Thioredoxin, a mediator of growth inhibition, maps to 9q31

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.

Cardiac transcriptional response to acute and chronic angiotensin II treatments

Exposure of experimental animals to increased angiotensin II (ANG II) induces hypertension associated with cardiac hypertrophy, inflammation, and myocardial necrosis and fibrosis. Some of the most effective antihypertensive treatments are those that antagonize ANG II. We investigated cardiac gene expression in response to acute (24 h) and chronic (14 day) infusion of ANG II in mice; 24-h treatment induces hypertension, and 14-day treatment induces hypertension and extensive cardiac hypertrophy and necrosis. For genes differentially expressed in response to ANG II treatment, we tested for significant regulation of pathways, based on Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Microarray Pathway Profiler (GenMAPP) databases, as well as functional classes based on Gene Ontology (GO) terms. Both acute and chronic ANG II treatments resulted in decreased expression of mitochondrial metabolic genes, notably those for the electron transport chain and Krebs-TCA cycle; chronic ANG II treatment also resulted in decreased expression of genes involved in fatty acid metabolism. In contrast, genes involved in protein translation and ribosomal activity increased expression following both acute and chronic ANG II treatments. Some classes of genes showed differential response between acute and chronic ANG II treatments. Acute treatment increased expression of genes involved in oxidative stress and amino acid metabolism, whereas chronic treatments increased cytoskeletal and extracellular matrix genes, second messenger cascades responsive to ANG II, and amyloidosis genes. Although a functional linkage between Alzheimer disease, hypertension, and high cholesterol has been previously documented in studies of brain tissue, this is the first demonstration of induction of Alzheimer disease pathways by hypertension in heart tissue. This study provides the most comprehensive available survey of gene expression changes in response to acute and chronic ANG II treatment, verifying results from disparate studies, and suggests mechanisms that provide novel insight into the etiology of hypertensive heart disease and possible therapeutic interventions that may help to mitigate its effects.

Redox regulation by thioredoxin in cardiovascular diseases

Increasing evidence has indicated that the modulation of intracellular redox states has important aspects to cellular events, such as cellular proliferation, activation, growth inhibition, or death via the regulation of intracellular signal transduction and gene expression. Thioredoxin (TRX) is a multifunctional stress-inducible protein, which protects cells from various types of stresses. TRX has not only a scavenging activity of reactive oxygen species, but also a regulating activity of various intracellular molecules including transcription factors. We demonstrated that the serum TRX levels are correlated with the severity of heart failure, and are negatively correlated with left ventricular ejection fractions of patients with heart failure. The expression of TRX is enhanced in endothelial cells and macrophages in human atherosclerotic plaques, in balloon-injured rat arteries, and in damaged cardiomyocytes of rats with acute myocarditis. Overexpression of TRX in transgenic mice attenuates adriamycin-induced cardiotoxicity by reducing oxidative stresses. These findings suggest that TRX and the redox system modulated by TRX have an important role in cellular defense against oxidative stress in cardiovascular diseases.

The thioredoxin system?From science to clinic

The thioredoxin system-formed by thioredoxin reductase and its characteristic substrate thioredoxin-is an important constituent of the intracellular redox milieu. Interactions with many different metabolic pathways such as DNA-synthesis, selenium metabolism, and the antioxidative network as well as significant species differences render this system an attractive target for chemotherapeutic approaches in many fields of medicine-ranging from infectious diseases to cancer therapy. In this review we will present and evaluate the preclinical and clinical results available today. Current trends in drug development are emphasized.

Protein kinase C as a molecular target for cancer prevention by selenocompounds

Selenium is a very effective cancer-preventive agent, suppressing tumor promotion and early stages of tumor progression. However, the mechanisms by which selenium exerts these cancer-preventive actions are not known. Protein kinase C (PKC) is a receptor for certain tumor promoters and also plays a crucial role in events related to tumor progression. Therefore, it is not only a potential target for the cancer-preventive activity of selenium, but also it has the structural basis for interaction with selenium. Redox-active selenocompounds can inactivate PKC, particularly the Ca(2+)-dependent isozymes, by reacting with the critical cysteine-rich regions present within the catalytic domain while, in some cases, also reacting with the cysteine residues present within the zinc-fingers of the regulatory domain. The selenoprotein thioredoxin reductase (TR), acting through thioredoxin, reverses the inactivation of PKC induced by selenometabolites. Furthermore, TR, through a direct interaction involving its selenosulfur center with the zinc-thiolates of PKC, can reverse the redox modification of this kinase induced by selenometabolites. Thus the selenometabolite-induced toxicity is reversed by a selenoprotein, and therefore an interrelationship exists between these two mechanisms of selenium actions. Moreover, this also explains how a resistance to selenium develops in advanced tumor cells probably due to an overexpression of functional TR. Selenium-induced inactivation of PKC may, at least in part, be responsible for the selenium-induced inhibition of tumor promotion, cell growth, invasion, and metastasis, as well as for the induction of apoptosis.

Properties and biological activities of thioredoxins

The mammalian thioredoxins are a family of small (approximately 12 kDa) redox proteins that undergo NADPH-dependent reduction by thioredoxin reductase and in turn reduce oxidized cysteine groups on proteins. The two main thioredoxins are thioredoxin- 1, a cytosolic and nuclear form, and thioredoxin-2, a mitochondrial form. Thioredoxin-1 has been studied more. It performs many biological actions including the supply of reducing equivalents to thioredoxin peroxidases and ribonucleotide reductase, the regulation of transcription factor activity, and the regulation of enzyme activity by heterodimer formation. Thioredoxin-1 stimulates cell growth and is an inhibitor of apoptosis. Thioredoxins may play a role in a variety of human diseases including cancer. An increased level of thioredoxin-1 is found in many human tumors, where it is associated with aggressive tumor growth. Drugs are being developed that inhibit thioredoxin and that have antitumor activity.

Properties and biological activities of thioredoxins

The mammalian thioredoxins are a family of small (approximately 12 kDa) redox proteins that undergo NADPH-dependent reduction by thioredoxin reductase and in turn reduce oxidized cysteine groups on proteins. The two main thioredoxins are thioredoxin-1, a cytosolic and nuclear form, and thioredoxin-2, a mitochondrial form. Thioredoxin-1 has been studied more. It performs many biological actions including the supply of reducing equivalents to thioredoxin peroxidases and ribonucleotide reductase, the regulation of transcription factor activity, and the regulation of enzyme activity by heterodimer formation. Thioredoxin-1 stimulates cell growth and is an inhibitor of apoptosis. Thioredoxins may play a role in a variety of human diseases including cancer. An increased level of thioredoxin-1 is found in many human tumors, where it is associated with aggressive tumor growth. Drugs are being developed that inhibit thioredoxin and that have antitumor activity.

Physiological functions of thioredoxin and thioredoxin reductase

Thioredoxin, thioredoxin reductase and NADPH, the thioredoxin system, is ubiquitous from Archea to man. Thioredoxins, with a dithiol/disulfide active site (CGPC) are the major cellular protein disulfide reductases; they therefore also serve as electron donors for enzymes such as ribonucleotide reductases, thioredoxin peroxidases (peroxiredoxins) and methionine sulfoxide reductases. Glutaredoxins catalyze glutathione-disulfide oxidoreductions overlapping the functions of thioredoxins and using electrons from NADPH via glutathione reductase. Thioredoxin isoforms are present in most organisms and mitochondria have a separate thioredoxin system. Plants have chloroplast thioredoxins, which via ferredoxin-thioredoxin reductase regulates photosynthetic enzymes by light. Thioredoxins are critical for redox regulation of protein function and signaling via thiol redox control. A growing number of transcription factors including NF-kappaB or the Ref-1-dependent AP1 require thioredoxin reduction for DNA binding. The cytosolic mammalian thioredoxin, lack of which is embryonically lethal, has numerous functions in defense against oxidative stress, control of growth and apoptosis, but is also secreted and has co-cytokine and chemokine activities. Thioredoxin reductase is a specific dimeric 70-kDa flavoprotein in bacteria, fungi and plants with a redox active site disulfide/dithiol. In contrast, thioredoxin reductases of higher eukaryotes are larger (112-130 kDa), selenium-dependent dimeric flavoproteins with a broad substrate specificity that also reduce nondisulfide substrates such as hydroperoxides, vitamin C or selenite. All mammalian thioredoxin reductase isozymes are homologous to glutathione reductase and contain a conserved C-terminal elongation with a cysteine-selenocysteine sequence forming a redox-active selenenylsulfide/selenolthiol active site and are inhibited by goldthioglucose (aurothioglucose) and other clinically used drugs.

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 interferon-beta and tamoxifen combination induces apoptosis using thioredoxin reductase

Interferons (IFNs) suppress cell growth by inducing cellular genes. The anti-estrogen tamoxifen (Tam), binds to estrogen receptor and inhibits transcription of estrogen stimulated genes. In cells resistant to IFN-induced growth suppression, IFN/Tam combination causes cell death. We previously reported that the combination of IFN-beta and Tam was a more potent growth suppressor of human tumor xenografts than either agent alone. The IFN/Tam combination acts in a manner similar to the IFN/retinoic acid combination. Using a genetic technique, we have recently identified several genes associated with retinoid-IFN-induced mortality (GRIM). One such gene, GRIM-12, was identical to human thioredoxin reductase (TR). In the present study we have examined whether the IFN/Tam combination also requires GRIM-12 for inducing cell death. We report here that GRIM-12 is necessary for mediating the cell death effects of IFN/Tam, and its expression is induced by IFN/Tam at a post-transcriptional stage. Repression of GRIM-12 levels either by antisense expression or by dominant negative inhibitors caused resistance to IFN/Tam induced death and promoted cell growth. Overexpression of GRIM-12 increased IFN/Tam induced apoptosis. Thus, these studies have identified a critical role for GRIM-12 (TR) in apoptosis.

Thioredoxin reductase mediates cell death effects of the combination of beta interferon and retinoic acid

Interferons (IFNs) and retinoids are potent biological response modifiers. By using JAK-STAT pathways, IFNs regulate the expression of genes involved in antiviral, antitumor, and immunomodulatory actions. Retinoids exert their cell growth-regulatory effects via nuclear receptors, which also function as transcription factors. Although these ligands act through distinct mechanisms, several studies have shown that the combination of IFNs and retinoids synergistically inhibits cell growth. We have previously reported that IFN-beta-all-trans-retinoic acid (RA) combination is a more potent growth suppressor of human tumor xenografts in vivo than either agent alone. Furthermore, the IFN-RA combination causes cell death in several tumor cell lines in vitro. However, the molecular basis for these growth-suppressive actions is unknown. It has been suggested that certain gene products, which mediate the antiviral actions of IFNs, are also responsible for the antitumor actions of the IFN-RA combination. However, we did not find a correlation between their activities and cell death. Therefore, we have used an antisense knockout approach to directly identify the gene products that mediate cell death and have isolated several genes associated with retinoid-IFN-induced mortality (GRIM). In this investigation, we characterized one of the GRIM cDNAs, GRIM-12. Sequence analysis suggests that the GRIM-12 product is identical to human thioredoxin reductase (TR). TR is posttranscriptionally induced by the IFN-RA combination in human breast carcinoma cells. Overexpression of GRIM-12 causes a small amount of cell death and further enhances the susceptibility of cells to IFN-RA-induced death. Dominant negative inhibitors directed against TR inhibit its cell death-inducing functions. Interference with TR enzymatic activity led to growth promotion in the presence of the IFN-RA combination. Thus, these studies identify a novel function for TR in cell growth regulation.

Thioredoxin expression and localization in human cell lines: detection of full-length and truncated species

Thioredoxin (Trx) is an intracellular multifunctional 12-kDa protein with a reduction/oxidation (redox) active disulfide constitutively expressed by most cells of the human body. Trx can also be released by cells such as lymphocytes upon activation or oxidative stress exposure and exert a cocytokine and cytoprotective activity. In addition, a truncated 10-kDa form of Trx has been reported. In order to better understand the function of full-length and truncated Trx, we have produced, for the first time, specific monoclonal antibodies, which can discriminate between the two forms. Using these novel antibodies, designated alpha Trx1 to alpha Trx4, a panel of cell lines derived from human B and T lymphocytes, monocytes, granulocytes, and melanomas was analyzed by immunochemical techniques. The cellular distribution differed between the two forms. All lines contained full-length Trx, also located to a minor extent on the cell surface. One exception was the melanoma cell line FM28.4, which did not show any Trx expression. Truncated Trx was present in most cells in minimal amounts only, whereas the monocytic cell lines THP-1 and U-937 expressed high amounts on the cell surface, as shown by flow cytometric analysis of living cells and confocal laser-scanning microscopy. The biological importance and function of the short versus long forms of Trx as detected by the antibodies are discussed.

Redox regulation of cellular activation

Growing evidence has indicated that cellular reduction/oxidation (redox) status regulates various aspects of cellular function. Oxidative stress can elicit positive responses such as cellular proliferation or activation, as well as negative responses such as growth inhibition or cell death. Cellular redox status is maintained by intracellular redox-regulating molecules, including thioredoxin (TRX). TRX is a small multifunctional protein that has a redox-active disulfide/dithiol within the conserved active site sequence: Cys-Gly-Pro-Cys. Adult T cell leukemia-derived factor (ADF), which we originally defined as an IL-2 receptor alpha-chain/Tac inducer produced by human T cell lymphotrophic virus-I (HTLV-I)-transformed T cells, has been identified as human TRX. TRX/ADF is a stress-inducible protein secreted from cells. TRX/ADF has both intracellular and extracellular functions as one of the key regulators of signaling in the cellular responses against various stresses. Extracellularly, TRX/ADF shows a cytoprotective activity against oxidative stress-induced apoptosis and a growth-promoting effect as an autocrine growth factor. Intracellularly, TRX/ADF is involved in the regulation of protein-protein or protein-nucleic acid interactions through the reduction/oxidation of protein cysteine residues. For example, TRX/ADF translocates from the cytosol into the nucleus by a variety of cellular stresses, to regulate the expression of various genes through the redox factor-1 (Ref-1)/APEX. Further studies to clarify the regulatory roles of TRX/ADF and its target molecules may elucidate the intracellular signaling pathways in the responses against various stresses. The concept of "redox regulation" is emerging as an understanding of the novel mechanisms in the pathogenesis of several disorders, including viral infections, immunodeficiency, malignant transformation, and degenerative disease.

A gene for a novel zinc-finger protein expressed in differentiated epithelial cells and transiently in certain mesenchymal cells

We have identified a novel zinc-finger protein whose mRNA is expressed at high levels in the epidermal layer of the skin and in epithelial cells in the tongue, palate, esophagus, stomach, and colon of newborn mice. Expression in epithelial cells is first detected at the time of their differentiation during embryonic development. In addition, during early embryonic development there is expression in mesenchymal cells of the skeletal primordia and the metanephric kidney which is later down-regulated. The expression pattern suggests that the protein could be involved in terminal differentiation of several epithelial cell types and could also be involved in early differentiation of the skeleton and kidney. The carboxyl terminus of the protein contains three zinc fingers with a high degree of homology to erythroid krüppel-like factor and binds to DNA fragments containing CACCC motifs. The amino-terminal portion of the protein is proline and serine-rich and can function as a transcriptional activator. The chromosomal location of the gene was mapped using mouse interspecific backcrosses and was shown to localize to mouse chromosome 4 and to cosegregate with the thioredoxin gene.

A survey of the goat genome transcribed in the lactating mammary gland

To fulfill its primary function, which is to synthesize milk during the course of lactation, the mammary gland requires efficient transcriptional, translational, and secretory machineries involving multiple genes among which promising candidates underlying the genetic variation of milk production have to be found. With the aim of providing a first transcriptional profile of lactating mammary tissue, a non-normalized cDNA library has been constructed from the udder of a lactating goat. After having discarded cDNA clones encoding the major milk proteins the rapid characterization of genes expressed in this tissue, by automated partial cDNA sequencing, was used to analyze a total of 435 cDNA clones. Examination of the Expressed Sequence Tags (ESTs) for similarities with sequence databases identified 234 cDNAs corresponding to 140 unique genes or proteins. Eighty-three clones, not similar to any current database entries, representing 77 novel sequences unrelated to previously described genes, were thus identified. Tissue specificity and relative abundance of 18 of these 77 unidentified clones were examined by dot blot and RT-PCR experiments. Sequence data were subsequently used to assign six genes of unknown localization in the bovine genome, to synteny groups by use of bovine-hamster cell hybrids and PCR.