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

Bleomycin (BLM) is a useful anticancer agent sometimes associated with a diffuse pulmonary inflammation and fibrosis. Using an intratracheal model of BLM-induced pulmonary damage, we have further investigated alveolar macrophage (AM) activation following intratracheal BLM. From rats that had been treated with either a single, fibrogenic, intratracheal dose of BLM (BLM-AM) or a comparable volume of saline (C-AM), bronchoalveolar lavage fluid was collected, and AM were isolated using Percoll gradient centrifugation. Using a spectrophotometric assay, production of nitrites by AM was measured. C-AM released low levels of nitrites, whereas BLM-AM as well as C-AM activated in vitro with lipopolysaccharide released significant amounts of nitrites. The addition of N6-monomethylarginine, a substrate-specific inhibitor of the L-arginine-dependent effector mechanism in activated macrophages, reduced the amount of measurable nitrites released from both BLM-AM and activated C-AM. Similar results were observed when 12 x 10(6) RBC were added to the cocultures. In the presence of N6-monomethylarginine, BLM-AM had no effect on two consequences of BLM-AM-induced cytostatic activity, DNA synthesis inhibition and aconitase activity reduction in the L1210 target cell. These results suggest that reactive nitrogen intermediates measured as nitrites are important moieties in our in vivo model of macrophage activation. Further, the identification of this effector molecule presents possibilities for therapeutic and biochemical manipulations.
 ...
PMID:Role of reactive nitrogen intermediate production in alveolar macrophage-mediated cytostatic activity induced by bleomycin lung damage in rats. 170 56

Conditioned medium (CM) from cultures of cytotoxic activated macrophages causes inhibition of mitochondrial respiration, DNA synthesis, and aconitase activity in murine EMT-6 mammary adenocarcinoma cells by an L-arginine dependent effector mechanism. CM induces cytotoxicity and nitrite synthesis in EMT-6 cells in a dose dependent manner. We have identified the soluble factors in CM that induce cytotoxicity and synthesis of inorganic nitrogen oxides from L-arginine by EMT-6 cells. Using functional inhibition experiments, the activity of lipopolysaccharide (LPS), tumor necrosis factor alpha (TNF alpha), and interferon gamma (IFN gamma) in CM was investigated. The LPS inhibitor polymyxin B and TNF alpha antibody produced a modest decrease in nitrite production, while IFN gamma antibody markedly inhibited both nitrite production and cytostasis. Simultaneous treatment with polymyxin B, TNF alpha antibody, and IFN gamma antibody reduced EMT-6 cell nitrite production by 81%, and cytostasis by 74%. By Western blot, IFN gamma and TNF alpha were shown to be present in CM. When CM was subjected to hydrophobic interaction chromatography, a single peak of activity was eluted, and Western blot showed that the active fractions contained IFN gamma. Furthermore, IFN gamma antibody neutralized the activity in these chromatographic fractions. We conclude that induction of inorganic nitrogen oxide synthesis from L-arginine by the synergistic combination of IFN gamma, TNF alpha, and LPS accounts for most of the biologic activity of CM, and that IFN gamma is the major priming factor.
 ...
PMID:Activated macrophage conditioned medium: identification of the soluble factors inducing cytotoxicity and the L-arginine dependent effector mechanism. 190 65

Although nitric oxide (.N = O) biosynthesis is inducible in rat hepatocytes (HC), the physiological significance of .N = O production by these cells is unknown. Short exposure of HC to authentic .N = O led to a concentration-dependent inhibition of mitochondrial aconitase, NADH-ubiquinone oxidoreductase, and succinate-ubiquinone oxidoreductase (complexes I and II of the mitochondrial electron transport chain). Most susceptible to .N = O inhibition was mitochondrial aconitase, in which a reduction in enzyme activity to 20.2 +/- 1.6% of control was observed. In contrast to mitochondrial aconitase, cytosolic aconitase activity was not inhibited by .N = O. After exposure to a maximal inhibitory concentration of .N = O, mitochondrial aconitase activity recovered completely within 6 h. Complex I did not fully recover within this incubation period. Endogenous .N = O biosynthesis was induced in HC by a specific combination of cytokines and lipopolysaccharide. After 18 h of incubation with these stimuli, a significant inhibition of mitochondrial aconitase activity to 70.8 +/- 2.4% of controls was detected. However, this was due only in part to the action of .N = O. A non- .N = O-dependent inhibition of mitochondrial function appeared to be mediated by tumor necrosis factor.
 ...
PMID:Effect of exogenous and endogenous nitric oxide on mitochondrial respiration of rat hepatocytes. 190 97

L-Arginine is required for expression of the activated macrophage cytotoxic effector mechanism that causes inhibition of mitochondrial respiration, aconitase activity, and DNA synthesis in tumor target cells. This effector mechanism is active in the presence of L-arginine even when the cocultivation medium lacks all other amino acids and serum. Cytotoxic activated macrophage-induced inhibition of mitochondrial respiration in target cells is proportional to the concentration of L-arginine in the medium. L-Arginine must be present during the cocultivation period. Pretreatment of cytotoxic activated macrophages with L-arginine or posttreatment of the target cells after cocultivation is not effective. D-Arginine does not substitute for L-arginine and at high concentrations is a competitive inhibitor of the L-arginine-dependent effector mechanism. Other analogues that could not replace L-arginine include agmatine, argininic acid, arginine hydroxamate, and tosyl-L-arginine methyl ester. L-homoarginine, however, can effectively substitute for L-arginine. NG-monomethyl-L-arginine is a potent competitive inhibitor of this effector mechanism. High concentrations of lipopolysaccharide do not reverse inhibition of the L-arginine-dependent effector mechanism by NG-monomethyl-L-arginine. However, inhibition of the effector mechanism by NG-monomethyl-L-arginine can be overridden by increasing the concentration of L-arginine in the culture medium. We compared NGNG-dimethyl-L-arginine and NGN1G-dimethyl-L-arginine with NG-monomethyl-L-arginine as inhibitors of the L-arginine-dependent effector mechanism. The results show that the inhibitory effect of these guanidino methylated derivatives of L-arginine is highly determined by structure. Guanidine is a weak competitive inhibitor of the L-arginine-dependent effector mechanism. The requirement for L-arginine does not appear to be for protein synthesis, creatine biosynthesis, polyamine biosynthesis, or ADP ribosylation reactions. Bacterial lipopolysaccharide is effective as a second signal only when the cocultivation medium contains L-arginine, and this strict L-arginine dependency is not overridden by increasing the concentration of lipopolysaccharide. Bovine liver arginase, by competing for L-arginine in the cocultivation medium, inhibits the L-arginine-dependent activated macrophage cytotoxic effector mechanism.
 ...
PMID:L-arginine is required for expression of the activated macrophage effector mechanism causing selective metabolic inhibition in target cells. 243 29

We tested several monokines and muramyl dipeptide (MDP) to determine whether they induce the L-arginine-dependent effector mechanism in cultured murine macrophages. Recombinant interferon-gamma (rIFN-gamma) and recombinant tumor necrosis factor (rTNF) synergize to induce nitrite (NO2-) and nitrate (NO3-) synthesis from L-arginine as well as to cause inhibition of the iron-dependent enzyme aconitase in macrophages. Unlike rTNF, recombinant interleukin 1 (rIL 1) and rIL 6/B cell stimulatory factor 2 (rIL 6/BSF-2) did not act as cofactors when added to macrophages in the presence of rIFN-gamma. rIFN-gamma plus MDP induced the L-arginine-dependent effector mechanism in murine macrophages. However, induction by rIFN-gamma plus MDP was inhibited by anti-rTNF antibodies which suppressed both NO2-/NO3- synthesis and aconitase inhibition. This result indicates that endogenously produced TNF is involved in the induction of the L-arginine-dependent effector mechanism when MDP is the co-stimulant with rIFN-gamma. In contrast, anti-rTNF antibodies did not fully suppress the effect of combining rIFN-gamma and lipopolysaccharide, suggesting that, in this case, activation of the L-arginine-dependent effector pathway may involve more than induction of TNF synthesis by the macrophages. These results provide information, at a biochemical level, on a mechanism through which combination of IFN-gamma and TNF can modulate macrophage functions involved in the control of cell proliferation.
 ...
PMID:Interferon-gamma and tumor necrosis factor induce the L-arginine-dependent cytotoxic effector mechanism in murine macrophages. 314 79

Biosynthesis of nitric oxide (NO) from L-arginine modulates activity of iron-dependent enzymes, including mitochondrial acontiase, an [Fe-S] protein. We examined the effect of NO on the activity of iron regulatory factor (IRF), a cytoplasmic protein which modulates both ferritin mRNA translation and transferrin receptor mRNA stability by binding to specific mRNA sequences called iron responsive elements (IREs). Murine macrophages were activated with interferon-gamma and lipopolysaccharide to induce NO synthase activity and cultured in the presence or absence of NG-substituted analogues of L-arginine which served as selective inhibitors of NO synthesis. Measurement of the nitrite concentration in the culture medium was taken as an index of NO production. Mitochondria-free cytosols were then prepared and aconitase activity as well as IRE binding activity and induction of IRE binding activity were correlated and depended on NO synthesis after IFN-gamma and/or LPS stimulation. Authentic NO gas as well as the NO-generating compound 3-morpholinosydnonimine (SIN-1) also conversely modulated aconitase and IRE binding activities of purified recombinant IRF. These results provide evidence that endogenously produced NO may modulate the post-transcriptional regulation of genes involved in iron homeostasis and support the hypothesis that the [Fe-S] cluster of IRF mediates iron-dependent regulation.
 ...
PMID:Biosynthesis of nitric oxide activates iron regulatory factor in macrophages. 750 26

Iron-regulatory proteins (IRP1 and IRP2) are RNA-binding proteins that bind to stem-loop structures known as iron-responsive elements (IREs). IREs are located in the 5'- or 3'-untranslated regions (UTRs) of specific mRNAs that encode proteins involved in iron homeostasis. The binding of IRPs to 5' IREs represses translation of the mRNA, whereas the binding of IRPs to 3' IREs stabilizes the mRNA. IRP1 and IRP2 binding activities are regulated by intracellular iron levels. In addition, nitric oxide (NO.) increases the affinity of IRP1 for IREs. The role of NO. in the regulation of IRP1 and IRP2 in rat hepatoma cells was investigated by using the NO.-generating compound S-nitroso-N-acetylpenicillamine (SNAP), or by stimulating cells with multiple cytokines and lipopolysaccharide (LPS) to induce NO. production. Mitochondrial and IRP1 aconitase activities were decreased in cells producing NO(.). NO. increased IRE binding activity of IRP1, but had no effect on IRE binding activity of IRP2. The increase in IRE binding activity of IRP1 was coincident with the translational repression of ferritin synthesis. Transferrin receptor (TfR) mRNA levels were increased in cells treated with NO.-generating compounds, but not in cytokine- and LPS-treated cells. Our data indicate that IRP1 and IRP2 are differentially regulated by NO. in rat hepatoma cells, suggesting a role for IRP1 in the regulation of iron homeostasis in vivo during hepatic inflammation.
 ...
PMID:Differential regulation of IRP1 and IRP2 by nitric oxide in rat hepatoma cells. 863 20

Subversion of mitochondrial electron transport to the production of O2.- has been proposed as a mechanism of tumor necrosis factor (TNF)-mediated cell killing and to a lesser extent interleukin-1 (IL-1) and lipopolysaccharide (LPS) cytotoxicity. We utilized the O2.- -sensitive aconitases to measure changes in steady-state 02.- levels in the mitochondrial matrix and cytoplasm of cultured mammalian cells in response to these inflammatory mediators. TNF alpha did not measurably affect aconitase activity, and thus mitochondrial 02.- production, in either cultured human A549 cells or murine L929 cells while TNF alpha clearly caused cytotoxicity as revealed by impaired mitochondrial respiration. IL-1 alpha and Escherichia coli LPS also failed to affect the aconitase activity in A549 cells. Neither the O2.- scavenger Mn(III) TMPyP nor the H2O2 scavenger catalase protected L929 cells against the cytotoxicity of TNF alpha. In conclusion, TNF, IL-1, and LPS do not appear to exert cytotoxicity, or MnSOD gene induction effects, by eliciting mitochondrial O2.- production.
 ...
PMID:Failure of tumor necrosis factor and interleukin-1 to elicit superoxide production in the mitochondrial matrices of mammalian cells. 883 51

The iron regulatory proteins (IRPs) are an example of different proteins regulating the same metabolic process, iron uptake and metabolism. IRP1 is an iron-sulfur cluster-containing protein that can be converted from a cytosolic aconitase to an RNA binding posttranscriptional regulator in response to nitric oxide (NO). IRP2 lacks aconitase activity and its expression is decreased by NO signaling. In macrophages, NO is produced in response to such inflammatory ligands as interferon-gamma, which is expressed in response to mitogenic and antigenic stimuli, and lipopolysaccharide, a marker of bacterial invasion. Until recently, research results predict that the cellular response to increased NO production should be a decrease in ferritin synthesis, due to IRP1 binding to ferritin mRNA, and an increase in transferrin receptor biosynthesis, due to IRP1 binding to the transferrin mRNA. Surprisingly, however, macrophages exhibit decreased transferrin receptor concentration in response to inflammatory ligands. Bouton and Drapier discuss the physiological role and the mechanisms that may underlie this contradictory response.
 ...
PMID:Iron regulatory proteins as NO signal transducers. 1274 46

Iron regulatory protein-1 (IRP-1) is a bifunctional [4Fe-4S] protein that functions as a cytosolic aconitase or as a trans-regulatory factor controlling iron homeostasis at a post-transcriptional level. Because IRP-1 is a sensitive target protein for nitric oxide (NO), we investigated whether this protein is nitrated in inflammatory macrophages and whether this post-transcriptional modification changes its activities. RAW 264.7 macrophages were first stimulated with interferon-gamma and lipopolysaccharide (IFN-gamma/LPS) and then triggered by phorbol 12-myristate 13-acetate (PMA) in order to promote co-generation of NO* and O*2-.. IRP-1 was isolated by immunoprecipitation and analyzed for protein-bound nitrotyrosine by Western blotting. We show that nitration of endogenous IRP-1 in NO-producing macrophages boosted to produce O*2- was accompanied by aconitase inhibition and impairment of its capacity to bind the iron-responsive element (IRE) of ferritin mRNA. Lost IRE-binding activity was not recovered by exposure of IRP-1 to 2% 2-mercaptoethanol and was not due to protein degradation. Inclusion of cis-aconitate with cell extract to stabilize the [4Fe-4S] cluster of holo-IRP-1 rendered protein insensitive to nitration by peroxynitrite, suggesting that loss of [Fe-S] cluster and subsequent change of conformation are prerequisites for tyrosine nitration. IRP-1 nitration was strongly reduced when IFN-gamma/LPS/PMA-stimulated cells were incubated with myeloperoxidase inhibitors, which points to the contribution of the nitrite/H2O2/peroxidase pathway to IRP-1 nitration in vivo. Interestingly, under these conditions, IRP-1 recovered full IRE binding as assessed by treatment with 2% 2-mercaptoethanol. Peroxidase-mediated nitration of critical tyrosine residues, by holding IRP-1 in an inactive state, may constitute, in activated macrophages, a self-protecting mechanism against iron-induced toxicity.
 ...
PMID:Endogenous nitration of iron regulatory protein-1 (IRP-1) in nitric oxide-producing murine macrophages: further insight into the mechanism of nitration in vivo and its impact on IRP-1 functions. 1525 60


1 2 Next >>