Thioredoxin reductase regulates AP-1 activity as well as thioredoxin nuclear localization via active cysteines in response to ionizing radiation

B- and T-cell-specific inactivation of thioredoxin reductase 2 does not impair lymphocyte development and maintenance

Thioredoxin reductases (Txnrds) are a group of selenoenzymes participating in cellular redox regulation. Three Txnrd isoforms are known, each of which exhibits distinct cellular localisation and tissue-specific expression pattern. Txnrd1 is found in the cytoplasm, expression of Txnrd2 is restricted to mitochondria and Txnrd3 shows testis-specific expression. Recently, it was shown that Txnrd2 strongly affects the development of blood cells, since mouse embryos deficient for Txnrd2 are severely anaemic, show increased apoptosis in foetal liver and possess haematopoietic liver stem cells of reduced capacity to proliferate in vitro. However, because Txnrd2-deficient mice die at embryonic day 13.5, it was not known how this enzyme affects blood cell function in the adult animal. In the present study we show that conditional Txnrd2 knockouts generated using CD4- and CD19Cre transgenic mice lack Txnrd2 expression in CD4-- and CD19-positive T- and B-lymphocytes, respectively. However, the development and differentiation of both cell types in thymus and bone marrow was not significantly impaired. In addition, B-cell proliferation and activation in response to CD40 and IL-4 was unaltered in Txnrd2-deficient B-cells.

From selenium to selenoproteins: synthesis, identity, and their role in human health

The requirement of the trace element selenium for life and its beneficial role in human health has been known for several decades. This is attributed to low molecular weight selenium compounds, as well as to its presence within at least 25 proteins, named selenoproteins, in the form of the amino acid selenocysteine (Sec). Incorporation of Sec into selenoproteins employs a unique mechanism that involves decoding of the UGA codon. This process requires multiple features such as the selenocysteine insertion sequence (SECIS) element and several protein factors including a specific elongation factor EFSec and the SECIS binding protein 2, SBP2. The function of most selenoproteins is currently unknown; however, thioredoxin reductases (TrxR), glutathione peroxidases (GPx) and thyroid hormone deiodinases (DIO) are well characterised selenoproteins involved in redox regulation of intracellular signalling, redox homeostasis and thyroid hormone metabolism. Recent evidence points to a role for selenium compounds as well as selenoproteins in the prevention of some forms of cancer. A number of clinical trials are either underway or being planned to examine the effects of selenium on cancer incidence. In this review we describe some of the recent progress in our understanding of the mechanism of selenoprotein synthesis, the role of selenoproteins in human health and disease and the therapeutic potential of some of these proteins.

Inactivation of thioredoxin reductases reveals a complex interplay between thioredoxin and glutathione pathways in Arabidopsis development

NADPH-dependent thioredoxin reductases (NTRs) are key regulatory enzymes determining the redox state of the thioredoxin system. The Arabidopsis thaliana genome has two genes coding for NTRs (NTRA and NTRB), both of which encode mitochondrial and cytosolic isoforms. Surprisingly, plants of the ntra ntrb knockout mutant are viable and fertile, although with a wrinkled seed phenotype, slower plant growth, and pollen with reduced fitness. Thus, in contrast with mammals, our data demonstrate that neither cytosolic nor mitochondrial NTRs are essential in plants. Nevertheless, in the double mutant, the cytosolic thioredoxin h3 is only partially oxidized, suggesting an alternative mechanism for thioredoxin reduction. Plant growth in ntra ntrb plants is hypersensitive to buthionine sulfoximine (BSO), a specific inhibitor of glutathione biosynthesis, and thioredoxin h3 is totally oxidized under this treatment. Interestingly, this BSO-mediated growth arrest is fully reversible, suggesting that BSO induces a growth arrest signal but not a toxic accumulation of activated oxygen species. Moreover, crossing ntra ntrb with rootmeristemless1, a mutant blocked in root growth due to strongly reduced glutathione synthesis, led to complete inhibition of both shoot and root growth, indicating that either the NTR or the glutathione pathway is required for postembryonic activity in the apical meristem.

Paraquat Increases Cyanide-insensitive Respiration in Murine Lung Epithelial Cells by Activating an NAD(P)H:Paraquat Oxidoreductase

Pulmonary fibrosis is one of the most severe consequences of exposure to paraquat, an herbicide that causes rapid alveolar inflammation and epithelial cell damage. Paraquat is known to induce toxicity in cells by stimulating oxygen utilization via redox cycling and the generation of reactive oxygen intermediates. However, the enzymatic activity mediating this reaction in lung cells is not completely understood. Using self-referencing microsensors, we measured the effects of paraquat on oxygen flux into murine lung epithelial cells. Paraquat (10-100 microm) was found to cause a 2-4-fold increase in cellular oxygen flux. The mitochondrial poisons cyanide, rotenone, and antimycin A prevented mitochondrial- but not paraquat-mediated oxygen flux into cells. In contrast, diphenyleneiodonium (10 microm), an NADPH oxidase inhibitor, blocked the effects of paraquat without altering mitochondrial respiration. NADPH oxidases, enzymes that are highly expressed in lung epithelial cells, utilize molecular oxygen to generate superoxide anion. We discovered that lung epithelial cells possess a distinct cytoplasmic diphenyleneiodonium-sensitive NAD(P)H:paraquat oxidoreductase. This enzyme utilizes oxygen, requires NADH or NADPH, and readily generates the reduced paraquat radical. Purification and sequence analysis identified this enzyme activity as thioredoxin reductase. Purified paraquat reductase from the cells contained thioredoxin reductase activity, and purified rat liver thioredoxin reductase or recombinant enzyme possessed paraquat reductase activity. Reactive oxygen intermediates and subsequent oxidative stress generated from this enzyme are likely to contribute to paraquat-induced lung toxicity.

Evaluation of anin vitro model of androgen ablation and identification of the androgen responsive proteome in LNCaP cells

Proteins responsive to androgen and anti-androgen may be involved in the development and progression of prostate cancer and the ultimate failure of androgen-ablation therapy. These proteins represent potential diagnostic and therapeutic targets for improved management of prostate cancer. We have investigated the effect of androgen (R1881) and anti-androgen (bicalutamide) on the androgen-responsive prostate cancer LNCaP cell line using a quantitative gel-based proteomic approach. Prior to analysis, the in vitro system was evaluated for reproducibility and validated by appropriate molecular responses to treatment. Six replicate samples were independently generated and analysed by 2-D DIGE. According to strict statistical criteria, 197 spots were differentially expressed, of which we have successfully identified 165 spots corresponding to 125 distinct proteins. Following androgen supplementation, 108 spots (68 proteins) were increased and 57 spots (39 proteins) were decreased. Essentially no difference was observed between control and anti-androgen-treated samples, confirming the absence of "off-target" effects of bicalutamide. Identified proteins were involved in diverse processes including the stress response and intracellular signalling. The potential contribution to disease of these processes and identified constituent proteins are discussed. This rigorous, statistically supported study of androgen responses has provided a number of potential candidates for development as diagnostic/prognostic markers and drug targets.

Cooperative activity of Ref-1/APE and ERp57 in reductive activation of transcription factors

ERp57, a protein disulfide isomerase localized mainly in the endoplasmic reticulum, has also been found in lesser amounts in the cytosol and nucleus, where its function is still not characterized. We report here that ERp57 displays affinity for Ref-1, a protein involved in DNA repair as well as in the reduction and activation of transcription factors. Immunoprecipitation experiments showed that Ref-1 and ERp57 also interact in vivo in at least three types of cultured human cells, namely HepG2, M14, and Raji. Oxidative stress increased the amount of nuclear Ref-1 associated with ERp57. Moreover, ERp57 reduced by the thioredoxin-reductase/thioredoxin system stimulated the binding of AP-1 to its consensus sequence on DNA, and HeLa cells stably transfected and overexpressing ERp57 were protected against hydrogen peroxide-induced cell killing. Accordingly, ERp57 appears to cooperate with Ref-1 in the regulation of gene expression mediated by redox-sensitive transcription factors and in the adaptive response of the cell to oxidative insult.

Inhibition of ICAM-1 expression by garlic component, allicin, in gamma-irradiated human vascular endothelial cells via downregulation of the JNK signaling pathway

Ionizing radiation used in cancer therapy frequently exerts damaging effects on normal tissues and induces a complex response including inflammation. Since the upregulation of adhesion molecules on endothelial cell surface has been known to be associated with inflammation and our previous data showed that irradiation enhanced adhesion molecules expression, interfering with the expression of adhesion molecules may be an important therapeutic target of inflammatory diseases. We examined the effect of allicin, a major component of garlic, on the induction of intercellular adhesion molecule-1 (ICAM-1) by gamma-irradiation (gamma IR) and the mechanisms of its effect in gamma-irradiated human umbilical vein endothelial cells (HUVECs). HUVECs were pretreated for 20 h with allicin (0.01-1 micro g/ml) and then exposed to 8 Gy radiation. Allicin significantly inhibited gamma IR-induced surface expression of ICAM-1 and ICAM mRNA in a dose-dependent manner. In addition, pretreatment with allicin resulted in the decrease of AP-1 activation and phosphorylation of the c-Jun NH2-terminal kinase (JNK) induced by gamma IR. These results suggest that allicin downregulates gamma IR-induced ICAM-1 expression via inhibition of both AP-1 activation and the JNK pathway and may be considered in therapeutic strategies for the management of patients treated with radiation therapy.

OSU-03012 promotes caspase-independent but PERK-, cathepsin B-, BID-, and AIF-dependent killing of transformed cells

We determined one mechanism by which the putative phosphoinositide-dependent kinase (PDK)-1 inhibitor 2-amino-N-{4-[5-(2-phenanthrenyl)-3-(trifluoromethyl)-1H-pyrazol-1-yl]-phenyl}acetamide (OSU-03012) killed primary human glioma and other transformed cells. OSU-03012 caused a dose-dependent induction of cell death that was not altered by p53 mutation, expression of ERBB1 vIII, or loss of phosphatase and tensin homolog deleted on chromosome 10 function. OSU-03012 promoted cell killing to a greater extent in glioma cells than in nontransformed astrocytes. OSU-03012 and ionizing radiation caused an additive, caspase-independent elevation in cell killing in 96-h viability assays and true radiosensitization in colony formation assays. In a cell type-specific manner, combined exposure to OSU-03012 with a mitogen-activated protein kinase kinase 1/2 inhibitor, phosphoinositide 3-kinase/AKT inhibitors, or parallel molecular interventions resulted in a greater than additive induction of cell killing that was independent of AKT activity and caspase function. OSU-03012 lethality as a single agent or when combined with signaling modulators was not modified in cells lacking expression of BIM or of BAX/BAK. OSU-03012 promoted the release of cathepsin B from the lysosomal compartment and release of AIF from mitochondria. Loss of BH3-interacting domain (BID) function, overexpression of BCL(XL), and inhibition of cathepsin B function suppressed cell killing and apoptosis-inducing factor (AIF) release from mitochondria. In protein kinase R-like endoplasmic reticulum kinase-/- cells, the lethality of OSU-03012 was attenuated which correlated with reduced cleavage of BID and with suppression of cathepsin B and AIF release into the cytosol. Our data demonstrate that OSU-03012 promotes glioma cell killing that is dependent on endoplasmic reticulum stress, lysosomal dysfunction, and BID-dependent release of AIF from mitochondria, and whose lethality is enhanced by irradiation or by inhibition of protective signaling pathways.

Thioredoxin-mediated negative autoregulation of peroxisome proliferator-activated receptor alpha transcriptional activity

PPARalpha, a member of the nuclear receptor superfamily, and thioredoxin, a critical redox-regulator in cells, were found to form a negative feedback loop, which autoregulates transcriptional activity of PPARalpha. Thioredoxin was identified as a target gene of PPARalpha. Activation of PPARalpha leads to increase of thioredoxin expression as well as its translocation from cytoplasm to nucleus, whereas ectopic overexpression of thioredoxin in the nucleus dramatically inhibited both constitutive and ligand-dependent PPARalpha activation. As PPARalpha-target genes, the expression of muscle carnitine palmitoyltransferase I, medium chain acyl CoA dehydrogenase, and apolipoprotein A-I were significantly down-regulated by nucleus-targeted thioredoxin at transcriptional or protein level. The suppression of PPARalpha transcriptional activity by Trx could be enhanced by overexpression of thioredoxin reductase or knockdown of thioredoxin-interacting protein, but abrogated by mutating the redox-active sites of thioredoxin. Mammalian one-hybrid assays showed that thioredoxin inhibited PPARalpha activity by modulating its AF-1 transactivation domain. It was also demonstrated by electrophoretic mobility-shift assay that thioredoxin inhibited the binding of PPARalpha to the PPAR-response element. Together, it is speculated that the reported negative-feedback loop may be essential for maintaining the homeostasis of PPARalpha activity.

Effect of isothiocyanates on nuclear accumulation of NF-kappaB, Nrf2, and thioredoxin in caco-2 cells

Early effects (only 1 h of exposure) of three isothiocyanates (benzyl, phenylethyl, and sulforaphane) on nuclear accumulation of thioredoxin, APE/Ref-1, and transcription factors NF-kappaB and Nrf2, as well as production of reactive oxygen species (ROS) and reduced glutathione levels were examined in human adenocarcinoma Caco-2 cells. Nuclear increase of NF-kappaB, Nrf2, and thioredoxin contents was observed in all isothiocyanate-treated cells, whereas the nuclear Ref-1 and cytoplasmic Keap1 contents were not changed. Sulforaphane was the most potent inducer of Nrf2 nuclear accumulation (10 microM, 1.9-fold) and NF-kappaB nuclear accumulation at higher concentration (25 microM, 6.3-fold). In contrast, benzyl isothiocyanate induced more thioredoxin nuclear accumulation (10 microM, 2.9-fold), increased production of ROS, and gave the greatest induction of thioredoxin reductase 1 mRNA (10 microM, 10.2-fold), whereas phenylethyl isothiocyanate was more potent in the depletion of reduced glutathione levels. These results show that different individual isothiocyanates may possess some different activities in nuclear accumulation of thioredoxin, NF-kappaB, Nrf2, and production of ROS.

Linking tumor cell cytotoxicity to mechanism of drug action: an integrated analysis of gene expression, small-molecule screening and structural databases

An integrated, bioinformatic analysis of three databases comprising tumor-cell-based small molecule screening data, gene expression measurements, and PDB (Protein Data Bank) ligand-target structures has been developed for probing mechanism of drug action (MOA). Clustering analysis of GI50 profiles for the NCI's database of compounds screened across a panel of tumor cells (NCI60) was used to select a subset of unique cytotoxic responses for about 4000 small molecules. Drug-gene-PDB relationships for this test set were examined by correlative analysis of cytotoxic response and differential gene expression profiles within the NCI60 and structural comparisons with known ligand-target crystallographic complexes. A survey of molecular features within these compounds finds thirteen conserved Compound Classes, each class exhibiting chemical features important for interactions with a variety of biological targets. Protein targets for an additional twelve Compound Classes could be directly assigned using drug-protein interactions observed in the crystallographic database. Results from the analysis of constitutive gene expressions established a clear connection between chemo-resistance and overexpression of gene families associated with the extracellular matrix, cytoskeletal organization, and xenobiotic metabolism. Conversely, chemo-sensitivity implicated overexpression of gene families involved in homeostatic functions of nucleic acid repair, aryl hydrocarbon metabolism, heat shock response, proteasome degradation and apoptosis. Correlations between chemo-responsiveness and differential gene expressions identified chemotypes with nonselective (i.e., many) molecular targets from those likely to have selective (i.e., few) molecular targets. Applications of data mining strategies that jointly utilize tumor cell screening, genomic, and structural data are presented for hypotheses generation and identifying novel anticancer candidates.

Thioredoxin and lipoic acid catalyze the denitrosation of low molecular weight and protein S-nitrosothiols

The nitrosation of cellular thiols has attracted much interest as a regulatory mechanism that mediates some of the pathophysiological effects of nitric oxide (NO). In cells, virtually all enzymes contain cysteine residues that can be subjected to S-nitrosation, whereby this process often acts as an activity switch. Nitrosation of biological thiols is believed to be mediated by N2O3, metal-nitrosyl complexes, and peroxynitrite. To date, however, enzymatic pathways for S-denitrosation of proteins have not been identified. Herein, we present experimental evidence that two ubiquitous cellular dithiols, thioredoxin and dihydrolipoic acid, catalyze the denitrosation of S-nitrosoglutathione, S-nitrosocaspase 3, S-nitrosoalbumin, and S-nitrosometallothionenin to their reduced state with concomitant generation of nitroxyl (HNO), the one-electron reduction product of NO. In these reactions, formation of NO and HNO was assessed by ESR spectrometry, potentiometric measurements, and quantification of hydroxylamine and sodium nitrite as end reaction products. Nitrosation and denitrosation of caspase 3 was correlated with its proteolytic activity. We also report that thioredoxin-deficient HeLa cells with mutated thioredoxin reductase denitrosate S-nitrosothiols less efficiently. We conclude that both thioredoxin and dihydrolipoic acid may be involved in the regulation of cellular S-nitrosothiols.

Short-Interfering RNA-Mediated Silencing of Thioredoxin Reductase 1 Alters the Sensitivity of HeLa Cells toward Cadmium

The mammalian thioredoxin reductase (TrxR) is a selenocysteine-containing flavoprotein that regulates the thioredoxin system, one of the major systems that maintain the intracellular redox balance. We previously reported that cytosolic TrxR (TrxR1), one of three mammalian TrxR isozymes, was induced by treatment with cadmium. In the present study, to study the role of cadmium-induced TrxR1 in cellular defense, we silenced the expression of TrxR1 in HeLa cells by using small interfering RNA and examined the effect of TrxR1 silencing on the sensitivity of the cells toward cadmium. We found that the gene silencing of TrxR1 had a dual effect on cadmium-induced cell death, depending on the concentration of cadmium. The TrxR1 silencing increased the sensitivity toward a low dose (less than 10 microM) of cadmium but decreased the sensitivity toward a high dose of cadmium. These results suggested that TrxR1 might play an important role in the cellular defense system against cadmium in two ways. TrxR1 might rescue the cells from a low dose of cadmium-induced moderate injury, while it might promote the death of cells severely injured by a high dose of cadmium.

Redox-sensitive signaling factors as a novel molecular targets for cancer therapy

Tumor cells undergoing proliferation, de-differentiation and progression depend on a complex set of respiratory pathways to generate the necessary energy. The metabolites from these pathways produce significant oxidative stress and must be buffered to prevent permanent cell damage and cell death. It is now clear that, in order to cope with and defend against the detrimental effects of oxidative stress, a series of redox-sensitive, pro-survival signaling pathways and factors regulate a complex intracellular redox buffering network. This review develops the hypothesis that tumor cells use these redox-sensitive, pro-survival signaling pathways and factors - up-regulated due to increased tumor cell respiration - to evade the damaging and cytotoxic effects of specific anticancer agents. It further suggests that redox-sensitive, signaling factors may be potential novel targets for drug discovery.

Altered thioredoxin subcellular localization and redox status in MCF-7 cells following 1,25-dihydroxyvitamin D3 treatment

1,25-Dihydroxyvitamin D(3) (1,25D) induces apoptosis in MCF-7 cells via the intrinsic pathway involving bax translocation to mitochondria, cytochrome c release and reactive oxygen species (ROS) generation. Vitamin D up-regulated protein 1 (VDUP1), an apoptotic regulatory gene induced by 1,25D in HL-60 cells, is a negative regulator of thioredoxin (Trx1), a redox protein which neutralizes ROS and protects against oxidative stress induced apoptosis. Due to the involvement of oxidative stress in 1,25D mediated apoptosis, we analyzed whether VDUP1 or Trx1 are altered by 1,25D in MCF-7 cells. In contrast to HL-60 cells, VDUP1 mRNA was not up-regulated by 1,25D in MCF-7 cells, indicating that transcriptional up-regulation of this gene is not required for 1,25D mediated apoptosis. 1,25D did not affect the expression or activity of Trx1 in MCF-7 cells, however, Trx1 activity was higher in MCF-7 cells selected for resistance to 1,25D mediated apoptosis. In untreated MCF-7 cells, Trx1 was present only in the cytosol, and the majority was in the oxidized state. In 1,25D treated MCF-7 cells, Trx1 was present in both cytosol and nucleus, and the nuclear Trx1 pool was in the reduced state. Nuclear localization of Trx1 in 1,25D treated MCF-7 cells was confirmed by immunofluorescent microscopy. Although redox status is known to alter the ability of Trx1 to bind apoptosis signal regulating kinase 1 (ASK1), no changes in ASK1 transcript or protein levels were observed in 1,25D treated MCF-7 cells. Collectively, these studies indicate that although VDUP1 and ASK1 are not altered by 1,25D, changes in redox status and sub-cellular distribution of Trx1 occurs during 1,25D mediated apoptosis of MCF-7 cells.

Inhibition of thioredoxin reductase but not of glutathione reductase by the major classes of alkylating and platinum-containing anticancer compounds

Mammalian thioredoxin reductase (TrxR) is important for cell proliferation, antioxidant defense, and redox signaling. Together with glutathione reductase (GR) it is the main enzyme providing reducing equivalents to many cellular processes. GR and TrxR are flavoproteins of the same enzyme family, but only the latter is a selenoprotein. With the active site containing selenocysteine, TrxR may catalyze reduction of a wide range of substrates, but can at the same time easily be targeted by electrophilic compounds due to the extraordinarily high reactivity of a selenolate moiety. Here we addressed the inhibition of the enzyme by major anticancer alkylating agents and platinum-containing compounds and we compared it to that of GR. We confirmed prior studies suggesting that the nitrosourea carmustine can inhibit both GR and TrxR. We next found, however, that nitrogen mustards (chlorambucil and melphalan) and alkyl sulfonates (busulfan) efficiently inhibited TrxR while these compounds, surprisingly, did not inhibit GR. Inhibitions were concentration and time dependent and apparently irreversible. Anticancer anthracyclines (daunorubicin and doxorubicin) were, in contrast to the alkylating agents, not inhibitors but poor substrates of TrxR. We also found that TrxR, but not GR, was efficiently inhibited by both cisplatin, its monohydrated complex, and oxaliplatin. Carboplatin, in contrast, could not inhibit any of the two enzymes. These findings lead us to conclude that representative compounds of the major classes of clinically used anticancer alkylating agents and most platinum compounds may easily target TrxR, but not GR. The TrxR inhibition should thereby be considered as a factor that may contribute to the cytotoxicity seen upon clinical use of these drugs.

Direct association of hepatopoietin with thioredoxin constitutes a redox signal transduction in activation of AP-1/NF-κB

It has been demonstrated that growth factors quiescin Q6 family was created by the fusion of the sulfhydryl oxidase fragment of the yeast essential for respiration and vegetative growth (ERV)1 prototype [an orthologue of hepatopoietin (HPO)] and thioredoxin (TRX)/disulfide isomerase domain during evolution. In this paper, our results demonstrated that two components of this composite protein, i.e., HPO and TRX, were involved in the same signal transduction and interacted physically in eukaryocyte. When HPO and TRX were cotransfected into COS7 cells, the activity of activator protein-1 (AP-1) and NF-kappaB was evidently enhanced compared with the transfection with HPO or TRX alone, at the same time, the phosphorylation of c-Jun was increased. They were colocalized in the cells. By Co-IP and GST pull-down experiments, we found that HPO could physically interact with TRX, which was also confirmed by yeast two-hybrid assay. By further investigation, we found both HPO and TRX were sensitive to cellular oxidative state. HPO dimer is in its natural state and could be reduced by dithiothreitol (DTT) in vitro and in vivo. Under the treatment of oxidants such as H(2)O(2) and diamide, the amount of HPO monomer was decreased significantly and assembled into dimer, and the free thiol in TRX was oxidized. HPO could transfer oxidizing equivalents to TRX via direct thiol-disulfide exchange in vitro, the redox state of TRX was also affected by HPO in vivo. Taken together, it was implicated that the oxidizing equivalents might flow from HPO to TRX and then to substrate protein by the dimerization of HPO, and its interaction with TRX finally activates the redox-sensitive transcription factor, suggesting a new redox signal pathway conducted by thiol-disulfide transformation in eukaryocytic cytoplasm.

The neuronal differentiation process involves a series of antioxidant proteins

Involvement of individual antioxidant proteins (AOXP) and antioxidants in the differentiation process has been already reported. A systematic search strategy for detecting differentially regulated AOXP in neuronal differentiation, however, has not been published so far. The aim of this study was to provide an analytical tool identifying AOXP and to generate a differentiation-related AOXP expressional pattern. The undifferentiated N1E-115 neuroblastoma cell line was switched into a neuronal phenotype by DMSO treatment and used for proteomic experiments: We used two-dimensional gel electrophoresis followed by unambiguous mass spectrometrical (MALDI-TOF-TOF) identification of proteins to generate a map of AOXP. 16 AOXP were unambiguously determined in both cell lines; catalase, thioredoxin domain-containing protein 4 and hypothetical glutaredoxin/glutathione S-transferase C terminus-containing protein were detectable in the undifferentiated cells only. Five AOXP were observed in both, undifferentiated and differentiated cells and thioredoxin, thioredoxin-like protein p19, thioredoxin reductase 1, superoxide dismutases (Mn and Cu-Zn), glutathione synthetase, glutathione S-transferase P1 and Mu1 were detected in differentiated cells exclusively. Herein a differential expressional pattern is presented that reveals so far unpublished antioxidant principles involved in neuronal differentiation by a protein chemical approach, unambiguously identifying AOXP. This finding not only shows concomitant determination of AOXP but also serves as an analytical tool and forms the basis for design of future studies addressing AOXP and differentiation per se.

Thioredoxin reductase as a novel molecular target for cancer therapy

Tumor cell proliferation, de-differentiation, and progression depend on a complex combination of altered cell cycle regulation, excessive growth factor pathway activation, and decreased apoptosis. The understanding of these complex mechanisms should lead to the identification of potential targets for therapeutic intervention. Redox-sensitive signaling factors also regulate multiple cellular processes including proliferation, cell cycle, and pro-survival signaling cascades, suggesting their potential as molecular targets for anticancer agents. These observations suggest that redox-sensitive signaling factors may be potential novel molecular markers. We hypothesized that thioredoxin reductase-1 (TR), a component of several redox-regulated pathways, may represent a potential molecular target candidate in response to agents that induce oxidative stress. There have been numerous biological studies over the last decade investigating the cell biological, biochemical, and genetic properties of TR both in culture and in in vivo models. In addition, using a series of permanent cell lines that express either a wild-type TR or a dominant mutant TR gene or a chemical agent that inhibits TR we demonstrated that TR meets most criteria that would identify a molecular target. Based on these results we believe TR is a potential molecular target and discuss potential clinical possibilities.

Cytoplasmic thioredoxin reductase is essential for embryogenesis but dispensable for cardiac development

Two distinct thioredoxin/thioredoxin reductase systems are present in the cytosol and the mitochondria of mammalian cells. Thioredoxins (Txn), the main substrates of thioredoxin reductases (Txnrd), are involved in numerous physiological processes, including cell-cell communication, redox metabolism, proliferation, and apoptosis. To investigate the individual contribution of mitochondrial (Txnrd2) and cytoplasmic (Txnrd1) thioredoxin reductases in vivo, we generated a mouse strain with a conditionally targeted deletion of Txnrd1. We show here that the ubiquitous Cre-mediated inactivation of Txnrd1 leads to early embryonic lethality. Homozygous mutant embryos display severe growth retardation and fail to turn. In accordance with the observed growth impairment in vivo, Txnrd1-deficient embryonic fibroblasts do not proliferate in vitro. In contrast, ex vivo-cultured embryonic Txnrd1-deficient cardiomyocytes are not affected, and mice with a heart-specific inactivation of Txnrd1 develop normally and appear healthy. Our results indicate that Txnrd1 plays an essential role during embryogenesis in most developing tissues except the heart.

Overexpression of Enzymatically Active Human Cytosolic and Mitochondrial Thioredoxin Reductase in HEK-293 Cells

The mammalian thioredoxin reductases (TrxR) are selenoproteins containing a catalytically active selenocysteine residue (Sec) and are important enzymes in cellular redox control. The cotranslational incorporation of Sec, necessary for activity, is governed by a stem-loop structure in the 3'-untranslated region of the mRNA and demands adequate selenium availability. The complicated translation machinery required for Sec incorporation is a major obstacle in isolating mammalian cell lines stably overexpressing selenoproteins. In this work we report on the development and characterization of stably transfected human embryonic kidney 293 cells that overexpress enzymatically active selenocysteine-containing cytosolic TrxR1 or mitochondrial TrxR2. We demonstrate that the overexpression of selenium-containing TrxR1 results in lower expression and activity of the endogenous selenoprotein glutathione peroxidase and that the activity of overexpressed TrxRs, rather than the protein amount, can be increased by selenium supplementation in the cell growth media. We also found that the TrxR-overexpressing cells grew slower over a wide range of selenium concentrations, which was an effect apparently not related to increased apoptosis nor to fatally altered intracellular levels of reactive oxygen species. Most surprisingly, the TrxR1- or TrxR2-overexpressing cells also induced novel expression of the epithelial markers CK18, CK-Cam5.2, and BerEP4, suggestive of a stimulation of cellular differentiation.

Oxidative stress, redox, and the tumor microenvironment

Cellular metabolism is critical for the generation of energy in biological systems; however, as a result of electron transfer reactions, reactive oxygen species (ROS) are generated in aerobic cells. Although low amounts of ROS are easily tolerated by the cell, abnormally high levels of ROS induce oxidative stress. ROS are also produced after exposure to ionizing radiation, selected chemotherapeutic agents, hyperthermia, inhibition of antioxidant enzymes, or depletion of cellular reductants such as NADPH and glutathione. Oxidative stress such as ionizing radiation produces a variety of highly reactive free radicals that damage cells, initiate signal transduction pathways, and alter gene expression. Cells are capable of countering the effects of oxidative stress by virtue of a complex redox buffering system. With respect to the radiation treatment of cancer, components of the cellular redox armamentarium may be targeted to enhance cell killing in the case of tumors and/or protection in the case of normal tissues.

Identification of a novel partner of duox: EFP1, a thioredoxin-related protein

H(2)O(2) is a crucial substrate of thyroproxidase (TPO) to iodinate thyroglobulin and synthesize thyroid hormones in thyroid. ThOX proteins (thyroid oxidase) also called Duox are believed to be responsible for H(2)O(2) generation. Duoxs expressed in transfected cells do not generate an active system, nor permit their membrane localization suggesting that other proteins are required to fulfill these functions. In this study, we demonstrate interactions of Duoxs with TPO and with p22(phox) without any effect on Duox activity. By yeast two-hybrid method using EF-hand fragment of dog Duox1 as the bait we have isolated EFP1 (EF-hand binding protein 1), one partner of Duoxs that belongs to the thioredoxin-related protein family. EFP1 shares moderate similarities with other members of thioredoxin-related proteins, but the characteristic active site and the folding structures are well conserved. EFP1 can be co-immunoprecipitated with Duoxs in transfected COS cells as well as in primary cultured human thyrocytes. It interacts also with TPO but not thyroglobulin. Immunofluorescence studies show that EFP1 and Duox proteins are co-localized inside the transfected cells, suggesting that EFP1 is not sufficient to induce either the expression of Duox at the plasma membrane or to permit H(2)O(2) production. EFP1 and Duox mRNA share similar distribution in nine different tissues. These results suggest that EFP1 could be one of the partners in the assembly of the multiprotein complex constituting the thyroid H(2)O(2) generating system but is certainly not sufficient to permit H(2)O(2) generation.

Thioredoxin reductase as a potential molecular target for anticancer agents that induce oxidative stress

Redox-sensitive signaling factors regulate multiple cellular processes, including proliferation, cell cycle, and prosurvival signaling cascades, suggesting their potential as molecular targets for anticancer agents. It is logical to set constraints that a molecular target should meet at least one of the following criteria: (1) inhibition of prosurvival signaling pathways; (2) inhibition of cell cycle progression; or (3) enhancement of the cytotoxic effects of anticancer agents. Therefore, we hypothesized that thioredoxin reductase 1 (TR), a component of several redox-regulated pathways, might represent a potential molecular target candidate in response to agents that induce oxidative stress. To address this issue, permanent cell lines overexpressing either the wild-type (pCXN2-myc-TR-wt) or a Cys-Ser mutant (pCXN2-myc-mTR) TR gene were used, as were parental HeLa cells treated with 1-methyl-1-propyl-2-imidazolyl disulfide (IV-2), a pharmacologic inhibitor of TR. Cells were exposed to the oxidative stressors, H2O2 and ionizing radiation (IR), and analyzed for changes in signal transduction, cell cycle, and cytotoxicity. Analysis of HeLa cells overexpressing the pCXN2-myc-TR-wt gene showed increased basal activity of nuclear factor kappaB (NFkappaB) and activator protein (AP-1), whereas HeLa cells expressing a pCXN2-myc-mTR gene and HeLa cells treated with IV-2 were unable to induce NFkappaB or AP-1 activity following H2O2 or IR exposure. Fluorescence-activated cell sorting analysis showed a marked accumulation of pCXN2-myc-mTR cells in the late G1 phase, whereas pCXN2-myc-TR-wt cells showed a decreased G1 subpopulation. Chemical inhibition of TR with IV-2 also completely inhibited cellular proliferation at concentrations between 10 and 25 micromol/L, resulting in a G1 phase cell cycle arrest consistent with the results from cells expressing the pCXN2-myc-mTR gene. Following exposure to H2O2 and IR, pCXN2-myc-mTR- and IV-2-treated cells were significantly more sensitive to oxidative stress-induced cytotoxicity as measured by clonogenic survival assays. Finally, IV-2-treated cells showed increased tumor cell death when treated with H2O2 and IR. These results identify TR as a potential target to enhance the cytotoxic effects of agents that induce oxidative stress, including IR.

Selenium and brain function: a poorly recognized liaison

Molecular biology has recently contributed significantly to the recognition of selenium (Se)2 and Se-dependent enzymes as modulators of brain function. Increased oxidative stress has been proposed as a pathomechanism in neurodegenerative diseases including, among others, Parkinson's disease, stroke, and epilepsy. Glutathione peroxidases (GPx), thioredoxin reductases, and one methionine-sulfoxide-reductase are selenium-dependent enzymes involved in antioxidant defense and intracellular redox regulation and modulation. Selenium depletion in animals is associated with decreased activities of Se-dependent enzymes and leads to enhanced cell loss in models of neurodegenerative disease. Genetic inactivation of cellular GPx increases the sensitivity towards neurotoxins and brain ischemia. Conversely, increased GPx activity as a result of increased Se supply or overexpression ameliorates the outcome in the same models of disease. Genetic inactivation of selenoprotein P leads to a marked reduction of brain Se content, which has not been achieved by dietary Se depletion, and to a movement disorder and spontaneous seizures. Here we review the role of Se for the brain under physiological as well as pathophysiological conditions and highlight recent findings which open new vistas on an old essential trace element.

An Alternative Splicing Variant of the Selenoprotein Thioredoxin Reductase Is a Modulator of Estrogen Signaling

The selenoprotein thioredoxin reductase (TrxR1) is an integral part of the thioredoxin system. It serves to transfer electrons from NADPH to thioredoxin leading to its reduction. Interestingly, recent work has indicated that thioredoxin reductase can regulate the activity of transcription factors such as p53, hypoxia-inducible factor, and AP-1. Here, we describe that an alternative splicing variant of thioredoxin reductase (TrxR1b) containing an LXXLL peptide motif, is implicated in direct binding to nuclear receptors. In vitro interaction studies revealed direct interaction of the TrxR1b with the estrogen receptors alpha and beta. Confocal microscopy analysis showed nuclear colocalization of the TrxR1b with both estrogen receptor alpha and beta in estradiol-17beta-treated cells. Transcriptional studies demonstrated that TrxR1b can affect estrogen-dependent gene activation differentially at classical estrogen response elements as compared with AP-1 response elements. Based on these results, we propose a model where thioredoxin reductase directly influences the estrogen receptor-coactivator complex assembly on non-classical estrogen response elements such as AP-1. In summary, our results suggest that TrxR1b is an important modulator of estrogen signaling.

Hepatitis C virus NS3 protein up-regulates expression of thioredoxin reductase 1 gene

AIM: To investigate the transactivating effect of HCV NS3 protein on TXNRD1 gene promoter and the molecular biological mechanisms of HCV NS3 protein in HCV pathogeneicity.

METHODS: Polymerase chain reaction (PCR) technique was employed to amplify the sequence of TXNRD1 promoter from HepG2 genomic DNA, and the product was subcloned into pCAT3-Basic by Kpn I and Xho I, named pCAT3-TXNRD1p. pCAT3-TXNRD1p was transfected into the hepatoblastoma cell line HepG2, then cotransfected with pcDNA3.1(-)-NS3 by FuGENE 6 transfection reagents. The HepG2 cells transfected with pCAT3-Basic was used as negative control. The activity of CAT in HepG2 cells transfected was detected by an ELISA kit after 48 hours, which reflected the transactivating function of HCV NS3 protein to TXNRD1 gene promoter.

RESULTS: The expression vector pcDNA3.1(-)-NS3 and report vector pCAT3-TXNRD1p were constructed and confirmed by restriction enzyme digestion and sequencing. The expression of CAT in HepG2 cells co-transfected with pCAT3-TXNRD1p and pcDNA3.1(-)-NS3 is 9 times as higher as that of pCAT3-Basic, and twice as higher as that of pCAT3-TXNRD1p.

CONCLUSION: HCV NS3 protein can transactivate TXNRD1 promoter, and therefore up-regulate the expression of TXNRD1 gene.

Identification of novel molecular candidates for fatty liver in the hyperlipidemic mouse model, HcB19

The inbred HcB19 mouse strain expresses a truncated form of thioredoxin interacting protein and is phenotypically characterized by fatty liver and elevated plasma triglycerides and VLDL. Recently, these mice have been proposed as an animal model for familial combined hyperlipidemia. The aim of the present study was identification of hepatic proteins specifically associated with the presence of fatty liver. Eighteen differential proteins were detected in whole-liver homogenate from HcB19, or the parental strain C3H, using 2D electrophoresis, and 11 of those were successfully identified by mass spectrometry. Five of the identified differential proteins were mitochondrial, two peroxisomal, two cytosolic, and two secretory. Four differential proteins were novel in the fatty liver proteome [i.e., aconitase, succinate dehydrogenase, propionyl CoA carboxylase alpha chain (PCCA), and 3-hydroxyanthranilate 3,4 dioxygenase (3HAAO)]. Of these, PCCA and 3HAAO are of particular interest because of their known functions in nicotinic acid metabolism (3HAAO) and ketogenesis (PCCA). We have newly identified several differential proteins in the hepatic proteome of mice with fatty liver, including PCCA and 3HAAO, and confirmed differential expression of previously reported proteins. These individual proteins, PCCA and 3HAAO, can be important in development of fatty liver or in the expression of hyperlipidemia.

Isolation and characterization of two nuclear genes encoding glutathione and thioredoxin reductases from the yeast Kluyveromyces lactis

Response to oxidative stress has been hitherto scarcely studied in the respiratory yeast Kluyveromyces lactis. The genes coding for reductases of glutathione and thioredoxin, KlGLR1 and KlTRR1, respectively, have been cloned and characterized in this work. H(2)O(2) treatment increased transcription and enzyme activity of KlTRR1 but not of KlGLR1, suggesting a different situation from that reported for the fermentative yeast Saccharomyces cerevisiae. A consensus for Yap1p binding is functional in the KlTRR1 promoter.

Secondary structure and stability of the selenocysteine insertion sequences (SECIS) for human thioredoxin reductase and glutathione peroxidase

We have used high resolution NMR and thermodynamics to characterize the secondary structure and stability of the selenocysteine insertion sequences (SECIS) of human glutathione peroxidase (58 nt) and thioredoxin reductase (51 nt). These sequences are members of the two classes of SECIS recently identified with two distinct structures capable of directing selenocysteine incorporation into proteins in eukaryotes. UV melting experiments showed a single cooperative and reversible transition for each RNA, which indicates the presence of stable secondary structures. Despite their large size, the RNAs gave well resolved NMR spectra for the exchangeable protons. Using NOESY, the imino protons as well as the cytosine amino protons of all of the Watson-Crick base pairs were assigned. In addition, a number of non-canonical base pairs including the wobble G.U pairs were identified. The interbase-pair NOEs allowed definition of the hydrogen-bonded structure of the oligonucleotides, providing an experimental model of the secondary structure of these elements. The derived secondary structures are consistent with several features of the predicted models, but with some important differences, especially regarding the conserved sequence motifs.

Indomethacin and ibuprofen induce Hsc70 nuclear localization and activation of the heat shock response in HeLa cells

It has been established that non-steroidal anti-inflammatory drugs (NSAIDs), such as sodium salicylate, sulindac, ibuprofen, and indomethacin, induce anti-inflammatory and anti-proliferative effects independent of cyclooxygenase. These cyclooxygenase-independent pharmacodynamic effects appear to regulate several signaling pathways involving proliferation, apoptosis, and heat shock response. However, the mechanisms of these actions remain an area of ongoing investigation. Hsc70 is a cytoplasmic chaperone protein involved in folding and trafficking of client proteins to different subcellular compartments, plays roles in signal transduction and apoptosis processes, and translocates to the nucleus following exposure to heat shock. Since NSAIDs induce some aspects of the heat shock response, we hypothesized that they may also induce Hsc70 nuclear translocation. Western immunoblotting and indirect cellular immunofluorescence showed that indomethacin and ibuprofen induce Hsc70 nuclear translocation at concentrations previously shown to induce HSF DNA-binding activity. Chemical inhibition of both p38(MAPK) and Erk42/44 had no effect on localization patterns. In addition, while indomethacin has been shown to behave as an oxidative stressor, the radical scavenging agent, N-acetyl cysteine, did not inhibit nuclear translocation. These results indicate that induction of the heat shock response by NSAIDs occurs at concentrations fivefold greater than those required to inhibit cyclooxygenase activity, suggesting a cyclooxygenase-independent mechanism, and in the presence or absence of kinase inhibitors and a free radical scavenger, suggesting independence of Erk42/44 or p38(MAPK) activities and intracellular oxidoreductive state.

APE/Ref-1 and the mammalian response to genotoxic stress

Human apurinic/apyrimidinic endonuclease/redox factor-1 (hAPE/Ref-1) is a multifunctional protein involved in the repair of DNA damaged by oxidative or alkylating compounds as well as in the regulation of stress inducible transcription factors such as AP-1, NF-kappaB, HIF-1 and p53. With respect to transcriptional regulation, both redox dependent and independent mechanisms have been described. APE/Ref-1 also acts as a transcriptional repressor. Recent data indicate that APE/Ref-1 negatively regulates the activity of the Ras-related GTPase Rac1. How these different physiological activities of APE/Ref-1 are coordinated is poorly understood. So far, convincing evidence is available that the expression of the APE/Ref-1 gene is inducible by oxidative stress and that overexpressed APE/Ref-1 protein protects cells against the genotoxic and cell killing effects of reactive oxygen species (ROS), whereas down-regulation sensitizes cells. Therefore, APE/Ref-1 can be considered to be part of an adaptive cellular response mechanism to oxidative genotoxic stress. The physiological relevance of increase of either the repair or redox activity of APE/Ref-1 for this adaptive response is unclear. Data will be shown that transfection of the truncated protein exhibiting either one of the activities provoked increase of resistance. Since APE/Ref-1 expression level and intracellular localization is variable in different types of tumors and frequently found to be different in non-malignant compared to the corresponding malignant human tissue, the protein is thought to be a diagnostic and prognostic tumor marker. Because of its involvement in DNA repair and apoptosis-related signaling mechanisms, APE/Ref-1 is also being discussed as a novel target for tumor-therapeutic approaches.

Thioredoxin reductase 1 expression in colon cancer: discrepancy between in vitro and in vivo findings

Thioredoxin and thioredoxin reductase 1 (TR1) are redox proteins that have been implicated in cellular events such as proliferation, transformation, and apoptosis. Analysis of the expression and localization of TR1 in different normal and cancer cell lines and in colon tissues (normal, neoplastic, or inflamed) was performed using reverse transcription-PCR and in situ hybridization. TR1 mRNA was expressed in all analyzed tissues with TR mRNA-positive cells restricted to the stroma of colon crypts, partly being CD3 or CD56 positive. In neoplastic areas of colonic cancer tissue, a loss of TR was obvious. None of the epithelial cells in colonic mucosa expressed TR mRNA, whereas more than 70% of HT-29 cells grown in monolayer were positive for TR. In contrast, HT-29 cells, grown as spheroids or as tumors in SCID mice, were negative for TR. In contrast to these in vitro findings and previous studies, there is no evidence that TR plays a significant role in vivo in normal cell growth in colonic epithelial cells. The mechanism underlying the loss of TR1-positive/CD3-positive/CD56-positive cells or the biologic consequence of this phenomenon observed in neoplastic colonic tissue remains to be clarified.

Intracellular renin and the nature of intracrine enzymes

Recently, the binding of renin and prorenin to cellular receptors with the subsequent generation of second messengers and the production of physiological effects has been demonstrated. In addition, the internalization of prorenin by target cells has been associated with increased cellular synthesis of angiotensin and cardiac pathology. Also, a renin transcript lacking the sequences encoding a secretory signal has been reported, and this transcript appears to produce a renin that acts in the cell that synthesized it. Some years ago, we coined the term intracrine for a peptide hormone or factor that acts in the intracellular space either after internalization or retention in its cell of synthesis. Thus defined, a wide variety of peptides display intracrine functionality, including hormones, growth factors, transcription factors, and enzymes. For example, considerable evidence indicates that angiotensin II is an intracrine. Also, general principles of intracrine functionality have been developed. Thus, recent evidence demonstrates that the prorenin/renin molecule is an intracrine enzyme. Here, the actions of intracrine enzymes (angiogenin, phosphoglucose isomerase, phospholipase A2, granzyme A and B, thioredoxin, platelet-derived endothelial growth factor, and serine protease inhibitors) are reviewed. The relation of prorenin/renin to other intracrine enzymes, and to intracrines in general, is discussed.

Loss of activity of the selenoenzyme thioredoxin reductase causes induction of hepatic heme oxygenase-1

The stress response enzyme heme oxygenase (HO)-1 is induced in livers of selenium-deficient rodents, probably to compensate for loss of certain selenoproteins. We sought to identify those selenoproteins. Selenium-replete mice with genetic deletion of selenoprotein P or glutathione peroxidase-1 did not have elevated hepatic HO activity, thus ruling out involvement of those selenoproteins in HO-1 induction by selenium deficiency. However, inhibition of thioredoxin reductase (TrxR) by a low dose of gold in the form of aurothioglucose led to induction of hepatic HO activity. Moreover, further induction by phenobarbital was observed. This HO-1 induction pattern is also seen in selenium-deficient mice. In the rat hepatoma cell line H4IIE, inhibition of TrxR by aurothioglucose or by 1-chloro-2,4-dinitrobenzene led to induction of HO-1. We conclude that loss of TrxR is responsible for the induction of HO-1 by selenium deficiency.

Overexpression of thioredoxin reductase 1 regulates NF-?B activation

Thioredoxin reductase (TrxR) is a flavoprotein that contains a C-terminal penultimate selenocysteine (Sec) and has an ability to reduce thioredoxin (Trx), which regulates the activity of NF-kappa B. To date, three TrxR isozymes, TrxR1, TrxR2, and TrxR3, have been identified. In the present study, we found that among these isozymes only TrxR1 was induced by tumor necrosis factor-alpha (TNF alpha) in vascular endothelial cells. Furthermore, the overexpression of TrxR1 enhanced TNF alpha-induced DNA-binding activity of NF-kappa B and NF-kappa B-dependent gene expression. The catalytic Sec residue of TrxR1, which is essential for reducing Trx, was required for this NF-kappa B activation, and aurothiomalate, an inhibitor of TrxR, suppressed TNF alpha-induced activation of NF-kappa B and the expression of NF-kappa B-targeted proinflammatory genes such as E-selectin and cyclooxygenase-2. These results suggest that TrxR1 may act as a positive regulator of NF-kappa B and may play an important role in the cellular inflammatory response.