Regulatory role for a novel human thioredoxin peroxidase in NF-kappaB activation

Redox regulation in the extracellular environment

The oxidizing nature of the extracellular environment is vastly different from the highly reducing nature of the intracellular compartment. The redox potential of the cytosolic compartment of the intracellular environment limits disulfide bond formation, whereas the oxidizing extracellular environment contains proteins rich in disulfide bonds. If not for an extracellular antioxidant system to eliminate reactive oxygen and nitrogen species, lipid peroxidation and protein oxidation would become excessive, resulting in cellular damage. Many reviews have focused on the role of intracellular antioxidants in the elimination of oxidative stress, but this one will focus on the coordinated action of both intracellular and extracellular antioxidants in limiting cellular oxidant stress.

Emerging potential of thioredoxin and thioredoxin interacting proteins in various disease conditions

Reactive oxygen species (ROS) are known to be mediators of intracellular signaling pathways. However the excessive production of ROS may be detrimental to the cell as a result of the increased oxidative stress and loss of cell function. Hence, well tuned, balanced and responsive antioxidant systems are vital for proper regulation of the redox status of the cell. The cells are normally able to defend themselves against the oxidative stress induced damage through the use of several antioxidant systems. Even though the free radical scavenging enzymes such as superoxide dismutase (SOD) and catalase can handle huge amounts of reactive oxygen species, should these systems fail some reactive molecules will evade the detoxification process and damage potential targets. In such a scenario, cells recruit certain small molecules and proteins as 'rescue specialists' in case the 'bodyguards' fail to protect potential targets from oxidative damage. The thioredoxin (Trx) system thus plays a vital role in the maintenance of a reduced intracellular redox state which is essential for the proper functioning of each individual cell. Trx alterations have been implicated in many diseases such as cataract formation, ischemic heart diseases, cancers, AIDS, complications of diabetes, hypertension etc. The interactions of Trx with many different proteins and different metabolic and signaling pathways as well as the significant species differences make it an attractive target for therapeutic intervention in many fields of medical science. In this review, we present, the critical roles that thioredoxins play in limiting oxidant stress through either its direct effect as an antioxidant or through its interactions with other key signaling proteins (thioredoxin interacting proteins) and its implications in various disease models.

Proteomics analysis of cells in whole saliva from oral cancer patients via value-added three-dimensional peptide fractionation and tandem mass spectrometry

Whole human saliva possesses tremendous potential in clinical diagnostics, particularly for conditions within the oral cavity such as oral cancer. Although many have studied the soluble fraction of whole saliva, few have taken advantage of the diagnostic potential of the cells present in saliva, and none have taken advantage of proteomics capabilities for their study. We report on a novel proteomics method with which we characterized for the first time cells contained in whole saliva from patients diagnosed with oral squamous cell carcinoma. Our method uses three dimensions of peptide fractionation, combining the following steps: preparative IEF using free flow electrophoresis, strong cation exchange step gradient chromatography, and microcapillary reverse-phase liquid chromatography. We determined that the whole saliva samples contained enough cells, mostly exfoliated epithelial cells, providing adequate amounts of total protein for proteomics analysis. From a mixture of four oral cancer patient samples, the analysis resulted in a catalogue of over 1000 human proteins, each identified from at least two peptides, including numerous proteins with a role in oral squamous cell carcinoma signaling and tumorigenesis pathways. Additionally proteins from over 30 different bacteria were identified, some of which putatively contribute to cancer development. The combination of preparative IEF followed by strong cation exchange chromatography effectively fractionated the complex peptide mixtures despite the closely related physiochemical peptide properties of these separations (pI and solution phase charge, respectively). Furthermore compared with our two-step method combining preparative IEF and reverse-phase liquid chromatography, our three-step method identified significantly more cellular proteins while retaining higher confidence protein identification enabled by peptide pI information gained through IEF. Thus, for detecting salivary markers of oral cancer and possibly other conditions of the oral cavity, the results confirm both the potential of analyzing the cells in whole saliva and doing so with our proteomics method.

The human peripheral blood mononuclear cell proteome responds to a dietary flaxseed-intervention and proteins identified suggest a protective effect in atherosclerosis

Flaxseed is one of the richest sources of lignans that are converted to enterolactone by the intestinal microflora. Enterolactone has been suggested to be the prime active compound mediating atherosclerosis-protective effects that were shown for flaxseed. The effects of a 1-wk intervention with 0.4 g of flaxseed/kg body weight per day on enterolactone plasma levels in seven healthy men revealed that all participants (PAs) responded with enhanced enterolactone plasma levels. Proteome analysis of peripheral blood mononuclear cells (PBMC) from donors before, during, and after the intervention showed that flaxseed consumption affected significantly the steady-state levels of 16 proteins of which four were altered in a similar manner when blood mononuclear cells were exposed ex vivo to enterolactone. Enhanced levels of peroxiredoxin and reduced levels of the long-chain fatty acid beta-oxidation multienzyme complex may be taken as indicators of a reduced oxidative stress whereas reduced levels of glycoprotein IIIa/II could indicate improved protection from thrombotic and inflammatory processes. In conclusion, the blood mononuclear cell proteome responds to dietary flaxseed intake with changes in a number of atherosclerosis-relevant proteins that may be taken as biomarkers of exposure and some of these changes observed can be attributed to the action of the lignan metabolite enterolactone.

Modulation of the host cell proteome by the intracellular apicomplexan parasite Toxoplasma gondii

To investigate how intracellular parasites manipulate their host cell environment at the molecular level, we undertook a quantitative proteomic study of cells following infection with the apicomplexan parasite Toxoplasma gondii. Using conventional two-dimensional electrophoresis, difference gel electrophoresis (DIGE), and mass spectrometry, we identified host proteins that were consistently modulated in expression following infection. We detected modification of protein expression in key metabolic pathways, including glycolysis, lipid and sterol metabolism, mitosis, apoptosis, and structural-protein expression, suggestive of global reprogramming of cell metabolism by the parasite. Many of the differentially expressed proteins had not been previously implicated in the response to the parasite, while others provide important corroborative protein evidence for previously proposed hypotheses of pathogen-cell interactions. Significantly, over one-third of all modulated proteins were mitochondrial, and this was further investigated by DIGE analysis of a mitochondrion-enriched preparation from infected cells. Comparison of our proteomic data with previous transcriptional studies suggested that a complex relationship exits between transcription and protein expression that may be partly explained by posttranslational modifications of proteins and revealed the importance of investigating protein changes when interpreting transcriptional data. To investigate this further, we used phosphatase treatment and DIGE to demonstrate changes in the phosphorylation states of several key proteins following infection. Overall, our findings indicate that the host cell proteome responds in a dramatic way to T. gondii invasion, in terms of both protein expression changes and protein modifications, and reveal a complex and intimate molecular relationship between host and parasite.

Sulfiredoxin, the cysteine sulfinic acid reductase specific to 2-Cys peroxiredoxin: its discovery, mechanism of action, and biological significance

Peroxiredoxin (Prx) is a family of bifunctional proteins that exhibit peroxidase and chaperone activities. Prx proteins contain a conserved Cys residue that undergoes a redox change between thiol and disulfide states. 2-Cys Prx enzymes, a subgroup of Prx family, are intrinsically susceptible to reversible hyperoxidation to cysteine sulfinic acid during catalysis. Cysteine hyperoxidation of Prx was shown to result in loss of peroxidase activity and a concomitant gain of chaperone activity. Reduction of sulfinic Prx enzymes, the first known biological example of such a reaction, is catalyzed by sulfiredoxin (Srx) in the presence of ATP. Srx appears to exist solely to support the reversible sulfinic modification of 2-Cys Prx enzymes. Srx specifically binds to 2-Cys Prx enzymes by recognizing several critical surface-exposed residues of the Prxs, and transfer the gamma-phosphate of ATP to their sulfinic moiety, using its conserved cysteine as the phosphate carrier. The resulting sulfinic phosphoryl ester is reduced to cysteine after oxidation of four thiol equivalents.

Expression of peroxiredoxin I in plasma cells of oral inflammatory diseases

The participation of reactive oxygen species (ROS) in the immune response, both as pathogen killers and as mediators of signaling pathways, is well established. However, little is known about the enzymes responsible for ROS elimination in immune cells. Peroxiredoxin I (PrdxI) is a multifunctional enzyme that exhibits thioredoxin-dependent peroxidase activity. It has been described as a major hydrogen peroxide (H(2)O(2))-inducible protein in mouse peritoneal macrophages. In order to characterize its participation in the antioxidant defense of inflammatory/immune cells in greater detail, we evaluated its expression at sites of the oral cavity affected by inflammatory disorders induced by different agents (infectious, chemical, mechanical or tumor). In this study we demonstrated, by immunohistochemistry, that PrdxI is expressed in plasma cells, but not in B lymphocytes, regardless of the inflammation-inducing agent. We suggest that PrdxI induction could be considered a crucial part of the cellular adaptive response to the B-cell differentiation process to cope with the additional H(2)O(2) associated with massive disulfide bond formation during immunoglobulin folding in the endoplasmic reticulum of plasma cells. PrdxI could diminish the tissue damage that accompanies inflammation.

Nuclear and cytoplasmic peroxiredoxin-1 differentially regulate NF-kappaB activities

Peroxiredoxins (Prx) are widely distributed and abundant proteins, which control peroxide concentrations and related signaling mechanisms. Prx1 is found in the cytoplasm and nucleus, but little is known about compartmentalized Prx1 function during redox signaling and oxidative stress. We targeted expression vectors to increase Prx1 in nuclei (NLS-Prx1) and cytoplasm (NES-Prx1) in HeLa cells. Results showed that NES-Prx1 inhibited NF-kappaB activation and nuclear translocation. In contrast, increased NLS-Prx1 did not affect NF-kappaB nuclear translocation but increased activity of a NF-kappaB reporter. Both NLS-Prx1 and NES-Prx1 inhibited NF-kappaB p50 oxidation, suggesting that oxidation of the redox-sensitive cysteine in p50's DNA-binding domain is regulated via peroxide metabolism in both compartments. Interestingly, following treatment with H(2)O(2), nuclear thioredoxin-1 (Trx1) redox status was protected by NLS-Prx1, and cytoplasmic Trx1 was protected by NES-Prx1. Compartmental differences from increasing Prx1 show that the redox poise of cytoplasmic and nuclear thiol systems can be dynamically controlled through peroxide elimination. Such spatial resolution and protein-specific redox differences imply that the balance of peroxide generation/metabolism in microcompartments provides an important specific component of redox signaling.

Carbonylation of adipose proteins in obesity and insulin resistance: identification of adipocyte fatty acid-binding protein as a cellular target of 4-hydroxynonenal

Obesity is a state of mild inflammation correlated with increased oxidative stress. In general, pro-oxidative conditions lead to production of reactive aldehydes such as trans-4-hydroxy-2-nonenal (4-HNE) and trans-4-oxo-2-nonenal implicated in the development of a variety of metabolic diseases. To investigate protein modification by 4-HNE as a consequence of obesity and its potential relationship to the development of insulin resistance, proteomics technologies were utilized to identify aldehyde-modified proteins in adipose tissue. Adipose proteins from lean insulin-sensitive and obese insulin-resistant C57Bl/6J mice were incubated with biotin hydrazide and detected using horseradish peroxidase-conjugated streptavidin. High carbohydrate, high fat feeding of mice resulted in a approximately 2-3-fold increase in total adipose protein carbonylation. Consistent with an increase in oxidative stress in obesity, the abundance of glutathione S-transferase A4 (GSTA4), a key enzyme responsible for metabolizing 4-HNE, was decreased approximately 3-4-fold in adipose tissue of obese mice. To identify specific carbonylated proteins, biotin hydrazide-modified adipose proteins from obese mice were captured using avidin-Sepharose affinity chromatography, proteolytically digested, and subjected to LC-ESI MS/MS. Interestingly enzymes involved in cellular stress response, lipotoxicity, and insulin signaling such as glutathione S-transferase M1, peroxiredoxin 1, glutathione peroxidase 1, eukaryotic elongation factor 1alpha-1 (eEF1alpha1), and filamin A were identified. The adipocyte fatty acid-binding protein, a protein implicated in the regulation of insulin resistance, was found to be carbonylated in vivo with 4-HNE. In vitro modification of adipocyte fatty acid-binding protein with 4-HNE was mapped to Cys-117, occurred equivalently using either the R or S enantiomer of 4-HNE, and reduced the affinity of the protein for fatty acids approximately 10-fold. These results indicate that obesity is accompanied by an increase in the carbonylation of a number of adipose-regulatory proteins that may serve as a mechanistic link between increased oxidative stress and the development of insulin resistance.

Proteomic analysis of proteins differentially expressed in preeclamptic trophoblasts

AIMS

To identify differential trophoblastic proteins associated with preeclampsia (PE) by proteomic analysis.

METHODS

We isolated and purified placental trophoblasts from normotensive pregnant women and patients with PE by a continuous Percoll gradient. The expression of proteins was determined by sliver staining after two-dimensional polyacrylamide gel electrophoresis (2D-PAGE). Proteins of interest were identified using matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF-MS).

RESULTS

The overall trophoblastic protein expression patterns in preeclamptic and corresponding normotensive placentas were quite similar except for some areas. Of 34 differentially expressed protein spots (p < 0.05 by paired t-test), seven differential proteins from nine spots were identified by MALDI-TOF-MS. The expression of the following proteins was repressed (p < 0.01): disulfide isomerase ER-60, peroxiredoxin 2, and Delta3,5-Delta2,4-dienoyl-CoA isomerase. Four proteins (protein disulfide isomerase precursor, endoplasmic reticulum resident protein, dihydrolipoyl dehydrogenase and TIM21-like protein) were found to be significantly upregulated in PE (p < 0.01).

CONCLUSION

We identified several proteins with significant altered expression in PE using 2D-PAGE. This method is a powerful technique with which to search for not only quantitative but also qualitative changes in a biological process of interest.

Transcriptome analysis of the salivary glands of Dermacentor andersoni Stiles (Acari: Ixodidae)

Amongst blood-feeding arthropods, ticks of the family Ixodidae (hard ticks) are vectors and reservoirs of a greater variety of infectious agents than any other ectoparasite. Salivary glands of ixodid ticks secrete a large number of pharmacologically active molecules that not only facilitate feeding but also promote establishment of infectious agents. Genomic, proteomic and immunologic characterization of bioactive salivary gland molecules are, therefore, important as they offer new insights into molecular events occurring at the tick-host interface and they have implications for development of novel control strategies. The present work uses complementary DNA (cDNA) sequence analysis to identify salivary gland transcripts expressed by the Rocky Mountain wood tick, Dermacentor andersoni, a vector of the human pathogens causing Rocky Mountain spotted fever, Colorado tick fever, tularemia, and Powassan encephalitis as well as the veterinary pathogen Anaplasma marginale. Dermacentor andersoni is also capable of inducing tick paralysis. Automated single-pass DNA sequencing was conducted on 1440 randomly selected cDNA clones from the salivary glands of adult female D. andersoni collected during the early stages of feeding (18-24h). Analysis of the expressed sequence tags (ESTs) resulted in 544 singletons and 218 clusters with more than one quality read and attempts were made to assign putative functions to tick genes based on amino acid identity to published protein databases. Approximately 25.6% (195) of the sequences showed limited or no homology to previously identified gene products. A number of novel sequences were identified which presented significant sequence similarity to mammalian genes normally associated with extracellular matrix (ECM), regulation of immune responses, tumor suppression, and wound healing. Several coding sequences possessed various degrees of homology to previously described proteins from other tick species. Preliminary nucleotide variation analysis of these and other tick sequences suggests extensive nucleotide diversity, which has implications for evolution of tick feeding. Intra-species diversity studies can be a promising tool for identifying sequence variations potentially associated with phenotypic traits affecting vector-host-pathogen interactions.

γ-Tocotrienol Inhibits Nuclear Factor-κB Signaling Pathway through Inhibition of Receptor-interacting Protein and TAK1 Leading to Suppression of Antiapoptotic Gene Products and Potentiation of Apoptosis

Unlike the tocopherols, the tocotrienols, also members of the vitamin E family, have an unsaturated isoprenoid side chain. In contrast to extensive studies on tocopherol, very little is known about tocotrienol. Because the nuclear factor-kappaB (NF-kappaB) pathway has a central role in tumorigenesis, we investigated the effect of gamma-tocotrienol on the NF-kappaB pathway. Although gamma-tocotrienol completely abolished tumor necrosis factor alpha (TNF)-induced NF-kappaB activation, a similar dose of gamma-tocopherol had no effect. Besides TNF, gamma-tocotrienol also abolished NF-kappaB activation induced by phorbol myristate acetate, okadaic acid, lipopolysaccharide, cigarette smoke, interleukin-1beta, and epidermal growth factor. Constitutive NF-kappaB activation expressed by certain tumor cells was also abrogated by gamma-tocotrienol. Reducing agent had no effect on the gamma-tocotrienol-induced down-regulation of NF-kappaB. Mevalonate reversed the NF-kappaB inhibitory effect of gamma-tocotrienol, indicating the role of hydroxymethylglutaryl-CoA reductase. Gamma-tocotrienol blocked TNF-induced phosphorylation and degradation of IkappaBalpha through the inhibition of IkappaBalpha kinase activation, thus leading to the suppression of the phosphorylation and nuclear translocation of p65. gamma-Tocotrienol also suppressed NF-kappaB-dependent reporter gene transcription induced by TNF, TNFR1, TRADD, TRAF2, TAK1, receptor-interacting protein, NIK, and IkappaBalpha kinase but not that activated by p65. Additionally, the expressions of NF-kappaB-regulated gene products associated with antiapoptosis (IAP1, IAP2, Bcl-xL, Bcl-2, cFLIP, XIAP, Bfl-1/A1, TRAF1, and Survivin), proliferation (cyclin D1, COX2, and c-Myc), invasion (MMP-9 and ICAM-1), and angiogenesis (vascular endothelial growth factor) were down-regulated by gamma-tocotrienol. This correlated with potentiation of apoptosis induced by TNF, paclitaxel, and doxorubicin. Overall, our results demonstrate that gamma-tocotrienol inhibited the NF-kappaB activation pathway, leading to down-regulation of various gene products and potentiation of apoptosis.

Mutual cross-talk between reactive oxygen species and nuclear factor-kappa B: molecular basis and biological significance

Reactive oxygen species (ROS) are emerging as key effectors in signal transduction. This role of ROS is especially evident in the pathways leading to programmed cell death (PCD) elicited in response to certain stress stimuli and cytokines. In these pathways, cytotoxic ROS signaling appears to be mediated in part by activation of the c-Jun-N-terminal kinase (JNK) mitogen-activated protein kinase (MAPK) cascade. Another pathway that is under ROS-mediated control in some systems is that leading to activation of transcription factor nuclear factor-kappa B (NF-kappaB), which is a central regulator of immunity, inflammation and cell survival. Remarkably, new evidence has unveiled the existence of a reciprocal, negative control that NF-kappaB exerts on ROS and JNK activities. This NF-kappaB-imposed restraint on ROS and JNK signaling is crucial for antagonism of PCD elicited by the proinflammatory cytokine tumor necrosis factor (TNF)alpha and likely other triggers. Effectors of this antagonistic cross-talk between NF-kappaB and ROS/JNK pathways have recently been identified. Because of the key roles that the prosurvival function of NF-kappaB plays in organismal physiology and disease, gaining a further mechanistic understanding of this cross-talk and NF-kappaB-dependent survival may be key to developing new therapies for the treatment of widespread human illnesses, such as cancer and chronic inflammatory conditions.

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

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

Functional analysis of the nuclear proteome of human A549 alveolar epithelial cells by HPLC-high resolution 2-D gel electrophoresis

The airway epithelial cell plays a central role in coordinating airway inflammatory responses, where significant changes in the proteome occur in response to infectious stimuli. To further understand the spectrum of proteins and the biological processes they control, we have initially determined the nuclear proteome of human type II-like alveolar epithelial cells (A549) using a sequential method of organellar enrichment followed by HPLC prefractionation prior to 2-DE-based protein identification using MALDI-TOF MS. This approach yielded 719 high-confidence identifications, 433 mapping to unique gene identifiers. Expert classification showed that these proteins controlled chromatin remodeling, protein refolding, cytoskeletal structure, membrane function, metabolic processes, mitochondrial function, RNA binding, protein synthesis, signaling, and transcription factor activities. The proteins were mapped to gene ontology classifications, where metabolism and catalytic activity functions were significantly enriched, representing 43 and 32% of the protein set, respectively. Pathways analysis indicated a protein network affecting tumor necrosis factor-nuclear factor-kappaB signaling pathway interacting with intermediate cytoskeletal filaments. Forty-five proteins of unknown function were subjected to domain analysis and inferred to have additional nuclear functions controlling purine nucleotide metabolism and protein-protein interactions. This database represents the most comprehensive data set of mammalian nuclear proteins and will serve as a foundation for further discovery.

The tert-butylhydroquinone-mediated activation of the human thioredoxin gene reveals a novel promoter structure

Thioredoxin is a redox-active protein that plays multiple roles in regulating cell growth, cell signalling and apoptosis. Here, we have demonstrated that a complex mechanism involving multiple regulatory elements is involved in the tBHQ [tert-butylhydroquinone or 2,5-di-(t-butyl)-1,4-hydroquinone]-mediated activation of the thioredoxin gene. Luciferase assays, utilizing various wild-type and mutated thioredoxin promoter fragments, revealed roles for the ORE (oxidative stress responsive element), ARE (antioxidant responsive element), three Sp1 (specificity protein 1)-binding sites and the TATA box in the activation of the thioredoxin gene by tBHQ. The ORE required the presence of the ARE to elicit its response, whereas the independent removal of three Sp1-binding sites and the TATA box also decreased activation of the thioredoxin gene, with mutation of the TATA box having the greatest effect. Real-time RT (reverse transcriptase)-PCR analysis also revealed varying roles for two TSSs (transcription start sites) in the activation of the thioredoxin gene by tBHQ. Transcription was initiated from both TSSs; however, different response rates and fold inductions were observed. Together, these results suggest that the thioredoxin gene is controlled by a novel arrangement of two overlapping core promoter regions, one containing a TATA box and the other TATA-less. Altering the intracellular levels of thioredoxin in a breast cancer cell line also influenced the induction of thioredoxin transcription in response to tBHQ. Stable transfections with a redox-inactive thioredoxin mutant produced 3.6 times higher induction levels of thioredoxin transcription compared with control cells, indicating an intrinsic form of control of promoter activity by the thioredoxin system itself.

Molecular pathways leading to oxidative stress-induced phosphorylation of Akt

Oxidative stress can activate a variety of intracellular signaling pathways. The authors previously reported the CaM-K inhibitor KN-93 inhibited hydrogen peroxide-induced phosphorylation of Akt on threonine 308 (T308). In this report they demonstrate that phosphorylation of T308 in response to hydrogen peroxide treatment is not inhibited by LY294002, suggesting that phosphorylation of this residue in response to oxidative stress is largely PI3K independent. In contrast, hydrogen peroxide-induced phosphorylation of Akt on serine 473 (S473) was downregulated by both PI3K and CaM-K inhibition, indicating that hydrogen peroxideinduced phosphorylation of Akt on S473 was largely dependent on both PI3K and a CaM-K activity. Further, it is reported that p56(Lck) had a substantial role in hydrogen peroxide-induced phosphorylation of S473, but only a minimal role in hydrogen peroxide-induced phosphorylation of T308. These data suggest that in response to hydrogen peroxide, two pathways are activated in Jurkat T lymphocytes that converge to result in the phosphorylation of Akt on S473 and T308. One pathway involves the CaM-Ks that may directly phosphorylate Akt on T308. In this pathway, neither the Src kinases nor PI3K are required. The other pathway mediated by hydrogen peroxide results in the phosphorylation of Akt on S473 and requires CaM-K, PI3K, and Src activity.

Peroxiredoxin genes are not induced in myeloid leukemia cells exposed to ionizing radiation

Peroxiredoxins (Prx) comprise an extended family of small antioxidant proteins which conserve a thioredoxin-dependent catalytic function that can contribute to cell protection from reactive oxygen species (ROS). ROS generation is one of the deleterious intracellular effects of ionizing radiation, but the role of Prx during radiation treatment has not been extensively explored. Present experiments measure effects of ionizing radiation on expression of human Prx types I (PAGA), II (NKEF-B) and IV (AOE372) in human myeloid leukemia cells (K562). Prx gene transcription was analyzed by amplifying with RT-PCR cDNAs complementary to each Prx-specific coding sequence and by identifying the derived products with Southern blotting procedure. Transcripts of GAPDH were used as the endogenous standard for semi-quantitative comparisons. No consistent increase in Prx gene expression was detected at time intervals up to 72 h after gamma radiation doses that caused cell cycle arrest and nuclear damage (maximum 20 Gy). Immunoblots also were consistent with a prolonged expression or stability of the Prx I/II proteins. Similarly, a cytotoxic concentration of the oxidant hemin, which stimulates rapid hemoglobinization of K562 cells, caused no induction of Prx gene expression. Our results indicate a high Prx stability in human radio-resistant leukemia cells.

The thioredoxin system in retroviral infection and apoptosis

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

Thioredoxin induced antioxidant gene expressions in human lens epithelial cells

Thioredoxin (Trx) is one of the major redox-regulating proteins. It catalyzes dithiol/disulfide exchange reactions and displays many unique intracellular and extracellular activities thereby controlling multiple mammalian cell functions. In the present study we examine the effect of exogenous Trx on the expression of several antioxidant genes in human lens epithelial (HLE B3) cells. mRNA levels for gene expression were monitored by RT-PCR and real-time PCR while protein levels were measured by western blot analysis. We have found that recombinant human Trx (hTrx)-treated HLE B3 cells have a simultaneous increase in mRNA expressions of mitochondrial manganese superoxide dismutase (MnSOD), thioltranferase 1 (TTase 1) or glutaredoxin 1 (Grx1), mitochondrial thioltransferase (TTase 2) or glutaredoxin 2 (Grx2), and thioredoxin peroxidase IV (Prx IV). The increased MnSOD and TTase 1 mRNA expressions were accompanied with their respective increases in protein levels. Other antioxidant genes, including Cu/ZnSOD, catalase, glutathione peroxidase 1 (GPx1), thioredoxin reductase 1 (TrxR1), thioredoxin peroxidase III (Prx III), and gamma-glutamyl cysteine synthetase were not affected. The ability of Trx to induce selectively these antioxidant genes in the absence of oxidative stress suggest a cytokine/growth factor-like new physiological role of hTrx in HLE B3 cells. Our data also provide evidence of a strong antioxidant defense system in HLE B3 cells that can be activated by extracellular hTrx, as well as of a possible link between the thioredoxin (Trx) and glutathione (GSH) redox regulating systems in these cells.

The antioxidant glutathione peroxidase family and spermatozoa: a complex story

Oxidative damage is one threat spermatozoa have to face during epididymal maturation and storage. However, it is clear that reactive oxygen species (ROS) are also central for sperm physiology in processes such as sperm maturation and capacitation. It is therefore essential that there exists around sperm cells a fine balance between ROS production and recycling. To do so, sperm cells and epididymal epithelial cells rely on common enzymatic ROS scavengers such as superoxide dismutase (SOD), glutathione peroxidases (GPX) and catalase (CAT) as well as more specific types such as indoleamine dioxygenase (IDO). Among the catalytic triad (SOD/GPX/CAT), the glutathione peroxidase protein family occupies a peculiar position, since several GPX have been found to be present on and around epididymal transiting sperm cells. Here, we will review our present knowledge regarding GPX expression, presence and putative role(s) within the epididymis and on spermatozoa. Taking into account our recent findings regarding the epididymal expression of indoleamine dioxygenase in mouse we will also discuss how we think this superoxide anion recycling enzyme completes the complex ROS generation/recycling balance in this organ.

Yeast oxidative stress response. Influences of cytosolic thioredoxin peroxidase I and of the mitochondrial functional state

We investigated the changes in the oxidative stress response of yeast cells suffering mitochondrial dysfunction that could impair their viability. First, we demonstrated that cells with this dysfunction rely exclusively on cytosolic thioredoxin peroxidase I (cTPxI) and its reductant sulfiredoxin, among other antioxidant enzymes tested, to protect them against H2O2-induced death. This cTPxI-dependent protection could be related to its dual functions, as peroxidase and as molecular chaperone, suggested by mixtures of low and high molecular weight oligomeric structures of cTPxI observed in cells challenged with H2O2. We found that cTPxI deficiency leads to increased basal sulfhydryl levels and transcriptional activation of most of the H2O2-responsive genes, interpreted as an attempt by the cells to improve their antioxidant defense. On the other hand, mitochondrial dysfunction, specifically the electron transport blockage, provoked a huge depletion of sulfhydryl groups after H2O2 treatment and reduced the H2O2-mediated activation of some genes otherwise observed, impairing cell defense and viability. The transcription factors Yap1 and Skn7 are crucial for the antioxidant response of cells under inhibited electron flow condition and probably act in the same pathway of cTPxI to protect cells affected by this disorder. Yap1 cellular distribution was not affected by cTpxI deficiency and by mitochondrial dysfunction, in spite of the observed expression alterations of several Yap1-target genes, indicating alternative mechanisms of Yap1 activation/deactivation. Therefore, we propose that cTPxI is specifically important in the protection of yeast with mitochondrial dysfunction due to its functional versatility as an antioxidant, chaperone and modulator of gene expression.

A mosquito 2-Cys peroxiredoxin protects against nitrosative and oxidative stresses associated with malaria parasite infection

Malaria parasite infection in anopheline mosquitoes induces nitrosative and oxidative stresses that limit parasite development, but also damage mosquito tissues in proximity to the response. Based on these observations, we proposed that cellular defenses in the mosquito may be induced to minimize self-damage. Specifically, we hypothesized that peroxiredoxins (Prxs), enzymes known to detoxify reactive oxygen species (ROS) and reactive nitrogen oxide species (RNOS), protect mosquito cells. We identified an Anopheles stephensi 2-Cys Prx ortholog of Drosophila melanogaster Prx-4783, which protects fly cells against oxidative stresses. To assess function, AsPrx-4783 was overexpressed in D. melanogaster S2 and in A. stephensi (MSQ43) cells and silenced in MSQ43 cells with RNA interference before treatment with various ROS and RNOS. Our data revealed that AsPrx-4783 and DmPrx-4783 differ in host cell protection and that AsPrx-4783 protects A. stephensi cells against stresses that are relevant to malaria parasite infection in vivo, namely nitric oxide (NO), hydrogen peroxide, nitroxyl, and peroxynitrite. Further, AsPrx-4783 expression is induced in the mosquito midgut by parasite infection at times associated with peak nitrosative and oxidative stresses. Hence, whereas the NO-mediated defense response is toxic to both host and parasite, AsPrx-4783 may shift the balance in favor of the mosquito.

2-DE proteome analysis of a proliferating and differentiating human neuronal stem cell line (ReNcell VM)

The proteome of a proliferating human stem cell line was analyzed and then utilized to detect stem cell differentiation-associated changes in the protein profile. The analysis was conducted with a stable human fetal midbrain stem cell line (ReNcell VM) that displays the properties of a neural stem cell. Therefore, acquisition of proteomic data should be representative of cultured human neural stem cells (hNSCs) in general. Here we present a 2-DE protein-map of this cell line with annotations of 402 spots representing 318 unique proteins identified by MS. The subsequent proteome profiling of differentiating cells of this stem cell line at days 0, 4 and 7 of differentiation revealed changes in the expression of 49 identified spots that could be annotated to 45 distinct proteins. This differentiation-associated expression pattern was validated by Western blot analysis for transgelin-2, proliferating cell nuclear antigen, as well as peroxiredoxin 1 and 4. The group of regulated proteins also included NudC, ubiquilin-1, STRAP, stress-70 protein, creatine kinase B, glial fibrillary acidic protein and vimentin. Our results reflect the large rearrangement of the proteome during the differentiation process of the stem cells to terminally differentiated neurons and offer the possibility for further characterization of specific targets driving the stem cell differentiation.

Specific protein interaction of human Pag with Omi/HtrA2 and the activation of the protease activity of Omi/HtrA2

The human PAG gene product (hPag), one member of the TSA/AhpC family, is overexpressed by oxidative stress, which causes apoptosis. To investigate the apoptotic signal transduction mediated by hPag, hPag-binding protein was screened using the yeast two-hybrid system. Omi/HtrA2 was identified as the hPag-binding protein. Omi/HtrA2, a potent proapoptotic factor, is released from the mitochondria into the cytoplasm as the mature form showing serine protease activity during apoptosis in response to oxidative stress. We found that hPag was able to interact with the mature form of Omi/HtrA2, not with the precursor form of Omi/HtrA2. The binding of Omi/HtrA2 to hPag was shown to involve the PDZ-binding domain in Omi/HtrA2. Also, the carboxyl-terminal domain of hPag was shown to be critical for the protein interaction. Using the yeast two-hybrid system and in vitro binding assay, the reduced form of hPag was able to interact with Omi/HtrA2. Interestingly, the protease activity given by the mature form of Omi/HtrA2 was significantly activated by the binding to hPag. Taken together, these results suggest that the specific protein interaction may participate as a molecular switch in modulating cell death in response to oxidative stress.

Gene hunting in hypoxia and exercise

New technologies in genomics and proteomics are revolutionizing the study of adaptation to environmental stress. These approaches provide a comprehensive overview of the responses of thousands of genes/proteins to stress and enormously expand our view of the molecular and metabolic changes that underlie physiological responses. Several new technologies can help physiological labs to become gene hunters. DNA array screening is particularly effective for two purposes: (1) identifying coordinated responses by functional groups of gene/proteins such as multiple members of a signal transduction cascade or enzymes of a metabolic pathway, and (2) highlighting cell functions that have never before been linked with the stress under consideration. We have shown that heterologous screening of DNA arrays can be a highly effective method of gene hunting for the comparative biochemist provided that it is followed up by species-specific analyses including PCR to quantify transcript levels and Western blotting to analyze protein responses. Recent work in my lab has used cDNA array screening to evaluate responses to low oxygen by multiple hypoxia/anoxia tolerant systems, revealing common gene responses across phylogeny. Analysis of vertebrate facultative anaerobiosis in freshwater turtles reveals an interesting mixture of gene responses, including up-regulation of antioxidant enzymes, protease inhibitors, and proteins of iron metabolism; a few of these are coordinated by the hypoxia inducible factor in other systems but most are not. Array screening is also providing new insights into how exercise stimulates the growth of differentiated muscle cells and studies in our lab are identifying the gene responses associated with "anti-exercise"--gene up-regulation that aids hibernating mammals to maintain their muscle mass despite months of inactivity.

Mitochondrial targeting of growth suppressor protein DLC2 through the START domain

Deleted in liver cancer 2 (DLC2) is a candidate tumor suppressor frequently found to be deleted in hepatocellular carcinoma. In this study, we determined the subcellular localization of DLC2. Co-localization and biochemical fractionation studies revealed that DLC2 localized to mitochondria. In addition, the DLC2-containing cytoplasmic speckles were in proximity to lipid droplets. A DLC2 mutant containing the steroidogenic acute regulatory protein-related lipid transfer (START) domain only showed a localization pattern identical to that of DLC2. Taken together, we have provided the first evidence for mitochondrial localization of DLC2 through the START domain. These findings might have implications in liver physiology and carcinogenesis.

Analysis of NOD2-mediated proteome response to muramyl dipeptide in HEK293 cells

NOD2, a cytosolic receptor for the bacterial proteoglycan fragment muramyl dipeptide (MDP), plays an important role in the recognition of intracellular pathogens. Variants in the bacterial sensor domain of NOD2 are genetically associated with an increased risk for the development of Crohn disease, a human chronic inflammatory bowel disease. In the present study, global protein expression changes after MDP stimulation were analyzed by two-dimensional PAGE of total protein extracts of human cultured cells stably transfected with expression constructs encoding for wild type NOD2 (NOD2(WT)) or the disease-associated NOD2 L1007fsinsC (NOD2(SNP13)) variant. Differentially regulated proteins were identified by matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry (MS) peptide mass fingerprinting and MALDI MS/MS. The limited overlap in the responses of the NOD2-overexpressing cell lines to MDP included a down-regulation of heat shock 70-kDa protein 4. A complex pro-inflammatory program regulated by NOD2(WT) that encompasses a regulation of key genes involved in protein folding, DNA repair, cellular redox homeostasis, and metabolism was observed both under normal growth conditions and after stimulation with MDP. By using the comparison of NOD2(WT) and disease-associated NOD2(SNP13) variant, we have identified a proteomic signature pattern that may further our understanding of the influence of genetic variations in the NOD2 gene in the pathophysiology of chronic inflammatory bowel disease.

Activity assay of mammalian 2-cys peroxiredoxins using yeast thioredoxin reductase system

2-Cys peroxiredoxin (Prx) is a novel cellular peroxidase that reduces peroxides in the presence of thioredoxin, thioredoxin reductase, and nicotinamide adenine dinucleotide phosphate (NADPH) and that functions in H(2)O(2)-mediated signal transduction. Recent studies have shown that 2-cys Prx can be inactivated by cysteine overoxidation in conditions of oxidative stress. Therefore, peroxidase activity, rather than the protein level, of 2-cys Prx is the more important measure to predict its cellular function. Here, we introduce a modified activity assay method for mammalian 2-cys Prx based on yeast nonselenium thioredoxin reductase. Yeast thioredoxin reductase is expressed in Escherichia coli cells and purified at high yield (40 mg/L of culture broth) as an active flavoprotein by combined diethyl aminoethyl (DEAE) and phenyl hydrophobic chromatography. The optimal concentrations of yeast thioredoxin and thioredoxin reductase required to achieve maximum mammalian 2-cys Prx activity are 3.0 and 1.5 microM, respectively. This modified assay method is useful for measuring 2-cys Prx activity in cell lysates and can also be adapted for a 96-well plate reader for high-throughput screening of chemical compounds that target 2-cys Prx.

Peroxisomal proteomics, a new tool for risk assessment of peroxisome proliferating pollutants in the marine environment

In an attempt to improve the detection of peroxisome proliferation as a biomarker in environmental pollution assessment, we have applied a novel approach based on peroxisomal proteomics. Peroxisomal proteins from digestive glands of mussels Mytilus galloprovincialis were analyzed using 2-DE and MS. We have generated a reference 2-DE map from samples obtained in a well-studied reference area and compared this with peroxisomal proteomes from other sequenced genomes. In addition, by comparing 2-DE maps from control samples with samples obtained in a polluted area, we have characterized the peroxisome proliferation expression pattern associated with exposure to a polluted environment. Over 100 spots were reproducibly resolved per 2-DE map; 55 differentially expressed spots were quantitatively detected and analyzed, and 14 of these showed an increase in protein expression of more than fourfold. Epoxide hydrolase, peroxisomal antioxidant enzyme, and sarcosine oxidase (SOX) have been identified by ESI MS/MS, and acyl-CoA oxidase, multifunctional protein, and Cu,Zn-superoxide dismutase were immunolocalized by Western blotting. Our results indicate that a peroxisomal protein pattern associated to marine pollutant exposure can be generated, and this approach may have a greater potential as biomarker than traditional, single-protein markers.

IL-16 Is Critical forTropheryma whippleiReplication in Whipple’s Disease

Whipple's disease (WD) is a rare systemic disease caused by Tropheryma whipplei. We showed that T. whipplei was eliminated by human monocytes but replicated in monocyte-derived macrophages (Mphi) by inducing an original activation program. Two different host molecules were found to be key elements for this specific pattern. Thioredoxin, through its overexpression in infected monocytes, was involved in bacterial killing because adding thioredoxin to infected Mphi inhibited bacterial replication. IL-16, which was up-regulated in Mphi, enabled T. whipplei to replicate in monocytes and increased bacterial replication in Mphi. In addition, anti-IL-16 Abs abolished T. whipplei replication in Mphi. IL-16 down-modulated the expression of thioredoxin and up-regulated that of IL-16 and proapoptotic genes. In patients with WD, T. whipplei replication was higher than in healthy subjects and was related to high levels of circulating IL-16. Both events were corrected in patients who successfully responded to antibiotics treatment. This role of IL-16 was not reported previously and gives an insight into the understanding of WD pathophysiology.

Redox system expression in the motor neurons in amyotrophic lateral sclerosis (ALS): immunohistochemical studies on sporadic ALS, superoxide dismutase 1 (SOD1)-mutated familial ALS, and SOD1-mutated ALS animal models

Peroxiredoxin-ll (Prxll) and glutathione peroxidase-l (GPxl) are regulators of the redox system that is one of the most crucial supporting systems in neurons. This system is an antioxidant enzyme defense system and is synchronously linked to other important cell supporting systems. To clarify the common self-survival mechanism of the residual motor neurons affected by amyotrophic lateral sclerosis (ALS), we examined motor neurons from 40 patients with sporadic ALS (SALS) and 5 patients with superoxide dismutase 1 (SOD1)-mutated familial ALS (FALS) from two different families (frame-shift 126 mutation and A4 V) as well as four different strains of the SOD1-mutated ALS models (H46R/G93A rats and G1H/G1L-G93A mice). We investigated the immunohistochemical expression of Prxll/GPxl in motor neurons from the viewpoint of the redox system. In normal subjects, Prxll/GPxl immunoreactivity in the anterior horns of the normal spinal cords of humans, rats and mice was primarily identified in the neurons: cytoplasmic staining was observed in almost all of the motor neurons. Histologically, the number of spinal motor neurons in ALS decreased with disease progression. Immunohistochemically, the number of neurons negative for Prxll/GPxl increased with ALS disease progression. Some residual motor neurons coexpressing Prxll/GPxl were, however, observed throughout the clinical courses in some cases of SALS patients, SOD1-mutated FALS patients, and ALS animal models. In particular, motor neurons overexpressing Prxll/GPxl, i.e., neurons showing redox system up-regulation, were commonly evident during the clinical courses in ALS. For patients with SALS, motor neurons overexpressing Prxll/GPxl were present mainly within approximately 3 years after disease onset, and these overexpressing neurons thereafter decreased in number dramatically as the disease progressed. For SOD1-mutated FALS patients, like in SALS patients, certain residual motor neurons without inclusions also overexpressed Prxll/GPxl in the short-term-surviving FALS patients. In the ALS animal models, as in the human diseases, certain residual motor neurons showed overexpression of Prxll/GPxl during their clinical courses. At the terminal stage of ALS, however, a disruption of this common Prxll/GPxl-overexpression mechanism in neurons was observed. These findings lead us to the conclusion that the residual ALS neurons showing redox system up-regulation would be less susceptible to ALS stress and protect themselves from ALS neuronal death, whereas the breakdown of this redox system at the advanced disease stage accelerates neuronal degeneration and/or the process of neuronal death.

Characterization of neural cell types expressing peroxiredoxins in mouse brain

The differential expression patterns of antioxidant enzymes observed in the brains of patients with neurodegenerative diseases suggest an important role for reactive oxygen species and antioxidant enzymes in neurodegeneration. The six mammalian peroxiredoxins (Prxs) comprise a novel family of anti-oxidative proteins that are widely distributed in most tissues, but few studies of Prx in brain tissue have been reported. The specific histology of the neural cell types in which Prxs are expressed is an important issue related to biological function and defense against oxidative stress in the brain. This study analyzed mouse brain neural cell types expressing Prx isoforms using single- or double-label immunohistochemical techniques. In neurons, immunoreactivity for Prx II-V was observed in the cytoplasm. In particular, Prx II was found in the habenular nuclei, and Prx III and V were found in the stratum lucidum of the hippocampus. Astrocytes and microglia were immunoreactive only for Prx VI and Prx I, respectively. Prx I and IV immunoreactivity was apparent in oligodendrocytes, where it was principally localized in the nuclei. The observed distribution of Prx isoforms in the mammalian brain may be indicative of their specific roles in their preferred neural cell types and subcellular locales. The results of this study will help in unraveling the physiological and pathophysiological roles of the different Prx isoforms in neural function.

Peroxiredoxins: a historical overview and speculative preview of novel mechanisms and emerging concepts in cell signaling

The observation that purified yeast glutamine synthetase is rapidly inactivated in a thiol-containing buffer yet retains activity in crude extracts containing the same thiol led to our discovery of an enzyme that protects against oxidation in a thiol-containing system. This novel antioxidant enzyme was shown to reduce hydroperoxides and, more recently, peroxynitrite with the use of electrons provided by a physiological thiol like thioredoxin. It defined a family of proteins, present in organisms from all kingdoms, that was named peroxiredoxin (Prx). All Prx enzymes contain a conserved Cys residue that undergoes a cycle of peroxide-dependent oxidation and thiol-dependent reduction during catalysis. Mammalian cells express six isoforms of Prx (Prx I to VI), which are classified into three subgroups (2-Cys, atypical 2-Cys, and 1-Cys) based on the number and position of Cys residues that participate in catalysis. The relative abundance of Prx enzymes in mammalian cells appears to protect cellular components by removing the low levels of peroxides produced as a result of normal cellular metabolism. During catalysis, the active site cysteine is occasionally overoxidized to cysteine sulfinic acid. Contrary to the general belief that oxidation to the sulfinic state is an irreversible process in cells, studies on the fate of the overoxidized Prx species revealed a mechanism by which the catalytically active thiol form is recovered. This sulfinic reduction is a slow, ATP-dependent process that is specific to 2-Cys Prx isoforms. This reversible overoxidation may represent an adaptation unique to eukaryotic cells that accommodates the intracellular messenger function of H(2)O(2), but experimental validation of such speculation is yet to come.

Peroxiredoxins, oxidative stress, and cell proliferation

Peroxiredoxins (Prxs) are a family of multifunctional antioxidant thioredoxin-dependent peroxidases that have been identified in a large variety of organisms. The major functions of Prxs comprise cellular protection against oxidative stress, modulation of intracellular signaling cascades that apply hydrogen peroxide as a second messenger molecule, and regulation of cell proliferation. In the present review, we discuss pertinent findings on the protein structure, the cell- and tissue-specific distribution, as well as the subcellular localization of Prxs. A particular emphasis is put on Prx I, which is the most abundant and ubiquitously distributed member of the mammalian Prxs. Major transcriptional and posttranslational regulatory mechanisms and signaling pathways that control Prx gene expression and activity are summarized. The interaction of Prx I with the oncogene products c-Abl and c-Myc and the regulatory role of Prx I for cell proliferation and apoptosis are highlighted. Recent findings on phenotypical alterations of mouse models with targeted disruptions of Prx genes are discussed, confirming the physiological functions of Prxs for antioxidant cell and tissue protection along with an important role as tumor suppressors.

High molecular mass proteome of androgen-independent prostate cancer

We made a comprehensive study of protein expression of androgen-independent (AI) prostate cancer by means of agarose two-dimensional gel electrophoresis (agarose 2-DE) followed by liquid chromatography-tandem mass spectrometric analysis. The agarose 2-DE method being good at separating high molecular mass (HMM) proteins and alkaline ones, so we were able to successfully reveal differences between the proteomes of androgen-dependent (AD) tumors and those of AI tumors. During the creation of agarose 2-DE protein maps, we successfully identified 295 proteins (91.0%) out of 324 spots excised in total. Excluding redundant and mouse serum proteins, we considered the remaining 225 proteins to be related to the cancer. We divided the 225 cancer-related proteins into HMM and low molecular mass (LMM) groups by their molecular mass being above or below 80 kDa. Functional classification of the proteins in these two groups showed clear differences between the two: more than half (54.8%) of the HMM proteins, but less than one-third (29.1%) of the LMM ones were classified among transcription- or translation-related proteins. Eighteen proteins were regulated when the tumor progressed from an AD to an AI state. Five of these proteins, including antioxidant protein 2, superoxide dismutase 1, thioredoxin peroxidase, GTP-binding protein beta chain homolog, and the ha1225 gene product, had a function to protect cells against oxidant stress-induced apoptosis. We suggest that prevention against oxidative stress is one of the key points for prostate cancer to obtain androgen independency. We also found proteins that had not been previously reported in prostate cancer by use of genomic or conventional 2-DE based proteomic approaches. The proteomic approach, using agarose 2-DE focused on HMM proteins, has the capability to find novel biomarkers of prostate cancer.

Up-regulation of a thioredoxin peroxidase-like protein, proliferation-associated gene, in hibernating bats

Two-dimensional gel electrophoresis was used to assess differential protein expression between euthermic and hibernating states in heart of Myotis lucifugus. A hibernation-induced protein was identified by mass spectrometry as a thioredoxin peroxidase-like protein known as PAG. Western blotting confirmed up-regulation (>2-fold) and RT-PCR also revealed up-regulation (>5-fold) of pag mRNA. Cloning revealed a highly conserved sequence suggesting a conserved function for PAG. Oxidative stress markers, p-IkappaB-alpha (Ser 32) and p-HSP27 (Ser 78/82), were also up-regulated in heart and skeletal muscle during hibernation. Although there are selected increases in gene/protein expression during hibernation, general translation inhibition occurs as part of metabolic rate depression. This was confirmed by elevated levels of the inactive forms of the eIF2alpha (Ser 51) in both heart and skeletal muscle (2- to 5-fold higher than in euthermia) and the eEF2 (Thr 51) in skeletal muscle (a 15-fold increase). This study suggests that hibernators may use up-regulation of specific proteins to counteract oxidative stress.

Thioredoxin peroxidase secreted by Fasciola hepatica induces the alternative activation of macrophages

Alternatively activated macrophages (AAMphi) are primarily associated with the chronic stages of parasitic infections and the development of a polarized Th2 response. We have shown that Fasciola hepatica infection of BALB/c mice induces a polarized Th2 response during both the latent and chronic stage of disease. The activation status of macrophages was analyzed in this model of helminth infection by evaluating the expression of genetic markers of alternative activation, namely, Fizz1, Ym1, and Arg1. AAMphi were recruited to the peritoneum of mice within 24 h of F. hepatica infection and after intraperitoneal injection of parasite excretory-secretory (ES) products. Administration of a recombinant antioxidant thioredoxin peroxidase (TPx), which is contained within the ES products, also induced the recruitment of AAMphi to the peritoneum. In vitro studies showed that this recombinant TPx directly converts RAW 264.7 macrophages to an alternatively activated phenotype characterized by the production of high levels of interleukin-10 (IL-10), prostaglandin E(2), corresponding with low levels of IL-12. Our data suggest that the Th2 responses induced by the helminth F. hepatica are mediated through the secretion of molecules, one of which is TPx, that induce the recruitment and alternative activation of macrophages.

IDENTIFICATION OF OXIDATIVE STRESS-RELATED PROTEINS FOR PREDICTIVE SCREENING OF HEPATOTOXICITY USING A PROTEOMIC APPROACH

We investigated the effects of three hepatotoxicants, acetaminophen (APAP), amiodarone (AD) and tetracycline (TC), on protein expression in primary cultured rat hepatocytes with toxicoproteomic approach, which is two-dimensional gel electrophoresis (2DE) and mass spectrometry. The objectives of this study were to search for alternative toxicity biomarkers which could be detected with high sensitivity prior to the appearance of morphological changes or alterations of analytical conventional biomarkers. The related proteins in the process of cell degeneration/necrosis such as cell death, lipid metabolism and lipid/carbohydrate metabolism were mainly affected under exposure to APAP, AD and TC, respectively. Among the differentially expressed proteins, several oxidative stress-related proteins were clearly identified after 24-hr exposure, even though they were not affected for 6-hr exposure. They were glutathione peroxidase (GPX) as a down-regulated protein as well as peroxiredoxin 1 (PRX1) and peroxiredoxin 2 (PRX2) as up-regulated proteins, which are known to serve as antioxidative enzymes in cells. These findings suggested that the focused proteins, GPX and PRXs, could be utilized as biomarkers of hepatotoxicity, and they were useful for setting high throughput screening methods to assess hepatotoxicity in the early stage of drug discovery.

Redox regulation of lung development and perinatal lung epithelial function

Throughout gestation, low oxygen tensions are a dominant feature of the fetal environment and so may be important in sustaining a normal pattern of lung morphogenesis until the moment of birth. As breathing begins, the equilibration of the lung lumen to postnatal PO2 evokes a series of physiologic and morphogenic maturation events that are partially reversible by hypoxia. In this review, we discuss the experimental evidence that fetal and perinatal oxygen tensions differently influence lung morphogenesis through oxygen- and redox-responsive signaling pathways and identify five loci at which this regulation may occur: (I) proliferation of undifferentiated lung mesenchyme as governed by hypoxia-regulated transcription factors (HIF-1alpha, C/EBPbeta); (II) transient production of reactive oxygen species (ROS) and nuclear oxidation of the perinatal lung epithelium; (III) nuclear transport and oxidation of thioredoxin in hand with the acute activation of nuclear factor- kappaB (NF-kappaB); (IV) ROS-evoked chronic rise in intracellular glutathione and thioredoxin redox buffering capacity; and (V) NF-kappaB-dependent increase in transepithelial Na+ transport and lung lumenal fluid clearance. Although not exhaustive, this analysis leads us to the conclusion that redox events that occur in the lung during gestation, parturition, and the early neonatal period may dramatically influence the expression of genes and physiological events that are crucial to the successful transition from fetal to postnatal lung maturation.

Reduction of cysteine sulfinic acid by sulfiredoxin is specific to 2-cys peroxiredoxins

Cysteine residues of certain peroxiredoxins (Prxs) undergo reversible oxidation to sulfinic acid (Cys-SO2H) and the reduction reaction is catalyzed by sulfiredoxin (Srx). Specific Cys residues of various other proteins are also oxidized to sulfinic acid, suggesting that formation of Cys-SO2H might be a novel posttranslational modification that contributes to regulation of protein function. To examine the susceptibility of sulfinic forms of proteins to reduction by Srx, we prepared such forms of all six mammalian Prx isoforms and glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Purified sulfiredoxin reduced the sulfinic forms of the four 2-Cys members (Prx I to Prx IV) of the Prx family in vitro, but it did not affect those of Prx V, Prx VI, or GAPDH. Furthermore, Srx bound specifically to the four 2-Cys Prxs in vitro and in cells. Sulfinic forms of Prx I and Prx II, but not of Prx VI or GAPDH, present in H2O2-treated A549 cells were gradually reduced after removal of H2O2; overexpression of Srx increased the rate of the reduction of Prx I and Prx II but did not induce that of Prx VI or GAPDH. These results suggest that reduction of Cys-SO2H by Srx is specific to 2-Cys Prx isoforms. For proteins such as Prx VI and GAPDH, sulfinic acid formation might be an irreversible process that causes protein damage.

Nuclear heat shock response and novel nuclear domain 10 reorganization in respiratory syncytial virus-infected a549 cells identified by high-resolution two-dimensional gel electrophoresis

The pneumovirus respiratory syncytial virus (RSV) is a leading cause of epidemic respiratory tract infection. Upon entry, RSV replicates in the epithelial cytoplasm, initiating compensatory changes in cellular gene expression. In this study, we have investigated RSV-induced changes in the nuclear proteome of A549 alveolar type II-like epithelial cells by high-resolution two-dimensional gel electrophoresis (2DE). Replicate 2D gels from uninfected and RSV-infected nuclei were compared for changes in protein expression. We identified 24 different proteins by peptide mass fingerprinting after matrix-assisted laser desorption ionization-time of flight mass spectrometry (MS), whose average normalized spot intensity was statistically significant and differed by +/-2-fold. Notable among the proteins identified were the cytoskeletal cytokeratins, RNA helicases, oxidant-antioxidant enzymes, the TAR DNA binding protein (a protein that associates with nuclear domain 10 [ND10] structures), and heat shock protein 70- and 60-kDa isoforms (Hsp70 and Hsp60, respectively). The identification of Hsp70 was also validated by liquid chromatography quadropole-TOF tandem MS (LC-MS/MS). Separate experiments using immunofluorescence microscopy revealed that RSV induced cytoplasmic Hsp70 aggregation and nuclear accumulation. Data mining of a genomic database showed that RSV replication induced coordinate changes in Hsp family proteins, including the 70, 70-2, 90, 40, and 40-3 isoforms. Because the TAR DNA binding protein associates with ND10s, we examined the effect of RSV infection on ND10 organization. RSV induced a striking dissolution of ND10 structures with redistribution of the component promyelocytic leukemia (PML) and speckled 100-kDa (Sp100) proteins into the cytoplasm, as well as inducing their synthesis. Our findings suggest that cytoplasmic RSV replication induces a nuclear heat shock response, causes ND10 disruption, and redistributes PML and Sp100 to the cytoplasm. Thus, a high-resolution proteomics approach, combined with immunofluorescence localization and coupled with genomic response data, yielded unexpected novel insights into compensatory nuclear responses to RSV infection.

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.

PRDX4, a member of the peroxiredoxin family, is fused to AML1 (RUNX1) in an acute myeloid leukemia patient with a t(X;21)(p22;q22)

The AML1 gene (also known as RUNX1) at 21q22 codes for core binding factor (CBF) alpha, which forms a heterodimer with CBF beta that acts as a transcriptional activating factor. CBF is a critical regulator in the generation and differentiation of definitive hematopoietic stem cells and is frequently disrupted in leukemia through chromosome translocations. We cloned a novel AML1 partner gene, PRDX4, in an X;21 translocation in a 74-year-old male patient diagnosed with acute myeloid leukemia-M2. Chromosome analysis detected a t(X;21)(p22;q22) as the sole abnormality in bone marrow samples. The involvement of AML1 was confirmed by fluorescence in situ hybridization studies. Using 3' RACE-PCR, we cloned a fusion between exon 5 of AML1 and exon 2 of PRDX4. RT-PCR confirmed the fusion and detected another fusion between exon 6 of AML1 and exon 2 of PRDX4, indicating alternative splicing of exon 6 of AML1 in the fusion transcripts. PRDX4 is one of six peroxiredoxin-family genes that are highly conserved in eukaryotes and prokaryotes and are ubiquitously expressed. Peroxiredoxin genes exhibit thioredoxin-dependent peroxidase activity and have been implicated in a number of other cellular functions such as cell proliferation and differentiation. PRDX4 plays a regulatory role in the activation of the transcription factor NF-kappaB and is significantly down-regulated in acute promyelocytic leukemia. This is the first example of antioxidant enzyme involvement in a chromosome translocation in leukemia.

Peroxiredoxins, a novel protein family in lung cancer

Cigarette smoke, the major risk factor for lung cancer, induces an accumulation of reactive oxygen species. These have multiple effects on cell defense, cell proliferation and cell death. Thus, compounds involved in the regulators of redox balance can be hypothesized to play a fundamental role in both carcinogenesis and tumor progression. Here, we have evaluated the expressions of all 6 peroxiredoxins (Prxs I-VI) in lung carcinomas. Prxs represent a protein family with the capability of breaking down hydrogen peroxide; thus, they can participate in cellular antioxidant defense, regulate cell proliferation and increase drug resistance of cultured cells. Altogether 92 cases were investigated by immunohistochemistry, including 32 adenocarcinomas, 45 squamous cell, 9 small cell and 6 other carcinomas. Additionally, 11 cases with adenocarcinoma or squamous cell carcinoma were studied by Western analysis and/or by RT-PCR. Prxs I, II, IV and VI were particularly elevated in lung carcinomas as assessed by immunohistochemistry and/or RT-PCR. Western analysis revealed that Prxs I and IV were significantly elevated in tumors compared to nonmalignant tissue (p = 0.04 and 0.002, respectively). There were remarkable variations in Prx expression in various tumor subtypes, the most striking being Prx IV expression, which was mainly associated with adenocarcinoma. Elevated Prx VI expression was associated with high-grade squamous cell carcinoma (p = 0.03) and Prx II expression, with advanced tumor stage (p = 0.01). Our results suggest that Prxs may have effects on the progression of lung cancer.

The AlnB protein of the bioemulsan alasan is a peroxiredoxin

The bioemulsifier of Acinetobacter radioresistens KA53, referred to as alasan, is a high molecular weight complex of a polysaccharide and three proteins (AlnA, AlnB and AlnC). AlnA has previously been shown to be an OmpA-like protein that is largely responsible for the emulsifying activity of alasan. To further elucidate the nature of alasan, the gene coding for AlnB was cloned, sequenced and overexpressed in Escherichia coli. The overall 561 bp sequence of the hypothetical AlnB showed strong homology, including all conserved regions and residues known to be essential for enzymatic activity, to the ubiquitous family of thiol-specific antioxidant enzymes known as peroxiredoxins. Transgenic E. coli overexpressing AlnB exhibited increased resistance to cumene hydroperoxide both in liquid culture and on agar medium. Recombinant AlnB had no emulsifying activity but stabilized oil-in-water emulsion generated by AlnA.