Thioredoxin-dependent redox regulation of p53-mediated p21 activation

Protein-disulfide isomerase regulates the thyroid hormone receptor-mediated gene expression via redox factor-1 through thiol reduction-oxidation

Protein-disulfide isomerase (PDI) is a dithiol/disulfide oxidoreductase that regulates the redox state of proteins. We previously found that overexpression of PDI in rat pituitary tumor (GH3) cells suppresses 3,3',5-triiodothyronine (T(3))-stimulated growth hormone (GH) expression, suggesting the contribution of PDI to the T(3)-mediated gene expression via thyroid hormone receptor (TR). In the present study, we have clarified the mechanism of regulation by which TR function is regulated by PDI. Overexpression of wild-type but not redox-inactive mutant PDI suppressed the T(3)-induced GH expression, suggesting that the redox activity of PDI contributes to the suppression of GH. We considered that PDI regulates the redox state of the TR and focused on redox factor-1 (Ref-1) as a mediator of the redox regulation of TR by PDI. Interaction between Ref-1 and TRβ1 was detected. Overexpression of wild-type but not C64S Ref-1 facilitated the GH expression, suggesting that redox activity of Cys-64 in Ref-1 is involved in the TR-mediated gene expression. Moreover, PDI interacted with Ref-1 and changed the redox state of Ref-1, suggesting that PDI controls the redox state of Ref-1. Our studies suggested that Ref-1 contributes to TR-mediated gene expression and that the redox state of Ref-1 is regulated by PDI. Redox regulation of PDI via Ref-1 is a new aspect of PDI function.

The expression and functional characterization associated with cell apoptosis and proteomic analysis of the novel gene MLAA-34 in U937 cells

MLAA-34 is a novel acute monocytic leukemia (M5)-associated antigen (MLAA) that plays a role in the apoptosis of U937 cells. However, the expression and molecular mechanism of MLAA-34 in U937 cells remain largely unclear. Here, we utilized three strategies to gain insight into the expression and molecular functions of MLAA-34 and to identify its interacting proteins and pathways involved in the fine-tuning of the MLAA-34 response. Western blot analysis was performed to assess the expression of MLAA-34 in 41 cell lines and five mixed cell types, which revealed that MLAA-34 is most strongly expressed in U937 cells. Immunostaining indicated that MLAA-34 is localized in the cytoplasm and cell membrane. Furthermore, lentivirus-mediated overexpression of MLAA-34 in the U937 cell line led to significant suppression of apoptosis and increased the potential of tumorigenicity. Co-immunoprecipitation (Co-IP), shotgun and bioinformatic analysis identified 256 proteins and 225 of them were annotated by gene ontology categories. This analysis revealed 71 proteins involved in cell apoptosis or proliferation of biological processes and signaling pathways. Moreover, the effect of MLAA-34 apoptosis may be through interaction with the Ras, Wnt, calcium and chemokine signaling pathways and thirteen of the annotated proteins may interact with MLAA-34 and participate in carcinogenesis directly. This study provides a basis for a better understanding of the molecular mechanism and proteomics in the inhibition of apoptosis by MLAA-34 in U937 cells and indicates that MLAA-34 may be a potential candidate for the early diagnosis and therapeutic application of M5.

Regulation of cell survival and death by pyridine nucleotides

Pyridine nucleotides (PNs), such as NAD(H) and NADP(H), mediate electron transfer in many catabolic and anabolic processes. In general, NAD(+) and NADP(+) receive electrons to become NADH and NADPH by coupling with catabolic processes. These electrons are utilized for biologically essential reactions such as ATP production, anabolism and cellular oxidation-reduction (redox) regulation. Thus, in addition to ATP, NADH and NADPH could be defined as high-energy intermediates and "molecular units of currency" in energy transfer. We discuss the significance of PNs as energy/electron transporters and signal transducers, in regulating cell death and/or survival processes. In the first part of this review, we describe the role of NADH and NADPH as electron donors for NADPH oxidases (Noxs), glutathione (GSH), and thioredoxin (Trx) systems in cellular redox regulation. Noxs produce superoxide/hydrogen peroxide yielding oxidative environment, whereas GSH and Trx systems protect against oxidative stress. We then describe the role of NAD(+) and NADH as signal transducers through NAD(+)-dependent enzymes such as PARP-1 and Sirt1. PARP-1 is activated by damaged DNA in order to repair the DNA, which attenuates energy production through NAD(+) consumption; Sirt1 is activated by an increased NAD(+)/NADH ratio to facilitate signal transduction for metabolic adaption as well as stress responses. We conclude that PNs serve as an important interface for distinct cellular responses, including stress response, energy metabolism, and cell survival/death.

Thioredoxin and thioredoxin-interacting protein as prognostic markers for gastric cancer recurrence

AIM: To evaluate the potential of thioredoxin (TXN) and thioredoxin-interacting protein (TXNIP) expression as biomarkers for predicting gastric cancer recurrence.

METHODS: TXN and TXNIP expression levels were acquired from gene expression microarray data for 65 human gastric cancer tissues. We determined whether each gene expression level was associated with cancer recurrence and investigated the relationship between the two genes. For validation, the expression levels of TXN and TXNIP were measured by quantitative real-time reverse transcription polymerase chain reaction in 68 independent stage III gastric cancer patients. The correlation between gene expression and cancer prognosis was evaluated. Immunohistochemical staining was performed to investigate the protein expression levels of TXN and TXNIP and to characterize the expression patterns of each protein.

RESULTS: TXN was a prognosis-related gene (P = 0.009), whereas TXNIP, a TXN inhibitor, demonstrated a negative correlation with TXN in the gene expression microarray data. In the 68 stage III patients, the expression levels of both TXN and TXNIP had a statistically significant effect on recurrence-free survival (RFS, P = 0.008 and P = 0.036, respectively). The low TXN and high TXNIP expression group exhibited a better prognosis than the other groups, and the high TXN and low TXNIP expression group exhibited a poorer prognosis (P < 0.001 for RFS and P = 0.001 for overall survival). More than half of the patients in the simultaneously high TXN and low TXNIP expression group experienced a recurrence within 1 year after curative surgery, and the 5-year survival rate of the patients in this group was 29%, compared with 89% in the low TXN and high TXNIP expression group. The TXN protein was overexpressed in 65% of the gastric cancer tissues, whereas the TXNIP protein was underexpressed in 85% of the cancer cells. In a correlation analysis, TXN and TXNIP were highly correlated with many oncogenes and tumor suppressors as well as with genes related to energy, protein synthesis and autophagy.

CONCLUSION: TXN and TXNIP are promising prognostic markers for gastric cancer, and performing personalized adjuvant treatment based on TXN and TXNIP expression levels would be an effective practice in the treatment of gastric cancer.

Nuclear expression of thioredoxin-1 in the invasion front is associated with outcome in patients with gallbladder carcinoma

BACKGROUND

Multifunctional redox protein human thioredoxin (TRX-1) is reduced by thioredoxin reductase (TRX-R). The aim of the present study was to examine the distribution of TRX-1 and TRX-R expressions in gallbladder carcinoma (GBC) to clarify their usefulness as prognostic factors after surgical resection.

METHODS

Immunohistochemical staining for TRX-1 and TRX-R was performed in GBC tissue from 38 patients who underwent surgical resection, and TRX-1/TRX-R localization in relation to outcome was examined.

RESULTS

TRX-1 protein levels were significantly higher in GBC samples than in cholecystolithiasis samples (P = 0.0174). TRX-1 expression was observed in 100% (38/38) of tumour samples and in the nucleus in 76% (29/38), with nuclear expression in the invasion front observed in 45% (13/29). TRX-R expression was only detected in the cytoplasm of cancer cells and in the invasion front in 28 samples. In all of the samples, the depth of tumour invasion, lymph node metastasis, surgical margin, curability and nuclear expression of TRX-1 in the invasion front were significant prognostic factors by univariate analysis. In 27 selected patients who underwent curative resection, both TRX-1 nuclear expression and TRX-R cytoplasmic expression in the invasion front was a significantly prognostic factor.

CONCLUSION

TRX-1 nuclear expression in the GBC invasion front is a significant prognostic marker. Patients with both TRX-1 nuclear expression and TRX-R cytoplasmic expression in the tumour invasion front should be observed carefully even if after curative resection.

Nucleolar accumulation of APE1 depends on charged lysine residues that undergo acetylation upon genotoxic stress and modulate its BER activity in cells

The functional importance of APE1 nucleolar accumulation is described. It is shown that acetylation of Lys27–35, affecting local conformation, regulates APE1 function by 1) controlling its interaction with NPM1 and rRNA and its nucleolar accumulation, 2) modulating K6/K7 acetylation status, and 3) promoting APE1 BER activity in cells.

Apurinic/apyrimidinic endonuclease 1 (APE1) is the main abasic endonuclease in the base excision repair (BER) pathway of DNA lesions caused by oxidation/alkylation in mammalian cells; within nucleoli it interacts with nucleophosmin and rRNA through N-terminal Lys residues, some of which (K²⁷/K³¹/K³²/K³⁵) may undergo acetylation in vivo. Here we study the functional role of these modifications during genotoxic damage and their in vivo relevance. We demonstrate that cells expressing a specific K-to-A multiple mutant are APE1 nucleolar deficient and are more resistant to genotoxic treatment than those expressing the wild type, although they show impaired proliferation. Of interest, we find that genotoxic treatment induces acetylation at these K residues. We also find that the charged status of K²⁷/K³¹/K³²/K³⁵ modulates acetylation at K⁶/K⁷ residues that are known to be involved in the coordination of BER activity through a mechanism regulated by the sirtuin 1 deacetylase. Of note, structural studies show that acetylation at K²⁷/K³¹/K³²/K³⁵ may account for local conformational changes on APE1 protein structure. These results highlight the emerging role of acetylation of critical Lys residues in regulating APE1 functions. They also suggest the existence of cross-talk between different Lys residues of APE1 occurring upon genotoxic damage, which may modulate APE1 subnuclear distribution and enzymatic activity in vivo.

The role of redox environment in neurogenic development

The dynamic changes of cellular redox elements during neurogenesis allow the control of specific programs for selective lineage progression. There are many redox couples that influence the cellular redox state. The shift from a reduced to an oxidized state and vice versa may act as a cellular switch mechanism of stem cell mode of action from proliferation to differentiation. The redox homeostasis ensures proper functioning of redox-sensitive signaling pathways through oxidation/reduction of critical cysteine residues on proteins involved in signal transduction. This review presents the current knowledge on the relation between changes in the cellular redox environment and stem cell programming in the course of commitment to a restricted neural lineage, focusing on in vivo neurogenesis and in vitro neuronal differentiation. The first two sections outline the main systems that control the intracellular redox environment and make it more oxidative or reductive. The last section provides the background on redox-sensitive signaling pathways that regulate neurogenesis.

APE1/Ref-1 role in redox signaling: translational applications of targeting the redox function of the DNA repair/redox protein APE1/Ref-1

The heterogeneity of most cancers diminishes the treatment effectiveness of many cancer-killing regimens. Thus, treatments that hold the most promise are ones that block multiple signaling pathways essential to cancer survival. One of the most promising proteins in that regard is APE1, whose reduction-oxidation activity influences multiple cancer survival mechanisms, including growth, proliferation, metastasis, angiogenesis, and stress responses. With the continued research using APE1 redox specific inhibitors alone or coupled with developing APE1 DNA repair inhibitors it will now be possible to further delineate the role of APE1 redox, repair and protein-protein interactions. Previously, use of siRNA or over expression approaches, while valuable, do not give a clear picture of the two major functions of APE1 since both techniques severely alter the cellular milieu. Additionally, use of the redox-specific APE1 inhibitor, APX3330, now makes it possible to study how inhibition of APE1's redox signaling can affect multiple tumor pathways and can potentiate the effectiveness of existing cancer regimens. Because APE1 is an upstream effector of VEGF, as well as other molecules that relate to angiogenesis and the tumor microenvironment, it is also being studied as a possible treatment for agerelated macular degeneration and diabetic retinopathy. This paper reviews all of APE1's functions, while heavily focusing on its redox activities. It also discusses APE1's altered expression in many cancers and the therapeutic potential of selective inhibition of redox regulation, which is the subject of intense preclinical studies.

The effects of chromium(VI) on the thioredoxin system: implications for redox regulation

Hexavalent chromium [Cr(VI)] compounds are highly redox active and have long been recognized as potent cytotoxins and carcinogens. The intracellular reduction of Cr(VI) generates reactive Cr intermediates, which are themselves strong oxidants, as well as superoxide, hydrogen peroxide, and hydroxyl radical. These probably contribute to the oxidative damage and effects on redox-sensitive transcription factors that have been reported. However, the identification of events that initiate these signaling changes has been elusive. More recent studies show that Cr(VI) causes irreversible inhibition of thioredoxin reductase (TrxR) and oxidation of thioredoxin (Trx) and peroxiredoxin (Prx). Mitochondrial Trx2/Prx3 are more sensitive to Cr(VI) treatment than cytosolic Trx1/Prx1, although both compartments show thiol oxidation with higher doses or longer treatments. Thiol redox proteomics demonstrate that Trx2, Prx3, and Trx1 are among the most sensitive proteins in cells to Cr(VI) treatment. Their oxidation could therefore represent initiating events that have widespread implications for protein thiol redox control and for multiple aspects of redox signaling. This review summarizes the effects of Cr(VI) on the TrxR/Trx system and how these events could influence a number of downstream redox signaling systems that are influenced by Cr(VI) exposure. Some of the signaling events discussed include the activation of apoptosis signal regulating kinase and MAP kinases (p38 and JNK) and the modulation of a number of redox-sensitive transcription factors including AP-1, NF-κB, p53, and Nrf2.

Modulation of transcription factor Nrf2 in an in vitro model of traumatic brain injury

Traumatic brain injury (TBI) afflicts approximately 1.4 million people in the United States and TBIs have been labeled a major cause of death and disability on a global scale. Regulatory responses in a variety of neuronal loss conditions have supported the protective involvement of the nuclear factor (erythroid-derived 2)-like 2 (Nrf2) transcription factor. Nrf2 regulates antioxidant enzyme genes, and an increase in Nrf2 expression may counteract oxidative damage that results from TBI. Elevated Nrf2 may ultimately act through the upregulation of downstream target genes such as thioredoxin (Trx) and heat-shock protein-70 (HSP70) and this may reduce neuronal loss. We performed multiple mild biaxial stretch injuries to neuroblastoma cells in culture, and examined the effects of the Nrf2 activator, tert-butylhydroquinone (tBHQ). We also compared the stretch injury to oxidative insult. We confirmed that Trx and HSP70 were upregulated by treatment with tBHQ. We observed that tBHQ protected neurons from either insult, and that this was evident by different measures of cell viability and a decrease in annexin V binding. Neuronal health after insult was improved approximately 50% by tBHQ, indicating that neurons exposed to TBI in vitro can be protected.

Role of thioredoxin in lung disease

Thioredoxin system is a ubiquitous thiol oxidoreductase system that regulates cellular reduction/oxidation (redox) status. It includes thioredoxin (Trx), thioredoxin reductase (TrxR), and NADPH. Trx plays an essential role in cell function by limiting oxidative stress directly via antioxidant effects and indirectly by proteins interaction with key signal transduction molecules. A variety of signaling molecules have been implicated in the cytoprotection conferred by Trx, such as autophagic proteins, p38 mitogen-activated protein kinase, nuclear factor-κB, phosphatidylinositol 3-kinase. Recent studies indicated that Trx may contribute to the pathogenesis of COPD, asthma and lung injury. Enhanced Trx expression or application of recombinant Trx afforded protection in preclinical models of pulmonary tissue injury, which suggested Trx may be used in future therapeutic applications. The focus of this review is on the significance of Trx in various pulmonary diseases, which as a potential therapeutic strategy to protect against oxidative stress and inflammation.

Reactive oxygen species (ROS) homeostasis and redox regulation in cellular signaling

Reactive oxygen species (ROS) are generated during mitochondrial oxidative metabolism as well as in cellular response to xenobiotics, cytokines, and bacterial invasion. Oxidative stress refers to the imbalance due to excess ROS or oxidants over the capability of the cell to mount an effective antioxidant response. Oxidative stress results in macromolecular damage and is implicated in various disease states such as atherosclerosis, diabetes, cancer, neurodegeneration, and aging. Paradoxically, accumulating evidence indicates that ROS also serve as critical signaling molecules in cell proliferation and survival. While there is a large body of research demonstrating the general effect of oxidative stress on signaling pathways, less is known about the initial and direct regulation of signaling molecules by ROS, or what we term the "oxidative interface." Cellular ROS sensing and metabolism are tightly regulated by a variety of proteins involved in the redox (reduction/oxidation) mechanism. This review focuses on the molecular mechanisms through which ROS directly interact with critical signaling molecules to initiate signaling in a broad variety of cellular processes, such as proliferation and survival (MAP kinases, PI3 kinase, PTEN, and protein tyrosine phosphatases), ROS homeostasis and antioxidant gene regulation (thioredoxin, peroxiredoxin, Ref-1, and Nrf-2), mitochondrial oxidative stress, apoptosis, and aging (p66Shc), iron homeostasis through iron-sulfur cluster proteins (IRE-IRP), and ATM-regulated DNA damage response.

Characterization of the redox activity and disulfide bond formation in apurinic/apyrimidinic endonuclease

Apurinic/apyrimidinic endonuclease (APE1) is an unusual nuclear redox factor in which the redox-active cysteines identified to date, C65 and C93, are surface inaccessible residues whose activities may be influenced by partial unfolding of APE1. To assess the role of the five remaining cysteines in APE1's redox activity, double-cysteine mutants were analyzed, excluding C65A, which is redox-inactive as a single mutant. C93A/C99A APE1 was found to be redox-inactive, whereas other double-cysteine mutants retained the same redox activity as that observed for C93A APE1. To determine whether these three cysteines, C65, C93, and C99, were sufficient for redox activity, all other cysteines were substituted with alanine, and this protein was shown to be fully redox-active. Mutants with impaired redox activity failed to stimulate cell proliferation, establishing an important role for APE1's redox activity in cell growth. Disulfide bond formation upon oxidation of APE1 was analyzed by proteolysis of the protein followed by mass spectrometry analysis. Within 5 min of exposure to hydrogen peroxide, a single disulfide bond formed between C65 and C138 followed by the formation of three additional disulfide bonds within 15 min; 10 total disulfide bonds formed within 1 h. A single mixed-disulfide bond involving C99 of APE1 was observed for the reaction of oxidized APE1 with thioredoxin (TRX). Disulfide-bonded APE1 or APE1-TRX species were further characterized by size exclusion chromatography and found to form large complexes. Taken together, our data suggest that APE1 is a unique redox factor with properties distinct from those of other redox factors.

Tumor suppressor genes and ROS: complex networks of interactions

Tumor suppressor genes regulate diverse cellular activities including DNA damage repair, cell cycle arrest, mitogenic signaling, cell differentiation, migration, and programmed cell death. In this review the tumor suppressor genes p53, FoxO, retinoblastoma (RB), p21, p16, and breast cancer susceptibility genes 1 and 2 (BRCA1 and BRCA2) and their roles in oxidative stress are summarized with a focus on the links and interplay between their pathways and reactive oxygen species (ROS). The results of a number of studies have demonstrated an antioxidant role for tumor suppressor proteins, activating the expression of some well-known antioxidant genes in response to oxidative stress. On the other hand, recent studies have revealed a pro-oxidant role for p53 by which cellular ROS are increased by enhanced transcription of proapoptotic genes. A tightly regulated feedback loop between ROS and FoxO proteins, with ROS regulating FoxO activity through posttranslational modifications and protein interactions and FoxO controlling intracellular ROS levels, has been demonstrated. Furthermore, these studies have shown that FoxO transcription factors and p38 mitogen-activated protein kinases may interact with the RB pathway under stress conditions. In addition, cellular senescence studies established an unexpected role for ROS in inducing and maintaining senescence-induced tumor suppression that blocks cytokinesis to ensure senescent cells never divide again. p21 and p16 have been shown to act as tumor suppressor proteins and this function extends beyond cell cycle control and includes important roles in regulating oxidative stress. Consequently, these important interactions indicate a critical potential role for tumor suppressor genes in the cellular response against oxidative stress and emphasize links between ROS and tumor suppressor genes that might be therapeutic targets in oxidative damage-associated diseases.

Hydrogen sulfide-releasing aspirin suppresses NF-κB signaling in estrogen receptor negative breast cancer cells in vitro and in vivo

Hormone-dependent estrogen receptor positive (ER+) breast cancers generally respond well to anti-estrogen therapy. Unfortunately, hormone-independent estrogen receptor negative (ER-) breast cancers are aggressive, respond poorly to current treatments and have a poor prognosis. New approaches and targets are needed for the prevention and treatment of ER- breast cancer. The NF-κB signaling pathway is strongly implicated in ER- tumor genesis, constituting a possible target for treatment. Hydrogen sulfide-releasing aspirin (HS-ASA), a novel and safer derivative of aspirin, has shown promise as an anti-cancer agent. We examined the growth inhibitory effect of HS-ASA via alterations in cell proliferation, cell cycle phase transitions, and apoptosis, using MDA-MB-231 cells as a model of triple negative breast cancer. Tumor xenografts in mice, representing human ER- breast cancer, were evaluated for reduction in tumor size, followed by immunohistochemical analysis for proliferation, apoptosis and expression of NF-κB. HS-ASA suppressed the growth of MDA-MB-231 cells by induction of G(0)/G(1) arrest and apoptosis, down-regulation of NF-κB, reduction of thioredoxin reductase activity, and increased levels reactive oxygen species. Tumor xenografts in mice, were significantly reduced in volume and mass by HS-ASA treatment. The decrease in tumor mass was associated with inhibition of cell proliferation, induction of apoptosis and decrease in NF-κB levels in vivo. HS-ASA has anti-cancer potential against ER- breast cancer and merits further study.

Antitumor indolequinones induced apoptosis in human pancreatic cancer cells via inhibition of thioredoxin reductase and activation of redox signaling

Indolequinones (IQs) were developed as potential antitumor agents against human pancreatic cancer. IQs exhibited potent antitumor activity against the human pancreatic cancer cell line MIA PaCa-2 with growth inhibitory IC(50) values in the low nanomolar range. IQs were found to induce time- and concentration-dependent apoptosis and to be potent inhibitors of thioredoxin reductase 1 (TR1) in MIA PaCa-2 cells at concentrations equivalent to those inducing growth-inhibitory effects. The mechanism of inhibition of TR1 by the IQs was studied in detail in cell-free systems using purified enzyme. The C-terminal selenocysteine of TR1 was characterized as the primary adduction site of the IQ-derived reactive iminium using liquid chromatography-tandem mass spectrometry analysis. Inhibition of TR1 by IQs in MIA PaCa-2 cells resulted in a shift of thioredoxin-1 redox state to the oxidized form and activation of the p38/c-Jun NH(2)-terminal kinase (JNK) mitogen-activated protein kinase (MAPK) signaling pathway. Oxidized thioredoxin is known to activate apoptosis signal-regulating kinase 1, an upstream activator of p38/JNK in the MAPK signaling cascade and this was confirmed in our study providing a potential mechanism for IQ-induced apoptosis. These data describe the redox and signaling events involved in the mechanism of growth inhibition induced by novel inhibitors of TR1 in human pancreatic cancer cells.

S-glutathionylation of cysteine 99 in the APE1 protein impairs abasic endonuclease activity

Human apurinic/apyrimidinic (AP) endonuclease 1 (APE1) is a central participant in the base excision repair pathway, exhibiting AP endonuclease activity that incises the DNA backbone 5' to an abasic site. Besides its prominent role as a DNA repair enzyme, APE1 was separately identified as a protein called redox effector factor 1, which is able to enhance the DNA binding activity of several transcription factors through a thiol-exchange-based reduction-oxidation mechanism. In the present study, we found that human APE1 is S-glutathionylated under conditions of oxidative stress both in the presence of glutathione in vitro and in cells. S-glutathionylated APE1 displayed significantly reduced AP endonuclease activity on abasic-site-containing oligonucleotide substrates, a result stemming from impaired DNA binding capacity. The combination of site-directed mutagenesis, biochemical assays, and mass spectrometric analysis identified Cys99 in human APE1 as the critical residue for the S-glutathionylation that leads to reduced AP endonuclease activity. This modification is reversible by reducing agents, which restore APE1 incision function. Our studies describe a novel posttranslational modification of APE1 that regulates the DNA repair function of the protein.

Redox control and interplay between p53 isoforms: roles in the regulation of basal p53 levels, cell fate, and senescence

The p53 tumor suppressor protein has achieved stardom in molecular oncology owing to frequent inactivation in a large range of cancers. Known as a factor activated by multiple forms of stress and causing a broad suppressive response to DNA damage, its regulation and functions in basal (non-stress) conditions has received relatively little attention. We summarize recent findings highlighting roles of p53 in physiological processes such as stem cell maintenance, development, aging and senescence, and regulation of basal oxidative cell metabolism. We suggest that these properties are regulated through two integrated biochemical systems: the redox-sensing capacity of the p53 protein (due to its structural features and its regulation by redox factors such as thioredoxin, metallothioneins, or the redox-repair enzyme APE1/ref-1), and the expression of p53 as multiple isoforms with antagonist effects. We propose that interactions between p53 and its isoforms Δ40p53 or Δ133p53 play critical roles in intracellular signaling by reactive oxygen species. We also discuss evidence that p53 controls energy production by repressing glycolysis and enhancing mitochondrial oxidative metabolism. Together, these mechanisms suggest that p53 acts not only as a "guardian of the genome" against DNA damage but also as a finely-tuned regulator of redox-dependent physiological processes.

Interaction of p53 with tumor suppressive and oncogenic signaling pathways to control cellular reactive oxygen species production

p53 is a crucial transcription factor with tumor suppressive properties that elicits its function through specific target genes. It constitutes a pivotal system that integrates information received by many signaling pathways and subsequently orchestrates cell fate decisions, namely, growth-arrest, senescence, or apoptosis. Reactive oxygen species (ROS) production in cells can play a key role in signal transduction, being able to trigger different processes as cell death or cell proliferation. Sustained oxidative stress can induce genomic instability and collaborates with cancer development, whereas acute enhancement of high ROS levels leads to toxic oxidative cell damage and cell death. Here, it has been considered p53 broad potential contribution through its ability to regulate selected key cancer signaling pathways, where ROS participate as inductors or effectors of the final biological outcome. Further, we have discussed how p53 could play a role in preventing potentially harmful oxidative state and cell proliferation by pro-oncogenic pathways such as PI3K/AKT/mTOR and WNT/β-catenin or under hypoxia state. In addition, we have considered potential mechanisms by which p53 could collaborate with signal transduction pathways such as transforming growth factor-β (TGF-β) and stress-activated protein kinases (SAPK) that produce ROS, to stop or eliminate uncontrolled proliferating cells.

Knock-in reconstitution studies reveal an unexpected role of Cys-65 in regulating APE1/Ref-1 subcellular trafficking and function

Apurinic/apyrimidinic endonuclease 1/redox factor-1 (APE1) protects cells from oxidative stress via the base excision repair pathway and as a redox transcriptional coactivator. It is required for tumor progression/metastasis, and its up-regulation is associated with cancer resistance. Loss of APE1 expression causes cell growth arrest, mitochondrial impairment, apoptosis, and alterations of the intracellular redox state and cytoskeletal structure. A detailed knowledge of the molecular mechanisms regulating its different activities is required to understand the APE1 function associated with cancer development and for targeting this protein in cancer therapy. To dissect these activities, we performed reconstitution experiments by using wild-type and various APE1 mutants. Our results suggest that the redox function is responsible for cell proliferation through the involvement of Cys-65 in mediating APE1 localization within mitochondria. C65S behaves as a loss-of-function mutation by affecting the in vivo folding of the protein and by causing a reduced accumulation in the intermembrane space of mitochondria, where the import protein Mia40 specifically interacts with APE1. Treatment of cells with (E)-3-(2-[5,6-dimethoxy-3-methyl-1,4-benzoquinonyl])-2-nonyl propenoic acid, a specific inhibitor of APE1 redox function through increased Cys-65 oxidation, confirm that Cys-65 controls APE1 subcellular trafficking and provides the basis for a new role for this residue.

Targeting NF-κB and HIF-1 pathways for the treatment of cancer: part II

Hypoxia that originates from disturbed growth of solid tumors initiates a cascade of intracellular events engaging hypoxia-inducible factors, HIF-1 and HIF-2. Overexpression of HIF has been confirmed in solid tumors and was unfortunately accompanied with chemo- and radioresistance observed in many patients. Multiple cellular pathways resulting in HIF activation could be successfully inhibited by use of different kinds of drugs (e.g. topotecan, heat shock protein 90 and mTOR inhibitors, YC-1, pleurotin or 2-methoxyestradiol), which are being subjected into intensive investigation in clinical trials.

CNS peroxiredoxins and their regulation in health and disease

Oxidative stress is thought to be a contributing factor in many chronic neurodegenerative pathologies, as well as acute cerebrovascular disorders such as stroke. Peroxiredoxins are a family of antioxidant enzymes that reduce peroxides directly through the use of a redox active cysteine within their active site, which in the process becomes oxidized. In order to cycle back to the reduced state, many peroxiredoxins rely on thiol-dependent reduction by the ubiquitous antioxidant enzyme thioredoxin. Peroxiredoxins, together with thioredoxin and thioredoxin's own 'recycling enzyme', thioredoxin reductase, represent an antioxidant enzymic system of growing significance in the context of neuronal physiology and pathology. Overexpression, knockdown, and knockout approaches have demonstrated an important role for peroxiredoxins in protecting neurons from oxidative insults. It is also becoming clear that neuronal peroxiredoxins are subjected to post-translational modifications that impair function as part of disease pathology. Conversely, components of this pathway are also subject to dynamic upregulation such as via endogenous synaptic activity-dependent signaling and induction of the Nrf2-dependent Phase II response. As such, the thioredoxin-peroxiredoxin system represents a potential therapeutic target for central nervous system disorders associated with oxidative stress.

Thioredoxin 1 as a subcellular biomarker of redox imbalance in human prostate cancer progression

We determined protein levels and subcellular distribution of thioredoxin 1 (Trx1) in human prostate tissues using tissue microarrays and analyzed redox changes in Trx1 in the nucleus and cytoplasm in cell culture models with a redox Western blot technique. We demonstrated increased nuclear Trx1 levels in high- versus low-grade human prostate cancers. Despite increased protein levels, the oxidized forms of nuclear Trx1 were higher in prostate cancer cell lines compared to their benign counterparts, suggesting that nuclear redox imbalance occurred selectively in cancer cells. A growth-stimulating dose of androgen caused transient oxidation of Trx1 in androgen-responsive prostate cancer cells only, suggesting a loss of both androgen- and redox-signaling mechanisms during cancer progression. Androgen-independent PC3 cells showed a significant increase in nuclear and cytoplasmic Trx1 protein levels, but a significant decrease in total Trx activity. Trx1 redox state and activity correlated with the sensitivity of prostate cancer cells to pro-oxidant agents, and downregulation of Trx1 sensitized cancer cells to these agents. Our findings suggest that loss of Trx function because of oxidation and corresponding redox imbalance may play important roles in prostate cancer progression and response to therapies; and Trx1 may serve as a biomarker of subcellular redox imbalance in prostate cancer.

Chloroethyl urea derivatives block tumour growth and thioredoxin-1 nuclear translocation

Aryl chloroethyl ureas (CEUs) are new protein alkylating agents exhibiting anticancer activity both in vitro and in vivo. We report herein that 14C-labeled CEU derivatives, designated CEU-025 and CEU-027, covalently bind to thioredoxin-1 (TRX1). Covalent binding of these molecules slightly decreases the disulfide-reducing activity of recombinant TRX1, when compared with the effect of strong thioalkylating agents such as N-ethylmaleimide. Moreover, site-directed mutagenesis and diamide competition assays demonstrated that TRX1 cysteinyl residues are not the prime targets of CEUs. CEU-025 abrogates the nuclear translocation of TRX1 in human cancer cells. In addition, we show that CEU-025 can block TRX1 nuclear translocation induced by cisplatin. Unexpectedly, pretreatment with sublethal CEU-025 concentrations that block TRX1 nuclear translocation protected the cells against cisplatin cytotoxicity. Overexpression of TRX1 in HT1080 fibrosarcoma cells attenuated CEU-025 cytotoxicity, while its suppression using TRX1-specific siRNA increased the effects of CEU-025, suggesting that loss of function of TRX1 is involved, at least in part, in the cytotoxic activity of CEU-025. These results suggest that CEU-025 and CEU-027 exhibit anticancer activity through a novel, unique mechanism of action. The importance of TRX1 and the dependence of the cytotoxicity of CEU-025 and CEU-027 on TRX1 intracellular localization are also discussed.

Redox control of protein-DNA interactions: from molecular mechanisms to significance in signal transduction, gene expression, and DNA replication

Protein-DNA interactions play a key role in the regulation of major cellular metabolic pathways, including gene expression, genome replication, and genomic stability. They are mediated through the interactions of regulatory proteins with their specific DNA-binding sites at promoters, enhancers, and replication origins in the genome. Redox signaling regulates these protein-DNA interactions using reactive oxygen species and reactive nitrogen species that interact with cysteine residues at target proteins and their regulators. This review describes the redox-mediated regulation of several master regulators of gene expression that control the induction and suppression of hundreds of genes in the genome, regulating multiple metabolic pathways, which are involved in cell growth, development, differentiation, and survival, as well as in the function of the immune system and cellular response to intracellular and extracellular stimuli. It also discusses the role of redox signaling in protein-DNA interactions that regulate DNA replication. Specificity of redox regulation is discussed, as well as the mechanisms providing several levels of redox-mediated regulation, from direct control of DNA-binding domains through the indirect control, mediated by release of negative regulators, regulation of redox-sensitive protein kinases, intracellular trafficking, and chromatin remodeling.

Generation of double-labeled reporter cell lines for studying co-dynamics of endogenous proteins in individual human cells

Understanding the dynamic relationship between components of a system or pathway at the individual cell level is a current challenge. To address this, we developed an approach that allows simultaneous tracking of several endogenous proteins of choice within individual living human cells. The approach is based on fluorescent tagging of proteins at their native locus by directed gene targeting. A fluorescent tag-encoding DNA is introduced as a new exon into the intronic region of the gene of interest, resulting in expression of a full-length fluorescently tagged protein. We used this approach to establish human cell lines simultaneously expressing two components of a major antioxidant defense system, thioredoxin 1 (Trx) and thioredoxin reductase 1 (TrxR1), labeled with CFP and YFP, respectively. We find that the distributions of both proteins between nuclear and cytoplasmic compartments were highly variable between cells. However, the two proteins did not vary independently of each other: protein levels of Trx and TrxR1 in both the whole cell and the nucleus were substantially correlated. We further find that in response to a stress-inducing drug (CPT), both Trx and TrxR1 accumulated in the nuclei in a manner that was highly temporally correlated. This accumulation considerably reduced cell-to-cell variability in nuclear content of both proteins, suggesting a uniform response of the thioredoxin system to stress. These results indicate that Trx and TrxR1 act in concert in response to stress in regard to both time course and variability. Thus, our approach provides an efficient tool for studying dynamic relationship between components of systems of interest at a single-cell level.

Cys-141 glutathionylation of human p53: Studies using specific polyclonal antibodies in cancer samples and cell lines

Previously, we reported that human p53 is functionally inactivated by S-glutathionylation at Cys-141 during oxidative and DNA-damaging treatments. Here, we describe the presence of thiolated p53 and the dynamic nature of this modification in human tissues using unique and specific polyclonal antibodies raised against a 12-residue p53 peptide bearing a mixed disulfide at Cys-141. The affinity- purified antibodies (glut-p53) were sequence-specific in that they recognized the antigenic peptide but not the unthiolated peptide or a scrambled glutathionylated peptide in ELISAs. On immunoblots, the purified antibodies did not react with native p53 or recombinant p53 (rp53), but readily detected the glutathionylated or cysteinylated or ethanethiol-treated rp53 only under nonreducing conditions. Untreated HCT116 cells showed low levels of glut-p53, which increased markedly after H(2)O(2), diamide, cisplatin, and doxorubicin treatments. Glut-p53 levels decreased sharply after cells were passed into oxidant-free medium, suggesting efficient dethiolation. The mutant p53 present in HT29 and T47D human cancer cells was also recognized. In vitro, the glut-p53 was rapidly degraded by rabbit reticulocyte lysates. Human prostate and prostate cancer tissues showed an abundant presence of glut-p53 in luminal epithelium, a site well known to generate ROS. Melanoma and colon cancer samples were also positive for glut-p53. The availability of the thiolation-specific antibodies should enhance our knowledge of p53 regulation in redox-perturbed states found in various diseases including cancer.

Redox control systems in the nucleus: mechanisms and functions

Proteins with oxidizable thiols are essential to many functions of cell nuclei, including transcription, chromatin stability, nuclear protein import and export, and DNA replication and repair. Control of the nuclear thiol-disulfide redox states involves both the elimination of oxidants to prevent oxidation and the reduction of oxidized thiols to restore function. These processes depend on the common thiol reductants, glutathione (GSH) and thioredoxin-1 (Trx1). Recent evidence shows that these systems are controlled independent of the cytoplasmic counterparts. In addition, the GSH and Trx1 couples are not in redox equilibrium, indicating that these reductants have nonredundant functions in their support of proteins involved in transcriptional regulation, nuclear protein trafficking, and DNA repair. Specific isoforms of glutathione peroxidases, glutathione S-transferases, and peroxiredoxins are enriched in nuclei, further supporting the interpretation that functions of the thiol-dependent systems in nuclei are at least quantitatively distinct, and probably also qualitatively distinct, from similar processes in the cytoplasm. Elucidation of the distinct nuclear functions and regulation of the thiol redox pathways in nuclei can be expected to improve understanding of nuclear processes and also to provide the basis for novel approaches to treat aging and disease processes associated with oxidative stress in the nuclei.

Functional aspects of redox control during neuroinflammation

Neuroinflammation is a CNS reaction to injury in which some severe pathologies, regardless of their origin, converge. The phenomenon emphasizes crosstalk between neurons and glia and reveals a complex interaction with oxidizing agents through redox sensors localized in enzymes, receptors, and transcription factors. When oxidizing pressures cause reversible molecular changes, such as minimal or transitory proinflammatory cytokine overproduction, redox couples provide a means of translating the presence of reactive oxygen or nitrogen species into useful signals in the cell. Additionally, thiol-based redox sensors convey information about localized changes in redox potential induced by physiologic or pathologic situations. They are susceptible to oxidative changes and become key events during neuroinflammation, altering the course of a signaling response or the behavior of specific transcription factors. When oxidative stress augments the pressure on the intracellular environment, the effective reduction potential of redox pairs diminishes, and cell signaling shifts toward proinflammatory and proapoptotic signals, creating a vicious cycle between oxidative stress and neuroinflammation. In addition, electrophilic compounds derived from the oxidative cascade react with key protein thiols and interfere with redox signaling. This article reviews the relevant functional aspects of redox control during the neuroinflammatory process.

Gold compounds as anticancer agents: chemistry, cellular pharmacology, and preclinical studies

Gold compounds are a class of metallodrugs with great potential for cancer treatment. During the last two decades, a large variety of gold(I) and gold(III) compounds are reported to possess relevant antiproliferative properties in vitro against selected human tumor cell lines, qualifying themselves as excellent candidates for further pharmacological evaluation. The unique chemical properties of the gold center confer very interesting and innovative pharmacological profiles to gold-based metallodrugs. The primary goal of this review is to define the state of the art of preclinical studies on anticancer gold compounds, carried out either in vitro or in vivo. The available investigations of anticancer gold compounds are analyzed in detail, and particular attention is devoted to underlying molecular mechanisms. Notably, a few biophysical studies reveal that the interactions of cytotoxic gold compounds with DNA are generally far weaker than those of platinum drugs, implying the occurrence of a substantially different mode of action. A variety of alternative mechanisms were thus proposed, of which those involving either direct mitochondrial damage or proteasome inhibition or modulation of specific kinases are now highly credited. The overall perspectives on the development of gold compounds as effective anticancer drugs with an innovative mechanism of action are critically discussed on the basis of the available experimental evidence.

Role of thioredoxin reductase 1 and thioredoxin interacting protein in prognosis of breast cancer

Introduction

The purpose of this work was to study the prognostic influence in breast cancer of thioredoxin reductase 1 (TXNRD1) and thioredoxin interacting protein (TXNIP), key players in oxidative stress control that are currently evaluated as possible therapeutic targets.

Methods

Analysis of the association of TXNRD1 and TXNIP RNA expression with the metastasis-free interval (MFI) was performed in 788 patients with node-negative breast cancer, consisting of three individual cohorts (Mainz, Rotterdam and Transbig). Correlation with metagenes and conventional clinical parameters (age, pT stage, grading, hormone and ERBB2 status) was explored. MCF-7 cells with a doxycycline-inducible expression of an oncogenic ERBB2 were used to investigate the influence of ERBB2 on TXNRD1 and TXNIP transcription.

Results

TXNRD1 was associated with worse MFI in the combined cohort (hazard ratio = 1.955; P < 0.001) as well as in all three individual cohorts. In contrast, TXNIP was associated with better prognosis (hazard ratio = 0.642; P < 0.001) and similar results were obtained in all three subcohorts. Interestingly, patients with ERBB2-status-positive tumors expressed higher levels of TXNRD1. Induction of ERBB2 in MCF-7 cells caused not only an immediate increase in TXNRD1 but also a strong decrease in TXNIP. A subsequent upregulation of TXNIP as cells undergo senescence was accompanied by a strong increase in levels of reactive oxygen species.

Conclusions

TXNRD1 and TXNIP are associated with prognosis in breast cancer, and ERBB2 seems to be one of the factors shifting balances of both factors of the redox control system in a prognostic unfavorable manner.

Thiol redox transitions by thioredoxin and thioredoxin-binding protein-2 in cell signaling

The cellular thiol redox state is a crucial mediator of metabolic, signaling and transcriptional processes in cells, and an exquisite balance between the oxidizing and reducing states is essential for the normal function and survival of cells. Reactive oxygen species (ROS) are widely known to function as a kind of second messenger for intracellular signaling and to modulate the thiol redox state. Thiol reduction is mainly controlled by the thioredoxin (TRX) system and glutathione (GSH) systems as scavengers of ROS and regulators of the protein redox states. The thioredoxin system is composed of several related molecules interacting through the cysteine residues at the active site, including thioredoxin, thioredoxin-2, a mitochondrial thioredoxin family, and transmembrane thioredoxin-related protein (TMX), an endoplasmic reticulum (ER)-specific thioredoxin family. Thioredoxin couples with thioredoxin-dependent peroxidases (peroxiredoxin) to scavenge hydrogen peroxide. In addition, thioredoxin does not simply act only as a scavenger of ROS but also as an important regulator of oxidative stress response through protein-protein interaction. The interaction of thioredoxin and thioredoxin-binding proteins such as thioredoxin-binding protein-2 (TBP-2, also called as Txnip or VDUP1), apoptosis signal kinase (ASK-1), redox factor 1 (Ref-1), Forkhead box class O 4 (FoxO4), and nod-like receptor proteins (NLRPs) suggested unconventional functions of thioredoxin and a novel mechanism of redox regulation. Here, we introduce the central mechanism of thiol redox transition in cell signaling regulated by thioredoxin and related molecules.

Thiol redox systems and protein kinases in hepatic stellate cell regulatory processes

Hepatic stellate cells (HSC) are the major producers of collagen in the liver and their conversion from resting cells to a proliferating, contractile and fibrogenic phenotype ('activation') is a critical step, leading to liver fibrosis characterized by deposition of excessive extracellular matrix. Cytokines, growth factors, reactive oxygen and nitrogen species (ROS/RNS), lipid peroxides and their products deriving from hepatocytes, Kupffer cells and other cells converge on HSC and influence their activation. This review focuses on glutathione and thioredoxin pathways, with particular emphasis on their role in HSC. These two systems have been shown to act in the metabolism of hydrogen peroxide, control of thiol redox balance and regulation of signalling pathways. Particular attention is paid to mitochondria and NADPH oxidase. Detailed knowledge of specific signalling, redox conditions and apoptotic processes will be of help in devising proper pharmacological treatments for liver fibrosis.

Redox regulation of DNA repair: implications for human health and cancer therapeutic development

Redox reactions are known to regulate many important cellular processes. In this review, we focus on the role of redox regulation in DNA repair both in direct regulation of specific DNA repair proteins as well as indirect transcriptional regulation. A key player in the redox regulation of DNA repair is the base excision repair enzyme apurinic/apyrimidinic endonuclease 1 (APE1) in its role as a redox factor. APE1 is reduced by the general redox factor thioredoxin, and in turn reduces several important transcription factors that regulate expression of DNA repair proteins. Finally, we consider the potential for chemotherapeutic development through the modulation of APE1's redox activity and its impact on DNA repair.

The missing zinc: p53 misfolding and cancer

The p53 tumor suppressor is a transcription factor that contains a single zinc ion near its DNA binding interface. Zn(2+) is required for site-specific DNA binding and proper transcriptional activation. In addition to its functional significance, zinc plays a dominant role in determining whether p53 folds productively or misfolds. Insufficient zinc and excess zinc cause p53 to misfold by distinct mechanisms which both result in functional loss. The zinc-binding status of p53 in the cell is impacted significantly by the presence of tumorigenic mutations and by metal ion homeostasis. This review discusses mechanisms by which zinc modulates folding and misfolding of p53, how improper metal binding and release leads to loss of function and cancer, and how misfolding can be rescued by metallochaperones.

The roles of thioredoxin and thioredoxin-binding protein-2 in endometriosis

BACKGROUND

Oxidative stress is considered to be involved in the establishment and development of endometriosis. Thioredoxin (TRX) is an endogenous redox regulator that protects cells against oxidative stress, and TRX-binding protein-2 (TBP-2) is a negative regulator of TRX in the biological function and expression. The aim of this study was to investigate the roles of TRX and TBP-2 in the pathophysiology of endometriosis.

METHODS

A total of 35 patients with histologically confirmed endometriosis and 31 patients without endometriosis participated in this study. Real-time polymerase chain reaction was used to quantify TRX and TBP-2 mRNA levels, and immunohistochemistry (IHC) was used to assess TRX and TBP-2 protein localization in the endometrium. Serum and peritoneal fluid levels of TRX and TBP-2 were measured using a specific commercial ELISA.

RESULTS

There were no significant differences in TRX mRNA levels in the endometrium of patients with endometriosis and the control groups. However, TBP-2 mRNA levels in the endometrium were lower, and the TRX to TBP-2 ratio was higher in patients with endometriosis than in the control group. In particular, the TRX to TBP-2 ratio was significantly higher during late secretory and menstrual phase in patients with endometriosis compared with the control group. IHC studies also showed the decreased TBP-2 immunoreactivity in patients with endometriosis compared with the control group. There was no correlation between TRX and TBP-2 mRNA levels in patients with endometriosis, whereas TRX mRNA levels were positively correlated with TBP-2 mRNA levels in the control group. There were no significant differences between the two groups in TRX and TBP-2 levels in serum or peritoneal fluid.

CONCLUSIONS

Aberrant expression of TRX and TBP-2 in the endometrium may be associated with the establishment of endometriosis.

Thioredoxin regulates cell cycle via the ERK1/2-cyclin D1 pathway

Thioredoxin (TRX) is a key component of redox regulation and has been indicated to play an essential role in cell survival and growth. Here, we investigated the molecular mechanism of TRX in the regulation of cell survival and growth by using RNA interference (RNAi) in A549 lung cancer and MCF7 breast cancer cells. TRX knockdown did not significantly increase the basal level of cell death without exposure to stress, but CDDP-induced cell death was enhanced. Meanwhile, TRX knockdown resulted in significant cell-cycle arrest at the G(1) phase. Cyclin D1 expression was reduced by TRX knockdown at the protein and mRNA levels. TRX knockdown caused suppression of activation of the cyclin D1 promoter through elements including AP-1. TRX knockdown also reduced the levels of phosphorylated ERK1/2 and the nuclear translocation of ERK 1/2 induced by EGF. These results suggest that TRX is an important regulator of the cell cycle in the G(1) phase via cyclin D1 transcription and the ERK/AP-1 signaling pathways.

Thioredoxin and thioredoxin reductase influence estrogen receptor alpha-mediated gene expression in human breast cancer cells

Accumulation of reactive oxygen species (ROS) in cells damages resident proteins, lipids, and DNA. In order to overcome the oxidative stress that occurs with ROS accumulation, cells must balance free radical production with an increase in the level of antioxidant enzymes that convert free radicals to less harmful species. We identified two antioxidant enzymes, thioredoxin (Trx) and Trx reductase (TrxR), in a complex associated with the DNA-bound estrogen receptor alpha (ERalpha). Western analysis and immunocytochemistry were used to demonstrate that Trx and TrxR are expressed in the cytoplasm and in the nuclei of MCF-7 human breast cancer cells. More importantly, endogenously expressed ERalpha, Trx, and TrxR interact and ERalpha and TrxR associate with the native, estrogen-responsive pS2 and progesterone receptor genes in MCF-7 cells. RNA interference assays demonstrated that Trx and TrxR differentially influence estrogen-responsive gene expression and that together, 17beta-estradiol, Trx, and TrxR alter hydrogen peroxide (H(2)O(2)) levels in MCF-7 cells. Our findings suggest that Trx and TrxR are multifunctional proteins that, in addition to modulating H(2)O(2) levels and transcription factor activity, aid ERalpha in regulating the expression of estrogen-responsive genes in target cells.

Redox regulation of cell survival by the thioredoxin superfamily: an implication of redox gene therapy in the heart

Reactive oxygen species (ROS) are the key mediators of pathogenesis in cardiovascular diseases. Members of the thioredoxin superfamily take an active part in scavenging reactive oxygen species, thus playing an essential role in maintaining the intracellular redox status. The alteration in the expression levels of thioredoxin family members and related molecules constitute effective biomarkers in various diseases, including cardiovascular complications that involve oxidative stress. Thioredoxin, glutaredoxin, peroxiredoxin, and glutathione peroxidase, along with their isoforms, are involved in interaction with the members of metabolic and signaling pathways, thus making them attractive targets for clinical intervention. Studies with cells and transgenic animals have supported this notion and raised the hope for possible gene therapy as modern genetic medicine. Of all the molecules, thioredoxins, glutaredoxins, and peroxiredoxins are emphasized, because a growing body of evidence reveals their essential and regulatory role in several steps of redox regulation. In this review, we discuss some pertinent observations regarding their distribution, structure, functions, and interactions with the several survival- and death-signaling pathways, especially in the myocardium.

Thioredoxin-related protein 14, a new member of the thioredoxin family with disulfide reductase activity: implication in the redox regulation of TNF-alpha signaling

Thioredoxin-related protein 14 (TRP14) is a novel 14-kDa disulfide reductase with two active site Cys residues in its WCPDC motif, which is comparable to the WCGPC motif of thioredoxin (Trx). Although the active site cysteine of TRP14 is sufficiently nucleophilic, its redox potential is similar to that of Trx1, and it receives the electrons from Trx reductase 1 (TrxR1) as does Trx1. TRP14 does not target the same substrate as Trx1, suggesting that TRP14 and Trx1 might act on distinct substrate proteins. Comparison of the crystal structures of TRP14 and Trx1 reveals distinct surface structures in the vicinity of their active sites. Both TRP14 and Trx1 inhibit the pathways of nuclear factor-kappaB (NF-kappaB), mitogen-activated protein kinases, and apoptosis in cells stimulated with tumor necrosis factor-alpha (TNF-alpha), but they appear to do so by acting on target proteins, some of which do not overlap. TRP14 inhibits the TNF-alpha-induced NF-kappaB activation to a greater extent than Trx1. The dynein light chain LC8 was identified as a new target of disulfide reductase activity of TRP14, and LC8 was shown to bind IkappaBalpha in a redox-dependent manner, thereby preventing its phosphorylation by IkappaB kinase. These findings elucidate the molecular mechanism by which NF-kappaB activation is regulated through TRP14.

Effect of thioredoxin deletion and p53 cysteine replacement on human p53 activity in wild-type and thioredoxin reductase null yeast

Reporter gene transactivation by human p53 is inhibited in budding yeast lacking the TRR1 gene encoding thioredoxin reductase. To investigate the role of thioredoxin in controlling p53 activity, the level of reporter gene transactivation by p53 was determined in yeast lacking the TRX1 and TRX2 genes encoding cytosolic thioredoxin. Surprisingly, p53 activity was unimpaired in yeast lacking thioredoxin. Subsequent analyses showed that thioredoxin deletion suppressed the inhibitory effect of thioredoxin reductase deletion, suggesting that accumulation of oxidized thioredoxin in mutant yeast was necessary for p53 inhibition. Purified human thioredoxin and p53 interacted in vitro (Kd = 0.9 microM thioredoxin). To test the idea that dithio-disulfide exchange reactions between p53 and thioredoxin were responsible for p53 inhibition in mutant yeast, each p53 cysteine was changed to serine, and the effect of the substitution on p53 activity in TRR1 and Deltatrr1 yeast was determined. Substitutions at Zn-coordinating cysteines C176, C238, or C242 resulted in p53 inactivation. Unexpectedly, substitution at cysteine C275 also inactivated p53, which was the first evidence for a non-zinc-coordinating cysteine being essential for p53 function. Cysteine substitutions at six positions (C124, C135, C141, C182, C229, and C277) neither inactivated p53 nor relieved the requirement for thioredoxin reductase. Furthermore, no tested combination of these six cysteine substitutions relieved thioredoxin reductase dependence. The results suggested that p53 dependence on thioredoxin reductase either was indirect, perhaps mediated by an upstream activator of p53, or was due to oxidation of one or more of the four essential cysteines.

Patulin-induced oxidative DNA damage and p53 modulation in HepG2 cells

Patulin (PAT) is a mycotoxin produced by certain species of Penicillium and Aspergillus. The aim of this study was to assess PAT-induced DNA damage and to clarify the mechanisms, using human hepatoma G2 (HepG2) cells. PAT caused significant increase of DNA migration in single cell gel electrophoresis assay. To elucidate the role of glutathione (GSH), the intracellular GSH level was modulated by pre-treatment with buthionine-(S, R)-sulfoximine, a specific GSH synthesis inhibitor. It was observed that PAT significantly induced DNA damage in GSH-depleted HepG2 cells at lower concentrations. PAT induced the increased levels of reactive oxygen species and depletion of GSH in HepG2 cells using 2,7-dichlorofluorescein diacetate and 0-phthalaldehyde, respectively. PAT significantly increased the levels of 8-hydroxydeoxyguanosine and thiobarbituric acid-reactive substances in HepG2 cells. Also, PAT-induced p53 protein accumulation was observed in HepG2 cells, suggesting that the activation of p53 appeared to have been a downstream response to the PAT-induced DNA damage. These results demonstrate that PAT causes DNA strand breaks in HepG2 cells, probably through oxidative stress. Both GSH, as a main intracellular antioxidant, and p53 protein are responsible for cellular defense against PAT-induced DNA damage.

Endogenous and exogenous thioredoxin 1 prevents goblet cell hyperplasia in a chronic antigen exposure asthma model

BACKGROUND

Goblet cell hyperplasia with mucus hypersecretion contribute to increased morbidity and mortality in bronchial asthma. We have reported that thioredoxin 1 (TRX1), a redox (reduction/oxidation)-active protein acting as a strong antioxidant, inhibits pulmonary eosinophilic inflammation and production of chemokines and Th2 cytokines in the lungs, thus decreasing airway hyperresponsiveness (AHR) and airway remodeling in mouse asthma models. In the present study, we investigated whether endogenous or exogenous TRX1 inhibits goblet cell hyperplasia in a mouse asthma model involving chronic exposure to antigen.

METHODS

We used wild-type Balb/c mice and Balb/c background human TRX1-transgenic mice constitutively overproducing human TRX1 protein in the lungs. Mice were sensitized 7 times (days 0 to 12) and then challenged 9 times with ovalbumin (OVA) (days 19 to 45). Every second day from days 18 to 44 (14 times) or days 35 to 45 (6 times), Balb/c mice were treated with 40 microg recombinant human TRX1 (rhTRX1) protein. Goblet cells in the lungs were examined quantitatively on day 34 or 45.

RESULTS

Goblet cell hyperplasia was significantly prevented in TRX1-transgenic mice in comparison with TRX1 transgene-negative mice. rhTRX1 administration during OVA challenge (days 18 to 44) significantly inhibited goblet cell hyperplasia in OVA-sensitized and -challenged wild-type mice. Moreover, rhTRX1 administration after the establishment of goblet cell hyperplasia (days 35 to 45) also significantly ameliorated goblet cell hyperplasia in OVA-sensitized and -challenged wild-type mice.

CONCLUSIONS

Our results suggest that TRX1 prevents the development of goblet cell hyperplasia, and also ameliorates established goblet cell hyperplasia.