NF-kappaB and AP-1 activation by nitric oxide attenuated apoptotic cell death in RAW 264.7 macrophages

Regulation of the hypoxia-inducible factor 1alpha by the inflammatory mediators nitric oxide and tumor necrosis factor-alpha in contrast to desferroxamine and phenylarsine oxide

Hypoxic/ischemic conditions provoke activation of the hypoxia-inducible factor-1 (HIF-1), which functions as a transcription factor. HIF-1 is composed of the HIF-1alpha and -beta subunits, and stability regulation occurs via accumulation/degradation of HIF-1alpha with the notion that a prolyl hydroxylase accounts for changes in protein level. In addition, there is evidence that HIF-1 is up-regulated by diverse agonists during normoxia. We investigated the impact of inflammatory mediators nitric oxide (NO) and tumor necrosis factor-alpha (TNF-alpha) on HIF-1alpha regulation. For comparison, LLC-PK(1) cells were exposed to hypoxia, stimulated with desferroxamine (DFX, known to mimic hypoxia), and the thiol-cross-linking agent phenylarsine oxide (PAO). Although all stimuli elicited HIF-1alpha stabilization with differences in the time-dependent accumulation pattern, significant variations appeared with regard to signaling. With the use of a superoxide anion (O(2-)) generator, we established an O(2-)-sensitive pathway that blocked HIF-1alpha stabilization in response to NO and TNF-alpha while DFX- and PAO-evoked HIF-1alpha stabilization appeared O(2-)-insensitive. NO and TNF-alpha signaling required phosphorylation events, especially activation of the phosphatidylinositol 3-kinase/Akt, which is in contrast to DFX and PAO. Based on HIF-1-dependent luciferase reporter gene analysis, it was found that, in contrast to NO and TNF-alpha, PAO resembled a stimulus that induced a dysfunctional HIF-1 complex. These data indicate that diverse agonists activate HIF-1alpha under normoxic conditions by employing different signaling pathways.

Regulation of inhibitor of apoptosis expression by nitric oxide and cytokines: relation to apoptosis induction in rat mesangial cells and raw 264.7 macrophages

Mesangial cells and RAW 264.7 macrophages respond to different nitric oxide (NO) donors within 16 to 24 h or 6 to 8 h, respectively, with apoptotic cell death. RAW 264.7 macrophages also die in response to endogenous NO production. In contrast, endogenous NO production fails to significantly induce cell death in mesangial cells. It was hypothesized that differences in the expression of antiapoptotic proteins, in particular the inhibitor of apoptosis (IAP) protein family, might be responsible for this cell type-specific behavior. Therefore, IAP expression was investigated in relation to apoptosis induction in response to NO and cytokines in both cell types. In mesangial cells, interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha induced cellular inhibitor of apoptosis 1 (cIAP1) mRNA expression within 3 h. In contrast, X chromosome-linked inhibitor of apoptosis (XIAP) mRNA levels remained unaffected by cytokines. Although coincubation of cells with IL-1beta and tumor necrosis factor-alpha or IL-1beta and basic fibroblast growth factor resulted in synergistic induction of inducible NO synthase, comparable potentiating effects on cIAP1 induction were absent. Exogenously released NO from NO donors promoted cIAP1 mRNA upregulation in mesangial cells, whereas XIAP mRNA was downregulated. However, the changes observed on the mRNA level were not adequately translated to the protein level, and corresponding values for cIAP1 and XIAP were only slightly affected. In contrast, in lipopolysaccharide/interferon-gamma-stimulated RAW 264.7 macrophages, massive NO-dependent downregulation of cIAP1 and XIAP protein levels, which correlated temporally with the induction of apoptosis, was observed. This effect was at least partially reversed by N(G)-monomethyl-L-arginine, an inhibitor of NO synthase activity. In summary, a direct correlation between the downregulation of IAP protein levels and the induction of apoptosis by endogenous NO was observed in macrophages. In contrast, a stable level of IAP protein in mesangial cells might represent a mechanism for the resistance of the cells to endogenously produced NO.

Transcription factors p53 and HIF-1alpha as targets of nitric oxide

It is widely recognized that the production of nitric oxide (NO) from L-arginine metabolism is an essential determinate of diverse signalling cascades throughout the body, with a major impact during nonspecific host defence. Biological actions of NO and derived species comprise physiological as well as pathological entities, with an impressive and steadily growing number of signalling pathways and/or protein targets being involved. It is now appreciated that NO not only acts as an effector molecule but also as an autocrine as well as paracrine modulator of rapid and delayed cellular responses. Among multiple targets the tumour suppressor p53 and the hypoxia inducible factor-1alpha (HIF-1alpha) emerged. Accumulation of p53 in response to NO delivery may account for an interference in cell cycle progression and/or initiation of apoptosis that is found in close correlation with inducible NO synthase (NOS) expression. Quite similarly, accumulation of HIF-1alpha not only occurs during hypoxia, but also under conditions of NO delivery, thus mimicking a situation of reduced oxygen availability. Interestingly, p53 and HIF-1alpha share regulatory elements that cause protein stabilization in part as a result of impaired ubiquitin-evoked protein degradation. Here, we summarize current knowledge on the impact of NO on p53- and HIF-1alpha-stabilization and we will discuss pathophysiological consequences. These examples may help to shape and refine current concepts of NO action with an emphasis on transcription factor regulation.

Nitric oxide suppresses IL-8 transcription by inhibiting c-Jun N-terminal kinase-induced AP-1 activation

The role of activator protein-1 (AP-1) in tumor necrosis factor-alpha (TNF-alpha)-induced interleukin-8 (IL-8) gene expression was evaluated. We showed that TNF-alpha activates AP-1 in the transformed endothelial cell line ECV304 by transient transfections of IL-8 promoter construct pGL-3BF(2). Mutation of either the AP-1 site or the NF-IL-6 site on the IL-8 promoter suppressed the TNF-alpha-induced activation, suggesting cooperation between these transcription factors and transcription factor NF-kappaB. Overexpression of dominant negative mutants of c-Jun suppressed AP-1-driven transcription of the IL-8 promoter following stimulation by TNF-alpha, suggesting that cooperative interaction between AP-1 and NF-kappaB is essential for IL-8 transcription in the presence of TNF-alpha. We also showed that nitric oxide (NO), in the form of an exogenous NO donor, suppressed the level of activation of the AP-1 subunit, c-Jun, by down-regulation of c-Jun NH2 terminal kinase. This down-regulation could be the putative mechanism of action for NO-mediated inhibition of IL-8 secretion in activated endothelium. These observations suggest for the first time that NO has broad suppressive activities on various proinflammatory effectors in activated endothelium.

Ergolide, sesquiterpene lactone from Inula britannica, inhibits inducible nitric oxide synthase and cyclo-oxygenase-2 expression in RAW 264.7 macrophages through the inactivation of NF-kappaB

We investigated the mechanism of suppression of inducible nitric oxide synthase (iNOS) and cyclo-oxygenase-2 (COX-2) by ergolide, sesquiterpene lactone from Inula britannica. iNOS activity in cell-free extract of LPS/IFN-gamma-stimulated RAW 264.7 macrophages was markedly attenuated by the treatment with ergolide. Its inhibitory effect on iNOS was paralleled by decrease in nitrite accumulation in culture medium of LPS/IFN-gamma-stimulated RAW 264.7 macrophages in a concentration-dependent manner. However, its inhibitory effect does not result from direct inhibition of the catalytic activity of NOS. Ergolide markedly decreased the production of prostaglandin E(2) (PGE(2)) in cell-free extract of LPS/IFN-gamma-stimulated RAW 264.7 macrophages in a concentration-dependent manner, without alteration of the catalytic activity of COX-2 itself. Ergolide decreased the level of iNOS and COX-2 protein, and iNOS mRNA caused by stimulation of LPS/IFN-gamma in a concentration-dependent manner, as measured by Western blot and Northern blot analysis, respectively. Ergolide inhibited nuclear factor-kappaB (NF-kappaB) activation, a transcription factor necessary for iNOS and COX-2 expression in response to LPS/IFN-gamma. This effect was accompanied by the parallel reduction of nuclear translocation of subunit p65 of NF-kappaB as well as IkappaB-alpha degradation. In addition, these effects were completely blocked by treatment of cysteine, indicating that this inhibitory effect of ergolide could be mediated by alkylation of NF-kappaB itself or an upstream molecule of NF-kappaB. Ergolide also directly inhibited the DNA-binding activity of active NF-kappaB in LPS/IFN-gamma-pretreated RAW 264.7 macrophages. These results demonstrate that the suppression of NF-kappaB activation by ergolide might be attributed to the inhibition of nuclear translocation of NF-kappaB resulted from blockade of the degradation of IkappaB and the direct modification of active NF-kappaB, leading to the suppression of the expression of iNOS and COX-2, which play important roles in inflammatory signalling pathway.

Cot kinase induces cyclooxygenase-2 expression in T cells through activation of the nuclear factor of activated T cells

Cyclooxygenase-2 (COX-2) is induced in human T lymphocytes upon T cell receptor triggering. Here we report that Cot kinase, a mitogen-activated protein kinase kinase kinase involved in T cell activation, up-regulates COX-2 gene expression in Jurkat T cells. Induction of COX-2 promoter activity by Cot kinase occurred mainly through activation of the nuclear factor of activated T cells (NFAT). Mutation of the distal (-105/-97) and proximal (-76/-61) NFAT response elements in the COX-2 promoter abolished the activation induced by Cot kinase. Even more, coexpression of a dominant negative version of NFAT inhibited Cot kinase-mediated COX-2 promoter activation, whereas cotransfection of a constitutively active version of the calcium-dependent phosphatase calcineurin synergizes with Cot kinase in the up-regulation of COX-2 promoter-driven transcription. Strikingly, Cot kinase increased transactivation mediated by a GAL4-NFAT fusion protein containing the N-terminal transactivation domain of NFATp. In contrast to phorbol ester plus calcium ionophore A23187, Cot kinase increases both COX-2 promoter activity and NFAT-mediated transactivation in a cyclosporin A-independent manner. These data indicate that Cot kinase up-regulates COX-2 promoter-driven transcription through the NFAT response elements, being the Cot kinase-induced NFAT-dependent transactivation presumably implicated in this up-regulation.

Suppression by a sesquiterpene lactone from Carpesium divaricatum of inducible nitric oxide synthase by inhibiting nuclear factor-kappaB activation

Excessive nitric oxide (NO) produced by inducible NO synthase (iNOS) acts as a causative regulator in various inflammatory disease states. Carpesium divaricatum has been used in Korean traditional herbal medicine for its antipyretic, analgesic, vermifugic, and anti-inflammatory properties. We investigated the molecular mechanism for the suppression of lipopolysaccharide/interferon-gamma (LPS/IFN-gamma)-induced NO production in RAW 264.7 macrophages by the sesquiterpene lactone 2beta,5-epoxy-5,10-dihydroxy-6alpha-angeloyloxy-9beta-isobutyloxy-germacran-8alpha,12-olide (C-1), which has been identified recently as a new compound from C. divaricatum. C-1 decreased NO production in LPS/IFN-gamma-stimulated RAW 264.7 cells in a concentration-dependent manner, with an IC50 of approximately 2.16 microM; however, it had no direct effect on the iNOS activity of fully LPS/IFN-gamma-stimulated RAW 264.7 cells. Furthermore, treatment with C-1 led to a decrease in iNOS protein and mRNA. These effects appear to be due to inhibition of nuclear factor-kappaB (NF-kappaB) activation through a mechanism involving stabilization of the NF-kappaB/inhibitor of the kappaB (I-kappaB) complex, since inhibition of NF-kappaB DNA binding activity by C-1 was accompanied by a parallel reduction of nuclear translocation of subunit p65 of NF-kappaB and I-kappaBalpha degradation. Taken together, the results suggest that the ability of C-1 to inhibit iNOS gene expression may be responsible, in part, for its anti-inflammatory effects.

Biphasic regulation of NF-kappa B activity underlies the pro- and anti-inflammatory actions of nitric oxide

Expression of inducible NO synthase (iNOS) by macrophages is a prerequisite for the production of high output NO, which mediates many bactericidal and tumoricidal actions of these immune cells. The expression of iNOS in mammalian cells is governed predominantly by the transcription factor, NF-kappa B, which regulates the expression of many host defense proteins. In the present study, we characterize a novel, biphasic effect of NO on NF-kappa B activity in murine macrophages. This mechanism depends on the local concentration of NO and enables it both to up- and down-regulate the expression of host defense proteins including iNOS, cyclooxygenase-2, and IL-6. This biphasic activity of NO appears to play a pivotal role in the time course of activation of these immune cells and, by inference, in facilitating the initiation of a defense response against pathogenic stimuli and in its termination to limit tissue damage. This mechanism may explain at least in part the reported ability of NO to act in both a pro- and anti-inflammatory manner.

Role of nitric oxide in carcinogenesis and tumour progression

Nitric oxide (NO) is a short-lived molecule required for many physiological functions, produced from L-arginine by NO synthases (NOS). It is a free radical, producing many reactive intermediates that account for its bioactivity. Sustained induction of the inducible form of NOS (iNOS) in chronic inflammation may be mutagenic, through NO-mediated DNA damage or hindrance to DNA repair, and thus potentially carcinogenic. Expression of iNOS is positively associated with P53 mutation in tumours of the colon, lung, and oropharynx. Progression of a large majority of human and experimental tumours seems to be stimulated by NO resulting from activation of iNOS or constitutive NOS, whereas inhibition is documented in others. This discrepancy is largely explained by differential sensitivity of tumour cells to NO-mediated cytostasis or apoptosis and clonal evolution of NO-resistant and NO-dependent cells. P53 mutation or loss is one of many events linked with NO resistance and dependence. NO can stimulate tumour growth and metastasis by promoting migratory, invasive, and angiogenic abilities of tumour cells, which may also be triggered by activation of cyclo-oxygenase (COX)-2. Thus, selective inhibitors of NOS, COX, or both may have a therapeutic role in certain cancers.

Redundancy in the signaling pathways and promoter elements regulating cyclooxygenase-2 gene expression in endotoxin-treated macrophage/monocytic cells

Macrophage expression of cyclooxygenase-2 (COX-2), the inducible isoform of COX, is up-regulated by pro-inflammatory stimuli both in vivo and in vitro. Here we investigated the mechanisms regulating COX-2 gene expression in macrophage/monocytic cells. Lipopolysaccharide (LPS) is known to induce de novo COX-2 mRNA expression in these cells. Transient cotransfections with a COX-2 promoter-luciferase construct and different expression vectors showed that LPS up-regulates COX-2 transcription through both mitogen-activated protein kinase (MAPK) and protein kinase C (PKC) pathways. Cotransfections with expression vectors for dominant negative mutants of MAPK and PKC isoforms did not suppress the effects of LPS on COX-2. Electrophoretic mobility shift assays and transient transfection experiments with deleted and mutated variants of a COX-2 promoter-luciferase construct showed that NFkappaB, NF-IL6, and CRE promoter sites mediate gene transcription independently in response to LPS treatment. In these experiments, isolated NFkappaB, NF-IL6, and CRE promoter sites were less effective than the intact promoter in mediating COX-2 transcription. Cotransfections with mutated COX-2 promoter-luciferase constructs and expression vectors showed that each one of these promoter elements can be activated by LPS through both MAPK and PKC pathways to induce gene expression. In summary, there is redundancy in the signaling pathways and promoter elements regulating COX-2 transcription in endotoxin-treated cells of macrophage/monocytic lineage.

Nitric oxide augments release of chemokines from monocytic U937 cells: modulation by anti-inflammatory pathways

Nitric oxide (NO) appears to act as an inflammatory mediator on monocytic cells. Exogenous NO augmented release of chemokines from human promonocytic U937 cells and peripheral blood mononuclear cells. Pharmacological strategies aiming at modulation of NO-induced release of interleukin-8 (IL-8) were investigated in U937 cells in detail. Release of IL-8 was down-regulated by transforming growth factor beta2 (TGF-beta2), by the protein tyrosine-kinase inhibitor genistein, and via rises in intracellular cyclic AMP, generated by prostaglandin E(2), rolipram, pentoxifylline, forskolin, or dibutyryl-cyclic AMP. In addition, incubation with the synthetic glucocorticoid dexamethasone or suppression of activity of p38 mitogen-activated protein (MAP) kinases by SB-203580 modulated release of IL-8. Activation of p38 MAP kinases was confirmed by the demonstration of an augmented appearance of phosphorylated p38 in the presence of NO. The present data suggest that exposure to exogenous NO resembles activation of U937 cells by proinflammatory stimuli. The anti-inflammatory cytokine TGF-beta2, as well as anti-inflammatory or immunosuppressive agents such as genistein, pentoxifylline, rolipram, dexamethasone, and SB-203580 modulate inflammatory, chemokine-inducing actions of NO.

Expression of cyclooxygenase-2 and nitrotyrosine in human gastric mucosa before and after Helicobacter pylori eradication

To determine whether cure of Helicobacter pylori infection influences the expression of COX-2 and nitrotyrosine in the distal stomach of humans, biopsy specimens were examined immunohistochemically. H. pylori infection was determined using a rapid urease test, culture and histology. Positive staining of COX-2/nitrotyrosine in the epithelium was expressed as the percentage of stained cells to the total epithelial cells. There was a significant increase in COX-2/nitrotyrosine staining in H. pylori -positive subjects compared with H. pylori -negative subjects. Cure of the infection resulted in a significant decrease in both COX-2/nitrotyrosine staining in all patients (52.1+/-12.1% vs 15. 4+/-7.2%, P<0.001; and 57.3+/-13.6% vs 36.1+/-18.0%, P<0.01, respectively). However, immunoreactivity of COX-2/nitrotyrosine was observed in all cases with intestinal metaplasia even after the cure of H. pylori infection.Thus, cure of H. pylori infection may decrease the risk of gastric carcinogenesis due to COX-2 and NO-related compounds in gastric mucosa but not in those patients with intestinal metaplasia.

Salmonella-induced caspase-2 activation in macrophages: a novel mechanism in pathogen-mediated apoptosis

The enterobacterial pathogen Salmonella induces phagocyte apoptosis in vitro and in vivo. These bacteria use a specialized type III secretion system to export a virulence factor, SipB, which directly activates the host's apoptotic machinery by targeting caspase-1. Caspase-1 is not involved in most apoptotic processes but plays a major role in cytokine maturation. We show that caspase-1-deficient macrophages undergo apoptosis within 4-6 h of infection with invasive bacteria. This process requires SipB, implying that this protein can initiate the apoptotic machinery by regulating components distinct from caspase-1. Invasive Salmonella typhimurium targets caspase-2 simultaneously with, but independently of, caspase-1. Besides caspase-2, the caspase-1-independent pathway involves the activation of caspase-3, -6, and -8 and the release of cytochrome c from mitochondria, none of which occurs during caspase-1-dependent apoptosis. By using caspase-2 knockout macrophages and chemical inhibition, we establish a role for caspase-2 in both caspase-1-dependent and -independent apoptosis. Particularly, activation of caspase-1 during fast Salmonella-induced apoptosis partially relies on caspase-2. The ability of Salmonella to induce caspase-1-independent macrophage apoptosis may play a role in situations in which activation of this protease is either prevented or uncoupled from the induction of apoptosis.

Attenuation of macrophage apoptosis by the cAMP-signaling system

Previous studies revealed that expression and activation of cyclooxygenase-2 (Cox-2) conveyed a protective principle in murine macrophages, thus attenuating pro-apoptotic actions of chemotherapeutic agents or programmed cell death as a result of massive nitric oxide (NO) generation. Expression of Cox-2 was achieved by treatment of cells with lipopolysaccharide/interferon-gamma or nontoxic doses of NO releasing agents. We reasoned E-type prostanoid formation, and in turn an intracellular cAMP increase as the underlying protective mechanism. To prove our hypothesis, we analyzed the effects of lipophilic cAMP-analogs on NO, cisplatin, or etoposide induced apoptosis in RAW 264.7 macrophages. Selected apoptotic parameters comprised DNA fragmentation (diphenylamine assay), annexin V staining of phosphatidylserine, caspase activity (quantitated by the cleavage of a fluorogenic caspase-3-like substrate Ac-DEVD-AMC), and mitochondrial membrane depolarisation (delta psi). Western blots detected accumulation of the tumor suppressor protein p53, relocation of cytochrome c to the cytosol, and expression of the anti-apoptotic protein Bcl-xL. Prestimulation with lipophilic cAMP-analogs attenuated apoptosis with the notion that cell death parameters were basically absent. To verify gene induction by cAMP in association with protection we established activation of cAMP response element binding protein (CREB) by gel-shift analysis and moreover, treated macrophages with oligonucleotides containing a cAMP-responsive element (CRE) in order to scavenge CREB. Decoy oligonucleotides, but not control oligonucleotides, attenuated cAMP-evoked protection and reestablished pro-apoptotic parameters. We conclude that gene induction by cAMP protects macrophages towards apoptosis that occurs as a result of excessive NO formation or addition of chemotherapeutica. Attenuating programmed cell death by the cAMP-signaling system may be found in association with Cox-2 expression and tumor formation.

Requirement of the inducible nitric oxide synthase pathway for IL-1-induced osteoclastic bone resorption

Nitric oxide has been suggested to be involved in the regulation of bone turnover, especially in pathological conditions characterized by release of bone-resorbing cytokines. The cytokine IL-1 is thought to act as a mediator of periarticular bone loss and tissue damage in inflammatory diseases such as rheumatoid arthritis. IL-1 is a potent stimulator of both osteoclastic bone resorption and expression of inducible nitric oxide synthase (iNOS) in bone cells and other cell types. In this study, we investigated the role that the iNOS pathway plays in mediating the bone-resorbing effects of IL-1 by studying mice with targeted disruption of the iNOS gene. Studies in vitro and in vivo showed that iNOS-deficient mice exhibited profound defects of IL-1-induced osteoclastic bone resorption but responded normally to calciotropic hormones such as 1,25 dihydroxyvitamin D3 and parathyroid hormone. Immunohistochemical studies and electrophoretic mobility shift assays performed on bone marrow cocultures from iNOS-deficient mice showed abnormalities in IL-1-induced nuclear translocation of the p65 component of NFkappaB and in NFkappaB-DNA binding, which were reversed by treatment with the NO donor S-nitroso-acetyl penicillamine. These results show that the iNOS pathway is essential for IL-1-induced bone resorption and suggest that the effects of NO may be mediated by modulating IL-1-induced nuclear activation of NFkappaB in osteoclast precursors.

Activation of the nitric oxide synthase 2 pathway in the response of bone marrow stromal cells to high doses of ionizing radiation

Reverse transcription-polymerase chain reaction and immunofluorescence analysis of D2XRII murine bone marrow stromal cells showed that gamma irradiation with doses of 2-50 Gy from (137)Cs stimulated expression of nitric oxide synthase 2 (Nos2, also known as iNos). The activation of Nos2 was accompanied by an increase in the fluorescence of 4,5-diaminofluorescein diacetate, a nitric oxide trap, and accumulation of 3-nitrotyrosine within cellular proteins in a dose-dependent manner. These effects were inhibited by actinomycin D and by N-[3-(aminomethyl)benzyl]acetamidine dihydrochloride, a specific inhibitor of Nos2. The induction of Nos2 expression and Nos2-dependent release of nitric oxide in D2XRII cells was observed within 24 h after irradiation and was similar in magnitude to that observed in cultures incubated with Il1b and Tnf. We conducted (1) confocal fluorescence imaging of 3-nitrotyrosine in bone marrow cells of irradiated C57BL/6J mice and (2) 3-nitrotyrosine fluorescence imaging of FDC-P1JL26 hematopoietic cells that were cocultured with previously irradiated D2XRII bone marrow stromal cells. Exposure to ionizing radiation increased the production of 3-nitrotyrosine in irradiated bone marrow cells in vivo and in nonirradiated FDC-P1JL26 cells cocultured with irradiated D2XRII cells for 1 or 4 h. We suggest that nitrative/oxidative stress to the transplanted multilineage hematopoietic cells due to exposure to nitric oxide released by host bone marrow stromal cells may contribute to the genotoxic events associated with malignant alterations in bone marrow tissue of transplant recipients who are prepared for engraftment by total-body irradiation.

Nitric oxide: an inhibitor of NF-kappaB/Rel system in glial cells

Nitric oxide (NO) has been reported to regulate NF-kappaB, one of the best-characterized transcription factors playing important roles in many cellular responses to a large variety of stimuli. NO has been suggested to induce or inhibit the activation of NF-kappaB, its effect depending, among others, on the cell type considered. In this review, the inhibitory effect of NO on NF-kappaB (and subsequent suppression of NF-kappaB-dependent gene expression) in glial cells is reported. In particular, exogenous and endogenous NO has been observed to keep NF-kappaB suppressed, thus preventing the expression of NF-kappaB-induced genes, such as inducible NO synthase itself or HIV-1 long terminal repeat. Furthermore, the possible molecular mechanisms of NO-mediated NF-kappaB inhibition are discussed. More specifically, NO has been reported to suppress NF-kappaB activation inducing and stabilizing the NF-kappaB inhibitor, IkappaB-alpha. On the other hand, NO may inhibit NF-kappaB DNA binding through S-nitrosylation of cysteine residue (i. e., Cys62) of the p50 subunit. As a whole, a novel concept that the balance of intracellular NO levels may control the induction of NF-kappaB in glial cells has been hypothesized.

Expression of a functional inducible nitric oxide synthase in hairy cell leukaemia and ESKOL cell line

The expression of nitric oxide synthase (NOS) isoforms was investigated in the established ESKOL hairy cell line and in leukemic cells of patients with hairy cell leukemia (HCL). By reverse transcription-polymerase chain reaction (RT-PCR), these cells were found to spontaneously express inducible NOS (iNOS)-specific mRNA, but not endothelial constitutive NOS (ecNOS) mRNA. The iNOS protein was detected by immunofluorescence in the cytoplasm of permeabilized leukemic cells and ESKOL cells, using different anti-iNOS monoclonal antibodies. A protein of 135 kDa was identified by Western blotting in ESKOL and HCL lysates, confirming the presence of an iNOS in these cells. Cytosolic homogenates displayed NOS catalytic activity, as measured by the conversion of 14C-labelled L-arginine into 14C L-citrulline and by detection in situ using the DAF-2DA (diaminofluorescein diacetate) NO-sensitive fluorescent probe. Ligation of CD23 (low affinity IgE receptor) was found to increase iNOS expression in ESKOL and conversely to decrease the percentage of cells undergoing apoptosis, as measured by the percentage of cells expressing annexin V. These results indicate that, as in chronic B cell lymphocytic leukemia cells (B-CLL) a functional iNOS is expressed constitutively in hairy cells that contributes to protecting these tumoral cells from apoptosis.

Limitation of nitric oxide production: cells from lymph node and spleen exhibit distinct difference in nitric oxide production

Many types of cells in the immune system have been found to produce nitric oxide (NO), which performs multiplex functions. However, in myelin basic protein peptide 68-86 (MBP 68-86)-induced experimental autoimmune encephalomyelitis (EAE) in Lewis rats, we found that elevated NO production was generated from spleen cells (SC), not from lymph node cells (LNC). LNC expressed lower NO synthase 2 (NOS2) and produced lower levels of NO than SC upon MBP 68-86 stimulation. Expression of B7-1(CD80) and B7-2(CD86) molecules was much lower on LNC than on SC. Blocking of B7-1 or B7-2 ligation resulted in reduced NO production by SC. Unlike SC, LNC were resistant to interferon-gamma- or lipopolysaccharide-induced NO production. NO derived from SC suppressed cell proliferation and induced apoptosis in vitro. Addition of N(omega)-nitrol-L-arginine methylester (L-NAME) into cell cultures promoted cell expansion and reduced apoptosis. These results indicate that NO production originates from SC, but not from LNC. Low expression of co-stimulatory molecules and NOS2 of LNC limits NO induction. The high levels of NO derived from SC are involved in the self-limiting mechanisms of autoimmune responses by inhibiting cell expansion and promoting cell apoptosis.

Reactive oxygen and reactive nitrogen intermediates in innate and specific immunity

Nitric oxide, nitric oxide derivatives and reactive oxygen intermediates are toxic molecules of the immune system which contribute to the control of microbial pathogens and tumors. There is recent evidence for additional functions of these oxygen metabolites in innate and adaptive immunity; these functions include the modulation of the cytokine response of lymphocytes and the regulation of immune cell apoptosis, as well as immunodeviating effects. Components of several signal transduction pathways have been identified as intracellular targets for reactive nitrogen and oxygen intermediates.

Nitric oxide inhibits growth of glomerular mesangial cells: role of the transcription factor EGR-1

Nitric oxide inhibits growth of glomerular mesangial cells: Role of the transcription factor Egr-1.

BACKGROUND

In previous studies, we found a close link of early growth response gene-1 (Egr-1) expression to mesangial cell (MC) proliferation. Antiproliferative agents inhibited mitogen-induced Egr-1 expression. Here we investigated the effect of S-nitrosoglutathione (GSNO) on the proliferation of MCs, specifically asking how GSNO regulates the transcription factor Egr-1, which we have previously shown to be critical for the induction of MC mitogenesis.

METHODS

The proliferation of MCs was measured by thymidine incorporation and cell counting. Egr-1 mRNA and protein levels were detected by Northern and Western blots. Electrophoretic mobility shift assays (EMSAs) and chloramphenicol acetyltransferase (CAT) assays were performed to test whether GSNO modulates DNA binding and transcriptional activation of Egr-1.

RESULTS

GSNO strongly inhibited serum-induced MC proliferation (-84% at 1 mmol/L). A mild inhibition of serum-induced Egr-1 mRNA was observed at GSNO concentrations from 50 to 200 micromol/L, whereas mRNA levels increased again at concentrations above 500 micromol/L. This increased mRNA expression, however, was not translated into Egr-1 protein. Instead, Egr-1 protein induction was inhibited (-40%). EMSAs indicated that GSNO inhibited specific binding of Egr-1 to its DNA consensus sequence. Moreover, transcriptional activation by Egr-1 in CAT assays using a reporter plasmid bearing three Egr-1 binding sites was strongly suppressed by GSNO.

CONCLUSIONS

Our data identify GSNO as a potent inhibitor of MC growth with potential beneficial effects in proliferative glomerular diseases. This antimitogenic property is mediated at least in part by inhibitory effects of GSNO on Egr-1 protein levels and by reducing the ability of Egr-1 to activate transcription by impairing its DNA binding activity.

Implications of inducible nitric oxide synthase expression and enzyme activity

We summarize here our current knowledge about inducible nitric oxide synthase (NOS) activity in human diseases and disorders. As basic research discovers more and more effects of low or high concentrations of NO toward molecular and cellular targets, successful therapies involving inhibition of NO synthesis or application of NO to treat human diseases are still lacking. This is in part due to the fact that the impact of NO on cell function or death are complex and often even appear to be contradictory. NO may be cytotoxic but may also protect cells from a toxic insult; it is apoptosis-inducing but also exhibits prominent anti-apoptotic activity. NO is an antioxidant but may also compromise the cellular redox state via oxidation of thiols like glutathione. NO may activate specific signal transduction pathways but is also reported to inhibit exactly these, and NO may activate or inhibit gene transcription. The situation may even be more complicated, because NO, depending on its concentration, may react with oxygen or the superoxide anion radical to yield reactive species with a much broader chemical reaction spectrum than NO itself. Thus, the action of NO during inflammatory reactions has to be considered in the context of timing and duration of its synthesis as well as stages and specific events in inflammation.

Control of apoptosis by Rel/NF-kappaB transcription factors

Apoptosis is a physiological process critical for organ development, tissue homeostasis, and elimination of defective or potentially dangerous cells in complex organisms. Apoptosis can be initiated by a wide variety of stimuli, which activate a cell suicide program that is constitutively present in most vertebrate cells. In diverse cell types, Rel/NF-kappaB transcription factors have been shown to have a role in regulating the apoptotic program, either as essential for the induction of apoptosis or, perhaps more commonly, as blockers of apoptosis. Whether Rel/NF-kappaB promotes or inhibits apoptosis appears to depend on the specific cell type and the type of inducer. An understanding of the role of Rel/NF-kappaB transcription factors in controlling apoptosis may lead to the development of therapeutics for a wide variety of human diseases, including neurodegenerative and immune diseases, and cancer.