Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P43026 (lipopolysaccharide)
 62,215 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The significance of lipid rafts in lipopolysaccharide (LPS) signaling in macrophages was studied through isolation of them by gradient centrifugation and subsequent visualization of signal molecules using antibodies. LPS signaling is initiated by binding to Toll-like receptor-4 (TLR4) and the co-receptor CD-14, leading to activation of downstream targets, such as MAP kinases. In this study, we show that LPS causes translocation of CD-14 and MAP kinases (ERK-2 and p38) to lipid rafts in the macrophage cell line RAW 264.7. The adaptor proteins MyD88 and Gab-2, on the other hand, were not detected in the lipid raft fractions. These results indicate that lipid rafts play a role in LPS-induced signaling in macrophages.
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PMID:The role of lipid rafts in LPS-induced signaling in a macrophage cell line. 1590 59

Sponges (phylum Porifera) are the phylogenetically oldest metazoa; as filter feeders, they are abundantly exposed to marine microorganisms. Here we present data indicating that the demosponge Suberites domuncula is provided with a recognition system for gram-negative bacteria. The lipopolysaccharide (LPS)-interacting protein was identified as a receptor on the sponge cell surface, which recognizes the bacterial endotoxin LPS. The cDNA was isolated, and the protein (Mr 49,937) was expressed. During binding to LPS, the protein dimerizes and interacts with MyD88, which was also identified and cloned. The sponge MyD88 (Mr 28,441) is composed of two protein interaction domains, a Toll/interleukin-1 receptor domain (found in MyD88 and in Toll-like receptors) and a death domain (present in MyD88 and interleukin-1 receptor-associated kinase). Northern blot experiments and in situ hybridization studies showed that after LPS treatment, the level of the LPS-interacting protein remains unchanged, whereas MyD88 is strongly up-regulated. A perforin-like molecule (Mr 74,171), the macrophage-expressed protein, was identified as an executing molecule of this pathway. This gene is highly expressed after LPS treatment, especially at the surfaces of the animals. The recombinant protein possesses biological activity and eliminates gram-negative bacteria; it is inactive against gram-positive bacteria. These data indicate that S. domuncula is provided with an innate immune system against gram-negative bacteria; the ligand LPS (a pathogen-associated molecular pattern) is recognized by the pattern recognition receptor (LPS-interacting protein), which interacts with MyD88. A signal transduction is established, which results in an elevated expression of MyD88 as well as of the macrophage-expressed protein as an executing protein.
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PMID:Innate immune defense of the sponge Suberites domuncula against bacteria involves a MyD88-dependent signaling pathway. Induction of a perforin-like molecule. 1592 43

Up to date, few successes have been achieved to identify the signaling molecules directly from immune cells due to their low-abundance and dynamic nature. Here, we designed an in vivo dual-tagging quantitative approach that integrated epitope-tagging which allows single affinity purification of the natural complexes formed at real-time, and amino acid-coded mass tagging (AACT) that assists mass spectrometry-based quantitative measurement, to identify the specific components of a signaling complex formed in macrophage cells upon lipopolysaccharide (LPS) stimulation. The sensitivity and accuracy of this quantitative method are significantly higher than those of tandem affinity purification, because the multiple step of purifications are avoided to preserve weakly interacting molecules. We identified a number of proteins that interact with MyD88, a critical adaptor protein in innate immune response, in macrophages upon stimulation. Among those newly identified MyD88-interacting partners, FLAP-1 was found to be an activator of NF-kappaB, the key transcription factor in immune response. This integrated approach provides global information on the functional link between MyD88 and other proteins in transducing the TLR-mediated signal and is generally applicable to in vivo analyses of other signaling pathways.
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PMID:In vivo dual-tagging proteomic approach in studying signaling pathways in immune response. 1595 41

The interleukin-1 (IL-1) receptor-associated kinase 1 (IRAK1) is a member of the IRAK kinase family that plays a pivotal role in the Toll/IL-1 receptor (TIR) family signaling cascade. We have identified a novel splice variant, IRAK1c, which lacks a region encoded by exon 11 of the IRAK1 gene. IRAK1c expression was confirmed by both RNA and protein detection. Although both IRAK1 and IRAK1c are expressed in most tissues tested, IRAK1c is the predominant form of IRAK1 expressed in the brain. Unlike IRAK1, IRAK1c lacks kinase activity and cannot be phosphorylated by IRAK4. However, IRAK1c retains the ability to strongly interact with IRAK2, MyD88, Tollip, and TRAF6. Overexpression of IRAK1c suppressed NF-kappaB activation and blocked IL-1beta-induced IL-6 as well as lipopolysaccharide- and CpG-induced tumor necrosis factor alpha production in multiple cellular systems. Mechanistically, we provide evidence that IRAK1c functions as a dominant negative by failing to be phosphorylated by IRAK4, thus remaining associated with Tollip and blocking NF-kappaB activation. The presence of a regulated, alternative splice variant of IRAK1 that functions as a kinase-dead, dominant-negative protein adds further complexity to the variety of mechanisms that regulate TIR signaling and the subsequent inflammatory response.
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PMID:A novel splice variant of interleukin-1 receptor (IL-1R)-associated kinase 1 plays a negative regulatory role in Toll/IL-1R-induced inflammatory signaling. 1602 89

The genetic basis of hyper-IgE syndrome (HIES), also known as Job syndrome, a primary immunodeficiency associated with recurrent skin and pulmonary infections, is unknown. We hypothesized that HIES is due to a defect in the Toll-like receptor signaling pathway. We used a whole blood cytokine assay to compare inflammatory responses to stimulation with specific Toll-like receptor (TLR) pathway agonists in four individuals with HIES and nine healthy controls. Production of tumor necrosis factor-alpha, interleukin (IL)-1beta, IL-6, and IL-12 was not impaired in response to stimulation with lipopolysaccharide, peptidoglycan, zymosan, lipoteichoic acid, Staphylococcus aureus, Escherichia coli, or Streptococcus pneumoniae. Interferon (IFN)-gamma was reduced in HIES subjects in response to each of these stimuli. We sequenced several candidate genes from the TLR pathway in HIES individuals to determine whether any mutations were associated with this syndrome. No novel mutations or polymorphisms were found in the coding regions of TLR1, TLR2, TLR6, MyD88, or TRAF6. In summary, although HIES individuals had an IFN-gamma secretion defect, they also produced normal levels of several TLR-regulated proinflammatory cytokines. No unique mutations or polymorphisms were observed in several candidate genes from the TLR pathway. Our studies do not support a role for a defective TLR response in HIES individuals.
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PMID:Hyper-IgE syndrome is not associated with defects in several candidate toll-like receptor pathway genes. 1611 32

Rip1 is required for IkappaB kinase activation in response to tumor necrosis factor alpha (TNF-alpha) and has been implicated in the Toll-like receptor 3 (TLR3) response to double-stranded RNA. Cytokine production is impaired when rip1-/- cells are treated with TNF-alpha, poly(I-C), or lipopolysaccharide, implicating Rip1 in the Trif-dependent TLR3 and TLR4 pathways. To examine the role of Rip1 in the Trif-dependent TLR4 pathway, we generated rip1-/- MyD88-/- cells. Lipopolysaccharide failed to stimulate NF-kappaB activation in rip1-/-MyD88-/- cells, revealing that Rip1 is also required for the Trif-dependent TLR4-induced NF-kappaB pathway. In addition to activating NF-kappaB, TLR3/4 pathways also stimulate interferon regulatory factor 3 activation. However, we find that Rip1 expression stimulates NF-kappaB but not interferon regulatory factor 3 activity. In the TNF-alpha pathway, Rip1 interacts with the E3 ubiquitin ligase Traf2 and is modified by polyubiquitin chains. Upon TLR3 activation, Rip1 is also modified by polyubiquitin chains and is recruited to TLR3 along with Traf6 and the ubiquitin-activated kinase Tak1. These studies suggest that Rip1 uses a similar, ubiquitin-dependent mechanism to activate IkappaB kinase-beta in response to TNF-alpha and TLR3 ligands.
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PMID:Rip1 mediates the Trif-dependent toll-like receptor 3- and 4-induced NF-{kappa}B activation but does not contribute to interferon regulatory factor 3 activation. 1611 77

Bacterial lipopolysaccharide (LPS) activates Toll-like receptor 4 (TLR4) leading to the expression of inflammatory gene products. Src-family tyrosine kinases (STKs) are known to be activated by LPS in monocytes/macrophages. Therefore, we determined the role of STKs in TLR4 signaling pathways and target gene expression in macrophages. The activation of NFkappaB, and p38 MAPK, and the expression of inducible nitric oxide synthase (iNOS) induced by LPS were not affected in macrophages deficient in three STKs (Lyn, Hck, and Fgr). These results suggest that the deletion of the three STKs among possibly nine STKs is not sufficient to abolish total activity of STKs possibly due to the functional redundancy of other STKs present in macrophages. However, two structurally unrelated pan-inhibitors of STKs, PP1 and SU6656, suppressed LPS-induced iNOS expression in MyD88-knockout as well as wild-type macrophages. The suppression of iNOS expression by the inhibitors was correlated with the downregulation of IFNbeta (a MyD88-independent gene) expression and subsequent decrease in STAT1 phosphorylation. Moreover, PP1 suppressed the expression of IFNbeta and iNOS induced by TRIF, a MyD88-independent adaptor of TLR4. PP1 suppressed STAT1 phosphorylation induced by LPS, but not by IFNbeta suggesting that STKs are involved in the primary downstream signaling pathways of TLR4, but not the secondary signaling pathways downstream of IFNbeta receptor. Together, these results demonstrate that STKs play a positive regulatory role in TLR4-mediated iNOS expression in a MyD88-independent (TRIF-dependent) manner. These results provide new insight in understanding the role of STKs in TLR4 signaling pathways and inflammatory target gene expression.
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PMID:The regulation of the expression of inducible nitric oxide synthase by Src-family tyrosine kinases mediated through MyD88-independent signaling pathways of Toll-like receptor 4. 1614 Feb 74

The activation dynamics of the transcription factor NF-kappaB exhibit damped oscillatory behavior when cells are stimulated by tumor necrosis factor-alpha (TNFalpha) but stable behavior when stimulated by lipopolysaccharide (LPS). LPS binding to Toll-like receptor 4 (TLR4) causes activation of NF-kappaB that requires two downstream pathways, each of which when isolated exhibits damped oscillatory behavior. Computational modeling of the two TLR4-dependent signaling pathways suggests that one pathway requires a time delay to establish early anti-phase activation of NF-kappaB by the two pathways. The MyD88-independent pathway required Inferon regulatory factor 3-dependent expression of TNFalpha to activate NF-kappaB, and the time required for TNFalpha synthesis established the delay.
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PMID:Achieving stability of lipopolysaccharide-induced NF-kappaB activation. 1616 16

Inflammatory lipid mediators such as prostaglandins and leukotrienes play crucial roles in the pathogenesis of bacterial lipopolysaccharide (LPS)-induced inflammation. Cytosolic phospholipase A(2) (cPLA(2)) is a key enzyme in the generation of pro-inflammatory lipid mediators. Here, we found that Toll-like receptor 4 (TLR4) is essential for LPS-induced cPLA(2) activation and lipid release. Inhibition of TLR4 protein expression by TLR4 small interfering RNA or neutralization of TLR4 by the specific antibody against TLR4/MD2 blocked cPLA(2) phosphorylation and cPLA(2)-hydrolyzed arachidonic acid release. Furthermore, activation of the TLR4 signaling pathway by LPS regulated cPLA(2) activation and lipid release. cPLA(2) phosphorylation and cPLA(2)-hydrolyzed lipid release were significantly impaired when TLR4 adaptor protein, either MyD88 or TRIF, was knocked down in LPS-stimulated macrophages. Similarly, LPS-induced arachidonate release was inhibited in cells transfected with a dominant-negative MyD88 or TRIF construct. Subsequently, cPLA(2) activation could be suppressed by inhibition of the TLR4 adaptor protein-directed p38 and ERK MAPK pathways. These findings suggest that, in LPS-induced inflammation, the TLR4-mediated MyD88- and TRIF-dependent MAPK pathways result in cPLA(2) activation and production of pro-inflammatory lipid mediators.
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PMID:Toll-like receptor 4 signaling regulates cytosolic phospholipase A2 activation and lipid generation in lipopolysaccharide-stimulated macrophages. 1617 25

Protein farnesyltransferase inhibitors (FTIs) have shown clinical responses in hematologic malignancies, but the mechanisms are unclear. To better understand potential mechanisms of action, we have studied effects of the FTI tipifarnib on inflammatory responses in vitro and in vivo. In a human leukemia cell line THP-1, tipifarnib inhibited lipopolysaccharide (LPS)-induced transcription of chemokines [monocyte chemotactic protein (MCP)-1 and MCP-2], cytokines [interleukin (IL)-1beta, IL-6, and interferon (IFN)beta], signaling molecules (MyD88 and STAT-1), proteases [matrix metalloproteinase (MMP-9)], and receptors (urokinase receptor). Tipifarnib also inhibited LPS-induced secretion of MMP-9, IL-6, MCP-1, and IL-1beta in THP-1 cells. In primary human peripheral blood mononuclear cells, dose-dependent inhibition of LPS-induced tumor necrosis factor (TNF)-alpha, IL-6, MCP-1, and IL-1beta by tipifarnib was observed with no evidence of cytotoxicity. Similar results were obtained in vivo in a murine model of LPS-induced inflammation, where pretreatment with tipifarnib resulted in significant inhibition of TNF-alpha, IL-6, MCP-1, IL-1beta, and MIP-1alpha production. Tipifarnib had no effect in vitro or in vivo on LPS-induced IL-8. Studies in THP-1 cells to address potential mechanism(s) showed that tipifarnib partially inhibited LPS-induced p38 phosphorylation. Tipifarnib significantly inhibited inhibitory subunit of nuclear factor-kappaB (NF-kappaB) (IkappaB)-alpha degradation and p65 nuclear translocation induced by LPS, but not by tumor necrosis factor-alpha, IL-1alpha, or toll-like receptor (TLR)2 ligand, suggesting that the target for inhibition of NF-kappaB activation was exclusive to the LPS/TLR4 signal pathway. The extent of IkappaB-alpha degradation inhibition did not correlate with inhibition of Ras farnesylation, indicating that Ras was not the target for the observed anti-inflammatory activity of tipifarnib. Our findings differ from those for other FTIs, which may have relevance for their dissimilar activity in specific tumor repertoires.
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PMID:Anti-inflammatory activity in vitro and in vivo of the protein farnesyltransferase inhibitor tipifarnib. 1635 5


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