Inactivation of glutathione peroxidase activity contributes to UV-induced squamous cell carcinoma formation

GPX2 promotes EMT and metastasis in non-small cell lung cancer by activating PI3K/AKT/mTOR/Snail signaling axis

Lung cancer, with non-small cell lung cancer (NSCLC) being the main subtype, is the leading cause of cancer death worldwide, which is mainly due to the cancer metastasis. Glutathione peroxidase 2 (GPX2), an antioxidant enzyme, is involved in tumor progression and metastasis. Nevertheless, the role of GPX2 in NSCLC metastasis has not been clarified. In this study, we found that GPX2 expression was elevated in NSCLC tissues and high GPX2 expression was correlated with poor prognosis in patients with NSCLC. In addtion, GPX2 expression was related to the patient's clinicopathological features, including lymph node metastasis, tumor size, and TNM stage. Overexpression of GPX2 promoted epithelial-mesenchymal transition (EMT), migration, and invasion of NSCLC cells in vitro. Knockdown of GPX2 showed the opposite effects in vitro and inhibited the metastasis of NSCLC cells in nude mice. Furthermore, GPX2 reduced reactive oxygen species (ROS) accumulation and activated the PI3K/AKT/mTOR/Snail signaling axis. Therefore, our results indicate that GPX2 promotes EMT and metastasis of NSCLC cells by activating the PI3K/AKT/mTOR/Snail signaling axis via the removal of ROS. GPX2 may be an effective diagnostic and prognostic biomarker for NSCLC.

Galactomyces Ferment Filtrate Potentiates an Anti-Inflammaging System in Keratinocytes

Skincare products play a crucial role in preventing the dry skin induced by various causes. Certain ingredients can help to improve the efficacy of skincare products. Galactomyces ferment filtrate (GFF) is such a functional ingredient. Its use originated from the empirical observation that the hands of sake brewers who deal with yeast fermentation retain a beautiful and youthful appearance. Consequently, skincare products based on GFF are widely used throughout the world. Recent studies have demonstrated that GFF activates an aryl hydrocarbon receptor (AHR) and upregulates the expression of filaggrin, a pivotal endogenous source of natural moisturizing factors, in epidermal keratinocytes. It also activates nuclear factor erythroid-2-related factor 2 (NRF2), the antioxidative master transcription factor, and exhibits potent antioxidative activity against oxidative stress induced by ultraviolet irradiation and proinflammatory cytokines, which also accelerate inflammaging. GFF-mediated NRF2 activation downregulates the expression of CDKN2A, which is known to be overexpressed in senescent keratinocytes. Moreover, GFF enhances epidermal terminal differentiation by upregulating the expression of caspase-14, claudin-1, and claudin-4. It also promotes the synthesis of the antiinflammatory cytokine IL-37 and downregulates the expression of proallergic cytokine IL-33 in keratinocytes. In addition, GFF downregulates the expression of the CXCL14 and IL6R genes, which are involved in inflammaging. These beneficial properties might underpin the potent barrier-protecting and anti-inflammaging effects of GFF-containing skin formulae.

The beginning of GPX2 and 30 years later

We published the first paper to characterize GPX2 (aka GSHPx-GI) as a selenoenzyme with glutathione peroxidase activity in 1993. Among the four Se-GPX isozymes, GPX1-4, GPX1 and GPX2 are closely related in terms of structure, substrate specificities, and subcellular localization. What sets them apart are distinct patterns of gene regulation, tissue distribution and response to selenium. While we identified the digestive tract epithelium as the main site of GPX2 expression, later work has shown GPX2 is found more widely in epithelial tissues with concentration of expression in stem cell and proliferative compartments. GPX2 expression is regulated over a wide range of levels by many pathways, including NRF2, WNT, p53, RARE and this often results in attaching undue significance to GPX2 as GPX2 is only a part of a system of hydroperoxidase activities, including GPX1, peroxiredoxins and catalase. These other activities may play equal or greater roles, particularly in cell lines cultured without selenium supplementation and often with very low GPX2 levels. This could be assessed by examining levels of mRNA and protein among these various peroxidases at the outset of studies. As an example, it was found that GPX1 responds to the absence of GPX2 in mouse ileum and colon epithelium with higher expression. As such, both Gpx1 and Gpx2 had to be knocked out in mice to produce ileocolitis. However, we note that the actual role of GPX1 and GPX2 in relation to peroxiredoxin function is unclear. There may be an interdependence that requires only low amounts of GPX1 and/or GPX2 in a supporting role to maintain proper peroxiredoxin function. GPX2 levels may be prognostic for cancer progression in colon, breast, prostate and liver, however, there is no consistent trend for higher or lower levels to be favorable.

Loss of Interleukin-6 Influences Transcriptional Immune Signatures and Alters Bacterial Colonization in the Skin

The skin functions as a protective barrier to inhibit the entry of foreign pathogens, all the while hosting a diverse milieu of microorganisms. Over time, skin cells, immune cells, cytokines, and microbes interact to integrate the processes of maintaining the skin's physical and immune barrier. In the present study, the basal expression of two immunologically divergent mouse strains C57BL/6 and BALB/c, as well as a strain on the C57 background lacking IL-6, was characterized. Additionally, cutaneous antimicrobial gene expression profiles and skin bacterial microbiome were assessed between strains. Total RNA sequencing was performed on untreated C57BL/6 (control), BALB/c, and IL-6-deficient skin samples and found over 3,400 genes differentially modulated between strains. It was found that each strain modulated its own transcriptional "profile" associated with skin homeostasis and also influenced the overall bacterial colonization as indicated by the differential phyla present on each strain. Together, these data not only provide a comprehensive view of the transcriptional changes in homeostatic skin of different mouse strains but also highlight the possible influence of the strain differences (e.g., Th1/Th2 balance) as well as a role for IL-6 in overall skin immunity and resident microbial populations.

Tumor Tissue Oxidative Stress Changes and Na, K-ATPase Evaluation in Head and Neck Squamous Cell Carcinoma

Changes in metabolism are mechanisms that are largely implicated in the development, progression, and metastasis of head and neck squamous cell carcinoma (HNSCC) and also in resistance to different anticancer therapies. Identification of biomarkers for differentiation between cancerous and normal epithelium, treatment design and prognosis remain a vital issue in the field of head and neck cancer. The present study analyzed the main biochemical changes that occur in HNSCC tumors by through mechanisms involving oxidative stress. The release of substances reactive to thiobarbituric acid was significantly lower in HNSCC tumor tissue as compared to healthy tissue. The assays related to the lipid profile assays showed changes in membrane biophysics of tumor cells due to an increase in total phospholipids and total cholesterol, as well as an increased activity and expression of the α1 subunit of Na, K-ATPase, which is fundamental in the process of carcinogenesis. The modulation of the antioxidant system was also affected, with a decrease in the catalytic activity of the enzymes superoxide dismutase (SOD) and glutathione peroxidase (GPx), as well as a reduction of glutathione (GSH) content and an increase in H₂O₂ content. A reduction in catalase (CAT) activity was observed. The data presented here are in accordance with important findings described by us in a previous study, involving the same individuals, but with a focus on the damage generated in red blood cells, resulting from tumor installation. Therefore, it was possible to conclude that the biochemical alterations found in HNSCC cells are fundamental for transformation and maintenance of the tumor cell and once it is installed, it is also capable of generating injuries in the patients' red blood cells. Our data demonstrate that this could be a promising biomarker for HNSCC.

Aging lens epithelium is susceptible to ferroptosis

Age-related cataracts (ARC) are the primary cause of blindness worldwide, and oxidative stress is considered the central pathogenesis of age-related cataractogenesis. Interestingly, ample evidence suggests that there is no remarkable apoptosis present in aged and cataractous human lenses despite the profound disruption of redox homeostasis, raising an essential question regarding the existence of other cell death mechanisms. Here we sought to explore the lens epithelial cell's (LEC) susceptibility to ferroptosis after documentation has concluded that aged and cataractous human lenses manifest with increased reactive oxygen species (ROS) formation, elevated lipid peroxidation, and accumulative intracellular redox-active iron, constituting the three hallmarks of ferroptosis during aging and cataractogenesis. Here we show that very low concentrations of system Xc- inhibitor Erastin (0.5 μM) and glutathione peroxidase 4 (GPX4) inhibitor RSL3 (0.1 μM) can drastically induce human LEC (FHL124) ferroptosis in vitro and mouse lens epithelium ferroptosis ex vivo. Depletion of intracellular glutathione (GSH) in human LECs and mouse lens epithelium significantly sensitizes ferroptosis, particularly under RSL3 challenge. Intriguingly, both human LECs and the mouse lens epithelium demonstrate an age-related sensitization of ferroptosis. Transcriptome analysis indicates that clusters of genes are up-or down-regulated in aged LECs, impacting cellular redox and iron homeostases, such as downregulation of both cystine/glutamate antiporter subunits SLC7A11 and SLC3A2 and iron exporter ferroportin (SLC40A1). Here, for the first time, we are suggesting that LECs are highly susceptible to ferroptosis. Moreover, aged and cataractous human lenses may possess more pro-ferroptotic criteria than any other organ in the human body.

Association of blood mercury levels with nonmelanoma skin cancer in the U.S.A. using National Health and Nutrition Examination Survey data (2003-2016)

BACKGROUND

Some studies have reported increased incidence or mortality of lung and brain cancers associated with occupations involving potential mercury exposure. Epidemiological evidence related to skin cancer is also limited.

OBJECTIVES

To investigate the association between blood mercury (Hg) levels and nonmelanoma skin cancer (NMSC).

METHODS

We used National Health and Nutrition Examination Survey data from 2003 to 2016. The exposures were blood total (tHg), inorganic (iHg) and methylmercury (MeHg). The outcome was a self-reported diagnosis of NMSC. We included participants aged ≥ 20 years who had information on blood mercury and sociodemographic factors. We conducted a logistic regression analysis to estimate odds ratios (ORs) and 95% confidence intervals (CIs) for the risk of NMSC associated with quartiles of blood Hg, after adjusting for the sociodemographic factors and survey year.

RESULTS

The number of participants was 29 413; mean age was 49 years and 52% were female. Compared with those with a tHg ≤ 0·47 μg L^-1 (Q1), those with a tHg > 1·74 μg L^-1 (Q4) had nearly double the odds of NMSC (OR 1·79, 95% CI 1·19-2·71; P_trend = 0·004). Similarly, those in the highest quartile of MeHg (> 1·44 μg L^-1 ) had 1·7 times greater odds of NMSC (OR 1·74, 95% CI 1·13-2·70; P_trend = 0·01) than those in the lowest quartile (≤ 0·21 μg L^-1 ). iHg levels were nonsignificantly positively associated with NMSC (P_trend = 0·08).

CONCLUSIONS

We found that higher blood tHg and MeHg levels were associated with a higher prevalence of NMSC. Linked Comment: Taylor. Br J Dermatol 2020; 183:413-414.

Thymosin alpha-1; a natural peptide inhibits cellular proliferation, cell migration, the level of reactive oxygen species and promotes the activity of antioxidant enzymes in human lung epithelial adenocarcinoma cell line (A549)

This research was conducted to investigate the biochemical effects of thymosin alpha-1 using human lung cancer cells (A549). The A549 cells were treated with different concentrations of Thα1 for 24 h and the growth, inhibition of cells was determined. Thα1 revealed anti-proliferative effect at 24 and 48 μg/ml after 24 h. Furthermore, it indicated antioxidant properties by significantly enhancing the activity of catalase (12 μg/ml), superoxide dismutase (6 and 12 μg/ml), and glutathione peroxidase (3, 6 and 12 μg/ml) and reducing the production of cellular ROS. Our results showed that Thα1 inhibits the migration of A549 cells in a concentration-dependent manner after 24 and 48 h. Moreover, the effect of Thα1 on apoptosis was investigated by Hoechst 33342 staining and cell cycle analysis. Results demonstrated no significant effect on the induction of apoptosis in A549 cells. In conclusion, our results showed the antioxidant properties of Thα1 on A549 cancer cells.

Regulation and function of avian selenogenome

BACKGROUND

Selenium (Se) is an essential micronutrient required by avian species. Dietary Se/vitamin E deficiency induces three classical diseases in chicks: exudative diathesis, nutritional pancreatic atrophy, and nutritional muscular dystrophy.

SCOPE OF REVIEW

This review is to summarize and analyze the evolution, regulation, and function of avian selenogenome and selenoproteome and their relationship with the three classical Se/vitamin E deficiency diseases.

MAJOR CONCLUSIONS

There are 24 selenoproteins confirmed in chicks, with two avian-specific members (SELENOU and SELENOP2) and two missing mammalian members (GPX6 and SELENOV). There are two forms of SELENOP containing 1 or 13 selenocysteine residues. In addition, a Gallus gallus gene was conjectured to be the counterpart of the human SEPHS2. Expression of selenoprotein genes in the liver, pancreas, and muscle of chicks seemed to be highly responsive to dietary Se changes. Pathogeneses of the Se/vitamin E deficient diseases in the chicks were likely produced by missing functions of selected selenoproteins in regulating cellular and tissue redox balance and inhibiting oxidative/reductive stress-induced cell death.

GENERAL SIGNIFICANCE

Gene knockout models, similar to those of rodents, will help characterize the precise functions of avian selenoproteins and their comparisons with those of mammalian species.

Involvement of NADPH oxidase 1 in UVB-induced cell signaling and cytotoxicity in human keratinocytes

Members of NADPH oxidase (Nox) enzyme family are important sources of reactive oxygen species (ROS) and are known to be involved in several physiological functions in response to various stimuli including UV irradiation. UVB-induced ROS have been associated with inflammation, cytotoxicity, cell death, or DNA damage in human keratinocytes. However, the source and the role of UVB-induced ROS remain undefined.

Here, we show that Nox1 is involved in UVB-induced p38/MAPK activation and cytotoxicity via ROS generation in keratinocytes. Nox1 knockdown or inhibitor decreased UVB-induced ROS production in human keratinocytes. Nox1 knockdown impaired UVB-induced p38 activation, accompanied by reduced IL-6 levels and attenuated cell toxicity. Treatment of cells with N-acetyl-L-cysteine (NAC), a potent ROS scavenger, suppressed p38 activation as well as consequent IL-6 production and cytotoxicity in response to UVB exposure. p38 inhibitor also suppressed UVB-induced IL-6 production and cytotoxicity. Furthermore, the blockade of IL-6 production by IL-6 neutralizing antibody reduced UVB-induced cell toxicity.

In vivo assay using wild-type mice, the intradermal injection of lysates from UVB-irradiated control cells, but not from UVB-irradiated Nox1 knockdown cells, induced inflammatory swelling and IL-6 production in the skin of ears. Moreover, administration of Nox1 inhibitor suppressed UVB-induced increase in IL-6 mRNA expression in mice skin.

Collectively, these data suggest that Nox1-mediated ROS production is required for UVB-induced cytotoxicity and inflammation through p38 activation and inflammatory cytokine production, such as IL-6. Thus, our findings suggest Nox1 as a therapeutic target for cytotoxicity and inflammation in response to UVB exposure.

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Nox1 knockdown decreased UVB-increased cellular ROS in keratinocytes.

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Nox1 knockdown suppressed UVB-induced p38 activation, accompanied by reduced in IL-6 levels and attenuated cell toxicity.

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UVB-induced cytotoxicity is involved in p38/MAPK pathway and IL-6 production, which is partially dependent on Nox1-generated ROS.

Selenium-Dependent Glutathione Peroxidases During Tumor Development

Five out of eight human glutathione peroxidases (GPxes) are selenoproteins and thus their expression depends on the selenium (Se) supply. Most Se-dependent GPxes are downregulated in tumor cells, while only GPx2 is considerably upregulated. Whether expression profiles of GPxes predict tumor development and patient survival is controversially discussed. Also, results from in vitro and in vivo studies modulating the expression of GPx isoforms provide evidence for both anti- and procarcinogenic mechanisms. GPxes are able to reduce hydroperoxides, which otherwise would damage DNA, possibly resulting in DNA mutations, modulate redox-sensitive signaling pathways affecting proliferation, differentiation, and cellular metabolism or initiate cell death. Considering these different processes, the role and functions of individual Se-dependent GPx isoforms will be discussed herein in the context of tumorigenesis.

Contribution of mammalian selenocysteine-containing proteins to carcinogenesis

Oxidative stress caused by a sharp growth of free radicals in the organism is a major cause underlying the occurrence of all kinds of malignant formations. Selenium is an important essential trace element found in selenoproteins in the form of selenocysteine, an amino acid differing from cysteine for the presence of selenium instead of sulfur and making such proteins highly active. To date the role of selenium has been extensively investigated through studying the functions of selenoproteins in carcinogenesis. Analysis of the obtained results clearly demonstrates that selenoproteins can act as oncosuppressors, but can also, on the contrary, favor the formation of malignant tumors.

Paradoxical Roles of Antioxidant Enzymes: Basic Mechanisms and Health Implications

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are generated from aerobic metabolism, as a result of accidental electron leakage as well as regulated enzymatic processes. Because ROS/RNS can induce oxidative injury and act in redox signaling, enzymes metabolizing them will inherently promote either health or disease, depending on the physiological context. It is thus misleading to consider conventionally called antioxidant enzymes to be largely, if not exclusively, health protective. Because such a notion is nonetheless common, we herein attempt to rationalize why this simplistic view should be avoided. First we give an updated summary of physiological phenotypes triggered in mouse models of overexpression or knockout of major antioxidant enzymes. Subsequently, we focus on a series of striking cases that demonstrate "paradoxical" outcomes, i.e., increased fitness upon deletion of antioxidant enzymes or disease triggered by their overexpression. We elaborate mechanisms by which these phenotypes are mediated via chemical, biological, and metabolic interactions of the antioxidant enzymes with their substrates, downstream events, and cellular context. Furthermore, we propose that novel treatments of antioxidant enzyme-related human diseases may be enabled by deliberate targeting of dual roles of the pertaining enzymes. We also discuss the potential of "antioxidant" nutrients and phytochemicals, via regulating the expression or function of antioxidant enzymes, in preventing, treating, or aggravating chronic diseases. We conclude that "paradoxical" roles of antioxidant enzymes in physiology, health, and disease derive from sophisticated molecular mechanisms of redox biology and metabolic homeostasis. Simply viewing antioxidant enzymes as always being beneficial is not only conceptually misleading but also clinically hazardous if such notions underpin medical treatment protocols based on modulation of redox pathways.

GPX2 underexpression indicates poor prognosis in patients with urothelial carcinomas of the upper urinary tract and urinary bladder

PURPOSE

Oxidative stress is believed to be one of the important etiologies in carcinogenesis that has not been systemically investigated in urothelial carcinoma (UC). Through data mining from a published transcriptomic database of UC of urinary bladders (UBUCs) (GSE31684), glutathione peroxidase 2 (GPX2) was identified as the most significant downregulated gene among those response to oxidative stress (GO:0006979). We therefore analyze GPX2 transcript and protein expressions and its clinicopathological significance.

METHODS

Real-time RT-PCR assay was used to detect GPX2 mRNA level in 20 fresh UBUC specimens. Immunohistochemistry was used to determine GPX2 protein expression in 340 urothelial carcinomas of upper tracts (UTUCs) and 295 UBUCs with mean/median follow-up of 44.7/38.9 and 30.8/23.1 months, respectively. Its expression status was further correlated with clinicopathological features and evaluated for its impact on disease-specific survival and metastasis-free survival (MeFS).

RESULTS

Decrease in GPX2 transcript level was associated with both higher pT and positive nodal status in 20 UBUCs (all p < 0.05). GPX2 protein underexpression was also significantly associated with advanced pT status, nodal metastasis, high histological grade, vascular invasion, and frequent mitoses in both groups of UCs (all p < 0.05). GPX2 underexpression not only predicted dismal DDS and MeFS at univariate analysis, but also implicated worse DDS (UTUC, p = 0.002; UBUC, p = 0.029) and MeFS (UTUC, p = 0.001; UBUC, p = 0.032) in multivariate analysis.

CONCLUSIONS

GPX2 underexpression is associated with advanced tumor status and implicated unfavorable clinical outcome of UCs, suggesting its role in tumor progression and may serve as a theranostic biomarker of UCs.

Selenoproteins: molecular pathways and physiological roles

Selenium is an essential micronutrient with important functions in human health and relevance to several pathophysiological conditions. The biological effects of selenium are largely mediated by selenium-containing proteins (selenoproteins) that are present in all three domains of life. Although selenoproteins represent diverse molecular pathways and biological functions, all these proteins contain at least one selenocysteine (Sec), a selenium-containing amino acid, and most serve oxidoreductase functions. Sec is cotranslationally inserted into nascent polypeptide chains in response to the UGA codon, whose normal function is to terminate translation. To decode UGA as Sec, organisms evolved the Sec insertion machinery that allows incorporation of this amino acid at specific UGA codons in a process requiring a cis-acting Sec insertion sequence (SECIS) element. Although the basic mechanisms of Sec synthesis and insertion into proteins in both prokaryotes and eukaryotes have been studied in great detail, the identity and functions of many selenoproteins remain largely unknown. In the last decade, there has been significant progress in characterizing selenoproteins and selenoproteomes and understanding their physiological functions. We discuss current knowledge about how these unique proteins perform their functions at the molecular level and highlight new insights into the roles that selenoproteins play in human health.

Combinative effects of thanh hao miet giap thang (sweet wormwood and tortoise shell decoction) ingredients on antioxidative activity in vitro

BACKGROUND

Traditional formulae usually exhibit therapeutic effects through the combinations of different ingredients. The purpose of this study was to investigate in vitro anti-oxidative activity of Thanh Hao Miet Giap Thang (THMGT) (Sweet Wormwood and Tortoise Shell Decoction) formula and the interactions of its ingredients leading to the overall anti-oxidative effect.

MATERIALS AND METHODS

We prepared 31 combinations containing two to four of the five ingredients including Herba Artemisia apiacea L (HbA), Carapax Trionycis (Tryonix sinensis) (CT), Rhizoma Anemarrhenae (Anemarrhena asphodeloides) (RzA), Radix Rehmanniae (Rehmannia glutinosa Libosch) (RdR), Moutan Cortex (Paeonia suffruticosa) (MC). These combinations were tested for anti-oxidative activity using DCFH-DA and DPPH assays on Hep G2 cells. We also analyzed changes in expression of genes involved in antioxidant defense system including Nuclear Factor Erythroid-Derived 2-Like 2 (NFE2L2), catalase (CAT), heme oxygenase-1 (HO-1), glutathione peroxidase (GPx), cytoplasmic superoxide dismutase (SOD1), mitochondrial superoxide dismutase (SOD2).

RESULTS

The complete formula and all combinations containing Moutan Cortex showed high antioxidant activity in both radical solution-based chemical assay and cellular-based assay. On the contrary, Carapax Trionycis displayed inhibitory effect on the overall antioxidant activity when present in a combination, an effect clearly emphasized in cellular-based assay. Hep G2 cells treated with the formula showed increased gene expression of HO-1 and SOD2 while expression of CAT, SOD1, GPx was unchanged.

CONCLUSION

Our results suggested that THMGT had anti-oxidative activity essentially through intrinsic reducing capacities and the overall activity of the formula resulted from enhancing and inhibiting interactions of ingredients.

Nutritional countermeasures targeting reactive oxygen species in cancer: from mechanisms to biomarkers and clinical evidence

Reactive oxygen species (ROS) exert various biological effects and contribute to signaling events during physiological and pathological processes. Enhanced levels of ROS are highly associated with different tumors, a Western lifestyle, and a nutritional regime. The supplementation of food with traditional antioxidants was shown to be protective against cancer in a number of studies both in vitro and in vivo. However, recent large-scale human trials in well-nourished populations did not confirm the beneficial role of antioxidants in cancer, whereas there is a well-established connection between longevity of several human populations and increased amount of antioxidants in their diets. Although our knowledge about ROS generators, ROS scavengers, and ROS signaling has improved, the knowledge about the direct link between nutrition, ROS levels, and cancer is limited. These limitations are partly due to lack of standardized reliable ROS measurement methods, easily usable biomarkers, knowledge of ROS action in cellular compartments, and individual genetic predispositions. The current review summarizes ROS formation due to nutrition with respect to macronutrients and antioxidant micronutrients in the context of cancer and discusses signaling mechanisms, used biomarkers, and its limitations along with large-scale human trials.

The effect of deposition Se on the mRNA expression levels of GPxs in goats from a Se-enriched county of China

Previous studies revealed that Se was an important regulatory factor for glutathione peroxidase (GPx) genes. However, the relationship between Se concentrations and mRNA expression levels of GPxs were unclear in goats, especially the goats living in natural Se-enriched area. Thus, the aim of this study was to determine the Se concentrations and the mRNA expression levels of GPx-1, GPx-2, GPx-3, and GPx-4 in goats from Ziyang County (ZY-H and ZY-L goats) and Baoji City (BJ-P goats), which were Se-rich region and Se-poor region in China, respectively. Atomic fluorescence spectrometry was used as an essential method to determine the Se concentrations in heart, liver, spleen, lung, kidney, longissimus, biceps femoris, and serum, and the gene expressions were quantified in mRNA samples extracted from the above tissues by real-time quantitative reverse transcription-polymerase chain reaction. We found that the Se concentrations in ZY-H and ZY-L goats were higher than that in BJ-P goats significantly (P < 0.05), and the pertinence relations of Se levels between serum and heart, liver, spleen, and kidney were significant (P < 0.05). The mRNA levels of GPx-1 in ZY-H and ZY-L goats were higher than that in BJ-P goats very significantly (P < 0.01) except for longissimus (P < 0.05). Our results indicated a significant trend for GPx-2 in the direction of increasing mRNA levels with increasing Se concentrations in goats but had no statistical significance (P > 0.05) in our experimental conditions. As to GPx-3, its mRNA expression in spleen, lung, and kidney (P < 0.05) were upregulated and were consensual to high Se contents in ZY-H goats, but no significant effects were observed in heart, liver, longissimus, and biceps femoris among our three groups (P > 0.05). The mRNA levels of GPx-4 in heart, liver, lung, and kidney of ZY-H and ZY-L goats were higher than that of BJ-P goats (P < 0.05), and the difference was very significant in lung especially (P < 0.01), but no change in spleen, longissimus, and biceps femoris (P > 0.05). In summary, these data suggested that the goats living in Ziyang County were rich in Se, and the deposition Se played important roles in the mRNA expression of GPx-1, GPx-3, and GPx-4 in certain tissues of goats differentially.

A light-activated NO donor attenuates anchorage independent growth of cancer cells: Important role of a cross talk between NO and other reactive oxygen species

It is established that high concentrations of nitric oxide(1) (NO), as released from activated macrophages, induce apoptosis in breast cancer cells. In this study, we assessed the potential of a light-activated NO donor [(Me2bpb)Ru(NO)(Resf)], a recently reported apoptototic agent, in suppressing the anchorage independent growth potentials of an aggressive human breast cancer cell line. Our results demonstrated the down regulation of anchorage independent growth by light activated NO treatment in the aggressive human breast cancer cell line MDA-MB-231 and afforded insight into the associated mechanism(s). The investigation revealed an up-regulation of the bioactivity of catalase with an accompanied reduction in the endogenous levels of H2O2, a direct substrate of catalase and a recently identified endogenous growth modulator in breast cancer cells. An earlier publication reported that endogenous superoxide (O2(-)) in human breast cancer cells constitutively inhibits catalase bioactivity (at the level of its protein), resulting in increased H2O2 levels. Interestingly in this study, O2(-) was also found to be down- regulated following NO treatment providing a basis for the observed increase in catalase bioactivity. Cells silenced for the catalase gene exhibited compromised reduction in anchorage independent growth upon light activated NO treatment. Collectively this study detailed a mechanistic cross talk between exogenous NO and endogenous ROS in attenuating anchorage independent growth.

Selenium for the prevention of cutaneous melanoma

The role of selenium (Se) supplementation in cancer prevention is controversial; effects often depend on the nutritional status of the subject and on the chemical form in which Se is provided. We used a combination of in vitro and in vivo models to study two unique therapeutic windows for intervention in the process of cutaneous melanomagenisis, and to examine the utility of two different chemical forms of Se for prevention and treatment of melanoma. We studied the effects of Se in vitro on UV-induced oxidative stress in melanocytes, and on apoptosis and cell cycle progression in melanoma cells. In vivo, we used the HGF transgenic mouse model of UV-induced melanoma to demonstrate that topical treatment with l-selenomethionine results in a significant delay in the time required for UV-induced melanoma development, but also increases the rate of growth of those tumors once they appear. In a second mouse model, we found that oral administration of high dose methylseleninic acid significantly decreases the size of human melanoma xenografts. Our findings suggest that modestly elevation of selenium levels in the skin might risk acceleration of growth of incipient tumors. Additionally, certain Se compounds administered at very high doses could have utility for the treatment of fully-malignant tumors or prevention of recurrence.

Selenoproteins and Cancer Prevention

The discovery of multiple selenoproteins has raised tantalizing questions about their role in maintaining normal cellular function. Unfortunately, many of these remain inadequately investigated. While they have a role in maintaining redox balance, other functions are becoming increasingly recognized. As the roles of these selenoproteins are further characterized, a better understanding of the true physiological significance of this trace element will arise. This knowledge will be essential in defining optimum intakes to achieve cellular homeostasis in order to optimize health, including a reduction in cancer, for diverse populations. Human variation in the response to selenium likely reflects significant interactions between the type and amounts of selenium consumed with the genome and a host of environmental factors including the totality of the diet, as discussed in this review.

The yin and yang of nrf2-regulated selenoproteins in carcinogenesis

The NF-E2-related factor-2 (Nrf2) is a transcription factor which regulates the major cellular defense systems and thereby contributes to the prevention of many diseases including cancer. Selenium deficiency is associated with a higher cancer risk making also this essential trace element a promising candidate for cancer prevention. Two selenoproteins, thioredoxin reductase-1 (TrxR1) and glutathione peroxidase-2 (GPx2), are targets for Nrf2. Selenium deficiency activates Nrf2 as does a TrxR1 knockout making a synergism between both systems plausible. Although this might hold true for healthy cells, the interplay may turn into the opposite in cancer cells. The induction of the detoxifying and antioxidant enzymes by Nrf2 will make cancer cells chemoresistant and will protect them against oxidative damage. The essential role of TrxR1 in maintaining proliferation makes its upregulation in cancer cells detrimental. The anti-inflammatory potential of GPx2 will help to inhibit cancer initiation and inflammation-triggered promotion, but its growth supporting potential will also support tumor growth. This paper considers beneficial and adverse consequences of the activation of Nrf2 and the selenoproteins which appear to depend on the cancer stage.

The role of the E2F transcription factor family in UV-induced apoptosis

The E2F transcription factor family is traditionally associated with cell cycle control. However, recent data has shown that activating E2Fs (E2F1-3a) are potent activators of apoptosis. In contrast, the recently cloned inhibitory E2Fs (E2F7 and 8) appear to antagonize E2F-induced cell death. In this review we will discuss (i) the potential role of E2Fs in UV-induced cell death and (ii) the implications of this to the development of UV-induced cutaneous malignancies.

Nitroxides as cancer imaging agents

Nitroxides are low molecular weight (150-400 Da) superoxide dismutase mimics that exhibit antioxidant, radical scavenging, and radioprotective activity. Additionally, the paramagnetic nature of nitroxides makes them viable as both spin probes for electron paramagnetic resonance imaging as well as contrast agents for magnetic resonance imaging. These imaging techniques enable in vivo monitoring of nitroxide metabolism. In biological systems, nitroxide metabolism occurs predominantly via reduction of the nitroxide to a hydroxylamine. The rate of nitroxide reduction can increase or decrease due to either oxidative stress, suggesting that nitroxides can provide an imaging-based assay of tissue redox status. The current review briefly summarizes the potential clinical applications of nitroxides, and focuses on the biochemical and tumor microenvironmental factors that affect the rate of nitroxide reduction. The potential therapeutic applications and bio-reduction mechanisms are discussed in the context of their relevance to oncology.

The Roles of Glutathione Peroxidases during Embryo Development

Embryo development relies on the complex interplay of the basic cellular processes including proliferation, differentiation, and apoptotic cell death. Precise regulation of these events is the basis for the establishment of embryonic structures and the organ development. Beginning with fertilization of the oocyte until delivery the developing embryo encounters changing environmental conditions such as varying levels of oxygen, which can give rise to reactive oxygen species (ROS). These challenges are met by the embryo with metabolic adaptations and by an array of anti-oxidative mechanisms. ROS can be deleterious by modifying biological molecules including lipids, proteins, and nucleic acids and may induce abnormal development or even embryonic lethality. On the other hand ROS are vital players of various signaling cascades that affect the balance between cell growth, differentiation, and death. An imbalance or dysregulation of these biological processes may generate cells with abnormal growth and is therefore potentially teratogenic and tumorigenic. Thus, a precise balance between processes generating ROS and those decomposing ROS is critical for normal embryo development. One tier of the cellular protective system against ROS constitutes the family of selenium-dependent glutathione peroxidases (GPx). These enzymes reduce hydroperoxides to the corresponding alcohols at the expense of reduced glutathione. Of special interest within this protein family is the moonlighting enzyme glutathione peroxidase 4 (Gpx4). This enzyme is a scavenger of lipophilic hydroperoxides on one hand, but on the other hand can be transformed into an enzymatically inactive cellular structural component. GPx4 deficiency - in contrast to all other GPx family members - leads to abnormal embryo development and finally produces a lethal phenotype in mice. This review is aimed at summarizing the current knowledge on GPx isoforms during embryo development and tumor development with an emphasis on GPx4.

Adaptive dysfunction of selenoproteins from the perspective of the triage theory: why modest selenium deficiency may increase risk of diseases of aging

The triage theory proposes that modest deficiency of any vitamin or mineral (V/M) could increase age-related diseases. V/M-dependent proteins required for short-term survival and/or reproduction (i.e., "essential") are predicted to be protected on V/M deficiency over other "nonessential" V/M-dependent proteins needed only for long-term health. The result is accumulation of insidious damage, increasing disease risk. We successfully tested the theory against published evidence on vitamin K. Here, we review about half of the 25 known mammalian selenoproteins; all of those with mouse knockout or human mutant phenotypes that could be used as criteria for a classification of essential or nonessential. Five selenoproteins (Gpx4, Txnrd1, Txnrd2, Dio3, and Sepp1) were classified as essential and 7 (Gpx1, Gpx 2, Gpx 3, Dio1, Dio2, Msrb1, and SelN) nonessential. On modest selenium (Se) deficiency, nonessential selenoprotein activities and concentrations are preferentially lost, with one exception (Dio1 in the thyroid, which we predict is conditionally essential). Mechanisms include the requirement of a special form of tRNA sensitive to Se deficiency for translation of nonessential selenoprotein mRNAs except Dio1. The same set of age-related diseases and conditions, including cancer, heart disease, and immune dysfunction, are prospectively associated with modest Se deficiency and also with genetic dysfunction of nonessential selenoproteins, suggesting that Se deficiency could be a causal factor, a possibility strengthened by mechanistic evidence. Modest Se deficiency is common in many parts of the world; optimal intake could prevent future disease.

Loss of E2F7 expression is an early event in squamous differentiation and causes derepression of the key differentiation activator Sp1

Squamous differentiation is controlled by key transcription factors such as Sp1 and E2F. We have previously shown that E2F1 can suppress transcription of the differentiation-specific gene, transglutaminase type 1 (TG1), by an indirect mechanism mediated by Sp1. Transient transfection of E2F1-E2F6 indicated that E2F-mediated reduction of Sp1 transcription was not responsible for E2F-mediated suppression of squamous differentiation. However, we found that E2F4 and E2F7, but not E2Fs 1, 2, 3, 5, or 6, could suppress the activation of the Sp1 promoter in differentiated keratinocytes (KCs). E2F4-mediated suppression could not be antagonized by E2Fs 1, 2, 3, 5, or 6 and was localized to a region of the human Sp1 promoter spanning -139 to + 35 bp. Chromatin immunoprecipitation analysis, as well as transient overexpression and short hairpin RNA knockdown experiments indicate that E2F7 binds to a unique binding site located between -139 and -119 bp of the Sp1 promoter, and knockdown of E2F7 in proliferating KCs leads to a derepression of Sp1 expression and the induction of TG1. In contrast, E2F4 knockdown in proliferating KCs did not alter Sp1 expression. These data indicate that loss of E2F7 during the initiation of differentiation leads to the derepression of Sp1 and subsequent transcription of differentiation-specific genes such as TG1.

Loss of GPx2 increases apoptosis, mitosis, and GPx1 expression in the intestine of mice

Localization of glutathione peroxidase 2 (GPx2), the gastrointestinal form of GPx's, in the intestinal crypt epithelium points to a specific but so-far unknown function of this particular GPx. Therefore, the consequences of a GPx2 knockout were tested in mice fed a selenium-restricted, Se-adequate, or Se-supplemented diet. An unexpected increase in total GPx activity was found throughout the intestine in selenium-fed GPx2 knockout (KO) animals. Immunohistochemistry revealed a strong increase in GPx1 in the colon and ileum, especially in crypt bases where typically GPx2 is localized. GPx1 mRNA was not enhanced in GPx2 KO, indicating that up-regulation most probably occurs at the translational level. Loss of GPx2 was accompanied by an increase in apoptotic cells at colonic crypt bases, an area essential for the self-renewal of the intestinal epithelium, particularly under selenium restriction. Additionally, mitotic cells increased in the middle parts of the crypts, indicating an extension of the proliferative area. These findings corroborate a role for GPx2 in regulating mucosal homeostasis. In GPx2 KO mice, an increase in GPx1 can only partially compensate for GPx2, even under selenium supplementation, indicating that GPx2 is the major antiapoptotic GPx in the colon. These data explain why spontaneous ileocolitis becomes manifested only if both Gpx2 and Gpx1 are deleted.

Oxidative stress and regulation of anti-oxidant enzymes in cytochrome P4502E1 transgenic mouse model of non-alcoholic fatty liver

BACKGROUND AND AIM

Reactive oxygen species produced by cytochrome P4502E1 (CYP2E1) are believed to play a role in pathophysiology of non-alcoholic fatty liver disease (NAFLD). However, little is known about the expression, protein content and activity of anti-oxidant enzymes and the role of inducible nitric oxide synthase (iNOS), a source of reactive nitrogen species, in NAFLD. In the present study, we evaluate gene expression, protein content and activity of anti-oxidant enzymes, and iNOS, in a CYP2E1 overexpressing model of non-alcoholic fatty liver (NAFL).

METHODS

Non-transgenic (nTg) and CYP2E1 transgenic (Tg) mice were fed rodent chow for 8 months. Alanine aminotransferase (ALT), aspartate aminotransferase (AST), liver triglycerides, malondialdehyde and protein carbonyls were measured. Gene expression of NF-E2-related factor (Nrf2), superoxide dismutase-1, -2 (SOD-1,2), catalase (CAT), glutathione peroxidase (GPx), heme oxygenase-1 (HO-1) and iNOS were determined. Protein content, activity and nitrosylation of the enzymes were also measured.

RESULTS

Tg mice had greater CYP2E1 activity and histological liver injury. MDA and protein carbonyls were increased, indicating insufficient anti-oxidant response. Gene expression of Nrf2, CAT, GPx, HO-1 and iNOS were significantly increased. Protein content and enzyme activities of most anti-oxidant enzymes were not correspondingly increased. iNOS activity and nitrosylation of CAT and SOD was greater in Tg mice liver.

CONCLUSION

Hepatocyte-specific CYP2E1 overexpression results in increased oxidative stress and nitrosative stress. Several anti-oxidant enzymes are upregulated. Failure of corresponding increase in total protein and activity of anti-oxidant enzymes suggests modification/degradation, possibly by nitrosylation, due to increased iNOS activity in a CYP2E1 overexpressing NAFL mouse model.

Antioxidant enzymes and lipid peroxidation in endometrium of patients with polyps, myoma, hyperplasia and adenocarcinoma

BACKGROUND

Oxidative stress and impaired antioxidant system have been proposed as a potential factors involved in the pathophysiology of diverse disease states, including carcinogenesis. In this study, we explored the lipid peroxidation levels and antioxidant enzyme activities in women diagnosed with different forms of gynecological diseases in order to evaluate the antioxidant status in endometrium of such patients.

METHODS

Endometrial tissues of gynecological patients with different diagnoses were collected and subjected to assays for superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase and lipid hydroperoxides.

RESULTS

Superoxide dismutase activity was significantly decreased (50% in average) in hyperplastic and adenocarcinoma patients. Activities of both glutathione peroxidase and glutathione reductase were increased 60% and 100% on average, in hyperplastic patients, while in adenocarcinoma patients only glutathione reductase activity was elevated 100%. Catalase activity was significantly decreased in adenocarcinoma patients (47%). Lipid hydroperoxides level was negatively correlated to superoxide dismutase and catalase activities, and positively correlated to glutathione peroxidase and glutathione reductase activities.

CONCLUSIONS

This study provided the first comparison of antioxidant status and lipid peroxidation in endometrial tissues of patients with polyps, myoma, hyperplasia and adenocarcinoma. The results showed that patients with premalignant (hyperplastic) and malignant (adenocarcinoma) lesions had enhanced lipid peroxidation and altered uterine antioxidant enzyme activities than patients with benign uterine diseases, polyps and myoma, although the extent of disturbance varied with the diagnosis. Further investigation is needed to clarify the mechanisms responsible for the observed alterations and whether lipid hydroperoxide levels and antioxidant enzyme activities in uterus of gynecological patients might be used as additional parameter in clinical evaluation of gynecological disorders.

Antioxidant enzymes and lipid peroxidation in endometrium of patients with polyps, myoma, hyperplasia and adenocarcinoma

BACKGROUND

Oxidative stress and impaired antioxidant system have been proposed as a potential factors involved in the pathophysiology of diverse disease states, including carcinogenesis. In this study, we explored the lipid peroxidation levels and antioxidant enzyme activities in women diagnosed with different forms of gynecological diseases in order to evaluate the antioxidant status in endometrium of such patients.

METHODS

Endometrial tissues of gynecological patients with different diagnoses were collected and subjected to assays for superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase and lipid hydroperoxides.

RESULTS

Superoxide dismutase activity was significantly decreased (50% in average) in hyperplastic and adenocarcinoma patients. Activities of both glutathione peroxidase and glutathione reductase were increased 60% and 100% on average, in hyperplastic patients, while in adenocarcinoma patients only glutathione reductase activity was elevated 100%. Catalase activity was significantly decreased in adenocarcinoma patients (47%). Lipid hydroperoxides level was negatively correlated to superoxide dismutase and catalase activities, and positively correlated to glutathione peroxidase and glutathione reductase activities.

CONCLUSIONS

This study provided the first comparison of antioxidant status and lipid peroxidation in endometrial tissues of patients with polyps, myoma, hyperplasia and adenocarcinoma. The results showed that patients with premalignant (hyperplastic) and malignant (adenocarcinoma) lesions had enhanced lipid peroxidation and altered uterine antioxidant enzyme activities than patients with benign uterine diseases, polyps and myoma, although the extent of disturbance varied with the diagnosis. Further investigation is needed to clarify the mechanisms responsible for the observed alterations and whether lipid hydroperoxide levels and antioxidant enzyme activities in uterus of gynecological patients might be used as additional parameter in clinical evaluation of gynecological disorders.

Absence of inflammatory response from upper airway epithelial cells after X irradiation

Radiotherapy of head and neck tumors causes adverse reactions in normal tissue, especially mucositis. The dose- and time-dependent response of upper airway cells to X radiation should be analyzed in terms of the pro-inflammatory potential. Immortalized BEAS-2B lung epithelial cells were treated with 2, 5 and 8 Gy. Out of 1232 genes, those that were transcribed differentially after 2, 6 and 24 h were assigned to biological themes according to the Gene Ontology Consortium. Enrichment of differentially regulated gene clusters was determined with GOTree ( http://bioinfo.vanderbilt.edu/gotm ). Eleven cytokines were measured in culture supernatants. The cell cycle response up to 24 h and induction of apoptosis up to 4 days after exposure were determined by flow cytometry. A significant dose- and time-dependent gene activation was observed for the categories response to DNA damage, oxidative stress, cell cycle arrest and cell death/apoptosis but not for immune/inflammatory response. This correlated with functional G(2) arrest and apoptosis. Pro-inflammatory cytokines accumulated in supernatants of control cells but not of X-irradiated cells. The complex gene expression pattern of X-irradiated airway epithelial cells is accompanied by cell cycle arrest and induction of apoptosis. In vivo, this may impair the epithelial barrier. mRNA and protein expression suggest at most an indirect contribution of epithelial cells to early radiogenic mucositis.

Glutathione peroxidases in different stages of carcinogenesis

Cancer cells produce high amounts of reactive oxygen species (ROS) and evade apoptosis. Hydroperoxides support proliferation, invasion, migration and angiogenesis, but at higher levels induce apoptosis, thus being pro- and anti-carcinogenic. Accordingly, glutathione peroxidases (GPxs) regulating hydroperoxide levels might have dual roles too. GPx1, clearly an antioxidant enzyme, is down-regulated in many cancer cells. Its main role would be prevention of cancer initiation by ROS-mediated DNA damage. GPx2 is up-regulated in cancer cells. GPx1/GPx2 double knockout mice develop colitis and intestinal cancer. However, GPx2 knockdown cancer cells grow better in vitro and in vivo probably reflecting the physiological role of GPx2 in intestinal mucosa homeostasis. GPx2 counteracts COX-2 expression and PGE(2) production, which explains its potential to inhibit migration and invasion of cultured cancer cells. Overexpression of GPx3 inhibits tumor growth and metastasis. GPx4 is decreased in cancer tissues. GPx4-overexpressing cancer cells have low COX-2 activity and tumors derived therefrom are smaller than from control cells and do not metastasize. Collectively, GPxs prevent cancer initiation by removing hydroperoxides. GPx4 inhibits but GPx2 supports growth of established tumors. Metastasis, but also apoptosis, is inhibited by all GPxs. GPx-mediated regulation of COX/LOX activities may be relevant to early stages of inflammation-mediated carcinogenesis.

Molecular mechanisms by which selenoproteins affect cancer risk and progression

Selenoproteins comprise a unique class of proteins that contain selenium in the form of selenocysteine. Several selenoproteins have been implicated in the risk or development of cancers in humans by genetic data. These include Selenoprotein P, 3 members of the glutathione peroxidase family of anti-oxidant enzymes and Sep15. At-risk alleles in the germline indicate a likely role in determining susceptibility to cancer, while loss of heterozygosity or chromosomal epigenetic silencing indicate that the reduction in the levels of the corresponding proteins contribute to malignant progression. Lower levels of these proteins are likely to be detrimental due to the resulting cellular stress and perturbations in important regulatory signaling pathways. The genetic data indicating the involvement of these selenoproteins in cancer etiology are discussed, as are the possible mechanisms by which these genes might promote carcinogenesis.

E2F7 can regulate proliferation, differentiation, and apoptotic responses in human keratinocytes: implications for cutaneous squamous cell carcinoma formation

The E2F family of transcription factors plays a crucial role in the regulation of genes involved in cell proliferation, differentiation, and apoptosis. In keratinocytes, the inhibition of E2F is a key step in the control and initiation of squamous differentiation. Because the product of the recently identified E2F7a/E2F7b gene has been shown to repress E2F-regulated promoters, and to be abundant in skin, we examined its role in the epidermis. Our results indicate that E2F7b mRNA expression is selectively associated with proliferation-competent keratinocytes. Moreover, E2F7 was able to antagonize E2F1-induced proliferation and apoptosis. In contrast, although E2F7 was able to inhibit proliferation and initiate differentiation, it was unable to antagonize the differentiation suppression induced by E2F1. These data indicate that E2F7-mediated suppression of proliferation and apoptosis acts through E2F1-dependent pathways, whereas E2F7-induced differentiation acts through an E2F1-independent pathway. These data also suggest that proliferation, differentiation, and survival of primary human keratinocytes can be controlled by the relative ratio of E2F1 to E2F7. Because deregulated proliferation, differentiation, and apoptosis are hallmarks of cancer, we examined the expression levels of E2F1 and E2F7 in cutaneous squamous cell carcinomas (CSCC). We found that both genes were overexpressed in CSCCs compared with normal epidermis. Furthermore, inhibition of E2F7 in a SCC cell line sensitized the cells to UV-induced apoptosis and doxorubicin-induced apoptosis. Combined, these data suggest that the selected disruption of E2F1 and E2F7 in keratinocytes is likely to contribute to CSCC formation and may prove to be a viable therapeutic target.

GPx2 counteracts PGE2 production by dampening COX-2 and mPGES-1 expression in human colon cancer cells

GPx2, the gastrointestinal glutathione peroxidase, is a selenoprotein predominantly expressed in the intestine. An anti-inflammatory and anticarcinogenic potential has been inferred from the development of colitis and intestinal cancer in GPx1 and GPx2 double knockout mice. Further, induction by Nrf2 activators classifies GPx2 as a protective enzyme. In contrast, enhanced COX-2 expression is consistently associated with inflammation. The antagonistic roles and an intriguing co-localization of GPx2 and COX-2 prompted us to investigate their possible mutual regulation. Both enzymes were upregulated in tissues of patients with colorectal cancer and colitis, and co-localized in the endoplasmic reticulum. A stable knockdown of GPx2 in HT-29 cells by siRNA resulted in a high basal and IL-1-induced expression of COX-2 and mPGES-1, enzymes required for the production of the pro-inflammatory PGE(2). Accordingly, si-GPx2 cells released high concentrations of PGE(2). Observed effects were specific for GPx2, since COX-2 and mPGES-1 expression was not affected by selenium-deprivation which resulted in the disappearance of GPx1. It is concluded that GPx2 by compartmentalized removal of hydroperoxides silences COX-2 activity and suppresses PGE(2)-dependent COX-2 expression. Thus, GPx2 may prevent undue responses to inflammatory stimuli and, in consequence, inflammation-driven initiation of carcinogenesis.

Selenium compounds and selenoproteins in cancer

An adequate selenium (Se) status has for long been considered to prevent the development of various forms of cancer. However, underlying molecular mechanisms remained unknown. In mammals, selenium exerts its functions as selenocysteine incorporated into selenoproteins. Therefore, Se compounds can either act as Se source for selenoproteins or, depending on their chemical forms, in distinct ways. Most potent chemopreventive effects have been attributed to compounds in which the Se moiety is methylated. These compounds are able to induce phase 2 enzymes which are involved in the cellular defense system that is regulated by the Nrf2 transcription factor. Selenoproteins best studied in cancer development are members of the glutathione peroxidase (GPx) and thioredoxin reductase (TrxR) family. In various cancer cells and tissues, GPx2 and/or TrxR1 are up-regulated. Interestingly, both enzymes are targets of Nrf2. An enhanced expression of these enzymes may represent a mechanism to counteract carcinogenic pathways. They may, however, also provide a selective advantage for pre-existing tumor cells in guaranteeing survival and continuous proliferation.

Reactive species: a cell damaging rout assisting to chemical carcinogens

Reactive oxygen and nitrogen species (ROS and RNS) are known to contribute as pathogenic factors to the development of chronic progressive diseases at various stages. The present review discusses the role of oxidative stress in chemically induced cancer development and progression. Reactive species are capable of inducing DNA damage that eventually may contribute to cell transformation and tumor initiation. ROS and RNS are also associated with tumor promotion and progression. Both endogenous processes and redox-cycling of xenobiotic compounds have been shown to result in oxidative DNA damage. In addition, several exocyclic DNA adducts represent secondary DNA damage caused by products of lipid peroxidation in the course of oxidative cellular stress. Due to their intrinsic ability to catalyze redox reactions, transition metals, and quinones from various classes of xenobiotics or endogenous compounds are important mediators of oxidative stress and thus likely of being involved in DNA damage, lipid peroxidation, cell transformation, and tumor development.

Gpx2 is an overexpressed gene in rat breast cancers induced by three different chemical carcinogens

Gene expression alterations are essential for the process of carcinogenesis. A carcinogen may have specific mechanisms for inducing tumors, which may involve inducing characteristic gene expression alterations. In this study, we attempted to identify genes crucial for mammary carcinogenesis. For this purpose, we used human c-Ha-ras proto-oncogene transgenic rats (Hras128), which are highly sensitive to mammary carcinogens including N-methyl-N-nitrosourea, 7,12-dimethyl benz[a]anthracene, and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine. DNA microarray analysis revealed that glutathione peroxidase 2 (Gpx2) was commonly up-regulated in the mammary carcinomas induced by the three different carcinogens, and its up-regulation was confirmed by quantitative reverse transcriptase-PCR and Western blotting analysis. In addition, expression of GPX2 was recognized in all 41 immunohistochemically examined cases of human breast cancer. Forced suppression of GPX2 expression by siRNA resulted in significant growth inhibition in both rat and human mammary carcinoma cell lines with wild-type p53 cells. Thus, these data suggested that GPX2 may be involved in mammary carcinogenesis and cell proliferation in both rats and humans, indicating that GPX2 may be a novel target for the prevention and therapy of breast cancer.