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1.
Monocytes/macrophages exposed to LPS show reduced responses to second stimulation with LPS, which is termed LPS tolerance. In this study, we investigated molecular mechanism of LPS tolerance in macrophages. Mouse peritoneal macrophages pre-exposed to LPS exhibited reduced production of inflammatory cytokines in a time- and dose-dependent manner. Activation of neither IL-1 receptor-associated kinase nor NF-kappaB was observed in macrophages that became tolerant by LPS pretreatment, indicating that the proximal event in Toll-like receptor 4 (TLR4)-MyD88-dependent signaling is affected in tolerant macrophages. Although TLR4 mRNA expression significantly decreased within a few hours of LPS pretreatment and returned to the original level at 24 h, the surface TLR4 expression began to decrease within 1 h, with a gradual decrease after that, and remained suppressed over 24 h. A decrease in inflammatory cytokine production in tolerant macrophages well correlates with down-regulation of the surface TLR4 expression, which may explain one of the mechanisms for LPS tolerance.  相似文献
2.
The human MD-2 molecule is associated with the extracellular domain of human Toll-like receptor 4 (TLR4) and greatly enhances its LPS signaling. The human TLR4-MD-2 complex thus signals the presence of LPS. Little is known, however, about cell surface expression and LPS signaling of the TLR4-MD-2 complex in vivo. We cloned mouse MD-2 molecularly and established a unique mAb MTS510, which reacted selectively with mouse TLR4-MD-2 but not with TLR4 alone in flow cytometry. Mouse MD-2 expression in TLR4-expressing cells enhanced LPS-induced NF-kappaB activation, which was clearly inhibited by MTS510. Thioglycolate-elicited peritoneal macrophages expressed TLR4-MD-2, which was rapidly down-regulated in the presence of LPS. Moreover, LPS-induced TNF-alpha production by peritoneal macrophages was inhibited by MTS510. Collectively, the TLR4-MD-2 complex is expressed on macrophages in vivo and senses and signals the presence of LPS.  相似文献
3.
M Miyake  S I Hakomori 《Biochemistry》1991,30(13):3328-3334
The biochemical basis of cell motility has been viewed as a complex process involving cell surface membrane proteins, integrin receptors, growth factors and their receptors, and cytoskeletal components [Rosen & Goldberg (1989) In Vitro 25, 1079]. The possible involvement of glycoconjugates at the cell surface in controlling cell motility has not been systematically investigated. We addressed this question using functional monoclonal antibodies (MAbs), which inhibit cell motility and the metastatic potential of tumor cells, as probes. Two such MAbs, derived from two independent processes of immunization and selection, were found to directed to a common specific carbohydrate structure, Fuc alpha 1----2Gal beta 1----R. MAb MIA-15-5 was established after immunization of mice with small cell lung carcinoma line PC7 and selected on the basis of inhibition of U937 and HEL cell migration. MAb MIA-22-20 was established after immunization with lung adenocarcinoma line MAC-10 and selected on the basis of inhibition of MAC-10 cell migration. These two MAbs were both IgM and were consistently reactive with the Fuc alpha 1----2Gal beta 1----R structure, regardless of the identity of the R group. Various other anti-H MAbs, specific to carrier isotype, did not affect cell motility. MAb MIA-15-5 reacted with 30-40% of high-metastatic variant BL6 of mouse melanoma B16 line but with only less than 5% of low-metastatic variant F1. Metastatic deposition to lung after injection of BL6 cells was inhibited if MAb MIA-15-5 was injected within 3 h but was not inhibited by injection of other anti-H antibodies under the same conditions.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献
4.
The complex consisting of Toll-like receptor 4 (TLR4) and associated MD-2 signals the presence of lipopolysaccharide (LPS) when it is expressed in cell lines. We here show that normal human mononuclear cells express TLR4 and signal LPS via TLR4. CD14 is a molecule that binds to LPS and facilitates its signaling. Little is known, however, about the relationship of CD14 with TLR4-MD-2. We show that CD14 helps TLR4-MD-2 to sense and signal the presence of LPS. CD14 has also been implicated in recognition of apoptotic cells, which leads to phagocytosis without activation. Membrane phospholipids such as phosphatidylserine (PS) or phosphatidylinositol (PtdIns) are thought to serve as the ligands for CD14 in apoptotic cells. We find that PtdIns acts as an LPS antagonist in the signaling via TLR4-MD-2. TLR4-MD-2 seems to discriminate LPS from phospholipids. The signaling via TLR4-MD-2 is thus regulated by CD14 and phospholipid such as PtdIns.  相似文献
5.
PROTEIN METHYLATION BY CEREBRAL TISSUE   总被引:6,自引:2,他引:4  
Abstract— Transfer of the methyl group of S -adenosyl [Me-14C]methionine into cerebral proteins, an encephalitogenic protein and histones was studied using extracts of bovine and rat brains. The brain extract contains multiple substrate proteins and their lysine and arginine residues were methylated to form Ne-mono-, -di- and -trimethyl-lysine and N G-mono-, N G, N G- and NG,NG-dimethylarginine residues respectively, at different rates. The enzyme which catalyses the methylation of arginine residues was differentiated by ammonium sulphate fractionation from that methylating lysine residues. Methylation of arginine and lysine residues of proteins was stepwise in general, from mono- to dimethyl-arginine and from mono- to di- and trimethyl-lysines. Two different enzymes which methylate histone and the encephalitogenic basic protein respectively were obtained from the cytoplasmic fraction of rat brain and their enzymic properties were examined.  相似文献
6.
A multipotential stem-cell-type cell line (RT4-AC) isolated from a rat peripheral neurotumor differentiates in culture into two neuronal-type cells (RT4-B and RT4-E) or into a glial-type cell (RT4-D). The neuronal classification of RT4-B and RT4-E cells is based on their positive response to veratridine in the tetrodotoxin-sensitive Na+-influx and Rb+-efflux assays and on the action potential observed upon hyperpolarized stimulation. In addition, these neuronal cell types do not synthesize two glial proteins, S100 protein (S100P) and glial fibrillary acidic protein (GFAP). The glial classification of RT4-D is based on the syntheses of S100P and GFAP. Additionally, RT4-D does not display veratridine-activated Na+ influx and Rb+ efflux nor action potential. The stem cell type, RT4-AC, expresses both neuronal and glial properties to a lesser degree. In the neuronal-type cell lines of the RT4 family (RT4-B and RT4-E), the large veratridine-activated Na+ influx can further be stimulated by scorpion toxin. The Na+ influx of the stem cell (RT4-AC), however, is only slightly stimulated by veratridine alone, but greatly stimulated by the addition of veratridine and scorpion toxin. These observations suggest that a progressive differentiation of voltage-dependent Na+ channels may have occurred by the cell-type conversion from the stem cell type to the neuronal cell types. The exact nature of the change in Na+ channels is currently not known.  相似文献
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9.
Binding specificity of histone-like HU alpha protein to supercoiled DNA was examined by gel retardation assay and chemical probing with OsO4. The latter method was proved to be a unique means for detecting torsional tension restrained in supercoiled plasmid in the presence of HU alpha. It was shown that HU alpha protein has preferential affinity to negatively supercoiled DNA relative to relaxed, nicked and linearized DNAs. There were two modes for binding of HU alpha to the supercoiled DNA: one was the binding associated with topological changes in DNA and the other was relatively strong binding, probably specific to certain particular structures of DNA. It was suggested that HU in vivo interacts preferentially with the regions deformed under torsional stress or with the metabolically active regions along DNA.  相似文献
10.
Experimental autoimmune encephalomyelitis (EAE) is a Th1 cell-mediated autoimmune disease that can be protected against by stimulating regulatory cells. Here we examined whether EAE can be purposefully modulated by stimulating Valpha14 NK T cells with the CD1d-restricted ligand alpha-galactosylceramide (alpha-GC). EAE induced in wild-type C57BL/6 (B6) mice was not appreciably altered by injection of alpha-GC. However, EAE induced in IL-4 knockout mice and IFN-gamma knockout mice was enhanced or suppressed by alpha-GC, respectively. This indicates that the IL-4 and IFN-gamma triggered by alpha-GC may play an inhibitory or enhancing role in the regulation of EAE. We next studied whether NK T cells of wild-type mice may switch their Th0-like phenotype toward Th1 or Th2. Notably, in the presence of blocking B7.2 (CD86) mAb, alpha-GC stimulation could bias the cytokine profile of NK T cells toward Th2, whereas presentation of alpha-GC by CD40-activated APC induced a Th1 shift of NK T cells. Furthermore, transfer of the alpha-GC-pulsed APC preparations suppressed or enhanced EAE according to their ability to polarize NK T cells toward Th2 or Th1 in vitro. These results have important implications for understanding the role of NK T cells in autoimmunity and for designing a therapeutic strategy targeting NK T cells.  相似文献
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