Inactivation of ribonucleotide reductase by nitric oxide

The use of thiols by ribonucleotide reductase

Ribonucleotide reductase (RNR) catalyzes the rate-limiting de novo synthesis of 2'-deoxyribonucleotides from the corresponding ribonucleotides and thereby provides balanced deoxyribonucleotide pools required for error-free DNA replication and repair. The essential role of RNR in DNA synthesis and the use of DNA as genetic material has made it an important target for the development of anticancer and antiviral agents. The most well known feature of the universal RNR reaction in all kingdoms of life is the involvement of protein free radicals. Redox-active cysteines, thiyl radicals, and thiol redox proteins of the thioredoxin superfamily play major roles in the catalytic mechanism. The involvement of cysteine residues in catalysis is common to all three classes of RNR. Taking account of the recent progress in this field of research, this review focuses on the use of thiols in the redox mechanism of RNR enzymes.

Nitric oxide and frataxin: two players contributing to maintain cellular iron homeostasis

BACKGROUND

Nitric oxide (NO) is a signalling and physiologically active molecule in animals, plants and bacteria. The specificity of the molecular mechanism(s) involved in transducing the NO signal within and between cells and tissues is still poorly understood. NO has been shown to be an emerging and potent signal molecule in plant growth, development and stress physiology. The NO donor S-nitrosoglutathion (GSNO) was shown to be a biologically active compound in plants and a candidate for NO storage and/or mobilization between plant tissues and cells. NO has been implicated as a central component in maintaining iron bioavailavility in plants.

SCOPE AND CONCLUSIONS

Iron is an essential nutrient for almost all organisms. This review presents an overview of the functions of NO in iron metabolism in animals and discusses how NO production constitutes a key response in plant iron sensing and availability. In plants, NO drives downstream responses to both iron deficiency and iron overload. NO-mediated improvement of iron nutrition in plants growing under iron-deficient conditions represents a powerful tool to cope with soils displaying low iron availability. An interconversion between different redox forms based on the iron and NO status of the plant cells might be the core of a metabolic process driving plant iron homeostasis. Frataxin, a recently identified protein in plants, plays an important role in mitochondria biogenesis and in maintaining mitochondrial iron homeostasis. Evidence regarding the interaction between frataxin, NO and iron from analysis of frataxin knock-down Arabidopsis thaliana mutants is reviewed and discussed.

Synthesis, characterization and cytotoxic/cytostatic activity of La(III) and Dy(III) complexes

New La(III) and Dy(III) complexes of deprotonated 4-hydroxy-3[1-(4-nitrophenyl)-3-oxobutyl]-2H-1-benzopyran-2-one (Acenocoumarol) were synthesized and characterized using FT-IR, FT-Raman, (1)H NMR spectra, and elemental analyses. The ligand and its lanthanide(III) complexes were tested for their cytotoxic/cytostatic activity against two tumor cell lines and peritoneal mouse macrophages. The La(III) and Dy(III) complexes exhibit good activity against melanoma B16 and fibrosarcoma L929 and they are stronger inhibitors of tumor cell proliferation compared to the ligand without influencing normal cell viability and NO release by mouse peritoneal macrophages.

The effect of nitric oxide on vaccinia virus-encoded ribonucleotide reductase

Growth inhibition of the DNA virus vaccinia (VACV) by NO is known to occur at the level of DNA synthesis. This inhibition is partially reversed by addition of deoxyribonucleosides, suggesting that NO or NO-related species inhibit viral ribonucleotide reductase (RR). However, the effect of NO on VACV-encoded RR or other DNA-synthesizing enzymes has not been demonstrated. In order to study the effects of NO on VACV-encoded RR, DNA polymerase (DNA pol) and thymidine kinase (TK), we generated a VACV recombinant expressing murine macrophage iNOS under control of a VACV early/late promoter p7.5. Using this recombinant, we demonstrate that expression of iNOS and the resulting production of NO inhibit activity of the viral RR, but not of viral DNA pol and TK. This NO-mediated inhibition of viral RR occurred around the same time as the increase of ADP levels, while it preceded the block in VACV DNA synthesis and the decrease of ATP levels. In addition, we tested the effects of DPTA/NONOate on the growth of different VACV mutants. Fold-inhibition of the growth of VACV deletion mutant for TK was comparable to that of wild-type VACV. VACV containing amplification of the gene for the small subunit of RR appeared to be least sensitive to DPTA/NONOate, while VACV deletion mutant for the large subunit of RR was most sensitive. The results provide a direct evidence for NO-mediated inhibition of VACV-encoded RR.

Nitric oxide stress induces different responses but mediates comparable protein thiol protection in Bacillus subtilis and Staphylococcus aureus

The nonpathogenic Bacillus subtilis and the pathogen Staphylococcus aureus are gram-positive model organisms that have to cope with the radical nitric oxide (NO) generated by nitrite reductases of denitrifying bacteria and by the inducible NO synthases of immune cells of the host, respectively. The response of both microorganisms to NO was analyzed by using a two-dimensional gel approach. Metabolic labeling of the proteins revealed major changes in the synthesis pattern of cytosolic proteins after the addition of the NO donor MAHMA NONOate. Whereas B. subtilis induced several oxidative stress-responsive regulons controlled by Fur, PerR, OhrR, and Spx, as well as the general stress response controlled by the alternative sigma factor SigB, the more resistant S. aureus showed an increased synthesis rate of proteins involved in anaerobic metabolism. These data were confirmed by nuclear magnetic resonance analyses indicating that NO causes a drastically higher increase in the formation of lactate and butanediol in S. aureus than in B. subtilis. Monitoring the intracellular protein thiol state, we observed no increase in reversible or irreversible protein thiol modifications after NO stress in either organism. Obviously, NO itself does not cause general protein thiol oxidations. In contrast, exposure of cells to NO prior to peroxide stress diminished the irreversible thiol oxidation caused by hydrogen peroxide.

Rapid and quantitative activation of Chlamydia trachomatis ribonucleotide reductase by hydrogen peroxide

We recently showed that the class Ic ribonucleotide reductase (RNR) from the human pathogen Chlamydia trachomatis ( Ct) uses a Mn (IV)/Fe (III) cofactor in its R2 subunit to initiate catalysis [Jiang, W., Yun, D., Saleh, L., Barr, E. W., Xing, G., Hoffart, L. M., Maslak, M.-A., Krebs, C., and Bollinger, J. M., Jr. (2007) Science 316, 1188-1191]. The Mn (IV) site of the novel cofactor functionally replaces the tyrosyl radical used by conventional class I RNRs to initiate substrate radical production. As a first step in evaluating the hypothesis that the use of the alternative cofactor could make the RNR more robust to reactive oxygen and nitrogen species [RO(N)S] produced by the host's immune system [Högbom, M., Stenmark, P., Voevodskaya, N., McClarty, G., Gräslund, A., and Nordlund, P. (2004) Science 305, 245-248], we have examined the reactivities of three stable redox states of the Mn/Fe cluster (Mn (II)/Fe (II), Mn (III)/Fe (III), and Mn (IV)/Fe (III)) toward hydrogen peroxide. Not only is the activity of the Mn (IV)/Fe (III)-R2 intermediate stable to prolonged (>1 h) incubations with as much as 5 mM H 2O 2, but both the fully reduced (Mn (II)/Fe (II)) and one-electron-reduced (Mn (III)/Fe (III)) forms of the protein are also efficiently activated by H 2O 2. The Mn (III)/Fe (III)-R2 species reacts with a second-order rate constant of 8 +/- 1 M (-1) s (-1) to yield the Mn (IV)/Fe (IV)-R2 intermediate previously observed in the reaction of Mn (II)/Fe (II)-R2 with O 2 [Jiang, W., Hoffart, L. M., Krebs, C., and Bollinger, J. M., Jr. (2007) Biochemistry 46, 8709-8716]. As previously observed, the intermediate decays by reduction of the Fe site to the active Mn (IV)/Fe (III)-R2 complex. The reaction of the Mn (II)/Fe (II)-R2 species with H 2O 2 proceeds in three resolved steps: sequential oxidation to Mn (III)/Fe (III)-R2 ( k = 1.7 +/- 0.3 mM (-1) s (-1)) and Mn (IV)/Fe (IV)-R2, followed by decay of the intermediate to the active Mn (IV)/Fe (III)-R2 product. The efficient reaction of both reduced forms with H 2O 2 contrasts with previous observations on the conventional class I RNR from Escherichia coli, which is efficiently converted from the fully reduced (Fe 2 (II/II)) to the "met" (Fe 2 (III/III)) form [Gerez, C., and Fontecave, M. (1992) Biochemistry 31, 780-786] but is then only very inefficiently converted from the met to the active (Fe 2 (III/III)-Y (*)) form [Sahlin, M., Sjöberg, B.-M., Backes, G., Loehr, T., and Sanders-Loehr, J. (1990) Biochem. Biophys. Res. Commun. 167, 813-818].

Induction and regulation of CD4+ T cell subsets

It is now generally accepted that CD4+ T cells can be divided into at least two distinct subsets: Th1 and Th2. Th1 cells characteristically secrete interleukin 1 (IL-2) and gamma-interferon (IFN-gamma) whereas Th2 cells produce mainly IL-4, IL-5 and IL-10. Studies from many laboratories have demonstrated that the balance between these two subsets of T cells frequently determines the outcome of infectious and autoimmune diseases. Several factors influence the preferential induction and regulation of Th1 or Th2 cells in vitro and in vivo. Mice were infected with the protozoan parasite Leishmania to show that the gene encoding a major surface glycoprotein of the parasite, delivered orally in a plasmid carried by an auxotrophic Salmonella typhimurium vaccine strain (BRD509), preferentially induced Th1 cells and protective immunity against a challenge infection. The protective effect of the vaccine was augmented by administration of BRD509 carrying the genes encoding IL-2, IFN-gamma or tumour necrosis factor alpha. Cloned mouse Th1 cells specific for malarial antigens have been used to show that nitric oxide (NO) can inhibit the production of IFN-gamma by Th1 cells. Oral delivery of antigen and selective cytokines may preferentially induce CD4+ T cell subsets. Modulation of NO synthesis may further influence this induction and sustain such selective responses leading to effective therapy.

Glutathione-dependent alcohol dehydrogenase AdhC is required for defense against nitrosative stress in Haemophilus influenzae

In Haemophilus influenzae Rd KW20, we identified a gene, adhC, which encodes a class III alcohol dehydrogenase (AdhC) and has S-nitrosoglutathione reductase activity. adhC exists on an operon with estD, which encodes an esterase. Divergent to the adhC-estD operon is the Haemophilus influenzae nmlR gene (nmlR(HI)), which encodes a MerR family regulator that is homologous to the Neisseria MerR-like regulator (NmlR). Analysis of an nmlR(HI) mutant indicated that expression of the adhC-estD operon is regulated by NmlR(HI) in strain Rd KW20. Chromosomal inactivation of either adhC or nmlR(HI) resulted in sensitivity to S-nitrosoglutathione and decreased S-nitrosoglutathione reductase activity. Examination of the NmlR(HI)-AdhC system in the genome sequences of nontypeable H. influenzae strains R2846, R2866, and 86-028NP identified significant variations. The adhC gene of 86-028NP was predicted to be nonfunctional due to a premature stop codon. Polymorphisms in the operator/promoter region of R2866 resulted in reduced enzyme activity. This correlated with an increased sensitivity to S-nitrosoglutathione. The adhC-nmlR(HI) system was examined in thirty-three clinical isolates (both capsular and nontypeable strains). Nucleic acid sequence data showed that only strain 86-028NP contained a premature stop codon. There were some variations in the DNA sequence of the operator/promoter region which altered the nmlR(HI) promoter. However, the clinical isolates still possessed S-nitrosoglutathione reductase activity and showed at least the equivalent ability to grow in the presence of S-nitrosoglutathione as Rd KW20. These data suggest that the nmlR(HI)-adhC system has a role in the defense against nitrosative stress in Haemophilus influenzae.

A manganese(IV)/iron(III) cofactor in Chlamydia trachomatis ribonucleotide reductase

In a conventional class I ribonucleotide reductase (RNR), a diiron(II/II) cofactor in the R2 subunit reacts with oxygen to produce a diiron(III/IV) intermediate, which generates a stable tyrosyl radical (Y*). The Y* reversibly oxidizes a cysteine residue in the R1 subunit to a cysteinyl radical (C*), which abstracts the 3'-hydrogen of the substrate to initiate its reduction. The RNR from Chlamydia trachomatis lacks the Y*, and it had been proposed that the diiron(III/IV) complex in R2 directly generates the C* in R1. By enzyme activity measurements and spectroscopic methods, we show that this RNR actually uses a previously unknown stable manganese(IV)/iron(III) cofactor for radical initiation.

Immunoregulatory and antimicrobial effects of nitrogen oxides

The therapeutic effects of inhaled nitric oxide (NO) therapy are thought to be restricted to the pulmonary vasculature because of rapid inactivation of NO by hemoglobin in the bloodstream. However, recent data suggest that inhaled NO may not only be scavenged by the heme iron of hemoglobin but also may react with protein thiols in the bloodstream, including cysteine-93 of the hemoglobin B subunit. Reaction of NO with protein or peptide thiols is termed S-nitrosylation and results in the formation of relatively stable protein S-nitrosothiols that carry NO bioactivity to distal organs. Thus, inhaled NO-induced protein S-nitrosylation may allow inhaled NO to have multiple as yet undiscovered physiologic and pathophysiologic effects outside of the lung. Here we review the immunoregulatory and antimicrobial functions of NO and the potential effects of inhaled NO therapy on host defense.

Role of epithelial nitric oxide in airway viral infection

The airway mucosal epithelium is the first site of virus contact with the host, and the main site of infection and inflammation. Nitric oxide (NO) produced by the airway epithelium is vital to antiviral inflammatory and immune defense in the lung. Multiple mechanisms function coordinately to support high-level basal NO synthesis in healthy airway epithelium and further induction of NO synthesis in the infected airway of normal hosts. Hosts deficient in NO synthesis, such as those patients with cystic fibrosis, have impaired antiviral defense and may benefit from therapies to augment NO levels in the airways.

Antibodies against nitric oxide damaged poly L-tyrosine and 3-nitrotyrosine levels in systemic lupus erythematosus

Alterations in the amino acid structure or sequence can generate neo-epitopes from self-proteins causing autoaggressive immune attack. Reactive nitrogen species are an important factor that induces post-translational modification of proteins by cellular reduction and oxidation mechanism; cysteinyl-nitrosylation or tyrosine nitration leading to potentially pathogenic pathways. It was thought of interest to investigate the immunogenicity of nitrated poly L-tyrosine vis-á-vis its possible role in the induction of antibodies in systemic lupus erythematosus (SLE). Commercially available poly L-tyrosine was exposed to nitrating species and the damage was monitored by UV spectroscopy and alkaline gel electrophoresis. The results indicated the formation of 3-nitrotyrosine. Nitrated poly L-tyrosine induced higher titre antibodies as compared to the native form. Nitrated poly L-tyrosine was recognized by the autoantibodies present in the sera of patients suffering from SLE by enzyme immunoassays and band shift assay. The possible role of nitrated self-proteins has been discussed in the production of circulating anti-DNA antibodies in SLE.

Nitrogen monoxide (NO)-mediated iron release from cells is linked to NO-induced glutathione efflux via multidrug resistance-associated protein 1

Nitrogen monoxide (NO) plays a role in the cytotoxic mechanisms of activated macrophages against tumor cells by inducing iron (Fe) release. We have shown that NO-mediated Fe efflux from cells required glutathione (GSH), and we have hypothesized that a GS-Fe-NO complex was released. Hence, we studied the role of the GSH-conjugate transporter multidrug resistance-associated protein 1 (MRP1) in NO-mediated Fe efflux. MCF7-VP cells overexpressing MRP1 exhibited a 3- to 4-fold increase in NO-mediated 59Fe and GSH efflux compared with WT cells (MCF7-WT) over 4 h. Similar results were found for other MRP1-overexpressing cell types but not those expressing another drug efflux pump, P-glycoprotein. NO-mediated 59Fe and GSH efflux were temperature- and energy-dependent and were significantly decreased by the GSH-depleting agent and MRP1 transport inhibitor L-buthionine-[S,R]-sulfoximine. Other MRP1 inhibitors, MK571, probenecid, and difloxacin, significantly inhibited NO-mediated 59Fe release. EPR spectroscopy demonstrated the dinitrosyl-dithiol-Fe complex (DNIC) peak in NO-treated cells was increased by MRP1 inhibitors, indicating inhibited DNIC transport from cells. The extent of DNIC accumulation correlated with the ability of MRP1 inhibitors to prevent NO-mediated 59Fe efflux. MCF7-VP cells were more sensitive than MCF7-WT cells to growth inhibition by effects of NO, which was potentiated by L-buthionine-[S,R]-sulfoximine. These data indicate the importance of GSH in NO-mediated inhibition of proliferation. Collectively, NO stimulates Fe and GSH efflux from cells via MRP1. Active transport of NO by MRP1 overcomes diffusion that is inefficient and nontargeted, which has broad ramifications for understanding NO biology.

Nitric oxide and endoplasmic reticulum stress

Nitric oxide (NO) is a multifunctional biomolecule involved in a variety of physiological and pathological processes, including regulation of blood vessel dilatation and anti-arteriosclerotic effects. However, a large amount of NO is toxic to the host and causes several diseases such as apoptosis, septic shock, and diabetes mellitus. Inducible-form NO synthase is induced in inflammatory diseases, including insulitis and arteriosclerosis. Endoplasmic reticulum (ER) stress pathway was first identified as a cellular response pathway induced by the accumulation of unfolded proteins in ER to preserve ER functions. Later it was found that ER stress pathway is also activated by various cellular stresses to protect cells, but when stresses are severe, apoptosis is induced to remove damaged cells. It is reported that NO and reactive oxygen species disturb ER functions, then ER stress-mediated apoptosis pathway is activated. CHOP/GADD153, which belongs to C/EBP transcription factor family, is induced in this process and mediates apoptosis. ER stress pathway induced by NO can be involved in the pathogenesis of various vascular diseases.

HIF-1alpha and iNOS levels in crucian carp gills during hypoxia-induced transformation

Hypoxia inducible factor 1 alpha (HIF-1alpha) initiates expression of a wide variety of genes, some of which are involved in apoptosis and cell cycle arrest. We have previously shown that crucian carp increases its respiratory surface area 7.5-fold in response to hypoxia. This change is due to apoptosis and cell cycle arrest in specific parts of its gills. Here we have characterized crucian carp HIF-1alpha, and measured mRNA, protein and DNA binding levels during hypoxia exposure in crucian carp gills. We have also measured an HIF-1alpha-induced gene, the inducible nitric oxide synthase (iNOS), which has the ability to initiate apoptosis and cell cycle arrest. Crucian carp HIF-1alpha was found to have all critical domains known to be important for function. Comparison of the peptide sequence with other species indicated high similarity with other cyprinid fish, but a pronounced variation compared to the salmonid, rainbow trout. Further, we found HIF-1alpha protein to be stabilized during hypoxia. Further, HIF-1alpha was often present in normoxia, and showed marked individual weight-dependent variation. We found no alteration of iNOS mRNA levels during hypoxia exposure. These findings suggest HIF-1alpha involvement in hypoxia-induced change of respiratory surface area in crucian carp gills. However, its activity does not seem to be mediated through iNOS.

Nitric Oxide in Salmonella and Escherichia coli Infections

This review discusses the role that nitric oxide (NO) and its congeners play on various stages in the pathophysiology of Escherichia coli and Salmonella infections, with special emphasis on the regulatory pathways that lead to high NO synthesis, the role of reactive nitrogen species (RNS) in host resistance, and the bacterial molecular targets and defense mechanisms that protect enteric bacteria against the nitrosative stress encountered in diverse host anatomical sites. In general, NO can react directly with prosthetic groups containing transition metal centers, with other radicals, or with sulfhydryl groups in the presence of an electron acceptor. Binding to iron complexes is probably the best characterized direct reaction of NO in biological systems. The targets of RNS are numerous. RNS can facilitate oxidative modifications including lipid peroxidation, hydroxylation, and DNA base and protein oxidation. In addition, RNS can inflict nitrosative stress through the nitrosation of amines and sulfhydryls. Numerous vital bacterial molecules can be targeted by NO. It is therefore not surprising that enteropathogenic bacteria are armed with a number of sensors to coordinate the protective response to nitrosative stress, along with an assortment of antinitrosative defenses that detoxify, repair, or avoid the deleterious effects of RNS encountered within the host. NO and NO-derived RNS play important roles in innate immunity to Salmonella and E. coli. Enzymatic NO production by NO synthases can be enhanced by microbial and other inflammatory stimuli and it exerts direct antimicrobial actions as well as immunomodulatory and vasoregulatory effects.

Inhibition of radiation induced nitration by curcumin and nicotinamide in mouse macrophages

Nitric oxide plays an important role in inflammation and carcinogenesis and has now been implicated as an important signaling molecule under normal physiological conditions also. Increased nitric oxide (NO) results in increased nitration of proteins at tyrosine, which can cause protein dysfunction or alterations in signal transduction pathways. Irradiation of Lipopolysaccharide (LPS) activated mouse peritoneal macrophages was found to increase NO production, inducible nitric oxide synthase (iNOS) expression and nitration of proteins. The increase in iNOS expression was very less when compared to increase in NO production, indicating the possibility of post-translational activation of iNOS by LPS and ionising radiation. The addition of curcumin, nicotinamide and Jun N-terminal kinase (JNK) inhibitor, SP 600125, reduced the levels of NO, iNOS expression and nitration of proteins in macrophages. Closer scrutiny of the inhibition pattern of these modulators revealed that although the JNK inhibitor did not result in significant decrease in iNOS expression it led to a significant decrease in NO production, implying the possible involvement of JNK in the regulation of iNOS activity. Curcumin and JNK inhibitor directly inhibited the nitration of proteins and JNK inhibitor and curcumin, when added together, did not show synergistic effect.

Involvement of phospholipid, biomembrane integrity, and NO peroxidase activity in the NO catabolism by cytochrome c oxidase

The physiological regulation of mitochondrial respiration by NO has been reported to result from the reversible binding of NO to the two-electron reduced binuclear center (Fe(2+)(a3)-Cu(1+)(B)) of cytochrome c oxidase (CcO). Although the role of CcO and its derived catalytic intermediates in the catabolism of NO has been documented, little has been established for the enzyme in its fully oxidized state (Fe(3+)(a3)-Cu(2+)(B)). We report: (1) CcO, in its fully oxidized state, represents the major component of the mitochondrial electron transport chain for NO consumption as controlled by the binding of NO to its binuclear center. Phospholipid enhances NO consumption by fully oxidized CcO, whereas the consumption of NO is slowed down by membrane structure and membrane potential when CcO is embedded in the phospholipid bilayer. (2) In the presence of H(2)O(2), CcO was shown to serve as a mitochondria-derived NO peroxidase. A CcO-derived protein radical intermediate was induced and involved in the modulation of NO catabolism.

Endothelial nitric oxide synthase upregulation in the cochlea of the guinea pig after intratympanic gentamicin injection

Single-shot transtympanic gentamicin therapy has become a popular treatment modality for Meniere's disease despite the known possible ototoxic properties of this drug. It was shown recently that NO production and iNOS were upregulated after gentamicin application, which was interpreted as a possible effect of ototoxicity. In this study we analyzed the expression of eNOS after gentamicin application to determine a possible correlation of this enzyme with gentamicin-induced ototoxicity. We compared eNOS expression in gentamicin-treated and non-treated guinea pigs in the second turn of the cochlea, an area corresponding to speech perception in humans. Gentamicin (4 mg) was injected intratympanically into the middle ear of guinea pigs ( n =3) and the reduction of the hearing threshold level was determined by recording acoustic-evoked potentials (AEP) before and 5 days after gentamicin application. Morphological alterations in the organ of Corti were analyzed by light and electron microscopy. Gold-labeled anti-eNOS antibodies were counted in eight different cell areas for quantification of eNOS expression. Seven animals were analyzed as controls. After gentamicin application, a deterioration of hearing level was observed varying from 10 to 30 dB. A high degree of vacuolization was identified in the third row of outer hair cells. At the subcellular level, the subsurface cisterns in outer hair cells were dissociated from the basolateral cell membrane, and the mitochondrial membranes were frequently damaged. Statistically significant upregulation of eNOS was observed in all cell types analyzed. Depending on the various cell types the amount of gold-labeled eNOS antibodies was 2.5 to 5.7 times higher after gentamicin application. We observed significant eNOS upregulation after gentamicin application in the cochlea, in conjunction with cellular damages and decreased hearing.

Reactive species-mediated regulation of cell signaling and the cell cycle: the role of MAPK

Cardiovascular disease development is significantly influenced by the effects of reactive species (RS). By virtue of their controlled production, regulation, and reactive nature, RS play important roles in the modulation of cellular signaling, growth, and death in the vasculature. Concentration gradients are important in determining the effects of RS. Low to moderate concentrations of RS act as mediators in signaling cascades and gene regulation, whereas high levels of RS cause cellular damage and death. Because a dual redox regulation state seems to exist in several signaling cascades, e.g., RS often induce upstream initiating events, whereas downstream events are reliant on reductive processes, alterations in cellular redox states influence the activation/inactivation of signaling events and transcription factors. In this review, the relationships between RS, specific signal transduction pathways, and aspects of cell-cycle control are discussed.

Cross-talk between nitric oxide and transforming growth factor-beta1 in malaria

Malaria has re-emerged as a global health problem, leading to an increased focus on the cellular and molecular biology of the mosquito Anopheles and the parasite Plasmodium with the goal of identifying novel points of intervention in the parasite life cycle. Anti-parasite defenses mounted by both mammalian hosts and Anopheles can suppress the growth of Plasmodium. Nonetheless, the parasite is able to escape complete elimination in vivo, perhaps by thwarting or co-opting these mechanisms for its own survival, as do numerous other pathogens. Among the defense systems used by the mammalian host against Plasmodium is the synthesis of nitric oxide (NO), catalyzed by an inducible NO synthase (iNOS). Nitric oxide produced by the action of an inducible Anopheles stephensi NO synthase (AsNOS) may be central to the anti-parasitic arsenal of this mosquito. In mammals, iNOS can be modulated by members of the transforming growth factor-beta (TGF-beta) cytokine superfamily. Transforming growth factor-beta is produced as an inactive precursor that is activated following dissociation of certain inhibitory proteins, a process that can be promoted by reaction products of NO as well as by hemin. Ingestion by Anopheles of blood containing Plasmodium initiates parasite development, blood digestion which results in the accumulation of hematin (hemin) in the insect midgut, and induction of both AsNOS and TGF-beta-like (As60A) gene expression in the midgut epithelium. Active mammalian TGF-beta1 can be detected in the A. stephensi midgut up to 48h post-ingestion and latent TGF-beta1 can be activated by midgut components in vitro, a process that is potentiated by NO and that may involve hematin. Further, mammalian TGF-beta1 is perceived as a cytokine by A. stephensi cells in vitro and can alter Plasmodium development in vivo. Bloodfeeding by Anopheles, therefore, results in a juxtaposition of evolutionarily conserved mosquito and mammalian TGF-beta superfamily homologs that may influence transmission dynamics of Plasmodium in endemic regions.

Repair of cytokine-induced DNA damage in cultured rat islets of Langerhans

Treatment of cultured rat pancreatic islets of Langerhans with the combined cytokines interleukin-1beta (IL-1beta), interferon gamma (IFN gamma) and tumour necrosis factor alpha (TNF alpha) leads to DNA damage including strand breakage. We have investigated the nature of this damage and its repairability. When islets are further incubated for 4 h in fresh medium, the level of cytokine-induced strand breakage remains constant. If the nitric oxide synthase inhibitor N(G)-monomethyl-L-arginine (NMMA) is present during cytokine treatment, then strand breakage is prevented. If NMMA is added following, rather than during,the cytokine treatment and islets are incubated for 4 h, further nitric oxide synthesis is prevented and most cytokine-induced strand breaks are no longer seen. To investigate DNA repair following cytokine treatment, cells were transferred to fresh medium and incubated for 4 h in the presence of hydroxyurea (HU) and 1-beta-D-arabinosyl cytosine (AraC), as inhibitors of strand rejoining. In the presence of these inhibitors there was an accumulation of strand breaks that would otherwise have been repaired. However, when further nitric oxide synthesis was inhibited by NMMA, significantly less additional strand breakage was seen in the presence of HU and AraC. We interpret this, as indicating that excision repair of previously induced base damage did not contribute significantly to strand breakage. Levels of oxidised purines, as indicated by formamidopyrimidine glycosylase (Fpg) sensitive sites, were not increased in cytokine-treated islets. We conclude that in these primary insulin-secreting cells: (a) the DNA damage induced by an 18h cytokine treatment is prevented by an inhibitor of nitric oxide synthase, (b) much of the damage is in the form of apparent strand breaks rather than altered bases such as oxidised purines, (c) substantial repair is ongoing during the cytokine treatment and this repair is not inhibited in the presence of nitric oxide.

Platelet--cancer interactions: mechanisms and pharmacology of tumour cell-induced platelet aggregation

During haematogenous metastasis, cancer cells migrate to the vasculature and interact with platelets resulting in tumour cell-induced platelet aggregation (TCIPA). We review: 1. The biological and clinical significance of TCIPA; 2. Molecular mechanisms involved in platelet aggregation by cancer cells; 3. Strategies for pharmacological regulation of these interactions. We conclude that pharmacological regulation of platelet-cancer cell interactions may reduce the impact of TCIPA on cancer biology.

IL-15 induces IFN-beta and iNOS gene expression, and antiviral activity of murine macrophage RAW 264.7 cells

The effects of interleukine-15 (IL-15) on macrophage activation and antiviral activity have been investigated in this study. We have provided evidence that IL-15 stimulates murine macrophage RAW 264.7 cells to release nitric oxide (NO) and inhibit vaccinia virus (VV) replication in bystander human 293 cells in a dose-dependent manner. The IL-15-induced antiviral activity was partially mediated by NO, as blocking NO production by NO synthase (iNOS) inhibitor NG-monomethyl-L-arginine acetate (L-NMA) partially restored the virus replication. Interferon-gamma (IFN-gamma) was not detectable by ELISA in the cell supernatant of IL-15-activated macrophages or in the co-cultures of macrophages and infected bystander cells. Neutralizing anti-IFN-gamma, anti-IFN-gamma receptor R2, anti-TNF-alpha, or anti-IL-12 antibodies had no effect on NO production or antiviral activity. In contrast, neutralizing anti-IFN-alpha/beta antibody completely restored the VV replication and reduced the NO level to one third of that in the control. Elevated mRNA levels of IFN-beta and iNOS genes were detected in IL-15-activated RAW 264.7 cells by RT-PCR. Our data suggest that IL-15 is capable of inducing IFN-beta, which could participate in NO-mediated antiviral effect.

Antimicrobial reactive oxygen and nitrogen species: concepts and controversies

Phagocyte-derived reactive oxygen and nitrogen species are of crucial importance for host resistance to microbial pathogens. Decades of research have provided a detailed understanding of the regulation, generation and actions of these molecular mediators, as well as their roles in resisting infection. However, differences of opinion remain with regard to their host specificity, cell biology, sources and interactions with one another or with myeloperoxidase and granule proteases. More than a century after Metchnikoff first described phagocytosis, and more than four decades after the discovery of the burst of oxygen consumption that is associated with microbial killing, the seemingly elementary question of how phagocytes inhibit, kill and degrade microorganisms remains controversial. This review updates the reader on these concepts and the topical questions in the field.

Activation of the nitric oxide response in gilthead seabream after experimental infection with Photobacterium damselae subsp. piscicida

Inoculation of small gilthead seabream (Sparus aurata) (30-75 g body weight) with a sublethal dose of different Photobacterium damselae subsp. piscicida (Pdp) strains (DI-21 and 94/99) induced an increase in serum concentrations of stable nitric oxide (NO) metabolites lasting from 6 h to six days post-infection, with a peak at 24 h. In contrast, no such response was detected in larger fish (150-600 g). Since the virulence of Pdp correlates with the presence of a polysaccharide capsular layer which can be induced by growing the bacteria in medium supplemented with 1% glucose (C+ forms), the effect of the presence of an enhanced capsular layer on the NO response in small fish was also evaluated. Although, all bacteria induced a similar rapid (6 h) and sustained (up to six days) NO response, serum concentrations of nitrites and citrulline were significantly increased in fish infected with the Pdp strains grown in glucose-supplemented medium. When the NO response of fish infected with the C+ form of Pdp was blocked by prior injection of the inhibitor L-NAME, the LD(50) was reduced by over 10-fold and the mean time to death was also markedly reduced. Considering that (i) pasteurellosis only affects gilthead seabream with body weights below 100 g; (ii) capsulated Pdp are more resistant to the bactericidal action of NO and peroxynitrites than non-capsulated strains; and (iii) blocking the NO response of the fish results in greater susceptibility to Pdp, it seems reasonable to propose that the sustained NO response reported in this study represents a relevant protective mechanism of juvenile gilthead seabream against pasteurellosis.

Depletion of deoxyribonucleoside triphosphate pools in tumor cells by nitric oxide

Nitric oxide displays pro- and anti-tumor activities, prompting further studies to better understand its precise role. Nitric oxide inhibits ribonucleotide reductase (RnR), the limiting enzyme for de novo dNTP synthesis. We report here the first detailed analysis of dNTP variations induced in tumor cells by NO. NO prodrugs induced a depletion in dNTP pools and an activation of the pyrimidine salvage pathway, as did hydroxyurea, the prototypic RnR inhibitor. In the presence of dipyridamole, which blocked salvaged dNTP synthesis, depletion of dNTP pools was also observed in tumor cells cocultured with macrophages expressing the high-output iNOS activity. This effect was rapid, reversible, blocked by NO scavengers, and cGMP independent. It was quantitatively correlated to iNOS activity. In the absence of dipyridamole, NO still induced a decrease in dATP concentration in tumor cells cocultured with macrophages, whereas surprisingly, concentrations of dCTP and dTTP expanded considerably, resulting in a strong imbalance in dNTP pools. NO prodrugs did not cause such an increase in pyrimidine dNTP, suggesting that pyrimidine nucleosides were released by NO-injured macrophages. Altered dNTP levels have been reported to promote mutagenesis and apoptosis. It is suggested that abnormal changes in dNTP pools in tumors might contribute to NO-dependent toxicity.

Formation of protein tyrosine ortho-semiquinone radical and nitrotyrosine from cytochrome c-derived tyrosyl radical

Oxidative alteration of mitochondrial cytochrome c (cyt c) has been linked to disease pathophysiology and is one of the causative factors for pro-apoptotic events. Hydrogen peroxide induces a short-lived cyt c-derived tyrosyl radical as detected by the electron spin resonance (ESR) spin-trapping technique. This investigation was undertaken to characterize the fate and consequences of the cyt c-derived tyrosyl radical. The direct ESR spectrum from the reaction of cyt c with H(2)O(2) revealed a single-line signal with a line width of approximately 10 G. The detected ESR signal could be prevented by pretreatment of cyt c with iodination, implying that the tyrosine residue of cyt c was involved. The ESR signal can be enhanced and stabilized by a divalent metal ion such as Zn(2+), indicating the formation of the protein tyrosine ortho-semiquinone radical (ToQ.). The production of cyt c-derived ToQ. is inhibited by the spin trap, 2-methyl-2-nitrosopropane (MNP), suggesting the participation of tyrosyl radical in the formation of the ortho-semiquinone radical. The endothelium relaxant factor nitric oxide is well known to mediate mitochondrial respiration and apoptosis. The consumption of NO by cyt c was enhanced by addition of H(2)O(2) as verified by inhibition electrochemical detection using an NO electrode. The rate of NO consumption in the system containing cyt c/NO/H(2)O(2) was decreased by the spin traps 5,5-dimethyl pyrroline N-oxide and MNP, suggesting NO trapping of the cyt c-derived tyrosyl radical. The above result was further confirmed by NO quenching of the ESR signal of the MNP adduct of cyt c tyrosyl radical. Immunoblotting analysis of cyt c after exposure to NO in the presence of H(2)O(2) revealed the formation of 3-nitrotyrosine. The addition of superoxide dismutase did not change the cyt c nitration, indicating that it is peroxynitrite-independent. The results of this study may provide useful information in understanding the interconnection among cyt c, H(2)O(2), NO, and apoptosis.

The Role of the Flavodiiron Proteins in Microbial Nitric Oxide Detoxification

The flavodiiron proteins (first named as A-type flavoproteins) constitute a large superfamily of enzymes, widespread among anaerobic and facultative anaerobic prokaryotes, from both the Archaea and Bacteria domains. Noticeably, genes encoding for homologous enzymes are also present in the genomes of some pathogenic and anaerobic amitochondriate protozoa. The fingerprint of this enzyme family is the conservation of a two-domain structural core, built by a metallo-beta-lactamase-like domain, at the N-terminal region, harbouring a non-heme diiron site, and a flavodoxin-like domain, containing one FMN moiety. These enzymes have a significant nitric oxide reductase activity, and there is increasing evidence that they are involved in microbial resistance to nitric oxide. In this review, we will discuss available data for this novel family of enzymes, including their physicochemical properties, structural and phylogenetic analyses, enzymatic properties and the molecular genetic approaches so far used to tackle their function.

Synapses between parallel fibres and stellate cells express long-term changes in synaptic efficacy in rat cerebellum

Various forms of synaptic plasticity underlying motor learning have already been well characterized at cerebellar parallel fibre (PF)-Purkinje cell (PC) synapses. Inhibitory interneurones play an important role in controlling the excitability and synchronization of PCs. We have therefore tested the possibility that excitatory synapses between PFs and stellate cells (SCs) are also able to exhibit long-term changes in synaptic efficacy. In the present study, we show that long-term potentiation (LTP) and long-term depression (LTD) were induced at these synapses by a low frequency stimulation protocol (2 Hz for 60 s) and that pairing this low frequency stimulation protocol with postsynaptic depolarization induced a marked shift of synaptic plasticity in favour of LTP. This LTP was cAMP independent, but required nitric oxide (NO) production from pre- and/or postsynaptic elements, depending on the stimulation or pairing protocol used, respectively. In contrast, LTD was not dependent on NO production but it required activation of postsynaptic group II and possibly of group I metabotropic glutamate receptors. Finally, stimulation of PFs at 8 Hz for 15 s also induced LTP at PF-SC synapses. But in this case, LTP was cAMP dependent, as was also observed at PF-PC synapses for presynaptic LTP induced in the same conditions. Thus, long-term changes in synaptic efficacy can be accomplished by PF-SCs synapses as well as by PF-PC synapses, suggesting that both types of plasticity might co-operate during cerebellar motor learning.

Activation of DNA biosynthesis in human hepatoblastoma HEPG2 cells by the nitric oxide donor, sodium nitroprusside

The role of nitric oxide (NO) in carcinogenesis is controversial as it has been shown to both stimulate and inhibit tumour growth. Also, there are contradictory opinions regarding the effects of NO on the proliferation of normal and tumour cells. The aim of our study was to use an in vitro model to determine the influence of exogenous NO donors on DNA biosynthesis by measuring [3H] thymidine incorporation in human hepatoblastoma cells (HepG2). The studies were conducted with the following NO precursors: sodium nitroprusside (SNP), S-nitrosoglutathione, and nitroglycerine (NTG). Out of all three NO donors, SNP increased NO levels and strongly stimulated DNA biosynthesis. A SNP concentration of 150 microM induced optimal NO levels necessary for the activation of DNA biosynthesis. Lower levels of DNA biosynthesis (118% increase over the control) were observed in the presence of NTG, whereas S-nitrosoglutathione had no effect. Antioxidants such as thiol-containing drugs, N-acetylcysteine and tocopherol, proved to be the most efficient co-activators of SNP-induced DNA synthesis. On the other hand, supplementing the SNP-containing medium with compounds that induce oxidative stress and lower the level of -SH groups such as hydrogen peroxide, doxorubicin, and N-ethylmaleimide, led to the inhibition of DNA synthesis. Therefore, our results firmly confirm the hypothesis that biological effects of exogenous NO donors depends on the redox status of the cell.

Toxicity of nitric oxide and peroxynitrite to Photobacterium damselae subsp. piscicida

Virulent strains of Photobacterium damselae subsp. piscicida (Pdp) were grown in media with or without glucose supplementation (to enhance polysaccharide capsule formation) and the bactericidal action of nitric oxide (NO) and peroxynitrites was evaluated in a cell-free assay. Treatment with the NO-donor S-nitroso-acetyl-penicillamine (SNAP) induced a dose-and time-dependent decrease in Pdp survival. This effect was greater for strains grown without glucose supplementation (C forms) than for their counterparts grown with glucose supplementation (C(+) forms). Addition of superoxide anion (O2(-)) generating systems (Xanthine/Xanthine oxidase, glucose/glucose oxidase) to the culture media further enhanced the bactericidal effect of NO. A similar bactericidal effect, with the same pattern of sensitivity, was observed when C+ and C forms of the bacteria were treated with 3-morpholino-sydonimide hydrochloride (SIN-1), a compound which simultaneously generates NO and O2(-). Addition of superoxide dismutase (SOD) or SOD plus catalase (CAT) did not fully reverse the toxic action of SIN-1 and the bactericidal effect was similar for both C and C(+) forms suggesting that while NO alone is sufficient to cause damage in all strains of the pathogen tested, growth in glucose supplemented medium enhanced protection to reactive oxygen intermediates rather than NO.

Macrophage endothelial nitric-oxide synthase autoregulates cellular activation and pro-inflammatory protein expression

Expression of inducible nitric-oxide (NO) synthase (iNOS) and "high-output" production of NO by macrophages mediates many cytotoxic actions of these immune cells. However, macrophages have also been shown to express a constitutive NOS isoform, the function of which remains obscure. Herein, bone marrow-derived macrophages (BMDMØs) from wild-type and endothelial NOS (eNOS) knock-out (KO) mice have been used to assess the role of this constitutive NOS isoform in the regulation of macrophage activation. BMDMØs from eNOS KO animals exhibited reduced nuclear factor-kappaB activity, iNOS expression, and NO production after exposure to lipopolysaccharide (LPS) as compared with cells derived from wild-type mice. Soluble guanylate cyclase (sGC) was identified in BMDMØs at a mRNA and protein level, and activation of cells with LPS resulted in accumulation of cyclic GMP. Moreover, the novel non-NO-based sGC activator, BAY 41-2272, enhanced BMDMØ activation in response to LPS, and the sGC inhibitor 1H-(1,2,4)oxadiazolo(4,3-a)quinoxalin-1-one attenuated activation. These observations provide the first demonstration of a pathophysiological role for macrophage eNOS in regulating cellular activation and suggest that NO derived from this constitutive NOS isoform, in part via activation of sGC, is likely to play a pivotal role in the initiation of an inflammatory response.

A mechanism by which nitric oxide accelerates the rate of oxidative DNA damage in Escherichia coli

The presence of nitric oxide (NO) greatly accelerates the rate at which hydrogen peroxide (H2O2) kills Escherichia coli. Workers have suggested that this effect may be important in the process of bacteriocide by phagocytes. The goal of this study was to determine the mechanism of this synergism. The filamentation of the dead cells, and their protection by cell-permeable iron chelators, indicated that NO/H2O2 killed cells by damaging their DNA through the Fenton reaction. Indeed, the number of DNA lesions was far greater when NO was present during H2O2 exposure. In the Fenton reaction, free intracellular iron transfers electrons from adventitious donors to H2O2, producing hydroxyl radicals. Although NO damaged the [Fe-S] clusters of dehydratases, this did not increase the amount of free iron and was therefore not the reason for acceleration of Fenton chemistry. However, NO also blocked respiration, an event that previous studies have shown can stimulate oxidative DNA damage. The resultant accumulation of NADH accelerates the reduction of free flavins by flavin reductase, and these reduced flavins drive Fenton chemistry by transferring electrons to free iron. Indeed, mutants lacking the respiratory quinol oxidases were sensitive to H2O2, and NO did not have any further effect. Further, mutants that lack flavin reductase were resistant to NO/H2O2, and overproducing strains were hypersensitive. We discuss the possibility that H2O2 and NO synergize when macrophages attack captive bacteria.

Impaired innate host defense causes susceptibility to respiratory virus infections in cystic fibrosis

Viral infection is the primary cause of respiratory morbidity in cystic fibrosis (CF) infants. Here, we identify that host factors allow increased virus replication and cytokine production, providing a mechanism for understanding the severity of virus disease in CF. Increased virus is due to lack of nitric oxide synthase 2 (NOS2) and 2', 5' oligoadenylate synthetase (OAS) 1 induction in response to virus or IFNgamma. This can be attributed to impairment of activation of signal transducer and activator of transcription (STAT)1, a fundamental component to antiviral defense. NO donor or NOS2 overexpression provides protection from virus infection in CF, suggesting that NO is sufficient for antiviral host defense in the human airway and is one strategy for antiviral therapy in CF children.

Synthesis of 3'- and 5'-nitrooxy pyrimidine nucleoside nitrate esters: "nitric oxide donor" agents for evaluation as anticancer and antiviral agents

A group of 3'-O-nitro-2'-deoxyuridines, 3'-O-nitro-2'-deoxycytidines, and 5'-O-nitro-2'-deoxyuridines possessing a variety of substituents (H, Me, F, I) at the C-5 position were synthesized for evaluation as anticancer/antiviral agents that have the ability to concomitantly release cytotoxic nitric oxide (*NO). Although these compounds generally released a greater percent of *NO than the reference drug isosorbide dinitrate upon incubation in the presence of l-cysteine, or serum, their cytotoxicity (CC(50) = 10(-3) to 10(-6) M range) was comparable to 5-iodo-2'-deoxyuridine, but weaker than 5-fluoro-2'-deoxyuridine, against a variety of cancer cell lines. No differences in cytotoxicity against nontransfected (KBALB, 143B), and the corresponding transfected (KBALB-STK, 143B-LTK) cancer cell lines possessing the herpes simplex virus type 1 (HSV-1) thymidine kinase gene (TK(+)) were observed, indicating that expression of the viral TK enzyme did not provide a gene therapeutic effect. These nitrate esters were inactive antiviral agents except for 5-iodo-3'-O-nitro-2'-deoxyuridine that showed modest activity against HSV-1, HSV-2, and vaccinia virus.

Effects of nitrogen monoxide and carbon monoxide on molecular and cellular iron metabolism: mirror-image effector molecules that target iron

Many effector functions of nitrogen monoxide (NO) and carbon monoxide (CO) are mediated through their high-affinity for iron (Fe). In this review, the roles of NO and CO are examined in terms of their effects on the molecular and cellular mechanisms involved in Fe metabolism. Both NO and CO avidly form complexes with a plethora of Fe-containing molecules. The generation of NO and CO is mediated by the nitric oxide synthase and haem oxygenase (HO) families of enzymes respectively. The effects of NO on Fe metabolism have been well characterized, whereas knowledge of the effects of CO remains within its infancy. In terms of the role of NO in Fe metabolism, one of the best characterized interactions includes its effect on the iron regulatory proteins. These molecules are mRNA-binding proteins that control the expression of the transferrin receptor 1 and ferritin, molecules that are involved in Fe uptake and storage respectively. Apart from this, activated macrophages impart their cytotoxic activity by generating NO, which results in marked Fe mobilization from tumour-cell targets. This deprives the cell of the Fe that is required for DNA synthesis and energy production. Considering that HO degrades haem, resulting in the release of CO, Fe(II) and biliverdin, it is suggested that a CO-Fe complex will form. This may account for the rapid Fe mobilization observed from macrophages after haemoglobin catabolism. Intriguingly, overexpression of HO results in cellular Fe mobilization, suggesting that CO has a similar effect to NO on Fe trafficking. Preliminary evidence suggests that, like NO, CO plays important roles in Fe metabolism.

Nitric oxide inhibits spleen cell proliferative response after burn injury by inducing cytostasis, apoptosis, and necrosis of activated T lymphocytes: role of the guanylate cyclase

We previously showed that an overproduction of nitric oxide (NO) by macrophages was responsible for the collapse of lymphoproliferative responses after burn injury in rats. First, we demonstrate here that 10 days post-burn, the inhibition of splenocyte response to concanavalin-A results from cytostatic, apoptotic, and necrotic effects of NO on activated T cells. This was evidenced by various criteria at the levels of DNA, mitochondria, and plasma membrane. Inhibition of NO synthase by S-methylisothiourea (10 microM) normalized all the parameters. Second, we show that two soluble guanylate cyclase (sGC) inhibitors, LY83583 and ODQ, restored the proliferative response in a concentration-dependent manner. LY83583 (0.5 microM) rescued T cells from apoptosis. Similar results were obtained with KT5823 (5 microM) a specific inhibitor of protein kinase G (PKG). In contrast, neither LY83583 nor KT5823 inhibited NO-induced necrosis. These results suggest that NO blocked T cells in the G1 phase and induced apoptosis through a sGC-PKG-dependent pathway and necrosis through an independent one.

A DNA microarray study of nitric oxide-induced genes in mouse hepatocytes: implications for hepatic heme oxygenase-1 expression in ischemia/reperfusion

Nitric oxide (NO) can modulate numerous genes directly; however, some genes may be modulated only in the presence of the inflammatory stimuli that increase the expression of the inducible nitric oxide synthase (iNOS). One method by which to examine changes in NO-mediated gene expression is to carry out a gene array analysis on NO-nai;ve cells. Herein, we report a gene array analysis on mRNA from iNOS-null (iNOS(-/-)) mouse hepatocytes harvested from mice exposed to NO by infection with an adenovirus expressing human iNOS (Ad-iNOS). Of the 6500 genes on this array, only approximately 200 were modulated either up or down by the increased iNOS activity according to our criteria for significance. Several clearly defined families of genes were modulated, including genes coding for proinflammatory transcription factors, cytokines, cytokine receptors, proteins associated with cell proliferation and cellular energetics, as well as proteins involved in apoptosis. Our results suggest that iNOS has a generally anti-inflammatory and anti-apoptotic role in hepatocytes but also acts to suppress proliferation and protein synthesis. The expression of iNOS results in increased expression of stress-related proteins, including heme oxygenase-1 (HO-1). We used HO-1 to confirm that a significant change identified by an analysis could be demonstrated as significant in cells and tissues. The elevation of HO-1 was confirmed at the protein level in hepatocytes in vitro. Furthermore, iNOS(-/-) mice experienced greatly increased liver injury subsequent to intestinal ischemia/reperfusion injury, associated with an inability to upregulate HO-1. This is the first study to address the global gene changes induced by iNOS in any cell type, and the findings presented herein may have clinical relevance for conditions such as septic or hemorrhagic shock in which hepatocytes, NO, and HO-1 play a crucial role.

The mechanism of nitrogen monoxide (NO)-mediated iron mobilization from cells. NO intercepts iron before incorporation into ferritin and indirectly mobilizes iron from ferritin in a glutathione-dependent manner

Nitrogen monoxide (NO) is a cytotoxic effector molecule produced by macrophages that results in Fe mobilization from tumour target cells which inhibits DNA synthesis and mitochondrial respiration. It is well known that NO has a high affinity for Fe, and we showed that NO-mediated Fe mobilization is markedly potentiated by glutathione (GSH) generated by the hexose monophosphate shunt [Watts, R.N. & Richardson, D.R. (2001) J. Biol. Chem. 276, 4724-4732]. We hypothesized that GSH completes the coordination shell of an NO[bond]Fe complex that is released from the cell. In this report we have extended our studies to further characterize the mechanism of NO-mediated Fe mobilization. Native PAGE 59Fe-autoradiography shows that NO decreased ferritin-59Fe levels in cells prelabelled with [59Fe]transferrin. In prelabelled cells, ferritin-59Fe levels increased 3.5-fold when cells were reincubated with control media between 30 and 240 min. In contrast, when cells were reincubated with NO, ferritin-59Fe levels decreased 10-fold compared with control cells after a 240-min reincubation. However, NO could not remove Fe from ferritin in cell lysates. Our data suggest that NO intercepts 59Fe on route to ferritin, and indirectly facilitates removal of 59Fe from the protein. Studies using the GSH-depleting agent, L-buthionine-(S,R)-sulphoximine, indicated that the reduction in ferritin-59Fe levels via NO was GSH-dependent. Competition experiments with NO and permeable chelators demonstrated that both bind a similar Fe pool. We suggest that NO requires cellular metabolism in order to effect Fe mobilization and this does not occur via passive diffusion down a concentration gradient. Based on our results, we propose a model of glucose-dependent NO-mediated Fe mobilization.

The iron metabolism of neoplastic cells: alterations that facilitate proliferation?

For many years it has been known that neoplastic cells express high levels of the transferrin receptor 1 (TfR1) and internalize iron (Fe) from transferrin (Tf) at a tremendous rate. Considering the high requirement of neoplastic cells for Fe, understanding its metabolism is vital in terms of devising potential new therapies. Apart from TfR1, a number of molecules have been identified that may have roles in Fe metabolism and cellular proliferation. These molecules include transferrin (Tf), the oestrogen-inducible transferrin receptor-like protein, transferrin receptor 2 (TfR2), melanotransferrin (MTf), ceruloplasmin, and ferritin. In the present review these latter molecules are discussed in terms of their potential functions in tumour cell Fe metabolism and proliferation. Further studies are essential to determine the specific roles of these proteins in the pathogenesis of cancer.