Mammalian peroxiredoxin isoforms can reduce hydrogen peroxide generated in response to growth factors and tumor necrosis factor-alpha

Human thioredoxin-1 ameliorates experimental murine colitis in association with suppressed macrophage inhibitory factor production

BACKGROUND & AIMS

Thioredoxin-1 (TRX) is a small multifunctional protein with antioxidative and redox-regulating functions. In this study, we investigated the significance of TRX in patients with inflammatory bowel disease (IBD) and the ability and mechanism to ameliorate experimental colitis.

METHODS

Serum TRX and macrophage migration inhibitory factor (MIF) levels were measured in patients with IBD. The effects of TRX were evaluated in a dextran sulfate sodium (DSS)-induced colitis model by comparing TRX-overexpressing transgenic (TRX-TG) and control mice. We further evaluated the effect of recombinant human TRX (rhTRX) administration on DSS-induced colitis and colonic inflammation of interleukin (IL)-10 knockout (IL-10 KO) mice. Colonic inflammation was examined clinically and histologically. Proinflammatory cytokine levels were examined in colonic tissues, and MIF levels were measured in colonic tissues and sera in mice. The effect of TRX on MIF production was also analyzed in vitro.

RESULTS

Serum TRX and MIF levels were significantly higher in patients with IBD than normal controls, and TRX levels correlated with disease activity. TRX significantly ameliorated DSS-induced colitis and colonic inflammation of IL-10 KO mice. Increase of tumor necrosis factor-alpha and interferon-gamma in colonic tissues was significantly suppressed in TRX-TG mice compared with wild-type mice. MIF levels in colonic tissues and sera were significantly lower in TRX-TG mice than in wild-type mice, irrespective of DSS administration. Anti-TRX treatment exacerbated DSS-induced colitis. In vitro studies demonstrated that rhTRX suppressed MIF production in human monocyte cells.

CONCLUSIONS

TRX might have a potential as a novel therapeutic agent for the treatment of IBD.

Modulation of vascular smooth muscle signaling by reactive oxygen species

Modulation of signaling in vascular cells by reactive oxygen species (ROS) affects many aspects of cellular function, including growth, migration, and contraction. NADPH oxidases, important sources of ROS, regulate many growth-specific and migration-related signaling pathways. Identifying the precise intracellular targets of ROS enhances understanding of their role in cardiovascular physiology and pathophysiology.

Prx1 suppresses radiation-induced c-Jun NH2-terminal kinase signaling in lung cancer cells through interaction with the glutathione S-transferase Pi/c-Jun NH2-terminal kinase complex

Radiotherapy is one of the major treatment modalities for lung cancer. Cell killing by ionizing radiation is mediated primarily through the reactive oxygen species (ROS) and ROS-driven oxidative stress. Prx1, a peroxiredoxin family member, was shown to be frequently elevated in lung cancer cells and tissues. Although the antioxidant function of Prx1 is expected to affect the radiotherapy response of lung cancer, the physiologic significance of its peroxidase activity in irradiated cells is unclear because the catalytic Cys52 is easily inactivated by ROS due to its overoxidation to sulfinic or sulfonic acid. In this study, we investigated the role of Prx1 in radiation sensitivity of human lung cancer cells, with special emphasis on the redox status of the catalytic Cys52. We found that overexpression of Prx1 enhances the clonogenic survival of irradiated cells and suppresses ionizing radiation-induced c-Jun NH2-terminal kinase (JNK) activation and apoptosis. The peroxidase activity of Prx1, however, is not essential for inhibiting JNK activation. The latter effect is mediated through its association with the glutathione S-transferase pi (GSTpi)-JNK complex, thereby preventing JNK release from the complex. Reduced JNK activation is observed when the peroxidase activity of Prx1 is compromised by Cys52 overoxidation or in the presence of the Cys52 to Ser52 mutant (Prx1C52S) lacking peroxidase activity. We show that both Prx1 and Prx1C52S interact with the GSTpi-JNK complex and suppress the release of JNK from the complex. Our study provides new insight into the antiapoptotic function of Prx1 in modulating radiosensitivity and provides the impetus to monitor the influence of Prx1 levels in the management of lung cancer.

Proteomic analysis of pulmonary sclerosing hemangioma

Sclerosing hemangioma (SH) is a rare benign pulmonary tumor derived from the primitive respiratory epithelium. However, the pathogenesis of SH has not yet been clear. Surfactant protein, thyroid transcription factor-1, epithelial membrane antigen, cytokeratin, and vimentin have been identified in SH by immunohistochemistry and electron microscopy. To identify proteins specifically regulated in SH, 2-D PAGE was performed using SH and paired normal tissues. Ten selected differentially expressed protein spots were identified by PMF, MALDI-TOF-MS, and database searching. Apolipoprotein A-1, antizyme inhibitor, heat shock 27-kDa protein 1, and antioxidant proteins, such as peroxiredoxin II (Prx II) and GST, were identified among the down-regulated proteins in SH. Western blot and immunohistochemistry confirmed reduced expressions of Prx II and GST in SH versus normal lung tissue. This study is the first report on the reduced expressions of Prx II and GST in SH.

Dual role of peroxiredoxin I in macrophage-derived foam cells

We and others have shown that foam cell formation initiated by exposing macrophages to oxidized low density lipoprotein (oxLDL) triggers the differential expression of a number of proteins. Specifically, our experiments have identified peroxiredoxin I (Prx I) as one of these up-regulated proteins. The peroxiredoxins, a family of peroxidases initially described for their antioxidant capability, have generated recent interest for their potential to regulate signaling pathways. Those studies, however, have not examined peroxiredoxin for a potential dual functionality as both cytoprotective antioxidant and signal modulator in a single, oxidant-stressed system. In this report, we examine the up-regulation of Prx I in macrophages in response to oxLDL exposure and its ability to function as both antioxidant enzyme and regulator of p38 MAPK activation. As an antioxidant, induction of Prx I expression led to improved cell survival following treatment with oxLDL or tert-butyl hydroperoxide. The improved survival coincided with a decrease in measurable reactive oxygen species (ROS), and both the increased survival and reduced ROS were reversed by Prx I small interfering RNA transfection. Additionally, our data show that activation of p38 MAPK in oxLDL-treated macrophages was dependent on the up-regulation of Prx I. Reduction of Prx I expression by small interfering RNA transfection resulted in a significant decrease in p38 MAPK activation, whereas the up-regulation of Prx I expression with either oxLDL or ethoxyquin led to increased p38 MAPK activation. These results are consistent with multiple roles for Prx I in macrophage-derived foam cells that include functionality as both an antioxidant and a regulator of oxidant-sensitive signal transduction.

Evaluation of the molecular mechanisms involved in the gain of function of a Li-Fraumeni TP53 mutation

The TP53 tumor suppressor gene is the most frequent target for genetic alterations in human cancer. TP53 gene alterations may result in the gain of oncogenic functions such as neoangiogenesis and resistance to therapy. The TP53 germ line mutation c.659A>C (p.Y220S) was identified in stored DNA from related patients with Li-Fraumeni syndrome (LFS) who died after developing clinically aggressive tumors. All of the patients were treated with protocols that included doxorubicin hydrochloride (DX) as a pivotal drug. To define the in vitro mutational phenotype of this germ line mutation, we used murine fibroblasts explanted from wild-type (wt) and p53 knockout (KO) mice from the same littermate. p53Y220S and p53R175H fibroblasts, obtained from p53KO fibroblasts transfected with expression vectors encoding the human Y220S and R175H p53 mutants, respectively, exhibited resistance to DX treatment. Moreover, p53Y220S fibroblasts exhibited angiogenetic properties, and after DX treatment, p53Y220S failed to translocate into the nucleus and showed an increase in its cytosolic levels. DX treatment does not influence p53 distribution within the nuclear and cytosolic compartments in p53R175H fibroblasts. Peroxiredoxin II (Prx II), a protein that is involved in eliminating reactive oxygen species (ROS), showed increased expression intensity in p53Y220S fibroblasts after DX treatment, as observed by two-dimensional electrophoresis analysis. Moreover, Thioredoxin (Trx), a protein that cooperates with Prx II, is overexpressed in p53Y220S mutants under basal conditions. These data suggest a relationship between the presence of the p53Y220S mutation and enhanced levels of Prx II and Trx in mutant fibroblasts. Since one of the mechanisms of the DX antitumor effect has been ascribed to production of ROS, future studies will evaluate the involvement of PrxII and Trx in the chemoresistance of p53Y220S fibroblasts to DX.

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

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

Thioredoxin networks in the malarial parasite Plasmodium falciparum

The intraerythrocytic protozoan parasite Plasmodium falciparum is responsible for more than 500 million clinical cases of tropical malaria annually. Although exposed to high fluxes of reactive oxygen species, Plasmodium lacks the antioxidant enzymes catalase and glutathione peroxidase. Thus, the parasite depends on the antioxidant capacity of its host cell and its own peroxidases. These are fuelled by the thioredoxin system and are considered to represent the major defense line against peroxides. Five peroxidases that act in different compartments have been described in P. falciparum. They include two typical 2-Cys peroxiredoxins (Prx), a 1-Cys Prx, the so-called antioxidant protein (AOP), which is a further Prx acting on the basis of a 1-Cys mechanism, and a glutathione peroxidase-like thioredoxin peroxidase. Because of their central function in redox regulation and antioxidant defense, some of these proteins might represent highly interesting targets for structure-based drug development. In this article we summarize the present knowledge on the thioredoxin and peroxiredoxin metabolism in malaria parasitized red blood cells. We furthermore report novel data on the biochemical and kinetic characterization of different thioredoxins, of AOP, and of the classic 1-Cys peroxiredoxin of P. falciparum.

SOD2-deficiency sideroblastic anemia and red blood cell oxidative stress

Iron overload is a feature of an array of human disorders such as sideroblastic anemias, a heterogeneous group of erythropoietic disorders without identified cause in most cases. However, sideroblastic anemias appear to result from a disturbance at the interface between mitochondrial function and iron metabolism. A defining feature is excessive iron deposition within mitochondria of developing red cells, the consequences of which are an increase in cellular free radicals production, increased damage to proteins, and reduced cell survival. Because of its mitochondrial location, superoxide dismutase (SOD2) is the principal defense against the toxicity of superoxide anions generated by the oxidative phosphorylation. We have used hematopoietic stem cell transplantation to study blood cells lacking SOD2. We became interested in the role SOD2 plays in the metabolism of superoxide anions during erythroid development, as anemia is the major phenotype in transplanted animals. Our exploration of this model suggests that oxidative stress-and in particular, mitochondrial- derived oxidants-plays an important role in the pathogenesis of the human disorder, sideroblastic anemia. Here we review the relation between mitochondrial dysfunction and sideroblastic anemia, describe several methods for assessing oxidative damage to mature or developing red cells, present data on, and discuss the potential of antioxidant therapy for this disorder.

Mitochondrial NADP+-dependent isocitrate dehydrogenase protects cadmium-induced apoptosis

Cadmium is known to exhibit high affinity for thiol groups and may therefore severely disturb many cellular functions. We have demonstrated that the control of mitochondrial redox balance and oxidative damage is one of the primary functions of mitochondrial NADP+-dependent isocitrate dehydrogenase (IDPm). When exposed to cadmium, IDPm was susceptible to loss of enzyme activity and structural alterations. Site-directed mutagenesis confirms that binding of cadmium occurs to a Cys379 of IDPm. We examined the antioxidant mechanism-mediated protective role of IDPm against cadmium-induced apoptosis with human embryonic kidney 293 cells transfected with the IDPm cDNA in sense and antisense orientations. As a result, we observed a clear inverse relationship between the amount of IDPm expressed in target cells and their susceptibility to cadmium-induced modulation of cellular redox status and apoptosis. In addition, loss of glutaredoxin (Grx, thioltransferase) activity by cadmium was more pronounced in antisense cells compared with the sense cells. When oxalomalate, a competitive inhibitor of IDPm, was administered to mice, inhibition of IDPm and Grx and enhanced susceptibility to apoptosis were observed upon their exposure to cadmium. These results suggest that IDPm plays an important protective role in cadmium-induced apoptosis by maintaining cellular redox status and by protection of Grx activity.

Enhanced expression of peroxiredoxin I and VI correlates with development, recurrence and progression of human bladder cancer

PURPOSE

PRDXs are antioxidant enzymes that have an important role in cell differentiation, proliferation and apoptosis. We investigated whether PRDX I and VI expression is related to bladder cancer.

MATERIALS AND METHODS

PRDX I and VI mRNA levels were examined in 149 tumor specimens in patients with primary bladder cancer, in 19 specimens with corresponding normal-appearing bladder mucosa surrounding cancer and in 18 with normal bladder mucosa using real-time polymerase chain reaction.

RESULTS

PRDX I and VI expression in bladder cancer (0.6644 and 0.1455 pg/ml) was significantly higher than in normal tissue (0.0278 and 0.0542 pg/ml, each p <0.05) and higher than in corresponding normal bladder mucosa surrounding cancer (0.2353 and 0.0304 pg/ml, respectively, each p <0.0005). PRDX I and VI expression was enhanced in patients with no recurrence (0.8148 and 0.2232 pg/ml) and no progression (0.7405 and 0.1716 pg/ml) compared with levels in those with recurrence (0.4314 and 0.0588 pg/ml) and progression (0.4338 and 0.0668 pg/ml, respectively, each p <0.05). PRDX I and VI expression did not correlate with disease-free survival in patients with bladder cancer.

CONCLUSIONS

Enhanced PRDX I and VI expression is strongly associated with bladder cancer development. Moreover, enhanced PRDX I and VI expression is also positively associated with a low rate of bladder cancer recurrence and progression. It might be useful as a marker for assessing the recurrence or progression of human bladder cancer.

Oxidative/nitrosative stress and peroxiredoxin 2 are associated with grade and prognosis of human renal carcinoma

Peroxiredoxins (Prxs) 1-6 were assessed in 138 renal cell carcinomas (RCC) using immunohistochemistry and selected samples by Western blotting analysis. Oxidative/nitrosative damage was evaluated using nitrotyrosine immunoreactivity. The expressions of Prxs were correlated with tumor grade and survival and nitrotyrosine reactivity. Non-malignant kidney tubular cells showed positivity with variable intensity for all six Prxs. In RCCs, most cases were positive for Prxs 1 and 2, while only 15-20% of tumors showed expression for Prxs 3 and 4. Prx 2 was associated with tumors of a lower grade (p=0.009) and with a lower frequency of distant metastases (p=0.046). Patients with tumors expressing Prx2 had better prognosis (p=0.027). Instead, nitrotyrosine was significantly associated with high grade tumors (p=0.001). Compared with the non-malignant kidney tubular cells, low Prx expression in the tumor cells can make them more susceptible to oxidative damage. Prx 2 was more abundantly expressed in low grade tumors, suggesting that this protein could play a role in preventing the development of oxidative damage, which in turn can lead to the activation of pathways leading to aggressive tumors.

Overexpression of mitochondrial peroxiredoxin-3 prevents left ventricular remodeling and failure after myocardial infarction in mice

BACKGROUND

Mitochondrial oxidative stress and damage play major roles in the development and progression of left ventricular (LV) remodeling and failure after myocardial infarction (MI). We hypothesized that overexpression of the mitochondrial antioxidant, peroxiredoxin-3 (Prx-3), could attenuate this deleterious process.

METHODS AND RESULTS

We created MI in 12- to 16-week-old, male Prx-3-transgenic mice (TG+MI, n=37) and nontransgenic wild-type mice (WT+MI, n=39) by ligating the left coronary artery. Prx-3 protein levels were 1.8 times higher in the hearts from TG than WT mice, with no significant changes in other antioxidant enzymes. At 4 weeks after MI, LV thiobarbituric acid-reactive substances in the mitochondria were significantly lower in TG+MI than in WT+MI mice (mean+/-SEM, 1.5+/-0.2 vs 2.2+/-0.2 nmol/mg protein; n=8 each, P<0.05). LV cavity dilatation and dysfunction were attenuated in TG+MI compared with WT+MI mice, with no significant differences in infarct size (56+/-1% vs 55+/-1%; n=6 each, P=NS) and aortic pressure between groups. Mean LV end-diastolic pressures and lung weights in TG+MI mice were also larger than those in WT+sham-operated mice but smaller than those in WT+MI mice. Improvement in LV function in TG+MI mice was accompanied by a decrease in myocyte hypertrophy, interstitial fibrosis, and apoptosis in the noninfarcted LV. Mitochondrial DNA copy number and complex enzyme activities were significantly decreased in WT+MI mice, and this decrease was also ameliorated in TG+MI mice.

CONCLUSIONS

Overexpression of Prx-3 inhibited LV remodeling and failure after MI. Therapies designed to interfere with mitochondrial oxidative stress including the antioxidant Prx-3 might be beneficial in preventing cardiac failure.

Glutathione regulates susceptibility to oxidant-induced mitochondrial DNA damage in human lymphocytes

Oxidative damage to mitochondrial DNA (mtDNA) interferes with the expression of mitochondrial-encoded subunits of the electron transport complexes of oxidative phosphorylation. MtDNA is protected by several mitochondrial antioxidant systems, but the specific importance of glutathione is unknown. We hypothesized that glutathione protects mtDNA from oxidative damage in human blood lymphocytes and that glutathione depletion increases susceptibility to mtDNA depletion, which increases vulnerability to apoptosis. MtDNA damage was measured in human blood lymphocytes exposed to tert-butyl-hydroperoxide (t-BOOH) or t-BOOH plus the glutathione analog, glutathione ethyl ester (GEE). Mitochondrial oxidative stress, mtDNA damage, and susceptibility to apoptosis were analyzed after glutathione depletion with buthionine sulfoximine (BSO). The data show selective damage to lymphocyte mtDNA at low concentrations of tBOOH that is attenuated by glutathione supplementation. Moreover, inhibition of glutathione synthesis led to lymphocyte ROS generation and mtDNA damage, and increased susceptibility to receptor-mediated apoptosis. These findings implicate the glutathione system in maintaining mtDNA integrity and resistance to apoptosis in lymphocytes and suggest that assessment of mtDNA damage in blood lymphocytes may be a useful marker of oxidative stress in humans.

Inhibition of lung tumor growth and augmentation of radiosensitivity by decreasing peroxiredoxin I expression

PURPOSE

In this study, we examined the role of peroxiredoxin I (Prx I) in lung cancer cell growth in vitro and in vivo and its influence on these tumor cells' sensitivity to radiotherapy.

METHODS AND MATERIALS

We established stable transfectants of A549 (p53+) and H1299 (p53-) lung carcinoma cell lines with Prx I antisense to downregulate their Prx I protein. We then examined their in vitro biologic changes and used nude mice xenografts of these cell lines to compare tumor invasion, spontaneous metastatic capacity, and sensitivity to radiotherapy.

RESULTS

The Prx I antisense transfectants of both cell lines showed a significant reduction in Prx I protein production. Prx I antisense transfectants grew more slowly than did the wild type. As xenografts in mice, A549 Prx I antisense transfectants showed a threefold delay in the generation of palpable tumors. The incidence of spontaneous metastasis of Prx I antisense transfectants was significantly less than that of the wild-type cells. Furthermore, irradiation of Prx I antisense transfectants caused more than twice the growth delay compared with the wild type.

CONCLUSION

The results of these studies suggest that inactivation of Prx I may be a promising approach to improve the treatment outcome of patients with lung cancer.

Molecular mechanism of the reduction of cysteine sulfinic acid of peroxiredoxin to cysteine by mammalian sulfiredoxin

Among many proteins with cysteine sulfinic acid (Cys-SO2H) residues, the sulfinic forms of certain peroxiredoxins (Prxs) are selectively reduced by sulfiredoxin (Srx) in the presence of ATP. All Srx enzymes contain a conserved cysteine residue. To elucidate the mechanism of the Srx-catalyzed reaction, we generated various mutants of Srx and examined their interaction with PrxI, their ATPase activity, and their ability to reduce sulfinic PrxI. Our results suggest that three surface-exposed amino acid residues, corresponding to Arg50, Asp57, and Asp79 of rat Srx, are critical for substrate recognition. The presence of the sulfinic form (but not the reduced form) of PrxI induces the conserved cysteine of Srx to take the gamma-phosphate of ATP and then immediately transfers the phosphate to the sulfinic moiety of PrxI to generate a sulfinic acid phosphoryl ester (Prx-Cys-S(=O)OPO3(2-)). This ester is reductively cleaved by a thiol molecule (RSH) such as GSH, thioredoxin, and dithiothreitol to produce a disulfide-S-monoxide (Prx-Cys-S(=O)-S-R). The disulfide-S-monoxide is further reduced through the oxidation of three thiol equivalents to complete the catalytic cycle and regenerate Prx-Cys-SH.

Thioredoxins in bacteria: functions in oxidative stress response and regulation of thioredoxin genes

Thioredoxins fulfill a number of different important cellular functions in all living organisms. In bacteria, thioredoxin genes are often regulated by external factors. In turn, thioredoxins influence the expression of many other genes. The multiple and important functions of thioredoxins in cells necessitate to appropriately adjust their level. This review outlines different strategies that have evolved for the regulation of bacterial thioredoxin genes. It also summarizes effects of thioredoxins on gene regulation and presents a recent model for a redox-dependent gene regulation that is mediated by thioredoxins.

Proteome analysis of hepatocellular carcinoma by laser capture microdissection

Hepatocellular carcinoma (HCC) is one of the most frequent visceral neoplasia worldwide and is a multifactorial and multistage pathogenesis that finally leads to the deregulation of cell homeostasis. Laser capture microdissection (LCM) may allow a more ready identification of differences in protein expression in selected cell types or areas of tissue, and microscopic regions as small as 3-5 microm in diameter can be sampled. Here we applied the LCM to the proteomic study of hepatitis B-related HCC and surrounding non-tumor tissues. Proteome alterations were observed using 2-DE and ESI-MS/MS, and alterations in the proteome were examined. Twenty protein spots were selected, of which 11 proteins were significantly altered in the HCC compared with the surrounding non-tumor tissues. Of the proteins that were selected, peroxiredoxin 2, apolipoprotein A-I precursor, 3-hydroxyacyl-CoA dehydrogenase type II, and 14.5-kDa translational inhibitor protein appear to be novel candidates as useful hepatitis B-related HCC markers. This study indicates that LCM is a useful technological method in the proteomic study of cancer tissue. The proteins revealed in this experiment can be used in the future for studies pertaining to hepatocarcinogenesis, or as diagnostic markers and therapeutic targets for HCC associated with hepatitis B virus infection.

High expression of antioxidant proteins in dendritic cells: possible implications in atherosclerosis

Dendritic cells (DCs) display the unique ability to activate naive T cells and to initiate primary T cell responses revealed in DC-T cell alloreactions. DCs frequently operate under stress conditions. Oxidative stress enhances the production of inflammatory cytokines by DCs. We performed a proteomic analysis to see which major changes occur, at the protein expression level, during DC differentiation and maturation. Comparative two-dimensional gel analysis of the monocyte, immature DC, and mature DC stages was performed. Manganese superoxide dismutase (Mn-SOD) reached 0.7% of the gel-displayed proteins at the mature DC stage. This important amount of Mn-SOD is a primary antioxidant defense system against superoxide radicals, but its product, H(2)O(2), is also deleterious for cells. Peroxiredoxin (Prx) enzymes play an important role in eliminating such peroxide. Prx1 expression level continuously increased during DC differentiation and maturation, whereas Prx6 continuously decreased, and Prx2 peaked at the immature DC stage. As a consequence, DCs were more resistant than monocytes to apoptosis induced by high amounts of oxidized low density lipoproteins containing toxic organic peroxides and hydrogen peroxide. Furthermore DC-stimulated T cells produced high levels of receptor activator of nuclear factor kappaB ligand, a chemotactic and survival factor for monocytes and DCs. This study provides insights into the original ability of DCs to express very high levels of antioxidant enzymes such as Mn-SOD and Prx1, to detoxify oxidized low density lipoproteins, and to induce high levels of receptor activator of nuclear factor kappaB ligand by the T cells they activate and further emphasizes the role that DCs might play in atherosclerosis, a pathology recognized as a chronic inflammatory disorder.

Regulation of replicative senescence by NADP+ -dependent isocitrate dehydrogenase

The free radical hypothesis of aging postulates that senescence is due to an accumulation of cellular oxidative damage, caused largely by reactive oxygen species that are produced as by-products of normal metabolic processes. Recently, we demonstrated that the control of cytosolic and mitochondrial redox balance and the cellular defense against oxidative damage is one of the primary functions of cytosolic (IDPc) and mitochondrial NADP+ -dependent isocitrate dehydrogenase (IDPm) by supplying NADPH for antioxidant systems. In this paper, we demonstrate that modulation of IDPc or IDPm activity in IMR-90 cells regulates cellular redox status and replicative senescence. When we examined the regulatory role of IDPc and IDPm against the aging process with IMR-90 cells transfected with cDNA for IDPc or IDPm in sense and antisense orientations, a clear inverse relationship was observed between the amount of IDPc or IDPm expressed in target cells and their susceptibility to senescence, which was reflected by changes in replicative potential, cell cycle, senescence-associated beta-galactosidase activity, expression of p21 and p53, and morphology of cells. Furthermore, lipid peroxidation, oxidative DNA damage, and intracellular peroxide generation were higher and cellular redox status shifted to a prooxidant condition in the cell lines expressing the lower level of IDPc or IDPm. The results suggest that IDPc and IDPm play an important regulatory role in cellular defense against oxidative stress and in the senescence of IMR-90 cells.

Regulation of reactive oxygen species, DNA damage, and c-Myc function by peroxiredoxin 1

Overexpression of c-Myc results in transformation and multiple other phenotypes, and is accompanied by the deregulation of a large number of target genes. We previously demonstrated that peroxiredoxin 1 (Prdx1), a scavenger of reactive oxygen species (ROS), interacts with a region of the c-Myc transcriptional regulatory domain that is essential for transformation. This results either in the suppression or enhancement of some c-Myc functions and in the altered expression of select target genes. Most notably, c-Myc-mediated transformation is inhibited, implying a tumor suppressor role for Prdx1. Consistent with this, prdx1-/- mice develop age-dependent hemolytic anemias and/or malignancies. We now show that erythrocytes and embryonic fibroblasts from these animals contain higher levels of ROS, and that the latter cells show evidence of c-Myc activation, including the ability to be transformed by a ras oncogene alone. In contrast, other primary cells from prdx1-/- mice do not have elevated ROS, but nonetheless show increased oxidative DNA damage. This apparent paradox can be explained by the fact that ROS localize primarily to the cytoplasm of prdx1+/+ cells, whereas in prdx1-/- cells, much higher levels of nuclear ROS are seen. We suggest that increased DNA damage and tumor susceptibility in prdx1-/- animals results from this shift in intracellular ROS. prdx1-/- mice should be useful in studying the role of oxidative DNA damage in the causation of cancer and its prevention by antioxidants. They should also help in studying the relationship between oncogenes such as c-Myc and DNA damage.

Phosphorylation and concomitant structural changes in human 2-Cys peroxiredoxin isotype I differentially regulate its peroxidase and molecular chaperone functions

The H2O2-catabolizing peroxidase activity of human peroxiredoxin I (hPrxI) was previously shown to be regulated by phosphorylation of Thr90. Here, we show that hPrxI forms multiple oligomers with distinct secondary structures. HPrxI is a dual function protein, since it can behave either as a peroxidase or as a molecular chaperone. The effects of phosphorylation of hPrxI on its protein structure and dual functions were determined using site-directed mutagenesis, in which the phosphorylation site was substituted with aspartate to mimic the phosphorylated status of the protein (T90D-hPrxI). Phosphorylation of the protein induces significant changes in its protein structure from low molecular weight (MW) protein species to high MW protein complexes as well as its dual functions. In contrast to the wild type (WT)- and T90A-hPrxI, the T90D-hPrxI exhibited a markedly reduced peroxidase activity, but showed about sixfold higher chaperone activity than WT-hPrxI.

2-Cys peroxiredoxin function in intracellular signal transduction: therapeutic implications

H(2)O(2) is a reactive oxygen species that has drawn much interest because of its role as a second messenger in receptor-mediated signaling. Mammalian 2-Cys peroxiredoxins have been shown to eliminate efficiently the H(2)O(2) generated in response to receptor stimulation. 2-Cys peroxiredoxins are members of a novel peroxidase family that catalyze the H(2)O(2) reduction reaction in the presence of thioredoxin, thioredoxin reductase and NADPH. Several lines of evidence suggest that 2-Cys peroxiredoxins have dual roles as regulators of the H(2)O(2) signal and as defenders of oxidative stress. In particular, 2-Cys peroxiredoxin appears to provide selective, specific and localized control of receptor-mediated signal transduction. Thus, the therapeutic potential of 2-Cys peroxiredoxins is clear for diseases, such as cancer and cardiovascular diseases, that involve reactive oxygen species.

Antioxidant-like protein 1 is altered in non-pyramidal cells and expressed in astrocytes in the gerbil hippocampal CA1 region after transient forebrain ischemia

In the present study, we observed chronological changes of antioxidant-like protein 1 (AOP-1) in the gerbil hippocampal CA1 region after 5 min of transient forebrain ischemia using immunohistochemistry and western blot. AOP-1 was significantly altered in the CA1 region after transient ischemia. In the sham-operated group, AOP-1 immunoreactivity was detected in pyramidal and non-pyramidal cells of the CA1 region. At 30 min after ischemic insult, AOP-1 immunoreactivity and protein level was decreased in the CA1 region. At 12 h after ischemic insult, AOP-1 immunoreactivity and protein level was highest in this region. At this time, after ischemia, AOP-1 immunoreactivity in non-pyramidal cells was high compared to the sham-operated group. Based on double immunofluorescence study, AOP-1-immunoreactive neurons were identified as GABAergic, which were stained with GAD or parvalbumin. Thereafter, AOP-1 immunoreactivity and protein levels were decreased time-dependently. From 4 days after ischemic insult, AOP 1 immunoreactivity was generally expressed in astrocytes. Five days after ischemic insult, AOP-1 immunoreactivity and protein level was increased again to 1.4 folds compared to that of the sham-operated group. In brief, AOP-1 immunoreactivity was increased in GABAergic non-pyramidal cells in the hippocampal CA1 region at early time after ischemic insult and was expressed in astrocytes at late time after ischemia. This result suggests that AOP-1 may be important role in homeostasis of GABAergic neurons because these neurons are resistant to ischemic damage.

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

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

Impaired homeostasis and phenotypic abnormalities in Prdx6-/-mice lens epithelial cells by reactive oxygen species: increased expression and activation of TGFbeta

PRDX6, a member of the peroxiredoxins (PRDXs) family, is a key player in the removal of reactive oxygen species (ROS). Using targeted inactivation of the Prdx6 gene, we present evidence that the corresponding protein offsets the deleterious effects of ROS on lens epithelial cells (LECs) and regulates gene expression by limiting its levels. PRDX6-depleted LECs displayed phenotypic alterations and elevated alpha-smooth muscle actin and betaig-h3 expression (markers for cataractogenesis), indistinguishable from transforming growth factor beta (TGFbeta)-induced changes. Biochemical assays disclosed enhanced levels of ROS, as well as high expression and activation of TGFbeta1 in Prdx6-/- LECs. A CAT assay revealed transcriptional repression of lens epithelium-derived growth factor (LEDGF), HSP27, and alphaB-crystallin promoter activities in these cells. A gel mobility shift assay demonstrated the attenuation of LEDGF binding to heat shock or stress response elements present in these genes. A supply of PRDX6 toPrdx6-/- LECs reversed these changes. Based on the above data, we propose a rheostat role for PRDX6 in regulating gene expression by controlling the ROS level to maintain cellular homeostasis.

Oxalomalate, a competitive inhibitor of NADP+-dependent isocitrate dehydrogenase, regulates heat shock-induced apoptosis

Heat shock may increase oxidative stress due to increased production of reactive oxygen species and/or the promotion of cellular oxidation events. Recently, we demonstrated that the control of cytosolic and mitochondrial redox balance and the cellular defense against oxidative damage is one of the primary functions of NADP(+)-dependent isocitrate dehydrogenase (ICDH) by supplying NADPH for antioxidant systems. The protective role of ICDH against heat shock-induced apoptosis in U937 cells was investigated in the control and the cells pre-treated with oxalomalate, a competitive inhibitor of ICDH. Upon exposure to heat shock, there was a distinct difference between the control cells and the cells pre-treated with 3mM oxalomalate for 3h in regard to apoptotic parameters, cellular redox status, and mitochondrial function. The oxalomalate pre-treated cells showed significant enhancement of apoptotic features such as activation of caspase-3, up-regulation of Bax, and down-regulation of Bcl-2 compared to the control cells upon exposure to heat shock. This study indicates that ICDH may play an important role in regulating the apoptosis induced by heat shock presumably through maintaining the cellular redox status.

The contemporary role of antioxidant therapy in attenuating liver ischemia-reperfusion injury: a review

Oxidative stress is an important factor in many pathological conditions such as inflammation, cancer, ageing and organ response to ischemia-reperfusion. Humans have developed a complex antioxidant system to eliminate or attenuate oxidative stress. Liver ischemia-reperfusion injury occurs in a number of clinical settings, including liver surgery, transplantation, and hemorrhagic shock with subsequent fluid resuscitation, leading to significant morbidity and mortality. It is characterized by significant oxidative stress but accompanied with depletion of endogenous antioxidants. This review has 2 aims: firstly, to highlight the clinical significance of liver ischemia-reperfusion injury, the underlying mechanisms and the main pathways by which the antioxidants function, and secondly, to describe the new developments that are ongoing in antioxidant therapy and to present the experimental and clinical evidence about the role of antioxidants in modulating hepatic ischemia-reperfusion injury.

Mitochondrial inhibition and oxidative stress: reciprocating players in neurodegeneration

Although the etiology for many neurodegenerative diseases is unknown, the common findings of mitochondrial defects and oxidative damage posit these events as contributing factors. The temporal conundrum of whether mitochondrial defects lead to enhanced reactive oxygen species generation, or conversely, if oxidative stress is the underlying cause of the mitochondrial defects remains enigmatic. This review focuses on evidence to show that either event can lead to the evolution of the other with subsequent neuronal cell loss. Glutathione is a major antioxidant system used by cells and mitochondria for protection and is altered in a number of neurodegenerative and neuropathological conditions. This review also addresses the multiple roles for glutathione during mitochondrial inhibition or oxidative stress. Protein aggregation and inclusions are hallmarks of a number of neurodegenerative diseases. Recent evidence that links protein aggregation to oxidative stress and mitochondrial dysfunction will also be examined. Lastly, current therapies that target mitochondrial dysfunction or oxidative stress are discussed.

Proteomic profiling for cancer progression: Differential display analysis for the expression of intracellular proteins between regressive and progressive cancer cell lines

Tumor development and progression consist of a series of complex processes involving multiple changes in gene expression (Paolo et al. Physiol. Rev., 1993, 73, 161-195; Lance et al. Cell., 1991, 64, 327-336). Tumor cells acquire an invasive and metastatic phenotype that is the main cause of death for cancer patients. Therefore, for early diagnosis and effective therapeutic intervention, we need to detect the alterations associated with transition from benign to malignant tumor cells on a molecular basis. To unravel alterations concerned with tumor progression, the proteomic approach has attracted great attention because it can identify qualitative and quantitative changes in protein composition, including post-translational modifications. In this study, we performed proteomic differential display analysis for the expression of intracellular proteins in the regressive cancer cell line QR-32 and the inflammatory cell-promoting progressive cancer cell line QRsP-11 of murine fibrosarcoma by two-dimensional gel electrophoresis and mass spectrometry using an Agilent 1100 LC/MSD Trap XCT. We found 11 protein spots whose expression was different between QR-32 and QRsP-11 cells and identified nine proteins, seven of which, calreticulin precursor, tropomyosin 1 alpha chain, annexin A5, heat shock protein (HSP)90-alpha, HSP90-beta, PEBP, and Prx II, were over-expressed, and two, Anp32e and HDGF, which were down-regulated. The results suggest an important complementary role for proteomics in identification of molecular abnormalities in tumor progression.

Proteomic analysis of supernatants of stored red blood cell products

BACKGROUND

The development of the red blood cell (RBC) storage lesion remains incompletely understood. To gain a greater insight into the mechanisms involved, a proteomics analysis was used to identify proteins that accumulate in supernatants of standard nonleukoreduced RBC products (S-RBCs) and prestorage leukofiltered RBC products (LF-RBCs) during storage.

STUDY DESIGN AND METHODS

S-RBCs and LF-RBCs were collected and stored in accordance with standard blood bank procedures. Supernatant samples were collected at fortnightly intervals until product expiry (at Day 42). Maps of supernatant proteins were generated by two-dimensional (2D)-gel electrophoresis and selected proteins were identified by mass spectrometry.

RESULTS

2D-gel mapping revealed that greater numbers of proteins accumulated in supernatants of S-RBCs compared to LF-RBCs. Abundant plasma proteins were strongly represented in both products. Several potentially bioactive proteins were found to predominantly accumulate in supernatant of S-RBCs. Among these, a promoter of neutrophil adhesion and an acute-phase scavenger protein were identified. In contrast, proteins found to accumulate predominantly in supernatant of LF-RBCs were RBC-regulatory proteins.

CONCLUSION

Proteomics provides a valuable approach to examine storage-related effects on RBCs. Such analytical approaches may help to elucidate the mechanisms involved in the RBC storage lesion and provide insights into the biologic consequences of transfusion of stored RBC products.

The modulation of thiol redox state affects the production and metabolism of hydrogen peroxide by heart mitochondria

In rat heart mitochondria, auranofin, arsenite, diamide, and BCNU increase H2O2 formation, further stimulated by antimycin. However, in submitochondrial particles, H2O2 formation and oxygen uptake are not affected, indicating that these substances do not alter respiration. Mitochondria are also able to rapidly metabolize added H2O2 in a process partially prevented by BCNU or auranofin. Calcium does not modify the production of H2O2 and the mitochondrial thioredoxin system is not affected by calcium ions. Auranofin, arsenite, and diamide determine a large mitochondrial permeability transition, while BCNU and acetoacetate are ineffective. Thiols and glutathione are modified only by BCNU and diamide. However, all the compounds tested cause the release of cytochrome c that occurs also in the absence of mitochondrial swelling. In conclusion, the compounds utilized share the common feature of shifting the mitochondrial thiol-linked redox balance towards a more oxidized condition that is responsible of the observed effects.

Dual role of vitamin C in an oxygen-sensitive system: discrepancy between DNA damage and cell death

Although vitamin C is considered to act both as pro-oxidant and antioxidant, the mechanisms underlying these actions are still unclear. Using the oxygen-sensitive system of a strict anaerobe, Prevotella melaninogenica, we investigated both the pro-oxidant and antioxidant mechanisms of vitamin C. In the presence of vitamin C, the 8-hydroxydeoxyguanosine (8OHdG) formation induced by oxygen exposure was enhanced, probably due to the action of vitamin C on hydrogen peroxide generated during oxygen exposure: while catalase almost completely suppressed the enhancing effect of vitamin C, 8OHdG formation induced by hydrogen peroxide was enhanced by vitamin C. By contrast, the presence of vitamin C inhibited bacterial cell death, membrane damage, and lipid peroxidation induced by oxygen exposure. Sodium azide showed similar effects to vitamin C, thus the antioxidant action of vitamin C may be due to its quenching of the singlet oxygen generated in this system. Both the pro-oxidant and antioxidant effects of vitamin C were observed only in acidic conditions.

Role of the redox protein thioredoxin in cytoprotective mechanism evoked by (-)-deprenyl

Through the inhibition of monoamine oxidase type B (MAO-B), (-)-deprenyl (selegiline) prevents the conversion of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to the toxic metabolite 1-methyl-4-phenylpyridinium ion (MPP+) and also prevents the neurotoxicity in the dopaminergic neurons in animal models. Cumulative observations suggest that selegiline may also protect against MPP+-induced neurotoxicity, possibly through the induction of pro-survival genes. We have observed that thioredoxin (Trx) mediates the induction of mitochondrial manganese superoxide dismutase (MnSOD) and Bcl-2 during preconditioning-induced hormesis. We therefore investigated whether the redox protein Trx plays any role in the neuroprotective mechanism of selegiline against MPP+-induced cytotoxicity in human SH-SY5Y neuroblastoma cells and also in primary neuronal cultures of mouse midbrain dopaminergic neurons. After confirming that selegiline protects against MPP+-induced cytotoxicity, we observed further that selegiline, at 1 microM or less, induced Trx for protection against oxidative injury caused by MPP+. The induction of Trx was blocked by protein kinase A (PKA) inhibitor and mediated by a PKA-sensitive phospho-activation of mitogen-activated protein (MAP) kinase Erk1/2 and the transcription factor c-Myc. Selegiline-induced Trx and associated neuroprotection were concomitantly blocked by the antisense against Trx mRNA, but not the sense or antisense mutant phosphothionate oligonucleotides, not only in human SH-SY5Y cells but also in mouse primary neuronal culture of midbrain dopaminergic neurons. Furthermore, the redox cycling of Trx may mediate the protective action of selegiline because the inhibition of Trx reductase by 1-chloro-2,4-dinitrobenzene ameliorated the effect of selegiline. Trx (1 microM) consistently increased the expression of mitochondrial proteins MnSOD and Bcl-2, supporting cell survival (Andoh et al., 2002). In conclusion, without modifying MAO-B activity, selegiline augments the gene induction of Trx, leading to elevated expression of antioxidative MnSOD and antiapoptotic Bcl-2 proteins for protecting against MPP+-induced neurotoxicity.

Cellular defense against heat shock-induced oxidative damage by mitochondrial NADP+ -dependent isocitrate dehydrogenase

Heat shock may increase oxidative stress due to increased production of reactive oxygen species and/or the promotion of cellular oxidation events. Mitochondrial NADP+ -dependent isocitrate dehydrogenase (IDPm) produces NADPH, an essential reducing equivalent for the antioxidant system. The protective role of IDPm against heat shock in HEK293 cells, an embryonic kidney cell line, was investigated in control and cells transfected with the cDNA for IDPm, where IDPm activity was 6-7 fold higher than that in the control cells carrying the vector alone. Upon exposure to heat shock, the viability was lower and the protein oxidation, lipid peroxidation and oxidative DNA damage were higher in control cells as compared to HEK293 cells in which IDPm was over-expressed. We also observed the significant difference in the cellular redox status reflected by the endogenous production of reactive oxygen species, NADPH pool and GSH recycling between two cells. The results suggest that IDPm plays an important role as an antioxidant defense enzyme in cellular defense against heat shock through the removal of reactive oxygen species.

A comparative proteomic analysis of the rat brain during rebound hyperphagia induced by space-restriction

Although neurochemical changes have been reported in the brain in animal models of binge eating, biochemical changes of specific proteins in the brain are unknown. Our aim was to elucidate brain proteins altered in rats during enhanced rebound hyperphargia. Rats were deprived of food for 22 h/day for 6 days, then allowed free access to food for 24 h in normal cages (rebound hyperphargia) or in space-restricted cages (enhanced rebound hyperphargia). Proteins extracted from the rat brain were separated by two-dimensional gel electrophoresis, and compared with those from control rats freely fed for 7 days in normal cages. Proteins expressed differently from controls were identified by N-terminal amino acid sequencing and mass fingerprinting using a MALDI-TOF mass spectrometer. Among proteins in the corpus striatum, frontal lobe, hippocampus and thalamus/hypothalamus, ubiquitin C-terminal hydrolase L1 and peroxiredoxin 2 decreased in the hippocampus and phosphatidylethanolamine-binding protein increased in the thalamus/hypothalamus of rats with the enhanced rebound hyperphargia induced by space-restriction. In this study, we first demonstrated that three brain proteins changed in rats during enhanced rebound hyperphagia. These proteins might have pathophysiologic relevance to binge eating.

Characterization of neural cell types expressing peroxiredoxins in mouse brain

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

A proteomic investigation into etoposide chemo-resistance of neuroblastoma cell lines

Neuroblastoma, one of the most common pediatric solid tumors, originates from the peripheral sympathetic nervous system and is responsible for approximately 15% of all childhood cancer deaths. Among the several antineoplastic drugs used in neuroblastoma chemotherapeutic protocols, topoisomerase inhibitors (i.e., etoposide) represent the most commonly used. Several resistance mechanisms limit the clinical success of topoisomerase-targeting drugs, mainly reducing the ability of neoplastic cells to start programmed cell death when exposed to antineoplastic drugs. The aim of this study was to determine, by means of proteomics, potential markers of etoposide resistance in human neuroblastoma cell lines as well as to investigate protein levels and modifications possibly involved in the onset of resistance. The etoposide resistant clone showed overexpression of the following proteins: peroxiredoxin 1, beta-galactoside soluble lectin binding protein, vimentin (three protein spots), heat shock 27 kDa protein (two protein spots) and heterogeneous nuclear ribonucleoprotein K. In addition, we also found down-regulation of dUTP pyrophosphatase. This investigation might represent a first step towards the development of novel prognostic markers of neuroblastoma chemotherapy.

Redox activation of mitochondrial intermembrane space Cu,Zn-superoxide dismutase

The localization of Cu,Zn-superoxide dismutase in the mitochondrial intermembrane space suggests a functional relationship with superoxide anion (O2*-) released into this compartment. The present study was aimed at examining the functionality of Cu,Zn-superoxide dismutase and elucidating the molecular basis for its activation in the intermembrane space. Intact rat liver mitochondria neither scavenged nor dismutated externally generated O2*-, unless the mitochondrial outer membrane was disrupted selectively by digitonin. The activation of the intermembrane space Cu,Zn-superoxide dismutase following the disruption of mitochondrial outer membrane was largely inhibited by bacitracin, an inhibitor of protein disulphide-isomerase. Thiol alkylating agents, such as N-methylmaleimide or iodoacetamide, decreased intermembrane space Cu,Zn-superoxide dismutase activation during, but not after, disruption of the outer membrane. This inhibitory effect was overcome by exposing mitochondria to low micromolar concentrations of H2O2 before disruption of the outer membrane in the presence of the alkylating agents. Moreover, H2O2 treatment alone enabled intact mitochondria to scavenge externally generated O2*-. These findings suggest that intermembrane space Cu,Zn-superoxide dismutase is inactive in intact mitochondria and that an oxidative modification of its critical thiol groups is necessary for its activation.

Proteasome inhibition by lactacystin in primary neuronal cells induces both potentially neuroprotective and pro-apoptotic transcriptional responses: a microarray analysis

Although inhibition of the ubiquitin proteasome system has been postulated to play a key role in the pathogenesis of neurodegenerative diseases, studies have also shown that proteasome inhibition can induce increased expression of neuroprotective heat-shock proteins (HSPs). The global gene expression of primary neurons in response to treatment with the proteasome inhibitor lactacystin was studied to identify the widest range of possible pathways affected. Our results showed changes in mRNA abundance, both at different time points after lactacystin treatment and at different lactacystin concentrations. Genes that were differentially up-regulated at the early time point but not when most cells were undergoing apoptosis might be involved in an attempt to reverse proteasome inhibitor-mediated apoptosis and include HSP70, HSP22 and cell cycle inhibitors. The up-regulation of HSP70 and HSP22 appeared specific towards proteasome inhibitor-mediated cell death. Overexpression of HSP22 was found to protect against proteasome inhibitor-mediated loss of viability by up to 25%. Genes involved in oxidative stress and the inflammatory response were also up-regulated. These data suggest an initial neuroprotective pathway involving HSPs, antioxidants and cell cycle inhibitors, followed by a pro-apoptotic response possibly mediated by inflammation, oxidative stress and aberrant activation of cell cycle proteins.

Galpha12/13-mediated production of reactive oxygen species is critical for angiotensin receptor-induced NFAT activation in cardiac fibroblasts

Angiotensin II (Ang II) activates multiple signaling pathways leading to hyperplasia of cardiac fibroblasts. Reactive oxygen species (ROS) produced by Ang II stimulation are assumed to play pivotal roles in this process. Here, we show that ROS mediate Ang II-induced activation of nuclear factor of activated T cells (NFAT) in rat cardiac fibroblasts. Ang II-induced NFAT activation was suppressed by diphenyleneiodonium (an NADPH oxidase inhibitor), dominant negative (DN)-Rac, DN-p47(phox), and an inhibitor of Galpha(12/13) (Galpha(12/13)-specific regulator of G protein signaling domain of p115RhoGEF, p115-regulator of G protein signaling (RGS)). Stimulation of Ang II receptor increased the intracellular ROS level in a Rac- and p47(phox)-dependent manner. Because p115-RGS suppressed Ang II-induced Rac activation, Ang II receptor-coupled Galpha(12/13) mediated NFAT activation through ROS production by Rac activation. Ang II-induced nuclear translocation of the green fluorescent protein (GFP)-tagged amino-terminal region of NFAT4 (GFP-NFAT4) was suppressed by p115-RGS or BAPTA but not by diphenyleneiodonium. The expression of constitutively active (CA)-Galpha(12/13), CA-G translocation alpha(13), or CA-Rac increased the nuclear of GFP-NFAT4. These results suggest that NFAT activity is regulated by both Ca(2+)-dependent and ROS-dependent pathways. Furthermore, activation of c-Jun NH(2)-terminal kinase (JNK) induced by Ang II stimulation is required for NFAT activation because Ang II-induced NFAT activation was inhibited by SP600125, a selective JNK inhibitor. These results indicate that Ang II stimulates the nuclear translocation and activation of NFAT by integrated pathways including the activation of Galpha(12/13), Rac, NADPH oxidase, and JNK and that Galpha(12/13)-mediated ROS production is essential for NFAT transcriptional activation.

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

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

Peroxiredoxin I expression in tongue squamous cell carcinomas as involved in tumor recurrence

Peroxiredoxin (Prx) I is an antioxidant protein expressed in proliferating cells. We investigated Prx I as marker for tongue cancer status by correlating clinical features with Prx I expression. Samples from 132 patients with squamous cell carcinoma in the tongue were examined by immunohistochemistry with an anti-Prx I antibody. Correlations between Prx I expression and the clinical features of tumors were statistically determined using univariate and multivariate analyses. Univariate analysis showed Prx I was significantly associated with local recurrence (P=0.033). By multiple logistic regression analysis, Prx I expression was associated with local recurrence (odds ratio: 2.84; 95% confidence interval: 1.09-7.43; P=0.034) and lymph node recurrence (odds ratio: 2.86; 95% confidence interval: 1.02-8.01; P=0.046). Our results suggested that Prx I expression indicates tumors with a high potential for recurrence. Prx I may be used clinically to guide treatment for squamous cell carcinoma of the tongue.

In vitro glucose-induced cataract in copper-zinc superoxide dismutase null mice

The purpose of this study was to evaluate the involvement of the superoxide radical in glucose-induced cataract using lenses from mice lacking the cytosolic copper-zinc superoxide dismutase (SOD1). Lenses from wild-type mice and SOD1 null mice were kept in organ culture with either 5.6 or 55.6 mM glucose for 6 days. The cataract formation was followed with digital image analysis and ocular staging. The lens damage was further quantified by analysis of the leakage of lactate dehydrogenase into the medium by the uptake of 86Rb and by determining the water content of the lenses. The formation of superoxide radicals in the lenses was assessed with lucigenin-derived chemiluminescence. Immunohistochemical staining for SOD1 was also performed on murine lenses. The SOD1 null lenses exposed to high glucose developed more cataract showed an increased leakage of lactate dehydrogenase and developed more oedema compared to the control lenses. At 5.6 mM glucose there was no difference between the SOD1 null and wild-type lenses. Staining for SOD1 was seen primarily in the cortex of the wild-type lens. This in vitro model suggests an involvement of the superoxide radical and a protective effect of SOD1 in glucose-induced cataract formation.

Regulation of PDGF signalling and vascular remodelling by peroxiredoxin II

Platelet-derived growth factor (PDGF) is a potent mitogenic and migratory factor that regulates the tyrosine phosphorylation of a variety of signalling proteins via intracellular production of H2O2 (refs 1, 2-3). Mammalian 2-Cys peroxiredoxin type II (Prx II; gene symbol Prdx2) is a cellular peroxidase that eliminates endogenous H2O2 produced in response to growth factors such as PDGF and epidermal growth factor; however, its involvement in growth factor signalling is largely unknown. Here we show that Prx II is a negative regulator of PDGF signalling. Prx II deficiency results in increased production of H2O2, enhanced activation of PDGF receptor (PDGFR) and phospholipase Cgamma1, and subsequently increased cell proliferation and migration in response to PDGF. These responses are suppressed by expression of wild-type Prx II, but not an inactive mutant. Notably, Prx II is recruited to PDGFR upon PDGF stimulation, and suppresses protein tyrosine phosphatase inactivation. Prx II also leads to the suppression of PDGFR activation in primary culture and a murine restenosis model, including PDGF-dependent neointimal thickening of vascular smooth muscle cells. These results demonstrate a localized role for endogenous H2O2 in PDGF signalling, and indicate a biological function of Prx II in cardiovascular disease.

Role of 15-DeoxyΔ12,14Prostaglandin J2and Nrf2 Pathways in Protection against Acute Lung Injury

RATIONALE

Acute lung injury (ALI) is a disease process that is characterized by diffuse inflammation in the lung parenchyma. Recent studies demonstrated that cyclooxygenase-2 (COX-2) induced at the late phase of inflammation aids in the resolution of inflammation by generating 15-deoxy-delta(12,14)-prostaglandin J2 (15d-PGJ2). Transcription factor Nrf2 is activated by electrophiles and exerts antiinflammatory effects by inducing the gene expression of antioxidant and detoxification enzymes.

OBJECTIVES

Because 15d-PGJ2 is an endogenous electrophile, we hypothesized that it protects against ALI by activating Nrf2.

METHODS

To test this hypothesis, we generated a reversible ALI model by intratracheal injection of carrageenin, an inducer of acute inflammation, whose stimulation has been known to induce COX-2.

MAIN RESULTS

We found that ALI induced by carrageenin was markedly exacerbated in Nrf2-knockout mice, compared with wild-type mice. Analysis of bronchoalveolar lavage fluids also revealed that the magnitude and the duration of acute inflammation, indicated by albumin concentration and the number of neutrophils, were significantly enhanced in Nrf2-knockout mice. Treatment of wild-type mice with NS-398, a selective COX-2 inhibitor, significantly exacerbated ALI to the level of Nrf2-knockout mice. In the lungs of NS-398-treated wild-type mice, both the accumulation of 15d-PGJ2 and the induction of Nrf2 target antioxidant genes were significantly attenuated. Exogenous administration of 15d-PGJ2 reversed the exacerbating effects of NS-398 with the induction of antioxidant genes.

CONCLUSIONS

These results demonstrated in vivo that 15d-PGJ2 plays a protective role against ALI by exploiting the Nrf2-mediated transcriptional pathway.

G alpha 12/13- and reactive oxygen species-dependent activation of c-Jun NH2-terminal kinase and p38 mitogen-activated protein kinase by angiotensin receptor stimulation in rat neonatal cardiomyocytes

In the present study, we examined signal transduction mechanism of reactive oxygen species (ROS) production and the role of ROS in angiotensin II-induced activation of mitogen-activated protein kinases (MAPKs) in rat neonatal cardiomyocytes. Among three MAPKs, c-Jun NH(2)-terminal kinase (JNK) and p38 MAPK required ROS production for activation, as an NADPH oxidase inhibitor, diphenyleneiodonium, inhibited the activation. The angiotensin II-induced activation of JNK and p38 MAPK was also inhibited by the expression of the Galpha(12/13)-specific regulator of G protein signaling (RGS) domain, a specific inhibitor of Galpha(12/13), but not by an RGS domain specific for Galpha(q). Constitutively active Galpha(12)- or Galpha(13)-induced activation of JNK and p38 MAPK, but not extracellular signal-regulated kinase (ERK), was inhibited by diphenyleneiodonium. Angiotensin II receptor stimulation rapidly activated Galpha(13), which was completely inhibited by the Galpha(12/13)-specific RGS domain. Furthermore, the Galpha(12/13)-specific but not the Galpha(q)-specific RGS domain inhibited angiotensin II-induced ROS production. Dominant negative Rac inhibited angiotensin II-stimulated ROS production, JNK activation, and p38 MAPK activation but did not affect ERK activation. Rac activation was mediated by Rho and Rho kinase, because Rac activation was inhibited by C3 toxin and a Rho kinase inhibitor, Y27632. Furthermore, angiotensin II-induced Rho activation was inhibited by Galpha(12/13)-specific RGS domain but not dominant negative Rac. An inhibitor of epidermal growth factor receptor kinase AG1478 did not affect angiotensin II-induced JNK activation cascade. These results suggest that Galpha(12/13)-mediated ROS production through Rho and Rac is essential for JNK and p38 MAPK activation.

Controlled elimination of intracellular H(2)O(2): regulation of peroxiredoxin, catalase, and glutathione peroxidase via post-translational modification

The predominant enzymes responsible for elimination of hydrogen peroxide (H(2)O(2)) in cells are peroxiredoxins (Prxs), catalase, and glutathione peroxidases (GPxs). Evidence suggests that catalytic activities of certain isoforms of these H(2)O(2)-eliminating enzymes are extensively regulated via posttranslational modification. Prx I and Prx II become inactivated when phosphorylated on Thr(90) by cyclin B-dependent kinase Cdc2. In addition, the active-site cysteine of Prx I-IV undergoes a reversible sulfinylation (oxidation to cysteine sulfinic acid) in cells. Desulfinylation (reduction to cysteine) is achieved by a novel enzyme named sulfiredoxin. c-Abl and Arg nonreceptor protein tyrosine kinases associate with catalase in cells treated with H(2)O(2) by mechanisms involving the SH3 domains of the kinases and the Pro(293)PheAsnPro motif of catalase and activate catalase by phosphorylating it on Tyr(231) and Tyr(386). Similarily, GPx1 is activated by c-Abl- and Arg-mediated phosphorylation. The tyrosine phosphorylation is critical for ubiquitination-dependent degradation of catalase.

Peroxiredoxins, oxidative stress, and cell proliferation

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