Redox modulation of AP-2 DNA binding activity in vitro

Crucial role of the transcription factors family activator protein 2 in cancer: current clue and views

The transcription factor family activator protein 2 (TFAP2) is vital for regulating both embryonic and oncogenic development. The TFAP2 family consists of five DNA-binding proteins, including TFAP2A, TFAP2B, TFAP2C, TFAP2D and TFAP2E. The importance of TFAP2 in tumor biology is becoming more widely recognized. While TFAP2D is not well studied, here, we mainly focus on the other four TFAP2 members. As a transcription factor, TFAP2 regulates the downstream targets directly by binding to their regulatory region. In addition, the regulation of downstream targets by epigenetic modification, posttranslational regulation, and interaction with noncoding RNA have also been identified. According to the pathways in which the downstream targets are involved in, the regulatory effects of TFAP2 on tumorigenesis are generally summarized as follows: stemness and EMT, interaction between TFAP2 and tumor microenvironment, cell cycle and DNA damage repair, ER- and ERBB2-related signaling pathway, ferroptosis and therapeutic response. Moreover, the factors that affect TFAP2 expression in oncogenesis are also summarized. Here, we review and discuss the most recent studies on TFAP2 and its effects on carcinogenesis and regulatory mechanisms.

The biological characteristics of transcription factors AP-2α and AP-2γ and their importance in various types of cancers

The Activator Protein 2 (AP-2) transcription factor (TF) family is vital for the regulation of gene expression during early development as well as carcinogenesis process. The review focusses on the AP-2α and AP-2γ proteins and their dualistic regulation of gene expression in the process of carcinogenesis. Both AP-2α and AP-2γ influence a wide range of physiological or pathological processes by regulating different pathways and interacting with diverse molecules, i.e. other proteins, long non-coding RNAs (lncRNA) or miRNAs. This review summarizes the newest information about the biology of two, AP-2α and AP-2γ, TFs in the carcinogenesis process. We emphasize that these two proteins could have either oncogenic or suppressive characteristics depending on the type of cancer tissue or their interaction with specific molecules. They have also been found to contribute to resistance and sensitivity to chemotherapy in oncological patients. A better understanding of molecular network of AP-2 factors and other molecules may clarify the atypical molecular mechanisms occurring during carcinogenesis, and may assist in the recognition of new diagnostic biomarkers.

JAK2V617F mediates resistance to DNA damage-induced apoptosis by modulating FOXO3A localization and Bcl-xL deamidation

The JAK2V617F mutation is found in most patients with a myeloproliferative neoplasm (MPN). This gain-of-function mutation dysregulates cytokine signaling and is associated with increased accumulation of DNA damage, a process likely to drive disease evolution. JAK2V617F inhibits NHE-1 upregulation in response to DNA damage and consequently represses Bcl-xL deamidation and apoptosis, thus giving rise to inappropriate cell survival. However, the mechanism whereby NHE-1 expression is inhibited by JAK2V617F is unknown. In this study, we demonstrate that the accumulation of reactive oxygen species (ROS) in cells expressing JAK2V617F compromises the NHE-1/Bcl-xL deamidation pathway by repressing NHE-1 upregulation in response to DNA damage. In JAK2V617F-positive cells, increased ROS levels results from aberrant PI3K signaling, which decreases nuclear localization of FOXO3A and decreases catalase expression. Furthermore, when compared with autologous control erythroblasts, clonally derived JAK2V617F-positive erythroblasts from MPN patients displayed increased ROS levels and reduced nuclear FOXO3A. However, in hematopoietic stem cells (HSCs), FOXO3A is largely localized within the nuclei despite the presence of JAK2V617F mutation, suggesting that JAK2-FOXO signaling has a different effect on progenitors compared with stem cells. Inactivation of FOXO proteins and elevation of intracellular ROS are characteristics common to many cancers, and hence these findings are likely to be of relevance beyond the MPN field.

Insights into the fish thioredoxin system: expression profile of thioredoxin and thioredoxin reductase in rainbow trout (Oncorhynchus mykiss) during infection and in vitro stimulation

Production of reactive oxygen species (ROS) is the first biological response during a disease outbreak and after injury. ROS are highly reactive molecules that can either endanger cell homeostasis or mediate cell signaling in several physiological pathways, including the immune response. Thioredoxin (Trx) and thioredoxin reductase (TrxR) are the essential components of the thioredoxin system, one of the main intracellular redox systems and are therefore important regulators of ROS accumulation. Through the regulation of the intracellular redox milieu, the thioredoxin system plays a key role within the immune system, linking immunology and free radical science. In this study we have firstly identified TrxRs in fish and used this new sequence information to reevaluate the evolution of the thioredoxin system within the vertebrate lineage. We next measured the expression of rainbow trout (Oncorhynchus mykiss) Trx and TrxR transcripts during infection in vivo and in vitro after stimulation of a macrophage cell line and primary macrophage cultures with pathogen associated molecular patterns (PAMPs). Our results showed that both Trx and TrxR were induced during infection at the transcriptional level, confirming their likely involvement in the innate immune response of fish. Since TrxRs are selenium-containing proteins (selenoproteins), we also measured the modulation of their expression upon organic and inorganic selenium exposure in vitro. TrxR was found to be responsive to selenium exposure in vitro, suggesting that it may represent a key mediator in the selenium modulation of innate immunity. In conclusion, our study highlights the need to investigate the involvement of the cell antioxidant pathways, especially the thioredoxin system, within the immune system of vertebrate species.

Diagnostic correlation between the expression of the DNA repair enzyme N-methylpurine DNA glycosylase and esophageal adenocarcinoma onset: a retrospective pilot study

EAC in its early stages, when it can potentially be cured, is rarely symptomatic and is associated with high mortality rates because in part of late-stage diagnosis. Given that DNA repair is an important contributory factor of early-stage malignancy, our study focused on the expression of the base excision repair enzyme N-methylpurine DNA glycosylase (MPG) in EAC disease onset. MPG messenger RNA (mRNA) expression levels were determined using quantitative reverse transcriptase polymerase chain reaction from a maximum of 72 patient samples. Immunohistochemistry was further utilized for the detection of MPG protein, and semiquantitative analysis performed using an H-score approach was carried out on a total of 130 archival tissue samples of different esophageal pathologies. Nuclear localized MPG protein was detected in all nonmalignant tissues derived from the enterohepatic system, with H-score values of 3.9-5.5 ± 0.4-1.0. In cancerous tissues derived from the enterohepatic system, a 9.5-fold increase in the level of MPG mRNA expression was specifically observed in the malignant regions located within the esophagus region. Further analysis revealed a 9- and 14-fold increase in MPG mRNA expression in EAC tumor, node, metastasis stages II and III, respectively, suggesting MPG expression to correlate with EAC disease progression. Immunohistochemistry analysis further showed a sevenfold significant increase in MPG protein expression in EAC tissues. Intriguingly, there was a fivefold significant decrease in nuclear localized MPG protein expression in tissues derived from Barrett's esophagus and low-grade dysplasia. Such findings highlight a complex regulatory pattern governing DNA glycosylase base excision repair initiation, as normal tissue undergoes Barrett's metaplasia and later dedifferentiates to EAC. Indeed, disease-stage-specific alterations in the expression of MPG may highlight a potential role for MPG in determining EAC onset and thus potentially be of clinical relevance for early disease detection and increased patient survival.

Penaeus monodon thioredoxin restores the DNA binding activity of oxidized white spot syndrome virus IE1

AIMS

In this study we identified viral gene targets of the important redox regulator thioredoxin (Trx), and explored in depth how Trx interacts with the immediate early gene #1 (IE1) of the white spot syndrome virus (WSSV).

RESULTS

In a pull-down assay, we found that recombinant Trx bound to IE1 under oxidizing conditions, and a coimmunoprecipitation assay showed that Trx bound to WSSV IE1 when the transfected cells were subjected to oxidative stress. A pull-down assay with Trx mutants showed that no IE1 binding occurred when cysteine 62 was replaced by serine. Electrophoretic mobility shift assay (EMSA) showed that the DNA binding activity of WSSV IE1 was downregulated under oxidative conditions, and that Penaeus monodon Trx (PmTrx) restored the DNA binding activity of the inactivated, oxidized WSSV IE1. Another EMSA experiment showed that IE1's Cys-X-X-Cys motif and cysteine residue 55 were necessary for DNA binding. Measurement of the ratio of reduced glutathione to oxidized glutathione (GSH/GSSG) in WSSV-infected shrimp showed that oxidative stress was significantly increased at 48 h postinfection. The biological significance of Trx was also demonstrated in a double-strand RNA Trx knockdown experiment where suppression of shrimp Trx led to significant decreases in mortality and viral copy numbers.

INNOVATION AND CONCLUSION

WSSV's pathogenicity is enhanced by the virus' use of host Trx to rescue the DNA binding activity of WSSV IE1 under oxidizing conditions.

Oxidative stress and redox modulation potential in type 1 diabetes

Redox reactions are imperative to preserving cellular metabolism yet must be strictly regulated. Imbalances between reactive oxygen species (ROS) and antioxidants can initiate oxidative stress, which without proper resolve, can manifest into disease. In type 1 diabetes (T1D), T-cell-mediated autoimmune destruction of pancreatic β-cells is secondary to the primary invasion of macrophages and dendritic cells (DCs) into the islets. Macrophages/DCs, however, are activated by intercellular ROS from resident pancreatic phagocytes and intracellular ROS formed after receptor-ligand interactions via redox-dependent transcription factors such as NF-κB. Activated macrophages/DCs ferry β-cell antigens specifically to pancreatic lymph nodes, where they trigger reactive T cells through synapse formation and secretion of proinflammatory cytokines and more ROS. ROS generation, therefore, is pivotal in formulating both innate and adaptive immune responses accountable for islet cell autoimmunity. The importance of ROS/oxidative stress as well as potential for redox modulation in the context of T1D will be discussed.

Expression of thioredoxin-1 and hypoxia inducible factor-1α in cerebral arteriovenous malformations: Possible role of redox regulatory factor in neoangiogenic property

Background:

Recently it is reported that proliferative activity remains in vascular walls of cerebral arteriovenous malformations (AVMs). These reports indicate that endothelial cells in AVMs have the neoangiogenic property. In this study, we assess the role of thioredoxin-1 (Trx-1) and hypoxia-inducible factor 1a (HIF-1α) in AVMs. These factors are reported to play a role in neoangiogenesis.

Methods:

We analyzed the expressions of Trx1 in the specimens of human cerebral AVMs. In addition, we also analyzed the expression of HIF-1α in these specimens by immunohistochemical method and RT-PCR. Furthermore, we assessed the effect of redox state and expression of Trx-1 during neoangiogenesis using in vitro angiogenesis assay.

Findings:

Trx-1 and HIF-1α immunoreactivity was detected in almost all 17 specimens of AVMs. Trx-1 and HIF-1α immunoreactive cells were distributed mainly endothelium of intranidal arteries and enlarged veins with thickened vascular walls. Double staining shows that Trx-1 and VEGF (vascular endothelial growth factor) immunoreactivity were colocalized in the same cells. These cells were considered to be endothelial cells. HIF-1α immunoreactivity was also colocalized with VEGF immunoreactivity in endothelium. As for influencing factors, the presence of deep drainers and convulsion significantly associated with HIF-1α expression. Trx-1 assessed by western blotting decreased at 6 hours and 12 hours after plating on Matrigel, which is a model of angiogenesis.

Conclusions:

We have shown that the endothelial induction of Trx-1 and HIF-1α in cerebral AVMs. Based on all findings obtained in this study, Trx-1 may affect the neoangiogenic property of cerebral AVMs.

Roles of AP-2 transcription factors in the regulation of cartilage and skeletal development

During embryogenesis, most of the mammalian skeletal system is preformed as cartilaginous structures that ossify later. The different stages of cartilage and skeletal development are well described, and several molecular factors are known to influence the events of this enchondral ossification, especially transcription factors. Members of the AP-2 family of transcription factors play important roles in several cellular processes, such as apoptosis, migration and differentiation. Studies with knockout mice demonstrate that a main function of AP-2s is the suppression of terminal differentiation during embryonic development. Additionally, the specific role of these molecules as regulators during chondrogenesis has been characterized. This review gives an overview of AP-2s, and discusses the recent findings on the AP-2 family, in particular AP-2alpha, AP-2beta, and AP-2epsilon, as regulators of cartilage and skeletal development.

Involvement of protein kinase D in phosphorylation and increase of DNA binding of activator protein 2 alpha to downregulate ATP-binding cassette transporter A1

BACKGROUND

Activator protein (AP) 2alpha negatively regulates expression of ABCA1 gene through Ser-phosphorylation of AP2alpha (Circ Res. 2007;101:156-165). Potential specific Ser-phosphorylation sites for this reaction were investigated in human AP2alpha.

METHODS AND RESULTS

The phosphorylation was shown mediated by PKD, and Ser258 and Ser326 were found in its specific phosphorylation sequence segment in AP2alpha. PKD phosphorylated Ser258 more than Ser326 and induced its binding to the ABCA1 promoter. These reactions and AP2alpha-induced suppression of the ABCA1 promoter activity were reversed by mutation of Ser258 more than Ser326 mutation. Knockdown of PKD by siRNA reduced the AP2alpha Ser-phosphorylation, and increased ABCA1 expression and HDL biogenesis. Gö6983 inhibited PKD more selectively than PKC in THP-1 and HEK 293 cells and in mice, and increased ABCA1 expression, HDL biogenesis, and plasma HDL level.

CONCLUSIONS

PKD phosphorylates AP2alpha to negatively regulate expression of ABCA1 gene to increase HDL biogenesis. The major functional phosphorylation of AP2alpha was identified at Ser258 by PKD, in the AP2alpha basic domain highly conserved among species and all 5 subtypes of AP2. PKD/AP2 system can be a potent pharmacological target for prevention of atherosclerosis.

Resveratrol regulates the expression of NHE-1 by repressing its promoter activity: critical involvement of intracellular H2O2 and caspases 3 and 6 in the absence of cell death

Na(+)/H(+) exchanger-1 (NHE-1) overexpression is associated with carcinogenesis and is an attractive target for intervention. We report that the chemopreventive agent resveratrol (RSV) downregulates NHE-1 in a caspase-dependent manner without inducing cell death. Resveratrol triggered early activation of caspase 3 and late activation of caspase 6, which were not inter-dependent. Whereas, caspase 3 activation appeared to be a direct effect of resveratrol, caspase 6 activation was mediated via intracellular hydrogen peroxide production and iron. Moreover, downregulation of NHE-1 expression was a function of resveratrol-induced repression of NHE-1 gene promoter activity. RNAi-mediated silencing of caspase 3 or 6 blocked the effect of resveratrol on NHE-1 expression, however the effect on NHE-1 promoter was observed at different phases of promoter repression with caspase 3 controlling the early phase (4-12 h) and caspase 6 regulating the late phase (12-24 h). Scavenging hydrogen peroxide or iron only reversed the late phase of resveratrol-induced NHE-1 promoter repression. Finally, an AP2 binding region within NHE-1 gene promoter was identified as the target of resveratrol. Collectively, these data could explain the anti-cancer activity of resveratrol in the light of the association of increased NHE-1 expression with carcinogenesis.

Oxidative repression of NHE1 gene expression involves iron-mediated caspase activity

The mechanism of Na(+)/H(+) exchanger 1 (NHE1) gene repression upon exposure of cells to non-apoptotic concentrations of hydrogen peroxide (H(2)O(2)) was investigated. We show that continuous presence of H(2)O(2) was not required for inhibition of NHE1 promoter activity. However, the downregulation of NHE1 promoter activity and protein expression was abrogated by the presence of beta mercaptoethanol (betaME) and dithiothreitol. The pan-caspase inhibitor zVAD-fmk also blocked the effect of H(2)O(2) on NHE1 promoter activity and expression, but unlike betaME, caspase inhibition was ineffective in rescuing the early phase of NHE1 repression. Interestingly, the effect of caspase inhibition was observed only after 9 h of exposure to H(2)O(2) and completely restored NHE1 promoter activity by 18-24 h. Using tetrapeptide inhibitors of a variety of caspases and siRNA-mediated gene silencing, caspases 3 and 6 were identified as mediators of H(2)O(2)-induced NHE1 repression, independent of initiator/amplifier caspase activation. Furthermore, incubation of cells with the iron chelator, desferioxamine, not only blocked the activities of caspases 3 and 6, but also affected NHE1 promoter and protein expression in a manner similar to zVAD-fmk. These data show that a mild oxidative stress represses NHE1 promoter activity and expression via an early oxidation phase blocked by reducing agents, and a late phase requiring an iron-dependent increase in caspases 3 and 6 activities.

Reactive oxygen species and antioxidant mechanisms in human tissues and their relation to malignancies

Reactive oxygen species (ROS) are formed in mammalian cells as a consequence of aerobic respiration. Despite multiple conserved redox modulating systems, a given proportion of ROS continuously escape from the mitochondrial respiratory chain, being sufficiently potent to damage cells in various ways, including numerous carcinogenic DNA mutations. Oxidative stress resulting from an imbalanced ratio between ROS production and detoxification may also disturb physiological signal transduction, lead to chain reactions in lipid layers, and damage DNA repair enzymes. The significance of ROS and antioxidant systems in carcinogenesis is still complicated and in many ways contradictory. Enhanced antioxidant mechanisms in tumor cells in vivo have been implicated in chemoresistance and lead to poor prognosis, whereas most in vitro studies have reported tumor-suppressing properties of antioxidant enzymes. The present review aims to clarify the significance of oxidative stress and the role of cell redox state modulating systems in human malignancies in light of the current literature.

AP-2alpha and AP-2gamma are transcriptional targets of p53 in human breast carcinoma cells

Activating enhancer-binding protein 2alpha (AP-2alpha) and activating enhancer-binding protein 2gamma (AP-2gamma) are transcription factors that bind GC-rich consensus sequences and regulate the expression of many downstream genes. AP-2alpha and AP-2gamma interact with p53 both physically and functionally. Expression microarray results in human breast carcinoma cells with forced p53 expression revealed AP-2gamma as a putative transcriptional target of p53. To confirm and extend these findings we measured the effects of forced p53 expression in human breast carcinoma cells by real-time reverse transcription-PCR, Western blotting, electrophoretic gel mobility shift assays, promoter reporter, chromatin immunoprecipitation and chromatin accessibility assays. Wild-type p53 expression rapidly induced not only AP-2gamma but also AP-2alpha mRNA. The subsequent increase in these proteins led to increased AP-2 DNA-binding and transactivating activity. Candidate p53-binding sites were identified in the AP-2alpha and AP-2gamma promoters. p53 binding to these cis-elements in vivo was also observed, together with a relaxation of chromatin structure in these regions. Finally, expression of either AP-2alpha or gamma inhibited growth of human breast carcinoma cells in vitro. Taken together, our findings indicate that these AP-2 genes are targets for transcriptional activation by p53 and suggest that AP-2 proteins may mediate some of the downstream effects of p53 expression such as inhibition of proliferation.

The AP-2 family of transcription factors

AP-2 transcription factors are involved in cell-type-specific stimulation of proliferation and the suppression of terminal differentiation during embryonic development. Members of the family are found in mammals (with five different proteins in human and mice), frogs and fish, as well as protochordates, insects and nematodes.

The AP-2 family of transcription factors consists of five different proteins in humans and mice: AP-2α, AP-2β, AP-2γ, AP-2δ and AP-2ε. Frogs and fish have known orthologs of some but not all of these proteins, and homologs of the family are also found in protochordates, insects and nematodes. The proteins have a characteristic helix-span-helix motif at the carboxyl terminus, which, together with a central basic region, mediates dimerization and DNA binding. The amino terminus contains the transactivation domain. AP-2 proteins are first expressed in primitive ectoderm of invertebrates and vertebrates; in vertebrates, they are also expressed in the emerging neural-crest cells, and AP-2α^-/- animals have impairments in neural-crest-derived facial structures. AP-2β is indispensable for kidney development and AP-2γ is necessary for the formation of trophectoderm cells shortly after implantation; AP-2α and AP-2γ levels are elevated in human mammary carcinoma and seminoma. The general functions of the family appear to be the cell-type-specific stimulation of proliferation and the suppression of terminal differentiation during embryonic development.

Role of mitogen-activated protein kinase pathway in reactive oxygen species-mediated endothelin-1-induced beta-myosin heavy chain gene expression and cardiomyocyte hypertrophy

Endothelin-1 (ET-1) has been found to increase cardiac beta-myosin heavy chain (beta-MyHC) gene expression and induce hypertrophy in cardiomyocytes. ET-1 has been demonstrated to increase intracellular reactive oxygen species (ROS) in cardiomyocytes. The exact molecular mechanism by which ROS regulate ET-1-induced beta-MyHC gene expression and hypertrophy in cardiomyocytes, however, has not yet been fully described. We aim to elucidate the molecular regulatory mechanism of ROS on ET-1-induced beta-MyHC gene expression and hypertrophic signaling in neonatal rat cardiomyocytes. Following stimulation with ET-1, cultured neonatal rat cardiomyocytes were examined for 3H-leucine incorporation and beta-MyHC promoter activities. The effects of antioxidant pretreatment on ET-1-induced cardiac hypertrophy and mitogen-activated protein kinase (MAPKs) phosphorylation were studied to elucidate the redox-sensitive pathway in cardiomyocyte hypertrophy and beta-MyHC gene expression. ET-1 increased 3H-leucine incorporation and beta-MyHC promoter activities, which were blocked by the specific ET(A) receptor antagonist BQ-485. Antioxidants significantly reduced ET-1-induced 3H-leucine incorporation, beta-MyHC gene promoter activities and MAPK (extracellular signal-regulated kinase, p38, and c-Jun NH2 -terminal kinase) phosphorylation. Both PD98059 and SB203580 inhibited ET-1-increased 3H-leucine incorporation and beta-MyHC promoter activities. Co-transfection of the dominant negative mutant of Ras, Raf, and MEK1 decreased the ET-1-induced beta-MyHC promoter activities, suggesting that the Ras-Raf-MAPK pathway is required for ET-1 action. Truncation analysis of the beta-MyHC gene promoter showed that the activator protein-2 (AP-2)/specificity protein-1 (SP-1) binding site(s) were(was) important cis-element(s) in ET-1-induced beta-MyHC gene expression. Moreover, ET-1-induced AP-2 and SP-1 binding activities were also inhibited by antioxidant. These data demonstrate the involvement of ROS in ET-1-induced hypertrophic responses and beta-MyHC expression. ROS mediate ET-1-induced activation of MAPK pathways, which culminates in hypertrophic responses and beta-MyHC expression.

Oxidized linoleic acid regulates expression and shedding of syndecan-4

Syndecan-4, a heparan sulfate proteoglycan that is widely expressed in the vascular wall and as a cell surface receptor, modulates events relevant to acute tissue repair, including cell migration and proliferation, cell-substrate interactions, and matrix remodeling. While syndecan-4 expression is regulated in response to acute vascular wall injury, its regulation under chronic proatherogenic conditions such as those characterized by prolonged exposure to oxidized lipids has not been defined. In this investigation, arterial smooth muscle cells were treated with 13-hydroperoxy-9,11-octadecadienoic acid (HPODE) and 13-hydroperoxy-10,12-octadecadienoic acid, oxidized products of linoleic acid, which is the major oxidizable fatty acid in LDL. Both oxidized fatty acids induced a dose-dependent, rapid upregulation of syndecan-4 mRNA expression that was not attenuated by cycloheximide. This response was inhibited by pretreatment with N-acetylcysteine, catalase, or MEK1/2 inhibitors, but not by curcumin or lactacystin, known inhibitors of NF-κB. These data suggest that oxidized linoleic acid induces syndecan-4 mRNA expression through the initial generation of intracellular hydrogen peroxide with subsequent activation of the extracellular signal-regulated kinase signaling pathway via MEK1/2. Notably, the HPODE-induced enhancement of syndecan-4 mRNA was accompanied by accelerated shedding of syndecan-4. In principle, alterations in both the cell surface expression and shedding of syndecan-4 may augment a variety of proatherogenic events that occur in response to oxidized lipids.

Characterization of the promoter of the mouse c-Jun NH2-terminal/stress-activated protein kinase alpha gene

We report the isolation of the mouse JNK/SAPKalpha gene, the determination of its exon/intron organization and the characterization of its promoter region. The mouse JNK/SAPKalpha gene spans a region of 36 kbp and contains 13 exons, which represent about 8% of the gene sequence. Major JNK/SAPKalpha splice variants (I and II) are generated by alternative splicing of exons 7 and 8, respectively, whereas minor variants (III and IV) are generated using cryptic sites located inside exon 9. The regulatory elements of the JNK/SAPKalpha gene are located in a 400-bp region placed upstream of the first exon. The gene lacks a TATA element and the initiation of transcription is located inside a 1-kbp CG island. Two regulatory regions located at -98/-69 and -69/-30 were defined by deletion analysis of the promoter.

Thioredoxin-1 binds to the C2 domain of PTEN inhibiting PTEN's lipid phosphatase activity and membrane binding: a mechanism for the functional loss of PTEN's tumor suppressor activity

Thioredoxin-1 (Trx-1) is a 12 kDa redox protein that is overexpressed in a large number of human tumors. Elevated Trx-1 is associated with increased tumor cell proliferation, inhibited apoptosis, aggressive tumor growth, and decreased patient survival. The molecular mechanisms for the promotion of tumorigenesis by Trx-1 are not known. PTEN is a major tumor suppressor of human cancer that acts by hydrolyzing membrane phosphatidylinositol (PtdIns)-3-phosphates, thus, preventing the activation of the survival signaling kinase Akt by PtdIns-3-kinase. We show that Trx-1 binds in a redox dependent manner to PTEN to inhibit its PtdIns-3-phosphatase activity which results in increased Akt activation in cells. Molecular docking and site-specific mutation studies show that the binding of Trx-1 to PTEN occurs through a disulfide bond between the active site Cys(32) of Trx-1 and Cys(212) of the C2 domain of PTEN leading to steric interference by bound Trx-1 of the catalytic site of PTEN and of the C2 lipid membrane-binding domain. The results of the study suggest that the increased levels of Trx-1 in human tumors could lead to functional inhibition of PTEN tumor suppressor activity providing an additional mechanism for tumorigenesis with loss of PTEN activity.

Activator protein 2alpha associates with adenomatous polyposis coli/beta-catenin and Inhibits beta-catenin/T-cell factor transcriptional activity in colorectal cancer cells

In most human colorectal cancers, mutations in the adenomatous polyposis coli gene (APC) or CTNNB1 constitutively activate the beta-catenin/T-cell factor (TCF)/lymphoid enhancer factor (LEF) signaling pathway. Here, we show that the transcription factor activator protein (AP)-2alpha inhibited a beta-catenin/TCF-responsive reporter in human embryonic kidney 293 cells and in two human colorectal cancer lines, despite the fact that beta-catenin and TCF-4 protein levels were unchanged in the nucleus. Co-immunoprecipitation studies revealed that AP-2alpha formed a complex with APC and beta-catenin and that AP-2alpha disrupted beta-catenin/TCF-4 interactions in the nucleus. Thus, AP-2alpha.APC.beta-catenin complex formation appears to suppress beta-catenin transactivation by shifting the pool of nuclear beta-catenin toward an inactive form, having reduced binding to TCF/LEF transcription factors. Glutathione S-transferase pull-down assays showed that AP-2alpha physically associated with APC rather than with beta-catenin, and the AP-2alpha binding site was identified in the N terminus of APC, involving both the heptad and armadillo repeat domains, whereas the APC binding site in AP-2alpha was in the basic region of the C-terminal DNA binding domain. These findings provide the first evidence for a specific interaction between the tumor suppressor protein APC and the transcription factor AP-2alpha, and they suggest a link between the Wnt signaling pathway and various other pathways of development and differentiation associated with AP-2alpha.

Redox regulation of DNA binding activity of DREF (DNA replication-related element binding factor) in Drosophila

DREF [DRE (DNA replication-related element) binding factor] is an 80 kDa polypeptide homodimer which plays an important role in regulating cell proliferation-related genes. Both DNA binding and dimer formation activities are associated with residues 16-115 of the N-terminal region. However, the mechanisms by which DREF dimerization and DNA binding are regulated remain unknown. Here, we report that the DNA binding activity of DREF is regulated by a redox mechanism, and that the cysteine residues are involved in this regulation. Electrophoretic mobility shift analysis using Drosophila Kc cell extracts or recombinant DREF proteins indicated that the DNA binding domain is sufficient for redox regulation. Site-directed mutagenesis and transient transfection assays showed that Cys59 and/or Cys62 are critical both for DNA binding and for redox regulation, whereas Cys91 is dispensable. In addition, experiments using Kc cells indicated that the DNA binding activity and function of DREF are affected by the intracellular redox state. These findings give insight into the exact nature of DREF function in the regulation of target genes by the intracellular redox state.

Molecular regulation of angiogenesis and tumorigenesis by signal transduction pathways: evidence of predictable and reproducible patterns of synergy in diverse neoplasms

A large number of oncogenes, tumor suppressor genes, and signal transduction pathways have been described. Currently, a framework that allows prediction of tumor behavior based upon oncogenes, tumor suppressors, and signal transduction pathways is lacking. In 1869, Mendeleev published a periodic table of elements which allowed prediction of properties of elements based upon atomic weights that allowed prediction of chemical and physical properties of elements yet to be discovered. In this paper, I will discuss recurrent patterns of synergy found in the literature and our laboratory between tumor suppressor genes, oncogenes, and signaling pathways that allows one to predict the signaling pathway in a given tumor based upon the inactivation of a tumor suppressor gene. These patterns can be found in multiple different human neoplasms. Conversely, one can predict the inactivation of a tumor suppressor based upon the activation status of a signaling pathway. This knowledge can be used by a clinician or pathologist with access to immunohistochemistry to make predictions based upon simple technologies and determine the signaling pathways involved in a patient's tumor. These strategies may be useful in the design of prevention and treatment strategies for cancer.

Regulation of alpha7-integrin expression in vascular smooth muscle by injury-induced atherosclerosis

Injury of vascular smooth muscle cells (VSMCs) by allylamine (AAM) leads to phenotypic changes associated with atherogenic progression including increased proliferation, migration, and alterations in cell adhesion. In the present study, the relationship between AAM-induced vascular injury and expression of the alpha(7)-integrin subunit was investigated. The alpha(7)-mRNA and protein expression were examined using real-time RT-PCR, fluorescence-activated cell sorting analysis (FACS), immunohistochemistry, and immunoblotting. In cultured VSMCs from aortas of AAM-treated rats (70 mg/kg for 20 days), alpha(7)-mRNA levels were increased more than twofold compared with control cells. No change was seen in beta(1)-integrin expression. FACS analysis revealed increased cell surface expression of alpha(7)-protein (25 +/- 9%; *P < 0.05). AAM treatment of naive VSMCs enhanced alpha(7)-mRNA expression (2.4 +/- 0.7-fold, mean +/- SE; *P < 0.05). The increased alpha(7)-mRNA expression was attenuated by the amine oxidase inhibitor semicarbazide and the antioxidant pyrrolidine dithiocarbamate, which confirms a role for oxidative stress in modulating alpha(7)-expression. In vivo alpha(7)-mRNA and protein expression were enhanced in the aortas of AAM-treated rats. In addition, increased alpha(7)-integrin expression facilitated AAM VSMC adhesion to laminin more efficiently compared with control (51 +/- 2%; *P < 0.05). Chemical injury induced by AAM significantly enhances alpha(7)-integrin expression in VSMCs. These findings implicate for the first time the expression of alpha(7)-integrin during the response of VSMCs to vascular injury.

Cerivastatin inhibits proliferation of interleukin-1β-induced rat mesangial cells by enhanced formation of nitric oxide

The antiproliferative effect of statins on mesangial cells could represent a new therapeutic approach in glomerulonephritis. We studied in rat mesangial cells whether the antiproliferative action of cerivastatin on mesangial cells may be mediated by mesangial nitric oxide (NO) formation due to the inducible NO synthase (iNOS) or by induction of cyclooxygenase-2. Mesangial cells were stimulated with interleukin-1 beta and treated with cerivastatin for 24 h. Cell proliferation was examined by bromodeoxy-uridine (BrdU) incorporation, and nitrite and prostaglandin production was measured in supernatants as a means for iNOS or cyclooxygenase-2 activity. iNOS and cyclooxygenase-2 expression was quantified by Northern and Western blot analyses. Cerivastatin (0.0625 microM) significantly inhibited DNA synthesis in interleukin-1 beta-stimulated mesangial cells without altering cell viability. Interleukin-1 beta-induced nitrite production was twofold increased by 0.05 microM cerivastatin, and this effect could be reversed by addition of 100 microM mevalonate. iNOS mRNA levels increased sixfold (33% of maximum) in cerivastatin-treated mesangial cells as compared with vehicle-treated controls (3.5% of maximum). iNOS and cyclooxygenase-2 protein expression increased threefold (iNOS: 2.77+/-0.53/cyclooxygenase-2: 3.49+/-1.25). The NOS inhibitors N-methyl-L-arginine (L-NMMA) and L-N6-(1-iminoethyl)lysine (L-NIL) reversed the antiproliferative effect of cerivastatin. The cyclooxygenase-2 inhibitor celecoxib did not alter DNA synthesis and iNOS or cyclooxygenase-2 expression, but blocked prostacyclin production in interleukin-1 beta and cerivastatin-treated mesangial cells. In conclusion, cerivastatin increased cytokine-induced iNOS and cyclooxygenase-2 expression, thus constituting NO-regulated growth inhibition of mesangial cells.

Redox factor-1 contributes to the regulation of progression from G0/G1 to S by PDGF in vascular smooth muscle cells

Redox factor-1 (Ref-1/APE), a multifunctional DNA base excision repair and redox regulation enzyme, plays an important role in oxidative signaling, transcription factor regulation, and cell cycle control. We hypothesized that Ref-1 plays a regulatory role in smooth muscle cell (SMC) proliferation induced by PDGF. Ref-1 antisense oligodeoxynucleotides (AODN), which diminished the level of Ref-1 protein in SMCs by approximately 50%, inhibited PDGF-BB (composed of the homodimer of B-polypeptide chain)-induced [3H]thymidine incorporation compared with control oligodeoxynucleotides. Ref-1 AODN inhibited PDGF-BB-induced S phase entry by approximately 63%, which was overcome by overexpression of Ref-1 by adenoviral-mediated gene transfer. Overexpression of Ref-1 alone without PDGF enhanced SMC entry into the S phase. Furthermore, decreasing Ref-1 protein by treatment of SMCs with Ref-1 AODN, or by immunodepletion of Ref-1 from nuclear extracts, inhibited PDGF-BB-induced activator protein-1 (AP-1) DNA binding activity. Chemical reduction restored the AP-1 DNA binding in Ref-1-depleted nuclear extracts. These results suggest that Ref-1 contributes to the regulation of PDGF-BB-stimulated cell cycle progression from G0/G1 to S in SMCs, with one of the possible steps being redox-regulation of AP-1 by Ref-1 protein.

Role and regulation of the thrombin receptor (PAR-1) in human melanoma

To determine treatment strategies and predict the clinical outcome of patients with melanoma it is important to understand the etiology of this disease. Recently, there has been some insight into molecular basis of melanoma including identification of a few of the regulatory factors and genes involved in this disease. For instance, the transcription factor AP-2 plays a tumor suppressor-like role in melanoma progression by regulating genes involved in tumor growth and metastasis. Previously, we have shown that the progression of human melanoma to the metastatic phenotype is associated with loss of AP-2 expression and deregulation of target genes such as MUC18/MCAM, c-KIT, and MMP-2. Increasing evidence demonstrates that the thrombin receptor (protease-activated receptor-1, PAR-1) plays a major role in tumor invasion and contributes to the metastatic phenotype of human melanoma. This review focuses on the role of the thrombin receptor in melanoma and its regulation by AP-2. We show that loss of AP-2 expression in metastatic melanoma cells correlates with overexpression of the thrombin receptor. Our analysis of AP-2/Sp1 complexes within the regulatory region of the thrombin receptor demonstrates that AP-2 binds the proximal 3' region of the promoter and diminishes PAR-1 expression. Levels of AP-2 and Sp1 proteins in a panel of melanoma cell lines demonstrated a marked decrease in the ratio of AP-2/Sp1, a decrease that correlated with overexpression of PAR-1 in metastatic melanoma cells. We propose that loss of AP-2 results in increased expression of the thrombin receptor, which subsequently contributes to the metastatic phenotype of melanoma by upregulating the expression of adhesion molecules, proteases, and angiogenic molecules.

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.

Oxidative stress and stress-activated signaling pathways: a unifying hypothesis of type 2 diabetes

In both type 1 and type 2 diabetes, the late diabetic complications in nerve, vascular endothelium, and kidney arise from chronic elevations of glucose and possibly other metabolites including free fatty acids (FFA). Recent evidence suggests that common stress-activated signaling pathways such as nuclear factor-kappaB, p38 MAPK, and NH2-terminal Jun kinases/stress-activated protein kinases underlie the development of these late diabetic complications. In addition, in type 2 diabetes, there is evidence that the activation of these same stress pathways by glucose and possibly FFA leads to both insulin resistance and impaired insulin secretion. Thus, we propose a unifying hypothesis whereby hyperglycemia and FFA-induced activation of the nuclear factor-kappaB, p38 MAPK, and NH2-terminal Jun kinases/stress-activated protein kinases stress pathways, along with the activation of the advanced glycosylation end-products/receptor for advanced glycosylation end-products, protein kinase C, and sorbitol stress pathways, plays a key role in causing late complications in type 1 and type 2 diabetes, along with insulin resistance and impaired insulin secretion in type 2 diabetes. Studies with antioxidants such as vitamin E, alpha-lipoic acid, and N-acetylcysteine suggest that new strategies may become available to treat these conditions.

Accumulation of glutathione disulfide mediates NF-kappaB activation during immune stimulation with CpG DNA

Innate immune cells recognize pathogens by detecting molecular patterns that are distinct from those of the host. One such pattern is unmethylated CpG dinucleotides, which are common in bacterial DNA but not in vertebrate genomes. Macrophages respond to such CpG motifs in bacterial DNA or synthetic oligodeoxynucleotides (ODN) by inducing NF-kappaB and secreting proinflammatory cytokines, such as interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha), but the mechanisms regulating this have been unclear. CpG ODN-stimulated cells produce reactive oxygen species (ROS) and have a decreased ratio of intracellular glutathione/glutathione disulfide (GSH/GSSG), indicating a shift to a more oxidized intracellular redox state. To determine whether this may play a role in mediating the CpG-induced macrophage activation, the GSH/GSSG redox state was manipulated in the murine macrophagelike cell line RAW264.7. Treatment of cells with BCNU to inhibit glutathione reductase (GR) enhanced the CpG-induced intracellular oxidation and decreased the GSH/GSSG, with increased activation of NF-kappaB and a doubling in the CpG-induced production of IL-6 and TNF-alpha. Experimental manipulation of the intracellular GSSG concentration during inhibition of cellular prooxidant production demonstrated that increased intracellular GSSG is a primary signal that is directly or indirectly required for CpG-induced NF-kappaB activation but is not in itself sufficient to trigger this in the absence of CpG ODN. These data suggest the existence of a second CpG-induced intracellular signal, independent of GSSG, mediating the activation of innate immunity by bacterial DNA.

v-Ha-ras mitogenic signaling through superoxide and derived reactive oxygen species

The ras proto-oncogene is frequently mutated in human tumors and functions to constitutively stimulate signal transduction cascades, resulting in unchecked proliferation and malignant transformation. In certain cells, superoxide functions as a signal-transduction messenger, mediating the downstream effects of ras and rac. We demonstrated previously that v-Ha-ras-transfected rat kidney epithelial cells (RECs) overproduced superoxide anion and that this superoxide production was mediated by ras. In the present study, we further demonstrated that v-Ha-ras overexpression transformed immortal nonmalignant RECs into malignant cancer cells; v-Ha-ras-transfected cells formed clones in soft agar, had high plating efficiency, and formed tumors in nude mice. Our data suggest that superoxide radical plays a role in ras-induced transformation; modulation of intracellular superoxide level by overexpression of manganese-containing superoxide dismutase or copper- and zinc-containing superoxide dismutase inhibited ras-induced transformation, as evidenced by in vitro studies of plating efficiency and by in vivo studies of tumor formation in nude mice. Overexpression of catalase (CAT) alone was found to have little effect on tumor cell growth, but overexpression of glutathione peroxidase 1 (GPx1) completely suppressed tumor cell growth in nude mice. This finding suggests that peroxides removed by GPx1, but not by CAT, are also involved in ras-induced transformation.

The roles of thioredoxin in protection against oxidative stress-induced apoptosis in SH-SY5Y cells

Using models of serum deprivation and 1-methyl-4-phenylpyridinium (MPP(+)), we investigated the mechanism by which thioredoxin (Trx) exerts its antiapoptotic protection in human neuroblastoma cells (SH-SY5Y) and preconditioning-induced neuroprotection. We showed that SH-SY5Y cells are highly sensitive to oxidative stress and responsive to both extracellularly administered and preconditioning-induced Trx. Serum deprivation and MPP(+) produced an elevation in the hydroxyl radicals, malondialdehyde and 4-hydroxy-2,3-nonenal (HNE), causing the cells to undergo mitochondria-mediated apoptosis. Trx in the submicromolar range blocked the observed apoptosis via a multiphasic protection mechanism that includes the suppression of cytochrome c release (most likely via the induction of Bcl-2), the inhibition of procaspase-9 and procaspase-3 activation, and the elevated level of Mn-SOD. The reduced form of Trx suppresses the serum-free-induced hydroxyl radicals, lipid peroxidation, and apoptosis, indicating that H(2)O(2) is removed by Trx peroxidase. The participation of Trx in preconditioning-induced neuroprotection is supported by the observation that inhibition of Trx synthesis with antisense oligonucleotides or of Trx reductase drastically reduced the hormesis effect. This effect of Trx-mediated hormesis against oxidative stress-induced apoptosis is striking. It induced a 30-fold shift in LD(50) in the MPP(+)-induced neurotoxicity.

Isolation and characterization of an extended thioredoxin h from poplar

A cDNA coding for a thioredoxin h has been isolated from a xylem/phloem poplar cDNA library by RACE-PCR. The nucleotide sequence called popTrx-h2 is homologous to other thioredoxins h isolated from plants but differs from the other thioredoxins h by presenting a 30 amino acid long N-terminus extension. A variant of this cDNA lacking the N-terminal extension was also generated by PCR. Both cDNAs have been introduced into an expression plasmid (pET-3d) and the recombinant proteins have been expressed to a high level and purified from Escherichia coli cells. Protein sequencing showed that a part of the N-terminal extension was cleaved in the E. coli cells, with the first 19 amino acids missing, suggesting the presence of a putative cleavage site in the N-terminal extension of popTrx-h2. Both recombinant proteins display unusual catalytic properties compared to other thioredoxins h characterized so far, i.e. a weak reduction by Arabidopsis thaliana NADPH-dependent thioredoxin reductase, and a weak activation of the chloroplastic NADP-malate dehydrogenase, a non-physiological target enzyme. Northern blot experiments indicate that the transcripts of popTrx-h2 are present in leaves and roots, albeit at a lower level compared to the earlier characterized popTrx-h1.

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.

V-Ha-Ras overexpression induces superoxide production and alters levels of primary antioxidant enzymes

Reactive oxygen species have been shown to play important roles in v-Ha-Ras mitogenic signaling. We hypothesized that v-Ha-Ras overexpression would induce superoxide production, and therefore modify expression of the primary antioxidant enzyme system. We have demonstrated that immortal rat kidney epithelial cells stably transduced with constitutively active v-Ha-ras produced significantly larger amounts of superoxide radical than wild-type or vector-transfected control cells. The levels of the primary antioxidant enzymes copper- and zinc-containing superoxide dismutase, manganese-containing superoxide dismutase, catalase, and glutathione peroxidase were increased in the superoxide-overproducing cells. DNA-binding activities of the transcription factors activator protein-1, activator protein-2, and nuclear factor-kappaB were all enhanced in the superoxide-overproducing cells. These v-Ha-ras transduced cells also had a shortened cell doubling time and higher plating efficiency, and displayed greater constitutive levels of phosphorylated mitogen-activated protein kinases. These data demonstrate that v-Ha-Ras overexpression increases superoxide production and this apparently affects a wide variety of cell signaling and redox systems.

Transcription factor AP-2alpha is preferentially cleaved by caspase 6 and degraded by proteasome during tumor necrosis factor alpha-induced apoptosis in breast cancer cells

Several reports have linked activating protein 2alpha (AP-2alpha) to apoptosis, leading us to hypothesize that AP-2alpha is a substrate for caspases. We tested this hypothesis by examining the effects of tumor necrosis factor alpha (TNF-alpha) on the expression of AP-2 in breast cancer cells. Here, we provide evidence that TNF-alpha downregulates AP-2alpha and AP-2gamma expression posttranscriptionally during TNF-alpha-induced apoptosis. Both a general caspase antagonist (zVADfmk) and a caspase 6-preferred antagonist (zVEIDfmk) inhibited TNF-alpha-induced apoptosis and AP-2alpha downregulation. In vivo tests showed that AP-2alpha was cleaved by caspases ahead of the DNA fragmentation phase of apoptosis. Recombinant caspase 6 cleaved AP-2alpha preferentially, although caspases 1 and 3 also cleaved it, albeit at 50-fold or higher concentrations. Activated caspase 6 was detected in TNF-alpha-treated cells, thus confirming its involvement in AP-2alpha cleavage. All three caspases cleaved AP-2alpha at asp(19) of the sequence asp-arg-his-asp (DRHD(19)). Mutating D(19) to A(19) abrogated AP-2alpha cleavage by all three caspases. TNF-alpha-induced cleavage of AP-2alpha in vivo led to AP-2alpha degradation and loss of DNA-binding activity, both of which were prevented by pretreatment with zVEIDfmk. AP-2alpha degradation but not cleavage was inhibited in vivo by PS-431 (a proteasome antagonist), suggesting that AP-2alpha is degraded subsequent to cleavage by caspase 6 or caspase 6-like enzymes. Cells transfected with green fluorescent protein-tagged mutant AP-2alpha are resistant to TNF-alpha-induced apoptosis, further demonstrating the link between caspase-mediated cleavage of AP-2alpha and apoptosis. This is the first report to demonstrate that degradation of AP-2alpha is a critical event in TNF-alpha-induced apoptosis. Since the DRHD sequence in vertebrate AP-2 is widely conserved, its cleavage by caspases may represent an important mechanism for regulating cell survival, proliferation, differentiation, and 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.

Constitutive activation of transcription factor AP-2 is associated with decreased MnSOD expression in transformed human lung fibroblasts

Activator protein-2 (AP-2) is a transcription factor with transactivating and transrepressing potential in different promoter contexts. AP-2 contains seven cysteines, and its in vitro DNA binding activity is redox-sensitive. Superoxide dismutase-2 (SOD2), which encodes the antioxidant enzyme manganese superoxide dismutase (MnSOD), is a putative tumor suppressor gene whose loss of expression is associated with the malignant phenotype. SOD2 promoter mutations that generate new AP-2 sites are associated with loss of MnSOD expression in cancer cells. In the current study, we have identified an inverse expression pattern between AP-2 and MnSOD in normal versus transformed human cells. MRC5 cells are a normal human lung fibroblast cell strain that is mortal and senesces after a certain number of passages in vitro. MRC5-VA is a simian virus transformed variant of MRC5. We determined the levels of expression of MnSOD and AP-2 in these two cell types at the levels of mRNA, protein, and activity. Our results indicated that MnSOD expression was significantly decreased in MRC5-VA cells compared with MRC5 cells at each level of investigation, whereas AP-2 showed an opposing pattern of expression and DNA binding activity. These results suggest that AP-2 may participate in the mechanism(s) underlying decreased expression of SOD2 in transformed cells.

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.

Expression of novel antioxidant thioredoxin-2 in the rat brain

Thioredoxins are a class of small redox-regulating proteins that have been implicated in the control of various aspects of cellular functions and seem to be one of the key regulators of signalling in the cellular responses to various stresses. Thioredoxin-2 (Trx2) is a novel mammalian thioredoxin which, in contrast to previously known cytosolic thioredoxin (Trx1), has been localized to the mitochondria. Trx2 is abundantly expressed in skeletal muscle, heart and adrenal gland, as well as in some other peripheral tissues with high metabolic activity. Using in situ hybridization and immunohistochemistry, we have studied the distribution and regulation of Trx2 expression in the rat brain. Trx2 mRNA and protein are highly expressed in the neurons in several brain regions, including the olfactory bulb, frontal cortex, hippocampus, some hypothalamic and thalamic nuclei, cerebellum and numerous brainstem nuclei. In addition, the Trx2 mRNA expression in paraventricular hypothalamic nucleus and reticular thalamic nucleus was found to be sensitive to peripheral glucocorticoids, as dexamethasone treatment caused significant elevation of Trx2 mRNA level in this area. No changes in other brain areas were observed after dexamethasone treatment. These findings implicate a significant regulatory and/or protective function of Trx2 in the nervous system.

Redox control of caspase-3 activity by thioredoxin and other reduced proteins

Caspases are cysteine proteinases that play a critical role in the execution phase of apoptosis. The active site cysteine residue must be reduced for caspase activity. Thioredoxins are redox proteins that catalyze the reduction of cysteine residues. We have examined the ability of various recombinant human thioredoxins to activate caspase-3. The EC(50) for caspase-3 activation by reduced thioredoxin-1 was 2.5 microM, by reduced glutathione 1.0 mM and by dithiothreitol 3.5 mM. A catalytic site redox-inactive mutant thioredoxin-1 was almost as active as thioredoxin-1 in activating caspase-3. Caspase activation was shown to correlate with the number of reduced cysteine residues in the thioredoxins. Reduced insulin and serum albumin were as effective on a molar basis as thioredoxin-1 in activating caspase-3. Thus, caspase-3 activation is not a specific effect of thioredoxins but is a property shared by other reduced proteins.

Oxidative stress and gene regulation

Reactive oxygen species are produced by all aerobic cells and are widely believed to play a pivotal role in aging as well as a number of degenerative diseases. The consequences of the generation of oxidants in cells does not appear to be limited to promotion of deleterious effects. Alterations in oxidative metabolism have long been known to occur during differentiation and development. Experimental perturbations in cellular redox state have been shown to exert a strong impact on these processes. The discovery of specific genes and pathways affected by oxidants led to the hypothesis that reactive oxygen species serve as subcellular messengers in gene regulatory and signal transduction pathways. Additionally, antioxidants can activate numerous genes and pathways. The burgeoning growth in the number of pathways shown to be dependent on oxidation or antioxidation has accelerated during the last decade. In the discussion presented here, we provide a tabular summary of many of the redox effects on gene expression and signaling pathways that are currently known to exist.