Thioredoxin peroxidase is a novel inhibitor of apoptosis with a mechanism distinct from that of Bcl-2

Role of mitochondrial phospholipid hydroperoxide glutathione peroxidase (PHGPx) as an antiapoptotic factor

Phospholipid hydroperoxide glutathione peroxidase (PHGPx) is a unique antioxidant enzyme that markedly reduces lipid hydroperoxide generated in biomembranes. Overexpression of mitochondrial PHGPx potentially suppresses the release of cytochrome c (cyt. c) from mitochondria and apoptosis. The hydroperoxide level in mitochondria was elevated in 2-deoxyglucose (2DG)-induced apoptosis, but not in apoptosis-resistant cells in which mitochondrial PHGPx was overexpressed. From studies of the overexpression of PHGPx, the generation of hydrogen peroxide and lipid hydroperoxide in mitochondria might be important triggers of apoptosis. In particular lipid hydroperoxide could be involved in the initiation of cyt. c liberation from mitochondria in 2DG-induced apoptosis since lipid hydroperoxide is a primary substrate for PHGPx. The release of cyt. c from mitochondria is an important proapoptotic signal in the mitochondrial death pathway. Several reports demonstrated the reactive oxgen species could be involved in cyt. c liberation, although its mechanism is still unknown. Cardiolipin (CL), which exclusively locates in the innermembrane of mitochondria, shows strong affinity for cyt. c is required for the adenine nucleotide translocator (ANT) that controls the opening and closing of the permeability transition pore. Association of cyt. c with CL is lost upon peroxidation. CL hydroperoxide (CLOOH), in contrast to CL, does not bind to cyt. c. Furthermore, CLOOH can open the permeability transion pore by the inactivation of ANT. These previous results suggest that mitochondrial PHGPx inhibits the release of cyt. c from mitochondria by the scavenging CLOOH and could prevent apoptosis.

The responses of Ht22 cells to oxidative stress induced by buthionine sulfoximine (BSO)

Background

glutathione (GSH) is the most abundant thiol antioxidant in mammalian cells. It directly reacts with reactive oxygen species (ROS), functions as a cofactor of antioxidant enzymes, and maintains thiol redox potential in cells. GSH depletion has been implicated in the pathogenesis of neurological diseases, particularly to Parkinson's disease (PD). The purpose of this study was to investigate the change of cellular antioxidant status and basic cell functions in the relatively early stages of GSH depletion.

Results

in this study, GSH was depleted by inhibition of glutamylcysteine synthetase using buthionine sulfoximine (BSO) treatment in Ht22, a neuronal cell line derived from mouse hippocampus. Treatment with BSO produced dose-dependent decreases in total GSH level, Fe3+-reducing ability (FRAP assay), Cu2+-reducing ability (Antioxidant Potential, AOP assay), and ABTS free radical scavenging ability (ABTS assay) of the cells, but the sensitivity of these indicators to dosage varied considerably. Most of the changes were completed during the first 8 hours of treatment. Cell viability was tested by MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromid) assay, and cells at lower density in culture were found to be more sensitive to GSH depletion. The activity of antioxidant enzymes, such as glutathione peroxidase (GPx), glutathione reductase (GR), and copper/zinc superoxide dismutase (Cu/Zn-SOD) were affected by GSH depletion. A cDNA expression array assay of the effects of BSO treatment showed significantly decreased mRNA level for 3 genes, and significantly increased mRNA level for 10 genes, including the antioxidant enzymes Cu/Zn-SOD and thioredoxin peroxidase 2 (TPxII).

Conclusions

the study suggests that there are BSO-sensitive and BSO-resistant pools of GSH in Ht22 cells, and that different categories of antioxidant react differently to GSH depletion. Further, the effect of GSH status on cell viability is cell density dependent. Finally, the alterations in expression or activity of several antioxidant enzymes provide insight into the various cellular responses to GSH depletion.

Mitochondrial function in cardiomyocytes: target for cardioprotection

PURPOSE OF REVIEW

Cardiac diseases including ischemic heart disease, cardiomyopathy, hypertension, atherosclerosis and congestive heart failure are associated with cardiac cell death as a result of both necrosis and apoptosis. Mitochondria play an essential role in deciding whether a cell lives or dies. This review summarizes current knowledge on the mechanisms by which mitochondria exert such decision-making power.

RECENT FINDINGS

A wide variety of factors, either directly or indirectly, function in a synchronized manner to regulate the death versus survival signals. Mitochondrial bioenergetics and permeability transition pore plays a crucial role in this process, although several redox-sensitive genes, proteins and transcription factors, such as Bcl-2, Bax, nuclear factor kappa B, regulate the decision-making power of mitochondria, which have the final authority to decide whether a cell lives or dies. Mitochondrially generated reactive oxygen species are critically involved in the decision-making process, by functioning both as executioner by damaging the biomolecules, or as savior by virtue of their ability to perform redox signaling.

SUMMARY

It appears that mitochondria regulate the life and death of cardiac cells by manipulating several factors, including bioenergetics, mitochondrial permeability transition pore and redox-sensing genes. Redox signaling is likely to be critically involved in this process.

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.

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.

Glucose repression ofPRX1expression is mediated by Tor1p and Ras2p through inhibition of Msn2/4p inSaccharomyces cerevisiae

Expression of mitochondrial thioredoxin peroxidase (Prx1p) from Saccharomyces cerevisiae is subjected to complex transcriptional regulation and is responsive to the levels of several compounds such as glucose and peroxides. We have previously shown that glucose represses the expression of mitochondrial thioredoxin peroxidase gene (PRX1) in a process mediated by cAMP/protein kinase A (PKA) and Msn2/4p. Here, we show by northern blot and reporter gene (beta-galactosidase) assays that deletion of genes encoding Tor1p and Ras2p resulted in increased PRX1 expression, indicating that these proteins are also mediators of the glucose repression effect. We also identified the position of the stress transcription responsive element (STRE) in the PRX1 promoter, which is recognized by Msn2p and Msn4p activators. Mutation of AGGGG sequence at position -116 to -112 caused a high drop in PRX1 expression under respiratory conditions and in strains containing deletions of TOR1 or RAS2, confirming the finding that this sequence is a STRE.

Identification of a novel partner of duox: EFP1, a thioredoxin-related protein

H(2)O(2) is a crucial substrate of thyroproxidase (TPO) to iodinate thyroglobulin and synthesize thyroid hormones in thyroid. ThOX proteins (thyroid oxidase) also called Duox are believed to be responsible for H(2)O(2) generation. Duoxs expressed in transfected cells do not generate an active system, nor permit their membrane localization suggesting that other proteins are required to fulfill these functions. In this study, we demonstrate interactions of Duoxs with TPO and with p22(phox) without any effect on Duox activity. By yeast two-hybrid method using EF-hand fragment of dog Duox1 as the bait we have isolated EFP1 (EF-hand binding protein 1), one partner of Duoxs that belongs to the thioredoxin-related protein family. EFP1 shares moderate similarities with other members of thioredoxin-related proteins, but the characteristic active site and the folding structures are well conserved. EFP1 can be co-immunoprecipitated with Duoxs in transfected COS cells as well as in primary cultured human thyrocytes. It interacts also with TPO but not thyroglobulin. Immunofluorescence studies show that EFP1 and Duox proteins are co-localized inside the transfected cells, suggesting that EFP1 is not sufficient to induce either the expression of Duox at the plasma membrane or to permit H(2)O(2) production. EFP1 and Duox mRNA share similar distribution in nine different tissues. These results suggest that EFP1 could be one of the partners in the assembly of the multiprotein complex constituting the thyroid H(2)O(2) generating system but is certainly not sufficient to permit H(2)O(2) generation.

Characterization of mammalian sulfiredoxin and its reactivation of hyperoxidized peroxiredoxin through reduction of cysteine sulfinic acid in the active site to cysteine

Peroxiredoxins (Prxs) are a family of peroxidases that reduce hydroperoxides. The cysteine residue in the active site of certain eukaryotic Prx enzymes undergoes reversible oxidation to sulfinic acid (Cys-SO2H) during catalysis, and sulfiredoxin (Srx) has been identified as responsible for reversal of the resulting enzyme inactivation in yeast. We have now characterized mammalian orthologs of yeast Srx with an assay based on monitoring of the reduction of sulfinic Prx by immunoblot analysis with antibodies specific for the sulfinic state. Sulfinic reduction by mammalian Srx was found to be a slow process (kcat = 0.18/min) that requires ATP hydrolysis. ATP could be efficiently replaced by GTP, dATP, or dGTP but not by CTP, UTP, dCTP, or dTTP. Both glutathione and thioredoxin are potential physiological electron donors for the Srx reaction, given that their Km values (1.8 mM and 1.2 microM, respectively) are in the range of their intracellular concentrations, and the Vmax values obtained with the two reductants were similar. Although its pKa is relatively low (approximately 7.3), the active site cysteine of Srx remained reduced even when the active site cysteine of most Prx molecules became oxidized. Finally, depletion of human Srx by RNA interference suggested that Srx is largely responsible for reduction of the Cys-SO2H of Prx in A549 human cells.

Overexpression of antioxidant enzyme peroxiredoxin 5 protects human tendon cells against apoptosis and loss of cellular function during oxidative stress

Oxidative stress and apoptosis are implicated in tendon degeneration. Peroxiredoxin 5 (PRDX5) is a novel thioredoxin peroxidase recently identified in mammals, participating directly in eliminating hydrogen peroxide (H(2)O(2)) and neutralizing other reactive oxygen species (ROS). We have previously reported that PRDX5 is upregulated in degenerative human tendon. However, the effects of this upregulation on human tendon cell function remain unknown, in particular, with regards to oxidative stress conditions. Here we report that exposure of human tendon cells to 50 microM H(2)O(2) for 24 h (in vitro oxidative stress) caused a significant increase in the percentage of apoptotic cells (P<0.05) as assessed by flow cytometric analysis of Annexin V binding, accompanied by increased PRXD5 mRNA and protein expression. Overexpression of PRDX5 in human tendon cells via transfection inhibited H(2)O(2)-induced tendon cell apoptosis by 46% (P<0.05), and prevented the decrease in tendon cell collagen synthesis which occurs under H(2)O(2) challenge, although the decrease in collagen synthesis was small. Results from our study indicate that the antioxidant enzyme PRDX5 plays a protective role in human tendon cells against oxidative stress by reducing apoptosis and maintaining collagen synthesis.

A proteomic approach to identify early molecular targets of oxidative stress in human epithelial lens cells

Oxidative stress is one of the most relevant contributors of cataractogenesis. To identify early protein targets of oxidative stress in lens cells, we used a differential proteomics approach to CD5A human epithelial lens cells treated with 500 microM H2O2 for 30 min. This dose of H2O2 was assayed to induce efficiently a block of cellular proliferation and to activate the oxidative stress-early inducible transcription factor EGR-1 (early growth response gene product 1), previously reported as stimulated factor in a model of cataractogenesis [Nakajima, Nakajima, Fukiage, Azuma and Shearer (2002) Exp. Eye Res. 74, 231-236]. We identified nine proteins, which sensitively reacted to H2O2 treatment by using two-dimensional gel electrophoresis and matrix-assisted laserdesorption ionization-time-of-flight-MS. In addition to cytoskeletal proteins (tubulin 1alpha and vimentin) and enzymes (phosphoglycerate kinase 1, ATP synthase beta, enolase alpha, nucleophosmin and heat-shock cognate 54 kDa protein), which presented quantitative differences in expression profiles, peroxiredoxin and glyceraldehyde 3-phosphate dehydrogenase showed changes in pI as a result of overoxidation. Mass-mapping experiments demonstrated the specific modification of peroxiredoxin I active-site cysteine into cysteic acid, thus providing an explanation for the increase in negative charge measured for this protein. With respect to other global differential approaches based on gene expression analysis, our results allowed us to identify novel molecular targets of oxidative stress in lens cells. These results indicate that a combination of different approaches is required for a complete functional understanding of the biological events triggered by oxidative stress.

A Peroxiredoxin Specifically Expressed in Two Types of Pharyngeal Neurons is Required for Normal Growth and Egg Production in Caenorhabditis elegans

A family of antioxidant proteins, the peroxiredoxins, serve two purposes, detoxification of reactive oxygen species and cellular signaling. Among the three peroxiredoxins of Caenorhabditis elegans (CePrx1-3), CePrx2 was found to have a very unusual expression pattern, restricted to only two types of pharyngeal neurons; namely, the single pharyngeal interneuron I4 and the sensory interneuron I2. CePrx1 and CePrx3-depleted worms showed no obvious phenotypic alterations, whereas worms devoid of CePrx2 were retarded developmentally and had a significantly reduced brood size. Other features, such as lifespan, pharyngeal activity or defecation rates were indistinguishable from those of wild-type worms. Recombinant CePrx2 revealed antioxidant activity, as it was able to detoxify hydrogen peroxide and butylhydroperoxide (t-BOOH), and to protect glutamine synthetase from inactivation by thiol-dependent metal-catalyzed oxidation. In addition, the molecule was able to act as a terminal peroxidase in the thioredoxin system. Expression of ceprx2 in C.elegans was induced after short-term exposure of worms to t-BOOH but survival of ceprx2 knockout mutants in the presence of reactive oxygen or nitrogen species was not impaired. Thus, CePrx2 may protect specifically the two types of neurons from oxidative damage or, more likely, plays a critical role in peroxide signaling in this nematode.

Proteomics and the haematologist

Understanding haematological malignancies at the protein level is important as the development of targeted treatments must be based on knowledge regarding the molecular pathogenesis of the tumour, inherited genetic variation and the mode of action of drugs. 'Proteomics' describes the analysis of the entire proteome of a cell or tissue and incorporates multiple technologies including Western blotting, two-dimensional gel electrophoresis, mass spectrometry, and ProteinChip-based technology. Although there are a limited number of studies to date in haematology those performed highlight the potential future impact of these technologies in the discovery of novel markers, proteins associated with drug resistance and the identification of tumour biomarkers which may facilitate the development of a rapid diagnostic test easily applicable in the clinical setting. Rapid large-scale analysis of the proteome in normal pathways and disease offers the opportunity of identification of potential diagnostic/prognostic markers and proteins associated with the malignant phenotype. This review discusses the current situation regarding the use of these technologies and the potential opportunities their future use may offer in the field of haematology.

Thioredoxin regulation of ischemic preconditioning

Thioredoxins are a class of small redox-regulating proteins that appear to play a crucial role in many oxidative stress-inducible degenerative diseases. A recent study demonstrated a reduction of thioredoxin-1 (Trx1) protein in the ischemic reperfused myocardium. When the same heart was adapted to ischemic stress by preconditioning with repeated cyclic episodes of small duration of ischemia and reperfusion, there was an increased induction of Trx1 expression. Inhibition of Trx1 expression resulted in reduced postischemic ventricular recovery and increased myocardial infarct size in the preconditioned heart. Corroborating these findings, transgenic mouse hearts overexpressing Trx1 were resistant to ischemic reperfusion injury as compared with the hearts from wild-type mice. Thus, it appears that thioredoxin plays a crucial role in cardioprotection induced by preconditioning.

TRAIL and Ceramide

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a clinically useful cytokine. TRAIL induces apoptosis in a wide variety of transformed cells, but does not cause toxicity to most normal cells. Recent studies show that death receptors (DR4 and DR5), decoy receptors (DcR1 and DcR2), and death inhibitors (FLIP, FAP-1, and IAP) are responsible for the differential sensitivity to TRAIL of normal and tumor cells. Several researchers have also shown that genotoxic agents, such as chemotherapeutic agents and ionizing radiation, enhance TRAIL-induced cytotoxicity by increasing DR5 gene expression or decreasing the intracellular level of FLIP, an antiapoptotic protein. Previous studies have shown that ceramide helps to regulate a cell's response to various forms of stress. Stress-induced alterations in the intracellular concentration of ceramide occur through the activation of a variety of enzymes that synthesize or catabolize ceramide. Increases in intracellular ceramide levels modulate apoptosis by acting through key proteases, phosphatases, and kinases. This review discusses the interaction between TRAIL and ceramide signaling pathways in regulating apoptotic death.

Overexpression of catalase or Bcl-2 delays or prevents alterations in phospholipid metabolism during glucocorticoid-induced apoptosis in WEHI7.2 cells

Dexamethasone-treated WEHI7.2 mouse thymoma cells readily undergo apoptosis. WEHI7.2 variants that overexpress catalase (CAT38) or Bcl-2 (Hb12) show a delay or lack of apoptosis, respectively, when treated with dexamethasone. This is accompanied by a delay or lack of cytochrome c release from the mitochondria suggesting that alterations in the signaling phase of apoptosis are responsible for the observed resistance. Because membranes are a rich source of signaling molecules, we have used 31P NMR spectroscopy to compare phospholipids and their metabolites in WEHI7.2, CAT38 and Hb12 cells after dexamethasone treatment. Increased lysophosphatidylcholine (lysoPtdC) content accompanied phosphatidylserine (PtdS) externalization in the WEHI7.2 cells. Both changes were delayed in CAT38 cells suggesting phosphatidylcholine (PtdC) metabolites may play a role in steroid-induced apoptotic signaling. The steroid-resistant Hb12 cells showed a dramatic increase in glycerophosphocholine (GPC) content, suggesting increased phospholipid turnover may contribute to the anti-apoptotic mechanism of Bcl-2.

Roles of reactive oxygen species, NF-kappaB, and peroxiredoxins in glycochenodeoxycholic acid-induced rat hepatocytes death

The aim of this study was to determine the roles of reactive oxygen species (ROS), NF-kappaB and antioxidants in glycochenodeoxycholic acid (GCDC, 0-400 micromol/l, 0.5- 3 h)-induced hepatocytes death. The differential uptake of ethidium bromide and acridine orange revealed that apoptotic death occurred dose-dependently in GCDC-treated hepatocytes whereas necrotic death was prominent especially at higher GCDC concentrations (> or =200 micromol/l). ROS generation measured fluorometrically either by a confocal laser microscope or by a microplate fluorescence reader was increased dose-dependently. The dose-dependent NF-kappaB activation with the significant IkappaB-alpha decrease preceded both hepatocyte cell death and the alteration of antioxidant enzymes. The Cu/Zn-SOD level among several antioxidants, we checked, remained unchanged. In contrast, the catalase level and its enzymatic activity were markedly decreased only at 400 micromol/l. The Prx I and Prx II, newly defined antioxidant enzymes reducing H(2)O(2) levels were decreased at the 200 and 400 micromol/l. These observations point to ROS generation in the GCDC-treated hepatocyte as the proximate event that triggers NF-kappaB activation, IkappaB-alpha proteolysis, Prx depletion, and finally cell death. And oxidative stress may be more related to necrotic cell death in GCDC-treated hepatocytes.

Enlargement and contracture of C2-ceramide channels

Ceramides are known to play a major regulatory role in apoptosis by inducing cytochrome c release from mitochondria. We have previously reported that ceramide, but not dihydroceramide, forms large and stable channels in phospholipid membranes and outer membranes of isolated mitochondria. C(2)-ceramide channel formation is characterized by conductance increments ranging from <1 to >200 nS. These conductance increments often represent the enlargement and contracture of channels rather than the opening and closure of independent channels. Enlargement is supported by the observation that many small conductance increments can lead to a large decrement. Also the initial conductances favor cations, but this selectivity drops dramatically with increasing total conductance. La(+3) causes rapid ceramide channel disassembly in a manner indicative of large conducting structures. These channels have a propensity to contract by a defined size (often multiples of 4 nS) indicating the formation of cylindrical channels with preferred diameters rather than a continuum of sizes. The results are consistent with ceramides forming barrel-stave channels whose size can change by loss or insertion of multiple ceramide columns.

Expression of peroxiredoxin II in vascular tumors of the skin: a novel vascular marker of endothelial cells

BACKGROUND

The peroxiredoxin (Prx) family consists of peroxidases to remove H(2)O(2) by using the thioredoxin system. In a previous study, Prx II was ubiquitously expressed in the epidermis and dermis including dermal vessels.

OBJECTIVE

This study aims to elucidate expression patterns of Prx II in benign and malignant vascular tumors.

METHODS

Immunohistochemical staining for Prx II, factor VIII-related antigen, and CD34 was performed in formalin-fixed specimens.

RESULTS

Prx II was strongly expressed in mature endothelial cells of benign vascular tumors, whereas it was expressed weakly or not expressed in immature endothelial cells in malignant tumors of Kaposi's sarcoma and angiosarcoma. The expression patterns of Prx II were similar to those of factor VIII-related antigen, rather than CD34.

CONCLUSIONS

Prx II can be used as a novel marker of endothelial cells and indicates that reactive oxygen may play a role in the pathogenesis of vascular tumors.

Arrested apoptosis of nurse cells during Hydra oogenesis and embryogenesis

During Hydra oogenesis, an aggregate of germ cells differentiates into one oocyte and thousands of nurse cells. Nurse cells display a number of features typical of apoptotic cells and are phagocytosed by the growing oocyte. Yet, these cells remain unchanged in morphology and number until hatching of the polyp, which can occur up to 12 months later. Treatments with caspase inhibitors can block oocyte development during an early phase of oogenesis, but not after nurse cell phagocytosis has taken place, indicating that initiation of nurse cell apoptosis is essential for oocyte development. The genomic DNA of the phagocytosed nurse cells in the oocyte and embryo shows large-scale fragmentation into 8- to 15-kb pieces, but there is virtually none of the internucleosomal degradation typically seen in apoptotic cells. The arrested nurse cells exhibit high levels of peroxidase activity and are prevented from entering the lysosomal pathway. After hatching of the polyp, apoptosis is resumed and the nurse cells are degraded within 3 days. During this final stage, nurse cells become TUNEL-positive and enter secondary lysosomes in a strongly degraded state. Our results suggest that nurse cell apoptosis consists of caspase-dependent and caspase-independent phases. The independent phase can be arrested at an advanced stage for several months, only to resume after the primary polyp hatches.

Cellular regulation by hydrogen peroxide

Substantial evidence suggests that the transient production of H(2)O(2) is an important signaling event triggered by the activation of various cell surface receptors. Understanding the intracellular messenger function of H(2)O(2) calls for studies of how receptor occupation elicits the production of H(2)O(2), what kinds of molecules are targeted by the produced H(2)O(2), and how H(2)O(2) is eliminated after the completion of its mission. Recent studies suggest that growth factor-induced H(2)O(2) production requires the activation of PtdIns 3-kinase. The essential role of PtdIns 3-kinase is likely to provide PI(3,4,5)P(3) that recruits and activates a guanine nucleotide exchange factor of Rac, which is required for the activation of NADPH oxidase. The targets of H(2)O(2) action include proteins that contain a reactive Cys residue. Thus, H(2)O(2) produced in response to growth factor causes inactivation of protein tyrosine phosphatases in various cells by oxidizing specifically the catalytic Cys. These results, together with other observations, indicate that the activation of a receptor tyrosine kinase per se by binding of the corresponding growth factor might not be sufficient to increase the steady-state level of protein tyrosine phosphorylation in cells. Rather, the concurrent inhibition of protein tyrosine phosphatases by H(2)O(2) might also be required. Peroxiredoxins, members of a newly discovered family of peroxidases, efficiently reduced the intracellular level of H(2)O(2) produced in the cells stimulated with various cell surface ligands. Furthermore, the activity of peroxiredoxin enzymes seems to be regulated via protein phosphorylation as in the case of many other intracellular messenger metabolizing enzymes.

Enhancement of mitochondrial oxidative stress and up-regulation of antioxidant protein peroxiredoxin III/SP-22 in the mitochondria of human pre-eclamptic placentae

A growing body of evidence indicates that the pathogenesis of pre-eclampsia is closely associated with oxidative stress occurring in mitochondria. In the present study, we evaluated the degree of mitochondrial lipid peroxidation by assessing the accumulation of 4-hydroxy-2-nonenal (HNE)-modified proteins and examined the expression of mitochondrial antioxidant protein peroxiredoxin III/SP-22 in normal and pre-eclamptic human placentae. The accumulation of HNE-modified proteins increased to a greater extent in both the mitochondria and cytosol of pre-eclamptic placentae than in those of normal placentae. Moreover, the accumulation of HNE-modified proteins was much more evident in the mitochondria than in the cytosol, indicating that lipid peroxidation occurred mainly in the mitochondria of pre-eclamptic placentae. The mRNA expression of peroxiredoxin III/SP-22 was increased about 2-fold in pre-eclamptic placentae compared to normal placentae. The protein levels of peroxiredoxin III/SP-22 were approximately 4-fold higher in pre-eclamptic placentae than in normal placentae. Immunohistochemistry of placental tissues showed that the levels of peroxiredoxin III/SP-22 protein were increased in the trophoblasts of floating villi, stromal cells of stem villi, and decidual cells in pre-eclamptic placentae. These results indicate that peroxiredoxin III/SP-22 plays a crucial role in the protection of placental function from oxidative stress occurring in mitochondria of pre-eclamptic placentae.

Effects of oxidative stress on human erythroid colony formation: Modulation by gamma-interferon

Evidence of increased oxidative stress is a hallmark of many chronic diseases associated with anemia. The current study was undertaken to evaluate the effects of oxidative stress on erythroid colony formation in vitro by bone marrow light density mononuclear cells (LDMN) and by peripheral blood derived cells enriched for erythroid colony forming units (CFU-E), and how these effects can be modified by a cytokine implicated in the anemia of chronic disease. When blood-derived and marrow cells were cultured with 50 microM H(2)O(2), CFU-E colony formation by blood-derived cells but not by marrow cells was significantly inhibited, suggesting a protective effect of marrow accessory cells. This inhibitory effect on peripheral blood-derived CFU-E was shown to be caspase-dependent. rhgammaIFN at concentrations which did not inhibit CFU-E colony formation sensitized LDMN marrow cells to inhibition by H(2)O(2). Exposure of LDMN marrow cells to rhgammaIFN at concentrations of 10 U/mL or higher significantly decreased the concentration of thioredoxin (Trx) in cell supernatant. Addition of recombinant Trx to LDMN marrow cells cultured with H(2)O(2) and rhgammaIFN partially (although not completely) reversed inhibition of CFU-E colony formation. These findings suggest that inflammatory cytokines implicated in the pathogenesis of the anemia of chronic disease may exert their effects at least in part through modulation of oxidative stress.

Genomic profiles and predictive biological networks in oxidant-induced atherogenesis

Atherogenic stimuli trigger complex responses in vascular smooth muscle cells (VSMCs) that culminate in activation/repression of overlapping signal transduction cascades involving oxidative stress. In the case of benzo[a]pyrene (BaP), a polycyclic aromatic hydrocarbon present in tobacco smoke, the atherogenic response involves interference with redox homeostasis by oxidative intermediates of BaP metabolism. The present studies were conducted to define genomic profiles and predictive gene biological networks associated with the atherogenic response of murine (aortic) VSMCs to BaP. A combined oxidant-antioxidant treatment regimen was used to identify redox-sensitive targets during the early course of the atherogenic response. Gene expression profiles were defined using cDNA microarrays coupled to analysis of variance and several clustering methodologies. A predictor algorithm was then applied to gain insight into critical gene-gene interactions during atherogenesis. Supervised and nonsupervised analyses identified clones highly regulated by BaP, unaffected by antioxidant, and neutralized by combined chemical treatments. Lymphocyte antigen-6 complex, histocompatibility class I component factors, secreted phosphoprotein, and several interferon-inducible proteins were identified as novel redox-regulated targets of BaP. Predictor analysis confirmed these relationships and identified immune-related genes as critical molecular targets of BaP. Redox-dependent patterns of gene deregulation indicate that oxidative stress plays a prominent role during the early stages of BaP-induced atherogenesis.

Rapid induction of cell death by selenium-compromised thioredoxin reductase 1 but not by the fully active enzyme containing selenocysteine

Mammalian thioredoxin reductases are selenoproteins. For native catalytic activity, these enzymes utilize a C-terminal -Gly-Cys-Sec-Gly-COOH sequence (where Sec is selenocysteine) forming a redox active selenenylsulfide/selenolthiol motif. A range of cellular systems depend upon or are regulated by thioredoxin reductase and its major protein substrate thioredoxin, including apoptosis signal-regulating kinase 1, peroxiredoxins, methionine sulfoxide reductase, and several transcription factors. Cytosolic thioredoxin reductase 1 (TrxR1) is moreover inhibited by various electrophilic anticancer compounds. TrxR1 is hence generally considered to promote cell viability. However, several recent studies have suggested that TrxR1 may promote apoptosis, and the enzyme was identified as GRIM-12 (gene associated with retinoid interferon-induced mortality 12). Transient transfection with GRIM-12/TrxR1 was also shown to directly induce cell death. To further analyze such effects, we have here employed lipid-mediated delivery of recombinant TrxR1 preparations into human A549 cells, thereby bypassing selenoprotein translation to facilitate assessment of the protein-related effects on cell viability. We found that selenium-deficient TrxR1, having a two-amino acid-truncated C-terminal -Gly-Cys-COOH motif, rapidly induced cell death (38 +/- 29% apoptotic cells after 4 h; p < 0.005 compared with controls). Cell death induction was also promoted by selenium-compromised TrxR1 derivatized with either cis-diamminedichloroplatinum (II) (cisplatin) or dinitrophenyl moieties but not by the structurally related non-selenoprotein glutathione reductase. In contrast, TrxR1 with intact selenocysteine could not promote cell death. The direct cellular effects of selenium-compromised forms of TrxR1 may be important for the pathophysiology of selenium deficiency as well as for the efficacy of antiproliferative drugs targeting the selenocysteine moiety of this enzyme.

Reversing the inactivation of peroxiredoxins caused by cysteine sulfinic acid formation

The active-site cysteine of peroxiredoxins is selectively oxidized to cysteine sulfinic acid during catalysis, which leads to inactivation of peroxidase activity. This oxidation was thought to be irreversible. However, by metabolic labeling of mammalian cells with 35S, we show that the sulfinic form of peroxiredoxin I, produced during the exposure of cells to H2O2, is rapidly reduced to the catalytically active thiol form. The mammalian cells' ability to reduce protein sulfinic acid might serve as a mechanism to repair oxidatively damaged proteins or represent a new type of cyclic modification by which the function of various proteins is regulated.

Aberrant expression of peroxiredoxin subtypes in neurodegenerative disorders

An increasing body of evidence indicates that oxidative stress and damage play a role in the pathogenesis of a number of diseases associated with neurodegeneration, including Down syndrome (DS), Alzheimer's disease (AD) and Pick's disease (PD). Although oxidative stress is a common element in these diseases, specific clinico-pathological phenotypes have been described for each disorder. Development of these phenotypes might be linked, among others, to differences in antioxidant response. The present study is designed to investigate expression of peroxiredoxins (Prxs), the newly characterized family of highly conserved antioxidant enzymes, and other antioxidant enzymes in frontal cortex and cerebellum of DS, AD and PD patients using the technique of proteomics. Levels of Prx I, Mn superoxide dismutase (SOD2) and glutathione-S-transferase omega1 in DS, AD and PD were not significantly different from that of controls in both brain regions investigated. In contrast, Prx II was significantly increased (P<0.05) in frontal cortex of DS, AD and PD, whereas Prx III was decreased in frontal cortex of DS (P<0.01) and PD (P<0.001). Interestingly, Prx VI displayed a significant increase (P<0.05) only in PD frontal cortex. The present data indicate that differential regulation of antioxidant enzymes exist in DS, AD and PD, suggestive of the diversity as well as distinct functional roles of these proteins. Moreover, while up-regulation of Prx II appears to provide evidence for the existence of compensatory response in increased cell loss, up-regulation of Prx VI may be used to discriminate PD from AD as well as DS.

A putative glutathione peroxidase of Drosophila encodes a thioredoxin peroxidase that provides resistance against oxidative stress but fails to complement a lack of catalase activity

Cellular defense systems against reactive oxygen species (ROS) include thioredoxin reductase (TrxR) and glutathione reductase (GR). They generate sulfhydryl-reducing systems which are coupled to antioxidant enzymes, the thioredoxin and glutathione peroxidases (TPx and GPx). The fruit fly Drosophila lacks a functional GR, suggesting that the thioredoxin system is the major source for recycling glutathione. Whole genome in silico analysis identified two non-selenium containing putative GPx genes. We examined the biochemical characteristics of one of these gene products and found that it lacks GPx activity and functions as a TPx. Transgene-dependent overexpression of the newly identified Glutathione peroxidase homolog with thioredoxin peroxidase activity (Gtpx-1) gene increases resistance to experimentally induced oxidative stress, but does not compensate for the loss of catalase, an enzyme which, like GTPx-1, functions to eliminate hydrogen peroxide. The results suggest that GTPx-1 is part of the Drosophila Trx antioxidant defense system but acts in a genetically distinct pathway or in a different cellular compartment than catalase.

Genetic redox preconditioning differentially modulates AP-1 and NF kappa B responses following cardiac ischemia/reperfusion injury and protects against necrosis and apoptosis

Reactive oxygen species have been established as key mediators of cardiac injury following ischemia/reperfusion (I/R). We hypothesized that superoxide formation at different subcellular locations following cardiac I/R injury may differentially regulate cellular responses that determine pathophysiologic outcomes. Recombinant adenoviruses expressing Cu/ZnSOD or MnSOD were utilized to modulate superoxide levels in the cytoplasmic or mitochondrial compartments, respectively, prior to coronary artery I/R injury in the rat heart. Ectopic expression of both MnSOD and Cu/ZnSOD afforded protection from I/R injury, as evidenced by a significant reduction in serum creatine kinase levels, infarct size, malondialdehyde levels, and apoptotic cell death in comparison to controls. MnSOD and Cu/ZnSOD expression also significantly altered the kinetics of NF kappa B and AP-1 activation following I/R injury, characterized by a delayed induction of NF kappa B and abrogated AP-1 response. Western blot analysis of Bcl-2, Bcl-xL, Bad, Caspase 3, PDK1, and phospho-Akt also revealed SOD-mediated changes in gene expression consistent with protection and decreased apoptosis. These findings support the notion that both mitochondrial and cytoplasmic-derived SOD induce changes in AP-1 and NF kappa B activity, creating an antiapoptotic microenvironment within cardiomyocytes that affords protection following I/R injury.

Advances in our understanding of peroxiredoxin, a multifunctional, mammalian redox protein

Organisms living under aerobic conditions have developed various anti-oxidative mechanisms to protect them from damage by reactive oxygen species (ROS). A novel family of anti-oxidative proteins, designated as peroxiredoxin (Prx), has been identified in the past two decades and currently comprises six members in mammals. They share a common reactive Cys residue in the N-terminal region, and are capable of serving as a peroxidase and involve thioredoxin and/or glutathione as the electron donor. Prx1 to Prx4 have an additional Cys residue in the conserved C-terminal region, and are cross members as judged by the amino acid sequence similarity. Prx5 also contains an additional Cys in its C-terminal region which is less conserved. On the other hand, Prx6 has only one unique Cys. These Prx family members are distributed in the cytosol, mitochondria, peroxisome and plasma, all of which are potential sites of ROS production. In addition to their role as a peroxidase, however, a body of evidence has accumulated to suggest that individual members also serve divergent functions which are associated with various biological processes such as the detoxification of oxidants, cell proliferation, differentiation and gene expression. It would be expected that these functions might not necessarily depend on peroxidase activity and, therefore, it seems likely that the divergence is due to unique molecular characteristics intrinsic to each member. A comparative study of the divergence would lead to a better understanding of the biological significance of the Prx family.

Accumulation of 8-oxoguanine in the cellular DNA and the alteration of the OGG1 expression during ischemia-reperfusion injury in the rat kidney

During ischemia-reperfusion (I/R) injury in the rat kidney, apoptosis was observed in the distal tubules of the cortico-medullary region and outer medulla (OM) while severe necrosis was seen in the proximal straight tubules of the OM. The majority of these changes disappeared within 2 weeks. We examined the contents of 8-oxo-2'-deoxyguanosine (8-oxo-dG), which is a major type of oxidative damage in DNA, in the rat kidney during I/R injury, and also investigated the expression level of the OGG1 gene encoding the 8-oxoguanine DNA glycosylase. High-performance liquid chromatography with an MS/MS analysis of the nuclear DNA revealed an immediate accumulation of 8-oxo-dG in the nuclear DNA prepared from the cortex and OM of the kidney 1h after I/R, and an immunohistochemical analysis demonstrated the immediate accumulation of 8-oxo-dG in the nuclei of renal tubular cells both in the cortex and OM. A delayed increase of cytoplasmic staining with anti-8-oxo-dG was observed only in the cortico-medulla and OM, where the cytoplasmic staining in the proximal tubular cells is higher than in the distal tubular cells. The level of cytoplasmic staining representing 8-oxo-dG in mitochondrial DNA, peaked at 6h after I/R and preceded the necrosis of proximal tubular cells in the OM. An RNase protection assay showed a high level of OGG1 mRNA in the normal kidney, and the level decreased within 3h only in the OM, and increased thereafter 1-7 days of I/R both in the cortex and OM. In situ hybridization showed higher levels of OGG1 mRNA expression in the renal tubules in the OM than in the cortex of the normal kidney, which decreased rapidly within 3h of I/R. Thus, the accumulation of 8-oxo-dG in the mitochondrial DNA rather than in nuclear DNA is likely to be involved in the pathogenic responses such as necrosis of renal tubular cells during I/R injury of the kidney, together with an altered level of OGG1 expression.

Biological significance of phospholipid hydroperoxide glutathione peroxidase (PHGPx, GPx4) in mammalian cells

Reactive oxygen species (ROS) are known mediators of intracellular signal cascades. Excessive production of ROS may lead to oxidative stress, loss of cell function, and cell death by apoptosis or necrosis. Lipid hydroperoxides are one type of ROS whose biological function has not yet been clarified. Phospholipid hydroperoxide glutathione peroxidase (PHGPx, GPx4) is a unique antioxidant enzyme that can directly reduce phospholipid hydroperoxide in mammalian cells. This contrasts with most antioxidant enzymes, which cannot reduce intracellular phospholipid hydroperoxides directly. In this review, we focus on the structure and biological functions of PHGPx in mammalian cells. Recently, molecular techniques have allowed overexpression of PHGPx in mammalian cell lines, from which it has become clear that lipid hydroperoxides also have an important function as activators of lipoxygenase and cyclooxygenase, participate in inflammation, and act as signal molecules for apoptotic cell death and receptor-mediated signal transduction at the cellular level.

Peroxiredoxins in antioxidant defense and redox regulation

Peroxiredoxins constitute a family of peroxidases that lack prosthetic groups or catalytically active heteroatoms. Instead, their peroxidatic activity is due to a strictly conserved cysteine that is activated within a novel catalytic triad in which the cysteine thiol is coordinated to an arginine and a threonine or serine residue. Donor substrates are thiol compounds which differ between subtypes of peroxiredoxins and species. In pathogenic trypanosomatids that lack heme- or seleno-peroxidases peroxiredoxins have been shown to represent the major devices to detoxify hydroperoxides and an equivalent role may be assumed for other protozoal parasites and many bacterial pathogens. In mammals equipped with more efficient peroxidases the peroxiredoxins appear to be responsible for the redox regulation of diverse metabolic processes. The substantial differences in the cosubstrate requirements of the peroxiredoxins of pathogenic microorganisms and their mammalian host may be exploited to selectively inhibit the antioxidant defense of pathogens. Thereby, the pathogen would be more readily eliminated by the innate immune response of the host's phagocytes.

Profiling substrate phosphorylation at the phosphopeptide level

The identification of substrates is a key aspect in the study of the biological function of protein kinases. The procedure here described is aimed at profiling substrate phosphorylation at the phosphopeptide level by sequentially involving (i). the assessment of the in vitro activity of individual protein kinases on a complex mix of immobilized proteins, (ii). the fractionation of the phosphopeptides being released upon proteolysis of substrates, and (iii). the final identification of the targeted sequences. In particular, the protein sample is spotted onto nitrocellulose membrane and then subjected to a solid-phase kinase assay in the presence of [32P]ATP, prior to solid-phase proteolytic digestion and two-dimensional phosphopeptide mapping. Radiolabeled phosphopeptides are subsequently isolated and sequenced to identify the substrates being targeted by the examined protein kinase. Using the gamma-isotype of p21-activated protein kinase (gamma-PAK) and its known in vitro substrates, I verified that both the specificity of substrate phosphorylation and its efficiency are similar upon solid- and liquid-phase conditions. To demonstrate the feasibility of the overall experimental system, I then employed a fairly crude cell extract as a source of candidate substrates and successfully identified the sequence of a putative substrate of gamma-PAK.

Ceramide in apoptosis: an overview and current perspectives

Recent years have witnessed significant advances in the understanding of the role of ceramide in apoptosis. This review summarizes these recent findings and discusses insights from studies of ceramide metabolism, topology, and effector actions. The recent identification of several genes for enzymes of ceramide metabolism, the development of mass spectrometric methods for ceramide analysis, and the increasing molecular and pharmacological tools to probe ceramide metabolism and function promise an accelerated phase in defining the molecular and biochemical details of the role of ceramide in apoptosis.

Glutathione and thioredoxin redox during differentiation in human colon epithelial (Caco-2) cells

Cellular redox, maintained by the glutathione (GSH)- and thioredoxin (Trx)-dependent systems, has been implicated in the regulation of a variety of biological processes. The redox state of the GSH system becomes oxidized when cells are induced to differentiate by chemical agents. The aim of this study was to determine the redox state of cellular GSH/glutathione disulfide (GSH/GSSG) and Trx as a consequence of progression from proliferation to contact inhibition and spontaneous differentiation in colon carcinoma (Caco-2) cells. Results showed a significant decrease in GSH concentration, accompanied by a 40-mV oxidation of the cellular GSH/GSSG redox state and a 28-mV oxidation of the extracellular cysteine/cystine redox state in association with confluency and increase in differentiation markers. The redox state of Trx did not change. Thus the two central cellular antioxidant and redox-regulating systems (GSH and Trx) were independently controlled. According to the Nernst equation, a 30-mV oxidation is associated with a 10-fold change in the reduced/oxidized ratio of a redox-sensitive dithiol motif. Therefore, the measured 40-mV oxidation of the cellular GSH/GSSG couple or the 28-mV oxidation of the extracellular cysteine/cystine couple should be sufficient to function in signaling or regulation of differentiation in Caco-2 cells.

Overexpression of protein kinase Czeta confers protection against antileukemic drugs by inhibiting the redox-dependent sphingomyelinase activation

Induction of apoptosis by chemotherapeutic drugs involves the sphingomyelin-ceramide (SM-CER) pathway. This signaling is critically dependent on reactive oxygen species (ROS) generation and p53/p56 Lyn activation. In this study, we have investigated the influence of protein kinase C (PKC) zeta overexpression on the SM-CER pathway in U937 human leukemia cell line. We show that PKCzeta overexpression resulted in delayed apoptosis and significant resistance to both 1-beta-D-arabinofuranosylcytosine (ara-C) and daunorubicin (DNR), but there was no significant protection against cell-permeant C(6)-CER. Moreover, PKCzeta overexpression abrogated drug-induced neutral sphingomyelinase stimulation and CER generation by inhibiting ROS production. We further investigated p53/p56 Lyn activation in PKCzeta-overexpressing U937 cells treated with ara-C or DNR. We demonstrate that PKCzeta inhibited p53/p56 Lyn phosphorylation and stimulation in drug- or H(2)O(2)-treated cells, suggesting that p53/p56 Lyn redox regulation is altered in PKCzeta-overexpressing cells. Finally, we show that PKCzeta-overexpressing U937 cells displayed accelerated H(2)O(2) detoxification. Altogether, our study provides evidence for the role of PKCzeta in the negative regulation of drug-induced SM-CER pathway.

Trends in selenium biochemistry

The biochemistry of selenium-containing natural products, including selenoproteins, is reviewed up to May 2002. Particular emphasis is placed on the assimilation of selenium from inorganic and organic selenium sources for selenoprotein synthesis, the catalytic role of selenium in enzymes, and medical implications of an unbalanced selenium supply. The review contains 393 references on key discoveries and recent progress.

Glutathione peroxidase-1 protects from CD95-induced apoptosis

Through the induction of apoptosis, CD95 plays a crucial role in the immune response and the elimination of cancer cells. Ligation of CD95 receptor activates a complex signaling network that appears to implicate the generation of reactive oxygen species (ROS). This study investigated the place of ROS production in CD95-mediated apoptosis and the role of the antioxidant enzyme glutathione peroxidase-1 (GPx1). Anti-CD95 antibodies triggered an early generation of ROS in human breast cancer T47D cells that was blocked by overexpression of GPx1 and inhibition of initiator caspase activation. Enforced expression of GPx1 also resulted in inhibition of CD95-induced effector caspase activation, DNA fragmentation, and apoptotic cell death. Resistance to CD95-mediated apoptosis was not due to an increased expression of anti-apoptotic molecules and could be reversed by glutathione-depleting agents. In addition, whereas the anti-apoptotic protein Bcl-xL prevented CD95-induced apoptosis in MCF-7 cells, it did not inhibit the early ROS production. Moreover, Bcl-xL but not GPx1 overexpression could suppress the staurosporine-induced late generation of ROS and subsequent cell death. Altogether, these findings suggest that GPx1 functions upstream of the mitochondrial events to inhibit the early ROS production and apoptosis induced by CD95 ligation. Finally, transgenic mice overexpressing GPx1 were partially protected from the lethal effect of anti-CD95, underlying the importance of peroxide formation (and GPx1) in CD95-triggered apoptosis.

Expression of the p75 TNF receptor is linked to TNF-induced NFkappaB translocation and oxyradical neutralization in glial cells

Tumor necrosis factor (TNF)-family cytokines induce reactive oxygen species (ROS) that injure vulnerable populations of brain cells. Among glia, oligodendrocytes are particularly susceptible to TNF-induced ROS whereas microglia are protected. We previously found that oligodendrocytes in vitro predominantly express the p55 type-1 TNF receptor, while microglial cells express both type-1 and p75 type-2 receptors. We hypothesized that differential TNF receptor expression and attendant signaling underlies the relative vulnerability of oligodendrocytes, versus microglia, to TNF-induced injury. To test this hypothesis, purified cultures of glial cells were incubated 0-48 hr with TNFalpha or lymphotoxin-alpha, following which levels of ROS, glutathione (GSH), nuclear factor kappa-B (NFkappaB) translocation, and anti-oxidant proteins and activity were measured. 48 hr exposure to TNF increased ROS levels 28% and decreased GSH levels 17% in oligodendrocytes, but decreased levels ROS levels 24% and increased GSH levels 112% increase in microglia. Thirty to 180 min exposure to TNF increased NFkappaB nuclear translocation to a greater extent and for a longer time in microglia versus oligodendrocytes, and this was followed 24-48 hr later with 3- to 13-fold increases in microglia manganese superoxide dismutase protein levels and 6-fold increases in enzyme activity. Collectively, these data suggest that signals transduced through the p75 receptor activate anti-oxidant mechanisms that protect microglia from TNF-induced injury. Lacking such signals, oligodendrocytes are considerably more vulnerable to the injurious effects of TNF.

Synthetic ceramides induce growth arrest or apoptosis by altering cellular redox status

Reactive oxygen species (ROS) and ceramide are each partly responsible for the signal transduction of a variety of extracellular agents. Furthermore, the application of synthetic, short-chain ceramides mimics the cellular responses to these extracellular agents. However, the significance of ROS involvement in ceramide signaling pathways is poorly understood. Here we describe that the cellular responses to C2-/C6-ceramide of growth arrest in U937 monocytes and apoptosis in Jurkat T-cells are preceded by a rise in mitochondrial peroxide production. In Jurkat T-cells, this is associated with a large time- and dose-dependent loss of cellular glutathione. However, in U937 monocytes, glutathione loss is transient. Differences in the magnitude and kinetics of this alteration in cellular redox state associate with discrete outcomes, namely growth arrest or apoptosis.

Inactivation of human peroxiredoxin I during catalysis as the result of the oxidation of the catalytic site cysteine to cysteine-sulfinic acid

By following peroxiredoxin I (Prx I)-dependent NADPH oxidation spectrophotometrically, we observed that Prx I activity decreased gradually with time. The decay in activity was coincident with the conversion of Prx I to a more acidic species as assessed by two-dimensional gel electrophoresis. Mass spectral analysis and studies with Cys mutants determined that this shift in pI was due to selective oxidation of the catalytic site Cys(51)-SH to Cys(51)-SO(2)H. Thus, Cys(51)-SOH generated as an intermediate during catalysis appeared to undergo occasional further oxidation to Cys(51)-SO(2)H, which cannot be reversed by thioredoxin. The presence of H(2)O(2) alone was not sufficient to cause oxidation of Cys(51) to Cys(51)-SO(2)H. Rather, the presence of complete catalytic components (H(2)O(2), thioredoxin, thioredoxin reductase, and NADPH) was necessary, indicating that such hyperoxidation occurs only when Prx I is engaged in the catalytic cycle. Likewise, hyperoxidation of Cys(172)/Ser(172) mutant Prx I required not only H(2)O(2), but also a catalysis-supporting thiol (dithiothreitol). Kinetic analysis of Prx I inactivation in the presence of a low steady-state level (<1 microm) of H(2)O(2) indicated that Prx I was hyperoxidized at a rate of 0.072% per turnover at 30 degrees C. Hyperoxidation of Prx I was also detected in HeLa cells treated with H(2)O(2).

A549 subclones demonstrate heterogeneity in toxicological sensitivity and antioxidant profile

In A549 cell culture, significant variability was found in sensitivity to actinomycin D. Using limiting dilution, actinomycin D-susceptible (G4S) and -resistant (D3R) subclones were isolated. G4S cells were also susceptible to protein synthesis inhibitors, a redox cycling quinone, and an electrophile with concomitant activation of caspases 3 and 9. D3R cells were resistant to these agents without caspase activation. Antioxidant profiles revealed that D3R cells had significantly higher glutathione and glutathione reductase activity but markedly lower catalase, glutathione peroxidase, and aldehyde reductase activities than G4S cells. Thus A549 cells contain at least two distinct subpopulations with respect to predisposition to cell death and antioxidant profile. Because sensitivities to agents and the antioxidant profile were inconsistent, mechanisms independent of antioxidants, including the apparent inability to activate caspases in D3R cells, may play an important role. Regardless, the results suggest that antioxidant profiles of asymmetrical cell populations cannot predict sensitivity to oxidants and warn that the use of single subclones is advisable for mechanistic studies using A549 or other unstable cell lines.

DNA microarray reveals increased expression of thioredoxin peroxidase in thioredoxin-1 transfected cells and its functional consequences

The mammalian thioredoxins are a family of small redox proteins that undergo NADPH dependent reduction by thioredoxin reductase. Reduced thioredoxins reduce oxidized cysteine groups on proteins including transcription factors to increase their binding to DNA, and is a source of reducing equivalents for enzymes such as thioredoxin peroxidase which removes H2O2 and alkyl peroxides. Thioredoxin-1 is over expressed in many human tumors where it is associated with aggressive tumor growth, inhibited apoptosis and decreased patient survival. Transfection of cells with thioredoxin-1 has been shown to increase cell growth and inhibit apoptosis. We have used DNA micro array to investigate the effects of thioredoxin-1 transfection on the expression of a panel of 520 redox, apoptosis and cell growth related genes in MCF-7 human breast cancer cells. One of the genes whose expression was increased as a result of thioredoxin-1 over expression was thioredoxin peroxidase-2. This increase was confirmed by Northern blotting. Transfection of mouse WEHI7.2 thymoma cells with human thioredoxin peroxidase-2 was found to protect the cells from apoptosis induced by H2O2 but not from apoptosis induced by dexamethasone, doxorubicin or etoposide. Thus, increased thioredoxin peroxidase-2 expression does not explain the widespread antiapoptotic effects of thioredoxin-1.

Ceramide channels increase the permeability of the mitochondrial outer membrane to small proteins

Ceramides are known to play a major regulatory role in apoptosis by inducing cytochrome c release from mitochondria. We have previously reported that C(2)- and C(16)-ceramide, but not dihydroceramide, form large channels in planar membranes (Siskind, L. J., and Colombini, M. (2001) J. Biol. Chem. 275, 38640-38644). Here we show that ceramides do not trigger a cytochrome c secretion or release mechanism, but simply raise the permeability of the mitochondrial outer membrane, via ceramide channel formation, to include small proteins. Exogenously added reduced cytochrome c was able to freely permeate the mitochondrial outer membrane with entry to and exit from the intermembrane space facilitated by ceramides in a dose- and time-dependent manner. The permeability pathways were eliminated upon removal of C(2)-ceramide by bovine serum albumin, thus ruling out a detergent-like effect of C(2)-ceramide on membranes. Ceramide channels were not specific to cytochrome c, as ceramides induced release of adenylate kinase, but not fumerase from isolated mitochondria, showing some specificity of these channels for the outer mitochondrial membrane. SDS-PAGE results show that ceramides allow release of intermembrane space proteins with a molecular weight cut-off of about 60,000. These results indicate that the ceramide-induced membrane permeability increases in isolated mitochondria are via ceramide channel formation and not a release mechanism, as the channels that allow cytochrome c to freely permeate are reversible, and are not specific to cytochrome c.

Regulation of peroxiredoxin I activity by Cdc2-mediated phosphorylation

Hydrogen peroxide is implicated as an intracellular messenger in various cellular responses such as proliferation and differentiation. Peroxiredoxin (Prx) I is a member of the peroxiredoxin family of peroxidases and contains a consensus site (Thr(90)-Pro-Lys-Lys) for phosphorylation by cyclin-dependent kinases (CDKs). This protein has now been shown to be phosphorylated specifically on Thr(90) by several CDKs, including Cdc2, in vitro. Phosphorylation of Prx I on Thr(90) reduced the peroxidase activity of this protein by 80%. The phosphorylation of Prx I in HeLa cells was monitored with the use of antibodies specific for Prx I phosphorylated on Thr(90). Immunoblot analysis with these antibodies of HeLa cells arrested at various stages of the cell cycle revealed that Prx I phosphorylation occurs in parallel with the activation of Cdc2; Prx I phosphorylation was thus marked during mitosis but virtually undetectable during interphase. Furthermore, when Cdc2 expression was reduced by RNA interference with cognate small interfering RNAs, Prx I phosphorylation was not observed in the cells synchronized in mitotic phase. The cytosolic location of Prx I likely prevents its interaction with activated CDKs until after the breakdown of the nuclear envelope during mitosis, when Cdc2 is the CDK that is most active. Phosphorylation of Prx I on Thr(90) both in vitro and in vivo was blocked by roscovitine, an inhibitor of CDKs. These results suggest that Cdc2-mediated phosphorylation and inactivation of Prx I and the resulting intracellular accumulation of H(2)O(2) might be important for progression of the cell cycle.

Protein levels of human peroxiredoxin subtypes in brains of patients with Alzheimer's disease and Down syndrome

Human peroxiredoxin (Prx) play important roles in eliminating hydrogen peroxide generated during cellular mechanisms using electrons from thioredoxin (Trx). Oxidative stress induced by reactive oxygen species (ROS) such as hydrogen peroxide has been implicated in the pathogenesis of several neurodegenerative diseases. We applied the proteomic approach to study protein levels of three subtypes of human Prx in brain regions from patients with Alzheimer's disease (AD) and Down Syndrome (DS). Protein levels of Prx-I and Prx-II were significantly increased in AD and DS. Protein levels of Prx-III, a mitochondrial protein, however, were significantly decreased. We conclude that increased protein levels of Prx-I and Prx-II could provide protection against neuronal cell death induced by hydrogen peroxide. Decreased protein levels of Prx-III could be caused by mitochondrial damage shown in AD and DS. Showing upregulated Prx protein levels provides evidence for the involvement of ROS in the pathogenesis of AD and DS.

Redox control of cell death

Cellular redox is controlled by the thioredoxin (Trx) and glutathione (GSH) systems that scavenge harmful intracellular reactive oxygen species (ROS). Oxidative stress also evokes many intracellular events including apoptosis. There are two major pathways through which apoptosis is induced; one involves death receptors and is exemplified by Fas-mediated caspase-8 activation, and another is the stress- or mitochondria-mediated caspase-9 activation pathway. Both pathways converge on caspase-3 activation, resulting in nuclear degradation and cellular morphological change. Oxidative stress induces cytochrome c release from mitochondria and activation of caspases, p53, and kinases, including apoptosis signal-regulating kinase 1 (ASK1), c-Jun N-terminal kinase, and p38 mitogen-activated protein kinase. Trx inhibits apoptosis signaling not only by scavenging intracellular ROS in cooperation with the GSH system, but also by inhibiting the activity of ASK1 and p38. Mitochondria-specific thioredoxin (Trx-2) and Trx peroxidases (peroxiredoxins) are suggested to regulate cytochrome c release from mitochondria, which is a critical early step in the apoptotis-signaling pathway. dATP/ATP and reducing factors including Trx determine the manifestation of cell death, apoptosis or necrosis, by regulating the activation process and the activity of redox-sensitive caspases. As mitochondria are the most redox-active organelle and indispensable for cells to initiate or inhibit the apoptosis process, the regulation of mitochondrial function is the central focus in the research field of apoptosis and redox.

Detection of cathepsin B up-regulation in neoplastic thyroid tissues by proteomic analysis

Nodular or multinodular goiter is the most common non-neoplastic thyroid disease and may be difficult to distinguish from true neoplastic thyroid diseases using microscopic criteria. We have used two-dimensional gel electrophoresis to study the protein patterns of thyroid tissues including normal thyroid, multinodular goiter, diffuse hyperplasia, follicular adenoma, follicular carcinoma and papillary carcinoma. Specific proteins, in the region of molecular mass 15-30 kDa and isoelectric point 4.5-6.5, were identified by electrospray tandem mass spectrometry and protein sequencing. The most distinctive protein found is cathepsin B, which could be detected as four spots, with differential expression in different thyroid diseases. In particular, two of these cathepsin B spots CB2 and CB3 are strongly up-regulated in neoplastic diseases, compared to non-neoplastic diseases. In addition, overexpression of ATP synthase D chain and prohibitin were observed in papillary carcinoma, which should allow it to be differentiated from follicular carcinoma. Changes in expression of other proteins were also observed in disease states compared to normal tissues, namely translationally controlled tumor protein, thioredoxin peroxidase 1, glutathione-S-transferase P, DJ-1 protein, superoxide dismutase (Cu, Zn), and heat shock protein 27, but these changes are less characteristic, so they do not allow the differentiation between neoplastic and non-neoplastic tissues. Thus, the proteomic approach is a useful diagnostic tool for studying diseases involving the thyroid nodule.

Proteomics analysis of cellular response to oxidative stress. Evidence for in vivo overoxidation of peroxiredoxins at their active site

The proteomics analysis reported here shows that a major cellular response to oxidative stress is the modification of several peroxiredoxins. An acidic form of the peroxiredoxins appeared to be systematically increased under oxidative stress conditions. Peroxiredoxins are enzymes catalyzing the destruction of peroxides. In doing so, a reactive cysteine in the peroxiredoxin active site is weakly oxidized (disulfide or sulfenic acid) by the destroyed peroxides. Cellular thiols (e.g. thioredoxin) are used to regenerate the peroxiredoxins to their active state. Tandem mass spectrometry was carried out to characterize the modified form of the protein produced in vivo by oxidative stress. The cysteine present in the active site was shown to be oxidized into cysteic acid, leading to an inactivated form of peroxiredoxin. This strongly suggested that peroxiredoxins behave as a dam upon oxidative stress, being both important peroxide-destroying enzymes and peroxide targets. Results obtained in a primary culture of Leydig cells challenged with tumor necrosis factor alpha suggested that this oxidized/native balance of peroxiredoxin 2 may play an active role in resistance or susceptibility to tumor necrosis factor alpha-induced apoptosis.