A classical enhancer element responsive to both lipopolysaccharide and interferon-gamma augments induction of the iNOS gene in mouse macrophages

Anti-Inflammatory Effects of Morinda citrifolia Extract against Lipopolysaccharide-Induced Inflammation in RAW264 Cells

Leaves of Morinda citrifolia (noni) have been used in Polynesian folk medicine for the treatment of pain and inflammation, and their juice is very popular worldwide as a functional food supplement. This study aimed to demonstrate that M. citrifolia seed extract exerts anti-inflammatory effects on RAW264 cells stimulated by lipopolysaccharide. To confirm the inhibitory effect of M. citrifolia seed extract, we assessed the production of nitric oxide (NO) and inflammatory cytokines. The M. citrifolia seed extract showed a significant inhibition of NO production, with no effect on cell viability, and was more active than M. citrifolia seed oil, leaf extract, and fruit extract. The M. citrifolia seed extract was found to reduce the expression of inducible NO synthase and tumor necrosis factor-alpha of pro-inflammatory cytokines. These results suggest that the anti-inflammatory effect of M. citrifolia seed extract is related to a reduction in the expression of inflammatory mediators and support its potential therapeutic use.

Badger macrophages fail to produce nitric oxide, a key anti-mycobacterial effector molecule

The European badger is recognised as a wildlife reservoir for bovine tuberculosis (bTB); the control of which is complex, costly and controversial. Despite the importance of badgers in bTB and the well-documented role for macrophages as anti-mycobacterial effector cells, badger macrophage (bdMφ) responses remain uncharacterised. Here, we demonstrate that bdMφ fail to produce nitric oxide (NO) or upregulate inducible nitric oxide synthase (iNOS) mRNA following Toll-like receptor (TLR) agonist treatment. BdMφ also failed to make NO after stimulation with recombinant badger interferon gamma (bdIFNγ) or a combination of bdIFNγ and lipopolysaccharide. Exposure of bdMφ to TLR agonists and/or bdIFNγ resulted in upregulated cytokine (IL1β, IL6, IL12 and TNFα) mRNA levels indicating that these critical pathways were otherwise intact. Although stimulation with most TLR agonists resulted in strong cytokine mRNA responses, weaker responses were evident after exposure to TLR9 agonists, potentially due to very low expression of TLR9 in bdMφ. Both NO and TLR9 are important elements of innate immunity to mycobacteria, and these features of bdMφ biology would impair their capacity to resist bTB infection. These findings have significant implications for the development of bTB management strategies, and support the use of vaccination to reduce bTB infection in badgers.

Both basal and enhancer κB elements are required for full induction of the mouse inducible nitric oxide synthase gene

The transcriptional regulatory region of the mouse inducible nitric oxide synthase (iNOS) gene has two KB elements, one enhancer-linked (KBII) and the other (KBI) proximal to its core promoter. Mutation of κBII substantially reduced the extent to which the iNOS promoter could be induced by LPS and interfered with augmented responsiveness of the promoter to LPS+IFN-γ. Mutation of KBI had a quantitatively less dramatic negative effect on LPS responsiveness and this construct still showed augmented responsiveness to LPS+IFN-γ. When both KB elements were mutated, inducibility by LPS and, in particular, by LPS+IFN-γ was paradoxically restored, compared with the mutated KBII alone, suggesting cooperative interactions among the transcription factors that trans-activate the iNOS gene. In vivo footprint analysis showed that both KB elements were bound by protein complexes when macrophages were stimulated with LPS ± IFN-γ. Furthermore, KBI was bound even in untreated cells, suggesting that KB binding proteins might also have a negative influence on expression of the gene. Both KBI and KBII were bound by NF-KB/Rel proteins found in nuclear extracts prepared from macrophages treated with LPS ± IFN-γ, although the specificity of binding to each element was different. Our results show that, while NF-KB/Rel proteins are required for maximal expression of the iNOS gene, alone they are not alone sufficient. Furthermore, the results reported here show that the augmentative effect of IFN-γ on the LPS-induced expression of the iNOS gene is not mediated through increased activation of NF-KB/Rel.

Mesenchymal stem cells use IDO to regulate immunity in tumor microenvironment

Mesenchymal stem cells (MSC) are present in most, if not all, tissues and are believed to contribute to tissue regeneration and the tissue immune microenvironment. Murine MSCs exert immunosuppressive effects through production of inducible nitric oxide synthase (iNOS), whereas human MSCs use indoleamine 2,3-dioxygenase (IDO). Thus, studies of MSC-mediated immunomodulation in mice may not be informative in the setting of human disease, although this critical difference has been mainly ignored. To address this issue, we established a novel humanized system to model human MSCs, using murine iNOS(-/-) MSCs that constitutively or inducibly express an ectopic human IDO gene. In this system, inducible IDO expression is driven by a mouse iNOS promoter that can be activated by inflammatory cytokine stimulation in a similar fashion as the human IDO promoter. These IDO-expressing humanized MSCs (MSC-IDO) were capable of suppressing T-lymphocyte proliferation in vitro. In melanoma and lymphoma tumor models, MSC-IDO promoted tumor growth in vivo, an effect that was reversed by the IDO inhibitor 1-methyl-tryptophan. We found that MSC-IDO dramatically reduced both tumor-infiltrating CD8(+) T cells and B cells. Our findings offer an important new line of evidence that interventional targeting of IDO activity could be used to restore tumor immunity in humans, by relieving IDO-mediated immune suppression of MSCs in the tumor microenvironment as well as in tumor cells themselves.

Identification of hamster inducible nitric oxide synthase (iNOS) promoter sequences that influence basal and inducible iNOS expression

IFN-γ/LPS-activated hamster (Mesocricetus auratus) macrophages express significantly less iNOS (NOS2) than activated mouse macrophages, which contributes to the hamster's susceptibility to intracellular pathogens. We determined a mechanism responsible for differences in iNOS promoter activity in hamsters and mice. The HtPP (1.2 kb) showed low basal and inducible promoter activity when compared with the mouse, and sequences within a 100-bp region (-233 to -133) of the mouse and hamster promoters influenced this activity. Moreover, within this 100 bp, we identified a smaller region (44 bp) in the mouse promoter, which recovered basal promoter activity when swapped into the hamster promoter. The mouse homolog (100-bp region) contained a cis-element for NF-IL-6 (-153/-142), which was absent in the hamster counterpart. EMSA and supershift assays revealed that the hamster sequence did not support the binding of NF-IL-6. Introduction of a functional NF-IL-6 binding sequence into the hamster promoter or its alteration in the mouse promoter revealed the critical importance of this transcription factor for full iNOS promoter activity. Furthermore, the binding of NF-IL-6 to the iNOS promoter (-153/-142) in vivo was increased in mouse cells but was reduced in hamster cells after IFN-γ/LPS stimulation. Differences in the activity of the iNOS promoters were evident in mouse and hamster cells, so they were not merely a result of species-specific differences in transcription factors. Thus, we have identified unique DNA sequences and a critical transcription factor, NF-IL-6, which contribute to the overall basal and inducible expression of hamster iNOS.

Characterization, anti-oxidative and anti-inflammatory effects of Costa Rican noni juice (Morinda citrifolia L.)

AIM OF THE STUDY

Noni fruit (Morinda citrifolia L.) juice has been used for more than 2000 years in Polynesia as a traditional folk medicine. The aim of the present study was to finely characterize noni juice from Costa Rica and to evaluate its anti-oxidative and anti-inflammatory activities.

MATERIALS AND METHODS

A microfiltrated noni juice was prepared with Costarican nonis. HPLC-DAD and Electro Spray Ionization Mass Spectrometric detection (HPLC-ESI-MS) were used to identify phenolic compounds and iridoids. The anti-oxidative activity of noni juice was measured in vitro by both Oxygen Radical Absorbance Capacity (ORAC) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging methods. The anti-inflammatory effects of noni juice were investigated in vitro by: measuring its effect on nitric oxide and prostaglandin E2 production by activated macrophages, evaluating its inhibitory activities on cyclooxygenase (COX)-1 and -2 and in vivo on a carrageenan-induced paw oedema model in rats.

RESULTS

Several polyphenols belonging to the coumarin, flavonoid and phenolic acid groups, and two iridoids were identified. Noni juice demonstrated a mean range free radical scavenging capacity. Furthermore, it also reduced carrageenan-induced paw oedema, directly inhibited cyclooxygenase COX-1 and COX-2 activities and inhibited the production of nitric oxide (NO) and prostaglandins E(2) (PGE(2)) in activated J774 cells, in a dose dependent manner.

CONCLUSIONS

This study showed that noni's biological effects include: (1) anti-oxidant properties probably associated with phenolic compounds, iridoids and ascorbic acid and (2) anti-inflammatory action through NO and PGE(2) pathways that might also be strengthened by anti-oxidant effects.

Differential induction of innate immune responses by synthetic lipid a derivatives

Recent studies have indicated that lipopolysaccharides (LPS) isolated from particular bacterial strains can bias innate immune responses toward different signal transduction pathways thereby eliciting unique patterns of cytokines. Heterogeneity in the structure of lipid A (the active component of LPS) and possible contaminations with other inflammatory components have made it difficult to confirm these observations and dissect molecular motifs that may be responsible for modulatory properties. To address these issues, we have examined, for the first time, the ability of a range of well defined synthetic lipid As and isolated LPS and lipid A preparations to induce the production of a wide range of cytokines in three different mouse cell types. It was found that, for a given compound, the potencies of production of the various cytokines differed significantly. An additive model, in which a chemical change in the structure of a compound effects the potencies of all cytokines in the same manner, could describe the potencies of the cytokines for all compounds. Thus, no evidence was found that the structure of lipid A can modulate the pattern of cytokine production. In addition, the statistical analysis showed that the relative ordering of the potencies of the compounds was identical in the different cell types and that structural features such as the presence of a 3-deoxy-D-manno-octulosonic acid moiety, anomeric phosphate, lipid length, and acylation pattern were important for pro-inflammatory activity. Finally, it was found that transcriptional and post-transcription control mechanisms determine potencies and efficacies of cytokine production in cell-specific manners.

Induction of iNOS by Chlamydophila pneumoniae requires MyD88-dependent activation of JNK

Innate immune cells produce NO via inducible NO synthase (iNOS) in response to certain infections or upon stimulation with cytokines such as IFN-gamma and TNF. NO plays an important role in host defense against intracellular bacteria including Chlamydophila pneumoniae as a result of its microbicidal activity. In MyD88-deficient mice, which succumb to C. pneumoniae infection, iNOS induction is impaired 6 days postinfection, although pulmonary levels of IFN-gamma and TNF are elevated as in wild-type mice at this time-point. Here, we demonstrate that induction of iNOS in macrophages upon C. pneumoniae infection is controlled by MyD88 via two pathways: NF-kappaB activation and phosphorylation of the MAPK JNK, which leads to the nuclear translocation of c-Jun, one of the two components of the AP-1 complex. In addition, phosphorylation of STAT1 and expression of IFN regulatory factor 1 (IRF-1) were delayed in the absence of MyD88 after C. pneumoniae infection but not after IFN-gamma stimulation. Taken together, our data show that for optimal induction of iNOS during C. pneumoniae infection, the concerted action of the MyD88-dependent transcription factors NF-kappaB and AP-1 and of the MyD88-independent transcription factors phosphorylated STAT1 and IRF-1 is required.

Heme oxygenase-1-derived carbon monoxide induces the Mycobacterium tuberculosis dormancy regulon

The mechanisms that allow Mycobacterium tuberculosis (Mtb) to persist in human tissue for decades and to then abruptly cause disease are not clearly understood. Regulatory elements thought to assist Mtb to enter such a state include the heme two-component sensor kinases DosS and DosT and the cognate response regulator DosR. We have demonstrated previously that O(2), nitric oxide (NO), and carbon monoxide (CO) are regulatory ligands of DosS and DosT. Here, we show that in addition to O(2) and NO, CO induces the complete Mtb dormancy (Dos) regulon. Notably, we demonstrate that CO is primarily sensed through DosS to induce the Dos regulon, whereas DosT plays a less prominent role. We also show that Mtb infection of macrophage cells significantly increases the expression, protein levels, and enzymatic activity of heme oxygenase-1 (HO-1, the enzyme that produces CO), in an NO-independent manner. Furthermore, exploiting HO-1(+/+) and HO-1(-/-) bone marrow-derived macrophages, we demonstrate that physiologically relevant levels of CO induce the Dos regulon. Finally, we demonstrate that increased HO-1 mRNA and protein levels are produced in the lungs of Mtb-infected mice. Our data suggest that during infection, O(2), NO, and CO are being sensed concurrently rather than independently via DosS and DosT. We conclude that CO, a previously unrecognized host factor, is a physiologically relevant Mtb signal capable of inducing the Dos regulon, which introduces a new paradigm for understanding the molecular basis of Mtb persistence.

Use of a murine cell line for identification of human nitric oxide synthase inhibitors

INTRODUCTION

Nitric oxide (NO) has been implicated in a wide range of physiological and pathological processes. Low concentrations of this mediator play homeostatic roles, whereas many acute and chronic responses are associated with excessive production of NO. This upregulation is due in part to the induction of inducible nitric oxide synthase (iNOS) by proinflammatory cytokines in several different cell types, including macrophages and their CNS derivative, microglia.

METHODS

The crystal structures of the oxygenase domains of mouse and human iNOS were superimposed using the "align by homology" feature in Sybyl (SYBYL 7.0, Tripos Inc.). NOS isoform expression was assessed by TaqMan, Western blotting, and activity assays.

RESULTS

We demonstrate that there is a high degree of three-dimensional overlap between the mouse and human iNOS active centers and propose that the murine isoform can serve as a suitable substitute for the human in assays. We also demonstrate that LPS stimulation of the mouse macrophage cell line RAW 264.7 induces the expression of iNOS, but not nNOS or eNOS, at the levels of mRNA transcription and protein expression. Furthermore, the pharmacology and calcium dependency of the NO formation support the finding that it is due to iNOS alone. Also reported is the demonstration of LPS-induced RAW 264.7 macrophages in simple cell-based and cell-free screening assays for iNOS inhibitors. Both assays were reproducible, as demonstrated by Z' factors of 0.69 and 0.71, and had high signal to noise ratios of 11- and 6-fold for the cell-based and cell-free assay, respectively.

DISCUSSION

Our computational analyses indicate that there is a high degree of three-dimensional overlap between the oxygenase domains of human and murine iNOS. This observation together with the selective induction of murine iNOS in RAW 264.7 macrophages demonstrates the potential utility of the mouse iNOS assay to identify inhibitors of the human enzyme.

Nitric oxide inhibits an interaction between JNK1 and c-Jun through nitrosylation

Nitric oxide (NO) has been shown to negatively regulate c-Jun N-terminal kinase (JNK) through S-nitrosylation. Here, we show that disruption of an interaction between JNK and its substrate c-Jun is an important mechanism underlying the NO-mediated inhibition of JNK signaling. Endogenous NO, which was generated by interferon-gamma treatment, suppressed anisomycin-stimulated JNK activity in microglial BV-2 cells. The interferon-gamma-induced suppression of JNK1 activation in BV-2 cells was prevented completely by treatment with N(G)-nitro-l-arginine, an inhibitor of NO synthase. A NO donor S-nitro-N-acetyl-dl-penicillamine (SNAP) inhibited JNK activity in vitro, and this inhibition was reversed by a thiol-reducing agent, dithiothreitol. Nitric oxide disrupts a physical interaction between JNK and its substrate c-Jun both in vitro and in intact cells without affecting an interaction between SEK1 and JNK. Collectively, our results suggest that the inhibition of the interaction between JNK and c-Jun may be an integral part of the mechanism underlying the negative regulation of the JNK signaling pathway by NO.

Kruppel-like factor 4 is a mediator of proinflammatory signaling in macrophages

Activation of macrophages is important in chronic inflammatory disease states such as atherosclerosis. Proinflammatory cytokines such as interferon-gamma (IFN-gamma), lipopolysaccharide (LPS), or tumor necrosis factor-alpha can promote macrophage activation. Conversely, anti-inflammatory factors such as transforming growth factor-beta1 (TGF-beta1) can decrease proinflammatory activation. The molecular mediators regulating the balance of these opposing effectors remain incompletely understood. Herein, we identify Kruppel-like factor 4 (KLF4) as being markedly induced in response to IFN-gamma, LPS, or tumor necrosis factor-alpha and decreased by TGF-beta1 in macrophages. Overexpression of KLF4 in J774a macrophages induced the macrophage activation marker inducible nitric-oxide synthase and inhibited the TGF-beta1 and Smad3 target gene plasminogen activator inhibitor-1 (PAI-1). Conversely, KLF4 knockdown markedly attenuated the ability of IFN-gamma, LPS, or IFN-gamma plus LPS to induce the iNOS promoter, whereas it augmented macrophage responsiveness to TGF-beta1 and Smad3 signaling. The KLF4 induction of the iNOS promoter is mediated by two KLF DNA-binding sites at -95 and -212 bp, and mutation of these sites diminished induction by IFN-gamma and LPS. We further provide evidence that KLF4 interacts with the NF-kappaB family member p65 (RelA) to cooperatively induce the iNOS promoter. In contrast, KLF4 inhibited the TGF-beta1/Smad3 induction of the PAI-1 promoter independent of KLF4 DNA binding through a novel antagonistic competition with Smad3 for the C terminus of the coactivator p300/CBP. These findings support an important role for KLF4 as a regulator of key signaling pathways that control macrophage activation.

LPS regulates a set of genes in primary murine macrophages by antagonising CSF-1 action

We previously reported that bacterial products such as LPS and CpG DNA down-modulated cell surface levels of the Colony Stimulating Factor (CSF)-1 receptor (CSF-1R) on primary murine macrophages in an all-or-nothing manner. Here we show that the ability of bacterial products to down-modulate the CSF-1R rendered bone marrow-derived macrophages (BMM) unresponsive to CSF-1 as assessed by Akt and ERK1/2 phosphorylation. Using toll-like receptor (tlr)9 as a model CSF-1-repressed gene, we show that LPS induced tlr9 expression in BMM only when CSF-1 was present, suggesting that LPS relieves CSF-1-mediated inhibition to induce gene expression. Using cDNA microarrays, we identified a cluster of similarly CSF-1 repressed genes in BMM. By real time PCR we confirmed that the expression of a selection of these genes, including integral membrane protein 2B (itm2b), receptor activity-modifying protein 2 (ramp2) and macrophage-specific gene 1 (mpg-1), were repressed by CSF-1 and were induced by LPS only in the presence of CSF-1. This pattern of gene regulation was also apparent in thioglycollate-elicited peritoneal macrophages (TEPM). LPS also counteracted CSF-1 action to induce mRNA expression of a number of transcription factors including interferon consensus sequence binding protein 1 (Icsbp1), suggesting that this mechanism leads to transcriptional reprogramming in macrophages. Since the majority of in vitro studies on macrophage biology do not include CSF-1, these genes represent a set of previously uncharacterised LPS-inducible genes. This study identifies a new mechanism of macrophage activation, in which LPS (and other toll-like receptor agonists) regulate gene expression by switching off the CSF-1R signal. This finding also provides a biological relevance to the well-documented ability of macrophage activators to down-modulate surface expression of the CSF-1R.

Reduction of nitric oxide synthase 2 expression by distamycin A improves survival from endotoxemia

NO synthase 2 (NOS2) plays an important role in endotoxemia through overproduction of NO. Distamycin A (Dist A) belongs to a class of drugs termed minor-groove DNA binders, which can inhibit transcription factor binding to AT-rich regions of DNA. We and others have previously shown that AT-rich regions of DNA surrounding transcription factor binding sites in the NOS2 promoter are critical for NOS2 induction by inflammatory stimuli in vitro. Therefore, we hypothesized that Dist A would attenuate NOS2 up-regulation in vivo during endotoxemia and improve animal survival. C57BL/6 wild-type (WT) mice treated with Dist A and LPS (endotoxin) showed significantly improved survival compared with animals treated with LPS alone. In contrast, LPS-treated C57BL/6 NOS2-deficient (NOS2-/-) mice did not benefit from the protective effect of Dist A on mortality from endotoxemia. Treatment with Dist A resulted in protection from hypotension in LPS-treated WT mice, but not in NOS2-/- mice. Furthermore, LPS-induced NOS2 expression was attenuated in vivo (WT murine tissues) and in vitro (primary peritoneal and RAW 264.7 murine macrophages) with addition of Dist A. Dist A selectively decreased IFN regulatory factor-1 DNA binding in the enhancer region of the NOS2 promoter, and this IFN regulatory factor-1 site is critical for the effect of Dist A in attenuating LPS induction of NOS2. Our data point to a novel approach in modulating NOS2 expression in vivo during endotoxemia and suggest the potential for alternative treatment approaches for critical illness.

Identification of cis-regulatory regions necessary for robust Nos2 promoter activity in glial cells: indirect role for NF-kappaB

Previous reports suggest the nitric-oxide synthase 2 (Nos2) promoter contains negative and positive cis-regulatory regions. This study identified such regions using rat C6 glial cells. Activity of the serially deleted rat Nos2 promoter fused to a luciferase reporter gene was found to vary with construct size independent of stimuli, decreasing markedly from 160 to 130 bp then increasing significantly from 110 to 94 bp. In contrast, time to peak activity was stimulus-dependent but size-independent; 4-8 h for a cytokine mixture or lipopolysaccharide + interferon-gamma, and 8-16 h for lipopolysaccharide + phorbol 12-myristate 13-acetate. Peak activity with heterologous promoters also varied; 4 h for 3.7 kb of the human Nos2A promoter, and 36 h for 1.8 kb of the murine promoter. Electrophoretic mobility shift assays and in vivo DNA footprinting data confirmed nuclear protein binding to promoter regions suspected of containing important regulatory sites based on reporter gene data. A binding site for NF-kappaB was not required for Nos2 promoter activity. These findings provide significant new information on the relative importance of different regions of the rat Nos2 promoter for transcriptional activation and nitric oxide production by glial cells and support the existence of cell- and species-specific mechanisms for transcriptional regulation of Nos2 activation.

A new NOS2 promoter polymorphism associated with increased nitric oxide production and protection from severe malaria in Tanzanian and Kenyan children

BACKGROUND

Nitric oxide (NO) is a mediator of immunity to malaria, and genetic polymorphisms in the promoter of the inducible NO synthase gene (NOS2) could modulate production of NO. We postulated that NOS2 promoter polymorphisms would affect resistance to severe malaria.

METHODS

We assessed genomic DNA from healthy children and from those diagnosed with malaria from Tanzania (n=47 and n=138, respectively) and Kenya (n=1106) for polymorphisms by single-stranded conformational polymorphism (SSCP) analysis and sequencing. We also measured in-vivo NO production in Tanzanian children.

FINDINGS

We identified a novel single nucleotide polymorphism, -1173 C-->T, in the NOS2 promoter that was significantly associated with protection from symptomatic malaria (odds ratio 0.12, 95% CI 0.03-0.48, p=0.0006) in 179 Tanzanian children, and significantly associated with protection from severe malarial anaemia (adjusted relative risk 0.25, 95% CI 0.09-0.66, p=0.0005) in 1106 Kenyan children studied over 5 years. The risk of parasitaemia was not significantly different in wild-type or -1173 C-->T individuals. -1173 C-->T protection in Tanzanians was independent of the previously recognised NOS2-954 G-->C polymorphism. The (CCTTT)(n) NOS2 polymorphism (Tanzania and Kenya) was not associated with severe malaria outcomes. -1173 C-->T was associated with increased fasting urine and plasma NO metabolite concentrations in Tanzanian children, suggesting that the polymorphism was functional in vivo. Interpretation The NOS2 promoter -1173 C-->T single nucleotide polymorphism is associated with protection against cerebral malaria and severe malarial anaemia. Increased NO production in individuals with the -1173 C-->T polymorphism lends support to a protective role for NO against these syndromes. Targeted interventions to increase NO delivery or production could provide novel preventive and therapeutic strategies against these major causes of mortality in African children.

Transcription factor complex formation and chromatin fine structure alterations at the murine c-fms (CSF-1 receptor) locus during maturation of myeloid precursor cells

Expression of the gene for the macrophage colony stimulating factor receptor (CSF-1R), c-fms, has been viewed as a hallmark of the commitment of multipotent precursor cells to macrophages. Lineage-restricted expression of the gene is controlled by conserved elements in the proximal promoter and within the first intron. To investigate the developmental regulation of c-fms at the level of chromatin structure, we developed an in vitro system to examine the maturation of multipotent myeloid precursor cells into mature macrophages. The dynamics of chromatin fine structure alterations and transcription factor occupancy at the c-fms promoter and intronic enhancer was examined by in vivo DMS and UV-footprinting. We show that the c-fms gene is already transcribed at low levels in early myeloid precursors on which no CSF-1R surface expression can be detected. At this stage of myelopoiesis, the formation of transcription factor complexes on the promoter was complete. By contrast, occupancy of the enhancer was acutely regulated during macrophage differentiation. Our data show that cell-intrinsic differentiation decisions at the c-fms locus precede the appearance of c-fms on the cell surface. They also suggest that complex lineage-specific enhancers such as the c-fms intronic enhancer regulate local chromatin structure through the coordinated assembly and disassembly of distinct transcription factor complexes.

A reverse nuclear factor-kappaB element in the rat type II nitric oxide synthase promoter mediates the induction by interleukin-1beta and interferon-gamma in rat aortic smooth muscle cells

The rat type II nitric oxide synthase (iNOS) promoter contains two nuclear factor-kappaB (NF-kappaB)-binding sites, one upstream (-965 to -956 bp) and one downstream (-107 to -98 bp), which are important for iNOS induction. We have identified a third NF-kappaB site located at -901 to -892 bp whose sequence is identical to that of the upstream site but with the opposite orientation ("the reverse NF-kappaB site"). We hypothesized that the reverse NF-kappaB site, like the other two sites, is important for iNOS induction. With the use of a rat iNOS promoter fragment of -906 to -887 bp as probe, electrophoretic mobility shift assays were performed on nuclear proteins extracted from rat aortic smooth muscle cells (RASMCs) treated with interleukin-1beta (IL-1beta, 100 U/ml) +/- interferon-gamma (IFN-gamma, 250 U/ml) for 30 min. IL-1beta, but not IFN-gamma, induced a DNA-protein complex that was supershifted by either anti-NF-kappaB p50 or anti-NF-kappaB p65 antibody. The functionality of the reverse NF-kappaB site was evaluated by mutation experiments and transfection assays. The wild-type and mutated -1.4 kb rat iNOS promoter-luciferase constructs were transfected into RASMCs. Compared with the wild type, reverse-NF-kappaB site (-901 to -892 bp) deletion, substitution of T for C at -894 bp, and substitution TTT for CCC at -896 to -894 bp decreased the IL-1beta-induced promoter activity by 67% (p < 0.001), 45% (p < 0.001), and 56% (p < 0.001), respectively. These deletion/substitutions also decreased the IL-1beta- and IFN-gamma-induced promoter activity by 74% (p < 0.001), 53%(p < 0. 001), and 63% (p < 0.001), respectively. In conclusion, a p50 and p65 NF-kappaB heterodimer binds to a reverse-NF-kappaB site on the rat iNOS promoter and contributes to iNOS induction by IL-1beta and IFN-gamma in RASMCs.

CCAAT/enhancer binding protein-beta trans-activates murine nitric oxide synthase 2 gene in an MTAL cell line

Nitric oxide production by nitric oxide synthase 2 (NOS2) has been implicated in epithelial cell injury from oxidative and immunologic stress. The NOS2 gene is transcriptionally activated by lipopolysaccharide (LPS) and cytokines in medullary thick ascending limb of Henle's loop (MTAL) cells and other cell types. The 5'-flanking region of the NOS2 gene contains a consensus element for CCAAT/enhancer binding proteins (C/EBP) at -150 to -142 that we hypothesized contributes to NOS2 trans-activation in the mouse MTAL cell line ST-1. Gel shift assays demonstrated LPS + interferon-gamma (IFN-gamma) induction of C/EBP family protein-DNA complexes in nuclei harvested from the cells. Supershift assays revealed that the complexes were comprised of C/EBPbeta, but not C/EBPalpha, C/EBPdelta, or C/EBPepsilon. NOS2 promoter-luciferase genes harboring deletion or mutation of the C/EBP box exhibited lower activities in response to LPS + IFN-gamma compared with wild-type NOS2 promoter constructs. Overexpression of a C/EBP-specific dominant-negative mutant limited LPS + IFN-gamma activation of the NOS2 promoter. In trans-activation assays, overexpression of C/EBPbeta stimulated basal NOS2 promoter activity. Thus C/EBPbeta appears to be an important trans-activator of the NOS2 gene in the MTAL.

Ascorbate-dependent enhancement of nitric oxide formation in activated macrophages

Macrophages activated with bacterial lipopolysaccharide (LPS) and cytokines produce nitric oxide through the induction of iNOS gene expression. Ascorbate increased NOx (nitrite and nitrate) formation by approximately 40% in a mouse macrophage-like cell line, J774.1, activated with LPS and interferon-gamma. Ascorbate alone exhibited no inductive activity toward NO formation. N(G)-Monomethyl-L-arginine inhibited nitrite formation in cells activated in the presence or absence of ascorbate. Northern and Western blotting analyses showed that both iNOS mRNA and protein steady-state levels were increased approximately twofold in cells activated in the presence of ascorbate compared to in cells activated only with the inducers. These data suggest that ascorbate increased NO production by increasing the amount of iNOS in the activated macrophages.

A protein-bound polysaccharide synergistic with lipopolysaccharide induces nitric oxide release and antioxidant enzyme activities in mouse peritoneal macrophages

The aim of this study is to examine whether polysaccharide krestin, a protein-bound polysaccharide, can prevent the progression of atherosclerosis and lipoperoxidative injury caused by oxidatively modified low density lipoprotein (Ox-LDL) to macrophages. The alterations of GSHPx (glutathione peroxidase), SOD (superoxide dismutase) activity and NO (nitric oxide) release in PSK-treated mouse peritoneal macrophages, and the effect of LPS on them were investigated. With peritoneal injection of PSK, the following were observed in the mouse peritoneal macrophages: 1) an increase in SeGSHPx activity, 2) elevation in non-SeGSHPx and SOD activity; 3) the enzyme activities were further improved by addition of lipopolysaccharide (LPS); and 4) much NO was found to be released by PSK-treated mouse peritoneal macrophages stimulated by LPS.

Diacerhein blocks iron regulatory protein activation in inflamed human monocytes

Iron Regulatory Proteins (IRPs), by modulating expression of ferritin, which stores excess iron in a non toxic form, and transferrin receptor, which controls iron uptake, are the main controller of cellular iron metabolism. During inflammation, modification of IRP activity may affect iron availability, free radical generation and cytokine gene response in inflammatory cells. In the present study we tested the effect of inflammatory stimuli on IRP function in a human monocytic-macrophagic cell line and the possibility of interfering with these pathways by using an antiinflammatory compound, diacerhein (DAR). IRP activity was enhanced by interferon gamma/lipopolysaccarhide (IFN/LPS), and this effect was consistently counteracted by increasing concentrations of DAR. No direct effect of DAR on IRP activity was found in vitro. However, in vivo, similar IRP activation was achieved by exposing cells to nitric oxide (NO) donors and the LPS/IFN-induced activation of IRP was reversed by NO inhibitors. Interestingly, NO-induced IRP activation was efficiently blocked by DAR. These data show for the first time that a clinically useful antiinflammatory compound, DAR, interferes with IRP activation by NO in inflammed human cells.

Nuclear translocation of NF-kappaB in lipopolysaccharide-treated macrophages fails to correspond to endotoxicity: evidence suggesting a requirement for a gamma interferon-like signal

Elucidation of a signal transduction pathway essential to lipopolysaccharide (LPS)-induced macrophage activation has the capacity to provide new targets for the treatment of septic shock. In this regard, activation of the transcription factor NF-kappaB is commonly thought to be critical to LPS-stimulated macrophage inflammatory mediator production, although certain immunological, genetic, and molecular evidence suggests that other factors are involved. To address this issue, we hypothesized that the degree of LPS-induced NF-kappaB mobilization should correlate with the murine endotoxicity of the species of LPS used for in vitro study. Therefore, using D-galactosamine-sensitized mice, we assessed the lethal potencies of eight LPS preparations from Escherichia, Salmonella, Klebsiella, Bacteroides, Pseudomonas, Neisseria, and Rhodobacter species as well as that of the endotoxin substructure lipid X. The lethal potencies of these LPS preparations varied by > 160-fold. Treatment of RAW 264.7 cells with the same LPS preparations induced levels of tumor necrosis factor alpha (TNF-alpha) and NO production that correlated with the LPS 50% lethal dose. The combined analysis of the levels of these two mediators produced in response to LPS in RAW cells was found to be a strong predictor of murine endotoxic lethality. Interestingly, while relatively nontoxic in mice, Rhodobacter capsulatus LPS stimulated RAW cell NF-kappaB-like DNA binding protein mobilization and TNF-alpha production to levels comparable to those of more toxic species of LPS but was unable to induce NO generation in RAW cells. These data indicate that neither NF-kappaB activation nor TNF-alpha production alone is a dependable predictor of LPS lethality. Additionally, cotreatment of RAW cells with the potent inflammatory mediator ADP had no effect on the ability of R. capsulatus LPS to stimulate NO production but significantly enhanced induction of NO production by the toxic species of LPS. In contrast, cotreatment of RAW cells or peritoneal macrophages with gamma interferon (IFN-gamma) normalized the abilities of both toxic and nontoxic LPS preparations to induce NO production, suggesting that selected preparations of LPS may preferentially generate an IFN-gamma-like signal that accounts for enhanced toxicity. In sum, the activation of NF-kappaB does not correspond to LPS lethality, thereby complicating models of macrophage activation that highlight NF-kappaB alone as a signal transduction factor necessary for LPS-mediated toxicity.

Upstream NF-kappaB site is required for the maximal expression of mouse inducible nitric oxide synthase gene in interferon-gamma plus lipopolysaccharide-induced RAW 264.7 macrophages

Transient transfection assays with various deletion mutants of the mouse inducible nitric oxide synthase (iNOS) promoter linked to a CAT reporter gene demonstrated that, besides the downstream NF-kappaB site, the region from -973 to -925 which contains a potential binding site for NF-kappaB (upstream NF-kappaB site) also mediated lipopolysaccharide (LPS)-inducibility in mouse macrophage cell line RAW 264.7. Site-specific mutation of three conserved nucleotides within the upstream NF-kappaB site abolished additional induction by LPS as well as maximal expression of iNOS by IFN-gamma plus LPS. In contrast, site-specific mutation of the downstream NF-kappaB site caused almost all reduction in expression of the reporter gene by LPS or LPS plus IFN-gamma. Electrophoretic mobility shift assays with the two NF-kappaB sites showed LPS-induced NF-kappaB binding to both probes and its higher affinity to the upstream NF-kappaB site. Taken together, these suggest that the upstream NF-kappaB site having enhancer function, besides the downstream NF-kappaB site as a core promoter, is essential for maximal expression of the iNOS gene.

Analysis of expression and promoter function of the human inducible nitric oxide synthase gene in DLD-1 cells and monkey hepatocytes

Upon cytokine induction, inducible nitric oxide synthase (iNOS) mRNA and enzyme activity in DLD-1 cells reached maximal levels at 6 and 8 h, respectively. A 3.7 kb 5'-flanking region of the human iNOS gene was used to prepare luciferase reporter constructs. Upon transfection of these constructs into DLD-1 cells and primary monkey hepatocytes, significant promoter activity was detected in the absence of cytokines, and this activity decreased with successive truncations of the human iNOS promoter. No increase in luciferase activity was observed after cytokine treatment, in spite of the fact that nuclear run-on analysis indicated that iNOS induction in DLD-1 cells was due, in part, to an increase in transcription rate. These results suggest that 3.7 kb of 5'-flanking DNA do not contain all of the elements required for transcriptional induction of the human iNOS gene. This differs from the mouse iNOS gene for which 1.7 kb of 5'-flanking DNA contain most or all of the elements that control iNOS expression in mouse macrophages. Thus, important cell- and species-specific mechanisms may exist for the control of iNOS expression.

In vivo footprinting of the mouse inducible nitric oxide synthase gene: inducible protein occupation of numerous sites including Oct and NF-IL6

A wide variety of cells usefully but sometimes destructively produce nitric oxide via inducible nitric oxide synthase (iNOS). Data obtained by gel shift analysis and reporter assays have linked murine iNOS gene induction by cytokines and bacterial products with the binding of a number of proteins to a proximal promoter, as well as to a distal enhancer of the iNOS gene. Nevertheless, these techniques do not necessarily reflect protein occupation of sites in vivo. To address this, we have used dimethyl sulphate in vivo footprinting to determine binding events in the two murine iNOS transcription control regions, using a classical lipopolysaccharide induction of RAW 264.7 macrophages. Protein-DNA interactions are absent before activation. Exposure to lipopolysaccharide induces protection at a NF-kappaB site and hypersensitivity at a shared gamma-activated site/interferon-stimulated response element within the enhancer. Protections are seen at a NF-IL6, and an Oct site within the promoter. We also observe modulations in guanine methylation at two regions which do not correspond to any known putative binding elements. Furthermore, we confirm the probable involvement of interferon regulatory factor-1 (binding to its -901 to -913 site) and the binding of NF-kappaB to its proximal site. Our data demonstrate an abundance of hitherto-unrecognised protein-DNA binding events upon simple lipopolysaccharide activation of the iNOS gene and suggests a role for protein-protein interactions in its transcriptional induction.