Summary and comparison of the signaling mechanisms of the Toll/interleukin-1 receptor family

LPS-induced IL-6, IL-8, VCAM-1, and ICAM-1 expression in human lymphatic endothelium

We have previously reported the TLR4 expression in human intestinal lymphatic vessels. In the study here, microarray analysis showed the expression of the TLR4, MD-2, CD14, MyD88, TIRAP, TRAM, IRAK1, and TRAF6 genes in cultured human neonatal dermal lymphatic microvascular endothelial cells (LEC). The microarray analysis also showed that LEC expressed genes of IL-6, IL-8, VCAM-1, and ICAM-1, and the real-time quantitative PCR analysis showed that mRNA production was increased by lipopolysaccharide (LPS). The LPS-induced IL-6, IL-8, VCAM-1, and ICAM-1 production in LEC was suppressed by the introduction of TLR4-specific small interfering RNA, and also by anti-TLR4, nobiletin, and CAPE pretreatment. These findings suggest that LEC has TLR4-mediated LPS recognition mechanisms that involve at least activation of NF-kappaB, resulting in increased expression of IL-6, IL-8, VCAM-1, and ICAM-1. Both the LPS effect on the gene expression and also the suppression by nobiletin and CAPE pretreatment on the protein production were larger in IL-6 and in VCAM-1 than in IL-8 and in ICAM-1 in LEC. The signal transduction of NF-kappaB and AP-1-dependent pathway may be more critical for the expression of IL-6 and VCAM-1 than that of IL-8 and ICAM-1 in LEC.

Cytomegalovirus immune evasion

Human cytomegalovirus (HCMV) has become a paradigm for viral immune evasion due to its unique multitude of immune-modulatory strategies. HCMV modulates the innate as well as adaptive immune response at every step of its life cycle. It dampens the induction of antiviral interferon-induced genes by several mechanisms. Further striking is the multitude of genes and strategies devoted to modulating and escaping the cellular immune response. Several genes are independently capable of inhibiting antigen presentation to cytolytic T cells by downregulating MHC class I. Recent data revealed an astounding variety of methods in triggering or inhibiting activatory and inhibitory receptors found on NK cells, NKT cells, T cells as well as auxiliary cells of the immune system. The multitude and complexity of these mechanisms is fascinating and continues to reveal novel insights into the host-pathogen interaction and novel cell biological and immunological concepts.

Role of TLR-4 in liver macrophage and endothelial cell responsiveness during acute endotoxemia

Liver macrophages and endothelial cells have been implicated in hepatotoxicity induced by endotoxin (ETX). In these studies, we analyzed the role of toll-like receptor 4 (TLR-4) in the response of these cells to acute endotoxemia. Treatment of control C3H/HeOuJ mice with ETX (3 mg/kg, i.p.) resulted in increased numbers of activated macrophages in the liver. This was associated with morphological changes in the cells and a rapid (within 3 h) induction of nitric oxide synthase-2, cyclooxygenase-2, microsomal PGE synthase-1, interleukin-1 beta and tumor necrosis factor alpha gene expression. In endothelial cells, acute endotoxemia led to increased expression of these genes, as well as 5-lipoxygenase. In contrast, liver sinusoidal cells from C3H/HeJ TLR-4 mutant mice were relatively unresponsive to ETX. Treatment of C3H/HeOuJ, but not C3H/HeJ mice with ETX, resulted in activation of transcription factors AP-1 and NF-kappaB in liver sinusoidal cells, which was evident within 3 h. Whereas in macrophages, transcription factor activation was transient, in endothelial cells, it persisted for 24 h. In C3H/HeOuJ mice treated with ETX, activation of p38 MAP kinase was also evident in macrophages and endothelial cells, and JNK kinase in macrophages. In contrast, reduced protein kinase B (AKT) was noted in macrophages. In C3H/HeJ mice, ETX administration also led to activation of p38 MAP kinase in macrophages with no effects on JNK, p44/42 MAP kinase or AKT. These studies demonstrate that liver macrophages and endothelial cells are highly responsive to acute endotoxemia. Moreover, this activity is largely dependent on TLR-4.

IL-1 receptor accessory protein is essential for IL-33-induced activation of T lymphocytes and mast cells

Lack of the IL-1 receptor accessory protein (IL-1RAcP) abrogates responses to IL-33 and IL-1 in the mouse thymoma clone EL-4 D6/76 cells. Reconstitution with full-length IL-1RAcP is sufficient to restore responsiveness to IL-33 and IL-1. IL-33 activates IL-1 receptor-associated kinase-1, cJun-N-terminal kinase, and the NF-kappaB pathway in an IL-1RAcP-dependent manner and results in IL-2 release. IL-33 is able to induce the release of proinflammatory cytokines in bone marrow-derived (BMD) mast cells, indicating that IL-33 may have a proinflammatory potential like its relatives IL-1 and IL-18, in addition to its Th2-skewing properties in the adaptive response described previously. Blocking of murine IL-1RAcP with the neutralizing antibody 4C5 inhibits response of mouse thymoma cells and BMD mast cells to IL-33. The interaction of either membrane-bound or soluble forms of IL-1RAcP and IL-33Ralpha-chain depends on the presence of IL-33, as demonstrated by coimmunoprecipitation assays. These data demonstrate that IL-1RAcP is indispensable for IL-33 signaling. Furthermore, they suggest that IL-1RAcP is used by more than one alpha-chain of the IL-1 receptor family and thus may resemble a common beta-chain of that family.

Evolving functions of endothelial cells in inflammation

Inflammation is usually analysed from the perspective of tissue-infiltrating leukocytes. Microvascular endothelial cells at a site of inflammation are both active participants in and regulators of inflammatory processes. The properties of endothelial cells change during the transition from acute to chronic inflammation and during the transition from innate to adaptive immunity. Mediators that act on endothelial cells also act on leukocytes and vice versa. Consequently, many anti-inflammatory therapies influence the behaviour of endothelial cells and vascular therapeutics influence inflammation. This Review describes the functions performed by endothelial cells at each stage of the inflammatory process, emphasizing the principal mediators and signalling pathways involved and the therapeutic implications.

Myocardial Matrix Remodeling and the Matrix Metalloproteinases: Influence on Cardiac Form and Function

It is now becoming apparent that dynamic changes occur within the interstitium that directly contribute to adverse myocardial remodeling following myocardial infarction (MI), with hypertensive heart disease and with intrinsic myocardial disease such as cardiomyopathy. Furthermore, a family of matrix proteases, the matrix metalloproteinases (MMPs) and the tissue inhibitors of MMPs (TIMPs), has been recognized to play an important role in matrix remodeling in these cardiac disease states. The purpose of this review is fivefold: 1) to examine and redefine the myocardial matrix as a critical and dynamic entity with respect to the remodeling process encountered with MI, hypertension, or cardiomyopathic disease; 2) present the remarkable progress that has been made with respect to MMP/TIMP biology and how it relates to myocardial matrix remodeling; 3) to evaluate critical translational/clinical studies that have provided a cause-effect relationship between alterations in MMP/TIMP regulation and myocardial matrix remodeling; 4) to provide a critical review and analysis of current diagnostic, prognostic, and pharmacological approaches that utilized our basic understanding of MMP/TIMPs in the context of cardiac disease; and 5) most importantly, to dispel the historical belief that the myocardial matrix is a passive structure and supplant this belief that the regulation of matrix protease pathways such as the MMPs and TIMPs will likely yield a new avenue of diagnostic and therapeutic strategies for myocardial remodeling and the progression to heart failure.

Pathogen-specific innate immune response

This chapter summarizes our studies on the three toll-like receptor pathways, namely TLR4, TLR2, and TLR3, induced by lipopolysaccharides (LPS), peptidoglycan (PGN), and double-stranded RNA (dsRNA) in antigen presenting cells (APC). The particular emphasis is on the activation of human innate immune responses via cytokine and chemokine production. Three different measurements have been performed on monocytic and dendritic cells as model APCs: (i) the expression of various cytokine and chemokine genes by real-time PCR, (ii) the release of the cytokines and chemokines by ELISA, and (iii) gene expression analysis by cytokine and chemokine pathway-specific and whole genome microarrays. Real-time PCR and ELISA enable us to identify cytokines and chemokines that are produced specifically upon LPS, PGN, or dsRNA stimulation. Subsequently, microarray studies and appropriate validation experiments help us to identify genes involved in the upstream pathways that cause the induction of cytokines and chemokines. It is evident that TLR4-LPS, TLR2-PGN, and TLR3-dsRNA pathways are distinguished by the specific set of cytokines and chemokines they induce as well as by the upstream signaling events.

Differential effects of anti-IL-1R accessory protein antibodies on IL-1alpha or IL-1beta-induced production of PGE(2) and IL-6 from 3T3-L1 cells

Soluble or cell-bound IL-1 receptor accessory protein (IL-1RAcP) does not bind IL-1 but rather forms a complex with IL-1 and IL-1 receptor type I (IL-1RI) resulting in signal transduction. Synthetic peptides to various regions in the Ig-like domains of IL-1RAcP were used to produce antibodies and these antibodies were affinity-purified using the respective antigens. An anti-peptide-4 antibody which targets domain III inhibited 70% of IL-1beta-induced productions of IL-6 and PGE(2) from 3T3-L1 cells. Anti-peptide-2 or 3 also inhibited IL-1-induced IL-6 production by 30%. However, anti-peptide-1 which is directed against domain I had no effect. The antibody was more effective against IL-1beta compared to IL-1alpha. IL-1-induced IL-6 production was augmented by coincubation with PGE(2). The COX inhibitor ibuprofen blocked IL-1-induced IL-6 and PGE(2) production. These results confirm that IL-1RAcP is essential for IL-1 signaling and that increased production of IL-6 by IL-1 needs the co-induction of PGE(2). However, the effect of PGE(2) is independent of expressions of IL-1RI and IL-1RAcP. Our data suggest that domain III of IL-1RAcP may be involved in the formation or stabilization of the IL-1RI/IL-1 complex by binding to epitopes on domain III of the IL-1RI created following IL-1 binding to the IL-1RI.

IL-1 receptor-mediated signal is an essential component of MyD88-dependent innate response to Mycobacterium tuberculosis infection

MyD88, the common adapter involved in TLR, IL-1, and IL-18 receptor signaling, is essential for the control of acute Mycobacterium tuberculosis (MTB) infection. Although TLR2, TLR4, and TLR9 have been implicated in the response to mycobacteria, gene disruption for these TLRs impairs only the long-term control of MTB infection. Here, we addressed the respective role of IL-1 and IL-18 receptor pathways in the MyD88-dependent control of acute MTB infection. Mice deficient for IL-1R1, IL-18R, or Toll-IL-1R domain-containing adaptor protein (TIRAP) were compared with MyD88-deficient mice in an acute model of aerogenic MTB infection. Although primary MyD88-deficient macrophages and dendritic cells were defective in cytokine production in response to mycobacterial stimulation, IL-1R1-deficient macrophages exhibited only a reduced IL-12p40 secretion with unaffected TNF, IL-6, and NO production and up-regulation of costimulatory molecules CD40 and CD86. Aerogenic MTB infection of IL-1R1-deficient mice was lethal within 4 wk with 2-log higher bacterial load in the lung and necrotic pneumonia but efficient pulmonary CD4 and CD8 T cell responses, as seen in MyD88-deficient mice. Mice deficient for IL-18R or TIRAP controlled acute MTB infection. These data demonstrate that absence of IL-1R signal leads to a dramatic defect of early control of MTB infection similar to that seen in the absence of MyD88, whereas IL-18R and TIRAP are dispensable, and that IL-1, together with IL-1-induced innate response, might account for most of MyD88-dependent host response to control acute MTB infection.

IRAK-2 participates in multiple toll-like receptor signaling pathways to NFkappaB via activation of TRAF6 ubiquitination

Toll-like receptor (TLR) signaling is known to involve interleukin-1 receptor-associated kinases (IRAKs), however the particular role of IRAK-2 has remained unclear. Further, although IRAK-1 was originally thought to be central for the TLR-NFkappaB signaling axis, recent data have shown that it is dispensable for NFkappaB activation for some TLRs and demonstrated an alternative role for it in interferon regulatory factor activation. Here we show that IRAK-2 is critical for the TLR-mediated NFkappaB activation pathway. The poxviral TLR antagonist A52 inhibited NFkappaB activation by TLR2, -3, -4, -5, -7, and -9 ligands, via its interaction with IRAK-2, while not affecting interferon regulatory factor activation. Knockdown of IRAK-2 expression by small interfering RNA suppressed TLR3, TLR4, and TLR8 signaling to NFkappaB in human cell lines, and importantly, TLR4-mediated chemokine production in primary human cells. IRAK-2 usage by different TLRs was distinct, because it acted downstream of the TLR adaptors MyD88 and Mal but upstream of TRIF. Expression of IRAK-2, but not IRAK-1, led to TRAF6 ubiquitination, an event critical for NFkappaB activation. Further, IRAK-2 loss-of-function mutants, which could not activate NFkappaB, were incapable of promoting TRAF6 ubiquitination. Thus we propose that IRAK-2 plays a more central role than IRAK-1 in TLR signaling to NFkappaB.

Interleukin-6 -174 promoter polymorphism does not influence IL-6 production after LPS and IL-1 beta stimulation in human umbilical cord vein endothelial cells

The IL-6 is a typical pleiotropic cytokine, which regulates T cell response, B cell differentiation and immunoglobulin production. Endothelial cells can produce large amounts of IL-6. SNP at position -174 (G/C) in the IL-6 promoter region was found to be associated with a series of complex diseases. In this study we analyzed whether IL-6 -174 G/C polymorphism has any effect on IL-6 production of in vitro cultured HUVECs. Thirty-three fresh umbilical cords were recruited from healthy pregnancies. The endothelial cells isolated from human umbilical cords were genotyped for IL-6 -174 SNP. C allele frequency was 0.379. The IL-6 production of each primary HUVEC line was measured after IL-1beta or LPS treatment by ELISA. Serial dilutions of the stimulating agents were applied and maximum amount of produced IL-6 (R(max)) and stimulator concentrations at half-maximal IL-6 response (MR(50)) were calculated for each of the cell lines. IL-6 production was not associated with IL-6 -174 SNP genotypes or with presence of C allele. Our results showed that IL-6 production of HUVEC after proinflammatory stimulation was not influenced by IL-6 -174 SNP. Further functional studies are required to compare differences and similarities in IL-6 -174 SNP dependent expression of IL-6 among various cell types.

Induction and evasion of the type I interferon response by cytomegaloviruses

Cytomegaloviruses represent supreme pathogens in that they are capable of occupying healthy mammalian hosts for life in the face of constant antiviral immune reactions. The inability of the host to eliminate the virus likely results from numerous counteractive strategies employed to disrupt the immune response. The role of type I interferon in the antiviral response has been well documented although only recently have the pathways of induction of this powerful cytokine been described. Cytomegaloviruses have been shown to both induce and be sensitive to the effects of type I interferon. Yet these viruses also possess numerous and varied phenotypes capable of inhibiting not only interferon induction but also interferon signaling and interferon-induced antiviral processes. The balance between induction and evasion of type I interferon responses by cytomegaloviruses is discussed in this review.

RhoE participates in the stimulation of the inflammatory response induced by ethanol in astrocytes

Astroglial cells are involved in the neuropathogenesis of several inflammatory diseases of the brain, where the activation of inflammatory mediators and cytokines plays an important role. We have previously demonstrated that ethanol up-regulates inflammatory mediators in both brain and astroglial cells. Since Rho GTPases are involved in inflammatory responses of astrocytes where loss of stress fibers takes place and RhoE/Rnd3 disorganizes the actin cytoskeleton, the aim of the present study was to investigate the implication of this protein in the stimulation of inflammatory signaling induced by ethanol. Our findings show that RhoE expression induces a decrease in both RhoA and Rac. In addition, RhoE not only induces actin cytoskeleton disorganization but it also stimulates both the IRAK/ERK/NF-kappaB pathway and the COX-2 expression associated with the inflammatory response in these cells. Our results also show that ethanol exposure induces RhoE signaling in astrocytes. Preincubation of astrocytes with GF109203X, an inhibitor of PKCs, reduces the RhoE levels and abolishes the ethanol-induced activation of IRAK, NF-kappaB and the COX-2 expression. Furthermore, RhoE overexpression restores ethanol responses in astrocytes treated with the PKCs inhibitor. Altogether, our findings suggest that this small GTPase is involved in the stimulation of the inflammatory signaling induced by ethanol in astrocytes. These findings provide new insights into the molecular mechanism involved in the inflammatory responses in astrocytes.

Plasminogen activation by fibroblasts from periodontal ligament and gingiva is not directly affected by chemokines in vitro

OBJECTIVE

Chronic inflammation in periodontal disease is associated with increased plasminogen activation and elevated levels of chemokines. It is unknown whether chemokines can regulate the activation of plasminogen via modulation of plasminogen activators (PA) and the corresponding plasminogen activator inhibitors (PAI) in periodontal tissue.

DESIGN

To establish a link between chemokines and activation of plasminogen, human periodontal ligament fibroblasts (PDL) and gingival fibroblasts (GF) were incubated with IL-8, monocyte chemoattractant protein-1, macrophage inflammatory protein-1alpha, and platelet factor-4, either alone or in the presence of the inflammatory mediators TGF-beta and IL-1. The potential of the cell lysates to activate plasminogen was based on kinetic studies with the substrate casein. Casein zymography was performed to determine the molecular sizes of the PA. Total PAI-1 in the cell-conditioned medium was quantified by immunoassay.

RESULTS

We report that the chemokines did not affect activation of plasminogen by PDL and GF. Even in the presence of TGF-beta which suppressed, and IL-1 which stimulated plasminogen activation, the chemokines had no direct effect. Inhibition of PA and plasmin, but not of matrix metalloproteinases and cysteine proteinases prevented caseinolysis. The plasminogen activation capacity of the cell lysates was represented by a single band with features of uPA. The immunoassay showed that the release of PAI-1 in PDL and GF remained unaffected by the chemokines, also when stimulated with TGF-beta.

CONCLUSIONS

These results suggest that plasminogen activation by PDL and GF is not directly affected by the chemokines even in the presence of the inflammatory mediators TGF-beta and IL-1.

Phosphorylation of IRF8 in a pre-associated complex with Spi-1/PU.1 and non-phosphorylated Stat1 is critical for LPS induction of the IL1B gene

Rapid induction of transcription is known to be mediated by factors which bind DNA following post-translational modification. We report here that non-tyrosine phosphorylated (NTP)-Stat1 is involved in a cooperative interaction with Spi-1/PU.1 and IRF8 to form a pre-associated, poised complex for IL1B gene induction. A double point mutation at a putative STAT binding site, which overlaps this composite Spi-1 x IRF8 site located in the LPS and IL-1 response element (LILRE), inhibited human IL1B LPS-dependent reporter activity to about 10 percent of the control wild type vector. Chromatin immunoprecipitation revealed stimulation-independent constitutive binding of IRF8, Spi-1 and NTP-Stat1 at the LILRE, while binding of C/EBP beta was activated at an adjacent C/EBP beta site after LPS stimulation. In contrast to Stat1, IRF8 was tyrosine phosphorylated following LPS treatment. Supporting the involvement of NTP-Stat1, LPS-induced IL1B reporter activity in monocytes was enhanced by ectopic expression of NTP-Stat1 Y701F. In contrast, co-expression of a Y211F IRF8 mutein functioned as a dominant-negative inhibitor of LPS-induced IL1B reporter activity. In vitro DNA binding using extracts from LPS-treated monocytes confirmed that the LILRE enhancer constitutively binds a trimolecular complex containing IRF8, Spi-1 and NTP-Stat1. Binding studies using in vitro-expressed proteins revealed that NTP-Stat1 enhanced the binding of Spi-1 and IRF8 to the LILRE. Co-expression of TRAF6, an LPS surrogate, with Spi-1 and IRF8 enhanced IL1B reporter activity in HEK293R cells, which was dramatically reduced when Y211F IRF8 was co-expressed. These results suggest that the rapid transcriptional induction of an important inflammatory gene is dependent upon constitutive cooperative binding of a Spi-1 x IRF8 x NTP-Stat1 complex to the LILRE, which primes the gene for immediate induction following IRF8 phosphorylation. Phosphorylation of chromatin pre-associated factors like IRF8 may be an important strategy for the rapid transcriptional activation of genes involved in innate immunity.

Natural and synthetic TLR7 ligands inhibit CpG-A- and CpG-C-oligodeoxynucleotide-induced IFN-alpha production

Plasmacytoid dendritic cells (pDCs) are unique with respect to their capacity to produce unsurpassed amounts of IFN-alpha and coexpress TLR7 and TLR9, mediating IFN-alpha production. Although TLRs are critical receptors of innate immunity, little is known about the immunological effects of TLR7/TLR9 costimulation. We have analyzed the effects of TLR7/TLR9 costimulation on IFN-alpha production by leukocytes and pDCs. Our experiments revealed that both synthetic (resiquimod and loxoribine) and natural (ssRNA40) TLR7 ligands abrogate CpG-A- and CpG-C-oligodeoxynucleotide (ODN)-induced IFN-alpha production by human leukocytes. Because TLR7 ligands themselves represent important IFN-alpha inducers, we demonstrated that substimulatory TLR7 ligand concentrations significantly inhibited CpG-A-induced IFN-alpha. Delayed addition of TLR7 ligands still resulted in complete suppression of CpG-A-ODN-induced IFN-alpha production, suggesting that the inhibition is unlikely to be caused by a kinetic uptake advantage. Unlike for CpG-A and CpG-C, TLR7 ligands did not inhibit CpG-B-ODN-induced IFN-alpha production. Experiments with purified human pDCs demonstrated that the inhibitory effects of TLR7/TLR9 costimulation were mediated directly by pDCs. Suppression of IFN-alpha production was not related to increased cell death and was also detectable in enriched mouse pDCs. Analyses of pDCs suggested that the TLR7 signal regulates the outcome of TLR7 ligand/CpG-A-ODN costimulation and can either inhibit (IFN-alpha) or promote (IL-8/CD40) cytokine and surface marker expression. Our data reveal for the first time a strong inhibitory effect of TLR7 stimulation on IFN-alpha production induced by CpG-A- and CpG-C-ODNs. These findings provide novel insight into the effects of TLR7/TLR9 costimulation and may support the development of novel TLR9 inhibitors.

Role of TLR4 tyrosine phosphorylation in signal transduction and endotoxin tolerance

In this study, we examined whether tyrosine phosphorylation of the Toll-IL-1 resistance (TIR) domain of Toll-like receptor (TLR) 4 is required for signaling and blocked in endotoxin tolerance. Introduction of the P712H mutation, responsible for lipopolysaccharide (LPS) unresponsiveness of C3H/HeJ mice, into the TIR domain of constitutively active mouse DeltaTLR4 and mutation of the homologous P714 in human CD4-TLR4 rendered them signaling-incompetent and blocked TLR4 tyrosine phosphorylation. Mutations of tyrosine residues Y674A and Y680A within the TIR domains of CD4-TLR4 impaired its ability to elicit phosphorylation of p38 and JNK mitogen-activated protein kinases, IkappaB-alpha degradation, and activation of NF-kappaB and RANTES reporters. Likewise, full-length human TLR4 expressing Y674A or Y680A mutations showed suppressed capacities to mediate LPS-inducible cell activation. Signaling deficiencies of the Y674A and Y680A TLR4s correlated with altered MyD88-TLR4 interactions, increased associations with a short IRAK-1 isoform, and decreased amounts of activated IRAK-1 in complex with TLR4. Pretreatment of human embryonic kidney (HEK) 293/TLR4/MD-2 cells with protein tyrosine kinase or Src kinase inhibitors suppressed LPS-driven TLR4 tyrosine phosphorylation, p38 and NF-kappaB activation. TLR2 and TLR4 agonists induced TLR tyrosine phosphorylation in HEK293 cells overexpressing CD14, MD-2, and TLR4 or TLR2. Induction of endotoxin tolerance in HEK293/TLR4/MD-2 transfectants and in human monocytes markedly suppressed LPS-mediated TLR4 tyrosine phosphorylation and recruitment of Lyn kinase to TLR4, but did not affect TLR4-MD-2 interactions. Thus, our data demonstrate that TLR4 tyrosine phosphorylation is important for signaling and is impaired in endotoxin-tolerant cells, and suggest involvement of Lyn kinase in these processes.

Glial-cytokine-neuronal interactions underlying the mechanisms of persistent pain

The emerging literature implicates a role for glia/cytokines in persistent pain. However, the mechanisms by which these non-neural elements contribute to CNS activity-dependent plasticity and pain are unclear. Using a trigeminal model of inflammatory hyperalgesia, here we provide evidence that demonstrates a mechanism by which glia interact with neurons, leading to activity-dependent plasticity and hyperalgesia. In response to masseter inflammation, there was an upregulation of glial fibrillary acidic proteins (GFAPs), a marker of astroglia, and interleukin-1beta (IL-1beta), a prototype proinflammatory cytokine, in the region of the trigeminal nucleus specifically related to the processing of deep orofacial input. The activated astroglia exhibited hypertrophy and an increased level of connexin 43, an astroglial gap junction protein. The upregulated IL-1beta was selectively localized to astrocytes but not to microglia and neurons. Local anesthesia of the masseter nerve prevented the increase in GFAP and IL-1beta after inflammation, and substance P, a prototype neurotransmitter of primary afferents, induced similar increases in GFAP and IL-1beta, which was blocked by a nitric oxide synthase inhibitor N(G)-nitro-L-arginine methyl ester. Injection of IL-1 receptor antagonist and fluorocitrate, a glial inhibitor, attenuated hyperalgesia and NMDA receptor phosphorylation after inflammation. In vitro application of IL-1beta induced NR1 phosphorylation, which was blocked by an IL-1 receptor antagonist, a PKC inhibitor (chelerythrine), an IP3 receptor inhibitor (2-aminoethoxydiphenylborate), and inhibitors of phospholipase C [1-[6-((17b-3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl]-1H-pyrrole-2,5-dione] and phospholipase A2 (arachidonyltrifluoromethyl ketone). These findings provide evidence of astroglial activation by tissue injury, concomitant IL-1beta induction, and the coupling of NMDA receptor phosphorylation through IL-1 receptor signaling.

Signal transduction in monocytes: the role of zinc ions

The availability of zinc has a regulatory role in the immune system. It can have either pro- or anti-inflammatory effects, which both seem to be a consequence of a direct interaction of zinc with the cytokine secretion by monocytes. In this review, the molecular basis for this effect, the interaction of zinc with the signal transduction of monocytes, is discussed. In particular, zinc seems to activate or inhibit several signaling pathways that interact with the signal transduction of pathogen sensing receptors, the so-called Toll-like receptors (TLR), which sense pathogen-derived molecular structures and, upon activation, lead to secretion of pro-inflammatory cytokines. The interaction of zinc with protein tyrosine phosphatases and protein kinase C, and a direct modulation of lipopolysaccharide binding to its receptor (TLR-4) all result in enhanced cytokine production. On the other hand, a complex interaction between zinc, NO and cyclic nucleotide signaling, and inhibition of interleukin-1 receptor associated kinase-1, and inhibitor of kappa B kinase all counteract the production of pro-inflammatory cytokines. A role for the zinc binding protein metallothionein as a regulator for intracellular zinc signaling is discussed. By acting on all these signaling molecules, the zinc status of monocytes can have a direct effect on inflammation.

Targeting bacterial endotoxin: two sides of a coin

The term sepsis describes a potentially lethal clinical condition that develops as a result of a dysregulated host response to bacterial infection. The most common bacterial component implicated in initiating the septic syndrome is a cell wall molecule derived from Gram-negative bacteria, known as lipopolysaccharide (LPS) or endotoxin. Like all mammals, humans are equipped with an LPS-sensing machinery consisting, primarily, of LPS-binding protein (LBP), CD14, a glycosylphosphatidylinositol (GPI)-anchored monocyte differentiation antigen, and toll-like receptor 4 (TLR4), a signal-transducing integral membrane protein. Modest stimulation of TLR4 facilitates the elimination of invading microorganisms. Potent TLR4 stimulation, however, produces severe reactions in the host, often leading to multiple organ failure and death. The search for pharmaceuticals that reduce mortality in septic patients has been a painstaking process. Thus far, only a few compounds have been found to significantly reduce mortality rates. Perhaps one of the more promising therapeutic strategies currently pursued is based on the identification of synthetic or naturally occurring substances that neutralize LPS or inhibit LPS-mediated activation of host immune cells, such as monocytes and macrophages. Here, we describe a number of diverse molecular structures with a capacity to either enhance or blunt LPS-induced monocyte activation. The underlying molecular mechanisms are discussed.

Gene expression profiles differentiate between sterile SIRS and early sepsis

INTRODUCTION

The systemic inflammatory response syndrome (SIRS) occurs frequently in critically ill patients and presents similar clinical appearances despite diverse infectious and noninfectious etiologies. Despite similar phenotypic expression, these diverse SIRS etiologies may induce divergent genotypic expressions. We hypothesized that gene expression differences are present between sepsis and uninfected SIRS prior to the clinical appearance of sepsis.

METHODS

Critically ill uninfected SIRS patients were followed longitudinally for the development of sepsis. All patients had whole blood collected daily for gene expression analysis by Affymetrix Hg_U133 2.0 Plus microarrays. SIRS patients developing sepsis were compared with those remaining uninfected for differences in gene expression at study entry and daily for 3 days prior to conversion to sepsis. Acceptance criteria for differentially expressed genes required: >1.2 median fold change between groups and significance on univariate and multivariate analysis. Differentially expressed genes were annotated to pathways using DAVID 2.0/EASE analysis.

RESULTS

A total of 12,782 (23.4%) gene probes were differentially expressed on univariate analysis 0 to 48 hours before clinical sepsis. 626 (1.1%) probes met acceptance criteria, corresponding to 459 unique genes, 65 (14.2%) down and 395 (85.8%) up expressed. These genes annotated to 10 pathways that functionally categorized to 4 themes involving innate immunity, cytokine receptors, T cell differentiation, and protein synthesis regulation.

CONCLUSIONS

Sepsis has a unique gene expression profile that is different from uninfected inflammation and becomes apparent prior to expression of the clinical sepsis phenotype.

IRAK-4 kinase activity is required for interleukin-1 (IL-1) receptor- and toll-like receptor 7-mediated signaling and gene expression

IRAK-4 is an essential component of the signal transduction complex downstream of the IL-1- and Toll-like receptors. Although regarded as the first kinase in the signaling cascade, the role of IRAK-4 kinase activity versus its scaffold function is still controversial. To investigate the role of IRAK-4 kinase function in vivo, "knock-in" mice were generated by replacing the wild type IRAK-4 gene with a mutant gene encoding kinase-deficient IRAK-4 protein (IRAK-4 KD). IRAK-4 kinase was rendered inactive by mutating the conserved lysine residues in the ATP pocket essential for coordinating ATP. Analyses of embryonic fibroblasts and macrophages obtained from IRAK-4 KD mice demonstrate lack of cellular responsiveness to stimulation with IL-1beta or a Toll-like receptor 7 (TLR7) agonist. IRAK-4 kinase deficiency prevents the recruitment of IRAK-1 to the IL-1 receptor complex and its subsequent phosphorylation and degradation. IRAK-4 KD cells are severely impaired in NFkappaB, JNK, and p38 activation in response to IL-1beta or TLR7 ligand. As a consequence, IL-1 receptor/TLR7-mediated production of cytokines and chemokines is largely absent in these cells. Additionally, microarray analysis identified IL-1beta response genes and revealed that the induction of IL-1beta-responsive mRNAs is largely ablated in IRAK-4 KD cells. In summary, our results suggest that IRAK-4 kinase activity plays a critical role in IL-1 receptor (IL-1R)/TLR7-mediated induction of inflammatory responses.

Interleukin-1beta-driven inflammation promotes the development and invasiveness of chemical carcinogen-induced tumors

The role of microenvironment interleukin 1 (IL-1) on 3-methylcholanthrene (3-MCA)-induced carcinogenesis was assessed in IL-1-deficient mice, i.e., IL-1beta(-/-), IL-1alpha(-/-), IL-1alpha/beta(-/-) (double knockout), and mice deficient in the naturally occurring inhibitor of IL-1, the IL-1 receptor antagonist (IL-1Ra). Tumors developed in all wild-type (WT) mice, whereas in IL-1beta-deficient mice, tumors developed slower and only in some of the mice. In IL-1Ra-deficient mice, tumor development was the most rapid. Tumor incidence was similar in WT and IL-1alpha-deficient mice. Histologic analyses revealed fibrotic structures forming a capsule surrounding droplets of the carcinogen in olive oil, resembling foreign body-like granulomas, which appeared 10 days after injection of 3-MCA and persisted until the development of local tumors. A sparse leukocyte infiltrate was found at the site of carcinogen injection in IL-1beta-deficient mice, whereas in IL-1Ra-deficient mice, a dense neutrophilic infiltrate was observed. Treatment of IL-1Ra-deficient mice with recombinant IL-1Ra but not with an inhibitor of tumor necrosis factor abrogated the early leukocytic infiltrate. The late leukocyte infiltrate (day 70), which was dominated by macrophages, was also apparent in WT and IL-1alpha-deficient mice, but was nearly absent in IL-1beta-deficient mice. Fibrosarcoma cell lines, established from 3-MCA-induced tumors from IL-1Ra-deficient mice, were more aggressive and metastatic than lines from WT mice; cell lines from IL-1-deficient mice were the least invasive. These observations show the crucial role of microenvironment-derived IL-1beta, rather than IL-1alpha, in chemical carcinogenesis and in determining the invasive potential of malignant cells.

IL-1beta induces alkaline phosphatase in human phagocytes

BACKGROUND

Alkaline phosphatase (ALPase) is found in blood plasma or serum and leukocytes and regulates intercellular processes, maintaining phosphoryl metabolites in a steady state, as well as synthesizing and hydrolyzing phosphate esters on membranes. ALPase supervises the active transport of inorganic phosphates, fats, proteins, carbohydrates and the sodium/potassium pump mechanisms. The formed elements of blood such as polymorphonuclear (PMNs) leucocytes, macrophages (MP) and some lymphocytes are high in ALPase concentrations.

METHODS

In this study we have tested whether the interleukin-1 receptor antagonist (IL-lra) could influence ALPase generation in IL-1beta or lipopolysaccharide (LPS)-stimulated neutrophils and MP. Human neutrophils were isolated from heparin-anticoagulated blood drawn from healthy individuals by centrifugation in a two-step gradient, Ficoll-Hypaque. ALPase activity was assessed spectrophotometrically in test tubes containing isolated neutrophils and adherence PBMCs treated with LPS, IL-1beta and IL-1ra, alone or in combination.

RESULTS

IL-lbeta or LPS enhanced ALPase in both PMNs and MP, whereas IL-1ra could not inhibit ALPase activity. We performed time course experiments at 0 min, 5 min, 1 h, 24 h, and 43 h (LPS 20 microg/mL, IL-1beta 10 ng/mL). No significant increase in ALPase activity was seen until 1 h; however, there was a rapid rise over the next few hours. In another set of experiments using IL-1ra (500 ng/mL), there was no difference between treated cells and control cells. The combination of IL-1beta plus IL-1ra did not reduce the ability of IL-1beta to induce ALPase activity.

CONCLUSIONS

These data suggest that IL-1beta stimulates ALPase through other mechanisms than the release of arachidonic acid products, which are inhibited by IL-lra.

Immunomodulatory drug CC-4047 is a cell-type and stimulus-selective transcriptional inhibitor of cyclooxygenase 2

COX2 (prostaglandin G/H synthase, PTGS2) is a well-validated target in the fields of both oncology and inflammation. Despite their significant toxicity profile, non-steroidal anti-inflammatory drugs (NSAIDs) have become standard of care in the treatment of many COX2-mediated inflammatory conditions. In this report, we show that one IMiDs((R)) immunomodulatory drug, CC-4047, can reduce the levels of COX2 and the production of prostaglandins (PG) in human LPS-stimulated monocytes. The inhibition of COX2 by CC-4047 occurs at the level of gene transcription, by reducing the LPS-stimulated transcriptional activity at the COX2 gene. Because it is a transcriptional rather than an enzymatic inhibitor of COX2, CC-4047 inhibition of PG production is not susceptible to competition by exogenous arachadonic acid (AA). The distinct mechanisms of action allow CC-4047 and a COX2-selective NSAID to work additively to block PG secretion from monocytes. CC-4047 does not, however, block COX2 induction in or prostacyclin secretion from IL-1beta stimulated human umbilical vein endothelial cells (HUVEC) cells, nor does it inhibit COX1 in either monocytes or HUVEC cells. CC-4047 also inhibits COX2 and PG production in monocytes derived from patients with sickle cell disease (SCD). Taken together, the data in this manuscript suggest CC-4047 will provide important anti-inflammatory benefit to patients and will improve the safety of NSAIDs in the treatment of SCD or other inflammatory conditions.

The death domain of IRAK-1: an oligomerization domain mediating interactions with MyD88, Tollip, IRAK-1, and IRAK-4

Ligand binding in the Toll-like/interleukin-1 receptor family results in the recruitment of an intracellular signaling complex. IRAK-1, which is centrally involved in this complex, is able to homo-oligomerize and to bind to Tollip and the adapters MyD88 and IRAK-4. The interactions of IRAK-1 with MyD88 or Tollip are mediated by the N-terminal part of IRAK-1, containing the death domain with the highly conserved threonine at position 66 (T66). Mutation of this amino acid into alanine or aspartic acid stabilized binding to MyD88, Tollip, and IRAK-4, allowing the definitive experimental proof, that all these interactions are mediated by the death domain of IRAK-1. Homo-oligomerization of IRAK-1, which is mediated by the death domain too, is not affected by mutation of T66. Finally, mutation of IRAK-1 at T66 not only allowed stable binding to the signaling adapters, but also enhanced its signaling capacity.

Toll-like receptor 4 polymorphism is associated with coronary stenosis but not with the occurrence of acute or old myocardial infarctions

OBJECTIVE

Atherosclerosis is considered to be a chronic inflammatory disease. Toll-like receptor 4 (TLR-4), a key mediator in activating inflammatory cascade, has an A-to-G functional polymorphism that changes aspartic acid to glycine at position 299. TLR-4 is activated by, for example, lipopolysaccharides. The purpose of this study was to investigate the role of a common Asp299Gly polymorphism of the TLR-4 gene in atherosclerosis.

MATERIAL AND METHODS

The study comprised autopsy material from 657 men (the Helsinki Sudden Death Study; mean age 53, range 33-70 years).

RESULTS

Fewer G-allele carriers had 3-vessel coronary artery disease compared with AA homozygotes (OR 0.32; 95 % CI, 0.12-0.88, p = 0.027), and they also had a lower mean value for maximal coronary stenosis (p = 0.019). TLR-4 polymorphism was not significantly associated with the occurrence of acute or old myocardial infarction (MI).

CONCLUSIONS

The G allele of the TLR-4 gene, which is associated with a lower inflammation response, was associated with a lower risk of coronary stenosis but not with the occurrence of MI and hence is not a major factor in the development of coronary atherosclerosis.

Interleukin-1beta-induced insulin resistance in adipocytes through down-regulation of insulin receptor substrate-1 expression

Inflammation is associated with obesity and insulin resistance. Proinflammatory cytokines produced by adipose tissue in obesity could alter insulin signaling and action. Recent studies have shown a relationship between IL-1beta level and metabolic syndrome or type 2 diabetes. However, the ability of IL-1beta to alter insulin signaling and action remains to be explored. We demonstrated that IL-1beta slightly increased Glut 1 translocation and basal glucose uptake in 3T3-L1 adipocytes. Importantly, we found that prolonged IL-1beta treatment reduced the insulin-induced glucose uptake, whereas an acute treatment had no effect. Chronic treatment with IL-1beta slightly decreased the expression of Glut 4 and markedly inhibited its translocation to the plasma membrane in response to insulin. This inhibitory effect was due to a decrease in the amount of insulin receptor substrate (IRS)-1 but not IRS-2 expression in both 3T3-L1 and human adipocytes. The decrease in IRS-1 amount resulted in a reduction in its tyrosine phosphorylation and the alteration of insulin-induced protein kinase B activation and AS160 phosphorylation. Pharmacological inhibition of ERK totally inhibited IL-1beta-induced down-regulation of IRS-1 mRNA. Moreover, IRS-1 protein expression and insulin-induced protein kinase B activation, AS160 phosphorylation, and Glut 4 translocation were partially recovered after treatment with the ERK inhibitor. These results demonstrate that IL-1beta reduces IRS-1 expression at a transcriptional level through a mechanism that is ERK dependent and at a posttranscriptional level independently of ERK activation. By targeting IRS-1, IL-1beta is capable of impairing insulin signaling and action, and could thus participate in concert with other cytokines, in the development of insulin resistance in adipocytes.

Contribution of GM-CSF on the enhancement of the T cell-stimulating activity of macrophages

Mycobacterium leprae is an intracellular parasitic organism that multiplies in macrophages (MØ). It inhibits the fusion of mycobacterial phagosome with lysosome and induces interleukin (IL)-10 production from macrophages. However, macrophages are heterogenous in various aspects. We examined macrophages that differentiated from monocytes using either recombinant (r) granulocyte-MØ colony-stimulating factor (GM-CSF) (these MØ are named as GM-MØ) or rMØ colony-stimulating factor (M-CSF) (cells named as M-MØ) in terms of the T cell-stimulating activity. Although both macrophages phagocytosed the mycobacteria equally, GM-MØ infected with M. leprae and subsequently treated with IFN-gamma- and CD40 ligand (L) stimulated T cells to produce interferon-gamma (IFN-gamma), but M-MØ lacked the ability to stimulate T cells. While M-MØ mounted a massive IL-10 production, GM-MØ did not produce the cytokine on infection with M. leprae. M. leprae-infected, IFN-gamma- and CD40L-treated GM-MØ expressed a higher level of HLA-DR and CD86 Ags than those of M-MØ, and expressed one of the dominant antigenic molecules of M. leprae, Major Membrane Protein-II on their surface. These results indicate that GM-CSF, but not M-CSF, contributes to the up-regulation of the T cell-stimulating activity of M. leprae-infected macrophages.

Involvement of phosphatidylinositol-phospholipase C in immune response to Salmonella lipopolysacharide in chicken macrophage cells (HD11)

The activation of phospholipases is one of the earliest key events in receptor-mediated cellular responses to a number of extracellular signaling molecules. Lipopolysaccharide (LPS) is a principle component of the outer membrane of Gram-negative bacteria and a prime target for recognition by the innate immune system. In the present study, we evaluated the role of specific phospholipase in the activation of a chicken macrophage cell line HD11 by LPS. Activation of HD11 cells by LPS results in induction of nitric oxide (NO). Using selective inhibitors, we have identified that phosphatidylinositol (PI)-phospholipase C (PI-PLC), but not phosphatidylcholine (PC)-phospholipase C (PC-PLC) nor PC-phospholipase D (PC-PLD), was required for LPS-induced NO production. Preincubation with PI-PLC selective inhibitors (U-73122 and ET-18-OCH3) abrogated LPS-induced NO production in HD11 cells, whereas PC-PLC inhibitor (D609), phosphatide phosphohydrolase inhibitor (propranolol), and PC-PLD inhibitor (n-butanol) had no inhibitory effects. We also showed that inhibition of protein kinase C (PKC) by selective inhibitors Ro 31-8220 and calphostin C and chelating intracellular Ca2+ by BAPTA-AM significantly reduced NO production in LPS-stimulated HD11 cells. Our results demonstrate that PI-PLC plays a critical role, most likely through activation of PKC pathway, in TLR4 mediated immune responses of avian macrophage cells to LPS.

HMGB1 signals through toll-like receptor (TLR) 4 and TLR2

In response to bacterial endotoxin (e.g., LPS) or endogenous proinflammatory cytokines (e.g., TNF and IL-1beta), innate immune cells release HMGB1, a late cytokine mediator of lethal endotoxemia and sepsis. The delayed kinetics of HMGB1 release makes it an attractive therapeutic target with a wider window of opportunity for the treatment of lethal systemic inflammation. However, the receptor(s) responsible for HMGB1-mediated production of proinflammatory cytokines has not been well characterized. Here we demonstrate that in human whole blood, neutralizing antibodies against Toll-like receptor 4 (TLR4, but not TLR2 or receptor for advanced glycation end product) dose-dependently attenuate HMGB1-induced IL-8 release. Similarly, in primary human macrophages, HMGB1-induced TNF release is dose-dependently inhibited by anti-TLR4 antibodies. In primary macrophages from knockout mice, HMGB1 activates significantly less TNF release in cells obtained from MyD88 and TLR4 knockout mice as compared with cells from TLR2 knockout and wild-type controls. However, in human embryonic kidney 293 cells transfected with TLR2 or TLR4, HMGB1 effectively induces IL-8 release only from TLR2 overexpressing cells. Consistently, anti-TLR2 antibodies dose-dependently attenuate HMGB1-induced IL-8 release in human embryonic kidney/TLR2-expressing cells and markedly reduce HMGB1 cell surface binding on murine macrophage-like RAW 264.7 cells. Taken together, our data suggest that there is a differential usage of TLR2 and TLR4 in HMGB1 signaling in primary cells and in established cell lines, adding complexity to studies of HMGB1 signaling which was not previously expected.

Regulation and function of IKK and IKK-related kinases

Members of the nuclear factor kappa B (NF-kappaB) family of dimeric transcription factors (TFs) regulate expression of a large number of genes involved in immune responses, inflammation, cell survival, and cancer. NF-kappaB TFs are rapidly activated in response to various stimuli, including cytokines, infectious agents, and radiation-induced DNA double-strand breaks. In nonstimulated cells, some NF-kappaB TFs are bound to inhibitory IkappaB proteins and are thereby sequestered in the cytoplasm. Activation leads to phosphorylation of IkappaB proteins and their subsequent recognition by ubiquitinating enzymes. The resulting proteasomal degradation of IkappaB proteins liberates IkappaB-bound NF-kappaB TFs, which translocate to the nucleus to drive expression of target genes. Two protein kinases with a high degree of sequence similarity, IKKalpha and IKKbeta, mediate phosphorylation of IkappaB proteins and represent a convergence point for most signal transduction pathways leading to NF-kappaB activation. Most of the IKKalpha and IKKbeta molecules in the cell are part of IKK complexes that also contain a regulatory subunit called IKKgamma or NEMO. Despite extensive sequence similarity, IKKalpha and IKKbeta have largely distinct functions, due to their different substrate specificities and modes of regulation. IKKbeta (and IKKgamma) are essential for rapid NF-kappaB activation by proinflammatory signaling cascades, such as those triggered by tumor necrosis factor alpha (TNFalpha) or lipopolysaccharide (LPS). In contrast, IKKalpha functions in the activation of a specific form of NF-kappaB in response to a subset of TNF family members and may also serve to attenuate IKKbeta-driven NF-kappaB activation. Moreover, IKKalpha is involved in keratinocyte differentiation, but this function is independent of its kinase activity. Several years ago, two protein kinases, one called IKKepsilon or IKK-i and one variously named TBK1 (TANK-binding kinase), NAK (NF-kappaB-activated kinase), or T2K (TRAF2-associated kinase), were identified that exhibit structural similarity to IKKalpha and IKKbeta. These protein kinases are important for the activation of interferon response factor 3 (IRF3) and IRF7, TFs that play key roles in the induction of type I interferon (IFN-I). Together, the IKKs and IKK-related kinases are instrumental for activation of the host defense system. This Review focuses on the functions of IKK and IKK-related kinases and the molecular mechanisms that regulate their activities.

The impact of interferon-beta treatment on the blood-brain barrier

Changes in the blood-brain barrier (BBB) are crucial to the pathogenesis of multiple sclerosis (MS). There are currently few established treatments for MS, and interferon-beta (IFN-beta) therapy is one of the most promising - proposed to act as an immunomodulator of the cytokine network reducing inflammatory damage. However, there is increasing evidence that direct effects on the BBB could also be relevant. This review surveys the evidence that IFN-beta stabilizes the BBB, and that this process itself might be the key target. Understanding IFN-beta-derived changes at the BBB will not only provide new insights in the pathogenesis of MS but will also be helpful to develop new, more-specific drugs for MS treatment.

Immunobiology of Toll-like receptors: emerging trends

Toll-like receptors (TLR), a family of evolutionarily conserved pathogen recognition receptors, play pivotal role as primary sensors of invading pathogens. TLR identify molecular motifs of infectious agents (pathogen associated molecular patterns) and elicit an effective defensive response against them. Mammalian TLR derive their name from the Drosophila Toll protein, with which they share sequence similarity. So far, expression of 10 TLR is known in humans. The adaptor proteins, myeloid differentiation factor 88 and Toll IL-1 receptor (TIR) domain containing adaptor inducing IFN-beta (TRIF) are the key players in the TLR signalling cascade leading to the activation of nuclear factor (NF)-kappaB and interferon regulatory factor-3, respectively. Targeted manipulation of the TLR signalling pathway has immense therapeutic potential and may eventually prove to be a boon in the development of innovative treatments for diverse disease conditions. There is accumulating evidence that TLR agonists have tremendous potential as novel therapeutic targets. In this review, we have discussed the immunobiology of TLR and emphasize significant advances made within the ever-expanding field of TLR that provide intriguing insights efficacious in unravelling the complexities associated with TLR.

Smad6 negatively regulates interleukin 1-receptor-Toll-like receptor signaling through direct interaction with the adaptor Pellino-1

Transforming growth factor-beta1 (TGF-beta1) is a potent cytokine with pleiotropic effects, including anti-inflammatory activity. Here we show that the signaling protein Smad6 bound to Pellino-1, an adaptor protein of mammalian interleukin 1 receptor (IL-1R)-associated kinase 1 (IRAK1), and thereby promoted TGF-beta-mediated anti-inflammatory effects. Smad6-Pellino-1 interaction abrogated signaling mediated by a complex of IRAK1, Pellino-1 and adaptor protein TRAF6 that formed after stimulation by IL-1beta treatment. Blockade of IRAK1-Pellino-1-TRAF6 signaling prevented degradation of the inhibitor IkappaBalpha and subsequent nuclear translocation of transcription factor NF-kappaB and thus expression of proinflammatory genes. 'Knockdown' of endogenous Smad6 expression by RNA interference reduced anti-inflammatory activity mediated by TGF-beta1 or the TGF-beta family member BMP-4. Thus Smad6 is a critical mediator of the TGF-beta-BMP pathway that mediates anti-inflammatory activity and negatively regulates IL-1R-Toll-like receptor signals.

Impaired maturation and function of dendritic cells by mycobacteria through IL-1beta

Dendritic cells (DC) are pivotal for initiation and regulation of innate and adaptive immune responses evoked by vaccination and natural infection. After infection, mycobacterial pathogens first encounter monocytes, which produce pro-inflammatory cytokines, including IL-1beta, TNF-alpha and IL-6. The role of these cytokines in DC maturation remains incompletely understood. Here, we show that maturation of DC from monocytes was impaired by pretreatment of monocytes with low doses of IL-1beta. Under these conditions, Mycobacterium leprae-infected DC failed to stimulate antigen-specific T cell responses. Expression of CD86 and CD83 and production of IL-12 in response to lipopolysaccharide and peptidoglycan were diminished. In contrast, these DC functions were not impaired by pretreatment with TNF-alpha, IL-6 or IL-10. When monocytes were infected with M. bovis Bacillus Calmette-Guérin, and subsequently differentiated to DC, the activity of these DC was suppressed as well. Thus, IL-1beta acts at early stages of differentiation of DC and impairs biological functions of DC at later stages. Therefore, production of IL-1beta by mycobacteria-infected antigen-presenting cells counteracts effective stimulation of innate and adaptive immune responses.

Extending the nuclear roles of IkappaB kinase subunits

The transcription factor NF-kappaB plays a key role in a wide variety of cellular processes such as innate and adaptive immunity, cellular proliferation, apoptosis and development. In unstimulated cells, NF-kappaB is sequestered in the cytoplasm through its tight association with inhibitory proteins called IkappaBs, comprising notably IkappaBalpha. A key step in NF-kappaB activation is the phosphorylation of IkappaBalpha by the so-called IkappaB kinase (IKK) complex, which targets the inhibitory protein for proteasomal degradation and allows the freed NF-kappaB to enter the nucleus where it can transactivate its target genes. The IKK complex is composed of two catalytic subunits called IKKalpha and IKKbeta, and a regulatory subunit called NEMO/IKKgamma. Despite their key role in mediating IkappaBalpha phosphorylation in the cytoplasm, recent works have provided evidence that IKK subunits also translocate into the nucleus to regulate NF-kappaB-dependent and -independent gene expression, paving the way of a novel and exciting field of research. In this review, we will describe the current knowledge in that research area.

PKC-δ mediates activation of ERK1/2 and induction of iNOS by IL-1β in vascular smooth muscle cells

Although the inflammatory cytokine interleukin-1β (IL-β) is an important regulator of gene expression in vascular smooth muscle (VSM), the signal transduction pathways leading to transcriptional activation upon IL-1β stimulation are poorly understood. Recent studies have implicated IL-1β-mediated ERK1/2 activation in the upregulation of type II nitric oxide synthase (iNOS) in VSM. We report that these events are mediated in a phospholipase C (PLC)- and protein kinase C (PKC)-δ-dependent manner utilizing a signaling mechanism independent of p21ras (Ras) and Raf1 activation. Stimulation of rat aortic VSM cells with IL-1β activated PLC-γ and pharmacological inhibition of PLC attenuated IL-1β-induced ERK1/2 activation and subsequent iNOS expression. Stimulation with IL-1β activated PKC-α and -δ, which was blocked using the PLC inhibitor U-73122. Pharmacological studies using isoform-specific PKC inhibitors and adenoviral overexpression of constitutively active PKC-δ indicated that ERK1/2 activation was PKC-α independent and PKC-δ dependent. Similarly, adenoviral overexpression of constitutively activated PKC-δ enhanced iNOS expression. IL-1β stimulation did not induce either Ras or Raf1 activity. The absence of a functional role for Ras and Raf1 related to ERK1/2 activation and iNOS expression was further confirmed by adenoviral overexpression of dominant-negative Ras and treatment with the Raf1 inhibitor GW5074. Taken together, we have outlined a novel transduction pathway implicating PKC-δ as a critical component of the IL-1-dependent activation of ERK in VSM cells.

NF-kappaB activation by reactive oxygen species: fifteen years later

The transcription factor NF-kappaB plays a major role in coordinating innate and adaptative immunity, cellular proliferation, apoptosis and development. Since the discovery in 1991 that NF-kappaB may be activated by H(2)O(2), several laboratories have put a considerable effort into dissecting the molecular mechanisms underlying this activation. Whereas early studies revealed an atypical mechanism of activation, leading to IkappaBalpha Y42 phosphorylation independently of IkappaB kinase (IKK), recent findings suggest that H(2)O(2) activates NF-kappaB mainly through the classical IKK-dependent pathway. The molecular mechanisms leading to IKK activation are, however, cell-type specific and will be presented here. In this review, we also describe the effect of other ROS (HOCl and (1)O(2)) and reactive nitrogen species on NF-kappaB activation. Finally, we critically review the recent data highlighting the role of ROS in NF-kappaB activation by proinflammatory cytokines (TNF-alpha and IL-1beta) and lipopolysaccharide (LPS), two major components of innate immunity.

Binding specificity of Toll-like receptor cytoplasmic domains

MyD88 participates in signal transduction by binding to the cytoplasmic Toll/IL-1 receptor (TIR) domains of activated Toll-like receptors (TLR). Yeast two-hybrid experiments reveal that the TIR domains of human TLR differ in their ability to associate with MyD88: The TIR of TLR2 binds to MyD88 but the TIR of the closely related TLR1, 6, or 10 do not. Using chimeric TIR domains, we define the critical region responsible for differential MyD88 binding, and use a computational analysis of the critical region to reveal the amino acids that differ between MyD88 binders and non-binders. Remarkably, a single missense mutation created in TLR1 (N672D) confers on it the ability to bind MyD88, without affecting its association with other proteins. Mutations identified as critical for MyD88 binding also affect signaling of TLR pairs in mammalian cells. To investigate the difference between MyD88 binders and non-binders, we identify novel interacting proteins for each cytoplasmic domain of TLR1, 2, 6, and 10. For example, heat shock protein (HSP)60 binds to TLR1 but not to TLR2, and HSP60 and MyD88 appear to bind the same region of the TIR domain. In summary, interactions between the TLR, MyD88, and novel associated proteins have been characterized.

MyD88 mediates neutrophil recruitment initiated by IL-1R but not TLR2 activation in immunity against Staphylococcus aureus

MyD88 is an important signaling adaptor for both TLR and IL-1R family members. Here, we evaluated the role of TLR2/MyD88 and IL-1R/MyD88 signaling in host defense against S. aureus by using a cutaneous infection model in conjunction with bioluminescent bacteria. We found that lesions of S. aureus-infected MyD88- and IL-1R-deficient mice were substantially larger with higher bacterial counts compared with wild-type mice. In contrast, TLR2-deficient mice had lesions that were only moderately larger with minimally higher bacterial counts. In addition, MyD88- and IL-1R- but not TLR2-deficient mice had severely decreased recruitment of neutrophils to the site of infection. This neutrophil recruitment was not dependent upon IL-1R/MyD88 signaling by recruited bone marrow-derived cells, suggesting that resident skin cells utilize IL-1R/MyD88 signaling to promote neutrophil recruitment.

NFkappaB signaling is induced by the oncoprotein Tio through direct interaction with TRAF6

The transcription factor NFkappaB is a major regulator of genes involved in inflammation and oncogenesis. NFkappaB is induced upon stimulation of cellular receptors coupled to different intracellular signaling molecules. Further downstream, TRAF6 links at least two receptor pathways to take control of IkappaB, the administrator of NFkappaB activity. Here we report on a strong NFkappaB activation by Tio, a unique herpesviral oncoprotein promoting transformation of human T cells in a Src-kinase-dependent manner. NFkappaB induction by Tio is independent of Src-kinase interaction and tyrosine phosphorylation of Tio. Mutation of a glutamic acid-rich motif at the N terminus of Tio, corresponding to a TRAF6 consensus binding motif, completely abrogated NFkappaB activation. Cotransfection of a dominant negative TRAF6 construct led to a decrease in NFkappaB activation. Furthermore, we provide evidence that TRAF6 directly binds to the Tio oncoprotein. Identification of TRAF6 as the direct target of Tio describes a novel mechanism for the constitutive activation of NFkappaB through an oncoprotein.

Phenol/water extract of Treponema socranskii subsp. socranskii as an antagonist of Toll-like receptor 4 signalling

Treponema socranskii is one of the most frequently found oral spirochaetes in periodontitis and endodontic infections. LPS or glycolipids from bacteria are potent stimulators of innate immune and inflammatory systems. In this study the bioactivity of a phenol/water extract from T. socranskii subsp. socranskii (TSS-P) was analysed. TSS-P showed minimal endotoxicity and no inducing potential for proinflammatory cytokines (TNF-α and IL-8) or for intercellular adhesion molecule-1 (ICAM-1) in human monocyte cell line THP-1 cells and primary cultured human gingival fibroblasts. Rather, it inhibited ICAM-1 expression and IL-8 secretion from cells stimulated by the LPS of Escherichia coli and Actinobacillus actinomycetemcomitans, which are known to be Toll-like receptor 4 (TLR4) agonists. However, this antagonistic activity was not shown in cells stimulated by peptidoglycan or IL-1β. As its antagonistic mechanism, TSS-P blocked the binding of E. coli LPS to LPS-binding protein (LBP) and CD14, which are molecules involved in the recruitment of LPS to the cell membrane receptor complex TLR4–MD-2 for the intracellular signalling of LPS. TSS-P itself did not bind to MD-2 or THP-1 cells, but inhibited the binding of E. coli LPS to MD-2 or to the cells in the presence of serum (which could be replaced by recombinant human LBP and recombinant human CD14). The results suggest that TSS-P acts as an antagonist of TLR4 signalling by interfering with the functioning of LBP/CD14.

Potentiation of caspase-1 activation by the P2X7 receptor is dependent on TLR signals and requires NF-kappaB-driven protein synthesis

The proinflammatory cytokines IL-1beta and IL-18 are inactive until cleaved by the enzyme caspase-1. Stimulation of the P2X7 receptor (P2X7R), an ATP-gated ion channel, triggers rapid activation of caspase-1. In this study we demonstrate that pretreatment of primary and Bac1 murine macrophages with TLR agonists is required for caspase-1 activation by P2X7R but it is not required for activation of the receptor itself. Caspase-1 activation by nigericin, a K+/H+ ionophore, similarly requires LPS priming. This priming by LPS is dependent on protein synthesis, given that cyclohexamide blocks the ability of LPS to prime macrophages for activation of caspase-1 by the P2X7R. This protein synthesis is likely mediated by NF-kappaB, as pretreatment of cells with the proteasome inhibitor MG132, or the IkappaB kinase inhibitor Bay 11-7085 before LPS stimulation blocks the ability of LPS to potentiate the activation of caspase-1 by the P2X7R. Thus, caspase-1 regulation in macrophages requires inflammatory stimuli that signal through the TLRs to up-regulate gene products required for activation of the caspase-1 processing machinery in response to K+-releasing stimuli such as ATP.