of Src family kinase expression or the use of specific kinase inhibitors blocked MyD88-dependent signaling and cytokine secretion, providing evidence that tyrosine phosphorylation is both CpG induced and an upstream requirement for the engagement of TLR9. The Src family pathway intersects the TLR9–MyD88 pathway by promoting the tyrosine phosphorylation of TLR9 and the recruitment of Syk to this receptor.

A comprehensive map of the toll-like receptor signaling network

Recognition of pathogen-associated molecular signatures is critically important in proper activation of the immune system. The toll-like receptor (TLR) signaling network is responsible for innate immune response. In mammalians, there are 11 TLRs that recognize a variety of ligands from pathogens to trigger immunological responses. In this paper, we present a comprehensive map of TLRs and interleukin 1 receptor signaling networks based on papers published so far. The map illustrates the possible existence of a main network subsystem that has a bow-tie structure in which myeloid differentiation primary response gene 88 (MyD88) is a nonredundant core element, two collateral subsystems with small GTPase and phosphatidylinositol signaling, and MyD88-independent pathway. There is extensive crosstalk between the main bow-tie network and subsystems, as well as feedback and feedforward controls. One obvious feature of this network is the fragility against removal of the nonredundant core element, which is MyD88, and involvement of collateral subsystems for generating different reactions and gene expressions for different stimuli.

SHP-1 inhibits LPS-mediated TNF and iNOS production in murine macrophages

Several lines of evidence have suggested that protein tyrosine phosphatases, including CD45 and SHP-1, regulate macrophage activation. Macrophages from mice lacking SHP-1 (motheaten mice) are hyper-responsive to many stimuli, suggesting that SHP-1 may negatively regulate macrophage activation. Herein we report that the repressible/inducible over-expression of wild-type SHP-1 in a subclone of RAW 264.7 macrophages (RAW-TT10 cells) inhibited both TNF secretion and iNOS protein accumulation in response to stimulation with lipopolysaccharide (LPS) and recombinant murine interferon-gamma and led to diminished LPS-mediated tyrosine phosphorylation of vav1. In contrast, expression of a truncated SHP-1 construct previously shown to interfere with endogenous SHP-1 function modestly augmented LPS-mediated TNF and iNOS production and did not inhibit vav1 tyrosine phosphorylation. Taken together, these data provide the first direct evidence that SHP-1 inhibits macrophage activation by LPS and suggest that this effect may be mediated in part by dephosphorylation of vav1.

Src protein tyrosine kinase family and acute inflammatory responses

Acute inflammatory responses are one of the major underlying mechanisms for tissue damage of multiple diseases, such as ischemia-reperfusion injury, sepsis, and acute lung injury. By use of cellular and molecular approaches and transgenic animals, Src protein tyrosine kinase (PTK) family members have been identified to be essential for the recruitment and activation of monocytes, macrophages, neutrophils, and other immune cells. Src PTKs also play a critical role in the regulation of vascular permeability and inflammatory responses in tissue cells. Importantly, animal studies have demonstrated that small chemical inhibitors for Src PTKs attenuate tissue injury and improve survival from a variety of pathological conditions related to acute inflammatory responses. Further investigation may lead to the clinical application of these inhibitors as drugs for ischemia-reperfusion injury (such as stroke and myocardial infarction), sepsis, acute lung injury, and multiple organ dysfunction syndrome.

Lipopolysaccharide-induced c-Src expression plays a role in nitric oxide and TNFalpha secretion in macrophages

As tyrosine kinases are indispensable in lipopolysaccharide (LPS)-induced macrophage activation, the myeloid-specific Src members (i.e. Lyn, Fgr and Hck) are speculated to play important roles in this process. However, the normal LPS responsiveness in lyn(-/-)fgr(-/-)hck(-/-) macrophages implicates the presence of an elusive, compensating tyrosine kinase(s). In this study, we demonstrate the upregulation of c-Src in Raw264.7 and peritoneal macrophages (PEMs) by LPS, which is inhibited by PP2 (an inhibitor for Src family kinases), pyrrolidinedithiocarbamate (PDTC; NF-kappaB inhibitor) and LY294002 (PI3K inhibitor). And this LPS-mediated c-Src induction is also observed in macrophages recovered from LPS-challenged rats. Intriguingly, PP2 attenuates the ability of PEMs to elicit COX-2 expression and nitric oxide production in response to LPS. Similar results are also observed when macrophages recovered from rats receiving either LPS alone or LPS and PP2 both are compared. Furthermore, administration of PP2 in Raw264.7 and animal models of sepsis greatly suppresses TNFalpha secretion and serum TNFalpha level, respectively. Therefore, we conclude that c-Src, with its LPS induction, has an unperceived role in transmitting LPS signaling in macrophages.

MyD88 adapter-like (Mal) is phosphorylated by Bruton's tyrosine kinase during TLR2 and TLR4 signal transduction

Members of the Toll-like receptor (TLR) family are essential players in activating the host innate immune response against infectious microorganisms. All TLRs signal through Toll/interleukin 1 receptor domain-containing adapter proteins. MyD88 adapter-like (Mal) is one such adapter that specifically is involved in TLR2 and TLR4 signaling. When overexpressed we have found that Mal undergoes tyrosine phosphorylation. Three possible phospho-accepting tyrosines were identified at positions 86, 106, and 187, and two mutant forms of Mal in which tyrosines 86 and 187 were mutated to phenylalanine acted as dominant negative inhibitors of NF-kappaB activation by lipopolysaccharide (LPS). Activation of THP-1 monocytic cells with the TLR4 agonist LPS and the TLR2 agonist macrophage-activating lipopeptide-2 induced phosphorylation of Mal on tyrosine residues. We found that the Bruton's tyrosine kinase (Btk) inhibitor LFM-A13 could block the endogenous phosphorylation of Mal on tyrosine in cells treated with macrophage-activating lipopeptide-2 or LPS. Furthermore, Btk immunoprecipitated from THP-1 cells activated by LPS could phosphorylate Mal. Our study therefore provides the first demonstration of the key role of Mal phosphorylation on tyrosine during signaling by TLR2 and TLR4 and identifies a novel function for Btk as the kinase involved.

The regulation of the expression of inducible nitric oxide synthase by Src-family tyrosine kinases mediated through MyD88-independent signaling pathways of Toll-like receptor 4

Bacterial lipopolysaccharide (LPS) activates Toll-like receptor 4 (TLR4) leading to the expression of inflammatory gene products. Src-family tyrosine kinases (STKs) are known to be activated by LPS in monocytes/macrophages. Therefore, we determined the role of STKs in TLR4 signaling pathways and target gene expression in macrophages. The activation of NFkappaB, and p38 MAPK, and the expression of inducible nitric oxide synthase (iNOS) induced by LPS were not affected in macrophages deficient in three STKs (Lyn, Hck, and Fgr). These results suggest that the deletion of the three STKs among possibly nine STKs is not sufficient to abolish total activity of STKs possibly due to the functional redundancy of other STKs present in macrophages. However, two structurally unrelated pan-inhibitors of STKs, PP1 and SU6656, suppressed LPS-induced iNOS expression in MyD88-knockout as well as wild-type macrophages. The suppression of iNOS expression by the inhibitors was correlated with the downregulation of IFNbeta (a MyD88-independent gene) expression and subsequent decrease in STAT1 phosphorylation. Moreover, PP1 suppressed the expression of IFNbeta and iNOS induced by TRIF, a MyD88-independent adaptor of TLR4. PP1 suppressed STAT1 phosphorylation induced by LPS, but not by IFNbeta suggesting that STKs are involved in the primary downstream signaling pathways of TLR4, but not the secondary signaling pathways downstream of IFNbeta receptor. Together, these results demonstrate that STKs play a positive regulatory role in TLR4-mediated iNOS expression in a MyD88-independent (TRIF-dependent) manner. These results provide new insight in understanding the role of STKs in TLR4 signaling pathways and inflammatory target gene expression.

Inhibition of SRC tyrosine kinases suppresses activation of nuclear factor-kappaB, and serine and tyrosine phosphorylation of IkappaB-alpha in lipopolysaccharide-stimulated raw 264.7 macrophages

Involvement of protein tyrosine kinases (PTK) in lipopolysaccharide (LPS)-induced nuclear factor-kappa B (NF-kappaB) activation has been demonstrated. Studies investigated the role of PTK and the underlying mechanisms by which PTK play a role in LPS induction of pathways leading to NF-kappaB activation in macrophages. Inhibitors of PTK-genistein, herbimycin A, or AG126-blocked LPS-induced NF-kappaB activation. Genistein also blocked pervanadate-induced NF-kappaB activation. Furthermore, Src TK selective inhibitors-damnacanthal or PP1-blocked LPS-induced NF-kappaB activation over a range of nanomolar concentrations. Genistein, damnacanthal, or PP1 blocked the LPS-induced serine phosphorylation, the degradation of IkappaB-alpha, and the consequent translocation of the p65 subunit of NF-kappaB to the nucleus. In addition to serine phosphorylation of IkappaB-alpha, LPS-induced NF-kappaB activation also required tyrosine phosphorylation of IkappaB-alpha. These TK inhibitors blocked substantially LPS induction of tyrosine phosphorylation of IkappaB-alpha. Furthermore, cSrc and Lck were physically associated with IkappaB-alpha. These results suggest that the LPS-induced NF-kappaB pathways are dependent on both serine and tyrosine phosphorylation of IkappaB-alpha, and that Src TK, such as cSrc and Lck, are key components of the LPS signaling pathway through at least two different mechanisms associated with NF-kappaB activation.

Inhibition of the Src and Jak Kinases Protects against Lipopolysaccharide-induced Acute Lung Injury

The cascade of cellular and molecular pathways mediating acute lung injury is complex and incompletely defined. Although the Src and Jak family of kinases is upregulated in LPS-induced murine lung injury, their role in the development of lung injury is unknown. Here we report that systemic inhibition of these kinases using specific small molecule inhibitors (PP2, SU6656, tyrphostin A1) significantly attenuated LPS-induced lung injury, as determined by histologic and capillary permeability assays. These inhibitors blocked LPS-dependent cytokine and chemokine production in the lung and in the serum. In contrast, lung-targeted inhibition of these kinases in the airway epithelium via adenoviral-mediated gene transfer of dominant negative Src or of suppressor of cytokine signaling (SOCS-1) disrupted lung cytokine production but had no effect on systemic cytokine production or lung vascular permeability. Mice were significantly protected from lethal LPS challenge by the small molecule inhibitors of Jak and Src kinase. Importantly, this protection was still evident even when the inhibitors were administered 6 hours after LPS challenge. Taken together, these observations suggest that Jak and Src kinases participate in acute lung injury and verify the potential of this class of selective tyrosine kinase inhibitors to serve as novel therapeutic agents for this disease.

Ribotoxic Stress Response to the Trichothecene Deoxynivalenol in the Macrophage Involves the Src Family Kinase Hck

Trichothecene mycotoxins and other translational inhibitors activate mitogen-activated protein kinase (MAPKs) by a mechanism called the "ribotoxic stress response," which drives both cytokine gene expression and apoptosis in macrophages. The purpose of this study was to identify upstream kinases involved in the ribotoxic stress response using the trichothecene deoxynivalenol (DON) and the RAW 264.7 macrophage as models. DON (100 to 1000 ng/ml) dose-dependently induced phosphorylation of c-Jun N-terminal protein kinase (JNK), extracellular signal-regulated kinase (ERK), and p38 MAPKs. MAPK phosphorylation in response to DON exposure occurred as early as 5 min, was maximal from 15 to 30 min, and lasted up to 8 h. Preincubation with inhibitors of protein kinase C, protein kinase A, or phospholipase C had no effect on DON-induced MAPK phosphorylation. In contrast, the Src family tyrosine kinase inhibitors, PP1 (4-amino-5-[4-methylphenyl)]-7-[t-butyl]pyrazolo[3,4-d]-pyrimidine) and, PP2 (4-amino-5-[4-chlorophenyl]-7-[t-butyl]pyrazolo[3,4-d]-pyrimidine) concentration-dependently impaired phosphorylation of all three MAPK families. PP1 suppressed DON-induced phosphorylation of the MAPK substrates c-jun, ATF-2, and p90(Rsk). MAPK phosphorylation by two other translational inhibitors, anisomycin and emetine, were similarly Src-dependent. PP1 reduced DON-induced increases in nuclear levels and binding activities of several transcription factors (NF-kappaB, AP-1, and C/EBP), which corresponded to decreases in TNF-alpha production, caspase-3 activation, and apoptosis. Tyrosine phosphorylation of hematopoeitic cell kinase (Hck), a Src found in macrophages, was detectable within 1 to 5 min after DON addition, and this was suppressed by PP1. Knockdown of Hck expression with siRNAs confirmed involvement of this Src in DON-induced TNF-alpha production and caspase activation. Taken together, activation of Hck and possibly other Src family tyrosine kinases are likely to be critical signals that precede both MAPK activation and induction of resultant downstream sequelae by DON and other ribotoxic stressors.

Soluble CD14 receptor expression and monocyte heterogeneity but not the C-260T CD14 genotype are associated with severe acute pancreatitis

OBJECTIVE

Soluble CD14 is derived from a membrane glycoprotein, and it enhances endothelial cytokine responses to lipopolysaccharide. We studied the role of soluble CD14 in the pathogenesis of the systemic inflammatory response associated with acute pancreatitis, to determine whether altered expression was due to a functional C-260T polymorphism in the CD14 promoter gene or altered monocyte heterogeneity.

DESIGN

Prospective case-matched study.

SETTING

Tertiary pancreatic treatment unit in the United Kingdom.

SUBJECTS

Patients with pancreatitis and controls.

INTERVENTIONS

DNA from 117 patients with pancreatitis (34 severe) and 263 controls underwent CD14 genotyping using restriction fragment length polymorphism-polymerase chain reaction.

MEASUREMENTS AND MAIN RESULTS

Peripheral venous blood samples at 24 and 72 hrs after the onset of abdominal pain were analyzed for sCD14 levels. Isolated peripheral blood mononuclear cells were phenotyped for CD14/CD16 receptor expression using immunofluorescence flow cytometry. Disease severity was assessed using Atlanta criteria, Acute Physiology Scores, and C-reactive protein.Soluble CD14 levels were higher in severe (24-hr median, 66.6 ng/mL; 72-hr median, 72.2 ng/mL) compared with mild attacks (24-hr median, 50.7 ng/mL; 72-hr median, 49.7 ng/mL, p < .001), although the latter was similar to controls (median, 51 ng/mL). Furthermore, soluble CD14 levels correlated with Acute Physiology Scores (p < .001) and C-reactive protein (p = .01).Peripheral blood mononuclear cells CD14++ (p = .008), CD14+/16+ (p = .003), and CD16++ (p = .015) receptor densities were all increased in severe attacks at 24 hrs. Early CD14+/16+ receptor density correlated with sCD14 (p < .001), Acute Physiology Scores (p < .001), and C-reactive protein (p = 0.006). The CD14 genotype prevalence in acute pancreatitis was similar to controls and failed to correlate with any variables studied.

CONCLUSIONS

Increased soluble CD14 expression is associated with the systemic inflammatory response to acute pancreatitis and an expansion of the proinflammatory CD14+/CD16+ monocyte subset. Its targeted disruption may afford some benefit in preventing the development of systemic complications.

Interleukin-10 suppression of myeloid cell activation--a continuing puzzle

Efforts to identify the signal transduction pathways used by interleukin-10 (IL-10) have resulted in limited success. The anti-inflammatory effects elicited by IL-10, and the mechanisms by which these are mediated, are still relatively unknown. Understanding the signalling mechanisms behind the suppression of cytokine expression by IL-10 could be of potential therapeutic interest. Although the consensus is that the Janus kinase, Jak1, as well as the signal transducer and activator of transcription STAT3 are central, much controversy exists about the participation and roles of many other signalling pathways targeted by IL-10. The mechanisms of cytokine suppression proposed by various groups have included transcriptional, post-transcriptional and post-translational regulation of IL-10 target genes; nevertheless no unifying model has emerged thus far. Here we would like to highlight novel findings and discuss their implications in the context of current understanding of IL-10 signalling.

Interleukin-8 production by THP-1 cells stimulated by Salmonella enterica serovar Typhimurium porins is mediated by AP-1, NF-κB and MAPK pathways

Interleukin-8 (IL-8) is released in response to inflammatory stimuli, such as bacterial products. Either porins or lipopolysaccharide (LPS) stimulated THP-1 cells to release IL-8 after 24 h. We have previously reported that stimulation of monocytic cells with Salmonella enterica serovar Typhimurium porins led to the activation of mitogen-activated protein kinase cascades and of protein tyrosine kinases (PTKs). In this report, we demonstrate, using two potent and selective inhibitors of MEK activation by Raf-1 (PD-098059) and p38 (SB-203580), that both ERK1/2 and p38 pathways play a key role in the production of IL-8 by porins and LPS. Porin-stimulated expression of activating protein 1 (AP-1) and correlated IL-8 release is also inhibited by PD-098059 or SB-203580 indicating that the Raf-1/MEK1-MEK2/MAPK cascade is required for their activation. Also PTKs modulate the pathway that control IL-8 gene expression, in fact its expression is abolished by tyrphostin. By using N-acetyl-leucinyl-leucinyl-norleucinal-H (ALLN) an inhibitor of nuclear factor-kappaB (NF-kappaB) activity, we also observed IL-8 release modulation. Our results elucidate some of the molecular mechanisms by which AP-1 and NF-kappaB regulate IL-8 release and open new strategies for the design of specific molecules that will modulate IL-8 effects in various infectious diseases.

Cross-linking of FcγR triggers shedding of the hemoglobin-haptoglobin scavenger receptor CD163

CD163, the hemoglobin (Hb)-haptoglobin scavenger receptor, is a monocyte/macrophage-restricted member of the scavenger receptor, cysteine-rich family of proteins. In addition to being expressed on the cell surface, a soluble form of CD163 has also been reported. Like tumor necrosis factor alpha (TNF-alpha), surface CD163 is proteolytically cleaved from the plasma membrane in response to lipopolysaccharide (LPS) stimulation. As cross-linking of the Fcgamma receptor (FcgammaR) is similarly known to induce TNF-alpha shedding, the effect of FcgammaR stimulation on CD163 shedding was investigated. We found that FcgammaR stimulation resulted in a rapid release of surface CD163 into the supernatant that was blocked by inhibitors of protein kinase C and tyrosine kinases. Although LPS and FcgammaR stimulation in short-term cultures suppressed CD163 mRNA expression, long-term cultures of monocytes treated with LPS-but not with a FcgammaR cross-linking reagent-resulted in an interleukin-10-dependent recovery of surface CD163 expression. These studies suggest that the presence of immune complexes in infection or autoimmunity may radically alter the nature of CD163-dependent monocyte/macrophage processes. This may be particularly important in disease states in which immune complexes and high levels of free Hb are present, such as in autoimmune hemolytic anemia, transfusion reactions, or infections by hemolytic bacteria.

Bruton’s tyrosine kinase (Btk)—the critical tyrosine kinase in LPS signalling?

The discovery of the Toll-like receptors (TLRs) has revolutionised the field of innate immunity. One unresolved question regarding LPS signalling is whether there is a role for tyrosine kinases downstream of the LPS receptor. Studies in mice deficient in Bruton's tyrosine kinase have previously shown that they are defective in their responses to LPS. Further investigation into the role of Btk in LPS signalling has directly implicated Btk downstream of TLR4, both with respect to p38 MAPK activation and activation of the transcription factor NFkappaB. In fact Btk is activated by LPS and has been shown to directly bind TLR4 and the key proximal signalling proteins involved in LPS-induced NFkappaB activation, MyD88, Mal and IRAK-1. These recent findings point to a direct role for Btk in LPS signal transduction and raise interesting questions regarding the mode of activation of Btk following LPS stimulation and the precise nature of the pathways activated downstream of Btk. A better understanding of how Btk functions in LPS signalling will have important implications for inflammatory and autoimmune disorders and therapies thereof.

Role of vav1- and src-related tyrosine kinases in macrophage activation by CpG DNA

Macrophage activation by CpG DNA requires toll-like receptor 9 and the adaptor protein MyD88. Gram-negative bacterial lipopolysaccharide also activates macrophages via a toll-like receptor pathway (TLR-4), but we and others have reported that lipopolysaccharide also stimulates tyrosine phosphorylation in macrophages. Herein we report that exposure of RAW 264.7 murine macrophages to CpG DNA (but not non-CpG DNA) provoked the rapid tyrosine phosphorylation of vav1. PP1, a selective inhibitor of src-related tyrosine kinases, blocked both the CpG DNA-mediated tyrosine phosphorylation of vav1 and the CpG DNA-mediated up-regulation of macrophage tumor necrosis factor secretion and inducible nitric-oxide synthase protein accumulation. Furthermore, we found that the inducible expression of any of three dominant interfering mutants of vav1 (a truncated protein, vavC; a form containing a point mutation in the regulatory tyrosine residue, vavYF174; and a form with an in-frame deletion of six amino acids required for the guanidine nucleotide exchange factor (GEF) activity of vav1 for rac family GTPases, vavGEFmt) consistently inhibited CpG DNA-mediated up-regulation of tumor necrosis factor secretion and inducible nitric-oxide synthase protein accumulation in RAW-TT10 macrophages. Finally, we determined that CpG DNA-mediated up-regulation of NF-kappaB activity (but not mitogen-activated protein kinase activation) was inhibited by preincubation with PP1 or by expression of the truncated vavC mutant. Taken together, our results indicate that the tyrosine phosphorylation of vav1 by a src-related tyrosine kinase or kinases plays an important role in the macrophage response to CpG DNA.

Prevention of lipopolysaccharide-induced microangiopathy by gp49B1: evidence for an important role for gp49B1 expression on neutrophils

gp49B1 is expressed on mast cells and inhibits immunoglobulin E–dependent activation and inflammation in vivo. We now show that gp49B1 is expressed on neutrophils and prevents neutrophil-dependent vascular injury in response to lipopolysaccharide (LPS). The intradermal (i.d.) injection of LPS into gp49B1-null (gp49B^−/−) but not gp49B1-sufficient (gp49B^+/+) mice elicited macroscopic hemorrhages by 24 h, which were preceded on microscopic analyses by significantly more intravascular thrombi (consisting of neutrophils, platelets, and fibrin) that occluded venules and by more tissue neutrophils than in gp49B^+/+ mice. However, there were no differences in the number of intact (nondegranulating) mast cells or the tissue levels of mediators that promote neutrophil recruitment. Hemorrhage was prevented by depleting neutrophils, blocking β2 integrin–intercellular adhesion molecule 1 interactions, or inhibiting coagulation. These characteristics indicate that gp49B^−/− mice are exquisitely sensitive to a local Shwartzman reaction (LSR) after a single i.d. injection of LPS, whereas in the classic LSR, a second exposure is required for increased β2 integrin function, intravascular neutrophil aggregation, formation of occlusive thrombi, and hemorrhage. Moreover, LPS increased gp49B1 expression on neutrophils in vivo. The results suggest that gp49B1 suppresses the LPS-induced increase in intravascular neutrophil adhesion, thereby providing critical innate protection against a pathologic response to a bacterial component.

Signal transduction pathways in mouse microglia N-11 cells activated by advanced glycation endproducts (AGEs)

Deposition of cross-linked insoluble protein aggregates such as amyloid plaques is characteristic for Alzheimer's disease. Microglial activation by these extracullar deposits has been proposed to play a crucial role in functional degeneration as well as cell death of neurones. A sugar-derived post-translational modification of long-lived proteins, advanced glycation endproducts (AGEs), activate specific signal transduction pathways, resulting in the up-regulation of various pro-inflammatory signals such as cytokines [interleukin-6 (IL-6), tumour necrosis factor-alpha (TNF-alpha)] and inducible nitric oxide synthase (iNOS). Our goal was to study AGE-activated signal transduction pathways involved in the induction of pro-inflammatory effectors in the murine microglial cell line N-11. Chicken egg albumin-AGE (CEA-AGE), used as model AGE, induces nitric oxide (NO), TNF-alpha and IL-6 production. The AGE receptor, RAGE, and the transcription factor, nuclear factor kappa B (NF-kappaB), appear to be involved in all pathways, since a neutralizing RAGE antibody and a peptide inhibiting NF-kappaB translocation down-regulated NO, TNF-alpha and IL-6 production. NO and TNF-alpha, but not IL-6 production appear to be regulated independently, since NOS inhibitors did not decrease TNF-alpha secretion and a neutralizing TNF-alpha antibody did not reduce NO production, while employment of NOS inhibitors reduced significantly the secretion of IL-6. Inhibition of the MAP-kinase-kinase (MEK) and phosphatidylinositol 3-kinase (PI3K) pathway, but not that of mitogen-activated protein kinase-p38 (MAPK-p38), reduced NO, TNF-alpha and IL-6 significantly, suggesting that simultaneous activation of the first two pathways is necessary for the AGE-induced induction of these pro-inflammatory stimuli.

Eukaryotic cell signaling and transcriptional activation induced by bacterial porins

The protein composition of the outer membrane of Gram-negative bacteria consists of about 20 immunochemically distinct proteins, termed outer membrane proteins (OMPs). Apart from their structural role, OMPs have been shown to have other functions, particularly with regard to transport, and have been classified as permeases and porins. Porins, during their interaction with the host, are immunogenic and also directly stimulate several cellular functions. Porins work both as molecules present on the bacterial surface and as molecules released by bacteria. Lipopolysaccharide and OMPs, the major structural macromolecular constituents of the outer membrane, carry out a fundamental role in the pathogenesis of Gram-negative infections. This brief review describes the multiple facets of the biological activities of porins both in vitro and in vivo, particularly focusing on their ability to induce the expression of cytokines and other factors that modulate cellular activities with either pathological or adaptive consequences. This brief discussion will focus on the signal transmission mechanisms induced by bacterial porins.

Mycosis fungoides shows concurrent deregulation of multiple genes involved in the TNF signaling pathway: an expression profile study

Mycosis fungoides (MF) is the most frequent type of cutaneous T-cell lymphoma, whose diagnosis and study is hampered by its morphologic similarity to inflammatory dermatoses (ID) and the low proportion of tumoral cells, which often account for only 5% to 10% of the total tissue cells. cDNA microarray studies using the CNIO OncoChip of 29 MF and 11 ID cases revealed a signature of 27 genes implicated in the tumorigenesis of MF, including tumor necrosis factor receptor (TNFR)-dependent apoptosis regulators, STAT4, CD40L, and other oncogenes and apoptosis inhibitors. Subsequently a 6-gene prediction model was constructed that is capable of distinguishing MF and ID cases with unprecedented accuracy. This model correctly predicted the class of 97% of cases in a blind test validation using 24 MF patients with low clinical stages. Unsupervised hierarchic clustering has revealed 2 major subclasses of MF, one of which tends to include more aggressive-type MF cases including tumoral MF forms. Furthermore, signatures associated with abnormal immunophenotype (11 genes) and tumor stage disease (5 genes) were identified.

Janus kinase 2 is involved in lipopolysaccharide-induced activation of macrophages

The mechanisms by which lipopolysaccharide (LPS) is recognized, and how such recognition leads to innate immune responses, are poorly understood. Stimulation with LPS induces the activation of a variety of proteins, including mitogen-activated protein kinases (MAPKs) and NF-kappaB. Activation of protein tyrosine kinases (PTKs) is also necessary for a number of biological responses to LPS. We used a murine macrophage-like cell line, RAW264.7, to demonstrate that Janus kinase (JAK)2 is tyrosine phosphorylated immediately after LPS stimulation. Anti-Toll-like receptor (TLR)4 neutralization antibody inhibits the phosphorylation of JAK2 and the c-Jun NH2-terminal protein kinase (JNK). Both the JAK inhibitor AG490 and the kinase-deficient JAK2 protein reduce the phosphorylation of JNK and phosphatidylinositol 3-kinase (PI3K) via LPS stimulation. Pharmacological inhibition of the kinase activity of PI3K with LY-294002 decreases the phosphorylation of JNK. Finally, we show that JAK2 is involved in the production of IL-1beta and IL-6. PI3K and JNK are also important for the production of IL-1beta. These results suggest that LPS induces tyrosine phosphorylation of JAK2 via TLR4 and that JAK2 regulates phosphorylation of JNK mainly through activation of PI3K. Phosphorylation of JAK2 via LPS stimulation is important for the production of IL-1beta via the PI3K/JNK cascade. Thus JAK2 plays a pivotal role in LPS-induced signaling in macrophages.