Distinct roles of thioredoxin in the cytoplasm and in the nucleus. A two-step mechanism of redox regulation of transcription factor NF-kappaB

Role of hydrogen peroxide in NF-kappaB activation: from inducer to modulator

Hydrogen peroxide (H2O2) has been implicated in the regulation of the transcription factor NF-kappaB, a key regulator of the inflammatory process and adaptive immunity. However, no consensus exists regarding the regulatory role played by H2O2. We discuss how the experimental methodologies used to expose cells to H2O2 produce inconsistent results that are difficult to compare, and how the steady-state titration with H2O2 emerges as an adequate tool to overcome these problems. The redox targets of H2O2 in the NF-kappaB pathway--from the membrane to the post-translational modifications in both NF-kappaB and histones in the nucleus--are described. We also review how H2O2 acts as a specific regulator at the level of the single gene, and briefly discuss the implications of this regulation for human health in the context of kappaB polymorphisms. In conclusion, after near 30 years of research, H2O2 emerges not as an inducer of NF-kappaB, but as an agent able to modulate the activation of the NF-kappaB pathway by other agents. This modulation is generic at the level of the whole pathway but specific at the level of the single gene. Therefore, H2O2 is a fine-tuning regulator of NF-kappaB-dependent processes, as exemplified by its dual regulation of inflammation.

Redox regulation of tumor necrosis factor signaling

Tumor necrosis factor-alpha (TNF) is a key cytokine that has been shown to play important physiologic (e.g., inflammation) and pathophysiologic (e.g., various liver pathologies) roles. In liver and other tissues, TNF treatment results in the simultaneous activation of an apoptotic pathway (i.e., TRADD, RIP, JNK) and a survival pathway mediated by NF-kappaB transcription of survival genes (i.e., GADD45beta, Mn-SOD, cFLIP). The cellular response (e.g., proliferation versus apoptosis) to TNF is determined by the balance between the apoptotic signaling pathway and the NF-kappaB survival pathway stimulated by TNF. Reactive oxygen species (ROS) are important modulators of signaling pathways and can regulate both apoptotic signaling and NF-kappaB transcription triggered by TNF. ROS are important in mediating the sustained activation of JNK, to help mediate apoptosis after TNF treatment. In some cells, ROS are second messengers that mediate apoptosis after TNF stimulation. Conversely, ROS can cause redox modifications that inhibit NF-kappaB activation, which can lead to cell death triggered by TNF. Consequently, the redox status of cells can determine the biologic response that TNF will induce in cells. In many liver pathologies, ROS generated extrinsically (e.g., inflammation) or intrinsically (i.e., drugs, toxins) may act in concert with TNF to promote hepatocyte death and liver injury through redox inhibition of NF-kappaB.

Redox regulation of nuclear post-translational modifications during NF-kappaB activation

The transcription factor NF-kappaB controls the expression of hundreds of genes involved in the regulation of the immune/inflammatory response, development, and apoptosis. In resting cells, NF-kappaB proteins are sequestered in the cytoplasm through their tight association with IkappaB proteins. NF-kappaB activation relies on the signal-induced IkappaB phosphorylation and degradation, thereby allowing the nuclear translocation of NF-kappaB proteins. In the nucleus, several post-translational modifications of NF-kappaB and chromatin remodeling of target genes are mandatory for NF-kappaB DNA binding and full transcription. Since 1991, reactive oxygen species (ROS) have been implicated in NF-kappaB activation. ROS enhance the cytoplasmic signaling pathways leading to NF-kappaB nuclear translocation, but reduction/oxidation (redox) also controls several key steps in the nuclear phase of the NF-kappaB program, including chromatin remodeling, recruitment of co-activators, and DNA binding. Here we describe the redox regulation of NF-kappaB activity in the nucleus.

Interaction of mitochondrial thioredoxin with glucocorticoid receptor and NF-kappaB modulates glucocorticoid receptor and NF-kappaB signalling in HEK-293 cells

Trx2 (mitochondrial thioredoxin) is an antioxidant and anti-apoptotic factor essential for cell viability. Trx1 (cytoplasmic thioredoxin) is a co-factor and regulator of redox-sensitive transcription factors such as the GR (glucocorticoid receptor) and NF-kappaB (nuclear factor kappaB). Both transcription factors have been detected in mitochondria and a role in mitochondrial transcription regulation and apoptosis has been proposed. In the present study, we show using SPR (surface plasmon resonance) and immunoprecepitation that GR and the p65 subunit of NF-kappaB are Trx2-interacting proteins. The interaction of Trx2 with GR is independent of the presence of GR ligand and of redox conditions. The p65 subunit of NF-kappaB can interact with Trx2 in the oxidized, but not the reduced, form. Using HEK (human embryonic kidney)-293 cell lines with increased or decreased expression of Trx2, we show that Trx2 modulates transcription of GR and NF-kappaB reporter genes. Moreover, Trx2 overexpression modulates the mRNA levels of the COX1 (cytochrome oxidase subunit I) and Cytb (cytochrome b), which are known to be regulated by GR and NF-kappaB. Increased expression of Trx2 differentially affects the expression of Cytb. The glucocorticoid dexamethasone potentiates the expression of Cytb, whereas TNFalpha (tumour necrosis factor alpha) down-regulates it. These results suggest a regulatory role for Trx2 in GR and NF-kappaB signalling pathways.

Mechanisms underlying the effects of melatonin intervention on acute necrotizing pancreatitis in rats

AIM: To investigate the relationship between the protective effects of melatonin pre-intervention for the pancreas and lungs and the expression of thioredoxin-1 (Trx-1) in rats with acute necrotizing pancreatitis (ANP).

METHODS: Seventy-two male Spraque-Dawley rats were randomly divided into three groups: normal control group, ANP group and melatonin treatment group. The ANP model rats were induced by giving rats three intraperitoneal injections of 6% L-arginine at a dose of 25 mL/kg body weight at an interval of 1 h. In the normal control group, normal rats were intraperitoneally injected with normal saline. Rats in the ANP group were intraperitoneally injected with normal saline one half hour before and after ANP induction, while rats in the melatonin treatment group were intraperitoneally injected with a single dose of 0.25% melatonin (20 mL/kg body weight) one half hour prior to ANP induction. Rats were sacrificed at 6, 12 and 24 h after the last L-arginine injection, respectively. The pancreas, lungs and blood samples were quickly taken. The pathological changes in the pancreas and lungs were observed and scored. The serum contents of Trx-1, IL-6, glutathione (GSH), total superoxide dismutase (T-SOD) and malondialdehyde (MDA) were measured.

RESULTS: Pathological analysis proved that L-arginine administration induced ANP successfully. Compared to the ANP group, pathological changes in the pancreas and lungs in the melatonin treatment group were significantly alleviated. Compared to the normal control group, serum Trx-1 contents in the ANP group were significantly decreased at 6- and 12-h time points but significantly increased at 24-h time point, exhibiting an initial decrease followed by a gradual increase. Serum Trx-1 contents in the melatonin treatment group at 6- and 12-h time points were significantly higher than those in the ANP group. Compared to the normal control group, serum IL-6 and MDA levels in the ANP group were significantly elevated, whereas serum T-SOD and GSH levels were significantly decreased. In contrast, serum IL-6 and MDA levels in the melatonin treatment group were significantly decreased while serum T-SOD and GSH levels were significantly increased when compared with the ANP group.

CONCLUSION: ANP can induce the expression of Trx-1. Melatonin pre-intervention is able to further promote the expression of Trx-1, increase serum Trx-1, SOD, and GSH levels and decrease serum IL-6 and MDA levels, thereby reducing pancreatic and pulmonary injury and exerting a protective effect for the pancreas and lungs in ANP rats.

Salmonella type III secretion effector SlrP is an E3 ubiquitin ligase for mammalian thioredoxin

Salmonella enterica encodes two virulence-related type III secretion systems in Salmonella pathogenicity islands 1 and 2, respectively. These systems mediate the translocation of protein effectors into the eukaryotic host cell, where they alter cell signaling and manipulate host cell functions. However, the precise role of most effectors remains unknown. Using a genetic screen, we identified the small, reduction/oxidation-regulatory protein thioredoxin as a mammalian binding partner of the Salmonella effector SlrP. The interaction was confirmed by affinity chromatography and coimmunoprecipitation. In vitro, SlrP was able to mediate ubiquitination of ubiquitin and thioredoxin. A Cys residue conserved in other effectors of the same family that also possess E3 ubiquitin ligase activity was essential for this catalytic function. Stable expression of SlrP in HeLa cells resulted in a significant decrease of thioredoxin activity and in an increase of cell death. The physiological significance of these results was strengthened by the finding that Salmonella was able to trigger cell death and inhibit thioredoxin activity in HeLa cells several hours post-infection. This study assigns a functional role to the Salmonella effector SlrP as a binding partner and an E3 ubiquitin ligase for mammalian thioredoxin.

Thioredoxin in human and experimental sepsis

INTRODUCTION

Thioredoxin (TRX) is assumed to be beneficial in acute inflammatory diseases because of its potent antioxidant properties and an inhibitory effect on neutrophil evasion into sites of inflammation.

OBJECTIVE

To compare plasma levels of thioredoxin in septic patients and to investigate the role of thioredoxin in a polymicrobial septic mouse model.

DESIGN AND INTERVENTIONS

A combined single-center noninterventional clinical observation study and randomized controlled experimental investigation.

SETTING

Intensive care unit of a university hospital and laboratories of four university hospitals.

MEASUREMENTS AND MAIN RESULTS

To evaluate the role of TRX in sepsis, we measured TRX in plasma of septic patients and compared its levels in survivors and patients who did not survive sepsis. In addition, we examined the effect of neutralization of endogenous TRX as well as of treatment with recombinant TRX in a mouse peritonitis model of cecal ligation and puncture (CLP). We found that the serum plasma levels of TRX were significantly higher in patients with sepsis compared with healthy individuals. Furthermore, nonsurvivors showed even higher TRX levels than survivors of sepsis. The CLP septic mouse model revealed that neutralization of endogenous TRX impaired survival of septic mice, whereas treatment with recombinant TRX after CLP strongly enhanced the survival of mice.

CONCLUSIONS

Our results therefore demonstrate a critical role for TRX in the septic inflammatory response and suggest TRX as a potential therapeutic target for septic shock.

Hindlimb unloading decreases thioredoxin-related antioxidant proteins and increases thioredoxin-binding protein-2 in rat skeletal muscle

To investigate role(s) of thioredoxin-related antioxidant proteins in disuse muscle atrophy, we examined the levels of thioredoxin-1 (Trx-1), peroxiredoxin-3/SP-22 (Prx-3) and thioredoxin-binding protein-2 (TBP-2) in rat soleus muscle subjected to hindlimb unloading (HU) for 2, 4, 7 or 14 days. The muscle weight loss was initially observed on day 4. The increases in aclorein- and malondialdehyde-modified proteins, and the decreases in the levels of Trx-1, Prx-3 and Mn-SOD were observed in the late phase of muscle atrophy, whereas, the increase in mRNA expression of TBP-2, a negative regulator of thioredoxin, preceded muscle atrophy. These findings suggest that the decrease of those antioxidant proteins, particularly a marked decrease of Trx-1, may be responsible for the enhanced oxidative damage during the late phase of disuse muscle atrophy. Furthermore, the increase in TBP-2 preceding the muscle atrophy may suppress the thioredoxin-mediated redox signaling, which can be an initial trigger leading to disuse muscle atrophy.

Thioredoxin-1 and endothelial cell aging: role in cardiovascular diseases

The thioredoxin-1 (Trx-1) system consists of two oxidoreductases, thioredoxin reductase and Trx-1. Trx-1 is a ubiquitously expressed oxidoreductase. The cellular functions of Trx-1 are wide range. They include protein disulfide reduction, DNA synthesis, protection from apoptosis, redox regulation of a variety of proteins, transcription factors and reduction of H(2)O(2), respectively. This review will first focus on the essential role for Trx-1 in different cardiovascular cells, namely smooth muscle cells, endothelial cells, and cardiomyocytes. Thereby, the review will demonstrate the predominant role of Trx-1 to limit oxidative stress directly due to reactive oxygen species scavenging and by protein-protein interaction with key signaling molecules. Second, this review will highlight the role of Trx-1 in cardiovascular aging, focusing on its importance on shear stress and the profound changes with age. Finally, the review will focus on important in vivo studies showing a protective role of Trx-1 in different cardiovascular diseases. Thus, the Trx system and Trx-1 could be important future targets to develop clinical therapies for cardiovascular disorders.

The anticancer agent chaetocin is a competitive substrate and inhibitor of thioredoxin reductase

We recently reported that the antineoplastic thiodioxopiperazine natural product chaetocin potently induces cellular oxidative stress, thus selectively killing cancer cells. In pursuit of underlying molecular mechanisms, we now report that chaetocin is a competitive and selective substrate for the oxidative stress mitigation enzyme thioredoxin reductase-1 (TrxR1) with lower K(m) than the TrxR1 native substrate thioredoxin (Trx; chaetocin K(m) = 4.6 +/- 0.6 microM, Trx K(m) = 104.7 +/- 26 microM), thereby attenuating reduction of the critical downstream ROS remediation substrate Trx at achieved intracellular concentrations. Consistent with a role for TrxR1 targeting in the anticancer effects of chaetocin, overexpression of the TrxR1 downstream effector Trx in HeLa cells conferred resistance to chaetocin-induced, but not to doxorubicin-induced, cytotoxicity. As the TrxR/Trx pathway is of central importance in limiting cellular reactive oxygen species (ROS)--and as chaetocin exerts its selective anticancer effects via ROS imposition--the inhibition of TrxR1 by chaetocin has potential to explain its selective anticancer effects. These observations have important implications not just with regard to the mechanism of action and clinical development of chaetocin and related thiodioxopiperazines, but also with regard to the utility of molecular targets within the thioredoxin reductase/thioredoxin pathway in the development of novel candidate antineoplastic agents.

Resveratrol: a promising agent in promoting cardioprotection against coronary heart diseaseThis article is one of a selection of papers from the NATO Advanced Research Workshop on Translational Knowledge for Heart Health (published in part 2 of a 2-part Special Issue)

The inverse association between alcohol intake and coronary heart disease has been consistently reported in cross-culture, case–control, and cohort studies. Over the past couple of decades, however, many studies have explained promising health benefits associated with wine consumption. Some studies suggest that red wine is more cardioprotective than white wine, possibly due to the increased content of flavanoid antioxidants found in red wine. Several experimental studies, including ours, support the evidence that these beneficial effects are due to resveratrol, the polyphenolic compound present in red wine. Many studies have provided evidence that resveratrol possesses antioxidant and antiapoptotic effects apart from activation of longevity proteins (such as SIRT-1). We have recently reported the angiogenic, antihypercholesterolemic, and antidiabetic effects of resveratrol and the mechanisms involved in reduced ventricular remodeling and increased cardiac functions. We have also shown different strategic target molecules involved in resveratrol-mediated cardioprotection. Therefore, this review discusses the potential effect of resveratrol and the mechanisms involved in resveratrol-mediated cardioprotection during myocardial infarction, hypercholesterolemia, and diabetes rendering its beneficial effects during health and disease.

Ecklonia cava ethanolic extracts inhibit lipopolysaccharide-induced cyclooxygenase-2 and inducible nitric oxide synthase expression in BV2 microglia via the MAP kinase and NF-kappaB pathways

Ecklonia cava (EC) is a brown alga that has demonstrated radical scavenging, bactericidal, tyrosinase inhibitory, and protease inhibitory activities. However, the molecular mechanisms underlying its anti-inflammatory action remain unclear. In the current study, we attempted to determine whether pretreatment with EC induces a significant inhibition of anti-inflammatory activity in lipopolysaccharide (LPS)-stimulated murine BV2 microglia. Our results indicate that EC inhibits LPS-induced nitric oxide (NO) and prostaglandin E(2) (PGE(2)) production in a concentration-dependent manner and inhibits inducible nitric oxide (iNOS) and cyclooxygenase (COX)-2 in BV2 microglia without significant cytotoxicity. EC treatment significantly reduced nuclear factor-kappaB (NF-kappaB) translocation and DNA-binding in LPS-stimulated BV2 microglia. This effect was mediated through the inhibition of the degradation of the inhibitor kappaB and by inhibition of the mitogen-activated protein kinase (MAPK) phosphorylation, at least in part by inhibiting the generation of reactive oxygen species. Our data also indicate that EC extracts exert anti-inflammatory effects by suppressing proinflammatory cytokines. Collectively, these results suggest that EC suppresses the induction of cytokines by LPS, as well as iNOS and COX-2 expression, by blocking NF-kappaB and MAPK activation. These findings provide mechanistic insights into the anti-inflammatory and neuroprotective actions of EC in BV2 microglia.

Sodium selenite increases the activity of the tumor suppressor protein, PTEN, in DU-145 prostate cancer cells

Epidemiological and clinical data suggest that selenium may prevent prostate cancer; however, the cellular effects of selenium in malignant prostate cells are not well understood. We previously reported that the activity of the tumor suppressor PTEN is modulated by thioredoxin (Trx) in a RedOx-dependent manner. In this study, we demonstrated that the activity of Trx reductase (TR) is increased by sevenfold in the human prostate cancer cell line, DU-145, after 5 days of sodium selenite (Se) treatment. The treatment of DU-145 cells with increasing concentrations of Se induced an increase in PTEN lipid phosphatase activity by twofold, which correlated with a decrease in phospho-ser(473)-Akt, and an increase in phospho-Ser(370)-PTEN levels. Se also increased casein kinase-2 (CK2) activity; and the use of apigenin, an inhibitor of CK2, revealed that the regulation of the tumor suppressor PTEN by Se may be achieved via both the Trx-TR system and the RedOx control of the kinase involved in the regulation of PTEN activity.

Thioredoxin and thioredoxin binding protein 2 in the liver

Thioredoxin (TRX) is a 12-kDa protein with redox-active dithiol in the active site -Cys-Gly-Pro-Cys- and constitutes a major thiol reducing system. TRX protects cells from stress-induced damage through antioxidative, antiapoptotic, and anti-inflammatory effect. In animal models, thioacetamide (TAA)-induced acute hepatitis and TAA-induced liver fibrosis was attenuated in TRX transgenic (TRXTG) mice. Plasma level of TRX is a good marker for hepatitis and nonalcoholic steatohepatitis (NASH) in human patients. Recently, we identified TRX binding protein 2 (TBP2) in a yeast two-hybrid screening. TBP2 regulates both the expression and reducing activity of TRX as well as cell growth. TBP2 knockout (TBP2KO) mice showed disorder in lipid metabolism. TBP2 plays a multiple role on cell growth and lipid and glucose metabolism. Thus, TRX and TBP2 play important roles in the pathophysiology of liver diseases, including NASH, indicating that ratio of TRX and TBP2 expression could be a novel marker of liver diseases like NASH.

The thioredoxin system: a key target in tumour and endothelial cells

Thioredoxin is a redox-sensitive molecule that has pleiotropic cellular effects, such as the control of proliferation, redox states and apoptosis, and is often upregulated in malignancy. The system controls the activation of a number of transcription factors through sulphydryl transfer and, through its activity on hypoxia inducible factor 1alpha, it is able to regulate vascular endothelial growth factor levels and hence angiogenesis. The thioredoxin protein has been shown to be upregulated in hypoxic regions of certain tumours, suggesting that inhibitors could potentially exhibit enhanced hypoxic toxicity and/or indirect anti-angiogenic effects. Evidence of this is becoming apparent in the literature. The current report reviews the thioredoxin system as an anticancer drug target and focuses upon two recent compounds, PMX464 and PX12, which reportedly inhibit this important pathway.

Oxidation and nuclear localization of thioredoxin-1 in sparse cell cultures

Reactive oxygen species (ROS) were once viewed only as mediators of toxicity, but it is now recognized that they also contribute to redox signaling through oxidation of specific cysteine thiols on regulatory proteins. Cells in sparse cultures have increased ROS relative to confluent cultures, but it is not known whether protein redox states are affected under these conditions. The purpose of the present study was to determine whether culture conditions affect the redox state of thioredoxin-1 (Trx1), the protein responsible for reducing most oxidized proteins in the cytoplasm and nucleus. The results showed that Trx1 was more oxidized in sparse HeLa cell cultures than in confluent cells. The glutathione pool was also more oxidized, demonstrating that both of the major cellular redox regulating systems were affected by culture density. In addition, the total amount of Trx1 protein was lower and the subcellular distribution of Trx1 was different in sparse cells. Trx1 in sparse cultures was predominantly nuclear whereas it was predominantly cytoplasmic in confluent cultures. This localization pattern was not unique to HeLa cells as it was also observed in A549, Cos-1 and HEK293 cells. These findings demonstrate that Trx1 is subject to changes in expression, redox state and subcellular localization with changing culture density, indicating that the redox environments of the cytoplasm and the nucleus are distinct and have different requirements under different culture conditions.

Thiol-independent action of mitochondrial thioredoxin to support the urea cycle of arginine biosynthesis in Schizosaccharomyces pombe

Thioredoxins usually perform a role as a thiol-disulfide oxidoreductase using their active-site cysteines. The fission yeast Schizosaccharomyces pombe contains two thioredoxins: Trx1 for general stress protection and Trx2 for mitochondrial functions. The Deltatrx2 mutant grows as well as the wild type on complex media containing glucose. However, on nonfermentable carbon source such as glycerol, the mutant did not grow, indicating a defect in mitochondrial function. The mutant also exhibited auxotrophy for arginine and cysteine on minimal medium. In order to find the reason for the unexpected arginine auxotrophy, we searched for multicopy suppressors and found that the arg3(+) gene encoding ornithine carbamoyltransferase (OCTase) in the urea cycle of the arginine biosynthetic pathway rescued the arginine auxotrophy. The levels of arg3(+) transcript, Arg3 protein, and OCTase activity were all decreased in Deltatrx2. Through immunocoprecipitation, we observed a direct interaction between Trx2 and Arg3 in cell extracts. The mutant forms of Trx2 lacking either one or both of the active site cysteines through substitution to serines also rescued the arginine auxotrophy and restored the decreased OCTase activity. They also rescued the growth defect of Deltatrx2 on glycerol medium. This contrasts with the thiol-dependent action of overproduced Trx2 in complementing glutathione reductase. Therefore, Trx2 serves multiple functions in mitochondria, protecting mitochondrial components against thiol-oxidative damage as a thiol-disulfide oxidoreductase, and supporting urea cycle and respiration in mitochondria in a manner independent of active site thiols.

Thioredoxin reductase-1 negatively regulates HIV-1 transactivating protein Tat-dependent transcription in human macrophages

Epidemiological studies suggest a correlation between severity of acquired immunodeficiency syndrome (AIDS) and selenium deficiency, indicating a protective role for this anti-oxidant during HIV infection. Here we demonstrate that thioredoxin reductase-1 (TR1), a selenium-containing pyridine nucleotide-disulfide oxidoreductase that reduces protein disulfides to free thiols, negatively regulates the activity of the HIV-1 encoded transcriptional activator, Tat, in human macrophages. We used a small interfering RNA approach as well as a high affinity substrate of TR1, ebselen, to demonstrate that Tat-dependent transcription and HIV-1 replication were significantly increased in human macrophages when TR1 activity was reduced. The increase in HIV-1 replication in TR1 small interfering RNA-treated cells was independent of the redox-sensitive transcription factor, NF-kappaB. These studies indicate that TR-1 acts as a negative regulator of Tat-dependent transcription. Furthermore, in vitro biochemical assays with recombinant Tat protein confirmed that TR1 targets two disulfide bonds within the Cys-rich motif required for efficient HIV-1 transactivation. Increasing TR1 expression along with other selenoproteins by supplementing with selenium suggests a potential inexpensive adjuvant therapy for HIV/AIDS patients.

Thioredoxin-1 and its natural inhibitor, vitamin D3 up-regulated protein 1, are differentially regulated by PPARalpha in human macrophages

Macrophage-derived reactive oxygen species contribute to the initiation and development of atherosclerosis. The cellular balance between oxidative and reductive states depends on the endogenous antioxidant capacity, with the thioredoxin-1 (Trx-1) system playing a major role. Peroxisome proliferator-activated receptor-alpha (PPARalpha) is expressed by human macrophages and exhibits anti-inflammatory properties. Here we show that the selective PPARalpha activator GW647 significantly increased the Trx-1 mRNA and protein expression in human macrophages as determined by quantitative polymerase chain reaction and Western immunoblotting. Consistently, the Trx-1 activity was significantly increased by PPARalpha activation. By contrast, PPARalpha activation led to the down-regulation of vitamin D(3) up-regulated protein 1 (VDUP-1), the physiological inhibitor of Trx-1. Analysis of the Trx-1 and VDUP-1 promoters with gene reporter assays, mutational analysis, gel shift assays and chromatin immunoprecipitation analyses revealed the presence of a functional response element specific for PPARalpha in the Trx-1 promoter and the presence of a functional activator protein 1 (AP-1) site in the VDUP-1 promoter. The interference of PPARalpha/retinoid X receptor alpha with the AP-1 transcription factor elements c-Jun/c-Fos resulted in the inhibition of AP-1 binding and down-regulation of the VDUP-1 gene expression. Finally, PPARalpha activation reduced the lidocaine-induced caspase-3 activity and apoptosis, which might be due to the VDUP-1-mediated regulation of the Bax/Bcl-2 ratio. Together these data indicate that stimulation of PPARalpha in human macrophages might reduce arterial inflammation through differential regulation of the Trx-1 and VDUP-1 gene expression.

Priming donor lungs with thioredoxin-1 attenuates acute allograft injury in a rat model of lung transplantation

BACKGROUND

Lung graft dysfunction and rejection are significant causes of morbidity and mortality in transplant recipients. Thioredoxin-1, a redox-regulatory protein, functions as an antioxidant in multiple organs, including lungs. We examined whether priming of the donor lungs with thioredoxin-1 before transplantation attenuates acute lung injury.

METHODS

Orthotopic left lung transplantation was performed from Lewis (donor) to Sprague-Dawley (recipient) rats. Donor lungs were perfused and stored in Perfadex solution (Vitrolife, Uppsala, Sweden), with or without purified thioredoxin-1. Changes in bronchoalveolar lavage (BAL) analysis, allograft oxygen exchange function, nuclear factor kappaB (NF-kappaB)/DNA binding, myeloperoxidase activities, and immunohistologic evaluation of neutrophils, macrophages, and cytotoxic T-cells (CD8(+)) infiltration were examined in post-transplant allograft (left) and native (right) lungs at Days 1 and 5.

RESULTS

BAL cell differential analysis showed significant increases in macrophages and neutrophils in allografts at Day 1 post-transplant. At Days 1 and 5, lymphocyte infiltration was significantly increased and myeloperoxidase and NF-kappaB/DNA binding activities were increased vs basal activities. Immunohistology staining revealed increased infiltration of macrophages, neutrophils, and CD8(+) T cell sub-sets. Pre-transplant priming of donor lungs with thioredoxin-1 improved oxygen exchange and attenuated NF-kappaB/DNA binding activity, and infiltration of macrophages, neutrophils, and CD8(+) T cell sub-sets in allografts at Days 1 and 5 post-transplant.

CONCLUSIONS

Priming of donor lungs with thioredoxin-1 before transplant attenuates acute allograft injury in a rat model of lung transplantation, and appears to be associated with the antioxidant function of thioredoxin-1 that limits early ischemia-reperfusion injury, NF-kappaB activation, and progressive infiltration of inflammatory and immune cells in allografts.

Redox control of endothelial function and dysfunction: molecular mechanisms and therapeutic opportunities

The endothelium is essential for the maintenance of vascular homeostasis. Central to this role is the production of endothelium-derived nitric oxide (EDNO), synthesized by the endothelial isoform of nitric oxide synthase (eNOS). Endothelial dysfunction, manifested as impaired EDNO bioactivity, is an important early event in the development of various vascular diseases, including hypertension, diabetes, and atherosclerosis. The degree of impairment of EDNO bioactivity is a determinant of future vascular complications. Accordingly, growing interest exists in defining the pathologic mechanisms involved. Considerable evidence supports a causal role for the enhanced production of reactive oxygen species (ROS) by vascular cells. ROS directly inactivate EDNO, act as cell-signaling molecules, and promote protein dysfunction, events that contribute to the initiation and progression of endothelial dysfunction. Increasing data indicate that strategies designed to limit vascular ROS production can restore endothelial function in humans with vascular complications. The purpose of this review is to outline the various ways in which ROS can influence endothelial function and dysfunction, describe the redox mechanisms involved, and discuss approaches for preventing endothelial dysfunction that may highlight future therapeutic opportunities in the treatment of cardiovascular disease.

Transgenic expression of S100A2 in hairless mouse skin enhances Cxcl13 mRNA in response to solar-simulated radiation

S100A2 is a homodimeric protein that undergoes oxidative cross-linking and translocation from the nucleus to the cytosol in the context of oxidative stress. Suggestive of a role for S100A2 in the cutaneous response to ultraviolet light, we found altered S100A2 immunostaining in photodamaged human skin, and crosslinking of S100A2 after ultraviolet A (UVA) irradiation of normal human keratinocytes (NHK). Skin from mice, rats, and rabbits did not contain S100A2 protein, whereas skin samples from pigs, frogs and humans were strongly positive. Survival after UVA irradiation was significantly greater in NHK compared to mouse keratinocytes, suggesting a protective role for S100A2. To test this hypothesis in vivo, we expressed S100A2 in SKH2/J hairless mice under the control of a bovine keratin 5 promoter, and compared responses of TG and WT mice from 1 to 7 days after a single dose (0.5-1 MED) of solar-simulated radiation (SSR) from UVA-340 bulbs. WT and TG mice manifested a similarly robust response to SSR, characterized by epidermal hyperplasia, marked induction of p21(WAF), and a twofold increase in p53. Thymine dimers (TD) were markedly increased in the epidermis and the dermis, but while over 95% of the epidermal TD were removed by 5-6 days, elevated dermal TD persisted nearly unchanged for 7 days. Global transcriptional profiling of WT and TG mice revealed strong induction of multiple transcripts, including keratins K6 and K16, defensin beta 3, S100A8, S100A9, Sprr2i and Sprr2f. However, the only S100A2-dependent difference we observed was an induction of Cxcl13 transcripts in TG, but not WT mice (4.4-fold vs. 0.7-fold, n = 3, P = 0.022). This finding was confirmed in an independent set of mice analyzed by quantitative RT-PCR (8.8-fold vs. 1.2-fold, n = 4, P = 0.001). The finding of persistent dermal DNA damage after suberythemal doses of SSR merits further study.

Peroxidase: a term of many meanings

Peroxidase research has been instrumental in defining the principles of chemical catalysis. By now, enzymes termed peroxidases represent a heterogeneous group of distinct enzyme families that operate by different catalytic principles and fulfill diverse biological functions, detoxifying H2O2 being just one of many aspects. H2O2 -dependent synthesis of secondary metabolites is the domain of heme peroxidases and related enzymes operating by transition metal catalysis, that often is mediated by free radical formation. Instead, the coenzyme-free glutathione peroxidases and peroxiredoxins only catalyze two-electron transitions and, thus, can reliably remove hydroperoxides without causing radical-mediated collateral damage. However, their ability to use hydroperoxides for the formation of specific disulfide bonds with and within particular proteins broadens their spectrum of biological activities to differentiation phenomena, redox regulation of metabolic processes, redox sensing, and signalling. The present Forum Editorial tries to guide the reader through the 190 years of equally bewildering and fascinating research on peroxidases up to the topical frontiers of the field that are addressed in this issue.

The role and regulation of Trxl, a cytosolic thioredoxin in Schizosaccharomyces pombe

The genome of fission yeast Schizosaccharomyces pombe harbors two genes for thioredoxins, trx1(+) and trx2(+), which encode cytosolic and mitochondrial thioredoxins, respectively. The Deltatrx1 mutant was found sensitive to diverse external stressors such as various oxidants, heat, and salt, whereas Deltatrx2 mutant was not sensitive except to paraquat, a superoxide generator. Both Deltatrx1 and Deltatrx2 mutants were more resistant to diamide, a thiol-specific oxidant, than the wild type. The trx1(+) gene expression was induced by H(2)O(2) and menadione, being mediated through a stress-responsive transcription factor Papl. In Deltatrx1 cells, the basal expression of Pap1-regulated genes were elevated, suggesting a role for Trxl as a reducer for oxidized (activated) Papl. The Deltatrx1 mutant exhibited cysteine auxotrophy, which can be overcome by adding sulfite. This suggests that Trxl serves as a primary electron donor for 3'-phosphoadenosine-5'-phosphosulfate (PAPS) reductase and thus is an essential protein for sulfur assimilation in S. pombe. These results suggest that, in contrast to Trx2 whose role is more confined to mitochondrial functions, Trxl plays a major role in protecting S. pombe against various stressful conditions and enables proper sulfur metabolism.

Glutathione in liver diseases and hepatotoxicity

Glutathione (GSH) is a major antioxidant as well as redox and cell signaling regulator. GSH guards cells against oxidative injury by reducing H(2)O(2) and scavenging reactive oxygen and nitrogen radicals. In addition, GSH-induced redox shift with or without ROS subjects some cellular proteins to varied forms of oxidation, altering the function of signal transduction and transcription factor molecules. Increasing evidence supports the important role of ROS and GSH in modulating multiple signaling pathways. TNF-alpha and Fas signaling, NF-kappaB, JNK and mitochondrial apoptotic pathways are the focus of this review. The redox regulation either can switch on/off or regulate the threshold for some crucial events in these pathways. Notably, mitochondrial GSH depletion induces increased mitochondrial ROS exposure which impairs bioenergetics and promotes mitochondrial permeability transition pore opening which is critical for cell death. Depending on the extent of mitochondrial damage, NF-kappaB inhibition and JNK activation, hepatocytes may either undergo different modes of cell death (apoptosis or necrosis) or be sensitized to cell-death stimuli (i.e. TNF-alpha). These processes have been implicated in the pathogenesis of many liver diseases.

Thioredoxin-like 6 protects retinal cell line from photooxidative damage by upregulating NF-kappaB activity

Apoptosis is the common pathway to photoreceptor cell death in many eye diseases including age-related macular degeneration which affects more than 8 million individuals in the United States alone. RdCVF, a truncated mouse thioredoxin is specifically expressed by rod photoreceptor cells and prevents the apoptosis of cone cells. However the protective mechanism of RdCVF and the implications of its human homologue, thioredoxin-like 6 (TXNL6), on the apoptosis of retinal cells remain unknown. In this study, we examined the function of TXNL6 and investigated its mechanism of protection using a cone photoreceptor cell line, 661W. We found that the photooxidative stress-induced degradation of NF-kappaB proteins is rescued by overexpression of TXNL6, which enabled the NF-kappaB transactivation activity. Furthermore, the overexpression of TXNL6 rescued the photooxidative stress-induced apoptosis of 661W cells. Interestingly, this protective effect was significantly blocked by NF-kappaB specific inhibitors demonstrating that TXNL6 exerts its protective effect against apoptosis via NF-kappaB. Taken together, our study shows that the TXNL6 probably protects retinal cells from photooxidative damage-induced apoptosis via upregulation of NF-kappaB activity. The identification of TXNL6 and the demonstration of its protective mechanism offer new insights into treatment possibilities for photoreceptor cell degradation.

Protein tyrosine phosphorylation and protein tyrosine nitration in redox signaling

Reversible phosphorylation of protein tyrosine residues by polypeptide growth factor-receptor protein tyrosine kinases is implicated in the control of fundamental cellular processes including the cell cycle, cell adhesion, and cell survival, as well as cell proliferation and differentiation. During the last decade, it has become apparent that receptor protein tyrosine kinases and the signaling pathways they activate belong to a large signaling network. Such a network can be regulated by various extracellular cues, which include cell adhesion, agonists of G protein-coupled receptors, and oxidants. It is well documented that signaling initiated by receptor protein tyrosine kinases is directly dependent on the intracellular production of oxidants, including reactive oxygen and nitrogen species. Accumulated evidence indicates that the intracellular redox environment plays a major role in the mechanisms underlying the actions of growth factors. Oxidation of cysteine thiols and nitration of tyrosine residues on signaling proteins are described as posttranslational modifications that regulate, positively or negatively, protein tyrosine phosphorylation (PTP). Early observations described the inhibition of PTP activities by oxidants, resulting in increased levels of proteins phosphorylated on tyrosine. Therefore, a redox circuitry involving the increasing production of intracellular oxidants associated with growth-factor stimulation/cell adhesion, oxidative reversible inhibition of protein tyrosine phosphatases, and the activation of protein tyrosine kinases can be delineated.

Does the oxidative stress in chronic obstructive pulmonary disease cause thioredoxin/peroxiredoxin oxidation?

The thioredoxin/peroxiredoxin system comprises a redox-regulated antioxidant family in human lung; its significance, regulation, or oxidation has not been evaluated in smoking-related lung diseases. Here, we present the expression of the thioredoxin/peroxiredoxin system in lung biopsies from normal lung (n = 14), smokers (n = 21), and patients with chronic obstructive pulmonary disease (COPD, n = 38), and assess the possible inactivation/oxidation of this system by nonreducing Western blotting, two-dimensional gel electrophoresis, and mass spectrometry. Our study shows that the thiol status of the Trx/Prx-system can be modulated in vitro, but it appears to have high resistance against the oxidative stress in COPD.

Identification of a subunit of NADH-dehydrogenase as a p49/STRAP-binding protein

Background

The p49/STRAP (or SRFBP1) protein was recently identified in our laboratory as a cofactor of serum response factor that contributes to the regulation of SRF target genes in the heart.

Results

In the present study, we report that NDUFAB1, a nuclear encoded subunit of NADH dehydrogenase, represented the majority of the cDNA clones that interacted with p49/STRAP in multiple screenings using the yeast two-hybrid system. The p49/STRAP and NDUFAB1 proteins interacted and co-localized with each other in the cell. The p49/STRAP protein contains four classic nuclear localization sequence motifs, and it was observed to be present predominantly in the nucleus. Overexpression of p49/STRAP altered the intracellular level of NAD, and reduced the NAD/NADH ratio. Overexpression of p49/STRAP also induced the deacetylation of serum response factor.

Conclusion

These data suggest that p49/STRAP plays a role in the regulation of intracellular processes such as cardiac cellular metabolism, gene expression, and possibly aging.

Redox compartmentalization in eukaryotic cells

Diverse functions of eukaryotic cells are optimized by organization of compatible chemistries into distinct compartments defined by the structures of lipid-containing membranes, multiprotein complexes and oligomeric structures of saccharides and nucleic acids. This structural and chemical organization is coordinated, in part, through cysteine residues of proteins which undergo reversible oxidation-reduction and serve as chemical/structural transducing elements. The central thiol/disulfide redox couples, thioredoxin-1, thioredoxin-2, GSH/GSSG and cysteine/cystine (Cys/CySS), are not in equilibrium with each other and are maintained at distinct, non-equilibrium potentials in mitochondria, nuclei, the secretory pathway and the extracellular space. Mitochondria contain the most reducing compartment, have the highest rates of electron transfer and are highly sensitive to oxidation. Nuclei also have more reduced redox potentials but are relatively resistant to oxidation. The secretory pathway contains oxidative systems which introduce disulfides into proteins for export. The cytoplasm contains few metabolic oxidases and this maintains an environment for redox signaling dependent upon NADPH oxidases and NO synthases. Extracellular compartments are maintained at stable oxidizing potentials. Controlled changes in cytoplasmic GSH/GSSG redox potential are associated with functional state, varying with proliferation, differentiation and apoptosis. Variation in extracellular Cys/CySS redox potential is also associated with proliferation, cell adhesion and apoptosis. Thus, cellular redox biology is inseparable from redox compartmentalization. Further elucidation of the redox control networks within compartments will improve the mechanistic understanding of cell functions and their disruption in disease.

Emerging potential of thioredoxin and thioredoxin interacting proteins in various disease conditions

Reactive oxygen species (ROS) are known to be mediators of intracellular signaling pathways. However the excessive production of ROS may be detrimental to the cell as a result of the increased oxidative stress and loss of cell function. Hence, well tuned, balanced and responsive antioxidant systems are vital for proper regulation of the redox status of the cell. The cells are normally able to defend themselves against the oxidative stress induced damage through the use of several antioxidant systems. Even though the free radical scavenging enzymes such as superoxide dismutase (SOD) and catalase can handle huge amounts of reactive oxygen species, should these systems fail some reactive molecules will evade the detoxification process and damage potential targets. In such a scenario, cells recruit certain small molecules and proteins as 'rescue specialists' in case the 'bodyguards' fail to protect potential targets from oxidative damage. The thioredoxin (Trx) system thus plays a vital role in the maintenance of a reduced intracellular redox state which is essential for the proper functioning of each individual cell. Trx alterations have been implicated in many diseases such as cataract formation, ischemic heart diseases, cancers, AIDS, complications of diabetes, hypertension etc. The interactions of Trx with many different proteins and different metabolic and signaling pathways as well as the significant species differences make it an attractive target for therapeutic intervention in many fields of medical science. In this review, we present, the critical roles that thioredoxins play in limiting oxidant stress through either its direct effect as an antioxidant or through its interactions with other key signaling proteins (thioredoxin interacting proteins) and its implications in various disease models.

Molecular modeling of the oxidized form of nuclear factor-κB suggests a mechanism for redox regulation of DNA binding and transcriptional activation

NF-kappa B is an important transcriptional regulator of numerous cellular genes, as well as viruses such as HIV-1. Oxidative stimuli in the cytosol are associated with nuclear translocation of NF-kappa B, whereas in the nucleus, reductive activation by thioredoxin is required for NF-kappa B to bind to DNA and activate target genes. Experimental structures of the reduced form of NF-kappa B bound to its DNA targets are available, from which we have modeled the oxidized form of NF-kappa B homodimer by removal of bound DNA, and modification via a hinge movement of a linker between the dimerization and DNA-binding domains of each subunit. These torsional motions enabled the formation of an inter-subunit disulfide bond between the Cys62 residues of each monomer; the resulting structure was refined using molecular dynamics simulation. The final model of oxidized, disulfide-bridged NF-kappaB is more compact than the open, reduced form. This may facilitate its nuclear translocation through small pores in the nuclear envelope, in response to oxidative stimuli in the cytosol. Furthermore, the inter-subunit disulfide blocks DNA from entering the active site of the oxidized dimer, explaining why subsequent reduction to the thiol form in the nucleus is essential for DNA binding and transcriptional activation to occur.

Novel anti-oxidative role of calreticulin in protecting A549 human type II alveolar epithelial cells against hypoxic injury

Short-term hypoxic pretreatment is an effective approach to protect the lung from subsequent prolonged hypoxic injury under conditions such as lung transplantation, shock, and trauma. However, the signaling pathways are not well understood. By use of high-throughput, two-dimensional electrophoresis combined with mass spectrometry, we found that short-term hypoxic treatment upregulated calreticulin (CRT), an endoplasmic-reticulum stress protein, in A549 human type II alveolar epithelial cells. Genetic manipulation of CRT expression in A549 cells through small interferring RNA inhibition or overexpression demonstrated a positive correlation between CRT expression level and cell viability in subsequent prolonged hypoxia, which indicates that CRT is a key mediator of short-term hypoxia-induced cell protection. Importantly, CRT overexpression prevented reactive oxygen species (ROS) accumulation during prolonged hypoxia by inducing the expression of thioredoxin (TRX), an antioxidant, in A549 cells. Furthermore, CRT promoted the nuclear translocation of nuclear factor-E2-related factor 2, the transcription factor of TRX. Finally, overexpressing an inactive TRX mutant reversed the effects of CRT on ROS accumulation and cell protection. Our results demonstrate that CRT stimulates the anti-oxidant pathway and contributes to short-term hypoxia-induced protection in A549 type II alveolar epithelial cells, which may have potential therapeutic ramifications for hypoxic pulmonary diseases.

Glutathione depletion activates mitogen-activated protein kinase (MAPK) pathways that display organ-specific responses and brain protection in mice

Because mitogen-activated protein kinases (MAPK) are downstream effectors of antioxidant responses, changes in GSH levels in an organism might induce organ-specific responses. To test our hypothesis, mice were treated intraperitoneally with L-buthionine-S-R-sulfoximine (BSO) to inhibit GSH synthesis. A time-related GSH depletion in the liver and kidney correlated with p38(MAPK) phosphorylation and induction of thioredoxin 1 (Tx-1) transcription. This positive regulation was associated with nuclear translocation of NF-kappaB and ATF-2 and c-Jun phosphorylation in the liver, but only c-Jun phosphorylation in the kidney. Increased levels of GSH were observed in the brain together with extracellular regulated kinase 2 (ERK2) activation, Nrf2 nuclear accumulation, and increases in transcription of Nrf2, xCT, gamma-glutamylcysteine synthetase (gammaGCSr), and Tx-1. Pretreatment with MAPK inhibitors SB203580 and U0126, or addition of the exogenous thiol N-acetylcysteine, abrogated both p38(MAPK) and ERK2 activation as well as downstream effects on gene expression. No effect on gammaGCSr was observed. These results indicate that in mice, GSH depletion is associated with p38(MAPK) phosphorylation in the liver and kidney and with ERK2 activation in the brain, in what could be considered part of the brain's protective response to thiol depletion.

Increased expression of thioredoxin-1, vascular endothelial growth factor, and redox factor-1 is associated with poor prognosis in patients with liver metastasis from colorectal cancer

We examined whether the expression of thioredoxin-1 (Trx-1) was associated with patient prognosis after liver resection for metastatic colorectal cancer. Eighty-four patients underwent resection of liver metastases from colorectal cancer, leaving no macroscopic evidence of residual tumor. Immunohistochemical study was performed to evaluate the relation among Trx-1, vascular endothelial growth factor (VEGF), and redox factor-1 (Ref-1) expression and the clinicopathologic characteristics and patient survival. Thirty-seven patients (44.0%) with Trx-1-positive metastases had shorter survival after primary liver resection (P = .0003) than the 47 patients (56.0%) with Trx-1-negative metastases. The percentage VEGF-positive and Ref-1-positive metastases was significantly higher in patients with Trx-1 expression (P = .0009 and .0002, respectively). Multivariate analysis revealed that Trx-1 expression was an independent prognostic factor. Expression of VEGF and Ref-1 is associated with Trx-1 overexpression, which is related to a poor prognosis in patients with liver metastases from colorectal cancer.

The txl1+ gene from Schizosaccharomyces pombe encodes a new thioredoxin-like 1 protein that participates in the antioxidant defence against tert-butyl hydroperoxide

Yeasts are equipped with several putative single-domain thioredoxins located in different subcellular compartments. However, additional proteins containing thioredoxin domains are also encoded by the yeast genomes as described for mammals and other eukaryotic organisms. We report here the characterization of the fission yeast orthologue thioredoxin-like 1 (txl1(+)), which has been previously identified in mammals. Similarly to the human protein, the fission yeast Txl1 is a two-domain protein comprising an N-terminal thioredoxin-like domain and a C-terminal domain of unknown function. Many other yeasts and fungi species contain homologues of txl1(+); however, there is no evidence of txl1(+) orthologues in either Saccharomyces cerevisiae or plants. Txl1 is found in both the nucleus and the cytoplasm of Schizosaccharomyces pombe cells and exhibits a strong reducing activity coupled to thioredoxin reductase. In humans, TXL1 expression is induced by glucose deprivation and overexpression of TXL1 confers resistance against this stress. In contrast, a Sz. pombe Deltatxl1 mutant was not affected in the response against glucose starvation but the Deltatxl1 mutant strain showed a clear hypersensitivity to alkyl hydroperoxide. The mRNA levels of txl1(+) in a h20 strain did not change in response to any oxidative insult (hydrogen peroxide or alkyl hydroperoxide) and the overexpression of an integrated copy of the wild-type txl1(+) gene did not confer a significant increased resistance against alkyl hydroperoxide. Overall, these results indicate that the Txl1 role in the cellular detoxification of alkyl hydroperoxide is exerted through a constitutive transcription of txl1(+).

Nuclear redox-signaling is essential for apoptosis inhibition in endothelial cells--important role for nuclear thioredoxin-1

OBJECTIVE

The redox regulator thioredoxin-1 (Trx) is a potent antioxidative enzyme and exerts important cellular functions. Physiological concentrations of reactive oxygen species (ROS) and of nitric oxide (NO) act as second messengers. Previously, we demonstrated that ROS and NO reduced apoptosis in a Trx-dependent manner. The aim of this study was to determine the underlying mechanisms.

METHODS AND RESULTS

First, we investigated the localization of Trx after H2O2 and NO. Both induced nuclear import of Trx, which required karyopherin-alpha. siRNA against karyopherin-alpha inhibited nuclear import of Trx. Analysis of the Trx amino acid sequence and subsequent immunoprecipitation studies revealed that Trx(K81/82E) is not imported into the nucleus under H2O2 treatment and Trx(K81/82/85E) was retained in the cytosol and induced cell death. Trx(K81/82E) abolished the antiapoptotic capacity of H2O2. Glutathione S-transferase P1 (GST-P1) was identified as one major target regulated by H2O2. siRNA against GST-P1 abolished the antiapoptotic effect of H2O2. Cysteine 69, but not cysteines 32 and 35, which are all required for the complete antiapoptotic function of Trx, is not imported into the nucleus.

CONCLUSION

H2O2-induced nuclear import of Trx depends on karyopherin-alpha and NO. Trx-dependent induction of GST-P1 expression is required for apoptosis inhibition in endothelial cells.

Nuclear factor-kappaB and the hepatic inflammation-fibrosis-cancer axis

Nuclear factor-kappaB (NF-kappaB) is a transcriptional regulator of genes involved in immunity, inflammatory response, cell fate, and function. Recent attention has focused on the pathophysiological role of NF-kappaB in the diseased liver. In vivo studies using rodent models of liver disease and cell-targeted perturbation of NF-kappaB activity have revealed complex and multicellular functions in hepatic inflammation, fibrosis, and the development of hepatocellular carcinoma - a process we have termed the "inflammation-fibrosis-cancer axis". This review summarizes the current state of knowledge and provides insight into the vast complexity of the hepatic NF-kappaB signaling system, which should provide a rich source of new therapeutic targets.

Disulfide Bond-mediated multimerization of Ask1 and its reduction by thioredoxin-1 regulate H(2)O(2)-induced c-Jun NH(2)-terminal kinase activation and apoptosis

Apoptosis signal-regulated kinase-1 (Ask1) lies upstream of a major redox-sensitive pathway leading to the activation of Jun NH(2)-terminal kinase (JNK) and the induction of apoptosis. We found that cell exposure to H(2)O(2) caused the rapid oxidation of Ask1, leading to its multimerization through the formation of interchain disulfide bonds. Oxidized Ask1 was fully reduced within minutes after induction by H(2)O(2). During this reduction, the thiol-disulfide oxidoreductase thioredoxin-1 (Trx1) became covalently associated with Ask1. Overexpression of Trx1 accelerated the reduction of Ask1, and a redox-inactive mutant of Trx1 (C35S) remained trapped with Ask1, blocking its reduction. Preventing the oxidation of Ask1 by either overexpressing Trx1 or using an Ask1 mutant in which the sensitive cysteines were mutated (Ask1-DeltaCys) impaired the activation of JNK and the induction of apoptosis while having little effect on Ask1 activation. These results indicate that Ask1 oxidation is required at a step subsequent to activation for signaling downstream of Ask1 after H(2)O(2) treatment.

Nuclear thioredoxin-1 is required to suppress cisplatin-mediated apoptosis of MCF-7 cells

Different cell line with increased thioredoxin-1 (Trx-1) showed a decreased or increased sensitivity to cell killing by cisplatin. Recently, several studies found that the subcellular localization of Trx-1 is closely associated with its functions. In this study, we explored the association of the nuclear Trx-1 with the cisplatin-mediated apoptosis of breast cancer cells MCF-7. Firstly, we found that higher total Trx-1 accompanied by no change of nuclear Trx-1 can not influence apoptosis induced by cisplatin in MCF-7 cells transferred with Trx-1 cDNA. Secondly, higher nuclear Trx-1 accompanied by no change of total Trx-1 can protect cells from apoptosis induced by cisplatin. Thirdly, high nuclear Trx-1 involves in the cisplatin-resistance in cisplatin-resistive cells. Meanwhile, we found that the mRNA level of p53 is closely correlated with the level of nuclear Trx-1. In summary, we concluded that the nuclear Trx-1 is required to resist apoptosis of MCF-7 cells induced by cisplatin, probably through up-regulating the anti-apoptotic gene, p53.

Nuclear and cytoplasmic peroxiredoxin-1 differentially regulate NF-kappaB activities

Peroxiredoxins (Prx) are widely distributed and abundant proteins, which control peroxide concentrations and related signaling mechanisms. Prx1 is found in the cytoplasm and nucleus, but little is known about compartmentalized Prx1 function during redox signaling and oxidative stress. We targeted expression vectors to increase Prx1 in nuclei (NLS-Prx1) and cytoplasm (NES-Prx1) in HeLa cells. Results showed that NES-Prx1 inhibited NF-kappaB activation and nuclear translocation. In contrast, increased NLS-Prx1 did not affect NF-kappaB nuclear translocation but increased activity of a NF-kappaB reporter. Both NLS-Prx1 and NES-Prx1 inhibited NF-kappaB p50 oxidation, suggesting that oxidation of the redox-sensitive cysteine in p50's DNA-binding domain is regulated via peroxide metabolism in both compartments. Interestingly, following treatment with H(2)O(2), nuclear thioredoxin-1 (Trx1) redox status was protected by NLS-Prx1, and cytoplasmic Trx1 was protected by NES-Prx1. Compartmental differences from increasing Prx1 show that the redox poise of cytoplasmic and nuclear thiol systems can be dynamically controlled through peroxide elimination. Such spatial resolution and protein-specific redox differences imply that the balance of peroxide generation/metabolism in microcompartments provides an important specific component of redox signaling.

Thioredoxin-2 affects lifespan and oxidative stress in Drosophila

Thioredoxins are proteins that have thiol-reducing activity and a characteristic conserved active site (WCGPC). They have several documented functions, e.g. roles in defences against oxidative stress and as electron donors for ribonucleotide-reductase. In Drosophila melanogaster there are three "classical" thioredoxins with the conserved active site: deadhead, ThioredoxinT and Thioredoxin-2. Here, we report the creation of null-mutations in the Thioredoxin-2 (Trx-2) gene. Characterization of two Trx-2 mutants indicated that Trx-2 affects the lifespan of D. melanogaster, and is involved in the organism's oxidative stress protection system. We found that the mutants have a shorter lifespan than wild-type flies, and thioredoxin double mutant flies showed lower tolerance to oxidative stress than wild-type flies, while flies carrying multiple copies of a Trx-2 rescue construct showed higher tolerance. These findings suggest that Trx-2 has modest or redundant functions in Drosophila physiology under unstressed conditions, but could be important during times of environmental stress.