Physiological functions of thioredoxin and thioredoxin reductase

Selenium distribution in a Se-enriched mushroom species of the genus Ganoderma

Data reported here show that Ganoderma lucidum could biotransform inorganic selenite in the substrate into organic forms by intergrating Se into proteins (56-61%) and polysaccharides (11-18%) and other components. Furthermore, water- and alkaline-soluble protein components were mainly responsible for the storage of organic Se, and Se-Met accounts for only a minor (8.2-18.3%) amount of the selenocompounds present in proteins. The molecular mass of most proteins or protein subunits containing Se was no more than 16 kDa. A low concentration of Se (<100 microg/g) in the substrate facilitated the synthesis of total protein and amino acids in G. lucidum, but a high concentration of Se (>150 microg/g) played a reverse role. Additionally, Se concentration in the culture had no significant effect on the distribution of the amino acids and proteins.

Purification, characterization, and immunolocalization of a thioredoxin reductase from adult Fasciola hepatica

Thioredoxin reductase (TrxR), an enzyme belonging to the flavoprotein family of pyridine nucleotide-disulfide oxidoreductases, was isolated from the deoxycholate-soluble extract of the common liver fluke, Fasciola hepatica. Purification to homogeneity of the 60-kDa enzyme from the adult worm was achieved by a combination of ammonium sulfate fractionation, anion exchange, and affinity chromatography on 2',5'-adenosine diphosphate-Sepharose. Using the 5,5'-dithiobis(2-nitrobenzoic acid) assay, the purified TrxR showed a specific activity of 7,117 U min(-1) mg(-1). The enzyme activity was completely inhibited by the presence of the gold compound aurothioglucose (IC50 = 120 nm), indicating that F. hepatica TrxR is a selenoenzyme. Also, the enzyme was capable of reducing disulfide bonds in insulin and was activated by the presence of the reduced form of flavin adenine dinucleotide, properties shared with mammalian TrxRs. Furthermore, the isolated enzyme showed very low glutaredoxin (Grx) activity (0.47 U mg(-1)), but no glutathione reductase activity was detected. Affinity-purified IgGs (20 microg ml(-1)) from the antisera produced against the purified TrxR inhibited its activity about 80% with respect to the control. The enzyme was immunolocalized in cells located within the parenchyma and in the testes, but it was not found in the tegument of the adult fluke.

Mitochondrial Thioredoxin System

Thioredoxin-2 (Trx2) is a mitochondrial protein-disulfide oxidoreductase essential for control of cell survival during mammalian embryonic development. This suggests that mitochondrial thioredoxin reductase-2 (TrxR2), responsible for reducing oxidized Trx2, may also be a key player in the regulation of mitochondria-dependent apoptosis. With this in mind, we investigated the effects of overexpression of TrxR2, Trx2, or both on mammalian cell responses to various apoptotic inducers. Stable transfectants of mouse Neuro2A cells were generated that overexpressed TrxR2 or an EGFP-TrxR2 fusion protein. EGFP-TrxR2 was enzymatically active and was localized in mitochondria. TrxR2 protein level and TrxR activity could be increased up to 6-fold in mitochondria. TrxR2 and EGFP-TrxR2 transfectants showed reduced growth rates as compared with control cells. This growth alteration was not due to cytotoxic effects nor related to changes in basal mitochondrial transmembrane potential (DeltaPsi(m)), reactive oxygen species production, or to other mitochondrial antioxidant components such as Trx2, peroxyredoxin-3, MnSOD, GPx1, and glutathione whose levels were not affected by increased TrxR2 activity. In response to various apoptotic inducers, the extent of DeltaPsi(m) dissipation, reactive oxygen species induction, caspase activation, and loss of viability were remarkably similar in TrxR2 and control transfectants. Excess TrxR2 did not prevent trichostatin A-mediated neuronal differentiation of Neuro2A cells nor did it protect them against beta-amyloid neurotoxicity. Neither massive glutathione depletion nor co-transfection of Trx2 and TrxR2 in Neuro2A (mouse), COS-7 (monkey), or HeLa (human) cells revealed any differential cellular resistance to prooxidant or non-oxidant apoptotic stimuli. Our results suggest that neither Trx2 nor TrxR2 gain of function modified the redox regulation of mitochondria-dependent apoptosis in these mammalian cells.

Reductive activation of ricin and ricin A-chain immunotoxins by protein disulfide isomerase and thioredoxin reductase

Intracellular activation of ricin and of the ricin A-chain (RTA) immunotoxins requires reduction of their intersubunit disulfide(s). This crucial event is likely to be catalyzed by disulfide oxidoreductases and precedes dislocation of the toxic subunit to the cytosol. We investigated the role of protein disulfide isomerase (EC 5.3.4.1, PDI), thioredoxin (Trx), and thioredoxin reductase (EC 1.8.1.9, TrxR) in the reduction of ricin and of a ricin A-chain immunotoxin by combining enzymatic assays, SDS-PAGE separation and immunoblotting. We found that, whereas PDI, Trx, and TrxR used separately were unable to directly reduce ricin and the immunotoxin, PDI and Trx in the presence of TrxR and NADPH could reduce both ricin and immunotoxin in vitro. PDI functioned only after pre-incubation with TrxR and the reductive activation of ricin was more efficient in the presence of glutathione. Similar results were obtained with microsomal membranes or crude cell extracts. Pre-incubation with the gold(I) compound auranofin, which irreversibly inactivates TrxR, resulted in a dose-dependent inhibition of ricin and immunotoxin reduction. Reductive activation of ricin and immunotoxin decreased or was abolished in microsomes depleted of TrxR and in cell extracts depleted of both PDI and Trx. Pre-incubation of U-937, Molt-3, Jurkat, and DU145 cells with auranofin significantly decreased ricin cytotoxicity with respect to mock-treated controls (P<0.05). Conversely, auranofin failed to protect cells from the toxicity of pre-reduced ricin which does not require intracellular reduction of disulfide between the two ricin subunits. We conclude that TrxR, by activating disulfide reductase activity of PDI, can ultimately lead to reduction/activation of ricin and immunotoxin in the cell.

Escherichia coli thioredoxin inhibition by cadmium: two mutually exclusive binding sites involving Cys32 and Asp26

Observations of thioredoxin inhibition by cadmium and of a positive role for thioredoxin in protection from Cd(2+) led us to investigate the thioredoxin-cadmium interaction properties. We used calorimetric and spectroscopic methods at different pH values to explore the relative contribution of putative binding residues (Cys32, Cys35, Trp28, Trp31 and Asp26) within or near the active site. At pH 8 or 7.5 two binding sites were identified by isothermal titration calorimetry with affinity constants of 10 x 10(6) m(-1) and 1 x 10(6) m(-1). For both sites, a proton was released upon Cd(2+) binding. One mole of Cd(2+) per mole of reduced thioredoxin was measured by mass spectrometry at these pH values, demonstrating that the two binding sites were partially occupied and mutually exclusive. Cd(2+) binding at either site totally inhibited the thiol-disulfide transferase activity of Trx. The absence of Cd(2+) interaction detected for oxidized or alkylated Trx and the inhibition of the enzymatic activity of thioredoxin by Cd(2+) supported the role of Cys32 at the first site. The fluorescence profile of Cd(2+)-bound thioredoxin differed, however, from that of oxidized thioredoxin, indicating that Cd(2+) was not coordinated with Cys32 and Cys35. From FTIR spectroscopy, we inferred that the second site might involve Asp26, a buried residue that deprotonates at a rather high and unusual pK(a) for a carboxylate (7.5/9.2). The pK(a) of the two residues Cys32 and Asp26 have been shown to be interdependent [Chivers, T. P. (1997) Biochemistry36, 14985-14991]. A mechanism is proposed in which Cd(2+) binding at the solvent-accessible thiolate group of Cys32 induces a decrease of the pK(a) of Asp26 and its deprotonation. Conversely, interaction between the carboxylate group of Asp26 and Cd(2+) at a second binding site induces Cys32 deprotonation and thioredoxin inhibition, so that Cd(2+) inhibits thioredoxin activity not only by binding at the Cys32 but also by interacting with Asp26.

Stress induction and mitochondrial localization of Oxr1 proteins in yeast and humans

Reactive oxygen species (ROS) are critical molecules produced as a consequence of aerobic respiration. It is essential for cells to control the production and activity of such molecules in order to protect the genome and regulate cellular processes such as stress response and apoptosis. Mitochondria are the major source of ROS within the cell, and as a result, numerous proteins have evolved to prevent or repair oxidative damage in this organelle. The recently discovered OXR1 gene family represents a set of conserved eukaryotic genes. Previous studies of the yeast OXR1 gene indicate that it functions to protect cells from oxidative damage. In this report, we show that human and yeast OXR1 genes are induced by heat and oxidative stress and that their proteins localize to the mitochondria and function to protect against oxidative damage. We also demonstrate that mitochondrial localization is required for Oxr1 protein to prevent oxidative damage.

Effect of high glucose on gene expression in mesangial cells: upregulation of the thiol pathway is an adaptational response

Pathological alterations in glomerular mesangial cells play a critical role in the development of diabetic nephropathy, the leading cause of end-stage renal disease. Molecular mechanisms mediating such alterations, however, remain to be fully understood. The present study first examined the effect of high glucose on the mRNA expression profile in rat mesangial cells using cDNA microarray. Based on variation-weighted criteria and with a false discovery rate of 4.3%, 459 of 17,664 cDNA elements examined were found to be upregulated and 151 downregulated by exposure to 25 mM d-glucose for 5 days. A large number of differentially expressed genes belonged to several functional categories, indicating high glucose had a profound effect on mesangial cell proliferation, protein synthesis, energy metabolism, and, somewhat unexpectedly, protein sorting and the cytoskeleton. Interestingly, several thiol antioxidative genes (glutathione peroxidase 1, peroxiredoxin 6, and thioredoxin 2) were found by microarray and confirmed by real-time PCR to be upregulated by high glucose. These changes suggested that the oxidative stress known to be induced in mesangial cells by high glucose might be buffered by upregulation of the thiol antioxidative pathway. Upregulation of thiol antioxidative genes also occurred in high-glucose-treated human mesangial cells and in glomeruli isolated from rats after 1 wk of streptozotocin-induced diabetes, but not in human proximal tubule cells. High glucose slightly increased lipid peroxidation and decreased the amount of reduced thiols in rat and human mesangial cells. Disruption of the thiol antioxidative pathway by two different thiol-oxidizing agents resulted in a three- to fivefold increase in high-glucose-induced lipid peroxidation. In summary, the present study provided a global view of the short-term effect of high glucose on mesangial cells at the level of mRNA expression and identified the upregulation of the thiol antioxidative pathway as an adaptational response of mesangial cells to high glucose.

Enhancement by effectors and substrate nucleotides of R1-R2 interactions in Escherichia coli class Ia ribonucleotide reductase

Ribonucleotide reductases are a family of essential enzymes that catalyze the reduction of ribonucleotides to their corresponding deoxyribonucleotides and provide cells with precursors for DNA synthesis. The different classes of ribonucleotide reductase are distinguished based on quaternary structures and enzyme activation mechanisms, but the components harboring the active site region in each class are evolutionarily related. With a few exceptions, ribonucleotide reductases are allosterically regulated by nucleoside triphosphates (ATP and dNTPs). We have used the surface plasmon resonance technique to study how allosteric effects govern the strength of quaternary interactions in the class Ia ribonucleotide reductase from Escherichia coli, which like all class I enzymes has a tetrameric alpha(2) beta(2) structure. The component alpha(2)called R1 harbors the active site and two types of binding sites for allosteric effector nucleotides, whereas the beta(2) component called R2 harbors the tyrosyl radical necessary for catalysis. Our results show that only the known allosteric effector nucleotides, but not non-interacting nucleotides, promote a specific interaction between R1 and R2. Interestingly, the presence of substrate together with allosteric effector nucleotide strengthens the complex 2-3 times with a similar free energy change as the mutual allosteric effects of substrate and effector nucleotide binding to protein R1 in solution experiments. The dual allosteric effects of dATP as positive allosteric effector at low concentrations and as negative allosteric effector at high concentrations coincided with an almost 100-fold stronger R1-R2 interaction. Based on the experimental setup, we propose that the inhibition of enzyme activity in the E. coli class Ia enzyme occurs in a tight 1:1 complex of R1 and R2. Most intriguingly, we also discovered that thioredoxin, one of the physiological reductants of ribonucleotide reductases, enhances the R1-R2 interaction 4-fold.

Nano red elemental selenium has no size effect in the induction of seleno-enzymes in both cultured cells and mice

We previous reported that a nano red elemental selenium (Nano-Se) in the range from 20 approximately 60 nm had similar bioavailability to sodium selenite (BioFactors 15 (2001) 27). We recently found that Nano-Se with different size had marked difference in scavenging an array of free radicals in vitro, the smaller the particle, the better scavenging activity (Free Radic. Biol. Med. 35 (2003) 805). In order to examine whether there is a size effect of Nano-Se in the induction of Se-dependent enzymes, a range of Nano-Se (5 approximately 200 nm) have been prepared based on the control of elemental Se atom aggregation. The sizes of Nano-Se particles were inversely correlated with protein levels in the redox system of selenite and glutathione. Different sizes of red elemental Se were prepared by adding varying amount of bovine serum albumin (BSA). Three different sizes of Nano-Se (5 approximately 15 nm, 20 approximately 60 nm, and 80 approximately 200 nm) have been chosen for the comparison of biological activity in terms of the induction of seleno-enzyme activities. Results showed that there was no significant size effect of Nano-Se from 5 to 200 nm in the induction of glutathione peroxidase (GPx), phospholipid hydroperoxide glutathione peroxidase (PHGPx) and thioredoxin reductase-1 (TrxR-1) in human hepatoma HepG2 cells and the livers of mice.

Protein disulfide bond formation in the cytoplasm during oxidative stress

The majority of disulfide-linked cytosolic proteins are thought to be enzymes that transiently form disulfide bonds while catalyzing oxidation-reduction (redox) processes. Recent evidence indicates that reactive oxygen species can act as signaling molecules by promoting the formation of disulfide bonds within or between select redox-sensitive proteins. However, few studies have attempted to examine global changes in disulfide bond formation following reactive oxygen species exposure. Here we isolate and identify disulfide-bonded proteins (DSBP) in a mammalian neuronal cell line (HT22) exposed to various oxidative insults by sequential nonreducing/reducing two-dimensional SDS-PAGE combined with mass spectrometry. By using this strategy, several known cytosolic DSBP, such as peroxiredoxins, thioredoxin reductase, nucleoside-diphosphate kinase, and ribonucleotide-diphosphate reductase, were identified. Unexpectedly, a large number of previously unknown DSBP were also found, including those involved in molecular chaperoning, translation, glycolysis, cytoskeletal structure, cell growth, and signal transduction. Treatment of cells with a wide range of hydrogen peroxide concentrations either promoted or inhibited disulfide bonding of select DSBP in a concentration-dependent manner. Decreasing the ratio of reduced to oxidized glutathione also promoted select disulfide bond formation within proteins from cytoplasmic extracts. In addition, an epitope-tagged version of the molecular chaperone HSP70 forms mixed disulfides with both beta4-spectrin and adenomatous polyposis coli protein in the cytosol. Our findings indicate that disulfide bond formation within families of cytoplasmic proteins is dependent on the nature of the oxidative insult and may provide a common mechanism used to control multiple physiological processes.

Oxidative inhibition of human soluble catechol-O-methyltransferase

A common polymorphism in the human gene for catechol-O-methyltransferase results in replacement of Val-108 by Met in the soluble form of the protein (s-COMT) and has been linked to breast cancer and neuropsychiatric disorders. The 108M and 108V variants are reported to differ in their thermal stability, with 108M COMT losing catalytic activity more rapidly. Because human s-COMT contains seven cysteine residues and includes CXXC and CXXS motifs that are associated with thiol-disulfide redox reactions, we examined the effects of reducing and oxidizing conditions on the enzyme. In the absence of a reductant 108M s-COMT lost activity more rapidly than 108V, whereas in the presence of 4 mm dithiothreitol (DTT) we found no significant differences in the stability of the two variants at 37 degrees C. DTT also restored most of the activity that was lost upon incubation at 37 degrees C in the absence of DTT. Mass spectrometry showed that cysteines 188 and 191 formed an intramolecular disulfide bond when s-COMT was incubated with oxidized glutathione, whereas cysteines 69, 95, 157, and 173 formed protein-glutathione adducts. Replacing Cys-95 by serine protected 108M s-COMT against inactivation in the absence of a reductant; C33S and Cys-188 mutations had little effect, and C69S was destabilizing. The sequences surrounding the reactive cysteine residues of human s-COMT and other proteins that form glutathione adducts at identified sites all include Pro and/or Gly and most include a hydrogen-bonding residue, suggesting that glutathiolation at conserved sites plays a physiologically important role.

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.

Proteomic analysis of thioredoxin-targeted proteins in Escherichia coli

Thioredoxin, a ubiquitous and evolutionarily conserved protein, modulates the structure and activity of proteins involved in a spectrum of processes, such as gene expression, apoptosis, and the oxidative stress response. Here, we present a comprehensive analysis of the thioredoxin-linked Escherichia coli proteome by using tandem affinity purification and nanospray microcapillary tandem mass spectrometry. We have identified a total of 80 proteins associated with thioredoxin, implicating the involvement of thioredoxin in at least 26 distinct cellular processes that include transcription regulation, cell division, energy transduction, and several biosynthetic pathways. We also found a number of proteins associated with thioredoxin that either participate directly (SodA, HPI, and AhpC) or have key regulatory functions (Fur and AcnB) in the detoxification of the cell. Transcription factors NusG, OmpR, and RcsB, not considered to be under redox control, are also associated with thioredoxin.

Up-regulation of the redox mediators thioredoxin and apurinic/apyrimidinic excision (APE)/Ref-1 in hypoxic microregions of invasive cervical carcinomas, mapped using multispectral, wide-field fluorescence image analysis

Thioredoxin and apurinic/apyrimidinic excision (APE)/ref-1 are important redox mediators in biochemical pathways that promote cell survival under adverse conditions including hypoxia and oxidative stress. For example, elevated levels occur surrounding vascular infarcts and protect from reperfusion injury. Because elevated thioredoxin or APE/ref-1 is also associated with resistance to certain forms of cancer treatment, we examined their tissue distribution in a series of 110 cervical carcinoma biopsies. Analysis was done using a quadruple fluorescence imaging technique, incorporating carbonic anhydrase IX (CAIX) immunofluorescence to outline hypoxic microregions and 4',6-diamidino-2-phenylindole to localize nuclear staining of thioredoxin and APE/ref-1. A scanning autostage was used to image the entire tissue section. Thioredoxin and APE/ref-1 levels were expressed as the average pixel brightness in tumor tissue, subdivided based on CAIX and 4',6-diamidino-2-phenylindole staining. Results showed that the nuclear and cytoplasmic levels of thioredoxin were similar, whereas APE/ref-1 expression was greater in nuclei. Neither of these markers was predictive of outcome in this series of patients treated with radical radiotherapy. Both proteins showed highly significant elevations in CAIX-positive regions compared to CAIX-negative regions, and there was a nonsignificant trend for this effect to be greater in adenocarcinomas compared to squamous cell carcinomas. Levels of APE/ref-1 decreased with increasing tumor grade, but the expression was similar in CAIX-positive regions of poorly differentiated tumors compared to moderately or well-differentiated tumors. Elevated expression of thioredoxin and APE/ref-1 might promote cancer cell survival in hypoxic microenvironments of cervical carcinomas.

Mechanism-based inactivation of thioredoxin reductase from Plasmodium falciparum by Mannich bases. Implication for cytotoxicity

Thioredoxin reductase (TrxR) is the homodimeric flavoenzyme that catalyzes reduction of thioredoxin disulfide (Trx). For Plasmodium falciparum, a causative agent of tropical malaria, TrxR is an essential protein which has been validated as a drug target. The high-throughput screening of 350000 compounds has identified Mannich bases as a new class of TrxR mechanism-based inhibitors. During catalysis, TrxR conducts reducing equivalents from the NADPH-reduced flavin to Trx via the two redox-active cysteine pairs, Cys88-Cys93 and Cys535'-Cys540', referred to as N-terminal and C-terminal cysteine pairs. The structures of unsaturated Mannich bases suggested that they could act as bisalkylating agents leading to a macrocycle that involves both C-terminal cysteines of TrxR. To confirm this hypothesis, different Mannich bases possessing one or two electrophilic centers were synthesized and first studied in detail using glutathione as a model thiol. Michael addition of glutathione to the double bond of an unsaturated Mannich base (3a) occurs readily at physiological pH. Elimination of the amino group, promoted by base-catalyzed enolization of the ketone, is followed by addition of a second nucleophile. The intermediate formed in this reaction is an alpha,beta-unsaturated ketone that can react rapidly with a second thiol. When studying TrxR as a target of Mannich bases, we took advantage of the fact that the charge-transfer complex formed between the thiolate of Cys88 and the flavin in the reduced enzyme can be observed spectroscopically. The data show that it is the C-terminal Cys 535'-Cys540' pair rather than the N-terminal Cys88-Cys93 pair that is modified by the inhibitor. Although alkylated TrxR is unable to turn over its natural substrate Trx, it can reduce low M(r) electron acceptors such as methyl methanethiolsulfonate by using its unmodified N-terminal thiols. On the basis of results with chemically distinct Mannich bases, a detailed mechanism for the inactivation of TrxR is proposed.

Evidence for intriguingly complex transcription of human thioredoxin reductase 1

Human thioredoxin reductase 1 (TrxR1, the TXNRD1 gene product) is a ubiquitously expressed selenoprotein with many important redox regulatory functions. In this study, we have further characterized the recently identified core promoter region of TXNRD1. One critical Sp1/Sp3 site was found to be important in A549 and HeLa cells, whereas another Sp1/Sp3 site and one Oct1 site bound transcription factors but were, nonetheless, dispensable for transcription. We also experimentally identified several 5'-region TXNRD1 transcript variants using 5'-RACE with cDNA derived from different tissues, and we analyzed all available TXNRD1-derived EST sequences. The results show that the core promoter governs transcription of the clear majority of TXNRD1 transcripts but also that alternative promoters may be activated under rare conditions or in specific cell types. Furthermore, extensive alternative splicing occured in the 5' region of TXNRD1. In total, 21 different transcripts were identified, potentially encoding five isoforms of TrxR1 carrying alternative N-terminal domains. One isoform encompassed a glutaredoxin domain, whereas another encoded a predicted mitochondrial localization signal. These results reveal that the human thioredoxin system is intriguingly complex. Cell-specific transcription of the TXNRD1 gene encoding different isoforms of TrxR1 must be taken into account to fully understand the functions of the human thioredoxin system.

Comparison of tumor marker CA 242 with CA 19-9 and carcinoembryonic antigen (CEA) in pancreatic cancer

BACKGROUND/AIMS

Although there are a variety of tumor markers used for diagnosis of pancreatic carcinoma, the sensitivity and specificity of those markers have not yet reached an ideal level. The aim of this study was to compare the diagnostic value of CA 242 with CA 19-9 and CEA in the patients with pancreatic cancer.

METHODOLOGY

Serum CA 242, CA 19-9 and CEA levels were determined in 135 subjects in the following groups: Pancreatic cancer (n = 40), cholangiocellular carcinoma (n = 15), hepatocellular carcinoma (n = 10), cirrhosis (n = 7), chronic active hepatitis (n = 7), choledochal stone (n = 12), chronic pancreatitis (n = 9), acute pancreatitis (n = 6), and healthy controls (n = 29).

RESULTS

An elevated serum CA 242 concentration (> 20 U/mL) was found in 30 out of 40 (70%) (mean; 2163 +/- 838 U/mL) patients with pancreas cancer, in 11 out of 15 patients with cholangiocellular carcinoma (93.3%) (mean 916 +/- 529 U/mL), in none of patients with hepatocellular carcinoma and healthy controls. Slightly elevated CA 242 concentration was found in 6 out of 41 patients with benign hepatobiliary and pancreatic disease (range 0.4-97.8 U/mL) (1 acute pancreatitis, 2 chronic pancreatitis, 1 cirrhosis, 2 choledochal stone). Mean serum CA 242, CA 19-9 and CEA levels of the pancreas cancer group were significantly higher than those of the other groups except the cholangiocellular carcinoma group. There was no significant difference between the stage of pancreas cancer regarding mean serum CA 242, CA 19-9 and CEA level. There was positive correlation between serum CA 242 and CA 19-9 level. In the pancreas cancer, the sensitivity of CA 242, CA 19-9 and CEA was 75%, 80%, 40%, respectively and the specificity of those markers was 85.5%, 67.5% and 73%, respectively.

CONCLUSIONS

In conclusion, the advantage of CA 242 compared to CA 19-9 is that its specificity is higher than that of CA 19-9 in the diagnosis of pancreas cancer.

Cystine uptake prevents production of hydrogen peroxide by Lactobacillus fermentum BR11

BspA is an abundant surface protein from Lactobacillus fermentum BR11, and is required for normal cystine uptake. In previous studies, a mutant strain deficient in BspA (L. fermentum PNG201) was found to be sensitive to oxidative stress. In this study, the biochemical basis for this was explored. It was found that under aerobic batch culture conditions in de Mann-Rogosa-Sharpe medium, both L. fermentum BR11 and PNG201 entered stationary phase due to hydrogen peroxide accumulation. However, this took place at a lower optical density for PNG201 than for BR11. Measurements of hydrogen peroxide levels revealed that the BspA mutant strain overproduces this compound. Addition of 6 mM cystine to aerobic cultures was found to prevent hydrogen peroxide production by both the BR11 and PNG201 strains, but lower cystine concentrations depressed hydrogen peroxide production in BR11 more efficiently than in PNG201. Each mole of cystine was able to prevent the production of several moles of hydrogen peroxide by L. fermentum BR11, suggesting that hydrogen peroxide breakdown is dependent upon a thiol that cycles between reduced and oxidized states. It was concluded that peroxide breakdown by L. fermentum BR11 is dependent upon exogenous cystine. It is most probable that the imported L-cystine is catabolized by a cystathionine lyase and then converted into a thiol reductant for a peroxidase.

An evolutionarily conserved gene required for proper microtubule architecture in Caenorhabditis elegans

Microtubules are involved in many cellular events during the cell cycle and also in a variety of early embryonic developmental processes. Their architecture and properties change dramatically during the cell cycle and are properly regulated. However, these regulatory mechanisms have not been fully elucidated. C05D11.3 gene of Caenorhabditis elegans encodes a low molecular weight protein that is evolutionarily conserved from yeasts to mammals. A mouse homolog of the C05D11.3 product, APACD (ATP binding protein associated with cell differentiation), contains a thioredoxin-like domain and P-loop, and is present in both the nucleus and the cytoplasm, showing often localization to centrosomes and midbody. In C. elegans, C05D11.3 is expressed throughout development with higher levels of expression in most cells of the nervous system and in vulva. C05D11.3 RNAi-treated embryos show apparent defects in pronuclear migration or nuclear-centrosome rotation, and exhibit little astral microtubules and defective small spindles. These results indicate that C05D11.3, an evolutionarily conserved gene, is essential for proper microtubule organization and function in C. elegans. This gene family may be a conserved regulator of microtubule dynamics and function.

Thioredoxin is associated with proliferation, p53 expression and negative estrogen and progesterone receptor status in breast carcinoma

We investigated the expression of thioredoxin and thioredoxin reductase in a large set of breast invasive and in situ carcinomas by immunohistochemistry. Additionally, NF-kappa B, p53 and proliferating cell nuclear antigen (PCNA) expression was studied. Thioredoxin and thioredoxin reductase expression was located in both cytoplasmic and nuclear compartments of the cell. Cytoplasmic thioredoxin positivity was found in 67 % and nuclear in 59 % of the cases, while thioredoxin reductase was found in 55 % and 6 % of cases, respectively. Ductal carcinomas showed stronger cytoplasmic thioredoxin immunoreactivity than lobular ones. Nuclear thioredoxin positivity was more often found in in situ lesions, and lobular carcinomas were more often negative than ductal ones. Both cytoplasmic and nuclear thioredoxin-positive cases had a high proliferation measured by PCNA staining. Positive nuclear immunostaining was associated with negative estrogen and progesterone receptor status. Cases with high p53 expression showed significantly higher nuclear thioredoxin positivity, but lower thioredoxin reductase positivity. Whilst thioredoxin or thioredoxin reductase was not associated with patient survival, cases showing both cytoplasmic and nuclear thioredoxin reductase-positive tumours had a shorter disease-free interval than those with negative immunostaining.

Thioredoxin system in premature and newborn biology

Thioredoxin is an important redox protein that is ubiquitously distributed. Thioredoxin exists in dynamic equilibrium between the oxidized and reduced forms, making it an ideal redox-regulatory protein. Thioredoxin, together with thioredoxin reductase and peroxiredoxins, forms a complete redox system that is similar to the glutathione system, but with distinct and divergent functions. This review provides a brief general summary of the thioredoxin system with particular emphasis on its role in premature birth and newborn physiology and disease states. Although extensive studies have examined the role of the thioredoxin system in antioxidant defense, cell proliferation, and signal transduction, further studies are needed to understand its role in embryogenesis and development. Such studies will facilitate our understanding of how thioredoxin may modulate newborn diseases via redox regulation.

Regulation of the mammalian selenoprotein thioredoxin reductase 1 in relation to cellular phenotype, growth, and signaling events

Reactive oxygen species (ROS) are generated as toxic by-products of aerobic metabolism, but are also essential biomolecules in cell signaling. The thioredoxin (Trx) system is a major enzymatic system modulating ROS levels and is important for redox regulation of cellular function. It consists of Trx and thioredoxin reductase (TrxR), which reduces Trx using NADPH. Most, if not all, of the functions of Trx depend on the activity of TrxR. Mammalian TrxR enzymes are selenoproteins with broad substrate specificities, and alteration of cytosolic TrxR1 expression and activity is likely to be an important determinant for the control of cellular redox regulation. TrxR1 activity in cells seems to be modulated by an intricate interplay, involving a housekeeping type promoter in combination with alternative splice variants and transcriptional start sites, posttranscriptional regulation through AU-rich elements, inactivation by electrophilic agents and by itself modulating the effects of several key signaling molecules. TrxR1 activity is also intimately linked with several aspects of selenium metabolism, and hence selenoprotein function in general. Here, we summarize the current knowledge of these different levels of TrxR1 regulation in diverse cell types and in response to growth and signaling events.

The mammalian testis-specific thioredoxin system

Redox control of cell physiology is one of the most important regulatory mechanisms in all living organisms. The thioredoxin system, composed of thioredoxin and thioredoxin reductase, has emerged as a key player in cellular redox-mediated reactions. For many years, only one thioredoxin system had been described in higher organisms, ubiquitously expressed in the cytoplasm of eukaryotic cells. However, during the last decade, we and others have identified and characterized novel thioredoxin systems with unique properties, such as organelle-specific localization in mitochondria or endoplasmic reticulum, tissue-specific distribution mostly in the testis, and features novel for thioredoxins, such as microtubule-binding properties. In this review, we will focus on the mammalian testis-specific thioredoxin system that comprises three thioredoxins exclusively expressed in spermatids (named Sptrx-1, Sptrx-2, and Sptrx-3) and an additional thioredoxin highly expressed in testis, but also present in lung and other ciliated tissues (Txl-2). The implications of these findings in the context of male fertility and testicular cancer, as well as evolutionary aspects, will be discussed.

The sufR gene (sll0088 in Synechocystis sp. strain PCC 6803) functions as a repressor of the sufBCDS operon in iron-sulfur cluster biogenesis in cyanobacteria

The suf operon is composed of four genes (sufB, sufC, sufD, and sufS) and is highly conserved in the genomes of cyanobacteria. Open reading frame sll0088 in Synechocystis sp. strain PCC 6803 is located near the 5' end of the suf operon but is transcribed in the direction opposite that of the suf operon. We previously reported the isolation of two independent suppressor strains of C14S(PsaC) that mapped to sll0088 and restored photoautotrophic growth. The protein encoded by sll0088 has two significant features: (i) a DNA-binding domain near the N terminus and (ii) four highly conserved cysteine residues near the C terminus. The protein has high sequence similarity to transcription regulatory proteins with a conserved DNA-binding domain and can be classified in the DeoR family of helix-loop-helix proteins. The protein falls into a further subclass that contains a C-X(12)-C-X(13)-C-X(14)-C motif near the C terminus, which may represent a metal-binding site. The expressed Sll0088 protein harbored an iron-sulfur cluster as shown by optical and electron paramagnetic resonance spectroscopy. Compared to the wild type, expression levels of the sufBCDS genes were elevated when cells were grown under conditions of oxidative and iron stress and were even higher in a null mutant of Synechococcus sp. strain PCC 7002 in which the sll0088 homolog was insertionally inactivated. In agreement with the proposed role of the sufBCDS genes in iron metabolism, the growth rate of the null mutant was significantly higher than that of the wild type under iron-limiting conditions. We propose that the protein encoded by sll0088 is a transcriptional repressor of the suf operon, and we name the gene sufR.

Transcriptional regulation of the Staphylococcus aureus thioredoxin and thioredoxin reductase genes in response to oxygen and disulfide stress

In this report we describe the cloning, organization, and promoter analysis of the Staphylococcus aureus thioredoxin (trxA) and thioredoxin reductase (trxB) genes and their transcription in response to changes in oxygen concentration and to oxidative stress compounds. Northern analysis showed that the S. aureus trxA and trxB genes were transcribed equally well in aerobic and anaerobic conditions. Several oxidative stress compounds were found to rapidly induce transcription of the trxA and trxB genes. The most pronounced effects were seen with diamide, a thiol-specific oxidant that promotes disulfide bond formation; menadione, a redox cycling agent; and tau-butyl hydroperoxide, an organic peroxide. In each case the induction was independent of the general stress sigma factor sigma(B). These studies show that the S. aureus trxA and trxB genes are upregulated following exposure to these oxidative stress agents, resulting in increased disulfide bond formation. In contrast, no effect of hydrogen peroxide on induction of the trxA and trxB genes was seen. We also show that the S. aureus thioredoxin reductase appears to be essential for growth. This observation, coupled with structural differences between the bacterial and mammalian thioredoxin reductases, suggests that it may serve as a target for the development of new antimicrobials.

Preconditioning potentiates redox signaling and converts death signal into survival signal

Reactive oxygen species (ROS) play a crucial role in the pathophysiology of ischemic heart disease by causing cardiac dysfunction and cell death. Several redox-sensitive anti- and pro-apoptotic transcription factors including NFkappaB and AP-1 progressively and steadily increase in the heart as a function of the duration of ischemia and reperfusion. When the heart is preconditioned to ischemic stress by repeated short-term ischemia and reperfusion, NFkappaB remains high while AP-1 is lowered to almost baseline value. The anti-apoptotic gene Bcl-2 is downregulated in the ischemic/reperfused heart, while it is upregulated in the adapted myocardium. Cardioprotective abilities of the preconditioning are abolished when heart is pre-perfused with N-acetyl cysteine, a scavenger for ROS, suggesting the role of ROS in redox signaling. Mammalian heart is protected by several defense systems which include among others, redox-regulated protein, thioredoxin. Reperfusion of ischemic myocardium results in the downregulation of thioredoxin 1 (Trx 1) expression, which was upregulated in the preconditioned myocardium. The increased expression of Trx 1 is completely blocked with an inhibitor of Trx 1, CDDP, which also abolished cardioprotection afforded by ischemic adaptation. The cardioprotective role of Trx 1 is confirmed further with transgenic mouse hearts overexpressing Trx 1. The Trx 1 mouse hearts displayed significantly improved post-ischemic ventricular recovery and reduced myocardial infarct size and apoptosis as compared to the corresponding wild-type mouse hearts. Taken together, preconditioning appears to potentiate redox signaling, which converts the "death signal" into "survival signal."

Thioredoxin, a regulator of gene expression

Cancer cells have high levels of thioredoxin (Trx) and of glyceraldehyde 3-phosphate dehydrogenase (GAPDH). Cells from patients with the cancer-prone disease Fanconi anemia (FA) exhibit reduced Trx levels. We found the activity of GAPDH to correlate directly with the endogenous Trx content and mRNA transcripts for GAPDH and TRx reduced in FA cells. The treatment of cells with reduced human Trx stimulated the synthesis of GAPDH mRNA. Similarly, the transfection of cells with an expression plasmid for Trx increased GAPDH mRNA synthesis. Trx treatment of cells and subsequent analysis of the differential gene expression by human cDNA arrays containing about 50 000 different PCR products resulted in more than 300 up- or downregulated genes. Two representative genes, GAPDH and IkappaBalpha/MAD-3, were further investigated to confirm their stimulation by Trx. Trx besides being the major carrier of redox potential of cells is also a regulator of gene expression on the transcriptional level. By regulation via Trx, cells are able to adapt to the prevailing redox conditions. These findings also enlighten the pathophysiology of FA in the respect that the characteristic diminution of Trx that results in the dysregulation of gene expression is a basis for the major symptoms of this disease.

Expression of the thioredoxin system in interstitial lung disease

The thioredoxin system containing thioredoxin (Trx) and thioredoxin reductase (TrxR) has profound effects on cell proliferation and protection against exogenous oxidants. The significance of the Trx system in human lung and lung diseases is, however, largely unresolved. Altogether, 66 specimens of human lung were investigated by immunohistochemistry for their expression of Trx and TrxR. The diseases included interstitial pneumonias such as usual interstitial pneumonia (UIP), desquamative interstitial pneumonia (DIP), and UIP associated with collagen vascular diseases (CVD-ILD), and granulomatous diseases such as sarcoidosis and allergic alveolitis. The ultrastructural localization of Trx and TrxR was analysed by immunoelectron microscopy. In healthy lung, Trx and TrxR were expressed in bronchial epithelium and alveolar macrophages. Trx and TrxR were highly concentrated in areas of metaplastic epithelium in UIP and in alveolar macrophages in DIP, though fibrotic areas in UIP were mainly negative. The expression of both enzymes was clearly weaker in CVD-ILD than in UIP. Granulomas of sarcoidosis showed moderate to intense Trx immunoreactivity. Ultrastructurally, Trx and TrxR were expressed diffusely in the cytosolic compartment and plasma membrane of metaplastic type II pneumocytes, macrophages, and bronchial epithelial cells. This study highlights the importance of Trx and TrxR in primary defence in bronchial epithelium, alveolar epithelium, and macrophages in human lung, but also indicates that elevated expression of these proteins may serve as markers of ongoing cell regeneration and inflammation.

Identification and Characterization of TRP14, a Thioredoxin-related Protein of 14 kDa

We have identified and characterized a 14-kDa human thioredoxin (Trx)-related protein designated TRP14. This cytosolic protein was expressed in all tissues and cell types examined, generally in smaller amounts than Trx1. Although TRP14 contains five cysteines, only the two Cys residues in its WCPDC motif were exposed and redox sensitive. Unlike Trx1, which was an equally good substrate for both Trx reductase 1 (TrxR1) and TrxR2, oxidized TRP14 was reduced by TrxR1 but not by TrxR2. Biochemical characterization of TRP14 suggested that, like Trx1, TRP14 is a disulfide reductase; its active site cysteine is sufficiently nucleophilic with the pK(a) value of 6.1; and its redox potential (-257 mV) is similar to those of other cellular thiol reductants. However, although TRP14 reduced small disulfide-containing peptides, it did not reduce the disulfides of known Trx1 substrates, ribonucleotide reductase, peroxiredoxin, and methionine sulfoxide reductase. These results suggest that TRP14 and Trx1 might act on distinct substrate proteins.

Effects of dietary selenium on glutathione peroxidase and thioredoxin reductase activity and recovery from cardiac ischemia-reperfusion

Glutathione peroxidase and thioredoxin reductase are selenocysteine-dependent enzymes that protect against oxidative injury. This study examined the effects of dietary selenium on the activity of these two enzymes in rats, and investigated the ability of selenium to modulate myocardial function post ischemia-reperfusion. Male wistar rats were fed diets containing 0, 50, 240 and 1000 microg/kg sodium selenite for 5 weeks. Langendorff perfused hearts isolated from these rats were subjected to 22.5 min global ischemia and 45 min reperfusion, with functional recovery assessed. Liver samples were collected at the time of sacrifice, and heart and liver tissues assayed for thioredoxin reductase and glutathione peroxidase activity. Selenium deficiency reduced the activity of both glutathione peroxidase and thioredoxin reductase systemically. Hearts from selenium deficient animals were more susceptible to ischemia-reperfusion injury when compared to normal controls (38% recovery of rate pressure product (RPP) vs. 47% recovery of RPP). Selenium supplementation increased the endogenous activity of thioredoxin reductase and glutathione peroxidase and resulted in improved recovery of cardiac function post ischemia reperfusion (57% recovery of RPP). Endogenous activity of glutathione peroxidase and thioredoxin reductase is dependent on an adequate supply of the micronutrient selenium. Reduced activity of these antioxidant enzymes is associated with significant reductions in myocardial function post ischemia-reperfusion.

The role of oxidative stress in chronic obstructive pulmonary disease

Tobacco smoke is the number one risk factor for chronic obstructive pulmonary disease (COPD) and contains a high concentration of oxidants. The lung has a high concentration of antioxidants and antioxidant enzymes; however, COPD patients show evidence of increased oxidative stress suggesting that endogenous antioxidants may be insufficient to prevent oxidative damage from cigarette smoke. The consequences of increased oxidative stress in the lung include increased transcription of inflammatory genes, increased protease activity, and increased mucus secretion. Oxidative stress is often associated with impaired skeletal muscle function and may be one of the causes of glucocorticoid resistance. While current pharmacologic approaches to the treatment of chronic obstructive pulmonary disease do not commonly include antioxidants, preclinical studies involving animal models suggest that antioxidant superoxide dismutase mimetics offer a potential new therapeutic approach to the prevention and treatment of chronic obstructive pulmonary disease.

Flavoprotein Disulfide Reductases: Advances in Chemistry and Function

The flavoprotein disulfide reductases represent a family of enzymes that show high sequence and structural homology. They catalyze the pyridine-nucleotide-dependent reduction of a variety of substrates, including disulfide-bonded substrates (lipoamide dehydrogenase, glutathione reductase and functional homologues, thioredoxin reductase, and alkylhydroperoxide reductase), mercuric ion (mercuric ion reductase), hydrogen peroxide (NADH peroxidase), molecular oxygen (NADH oxidase), and the reductive cleavage of a carbonyl-activated carbon-sulfur bond followed by carboxylation (2-ketopropyl-coenzyme-M carboxylase?oxidoreductase). They use at least one nonflavin redox center to transfer electrons from reduced pyridine nucleotide to their substrate through flavin adenine dinucleotide. The nature of the nonflavin redox center located adjacent to the flavin varies and three types have been identified: an enzymic disulfide (most commonly), an enzymic cysteine sulfenic acid (NADH peroxidase and NADH oxidase), and a mixed Cys-S-S-CoA disulfide (coenzyme A disulfide reductase). Selection of the particular nonflavin redox center and utilization of a second, or even a third, nonflavin redox center in some cases presumably represents the most efficient strategy for reduction of the individual substrate.

Oxidative stress in severe pulmonary hypertension

Severe pulmonary hypertension (PH) occurs in a primary or "unexplained" form and in a group of secondary forms associated with a number of diseases. Because the lung tissue from patients with severe PH demonstrates complex vascular lesions, which contain inflammatory cells, we wondered whether the lung tissue from patients with severe PH was "under oxidative stress." We used immunohistochemistry to localize nitrotyrosine and 8-hydroxy guanosine in the lung tissue sections from patients with primary and secondary PH. In some lung tissue extracts, the eicosanoid metabolites 5-oxo-eicosatetraenoic acid, leukotriene B4 5-hydroxyeicosatetraenoic acid (HETE), 12-HETE, and 15-HETE were measured using mass spectroscopy, and superoxide dismutase amount and activity were measured. Nitrotyrosine expression was ubiquitous in all PH lungs, and 5-oxo-eicosatetraenoic acid and HETE levels were elevated in the lungs of patients with severe PH but not in those lungs that were from the patients with severe PH treated chronically with prostacyclin. We conclude that indeed the lungs from patients with severe PH are under oxidative stress and that chronic prostacyclin infusion has an antiinflammatory effect on the lung tissue.

Thioredoxin reductase from the malaria mosquito Anopheles gambiae

The mosquito, Anopheles gambiae, is an important vector of Plasmodium falciparum malaria. Full genome analysis revealed that, as in Drosophila melanogaster, the enzyme glutathione reductase is absent in A. gambiae and functionally substituted by the thioredoxin system. The key enzyme of this system is thioredoxin reductase-1, a homodimeric FAD-containing protein of 55.3 kDa per subunit, which catalyses the reaction NADPH + H+ + thioredoxin disulfide-->NADP+ + thioredoxin dithiol. The A. gambiae trxr gene is located on chromosome X as a single copy; it represents three splice variants coding for two cytosolic and one mitochondrial variant. The predominant isoform, A. gambiae thioredoxin reductase-1, was recombinantly expressed in Escherichia coli and functionally compared with the wild-type enzyme isolated in a final yield of 1.4 U.ml(-1) of packed insect cells. In redox titrations, the substrate A. gambiae thioredoxin-1 (Km=8.5 microm, kcat=15.4 s(-1) at pH 7.4 and 25 degrees C) was unable to oxidize NADPH-reduced A. gambiae thioredoxin reductase-1 to the fully oxidized state. This indicates that, in contrast to other disulfide reductases, A. gambiae thioredoxin reductase-1 oscillates during catalysis between the four-electron reduced state and a two-electron reduced state. The thioredoxin reductases of the malaria system were compared. A. gambiae thioredoxin reductase-1 shares 52% and 45% sequence identity with its orthologues from humans and P. falciparum, respectively. A major difference among the three enzymes is the structure of the C-terminal redox centre, reflected in the varying resistance of catalytic intermediates to autoxidation. The relevant sequences of this centre are Thr-Cys-Cys-SerOH in A. gambiae thioredoxin reductase, Gly-Cys-selenocysteine-GlyOH in human thioredoxin reductase, and Cys-X-X-X-X-Cys-GlyOH in the P. falciparum enzyme. These differences offer an interesting approach to the design of species-specific inhibitors. Notably, A. gambiae thioredoxin reductase-1 is not a selenoenzyme but instead contains a highly unusual redox-active Cys-Cys sequence.

Human mitochondrial glutaredoxin reduces S-glutathionylated proteins with high affinity accepting electrons from either glutathione or thioredoxin reductase

Glutaredoxins catalyze glutathione-dependent thiol disulfide oxidoreductions via a GSH-binding site and active cysteines. Recently a second human glutaredoxin (Grx2), which is targeted to either mitochondria or the nucleus, was cloned. Grx2 contains the active site sequence CSYC, which is different from the conserved CPYC motif present in the cytosolic Grx1. Here we have compared the activity of Grx2 and Grx1 using glutathionylated substrates and active site mutants. The kinetic studies showed that Grx2 catalyzes the reduction of glutathionylated substrates with a lower rate but higher affinity compared with Grx1, resulting in almost identical catalytic efficiencies (k(cat)/K(m)). Permutation of the active site motifs of Grx1 and Grx2 revealed that the CSYC sequence of Grx2 is a prerequisite for its high affinity toward glutathionylated proteins, which comes at the price of lower k(cat). Furthermore Grx2 was a substrate for NADPH and thioredoxin reductase, which efficiently reduced both the active site disulfide and the GSH-glutaredoxin intermediate formed in the reduction of glutathionylated substrates. Using this novel electron donor pathway, Grx2 reduced low molecular weight disulfides such as CoA but with particular high efficiency glutathionylated substrates including GSSG. These results suggest an important role for Grx2 in protection and recovery from oxidative stress.

The amitochondriate eukaryote Trichomonas vaginalis contains a divergent thioredoxin-linked peroxiredoxin antioxidant system

Trichomonas is an amitochondriate parasitic protozoon specialized for an anaerobic lifestyle. Nevertheless, it is exposed to oxygen and is able to cope with the resultant oxidative stress. In the absence of glutathione, cysteine has been thought to be the major antioxidant. We now report that the parasite contains thioredoxin reductase, which functions together with thioredoxin and thioredoxin peroxidase to detoxify potentially damaging oxidants. Thioredoxin reductase and thioredoxin also reduce cystine and so may play a role in maintaining the cellular cysteine levels. The importance of the thioredoxin system as one of the major antioxidant defense mechanisms in Trichomonas was confirmed by showing that the parasite responds to environmental changes resulting in increased oxidative stress by up-regulating thioredoxin and thioredoxin peroxidases levels. Sequence data indicate that the thioredoxin reductase of Trichomonas differs fundamentally in structure from that of its human host and thus may represent a useful drug target. The protein is generally similar to thioredoxin reductases present in other lower eukaryotes, all of which probably originated through horizontal gene transfer from a prokaryote. The phylogenetic signal in thioredoxin peroxidase is weak, but evidence from trees suggests that this gene has been subject to repeated horizontal gene transfers from different prokaryotes to different eukaryotes. The data are thus consistent with the complexity hypothesis that predicts that the evolution of simple pathways such as the thioredoxin cascade are likely to be affected by horizontal gene transfer between species.

Absolute gene expression patterns of thioredoxin and glutaredoxin redox systems in mouse

This work provides the first absolute expression patterns of genes coding for all known components of both thioredoxin (Trx) and glutaredoxin (Grx) systems in mouse: Trx1, Trx2, Grx1, Grx2, TrxR1, TrxR2, thioredoxin/glutathione reductase, and glutathione reductase. We devised a novel assay that, combining the advantages of multiplex and real-time PCR, streamlines the quantitation of the actual mRNA copy numbers in whole-animal experiments. Quantitations reported establish differences among adult organs and embryonic stages, compare mRNA decay rates, explore the significance of alternative mRNA isoforms derived from TrxR1 and Grx2 genes, and examine the time-course expression upon superoxide stress promoted by paraquat. Collectively, these quantitations show: i) unique expression profiles for each transcript and mouse organ examined, yet with some general trends like the higher amounts of mRNA species coding for thioredoxins than those coding for the reductases that control their redox states and activities; ii) continuous expression during embryogenesis with outstanding up-regulations of Trx1 and TrxR1 mRNAs in specific temporal sequences; iii) drastic differences in mRNA stability, liver decay rates range from 2.8 h (thioredoxin/glutathione reductase) to >/= 35 h (Trx1 and Trx2), and directly correlate with mRNA steady-state values; iv) testis-specific differences in the amounts (relative to total isoforms) of transcripts yielding the mitochondrial Grx2a and 67-kDa TrxR1 variants; and v) coordinated up-regulation of TrxR1 and glutathione reductase mRNAs in response to superoxide stress in an organ-specific manner. Further insights into in vivo roles of these redox systems should be gained from more focused studies of the mechanisms underlying the vast differences reported here at the transcript level.

Cloning and developmental analysis of murid spermatid-specific thioredoxin-2 (SPTRX-2), a novel sperm fibrous sheath protein and autoantigen

Thioredoxins compose a growing family of proteins that participate in different cellular processes via redox-mediated reactions. We report here the cloning, developmental expression, and location of murid Sptrx-2. Mouse and rat SPTRX-2 proteins display a high homology to their human ortholog in the thioredoxin and NDP kinase domains, and the coding genes are located at syntenic positions. Northern blotting and in situ hybridization confirmed the testis-specific expression of murine Sptrx-2 mRNA, mostly in round spermatids. Immunohistochemical analysis of the 19 steps of rat spermiogenesis showed that SPTRX-2 expression becomes prominent in the cytoplasmic lobe of step 15-18 spermatids and diminishes in step 19 just before spermiation. However, in the spermatid tail, SPTRX-2 immunoreactivity increased from step 15 to 19 and was confined to the principal piece. By immunogold electron microscopy, SPTRX-2 was first detected scattered throughout the cytoplasm of the axoneme in step 14-15 spermatids, but began to be incorporated by step 16 into the fibrous sheath (FS). During steps 17-18, the labeling increased over the ribs and columns of the assembled FS. It peaked in step 19 and remained in the FS of epididymal spermatozoa. Immunoblots of isolated FS obtained from spermatozoa confirmed that SPTRX-2 is an integral component of the FS and a post-obstruction autoantigen in vasectomized rats. Our data indicate that SPTRX-2 incorporation into the FS lags well behind FS assembly, suggesting it is required during the final stages of sperm tail maturation in the testis and/or epididymis, where extensive disulfide bonding of FS proteins occurs.

Interactions of quinones with thioredoxin reductase: a challenge to the antioxidant role of the mammalian selenoprotein

Mammalian thioredoxin reductases (TrxR) are important selenium-dependent antioxidant enzymes. Quinones, a wide group of natural substances, human drugs, and environmental pollutants may act either as TrxR substrates or inhibitors. Here we systematically analyzed the interactions of TrxR with different classes of quinone compounds. We found that TrxR catalyzed mixed single- and two-electron reduction of quinones, involving both the selenium-containing motif and a second redox center, presumably FAD. Compared with other related pyridine nucleotide-disulfide oxidoreductases such as glutathione reductase or trypanothione reductase, the k(ca)(t)/K(m) value for quinone reduction by TrxR was about 1 order of magnitude higher, and it was not directly related to the one-electron reduction potential of the quinones. A number of quinones were reduced about as efficiently as the natural substrate thioredoxin. We show that TrxR mainly cycles between the four-electron reduced (EH(4)) and two-electron reduced (EH(2)) states in quinone reduction. The redox potential of the EH(2)/EH(4) couple of TrxR calculated according to the Haldane relationship with NADPH/NADP(+) was -0.294 V at pH 7.0. Antitumor aziridinylbenzoquinones and daunorubicin were poor substrates and almost inactive as reversible TrxR inhibitors. However, phenanthrene quinone was a potent inhibitor (approximate K(i) = 6.3 +/- 1 microm). As with other flavoenzymes, quinones could confer superoxide-producing NADPH oxidase activity to mammalian TrxR. A unique feature of this enzyme was, however, the fact that upon selenocysteine-targeted covalent modification, which inactivates its normal activity, reduction of some quinones was not affected, whereas that of others was severely impaired. We conclude that interactions with TrxR may play a considerable role in the complex mechanisms underlying the diverse biological effects of quinones.

Attenuation of nitrate tolerance and oxidative stress by an angiotensin II receptor blocker in patients with coronary spastic angina

BACKGROUND

Nitrates are widely used to treat coronary artery disease, but their therapeutic value is compromised by the rapid development of tolerance. Recently, the renin-angiotensin system has been suggested to play an important role in the development of nitrate tolerance.

METHODS AND RESULTS

Sixty-four patients with coronary spastic angina were investigated to clarify the effect of angiotensin II type 1 receptor blocker (ARB) therapy on nitrate tolerance. Transdermal nitroglycerin (10 mg/d) and an ARB (candesartan, 8 mg/d) were administered to 21 patients (GTN+ARB group) for 3 days, whereas transdermal nitroglycerin and placebo were administered to 19 patients (GTN group). Another 18 patients were treated with placebo skin patches and placebo tablets for 3 days (control group). The brachial artery response to incremental doses of intravenous nitroglycerin (0.01, 0.1, and 1.0 micro;g/kg) was measured by ultrasound before and after transdermal nitroglycerin therapy. Before treatment, the arterial diameter was increased by nitroglycerin injection in each group. After treatment, the increase of arterial diameter was significantly suppressed in the GTN group but not in the control or GTN+ARB groups. The plasma level of thioredoxin (a marker of oxidative stress) was increased in the GTN group after treatment (P<0.01) but not in the control or GTN+ARB groups.

CONCLUSIONS

An ARB suppressed the development of nitrate tolerance during transdermal nitroglycerin therapy. These results suggest that increased oxidative stress induced by activation of angiotensin II may play an important role in the development of nitrate tolerance.

The potentiation role of hepatopoietin on activator protein-1 is dependent on its sulfhydryl oxidase activity

Hepatopoietin (HPO) is a novel hepatotrophic growth factor that stimulates hepatocyte proliferation by two pathways. In the first, intracellular HPO specifically modulates the activator protein-1 (AP-1) pathway through JAB1 (Jun activation domain-binding protein 1), whereas in the second, extracellular HPO triggers the mitogen-activated protein kinase pathway by binding its specific receptor on the cell surface. In this report we demonstrate that HPO is a flavin-linked sulfhydryl oxidase, and the invariant CXXC (Cys-Xaa-Xaa-Cys) motif in HPO is essential for the enzyme activity of HPO but not for its dimerization nor for its binding ability with JAB1. Two intramolecular disulfides were identified in HPO by mass spectrometry, one of which is formed by the redox CXXC cysteine residues. HPO site-directed mutants (Cys/Ser) at active sites, which lost sulfhydryl oxidase activity, could not increase c-Jun phosphorylation and failed to potentiate JAB1-mediated AP-1 activation. However, the mutants still have mitogenic stimulation and mitogen-activated protein kinase activation effects on HepG2 cells. Thus, it can be concluded that the potentiation role of HPO on AP-1 is dependent on its sulfhydryl oxidase activity.

Variability of antioxidant-related gene expression in the airway epithelium of cigarette smokers

Cigarette smoking is the major risk factor for developing chronic bronchitis, yet only 15-20% of smokers develop this disorder. Because oxidants are the major mechanism of smoking-induced airway damage, we hypothesized that smoking is associated with upregulation of various antioxidant-related genes in the airway epithelium, but the magnitude of the response shows high inter-individual variability. Microarray analysis was used to assess levels of expression of 44 antioxidant-related genes in four categories (catalase/superoxide dismutase family; glutathione metabolism; redox balance; and pentose phosphate cycle) in bronchoscopy-obtained airway epithelium of matched cohorts (13 current smokers, 9 nonsmokers), none of whom had lung disease. There was minimal variation in gene expression levels within the same individual (right versus left lung or over time), but significant upregulation of 16/44 antioxidant-related genes in smoker epithelium compared with nonsmokers. Subgroups of smokers were identified with clusters of expression levels of antioxidant-related genes. We propose that the antioxidant-related genes demonstrating the most variability in the level of expression in smokers may be useful genetic markers in epidemiologic studies assessing susceptibility to smoking-induced chronic bronchitis.

Redox regulation in the lens

The high content of glutathione (GSH) in the lens is believed to protect thiols in structural proteins and enzymes for proper biological functions. The lens has both biosynthetic and regenerating systems for GSH to maintain its large pool size. However, ageing lenses or lenses under oxidative stress show an extensively diminished size of GSH pool with some protein thiols being S-thiolated by oxidized non-protein thiols to form protein-thiol mixed disulfides, either as protein-S-S-glutathione (PSSG) or protein-S-S-cysteine (PSSC) or protein-S-S-gamma-glutamylcysteine. It was shown in an H(2)O(2)-induced cataract model that PSSG formation precedes a cascade of events before cataract formation, starting with protein disulfide crosslinks, protein solubility loss and high molecular weight aggregation. Furthermore, this early oxidative damage in protein thiols can be spontaneously reversed in H(2)O(2) pretreated lenses if the oxidant is removed in time. This dethiolation process appears to have mediated through a redox-regulating enzyme, thioltransferase (TTase), which is ubiquitously present in microbial, plant and animal tissues, including the lens. The GSH-dependent, low molecular weight (11.8 kDa) cytosolic enzyme plays an important role in oxidative defense and can modulate key metabolic enzymes in the glycolytic pathway. The enzyme repairs oxidatively damaged proteins/enzymes through its unique catalytic site with a vicinal cysteine moiety, which can specifically dethiolate protein-S-S-glutathione and restore protein free SH groups for proper enzymatic or protein functions. Most importantly, it has been demonstrated that thioltransferase has a remarkable resistance to oxidation (H(2)O(2)) in cultured human and rabbit lens epithelial cells under oxidative stress conditions when other oxidation defense systems of GSH peroxidase and GSH reductase are severely inactivated. A second repair enzyme, thioredoxin (TRx), which is NADPH-dependent, is widely found in many lower and higher life forms of life. It can dethiolate protein disulfides and thus is an extremely important regulator for redox homeostasis in the cells. Thioredoxin has been recently found in the lens and has been shown to participate in the repair process of oxidatively damaged lens proteins/enzymes. These two enzymes may work synergistically to regulate and repair thiols in lens proteins and enzymes, keeping a balanced redox potential to maintain the function of the lens.

Adenoviral transfection of hepatocytes with the thioredoxin gene confers protection against apoptosis and necrosis

A recombinant adenovirus vector containing the human thioredoxin (TRX) gene was constructed using the Cre-loxP recombination system and used to transfect rat hepatocytes with very high efficiency. The TRX gene was expressed in a dose-dependent manner and significantly modulated rat cellular functions. The TRX gene conferred resistance to oxidative stress, such as hydrogen peroxide treatment, on the host hepatocytes. FACS analysis of DNA fragmentation showed that the TRX gene suppressed hepatocyte apoptosis. It also significantly extended the life span of hepatocytes cultured conventionally on polystyrene plates. Liver-specific functions were maintained in the viability-modulated hepatocytes. Moreover, TRX expression did not affect hepatocyte spheroid formation and it extensively suppressed necrosis in the internal cells. Thus, the transfection of hepatocytes with the TRX gene successfully confers global maintenance of liver functions. These findings provide important information for the development of bioartificial liver support systems and gene therapy for liver diseases.

Immunohistochemical determination of thioredoxin and glutaredoxin distribution in the human cervix, and possible relation to cervical ripening

Thioredoxin (Trx) and glutaredoxin (Grx) are dithiol redox enzymes, catalyzing general thiol-disulfide oxidoreductions apart from being hydrogen donors for ribonucleotide reductase, an enzyme essential for DNA synthesis. In mammals, isoenzymes of Trx and Grx are found in the cytoplasm (Trx1 and Grx1) or in mitochondria (Trx2 and Grx2). Trx and Grx play a role in cellular defence against oxidative stress and in redox regulation of cellular function. The localization and levels of human Trx1 and human Grx1 have been determined in the human cervix by immunohistochemistry and image analysis. Cervical biopsies were obtained from five non-pregnant, five term pregnant and five postpartum women. The levels of both Trx1 and Grx1 were increased in the nuclei (after translocation from the cytoplasm) of stromal cells in cervices from the term pregnant group as compared to the non-pregnant group, but the levels in the postpartum group did not differ significantly from those of the other two groups. These results are in agreement with our previous data on the mRNA expression of these two redox enzymes. The increased levels of the redox enzymes in term pregnancy suggest that they can be regulating factors involved in the process of cervical ripening, e.g. transcription factors and enzymes. Secreted Trx may participate in removing inhibitors of collagen-degrading metalloproteinases.