Cloning and characterization of a 23-kDa stress-induced mouse peritoneal macrophage protein

Peroxiredoxin-1 as a molecular chaperone that regulates glutathione S-transferase P1 activity and drives mutidrug resistance in ovarian cancer cells

Ovarian cancer is among the most prevalent gynecological malignancies around the globe. Nonetheless, chemoresistance continues to be one of the greatest obstacles in the treatment of ovarian cancer. Therefore, understanding the mechanisms of chemoresistance and identifying new treatment options for ovarian cancer patients is urgently required. In this study, we found that the mRNA and protein expression levels of PRDX1 were significantly increased in cisplatin resistant A2780/CDDP cells. Cell survival assays revealed that PRDX1 depletion substantially increased ovarian cancer cell sensitivity to cisplatin, docetaxel, and doxorubicin. Additionally, PRDX1 significantly increased GSTP1 activity, resulting in multidrug resistance. Biochemical experiments showed that PRDX1 interacted with GSTP1 through Cysteine 83, which regulated GSTP1 activity as well as chemotherapy resistance in ovarian cancer cells. Our findings indicate that the molecular chaperone activity of PRDX1 is a promising new therapeutic target for ovarian cancer.

Potential of NRF2 Pathway in Preventing Developmental and Reproductive Toxicity of Fine Particles

Air pollution is associated with significant adverse health effects. Recent studies support the idea that inhalation of fine particles can instigate extrapulmonary effects on the cardiovascular system through several pathways. The systemic transfer of ultrafine particles (UFPs) or soluble particle components (organic compounds and metals) is of particular concern. An integral role of reactive oxygen species (ROS)-dependent pathways has been suggested in systemic inflammatory responses and vascular dysfunction at the molecular level. Accumulating lines of evidence suggest that fine particles affect fetal development, giving rise to low birth weight and a reduction in fetal growth, and also affect the immune, cardiovascular, and central nervous systems. Oxidative stress plays an important role in fine particles toxicity; pre-treatment with antioxidants partially suppresses the developmental toxicity of fine particles. On the other hand, Nuclear factor erythroid-derived 2-like 2 (Nfe2l2), also known as NRF2, is a transcription factor essential for inducible and/or constitutive expression of phase II and antioxidant enzymes. Studies using Nrf2-knockout mice revealed that NRF2 dysfunction is intimately involved in the pathogenesis of various human diseases. Multiple single nucleotide polymorphisms (SNPs) have been detected in human NRF2 locus. An NRF2 gene SNP (−617C > A; rs6721961), located in the upstream promoter region, affects the transcriptional level of NRF2 and thereby the protein level and downstream gene expression. It has been reported that the SNP-617 is associated with various diseases. The onset and exacerbation of the diseases are regulated by genetic predisposition and environmental factors; some people live in the air-polluted environment but are not affected and remain healthy, suggesting the presence of individual differences in the susceptibility to air pollutants. NRF2 polymorphisms may also be associated with the fetal effects of fine particles exposure. Screening high-risk pregnant women genetically susceptible to oxidative stress and prevention by antioxidant interventions to protect fetal development in air-polluted areas should be considered. This article reviews the recent advances in our understanding of the fetal health effects of fine particles and describes potential chemoprevention via the NRF2 pathway to prevent the developmental and reproductive toxicity of fine particles.

Peroxiredoxin 1 Interacts with TBK1/IKKε and Negatively Regulates Pseudorabies Virus Propagation by Promoting Innate Immunity

Peroxiredoxin 1 (PRDX1) is a cellular antioxidant enzyme that is crucial for diverse fundamental biological processes, such as autophagy, inflammation, and carcinogenesis. However, molecular mechanisms underpinning its diverse roles are not well understood. Here, we report that PRDX1 positively regulates interferon (IFN) induction and that pseudorabies virus (PRV) targets PRDX1 to evade IFN induction. PRV UL13 encodes a serine/threonine kinase important for PRV infection, although its biological function remains obscure. We identified PRDX1 as a UL13-interacting protein. Virological and biochemical assays demonstrate that PRDX1 promotes IFN induction by interacting with TANK-binding kinase 1 (TBK1) and IκB kinase ε (IKKε). Conversely, UL13 accelerates PRDX1 degradation via the ubiquitin-proteosome pathway in a kinase-dependent manner. In doing so, PRV inhibits IFN induction during productive infection, which requires PRDX1 expression. This study uncovers an essential role of PRDX1 in the innate immune response and reveals a new viral immune evasion strategy to counteract cellular defenses. IMPORTANCE PRV interacts with numerous cellular proteins during productive infection. Here, we demonstrated the interaction of viral protein UL13 with the antioxidant enzyme PRDX1, which functions in multiple signal transduction pathways. We found that PRDX1 participates in the type I IFN pathway by interacting with TBK1 and IKKε, thereby negatively regulating PRV propagation. However, UL13 ubiquitinates PRDX1, which routes PRDX1 into proteasomes for degradation and effectively reduces its expression. These results illuminate the fundamental role that PRDX1 plays in the IFN pathway, and they identify a potential target for the control of PRV infection.

Peroxiredoxin-1 aggravates lipopolysaccharide-induced septic shock via promoting inflammation

Septic shock induced by lipopolysaccharide (LPS) is characterized by serious systemic inflammatory response and robust production of pro-inflammatory cytokines from activated macrophages. Damage-associated molecular patterns (DAMPs) secreted by activated macrophages are key contributors to septic shock. However, the current knowledge on those DAMPs that promote inflammatory response under LPS-induced septic shock remains poorly understood. Here, we report that Peroxiredoxin 1 (Prdx1) plays a detrimental role in LPS-induced septic shock. Intraperitoneal injection of LPS elicited a progressive course of septic shock in mice, which was characterized by significant lethality along with robust production of cytokines (IL-1β, IL-6 and TNF-α). Removal of Prdx1 strongly protected mice from LPS-induced death, and decreased IL-1β, IL-6 and TNF-α productions. Additionally, primary macrophages deficient in Prdx1 are less able to produce much more IL-1β, IL-6 and TNF-α. Collectively, we provide a demonstration for Prdx1 contributing to LPS-induced septic shock likely via promoting inflammation.

The interactome of 2-Cys peroxiredoxins in Plasmodium falciparum

Peroxiredoxins (Prxs) are crucially involved in maintaining intracellular H2O2homeostasis via their peroxidase activity. However, more recently, this class of proteins was found to also transmit oxidizing equivalents to selected downstream proteins, which suggests an important function of Prxs in the regulation of cellular protein redox relays. Using a pull-down assay based on mixed disulfide fishing, we characterized the thiol-dependent interactome of cytosolic Prx1a and mitochondrial Prx1m from the apicomplexan malaria parasitePlasmodium falciparum(Pf). Here, 127 cytosolic and 20 mitochondrial proteins that are components of essential cellular processes were found to interact withPfPrx1a andPfPrx1m, respectively. Notably, our data obtained with active-site mutants suggests that reducing equivalents might also be transferred from Prxs to target proteins. Initial functional analyses indicated that the interaction with Prx can strongly impact the activity of target proteins. The results provide initial insights into the interactome of Prxs at the level of a eukaryotic whole cell proteome. Furthermore, they contribute to our understanding of redox regulatory principles and thiol-dependent redox relays of Prxs in subcellular compartments.

Circulating Peroxiredoxin-1 is a novel damage-associated molecular pattern and aggravates acute liver injury via promoting inflammation

Sterile inflammation is initiated by damage-associated molecular patterns (DAMPs) and a key contributor to acute liver injury (ALI). However, the current knowledge on those DAMPs that activate hepatic inflammation under ALI remains incomplete. We report here that circulating peroxiredoxin-1 (Prdx1) is a novel DAMP for ALI. Intraperitoneal injection of acetaminophen (APAP) elicited a progressive course of ALI in mice, which was developed from 12 to 24 h post injection along with liver inflammation evident by macrophage infiltration and upregulations of cytokines (IL-1β, IL-6 and TNF-α); these alterations were concurrently occurred with a robust and progressive production of serum Prdx1. Similar observations were also obtained in carbon tetrachloride (CCl₄)-induced ALI in mice. Removal of the source of serum Prdx1 protected mice deficient in Prdx1 from APAP and CCl₄-induced liver injury, and decreased macrophage infiltration, IL-1β, IL-6 and TNF-α production. As a result, Prdx1^-/- mice were strongly protected from APAP-induced death that was likely progressed from ALI. Additionally, intravenous re-introduction of recombinant Prdx1 (rPrdx1) in Prdx1^-/- mice reversed or reduced all the above events, demonstrating an important contribution of circulating Prdx1 to ALI. rPrdx1 potently induced in primary macrophages the expression of pro-IL-1β, IL-6, TNF-α, and IL-1β through the NF-κB signaling as well as the NOD-like receptor family pyrin domain containing 3 (NLRP3) inflammasome signaling, evident by caspase-1 activation. Furthermore, a significant elevation of serum Prdx1 was demonstrated in patients (n = 15) with ALI; the elevation is associated with ALI severity. Collectively, we provide the first demonstration for serum Prdx1 contributing to ALI.

The prognostic values of the peroxiredoxins family in ovarian cancer

Purpose: Peroxiredoxins (PRDXs) are a family of antioxidant enzymes with six identified mammalian isoforms (PRDX1–6). PRDX expression is up-regulated in various types of solid tumors; however, individual PRDX expression, and its impact on prognostic value in ovarian cancer patients, remains unclear.

Methods: PRDXs family protein expression profiles in normal ovarian tissues and ovarian cancer tissues were examined using the Human Protein Atlas database. Then, the prognostic roles of PRDX family members in several sets of clinical data (histology, pathological grades, clinical stages, and applied chemotherapy) in ovarian cancer patients were investigated using the Kaplan–Meier plotter.

Results: PRDXs family protein expression in ovarian cancer tissues was elevated compared with normal ovarian tissues. Meanwhile, elevated expression of PRDX3, PRDX5, and PRDX6 mRNAs showed poorer overall survival (OS); PRDX5 and PRDX6 also predicted poor progression-free survival (PFS) for ovarian cancer patients. Furthermore, PRDX3 played significant prognostic roles, particularly in poor differentiation and late-stage serous ovarian cancer patients. Additionally, PRDX5 predicted a lower PFS in all ovarian cancer patients treated with Platin, Taxol, and Taxol+Platin chemotherapy. PRDX3 and PRDX6 also showed poor PFS in patients treated with Platin chemotherapy. Furthermore, PRDX3 and PRDX5 indicated lower OS in patients treated with these three chemotherapeutic agents. PRDX6 predicted a poorer OS in patients treated with Taxol and Taxol+Platin chemotherapy.

Conclusion: These results suggest that there are distinct prognostic values of PRDX family members in patients with ovarian cancer, and that the expression of PRDX3, PRDX5, and PRDX6 mRNAs are a useful prognostic indicator in the effect of chemotherapy in ovarian cancer patients.

Peroxiredoxin I participates in the protection of reactive oxygen species-mediated cellular senescence

Peroxiredoxin I (Prx I) plays an important role as a reactive oxygen species (ROS) scavenger in protecting and maintaining cellular homeostasis; however, the underlying mechanisms are not well understood. Here, we identified a critical role of Prx I in protecting cells against ROS-mediated cellular senescence by suppression of p16^INK4a expression. Compared to wild-type mouse embryonic fibroblasts (WT-MEFs), Prx I^−/− MEFs exhibited senescence-associated phenotypes. Moreover, the aged Prx I^−/− mice showed an increased number of cells with senescence associated-β-galactosidase (SA-β-gal) activity in a variety of tissues. Increased ROS levels and SA-β-gal activity, and reduction of chemical antioxidant in Prx I^−/− MEF further supported an essential role of Prx I peroxidase activity in cellular senescence that is mediated by oxidative stress. The up-regulation of p16^INK4a expression in Prx I^−/− and suppression by overexpression of Prx I indicate that Prx I possibly modulate cellular senescence through ROS/p16^INK4a pathway.

Prdx1 (peroxiredoxin 1) deficiency reduces cholesterol efflux via impaired macrophage lipophagic flux

Oxidative stress activates macroautophagy/autophagy and contributes to atherogenesis via lipophagic flux, a form of lipid removal by autophagy. However, it is not known exactly how endogenous antioxidant enzymes are involved in lipophagic flux. Here, we demonstrate that the antioxidant PRDX1 (peroxiredoxin 1) has a crucial role in the maintenance of lipophagic flux in macrophages. PRDX1 is more highly expressed than other antioxidant enzymes in monocytes and macrophages. We determined that Prdx1 deficiency induced excessive oxidative stress and impaired maintenance of autophagic flux in macrophages. Prdx1-deficient macrophages had higher intracellular cholesterol mass and lower cholesterol efflux compared with wild type. This perturbation in cholesterol homeostasis was due to impaired lipophagic cholesterol hydrolysis caused by excessive oxidative stress, resulting in the inhibition of free cholesterol formation and the reduction of NR1H3 (nuclear receptor subfamily 1, group H, member 3) activity. Notably, impairment of both lipophagic flux and cholesterol efflux was restored by the 2-Cys PRDX-mimics ebselen and gliotoxin. Consistent with this observation, apoe ^−/− mice transplanted with bone marrow from prdx1^−/−apoe^−/− mice had increased plaque formation compared with apoe^−/− BM-transplanted recipients. This study reveals that PRDX1 is crucial to regulating lipophagic flux and maintaining macrophage cholesterol homeostasis against oxidative stress. We suggest that PRDX1-dependent control of oxidative stress may provide a strategy for treating atherosclerosis and autophagy-related human diseases.

Proteomic and transcriptomic studies of HBV-associated liver fibrosis of an AAV-HBV-infected mouse model

Background

Human hepatitis B virus (HBV) infection is an important public health issue in the Asia-Pacific region and is associated with chronic hepatitis, liver fibrosis, cirrhosis and even liver cancer. However, the underlying mechanisms of HBV-associated liver fibrosis remain incompletely understood.

Results

In the present study, proteomic and transcriptomic approaches as well as biological network analyses were performed to investigate the differentially expressed molecular signature and key regulatory networks that were associated with HBV-mediated liver fibrosis. RNA sequencing and 2DE-MALDI-TOF/TOF were performed on liver tissue samples obtained from HBV-infected C57BL/6 mouse generated via AAV8-HBV virus. The results showed that 322 genes and 173 proteins were differentially expressed, and 28 HBV-specific proteins were identified by comprehensive proteomic and transcriptomic analysis. GO analysis indicated that the differentially expressed proteins were predominantly involved in oxidative stress, which plays a key role in HBV-related liver fibrosis. Importantly, CAT, PRDX1, GSTP1, NXN and BLVRB were shown to be associated with oxidative stress among the differentially expressed proteins. The most striking results were validated by Western blot and RT-qPCR. The RIG-I like receptor signaling pathway was found to be the major signal pathway that changed during HBV-related fibrosis.

Conclusions

This study provides novel insights into HBV-associated liver fibrosis and reveals the significant role of oxidative stress in liver fibrosis. Furthermore, CAT, BLVRB, NXN, PRDX1, and IDH1 may be candidates for detection of liver fibrosis or therapeutic targets for the treatment of liver fibrosis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-017-3984-z) contains supplementary material, which is available to authorized users.

Multiple Functions and Regulation of Mammalian Peroxiredoxins

Peroxiredoxins (Prxs) constitute a major family of peroxidases, with mammalian cells expressing six Prx isoforms (PrxI to PrxVI). Cells produce hydrogen peroxide (H₂O₂) at various intracellular locations where it can serve as a signaling molecule. Given that Prxs are abundant and possess a structure that renders the cysteine (Cys) residue at the active site highly sensitive to oxidation by H₂O₂, the signaling function of this oxidant requires extensive and highly localized regulation. Recent findings on the reversible regulation of PrxI through phosphorylation at the centrosome and on the hyperoxidation of the Cys at the active site of PrxIII in mitochondria are described in this review as examples of such local regulation of H₂O₂ signaling. Moreover, their high affinity for and sensitivity to oxidation by H₂O₂ confer on Prxs the ability to serve as sensors and transducers of H₂O₂ signaling through transfer of their oxidation state to bound effector proteins.

Differential Cellular and Subcellular Localization of Heme-Binding Protein 23/Peroxiredoxin I and Heme Oxygenase-1 in Rat Liver

Heme-binding protein 23 (HBP23), also termed peroxiredoxin (Prx) I, and heme oxygenase-1 (HO-1) are distinct antioxidant stress proteins that are co-ordinately induced by oxidative stress. HBP23/Prx I has thioredoxin-dependent peroxidase activity with high binding affinity for the pro-oxidant heme, while HO-1 is the inducible isoform of the rate-limiting enzyme of heme degradation. We investigated the cellular and subcellular localization of both proteins in rat liver. Whereas by immunohistochemistry (IHC) a uniformly high level of HBP23/Prx I expression was observed in liver parenchymal and different sinusoidal cells, HO-1 expression was restricted to Kupffer cells. By immunoelectron microscopy using the protein A-gold technique, HBP23/Prx I immunoreactivity was detected in cytoplasm, nuclear matrix, mitochondria, and peroxisomes of parenchymal and non-parenchymal liver cell populations. In contrast, the secretory pathway, i.e., the endoplasmic reticulum and Golgi complex, was free of label. As determined by immunocytochemical (ICC) studies in liver cell cultures and by Western and Northern blotting analysis, HBP23/Prx I was highly expressed in cultures of isolated hepatocytes and Kupffer cells. In contrast, HO-1 was constitutively expressed only in Kupffer cell cultures but was also inducible in hepatocytes. These data suggest that HBP23/Prx I and HO-1 may have complementary antioxidant functions in different cell populations in rat liver.

Expression of cyclooxygenase-2, peroxiredoxin I, peroxiredoxin 6 and nuclear factor-κB in oral squamous cell carcinoma

Tumor development and progression are multistep processes that involve local tumor growth and invasion, followed by metastasis. The aggressiveness of the tumor is the major determinant of the mortality of oral cancer patients. The present study investigates whether the expression levels of cyclooxygenase-2 (COX-2), nuclear factor-κB (NF-κB), peroxiredoxin 1 (PRDX1) and PRDX6 are associated with the development, proliferation, differentiation and recurrence of oral squamous cell carcinoma (OSCC). The mRNA expression levels of COX-2, NF-κB, PRDX1 and PRDX6 were examined in 50 OSCC specimens and 19 normal oral mucosae by quantitative polymerase chain reaction (qPCR). qPCR analysis showed that the mRNA levels of COX-2 in OSCC were significantly higher than those in the normal oral mucosae (P=0.021). The expression levels of PRDX1 in high-stage tumors (T3 and T4) were significantly elevated compared with those in low-stage tumors (T1) (P=0.047). Additionally, the expression levels of NF-κB in the high-grade tumor were significantly elevated compared with those in the low-grade tumors (P=0.030). Overall, it was indicated that the expression of COX-2 is strongly associated with the development of OSCC. Moreover, the enhanced expression of PRDX1 and NF-κB may function in the progression of OSCC, which serves as a useful marker for prognosis in patients with oral cancer.

Dominant Role of Peroxiredoxin/JNK Axis in Stemness Regulation During Neurogenesis from Embryonic Stem Cells

Redox balance has been suggested as an important determinant of “stemness” in embryonic stem cells (ESCs). In this study, we demonstrate that peroxiredoxin (Prx) plays a pivotal role in maintenance of ESC stemness during neurogenesis through suppression of reactive oxygen species (ROS)-sensitive signaling. During neurogenesis, Prx I and Oct4 are expressed in a mutually dependent manner and their expression is abruptly downregulated by an excess of ROS. Thus, in Prx I−/− or Prx II−/− ESCs, rapid loss of stemness can occur due to spontaneous ROS overload, leading to their active commitment into neurons; however, stemness is restored by the addition of an antioxidant or an inhibitor of c-Jun N-terminal kinase (JNK). In addition, Prx I and Prx II appear to have a tight association with the mechanism underlying the protection of ESC stemness in developing teratomas. These results suggest that Prx functions as a protector of ESC stemness by opposing ROS/JNK cascades during neurogenesis. Therefore, our findings have important implications for understanding of maintenance of ESC stemness through involvement of antioxidant enzymes and may lead to development of an alternative stem cell-based therapeutic strategy for production of high-quality neurons in large quantity. Stem Cells  2014;32:998–1011

Thioredoxins, glutaredoxins, and peroxiredoxins--molecular mechanisms and health significance: from cofactors to antioxidants to redox signaling

Thioredoxins (Trxs), glutaredoxins (Grxs), and peroxiredoxins (Prxs) have been characterized as electron donors, guards of the intracellular redox state, and "antioxidants". Today, these redox catalysts are increasingly recognized for their specific role in redox signaling. The number of publications published on the functions of these proteins continues to increase exponentially. The field is experiencing an exciting transformation, from looking at a general redox homeostasis and the pathological oxidative stress model to realizing redox changes as a part of localized, rapid, specific, and reversible redox-regulated signaling events. This review summarizes the almost 50 years of research on these proteins, focusing primarily on data from vertebrates and mammals. The role of Trx fold proteins in redox signaling is discussed by looking at reaction mechanisms, reversible oxidative post-translational modifications of proteins, and characterized interaction partners. On the basis of this analysis, the specific regulatory functions are exemplified for the cellular processes of apoptosis, proliferation, and iron metabolism. The importance of Trxs, Grxs, and Prxs for human health is addressed in the second part of this review, that is, their potential impact and functions in different cell types, tissues, and various pathological conditions.

Amelioration of cisplatin-induced nephrotoxicity in peroxiredoxin I-deficient mice

PURPOSE

Cisplatin is one of the most potent chemotherapeutic agents used to treat cancer. However, cisplatin-induced nephrotoxicity, which is partly caused by oxidative damage, is a serious problem. We previously showed that murine embryonic fibroblasts deficient in Peroxiredoxin I (Prx I), a major Nrf2-linked anti-oxidant enzyme, are susceptible to cisplatin-induced cytotoxicity. In the present study, we examined the role of Prx I against cisplatin-induced renal injury in vivo using Prx I-null mice.

METHODS

Prx I-null mice and wild-type (WT) mice were given an intraperitoneal injection of cisplatin, and tissues were removed and evaluated histopathologically. In addition, gene and protein expression of efflux transporters was analyzed.

RESULTS

In contrast to an in vitro cell study, Prx I-null mice exhibited less cisplatin-induced renal damage than WT mice in histological and blood biochemical analyses. Moreover, Prx I-null mice showed a higher clearance rate of cisplatin than WT mice following intraperitoneal cisplatin injection. Consistent with these results, Prx I-null mice exhibited higher expression of renal efflux transporters Mrp2 and Mrp4 compared with WT mice under both basal and the cisplatin-induced conditions. We suggest the enhanced transcriptional activity of c-Myc in Prx I-null mice may partly contribute the enhanced expression of renal efflux transporters.

CONCLUSION

In summary, the enhanced clearance rate of cisplatin significantly attenuates nephrotoxicity in Prx I-null mice.

Characterization of the role of protein-cysteine residues in the binding with sodium arsenite

To better characterize the interaction of protein-cysteines with sodium arsenite, arsenic-binding proteins were identified from the arsenic-resistant Chinese hamster ovary cell line SA7 using a p-aminophenylarsine oxide (PAO)-agarose matrix in combination with proteomic techniques. Twenty of the isolated arsenic-binding proteins were further peptide-mapped by MALDI-Q-TOF-MS. The binding capacity of PAO-agarose-retained proteins was then verified by re-applying Escherichia coli overexpressed recombinant proteins with various numbers of cysteine residues onto the PAO-agarose matrix. The results showed that recombinant heat shock protein 27 (HSP27, with one cysteine residue), reticulocalbin-3 (RCN3, with no cysteine residue), galectin-1 (GAL1, with six cysteine residues), but not peroxiredoxin 6 (Prdx6, with one cysteine residue but not retained by the PAO-agarose matrix), were bound to the PAO-agarose matrix. The six free cysteine residues in GAL1 were individually or double-mutated to alanine by means of site-directed mutagenesis and subjected to CD and ICP-MS analysis. The binding capacity of GAL1 for sodium arsenite was significantly attenuated in C16A, C88A and all double mutant clones. Taken together, our current data suggest that the cysteine residues in GAL1 may play a critical role in the binding of arsenic, but that in the case of RCN3 and Prdx6, this interaction may be mediated by other factors.

Differential expression and function of peroxiredoxin 1 and peroxiredoxin 6 in cancerous MCF-7 and noncancerous MCF-10A breast epithelial cells

Peroxiredoxins are thiol-specific antioxidant proteins whose expression is elevated in several cancers. We compared the expression and function of Prdx1 and Prdx6 between the MCF-7 mammary adenocarcinoma cell line and the noncancerous MCF-10A cell line. We found elevated Prdx1 expression in MCF-7 cells and comparable expression of Prdx6. Suppression of Prdx1 and/or Prdx6 resulted in a modest increase in peroxide-induced cytotoxicity of MCF-7 cells, and a dramatic increase in MCF-10A cytotoxicity with and without hydrogen peroxide treatment. Our data confirm a cytoprotective role for peroxiredoxins and suggest a synergistic role for Prdx1 and Prdx6 in MCF-10A cells.

Novel roles of peroxiredoxins in inflammation, cancer and innate immunity

Peroxiredoxins possess thioredoxin or glutathione peroxidase and chaperone-like activities and thereby protect cells from oxidative insults. Recent studies, however, reveal additional functions of peroxiredoxins in gene expression and inflammation-related biological reactions such as tissue repair, parasite infection and tumor progression. Notably, peroxiredoxin 1, the major mammalian peroxiredoxin family protein, directly interacts with transcription factors such as c-Myc and NF-κB in the nucleus. Additionally, peroxiredoxin 1 is secreted from some cells following stimulation with TGF-β and other cytokines and is thus present in plasma and body fluids. Peroxiredoxin 1 is now recognized as one of the pro-inflammatory factors interacting with toll-like receptor 4, which triggers NF-κB activation and other signaling pathways to evoke inflammatory reactions. Some cancer cells release peroxiredoxin 1 to stimulate toll-like receptor 4-mediated signaling for their progression. Interestingly, peroxiredoxins expressed in protozoa and helminth may modulate host immune responses partly through toll-like receptor 4 for their survival and progression in host. Extracellular peroxiredoxin 1 and peroxiredoxin 2 are known to enhance natural killer cell activity and suppress virus-replication in cells. Peroxiredoxin 1-deficient mice show reduced antioxidant activities but also exhibit restrained tissue inflammatory reactions under some patho-physiological conditions. Novel functions of peroxiredoxins in inflammation, cancer and innate immunity are the focus of this review.

Sub-proteomic study on macrophage response to Candida albicans unravels new proteins involved in the host defense against the fungus

In previous proteomic studies on the response of murine macrophages against Candida albicans, many differentially expressed proteins involved in processes like inflammation, cytoskeletal rearrangement, stress response and metabolism were identified. In order to look for proteins important for the macrophage response, but in a lower concentration in the cell, 3 sub-cellular extracts were analyzed: cytosol, organelle/membrane and nucleus enriched fractions from RAW 264.7 macrophages exposed or not to C. albicans SC5314 for 3 h. The samples were studied using DIGE technology, and 17 new differentially expressed proteins were identified. This sub-cellular fractionation permitted the identification of 2 mitochondrion proteins, a membrane receptor, Galectin-3, and some ER related proteins, that are not easily detected in total cell extracts. Besides, the study of different fractions allowed us to detect, not only total increase in Galectin-3 protein amount, but its distinct allocation along the interaction. The identified proteins are involved in the pro-inflammatory and oxidative responses, immune response, unfolded protein response and apoptosis. Some of these processes increase the host response and others could be the effect of C. albicans resistance to phagocytosis. Thus, the sub-proteomic approach has been a very useful tool to identify new proteins involved in macrophage-fungus interaction. This article is part of a Special Issue entitled: Translational Proteomics.

The expression of antioxidant enzymes in the gingivae of type 2 diabetics with chronic periodontitis

OBJECTIVES

There is controversial evidence regarding the levels of antioxidant molecules in type 2 diabetes periodontitis patients. Thus, the aim of the present study was to evaluate the gene expression of antioxidant enzymes in the gingival tissue of poorly and well-controlled type 2 diabetic subjects with chronic periodontitis (CP).

DESIGN

Gingival biopsies were harvested from systemically and periodontally healthy subjects (n=12), systemically healthy subjects with CP (n=15), well-controlled (n=8) and poorly controlled (n=14) diabetic subjects with CP. The messenger RNA (mRNA) levels of peroxiredoxin (PRDX) 1 and 2, catalase (CAT), glutathione peroxidase (GPX1) and superoxide dismutase (SOD) 1 and 2 were measured by quantitative polymerase chain reaction (qPCR).

RESULTS

The results showed that PRDX1 and GPX1 were up-regulated by periodontitis (p<0.05), independently of the glycaemic status, whilst PRDX2 and SOD2 genes were slightly influenced by periodontitis, but significantly induced when periodontitis was associated with DM, especially under a poor glycaemic control (p<0.05). Moreover, CAT and SOD1 expressions were not significantly influenced by any of these inflammatory disorders (p>0.05).

CONCLUSION

In conclusion, both PRDX1 and GPX1 were overexpressed in CP whilst PRDX2 and SOD2 were up-regulated especially in the poorly controlled diabetic group with CP.

Multiple functions of peroxiredoxins: peroxidases, sensors and regulators of the intracellular messenger H₂O₂, and protein chaperones

Peroxiredoxins (Prxs) are a family of peroxidases that reduce peroxides, with a conserved cysteine residue (the peroxidatic Cys) serving as the site of oxidation by peroxides. Peroxides oxidize the peroxidatic Cys-SH to Cys-SOH, which then reacts with another cysteine residue (typically the resolving Cys [C(R)]) to form a disulfide that is subsequently reduced by an appropriate electron donor. On the basis of the location or absence of the C(R), Prxs are classified into 2-Cys, atypical 2-Cys, and 1-Cys Prx subfamilies. In addition to their peroxidase activity, members of the 2-Cys Prx subfamily appear to serve as peroxide sensors for other proteins and as molecular chaperones. During catalysis, the peroxidatic Cys-SOH of 2-Cys Prxs is occasionally further oxidized to Cys-SO(2)H before disulfide formation, resulting in inactivation of peroxidase activity. This hyperoxidation, which is reversed by the ATP-dependent enzyme sulfiredoxin, modulates the sensor and chaperone functions of 2-Cys Prxs. The peroxidase activity of 2-Cys Prxs is extensively regulated via tyrosine and threonine phosphorylation, which allows modulation of the local concentration of the intracellular messenger H(2)O(2). Finally, 2-Cys Prxs interact with a variety of proteins, with such interaction having been shown to modulate the function of the binding partners in a reciprocal manner.

Peroxidoxins: a new antioxidant family

Peroxidoxins are a recently described family of antioxidants. They have an ancient origin, being present in organisms as primitive as the archaea, and they appear to be ubiquitous in living cells. Here, Sharon McGonigle, John Dalton and Eric James review the present understanding of the functions and mechanism of action of these enzymes and suggest that these antioxidants may represent the ;missing link' in the metabolism of reactive oxygen species by some protozoan and helminth parasites. Also, by performing sequence comparisons of homologues entered in the public databases, they have classified the parasite peroxidoxins as 1-cys or 2-cys enzymes. The discovery of these antioxidants may change our understanding of how reactive oxygen species, of parasite or host origin, are managed by parasites.

Expression of peroxiredoxin I regulated by gonadotropins in the rat ovary

Objective

Peroxiredoxins (Prxs) play an important role in regulating cellular differentiation and proliferation in several types of mammalian cells. This report examined the expression of Prx isotype I in the rat ovary after hormone treatment.

Methods

Immature rats were injected with 10 IU of pregnant mare's serum gonadotropin (PMSG) to induce the growth of multiple preovulatory follicles and 10 IU of human chorionic gonadotropin (hCG) to induce ovulation. Immature rats were also treated with diethylstilbestrol (DES), an estrogen analogue, to induce the growth of multiple immature follicles. Northern blot analysis was performed to detect gene expression. Cell-type specific localization of Prx I mRNA were detected by in situ hybridization analysis.

Results

During follicle development, ovarian Prx I gene expression was detected in 3-day-old rats and had increased in 21-day-old rats. The levels of Prx I mRNA slightly declined one to two days following treatment with DES. A gradual increase in Prx I gene expression was observed in ovaries obtained from PMSG-treated immature rats. Furthermore, hCG treatment of PMSG-primed rats resulted in a gradual stimulation of Prx I mRNA levels by 24 hours (2.1-fold increase) following treatment, which remained high until 72 hours following treatment. In situ hybridization analysis revealed the expression of the Prx I gene in the granulosa cells of PMSG-primed ovaries and in the corpora lutea of ovaries stimulated with hCG for 72 hours.

Conclusion

These results demonstrate the gonadotropin and granulosa cell-specific stimulation of Prx I gene expression, suggesting its role as a local regulator of follicle development.

Secretome Analysis of Skeletal Myogenesis Using SILAC and Shotgun Proteomics

Myogenesis, the formation of skeletal muscle, is a multistep event that commences with myoblast proliferation, followed by cell-cycle arrest, and finally the formation of multinucleated myotubes via fusion of mononucleated myoblasts. Each step is orchestrated by well-documented intracellular factors, such as cytoplasmic signalling molecules and nuclear transcription factors. Regardless, the key step in getting a more comprehensive understanding of the regulation of myogenesis is to explore the extracellular factors that are capable of eliciting the downstream intracellular factors. This could further provide valuable insight into the acute cellular response to extrinsic cues in maintaining normal muscle development. In this paper, we survey the intracellular factors that respond to extracellular cues that are responsible for the cascades of events during myogenesis: myoblast proliferation, cell-cycle arrest of myoblasts, and differentiation of myoblasts into myotubes. This focus on extracellular perspective of muscle development illustrates our mass spectrometry-based proteomic approaches to identify differentially expressed secreted factors during skeletal myogenesis.

Aggravation of bleomycin-induced pulmonary inflammation and fibrosis in mice lacking peroxiredoxin I

Oxidative stress plays an important role in the pathogenesis of acute lung injury and pulmonary fibrosis. Peroxiredoxin (Prx) I is a cellular antioxidant enzyme induced under stress conditions. In the present study, the protective effects of Prx I on the development of bleomycin-induced acute pulmonary inflammation and pulmonary fibrosis were investigated using Prx I-deficient mice. Survival of Prx I-deficient mice after bleomycin administration was significantly lower than that of wild-type mice, corresponding with enhanced acute pulmonary inflammation and fibrosis. The level of inflammatory cytokines and chemokines, such as TNF-α, macrophage inflammatory protein-2, and monocyte chemotactic protein-1, was significantly elevated in the bronchoalveolar lavage fluid of Prx I-deficient mice after bleomycin administration. Furthermore, the level of 8-isoprostane, an oxidative stress marker, and the concentration and alveolar macrophage expression of macrophage migration inhibitory factor were elevated in the lungs of Prx I-deficient mice after bleomycin administration. The exacerbation of bleomycin-induced pulmonary inflammation and fibrosis in Prx I-deficient mice was inhibited by treatment with N-acetyl-L-cysteine, a radical scavenger, or with (S,R)-3-(4-hydroxyphenyl)-4,5-dihydro-5-isoxazole acetic acid methyl ester, a tautomerase inhibitor of macrophage migration inhibitory factor. These findings suggest that mice lacking Prx I are highly susceptible to bleomycin-induced pulmonary inflammation and fibrosis because of increases in pulmonary oxidant levels and macrophage migration inhibitory factor activity in response to bleomycin.

Microglial peroxiredoxin V acts as an inducible anti-inflammatory antioxidant through cooperation with redox signaling cascades

Reactive oxygen species (ROS) actively participate in microglia-mediated pathogenesis as pro-inflammatory molecules. However, little is known about the involvement of specific antioxidants in maintaining the microglial oxidative balance. We demonstrate that microglial peroxiredoxin (Prx) 5 expression is up-regulated by lipopolysaccharide (LPS) through activation of the ROS-sensitive signaling pathway and is involved in attenuation of both microglial activation and nitric oxide (NO) generation. Unlike in stimulation of oxidative insults with paraquat and hydrogen peroxide, Prx V expression is highly sensitive to LPS-stimulation in microglia. Reduction of ROS level by treatment with either NADPH oxidase inhibitor or antioxidant ablates LPS-mediated Prx V up-regulation in BV-2 microglial cells and is closely associated with the activation of the c-jun N-terminal kinase (JNK) signaling pathway. This suggests the involvement of ROS/JNK signaling in LPS-mediated Prx V induction. Furthermore, NO induces Prx V up-regulation that is ablated by the addition of inducible nitric oxide synthase inhibitor or deleted mutation of inducible nitric oxide synthase in LPS-stimulated microglia. Therefore, these results suggest that Prx V is induced by cooperative action among the ROS, RNS, and JNK signaling cascades. Interestingly, knockdown of Prx V expression causes the acceleration of microglia activation, including augmented ROS generation and JNK-dependent NO production. In summary, we demonstrate that Prx V plays a key role in the microglial activation process through modulation of the balance between ROS/NO generation and the corresponding JNK cascade activation.

[Peroxiredoxins, a new family of antioxidant proteins]

Current ideas are discussed about the structures and mechanisms of action of proteins that have been united at present into a family of thiol-specific antioxidants or peroxiredoxins, which protect the cells of different organisms from the action of hydrogen peroxide. Peroxiredoxins fulfill the same function as antioxidant enzymes such as catalases and glutathione-dependent peroxidases; however, their catalytic activity is lower than that of these enzymes. The level of expression of genes of peroxiredoxins is increased in many pathological states accompanied by oxidative stress, and today there is direct evidence for the important role of peroxiredoxins in the vital activity of cells.

Induction of peroxiredoxin I gene expression by LPS involves the Src/PI3K/JNK signalling pathway

Peroxiredoxin I (Prx I) belongs to a family of proteins with thiol-dependent peroxidase activity and is involved in the cellular protection against oxidative stress, the modulation of intracellular signalling cascades as well as the regulation of cell proliferation and apoptosis. In RAW 264.7 mouse macrophage cells Prx I was up-regulated on the mRNA and protein level by lipopolysaccharide (LPS). Treatment of cells with LPS increased the phosphorylation of c-Jun-NH(2) terminal kinase (JNK) and protein kinase B (PKB). Both SP600125, an inhibitor of JNK, and LY294002, an inhibitor of phosphoinositide 3-kinase (PI3K), dose-dependently decreased LPS-induced Prx I mRNA expression. Furthermore, up-regulation of Prx I mRNA by LPS was diminished by the Src tyrosine kinase inhibitor PP2 and the iNOS inhibitor L-NMMA. LPS-dependent induction of Prx I is likely mediated by an activator protein-1 site within the Prx I promoter region binding JunB and c-Fos. In contrast, NFkappaB was not involved in the activation of Prx I transcription. Our results suggest that the up-regulation of Prx I gene expression by LPS is part of the cellular response to stress and may protect against oxidative stress-related injury in RAW 264.7 cells.

Peroxiredoxin I plays a protective role against cisplatin cytotoxicity through mitogen activated kinase signals

The anticancer agent cis-diamminedichloroplatinum (cisplatin) is a first-line chemotherapeutic agent for oral cancer. Cell exposure to cisplatin is associated with increased oxidative stress and post-translational changes in components of apoptosis pathways, including p38 Mitogen-activated protein kinase (MAPK), c-Jun-NH2-kinase (JNK), and extracellular signal-regulated kinase (ERK). Peroxiredoxin (Prx) I is an oxidative stress-inducible protein expressed in many tissues and important for reducing reactive oxygen species in vivo; however, whether Prx I helps protect cells from cisplatin injury is unknown. In this report, we examined the effects of Prx I on cell sensitivity to cisplatin-induced apoptosis. Mouse embryo fibroblasts (MEFs) derived from Prx I-deficient mice showed increased cisplatin-induced apoptosis compared with wild-type MEFs. Cisplatin treatment also led to increased activation of p38 MAPK and JNK, and reduced ERK phosphorylation in Prx I-deficient MEFs compared with wild-type MEFs. Furthermore, JNK- and ERK-specific inhibitors protected the Prx I-deficient MEFs from cisplatin-induced apoptosis, but Prx I-deficient MEFs remained more sensitive than wild-type MEFs when treated with a p38 MAPK-specific inhibitor. These findings indicate that Prx I modulates the cisplatin-evoked activation of MAPKs that lead to apoptosis, and Prx I may thus represent a useful target as a protective therapy against cisplatin cytotoxicity.

Peroxiredoxin I is a negative regulator of Th2-dominant allergic asthma

Peroxiredoxin (Prx) I, a ubiquitous antioxidant enzyme, is known to protect against inflammation; however, its role in the allergic inflammation remains unidentified. We determined whether intristic Prx I protects against allergic asthma traits using Prx-I knockout (-/-) mice. Prx I (-/-) and wild-type (WT) mice were immunized with ovalbumin (OVA) plus aluminum potassium sulfate (Alum: Th2 adjuvant) and subsequently challenged with OVA. Twenty-four hours after the last OVA challenge, leukocyte influx including eosinophils into bronchoalveolar lavage fluid was significantly greater in Prx I (-/-) mice compared to that in WT mice. On the other hand, when these mice were immunized with OVA+complete Freund's adjuvant (Th1 adjuvant), opposite phenomenon was observed. In the presence of OVA/Alum, peribronchial inflammatory leukocyte infiltration, cholinergic airway resistance, and the lung expression of interleukin (IL)-2 were significantly greater and that of interferon-gamma was significantly lesser in Prx I (-/-) than in WT mice. In vitro, OVA/Alum-sensitized Prx I (-/-) T cells proliferated more profoundly than WT T cells when they were cocultured with syngeneic bone marrow-generated dendritic cells. These results indicate that endogenous Prx I protects against allergen-related Th2-type airway inflammation and hyperresponsiveness, at least partly, via the suppression of the lung expression of IL-2 and regulation of the Th1/Th2 balance in addition to its antioxidative properties. Furthermore, Prx I can inhibit allergen-specific T-cell proliferation through immunological synapse. Our findings implicate an alternative therapeutic value of Prx I in the treatment of Th2-skewed allergic airway inflammatory diseases such as atopic asthma.

Regulation of reactive oxygen species homeostasis by peroxiredoxins and c-Myc

Peroxiredoxins (Prxs) are highly conserved proteins found in most organisms, where they function primarily to scavenge reactive oxygen species (ROS). Loss of the most ubiquitous member of the family, Prx1, is associated with the accumulation of oxidatively damaged DNA and a tumor-prone phenotype. Prx1 interacts with the transcriptional regulatory domain of the c-Myc oncoprotein and suppresses its transforming activity. The DNA damage in tissues of prx1-/- mice is associated in some cases with only modest increases in total ROS levels. However, these cells show dramatic increases in nuclear ROS and reduced levels of cytoplasmic ROS, which explains their mutational susceptibility. In the current work, we have investigated whether changes in other ROS scavengers might account for the observed ROS redistribution pattern in prx1-/- cells. We show approximately 5-fold increases in Prx5 levels in prx1-/- embryo fibroblasts relative to prx1+/+ cells. Moreover, Prx5 levels normalize when Prx1 expression is restored. Prx5 levels also appear to be highly dependent on c-Myc, and chromatin immunoprecipitation experiments showed differential occupancy of c-Myc and Prx1 complexes at E-box elements in the prx5 gene proximal promoter. This study represents a heretofore unreported mechanism for the c-Myc-dependent regulation of one Prx family member by another and identifies a novel means by which cells reestablish ROS homeostasis when one of these family members is compromised.

Oxidative stress in the regulation of normal and neoplastic hematopoiesis

Recent evidence suggests that oxidative stress contributes significantly to the regulation of hematopoietic cell homeostasis. In particular, red blood cells and hematopoietic stem cells are highly sensitive to deregulated accumulation of reactive oxygen species (ROS). Unchecked ROS accumulation often leads to hemolysis, that is, to destruction and shortened life span of red blood cells. In addition, the process of erythroid cell formation is sensitive to ROS accumulation. Similarly, ROS buildup in hematopoietic stem cells compromises their function as a result of potential damage to their DNA leading to loss of quiescence and alterations of hematopoietic stem cell cycling. These abnormalities may lead to accelerated aging of hematopoietic stem cells or to hematopoietic malignancies.

Peroxiredoxin1 prevents excessive endothelial activation and early atherosclerosis

The peroxiredoxin (Prdx) family of antioxidant enzymes uses redox-active cysteines to reduce peroxides, lipid hydroperoxides, and peroxynitrites. Prdx1 is known to be important to protect red blood cells against reactive oxygen species and in tumor prevention. In this study, the role of Prdx1 in inflammation, thrombosis, and atherosclerosis was investigated. Using intravital microscopy, we showed that the number of leukocytes rolling per minute in unstimulated veins was increased by 2.5-fold in Prdx1(-/-) compared to Prdx1(+/+) mice. In Prdx1(-/-) mice, 50% of leukocytes rolled at a velocity <10 mum/sec compared with 10% in Prdx1(+/+) mice, suggesting that adhesion molecule density on the endothelium may have been increased by Prdx1 deficiency. Indeed, endothelial P-selectin, soluble P-selectin, and von Willebrand factor in plasma were increased in Prdx1(-/-) mice compared to Prdx1(+/+) mice, indicating elevated Weibel-Palade body release. In contrast to this excessive endothelial activation, Prdx1(-/-) platelets showed no sign of hyperreactivity, and their aggregation both in vitro and in vivo was normal. We also examined the role of Prdx1 in the apoE(-/-) murine spontaneous model of atherosclerosis. Prdx1(-/-)/apoE(-/-) mice fed normal chow developed larger, more macrophage-rich aortic sinus lesions than Prdx1(+/+)/apoE(-/-) mice, despite similar amounts and size distributions of cholesterol in their plasma lipoproteins. Thus, Prdx1 protects against excessive endothelial activation and atherosclerosis, and the Prdx1(-/-) mice could serve as an animal model susceptible to chronic inflammation.

Protective effects of peroxiredoxin-1 at the injured blood-brain barrier

Reactive oxygen species (ROS) play a pivotal role in the development of neuroinflammatory disorders, such as multiple sclerosis (MS). Here, we studied the effect of ROS on protein expression in brain endothelial cells (BECs) using proteomic techniques and show that long-term exposure to ROS induces adaptive responses in BECs to counteract an oxidative attack. ROS induce differential protein expression in BECs, among which is peroxiredoxin-1 (Prx1). To further study the role of Prx1 we established a BEC line overexpressing Prx1. Our data indicate that Prx-1 overexpression protects BECs from ROS-induced cell death, reduces adhesion and subsequent transendothelial migration of monocytes by decreasing intercellular adhesion molecule-1 expression, and enhances the integrity of the BEC layer. Interestingly, vascular Prx1 immunoreactivity was markedly upregulated in inflammatory lesions of experimental autoimmune encephalomyelitis (EAE) animals and active demyelinating MS lesions. These findings indicate that enhanced vascular Prx1 expression may reflect the occurrence of vascular oxidative stress in EAE and MS. On the other hand, it may function as an endogenous defense mechanism to inhibit leukocyte infiltration and counteract ROS-induced cellular injury.

Peroxiredoxin I protects gastric mucosa from oxidative injury induced by H. pylori infection

BACKGROUND AND AIM

Helicobacter pylori (H. pylori) infection enhances the production of reactive oxygen species and peroxynitrite, thereby resulting in oxidative tissue damage. In this study, we examined the role of peroxiredoxin I (Prx I), a stress-induced antioxidant enzyme, in protecting gastric mucosa from H. pylori-induced gastric mucosal injury.

METHODS

Wild type (Prx I(+/+)) and Prx I-deficient type (Prx I(-/-)) mice were maintained for 2 to 12 months with or without infection of H. pylori, Sydney strain-1. Gastric mucosal expression of Prx I was assessed by immunoblot analysis and immunohistochemistry. The degree of gastritis was evaluated by the updated Sydney system and by mucosal levels of inflammatory cytokines (MIP-2, IL-1beta, and TNF-alpha). Oxidative DNA injury and apoptosis were analyzed by mucosal level of 8-hydroxy-2'-deoxyguanosine, and the number of apoptotic cells stained with a single-stranded DNA antibody, respectively.

RESULTS

H. pylori infection upregulated gastric mucosal Prx I expression in the Prx I(+/+) but not the Prx I(-/-) mice. H. pylori infection also induced more severe gastritis and a more prominent increase in MIP level, more marked oxidative DNA injury, and apoptosis in the Prx I(-/-) than the Prx I(+/+) mice. In the absence of H. pylori infection, no changes were demonstrated in gastric mucosa in either the Prx I(+/+) or the Prx I(-/-) mice.

CONCLUSION

These data suggest that H. pylori infection upregulates gastric mucosal Prx I expression, and further, that Prx I plays an important role in gastric mucosal protection against oxidative injury induced by H. pylori infection.

Inhibition of phorbol ester-dependent peroxiredoxin I gene activation by lipopolysaccharide via phosphorylation of RelA/p65 at serine 276 in monocytes

Peroxiredoxin I (Prx I) is an antioxidant enzyme with thioredoxin-dependent peroxidase activity which is involved in various cellular processes such as regulation of cell proliferation. Here, it is shown that the proinflammatory mediator lipopolysaccharide (LPS) inhibits the induction of Prx I expression and promoter activity by the phorbol ester 12-O-tetradecanoylphorbol- 13-acetate (TPA) in RAW264.7 monocytes, but not that of cyclooxygenase-2. LPS-dependent repression of Prx I induction by TPA was mediated via a newly identified kappaB site in the Prx I promoter, but the "classical" NF-kappaB cascade was not involved in this regulatory pathway, because IkappaB did not affect LPS-mediated Prx I repression. By contrast, phosphorylation of p65 at serine 276, which enhances the transcriptional activity of NF-kappaB, was up-regulated by TPA and was reduced by simultaneous exposure to LPS. Functional studies with Gal4-p65 constructs revealed that serine 276 is crucial to confer LPS-dependent repression of TPA-mediated induction of p65 transactivation. Finally, repression of TPA-dependent Prx I induction by LPS was mediated via Bruton's tyrosine kinase as indicated by studies with the pharmacological inhibitor LFM-A13. In summary, LPS-dependent inhibition of Prx I gene activation by TPA in monocytes is regulated via a pathway that involves phosphorylation of the NF-kappaB subunit p65 at serine 276.

Stress-induced peroxiredoxins

Some members of the Prx family are up-regulated in cells under stress conditions. Prx I is the major cytoplasmic Prx and is known as a stress-inducible antioxidant enzyme. Various stress agents or conditions activate Prx I gene expression in vitro and in vivo. The transcription factor Nrf2 and its inhibitor Keap1 play an essential role in the regulation of the stress-induced Prx I gene activation through the ARE/EpRE (antioxidant/electrophile response element). The expression levels of Prx II and III are also up-regulated under stress conditions, although the molecular mechanisms of their up-regulation have not yet been thoroughly studied. Gene expression of both Prx I and II is activated by X-ray irradiation of the testis. Mitochondrial Prx III is up-regulated by stress agents in both cultured cells and experimental animals. The up-regulation of the Prxs in cells and tissues under oxidative stress conditions is one of the cellular recovery responses after oxidative damage.

Expression of peroxiredoxin I in plasma cells of oral inflammatory diseases

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