The interleukin-1 receptor/Toll-like receptor superfamily: signal transduction during inflammation and host defense

Structural insights into the assembly and activation of IL-1β with its receptors

Interleukin 1β (IL-1β) is a key orchestrator of inflammation and host defense that exerts its effects through IL-1 receptor type I (IL-1RI) and IL-1 receptor accessory protein (IL-1RAcP). How IL-1RAcP is recruited by IL-1β-IL-1RI to form the signaling-competent complex remains elusive. Here we present the crystal structure of IL-1β bound to IL-1 receptor type II (IL-1RII) and IL-1RAcP. IL-1β-IL-1RII generated a composite binding surface to recruit IL-1RAcP. Biochemical analysis demonstrated that IL-1β-IL-1RI and IL-1β-IL-1RII interacted similarly with IL-1RAcP. It also showed the importance of two loops of IL-1 receptor antagonist (IL-1Ra) in determining its antagonism. Our results provide a structural basis for assembly and activation of the IL-1 receptor and offer a general cytokine-receptor architecture that governs the IL-1 family of cytokines.

Type I IL-1 receptor (IL-1RI) as potential new therapeutic target for bronchial asthma

The IL-1R/TLR family has been receiving considerable attention as potential regulators of inflammation through their ability to act as either activators or suppressors of inflammation. Asthma is a chronic inflammatory disease characterized by airway hyperresponsiveness, allergic inflammation, elevated serum total, allergen-specific IgE levels, and increased Th2 cytokine production. The discovery that the IL-1RI–IL-1 and ST2–IL-33 pathways are crucial for allergic inflammation has raised interest in these receptors as potential targets for developing new therapeutic strategies for bronchial asthma. This paper discusses the current use of neutralizing mAb or soluble receptor constructs to deplete cytokines, the use of neutralizing mAb or recombinant receptor antagonists to block cytokine receptors, and gene therapy from experimental studies in asthma. Targeting IL-1RI–IL-1 as well as ST2–IL-33 pathways may promise a disease-modifying approach in the future.

Enhancement of phagocytic activity of macrophage-like cells by pyrogallol-type green tea polyphenols through caspase signaling pathways

We investigated the phagocytosis-enhancing activity of green tea polyphenols, such as epigallocatechin gallate (EGCG), epigallocatechin (EGC), epicatechin gallate (ECG), epicatechin (EC) catechin (+C) and strictinin, using VD3-differentiated HL60 cells. EGCG, EGC, ECG and strictinin, but not EC and +C, increased the phagocytic activity of macrophage-like cells, and a caspase inhibitor significantly inhibited phagocytic activities. These results suggest that the pyrogallol-type structure in green tea polyphenols may be important for enhancement of the phagocytic activity through caspase signaling pathways.

Functional expression of IgG-Fc receptors in human airway smooth muscle cells

IgE-Fc receptors and IgG-Fc receptors are expressed on hematopoietic cells, but some evidence suggests that these receptors are also found on nonhematopoietic cells, including human airway smooth muscle (hASM) cells. Our study characterizes the expression of IgE-Fc receptors (FcεRI/CD23) and IgG-Fc receptors (FcγRs-I, -II, and -III) in cultured hASM cells by flow cytometry and Western blotting, and the functional activity of receptors was determined through quantification of cell proliferation and released cytokines. Expression of Fc receptor-linked intracellular signaling proteins and phosphorylation of the mitogen-activated protein kinases (MAPKs) extracellular signal-regulated kinase 1/2 and p38(MAPK) in hASM cells was examined by Western blotting. Expression of FcεRI and CD23 was not detectable in hASM cells. However, FcγRI and FcγRII were shown to be expressed on these cells. Specific antibodies, validated using transfected cell lines, revealed that the inhibitory IgG receptor, FcγRIIb, was the most abundant Fc receptor subtype expressed. Although cross-linking FcγR with heat-aggregated γ globulin (HAGG) did not induce detectable cell stimulation, pretreating hASM cells with HAGG significantly inhibited IL-1α-induced increases in cytokine levels and basic fibroblast growth factor-induced cell proliferation. This inhibitory effect of HAGG was abrogated by preincubation of cells with an anti-FcγRIIb antigen-binding fragment (Fab). Expression of proteins involved in the canonical FcγRIIb inhibitory signaling pathway was established in hASM cells. Pretreatment of hASM cells with HAGG significantly inhibited IL-1α- and basic fibroblast growth factor-induced extracellular signal-regulated kinase 1/2 and p38(MAPK) phosphorylation. This study identifies functional expression of FcγRIIb in hASM cells, with the potential to suppress their remodeling and immunomodulatory roles.

Helical assembly in the MyD88-IRAK4-IRAK2 complex in TLR/IL-1R signalling

MyD88, IRAK4 and IRAK2 are critical signalling mediators of the TLR/IL1-R superfamily. Here we report the crystal structure of the MyD88-IRAK4-IRAK2 death domain (DD) complex, which surprisingly reveals a left-handed helical oligomer that consists of 6 MyD88, 4 IRAK4 and 4 IRAK2 DDs. Assembly of this helical signalling tower is hierarchical, in which MyD88 recruits IRAK4 and the MyD88-IRAK4 complex recruits the IRAK4 substrates IRAK2 or the related IRAK1. Formation of these Myddosome complexes brings the kinase domains of IRAKs into proximity for phosphorylation and activation. Composite binding sites are required for recruitment of the individual DDs in the complex, which are confirmed by mutagenesis and previously identified signalling mutations. Specificities in Myddosome formation are dictated by both molecular complementarity and correspondence of surface electrostatics. The MyD88-IRAK4-IRAK2 complex provides a template for Toll signalling in Drosophila and an elegant mechanism for versatile assembly and regulation of DD complexes in signal transduction.

Computational modeling with forward and reverse engineering links signaling network and genomic regulatory responses: NF-kappaB signaling-induced gene expression responses in inflammation

Background

Signal transduction is the major mechanism through which cells transmit external stimuli to evoke intracellular biochemical responses. Diverse cellular stimuli create a wide variety of transcription factor activities through signal transduction pathways, resulting in different gene expression patterns. Understanding the relationship between external stimuli and the corresponding cellular responses, as well as the subsequent effects on downstream genes, is a major challenge in systems biology. Thus, a systematic approach is needed to integrate experimental data and theoretical hypotheses to identify the physiological consequences of environmental stimuli.

Results

We proposed a systematic approach that combines forward and reverse engineering to link the signal transduction cascade with the gene responses. To demonstrate the feasibility of our strategy, we focused on linking the NF-κB signaling pathway with the inflammatory gene regulatory responses because NF-κB has long been recognized to play a crucial role in inflammation. We first utilized forward engineering (Hybrid Functional Petri Nets) to construct the NF-κB signaling pathway and reverse engineering (Network Components Analysis) to build a gene regulatory network (GRN). Then, we demonstrated that the corresponding IKK profiles can be identified in the GRN and are consistent with the experimental validation of the IKK kinase assay. We found that the time-lapse gene expression of several cytokines and chemokines (TNF-α, IL-1, IL-6, CXCL1, CXCL2 and CCL3) is concordant with the NF-κB activity profile, and these genes have stronger influence strength within the GRN. Such regulatory effects have highlighted the crucial roles of NF-κB signaling in the acute inflammatory response and enhance our understanding of the systemic inflammatory response syndrome.

Conclusion

We successfully identified and distinguished the corresponding signaling profiles among three microarray datasets with different stimuli strengths. In our model, the crucial genes of the NF-κB regulatory network were also identified to reflect the biological consequences of inflammation. With the experimental validation, our strategy is thus an effective solution to decipher cross-talk effects when attempting to integrate new kinetic parameters from other signal transduction pathways. The strategy also provides new insight for systems biology modeling to link any signal transduction pathways with the responses of downstream genes of interest.

ERK activation by GM-CSF reduces effectiveness of p38 inhibitor on inhibiting TNFalpha release

Tumor necrosis factor alpha (TNFalpha), a pro-inflammatory factor, plays an important role in many inflammatory diseases. Inhibition of p38 is being pursued as a pharmaceutical treatment to reduce TNFalpha release. Since a variety of cytokines and factors may exist at different amounts in patients, we explored how differences in the cytokine environment impact p38 inhibitor potency. Cytokine co-stimulation with LPS was compared against LPS stimulation alone. In both differentiated U937 cells and peripheral monocytes, GM-CSF co-stimulation with LPS increased TNFalpha release and led to an increased residual TNFalpha levels with p38 inhibitor. Adding MEK inhibitor in the presence of p38 inhibitor further reduced TNFalpha release suggesting that the ERK pathway plays a role in GM-CSF induced reduction of the p38 inhibitor potency. When cells were stimulated with different concentrations of LPS and GM-CSF, the minimal TNFalpha level obtained by MEK inhibitor was not dependent on the stimulation condition; while it was dependent on GM-CSF level for p38 inhibitor. TNFalpha release in the presence of combinations of p38 and MEK inhibitors under different stimulation conditions was measured. A linear model was created using the initial relative ERK and p38 phosphorylation levels and p38 and MEK inhibitor concentrations to accurately predict released TNFalpha level, suggesting these four parameters are sufficient to predict TNFalpha levels. We then used the model to show that with same TNFalpha levels, higher ERK pathway activity reduces p38 inhibitor potency. These results suggest that p38 inhibitor will be a more potent anti-TNFalpha therapy for patients with low ERK pathway activity.

Role of cytokines as mediators and regulators of microglial activity in inflammatory demyelination of the CNS

As the resident innate immune cells of the central nervous system (CNS), microglia fulfil a critical role in maintaining tissue homeostasis and in directing and eliciting molecular responses to CNS damage. The human disease Multiple Sclerosis and animal models of inflammatory demyelination are characterized by a complex interplay between degenerative and regenerative processes, many of which are regulated and mediated by microglia. Cellular communication between microglia and other neural and immune cells is controlled to a large extent by the activity of cytokines. Here we review the role of cytokines as mediators and regulators of microglial activity in inflammatory demyelination, highlighting their importance in potentiating cell damage, promoting neuroprotection and enhancing cellular repair in a context-dependent manner.

MyD88-dependent TLR4 signaling is selectively impaired in alveolar macrophages from asymptomatic HIV+ persons

Alveolar macrophages (AMs) are the predominant effector cell in the lungs and contribute to a critical first line of defense against bacterial pathogens through recognition by pattern recognition receptors such as Toll-like receptor 4 (TLR4). TLR4-mediated tumor necrosis factor alpha (TNFalpha) release is significantly impaired in HIV(+) macrophages, but whether HIV impairs myeloid differentiation factor 88 (MyD88)-dependent and/or MyD-independent TLR4 signaling pathways in human macrophages is not known. Comparing human U937 macrophages with HIV(+) U1 macrophages (HIV-infected U937 subclone), the current study shows that HIV infection is associated with impaired macrophage TLR4-mediated signaling, specifically targeting the MyD88-dependent TLR4-mediated signaling pathway (reduced MyD88-interleukin-1 receptor-associated kinase [IRAK] interaction, IRAK phosphorylation, nuclear factor [NF]-kappaB nuclear translocation, and TNFalpha release) while preserving the MyD88-independent TLR4-mediated signaling pathway (preserved STAT1 phosphorylation, interferon regulatory factor [IRF] nuclear translocation, and interleukin-10 [IL-10] and RANTES release). Extracellular TLR4 signaling complex was intact (similar levels of CD14 and MD2), and similar patterns of response were observed in clinically relevant AMs from healthy and asymptomatic HIV(+) persons at high clinical risk of pneumonia. Taken together, these data support the concept that chronic HIV infection is associated with specific and targeted disruption of critical macrophage TLR4 signaling, which in turn may contribute to disease pathogenesis of bacterial pneumonia.

[Role of toll-like receptors in respiratory diseases]

There has been growing interest in the last 10 years in the study of innate immunity, in particular because of the possible role that toll-like receptors (TLR) may play in the pathogenesis of some respiratory disease such as for example, asthma, chronic obstructive pulmonary disease, and infections. TLR are a family of type 1 transmembrane proteins, responsible for recognizing molecular patterns associated with pathogens (PAMP, pathogen-associated molecular patterns), and expressed by a broad spectrum of infectious agents. This recognition leads to quick production of cytokines and chemokines which provides a long-lasting adaptive response to the pathogen. Currently, it is considered that the administration of drugs which modulate the activity of these receptors upwards or downwards may represent major therapeutic progress for handling these diseases. The aim of this review is to describe the different TLS, define their possible role in the pathogenesis of the main respiratory diseases and finally, speculate over the therapeutic possibilities which their modulation, agonist or antagonist, offers as possible therapeutic targets.

Tumor progression locus 2 (Map3k8) is critical for host defense against Listeria monocytogenes and IL-1 beta production

Tumor progression locus 2 (Tpl2, also known as Map3k8 and Cot) is a serine-threonine kinase critical in innate immunity, linking toll-like receptors (TLRs) to TNF production through its activation of ERK. Tpl2(-/-) macrophages have abrogated TNF production but overproduce IL-12 in response to TLR ligands. Despite enhanced IL-12 production, Tpl2(-/-) T cells have impaired IFN-gamma production. Therefore, the role of Tpl2 in a bona fide bacterial infection where all of these cytokines are important in host defense is unclear. To address this issue, we infected Tpl2(-/-) mice with the model pathogen Listeria monocytogenes. We found that Tpl2(-/-) mice infected i.v. with L. monocytogenes had increased pathogen burdens compared with wild-type mice and rapidly succumbed to infection. Enhanced susceptibility correlated with impaired signaling through TLR2 and nucleotide-binding oligomerization domain 2, two receptors previously shown to mediate Listeria recognition. Surprisingly, TNF production in response to infection was not significantly impaired, even though Tpl2 has been implicated in the regulation of TNF. We found that the role of Tpl2 has cell-type specific effects in regulating TNF and transduces signals from some, but not all, pattern recognition receptors (PRR). In contrast to the cell-type- and receptor-specific regulation of TNF, we found that Tpl2 is essential for IL-1beta production from both macrophages and dendritic cells. These studies implicate Tpl2 as an important mediator for collaboration of pattern recognition receptors with danger-associated molecular patterns to induce TNF and IL-1beta production and optimal host defense.

Identification of full length bovine TLR1 and functional characterization of lipopeptide recognition by bovine TLR2/1 heterodimer

Toll-like receptors (TLR) are highly conserved pattern recognition receptors of the innate immune system. Toll-like receptor 2 (TLR2) recognizes bacterial lipopeptides in a heterodimeric complex with TLR6 or TLR1, thereby discriminating between di- or triacylated lipopeptides, respectively. Previously, we found that HEK293 cells transfected with bovine TLR2 (boTLR2) were able to respond to diacylated lipopeptides but did not recognize triacylated lipopeptides, even after cotransfection with the so far published sequence of boTLR1. In this study we now could show that primary bovine cells were in general able to detect triacylated lipopetides. A closer investigation of the boTLR1 gene locus revealed an additional ATG 195 base pairs upstream from the published start codon. Its transcription would result in an N-terminus with high identity to human and murine TLR1 (huTLR1, muTLR1). Cloning and cotransfection of this longer boTLR1 with boTLR2 now resulted in the recognition of triacylated lipopeptides by HEK293 cells, thereby resembling the ex vivo observation. Analysis of the structure-activity relationship showed that the ester-bound acid chains of these lipopeptides need to consist of at least 12 carbon atoms to activate the bovine heterodimer showing similarity to the recognition by huTLR2/huTLR1. In contrast, HEK293 cell cotransfected with muTLR2 and muTLR1 could already be activated by lipopeptides with shorter fatty acids of only 6 carbon atoms. Thus, our data indicate that the additional N-terminal nucleotides belong to the full length and functionally active boTLR1 (boTLR1-fl) which participates in a species-specific recognition of bacterial lipopeptides.

MSK1 regulates the transcription of IL-1ra in response to TLR activation in macrophages

The activity of the pro-inflammatory cytokine IL (interleukin)-1 is closely regulated in vivo via a variety of mechanisms, including both the control of IL-1 production and secretion as well as naturally occurring inhibitors of IL-1 function, such as IL-1ra (IL-1 receptor antagonist). IL-1ra is homologous with IL-1, and is able to bind but not activate the IL-1 receptor. IL-1ra can be produced by a variety of cell types, and its production is stimulated by inflammatory signals. In the present study, we show that in macrophages the TLR (Toll-like receptor)-mediated induction of IL-1ra from both its proximal and distal promoters involves the p38 and ERK1/2 (extracellular-signal-regulated kinase 1/2) MAPK (mitogen-activated protein kinase) cascades. In addition, we show that MSK1 and 2 (mitogen- and stress-activated kinase 1 and 2), kinases activated by either ERK1/2 or p38 in vivo, are required for the induction of both IL-1ra mRNA and protein. MSKs regulate IL-1ra transcription via both IL-10-dependent and -independent mechanisms in cells. Consistent with this, knockout of MSK in mice was found to result in a decrease in IL-1ra production following LPS (lipopolysaccharide) injection. MSKs therefore act as important negative regulators of inflammation following TLR activation.

The remedial effect of soluble interleukin-1 receptor type II on endometriosis in the nude mouse model

OBJECTIVE

Recent studies have shown that the local expression of soluble interleukin (IL) -1 receptor type II (sIL-1 RII) in endometrial tissue of women with endometriosis is decreased, and the depression of IL-1 RII was more significant in infertile women than that in fertile women with endometriosis. In this research, we investigated the remedial effect of sIL-1-RII administration on endometriosis in the nude mouse model.

METHODS

NINETEEN NUDE MODEL MICE WITH ENDOMETRIOSIS WERE RANDOMLY DIVIDED INTO THREE GROUPS: group A was treated by intraperitoneal administration with only sIL-1 RII for two weeks, group B was similarly treated with only IL-1, and group C (control) was administered saline . After 2 weeks, the size of the ectopic endometrial lesions was calculated, and the expression of vascular endothelial growth factor (VEGF) and B-cell lymphoma leukemia-2 (Bcl-2) were detected by immunohistochemistry. The IL-8 and VEGF levels in the peritoneal fluid (PF) and serum were also measured by enzyme-linked immunosorbent assay (ELISA).

RESULTS

The mean size of ectopic endometrial lesion did not differ between the three groups (P > 0.05). Compared with the control, the expression of VEGF and Bcl-2 was significantly lower in group A, and higher in group B. In the three groups, the levels of IL-8 in the PF and serum were highest in group A, and lowest in group B.

CONCLUSION

sIL-1 RII may suppresse hyperplasia of ectopic endometriosis, perhaps by reducing the expression of certain cytokines, such as VEGF, IL-8, and Bcl-2, which could provide a new clinical strategy for the treatment of endometriosis.

Lysine 63-linked polyubiquitination of TAK1 at lysine 158 is required for tumor necrosis factor alpha- and interleukin-1beta-induced IKK/NF-kappaB and JNK/AP-1 activation

Transforming growth factor-beta-activated kinase 1 (TAK1) plays an essential role in the tumor necrosis factor alpha (TNFalpha)- and interleukin-1beta (IL-1beta)-induced IkappaB kinase (IKK)/nuclear factor-kappaB (NF-kappaB) and c-Jun N-terminal kinase (JNK)/activator protein 1 (AP-1) activation. Here we report that TNFalpha and IL-1beta induce Lys(63)-linked TAK1 polyubiquitination at the Lys(158) residue within the kinase domain. Tumor necrosis factor receptor-associated factors 2 and 6 (TRAF2 and -6) act as the ubiquitin E3 ligases to mediate Lys(63)-linked TAK1 polyubiquitination at the Lys(158) residue in vivo and in vitro. Lys(63)-linked TAK1 polyubiquitination at the Lys(158) residue is required for TAK1-mediated IKK complex recruitment. Reconstitution of TAK1-deficient mouse embryo fibroblast cells with TAK1 wild type or a TAK1 mutant containing a K158R mutation revealed the importance of this site in TNFalpha and IL-1beta-mediated IKK/NF-kappaB and JNK/AP-1 activation as well as IL-6 gene expression. Our findings demonstrate that Lys(63)-linked polyubiquitination of TAK1 at Lys(158) is essential for its own kinase activation and its ability to mediate its downstream signal transduction pathways in response to TNFalpha and IL-1beta stimulation.

Use of human bronchial epithelial cells (BEAS-2B) to study immunological markers resulting from exposure to PM(2.5) organic extract from Puerto Rico

Fine particulate air pollutants, mainly their organic fraction, have been demonstrated to be associated with cardiovascular and respiratory health problems. Puerto Rico has been reported to have the highest prevalence of pulmonary diseases (e.g., asthma) in the United States. The aim of this study was to assess, for the first time, the immunological response of human bronchial epithelial cells (BEAS-2B) to organic extracts isolated from airborne particulate matter (PM(2.5)) in Puerto Rico. Organic extracts from PM(2.5) collected throughout an 8-month period (2000-2001) were pooled (composite) in order to perform chemical analysis and biological activity testing. BEAS-2B cells were exposed to PM(2.5) organic extract to assess cytotoxicity, levels of cytokines and relative gene expression of MHC-II, hPXR and CYP3A5. Our findings show that organic PM(2.5) consist of toxic as well as bioactive components that can regulate the secretion of cytokines in BEAS-2B, which could modulate inflammatory response in the lung. Trace element analyses confirmed the presence of metals in organic extracts highlighting the relative high abundance of Cu and Zn in polar organic extracts. Polar organic extracts exhibited dose-dependant toxicity and were found to significantly induce the release of interleukin 6 (IL-6), IL-1beta and IL-7 while significantly inhibiting the secretion of IL-8, G-CSF and MCP-1. Moreover, MHC-II transcriptional activity was up-regulated after 24 h of exposure, whereas PXR and CYP3A5 were down-regulated. This research provides a new insight into the effects of PM(2.5) organic fractions on specific effectors and their possible role in the development of respiratory inflammatory diseases in Puerto Rico.

Adjuvant effects for oral immunization provided by recombinant Lactobacillus casei secreting biologically active murine interleukin-1{beta}

Vaccine delivery systems using lactic acid bacteria are under development, but their efficiency is insufficient. Autologous cytokines, such as interleukin-1beta (IL-1beta), are potential adjuvants for mucosal vaccines and can be provided by recombinant lactic acid bacteria. The aim of this study was the construction and evaluation of recombinant Lactobacillus casei producing IL-1beta as an adjuvant delivery agent. The recombinant strain was constructed using an expression/secretion vector plasmid, including a mature IL-1beta gene from mouse. The biological activity of the cytokine was confirmed by IL-8 production from Caco-2 cells. In response to the recombinant L. casei secreting IL-1beta, expression of IL-6 was detected in vivo using a ligated-intestinal-loop assay. The release of IL-6 from Peyer's patch cells was also detected in vitro. Intragastric immunization with heat-killed Salmonella enterica serovar Enteritidis (SE) in combination with IL-1beta-secreting lactobacilli resulted in relatively high SE-specific antibody production. In this study, it was demonstrated that recombinant L. casei secreting bioactive murine IL-1beta provided adjuvant effects for intragastric immunization.

Evaluation of candidate genes in a genome-wide association study of childhood asthma in Mexicans

BACKGROUND

More than 200 asthma candidate genes have been examined in human association studies or identified with knockout mouse approaches. However, many have not been systematically replicated in human populations, especially those containing a large number of tagging single nucleotide polymorphisms (SNPs).

OBJECTIVE

We comprehensively evaluated the association of previously implicated asthma candidate genes with childhood asthma in a Mexico City population.

METHODS

From the literature, we identified candidate genes with at least 1 positive report of association with asthma phenotypes in human subjects or implicated in asthma pathogenesis using knockout mouse experiments. We performed a genome-wide association study in 492 asthmatic children aged 5 to 17 years and both parents using the Illumina HumanHap 550v3 BeadChip. Separate candidate gene analyses were performed for 2933 autosomal SNPs in the 237 selected genes by using the log-linear method with a log-additive risk model.

RESULTS

Sixty-one of the 237 genes had at least 1 SNP with a P value of less than .05 for association with asthma. The 9 most significant results were observed for rs2241715 in the gene encoding TGF-beta1 (TGFB1; P = 3.3 x 10(-5)), rs13431828 and rs1041973 in the gene encoding IL-1 receptor-like 1 (IL1RL1; P = 2 x 10(-4) and 3.5 x 10(-4)), 5 SNPs in the gene encoding dipeptidyl-peptidase 10 (DPP10; P = 1.6 x 10(-4) to 4.5 x 10(-4)), and rs17599222 in the gene encoding cytoplasmic FMR1 interacting protein 2 (CYFIP2; P = 4.1 x 10(-4)). False discovery rates were less than 0.1 for all 9 SNPs. Multimarker analysis identified TGFB1, IL1RL1, the gene encoding IL-18 receptor 1 (IL18R1), and DPP10 as the genes most significantly associated with asthma.

CONCLUSIONS

This comprehensive analysis of literature-based candidate genes suggests that SNPs in several candidate genes, including TGFB1, IL1RL1, IL18R1, and DPP10, might contribute to childhood asthma susceptibility in a Mexican population.

Interleukin-1beta increases gap junctional communication among synovial fibroblasts via the extracellular-signal-regulated kinase pathway

BACKGROUND INFORMATION

The gap junction protein, Cx43 (connexin 43), has been implicated in the aetiology of osteoarthritis. Studies have revealed that the size and number of gap junctions increase in synovial biopsies from patients with osteoarthritis. Furthermore, pharmacological inhibition of Cx43 function has been shown to reduce IL-1beta (interleukin-1beta)-induced metalloproteinase production by synovial fibroblasts in vitro.

RESULTS

In the present study, we examined the link between IL-1beta and Cx43 function. We demonstrated that treatment of a rabbit synovial fibroblast cell line with IL-1beta markedly increased the level of the Cx43 protein in a concentration- and time-dependent manner. The impact on Cx43 protein levels appeared to occur post-transcriptionally, as mRNA levels are unaffected by IL-1beta administration. Additionally, we showed by fluorescence microscopy that IL-1beta alters the cellular distribution of Cx43 to cell-cell junctions and is concomitant with a striking increase in gap junction communication. Furthermore, we demonstrated that the increase in Cx43 protein, and the associated change in protein localization and gap junction communication following IL-1beta treatment, are dependent upon activation of the ERK (extracellular-signal-regulated kinase) signalling cascade.

CONCLUSION

These data show that IL-1beta acts through the ERK signalling cascade to alter the expression and function of Cx43 in synovial fibroblasts.

Lipid rafts and caveolin-1 coordinate interleukin-1beta (IL-1beta)-dependent activation of NFkappaB by controlling endocytosis of Nox2 and IL-1beta receptor 1 from the plasma membrane

Recent evidence suggests that signaling by the proinflammatory cytokine interleukin-1beta (IL-1beta) is dependent on reactive oxygen species derived from NADPH oxidase. Redox signaling in response to IL-1beta is known to require endocytosis of its cognate receptor (IL-1R1) following ligand binding and the formation of redox-active signaling endosomes that contain Nox2 (also called redoxosomes). The consequent generation of reactive oxygen species by redoxosomes is responsible for the downstream recruitment of IL-1R1 effectors (IRAK, TRAF6, and IkappaB kinase kinases) and ultimately for activation of the transcription factor NFkappaB. Despite this knowledge of the signaling events that occur downstream of redoxosome formation, an understanding of the mechanisms that coordinate the genesis of redoxosomes following IL-1beta stimulation has been lacking. Here, we demonstrate that lipid rafts play an important role in this process. We show that Nox2 and IL-1R1 localize to plasma membrane lipid rafts in the unstimulated state and that IL-1beta signals caveolin-1-dependent endocytosis of both proteins into the redoxosome. We also show that inhibiting lipid raft-mediated endocytosis prevents NFkappaB activation. Finally, we demonstrate that Vav1, a Rac1 guanine exchange factor and activator of Nox2, is recruited to lipid rafts following IL-1beta stimulation and that it is required for NFkappaB activation. Our results fill in an important mechanistic gap in the understanding of early IL-1R1 and Nox2 signaling events that control NFkappaB activation, a redox-dependent process important in inflammation.

Requirement for nuclear factor kappa B signalling in the interleukin-1-induced expression of the CCAAT/enhancer binding protein-delta gene in hepatocytes

Elevated circulating levels of acute phase proteins (APP) are associated with inflammation and inflammatory disorders such as cardiovascular disease. APP are mainly synthesised by hepatocytes and their transcription is induced by pro-inflammatory cytokines such as interleukin-1 (IL-1). The molecular mechanisms underlying the IL-1-induced expression of key transcription factors implicated in the regulation of APP are poorly understood. We have investigated this aspect using the CCAAT/enhancer binding protein-delta (C/EBPdelta) as a model gene. IL-1 induced the expression of C/EBPdelta mRNA and protein in the human hepatoma Hep3B cell line, a widely employed model system for studies on cytokine signalling in relation to the expression of APP. The IL-1-mediated induction of C/EBPdelta expression was attenuated in the presence of pharmacological inhibitors against c-Jun N-terminal kinase (JNK) (curcumin and SP600125), casein kinase 2 (CK2) (apigenin) and nuclear factor-kappaB (NF-kappaB) (NF-kappaB activation inhibitor). RNA interference assays showed significant attenuation of the IL-1-induced expression of C/EBPdelta following knockdown of the p50 and p65 subunits of NF-kappaB. IL-1 induced NF-kappaB DNA binding and activation by this transcription factor and this was attenuated by curcumin and apigenin. Taken together, these results suggest a potentially crucial role for NF-kappaB in the IL-1-induced expression of C/EBPdelta, and thereby downstream APP genes regulated by this transcription factor.

[Role of toll-like receptors in respiratory diseases]

There has been growing interest in the last 10 years in the study of innate immunity, in particular because of the possible role that toll-like receptors (TLR) may play in the pathogenesis of some respiratory diseases including, asthma, chronic obstructive pulmonary disease, and infections. TLR are a family of type 1 transmembrane proteins, responsible for recognising molecular patterns associated with pathogens (PAMP, pathogen-associated molecular patterns), and expressed by a broad spectrum of infectious agents. This recognition leads to a quick production of cytokines and chemokines which provides a long-lasting adaptive response to the pathogen. At present, it is considered //It is currently considered that the administration of drugs which modulate the activity of these receptors upwards or downwards may represent major therapeutic progress for handling these diseases.

The aim of this review is to describe the different TLS, define their possible role in the pathogenesis of the main respiratory diseases and finally, speculate over the therapeutic possibilities which their modulation, agonist or antagonist, offers as possible therapeutic targets.

A novel role for IkappaBzeta in the regulation of IFNgamma production

IkappaBzeta is a novel member of the IkappaB family of NFkappaB regulators, which modulates NFkappaB activity in the nucleus, rather than controlling its nuclear translocation. IkappaBzeta is specifically induced by IL-1beta and several TLR ligands and positively regulates NFkappaB-mediated transcription of genes such as IL-6 and NGAL as an NFkappaB binding co-factor. We recently reported that the IL-1 family cytokines, IL-1beta and IL-18, strongly synergize with TNFalpha for IFNgamma production in KG-1 cells, whereas the same cytokines alone have minimal effects on IFNgamma production. Given the striking similarities between the IL-1R and IL-18R signaling pathways we hypothesized that a common signaling event or gene product downstream of these receptors is responsible for the observed synergy. We investigated IkappaBzeta protein expression in KG-1 cells upon stimulation with IL-1beta, IL-18 and TNFalpha. Our results demonstrated that IL-18, as well as IL-1beta, induced moderate IkappaBzeta expression in KG-1 cells. However, TNFalpha synergized with IL-1beta and IL-18, whereas by itself it had a minimal effect on IkappaBzeta expression. NFkappaB inhibition resulted in decreased IL-1beta/IL-18/TNFalpha-stimulated IFNgamma release. Moreover, silencing of IkappaBzeta expression led to a specific decrease in IFNgamma production. Overall, our data suggests that IkappaBzeta positively regulates NFkappaB-mediated IFNgamma production in KG-1 cells.

Protein-tyrosine phosphatase-alpha and Src functionally link focal adhesions to the endoplasmic reticulum to mediate interleukin-1-induced Ca2+ signaling

Calcium (Ca2+) signaling by the pro-inflammatory cytokine interleukin-1 (IL-1) is dependent on focal adhesions, which contain diverse structural and signaling proteins including protein phosphatases. We examined here the role of protein-tyrosine phosphatase (PTP) alpha in regulating IL-1-induced Ca2+ signaling in fibroblasts. IL-1 promoted recruitment of PTPalpha to focal adhesions and endoplasmic reticulum (ER) fractions, as well as tyrosine phosphorylation of the ER Ca2+ release channel IP3R. In response to IL-1, catalytically active PTPalpha was required for Ca2+ release from the ER, Src-dependent phosphorylation of IP3R1 and accumulation of IP3R1 in focal adhesions. In pulldown assays and immunoprecipitations PTPalpha was required for the association of PTPalpha with IP3R1 and c-Src, and this association was increased by IL-1. Collectively, these data indicate that PTPalpha acts as an adaptor to mediate functional links between focal adhesions and the ER that enable IL-1-induced Ca2+ signaling.

TLR2-dependent inhibition of macrophage responses to IFN-gamma is mediated by distinct, gene-specific mechanisms

Mycobacterium tuberculosis uses multiple mechanisms to avoid elimination by the immune system. We have previously shown that M. tuberculosis can inhibit selected macrophage responses to IFN-γ through TLR2-dependent and -independent mechanisms. To specifically address the role of TLR2 signaling in mediating this inhibition, we stimulated macrophages with the specific TLR2/1 ligand Pam₃CSK₄ and assayed responses to IFN-γ. Pam₃CSK₄ stimulation prior to IFN-γ inhibited transcription of the unrelated IFN-γ-inducible genes, CIITA and CXCL11. Surface expression of MHC class II and secretion of CXCL11 were greatly reduced as well, indicating that the reduction in transcripts had downstream effects. Inhibition of both genes required new protein synthesis. Using chromatin immunoprecipitation, we found that TLR2 stimulation inhibited IFN-γ-induced RNA polymerase II binding to the CIITA and CXCL11 promoters. Furthermore, TATA binding protein was unable to bind the TATA box of the CXCL11 promoter, suggesting that assembly of transcriptional machinery was disrupted. However, TLR2 stimulation affected chromatin modifications differently at each of the inhibited promoters. Histone H3 and H4 acetylation was reduced at the CIITA promoter but unaffected at the CXCL11 promoter. In addition, NF-κB signaling was required for inhibition of CXCL11 transcription, but not for inhibition of CIITA. Taken together, these results indicate that TLR2-dependent inhibition of IFN-γ-induced gene expression is mediated by distinct, gene-specific mechanisms that disrupt binding of the transcriptional machinery to the promoters.

Activated macrophages induce hepcidin expression in HuH7 hepatoma cells

BACKGROUND

Hepcidin is an iron regulatory peptide produced by the liver in response to inflammation and elevated systemic iron. Recent studies suggest that circulating monocytes and resident liver macrophages--Küpffer cells--may influence both basal and inflammatory expression of hepcidin.

DESIGN AND METHODS

We used an in vitro co-culture model to investigate hepatocyte hepcidin regulation in the presence of activated THP1 macrophages. HuH7 hepatoma cells were co-cultured with differentiated THP1 macrophages for 24 h prior to the measurement of HuH7 hepcidin (HAMP) mRNA expression using quantitative polymerase chain reaction, and HAMP promoter activity using a luciferase reporter assay. Luciferase assays were performed using the wild type HAMP promoter, and constructs containing mutations in BMP/SMAD4, STAT3, C/EBP and E-BOX response elements. Neutralizing antibodies against interleukin-6, interleukin-1beta , and the bone morphogenetic protein inhibitor noggin were used to identify the macrophage-derived cytokines involved in the regulation of HAMP expression.

RESULTS

Co-culturing HuH7 cells with differentiated THP1 cells induced HAMP promoter activity and endogenous HAMP mRNA expression maximally after 24 h. This induction was fully neutralized in the presence of an interleukin-1beta antibody, and fully attenuated by mutations of the proximal C/EBP or BMP/SMAD4 response elements.

CONCLUSIONS

Our data suggest that the interleukin-1beta and bone morphogenetic protein signaling pathways are central to the regulation of HAMP expression by macrophages in this co-culture model.

Inflammatory cytokines IL-1β and TNF-α regulate p75NTR expression in CNS neurons and astrocytes by distinct cell-type-specific signalling mechanisms

The p75^NTR (where NTR is neurotrophin receptor) can mediate many distinct cellular functions, including cell survival and apoptosis, axonal growth and cell proliferation, depending on the cellular context. This multifunctional receptor is widely expressed in the CNS (central nervous system) during development, but its expression is restricted in the adult brain. However, p75^NTR is induced by a variety of pathophysiological insults, including seizures, lesions and degenerative disease. We have demonstrated previously that p75^NTR is induced by seizures in neurons, where it induces apoptosis, and in astrocytes, where it may regulate proliferation. In the present study, we have investigated whether the inflammatory cytokines IL (interleukin)-1β and TNF-α (tumour necrosis factor-α), that are commonly elevated in these pathological conditions, mediate the regulation of p75^NTR in neurons and astrocytes. We have further analysed the signal transduction pathways by which these cytokines induce p75^NTR expression in the different cell types, specifically investigating the roles of the NF-κB (nuclear factor κB) and p38 MAPK (mitogen-activated protein kinase) pathways. We have demonstrated that both cytokines regulate p75^NTR expression; however, the mechanisms governing this regulation are cytokine- and cell-type specific. The distinct mechanisms of cytokine-mediated p75^NTR regulation that we demonstrate in the present study may facilitate therapeutic intervention in regulation of this receptor in a cell-selective manner.

Modulation of TLR signaling by multiple MyD88-interacting partners including leucine-rich repeat Fli-I-interacting proteins

Emerging evidences suggest TLR-mediated signaling is tightly regulated by a specific chain of intracellular protein-protein interactions, some of which are yet to be identified. Previously we utilized a dual-tagging quantitative proteomics approach to uncover MyD88 interactions in LPS-stimulated cells and described the function of Fliih, a leucine-rich repeat (LRR) protein that negatively regulates NF-kappaB activity. Here we characterize two distinct LRR-binding MyD88 interactors, LRRFIP2 and Flap-1, and found that both are positive regulators of NF-kappaB activity. Upon LPS stimulation, LRRFIP2 was also found to positively regulate cytokine production in macrophages, suggesting a functional role in TLR4-mediated inflammatory response. Furthermore, we observed that immediately following LPS stimulation both LRRFIP2 and Flap-1 compete with Fliih for interacting with MyD88 to activate the signaling. By using a novel multiplex quantitative proteomic approach, we found that at endogenous levels these positive and negative regulators interact with MyD88 in a timely and orderly manner to differentially mediate the NF-kappaB activity through the course of signaling from initiation to prolongation, and to repression. Based on these data, we describe a mechanistic model in which selective modulation of TLR signaling is achieved by temporal and dynamic interactions of MyD88 with its regulators.

GCK is essential to systemic inflammation and pattern recognition receptor signaling to JNK and p38

Systemic inflammation arising from the organismal distribution of pathogen-associated molecular patterns is a major cause of clinical morbidity and mortality. Herein we report a critical and previously unrecognized in vivo role for germinal center kinase (GCK, genome nomenclature: map4k2), a mammalian Sterile 20 (STE20) orthologue, in PAMP signaling, and systemic inflammation. We find that disruption of gck in mice strongly impairs PAMP-stimulated macrophage cytokine and chemokine release and renders mice resistant to endotoxin-mediated lethality. Bone marrow transplantation studies show that hematopoietic cell GCK signaling is essential to systemic inflammation. Disruption of gck substantially reduces PAMP activation of macrophage Jun-N-terminal kinase (JNK) and p38 mitogen-activated protein kinases (MAPKs) via reduced activation of the MAPK-kinase-kinases (MAP3Ks) mixed lineage kinases (MLKs)-2 and -3. Extracellular signal-regulated kinase (ERK) and nuclear factor-kappaB (NF-kappaB) activation are largely unaffected. Thus, GCK is an essential PAMP effector coupling JNK and p38, but not ERK or NF-kappaB to systemic inflammation.

Prostaglandins and sickness behavior: old story, new insights

Previous evidence has shown that prostaglandins play a key role in the development of sickness behavior observed during inflammatory states. In particular, prostaglandin E2 (PGE2) is produced in the brain by a variety of inflammatory signals such as endotoxins or cytokines. Its injection has been also shown to induce symptoms of sickness behavior. The role of cyclooxygenase enzymes (COX), the rate-limiting enzymes converting arachidonic acid into prostaglandins, in sickness behavior has been extensively studied, and it has been demonstrated that strategies aiming at inhibiting these enzymes limit anorexia, body weight loss and fever in animals with inflammatory diseases. However, inhibiting COX activity may lead to negative gastric or cardiovascular effects, since COX enzymes play a role in the synthesis of others prostanoids with various and sometimes contrasting properties. Recently, prostaglandin E synthases (PGES), which specifically catalyze the final step of PGE2 biosynthesis, were characterized. Among these enzymes, the microsomal prostaglandin E synthase-1 (mPGES-1) was of a particular interest since it was shown to be up-regulated by inflammatory signals in a variety of cell types. Moreover, mPGES-1 was shown to be crucial for correct immune-to-brain communication and induction of fever and anorexia by pro-inflammatory agents. This review takes stock of previous knowledge and recent advances in understanding the role of prostaglandins and of their specific synthesizing enzymes in the molecular mechanisms underlying sickness behavior. The review concludes with a short summary of key questions that remain to be addressed and points out therapeutic developments in this research field.

The interleukin-1 receptor/Toll-like receptor superfamily: 10 years of progress

The interleukin-1 receptor (IL-1R)/Toll-like receptor (TLR) superfamily was first defined in 1998 as a family of proteins that contain the Toll-IL-1 receptor domain. At that time, there were a number of orphan receptors in the IL-1R branch, and the TLRs had yet to be shown to be key innate immune receptors that sense microbial products. We now know a great deal more about this superfamily, with the description of novel IL-1 family members such as IL-1F6 signaling via IL-1Rrp2 and IL33 signaling via ST2. Remarkable progress has been made in our understanding of the functions of the TLRs, leading to a renaissance of interest in innate immunity. The importance of IL-1 is also being rediscovered, with the observation that Nalp3 is a key regulator of caspase-1, the enzyme that processes pro-IL-1beta into the mature cytokine. This area has therefore proved very fruitful in terms of improving our knowledge of the molecular basis for innate immunity and inflammation, and we can anticipate further discoveries in the coming years.

Meprin A and meprin alpha generate biologically functional IL-1beta from pro-IL-1beta

The present study demonstrates that both oligomeric metalloendopeptidase meprin A purified from kidney cortex and recombinant meprin alpha are capable of generating biologically active IL-1beta from its precursor pro-IL-1beta. Amino-acid sequencing analysis reveals that meprin A and meprin alpha cleave pro-IL-1beta at the His(115)-Asp(116) bond, which is one amino acid N-terminal to the caspase-1 cleavage site and five amino acids C-terminal to the meprin beta site. The biological activity of the pro-IL-1beta cleaved product produced by meprin A, determined by proliferative response of helper T-cells, was 3-fold higher to that of the IL-1beta product produced by meprin beta or caspase-1. In a mouse model of sepsis induced by cecal ligation puncture that results in elevated levels of serum IL-1beta, meprin inhibitor actinonin significantly reduces levels of serum IL-1beta. Meprin A and meprin alpha may therefore play a critical role in the production of active IL-1beta during inflammation and tissue injury.

Pellino proteins contain a cryptic FHA domain that mediates interaction with phosphorylated IRAK1

Pellino proteins are RING E3 ubiquitin ligases involved in signaling events downstream of the Toll and interleukin-1 (IL-1) receptors, key initiators of innate immune and inflammatory responses. Pellino proteins associate with and ubiquitinate proteins in these pathways, including the interleukin-1 receptor associated kinase-1 (IRAK1). We determined the X-ray crystal structure of a Pellino2 fragment lacking only the RING domain. This structure reveals that the IRAK1-binding region of Pellino proteins consists largely of a previously unidentified forkhead-associated (FHA) domain. FHA domains are well-characterized phosphothreonine-binding modules, and this cryptic example in Pellino2 can drive interaction of this protein with phosphorylated IRAK1. The Pellino FHA domain is decorated with an unusual appendage or "wing" composed of two long inserts that lie within the FHA homology region. Delineating how this E3 ligase associates with substrates, and how these interactions are regulated by phosphorylation, is crucial for a complete understanding of Toll/IL-1 receptor signaling.

Live Borrelia burgdorferi spirochetes elicit inflammatory mediators from human monocytes via the Toll-like receptor signaling pathway

We investigated the mechanisms that lead to the production of proinflammatory mediators by human monocytes when these cells are exposed in vitro to live Borrelia burgdorferi spirochetes. We first focused on myeloid differentiation primary response protein 88 (MyD88), an adapter molecule that is essential in the Toll-like receptor (TLR) pathway. Real-time PCR, flow cytometry, and confocal microscopy experiments revealed that MyD88 was maximally expressed in THP-1 cells after 24-h stimulation of these cells with live B. burgdorferi. Silencing of the MYD88 gene by using small interfering RNA resulted in 24%, 35%, and 84% down-modulation of the production of tumor necrosis factor alpha (TNF-alpha), interleukin-8 (IL-8), and IL-6, respectively, in THP-1 cells stimulated with live B. burgdorferi. Specific silencing of the TLR1, TLR2, or TLR5 gene by RNA interference further revealed that silencing of the TLR1 and TLR2 genes alone or combined, but not the TLR5 gene, caused a downregulation of IL-6, IL-8, and TNF-alpha in live B. burgdorferi-stimulated THP-1 cells. Overall, similar results were obtained for THP-1 cells stimulated with purified lipoproteins. Our results indicate that the TLR pathway mediates, at least in part, the release of inflammatory mediators in human monocytes stimulated with live B. burgdorferi spirochetes and furthermore suggest that the TLR-dependent interaction between these cells and live spirochetes is mediated by spirochetal lipoproteins but not by flagellin.

The interleukin-1 receptor-associated kinase M selectively inhibits the alternative, instead of the classical NFkappaB pathway

The innate immunity signaling process is controlled by numerous positive and negative regulators. The interleukin-1 receptor-associated kinase M (IRAK-M) is one of the negative regulators that contribute to the attenuation of NFkappaB activation. The molecular mechanism involved, however, is poorly defined. In this report, we observed that IRAK-M selectively suppresses the NIK-IKKalpha-mediated alternative NFkappaB pathway. Deletion of IRAK-M led to NIK stabilization, favored the formation of the IKKalpha/IKKalpha homodimer instead of the IKKalpha/IKKbeta heterodimer, and enhanced RelB nuclear distribution. In contrast, p65 nuclear localization and phosphorylation was not affected by IRAK-M deficiency. IRAK-M-deficient cells exhibited increased expression of selected cytokines such as IL-6 and GM-CSF, as well as quickened resynthesis of IkappaBalpha. The increased expression of IL-6 and GM-CSF was ablated when RelB expression was knocked down using specific siRNA. We also demonstrated that the observed inhibitory effect of IRAK-M was primarily limited to the TLR2 ligand, instead of TLR4. Taken together, our findings suggest that IRAK-M negatively regulates the alternative NFkappaB pathway in a ligand-specific manner.

Nonmyocardial production of ST2 protein in human hypertrophy and failure is related to diastolic load

OBJECTIVES

This study was designed to investigate: 1) relationships between serum ST2 levels and hemodynamic/neurohormonal variables; 2) myocardial ST2 production; and the 3) expression of ST2, membrane-anchored ST2L, and its ligand, interleukin (IL)-33, in myocardium, endothelium, and leukocytes from patients with left ventricular (LV) pressure overload and congestive cardiomyopathy.

BACKGROUND

Serum levels of ST2 are elevated in heart failure. The relationship of ST2 to hemodynamic variables, source of ST2, and expression of ST2L and IL-33 in the cardiovascular system are unknown.

METHODS

Serum ST2 (pg/ml; median [25th, 75th percentile]) was measured in patients with LV hypertrophy (aortic stenosis) (n = 45), congestive cardiomyopathy (n = 53), and controls (n = 23). ST2 was correlated to N-terminal pro-brain natriuretic peptide, C-reactive protein, and hemodynamic variables. Coronary sinus and arterial blood sampling determined myocardial gradient (production) of ST2. The levels of ST2, ST2L, and IL-33 were measured (reverse transcriptase-polymerase chain reaction) in myocardial biopsies and leukocytes. The ST2 protein production was evaluated in human endothelial cells. The IL-33 protein expression was determined (immunohistochemistry) in coronary artery endothelium.

RESULTS

The ST2 protein was elevated in aortic stenosis (103 [65, 165] pg/ml, p < 0.05) and congestive cardiomyopathy (194 [69, 551] pg/ml, p < 0.01) versus controls (49 [4, 89] pg/ml) and correlated with B-type natriuretic peptide (r = 0.5, p < 0.05), C-reactive protein (r = 0.6, p < 0.01), and LV end-diastolic pressure (r = 0.38, p < 0.03). The LV ST2 messenger ribonucleic acid was similar in aortic stenosis and congestive cardiomyopathy versus control (p = NS). No myocardial ST2 protein gradient was observed. Endothelial cells secreted ST2. The IL-33 protein was expressed in coronary artery endothelium. Leukocyte ST2L and IL-33 levels were highly correlated (r = 0.97, p < 0.001).

CONCLUSIONS

In human hypertrophy and failure, serum ST2 correlates with the diastolic load. Though the heart, endothelium, and leukocytes express components of ST2/ST2L/IL-33 pathway, the source of circulating serum ST2 is extra-myocardial.

Welcome to the neighborhood: epithelial cell-derived cytokines license innate and adaptive immune responses at mucosal sites

There is compelling evidence that epithelial cells (ECs) at mucosal surfaces, beyond their role in creating a physical barrier, are integral components of innate and adaptive immunity. The capacity of these cells to license the functions of specific immune cell populations in the airway and gastrointestinal tract offers the prospect of novel therapeutic strategies to target multiple inflammatory diseases in which barrier immunity is dysregulated. In this review, we discuss the critical functions of EC-derived thymic stromal lymphopoietin (TSLP), interleukin-25 (IL-25), and IL-33 in the development and regulation of T-helper 2 (Th2) cytokine-dependent immune responses. We first highlight recent data that have provided new insights into the factors that control expression of this triad of cytokines and their receptors. In addition, we review their proinflammatory and immunoregulatory functions in models of mucosal infection and inflammation. Lastly, we discuss new findings indicating that despite their diverse structural features and differential expression of their receptors, TSLP, IL-25, and IL-33 cross-regulate one another and share overlapping properties that influence Th2 cytokine-dependent responses at mucosal sites.

Roles of caspase 1 and extracellular signal-regulated kinase in inflammation-induced inhibition of lacrimal gland protein secretion

PURPOSE

The purpose of the present study was to investigate the roles of caspase 1 and extracellular signal-regulated kinase (ERK) in inflammation-induced inhibition of lacrimal gland secretion.

METHODS

Lacrimal gland inflammation was induced by injection of lipopolysaccharide (LPS; to study the role of caspase 1) or IL-1beta (to study the role of ERK). Lacrimal gland protein secretion was measured using a spectrofluorometric assay. Caspase 1 and ERK activities in the lacrimal gland were measured by immunohistochemistry, Western blotting, or both. Aqueous tear production was measured using phenol red-impregnated cotton threads.

RESULTS

Injection of LPS into the lacrimal gland inhibited neurally and adrenergic agonist-induced protein secretion by 77% and 54%, respectively, and activated caspase 1. The degree of inhibition achieved by LPS was similar to that obtained with injection of IL-1beta. Inhibition of caspase 1 alleviated the inhibitory effect of LPS on lacrimal gland secretion. IL-1beta activated ERK in the lacrimal gland in vitro and in vivo, and this effect was blocked by UO126, an inhibitor of MEK, the ERK-activating enzyme. IL-1beta injection into the lacrimal gland inhibited aqueous tear production by 52% and inhibited neurally and adrenergic agonist-induced protein secretion by 80% and 55%, respectively. UO126 alleviated the inhibitory effect of IL-1beta on aqueous tear production and lacrimal gland protein secretion.

CONCLUSIONS

LPS inhibits lacrimal gland secretion by activating caspase 1, and IL-1beta activates the ERK pathway to inhibit lacrimal gland protein secretion and aqueous tear production.

Alterations in microRNA expression contribute to fatty acid-induced pancreatic beta-cell dysfunction

OBJECTIVE

Visceral obesity and elevated plasma free fatty acids are predisposing factors for type 2 diabetes. Chronic exposure to these lipids is detrimental for pancreatic beta-cells, resulting in reduced insulin content, defective insulin secretion, and apoptosis. We investigated the involvement in this phenomenon of microRNAs (miRNAs), a class of noncoding RNAs regulating gene expression by sequence-specific inhibition of mRNA translation.

RESEARCH DESIGN AND METHODS

We analyzed miRNA expression in insulin-secreting cell lines or pancreatic islets exposed to palmitate for 3 days and in islets from diabetic db/db mice. We studied the signaling pathways triggering the changes in miRNA expression and determined the impact of the miRNAs affected by palmitate on insulin secretion and apoptosis.

RESULTS

Prolonged exposure of the beta-cell line MIN6B1 and pancreatic islets to palmitate causes a time- and dose-dependent increase of miR34a and miR146. Elevated levels of these miRNAs are also observed in islets of diabetic db/db mice. miR34a rise is linked to activation of p53 and results in sensitization to apoptosis and impaired nutrient-induced secretion. The latter effect is associated with inhibition of the expression of vesicle-associated membrane protein 2, a key player in beta-cell exocytosis. Higher miR146 levels do not affect the capacity to release insulin but contribute to increased apoptosis. Treatment with oligonucleotides that block miR34a or miR146 activity partially protects palmitate-treated cells from apoptosis but is insufficient to restore normal secretion.

CONCLUSIONS

Our findings suggest that at least part of the detrimental effects of palmitate on beta-cells is caused by alterations in the level of specific miRNAs.

Lipopolysaccharide stimulation of trophoblasts induces corticotropin-releasing hormone expression through MyD88

OBJECTIVE

We hypothesized that intrauterine infection may lead to placental corticotrophin-releasing hormone (CRH) expression via Toll-like receptor signaling.

STUDY DESIGN

To test this hypothesis JEG3 cells were stimulated with lipopolysaccharide (LPS), chlamydial heat shock protein 60, and interleukin (IL)-1. CRH expression was assessed by reverse transcription polymerase chain reaction (RT-PCR). The signaling mechanisms that were involved were examined in transient transfection experiments with beta-galactosidase, CRH-luciferase, cyclic adenosine monophosphate (AMP) response element-luciferase, dominant-negative (DN)-myeloid differentiation primary response gene (MyD88) and DN-toll-IL-1-receptor domain containing adapter inducing interferon (TRIF) vectors. Luciferase activity was determined by luciferase assay. Beta-galactosidase assay was performed to determine transfection efficiency.

RESULTS

LPS, chlamydial heat shock protein 60, and IL-1 stimulation led to CRH expression in the JEG3 cells. LPS-induced CRH expression was not due to the autocrine effect of LPS-induced IL-1 because the supernatant from LPS-conditioned JEG3 cells did not induce CRH expression in the naïve cells. DN-MyD88, but not DN-TRIF, blocked the LPS-induced CRH expression. The cAMP response element did not play a role in LPS-induced CRH expression.

CONCLUSION

Toll-like receptor signaling 4 may induce placental CRH expression through MyD88.

Stimulation of Toll-like receptor 3 and 4 induces interleukin-1beta maturation by caspase-8

The cytokine interleukin (IL)-1beta is a key mediator of the inflammatory response and has been implicated in the pathophysiology of acute and chronic inflammation. IL-1beta is synthesized in response to many stimuli as an inactive pro-IL-1beta precursor protein that is further processed by caspase-1 into mature IL-1beta, which is the secreted biologically active form of the cytokine. Although stimulation of membrane-bound Toll-like receptors (TLRs) up-regulates pro-IL-1beta expression, activation of caspase-1 is believed to be mainly initiated by cytosolic Nod-like receptors. In this study, we show that polyinosinic:polycytidylic acid (poly[I:C]) and lipopolysaccharide stimulation of macrophages induces pro-IL-1beta processing via a Toll/IL-1R domain-containing adaptor-inducing interferon-beta-dependent signaling pathway that is initiated by TLR3 and TLR4, respectively. Ribonucleic acid interference (RNAi)-mediated knockdown of the intracellular receptors NALP3 or MDA5 did not affect poly(I:C)-induced pro-IL-1beta processing. Surprisingly, poly(I:C)- and LPS-induced pro-IL-1beta processing still occurred in caspase-1-deficient cells. In contrast, pro-IL-1beta processing was inhibited by caspase-8 peptide inhibitors, CrmA or vFLIP expression, and caspase-8 knockdown via RNAi, indicating an essential role for caspase-8. Moreover, recombinant caspase-8 was able to cleave pro-IL-1beta in vitro at exactly the same site as caspase-1. These results implicate a novel role for caspase-8 in the production of biologically active IL-1beta in response to TLR3 and TLR4 stimulation.

Crucial role for the Nalp3 inflammasome in the immunostimulatory properties of aluminium adjuvants

Aluminium adjuvants, typically referred to as 'alum', are the most commonly used adjuvants in human and animal vaccines worldwide, yet the mechanism underlying the stimulation of the immune system by alum remains unknown. Toll-like receptors are critical in sensing infections and are therefore common targets of various adjuvants used in immunological studies. Although alum is known to induce the production of proinflammatory cytokines in vitro, it has been repeatedly demonstrated that alum does not require intact Toll-like receptor signalling to activate the immune system. Here we show that aluminium adjuvants activate an intracellular innate immune response system called the Nalp3 (also known as cryopyrin, CIAS1 or NLRP3) inflammasome. Production of the pro-inflammatory cytokines interleukin-1beta and interleukin-18 by macrophages in response to alum in vitro required intact inflammasome signalling. Furthermore, in vivo, mice deficient in Nalp3, ASC (apoptosis-associated speck-like protein containing a caspase recruitment domain) or caspase-1 failed to mount a significant antibody response to an antigen administered with aluminium adjuvants, whereas the response to complete Freund's adjuvant remained intact. We identify the Nalp3 inflammasome as a crucial element in the adjuvant effect of aluminium adjuvants; in addition, we show that the innate inflammasome pathway can direct a humoral adaptive immune response. This is likely to affect how we design effective, but safe, adjuvants in the future.

Interferons and scleroderma-a new clue to understanding the pathogenesis of scleroderma?

Scleroderma or systemic sclerosis (SSc) is a complex disease characterized by vasculopathy and deregulated immune and fibroblast activation. The resulting excessive production of collagens and other extracellular matrix proteins by fibroblasts as well as the inflammatory response leads to the development of scleroderma. Recently, some emerging data have been showing a possible link between the type I and II interferons (IFNs) and SSc pathogenesis. IFNs are well-known immunomodulators and inhibitors of collagen production. However, IFN therapy also has been implicated in the development or exacerbation of several autoimmune diseases, including SSc. Some studies also showed an increase mRNA and protein levels of IFNs and several interferon stimulated genes in cells and tissues from SSc patients. In this review we discuss about a possible role for IFNs in SSc development and pathogenesis.

The IL-1 receptor accessory protein (AcP) is required for IL-33 signaling and soluble AcP enhances the ability of soluble ST2 to inhibit IL-33

Interleukin (IL)-33 (or IL-1F11) was recently identified as a ligand for the orphan IL-1 receptor family member T1/ST2 (ST2). IL-33 belongs to the IL-1 cytokine family and, upon binding to ST2, induces intracellular signals similar to those utilized by IL-1. The effects of other IL-1 family cytokines are mediated by their binding to a specific receptor and the recruitment of a co-receptor required for elicitation of signaling. The aim of this study was to characterize the co-receptor involved in IL-33 signaling. Immunoprecipitation confirmed that IL-33 specifically binds ST2 and revealed that cellular IL-1 receptor accessory protein (AcP) associates with ST2 in a ligand-dependent manner. Receptor binding measurements demonstrated that the affinity of mouse (m)IL-33 for ST2 is increased by 4-fold in presence of AcP. IL-33 dose-dependently stimulated IL-6 secretion from wild-type (WT) mast cells, while no effect of IL-33 was observed with mast cells derived from AcP-deficient mice. Finally, soluble (s)ST2-Fc and sAcP-Fc acted synergistically to inhibit IL-33 activity. These observations identify AcP as a shared co-receptor within the IL-1 family that is essential for IL-33 signaling and suggest a novel role for sAcP in modulating the activity of IL-33.

Plant receptor-like serine threonine kinases: roles in signaling and plant defense

Plants are hosts to a wide array of pathogens from all kingdoms of life. In the absence of an active immune system or combinatorial diversifications that lead to recombination-driven somatic gene flexibility, plants have evolved different strategies to combat both individual pathogen strains and changing pathogen populations. The receptor-like kinase (RLK) gene-family expansion in plants was hypothesized to have allowed accelerated evolution among domains implicated in signal reception, typically a leucine-rich repeat (LRR). Under that model, the gene-family expansion represents a plant-specific adaptation that leads to the production of numerous and variable cell surface and cytoplasmic receptors. More recently, it has emerged that the LRR domains of RLK interact with a diverse group of proteins leading to combinatorial variations in signal response specificity. Therefore, the RLK appear to play a central role in signaling during pathogen recognition, the subsequent activation of plant defense mechanisms, and developmental control. The future challenges will include determinations of RLK modes of action, the basis of recognition and specificity, which cellular responses each receptor mediates, and how both receptor and kinase domain interactions fit into the defense signaling cascades. These challenges will be complicated by the limited information that may be derived from the primary sequence of the LRR domain. The review focuses upon implications derived from recent studies of the secondary and tertiary structures of several plant RLK that change understanding of plant receptor function and signaling. In addition, the biological functions of plant and animal RLK-containing receptors were reviewed and commonalities among their signaling mechanisms identified. Further elucidated were the genomic and structural organizations of RLK gene families, with special emphasis on RLK implicated in resistance to disease and development.