Identification of a thioredoxin-related protein associated with plasma membranes

Domain-wise differentiation of Mycobacterium tuberculosis H37 Rv hypothetical proteins: A roadmap to discover bacterial survival potentials

Proteomic information revealed approximately 3,923 proteins in Mycobacterium tuberculosis H₃₇ Rv genome of which around ∼25% of proteins are hypothetical proteins (HPs). The present work comprises computational approaches to identify and characterize the HPs of M. tuberculosis that symbolize the putative target for rationale development of a drug or antituberculosis strategy. Proteins were primarily classified based on motif and domain information, which were further analyzed for the presence of virulence factors (VFs), determination of localization, and signal peptide/enzymatic cleavage sites. 863 HPs were found, and 599 HPs were finalized based on motifs, that is, GTP (525), Trx (47), SAM (14), PE-PGRS (5), and CBD (8). 80 HPs contain virulence factor (VF), 24 HPs localized in membrane region, and 4 HPs contain signal peptide/enzymatic cleavage sites. The overall parametric study finalizes four HPs Rv0679c, Rv0906, Rv3627c, and Rv3811 that also comprise GTPase domain. Structure prediction, structure-based function prediction, molecular docking and mutation analysis of selected proteins were done. Docking studies revealed that GTP and GTPase inhibitor (mac0182344) were docked with all four proteins with high affinities. In silico point mutation studies showed that substitution of aspartate with glycine within a GTPase motif showed the largest decrease in stability and pH differentiation also affects protein's stability. This analysis thus fixes a roadmap in the direction of finding potential target of this bacterium for drug development and enlightens the efficacy of GTP as a major regulator of Mycobacterial cellular pathways.

Peri/Epicellular Thiol Oxidoreductases as Mediators of Extracellular Redox Signaling

Significance: Supracellular redox networks regulating cell-extracellular matrix (ECM) and organ system architecture merge with structural and functional (catalytic or allosteric) properties of disulfide bonds. This review addresses emerging evidence that exported thiol oxidoreductases (TORs), such as thioredoxin, protein disulfide isomerases (PDIs), quiescin sulfhydryl oxidases (QSOX)1, and peroxiredoxins, composing a peri/epicellular (pec)TOR pool, mediate relevant signaling. pecTOR functions depend mainly on kinetic and spatial regulation of thiol-disulfide exchange reactions governed by redox potentials, which are modulated by exported intracellular low-molecular-weight thiols, together conferring signal specificity. Recent Advances: pecTOR redox-modulates several targets including integrins, ECM proteins, surface molecules, and plasma components, although clear-cut documentation of direct effects is lacking in many cases. TOR catalytic pathways, displaying common patterns, culminate in substrate thiol reduction, oxidation, or isomerization. Peroxiredoxins act as redox/peroxide sensors, contrary to PDIs, which are likely substrate-targeted redox modulators. Emerging evidence suggests important pecTOR roles in patho(physio)logical processes, including blood coagulation, vascular remodeling, mechanosensing, endothelial function, immune responses, and inflammation. Critical Issues: Effects of pecPDIs supporting thrombosis/platelet activation have been well documented and reached the clinical arena. Roles of pecPDIA1 in vascular remodeling/mechanosensing are also emerging. Extracellular thioredoxin and pecPDIs redox-regulate immunoinflammation. Routes of TOR externalization remain elusive and appear to involve Golgi-independent routes. pecTORs are particularly accessible drug targets. Future Directions: Further understanding mechanisms of thiol redox reactions and developing assays for assessing pecTOR redox activities remain important research avenues. Also, addressing pecTORs as disease markers and achieving more efficient/specific drugs for pecTOR modulation are major perspectives for diagnostic/therapeutic improvements.

[Main Cellular Redox Couples]

Most of the living cells maintain the continuous flow of electrons, which provides them by energy. Many of the compounds are presented in a cell at the same time in the oxidized and reduced states, forming the active redox couples. Some of the redox couples, such as NAD+/NADH, NADP+/NADPH, oxidized/reduced glutathione (GSSG/GSH), are universal, as they participate in adjusting of many cellular reactions. Ratios of the oxidized and reduced forms of these compounds are important cellular redox parameters. Modern research approaches allow setting the new functions of the main redox couples in the complex organization of cellular processes. The following information is about the main cellular redox couples and their participation in various biological processes.

Redox systems in Botrytis cinerea: impact on development and virulence

The thioredoxin system is of great importance for maintenance of cellular redox homeostasis. Here, we show that it has a severe influence on virulence of Botrytis cinerea, demonstrating that redox processes are important for host-pathogen interactions in this necrotrophic plant pathogen. The thioredoxin system is composed of two enzymes, the thioredoxin and the thioredoxin reductase. We identified two genes encoding for thioredoxins (bctrx1, bctrx2) and one gene encoding for a thioredoxin reductase (bctrr1) in the genome of B. cinerea. Knockout mutants of bctrx1 and bctrr1 were severely impaired in virulence and more sensitive to oxidative stress. Additionally, Δbctrr1 showed enhanced H2O2 production and retarded growth. To investigate the impact of the second major cellular redox system, glutathione, we generated deletion mutants for two glutathione reductase genes. The effects were only marginal; deletion of bcglr1 resulted in reduced germination and, correspondingly, to retarded infection as well as reduced growth on minimal medium, whereas bcglr2 deletion had no distinctive phenotype. In summary, we showed that the balanced redox status maintained by the thioredoxin system is essential for development and pathogenesis of B. cinerea, whereas the second major cellular redox system, the glutathione system, seems to have only minor impact on these processes.

Disulfide reduction in CD4 domain 1 or 2 is essential for interaction with HIV glycoprotein 120 (gp120), which impairs thioredoxin-driven CD4 dimerization

Human CD4 is a membrane-bound glycoprotein expressed on the surface of certain leukocytes, where it plays a key role in the activation of immunostimulatory T cells and acts as the primary receptor for human immunodeficiency virus (HIV) glycoprotein (gp120). Although growing evidence suggests that redox exchange reactions involving CD4 disulfides, potentially catalyzed by cell surface-secreted oxidoreductases such as thioredoxin (Trx) and protein disulfide isomerase, play an essential role in regulating the activity of CD4, their mechanism(s) and biological utility remain incompletely understood. To gain more insights in this regard, we generated a panel of recombinant 2-domain CD4 proteins (2dCD4), including wild-type and Cys/Ala variants, and used these to show that while protein disulfide isomerase has little capacity for 2dCD4 reduction, Trx reduces 2dCD4 highly efficiently, catalyzing the formation of conformationally distinct monomeric 2dCD4 isomers, and a stable, disulfide-linked 2dCD4 dimer. Moreover, we show that HIV gp120 is incapable of binding a fully oxidized, monomeric 2dCD4 in which both domain 1 and 2 disulfides are intact, but binds robustly to reduced counterparts that are the ostensible products of Trx-mediated isomerization. Finally, we demonstrate that Trx-driven dimerization of CD4, a process believed to be critical for the establishment of functional MHCII-TCR-CD4 antigen presentation complexes, is impaired when CD4 is bound to gp120. These observations reinforce the importance of cell surface redox activity for HIV entry and posit the intriguing possibility that one of the many pathogenic effects of HIV may be related to gp120-mediated inhibition of oxidoreductive CD4 isomerization.

Lymphocytes from rheumatoid arthritis patients have elevated levels of intracellular peroxiredoxin 2, and a greater frequency of cells with exofacial peroxiredoxin 2, compared with healthy human lymphocytes

Peroxiredoxin 2 has immune regulatory functions, but its expression in human peripheral blood lymphocytes and levels in extracellular fluid in healthy subjects and rheumatoid arthritis patients are poorly described. In the present study, the median intracellular peroxiredoxin 2 protein content of lymphocytes from rheumatoid arthritis patients was more than two-fold higher compared with healthy subjects’ lymphocytes. Intracellular peroxiredoxin 3 levels were similar in healthy and rheumatoid arthritis lymphocytes. Flow cytometry detected peroxiredoxin 2 on the surface of ca. 8% of T cells and ca. 56% of B cells (median % values) of all subjects analyzed. Exofacial thioredoxin-1 was also observed. In the total lymphocyte population from rheumatoid arthritis patients, few cells (median, 6%) displayed surface peroxiredoxin 2. In contrast, a significantly increased proportion of interleukin-17^+ve lymphocytes were exofacially peroxiredoxin 2^+ve (median, 39%). Prdx2 was also detected in human extracellular fluids. We suggest that crucial inflammatory cell subsets, i.e. interleukin-17^+ve T cells, exhibit increased exofacial redox-regulating enzymes and that peroxiredoxin 2 may be involved in the persistence of pro-inflammatory cells in chronic inflammation.

Thioredoxin-1 and protein disulfide isomerase catalyze the reduction of similar disulfides in HIV gp120

HIV-1 enters cells via interaction of the viral glycoprotein gp120, the host cell surface receptor CD4 and the co-receptors CCR5 or CXCR4. For entry, gp120 undergoes conformational changes that depend on the reduction of one or more disulfides. Previous studies indicate that protein disulfide isomerase (PDI), thioredoxin-1 (Trx1), and glutaredoxin-1 (Grx1) catalyze gp120 reduction, but their specific disulfide targets are not known. Here, it was demonstrated that PDI and Trx1 have similar gp120 disulfide targets as determined by labeling after reduction, but with some pattern differences, including overall stronger labeling with Trx1 than with PDI. Furthermore, uneven labeling of the residues of a disulfide may reflect altered accessibility by conformational changes upon the reduction process. Since both PDI and Trx1 may be involved in viral entry, compounds that target the host redox system or the viral gp120 were tested in vitro to investigate whether redox regulation is a target for anti-HIV therapy. Carbohydrate binding agents (CBAs), previously shown to bind gp120 and inhibit HIV entry, were now demonstrated to inhibit gp120 disulfide reduction. Auranofin, an inhibitor of thioredoxin reductase 1 (TrxR1), also showed inhibitory activity towards HIV infection, although close to its cytotoxic concentration. Our results demonstrate that both the host redox system and the viral surface glycoproteins are of interest for the development of new generations of anti-HIV therapeutics.

Regulation of the extracellular antioxidant selenoprotein plasma glutathione peroxidase (GPx-3) in mammalian cells

Plasma glutathione peroxidase (GPx-3) is a selenocysteine-containing extracellular antioxidant protein that catalyzes the reduction of hydrogen peroxide and lipid hydroperoxides. Selenoprotein expression involves the alternate recognition of a UGA codon as a selenocysteine codon and requires signals in the 3'-untranslated region (UTR), including a selenocysteine insertion sequence (SECIS), as well as specific translational cofactors. To ascertain regulatory determinants of GPx-3 expression and function, we generated recombinant GPx-3 (rGPX-3) constructs with various 3'-UTR, as well as a Sec73Cys mutant. In transfected Cos7 cells, the Sec73Cys mutant was expressed at higher levels than the wild type rGPx-3, although the wild type rGPx-3 had higher specific activity, similar to plasma purified GPx-3. A 3'-UTR with only the SECIS was insufficient for wild type rGPx-3 protein expression. Selenocompound supplementation and co-transfection with SECIS binding protein 2 increased wild type rGPx-3 expression. These results demonstrate the importance of translational mechanisms in GPx-3 expression.

Human glutaredoxin-1 catalyzes the reduction of HIV-1 gp120 and CD4 disulfides and its inhibition reduces HIV-1 replication

Reduction of intramolecular disulfides in the HIV-1 envelope protein gp120 occurs after its binding to the CD4 receptor. Protein disulfide isomerase (PDI) catalyzes the disulfide reduction in vitro and inhibition of this enzyme blocks viral entry. PDI belongs to the thioredoxin protein superfamily that also includes human glutaredoxin-1 (Grx1). Grx1 is secreted from cells and the protein has also been found within the HIV-1 virion. We show that Grx1 efficiently catalyzes gp120, and CD4 disulfide reduction in vitro, even at low plasma levels of glutathione. Grx1 catalyzes the reduction of two disulfide bridges in gp120 in a similar manner as PDI. Purified anti-Grx1 antibodies were shown to inhibit the Grx1 activity in vitro and block HIV-1 replication in cultured peripheral blood mononuclear cells. Also, the polyanion PRO2000, that was previously shown to prevent HIV entry, inhibits the Grx1- and PDI-dependent reduction of gp120 disulfides. Our findings suggest that Grx1 activity is important for HIV-1 entry and that Grx1 and the gp120 intramolecular disulfides are novel pharmacological targets for rational drug development.

Regulators of the neuropeptide-degrading enzyme, EC 3.4.24.15 (thimet oligopeptidase), in cerebrospinal fluid

Endopeptidase EC 3.4.24.15 (EP 24.15; thimet oligopeptidase) is a soluble metalloendopeptidase implicated in the metabolism of a number of neuropeptides, including neurotensin, gonadotropin-releasing hormone, and opioid peptides. We have shown previously that thiol reducing agents, such as dithiothreitol, activate EP 24.15 by mediating the conversion of inactive multimeric forms to active monomers and that this conversion involves the disruption of intermolecular disulfide bonds involving cysteine residues 246, 248, and 253. We have identified two components of cerebrospinal fluid that activate recombinant EP 24.15, but have no effect on a thiol-independent cysteine mutant form of the enzyme. The low molecular weight (<10 kDa) component co-elutes with glutathione by reversed-phase HPLC, whereas the high molecular weight component (>50 kDa) is sensitive to digestion with trypsin, suggesting it is proteinaceous in nature. These results suggest that EP 24.15 activity in the brain may be modulated by factors released into cerebrospinal fluid.

Disulfide bonds as switches for protein function

The prevailing view is that disulfide bonds have been added during evolution to enhance the stability of proteins that function in a fluctuating cellular environment. However, recent evidence indicates that disulfide bonds can be more than inert structural motifs. The function of some secreted soluble proteins and cell-surface receptors is controlled by cleavage of one or more of their disulfide bonds; this cleavage is mediated by catalysts or facilitators that are specific for their substrate.

Disulfide exchange in domain 2 of CD4 is required for entry of HIV-1

CD4, a member of the immunoglobulin superfamily of receptors that mediates cell-cell interactions in the immune system, is the primary receptor for HIV-1. The extracellular portion of CD4 is a concatenation of four immunoglobulin-like domains, D1 to D4. The D1, D2 and D4 domains each contain a disulfide bond. We show here that the D2 disulfide bond is redox-active. The redox state of the thiols (disulfide versus dithiol) appeared to be regulated by thioredoxin, which is secreted by CD4(+) T cells. Locking the CD4 and the thioredoxin active-site dithiols in the reduced state with a hydrophilic trivalent arsenical blocked entry of HIV-1 into susceptible cells. These findings indicate that redox changes in CD4 D2 are important for HIV-1 entry and represent a new target for HIV-1 entry inhibitors.

The role of the redox protein thioredoxin in cell growth and cancer

The thioredoxins are ubiquitous proteins containing a conserved -Trp-Cys-Gly-Pro-Cys-Lys- redox catalytic site. Mammalian thioredoxin family members include thioredoxin-1 (Trx1), mitochondrial thioredoxin-2 (Trx2), and a larger thioredoxin-like protein, p32TrxL. Thioredoxin is reduced by NADPH and thioredoxin reductase and, in turn reduces oxidized cysteine groups on proteins. When thioredoxin levels are elevated there is increased cell growth and resistance to the normal mechanism of programmed cell death. An increase in thioredoxin levels seen in many human primary cancers compared to normal tissue appears to contribute to increased cancer cell growth and resistance to chemotherapy. Mechanisms by which thioredoxin increases cell growth include an increased supply of reducing equivalents for DNA synthesis, activation of transcription factors that regulate cell growth, and an increase in the sensitivity of cells to other cytokines and growth factors. The mechanisms for the inhibition of apoptosis by thioredoxin are just now being elucidated. Because of its role in stimulating cancer cell growth and as an inhibitor of apoptosis, thioredoxin offers a target for the development of drugs to treat and prevent cancer.

The relative effectiveness of human plasma glutathione peroxidase as a catalyst for the reduction of hydroperoxides by glutathione

To reveal clues to the function of human plasma glutathione peroxidase (GPx), we investigated its catalytic effectiveness with a variety of hydroperoxides. Comparisons of hydroperoxides as substrates for plasma GPx based on the ratio of Vmax/Km were blocked by the limited solubility of the organic hydroperoxides, which prevented kinetic saturation of the enzyme at the chosen glutathione concentration. Therefore, we compared the hydroperoxides by the fold increase in the apparent first-order rate constants of their reactions with glutathione owing to catalysis by plasma GPx. The reductions of aromatic and small hydrophobic hydroperoxides (cumene hydroperoxide, t-amyl hydroperoxide, t-butyl hydroperoxide, paramenthane hydroperoxide) were better catalyzed by plasma GPx than were reductions of the more "physiological" substrates (linoleic acid hydroperoxide, hydrogen peroxide, peroxidized plasma lipids, and oxidized cholesterol).

Generation of angiostatin by reduction and proteolysis of plasmin. Catalysis by a plasmin reductase secreted by cultured cells

Extracellular manipulation of protein disulfide bonds has been implied in diverse biological processes, including penetration of viruses and endotoxin into cells and activation of certain cytokine receptors. We now demonstrate reduction of one or more disulfide bonds in the serine proteinase, plasmin, by a reductase secreted by Chinese hamster ovary or HT1080 cells. Reduction of plasmin disulfide bond(s) triggered proteolysis of the enzyme, generating fragments with the domain structure of the angiogenesis inhibitor, angiostatin. Two of the known reductases secreted by cultured cells are protein disulfide isomerase and thioredoxin, and incubation of plasmin with these purified reductases resulted in angiostatin fragments comparable with those generated from plasmin in cell culture. Thioredoxin-derived angiostatin inhibited proliferation of human dermal microvascular endothelial cells with half-maximal effect at approximately 0.2 microg/ml. Angiostatin made by cells and by purified reductases contained free sulfhydryl group(s), and S-carbamidomethylation of these thiol group(s) ablated biological activity. Neither protein disulfide isomerase nor thioredoxin were the reductases used by cultured cells, because immunodepletion of conditioned medium of these proteins did not affect angiostatin generating activity. The plasmin reductase secreted by HT1080 cells required a small cofactor for activity, and physiologically relevant concentrations of reduced glutathione fulfilled this role. These results have consequences for plasmin activity and angiogenesis, particularly in the context of tumor growth and metastasis. Moreover, this is the first demonstration of extracellular reduction of a protein disulfide bond, which has general implications for cell biology.

Thiol activation of endopeptidase EC 3.4.24.15. A novel mechanism for the regulation of catalytic activity

Endopeptidase EC 3.4.24.15 (EP24.15) is a thermolysin-like metalloendopeptidase involved in the regulated metabolism of a number of neuropeptides. Unlike other thermolysin-like peptidases EP24.15 displays a unique thiol activation, a mechanism that is not clearly understood. In this study we show that both recombinant and tissue-derived EP24.15 are activated up to 8-fold by low concentrations (0.1 mM) of dithiothreitol. Additionally, under non-reducing conditions, recombinant and native EP24.15 forms multimers that can be returned to the monomeric form by reduction. We have also shown that competitive inhibitor binding occurs only to the monomeric form, which indicates that catalytic site access is restricted in the multimeric forms. Through systematic site-directed mutagenesis we have identified that cysteine residues 246, 253, and possibly 248 are involved in the formation of these multimers. Furthermore, both a double mutant (C246S/C253S) and a triple mutant (C246S/C248S/C253S) are fully active in the absence of reducing agents, as measured by both inhibitor binding and hydrolysis. The formation and disruption of disulfide bonds involving these cysteine residues may be a mechanism by which EP24.15 activity is regulated through changes in intra- and extracellular redox potential.

Cloning and expression of a novel mammalian thioredoxin

We have isolated a 1276-base pair cDNA from a rat heart cDNA library that encodes a novel thioredoxin (Trx2) of 166 amino acid residues with a calculated molecular mass of 18.2 kDa. Trx2 possesses the conserved thioredoxin-active site, Trp-Cys-Gly-Pro-Cys, but lacks structural cysteines present in all mammalian thioredoxins. Trx2 also differs from the previously described rat thioredoxin (Trx1) by the presence of a 60-amino acid extension at the N terminus. This extension has properties characteristic for a mitochondrial translocation signal, and the cleavage at a putative mitochondrial peptidase cleavage site would give a mature protein of 12.2 kDa. Western blot analysis from cytosolic, peroxisomal, and mitochondrial rat liver cell fractions confirmed mitochondrial localization of Trx2. Northern blot and reverse transcriptase-polymerase chain reaction analyses revealed that Trx2 hybridized to a 1.3-kilobase message, and it was expressed in several tissues with the highest expression levels in heart, muscle, kidney, and adrenal gland. N-terminally truncated recombinant protein was expressed in bacteria and characterized biochemically. Trx2 possessed a dithiol-reducing enzymatic activity and, with mammalian thioredoxin reductase and NADPH, was able to reduce the interchain disulfide bridges of insulin. Furthermore, Trx2 was more resistant to oxidation than Trx1.

Detection of membrane associated thioredoxin on human cell lines

Thioredoxin (TRX) is a ubiquitous dithiol-oxidoreduction enzyme broadly expressed in cells from prokaryote to eukaryote organisms. Human thioredoxin (human TRX) gene, previously cloned in our laboratory, codes for a 12-kDa protein found in the culture supernatant of several hemopoietic human cell lines. This protein is secreted by a nonclassical pathway. The role of the secreted enzyme as a signalling soluble mediator was demonstrated, but nothing is known about a membrane associated form of thioredoxin which could be involved in cell/cell contacts and accessory signal function. Thus, we performed experiments to determine if human TRX is also expressed at the cell surface. We report here positive results based upon indirect immunofluorescence flow cytometric analysis of different human cell lines (HeLa, U 937, Jurkat, 3B6, Daudi and Raji) using a cross reactive sheep anti E. coli TRX polyclonal antibody demonstrating a significant expression of human TRX at the surface of human cells.

Heterologous expression and enzymatic properties of a selenium-independent glutathione peroxidase from the parasitic nematode Brugia pahangi

A full-length cDNA from the parasitic nematode Brugia pahangi encoding a secreted homolog of glutathione peroxidase in which the codon for the active site selenocysteine is substituted naturally by a cysteine codon has been expressed in Spodoptera frugiperda (insect) cells via Autographa californica nuclear polyhedrosis virus (baculovirus). The recombinant protein was glycosylated and secreted from the cells in tetrameric form. The purified protein showed glutathione peroxidase activity with a range of organic hydroperoxides, including L-alpha-phosphatidylcholine hydroperoxide, but no significant activity against hydrogen peroxide. Glutathione was the only thiol tested that served as a substrate for the enzyme, which showed no activity with the thioredoxin system (thioredoxin, thioredoxin reductase, and NADPH). No glutathione-conjugating activity was detected against a range of electrophilic compounds that are common substrates for glutathione S-transferases. The apparent (pseudo)m for glutathione was determined as 4.9 mM at a fixed concentration of linolenic acid hydroperoxide (3 microM). The enzyme showed low affinity for hydroperoxide substrates (apparent Km for linolenic acid hydroperoxide and L-alpha-phosphatidylcholine hydroperoxide of 3.8 and 9.7 mM, respectively at a fixed glutathione concentration of 3 mM).

Characterization of a thioredoxin-related surface protein

A surface-associated sulphydryl (thiol) protein (SASP) constitutively present in most nucleated cells was purified from human THP-1 monocytes and rat C6 glioma cells. The human protein was similar in mass and isoelectric point and had the same N-terminal amino acid sequence to adult T-cell leukemia-derived factor (ADF), a growth factor secreted by human lymphoid cells which is able to induce increased expression of interleukin-2 receptors. A further internal amino acid sequence, determined following cleavage of human SASP with cyanogen bromide, was also identical to the corresponding sequence deduced for ADF. Samples of SASP were able to reductively depolymerize human immunoglobulin, a property shared with thioredoxin, a ubiquitous protein, almost identical to ADF, with an essential function in many thiol-dependent reducing reactions. Furthermore, SASP purified from rat C6 glioma cells had an identical N-terminal amino acid sequence to that deduced for rat liver thioredoxin, showing that they were both members of the same family of proteins. The use of membrane-impermeable thiol reagents indicated that SASP was predominantly a cell-surface protein, and was not normally secreted. This SASP protein appeared to be a surface-associated form of thioredoxin that was constitutively present in a wide range of cells and was related to ADF, a secreted form of the same protein.

Neuroprotection by glial cells through adult T cell leukemia-derived factor/human thioredoxin (ADF/TRX)

Adult T cell leukemia-derived factor (ADF) is a human homologue of thioredoxin (TRX) with many biological functions and is induced by various stimuli and stress. In the central nervous system (CNS), expression of ADF/TRX occurs in glial cells during ischemia and reperfusion. We showed that ADF/TRX was actively released from U251 astrocytoma cells upon exposure to a low concentration of H2O2. The addition of conditioned medium from H2O2-stimulated U251 cells or recombinant ADF (rADF) to the culture medium promoted the survival of neurons from embryonic mouse cortex and striatum, but the addition of mutant ADF (mADF), which has no reducing activity, did not. In addition to rADF, incubation with two other thiol compounds, 2-mercaptoethanol (2-ME) and N-acetyl-L-cysteine (NAC), also increased the neuronal cell survival rate. In contrast, L-buthionine-(S,R)-sulfoximine (BSO), which inhibited the synthesis of glutathione (GSH), decreased the neuronal cell survival rate. Intracellular GSH was increased by incubation with rADF for 24 h, as it is with 2-ME and NAC. Redox active molecules such as thiol compounds may be survival factors for central neurons in vitro, and this capacity may be supplied by endogenous molecules, such as ADF/TRX and glutathione, under certain pathologic conditions in vivo.

Detection of adult T-cell leukemia-derived factor/human thioredoxin in human serum

Adult T-cell leukemia (ATL)-derived factor (ADF), originally defined as an inducer of interleukin-2 receptor/alpha-chain (IL-2R/p55) of human T-lymphotropic virus type I (HTLV-I) positive T cells, is a human homologue of redox-active coenzyme thioredoxin (Trx) of Escherichia coli. In this study, an enzymatic assay system based on the dithiol-dependent insulin-reducing activity of ADF/Trx was established (insulin-reducing assay) to determine the amount of ADF/Trx in human serum using NADPH and Trx reductase purified from human placenta. Insulin-reducing activity was detected in all of the serum samples from healthy volunteers (n = 30) screened by this assay, with a mean +/- SD of 10.9 +/- 2.4 U/l. This mean value corresponds with the concentration of 223 ng recombinant ADF/Trx (rADF/Trx)/ml. Human serum is known to contain several redox-active proteins with ADF/Trx motifs. To differentiate the contribution of these proteins and ADF/Trx to the insulin-reducing activity, the anti-rADF/Trx monoclonal antibody (mAb)-conjugated affinity column-depleted sera obtained from an identical source was used for analysis. The affinity column-depleted sera demonstrated a loss of over 99% of the original activity, while control column depleted sera lost less than 4%. Furthermore, the amount of affinity-purified ADF/Trx molecules eluted from the same column almost corresponded with the amount estimated by the insulin-reducing activity.(ABSTRACT TRUNCATED AT 250 WORDS)