A novel role of the fission yeast sulfiredoxin Srx1 in heme acquisition

The transporter Str3 promotes heme import in Schizosaccharomyces pombe cells that lack the heme receptor Shu1 and are deficient in heme biosynthesis. Under microaerobic conditions, the peroxiredoxin Tpx1 acts as a heme scavenger within the Str3-dependent pathway. Here, we show that Srx1, a sulfiredoxin known to interact with Tpx1, is essential for optimal growth in the presence of hemin. The expression of Srx1 is induced in response to low iron and repressed under iron repletion. Coimmunoprecipitation and bimolecular fluorescence complementation experiments show that Srx1 interacts with Str3. Although the interaction between Srx1 and Str3 is weakened, it is still observed in tpx1Δ mutant cells or when Str3 is coexpressed with a mutant form of Srx1 (mutD) that cannot bind Tpx1. Further analysis by absorbance spectroscopy and hemin-agarose pull-down assays confirms the binding of Srx1 to hemin, with an equilibrium constant value of 2.56 μM. To validate the Srx1-hemin association, we utilize a Srx1 mutant (mutH) that fails to interact with hemin. Notably, when Srx1 binds to hemin, it partially shields hemin from degradation caused by hydrogen peroxide. Collectively, these findings elucidate an additional function of the sulfiredoxin Srx1, beyond its conventional role in oxidative stress defense.

The sulfiredoxin-peroxiredoxin redox system regulates the stemness and survival of colon cancer stem cells

Cancer stem cells (CSCs) initiate tumor formation and are known to be resistant to chemotherapy. A metabolic alteration in CSCs plays a critical role in stemness and survival. However, the association between mitochondrial energy metabolism and the redox system remains undefined in colon CSCs. In this study, we assessed the role of the Sulfiredoxin-Peroxiredoxin (Srx-Prx) redox system and mitochondrial oxidative phosphorylation (OXPHOS) in maintaining the stemness and survival of colon CSCs. Notably, Srx contributed to the stability of PrxI, PrxII, and PrxIII proteins in colon CSCs. Increased Srx expression promoted the stemness and survival of CSCs and was important for the maintenance of the mitochondrial OXPHOS system. Furthermore, Nrf2 and FoxM1 led to OXPHOS activation and upregulated expression of Srx-Prx redox system-related genes. Therefore, the Nrf2/FoxM1-induced Srx-Prx redox system is a potential therapeutic target for eliminating CSCs in colon cancer.

The crystal structure of sulfiredoxin from Arabidopsis thaliana revealed a more robust antioxidant mechanism in plants

Typical 2-cysteine peroxiredoxins (2-Cys Prxs) are critical peroxidase sensors and could be deactivated by the hyperoxidation under oxidative stress. In plants, 2-Cys Prxs present at a high level in chloroplasts and are repaired by Sulfiredoxin. Whereas many studies have explored the mechanism of Sulfiredoxin from Homo sapiens (HsSrx), the molecular mechanism of Sulfiredoxin in plants with unique photosynthesis remains unclear. Here we report the crystal structure of Sulfiredoxin from Arabidopsis thaliana (AtSrx), which displayed a typical ParB/Srx fold with an ATP bound at a conservative nucleotide binding motif GCHR. Both the ADP binding pocket and the putative AtSrx-AtPrxA interaction surface of AtSrx are more positively charged comparing to HsSrx, suggesting a robust mechanism of AtSrx. These features illustrate the unique mechanisms of AtSrx, which are vital for figure out the strategies of plants to cope with oxidation stress.

Elucidation of the inhibition mechanism of sulfiredoxin using molecular modeling and development of its inhibitors

When intracellular reactive oxygen species (ROS) increase, cancer cells are more vulnerable to oxidative stress compared to normal cells; thus, the collapse of redox homeostasis can lead to selective death of cancer cells. Indeed, recent studies have shown that inhibition of sulfiredoxin (Srx), which participates in antioxidant mechanisms, induces ROS-mediated cancer cell death. In this paper, we describe how an Srx inhibitor, J14 (4-[[[4-[4-(2-chlor-ophenyl)-1-piperazinyl]-6-phenyl-2-pyrimidinyl]thio]methyl]-benzoic acid), interferes with the antioxidant activity of Srx at the molecular level. We searched for possible binding sites of Srx using a binding site prediction method and uncovered two possible inhibition mechanisms of Srx by J14. Using molecular dynamics simulations and binding free energy calculations, we confirmed that J14 binds to the ATP binding site; therefore, J14 acts as a competitive inhibitor of ATP, settling the question of the two mechanisms. Based on the inhibition mechanism revealed at the atomic level, we designed several derivatives of J14, which led to LMT-328 (4-(((4-(4-(2-Chlorophenyl)piperazin-1-yl)-6-(2,4-dihydroxy-5-isopropylphenyl)pyrimidin-2-yl)thio)methyl)benzoic acid), which is possibly an even more potent inhibitor than J14.

A lack of GluN2A-containing NMDA receptors confers a vulnerability to redox dysregulation: Consequences on parvalbumin interneurons, and their perineuronal nets

The GluN2A subunit of NMDA receptors (NMDARs) plays a critical role during postnatal brain development as its expression increases while Glun2B expression decreases. Mutations and polymorphisms in GRIN2A gene, coding for GluN2A, are linked to developmental brain disorders such as mental retardation, epilepsy, schizophrenia. Published data suggest that GluN2A is involved in maturation and phenotypic maintenance of parvalbumin interneurons (PVIs), and these interneurons suffer from a deficient glutamatergic neurotransmission via GluN2A-containing NMDARs in schizophrenia. In the present study, we find that although PVIs and their associated perineuronal nets (PNNs) appear normal in anterior cingulate cortex of late adolescent/young adult GRIN2A KO mice, a lack of GluN2A delays PNN maturation. GRIN2A KO mice display a susceptibility to redox dysregulation as sub-threshold oxidative stress and subtle alterations in antioxidant systems are observed in their prefrontal cortex. Consequently, an oxidative insult applied during early postnatal development increases oxidative stress, decreases the number of parvalbumin-immunoreactive cells, and weakens the PNNs in KO but not WT mice. These effects are long-lasting, but preventable by the antioxidant, N-acetylcysteine. The persisting oxidative stress, deficit in PVIs and PNNs, and reduced local high-frequency neuronal synchrony in anterior cingulate of late adolescent/young adult KO mice, which have been challenged by an early-life oxidative insult, is accompanied with microglia activation. Altogether, these indicate that a lack of GluN2A-containing NMDARs alters the fine control of redox status, leading to a delayed maturation of PNNs, and conferring vulnerability for long-term oxidative stress, microglial activation, and PVI network dysfunction.

Sulfiredoxin may promote metastasis and invasion of cervical squamous cell carcinoma by epithelial-mesenchymal transition

Sulfiredoxin (Srx), a novel oxidative stress-induced antioxidant protein, has been reported to be expressed in several human tumour tissues. However, the expression and functions of Srx in cervical squamous cell carcinoma remain unknown. Here, we proved that expression of Srx was upregulated in cervical tissues as revealed by immunohistochemistry, and revealed a close correlation between the protein's expression and the expression level of one core epithelial-mesenchymal transition marker, E-cadherin. We demonstrated that Srx was overexpressed in cervical squamous cell carcinoma and its expression level was closely correlated with lymph node metastasis and invasion of cervical squamous cell carcinoma. Meanwhile, Srx expression was negatively correlated with E-cadherin expression. The remission time (tumour-free status after surgery) of the Srx strong staining group was significantly shorter than that of the Srx weak staining group. We silenced Srx by short hairpin RNA in HeLa and SiHa cells. Diminished Srx expression upregulated E-cadherin expression. The cell invasion and migration activity in the ShSrx group were obviously decreased in HeLa and SiHa cells. Moreover, Srx regulated the expression of the other marker of epithelial-mesenchymal transition, vimentin. In conclusion, the study suggested that Srx was highly expressed in cervical squamous cell carcinoma and may promote invasion and metastasis of cervical squamous cell carcinoma via regulating epithelial-mesenchymal transition.

Sulfiredoxin involved in the protection of peroxiredoxins against hyperoxidation in the early hyperglycaemia

As a direct consequence of hyperglycaemia, the excessive generation of ROS is central to the pathogenesis of diabetic cardiomyopathy. We hypothesize that stimulation of high glucose (HG) results in an increased sulfiredoxin (Srx) expression, which regulates ROS signaling through reducing the hyperoxidized peroxiredoxins (Prxs). We show that hyperoxidized Prxs were initially reduced in the preliminary stage but then dramatically increased in advanced stage and these changes corresponded to a significant increase of Srx expression in the heart of diabetic rats. These time-dependent changes were also confirmed in neonatal cardiomyocytes and H9c2 cells treated with HG. Moreover, the reduction rate of hyperoxidized Prxs was greatly improved in the HG 24h group, which had an elevated expression of Srx. Our data also show that HG-induced AP1 activation and Srx expression were almost abolished by JNK inhibitor and N-acetylcysteine (NAC). In addition, siRNA-Srx suppressed HG-induced ANP and β-MHC gene expression. These observations suggest that activation of AP1 induced by HG is important for the expression of Srx and the reduction of hyperoxidized Prxs in cardiomyocytes. This Srx induction maybe is the pivotal compensatory protection mechanism against oxidative stress in diabetes or hyperglycaemia. Most interestingly, hyperoxidized Prxs/Srx pathway may be involved in the cardiac hypertrophy signaling of diabetes.

The Peroxiredoxin Family: An Unfolding Story

Peroxiredoxins (Prxs) are a large and conserved family of peroxidases that are considered to be the primary cellular guardians against oxidative stress in all living organisms. Prxs share a thioredoxin fold and contain a highly-reactive peroxidatic cysteine in a specialised active-site environment that is able to reduce their peroxide substrates. The minimal functional unit for Prxs are either monomers or dimers, but many dimers assemble into decameric rings. Ring structures can further form a variety of high molecular weight complexes. Many eukaryotic Prxs contain a conserved GGLG and C-terminal YF motif that confer sensitivity to elevated levels of peroxide, leading to hyperoxidation and inactivation. Inactive forms of Prxs can be re-reduced by the enzyme sulfiredoxin, in an ATP-dependent reaction. Cycles of hyperoxidation and reactivation are considered to play an integral role in a variety of H₂O₂-mediated cell signalling pathways in both stress and non-stress conditions. Prxs are also considered to exhibit chaperone-like properties when cells are under oxidative or thermal stress. The roles of various types of covalent modifications, e.g. acetylation and phosphorylation are also discussed. The ability of Prxs to assemble into ordered arrays such as nanotubes is currently being exploited in nanotechnology.

Effective killing of cancer cells and regression of tumor growth by K27 targeting sulfiredoxin

Cancer cells have been suggested to be more susceptible to oxidative damages and highly dependent on antioxidant capacity in comparison with normal cells, and thus targeting antioxidant enzymes has been a strategy for effective cancer treatment. Sulfiredoxin (Srx) is an enzyme that catalyzes the reduction of sulfinylated peroxiredoxins and thereby reactivates them. In this study we developed a Srx inhibitor, K27 (N-[7-chloro-2-(4-fluorophenyl)-4-quinazolinyl]-N-(2-phenylethyl)-β-alanine), and showed that it induces the accumulation of sulfinylated peroxiredoxins and oxidative stress, which leads to mitochondrial damage and apoptotic death of cancer cells. The effects of K27 were significantly reversed by ectopic expression of Srx or antioxidant N-acetyl cysteine. In addition, K27 led to preferential death of tumorigenic cells over non-tumorigenic cells, and suppressed the growth of xenograft tumor without acute toxicity. Our results suggest that targeting Srx might be an effective therapeutic strategy for cancer treatment through redox-mediated cell death.

Trapping redox partnerships in oxidant-sensitive proteins with a small, thiol-reactive cross-linker

A broad range of redox-regulated proteins undergo reversible disulfide bond formation on oxidation-prone cysteine residues. Heightened reactivity of the thiol groups in these cysteines also increases susceptibility to modification by organic electrophiles, a property that can be exploited in the study of redox networks. Here, we explored whether divinyl sulfone (DVSF), a thiol-reactive bifunctional electrophile, cross-links oxidant-sensitive proteins to their putative redox partners in cells. To test this idea, previously identified oxidant targets involved in oxidant defense (namely, peroxiredoxins, methionine sulfoxide reductases, sulfiredoxin, and glutathione peroxidases), metabolism, and proteostasis were monitored for cross-link formation following treatment of Saccharomyces cerevisiae with DVSF. Several proteins screened, including multiple oxidant defense proteins, underwent intermolecular and/or intramolecular cross-linking in response to DVSF. Specific redox-active cysteines within a subset of DVSF targets were found to influence cross-linking; in addition, DVSF-mediated cross-linking of its targets was impaired in cells first exposed to oxidants. Since cross-linking appeared to involve redox-active cysteines in these proteins, we examined whether potential redox partners became cross-linked to them upon DVSF treatment. Specifically, we found that several substrates of thioredoxins were cross-linked to the cytosolic thioredoxin Trx2 in cells treated with DVSF. However, other DVSF targets, like the peroxiredoxin Ahp1, principally formed intra-protein cross-links upon DVSF treatment. Moreover, additional protein targets, including several known to undergo S-glutathionylation, were conjugated via DVSF to glutathione. Our results indicate that DVSF is of potential use as a chemical tool for irreversibly trapping and discovering thiol-based redox partnerships within cells.

Mitochondrial H2O2 signaling is controlled by the concerted action of peroxiredoxin III and sulfiredoxin: Linking mitochondrial function to circadian rhythm

Mitochondria produce hydrogen peroxide (H₂O₂) during energy metabolism in most mammalian cells as well as during the oxidation of cholesterol associated with the synthesis of steroid hormones in steroidogenic cells. Some of the H₂O₂ produced in mitochondria is released into the cytosol, where it serves as a key regulator of various signaling pathways. Given that mitochondria are equipped with several H₂O₂-eliminating enzymes, however, it had not been clear how mitochondrial H₂O₂ can escape destruction by these enzymes for such release. Peroxiredoxin III (PrxIII) is the most abundant and efficient H₂O₂-eliminating enzyme in mitochondria of most cell types. We found that PrxIII undergoes reversible inactivation through hyperoxidation of its catalytic cysteine residue to cysteine sulfinic acid, and that release of mitochondrial H₂O₂ likely occurs as a result of such PrxIII inactivation. The hyperoxidized form of PrxIII (PrxIII-SO₂H) is reduced and reactivated by sulfiredoxin (Srx). We also found that the amounts of PrxIII-SO₂H and Srx undergo antiphasic circadian oscillation in mitochondria of the adrenal gland, heart, and brown adipose tissue of mice maintained under normal conditions. Cytosolic Srx was found to be imported into mitochondria via a mechanism that requires formation of a disulfide-linked complex with heat shock protein 90, which is likely promoted by H₂O₂ released from mitochondria. The imported Srx was found to be degraded by Lon protease in a manner dependent on PrxIII hyperoxidation state. The coordinated import and degradation of Srx underlie Srx oscillation and consequent PrxIII-SO₂H oscillation in mitochondria. The rhythmic change in the amount of PrxIII-SO₂H suggests that mitochondrial release of H₂O₂ is also likely a circadian event that conveys temporal information on steroidogenesis in the adrenal gland and on energy metabolism in heart and brown adipose tissue to cytosolic signaling pathways.

Mitochondrial H2O2 signaling is controlled by the concerted action of peroxiredoxin III and sulfiredoxin: Linking mitochondrial function to circadian rhythm

Mitochondria produce hydrogen peroxide (H₂O₂) during energy metabolism in most mammalian cells as well as during the oxidation of cholesterol associated with the synthesis of steroid hormones in steroidogenic cells. Some of the H₂O₂ produced in mitochondria is released into the cytosol, where it serves as a key regulator of various signaling pathways. Given that mitochondria are equipped with several H₂O₂-eliminating enzymes, however, it had not been clear how mitochondrial H₂O₂ can escape destruction by these enzymes for such release. Peroxiredoxin III (PrxIII) is the most abundant and efficient H₂O₂-eliminating enzyme in mitochondria of most cell types. We found that PrxIII undergoes reversible inactivation through hyperoxidation of its catalytic cysteine residue to cysteine sulfinic acid, and that release of mitochondrial H₂O₂ likely occurs as a result of such PrxIII inactivation. The hyperoxidized form of PrxIII (PrxIII-SO₂H) is reduced and reactivated by sulfiredoxin (Srx). We also found that the amounts of PrxIII-SO₂H and Srx undergo antiphasic circadian oscillation in mitochondria of the adrenal gland, heart, and brown adipose tissue of mice maintained under normal conditions. Cytosolic Srx was found to be imported into mitochondria via a mechanism that requires formation of a disulfide-linked complex with heat shock protein 90, which is likely promoted by H₂O₂ released from mitochondria. The imported Srx was found to be degraded by Lon protease in a manner dependent on PrxIII hyperoxidation state. The coordinated import and degradation of Srx underlie Srx oscillation and consequent PrxIII-SO₂H oscillation in mitochondria. The rhythmic change in the amount of PrxIII-SO₂H suggests that mitochondrial release of H₂O₂ is also likely a circadian event that conveys temporal information on steroidogenesis in the adrenal gland and on energy metabolism in heart and brown adipose tissue to cytosolic signaling pathways.

Sulfiredoxin inhibitor induces preferential death of cancer cells through reactive oxygen species-mediated mitochondrial damage

Recent studies have shown that many types of cancer cells have increased levels of reactive oxygen species (ROS) and enhance antioxidant capacity as an adaptation to intrinsic oxidative stress, suggesting that cancer cells are more vulnerable to oxidative insults and are more dependent on antioxidant systems compared with normal cells. Thus, disruption of redox homeostasis caused by a decline in antioxidant capacity may provide a method for the selective death of cancer cells. Here we show that ROS-mediated selective death of tumor cells can be caused by inhibiting sulfiredoxin (Srx), which reduces hyperoxidized peroxiredoxins, leading to their reactivation. Srx inhibitor increased the accumulation of sulfinic peroxiredoxins and ROS, which led to oxidative mitochondrial damage and caspase activation, resulting in the death of A549 human lung adenocarcinoma cells. Srx depletion also inhibited the growth of A549 cells like Srx inhibition, and the cytotoxic effects of Srx inhibitor were considerably reversed by Srx overexpression or antioxidants such as N-acetyl cysteine and butylated hydroxyanisol. Moreover, Srx inhibitor rendered tumorigenic ovarian cells more susceptible to ROS-mediated death compared with nontumorigenic cells and significantly suppressed the growth of A549 xenografts without acute toxicity. Our results suggest that Srx might serve as a novel therapeutic target for cancer treatment based on ROS-mediated cell death.

The aryl hydrocarbon receptor suppresses cigarette-smoke-induced oxidative stress in association with dioxin response element (DRE)-independent regulation of sulfiredoxin 1

The aryl hydrocarbon receptor (AhR) is a ubiquitously expressed receptor/transcription factor that mediates toxicological responses of environmental contaminants such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Emerging evidence indicates that the AhR suppresses apoptosis and proliferation independent of exogenous ligands, including suppression of apoptosis by cigarette smoke, a key risk factor for chronic obstructive pulmonary disease (COPD). As cigarette smoke is a potent inducer of oxidative stress, a feature that may contribute to the development of COPD, we hypothesized that the AhR prevents smoke-induced apoptosis by regulating oxidative stress. Utilizing primary lung fibroblasts derived from AhR(+/+) and AhR(-/-) mice as well as A549 human lung adenocarcinoma cells deficient in AhR expression (A549-AhR(ko)), we first show that AhR(-/-) fibroblasts and A549-AhR(ko) epithelial cells have a significant increase in cigarette smoke extract (CSE)-induced oxidative stress compared to wild type. CSE induced a significant increase in the mRNA expression of key antioxidant genes, including Nqo1 and Srxn1, predominantly in AhR(+/+) fibroblasts, with significantly less induction in AhR(-/-) cells. The induction of Srxn1, but not Nqo1, was independent of dioxin-response element (DRE) binding as AhR(DBD/DBD) lung fibroblasts, which express an AhR incapable of binding the DRE, increased Srxn1 to a degree similar to wild-type cells in response to CSE. There was no difference in Nrf2 expression or activation based on AhR expression. Lung fibroblasts derived from COPD subjects have significantly less AhR protein expression compared with both never-smokers (Normal) and smokers (At Risk). Consequently, COPD-derived fibroblasts were less robust in their induction of both Nqo1 and Srxn1 mRNA after exposure to CSE, which also failed to activate the AhR in the COPD fibroblasts. Taken together, these results support a new role for the AhR in regulating antioxidant defense in lung structural cells, such that low AhR expression may facilitate the development or progression of COPD.

In vivo parameters influencing 2-Cys Prx oligomerization: The role of enzyme sulfinylation

2-Cys Prxs are H₂O₂-specific antioxidants that become inactivated by enzyme hyperoxidation at elevated H₂O₂ levels. Although hyperoxidation restricts the antioxidant physiological role of these enzymes, it also allows the enzyme to become an efficient chaperone holdase. The critical molecular event allowing the peroxidase to chaperone switch is thought to be the enzyme assembly into high molecular weight (HMW) structures brought about by enzyme hyperoxidation. How hyperoxidation promotes HMW assembly is not well understood and Prx mutants allowing disentangling its peroxidase and chaperone functions are lacking. To begin addressing the link between enzyme hyperoxidation and HMW structures formation, we have evaluated the in vivo 2-Cys Prxs quaternary structure changes induced by H₂O₂ by size exclusion chromatography (SEC) on crude lysates, using wild type (Wt) untagged and Myc-tagged S. cerevisiae 2-Cys Prx Tsa1 and derivative Tsa1 mutants or genetic conditions known to inactivate peroxidase or chaperone activity or altering the enzyme sensitivity to hyperoxidation. Our data confirm the strict causative link between H₂O₂-induced hyperoxidation and HMW formation/stabilization, also raising the question of whether C_P hyperoxidation triggers the assembly of HMW structures by the stacking of decamers, which is the prevalent view of the literature, or rather, the stabilization of preassembled stacked decamers.

The sulfiredoxin-peroxiredoxin (Srx-Prx) axis in cell signal transduction and cancer development

Redox signaling is a critical component of cell signaling pathways that are involved in the regulation of cell growth, metabolism, hormone signaling, immune regulation and variety of other physiological functions. Peroxiredoxin (Prx) is a family of thiol-based peroxidase that acts as a regulator of redox signaling. Members of Prx family can act as antioxidants and chaperones. Sulfiredoxin (Srx) is an antioxidant protein that exclusively reduces over-oxidized typical 2-Cys Prx. Srx has different affinities for individual Prx and it also catalyzes the deglutathionylation of variety of substrates. Individual component of the Srx-Prx system plays critical role in carcinogenesis by modulating cell signaling pathways involved in cell proliferation, migration and metastasis. Expression levels of individual component of the Srx-Prx axis have been correlated with patient survival outcome in multiple cancer types. This review will summarize the molecular basis of differences in the affinity of Srx for individual Prx and the role of individual component of the Srx-Prx system in tumor progression and metastasis. This enhanced understanding of molecular aspects of Srx-Prx interaction and its role in cell signal transduction will help define the Srx-Prx system as a future therapeutic target in human cancer.

Role of sulfiredoxin in systemic diseases influenced by oxidative stress

Sulfiredoxin is a recently discovered member of the oxidoreductases family which plays a crucial role in thiol homoeostasis when under oxidative stress. A myriad of systemic disorders have oxidative stress and reactive oxygen species as the key components in their etiopathogenesis. Recent studies have evaluated the role of this enzyme in oxidative stress mediated diseases such as atherosclerosis, chronic obstructive pulmonary disease and a wide array of carcinomas. Its action is responsible for the normal functioning of cells under oxidative stress and the promotion of cell survival in cancerous cells. This review will highlight the cumulative effects of sulfiredoxin in various systemic disorders with a strong emphasis on its target activity and the factors influencing its expression in such conditions.

Study of the signaling function of sulfiredoxin and peroxiredoxin III in isolated adrenal gland: unsuitability of clonal and primary adrenocortical cells

Members of the peroxiredoxin (Prx) family of antioxidant enzymes are inactivated via hyperoxidation of the active site cysteine by the substrate H2O2 and are reactivated via an ATP-consuming process catalyzed by sulfiredoxin (Srx). PrxIII is reversibly inactivated by H2O2 produced by cytochrome P450 11B1 (CYP11B1) in mitochondria during corticosterone synthesis in the adrenal gland of mice injected with adrenocorticotropic hormone (ACTH). Inactivation of PrxIII triggers a sequence of events including accumulation of H2O2, activation of p38 mitogen-activated kinase (MAPK), inhibition of cholesterol transfer, and suppression of corticosterone synthesis. Srx expression is significantly induced by ACTH injection. The coupling of CYP11B1 activity to PrxIII inactivation and Srx induction provides a feedback regulatory mechanism for steroidogenesis that functions independently of the hypothalamic-pituitary-adrenal axis. Furthermore, the PrxIII-Srx regulatory pathway is critical for the circadian rhythm of corticosterone production. Although adrenocortical tumor cell lines such as Y-1 and H295R have been used extensively for studying the mechanism of steroidogenesis, those clonal cells were found to be unsuitable as an in vitro model for redox signaling because the amount of Srx in the cell lines is much higher than that in mouse adrenal gland and not affected by ACTH stimulation. Furthermore, the levels of PrxIII in the clonal cells are greatly reduced compared to that in the adrenal gland, and ACTH does not induce PrxIII hyperoxidation in the clonal cells. Primary adrenocortical cells isolated from the mouse adrenal gland were also found to be an invalid model because Srx levels are increased, along with decreased levels of hyperoxidized PrxIII, soon after isolation of these cells. Organ culture system is, however, appropriate for studying the PrxIII-Srx regulatory function as the levels of hyperoxidized PrxIII and Srx in the adrenal glands maintained overnight in culture medium are not changed.

Nuclear Nrf2 expression is related to a poor survival in pancreatic adenocarcinoma

The aim of this study was to investigate the expression of Nrf2, sulfiredoxin and DJ1 in pancreatic cancer. The expression of Nrf2, sulfiredoxin and DJ1 was studied immunohistochemically in a large set of pancreatic adenocarcinomas consisting of 103 cases. Eighty six percent of the cases showed cytoplasmic Nrf2 and 24% nuclear Nrf2 positivity. Sulfiredoxin positivity was observed in 54% and DJ1 positivity in all cases. Nuclear Nrf2 positivity had an association with sulfiredoxin (p=0.019) and was associated with a poor survival (p=0.010). Stage IV tumors tended to have a more nuclear Nrf2 expression (p=0.080). DJ1 expression was more often found in well-differentiated tumors (p=0.012), and DJ1 expression was associated with better survival (p=0.020). According to the results, nuclear Nrf2 expression predicts a worse survival in pancreatic adenocarcinoma, which is in keeping with its protection of cells against oxidative or xenobiotic stress. In accordance with Nrf2's regulation of the synthesis of sulfiredoxin, there was an association between them (p=0.019). DJ1 had no association with Nrf2, and its expression predicted a better survival of patients.

Peroxiredoxins and sulfiredoxin at the crossroads of the NO and H2O2 signaling pathways

Peroxiredoxins (Prxs) are a family of peroxidases that maintain thiol homeostasis by catalyzing the reduction of organic hydroperoxides, H2O2, and peroxynitrite. Eukaryotic 2-Cys-Prxs, also referred to as typical Prxs, can be inactivated by oxidation of the catalytic cysteine to sulfinic acid, which may regulate the intracellular messenger function of H2O2. A small redox protein, sulfiredoxin (Srx), has been shown to reduce sulfinylated 2-Cys-Prxs and thus to regenerate active 2-Cys-Prxs. We previously reported that cytokine-induced nitric oxide (NO) intervenes in this pathway by decreasing the level of 2-Cys overoxidation and by upregulating Srx through the activation of the transcription factor nuclear factor erythroid 2-related factor (Nrf2). Here, we describe the methods used to monitor the interplay between NO and H2O2 in the regulation of the Prx/Srx system in immunostimulated macrophages, which produce both reactive oxygen species and NO.

Nuclear factor E2-related factor 2 dependent overexpression of sulfiredoxin and peroxiredoxin III in human lung cancer

BACKGROUND/AIMS

Oxidative stress results in protein oxidation and is implicated in carcinogenesis. Sulfiredoxin (Srx) is responsible for the enzymatic reversal of inactivated peroxiredoxin (Prx). Nuclear factor E2-related factor 2 (Nrf2) binds to antioxidant responsive elements and upregulates the expression of Srx and Prx during oxidative stress. We aimed to elucidate the biological functions and potential roles of Srx in lung cancer.

METHODS

To study the roles of Srx and Prx III in lung cancer, we compared the protein levels of Nrf2, Prxs, thioredoxin, and Srx in 40 surgically resected human lung cancer tissues using immunoblot and immunohistochemical analyses. Transforming growth factor-β(1), tumor necrosis factor-α, and camptothecin treatment were used to examine Prx III inactivation in Mv1Lu mink lung epithelial cells and A549 lung cancer cells.

RESULTS

Prx I and Prx III proteins were markedly overexpressed in lung cancer tissues. A significant increase in the oxidized form of a cysteine sulfhydryl at the catalytic site of Prxs was found in carcinogenic lung tissue compared to normal lung tissue. Densitometric analyses of immunoblot data revealed significant Srx expression, which was higher in squamous cell carcinoma tissue (60%, 12/20) than in adenocarcinoma (20%, 4/20). Also, Nrf2 was present in the nuclear compartment of cancer cells.

CONCLUSIONS

Srx and Prx III proteins were markedly overexpressed in human squamous cell carcinoma, suggesting that these proteins may play a protective role against oxidative injury and compensate for the high rate of mitochondrial metabolism in lung cancer.