Sulfiredoxin is an AP-1 target gene that is required for transformation and shows elevated expression in human skin malignancies

Unraveling the role of sulfiredoxin-1 in early-onset preeclampsia: A key player in trophoblast ferroptosis

Preeclampsia (PE) significantly contributes to obstetric complications and maternal mortality, yet its pathogenesis and mechanisms are not well understood. Sulfiredoxin-1 (SRXN1) is known for its antioxidant activity and its role in defending against oxidative stress; it is also linked to various cancers. However, the role of SRXN1 in PE remains unclear. Our study found a significant decrease in SRXN1 levels in the serum and placental tissues of patients with early-onset preeclampsia (EOPE). Similarly, a PE-like mouse model showed reduced SRXN1 expression. Our in vitro experiments showed that reducing SRXN1 impaired trophoblast viability, decreased invasion and migration, and led to cell death, primarily through ferroptosis. These results are consistent with analyses of placental tissues from EOPE patients. In summary, lower SRXN1 levels during pregnancy contribute to trophoblast ferroptosis, potentially affecting the development and progression of EOPE.

Association of SRXN1 Receptor Gene Polymorphism with Susceptibility to Periodontitis

Background

Emerging evidence suggests that oxidative stress forms a key component in the etiopathogenesis of periodontitis. Literature evidence have shown potential antioxidants responsible for combating the pro-oxidants which stress the periodontium, but the peroxiredoxin-sulfiredoxin system is explored very minimally in periodontal disease. Thus, the present study was aimed to evaluate the genetic association of SRXN1 receptor gene polymorphism (rs6053666).

Materials and Methods

A total of 100 subjects were recruited for this study, which included 50 Periodontitis patients (Stage II and above based on the criteria of American Association of Periodontology-2018) and 50 periodontally healthy or mild gingivitis. Genomic DNA was extracted from the whole blood collected from the subjects. DNA was amplified using specific primers flanking the BtgI region of the SRXN1 receptor gene. The amplicon was further subjected to genotyping using restriction fragment length using BtgI enzyme. The genotype obtained based on the restriction fragment length polymorphism pattern was recorded and used for statistical analysis. The distribution of genotypes and allele frequencies in the periodontitis and control groups were compared using the Chi-square test. The risk associated with individual alleles or genotypes was calculated as the odds ratio with 95% confidence intervals. Statistical significance in all tests was determined at P < 0.05.

Results

The genotype frequency and distributions of SRXN1 receptor BtgI polymorphism did not differ significantly at ꭕ2df (P = 0.557). Our study results showed that homozygous and heterozygous mutant genotypes had no significant difference (CC vs. CT + TT) between the periodontitis patients and control group with a P = 0.4266. The detected frequency of CT (38% vs. 34%) and TT (42% vs. 52%) genotype showed no significant difference between control and test group. There was no significant difference in C allele (39% vs. 31%) and T allele (61% vs. 69%) between the test and control group.

Conclusion

The present study denotes that SRXN1 receptor gene polymorphism is not associated with periodontitis in the study group analyzed.

Apigenin Induced Apoptosis by Downregulating Sulfiredoxin Expression in Cutaneous Squamous Cell Carcinoma

Cutaneous squamous cell carcinoma (cSCC) is the second carcinoma in nonmelanoma skin cancer (NMSC). Sulfiredoxin (Srx) is an antioxidant protein with a role in maintaining redox homeostasis. And Srx has an oncogenic role in skin tumorigenesis. In the current study, we found that apigenin, as a natural flavonoid, downregulated the expression of Srx protein in cSCC cell lines. Apigenin also inhibited the ability of cell proliferation and migration and induced apoptosis in cSCC cell lines. Our results also showed that apigenin induced apoptosis via the activation of the mitogen-activated protein kinase (MAPK) signaling pathway, as well as downregulated Srx expression in cSCC cell lines. Importantly, the effect of downregulation Srx by apigenin has been rescued with the inhibitor of the MAPK signaling pathway intervention. And induced apoptosis by apigenin was partially attenuated by the addition of MAPK inhibitor, Binimetinib. Our research revealed that apigenin induced apoptosis by downregulation of Srx expression through regulating the MAPK signaling pathway in cSCC cells, thus providing evidence of its applicability as a potentially effective therapeutic agent for cSCC treatment.

Sulfiredoxin Promotes Cancer Cell Invasion through Regulation of the miR143-Fascin Axis

Intracellular antioxidant enzymes are critical for maintenance of redox homeostasis, but whether and how they contribute to the malignancy of cancer cells remains poorly understood. Sulfiredoxin (Srx) is a unique oxidoreductase in that it not only restores peroxidase activity of peroxiredoxins (Prxs) but also functions as a pivotal stimulator of oncogenic signaling. We found that abnormally high level of Srx promotes colorectal cancer (CRC) malignancy by stimulating gelatin degradation, invadopodia formation, and cell invasion. Fascin, an actin-bundling protein, was discovered and validated as one of the critical downstream targets of Srx activation. We demonstrated that depletion of Srx in CRC cells leads to upregulation of miR-143-3p, which mediates degradation of fascin mRNA through binding to conserved sites within the 3' untranslated region (UTR). Depletion of fascin in CRC cells recapitulates the effect of Srx loss, and restoration of fascin in Srx-depleted cells by miR-143-3p inhibitor or overexpression rescues defects in cell invasion. Therefore, our data demonstrate that the Srx-miR143-fascin axis plays a key role in promoting the malignancy of human CRC cells. In the future, the Srx-miR143-fascin axis can be used as a functional pathway to evaluate the efficacy of therapeutic drugs or be targeted to develop promising chemotherapeutics for treatment of CRC patients.

NRF2 and Key Transcriptional Targets in Melanoma Redox Manipulation

Melanocytes are dendritic, pigment-producing cells located in the skin and are responsible for its protection against the deleterious effects of solar ultraviolet radiation (UVR), which include DNA damage and elevated reactive oxygen species (ROS). They do so by synthesizing photoprotective melanin pigments and distributing them to adjacent skin cells (e.g., keratinocytes). However, melanocytes encounter a large burden of oxidative stress during this process, due to both exogenous and endogenous sources. Therefore, melanocytes employ numerous antioxidant defenses to protect themselves; these are largely regulated by the master stress response transcription factor, nuclear factor erythroid 2-related factor 2 (NRF2). Key effector transcriptional targets of NRF2 include the components of the glutathione and thioredoxin antioxidant systems. Despite these defenses, melanocyte DNA often is subject to mutations that result in the dysregulation of the proliferative mitogen-activated protein kinase (MAPK) pathway and the cell cycle. Following tumor initiation, endogenous antioxidant systems are co-opted, a consequence of elevated oxidative stress caused by metabolic reprogramming, to establish an altered redox homeostasis. This altered redox homeostasis contributes to tumor progression and metastasis, while also complicating the application of exogenous antioxidant treatments. Further understanding of melanocyte redox homeostasis, in the presence or absence of disease, would contribute to the development of novel therapies to aid in the prevention and treatment of melanomas and other skin diseases.

Clinico-pathological and prognostic implications of Srx, Nrf2, and PROX1 expression in gastric cancer and adjacent non-neoplastic mucosa - an immunohistochemical study

Introduction

Sulfiredoxin (Srx), which is an endogenous antioxidant substance which could, regulate the signaling pathways of reactive oxygen species. Nuclear factor erythroid 2-related factor 2 (Nrf2) is Cap-N-collar (CNC) transcription factors family member that have essential roles in regulation of antioxidant response. The transcription factor PROX1 is a transcription factor and a key regulatory protein in cancer development.

Aim of the study

To analyze levels of tissue expression of Srx, Nrf2, and PROX1 in gastric cancer and adjacent non-neoplastic gastric mucosa to clarify the relationship between their expression levels, clinical, pathological parameters and patients’ outcome. The results might lead to discovering novel targeted therapies to gastric cancers.

Material and methods

We included 70 paraffin-embedded samples: 50 specimens from gastric carcinomas and 20 specimens from adjacent non-neoplastic gastric mucosa. All samples are stained with Srx, Nrf2, and PROX1 using immunohistochemistry, correlated their expression with clinicopathological and prognostic parameters of patients.

Results

High levels of Srx and Nrf2 expression were positively associated with higher cancer grade (p = 0.006, 0.031 respectively), advanced stage (p < 0.001, 0.02 respectively), higher incidence of distant metastases (p = 0.029, 0.03 respectively) and dismal outcome (p < 0.001). High levels of PROX1 expression were associated with lower cancer grade (p = 0.005), absence of lymph nodes metastases (p = 0.023), early stage (p = 0.003), absence of relapse (p = 0.004), and favorable outcome (p < 0.001).

Conclusions

Srx and Nrf2 expression increase gastric cancer invasiveness, suggesting their utility as poor prognostic markers, but PROX1 serves as a favorable prognostic marker of gastric cancer patients.

SRXN1 stimulates hepatocellular carcinoma tumorigenesis and metastasis through modulating ROS/p65/BTG2 signalling

Sulfiredoxin 1 (SRXN1) is a pivotal regulator of the antioxidant response in eukaryotic cells. However, the role of SRXN1 in hepatocellular carcinoma (HCC) is far from clear. The present study aims to elucidate whether SRXN1 participates in tumorigenesis and metastasis of HCC and to determine the molecular mechanisms. We found that SRXN1 expression was up-regulated in HCC tissue samples and correlated with poor prognosis in HCC patients. We also observed that SRXN1 knockdown by transient siRNA transfection inhibited HCC cell proliferation, migration and invasion. Overexpression of SRXN1 increased HCC cell migration and invasion. B-cell translocation gene 2 (BTG2) was identified as a downstream target of SRXN1. Mechanistic studies revealed that SRXN1-depleted reactive oxygen species (ROS) modulated migration and invasion of HCC cells. In addition, the ROS/p65/BTG2 signalling hub was found to regulate the epithelial-mesenchymal transition (EMT), which mediates the pro-metastasis role of SRXN1 in HCC cells. In vivo experiments showed SRXN1 promotes HCC tumour growth and metastasis in mouse subcutaneous xenograft and metastasis models. Collectively, our results revealed a novel pro-tumorigenic and pro-metastatic function of SRXN1 in HCC. These findings demonstrate a rationale to exploit SRXN1 as a therapeutic target effectively preventing metastasis of HCC.

Sulfiredoxin as a Potential Therapeutic Target for Advanced and Metastatic Prostate Cancer

The incidence of prostate cancer (PCa) is increasing, and it is currently the second most frequent cause of death by cancer in men. Despite advancements in cancer therapies, new therapeutic approaches are still needed for treatment-refractory advanced metastatic PCa. Cross-species analysis presents a robust strategy for the discovery of new potential therapeutic targets. This strategy involves the integration of genomic data from genetically engineered mouse models (GEMMs) and human PCa datasets. Considering the role of antioxidant pathways in tumor initiation and progression, we searched oxidative stress-related genes for a potential therapeutic target for PCa. First, we analyzed RNA-sequencing data from Pb-Cre4; Pten^f/f mice and discovered an increase in sulfiredoxin (Srxn1) mRNA expression in high-grade prostatic intraepithelial neoplasia (PIN), well-differentiated adenocarcinoma (medium-stage tumors), and poor-differentiated adenocarcinoma (advanced-stage prostate tumors). The increase of SRXN1 protein expression was confirmed by immunohistochemistry in mouse prostate tumor paraffin samples. Analyses of human databases and prostate tissue microarrays demonstrated that SRXN1 is overexpressed in a subset of high-grade prostate tumors and correlates with aggressive PCa with worse prognosis and decreased survival. Analyses in vitro showed that SRXN1 expression is also higher in most PCa cell lines compared to normal cell lines. Furthermore, siRNA-mediated downregulation of SRXN1 led to decreased viability of PCa cells LNCaP. In conclusion, we identified the antioxidant enzyme SRXN1 as a potential therapeutic target for PCa. Our results suggest that the use of specific SRXN1 inhibitors may be an effective strategy for the adjuvant treatment of castration-resistant PCa with SRXN1 overexpression.

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.

Frugoside Induces Mitochondria-Mediated Apoptotic Cell Death through Inhibition of Sulfiredoxin Expression in Melanoma Cells

Malignant melanoma is the most life-threatening neoplasm of the skin. Despite the increase in incidence, melanoma is becoming more resistant to current therapeutic agents. The bioactive compound frugoside has been recently reported to inhibit growth when used in various cancer cells. However, this effect has not been demonstrated in melanoma. Here, we found that frugoside inhibited the rate of reduction of hyperoxidized peroxiredoxins (Prxs) by downregulating sulfiredoxin (Srx) expression. Furthermore, frugoside increased the accumulation of sulfinic Prxs and reactive oxygen species (ROS) and stimulated p-p38 activation, resulting in the mitochondria-mediated death of M14 and A375 human melanoma cells. The mitochondria-mediated cell death induced by frugoside was inhibited by the overexpression of Srx and antioxidants, such as N-acetyl cysteine and diphenyleneiodonium. In addition, we observed that frugoside inhibited tumor growth without toxicity through a M14 xenograft animal model. Taken together, our findings reveal that frugoside exhibits a novel antitumor effect based on a ROS-mediated cell death in melanoma cells, which may have therapeutic implications.

The redox regulator sulfiredoxin forms a complex with thioredoxin domain-containing 5 protein in response to ER stress in lung cancer cells

Sulfiredoxin (Srx) reduces hyperoxidized 2-cysteine-containing peroxiredoxins (Prxs) and protects cells against oxidative stress. Previous studies have shown that Srx is highly expressed in primary specimens of lung cancer patients and plays a pivotal role in lung tumorigenesis and cancer progression. However, the oncogenic mechanisms of Srx in cancer are incompletely understood. In this study, we found that Srx knockdown sensitizes lung cancer cells to endoplasmic reticulum (ER) stress-induced cell death. Through MS analysis, we determined that Srx forms a complex with the ER-resident protein thioredoxin domain-containing protein 5 (TXNDC5). Using reciprocal co-immunoprecipitation, immunofluorescence imaging, subcellular fractionation, and domain-mapping assays with site-specific mutagenesis and purified recombinant proteins, we further characterized the Srx-TXNDC5 interaction. In response to ER stress but not to oxidative stress, Srx exhibits an increased association with TXNDC5, facilitating the retention of Srx in the ER. Of note, TXNDC5 knockdown in lung cancer cells inhibited cell proliferation and repressed anchorage-independent colony formation and migration, but increased cell invasion and activation of mitogen-activated protein kinases. Using immunohistochemical staining, we demonstrate that TXNDC5 is highly expressed in patient-derived lung cancer specimens. Bioinformatics analysis of publicly available data sets revealed that those with high Srx levels have significantly shorter survival and that those with high TXNDC5 levels have longer survival. We conclude that the cellular levels of Srx and TXNDC5 may be useful as biomarkers to predict the survival of individuals with lung cancer.

Increased Sulfiredoxin Expression in Gastric Cancer Cells May Be a Molecular Target of the Anticancer Component Diallyl Trisulfide

Sulfiredoxin (Srx) is a newly discovered antioxidant enzyme playing a role in the catalytic reduction of oxidative modifications. Srx is overexpressed in a variety of cancers. It may promote carcinogenesis as well as tumor progression. In this study, we report for the first time that Srx expression might be positively associated with the development of gastric cancer and tumor malignancy. Immunohistochemistry showed that, compared to normal tissues (42%, 20/47), Srx expression in gastric tumors (85%, 40/47) was much more common (chi-square test, p<0.01). In addition, the staining of Srx was stronger in poorly differentiated gastric cancer than in well-differentiated gastric cancer. Western blotting showed that, in the gastric tumor cell line BGC823, the Srx protein was upregulated in response to H₂O₂ treatment, although it was inadequate to counteract the increased oxidative stress, as indicated by the gradually increasing level of malondialdehyde (MDA). In addition, Srx expression, MDA levels, and ROS levels in BGC823 cells were markedly inhibited upon treatment with diallyl trisulfide (DATS), a major constituent of garlic oil with proven anticancer effects. These results suggest that Srx may be an oxidative stress marker. Antioxidation may account for the anticancer potential of garlic.

Chemical proteomics reveals new targets of cysteine sulfinic acid reductase

Cysteine sulfinic acid or S-sulfinylation is an oxidative post-translational modification (OxiPTM) that is known to be involved in redox-dependent regulation of protein function but has been historically difficult to analyze biochemically. To facilitate the detection of S-sulfinylated proteins, we demonstrate that a clickable, electrophilic diazene probe (DiaAlk) enables capture and site-centric proteomic analysis of this OxiPTM. Using this workflow, we revealed a striking difference between sulfenic acid modification (S-sulfenylation) and the S-sulfinylation dynamic response to oxidative stress, which is indicative of different roles for these OxiPTMs in redox regulation. We also identified >55 heretofore-unknown protein substrates of the cysteine sulfinic acid reductase sulfiredoxin, extending its function well beyond those of 2-cysteine peroxiredoxins (2-Cys PRDX1-4) and offering new insights into the role of this unique oxidoreductase as a central mediator of reactive oxygen species-associated diseases, particularly cancer. DiaAlk therefore provides a novel tool to profile S-sulfinylated proteins and study their regulatory mechanisms in cells.

The Multifaceted Impact of Peroxiredoxins on Aging and Disease

SIGNIFICANCE

Peroxiredoxins (Prxs), a family of thiol-associated peroxidases, are purported to play a major role in sensing and managing hydrogen peroxide concentrations and transducing peroxide-derived signals. Recent Advances: Prxs can act as detoxifying factors and impart effects to cells that can be either sparing or suicidal. Advances have been made to address the qualitative changes in Prx function in response to quantitative changes in the signal level and to understand how Prx activity could be affected by their own substrates. Here we rationalize the basis for both positive and negative effects on signaling pathways and cell physiology, summarizing data from model organisms, including invertebrates.

CRITICAL ISSUES

Resolving the relationship between the promiscuous behavior of reactive oxygen species and the specificity of Prxs toward different targets in redox-sensitive signaling pathways is a key area of research. Attempts to understand Prx function and underlying mechanisms were conducted in vitro or in vivo under nonphysiological conditions, leaving the physiological relevance yet to be defined. Other issues: Why despite the high degree of homology and similarities in subcellular and tissue distribution between Prxs do they display differential effects on signaling? How is the specificity of post-translational protein modifications determined? Other than chaperone-like activity, how do hyperoxidized Prxs function?

FUTURE DIRECTIONS

Genetic models with mutated catalytic and resolving cysteines should be further exploited to dissect the functional significance of individual Prxs in their different states together with their alternative reducing partners. Such an analysis may then be extended to help identify Prx-specific targets.

Nrf2-activated expression of sulfiredoxin contributes to urethane-induced lung tumorigenesis

Lung cancer is the leading cause of cancer death worldwide. Cigarette smoking and exposure to chemical carcinogens are among the risk factors of lung tumorigenesis. In this study, we found that cigarette smoke condensate and urethane significantly stimulated the expression of sulfiredoxin (Srx) at the transcript and protein levels in cultured normal lung epithelial cells, and such stimulation was mediated through the activation of nuclear related factor 2 (Nrf2). To study the role of Srx in lung cancer development in vivo, mice with Srx wildtype, heterozygous or knockout genotype were subjected to the same protocol of urethane treatment to induce lung tumors. By comparing tumor multiplicity and volume between groups of mice with different genotype, we found that Srx knockout mice had a significantly lower number and smaller size of lung tumors. Mechanistically, we demonstrated that loss of Srx led to a decrease of tumor cell proliferation as well as an increase of tumor cell apoptosis. These data suggest that Srx may have an oncogenic role that contributes to the development of lung cancer in smokers or urethane-exposed human subjects.

Targeting Free Radicals in Oxidative Stress-Related Human Diseases

Cancer and Alzheimer's disease (AD) are characterized by (i) opposing biological mechanisms, (ii) an inverse correlation between their incidences, and (iii) oxidative stress being a common denominator of both diseases. Increased formation of reactive oxygen species (ROS) in cancer cells from oncogenic signaling and/or metabolic disturbances leads to upregulation of cellular antioxidant capacity to maintain ROS levels below a toxic threshold. Combining drugs that induce high levels of ROS with compounds that suppress cellular antioxidant capacity by depleting antioxidant systems [glutathione (GSH), superoxide dismutase (SOD), and thioredoxin (TRX)] and/or targeting glucose metabolism represents a potential anticancer strategy. In AD, free metals and/or Aβ:metal complexes may cause damage to biomolecules in the brain (via Fenton reaction), including DNA. Metal chelation, based on the application of selective metal chelators or metal delivery, may induce neuroprotective signaling and represents a promising therapeutic strategy. This review examines therapeutic strategies based on the modulation of oxidative stress in cancer and AD.

Sulfiredoxin May Promote Cervical Cancer Metastasis via Wnt/β-Catenin Signaling Pathway

The abnormal elevation of sulfiredoxin (Srx/SRXN1)-an antioxidant enzyme whose main function is to protect against oxidative stress-has been shown to be closely correlated with the progression of several types of cancer, including human cervical cancer. However, the molecular mechanism by which Srx promotes tumor progression, especially cancer metastasis in cervical cancer, has not been elucidated. Here, we show that Srx expression gradually increases during the progression of human cervical cancer and its expression level is closely correlated with lymph node metastasis. Our study also reveals a significant positive correlation between the expression of Srx and β-catenin in cervical cancer tissues. Loss-of-function studies demonstrate that Srx knockdown using a lentiviral vector-mediated specific shRNA decreases the migration and invasion capacity in HeLa (human papilloma virus 18 type cervical cancer cell line) and SiHa SiHa (cervical squamous cancer cell line). Notably, the exact opposite effects were observed in gain-of-function experiments in C-33A cells. Mechanistically, downregulation or upregulation of Srx leads to an altered expression of proteins associated with the Wnt/β-catenin signaling pathway. Furthermore, blockage of the Wnt/β-catenin signaling pathway contributed to attenuated Srx expression and resulted in significant inhibition of cell migration and invasion in cervical cancer cell lines. Combined, Srx might be an oncoprotein in cervical cancer, playing critical roles in activating the Wnt/β-catenin signaling pathway; it may therefore be a therapeutic target for cervical cancer.

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.

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.

Lgr4 is crucial for skin carcinogenesis by regulating MEK/ERK and Wnt/β-catenin signaling pathways

Lgr4 is a member of the leucine-rich, G protein-coupled receptor family of proteins, and has recently been shown to augment Wnt/β-catenin signaling via binding to Wnt agonists R-spondins. It plays an important role in skin development, but its involvement in skin tumorigenesis is unclear. Here, we report that mice deficient for Lgr4 are resistant to 12-O-tetradecanoyl-phorbol-13-acetate (TPA)-induced keratinocyte proliferation and papilloma formation. We show that TPA treatment activates MEK1, ERK1/2 and downstream effector AP-1 in wild-type (WT) epidermal cells and mice, but not in cells or mice where Lgr4 is depleted. Wnt/β-catenin signaling is also dramatically activated by TPA treatment, and this activation is abolished when Lgr4 is deleted. We provide evidences that blocking both MEK1/ERK1/2 and Wnt/β-catenin pathways prevents TPA-induced increase in the expression of Ccnd1 (cyclin D1), a known Wnt/β-catenin target gene, and that the activation of MEK1/ERK1/2 pathway lies upstream of Wnt/β-catenin signal pathway. Collectively, our findings identify Lgr4 as a critical positive factor for skin tumorigenesis by mediating the activation of MEK1/ERK1/2 and Wnt/β-catenin pathways.

Thioredoxin 1 protects astrocytes from oxidative stress by maintaining peroxiredoxin activity

Previous studies have demonstrated that thioredoxin 1 (Trx1) exerts neuroprotective effects against cerebral ischemia/reperfusion injury caused by oxidative stress. While Trx1 is known to maintain the anti-oxidant activity of 2-Cys peroxiredoxins (Prdxs), the underlying mechanisms of its protective effects have remained to be elucidated, which was the aim of the present study. For this, an in vitro ischemic model of hypoxemia lasting for 4 h, followed by 24 h of reperfusion was used. Primary astrocytes from neonatal rats were pre-treated with small interfering RNA targeting Trx1 prior to oxygen glucose deprivation/reperfusion (OGD/R). MTS and lactate dehydrogenase assays were performed to evaluate cell viability. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and western blot analysis were employed to assess the mRNA and protein expression levels of Prdx1-4 and Prdx-SO₃. Furthermore, a dual luciferase reporter assay was used to assess the interaction between activator protein-1 (AP-1) and Trx1. The present study demonstrated that OGD/R decreased the cell viability and increased cellular damage, which was more marked following Trx1 knockdown. The expression of Prdx1-4 and Prdx-SO₃ protein was higher in the cells subjected to OGD/R. Knockdown of Trx1 markedly decreased the levels of Prdx1-4 but increased Prdx-SO₃ mRNA and protein levels. The results of the present study also suggested that AP-1 directly activated the expression of Trx1. The present study demonstrated that Trx1 exerts its neuroprotective effects by preventing oxidative stress in astrocytes via maintaining Prdx expression.

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.

Dysregulation of redox-state-regulating enzymes in melanocytic skin tumours and the surrounding microenvironment

AIMS

To investigate redox-regulating enzymes that may have a special role in melanoma pathogenesis due to continuous exposure to microenvironment-produced and ultraviolet radiation-induced oxidative stress.

METHODS AND RESULTS

We assessed immunohistochemically the expression of antioxidant enzymes peroxiredoxins (Prxs) I-IV, sulfiredoxin (Srx) and redox-regulated proto-oncogene DJ-1 in material consisting of 30 benign naevi, 14 lentigo malignas and 67 malignant melanomas. Evaluation of immunostaining was performed with special attention paid to protein expression in different tumour compartments. In particular, the expression patterns of nuclear Prx I and Prx II and cytoplasmic DJ-1 were decreased significantly in melanomas compared with dysplastic and benign naevi. In multivariate analysis, several prognostic factors were identified: Prx III expression in the cytoplasm of stromal fibroblasts was associated with shortened melanoma-specific survival [hazard ratio (HR) 6.730; 95% confidence interval (CI) 1.579-28.689], while cytoplasmic Prx IV expression in endothelial cells (HR 6.563; 95% CI 1.750-24.620) and Srx expression in the cytoplasm of keratinocytes (HR 6.988; 95% CI 1.559-31.324) were associated with better prognosis independently of ulceration, thickness of melanoma or its diagnostic type.

CONCLUSIONS

Redox-regulating enzymes have the potential to serve as novel prognostic factors and targeting them may offer new therapeutic options in malignant melanoma.

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.

Tumor promoter-induced sulfiredoxin is required for mouse skin tumorigenesis

Sulfiredoxin (Srx), the exclusive enzyme that reduces the hyperoxidized inactive form of peroxiredoxins (Prxs), has been found highly expressed in several types of human skin cancer. To determine whether Srx contributed to skin tumorigenesis in vivo, Srx null mice were generated on an FVB background. Mouse skin tumorigenesis was induced by a 7,12-dimethylbenz[α]anthracene/12-O-tetradecanoylphorbol-13-acetate (DMBA/TPA) protocol. We found that the number, volume and size of papillomas in Srx(-/-) mice were significantly fewer compared with either wild-type (Wt) or heterozygous (Het) siblings. Histopathological analysis revealed more apoptotic cells in tumors from Srx(-/-) mice. Mechanistic studies in cell culture revealed that Srx was stimulated by TPA in a redox-independent manner. This effect was mediated transcriptionally through the activation of mitogen-activated protein kinase and Jun-N-terminal kinase. We also demonstrated that Srx was capable of reducing hyperoxidized Prxs to facilitate cell survival under oxidative stress conditions. These findings suggested that loss of Srx protected mice, at least partially, from DMBA/TPA-induced skin tumorigenesis. Therefore, Srx has an oncogenic role in skin tumorigenesis and targeting Srx may provide novel strategies for skin cancer prevention or treatment.

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.

Regulation of the human thioredoxin gene promoter and its key substrates: a study of functional and putative regulatory elements

BACKGROUND

The thioredoxin system maintains redox balance through the action of thioredoxin and thioredoxin reductase. Thioredoxin regulates the activity of various substrates, including those that function to counteract cellular oxidative stress. These include the peroxiredoxins, methionine sulfoxide reductase A and specific transcription factors. Of particular relevance is Redox Factor-1, which in turn activates other redox-regulated transcription factors.

SCOPE OF REVIEW

Experimentally defined transcription factor binding sites in the human thioredoxin and thioredoxin reductase gene promoters together with promoters of the major thioredoxin system substrates involved in regulating cellular redox status are discussed. An in silico approach was used to identify potential putative binding sites for these transcription factors in all of these promoters.

MAJOR CONCLUSIONS

Our analysis reveals that many redox gene promoters contain the same transcription factor binding sites. Several of these transcription factors are in turn redox regulated. The ARE is present in several of these promoters and is bound by Nrf2 during various oxidative stress stimuli to upregulate gene expression. Other transcription factors also bind to these promoters during the same oxidative stress stimuli, with this redundancy supporting the importance of the antioxidant response. Putative transcription factor sites were identified in silico, which in combination with specific regulatory knowledge for that gene promoter may inform future experiments.

GENERAL SIGNIFICANCE

Redox proteins are involved in many cellular signalling pathways and aberrant expression can lead to disease or other pathological conditions. Therefore understanding how their expression is regulated is relevant for developing therapeutic agents that target these pathways.

AP1 transcription factors in epidermal differentiation and skin cancer

AP1 (jun/fos) transcription factors (c-jun, junB, junD, c-fos, FosB, Fra-1, and Fra-2) are key regulators of epidermal keratinocyte survival and differentiation and important drivers of cancer development. Understanding the role of these factors in epidermis is complicated by the fact that each protein is expressed, at different levels, in multiple cells layers in differentiating epidermis, and because AP1 transcription factors regulate competing processes (i.e., proliferation, apoptosis, and differentiation). Various in vivo genetic approaches have been used to study these proteins including targeted and conditional knockdown, overexpression, and expression of dominant-negative inactivating AP1 transcription factors in epidermis. Taken together, these studies suggest that individual AP1 transcription factors have different functions in the epidermis and in cancer development and that altering AP1 transcription factor function in the basal versus suprabasal layers differentially influences the epidermal differentiation response and disease and cancer development.

Loss of sulfiredoxin renders mice resistant to azoxymethane/dextran sulfate sodium-induced colon carcinogenesis

Sulfiredoxin (Srx) is the enzyme that reduces the hyperoxidized inactive form of peroxiredoxins. To study the function of Srx in carcinogenesis in vivo, we tested whether loss of Srx protects mice from cancer development. Srx null mice were generated and colon carcinogenesis was induced by an azoxymethane (AOM) and dextran sulfate sodium (DSS) protocol. Compared with either wild-type (Wt) or heterozygotes, Srx(-/-) mice had significantly reduced rates in both tumor multiplicity and volume. Mechanistic studies reveal that loss of Srx did not alter tumor cell proliferation; however, increased apoptosis and decreased inflammatory cell infiltration were obvious in tumors from Srx null mice compared with those from Wt control. In addition to the AOM/DSS model, examination of Srx expression in human reveals a tissue-specific expression pattern. Srx expression was also demonstrated in tumors from colorectal cancer patients and the levels of expression were associated with patients' clinic stages. These data provide the first in vivo evidence that loss of Srx renders mice resistant to AOM/DSS-induced colon carcinogenesis, suggesting that Srx has a critical oncogenic role in cancer development, and Srx may be used as a marker for human colon cancer pathogenicity.

Loss of SPARC in bladder cancer enhances carcinogenesis and progression

Secreted protein acidic and rich in cysteine (SPARC) has been implicated in multiple aspects of human cancer. However, its role in bladder carcinogenesis and metastasis are unclear,with some studies suggesting it may be a promoter and others arguing the opposite. Using a chemical carcinogenesis model in Sparc-deficient mice and their wild-type littermates, we found that loss of SPARC accelerated the development of urothelial preneoplasia (atypia and dysplasia), neoplasia, and metastasis and was associated with decreased survival. SPARC reduced carcinogen-induced inflammation and accumulation of reactive oxygen species as well as urothelial cell proliferation. Loss of SPARC was associated with an inflammatory phenotype of tumor-associated macrophages and fibroblasts, with concomitant increased activation of urothelial and stromal NF-κB and AP1 in vivo and in vitro. Syngeneic spontaneous and experimental metastasis models revealed that tumor- and stroma-derived SPARC reduced tumor growth and metastasis through inhibition of cancer-associated inflammation and lung colonization. In human bladder tumor tissues, the frequency and intensity of SPARC expression were inversely correlated with disease-specific survival. These results indicate that SPARC is produced by benign and malignant compartments of bladder carcinomas where it functions to suppress bladder carcinogenesis, progression, and metastasis.

Mitochondrial thiols in the regulation of cell death pathways

SIGNIFICANCE

Regulation of mitochondrial H(2)O(2) homeostasis and its involvement in the regulation of redox-sensitive signaling and transcriptional pathways is the consequence of the concerted activities of the mitochondrial energy- and redox systems.

RECENT ADVANCES

The energy component of this mitochondrial energy-redox axis entails the formation of reducing equivalents and their flow through the respiratory chain with the consequent electron leak to generate [Formula: see text] and H(2)O(2). The mitochondrial redox component entails the thiol-based antioxidant system, largely accounted for by glutathione- and thioredoxin-based systems that support the activities of glutathione peroxidases, peroxiredoxins, and methionine sulfoxide reductase. The ultimate reductant for these systems is NADPH: mitochondrial sources of NADPH are the nicotinamide nucleotide transhydrogenase, isocitrate dehydrogenase-2, and malic enzyme. NADPH also supports the glutaredoxin activity that regulates the extent of S-glutathionylation of mitochondrial proteins in response to altered redox status.

CRITICAL ISSUES

The integrated network of these mitochondrial thiols constitute a regulatory device involved in the maintenance of steady-state levels of H(2)O(2), mitochondrial and cellular redox and metabolic homeostasis, as well as the modulation of cytosolic redox-sensitive signaling; disturbances of this regulatory device affects transcription, growth, and ultimately influences cell survival/death.

FUTURE DIRECTIONS

The modulation of key mitochondrial thiol proteins, which participate in redox signaling, maintenance of the bioenergetic machinery, oxidative stress responses, and cell death programming, provides a pivotal direction in developing new therapies towards the prevention and treatment of several diseases.

Peroxiredoxins, gerontogenes linking aging to genome instability and cancer

Age is the highest risk factor known for a large number of maladies, including cancers. However, it is unclear how aging mechanistically predisposes the organism to such diseases and which gene products are the primary targets of the aging process. Recent studies suggest that peroxiredoxins, antioxidant enzymes preventing tumor development, are targets of age-related deterioration and that bolstering their activity (e.g., by caloric restriction) extends cellular life span. This review focuses on how the peroxiredoxin functions (i.e., as peroxidases, signal transducers, and molecular chaperones) fit with contemporary theories of aging and whether peroxiredoxins could be targeted therapeutically in the treatment of age-associated cancers.

Sulfiredoxin redox-sensitive interaction with S100A4 and non-muscle myosin IIA regulates cancer cell motility

Sulfiredoxin (Srx) is a redox active protein that participates in the reduction of oxidized cysteine residues. Here we identify a novel function of Srx through its specific binding to S-glutathionylated S100A4 affecting its interaction with non-muscle myosin (NMIIA), thereby modulating the effect of S100A4 on NMIIA function and impacting cell adhesion and migration. Srx forms a complex with S100A4 (and has stronger affinity for S-glutathionylated S100A4), regulates its activity, and mediates redox regulation of the interaction of S100A4 with NMIIA. The consequence of this regulation is microfilament remodeling and altered cellular motility and adhesion. Srx-overexpressing cells had reduced levels of adhesion, decreased levels of Tyr(397)-phosphorylated focal adhesion kinase, and increased cell motility in wound healing assays. These results describe a novel redox-sensitive role for Srx in mediating complex protein interactions with plausible consequences for cancer cell motility.

Targeting of Noncanonical Wnt5a Signaling by AP-1 Blocker Dominant-Negative Jun When It Inhibits Skin Carcinogenesis

The transcription factor AP-1 (activator protein-1) regulates a number of genes that drive tumor promotion and progression. While basal levels of AP-1 activity are important for normal cell proliferation and cell survival, overactivated AP-1-dependent gene expression stimulates inflammation, angiogenesis, invasion, and other events that propel carcinogenesis. We seek to discover genes targeted by carcinogenesis inhibitors that do not also inhibit cell proliferation or survival. Transgenic TAM67 (dominant-negative c-Jun) inhibits mouse skin tumorigenesis and tumor progression without inhibiting cell proliferation or induced hyperproliferation. Expression profiling of wild-type and K14-TAM67 mouse epidermis has revealed a number of functionally significant genes that are induced by tumor promoters in wild-type mice but not in those expressing the AP-1 blocker. The current study now identifies Wnt5a signaling as a new target of TAM67 when it inhibits DMBA/TPA-induced carcinogenesis. Wnt5a is required to maintain the tumor phenotype in tumorigenic mouse JB6 cells and Ras-transformed human squamous carcinoma HaCaT-II4 cells, as Wnt5a knockdown suppresses anchorage-independent and tumor xenograft growth. The oncogenic Wnt5a-mediated pathway signals through activation of the protein kinase PKCα and oncogenic transcription factor STAT3 phosphorylation and not through the canonical Wnt/β-catenin pathway. Similar to Wnt5a knockdown, inhibitors of PKCα blocked STAT3 activation in both mouse JB6 and human HaCaT-II4 tumor cells. Moreover, expression of STAT3-regulated genes FAS, MMP3, IRF1, and cyclin D1 was suppressed with Wnt5a knockdown. Treatment of mouse Wnt5a knockdown cells with a PKCα-specific activator rescued phosphorylation of STAT3. Thus, Wnt5a signaling is required for maintaining the tumor phenotype in squamous carcinoma cells, Wnt5a targeting by the AP-1 blockade contributes to inhibition of skin carcinogenesis, and the signaling pathway traverses PKCα and STAT3 activation. Coordinate overactivation of Wnt5a expression and STAT3 signaling is observed in human skin and colon cancers as well as glioblastoma.

Role of sulfiredoxin as a regulator of peroxiredoxin function and regulation of its expression

Peroxiredoxins (Prxs) constitute a family of peroxidases in which cysteine serves as the primary site of oxidation during the reduction of peroxides. Members of the 2-Cys Prx subfamily of Prxs (Prx I to IV in mammals) are inactivated via hyperoxidation of the active-site cysteine to sulfinic acid (Cys-SO(2)H) during catalysis and are reactivated via an ATP-consuming reaction catalyzed by sulfiredoxin (Srx). This reversible hyperoxidation reaction has been proposed to protect H(2)O(2) signaling molecules from premature removal by 2-Cys Prxs or to upregulate the chaperone function of these enzymes. In addition to its sulfinic acid reductase activity, Srx catalyzes the removal of glutathione (deglutathionylation) from modified proteins. The physiological relevance of both the reversible hyperoxidation of 2-Cys Prxs and the deglutathionylation catalyzed by Srx remains unclear. Recent findings have revealed that Srx expression is induced in mammalian cells under a variety of conditions, such as in metabolically stimulated pancreatic β cells, in immunostimulated macrophages, in neuronal cells engaged in synaptic communication, in lung cells exposed to hyperoxia or cigarette smoke, in hepatocytes of ethanol-fed animals, and in several types of cells exposed to chemopreventive agents. Such induction of Srx in mammalian cells is regulated at the transcriptional level, predominantly via activator protein-1 and/or nuclear factor erythroid 2-related factor 2. Srx expression is also regulated at the translational level in Saccharomyces cerevisiae.

c-Jun-dependent sulfiredoxin induction mediates BDNF protection against mitochondrial inhibition in rat cortical neurons

In current study, we tested the hypothesis that c-Jun-dependent sulfiredoxin expression mediates protective effects of brain-derived neurotrophic factor (BDNF) against neurotoxicity induced by 3-nitropropionic acid (3-NP), a mitochondrial complex II inhibitor, in primary rat cortical cultures. We found that BDNF-dependent c-Jun expression and nuclear translocation required prior phosphorylation of extracellular signal-regulated kinase (ERK)1/2, but not Akt. BDNF also transiently activated the expression of sulfiredoxin, an ATP-dependent antioxidant enzyme, at both mRNA and protein levels. Furthermore, both c-Jun siRNA and ERK1/2 inhibitor PD98059 suppressed BDNF-induced sulfiredoxin expression. Finally, PD98059, c-Jun siRNA, and sulfiredoxin siRNA all abrogated BDNF-mediated 3-NP resistance. Together, these results established a signaling cascade of "BDNF → ERK1/2-Pi → c-Jun → sulfiredoxin → 3-NP resistance". We therefore conclude that c-Jun-induced sulfiredoxin mediates the BDNF-dependent neuroprotective effects against 3-NP toxicity in primary rat cortical neurons, at least in part.

Sulfiredoxin protein is critical for redox balance and survival of cells exposed to low steady-state levels of H2O2

Sulfiredoxin (Srx) is an enzyme that catalyzes the reduction of cysteine sulfinic acid of hyperoxidized peroxiredoxins (Prxs). Having high affinity toward H2O2, 2-Cys Prxs can efficiently reduce H2O2 at low concentration. We previously showed that Prx I is hyperoxidized at a rate of 0.072% per turnover even in the presence of low steady-state levels of H2O2. Here we examine the novel role of Srx in cells exposed to low steady-state levels of H2O2, which can be achieved by using glucose oxidase. Exposure of low steady-state levels of H2O2 (10-20 μm) to A549 or wild-type mouse embryonic fibroblast (MEF) cells does not lead to any significant change in oxidative injury because of the maintenance of balance between H2O2 production and elimination. In contrast, loss-of-function studies using Srx-depleted A549 and Srx-/- MEF cells demonstrate a dramatic increase in extra- and intracellular H2O2, sulfinic 2-Cys Prxs, and apoptosis. Concomitant with hyperoxidation of mitochondrial Prx III, Srx-depleted cells show an activation of mitochondria-mediated apoptotic pathways including mitochondria membrane potential collapse, cytochrome c release, and caspase activation. Furthermore, adenoviral re-expression of Srx in Srx-depleted A549 or Srx-/- MEF cells promotes the reactivation of sulfinic 2-Cys Prxs and results in cellular resistance to apoptosis, with enhanced removal of H2O2. These results indicate that Srx functions as a novel component to maintain the balance between H2O2 production and elimination and then protects cells from apoptosis even in the presence of low steady-state levels of H2O2.

Systemic remodeling of the redox regulatory network due to RNAi perturbations of glutaredoxin 1, thioredoxin 1, and glucose-6-phosphate dehydrogenase

BACKGROUND

Cellular clearance of reactive oxygen species is dependent on a network of tightly coupled redox enzymes; this network rapidly adapts to oxidative conditions such as aging, viral entry, or inflammation. Current widespread use of shRNA as a means to perturb specific redox couples may be misinterpreted if the targeted effects are not monitored in the context of potential global remodeling of the redox enzyme network.

RESULTS

Stable cell lines containing shRNA targets for glutaredoxin 1, thioredoxin 1, or glucose-6-phosphate dehydrogenase were generated in order to examine the changes in expression associated with altering cytosolic redox couples. A qRT PCR array revealed systemic off-target effects of altered antioxidant capacity and reactive oxygen species formation. Empty lentiviral particles generated numerous enzyme expression changes in comparison to uninfected cells, indicating an alteration in antioxidant capacity irrespective of a shRNA target. Of the three redox couples perturbed, glutaredoxin 1, attenuation produced the most numerous off-target effects with 10/28 genes assayed showing statistically significant changes. A multivariate analysis extracted strong co-variance between glutaredoxin 1 and peroxiredoxin 2 which was subsequently experimentally verified. Computational modeling of the peroxide clearance dynamics associated with the remodeling of the redox network indicated that the compromised antioxidant capacity compared across the knockdown cell lines was unequally affected by the changes in expression of off-target proteins.

CONCLUSIONS

Our results suggest that targeted reduction of redox enzyme expression leads to widespread changes in off-target protein expression, changes that are well-insulated between sub-cellular compartments, but compensatory in both the production of and protection against intracellular reactive oxygen species. Our observations suggest that the use of lentivirus can in itself have off-target effects on dynamic responses to oxidative stress due to the changes in species concentrations.

Nuclear factor erythroid-derived 2-like 2 (Nrf2) and DJ1 are prognostic factors in lung cancer

Nuclear factor erythroid-derived 2-like 2 (Nrf2) controls the expression of several enzymes that are protective against oxidative stress. We investigated the expression of nuclear factor erythroid-derived 2-like 2, DJ1 (Nrf2 stabilizer), and sulfiredoxin in a large set of lung carcinomas. The cases were analyzed immunohistochemically with antibodies to nuclear factor erythroid-derived 2-like 2, DJ1, and sulfiredoxin with the results being compared with histologic and clinical data. Significant differences were observed in the expression of DJ1 and sulfiredoxin between various types of lung tumors, while expression of nuclear factor erythroid-derived 2-like 2 was more constant. Patients with tumors with cytoplasmic (P = .033) or nuclear (P = .003) DJ1 positivity exhibited worse survival. Separately in squamous cell carcinomas, there was a tendency toward worse survival with both cytoplasmic (P = .013) and nuclear (P = .071) DJ1 positivity. Patients with a strong nuclear factor erythroid-derived 2-like 2 expression in their tumors had worse survival (P = .006). In the Cox regression analysis, nuclear factor erythroid-derived 2-like 2 was an independent prognostic factor (P = .012) along with the T status (P = .008) and DJ1 cytoplasmic positivity (P = .028). Interestingly, smokers and ex-smokers had significantly more sulfiredoxin expression in their tumors (P < .001); and in patients receiving cytostatic drugs or radiation therapy, sulfiredoxin expression predicted a poor prognosis (P = .038). Nuclear factor erythroid-derived 2-like 2 and its stabilizing protein DJ1 affect the prognosis of patients with lung cancer by inducing an elevated stress response to oxidative damage. There were differences in the expression of sulfiredoxin and DJ1 between different lung tumor types, suggesting that the pathways involved in combating oxidative stress vary in different lung cancer types.

Reduction of cysteine sulfinic acid in eukaryotic, typical 2-Cys peroxiredoxins by sulfiredoxin

The eukaryotic, typical 2-Cys peroxiredoxins (Prxs) are inactivated by hyperoxidation of one of their active-site cysteine residues to cysteine sulfinic acid. This covalent modification is thought to enable hydrogen peroxide-mediated cell signaling and to act as a functional switch between a peroxidase and a high-molecular-weight chaperone. Moreover, hyperoxidation has been implicated in a variety of disease states associated with oxidative stress, including cancer and aging-associated pathologies. A repair enzyme, sulfiredoxin (Srx), reduces the sulfinic acid moiety by using an unusual ATP-dependent mechanism. In this process, the Prx molecule undergoes dramatic structural rearrangements to facilitate repair. Structural, kinetic, mutational, and mass spectrometry-based approaches have been used to dissect the molecular basis for Srx catalysis. The available data support the direct formation of Cys sulfinic acid phosphoryl ester and protein-based thiosulfinate intermediates. This review discusses the role of Srx in the reversal of Prx hyperoxidation, the questions raised concerning the reductant required for human Srx regeneration, and the deglutathionylating activity of Srx. The complex interplay between Prx hyperoxidation, other forms of Prx covalent modification, and the oligomeric state also are discussed.

Nitric oxide activates an Nrf2/sulfiredoxin antioxidant pathway in macrophages

Peroxiredoxins (Prx's) are a family of peroxidases that maintain thiol homeostasis by catalyzing the reduction of organic hydroperoxides, H₂O₂, and peroxynitrite. Under conditions of oxidative stress, eukaryotic Prx's can be inactivated by the substrate-dependent oxidation of the catalytic cysteine to sulfinic acid, which may regulate the intracellular messenger function of H₂O₂. A small redox protein, sulfiredoxin (Srx), conserved only in eukaryotes, has been shown to reduce sulfinylated 2-Cys Prx's, adding to the complexity of the H₂O₂ signaling network. In this study, we addressed the regulation of Srx expression in immunostimulated primary macrophages that produce both reactive oxygen species (ROS) and nitric oxide (NO(•)). We present genetic evidence that NO-mediated Srx up-regulation is mediated by the transcription factor nuclear factor erythroid 2-related factor (Nrf2). We also show that the NO(•)/Srx pathway inhibits generation of ROS. These results reveal a link between innate immunity and H₂O₂ signaling. We propose that an NO(•)/Nrf2/Srx pathway participates in the maintenance of redox homeostasis in cytokine-activated macrophages and other inflammatory settings.

Identification and characterization of human leukocyte antigen class I ligands in renal cell carcinoma cells

The presentation of tumor antigen-derived peptides by human leukocyte antigen (HLA) class I surface antigens on tumor cells is a key prerequisite to trigger effective T-cell responses in cancer patients. Multiple complementary strategies like cDNA and serological expression cloning, reverse immunology and different 'ome'-based methods have been employed to identify potential T-cell targets. This report focuses on a ligandomic profiling approach leading to the identification of 49 naturally processed HLA class I peptide ligands presented on the cell surface of renal cell carcinoma (RCC) cells. The source proteins of the defined HLA ligands are classified according to their biological function and subcellular localization. Previously established cDNA microarray data of paired tissue specimen of RCC and renal epithelium assessed the transcriptional regulation for 28 source proteins. In addition, HLA-A2-restricted, peptide-specific T cells directed against a HLA ligand derived from sulfiredoxin-1 (SRXN1) were generated, which were able to recognize and lyse ligand-presenting target cells in a HLA class I-restricted manner. Furthermore, tumor-infiltrating T cells isolated from a RCC patient were also able to kill SRXN1 expressing tumor cells. Thus, this experimental strategy might be suited to define potential candidate biomarkers and novel targets for T-cell-based immunotherapies of this disease.

Sulfiredoxin-Peroxiredoxin IV axis promotes human lung cancer progression through modulation of specific phosphokinase signaling

Oxidative stress is known to cause tumorigenesis through induction of DNA and lipid damage. It also promotes cancer progression through a largely unknown mechanism. Sulfiredoxin (Srx) is a novel oxidative stress-induced antioxidant protein whose function in tumorigenesis and cancer progression has not been well studied. We report that Srx is highly expressed in human lung cancer. Knockdown of Srx reduces anchorage-independent colony formation, cell migration, and invasion of human lung cancer cells. Srx preferentially interacts with Peroxiredoxin (Prx) IV relative to other Prxs due to its intrinsic higher binding affinity. Knockdown of Prx IV recapitulates the phenotypic changes of depleting Srx. Disruption or enhancement of the Srx-Prx IV axis leads respectively to reduction or acceleration of tumor growth and metastasis formation in vivo. Through identification and validation of the downstream mediators we unraveled the Srx-mediated signaling network that traverses AP-1-activating and other phosphokinase signaling cascades. Our work reveals that the Srx-Prx IV axis is critical for lung cancer maintenance and metastasis, suggesting that targeting the Srx-Prx IV axis may provide unique effective strategies for cancer prevention and treatment.

Downregulation of AP-1 gene expression is an initial event in the oridonin-mediated inhibition of colorectal cancer: studies in vitro and in vivo

BACKGROUND AND AIM

Oridonin is the active ingredient isolated from the Chinese herb Rabdosia rubescens. We used both in vivo and in vitro approaches to elucidate the underlying mechanism of the oridonin-mediated inhibition of colorectal cancer.

METHODS

Two colorectal cell lines, Lovo and SW480, were treated with oridonin in solution. The effect of this treatment on the inhibition of the cell proliferation rate was determined by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide method. The changes in gene expression that occurred in both cell lines in response to treatment with oridonin were determined via an illumine expression sensor. Additionally, a colorectal cancer colostomy implantation model was established. Animals were injected intraperitoneally with an oridonin solution.

RESULTS

The treatment of Lovo and SW480 cells with oridonin inhibited cell proliferation in a dose-dependent manner. Furthermore, the rate of inhibition increased with prolonged treatment. The growth rate of the colorectal cancer colostomy implantation model was significantly lower than control cells when treated with oridonin (P<0.001), which meant that oridonin treatment had a significant effect on the tumor growth rate. In the tumor model, activator protein-1 (AP-1) was the only gene found to be downregulated after oridonin treatment by the gene expression sensor. After 4 weeks of treatment, AP-1, nuclear factor-κB (NF-κB) and P38 were all found to be downregulated.

CONCLUSIONS

Our study confirmed the inhibitory effects of oridonin on colorectal cancer. These results indicate that the downregulation of AP-1 might be an initial response to treatment by oridonin. This regulation could, in turn, affect the expression of the NF-κB and mitogen-activated protein kinase pathways, thereby inhibiting tumor growth.

Concerted action of sulfiredoxin and peroxiredoxin I protects against alcohol-induced oxidative injury in mouse liver

Peroxiredoxins (Prxs) are peroxidases that catalyze the reduction of reactive oxygen species (ROS). The active site cysteine residue of members of the 2-Cys Prx subgroup (Prx I to IV) of Prxs is hyperoxidized to cysteine sulfinic acid (Cys-SO(2) ) during catalysis with concomitant loss of peroxidase activity. Reactivation of the hyperoxidized Prx is catalyzed by sulfiredoxin (Srx). Ethanol consumption induces the accumulation of cytochrome P450 2E1 (CYP2E1), a major contributor to ethanol-induced ROS production in the liver. We now show that chronic ethanol feeding markedly increased the expression of Srx in the liver of mice in a largely Nrf2-dependent manner. Among Prx I to IV, only Prx I was found to be hyperoxidized in the liver of ethanol-fed wildtype mice, and the level of Prx I-SO(2) increased to ≈30% to 50% of total Prx I in the liver of ethanol-fed Srx(-/-) mice. This result suggests that Prx I is the most active 2-Cys Prx in elimination of ROS from the liver of ethanol-fed mice and that, despite the up-regulation of Srx expression by ethanol, the capacity of Srx is not sufficient to counteract the hyperoxidation of Prx I that occurs during ROS reduction. A protease protection assay revealed that a large fraction of Prx I is located together with CYP2E1 at the cytosolic side of the endoplasmic reticulum membrane. The selective role of Prx I in ROS removal is thus likely attributable to the proximity of Prx I and CYP2E1.

CONCLUSION

The pivotal functions of Srx and Prx I in protection of the liver in ethanol-fed mice was evident from the severe oxidative damage observed in mice lacking either Srx or Prx I.