Vitamin D3 up-regulated protein 1 mediates oxidative stress via suppressing the thioredoxin function

Gene expression pattern in apoptotic QGY-7703 cells induced by homoharringtonine

AIM

To classify the genes responsible for apoptosis in QGY-7703 cells induced by homoharringtonine (HHT).

METHODS

Apoptosis in QGY-7703 cells induced by HHT was demonstrated by DNA fragmentation and morphological observation. cDNA microarray technology was used to detect gene transcription, and the result of microarrays for genes was confirmed by RT-PCR.

RESULTS

Seventy-eight individual mRNA were identified and their transcription levels changed significantly. Those genes, of which 68% were upregulated and 32% were downregulated, were partially related to apoptosis. They were mostly oncogenes, tumor suppressors, enzymes, and kinases.

CONCLUSION

HHT is a potential drug in the treatment of liver cancer. TGF-beta, TNF, FAS, p38MAPK, and p53 apoptosis signaling pathways were activated during apoptosis in QGY-7703 cells. Such inducible genes may play important roles in apoptosis and deserve to be further studied.

Microarray studies of genomic oxidative stress and cell cycle responses in obstructive sleep apnea

Obstructive sleep apnea (OSA), the commonest form of sleep-disordered breathing, is characterized by recurrent episodes of intermittent hypoxia and sleep fragmentation. This study evaluated microarray measures of gene transcript levels in OSA subjects compared to age and BMI matched healthy controls. Measurements were obtained before and after: (a) a night of normal sleep in controls; and (b) a night of untreated apnea in OSA patients. All subjects underwent full polysomnography. mRNA from the whole blood samples was analyzed by HG-U133A and B Affymetrix GeneChip arrays using Spotfire 7.2 data analysis platform. After sleep in OSA patients, changes were noted in several genes involved in modulation of reactive oxygen species (ROS), including heme oxygenase 1, superoxide dismutase 1 and 2, and catalase. Changes were also observed in genes involved in cell growth, proliferation, and the cell cycle such as cell division cycle 25B, signaling lymphocyte activating molecule (SLAM), calgizzarin S100A11, B-cell translocation gene, Src-like adapter protein (SLAP), and eukaryotic translation initiation factor 4E binding protein 2. These overnight changes in OSA patients are suggestive of activation of several mechanisms to modulate, and adapt to, increased ROS developing in response to the frequent episodes of intermittent hypoxia.

Regulation of the bioavailability of thioredoxin in the lens by a specific thioredoxin-binding protein (TBP-2)

Thioredoxin (TRx) is known to control redox homeostasis in cells. In recent years, a specific TRx binding protein called thioredoxin binding protein-2 (TBP-2) was found in other cell types and it appeared to negatively regulate TRx bioavailability and thereby control TRx biological function. In view of the sensitivity of lens transparency to redox status, proper regulation of TRx bioavailability is of the utmost importance. This study was conducted to examine the presence and function of TBP-2 in human lens epithelial cells (HLE B3). We cloned human lens TBP-2 from a human cDNA library (GenBank accession number AY 594328) and showed that it is fully homologous to the human brain TBP-2 gene. The recombinant TBP-2 protein was partially purified and mass spectrometric analysis confirmed its sequence homology to that of brain TBP-2. Immunoprecipitates obtained from HLE B3 cells using anti-TRx and anti-TBP-2 antibodies showed the presence of TRx and TBP-2 in immunoprecipitates indicating the formation of a TRx-TBP-2 complex in vivo. Furthermore, under H(2)O(2)-stress conditions, TRx gene expression was transiently up-regulated while TBP-2 gene expression was inversely down-regulated as seen in both HLE B3 cells and in the epithelial cell layers from cultured pig lenses. Cells with overexpressed TBP-2 showed lower TRx activity, grew slower and were more susceptible to oxidative stress-induced apoptosis. This is the first report of the presence of a TRx-specific binding protein in the lens. Our data suggest that TBP-2 is likely a negative regulator for the bioavailability, and therefore, the overall function of TRx in the lens.

Investigation of TXNIP (thioredoxin-interacting protein) and TRX (thioredoxin) genes for growth-related traits in pigs

It is well known that TRX and its endogenous inhibitor TXNIP help sustain the cellular reduction/oxidation balance in response to various stresses and both play a crucial role in cell proliferation and growth. Five SNPs were found in TXNIP and these allowed us to map it by linkage to SSC4. Three of the SNPs were used for association analyses in three commercial pig populations (Duroc, Hampshire, and synthetic line) with more than 1200 animals. Both the single-marker and haplotype analyses revealed significant effects of TXNIP on hot carcass weight, test daily gain, and lifetime daily gain. TRX was mapped on SSC1 but no significant associations with growth-related traits were found in the synthetic pig line in which the SNP was informative. The expression levels of TXNIP and TRX were then detected in two groups (fast growth and slow growth, respectively) with different genetic backgrounds for growth. Compared with the slow-growth group, TXNIP expression was significantly lower in the fast-growth group, whereas a marked increase in TRX expression was observed in fast-growth group. Our findings suggest that TXNIP has effects on growth-related traits in pigs and further investigations will be necessary to elucidate the underlying mechanisms involved.

Oxygen sensing and redox signaling: the role of thioredoxin in embryonic development and cardiac diseases

It is important to regulate the oxygen concentration and scavenge oxygen radicals throughout the life of animals. In mammalian embryos, proper oxygen concentration gradually increases in utero and excessive oxygen is rather toxic during early embryonic development. Reactive oxygen species (ROS) are generated as by-products in the respiratory system and increased under inflammatory conditions. In the pathogenesis of a variety of adult human diseases such as cancer and cardiovascular disorders, ROS cause an enhancement of tissue injuries. ROS promote not only the development of atherosclerosis but also tissue injury during the reperfusion process. The thioredoxin (TRX) system is one of the most important mechanisms for regulating the redox balance. TRX is a small redox active protein distributed ubiquitously in various mammalian tissues and cells. TRX acts as not only an antioxidant but also an anti-inflammatory and an antiapoptotic protein. TRX is induced by oxidative stress and released from cells in response to oxidative stress. In various human diseases, the serum/plasma level of TRX is a well-recognized biomarker of oxidative stress. Here we discuss the roles of TRX on oxygen stress and redox regulation from different perspectives, in embryogenesis and in adult diseases focusing on cardiac disorders.

Genomewide identification of prednisolone-responsive genes in acute lymphoblastic leukemia cells

Glucocorticoids are keystone drugs in the treatment of childhood acute lymphoblastic leukemia (ALL). To get more insight in signal transduction pathways involved in glucocorticoid-induced apoptosis, Affymetrix U133A GeneChips were used to identify transcriptionally regulated genes on 3 and 8 hours of prednisolone exposure in leukemic cells of 13 children as compared with nonexposed cells. Following 3 hours of exposure no significant changes in gene expression could be identified. Following 8 hours of exposure, 51 genes were differentially expressed (P < .001 and false discovery rate < 10%) with 39 genes being up-regulated (median, 2.4-fold) and 12 genes were down-regulated (median, 1.7-fold). Twenty-one of those genes have not been identified before to be transcriptionally regulated by prednisolone. Two of the 3 most highly up-regulated genes were tumor suppressor genes, that is, thioredoxin-interacting protein (TXNIP; 3.7-fold) and zinc finger and BTB domain containing 16 (ZBTB16; 8.8-fold). About 50% of the differentially expressed genes were functionally categorized in 3 major routes, namely MAPK pathways (9 genes), NF-kappaB signaling (11 genes), and carbohydrate metabolism (5 genes). Biologic characterization of these genes and pathways might elucidate the action of glucocorticoids in ALL cells, possibly suggesting causes of glucocorticoid resistance and new potential targets for therapy.

Mitochondrial peroxiredoxins

Mitochondria are the major intracellular sites of oxygen consumption producing reactive oxygen species (ROS) as toxic by-products of oxidative phosphorylation, primarily via electron leakage from the respiratory chain. The resultant types of chemical damage to lipids, DNA and proteins are described as well as the broader implications for the involvement of ROS in disease onset and progression. The relative contributions of mitochondrial, enzyme-linked, antioxidant defence systems to tissue protection are also reviewed as is the emerging importance of the peroxiredoxin family in general to H2O2-mediated signalling The constituent enzymes of the mitochondrial PrxIII pathway are discussed in detail including the roles of PrxIII and PrxV in their capacities as typical 2-cys and atypical 2-cys thioredoxin-dependent hydroperoxide reductases, respectively. The structures and catalytic mechanisms of PrxIII and V are examined and some key properties of the reconstituted mitochondrial PrxIII pathway are highlighted with specific reference to the susceptibility of peroxiredoxins to inactivation at elevated H2O2 levels and their potential for participation in H2O2-mediated signalling responses. It is concluded that mitochondrial Prxs form a vital link in an integrated cellular antioxidant defence network that minimises ROS-mediated damage and ensures that cells mount appropriate responses to increased levels of oxidative stress via the upregulation of key cell signalling pathways.

Enhanced VDUP-1 gene expression by PPARγ agonist induces apoptosis in human macrophage

The fate and phenotype of lesion macrophages is regulated by cellular oxidative stress. Thioredoxin-1 (Trx-1) plays a major role in the regulation of cellular redox balance, with resultant effects on gene expression and cellular responses including cell growth and death. Trx-1 activity is inhibited by interaction with vitamin D-upregulated protein-1 (VDUP-1). Peroxisome proliferator-activated receptor gamma (PPARgamma) is expressed by human monocyte-derived macrophages (HMDM) and PPARgamma agonism has been reported to decrease expression of inflammatory genes and to promote apoptosis of these cells. To determine whether VDUP-1 may be involved in regulating the effects of PPARgamma agonists in macrophages, we investigated the effect of a synthetic PPARgamma agonist (GW929) on the expression of VDUP-1 in HMDM. GW929 concentration-dependently increased HMDM expression of VDUP-1 (mRNA and protein). Transfection of different fragments of the VDUP-1 promoter as well as gel shift analysis revealed the presence of functional PPARgamma response elements (PPRE) in the promoter. Under conditions in which PPAR agonism altered levels of VDUP-1, caspase-3 activity, and macrophage apoptosis were also elevated. The results suggest that PPARgamma activation stimulates apoptosis in human macrophages by altering the cellular redox balance via regulation of VDUP-1.

Thioredoxin and related molecules--from biology to health and disease

Thioredoxin and glutaredoxin systems in mammalian cells utilize thiol and selenol groups to maintain a reducing intracellular redox state acting as antioxidants and reducing agents in redox signaling with oxidizing reactive oxygen species. During the last decade, the functional roles of thioredoxin in particular have continued to expand, also including novel functions such as a secreted growth factor or a chemokine for immune cells. The role of thioredoxin and glutaredoxin in antioxidant defense and the role of thioredoxin in controlling recruitment of inflammatory cells offer potential use in clinical therapy. The fundamental differences between bacterial and mammalian thioredoxin reductases offer new principles for treatment of infections. Clinical drugs already in use target the active site selenol in thioredoxin reductases, inducing cell death in tumor cells. Thioredoxin and binding proteins (ASK1 and TBP2) appear to control apoptosis or metabolic states such as carbohydrate and lipid metabolism related to diseases such as diabetes and atherosclerosis.

Global gene expression changes underlying Stachybotrys chartarum toxin-induced apoptosis in murine alveolar macrophages: Evidence of multiple signal transduction pathways

The overall mechanism(s) underlying macrophage apoptosis caused by the toxins of the indoor mold Stachybotrys chartarum (SC) are not yet understood. In this direction, we report a microarray-based global gene expression profiling on the murine alveolar macrophage cell line (MH-S) treated with SC toxins for short (2 h) and long (24 h) periods, coinciding with the pre-apoptotic (<3 h) and progressed apoptotic stages of the treated cells, respectively. Microarray results on differential expression were validated by real-time RT-PCR analysis using representative gene targets. The toxin-regulated genes corresponded to multiple cellular processes, including cell growth, proliferation and death, inflammatory/immune response, genotoxic stress and oxidative stress, and to the underlying multiple signal transduction pathways involving MAPK-, NF-kB-, TNF-, and p53-mediated signaling. Transcription factor NF-kB showed dynamic temporal changes, characterized by an initial activation and a subsequent inhibition. Up-regulation of a battery of DNA damage-responsive and DNA repair genes in the early stage of the treatment suggested a possible role of genotoxic stress in the initiation of apoptosis. Simultaneous expression changes in both pro-survival genes and pro-apoptotic genes indicated the role of a critical balance between the two processes in SC toxin-induced apoptosis. Taken together, the results imply that multiple signaling pathways underlie the SC toxin-induced apoptosis in alveolar macrophages.

Thiol-based mechanisms of the thioredoxin and glutaredoxin systems: implications for diseases in the cardiovascular system

Reactive oxygen species (ROS) and the cellular thiol redox state are crucial mediators of multiple cell processes like growth, differentiation, and apoptosis. Excessive ROS production or oxidative stress is associated with several diseases, including cardiovascular disorders like ischemia-reperfusion. To prevent ROS-induced disorders, the heart is equipped with effective antioxidant systems. Key players in defense against oxidative stress are members of the thioredoxin-fold family of proteins. Of these, thioredoxins and glutaredoxins maintain a reduced intracellular redox state in mammalian cells by the reduction of protein thiols. The reversible oxidation of Cys-Gly-Pro-Cys or Cys-Pro(Ser)-Tyr-Cys active site cysteine residues is used in reversible electron transport. Thioredoxins and glutaredoxins belong to corresponding systems consisting of NADPH, thioredoxin reductase, and thioredoxin or NADPH, glutathione reductase, glutathione, and glutaredoxin, respectively. Thioredoxin as well as glutaredoxin activities appear to be very important for the progression and severity of several cardiovascular disorders. These proteins function not only as antioxidants, they inhibit or activate apoptotic signaling molecules like apoptosis signal-regulating kinase 1 and Ras or transcription factors like NF-kappaB. Thioredoxin activity is regulated by the endogenous inhibitor thioredoxin-binding protein 2 (TBP-2), indicating an important role of the balance between thioredoxin and TBP-2 levels in cardiovascular diseases. In this review, we will summarize cardioprotective effects of endogenous thioredoxin and glutaredoxin systems as well as the high potential in clinical applications of exogenously applied thioredoxin or glutaredoxin or the induction of endogenous thioredoxin and glutaredoxin systems.

Nitric Oxide–Dependent Suppression of Thioredoxin-Interacting Protein Expression Enhances Thioredoxin Activity

Objective— Cellular redox balance is regulated by enzymatic and nonenzymatic systems and freely diffusible nitric oxide (NO) promotes antioxidative mechanisms. We show the NO-dependent transcriptional regulation of the antioxidative thioredoxin system.

Methods and Results— Incubation of rat pulmonary artery smooth muscle cells (RPaSMC) with the NO donor compound S -nitroso-glutathione (GSNO, 100 μmol/L) suppressed thioredoxin-interacting protein (Txnip), an inhibitor of thioredoxin function, by 71±18% and enhanced thioredoxin reductase 2.7±0.2 fold (n=6; both P <0.001 versus control). GSNO increased thioredoxin activity (1.9±0.5-fold after 4 hours; P <0.05 versus control). Promoter deletion analysis revealed that NO suppression of Txnip transcription is mediated by cis -regulatory elements between −1777 and −1127 bp upstream of the start codon. Hyperglycemia induced Txnip promoter activity (3.9±0.2-fold; P <0.001) and abolished NO effects (−37.4±1.0% at 5.6 mmol/L glucose versus 12.4±2.1% at 22.4 mmol/L glucose; P <0.05). Immunoprecipitation experiments demonstrated that GSNO stimulation and mutation of thioredoxin at Cys69, a site of nitrosylation, had no effect on the Txnip/thioredoxin interaction.

Conclusions— NO can regulate cellular redox state by changing expression of Txnip and thioredoxin reductase. This represents a novel antioxidative mechanism of NO independent of posttranslational protein S -nitrosylation of thioredoxin.

Role of thioredoxin in cell growth through interactions with signaling molecules

The thioredoxin system helps maintain a reducing environment in cells, but thioredoxin functions as more than simply an antioxidant. Thioredoxin functions depend on the protein's redox state, as determined by two conserved cysteines. Key biologic activities of thioredoxin include antioxidant, growth control, and antiapoptotic properties, resulting from interaction with target molecules including transcription factors. Mechanisms by which thioredoxin regulates cell growth include binding to signaling molecules such as apoptosis signal-regulating kinase-1 (ASK-1) and thioredoxin-interacting protein (Txnip). The molecular interplay between thioredoxin, ASK-1, and Txnip potentially influences cell growth and survival in diverse human diseases such as cancer, diabetes, and heart disease. In this review, we focus on the structure of thioredoxin and its functional regulation of cell growth through the interactions with signaling molecules.

Thioredoxin in the cardiovascular system

The thioredoxin (TRX) system (TRX, TRX reductase, and NADPH) is a ubiquitous thiol oxidoreductase system that regulates cellular reduction/oxidation (redox) status. The impairment of cell redox state alters multiple cell pathways, which may contribute to the pathogenesis of cardiovascular disorders including hypertension, atherosclerosis, and heart failure. In this manuscript, we review the essential roles that TRX plays by limiting oxidative stress directly via antioxidant effects and indirectly by protein-protein interactions with key signaling molecules such as thioredoxin interacting protein (TXNIP). TRX and its endogenous regulators may represent important future targets to develop clinical therapies for diseases associated with oxidative stress.

Vitamin D3upregulated protein 1 (VDUP1) is a regulator for redox signaling and stress-mediated diseases

Vitamin D(3) upregulated protein 1 (VDUP1) is a 46-kDa multifunctional protein, initially isolated in HL-60 cells as a protein of which expression is upregulated by vitamin D(3) administration. Subsequently, it was identified independently by investigators from diverse scientific backgrounds as a thioredoxin binding protein that negatively regulates the expression and the activity of thioredoxin, and is thus involved in redox regulation. Further studies have revealed that VDUP1 plays multiple roles in a wide range of cellular processes such as proliferation or apoptosis. Recently, it has been reported that VDUP1 is also involved in the immune system via positive regulation of natural killer development. In addition, VDUP1 has been revealed to be associated with the fatty acid utilization. In the present review, we discuss the novel aspects of VDUP1 function as well as the historical background of VDUP1. Future studies will explore the diagnostic and therapeutic potential of modulating the function of VDUP1 in vivo.

Extracellular thioredoxin and thioredoxin-binding protein 2 in control of cancer

Thioredoxin-1 (TRX) is a redox-active protein with multiple intracellular and extracellular functions. Intracellular redox balance is maintained by the TRX family and its related molecules. Extracellular TRX shows cytoprotective effects, while truncated Trx80 has more mitogenic activity. Exogenously administered TRX does not promote the growth of cancer in vivo and shows anti-chemotactic effect for neutrophils and anti-inflammatory functions. Thioredoxin is released from cells in response to oxidative stress and TRX levels in plasma or serum are good markers for oxidative stress associated with cancer. Thioredoxin-binding protein 2 (TBP-2) is an endogenous negative regulator of TRX and a tumor suppressor.

Thioredoxin in cancer--role of histone deacetylase inhibitors

Increased levels of thioredoxin (Trx) occur in a number of human cancers, which may contribute to the resistance of cancers to therapy by scavenging reactive oxygen species (ROS) which are generated by various anti-cancer agents. Many human cancers have low levels of thioredoxin-binding protein (TBP-2). TBP-2 binds to Trx and blocks its reducing activity. Histone deacetylase inhibitors (HDACi) up-regulate TBP-2 in various transformed cells, associated with a decrease in Trx levels. Up-regulation of TBP-2 and decrease of Trx may contribute to the sensitivity of many hematologic and solid tumors to anti-cancer activity of HDACi.

Thioredoxin and ventricular remodeling

Increasing bodies of evidence indicate that reactive oxygen species (ROS) produced by mitochondria and other sources play an essential role in mediating ventricular remodeling after myocardial infarction and the development of heart failure. Antioxidants scavenge ROS, thereby maintaining the reduced environment of cells and inhibiting ventricular remodeling in the heart. Thioredoxin not only functions as a major antioxidant in the heart but also interacts with important signaling molecules and transcription factors, thereby modulating various cellular functions. The activity of thioredoxin is regulated by a variety of mechanisms, such as transcription, localization, protein-protein interaction, and post-translational modification. In this review, we will summarize the cardiac effects of thioredoxin and the mechanisms by which thioredoxin mediates inhibition of ventricular remodeling.

Redox regulation of human thioredoxin network

Oxidative stresses are largely mediated by intracellular protein oxidations by reactive oxygen species (ROS). Host cells are equipped with antioxidants that scavenge ROS. The cellular reduction/oxidation (redox) balance is maintained by ROS and antioxidants. Accumulating evidence suggests that the redox balance plays an important role in cellular signaling through the redox modification of cysteine residues in various important components of the signal transduction pathway. Thioredoxin (TRX) is a small protein playing important roles in cellular responses, including cell growth, cell cycle, gene expression, and apoptosis, to maintain the redox circumstance. Moreover, many recent papers have shown that the redox regulation by TRX is deeply involved in the pathogenesis of various oxidative stress-associated disorders. This review focuses on TRX and its related molecules, and discusses the role of TRX-dependent redox regulation in oxidative stress-induced signal transduction.

Thioredoxin interacting protein is increased in sensory neurons in experimental diabetes

Diabetic neuropathy is a major complication of diabetes and has multifactoral aetiology. The exact cause of damage is unknown although high glucose and oxidative stress are known to contribute significantly. In order to identify molecular targets of the disease and possibly new therapeutic targets, we previously examined the effect of diabetes on dorsal root ganglia (DRG) neurons using Affymetrix gene chip arrays. A number of individual genes and groups of genes were found to be dysregulated; the most significant of these was thioredoxin interacting protein (Txnip). This gene was found to have increased expression in DRG from diabetic rats with all durations of diabetes examined, including those that preceded the onset of functional changes such as decreased nerve conduction velocity. Increased Txnip expression therefore represents an early change in diabetic neuropathy that could, at least in part, be responsible for causing the initial functional deficits. This study confirmed the changes in Txnip expression at the mRNA and protein levels and identified the cell types responsible for the change. Furthermore we investigated the mechanism of diabetes-induced Txnip gene induction. Neither the antioxidant dexlipotam (R-lipoic acid) nor the p38 MAP kinase inhibitor SB239063 could prevent increases in Txnip expression despite reducing oxidative stress. However, treatment of rats with insulin prevented diabetes-induced increases in Txnip gene expression. These results indicate another mechanism by which diabetes may cause oxidative damage in peripheral nerve, and may represent a novel target for therapeutic intervention.

The interaction of thioredoxin with Txnip. Evidence for formation of a mixed disulfide by disulfide exchange

The thioredoxin system plays an important role in maintaining a reducing environment in the cell. Recently, several thioredoxin binding partners have been identified and proposed to mediate aspects of redox signaling, but the significance of these interactions is unclear in part due to incomplete understanding of the mechanism for thioredoxin binding. Thioredoxin-interacting protein (Txnip) is critical for regulation of glucose metabolism, the only currently known function of which is to bind and inhibit thioredoxin. We explored the mechanism of the Txnip-thioredoxin interaction and present evidence that Txnip and thioredoxin form a stable disulfide-linked complex. We identified two Txnip cysteines that are important for thioredoxin binding and showed that this interaction is consistent with a disulfide exchange reaction between oxidized Txnip and reduced thioredoxin. These cysteines are not conserved in the broader family of arrestin domain-containing proteins, and we demonstrate that the thioredoxin-binding property of Txnip is unique. These data suggest that Txnip is a target of reduced thioredoxin and provide insight into the potential role of Txnip as a redox-sensitive signaling protein.

Exenatide inhibits beta-cell apoptosis by decreasing thioredoxin-interacting protein

Exenatide (Ex-4) is a novel anti-diabetic drug that stimulates insulin secretion and enhances beta-cell mass, but the mechanisms involved are not fully understood. We found that Ex-4 protects INS-1 beta-cells against oxidative stress-induced apoptosis (TUNEL) and also reduces expression (mRNA and protein) of thioredoxin-interacting protein (TXNIP), a pro-apoptotic factor involved in beta-cell glucose toxicity and oxidative stress. This reduction was observed in INS-1 cells, mouse, and human islets as well as in wild-type mice receiving Ex-4 and was accompanied by decreased expression of the apoptotic factors caspase-3 and Bax. To determine whether Ex-4-mediated TXNIP reduction is critical for this inhibition of apoptosis, we stably overexpressed TXNIP in INS-1 cells, which completely blunted the anti-apoptotic Ex-4 effects. Thus, Ex-4 inhibits apoptosis by reducing TXNIP expression and early initiation of Ex-4 treatment may help preserve endogenous beta-cell mass, protect against oxidative stress, and delay type 2 diabetes progression.

The thioredoxin system in retroviral infection and apoptosis

Human thioredoxin (TRX) was first identified in human T-cell leukemia virus type I (HTLV-I)-positive T-cell lines and is associated with the pathophysiology of retroviral infections. TRX is a vital component of the thiol-reducing system and regulates various cellular function (redox regulation). Members of the TRX system regulate apoptosis through a wide variety of mechanisms. A family of thioredoxin-dependent peroxidases (peroxiredoxins) protects against apoptosis by scavenging hydrogen peroxide. Thioredoxin 2 is a critical regulator of cytochrome c release and mitochondrial apoptosis; transmembrane thioredoxin-related molecule (TMX) has a protective role in endoplasmic reticulum (ER) stress-induced apoptosis. TRX interacts with apoptosis signal-regulating kinase 1 (ASK1) and is a sensor of oxidative stress. Thioredoxin binding protein-2/vitamin D(3) upregulated protein 1 is a growth suppressor and its expression is suppressed in HTLV-I-transformed cells. Studies of these molecules of the TRX system provide novel insights into the apoptosis associated with retroviral diseases.

Heterogeneous Nuclear Ribonucleoprotein G Shows Tumor Suppressive Effect against Oral Squamous Cell Carcinoma Cells

PURPOSE

Heterogeneous nuclear ribonucleoproteins (hnRNP) are nucleic acid binding proteins involved in RNA processing. We found that hnRNP G is expressed in normal human oral epithelial cells while frequently not found in the cells derived from human oral squamous cell carcinomas (HOSCC). The current study was designed to test the hypothesis that hnRNP G is a tumor suppressor.

EXPERIMENTAL DESIGN

We investigated the expression levels of hnRNP G protein in normal, precancerous, and malignant oral tissues by in situ immunohistochemistry. In addition, wild-type or mutant hnRNP G was ectopically overexpressed in HOSCC cells and their effects on cellular replication kinetics, colonogenic efficiency, anchorage-independent growth, and in vivo tumorigenicity were determined.

RESULTS

In situ immunohistochemical staining showed robust presence of hnRNP G in the basal cell layers of normal oral epithelium but the level of its staining was markedly reduced in dysplastic or cancerous tissues. Ectopic expression of wild-type hnRNP G in cancer cells lacking hnRNP G expression or containing mutant hnRNP G resulted in severe retardation of proliferation, reduction of colonogenic efficiency, loss of anchorage-independent growth, and reduction of in vivo tumorigenicity in immunocompromised mice. In addition, hnRNP G overexpression led to up-regulation of the expression of TXNIP, a cell cycle inhibitory gene, and significantly reduced the expression of the genes that promote cellular proliferation, such as EGR1, JUND, JUNB, FOS, FOSL1, ROS, and KIT.

CONCLUSIONS

These results indicate that hnRNP G is a tumor suppressor against HOSCC but its mechanisms of action remain to be further investigated.

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

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

Thioredoxin-interacting protein (txnip) is a glucocorticoid-regulated primary response gene involved in mediating glucocorticoid-induced apoptosis

Glucocorticoid hormones induce apoptosis in lymphoid cells. This process is transcriptionally regulated and requires de novo RNA/protein synthesis. However, the full spectrum of glucocorticoid-regulated genes mediating this cell death process is unknown. Through gene expression profiling we discovered that the expression of thioredoxin-intereacting protein (txnip) mRNA is significantly induced by the glucocorticoid hormone dexamethasone not only in the murine T-cell lymphoma line WEHI7.2, but also in normal mouse thymocytes. This result was confirmed by Northern blot analysis in multiple models of dexamethasone-induced apoptosis. The induction of txnip mRNA by dexamethasone appears to be mediated through the glucocorticoid receptor as it is blocked in the presence of RU486, a glucocorticoid receptor antagonist. Deletion and mutation analysis of the txnip promoter identified a functional glucocorticoid response element in the txnip promoter. Reporter assays demonstrated that this glucocorticoid response element was necessary and sufficient for induction of txnip by dexamethasone. Expression of a GFP-TXNIP fusion protein was sufficient to induce apoptosis in WEHI7.2 cells, and repression of endogenous txnip by RNA interference inhibited dexamethasone-induced apoptosis in WEHI7.2 cells. Together, these findings indicate that txnip is a novel glucocorticoid-induced primary target gene involved in mediating glucocorticoid-induced apoptosis.

Genes associated with the formation of germ cells from embryonic stem cells in cultures containing different glucose concentrations

In a previous study, we established a system for visualizing the development of germ cells from mouse embryonic stem (ES) cells in culture using knock-in ES clones in which visual reporter genes were expressed from the mouse vasa homolog, Mvh. While assessing various culture conditions, we found that germ-cell formation was markedly depressed in low glucose medium. Using a repeated polymerase chain reaction (PCR) subtraction method, we identified genes that were differentially expressed in low versus high glucose media. Three genes that were predominantly expressed in high glucose medium, thioredoxin-interacting protein (Txnip), pituitary tumor-transforming gene 1 (Pttg), and RuvB-like protein 2 (RuvBl2), were further investigated. These genes were also found to be highly expressed in adult and embryonic gonads, and RuvBl2 in particular, which encodes an ATP-dependent DNA helicase, was specifically detected in the spermatocytes and spermatids of the adult testis as well as in primordial germ cells. Furthermore, using a green fluorescent protein (GFP) fusion construct, we found that RuvBl2 was expressed in both the nucleus and cytoplasm of testicular germ cells. These findings suggest a possible relationship between glucose metabolism and germ-cell development.

A yeast two-hybrid knockout strain to explore thioredoxin-interacting proteins in vivo

All organisms contain thioredoxin (TRX), a regulatory thiol:disulfide protein that reduces disulfide bonds in target proteins. Unlike animals and yeast, plants contain numerous TRXs for which no function has been assigned in vivo. Recent in vitro proteomic approaches have opened the way to the identification of >100 TRX putative targets, but of which none of the numerous plant TRXs can be specifically associated. In contrast, in vivo methodologies, including classical yeast two-hybrid (Y2H) systems, failed to reveal the expected high number of TRX targets. Here, we developed a yeast strain named CY306 designed to identify TRX targets in vivo by a Y2H approach. CY306 contains a GAL4 reporter system but also carries deletions of endogenous genes encoding cytosolic TRXs (TRX1 and TRX2) that presumably compete with TRXs introduced as bait. We demonstrate here that, in the CY306 strain, yeast TRX1 and TRX2, as well as Arabidopsis TRX introduced as bait, interact with known TRX targets or putative partners such as yeast peroxiredoxins AHP1 and TSA1, whereas the same interactions cannot be detected in classical Y2H strains. Thanks to CY306, we also show that TRXs interact with the phosphoadenosine-5-phosphosulfate (PAPS) reductase MET16 through a conserved cysteine. Moreover, interactions visualized in CY306 are highly specific depending on the TRX and targets tested. CY306 constitutes a relevant genetic system to explore the TRX interactome in vivo and with high specificity, and opens new perspectives in the search for new TRX-interacting proteins by Y2H library screening in organisms with multiple TRXs.

Catalytic Degradation of Vitamin D Up-regulated Protein 1 mRNA Enhances Cardiomyocyte Survival and Prevents Left Ventricular Remodeling after Myocardial Ischemia

Vitamin D3 up-regulated protein 1 (VDUP1) is a key mediator of oxidative stress on various cellular processes via downstream effects on apoptosis signaling kinase 1 (ASK1) and p38 mitogen-activated protein kinase (MAPK). Here, we report that VDUP1 expression is significantly increased in rat hearts following acute myocardial ischemia, suggesting it may have important regulatory effects on cardiac physiological processes during periods of oxidative stress. Transfection of H9C2 cardiomyoblasts with a sequence-specific VDUP1 DNA enzyme to down-regulate VDUP1 mRNA expression significantly reduced apoptosis and enhanced cell survival under conditions of H(2)O(2) stress, and these effects involved inhibition of ASK1 activity. Direct intracardiac injection of the DNA enzyme at the time of acute myocardial infarction reduced myocardial VDUP1 mRNA expression and resulted in prolonged reduction in cardiomyocyte apoptosis and ASK1 activity. Moreover, down-regulation of VDUP1 was accompanied by significant reduction in cardiac expression of pro-collagen type I alpha2 mRNA level, as well as marked reduction in myocardial scar formation. These features were accompanied by significant improvement in cardiac function. Together, these results suggest a direct role for VDUP1 in the adverse effects of ischemia and oxidative stress on cardiomyocyte survival, left ventricular collagen deposition, and cardiac function. Strategies to inhibit VDUP1 expression and/or function during acute ischemic events may be beneficial to cardiac functional recovery and prevention of left ventricular remodeling.

Impaired fatty acid utilization in thioredoxin binding protein-2 (TBP-2)-deficient mice: a unique animal model of Reye syndrome

Thioredoxin binding protein-2 (TBP-2) is a negative regulator of thioredoxin and has multiple regulatory functions in cellular redox, growth, differentiation, apoptosis, and aging. To investigate the function of TBP-2 in vivo, we generated mice with targeted inactivation of TBP-2 (TBP-2-/- mice). Here, we show that TBP-2 expression is markedly up-regulated during fasting in wild-type mice, while TBP-2-/- mice were predisposed to death with bleeding tendency, as well as hepatic and renal dysfunction as a result of 48 h of fasting. The fasting-induced death was rescued by supplementation of glucose but not by that of oleic acid, suggesting that inability of fatty acid utilization plays an important role in the anomaly of TBP-2-/- mice. In these mice, plasma free fatty acids levels are higher, whereas glucose levels are lower than those of wild-type mice. Compared with wild-type mice, TBP-2-/- mice showed increased levels of plasma ketone bodies, pyruvate and lactate, indicating that Krebs cycle-mediated fatty acid utilization is impaired. Because the fatal impairment of fatty acid utilization is a characteristically metabolic feature of Reye (-like) syndrome, TBP-2-/- mouse may represent a novel model for investigating the pathophysiology of these disorders.

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

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

Gene expression profiling in INS-1 cells overexpressing thioredoxin-interacting protein

Thioredoxin-interacting protein (TXNIP) is overexpressed in diabetes and has deleterious effects on pancreatic beta-cells and the cardiovascular system. TXNIP is a regulator of the cellular redox state, but has also been suggested to act as a transcriptional repressor. However, the genes and pathways regulated by TXNIP remain unknown. We therefore compared gene expression in INS-1 insulinoma beta-cells overexpressing TXNIP and control LacZ-overexpressing cells using the Affymetrix 230A rat chip. Analysis with the Bayes methodology revealed 98 differentially expressed genes, 90 of which were down-regulated, consistent with the predicted role of TXNIP as a repressor. Using the PathwayAssist software, we found that affected genes were involved in cell death/survival and insulin secretion, and confirmed these findings by real-time RT-PCR and by functional studies. Thus, aside from regulating the cellular redox, TXNIP does modulate overall gene transcription and thereby may further enhance beta-cell death and impair insulin secretion.

VDUP1: a potential mediator of expansion-induced lung growth and epithelial cell differentiation in the ovine fetus

The degree of fetal lung expansion is a critical determinant of fetal lung growth and alveolar epithelial cell (AEC) differentiation, although the mechanisms involved are unknown. As VDUP1 (vitamin D3-upregulated protein 1) can modulate cell proliferation, can induce cell differentiation, and is highly expressed in the lung, we have investigated the effects of fetal lung expansion on VDUP1 expression and its relationship to expansion-induced fetal lung growth and AEC differentiation in fetal sheep. Alterations in fetal lung expansion caused profound changes in VDUP1 mRNA levels in lung tissue. Increased fetal lung expansion significantly reduced VDUP1 mRNA levels from 100+/-8% in control fetuses to 37+/-4, 46+/-4, and 45+/-9% of control values at 2, 4, and 10 days of increased fetal lung expansion, respectively. Reduced fetal lung expansion increased VDUP1 mRNA levels from 100+/-16% in control fetuses to 162+/-16% of control values after 7 days. VDUP1 was localized to airway epithelium in small bronchioles, AECs, and some mesenchymal cells. Its expression was inversely correlated with cell proliferation during normal lung development (R2=0.972, P<0.002) as well as in response to alterations in fetal lung expansion (R2=0.956, P<0.001) and was positively correlated with SP-B expression during normal lung development (R2=0.803, P<0.0001) and following altered lung expansion (R2=0.817, P<0.001). We suggest that VDUP1 may be an important mediator of expansion-induced lung cell proliferation and AEC differentiation in the developing lung.

Two distinct mechanisms for loss of thioredoxin-binding protein-2 in oxidative stress-induced renal carcinogenesis

Thioredoxin is a major component of thiol-reducing system. Recently, we identified thioredoxin-binding protein-2 (TBP-2) as a negative regulator of thioredoxin. Here, we report the role of TBP-2 in oxidative renal tubular injury and the subsequent carcinogenesis by ferric nitrilotriacetate. TBP-2 was abundantly expressed in the rat kidney. Immunohistochemical analysis revealed that TBP-2 was present in association with nuclei and mitochondrial intermembrane space in the proximal tubular cells and coimmunoprecipitated with cytochrome c. After acute oxidative tubular damage, TBP-2 protein, but not messenger RNA, markedly decreased, demonstrating shortened half-life of this protein. Most cases of the induced renal cell carcinoma showed undetectable levels of TBP-2 protein, which was associated with the methylation of CpG island in the promoter region. Genome sequence analyses identified the poly-A tract in the 3' untranslated region as a mutation hot spot in this rather nonselective environment. Collectively, the amounts of TBP-2 protein were inversely associated with proliferation of tubular cells, as evaluated by proliferating cell nuclear antigen. These results suggest that loss of TBP-2 is essential for proliferation of not only neoplastic but also non-neoplastic renal tubular cells, and that TBP-2 is a target gene in oxidative stress-induced renal carcinogenesis by ferric nitrilotriacetate.

Tumor Suppressor VDUP1 Increases p27kip1 Stability by Inhibiting JAB1

Vitamin D3 up-regulated protein 1 (VDUP1) is a stress-response gene that is up-regulated by 1,25(OH)2D3 in many cells. It has been reported that VDUP1 expression is reduced in many tumor cells and the enforced expression of VDUP1 inhibits cell proliferation by arresting cell cycle progression. Here, we found that VDUP1-/- fibroblast cells proliferated more rapidly compared with wild-type cells with reduced expression of p27(kip1), a cyclin-dependent kinase inhibitor. JAB1 is known to interact with p27(kip1) and to decrease the stability of p27(kip1). VDUP1 interacted with JAB1 and restored JAB1-induced suppression of p27(kip1) stability. In this process, VDUP1 blocked the JAB1-mediated translocation of p27(kip1) from the nucleus to the cytoplasm. In addition, VDUP1 inhibited JAB1-mediated activator protein-1 activation and cell proliferation. Taken together, these results indicate that VDUP1 is a novel factor of p27(kip1) stability via regulating JAB1.

Identification and characterization of novel variants of the thioredoxin reductase 3 new transcript 1 TXNRD3NT1

We have identified and characterized a new gene sequence, TXNRD3NT1, whose transcripts, corresponding to the EST AA430236, were found by Affymetrix DNA chip analysis to be significantly down regulated in affected psoriatic tissue. The full-length cDNA of TXNRD3NT1 was isolated and characterized by combining 5'- and 3'-RACE (rapid amplication of cDNA ends) with screening a keratinocyte cDNA library, designing appropriate PCR primers, cloning amplified products, sequencing, and sequence analysis. Because part of this gene overlaps the previously described thioredoxin reductase 3 (TXNRD3) gene, we have named it TXNRD3NT1 (TXNRD3 new transcript 1). The full-length TXNRD3NT1 cDNA has 1133 nucleotides with a 251-bp 3-UTRand 2 poly(A)signal variants and 2 poly (A) sites. The TXNRD3NT1 cDNA ORF encodes for 133 amino acids, with the first four residues coding for a tubulin-beta mRNA autoregulation signal. Mapping the cDNA nucleotide sequence to the human genome sequence revealed that the TXNRD3NT1 gene has 4 exons located on Chromosome 3, at position 3q21. Exons 1 and 2 of the TXNRD3NT1 gene overlap with exons 15 and 16 of the thioredoxin reductase 2 gene which has different ORFs to that of TXNRD3NT1. The translation initiation codon ATG was found in exon 3 of the TXNRD3NT1 gene. RT-PCR showed that the full-length variant of the TXNRD3NT1 gene was expressed in only four issues (pancreas, esophagus, bone marrow, and keratinocytes) of the 30 different tissues tested. In most other tissues, an aberrant and truncated form of the transcript (i.e., missing exon 3 and part of exon 4) was detected. The result of a preliminary association study between psoriasis and single microsatellite marker of the TXNRD3NT1 gene suggests that it may not be a significant genetic determinant of psoriasis. However, we cannot exclude the possibility that other sequence variants may still exist within the TXNRD3NT1 gene. Sequence analysis of the TXNRD3NT1 gene from 8 psoriasis patients and 8 healthy controls revealed a number of synonymous SNPs that may be useful markers for future disease association studies.

Fluid shear stress inhibits vascular inflammation by decreasing thioredoxin-interacting protein in endothelial cells

Regions in the vasculature that are exposed to steady laminar blood flow are protected from atherosclerosis as compared with regions where flow is disturbed. We found that flow decreased TNF-mediated VCAM1 expression by inhibiting JNK and p38. JNK inhibition correlated with inhibition of apoptosis signal-regulating kinase 1 (ASK1), a JNK and p38 activator. Thioredoxin-interacting protein (TXNIP) is a stress-responsive protein that inhibits thioredoxin (TRX) activity. Since thioredoxin inhibits ASK1, we hypothesized that changes in TXNIP-TRX-ASK1 interactions mediate the antiinflammatory effects of flow. To explore this, we used perfused vessels and cultured ECs. Exposure of rabbit aortae or ECs to normal flow (12 dyn/cm2, 24 hours) was associated with decreased TXNIP expression and increased TRX activity compared with exposure to low flow (0.4 dyn/cm2). Normal flow inhibited TNF activation of JNK/p38 and VCAM1 expression. In cultured ECs, reduction of TXNIP expression by small interfering RNA increased TRX binding to ASK1 and inhibited TNF activation of JNK/p38 and VCAM1 expression. Conversely, overexpression of TXNIP stimulated JNK and p38. In aortae from TXNIP-deficient mice, TNF-induced VCAM1 expression was inhibited. The data suggest that TXNIP and TRX are key components of biomechanical signal transduction and establish them as potentially novel regulators of TNF signaling and inflammation in ECs.

Fluid shear stress inhibits vascular inflammation by decreasing thioredoxin-interacting protein in endothelial cells

Regions in the vasculature that are exposed to steady laminar blood flow are protected from atherosclerosis as compared with regions where flow is disturbed. We found that flow decreased TNF-mediated VCAM1 expression by inhibiting JNK and p38. JNK inhibition correlated with inhibition of apoptosis signal-regulating kinase 1 (ASK1), a JNK and p38 activator. Thioredoxin-interacting protein (TXNIP) is a stress-responsive protein that inhibits thioredoxin (TRX) activity. Since thioredoxin inhibits ASK1, we hypothesized that changes in TXNIP-TRX-ASK1 interactions mediate the antiinflammatory effects of flow. To explore this, we used perfused vessels and cultured ECs. Exposure of rabbit aortae or ECs to normal flow (12 dyn/cm2, 24 hours) was associated with decreased TXNIP expression and increased TRX activity compared with exposure to low flow (0.4 dyn/cm2). Normal flow inhibited TNF activation of JNK/p38 and VCAM1 expression. In cultured ECs, reduction of TXNIP expression by small interfering RNA increased TRX binding to ASK1 and inhibited TNF activation of JNK/p38 and VCAM1 expression. Conversely, overexpression of TXNIP stimulated JNK and p38. In aortae from TXNIP-deficient mice, TNF-induced VCAM1 expression was inhibited. The data suggest that TXNIP and TRX are key components of biomechanical signal transduction and establish them as potentially novel regulators of TNF signaling and inflammation in ECs.

Thioredoxin: a multifunctional antioxidant enzyme in kidney, heart and vessels

PURPOSE OF REVIEW

Recent studies indicate that an imbalance in cell redox state alters multiple cell pathways that may contribute to the pathogenesis of cardiovascular disorders including hypertension and renal failure.

RECENT FINDINGS

The thioredoxin system (thioredoxin, thioredoxin reductase, and NADPH) is a ubiquitous thiol oxidoreductase system that regulates cellular reduction/oxidation (redox) status. Thioredoxin plays an essential role in cell function by limiting oxidative stress directly via antioxidant effects and indirectly by protein-protein interactions with key signaling molecules such as thioredoxin-interacting protein (TXNIP). Examples include the findings that hyperglycemia and diabetes induce TXNIP and decrease thioredoxin activity, while steady blood flow decreases TXNIP and increases thioredoxin activity.

SUMMARY

Based on these findings we propose that thioredoxin and its endogenous regulators represent important future targets to develop clinical therapies for diseases associated with oxidative stress.

VDUP1 Is Required for the Development of Natural Killer Cells

Vitamin D3 upregulated protein 1 (VDUP1) is a stress-response gene that is upregulated by 1,25(OH)2D3 in tumor cells. The in vivo roles of VDUP1 were investigated by producing mice lacking VDUP1 (VDUP1-/- mice). VDUP1-/- mice showed minimal changes in the development of T and B cells, but there was a profound reduction in the numbers of natural killer (NK) cells. As well, these mice showed decreased NK activity. In the VDUP1-/- mice, the expression of CD122 was reduced, demonstrating that VDUP1 is required for CD122 expression and NK maturation. In addition, severe lymphoid hyperplasia in the small intestine was observed in VDUP1-/- mice. Taken together, these results suggest that VDUP1 is a critical factor for the development and function of NK cells in vivo.

Thioredoxin-interacting protein deficiency disrupts the fasting-feeding metabolic transition

Through a positional cloning approach, the thioredoxin-interacting protein gene (Txnip) was recently identified as causal for a form of combined hyperlipidemia in mice (Bodnar, J. S., A. Chatterjee, L. W. Castellani, D. A. Ross, J. Ohmen, J. Cavalcoli, C. Wu, K. M. Dains, J. Catanese, M. Chu, S. S. Sheth, K. Charugundla, P. Demant, D. B. West, P. de Jong, and A. J. Lusis. 2002. Positional cloning of the combined hyperlipidemia gene Hyplip1. Nat. Genet. 30: 110-116). We now show that Txnip-deficient mice in the fed state exhibit a metabolic profile similar to fasted mice, including increased levels of plasma ketone bodies and free fatty acids, decreased glucose, and increased hepatic expression of peroxisome proliferator-activated receptor-gamma coactivator-1alpha, phosphoenolpyruvate carboxykinase, glucose-6-phosphatase, and acyl-CoA oxidase. Dramatic differences in the expression of key metabolic enzymes were also observed in other tissues, and the fat-to-muscle ratio of Txnip-deficient mice was increased by approximately 40%. We demonstrate an effect of Txnip on the redox status, as the Txnip-deficient mice in the fed state had a significant increase in the ratio of NADH to NAD(+). Surprisingly, we observed that Txnip-deficient mice and wild-type mice had similar levels of thioredoxin activity, suggesting that the effects of Txnip deficiency may be mediated in part by other interactions. These results indicate a role for Txnip in the metabolic response to feeding and the maintenance of the redox status.

Thioredoxin modulates activator protein 1 (AP-1) activity and p27Kip1 degradation through direct interaction with Jab1

Thioredoxin (Trx) is a cellular redox enzyme that plays multiple roles in regulating cell growth and apoptosis. Jun activation domain-binding protein 1 (Jab1) was originally identified as a coactivator of activator protein 1 (AP-1) transcription and was also shown to promote degradation of the cyclin-dependent kinase inhibitor, p27Kip1. Recently, Jab1 expression was associated with the progression and poor prognosis of pituitary, epithelial ovarian, and breast cancers, suggesting that it plays a role in oncogenesis. Here, we report that Trx specifically interacts with and modulates the function of Jab1. Fluorescence resonance energy transfer and co-immunoprecipitation studies revealed that Trx and Jab1 colocalize and directly interact with each other. Further, Trx negatively regulates two important Jab1-controlled signaling pathways, activation of AP-1 transcription and degradation of p27Kip1, probably through a direct interaction between Trx and C-terminal of Jab1. The negative effect of Trx on AP-1 activity is Jab1-dependent, as it disappears when Jab1 levels are suppressed by an antisense approach. In addition, Trx competes with p27Kip1 for Jab1 binding. Taken together, our results suggest that Trx may regulate cell cycle and growth through a novel modulation of Jab1-mediated proliferation signals, further indicating that Trx may have the ability to control tumor progression.

Regulation of human osteoclast differentiation by thioredoxin binding protein-2 and redox-sensitive signaling

Differential expression of TBP-2 and Trx-1 occurs during osteoclastogenesis. Adenoviral overexpression of TBP-2 in osteoclast precursors inhibits Trx-1 expression, osteoclast formation, and AP-1 binding activity. TBP-2 and Trx-1 are key regulators of osteoclastogenesis.

INTRODUCTION

Thioredoxin binding protein-2 (TBP-2) negatively regulates thioredoxin-1 (Trx-1), a key endogenous modulator of cellular redox and signaling. In gene array analysis, we found that TBP-2 expression was reduced during human osteoclast differentiation compared with macrophage differentiation. Our aim was to determine the roles of TBP-2 and Trx-1 in human osteoclastogenesis and RANKL signaling.

MATERIALS AND METHODS

Osteoclasts or macrophages were generated from colony-forming unit-granulocyte macrophage (CFU-GM) precursors treated with sRANKL and macrophage-colony-stimulating factor (M-CSF), or M-CSF alone, respectively. Expression of TBP-2 and Trx-1 was quantified by real-time PCR and Western analysis. Adenoviral gene transfer was used to overexpress TBP-2 in precursors. NF-kappaB and activator protein 1 (AP-1) signaling was assessed with EMSA.

RESULTS

In the presence of sRANKL, expression of TBP-2 was decreased, whereas Trx-1 expression was increased. The antioxidant N-acetylcysteine reversed this pattern and markedly inhibited osteoclastogenesis. Adenoviral overexpression of human TBP-2 in precursors inhibited osteoclastogenesis and Trx-1 expression, inhibited sRANKL-induced DNA binding of AP-1, but enhanced sRANKL-induced DNA binding of NF-kappaB.

CONCLUSIONS

These data support significant roles for TBP-2 and the Trx system in osteoclast differentiation that are mediated by redox regulation of AP-1 transcription. A likely mechanism of stress signal induction of bone resorption is provided. Modulators of the Trx system such as antioxidants have potential as antiresorptive therapies.

Suboptimal action of NF-kappaB in Fanconi anemia cells results from low levels of thioredoxin

Electrophoretic mobility shift assays (EMSA) revealed that under standard cell culture conditions NF-kappaB was induced in Fanconi anemia fibroblasts in contrast to control cells. Dithiothreitol, a potent synthetic redox potential-delivering compound, when added to growing cells, prevented this induction of NF-kappaB and, simultaneously, chromosomal instability was reduced. Fanconi anemia cells possess low endogenous levels of the naturally occurring antioxidant thioredoxin. Transfection of Fanconi anemia cells with thioredoxin cDNA containing a nuclear localization signal prevented both spontaneous as well as mitomycin C-induced chromosomal instability. A promotor construct with two NF-kappaB binding sites in front of the CAT gene induced little CAT expression in cells with low thioredoxin content in spite of induced NF-kappaB. In cells with higher thioredoxin content CAT expression was increased. Cotransfection of the NF-kappaB-dependent CAT plasmid with the Trx/nuc-plasmid into FA fibroblasts increased the CAT expression to almost that of control cells, indicating that in this model system with diminished thioredoxin content NF-kappaB requires thioredoxin for binding to its specific promotor. Since Fanconi anemia cells have low thioredoxin contents, NF-kappaB-dependent genes are expressed insufficiently. This explains part of the pathophysiological processes observed in Fanconi anemia.

Importin alpha1 (Rch1) mediates nuclear translocation of thioredoxin-binding protein-2/vitamin D(3)-up-regulated protein 1

Thioredoxin-binding protein-2 (TBP-2)/vitamin D(3) up-regulated protein 1 is an endogenous molecule interacting with thioredoxin (TRX), negatively regulating TRX function, and being implicated in the suppression of tumor development and metastasis. We found that TBP-2 ectopically expressed in the breast cancer cell line MCF-7 was localized predominantly in the nucleus exhibiting growth suppressive activity. The nuclear accumulation of endogenous TBP-2 protein was also demonstrated when the cells were treated with an anti-cancer drug, suberoylanilide hydroxamic acid. To investigate the mechanism underlying the nuclear localization, we performed a yeast two-hybrid screening and identified importin alpha(1) (Rch1) as a protein interacting with TBP-2. The physical interaction between TBP-2 and Rch1 was confirmed with a glutathione S-transferase pull-down assay. The interaction of TBP-2 was specific to Rch1 among other importin alpha subfamilies (Qip1 and NPI-1), and amino acids 1-227 of TBP-2 were sufficient for both the interaction with Rch1 and the nuclear localization, although there is no typical nuclear localization signal in this sequence. The expression of short interfering RNA of Rch1 suppressed suberoylanilide hydroxamic acid-induced nuclear accumulation of TBP-2. Collectively, our results strongly suggest that an interaction with importin system is required for TBP-2 nuclear translocation and growth control tightly associated with TRX-dependent redox regulation of transcription factors.

Differentiation-associated redox-regulation in human B cell lines from stem cell/pro-B to plasma cell

Redox-regulation of receptors and transcription factors are important for lymphocyte activation, differentiation and apoptosis. Thioredoxin (Trx) is a key redox-regulating protein and oxidative stress sensor operating in synergy with Trx-reductase and protein disulfide isomerase (PDI). The expression of Trx, PDI, and the Trx-regulated transcription-factor Pax5 were analyzed in a panel of human B cell lines and were compared with that of the Bcl-2 family proteins, also redox-controlled. The panel included representative cells from various stages: FLEB14-4 (pro-B); REH and NALM-6 (pre-B); Rael and Daudi (small mature B); U-698 and NC0467.3 (B-blasts); LP-1, U-1996, and U-266 (plasma cells). We found a significant congruence and co-variation of Trx and Bcl-2 levels in the B-lineage, with high expression levels in early stages (pro-B and pre-B) and in the late stage representing terminally-differentiated plasma cells, whereas mid-stage small resting B cells showed a very low expression. PDI increased significantly in plasma-blasts and plasma cells, indicating its importance in the highly specialized immunoglobulin assembly-machinery, including disulfide-bond isomerization. Pax5 was expressed in early and mid-stages, but was silenced in terminal stages. We conclude that the high Trx and Bcl-2-expression early and late in the B cell maturation pathway reflects a redox-strategy favoring an increased survival potential of the B cells at those stages.

Mice Lacking Thioredoxin-interacting Protein Provide Evidence Linking Cellular Redox State to Appropriate Response to Nutritional Signals

Thioredoxin-interacting protein (Txnip) is a ubiquitous protein that binds with high affinity to thioredoxin and inhibits its ability to reduce sulfhydryl groups via NADPH oxidation. HcB-19 mice contain a nonsense mutation in Txnip that eliminates its expression. Unlike normal animals, HcB-19 mice have approximately 3-fold increase in insulin levels when fasted. The C-peptide/insulin ratio is normal, suggesting that the hyperinsulinemia is due to increased insulin secretion. Fasted HcB-19 mice are hypoglycemic, hypertriglyceridemic, and have higher than normal levels of ketone bodies. Ablation of pancreatic beta-cells with streptozotocin completely blocks the fasting-induced hypoglycemia/hypertriglyceridemia, suggesting that these abnormalities are due to excess insulin secretion. This is supported by increased hepatic mRNA levels of the insulin-inducible, lipogenic transcription factor sterol-responsive element-binding protein-1c and two of its targets, acetyl-CoA carboxylase and fatty acid synthase. During a prolonged fast, the hyperinsulinemia up-regulates lipogenesis but fails to down-regulate hepatic phosphoenolpyruvate carboxykinase mRNA expression. Hepatic ratios of reduced:oxidized glutathione, established regulators of gluconeogenic/glycolytic/lipogenic enzymes, were elevated 30% in HcB-19 mice, suggesting a loss of Txnip-enhanced sulfhydryl reduction. The altered hepatic enzymatic profiles of HcB-19 mice divert phosphoenolpyruvate to glyceroneogenesis and lipogenesis rather than gluconeogenesis. Our findings implicate Txnip-modulated sulfhydryl redox as a central regulator of insulin secretion in beta-cells and regulation of many of the branch-points of gluconeogenesis/glycolysis/lipogenesis.

Identification of novel differentially expressed genes by the effect of a high-fat n-6 diet in experimental breast cancer

In previous studies, we demonstrated that high corn oil diets promote the development of 7,12-dimethylbenz(alpha)anthracene (DMBA)-induced mammary tumors. In this study, we have investigated whether modulation of gene expression is one of the mechanisms by which this high-fat diet exerts such effects. Female Sprague-Dawley rats were induced with DMBA and fed normolipidic (3% corn oil) or high-fat (20% corn oil) diet. Screening of genes differentially expressed in adenocarcinomas from the high corn oil diet group compared to the control diet group was performed with cDNA microarrays. The resulting six upregulated and nine downregulated genes were validated by Northern blot and/or reverse transcription (RT)-polymerase chain reaction (PCR). Further investigation in a higher number of adenocarcinomas showed that in the high-fat n-6 diet group, where the tumor phenotype was verified to be more aggressive, the expression of submaxillary gland alpha-2u globulin, vitamin D(3)-upregulated protein 1 (VDUP1), H19, and the unknown function gene that codifies the expressed sequence tag (EST)-Rn.32385 was significantly decreased in comparison with the control group (C). These results, together with the fact that VDUP1, H19, and this globulin have been associated with cell proliferation and differentiation, open a new line of research about how the underexpression of these genes contributes to the stimulating effect of a high corn oil diet on experimental mammary carcinogenesis.

Hyperglycemia promotes oxidative stress through inhibition of thioredoxin function by thioredoxin-interacting protein

Increased intracellular reactive oxygen species (ROS) contribute to vascular disease and pro-atherosclerotic effects of diabetes mellitus may be mediated by oxidative stress. Several ROS-scavenging systems tightly control cellular redox balance; however, their role in hyperglycemia-induced oxidative stress is unclear. A ubiquitous antioxidative mechanism for regulating cellular redox balance is thioredoxin, a highly conserved thiol reductase that interacts with an endogenous inhibitor, thioredoxin-interacting protein (Txnip). Here we show that hyperglycemia inhibits thioredoxin ROS-scavenging function through p38 MAPK-mediated induction of Txnip. Overexpression of Txnip increased oxidative stress, while Txnip gene silencing restored thioredoxin activity in hyperglycemia. Diabetic animals exhibited increased vascular expression of Txnip and reduced thioredoxin activity, which normalized with insulin treatment. These results provide evidence for the impairment of a major ROS-scavenging system in hyperglycemia. These studies implicate reduced thioredoxin activity through interaction with Txnip as an important mechanism for vascular oxidative stress in diabetes mellitus.