Characterization and Functional Analysis of the Human Inducible Nitric Oxide Synthase Gene Promoter

Elucidation of the Mechanism Underlying the Anti-Inflammatory Properties of (S)-(+)-Carvone Identifies a Novel Class of Sirtuin-1 Activators in a Murine Macrophage Cell Line

The signaling pathways involved in age-related inflammation are increasingly recognized as targets for the development of preventive and therapeutic strategies. Our previous study elucidated the structure-activity relationship of monoterpene compounds derived from p-menthane as potential anti-inflammatory drugs and identified (S)-(+)-carvone as the most potent among the compounds tested. This study aims at identifying the molecular mechanism underlying the anti-inflammatory properties of (S)-(+)-carvone. The murine macrophage cell line, Raw 264.7, was stimulated with bacterial lipopolysaccharide (LPS) to simulate inflammation. Western blot was used to assess protein levels and post-translational modifications. The subcellular localization of NF-κB/p65 was visualized by immunocytochemistry. An in vitro fluorometric assay was used to measure Sirtuin-1 (SIRT1) activity. (S)-(+)-carvone inhibited LPS-induced JNK1 phosphorylation, but not that of p38 and ERK1/2 and also did not affect the phosphorylation and degradation of the NF-κB inhibitor, IκB-α. Accordingly, (S)-(+)-carvone did not affect LPS-induced phosphorylation of NF-κB/p65 on Ser536 and its nuclear translocation, but it significantly decreased LPS-induced IκB-α resynthesis, a NF-κB-dependent process, and NF-κB/p65 acetylation on lysine (Lys) 310. Deacetylation of that Lys residue is dependent on the activity of SIRT1, which was found to be increased by (S)-(+)-carvone, while its protein levels were unaffected. Taken together, these results show that (S)-(+)-carvone is a new SIRT1 activator with the potential to counteract the chronic low-grade inflammation characteristic of age-related diseases.

Exhaled nitric oxide and inducible nitric oxide synthase gene polymorphism in Japanese asthmatics

BACKGROUND

Inducible nitric oxide synthase (iNOS) induced by inflammatory cytokines and iNOS activity in bronchial epithelial cells is a major determinant of fractional exhaled nitric oxide (FeNO) levels. The aim of this study was to investigate the association of iNOS promoter gene polymorphisms and FeNO levels in Japanese asthmatics before the introduction of asthma treatment.

METHODS

Asthmatics were recruited from Fukushima Medical University Hospital. Genotyping of the pentanucleotide repeat (CCTTT)n and seven previously detected single nucleotide polymorphisms (SNPs) in the iNOS promoter lesion was performed. The relationships between the genotypes and FeNO levels before the introduction of asthma treatment were compared.

RESULTS

In 91 asthmatics, the number of microsatellite repeats ranged from 9 to 20 and showed a bimodal distribution. According to this distribution, asthmatics were divided into two groups: genotypes with at least one long allele with more than 14 repeats (L/s or L/L) and genotypes with both short alleles with 14 or fewer repeats (s/s). No significant differences were observed in each parameter between the two groups. The mean FeNO level before treatment was significantly higher in the L/s or L/L subjects than in the s/s subjects. After treatment, the lowest FeNO level did not differ between the two groups. Three SNPs detected in the Japanese subjects were not associated with FeNO levels.

CONCLUSIONS

The number of CCTTT repeats in the iNOS promoter region was associated with FeNO levels in asthmatics before treatment, suggesting the importance of iNOS genotype in the clinical application of FeNO for asthmatics.

Replacing the Promoter of the Murine Gene Encoding P-selectin with the Human Promoter Confers Human-like Basal and Inducible Expression in Mice

In humans and mice, megakaryocytes/platelets and endothelial cells constitutively synthesize P-selectin and mobilize it to the plasma membrane to mediate leukocyte rolling during inflammation. TNF-α, interleukin 1β, and LPS markedly increase P-selectin mRNA in mice but decrease P-selectin mRNA in humans. Transgenic mice bearing the entire human SELP gene recapitulate basal and inducible expression of human P-selectin and reveal human-specific differences in P-selectin function. Differences in the human SELP and murine Selp promoters account for divergent expression in vitro, but their significance in vivo is not known. Here we generated knockin mice that replace the 1.4-kb proximal Selp promoter with the corresponding SELP sequence (Selp(KI)). Selp(KI) (/) (KI) mice constitutively expressed more P-selectin on platelets and more P-selectin mRNA in tissues but only slightly increased P-selectin mRNA after injection of TNF-α or LPS. Consistent with higher basal expression, leukocytes rolled more slowly on P-selectin in trauma-stimulated venules of Selp(KI) (/) (KI) mice. However, TNF-α did not further reduce P-selectin-dependent rolling velocities. Blunted up-regulation of P-selectin mRNA during contact hypersensitivity reduced P-selectin-dependent inflammation in Selp(KI) (/-) mice. Higher basal P-selectin in Selp(KI) (/) (KI) mice compensated for this defect. Therefore, divergent sequences in a short promoter mediate most of the functionally significant differences in expression of human and murine P-selectin in vivo.

Toll-like receptor 9 deficiency protects mice against Pseudomonas aeruginosa lung infection

Pseudomonas aeruginosa is an opportunistic pathogen involved in nosocomial infections. While a number of studies have demonstrated the roles of TLR2, TLR4 and TLR5 in host defense againt P. aeruginosa infection, the implication of TLR9 in this process has been overlooked. Here, we show that P. aeruginosa DNA stimulates the inflammatory response through TLR9 pathway in both a cell line and primary alveolar macrophages (AMs). This activation requires asparagine endopeptidase- and endosomal acidification. Interestingly, TLR9^-/- mice resisted to lethal lung infection by P. aeruginosa, compared to WT C57BL/6 mice. The resistance of TLR9^-/- mice to P. aeruginosa infection was associated with: (i) a higher ability of TLR9^-/- AMs to kill P. aeruginosa; (ii) a rapid increase in the pro-inflammatory cytokines such as TNFα, IL-1β and IL-6 production; and (iii) an increase in nitric oxide (NO) production and inductible NO synthase expression in AMs. In addition, inhibition of both IL-1β and NO production resulted in a significant decrease of P. aeruginosa clearance by AMs. Altogether these results indicate that TLR9 plays a detrimental role in pulmonary host defense toward P. aeruginosa by reducing the AMs clearance activity and production of IL-1β and NO necessary for bacteria killing.

Sphingosine 1-phosphate counteracts the effects of interleukin-1β in human chondrocytes

Objective

The lipid mediator sphingosine 1-phosphate (S1P) is found in the synovial fluid of osteoarthritis (OA) patients. S1P protects bovine cartilage by counteracting the effects of interleukin-1β (IL-1β). This study was undertaken to examine the interaction of S1P and IL-1β in human OA chondrocytes.

Methods

Human cartilage was obtained from patients undergoing total knee joint replacement. Chondrocytes were cultured in monolayer and treated with IL-1β and S1P. Expression of S1P receptor subtypes and genes involved in cartilage degradation was evaluated using real-time polymerase chain reaction, immunohistochemistry, and Western blotting. S1P signaling was evaluated using inhibitors of S1P receptors and small interfering RNA (siRNA) knockdown of the S1P₂ receptor. Phosphorylation of MAP kinases and NF-κB in response to IL-1β and S1P was detected by Western blotting.

Results

S1P₂ was identified as the most prevalent S1P receptor subtype in human OA cartilage and chondrocytes in vitro. S1P reduced expression of inducible nitric oxide synthase (iNOS) in IL-1β–treated chondrocytes. Reduction of ADAMTS-4 and matrix metalloproteinase 13 expression by S1P correlated with S1P₂ expression. Pharmacologic inhibition of the S1P₂ receptor, but not the S1P₁ and S1P₃ receptors, abrogated the inhibition of iNOS expression. Similar results were observed using siRNA knockdown. S1P signaling inhibited IL-1β–induced phosphorylation of p38 MAPK.

Conclusion

In human chondrocytes, S1P reduces the induction of catabolic genes in the presence of IL-1β. Activation of the S1P₂ receptor counteracts the detrimental phosphorylation of p38 MAPK by IL-1β.

Regulation of nitrogen monoxide production in human malaria

The production of nitrogen monoxide (NO(*)) contributes to defence mechanisms of the immune system to fight infectious agents like bacteria and protozoa. The respective gene producing the NO(*) has to be carefully regulated so that an overwhelming response kills the pathogen but does not harm the host. A strong increase in the NO(*) production for efficient anti-microbial activity is achieved by the transcriptional up-regulation of the nitric oxide synthase 2 gene (NOS2 or inducible nitric oxide synthase, iNOS), which is regulated by a number of transcription factors that are vital in the regulation of many genes involved in the immune response. Binding sites for members of the nuclear factor-kappaB (NF-kappaB) and activator protein 1 (AP1) families have been detected and seem to fulfil their function in vitro. Genetic variants of the iNOS genes have been identified that are linked to NO(*) production and to the outcome of malaria in humans.

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.

Regulation of smooth muscle by inducible nitric oxide synthase and NADPH oxidase in vascular proliferative diseases

Inflammation plays a critical role in promoting smooth muscle migration and proliferation during vascular diseases such as postangioplasty restenosis and atherosclerosis. Another common feature of many vascular diseases is the contribution of reactive oxygen (ROS) and reactive nitrogen (RNS) species to vascular injury. Primary sources of ROS and RNS in smooth muscle are several isoforms of NADPH oxidase (Nox) and the cytokine-regulated inducible nitric oxide (NO) synthase (iNOS). One important example of the interaction between NO and ROS is the reaction of NO with superoxide to yield peroxynitrite, which may contribute to the pathogenesis of hypertension. In this review, we discuss the literature that supports an alternate possibility: Nox-derived ROS modulate NO bioavailability by altering the expression of iNOS. We highlight data showing coexpression of iNOS and Nox in vascular smooth muscle demonstrating the functional consequences of iNOS and Nox during vascular injury. We describe the relevant literature demonstrating that the mitogen-activated protein kinases are important modulators of proinflammatory cytokine-dependent expression of iNOS. A central hypothesis discussed is that ROS-dependent regulation of the serine/threonine kinase protein kinase Cdelta is essential to understanding how Nox may regulate signaling pathways leading to iNOS expression. Overall, the integration of nonphagocytic NADPH oxidase with cytokine signaling in general and in vascular smooth muscle in particular is poorly understood and merits further investigation.

Influence of the inducible nitric oxide synthase gene (NOS2A) on inflammatory bowel disease susceptibility

The great amount of nitric oxide (NO) produced by the inducible isoform of NO synthase (iNOS) exerts deleterious effects, and iNOS expression is raised in the colonic mucosa of inflammatory bowel disease (IBD) patients. This is the first association analysis of polymorphisms within the NOS2A extended gene with IBD susceptibility. We analyzed 336 patients of Crohn's disease (CD), 355 of ulcerative colitis (UC), and 536 healthy controls from a Spanish population. We tested a (CCTTT)n microsatellite, a (-/TAAA) insertion, and two single nucleotide polymorphisms (SNPs) flanking them (rs2779251 and rs2779248) in the NOS2A promoter, together with two SNPs in the coding region: one within exon 10, D385D (rs1137933), and another mapping to exon 16, S608L (rs2297518). Analysis of these markers evidenced differences among IBD patients and healthy controls. Allele (CCTTT) 13 is related to higher UC risk (p = 0.001; odds ratio [OR] [95% confidence interval, CI] = 1.64 [1.20-2.23]). Carriers of minor alleles of the two promoter SNPs analyzed showed an association with UC predisposition, and common allele homozygotes of the two exonic SNPs were more frequent among CD patients than among controls. Concordantly, one out of the three haplotypes carrying both exonic risk alleles was found to increase CD susceptibility (p = 0.007; OR [95%CI] = 1.74 [1.13-2.67]). Therefore, the NOS2A gene seems to be involved in IBD aetiology.

Nitric oxide synthase and cyclooxygenase interactions in cartilage and meniscus: relationships to joint physiology, arthritis, and tissue repair

Rheumatoid arthritis and osteoarthritis are painful and debilitating diseases with complex pathophysiology. There is growing evidence that pro-inflammatory cytokines (e.g., interleukin-1 and tumor necrosis factor alpha) and mediators (e.g., prostaglandins, leukotrienes, and nitric oxide) play critical roles in the development and perpetuation of tissue inflammation and damage in joint tissues such as articular cartilage and meniscus. While earlier studies have generally focused on cells of the synovium (especially macrophages), there is increasing evidence that chondrocytes and meniscal cells actively contribute to inflammatory processes. In particular, it is now apparent that mechanical forces engendered by joint loading are transduced to biological signals at the cellular level and that these signals modulate gene expression and biochemical processes. Here we give an overview of the interplay of cytokines and mechanical stress in the production of cyclooxygenases and prostaglandins; lipoxygenases and leukotrienes; and nitric oxide synthases and nitric oxide in arthritis, with particular focus on the interactions of these pathways in articular cartilage and meniscus.

Lack of association between NOS2 pentanucleotide repeat polymorphism and asthma phenotypes or exhaled nitric oxide concentration

Nitric oxide (NO) plays an immunoregulatory role in balancing cellular immunity. The expression of inducible nitric oxide synthase gene (NOS2) is upregulated upon exposure to proinflammatory cytokines and microbial exposure. The (CCTTT)n polymorphism in NOS2 promoter confers protection against infections and immunological disorders including atopy. We investigated the association between (CCTTT)n and asthma traits in Chinese children. Asthmatic children between 5 and 18 years of age and non-allergic controls were recruited. Plasma total and specific IgEs were measured by immunoassays, and exhaled NO concentration was quantified online by chemiluminescence. NOS2 (CCTTT)n was genotyped by GeneScan analysis. The mean (SD) age of 291 asthmatics and 172 controls were 11.1 (3.8) years and 11.6 (4.0) years, respectively (P = 0.259). NOS2 (CCTTT)n followed Hardy-Weinberg equilibrium in both groups, and its uni-modal allele distribution peaks at 12-repeat. Significant interethnic differences in (CCTTT)n alleles were observed, with our Chinese having less 13-repeat (Pc = 0.022) but more 17-repeat (Pc = 0.033) than Caucasians. The frequency of 14-repeat allele was similar in our Chinese as compared to Japanese (Pc = 0.32). Multivariate regression analyses failed to detect any association between this polymorphic marker and asthma diagnosis (P = 0.949), atopy (P = 0.305), IgE sensitization to aeroallergens (P > 0.2 for all), or FeNO (P = 0.847). These findings do not support NOS2 to be a major candidate gene for asthma or IgE-mediated allergic diseases in Chinese children.

Regulation of inducible nitric oxide synthase in proinflammatory cytokine-stimulated human primary astrocytes

The present study was undertaken to investigate the mechanism of expression of inducible nitric oxide synthase (iNOS) in human primary astrocytes. Among IL-1beta, TNF-alpha, and IFN-gamma, only IL-1beta alone was capable of inducing iNOS. Similarly, among different cytokine combinations, the combinations involving only IL-1beta as a partner were capable of inducing iNOS. The combination of IL-1beta and IFN-gamma (IL-IF) induced the expression of iNOS at the highest level. All three cytokines alone induced the activation of AP-1 while IL-1beta and TNF-alpha but not IFN-gamma induced the activation of NF-kappaB. However, among the three cytokines, only IL-1beta was capable of inducing the activation of CCAAT/enhancer-binding proteinbeta (C/EBPbeta), suggesting an essential role of C/EBPbeta in the expression of iNOS in astrocytes. Although IL-1beta and IFN-gamma alone induced the activation of AP-1, the combination of these two cytokines (IL-IF) markedly inhibited the activation of AP-1. Consistently, JNK-I, a specific inhibitor of JNK, inhibited IL-1beta-mediated activation of AP-1 and expression of iNOS. On the other hand, JNK-I had no effect on (IL-IF)-induced expression of iNOS, suggesting that the activation of AP-1 is involved only during the low level of iNOS induction by IL-1beta but not during the high level of induction by IL-IF. In contrast, the activation of gamma-activation site (GAS) was involved only during the high level of induction by IL-IF but not during the low level of induction by IL-1beta. However, the activation of NF-kappaB and C/EBPbeta was involved in the induction of iNOS by IL-1beta as well as by IL-IF.

Expression profile of a human inducible nitric oxide synthase promoter reporter in transgenic mice during endotoxemia

Inducible nitric oxide synthase (iNOS) is involved in many physiological and pathophysiological processes, including septic shock and acute kidney failure. Little is known about transcriptional regulation of the human iNOS gene in vivo under basal conditions or in sepsis. Accordingly, we developed transgenic mice carrying an insertional human iNOS promoter-reporter gene construct. In these mice, the proximal 8.3 kb of the human iNOS 5′-flanking region controls expression of the reporter gene of enhanced green fluorescent protein (EGFP). Patterns of human iNOS promoter/EGFP transgene expression in tissues were examined by fluorescence microscopy and immunoblotting. Endogenous murine iNOS was basally undetectable in kidney, intestine, spleen, heart, lung, liver, stomach, or brain. In contrast, EGFP from the transgene was basally expressed in kidney, brain, and spleen, but not the other tissues of the transgenic mice. Bacterial lipopolysaccharide induced endogenous iNOS expression in kidney, intestine, spleen, lung, liver, stomach, and heart, but not brain. In contrast, human iNOS promoter/EGFP transgene expression was induced above basal levels only in intestine, spleen, brain, stomach, and lung. Within kidney, human iNOS promoter/EGFP fluorescence was detected most prominently in proximal tubules of the outer cortex and collecting ducts and colocalized with endogenous mouse iNOS. Within the collecting duct, both endogenous iNOS and the human iNOS promoter/EGFP transgene were expressed in cells lacking aquaporin-2 immunoreactivity, consistent with expression in intercalated cells. Although it remains possible that essential regulatory elements reside in remote locations of the gene, our data concerning this 8.3-kb region provide the first in vivo evidence suggesting differential transcriptional control of the human iNOS gene in these organs and marked differences in transcriptional regulatory regions between the murine and human genes.

Induction of nitric oxide release from the human alveolar epithelial cell line A549: an in vitro correlate of innate immune response to Mycobacterium tuberculosis

In view of the presence of a large number of epithelial cells in the alveoli of the lung and their ability to produce various cytokines and chemokines, the possible role of alveolar epithelial cells in the innate immune response to tuberculosis was examined. The human alveolar epithelial cell line A549 was used as a model. The ability of A549 cells to induce nitric oxide (NO) in response to Mycobacterium tuberculosis infection was taken as an in vitro correlate of innate immunity. M. tuberculosis infection induced A549 cells to produce significant levels of NO and to express inducible nitric oxide synthase mRNA at 48 hr of infection. However, the amount of NO released at this point was not mycobactericidal. Cytokine stimulation (interferon-gamma, tumour necrosis factor-alpha, interleukin-1beta, alone or in combination) of the infected A549 cells induced a higher concentration of NO. The study of colony-forming units (CFU) as a measure of the mycobactericidal capacity of A549 cells revealed a reduction in CFU of M. tuberculosis by 39.29% (from 10.62 +/- 0.48 - 6.392 +/- 0.54) following cytokine stimulation of the infected cells. Interestingly gamma-irradiated M. tuberculosis H37Rv could also induce higher than basal level of NO. Therefore we examined mycobacterial antigenic components for their possible role in NO production. We observed that A549 cells produced significantly higher amounts of NO at 48 hr when treated with mycobacterial whole cell lysates, cell wall or cell membrane preparations. The release of NO and the resultant mycobactericidal activity could be further enhanced by simultaneously conditioning the M. tuberculosis infected A549 cells with cytokine and mycobacterial components. These results suggest that alveolar epithelial cells respond to their microenvironment, which is constituted of various cytokines and macrophage-processed antigens and may contribute to the innate immune response to tuberculosis.

Haplotypic relationship between SNP and microsatellite markers at the NOS2A locus in two populations

The density of genetic markers required for successful association mapping of complex diseases depends on linkage disequilibrium (LD) between non-functional markers and functional variants. The haplotypic relationship between stable markers and potentially unstable but highly informative markers (e.g. microsatellites) indicates that LD might be maintained over considerable genetic distance in non-African populations, supporting the use of such 'mixed marker haplotypes' in LD-based mapping, and allowing inferences to be drawn about human origins. We investigated sequence variation in the proximal 2.6 kb of the inducible nitric oxide synthase (NOS2A) promoter and the relationship between SNP haplotypes and a pentanucleotide microsatellite (the 'NOS2A(-2.6) microsatellite') in Gambians and UK Caucasians. UK Caucasians exhibited a subset of sequence diversity observed in Gambians, sharing four of 11 SNPs and a similar haplotypic structure. Five SNPs were found in the sequence of interspersed repetitive DNA elements. In both populations, there was dramatic loss of LD between SNP haplotypes and microsatellite alleles across a very short physical distance, suggesting a high intrinsic mutation rate of the NOS2A(-2.6) microsatellite, the SNP haplotypes are relatively ancient, or that this was a region of frequent recombination. Understanding locus- and population-specific LD is essential when designing and interpreting genetic association studies.

Nitric oxide synthesis in the kidney: isoforms, biosynthesis, and functions in health

Nitric oxide (NO) is a gaseous free radical that serves cell signaling, cellular energetics, host defense, and inflammatory functions in virtually all cells. In the kidney and vasculature, NO plays fundamental roles in the control of systemic and intrarenal hemodynamics, the tubuloglomerular feedback response, pressure natriuresis, release of sympathetic neurotransmitters and renin, and tubular solute and water transport. NO is synthesized from L-arginine by NO synthases (NOS). Because of its high chemical reactivity and high diffusibility, NO production by each of the 3 major NOS isoforms is regulated tightly at multiple levels from gene transcription to spatial proximity near intended targets to covalent modification and allosteric regulation of the enzyme itself. Many of these regulatory mechanisms have yet to be tested in renal cells. The NOS isoforms are distributed differentially and regulated in the kidney, and there remains some controversy over the specific expression of functional protein for the NOS isoforms in specific renal cell populations. Mice with targeted deletion of each of the NOS isoforms have been generated, and these each have unique phenotypes. Studies of the renal and vascular phenotypes of these mice have yielded important insights into certain vascular diseases, ischemic acute renal failure, the tubuloglomerular feedback response, and some mechanisms of tubular fluid and electrolyte transport, but thus far have been underexploited. This review explores the collective knowledge regarding the structure, regulation, and function of the NOS isoforms gleaned from various tissues, and highlights the progress and gaps in understanding in applying this information to renal and vascular physiology.

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.

Transcriptional activation of the human inducible nitric-oxide synthase promoter by Kruppel-like factor 6

Nitric oxide is a ubiquitous free radical that plays a key role in a broad spectrum of signaling pathways in physiological and pathophysiological processes. We have explored the transcriptional regulation of inducible nitric-oxide synthase (iNOS) by Krüppel-like factor 6 (KLF6), an Sp1-like zinc finger transcription factor. Study of serial deletion constructs of the iNOS promoter revealed that the proximal 0.63-kb region can support a 3-6-fold reporter activity similar to that of the full-length 16-kb promoter. Within the 0.63-kb region, we identified two CACCC sites (-164 to -168 and -261 to -265) that bound KLF6 in both electrophoretic mobility shift and chromatin immunoprecipitation assays. Mutation of both these sites abrogated the KLF6-induced enhancement of the 0.63-kb iNOS promoter activity. The binding of KLF6 to the iNOS promoter was significantly increased in Jurkat cells, primary T lymphocytes, and COS-7 cells subjected to NaCN-induced hypoxia, heat shock, serum starvation, and phorbol 12-myristate 13-acetate/ ionophore stimulation. Furthermore, in KLF6-transfected and NaCN-treated COS-7 cells, there was a 3-4-fold increase in the expression of the endogenous iNOS mRNA and protein that correlated with increased production of nitric oxide. These findings indicate that KLF6 is a potential transactivator of the human iNOS promoter in diverse pathophysiological conditions.

Nucleotide and haplotypic diversity of the NOS2A promoter region and its relationship to cerebral malaria

To assess the hypothesis that nitric oxide is critical in the pathogenesis of cerebral malaria, we analysed genetic variation in the proximal promoter region of NOS2A, the gene encoding inducible nitric oxide synthase. Sequencing 72 Gambian chromosomes revealed 11 single nucleotide polymorphisms in 2.5 kB (theta=8.6 x 10(-4)). Genotyping 104 nuclear families identified six common haplotypes. A single haplotype, uniquely defined by the NOS2A-1659T allele, was associated with cerebral malaria by a transmission disequilibrium test of 334 affected children and their parents (P=0.02). An independent case-control study of 505 different children from the same population replicated the allelic association with cerebral malaria (odds ratio: 1.31, P=0.04). Taken together these data indicate a weak but significant association of the NOS2A locus with susceptibility to cerebral malaria. Despite high linkage disequilibrium across the region studied, this association would not have been detected without the initial construction of a dense marker set for haplotype tagging.

Gemfibrozil, a lipid-lowering drug, inhibits the induction of nitric-oxide synthase in human astrocytes

Gemfibrozil, a lipid-lowering drug, inhibited cytokine-induced production of NO and the expression of inducible nitric-oxide synthase (iNOS) in human U373MG astroglial cells and primary astrocytes. Similar to gemfibrozil, clofibrate, another fibrate drug, also inhibited the expression of iNOS. Inhibition of human iNOS promoter-driven luciferase activity by gemfibrozil in cytokine-stimulated U373MG astroglial cells suggests that this compound inhibits the transcription of iNOS. Since gemfibrozil is known to activate peroxisome proliferator-activated receptor-alpha (PPAR-alpha), we investigated the role of PPAR-alpha in gemfibrozil-mediated inhibition of iNOS. Gemfibrozil induced peroxisome proliferator-responsive element (PPRE)-dependent luciferase activity, which was inhibited by the expression of DeltahPPAR-alpha, the dominant-negative mutant of human PPAR-alpha. However, DeltahPPAR-alpha was unable to abrogate gemfibrozil-mediated inhibition of iNOS suggesting that gemfibrozil inhibits iNOS independent of PPAR-alpha. The human iNOS promoter contains consensus sequences for the binding of transcription factors, including interferon-gamma (IFN-gamma) regulatory factor-1 (IRF-1) binding to interferon-stimulated responsive element (ISRE), signal transducer and activator of transcription (STAT) binding to gamma-activation site (GAS), nuclear factor-kappaB (NF-kappaB), activator protein-1 (AP-1), and CCAAT/enhancer-binding protein beta (C/EBPbeta); therefore, we investigated the effect of gemfibrozil on the activation of these transcription factors. The combination of interleukin (IL)-1beta and IFN-gamma induced the activation of NF-kappaB, AP-1, C/EBPbeta, and GAS but not that of ISRE, suggesting that IRF-1 may not be involved in cytokine-induced expression of iNOS in human astrocytes. Interestingly, gemfibrozil strongly inhibited the activation of NF-kappaB, AP-1, and C/EBPbeta but not that of GAS in cytokine-stimulated astroglial cells. These results suggest that gemfibrozil inhibits the induction of iNOS probably by inhibiting the activation of NF-kappaB, AP-1, and C/EBPbeta and that gemfibrozil, a prescribed drug for humans, may further find its therapeutic use in neuroinflammatory diseases.

Diacerhein and rhein prevent interleukin-1beta-induced nuclear factor-kappaB activation by inhibiting the degradation of inhibitor kappaB-alpha

Diacerhein and rhein are anthraquinone compounds that ameliorate the course of osteoarthritis. Recent reports also suggest that these compounds may have antiinflammatory properties, but the cellular mechanisms by which they exert antiosteoarthritic and possibly antiinflammatory effects are still incompletely understood. The purpose of this study was to investigate the ability of diacerhein and rhein to inhibit the activation of the transcription factor nuclear factor kappaB, induced by the proinflammatory cytokine interleukin-1beta, in primary monolayer cultures of bovine articular chondrocytes. We also studied the ability of diacerhein and rhein to prevent the expression of the inducible nitric oxide synthase gene, which is driven by nuclear factor-kappaB. We observed that interleukin-1beta induced the degradation of the inhibitor kappaB-alpha protein and the translocation of the protein p65 (a member of the nuclear factor-kappaB family) to the nucleus, which were inhibited by diacerhein and rhein, in a dose-dependent manner. Interleukin-1beta-induced nuclear factor-kappaB binding to a specific (gamma-(32)P)-labelled oligonucleotide probe was also inhibited by treatment of chondrocytes with diacerhein or rhein, as revealed by electrophoretic mobility shift assay. Inducible nitric oxide synthase mRNA and protein synthesis and nitric oxide production were also inhibited by diacerhein and rhein, in a dose-dependent manner. The half-maximal inhibitory concentrations of diacerhein and rhein, relative to nitric oxide production, were 8.2 microM ;and 7.7 microM, respectively. These results suggest that diacerhein and rhein inhibit nuclear factor-kappaB activation and, consequently, the expression of nuclear factor-kappaB-dependent genes, such as the inducible nitric oxide synthase gene, which can explain their antiosteoarthritic and antiinflammatory effects.

Proteomic analysis of cytokine induced proteins in human intestinal epithelial cells: implications for inflammatory bowel diseases

A role for cytokine regulated proteins in epithelial cells has been suggested in the pathogenesis of inflammatory bowel diseases (IBD). The aim of this study was to identify such cytokine regulated targets using a proteomic functional approach. Protein patterns from (35)S-radiolabeled homogenates of cultured colon epithelial cells were compared before and after exposure to interferon-gamma, interleukin-1beta and interleukin-6. Proteins were separated by two-dimensional polyacrylamide gel electrophoresis. Both autoradiographies and silver stained gels were analyzed. Proteins showing differential expression were identified by tryptic in-gel digestion and mass spectrometry. Metabolism related proteins were also investigated by Western blot analysis. Tryptophanyl-tRNA synthetase, indoleamine-2,3-dioxygenase, heterogeneous nuclear ribonucleoprotein JKTBP, interferon-induced 35kDa protein, proteasome subunit LMP2 and arginosuccinate synthetase were identified as cytokine modulated proteins in vitro. Using purified epithelial cells from patients, overexpression of indoleamine-2,3-dioxygenase, an enzyme involved in tryptophan metabolism, was confirmed in Crohn's disease as well as in ulcerative colitis, as compared to normal mucosa. No such difference was found in diverticulitis. Potentially, this observation opens new avenues in the treatment of IBD.

A repressor in the proximal human inducible nitric oxide synthase promoter modulates transcriptional activation

The human inducible nitric oxide synthase (iNOS or NOSII) gene is regulated through an extended and complex promoter. In this study, the transcriptional regulation of human NOSII is investigated in the human colon cell line HCT-8R. Stimulation with a cytokine mix (interferon-gamma, interleukin 1-beta, and tumor necrosis factor alpha) induces NOSII mRNA accumulation, as well as promoter activity in these cells. Several random deletions were performed within the proximal 7 kb of the promoter, which led to the identification of a region, whose deletion provokes a marked increase in transcriptional activity upon cytokine stimulation. Furthermore, this region is shown to repress a viral-driven luciferase construct, mainly at basal levels. An AP-1-like sequence present in this region that is specifically recognized by nuclear proteins is shown to be involved in the repressive effect. This element is capable of repressing a viral promoter, and its deletion augments cytokine-stimulated transcription. These findings are confirmed in various cell lines and suggest a general mechanism for the control of basal levels of NOSII expression, to avoid unnecessary toxicity under normal conditions.

Role of mitogen-activated protein kinases and tyrosine kinases on IL-1-Induced NF-kappaB activation and iNOS expression in bovine articular chondrocytes

Nitric oxide (NO), produced by the inducible isoform of the NO synthase (iNOS), plays an important role in the pathophysiology of arthritic diseases. This work aimed at elucidating the role of the mitogen-activated protein kinases (MAPK), p38MAPK and p42/44MAPK, and of protein tyrosine kinases (PTK) on interleukin-1beta (IL-1)-induced iNOS expression in bovine articular chondrocytes. The specific inhibitor of the p38MAPK, SB 203580, effectively inhibited IL-1-induced iNOS mRNA and protein synthesis, as well as NO production, while the specific inhibitor of the p42/44MAPK, PD 98059, had no effect. These responses to IL-1 were also inhibited by treatment of the cells with the tyrosine kinase inhibitors, genistein and tyrphostin B42, which also prevented IL-1-induced NF-kappaB activation. The p38MAPK inhibitor, SB 203580, had no effect on IL-1-induced NF-kappaB activation. Finally, the p42/44MAPK inhibitor, PD 98059, prevented IL-1-induced AP-1 activation in a concentration that did not inhibit iNOS expression. In conclusion, this study shows that (1) PTK are part of the signaling pathway that leads to IL-1-induced NF-kappaB activation and iNOS expression; (2) the p38MAPK cascade is required for IL-1-induced iNOS expression; (3) the p42/44MAPK and AP-1 are not involved in IL-1-induced iNOS expression; and (4) NF-kappaB and the p38MAPK lie on two distinct pathways that seem to be independently required for IL-1-induced iNOS expression. Hence, inhibition of any of these two signaling cascades is sufficient to prevent iNOS expression and the subsequent production of NO in articular chondrocytes.

(CCTTT)n repeat polymorphism in the NOS2 gene promoter is associated with atopy

BACKGROUND

Several studies have shown that nitric oxide (NO) plays a role in the regulation of the T(H)1/T(H)2 balance, indicating the potential for NO to contribute to the development of atopy and several other allergic diseases, including bronchial asthma. NO synthase 2 (NOS2) is critically involved in the synthesis of NO during several inflammatory states, and the gene encoding NOS2 is located at chromosome 17q11.2-q12, where 2 genome scans have identified a candidate locus for atopy and asthma.

OBJECTIVE

The 14-repeat allele of the (CCTTT)(n) repeat polymorphism in the NOS2 promoter region is a powerful enhancer of promoter activity in reporter constructs in vitro. We tested whether this potentially functional allele in the NOS2 gene influences the development of atopy and asthma.

METHODS

We studied a total of 497 unrelated Japanese subjects (141 nonatopic healthy controls, 102 atopic healthy controls, 56 nonatopic asthmatic subjects, and 198 atopic asthmatic subjects). The odds ratio (OR) was calculated for atopy and asthma in carriers of the 14-repeat allele through use of logistic regression models. Atopy was defined as a positive specific IgE level to at least 1 of 10 common inhaled allergens.

RESULTS

The 14-repeat allele was inversely associated with atopy (OR = 0.42, P < .01). The association remained significant when the model was controlled for asthmatic status (OR = 0.36, P < .01). This allele, however, was associated neither with the development of asthma nor with total serum IgE levels.

CONCLUSION

Our findings suggest that the (CCTTT)(n) repeat polymorphism in the promoter of the NOS2 gene that affects promoter activity is a risk factor for the development of atopy, and this genetic effect seems independent of asthma.

Cytokine-induced changes in chromatin structure and in vivo footprints in the inducible NOS promoter

Transcription of the human inducible nitric oxide synthase (iNOS) gene is regulated by inflammatory cytokines in a tissue-specific manner. To determine whether differences in cytokine-induced mRNA levels between pulmonary epithelial cells (A549) and hepatic biliary epithelial cells (AKN-1) result from different protein or DNA regulatory mechanisms, we identified cytokine-induced changes in DNase I-hypersensitive (HS) sites in 13 kb of the iNOS 5'-flanking region. Data showed both constitutive and inducible HS sites in an overlapping yet cell type-specific pattern. Using in vivo footprinting and ligation-mediated PCR to detect potential DNA or protein interactions, we examined one promoter region near -5 kb containing both constitutive and cytokine-induced HS sites. In both cell types, three in vivo footprints were present in both control and cytokine-treated cells, and each mapped within a constitutive HS site. The remaining footprint appeared only in response to cytokine treatment and mapped to an inducible HS site. These studies, performed on chromatin in situ, identify a portion of the molecular mechanisms regulating transcription of the human iNOS gene in both lung- and liver-derived epithelial cells.

Complex contribution of the 3'-untranslated region to the expressional regulation of the human inducible nitric-oxide synthase gene. Involvement of the RNA-binding protein HuR

Cytokine stimulation of human DLD-1 cells resulted in a marked expression of nitric-oxide synthase (NOS) II mRNA and protein accompanied by only a moderate increase in transcriptional activity. Also, there was a basal transcription of the NOS II gene, which did not result in measurable NOS II expression. The 3'-untranslated region (3'-UTR) of the NOS II mRNA contains four AUUUA motifs and one AUUUUA motif, known to destabilize the mRNAs of proto-oncogenes, nuclear transcription factors, and cytokines. Luciferase reporter gene constructs containing the NOS II 3'-UTR showed a significantly reduced luciferase activity. The embryonic lethal abnormal vision (ELAV)-like protein HuR was found to bind with high affinity to the adenylate/uridylate-rich elements of the NOS II 3'-UTR. Inhibition of HuR with antisense constructs reduced the cytokine-induced NOS II mRNA, whereas overexpression of HuR potentiated the cytokine-induced NOS II expression. This provides evidence that NOS II expression is regulated at the transcriptional and post-transcriptional level. Binding of HuR to the 3'-UTR of the NOS II mRNA seems to play an essential role in the stabilization of this mRNA.

Non-NF-kappaB elements are required for full induction of the rat type II nitric oxide synthase in vascular smooth muscle cells

We have investigated the role of the NF-kappaB binding sites and other promoter elements beyond NF-kappaB in iNOS induction in rat vascular smooth muscle cells (SMC). Rat aortic SMC transfected with iNOS promoter constructs with either mutation or deletion of the downstream NF-kappaB site exhibited about 50% reduction in promoter activity in response to a cytokine mixture, whereas either mutation or deletion of the upstream NF-kappaB site reduced promoter activity by 90%, suggesting that the latter site is the most important, and that co-existence of two NF-kappaB sites is necessary for iNOS induction. Nuclear NF-kappaB activity was robustly induced by TNF-alpha. However, TNF-alpha alone did not induce iNOS promoter activity, protein expression, or nitrite production, indicating that NF-kappaB activation alone is not sufficient for iNOS induction. The construct up to -890 bp, containing the downstream NF-kappaB site, exhibited little response to cytokines. The construct up to -1.0 kb, containing the two NF-kappaB sites exhibited only 22% of full promoter activity. The regions -1001 to -1368 bp and -2 to -2.5 kb contributed an additional 43 and 22% promoter activity, respectively. Internal deletion or reversal of the orientation of -1001 to -1368 bp in the full promoter resulted in 40% reduction in promoter activity. These data suggest that the co-existence of two NF-kappaB sites is essential for core promoter activity, but that full induction of the rat SMC iNOS gene requires other elements located between -1.0 to -1.37 and -2.0 to -2.5 kb of the promoter.

Genotyping and functional analysis of a polymorphic (CCTTT)(n) repeat of NOS2A in diabetic retinopathy

Accumulating evidence shows that the severity and rapidity of onset of diabetic retinopathy are influenced by genetic factors. Expression of the nitric oxide synthases is altered in the retinal vasculature in the early stages of diabetic retinopathy. We analyzed the allele distribution of a polymorphic pentanucleotide repeat within the 5' upstream promoter region of the NOS2A gene in samples of diabetic patients. In diabetic patients from Northern Ireland, the 14-repeat allele of the NOS2A marker was significantly associated with the absence of diabetic retinopathy. Carriers of this repeat had 0.21-fold the relative risk of developing diabetic retinopathy than noncarriers of this allele. They also had significantly fewer renal and cardiovascular complications. The ability of differing numbers of (CCTTT)(n) pentanucleotide repeats to induce transcription of the NOS2A gene was analyzed using a luciferase reporter gene assay in transfected colonic carcinoma cells. Interleukin 1beta (IL-1beta) induction was most effective in constructs carrying the 14-repeat allele. When cells were incubated in 25 mM glucose to mimic the diabetic state, IL-1beta induction was inhibited in all cases, but to a significantly lesser extent with the 14-repeat allele. These unique properties of the 14-repeat allele may confer selective advantages in diabetic individuals, which may delay or prevent microvascular complications of diabetes.

Blood mononuclear cell nitric oxide production and plasma cytokine levels in healthy gabonese children with prior mild or severe malaria

Plasmodium falciparum malaria is an important cause of morbidity and mortality in children. Factors that determine the development of mild versus severe malaria are not fully understood. Since host-derived nitric oxide (NO) has antiplasmodial properties, we measured NO production and NO synthase (NOS) activity in peripheral blood mononuclear cells (PBMC) from healthy Gabonese children with a history of prior mild malaria (PMM) or prior severe malaria (PSM) caused by P. falciparum. The PMM group had significantly higher levels of NOS activity in freshly isolated PBMC and higher NO production and NOS activity in cultured PBMC. The investigation of NO-modulating cytokines (e.g., interleukin 12, gamma interferon, tumor necrosis factor alpha [TNF-alpha], and transforming growth factor beta1) as an explanation for differing levels of NOS activity revealed that plasma levels of TNF-alpha were significantly higher in the PSM group. Our results suggest that NOS/ NO and TNF-alpha are markers for prior disease severity and important determinants of resistance to malaria.

Synergistic cytokine-induced nitric oxide production in human alveolar epithelial cells

Nitric oxide (NO) is an important mediator molecule in regulating normal airway function, as well as in the pathophysiology of inflammatory airway diseases. In addition, cytokines are potent messenger molecules at sites of inflammation. The specific relationship among IL-1beta, TNF-alpha, and IFN-gamma on iNOS induction and NO synthesis in human alveolar epithelial cells has not been determined. In addition, rigorous methods to determine potential synergistic action between the cytokines have not been employed. We exposed monolayer cultures of A549 cells to a factorial combination of three cytokines (IL-1beta, TNF-alpha, and IFN-gamma) and three concentrations (0, 5, and 100 ng/mL). TNF-alpha alone does not induce NO production directly; however, it does have a stimulatory effect on IL-1beta-induced NO production. IL-1beta and INF-gamma both induce NO production alone, yet at different concentration thresholds, and act synergistically when present together. In the presence of all three cytokines, the net effect of NO production exceeds the predicted additive effect of each individual cytokine and the two-way interactions. Several plausible mechanisms of synergy among IL-1beta, TNF-alpha, and IFN-gamma in NO production from human alveolar epithelial cells (A549) are proposed. In order to verify the proposed mechanisms of synergy, future experimental and theoretical studies must address several molecular steps through which the iNOS gene is expressed and regulated, as well as the expression and regulation of enzyme cofactors and substrates.

The role of protein phosphatases in the expression of inducible nitric oxide synthase in the rat hepatocyte

Previously, we demonstrated that nuclear factor-kappaB (NF-kappaB) mediates cytokine-induced hepatic inducible nitric oxide synthase (iNOS) expression. NF-kappaB activation is regulated by kinases and phosphatases whose function is only beginning to be understood. Therefore, experiments were performed to determine the role of protein phosphatases (PPase) in cytokine-induced iNOS expression. Hepatocytes were stimulated with cytokines in the presence or absence of tyrosine phosphatase inhibitors (pervanadate [PV], phenylarsine oxide [PAO]) and a serine-threonine phosphatase inhibitor (okadaic acid [OA]). Cytokines induced hepatocyte iNOS mRNA, protein, and NO2- production that was substantially decreased by the addition of the tyrosine phosphatase inhibitors (PAO and PV). The serine-threonine phosphatase inhibitor (OA) decreased NO release and protein levels in a concentration-dependent fashion; however, iNOS mRNA levels were not significantly reduced. Nuclear run-on experiments demonstrated that protein tyrosine phosphatases (PTPases) are required for iNOS transcription, while the serine-threonine phosphatase inhibitor (OA) had no effect on iNOS transcription. Electromobility shift assays (EMSAs) revealed that the tyrosine-phosphatase inhibitors blocked cytokine-induced NF-kappaB activation, while OA did not have a significant effect on NF-kappaB DNA binding activity. Therefore, tyrosine phosphatases are involved in the regulation of cytokine-induced activation of NF-kappaB, while serine-threonine phosphatases posttranscriptionally regulate iNOS translation. These results identify the regulatory role of specific protein phosphatases (PPases) in hepatic iNOS expression.

Distinct distribution and time-course changes in neuronal nitric oxide synthase and inducible NOS in the paraventricular nucleus following lipopolysaccharide injection

Nitric oxide (NO) is known to be involved in the modulation of neuroendocrine function. To clarify the role of different isoforms of NO synthase (NOS) in the neuroendocrine response to immune challenge, the expressions of neuronal NOS (nNOS) and inducible NOS (iNOS) genes in the hypothalamus following lipopolysaccharide (LPS) injection were examined using in situ hybridization. NOS activity was also determined by NADPH-diaphorase (NADPH-d) histochemistry. LPS (25 mg/kg) or sterile saline was injected intraperitoneally to male Wistar rats and the rats sacrificed 30 min, or 1, 2, 3, 5, 12 or 24 h after injection. nNOS mRNA expression in the paraventricular nucleus (PVN) was significantly increased 2 h after LPS injection. iNOS mRNA, which was not detected until 2 h after LPS injection, was significantly increased in the PVN 3 h after LPS injection. Both RNA expressions had returned to basal levels by 12 h after LPS injection. The number of NADPH-d positive cells was significantly increased 5 h after LPS injection. iNOS expression was more robust in parvocellular PVN, while nNOS was distributed mainly in the magnocellular PVN. Double in situ hybridization histochemistry revealed that some of the iNOS- (48.4%) or nNOS-positive cells (34. 3%) in the parvocellular PVN expressed CRF mRNA. The results demonstrate that LPS-induced sepsis causes significant increases in nNOS and iNOS gene expression with different time-courses and distributions, and that iNOS mRNA was more frequently co-localized with CRF-producing parvocellular neurons in the PVN. Thus, NO produced by iNOS and nNOS may play an important role in the neuroendocrine response to an immune challenge. Distinct differences in the distribution and time-course changes of iNOS and nNOS suggest different roles for the hypothalamic-pituitary-adrenal axis and/or neurohypophyseal system.

Role of interferon regulatory factor-1 and mitogen-activated protein kinase pathways in the induction of nitric oxide synthase-2 in retinal pigmented epithelial cells

Bovine retinal pigmented epithelial cells express an inducible nitric oxide synthase (NOS-2) after activation with interferon-gamma (IFN-gamma) and lipopolysaccharide (LPS). Experiments were performed to investigate the involvement of interferon regulatory factor-1 (IRF-1) on NOS-2 induction and its regulation by NOS-2 inhibitors such as pyrrolidine dithiocarbamate (PDTC), an antioxidant, or protein kinase inhibitors. Analysis by transitory transfections showed that LPS, alone or with IFN-gamma, stimulated activity of the murine NOS-2 promoter fragment linked upstream of luciferase and its suppression by PDTC and by the different protein kinase inhibitors, genistein (tyrosine kinase inhibitor), PD98059 (mitogen-actived protein (MAP) kinase kinase inhibitor), and SB 203580 (p38 MAP inhibitor). Using specific antibodies, we have confirmed that extracellular signal-regulated kinases and p38 MAP kinase were activated by LPS and IFN-gamma in retinal pigmented epithelial cells. Analysis by reverse transcriptase-polymerase chain reaction, Western blot, and electrophoretic mobility shift assay demonstrated that IFN-gamma alone or combined with LPS induced an accumulation of IRF-1 mRNA and protein and IRF-1 DNA binding. Transfections assays with the IRF-1 promoter showed an induction of this promoter with IFN-gamma, potentiated by LPS. The decrease of LPS/IFN-gamma-induced IRF-1 promoter activity, IRF-1 synthesis, and IRF-1 activation, by PDTC, genistein, PD98059, and SB 203580, could explained in part the inhibition of the NOS-2 induction by these compounds. Our results demonstrate that IRF-1 is necessary for NOS-2 induction by LPS and IFN-gamma and that its synthesis requires the involvement of a redox-sensitive step, the activation of tyrosine kinases, and extracellular signal-regulated kinases 1/2 and p38 MAP kinases.

Cytokine induction of NO synthase II in human DLD-1 cells: roles of the JAK-STAT, AP-1 and NF-kappaB-signaling pathways

1. In human epithelial-like DLD-I cells, nitric oxide synthase (NOS) II expression was induced by interferon-gamma (100 u ml(-1)) alone and, to a larger extent, by a cytokine mixture (CM) consisting of interferon-gamma, interleukin-1beta (50 u ml(-1)) and tumor necrosis factor-alpha (10 ng ml(-1)). 2. CM-induced NOS II expression was inhibited by tyrphostin B42 (mRNA down to 1%; nitrite production down to 0.5% at 300 microM) and tyrphostin A25 (mRNA down to 24%, nitrite production down to 1% at 200 microM), suggesting the involvement of janus kinase 2 (JAK-2). Tyrphostin B42 also blocked the CM-induced JAK-2 phosphorylation (kinase assay) and reduced the CM-stimulated STAT1alpha binding activity (gel shift analysis). 3. CM reduced the nuclear binding activity of transcription factor AP-1. A heterogenous group of compounds, that stimulated the expression of c-fos/c-jun, enhanced the nuclear binding activity of AP-1. This group includes the protein phosphatase inhibitors calyculin A, okadaic acid, and phenylarsine oxide, as well as the inhibitor of translation anisomycin. All of these compounds reduced CM-induced NOS II mRNA expression (to 9% at 50 nM calyculin A; to 28% at 500 nM okadaic acid; to 18% at 10 microM phenylarsine oxide; and to 19% at 100 ng ml(-1) anisomycin) without changing NOS II mRNA stability. In cotransfection experiments, overexpression of c-Jun and c-Fos reduced promoter activity of a 7 kb DNA fragment of the 5'-flanking sequence of the human NOS II gene to 63%. 4. Nuclear extracts from resting DLD-1 cells showed significant binding activity for transcription factor NF-kappaB, which was only slightly enhanced by CM. The NF-kappaB inhibitors dexamethasone (1 microM), 3,4-dichloroisocoumarin (50 microM), panepoxydone (5 microg ml(-1)) and pyrrolidine dithiocarbamate (100 microM) produced no inhibition of CM-induced NOS II induction. 5. We conclude that in human DLD-1 cells, the interferon-gamma-JAK-2-STAT1alpha pathway is important for NOS II induction. AP-1 (that is downregulated by CM) seems to be a negative regulator of NOS II expression. NF-kappaB, which is probably important for basal activity of the human NOS II promoter, is unlikely to function as a major effector of CM in DLD-1 cells.

Cytokine-mediated transcriptional induction of the human inducible nitric oxide synthase gene requires both activator protein 1 and nuclear factor kappaB-binding sites

The involvement of AP-1 and NF-kappaB transcription factors in cytokine-mediated induction of human inducible nitric oxide synthase (hiNOS) promoter activity was examined. Luciferase reporter plasmids, containing mutations in AP-1 and NF-kappaB sites, in a hiNOS promoter extending from -8.3 kilobase pairs (kb) to +168, were transiently expressed in A549 cells, and promoter activity was determined after treatment with a cytokine mixture (CM) containing interleukin 1-beta, interferon-gamma, and tumor necrosis factor-alpha. Mutation of the AP-1 heptad located -5301 base pairs upstream decreased gene activation by 90% in a -8.3-kb promoter and a shorter -5.574-kb promoter. Disruption of AP-1 (at -5115) or NF-kappaB (at -115 and -8283) sites reduced promoter activity by 45, 67, and 52%, respectively. Responsiveness to CM was decreased by 85% in constructs mutated in both NF-kappaB sites. By gel retardation analyses, CM increased AP-1- and NF-kappaB binding. Supershift analysis identified Jun D and Fra-2 as components of AP-1 complexes. Each kappaB site bound different complements of NF-kappaB/Rel family members (downstream site, Rel A/p50; upstream site, Rel A/Rel A). Rel A was maximally, whereas IkappaB-alpha was minimally, expressed in nuclei after 1 h of CM treatment, corresponding with the peak in NF-kappaB inding activity. Thus, AP-1 and NF-kappaB are important cis-elements for induction of hiNOS gene transcription.

Analysis of the cytokine-stimulated human inducible nitric oxide synthase (iNOS) gene: characterization of differences between human and mouse iNOS promoters

Expression of human inducible nitric oxide synthase (hiNOS) is under cytokine control and is transcriptionally regulated. The hiNOS and mouse iNOS (miNOS) genes are regulated differently by cytokines. To understand better the transcriptional regulation of the hiNOS gene, the 8.3-kb hiNOS promoter was characterized. Promoter activity was evaluated by transient transfection of hiNOS luciferase constructs in A549 human alveolar type II epithelium-like cells in the presence and absence of cytokines (IFN-gamma, IL-1 beta, and TNF-alpha). Important cytokine-responsive elements are located at -3665 to -5574 bp (containing two perfectly matched AP-1 sites which are not present in miNOS promoter) and -8093 to -8296 bp (one perfectly matched NF-kappa B site) of the hiNOS promoter region. Likely, these two AP-1 sites and the upstream NF-kappa B site are important in the transcriptional induction of hiNOS by cytokines. Our data demonstrate the molecular basis for the different cytokine-stimulated characteristics of hiNOS and miNOS genes.

Inducible nitric oxide synthase expression in smooth muscle cells and macrophages of human transplant coronary artery disease

BACKGROUND

The inducible isoform of the nitric oxide synthase (iNOS) produces large amounts of nitric oxide in response to cytokine stimulation. Previous investigations have demonstrated iNOS expression in the setting of acute and chronic rejection in experimental cardiac transplant models. The goal of this study was to investigate whether iNOS is upregulated in human transplant coronary artery disease (TCAD), a major cause of late mortality after cardiac transplantation.

METHODS AND RESULTS

We studied 15 patients with TCAD and 10 with normal coronary arteries. In situ hybridization and immunohistochemistry were used in tissue sections to localize iNOS mRNA and protein, respectively. The presence of peroxynitrite was indirectly assessed by immunostaining with an anti-nitrotyrosine antibody. Normal coronary arteries had no evidence of iNOS expression. In contrast, 30 of 36 coronary artery segments with TCAD (83%) were immunostained by the iNOS antibody. The presence of iNOS mRNA was demonstrated in these vessels by in situ hybridization. Specific cell markers identified iNOS-positive cells as neointimal macrophages and smooth muscle cells. Nitrotyrosine immunoreactivity colocalized with iNOS expression in arteries with TCAD, distributed in macrophages and smooth muscle cells.

CONCLUSIONS

iNOS mRNA and protein are expressed in human arteries with TCAD, where they are associated with extensive nitration of protein tyrosines. These findings indicate that the high-output nitric oxide pathway and possibly the oxidant peroxynitrite might be involved in the process leading to the development of TCAD.

Multiple NF-kappaB enhancer elements regulate cytokine induction of the human inducible nitric oxide synthase gene

The human inducible nitric oxide synthase (iNOS) gene is overexpressed in a number of human inflammatory diseases. Previously, we observed that the human iNOS gene is transcriptionally regulated by cytokines and demonstrated that the cytokine-responsive regions are upstream of -3.8 kilobase pairs (kb). Therefore, the purpose of this study was to further localize the functional enhancer elements and to assess the role of the transcription factor NF-kappaB in both human liver (AKN-1) and human lung (A549) epithelial cell lines. The addition of NF-kappaB inhibitors significantly suppressed cytokine-stimulated iNOS mRNA expression and NO synthesis, indicating that NF-kappaB is involved in the induction of the human iNOS gene. Analysis of the first 4.7 kb of the 5'-flanking region demonstrated basal promoter activity and failed to show any cytokine-inducible activity. However, promoter constructs extending to -5.8 and -7.2 kb revealed 2-3-fold and 4-5-fold induction, respectively, in the presence of cytokines. DNA sequence analysis from -3.8 to -7.2 kb identified five putative NF-kappaB cis-regulatory transcription factor binding sites upstream of -4.7 kb. Site-directed mutagenesis of these sites revealed that the NF-kappaB motif at -5.8 kb is required for cytokine-induced promoter activity, while the sites at -5.2, -5.5, and -6.1 kb elicit a cooperative effect. Electromobility shift assays using a site-specific oligonucleotide and nuclear extracts from cells stimulated with cytokine-mixture, tumor necrosis factor-alpha or interleukin-1beta, but not interferon-gamma, exhibited inducible DNA binding activity for NF-kappaB. These data indicate that NF-kappaB activation is required for cytokine induction of the human iNOS gene and identifies four NF-kappaB enhancer elements upstream in the human iNOS promoter that confer inducibility to tumor necrosis factor-alpha and interleukin-1beta.

Molecular cloning and analysis of the rat inducible nitric oxide synthase gene promoter in aortic smooth muscle cells

We have cloned five DNA fragments (-0.32, -0.48, -1.7, -3.2, and -5.1 kb) of the 5'-flanking region of the rat inducible nitric oxide synthase (iNOS) gene from rat genomic DNA. The functional importance of the 5'-flanking region was determined by transient expression of iNOS promoter-luciferase constructs in cultures of rat aortic smooth muscle cells. The -0.48 kb construct, containing one nuclear factor kappaB (NF-kappaB) binding site, expressed basal promoter activity but showed only a 1.5- and 1.7-fold increase in luciferase activity in response to lipopolysaccharide (LPS) or a cytokine mixture, respectively. However, the -3.2 kb construct (containing a second NF-kappaB binding site) showed full promoter activity with a 24-fold increase in response to LPS or cytokine mixture. The -5.1 kb construct showed no further increase in luciferase activity, suggesting that the 1.9 kb upstream of -3.2 kb may not be important in rat iNOS regulation. Rat iNOS promoter induction did not appear to be transcriptionally regulated by NO since NOS inhibitors did not affect induction. These data are in marked contrast to the mouse iNOS promoter in which a DNA sequence as short as a -85 bp, containing one NF-kappaB site, confers 10-fold inducibility by LPS. The present findings demonstrate that the rat iNOS gene is transcriptionally regulated by cytokines and LPS, but, unlike the mouse gene, the downstream NF-kappaB site does not appear to be a key region in responses to cytokines and LPS. These data suggest that the regulation of the rat gene may require the coexistence of at least two NF-kappaB sites or other elements upstream of -0.48 kb of the 5'-flanking region.

Acute and subacute effects of endotoxin on hypothalamic gaseous neuromodulators

Although two-way communication between the hypothalamus and the immune system in now well established, particularly for the hypothalamo-pituitary-adrenal axis, the role of the gaseous neurotransmitters nitric oxide (NO) and carbon monoxide (CO) is much less well understood in terms of hypothalamic function. These agents are an important part of the peripheral inflammatory response; and their synthetic enzymes, NO synthase (NOS) and heme oxygenase (HO), respectively, have been localized to the hypothalamic PVN and SON. The induced generation of both NO and CO leads to the suppression of CRH and vasopressin, the major stimulators of the HPA. Thus, the addition of hemin to hypothalamic explants is maximally active at 1 microM in attenuating the release of CRH and vasopressin, and this dose is also most effective in generating biliverdin and associated CO. CO generation is also able to stimulate cyclooxygenase to produce prostaglandin E2, an established intermediary in the cytokine-stimulated activation of the HPA. Finally, inducible NOS mRNA is specifically induced in the hypothalalmus in response to endotoxin, in parallel to interleukin-1. These data provide increasing evidence in favor of NO and CO as counterregulatory agents in the HPA response to immune activation.

Molecular characterization of rabbit CPP32 and its function in vascular smooth muscle cell apoptosis

Vascular remodeling in atherogenesis is marked not only by cellular proliferation and migration but is also impacted by apoptotic cell death. Extensive studies have focused on the signal transduction events leading to apoptosis. CPP32, a member of the caspase/interleukin-1 beta-converting enzyme (ICE) protease family, has emerged as a central player in several reports of apoptosis pathways. Vascular smooth muscle cells (SMC) undergo apoptosis after treatment with various stimuli, including nitric oxide (NO) donors, such as sodium nitroprusside (SNP, 0.1-1 mM). The aim of the present study was to evaluate the role of CPP32 in SNP-induced apoptosis of SMC. We isolated a rabbit CPP32 cDNA by using degenerate primers and polymerase chain reaction technique. The predicted protein encoded by this cDNA contains the conserved sequence (QACRG) necessary for covalent linkage to poly(ADP-ribose) polymerase (PARP) as well as the three amino acids responsible for substrate recognition and catalysis reported in other caspase members. Using a segment of this cDNA as a probe, we found no change of CPP32 mRNA in cultured arterial SMC before and after SNP treatment. We also measured the protease activity of CPP32 against a chromophore p-nitroaniline (pNA)-labeled substrate, DEVD-pNA. Our results showed a dose-dependent increase of CPP32 activity in SMC, with a maximal 10-fold increase after SNP treatment. Addition of a competitive CPP32 inhibitor, DEVD-CHO, produced a 50% reduction in maximal stimulation. Immunoblot analysis illustrated that SNP treatment induced proteolytic cleavage of CPP32 into its enzymatically active subunit p17 as well as the degradation of PARP into a 85-kDa fragment. We further demonstrated that incubation of cultured SMC with DEVD-CHO significantly reduced SNP-induced DNA fragmentation. DNA fragmentation analysis was carried out using several methods including a cell death detection enzyme-linked immunosorbent assay kit, in situ end labeling, and DNA electrophoresis in agarose gel. Our data indicate that CPP32 mRNA is constitutively expressed in rabbit SMC and activation of CPP32 protein has a pivotal role in SNP-induced SMC apoptosis.

Expression of nitric oxide synthase-2 in glia associated with CNS pathology

This chapter discusses the expression of nitric oxide synthase-2 (NOS-2) in glia associated with central nervous system (CNS) pathology. The production of nitric oxide (NO) in the nervous system is catalyzed by three, highly homologous isoforms of NO synthase (NOS). NOS-2, the dimeric, heme-containing, soluble protein whose activity is independent of a rise in intracellular calcium, is variously termed ‘inducible,’ ‘immunologic,’ and ‘macrophage NOS (macNOS).’ Nitric oxide inhibits not only NOS-2 activity but also regulates the level of NOS-2 messenger RNA (mRNA) expression through a mechanism involving NF-^K B. There is specific evidence for the glial expression of NOS-2 associated with neuronal injury and infection of the CNS and in neurodegenerative and demyelinating diseases. Direct injury in the CNS results in a reactive gliosis, characterized by the induction of the glial fibrillary acidic protein gene and changes in astrocyte morphology.

Control of nitric oxide production by endogenous TNF-alpha in mouse retinal pigmented epithelial and Muller glial cells

Since the induction of nitric oxide synthase (NOS) by lipopolysaccharide (LPS) has been suggested to be partially dependent of the synthesis of tumor necrosis factor alpha (TNF alpha), we have investigated in vitro the production of NO in retinal cells from mice deficient in Lymphotoxin alpha (LT alpha)/TNF alpha. Treatment of retinal Müller glial (RMG) and retinal pigmented epithelial (RPE) cells from both wild-type and knockout mice with LPS and interferon gamma (IFN gamma) induced NO synthesis as determined by nitrite release into the media and was correlated to an increase in NOS-2 mRNA levels, evaluated by RT-PCR. However, the level of nitrite and the accumulation of mRNA was always less in cells from LT alpha/TNF alpha knockout mice than in wild type mice. Simultaneous addition of TNF alpha restored the level of NO synthesis by RMG and RPE cells from LT alpha/TNF alpha knockout mice stimulated with LPS and IFN gamma to wild type levels. Transforming growth factor beta (TGF beta) blocked LPS/IFN gamma-induced NO production is RMG and RPE cells from wild-type and LT alpha/TNF alpha knockout mice. Our results demonstrate that induction of NO synthesis in RMG and RPE cells by LPS and IFN gamma is dependent in part on endogenous TNF alpha while inhibition of NO production by TGF beta does not require a modulation of TNF alpha synthesis.