Francisco Sobrino

Oxidative Stress Triggers STAT3 Tyrosine Phosphorylation and Nuclear Translocation in Human Lymphocytes

Oxidizing agents are powerful activators of factors responsible for the transcriptional activation of cytokine-encoding genes involved in tissue injury. In this study we show evidence that STAT3 is a transcription factor whose activity is modulated by H2O2 in human lymphocytes, in which endogenous catalase had previously been inhibited. H2O2-induced nuclear translocation of STAT3 to form sequence-specific DNA-bound complexes was evidenced by immunoblotting of nuclear fractions and electrophoretic mobility shift assays, and vanadate was found to strongly synergize with H2O2. Moreover, anti-STAT3 antibodies specifically precipitated a protein of 92 kDa that becomes phosphorylated on tyrosine upon lymphocyte treatment with H2O2. Phenylarsine oxide, a tyrosine phosphatase inhibitor, and genistein, a tyrosine kinase inhibitor, cooperated and cancelled, respectively, the H2O2-promoted STAT3 nuclear translocation. Evidence is also presented, using Fe2+/Cu2+ions, that ⋅OH generated from H2O2through Fenton reactions could be a candidate oxygen reactive species to directly activate STAT3. Present data suggest that H2O2 and vanadate are likely to inhibit the activity of intracellular tyrosine phosphatase(s), leading to enhanced STAT3 tyrosine phosphorylation and hence its translocation to the nucleus. These results demonstrate that the DNA binding activity of STAT3 can be modulated by oxidizing agents and provide a framework to understand the effects of oxidative stress on the JAK-STAT signaling pathway.

15-Deoxy-Δ12,14-prostaglandin J2 Induces Heme Oxygenase-1 Gene Expression in a Reactive Oxygen Species-dependent Manner in Human Lymphocytes

15-Deoxy-Δ12,14-prostaglandin J2 (15dPGJ2 has been recently proposed as a potent anti-inflammatory agent. However, the mechanisms by which 15dPGJ2 mediates its therapeutic effects in vivo are unclear. We demonstrate that 15dPGJ2 at micromolar (2.5–10 μm) concentrations induces the expression of heme oxygenase-1 (HO-1), an anti-inflammatory enzyme, at both mRNA and protein levels in human lymphocytes. In contrast, troglitazone and ciglitazone, two thiazolidinediones that mimic several effects of 15dPGJ2 through their binding to the peroxisome proliferator-activated receptor (PPAR)-γ, did not affect HO-1 expression, and the positive effect of 15dPGJ2 on this process was mimicked instead by other cyclopentenone prostaglandins (PG), such as PGD2 (the precursor of 15dPGJ2) and PGA1 and PGA2 which do not interact with PPAR-γ. Also, 15dPGJ2 enhanced the intracellular production of reactive oxygen species (ROS) and increased xanthine oxidase activity in vitro. Inhibition of intracellular ROS production by N-acetylcysteine, TEMPO, Me2SO, 1,10-phenanthroline, or allopurinol resulted in a decreased 15dPGJ2-dependent HO-1 expression in the cells. Furthermore, buthionine sulfoximine, an inhibitor of reduced glutathione synthesis, or Fe2+/Cu2+ ions enhanced the positive effect of 15dPGJ2 on HO-1 expression. On the other hand, the inhibition of phosphatidylinositol 3-kinase or p38 mitogen-activated protein kinase, or the blockade of transcription factor NF-κB activation, hindered 15dPGJ2-elicited HO-1 expression. Collectively, the present data suggest that 15dPGJ2 anti-inflammatory actions at pharmacological concentrations involve the induction of HO-1 gene expression through mechanisms independent of PPAR-γ activation and dependent on ROS produced via the xanthine/xanthine oxidase system and/or through Fenton reactions. Both phosphatidylinositol 3-kinase and p38 mitogen-activated protein kinase signaling pathways also appear implicated in modulation of HO-1 expression by 15dPGJ2.

Characterization of Calcineurin in Human Neutrophils INHIBITORY EFFECT OF HYDROGEN PEROXIDE ON ITS ENZYME ACTIVITY AND ON NF-κB DNA BINDING

We describe here a specific calcineurin activity in neutrophil lysates, which is dependent on Ca2+, inhibited by trifluoroperazine, and insensitive to okadaic acid. Immunoblotting experiments using a specific antiserum recognized both the A and B chains of calcineurin. Neutrophils treated with cyclosporin A or FK 506 showed a dose-dependent inhibition of calcineurin activity. The effect of oxidant compounds on calcineurin activity was also investigated. Neutrophils treated with hydrogen peroxide (H2O2), where catalase was inhibited with aminotriazole, exhibited a specific inhibition of calcineurin activity. However, the addition of reducing agents to neutrophil extracts partially reversed the inhibition caused by H2O2. A similar inhibitory effect of H2O2 on calcineurin activity was observed to occur in isolated lymphocytes. This is the first demonstration that redox agents modulate calcineurin activity in a cellular system. In addition, electrophoretic mobility shift assays revealed that lipopolysaccharide-induced activation of NF-κB in human neutrophils is inhibited by cell pretreatment with H2O2 in a dose-dependent manner. These data indicate that calcineurin activity regulates the functional activity of lipopolysaccharide-induced NF-κB/Rel proteins in human neutrophils. These data indicate a role of peroxides in the modulation of calcineurin activity and that the H2O2-dependent NF-κB inactivation in neutrophils occurs in concert with inhibition of calcineurin.

Stimulators of AMP-activated protein kinase inhibit the respiratory burst in human neutrophils

In the present study, we have examined the potential ability of 5′‐AMP‐activated protein kinase (AMPK) to modulate NADPH oxidase activity in human neutrophils. AMPK activated with either 5′‐aminoimidazole‐4‐carboxamide ribonucleoside (AICAR) or with 5′‐AMP significantly attenuated both phorbol 12‐myristate 13‐acetate (PMA) and formyl methionyl leucyl phenylalanine‐stimulated superoxide anion (O2 −) release by human neutrophils, consistently with a reduced translocation to the cell membrane and phosphorylation of a cytosolic component of NADPH oxidase, namely p47phox. AMPK was found to be present in human neutrophils and to become phosphorylated in response to either AICAR or other stimulators of its enzyme activity. Furthermore, AICAR also strongly reduced PMA‐dependent H2O2 release, and induced the phosphorylation of c‐jun N‐terminal kinase 1 (p46), p38 mitogen‐activated protein kinase and extracellular signal‐regulated kinase. Present data demonstrate for the first time that the activation of AMPK, in states of low cellular energy charge (such as under high levels of 5′‐AMP) or other signals, could be a factor contributing to reduce the host defense mechanisms.

Age-related changes in membrane lipid composition, fluidity and respiratory burst in rat peritoneal neutrophils

The O·2−. production has been studied in rat peritoneal neutrophils of different age (3, 12 and 24 months), in order to analyse whether the neutrophil respiratory burst is modified with increasing age. To stimulate NADPH oxidase, the enzyme responsible for the respiratory burst, two stimuli that act in different way have been used: phorbol myristate acetate (PMA) and N‐formyl‐methionyl‐leucyl‐phenylalanine (N‐FMLP). Production of O·2− decreased with age in neutrophils stimulated with N‐FMLP (about 40%), but not in the stimulated with PMA. No difference in NADPH oxidase activity was found with age. The NADPH is supplied to the respiratory burst mainly by the pentose phosphate shunt. A progressive and significant decrease in the two most important enzymes of this route, glucose‐6‐phosphate dehydrogenase and 6‐phosphogluconate dehydrogenase, was detected as a function of age; in spite of this reduction, the NADPH produced by cells from old animals seems not limiting for the O·2− production. The N‐FMLP‐induced decrease in the O·2− production may be related to the age‐dependent increase in the membrane fluidity observed. A decline in the cholesterol/phospholipid ratio and a rise in the total polyunsaturated fatty acids content were found, that correlated well with the increase in the membrane fluidity. The decrease (50%) of phosphatidylinositols in the 24‐month‐old animals may be also related to the age‐impairment in the respiratory burst found after stimulation with N‐FMLP. These studies suggest that the age‐related alterations in neutrophil may result in diminished neutrophil function and increased susceptibility to infection in the ageing.

NO induces a cGMP-independent release of cytochrome c from mitochondria which precedes caspase 3 activation in insulin producing RINm5F cells

Exposure of RINm5F cells to interleukin‐1β and to several chemical NO donors such as sodium nitroprusside (SNP), SIN‐1 and SNAP induce apoptotic events such as the release of cytochrome c from mitochondria, caspase 3 activation, Bcl‐2 downregulation and DNA fragmentation. SNP exposure led to transient activation of soluble guanylate cyclase (sGC) and prolonged protein kinase G (PKG) activation but apoptotic events were not attenuated by inhibition of the sGC/PKG pathway. Prolonged activation of the cGMP pathway by exposing cells to the dibutyryl analogue of cGMP for 12 h induced both apoptosis and necrosis, a response that was abolished by the PKG inhibitor KT5823. These results suggest that NO‐induced apoptosis in the pancreatic β‐cell line is independent of acute activation of the cGMP pathway.

Evidence for involvement of c-Src in the anti-apoptotic action of nitric oxide in serum-deprived RINm5F cells.

The mechanism by which nitric oxide (NO) protects from apoptosis is a matter of debate. We have shown previously that phosphorylation of tyrosine residues participates in the protection from apoptosis in insulin-producing RINm5F cells (Inorg. Chem. Commun. 3 (2000) 32). Since NO has been reported to activate the tyrosine kinase c-Src and this kinase is involved in the activation of protein kinase G (PKG) in some cell systems, we aimed at studying the contribution of c-Src and PKG systems in anti-apoptotic actions of NO in serum-deprived RINm5F cells. Here we report that exposure of serum-deprived cells to 10 microM DETA/NO results in protection from degradation of the anti-apoptotic protein Bcl-2, together with a reduction of cytochrome c release from mitochondria and caspase-3 inhibition. Studies with the inhibitors ODQ and KT-5823 revealed that these actions are dependent on both activation of guanylate cyclase and PKG. DETA/NO was also able to induce autophosphorylation and activation c-Src protein both in vivo and in vitro and active c-Src was able to induce tyrosine phosphorylation of Bcl-2 in vitro. The c-Src kinase inhibitor PP1 abrogated the actions of DETA/NO on cGMP formation, PKG activation, caspase activation, cytochrome c release from mitochondria, and Bcl-2 phosphorylation and degradation in serum-deprived cells. We thus propose that activation of c-Src is an early step in the chain of events that signal cGMP-dependent anti-apoptotic actions of NO in mitocohondria.

Modulation of IgE-dependent COX-2 gene expression by reactive oxygen species in human neutrophils

Cyclooxygenase (COX) is a key enzyme in prostaglandin (PG) synthesis. Up‐regulation of its COX‐2 isoform is responsible for the increased PG release, taking place under inflammatory conditions, and also, is thought to be involved in allergic and inflammatory diseases. In the present work, we demonstrate that COX‐2 expression becomes highly induced by anti‐immunoglobulin E (IgE) antibodies and by antigens in human neutrophils from allergic patients. This induction was detected at mRNA and protein levels and was accompanied by a concomitant PGE2 and thromboxane A2 release. We also show evidence that inhibitors of reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, such as 4‐(2‐aminoethyl)benzenesulphonyl fluoride and 4‐hydroxy‐3‐methoxyaceto‐phenone, completely cancelled anti‐IgE‐induced COX‐2 protein up‐regulation, suggesting that this process is mediated by reactive oxygen species (ROS) derived from NADPH oxidase activity. Moreover, the mitogen‐activated protein kinases (MAPKs), p38 and extracellular signal‐regulated kinase, and also, the transcription factor, nuclear factor (NF)‐κB, are involved in the up‐regulation of COX‐2 expression, as specific chemical inhibitors of these two kinases, such as SB203580 and PD098059, and of the NF‐κB pathway, such as N(α)‐benzyloxycarbonyl‐l‐leucyl‐l‐leucyl‐l‐leucinal, abolished IgE‐dependent COX‐2 induction. Evidence is also presented, using Fe2+/Cu2+ ions, that hydroxyl radicals generated from hydrogen peroxide through Fenton reactions could constitute candidate modulators able to directly trigger anti‐IgE‐elicited COX‐2 expression through MAPK and NF‐κB pathways. Present results underscore a new role for ROS as second messengers in the modulation of COX‐2 expression by human neutrophils in allergic conditions.

Activation of phagocytic cell NADPH oxidase by norfloxacin: a potential mechanism to explain its bactericidal action

The mechanisms underlying the bactericidal power of fluoroquinolones against intracellular parasites in host macrophages remain poorly understood. We have analyzed the effect of norfloxacin, a fluoroquinolone antibiotic, on the production of reactive oxygen intermediates (O2•− and H2O2) and NADPH oxidase activity in mouse macrophages. The generation of anion superoxide (O2•−) was found to be significantly greater in macrophages incubated with norfloxacin than in untreated controls. This enhancing effect of norfloxacin was dose‐dependent and reached maximal values within 10 min after its addition. The O2•− generated was mainly intracellular, as determined by the use of specific dyes, such as lucigenin and luminol, and able to diffuse freely through the cell membrane. Also, the production of H2O2 was increased in macrophages in response to norfloxacin. The positive effect of norfloxacin was associated to an enhanced mobilization of NADPH oxidase subunits p47phox and p67phox from the cytosol to the plasma membrane in phagocytic cells. The effect of the antibiotic persisted in vivo for several hours. These data support the notion that norfloxacin inhibits mycobacterial growth within phagocytic cells by enhancing intracellular production of O2•− and other reactive oxygen species.

Specific Allergens Enhance Elastase Release in Stimulated Neutrophils from Asthmatic Patients

Background: The presence of the three forms of IgE receptor – the heterotrimeric high-affinity receptor for IgE (FcΕRI), the low-affinity receptor for IgE (FcΕRII/CD23) and the Mac-2/IgE-binding protein (ΕBP) – has been demonstrated on human neutrophils. We have previously shown that specific allergens are able to activate functional responses by neutrophils from allergic patients sensitized to those allergens. Neutrophils are present at the sites of allergic inflammation. The primary (azurophilic) granules of neutrophils contain a variety of enzymes, such as elastase, that might potentiate inflammation. It is not known whether specific allergens are able to elicit elastase release by neutrophils from allergic patients. In addition, we attempted to evaluate the relationship between neutrophil degranulation and lung function of the patients, measured as FEV1. Methods: Neutrophils were challenged in vitro with the specific allergens that produced clinical symptoms in asthmatic patients. The cells were also challenged with allergen to which the patients were not sensitive. Neutrophils from normal subjects were challenged with allergens as control. Results: The in vitro challenge of neutrophils with allergens to which the patients were sensitive elicited a release of elastase by these cells. The in vitro activation of neutrophils was highly allergen specific; allergens other than those accounting for clinical symptoms did not evoke elastase release, and allergens were ineffective on neutrophils from healthy donors. A significant inverse correlation was observed between elastase release and patients’ lung function, measured as FEV1. Conclusion: An IgE-dependent mechanism might promote elastase release by neutrophils at allergic sites. There is a significant inverse relationship between levels of elastase released by neutrophils from allergic patients and lung function, as assessed by FEV1.