Regulation of 1-cys peroxiredoxin expression in lung epithelial cells

Peroxiredoxin 6 Knockout Mice Demonstrate Anxiety Behavior and Attenuated Contextual Fear Memory after Receiving Acute Immobilization Stress

Stress can elicit glucocorticoid release to promote coping mechanisms and influence learning and memory performance. Individual memory performance varies in response to stress, and the underlying mechanism is not clear yet. Peroxiredoxin 6 (PRDX6) is a multifunctional enzyme participating in both physiological and pathological conditions. Several studies have demonstrated the correlation between PRDX6 expression level and stress-related disorders. Our recent finding indicates that lack of the Prdx6 gene leads to enhanced fear memory. However, it is unknown whether PRDX6 is involved in changes in anxiety response and memory performance upon stress. The present study reveals that hippocampal PRDX6 level is downregulated 30 min after acute immobilization stress (AIS) and trace fear conditioning (TFC). In human retinal pigment epithelium (ARPE-19) cells, the PRDX6 expression level decreases after being treated with stress hormone corticosterone. Lack of PRDX6 caused elevated basal H₂O₂ levels in the hippocampus, basolateral amygdala, and medial prefrontal cortex, brain regions involved in anxiety response and fear memory formation. Additionally, this H₂O₂ level was still high in the medial prefrontal cortex of the knockout mice under AIS. Anxiety behavior of Prdx6^-/- mice was enhanced after immobilization for 30 min. After exposure to AIS before a contextual test, Prdx6^-/- mice displayed a contextual fear memory deficit. Our results showed that the memory performance of Prdx6^-/- mice was impaired when responding to AIS, accompanied by dysregulated H₂O₂ levels. The present study helps better understand the function of PRDX6 in memory performance after acute stress.

Peroxiredoxin 6 Inhibits Osteogenic Differentiation and Bone Formation Through Human Dental Pulp Stem Cells and Induces Delayed Bone Development

Aims: Peroxiredoxins (PRDXs) are thiol-specific antioxidant enzymes that regulate redox balance that are critical for maintaining the cellular potential for self-renewal and stemness. Stem cell-based regenerative medicine is a promising approach in tissue reconstruction. However, to obtain functional cells for use in clinical applications, stem cell technology still requires improvements. Results: In this study, we found that PRDX6 levels were decreased during osteogenic differentiation in human dental pulp stem cells (hDPSCs). hDPSCs stably expressing Myc-PRDX6 (hDPSC/myc-PRDX6) inhibited cell growth in hDPSCs during osteogenic differentiation and impaired osteogenic phenotypes such as alkaline phosphatase (ALP) activity, mineralized nodule formation, and osteogenic marker genes [ALP and osteocalcin (OCN)]. hDPSC cell lines stably expressing mutant glutathione peroxidase (PRDX6(C47S)) and independent phospholipase A2 (PRDX6(S32A)) were also generated. Each mutant form of PRDX6 abolished the impaired osteogenic phenotypes, the transforming growth factor-β-mediated Smad2 and p38 pathways, and RUNX2 expression. Furthermore, in vivo experiments revealed that hDPSC/myc-PRDX6 suppressed hDPSC-based bone regeneration in calvarial defect mice, and newborn PRDX6 transgenic mice exhibited delayed bone development and reduced RUNX2 expression. Innovation and Conclusion: These findings illuminate the effects of PRDX6 during osteogenic differentiation of hDPSCs, and also suggest that regulating PRDX6 may improve the clinical utility of stem cell-based regenerative medicine for the treatment of bone diseases. Antioxid. Redox Signal. 30, 1969-1982.

Peroxiredoxin6 in Endothelial Signaling

Peroxiredoxins (Prdx) are a ubiquitous family of highly conserved antioxidant enzymes with a cysteine residue that participate in the reduction of peroxides. This family comprises members Prdx1–6, of which Peroxiredoxin 6 (Prdx6) is unique in that it is multifunctional with the ability to neutralize peroxides (peroxidase activity) and to produce reactive oxygen species (ROS) via its phospholipase (PLA₂) activity that drives assembly of NADPH oxidase (NOX2). From the crystal structure, a C47 residue is responsible for peroxidase activity while a catalytic triad (S32, H26, and D140) has been identified as the active site for its PLA₂ activity. This paradox of being an antioxidant as well as an oxidant generator implies that Prdx6 is a regulator of cellular redox equilibrium (graphical abstract). It also indicates that a fine-tuned regulation of Prdx6 expression and activity is crucial to cellular homeostasis. This is specifically important in the endothelium, where ROS production and signaling are critical players in inflammation, injury, and repair, that collectively signal the onset of vascular diseases. Here we review the role of Prdx6 as a regulator of redox signaling, specifically in the endothelium and in mediating various pathologies.

Deficiency of peroxiredoxin 6 or inhibition of its phospholipase A2 activity impair the in vitro sperm fertilizing competence in mice

Prdx6 -/- male mice are subfertile, and the deficiency or inactivation of Peroxiredoxins (PRDXs) is associated with human male infertility. We elucidate the impact of the lack of PRDX6 or inhibition of its calcium-independent phospholipase A2 (Ca2+-iPLA2) activity by MJ33 on fertilization competence of mouse spermatozoa. Sperm motility, viability, fertilization and blastocyst rates were lower in Prdx6 -/- spermatozoa than in C57BL/6J wild-type (WT) controls (p ≤ 0.05). MJ33 inhibited the PRDX6 Ca2+-iPLA2 activity and reduced these parameters in WT spermatozoa compared with controls (p ≤ 0.05). Levels of lipid peroxidation and of superoxide anion (O2•─) were higher in Prdx6 -/- than in WT spermatozoa (p ≤ 0.05). MJ33 increased the levels of lipid peroxidation and mitochondrial O2•─ production in treated versus non-treated WT spermatozoa. Acrosome reaction, binding to zona pellucida and fusion with the oolemma were lower in Prdx6 -/- capacitated spermatozoa than WT capacitated controls and lower in WT spermatozoa treated with the PRDX6 inhibitor. In conclusion, the inhibition of the PRDX6 Ca2+-iPLA2 activity promotes an oxidative stress affecting viability, motility, and the ability of mouse spermatozoa to fertilize oocytes. Thus, PRDX6 has a critical role in the protection of the mouse spermatozoon against oxidative stress to assure fertilizing competence.

Peroxiredoxin 6 in the repair of peroxidized cell membranes and cell signaling

Peroxiredoxin 6 represents a widely distributed group of peroxiredoxins that contain a single conserved cysteine in the protein monomer (1-cys Prdx). The cys when oxidized to the sulfenic form is reduced with glutathione (GSH) catalyzed by the π isoform of GSH-S-transferase. Three enzymatic activities of the protein have been described:1) peroxidase with H2O2, short chain hydroperoxides, and phospholipid hydroperoxides as substrates; 2) phospholipase A2 (PLA2); and 3) lysophosphatidylcholine acyl transferase (LPCAT). These activities have important physiological roles in antioxidant defense, turnover of cellular phospholipids, and the generation of superoxide anion via initiation of the signaling cascade for activation of NADPH oxidase (type 2). The ability of Prdx6 to reduce peroxidized cell membrane phospholipids (peroxidase activity) and also to replace the oxidized sn-2 fatty acyl group through hydrolysis/reacylation (PLA2 and LPCAT activities) provides a complete system for the repair of peroxidized cell membranes.

Screening and functional analysis of the peroxiredoxin specifically expressed in Bursaphelenchus xylophilus--the causative agent of pine wilt disease

The pine wood nematode, Bursaphelenchus xylophilus, is the causal agent of pine wilt disease. Accurately differentiating B. xylophilus from other nematodes species, especially its related species B. mucronatus, is important for pine wood nematode detection. Thus, we attempted to identify a specific protein in the pine wood nematode using proteomics technology. Here, we compared the proteomes of B. xylophilus and B. mucronatus using Two-dimensional gel electrophoresis (2-DE) and matrix-assisted laser desorption/ionization-time-of-flight/time-of-flight (MALDI-TOF/TOF-MS) technologies. In total, 15 highly expressed proteins were identified in B. xylophilus compared with B. mucronatus. Subsequently, the specificity of the proteins identified was confirmed by PCR using the genomic DNA of other nematode species. Finally, a gene encoding a specific protein (Bx-Prx) was obtained. This gene was cloned and expressed in E. coli. The in situ hybridisation pattern of Bx-Prx showed that it was expressed strongly in the tail of B. xylophilus. RNAi was used to assess the function of Bx-Prx, the results indicated that the gene was associated with the reproduction and pathogenicity of B. xylophilus. This discovery provides fundamental information for identifying B. xylophilus via a molecular approach. Moreover, the purified recombinant protein has potential as a candidate diagnostic antigen of pine wilt disease, which may lead to a new immunological detection method for the pine wood nematode.

Keratinocyte growth factor and glucocorticoid induction of human peroxiredoxin 6 gene expression occur by independent mechanisms that are synergistic

AIMS

Peroxiredoxin 6 (Prdx6), a 1-cys Prdx has both peroxidase and phospholipase A2 activities, protecting against oxidative stress and regulating pulmonary surfactant phospholipid metabolism. This study determined the mechanism by which keratinocyte growth factor (KGF) and the glucocorticoid analogue, dexamethasone (Dex), induce increased Prdx6 expression.

RESULTS

Transcriptional activation by KGF in both A549 lung adenocarcinoma cells and rat lung alveolar epithelial type II (ATII) cells utilizes an antioxidant response element (ARE), located between 357 and 349 nucleotides before the PRDX6 translational start, that is also necessary for upregulation of the human PRDX6 promoter in response to oxidative stress. Activation is mediated by binding of the transcription factor, Nrf2, to the ARE as shown by experiments using siRNA against Nrf2 and by transfecting ATII cells isolated from lungs of Nrf2 null mice. KGF triggers the migration of Nrf2 from cytoplasm to nucleus where it binds to the PRDX6 promoter as shown by chromatin immunoprecipitation assays. Activation of transcription by Dex occurs through a glucocorticoid response element located about 750 nucleotides upstream of the PRDX6 translational start.

INNOVATION

This study demonstrates that KGF can activate an ARE in a promoter without reactive oxygen species involvement and that KGF and Dex can synergistically activate the PRDX6 promoter and protect cells from oxidative stress.

CONCLUSION

These two different activators work through different DNA elements. Their combined effect on transcription of the reporter gene is synergistic; however, at the protein level, the combined effect is additive and protects cells from oxidative damage.

Oxidative stress and the antioxidant enzyme system in the developing brain

Preterm infants are vulnerable to the oxidative stress due to the production of large amounts of free radicals, antioxidant system insufficiency, and immature oligodendroglial cells. Reactive oxygen species (ROS) play a pivotal role in the development of periventricular leukomalacia. The three most common ROS are superoxide (O2^•-), hydroxyl radical (OH^•), and hydrogen peroxide (H₂O₂). Under normal physiological conditions, a balance is maintained between the production of ROS and the capacity of the antioxidant enzyme system. However, if this balance breaks down, ROS can exert toxic effects. Superoxide dismutase, glutathione peroxidase, and catalase are considered the classical antioxidant enzymes. A recently discovered antioxidant enzyme family, peroxiredoxin (Prdx), is also an important scavenger of free radicals. Prdx1 expression is induced at birth, whereas Prdx2 is constitutively expressed, and Prdx6 expression is consistent with the classical antioxidant enzymes. Several antioxidant substances have been studied as potential therapeutic agents; however, further preclinical and clinical studies are required before allowing clinical application.

Expression of peroxiredoxin 1, 2, and 6 in the rat brain during perinatal development and in response to dexamethasone

Peroxiredoxins (Prdx), a family of antioxidant proteins, have important defensive roles in the degenerative brain diseases and neuronal cell death in adult subjects. However, little is known in the neonatal brain. Here, we studied the developmental expression of Prdxs and their response to dexamethasone in the perinatal rat brain. Prdx 1 expression increased during late gestations and peaked at postnatal-day 1, when its expression gradually decreased. Prdx 2 expression remained largely unchanged. Prdx 6 expression continually increased as growing. Using immunohistochemistry, each Prdx showed a strong expression in the cerebral cortex and hippocampus. Prdx 1 was strongly expressed in the corpus callosum. The dexamethasone injection increased the expression of Prdx 6. In conclusion, we reveal for the first time that Prdx 1, 2 and 6 are found in abundance in the perinatal rat brain and are differentially expressed during development. The expression of Prdx 6 was affected by dexamethasone treatment.

Antioxidant capacity develops with maturation in the deep-diving hooded seal

Maturation in hooded seals is characterized by the rapid development of their physiological diving capacity and is accompanied by increases in oxidant production but not oxidative damage. To test the hypothesis that the antioxidant system of hooded seals develops as they transition from a terrestrial to an aquatic environment, we obtained the complete cDNA sequence that encodes the NF-E2-related factor 2 (Nrf2), a central regulator of the antioxidant response, and compared Nrf2 mRNA and protein expression levels in muscle samples from neonate, weaned pups and adult hooded seals, along with glutathione (GSH) levels and the activity/protein content of the antioxidant enzymes catalase, glutathione peroxidase (GPx), peroxyredoxin VI (PrxVI), thioredoxin 1 (Trx1), thioredoxin reductase (TrxR), glutaredoxin 1 (Glrx1), glutathione disulphide reductase, glutathione S-transferase and glutamate-cysteine ligase. The Nrf2 of the hooded seal is 1822 bp long and encodes a protein of 606 amino acids with a leucine zipper domain and Keap1-mediated proteosomal degradation residues, which are key for Nrf2 function and regulation. Although neither Nrf2 mRNA nor Nrf2 nuclear protein content are higher in adults than in pups, GSH levels along with GPx, PrxVI, Trx1, TrxR and Glrx1 activity/protein content increase with maturation, suggesting that the potential for peroxide removal increases with development in hooded seals, and that these enzymes contribute to the regulation of the intracellular redox state and the prevention of oxidative damage in these deep-diving mammals.

Peroxiredoxin 6: a bifunctional enzyme with glutathione peroxidase and phospholipase A₂ activities

Peroxiredoxin 6 (Prdx6) is the prototype and the only mammalian 1-Cys member of the Prdx family. Major differences from 2-Cys Prdxs include the use of glutathione (GSH) instead of thioredoxin as the physiological reductant, heterodimerization with πGSH S-transferase as part of the catalytic cycle, and the ability either to reduce the oxidized sn-2 fatty acyl group of phospholipids (peroxidase activity) or to hydrolyze the sn-2 ester (alkyl) bond of phospholipids (phospholipase A(2) [PLA(2)] activity). The bifunctional protein has separate active sites for peroxidase (C47, R132, H39) and PLA(2) (S32, D140, H26) activities. These activities are dependent on binding of the protein to phospholipids at acidic pH and to oxidized phospholipids at cytosolic pH. Prdx6 can be phosphorylated by MAP kinases at T177, which markedly increases its PLA(2) activity and broadens its pH-activity spectrum. Prdx6 is primarily cytosolic but also is targeted to acidic organelles (lysosomes, lamellar bodies) by a specific targeting sequence (amino acids 31-40). Oxidant stress and keratinocyte growth factor are potent regulators of Prdx6 gene expression. Prdx6 has important roles in both antioxidant defense based on its ability to reduce peroxidized membrane phospholipids and in phospholipid homeostasis based on its ability to generate lysophospholipid substrate for the remodeling pathway of phospholipid synthesis.

Cloning and characterization of a 2-cys peroxiredoxin in the pine wood nematode, Bursaphelenchus xylophilus, a putative genetic factor facilitating the infestation

The pine wood nematode, Bursaphelenchus xylophilus, is an invasive plant parasitic nematode and a worldwide quarantine pest. An indigenous species in North America and the causal agent of pine wilt disease, B. xylophilus has devastated pine production in Southeastern Asia including Japan, China, and Korea since its initial introduction in the early 1900s. The reactive oxygen species (ROS) is the first line of defense utilized by host plants against parasites, while nematodes, counteractively, employ antioxidants to facilitate their infection. Peroxiredoxins (Prxs) are a large class of antioxidants recently found in a wide variety of organisms. In this report, a gene encoding a novel 2-cysteine peroxiredoxin protein in B. xylophilus was cloned and characterized. The 2-cysteine peroxiredoxin in B. xylophilus (herein refers to as "BxPrx") is highly conserved in comparison to 2-cysteine peroxiredoxins (Prx2s) in other nematodes, which have two conserved cysteine amino acids (Cp and Cr), a threonine-cysteine-arginine catalytic triad, and two signature motifs (GGLG and YF) sensitive to hydrogen peroxide. In silico assembly of BxPrx tertiary structure reveals the spatial configuration of these conserved domains and the simulated BxPrx 3-dimensional structure is congruent with its presumed redox functions. Although no signal peptide was identified, BxPrx was abundantly expressed and secreted under the B. xylophilus cuticle. Upon further analysis of this leader-less peptide, a single transmembrane α-helix composed of 23 consecutive hydrophobic amino acids was found in the primary structure of BxPrx. This transmembrane region and/or readily available ATP binding cassette transporters may facilitate the transport of non-classical BxPrx across the cell membrane. Recombinant BxPrx showed peroxidase activity in vitro reducing hydrogen peroxide using glutathione as the electron donor. The combined results from gene discovery, protein expression and distribution profiling (especially the "surprising" presence under the nematode cuticle), and recombinant antioxidant activity suggest that BxPrx plays a key role in combating the oxidative burst engineered by the ROS defense system in host plants during the infection process. In summary, BxPrx is a genetic factor potentially facilitating B. xylophilus infestation.

Protein expression profiling of lens epithelial cells from Prdx6-depleted mice and their vulnerability to UV radiation exposure

Oxidative stress is one of the causative factors in progression and etiology of age-related cataract. Peroxiredoxin 6 (Prdx6), a savior for cells from internal or external environmental stresses, plays a role in cellular signaling by detoxifying reactive oxygen species (ROS) and thereby controlling gene regulation. Using targeted inactivation of the Prdx6 gene, we show that Prdx6-deficient lens epithelial cells (LECs) are more vulnerable to UV-triggered cell death, a major cause of skin disorders including cataractogenesis, and these cells display abnormal protein profiles. PRDX6-depleted LECs showed phenotypic changes and formed lentoid body, a characteristic of terminal cell differentiation and epithelial-mesenchymal transition. Prdx6(-/-) LECs exposed to UV-B showed higher ROS expression and were prone to apoptosis compared with wild-type LECs, underscoring a protective role for Prdx6. Comparative proteomic analysis using fluorescence-based difference gel electrophoresis along with mass spectrometry and database searching revealed a total of 13 proteins that were differentially expressed in Prdx6(-/-) cells. Six proteins were upregulated, whereas expression of seven proteins was decreased compared with Prdx6(+/+) LECs. Among the cytoskeleton-associated proteins that were highly expressed in Prdx6-deficient LECs was tropomyosin (Tm)2beta. Protein blot and real-time PCR validated dramatic increase of Tm2beta and Tm1alpha expression in these cells. Importantly, Prdx6(+/+) LECs showed a similar pattern of Tm2beta protein expression after transforming growth factor (TGF)-beta or H(2)O(2) treatment. An extrinsic supply of PRDX6 could restore Tm2beta expression, demonstrating that PRDX6 may attenuate adverse signaling in cells and thereby maintain cellular homeostasis. Exploring redox-proteomics (Prdx6(-/-)) and characterization and identification of abnormally expressed proteins and their attenuation by PRDX6 delivery should provide a basis for development of novel therapeutic interventions to postpone ROS-mediated abnormal signaling deleterious to cells or tissues.

Comparative proteomics profile of osteoblasts cultured on dissimilar hydroxyapatite biomaterials: an iTRAQ-coupled 2-D LC-MS/MS analysis

Hydroxyapatite (HA) and its derived bioceramic materials have been widely used for skeletal implants and/or bone repair scaffolds. It has been reported that carbon nanotube (CNT) is able to enhance the brittle ceramic matrix without detrimental to the bioactivity. However, interaction between osteoblasts and these bioceramics, as well as the underlying mechanism of osteoblast proliferation on these bioceramic surfaces remain to be determined. Using iTRAQ-coupled 2-D LC-MS/MS analysis, we report the first comparative proteomics profiling of human osteoblast cells cultured on plane HA and CNT reinforced HA, respectively. Cytoskeletal proteins, metabolic enzymes, signaling, and cell growth proteins previous associated with cell adhesion and proliferation were found to be differentially expressed on these two surfaces. The level of these proteins was generally higher in cells adhered to HA surface, indicating a higher level of cellular proliferation in these cells. The significance of these findings was further assessed by Western blot analysis. The differential protein profile in HA and CNT strengthened HA established in our study should be valuable for future design of biocompatible ceramics.

Oxidant stress stimulates expression of the human peroxiredoxin 6 gene by a transcriptional mechanism involving an antioxidant response element

Peroxiredoxin 6 (Prdx6) is a unique antioxidant enzyme that can reduce phospholipid and other hydroperoxides. A549 cells, a human lung-derived cell line, express both Prdx6 and Nrf2, a transcription factor that binds to antioxidant-response elements (AREs) and promotes expression of antioxidant genes. Treatment of A549 cells with 500 microM H(2)O(2) increased Prdx6 mRNA levels 2.5-fold, whereas treatment with 400 microM H(2)O(2) or 200 microM tert-butylhydroquinone (t-BHQ) triggered a corresponding 2.5-fold increase in reporter gene activity in A549 cells transfected with the pSEAP2:Basic vector (BD Bioscience), containing 1524 nucleotides of the human Prdx6 promoter region. Deletion of a consensus ARE sequence present between positions 357 and 349 before the start of transcription led to a striking decrease in both basal and H(2)O(2)- or t-BHQ-induced activation in A549 cells and H(2)O(2)-induced activation in primary rat alveolar type II cells. Cotransfection with Nrf2 stimulated the Prdx6 promoter in an ARE-dependent manner, whereas it was negatively regulated by Nrf3. siRNA targeting Nrf2 down-regulated reporter gene expression, whereas siRNA targeting the Nrf2 repressor, Keap1, up-regulated it. Binding of Nrf2 to the ARE sequence in chromatin was confirmed by PCR after chromatin immunoprecipitation. These data demonstrate that the ARE within the Prdx6 promoter is a key regulator of basal transcription of the Prdx6 gene and of its inducibility under conditions of oxidative stress.

Investigating transcriptional regulation of Prdx6 in mouse liver cells

Prdx6, a unique member of the peroxiredoxin family of antioxidants, is highly expressed in liver and protects cells from oxidative damage by reducing H2O2 and various lipid peroxides. We investigated the transcriptional regulation of Prdx6 in the H2.35 mouse hepatocyte cell line and sought to determine the mechanism of basal and induced expression. We found that Prdx6 expression is down-regulated upon serum deprivation and subsequently induced in a time-dependent manner in response to KGF, TNF-alpha, dexamethasone, and H2O2. Inhibitors of both PKC and MEK largely prevented Prdx6 induction by KGF and, to a lesser extent, TNF-alpha. Interestingly, inhibition of NF-kappaB led to a marked increase in Prdx6 regulation in the absence or presence of inducers, suggesting a normal role for NF-kappaB in Prdx6 suppression. Using reporter constructs from the mouse gene, we found that the first 160 bp of the proximal promoter was sufficient for low levels of expression, and expression increased sixfold with 1200 bp of the proximal promoter. These regions were not, however, sufficient to mediate up-regulation by the known Prdx6 inducers in our system. Together, these data support multiple pathways of Prdx6 regulation and reveal important promoter regions that mediate its transcriptional regulation.

Peroxiredoxins in the lung with emphasis on peroxiredoxin VI

All six mammalian peroxiredoxins are expressed in the lung. Peroxiredoxin (Prx) VI is the isoform expressed at the highest level and its lung expression exceeds that for other organs. The predominant location of Prx VI is the cytosol and acidic organelles of Clara cells of the conducting airways and type II epithelial cells and macrophages in the alveoli. Prx I and VI show developmental induction of transcription at birth. PrxVI shares structural homology with other peroxiredoxins exhibiting a thioredoxin fold and a conserved catalytic Cys residue in the N-terminus of the protein. This enzyme is highly inducible by oxidative stress in both the neonatal and adult lung consistent with a role in antioxidant defense. Prx VI has several properties that distinguish its peroxidase activity from other peroxiredoxins: it can reduce phospholipid hydroperoxides in addition to other organic hydroperoxides and H2O2; the electron donor that serves to reduce the oxidized peroxidatic cysteine is not thioredoxin but GSH; instead of homodimerization, heterodimerization with pi-glutathione S-transferase is required for regeneration of the active enzyme. Prx VI also expresses a phospholipase A2 activity that is Ca2+-independent, maximal at acidic pH, and dependent on a serine-based catalytic triad and nucleophilic elbow at the surface of the protein. Models of altered Prx VI expression at the cellular, organ and whole animal levels have demonstrated that Prx VI functions as an important anti-oxidant enzyme with levels of protection that exceed those ascribed to GSH peroxidase (GPx1). The phospholipase A2 activity plays an important role in lung surfactant homeostasis and is responsible for the bulk of the degradation of internalized phosphatidylcholine and its resynthesis by the reacylation pathway. Expression of peroxiredoxins is elevated in several lung diseases including lung cancer, mesothelioma and sarcoidosis, although the mechanism for these alterations is not known. The unique properties of Prx VI enable it to play an important role in lung cell function.

Peroxiredoxins in gametogenesis and embryo development

Reactive oxygen species have been implicated in gametogenesis and embryo development in animals. As peroxiredoxins are now recognized as important protective antioxidant enzymes as well as modulators of hydrogen peroxide-mediated signaling, we addressed here the putative role of this novel family of peroxidases in gamete maturation and during embryogenesis in mammals and insects.

Towards a lung adenocarcinoma proteome map: Studies with SP-C/c-raf transgenic mice

We report mapping of proteins of adenocarcinomas of the lung as a result of overexpression of the oncogenically activated N-terminal deletion mutant c-raf-1 BxB through usage of the human SP-C promotor. Proteins from non-transgenic controls and tumors were extracted with a lysis buffer containing 5 mol/L urea, 2 mol/L thiourea, 40 mmol/L Tris, 4% CHAPS, 100 mmol/L DTT, 0.5% BioLyte 3-10, separated by 2-DE and studied by image analysis. On average, 300-600 protein spots per gel were excised and analyzed by MALDI-TOF and -TOF/TOF MS. More than 1000 of the CBB-stained proteins were identified and traced back to 100 different gene products, including many of their isoforms. We observed significant changes in the expression of proteins involved in cellular defense or glycolysis, and this included glutathione S-transferase, peroxiredoxin 6, and alpha-enolase, among others. Proteins associated with lung tumor growth and/or metastasis, i.e., lung carbonyl reductase, differed in expression, as did tumor-associated expression of cell adhesion and membrane-bound proteins such as vinculin. This map provides valuable insight into expression of pulmonary proteins associated with lung adenocarcinomas, some of which may be of utility as diagnostic markers in clinical trials.

Transcripts associated with Prdx6 (peroxiredoxin 6) and related genes in mouse

PRDX6 is a cytosolic member of the peroxiredoxin family of antioxidant proteins, which protect cells from oxidative damage by reducing cellular peroxides. Knockout studies and transgenic overexpression of Prdx6 in mice have demonstrated an important role for this protein in the defense against oxidative stress. Using Northern blotting with various Prdx6 probes, we have revealed the existence of multiple transcripts with distinct tissue distributions and regulation, including the major 1.4-kb transcript highly expressed in liver and lung, and two additional transcripts expressed primarily in liver. We hypothesized that these additional transcripts correspond either to alternative Prdx6 mRNAs or to highly related genes such as the intronless genes Aop2-rs1 and Aop2-rs2. A combination of Northern blotting, RACE, and EST and genomic sequence analysis has determined that all three liver transcripts are derived from the Prdx6 gene, as they are absent in Prdx6-null mice and differ in their 3' UTRs, suggesting the utilization of different transcription termination signal sequences which we have identified by sequence analysis. We found the Aop2-rs1 gene to be exclusively expressed in testis as a 1.2-kb transcript and have identified putative regulatory elements in its promoter. In contrast, Aop2-rs2 appears not to be expressed in any tissues, although we have evidence for the existence of other related genes that are expressed in a tissue-specific manner. Since the Prdx6 transcripts exhibit differential regulation in response to growth and oxidative stress, further investigation may reveal their distinct roles in the cell and mechanism of regulation.

Vitamin E differentially regulates the expression of peroxiredoxin-1 and -6 in alveolar type II cells

Vitamin E is the primary lipophilic antioxidant in mammals. Lack of vitamin E may lead to an increase of cytotoxic phospholipid-peroxidation products (PL-Ox). However, we could previously show that alimentary vitamin E-depletion in rats did not change the concentrations of dienes, hydroperoxides, and platelet-activating factor-related oxidation products in alveolar type II cells (TII cells). We hypothesized that vitamin E deficiency increases the activity of enzymes involved in the degradation of PL-Ox. Degradation of PL-Ox may be catalyzed by phospholipase A2, PAF-acetylhydrolase, or peroxiredoxins (Prx's). Alimentary vitamin E deficiency in rats increased the expression of Prx-1 at the mRNA and protein levels and the formation of Prx-SO3, but it did not change the expression of Prx-6 or the activity of phospholipase A2 and PAF-acetylhydrolase in TII cells. H2O2-induced oxidative stress in isolated TII cells activated protein kinase Calpha (PKCalpha) and increased the expression of Prx-1 and Prx-6. Inhibition of PKCalpha in isolated TII cells by long-time incubation with PMA inhibited PKCalpha and Prx-1 but not Prx-6. We concluded that the expression of Prx-1 and -6 is selectively regulated in TII cells; PKCalpha regulates the expression of Prx-1 but not Prx-6. Prx-6 expression may be closely linked to lipid peroxidation.

Gene expression profiling of NRF2-mediated protection against oxidative injury

Nuclear factor E2 p45-related factor 2 (NRF2) contributes to cellular protection against oxidative insults and chemical carcinogens via transcriptional activation of antioxidant/detoxifying enzymes. To understand the molecular basis of NRF2-mediated protection against oxidative lung injury, pulmonary gene expression profiles were characterized in Nrf2-disrupted (Nrf2(-/-)) and wild-type (Nrf2(+/+)) mice exposed to hyperoxia or air. Genes expressed constitutively higher in Nrf2(+/+) mice than in Nrf2(-/-) mice included antioxidant defense enzyme and immune cell receptor genes. Higher basal expression of heat shock protein and structural genes was detected in Nrf2(-/-) mice relative to Nrf2(+/+) mice. Hyperoxia enhanced expression of 175 genes (> or = twofold) and decreased expression of 100 genes (> or =50%) in wild-type mice. Hyperoxia-induced upregulation of many well-known/new antioxidant/defense genes (e.g., Txnrd1, Ex, Cp-2) and other novel genes (e.g., Pkc-alpha, Tcf-3, Ppar-gamma) was markedly greater in Nrf2(+/+) mice than in Nrf2(-/-) mice. In contrast, induced expression of genes encoding extracellular matrix and cytoskeletal proteins was higher in Nrf2(-/-) mice than in Nrf2(+/+) mice. These NRF2-dependent gene products might have key roles in protection against hyperoxic lung injury. Results from our global gene expression profiles provide putative downstream molecular mechanisms of oxygen tissue toxicity.

Variable overoxidation of peroxiredoxins in human lung cells in severe oxidative stress

Peroxiredoxins (Prxs) are a group of thiol containing proteins that participate both in signal transduction and in the breakdown of hydrogen peroxide (H(2)O(2)) during oxidative stress. Six distinct Prxs have been characterized in human cells (Prxs I-VI). Prxs I-IV form dimers held together by disulfide bonds, Prx V forms intramolecular bond, but the mechanism of Prx VI, so-called 1-Cys Prx, is still unclear. Here we describe the regulation of all six Prxs in cultured human lung A549 and BEAS-2B cells. The cells were exposed to variable concentrations of H(2)O(2), menadione, tumor necrosis factor-alpha or transforming growth factor-beta. To evoke glutathione depletion, the cells were furthermore treated with buthionine sulfoximine. Only high concentrations (300 microM) of H(2)O(2) caused a minor increase (<28%, 4 h) in the expression of Prxs I, IV, and VI. Severe oxidant stress (250-500 microM H(2)O(2)) caused a significant increase in the proportion of the monomeric forms of Prxs I-IV; this was reversible at lower H(2)O(2) concentrations (< or =250 microM). This recovery of Prx overoxidation differed among the various Prxs; Prx I was recovered within 24 h, but recovery required 48 h for Prx III. Overall, Prxs are not significantly modulated by mild oxidant stress or cytokines, but there is variable, though reversible, overoxidation in these proteins during severe oxidant exposure.

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.

Peroxiredoxin 6 is upregulated in bovine oocytes and cumulus cells during in vitro maturation: role of intercellular communication

Peroxiredoxins are peroxidases involved in antioxidant defense and intracellular signaling. Expression of transcripts coding for peroxiredoxin 6 (PRDX6) has been previously described to be upregulated in oocytes after in vitro maturation, a period during which general transcription decreases dramatically in oocytes. The aim of the present work was to evaluate PRDX6 regulation in bovine cumulus-oocyte complexes in relation to maturation and intercellular communication. PRDX6 expression was analyzed by reverse transcription-PCR and Western blotting in oocytes and cumulus cells before and after in vitro maturation. PRDX6 was found to be upregulated at the mRNA and protein levels in both cell types after maturation. The effect of paracrine and gap junctional communication on PRDX6 expression was then assessed by culturing cumulus clusters in the presence or absence of denuded oocytes. While PRDX6 upregulation in oocytes required intact cumulus-oocyte junctions, the presence of denuded oocytes was necessary but sufficient for the upregulation to occur in cumulus cells. Finally, the influence of recombinant mouse growth differentiation factor-9 (GDF-9) on PRDX6 expression in cumulus cells was studied. GDF-9 induced cumulus expansion and PRDX6 upregulation in bovine cumulus clusters. Altogether, our data suggest that PRDX6 upregulation in cumulus-oocyte complexes during in vitro maturation is mutually regulated by both cell types: PRDX6 upregulation in oocytes would require gap junctions with cumulus cells, while upregulation in cumulus would depend on secretion of oocyte paracrine factor(s) with GDF-9 being a likely candidate.

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.

Activation of the antioxidant enzyme 1-CYS peroxiredoxin requires glutathionylation mediated by heterodimerization with pi GST

1-cys peroxiredoxin (1-cysPrx), a member of the peroxiredoxin superfamily, can protect cells against membrane oxidation through glutathione (GSH)-dependent reduction of phospholipid hydroperoxides to corresponding alcohols. However, purified native or recombinant enzyme in vitro generally lacks GSH peroxidase (GPx) activity because of oxidation of its single conserved cysteine. Reduction of the resultant oxidized cysteine is difficult because of its protected location within the homodimer formed by the oxidized protein monomers. Partial purification of 1-cysPrx from bovine lung revealed the presence of pi GST in an active preparation, while purification to homogeneity yielded enzyme that inactivated with time. We show that heterodimerization of 1-cysPrx with GSH-saturated pi GST results in glutathionylation of the oxidized cysteine in 1-cysPrx followed by subsequent spontaneous reduction of the mixed disulfide and restoration of enzymatic activity. Maximum activation of 1-cysPrx occurred with a 1:1 molar ratio of GSH-saturated pi GST and a 2:1 molar ratio of GSH to 1-cysPrx. Liposome-mediated delivery of oxidized recombinant enzyme into NCI-H441 cells that lack 1-cysPrx but express pi GST resulted in 1-cysPrx activation, whereas activation in MCF7 cells required co-delivery of pi GST. Our data indicate a physiological mechanism for glutathionylation of the oxidized catalytic cysteine of 1-cysPrx by its heterodimerization with pi GST followed by its GSH-mediated reduction and enzyme activation.

Induction of 1-cys peroxiredoxin expression by oxidative stress in lung epithelial cells

1-Cys peroxiredoxin (1-cysPrx), a member of the peroxiredoxin family that contains a single conserved cysteine residue, reduces a broad spectrum of hydroperoxides. We studied changes in 1-cysPrx expression in rat lungs and lung cell lines in response to oxidative stress due to hyperoxia, H2O2, or paraquat. After 60 h of hyperoxia (>95% O2), mRNA and protein levels of 1-cysPrx and peroxidase activity were significantly elevated in rat lungs by approximately 1.5- to 2-fold compared with the control (P < 0.05). A similar induction of 1-cysPrx was observed in mouse lungs following exposure to O2 for 63 or 72 h; enzyme induction in mouse lungs was similar for wild-type and glutathione peroxidase 1 gene-targeted mice. H2O2 and paraquat treatment induced 1-cysPrx gene expression in L2 cells. Enzyme induction was attenuated by pretreatment with Trolox or N-acetylcysteine. Actinomycin D treatment showed that stability of 1-cysPrx mRNA was not altered in the presence of H2O2 or paraquat, indicating that increased expression with oxidative stress is regulated at the transcriptional level. These data indicate that the antioxidant enzyme 1-cysPrx is induced in lung cells by oxidative stress.

An antisense oligonucleotide to 1-cys peroxiredoxin causes lipid peroxidation and apoptosis in lung epithelial cells

1-cys peroxiredoxin (1-cysPrx), a member of the peroxiredoxin superfamily, reduces phospholipid hydroperoxides as well as organic peroxides and H(2)O(2). To determine the physiological function(s) of 1-cysPrx, we have used an antisense strategy to suppress endogenous 1-cysPrx in L2 cells, a rat lung epithelial cell line. A 25-base antisense morpholino oligonucleotide was designed to bind a complementary sequence overlapping the translational start site (-18 to +7) in the rat 1-cysPrx mRNA, blocking protein synthesis. Treatment with an antisense oligonucleotide for 48 h resulted in approximately 60% suppression of the 1-cysPrx protein content as measured by immunoblot analysis and an approximately 44% decrease of glutathione peroxidase activity as compared with random oligonucleotide treated and control (vehicle only) cells. Accumulation of phosphatidylcholine hydroperoxide in plasma membranes was demonstrated by high pressure liquid chromatography assay for conjugated dienes (260 pmol/10(6) cells for antisense versus 70 pmol/10(6) cells for random oligonucleotide and control cells) and by fluorescence of diphenyl-1-pyrenylphosphine, a probe for lipid peroxidation. The percentage of cells showing positive staining for annexin V and propidium iodide after antisense treatment was 40% at 28 h and 80% at 48 h. TdT-mediated dUTP nick end labeling assay at 48 h indicated DNA fragmentation in antisense-treated cells that was blocked by prior infection with adenovirus encoding 1-cysPrx or by pretreatment with a vitamin E analogue. The results indicate that 1-cysPrx can function in the intact cell as an antioxidant enzyme to reduce the accumulation of phospholipid hydroperoxides and prevent apoptotic cell death.