Selenoprotein P regulates 1-(4-Chlorophenyl)-benzo-2,5-quinone-induced oxidative stress and toxicity in human keratinocytes

Selenoprotein P inhibits cell proliferation and ROX production in HCC cells

Selenoprotein P (SEPP1) is a kind of secretory glycoproteins with an antioxidant effect during the development of some diseases. In this study, we attempted to observe the expression of SEPP1 in livers from the patients with hepatocellular carcinoma (HCC) and explore its effect on HCC cells. All the tissues from patients with HCC were obtained from Affiliated Hospital of Nantong University. Western blot and immunohistochemical results showed that SEPP1 was reduced in HCC liver tissues. Its expression was negatively correlated with Ki67 expression in tissues. The expression of SEPP1 in normal liver cell line was significantly higher than those in the liver cancer cell lines. Serum starvation and release experiment demonstrated that SEPP1 expression was reduced and PCNA expression was increased, when the serum was re-added into cell culture system and the cells were on a proliferation state. After SEPP1 over-expression plasmid was transfected into HepG2 cells, cell proliferation of HepG2 cells and PCNA expression level were all inhibited by SEPP1. Results obtained via 8-isoprostane ELISA further indicated that inhibited ROS level was found in HepG2 cells transfected with SEPP1 over-expression plasmid. In addition, RT-qPCR results demonstrated that GPX1 expression levels increased in HepG2 cells transfected with SEPP1 over-expression plasmid. In conclusion, SEPP1 may inhibit the proliferation of HCC cells, accompanied by the reduction of ROS production and the increasing of GPX1 expression.

2-Hydroxy-(4-methylseleno)butanoic Acid Is Used by Intestinal Caco-2 Cells as a Source of Selenium and Protects against Oxidative Stress

BACKGROUND

Selenium (Se) participates in different functions in humans and other animals through its incorporation into selenoproteins as selenocysteine. Inadequate dietary Se is considered a risk factor for several chronic diseases associated with oxidative stress.

OBJECTIVE

The role of 2-hydroxy-(4-methylseleno)butanoic acid (HMSeBA), an organic form of Se used in animal nutrition, in supporting selenoprotein synthesis and protecting against oxidative stress was investigated in an in vitro model of intestinal Caco-2 cells.

METHODS

Glutathione peroxidase (GPX) and thioredoxin reductase (TXNRD) activities, selenoprotein P1 protein (SELENOP) and gene (SELENOP) expression, and GPX1 and GPX2 gene expression were studied in Se-deprived (FBS removal) and further HMSeBA-supplemented (0.1-625 μM, 72 h) cultures. The effect of HMSeBA supplementation (12.5 and 625 μM, 24 h) on oxidative stress induced by H2O2 (1 mM) was evaluated by the production of reactive oxygen species (ROS), 4-hydroxy-2-nonenal (4-HNE) adducts, and protein carbonyl residues compared with a sodium selenite control (SS, 5 μM).

RESULTS

Se deprivation induced a reduction (P < 0.05) in GPX activity (62%), GPX1 expression, and both SELENOP (33%) and SELENOP expression. In contrast, an increase (P < 0.05) in GPX2 expression and no effect in TXNRD activity (P = 0.09) were observed. HMSeBA supplementation increased (P < 0.05) GPX activity (12.5-625 μM, 1.68-1.82-fold) and SELENOP protein expression (250 and 625 μM, 1.87- and 2.04-fold). Moreover, HMSeBA supplementation increased (P < 0.05) GPX1 (12.5 and 625 μM), GPX2 (625 μM), and SELENOP (12.5 and 625 μM) expression. HMSeBA (625 μM) was capable of decreasing (P < 0.05) ROS (32%), 4-HNE adduct (49%), and protein carbonyl residue (75%) production after H2O2 treatment.

CONCLUSION

Caco-2 cells can use HMSeBA as an Se source for selenoprotein synthesis, resulting in protection against oxidative stress.

Transcriptome analysis of airborne PM2.5-induced detrimental effects on human keratinocytes

Ambient air pollution is becoming more severe worldwide, posing a serious threat to human health. Fine airborne particles of particulate matter (PM_2.5) show higher cytotoxicity than other coarse fractions. Indeed, PM_2.5 induces cardiovascular or respiratory damage; however, few studies have evaluated the detrimental effect of PM_2.5 to normal human skin. We used a next-generation sequencing-based (RNA-Seq) method with transcriptome and Gene Ontology (GO) enrichment analysis to determine the harmful influences of PM_2.5 on human normal epidermal keratinocytes. DAVID analysis showed that the most significantly enriched GO terms were associated with epidermis-related biological processes such as "epidermis development (GO: 0008544)" and "keratinocyte differentiation (GO: 0030216)", suggesting that PM_2.5 has some deleterious effects to the human epidermis. In addition, Ingenuity Pathway Analysis predicted inflammation-related signaling as one of the major PM_2.5-induced signaling pathways, and pro-inflammatory cytokines as upstream regulators with symptoms similar to psoriasis as downstream effects. PM_2.5 caused considerable changes in the expression of pro-inflammatory cytokines and psoriatic skin disease-related genes, might lead to epidermal dysfunctions. Our results might help to understand the mechanism of air pollution-induced skin barrier perturbation and contribute to the development of a new strategy for the prevention or recovery of the consequent damage.

Cytochrome c adducts with PCB quinoid metabolites

Polychlorinated biphenyls (PCBs) are a group of 209 individual congeners widely used as industrial chemicals. PCBs are found as by-products in dye and paint manufacture and are legacy, ubiquitous, and persistent as human and environmental contaminants. PCBs with fewer chlorine atoms may be metabolized to hydroxy- and dihydroxy-metabolites and further oxidized to quinoid metabolites both in vitro and in vivo. Specifically, quinoid metabolites may form adducts on nucleophilic sites within cells. We hypothesized that the PCB-quinones covalently bind to cytochrome c and, thereby, cause defects in the function of cytochrome c. In this study, synthetic PCB quinones, 2-(4'-chlorophenyl)-1,4-benzoquinone (PCB3-pQ), 4-4'-chlorophenyl)-1,2-benzoquinone (PCB3-oQ), 2-(3', 5'-dichlorophenyl)-1,4-benzoquinone, 2-(3',4', 5'-trichlorophenyl)-1,4-benzoquinone, and 2-(4'-chlorophenyl)-3,6-dichloro-1,4-benzoquinone, were incubated with cytochrome c, and adducts were detected by liquid chromatography-mass spectrometry (LC-MS) and matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI TOF). Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) was employed to separate the adducted proteins, while trypsin digestion and liquid chromatography-tandem mass spectrometry (LC-MS/MS) were applied to identify the amino acid binding sites on cytochrome c. Conformation change of cytochrome c after binding with PCB3-pQ was investigated by SYBYL-X simulation and cytochrome c function was examined. We found that more than one molecule of PCB-quinone may bind to one molecule of cytochrome c. Lysine and glutamic acid were identified as the predominant binding sites. Software simulation showed conformation changes of adducted cytochrome c. Additionally, cross-linking of cytochrome c was observed on the SDS-PAGE gel. Cytochrome c was found to lose its function as electron acceptor after incubation with PCB quinones. These data provide evidence that the covalent binding of PCB quinone metabolites to cytochrome c may be included among the toxic effects of PCBs.

Succinate dehydrogenase activity regulates PCB3-quinone-induced metabolic oxidative stress and toxicity in HaCaT human keratinocytes

Polychlorinated biphenyls (PCBs) and their metabolites are environmental pollutants that are known to have adverse health effects. 1-(4-Chlorophenyl)-benzo-2,5-quinone (4-ClBQ), a quinone metabolite of 4-monochlorobiphenyl (PCB3, present in the environment and human blood) is toxic to human skin keratinocytes, and breast and prostate epithelial cells. This study investigates the hypothesis that 4-ClBQ-induced metabolic oxidative stress regulates toxicity in human keratinocytes. Results from Seahorse XF96 Analyzer showed that the 4-ClBQ treatment increased extracellular acidification rate, proton production rate, oxygen consumption rate and ATP content, indicative of metabolic oxidative stress. Results from a q-RT-PCR assay showed significant increases in the mRNA levels of hexokinase 2 (hk2), pyruvate kinase M2 (pkm2) and glucose-6-phosphate dehydrogenase (g6pd), and decreases in the mRNA levels of succinate dehydrogenase (complex II) subunit C and D (sdhc and sdhd). Pharmacological inhibition of G6PD-activity enhanced the toxicity of 4-ClBQ, suggesting that the protective function of the pentose phosphate pathway is functional in 4-ClBQ-treated cells. The decrease in sdhc and sdhd expression was associated with a significant decrease in complex II activity and increase in mitochondrial levels of ROS. Overexpression of sdhc and sdhd suppressed 4-ClBQ-induced inhibition of complex II activity, increase in mitochondrial levels of ROS, and toxicity. These results suggest that the 4-ClBQ treatment induces metabolic oxidative stress in HaCaT cells, and while the protective function of the pentose phosphate pathway is active, inhibition of complex II activity sensitizes HaCaT cells to 4-ClBQ-induced toxicity.

Down-regulation of peroxisome proliferator activated receptor γ coactivator 1α induces oxidative stress and toxicity of 1-(4-Chlorophenyl)-benzo-2,5-quinone in HaCaT human keratinocytes

Peroxisome proliferator activated receptor γ coactivator 1α (PGC-1α) is a transcriptional coactivator that is known to regulate oxidative stress response by enhancing the expression of antioxidant genes. We have shown previously that 1-(4-Chlorophenyl)-benzo-2,5-quinone (4-ClBQ), a quinone-metabolite of 4-monochlorobiphenyl (PCB3) induces oxidative stress and toxicity in human skin keratinocytes, and breast and prostate epithelial cells. In this study, we investigate whether PGC-1α regulates oxidative stress and toxicity in 4-ClBQ treated HaCaT human keratinocytes. Results showed significant down-regulation in the expression of PGC-1α and catalase in 4-ClBQ treated HaCaT cells. Down-regulation of PGC-1α expression was associated with 4-ClBQ induced increase in the steady-state levels of cellular reactive oxygen species (ROS) and toxicity. Overexpression of pgc-1α enhanced the expression of catalase and suppressed 4-ClBQ induced increase in cellular ROS levels and toxicity. These results suggest that pgc-1α mediates 4-ClBQ induced oxidative stress and toxicity in HaCaT cells presumably by regulating catalase expression.

Aflatoxin B1 Suppressed T-Cell Response to Anti-pig-CD3 Monoclonal Antibody Stimulation in Primary Porcine Splenocytes: A Role for the Extracellular Regulated Protein Kinase (ERK1/2) MAPK Signaling Pathway

The aim of the present study is to investigate whether aflatoxin B1 (AFB1)-induced immunotoxicity is associated with oxidative stress and the expression of extracellular regulated protein kinases (ERK) 1/2. The primary splenocytes isolated from healthy pigs were activated and proliferated by anti-pig-CD3 monoclonal antibodies (mAb) in the present experiment, which is an antigen-specific stimulant. Results indicated that cell proliferation and interleukin-2 (IL-2) production were significantly suppressed by AFB1 from 4 to 8 μg/mL in a dose-dependent manner compared to the control group. Furthermore, AFB1 significantly increased malondialdehyde (MDA) levels, decreased reduced glutathione (GSH) and total superoxide dismutase levels, and up-regulated p-ERK1/2 expression in the activated splenocytes. N-Acetyl-l-cysteine blocked anti-CD3-induced T-cell suppression by AFB1 through increasing intracellular concentrations of GSH levels, decreasing MDA levels, and down-regulated p-ERK1/2 expression, respectively. Inhibition of the ERK1/2 expression by ERK-specific iRNA attenuated the decrease of T-cell proliferation and IL-2 production induced by AFB1. It was concluded that AFB1 inhibits anti-CD3-induced lymphocyte proliferation and IL-2 production by the oxidative stress mediated ERK1/2 MAPK signaling pathway.

Redox-Mediated Suberoylanilide Hydroxamic Acid Sensitivity in Breast Cancer

AIMS

Vorinostat (suberoylanilide hydroxamic acid; SAHA) is a histone deacetylase inhibitor (HDACi) approved in the clinics for the treatment of T-cell lymphoma and with the potential to be effective also in breast cancer. We investigated the responsiveness to SAHA in human breast primary tumors and cancer cell lines.

RESULTS

We observed a differential response to drug treatment in both human breast primary tumors and cancer cell lines. Gene expression analysis of the breast cancer cell lines revealed that genes involved in cell adhesion and redox pathways, especially glutathione metabolism, were differentially expressed in the cell lines resistant to SAHA compared with the sensitive ones, indicating their possible association with drug resistance mechanisms. Notably, such an association was also observed in breast primary tumors. Indeed, addition of buthionine sulfoximine (BSO), a compound capable of depleting cellular glutathione, significantly enhanced the cytotoxicity of SAHA in both breast cancer cell lines and primary breast tumors.

INNOVATION

We identify and validate transcriptional differences in genes involved in redox pathways, which include potential predictive markers of sensitivity to SAHA.

CONCLUSION

In breast cancer, it could be relevant to evaluate the expression of antioxidant genes that may favor tumor resistance as a factor to consider for potential clinical application and treatment with epigenetic drugs (HDACis).

Selenoprotein P influences colitis-induced tumorigenesis by mediating stemness and oxidative damage

Patients with inflammatory bowel disease are at increased risk for colon cancer due to augmented oxidative stress. These patients also have compromised antioxidant defenses as the result of nutritional deficiencies. The micronutrient selenium is essential for selenoprotein production and is transported from the liver to target tissues via selenoprotein P (SEPP1). Target tissues also produce SEPP1, which is thought to possess an endogenous antioxidant function. Here, we have shown that mice with Sepp1 haploinsufficiency or mutations that disrupt either the selenium transport or the enzymatic domain of SEPP1 exhibit increased colitis-associated carcinogenesis as the result of increased genomic instability and promotion of a protumorigenic microenvironment. Reduced SEPP1 function markedly increased M2-polarized macrophages, indicating a role for SEPP1 in macrophage polarization and immune function. Furthermore, compared with partial loss, complete loss of SEPP1 substantially reduced tumor burden, in part due to increased apoptosis. Using intestinal organoid cultures, we found that, compared with those from WT animals, Sepp1-null cultures display increased stem cell characteristics that are coupled with increased ROS production, DNA damage, proliferation, decreased cell survival, and modulation of WNT signaling in response to H2O2-mediated oxidative stress. Together, these data demonstrate that SEPP1 influences inflammatory tumorigenesis by affecting genomic stability, the inflammatory microenvironment, and epithelial stem cell functions.

Ligand-independent activation of aryl hydrocarbon receptor signaling in PCB3-quinone treated HaCaT human keratinocytes

Aryl hydrocarbon receptor (AhR) is a ligand-dependent transcription factor that plays a critical role in metabolism, cell proliferation, development, carcinogenesis, and xenobiotic response. In general, dioxin-like polychlorinated biphenyls (PCBs) exhibit a ligand-dependent activation of AhR-signaling. Results from this study show that a quinone-derivative (1-(4-Chlorophenyl)-benzo-2,5-quinone; 4-ClBQ) of a non-dioxin like PCB (PCB3) also activates AhR-signaling. Treatments of HaCaT human keratinocytes with 4-ClBQ and dioxin-like PCB126 significantly increased AhR-target gene expression, CYP1A1 mRNA and protein levels. 4-ClBQ-induced increase CYP1A1 expression was associated with an increase in the nuclear translocation of AhR protein as well as an increase in the luciferase-reporter activity of a human CYP1A1 xenobiotic response element (XRE). 6,2',4'-Trimethoxyflavone (TMF), a well-characterized AhR-ligand antagonist significantly suppressed PCB126-induced increase in CYP1A1 expression, while the same treatment did not suppress 4-ClBQ-induced increase in CYP1A1 expression. However, siRNA-mediated down-regulation of AhR significantly inhibited 4-ClBQ-induced increase in CYP1A1 expression, suggesting that AhR mediates 4-ClBQ-induced increase in CYP1A1 expression. Interestingly, treatment with the antioxidant N-acetyl-l-cysteine significantly suppressed 4-ClBQ-induced increase in CYP1A1 expression. Furthermore, CYP1A1 expression also increased in cells treated with hydrogen peroxide. These results demonstrate that a ligand-independent and oxidative stress dependent pathway activates AhR-signaling in 4-ClBQ treated HaCaT cells. Because AhR signaling is believed to mediate xenobiotics response, our results may provide a mechanistic rationale for the use of antioxidants as effective countermeasure to environmental pollutant-induced adverse health effects.

Selenium and Human Health: Witnessing a Copernican Revolution?

In humans, selenium was hypothesized to lower the risk of several chronic diseases, mainly due to the antioxidant activity of selenium-containing proteins. Recent epidemiologic and laboratory studies, however, are changing our perception of the biological effects of this nutritionally essential trace element. We reviewed the most recent epidemiologic and biochemical literature on selenium, synthesizing the findings from these studies into a unifying view. Randomized trials have shown that selenium did not protect against cancer and other chronic diseases, but even increased the risk of specific neoplasms such as advanced prostate cancer and skin cancer, in addition to type 2 diabetes. Biochemical studies indicate that selenium may exert a broad pattern of toxic effects at unexpectedly low concentrations. Furthermore, its upregulation of antioxidant proteins (selenium-dependent and selenium-independent) may be a manifestation of self-induced oxidative stress. In conclusion, toxic effects of selenium species occur at lower concentrations than previously believed. Those effects may include a large range of proteomic changes and adverse health effects in humans. Since the effects of environmental exposure to this element on human health still remain partially unknown, but are potentially serious, the toxicity of selenium exposure should be further investigated and considered as a public health priority.

Direct interaction between selenoprotein P and tubulin

Selenium (Se), an essential trace element for human health, mainly exerts its biological function via selenoproteins. Among the 25 selenoproteins identified in human, selenoprotein P (SelP) is the only one that contains multiple selenocysteines (Sec) in the sequence, and has been suggested to function as a Se transporter. Upon feeding a selenium-deficient diet, mice lacking SelP develop severe neurological dysfunction and exhibit widespread brainstem neurodegeneration, indicating an important role of SelP in normal brain function. To further elucidate the function of SelP in the brain, SelP was screened by the yeast two-hybrid system from a human fetal brain cDNA library for interactive proteins. Our results demonstrated that SelP interacts with tubulin, alpha 1a (TUBA1A). The interaction between SelP and tubulin was verified by fluorescence resonance energy transfer (FRET) and co-immunoprecipitation (co-IP) assays. We further found that SelP interacts with the C-terminus of tubulin by its His-rich domain, as demonstrated by FRET and Isothermal Titration Calorimetry (ITC) assays. The implications of the interaction between SelP and tubulin in the brain and in Alzheimer's disease are discussed.

Selenoprotein P inhibits radiation-induced late reactive oxygen species accumulation and normal cell injury

PURPOSE

Radiation is a common mode of cancer therapy whose outcome is often limited because of normal tissue toxicity. We have shown previously that the accumulation of radiation-induced late reactive oxygen species (ROS) precedes cell death, suggesting that metabolic oxidative stress could regulate cellular radiation response. The purpose of this study was to investigate whether selenoprotein P (SEPP1), a major supplier of selenium to tissues and an antioxidant, regulates late ROS accumulation and toxicity in irradiated normal human fibroblasts (NHFs).

METHODS AND MATERIALS

Flow cytometry analysis of cell viability, cell cycle phase distribution, and dihydroethidium oxidation, along with clonogenic assays, were used to measure oxidative stress and toxicity. Human antioxidant mechanisms array and quantitative real-time polymerase chain reaction assays were used to measure gene expression during late ROS accumulation in irradiated NHFs. Sodium selenite addition and SEPP1 overexpression were used to determine the causality of SEPP1 regulating late ROS accumulation and toxicity in irradiated NHFs.

RESULTS

Irradiated NHFs showed late ROS accumulation (4.5-fold increase from control; P<.05) that occurs after activation of the cell cycle checkpoint pathways and precedes cell death. The mRNA levels of CuZn- and Mn-superoxide dismutase, catalase, peroxiredoxin 3, and thioredoxin reductase 1 increased approximately 2- to 3-fold, whereas mRNA levels of cold shock domain containing E1 and SEPP1 increased more than 6-fold (P<.05). The addition of sodium selenite before the radiation treatment suppressed toxicity (45%; P<.05). SEPP1 overexpression suppressed radiation-induced late ROS accumulation (35%; P<.05) and protected NHFs from radiation-induced toxicity (58%; P<.05).

CONCLUSION

SEPP1 mitigates radiation-induced late ROS accumulation and normal cell injury.