Yoshishige Urata

Melatonin induces γ-glutamylcysteine synthetase mediated by activator protein-1 in human vascular endothelial cells

Abstract In the present study, we show that melatonin induces the expression of γ-glutamylcysteine synthetase (γ-GCS), the rate-limiting enzyme of glutathione (GSH) synthesis, in ECV304 human vascular endothelial cells. One micromolar melatonin induced the expression of γ-GCS mRNA followed by an increase in the concentration of GSH with a peak at 24 h. An electrophoretic mobility shift assay showed that melatonin stimulates the DNA-binding activity of activator protein-1 (AP-1) as well as retinoid Z receptor/retinoid receptor-related orphan receptor α (RZR/RORα). ECV304 cells transiently transfected with a plasmid containing the γ-GCS promoter-luciferase construct showed increased luciferase activity when treated with melatonin. The melatonin-dependent luciferase activity was found in the γ-GCS promoter containing AP-1 site. The luciferase activity mediated by AP-1 was repressed in the promoter containing RZR/RORα site. In addition, cell cycle analysis showed that melatonin increases the number of cells in the G0/G1 phase; however, treatment of the cells with buthionine sulfoximine, a specific inhibitor of γ-GCS, abolished the effect of melatonin on the cell cycle, suggesting induction of cell arrest by melatonin requires GSH. As conclusion, induction of GSH synthesis by melatonin protects cells against oxidative stress and regulates cell proliferation.

Significance of Glutathione Depletion and Oxidative Stress in Early Embryogenesis in Glucose-Induced Rat Embryo Culture

Recent studies have demonstrated the protective effects of supplementing free oxygen radical scavenging enzymes against hyperglycemia-induced embryonic malformations. In this study, the glutathione (GSH)-dependent protection system in hyperglycemia-induced embryopathy was investigated. Rat embryos at the early head-fold stage (day 9.5) cultured in 66.7 mmol/l glucose for 48 h showed significant growth retardation and an increase in the frequency of malformations. The concentration of GSH and activity of the rate-limiting GSH-synthesizing enzyme, γ-glutamylcysteine synthetase (γ-GCS), significantly decreased in embryos exposed to hyperglycemia compared with controls (7.9 ± 0.6 vs. 12.5 ± 0.9 nmol/mg protein, P < 0.01 and 13.3 ± 1.9 vs. 22.6 ± 1.1 μU/mg protein, P < 0.01, respectively). Decreased activity of γ-GCS in embryos exposed to hyperglycemia was associated with decreased expression of γ-GCS mRNA levels. However, the activities of superoxide dismutase and glutathione peroxidase did not significantly change in these embryos. Extracellular and intracellular free oxygen radical formations estimated by Lucigenin-dependent chemoluminescence and flow cytometric analysis using 2′,7′-dichlorofluorescein diacetate increased in isolated embryonic cells taken from embryos cultured under hyperglycemia. Supplementation of 2 mmol/l GSH ester into the hyperglycemic culture nearly restored GSH concentration in these embryos (11.9 ± 0.5 vs. 12.5 ± 0.9 nmol/mg protein) and reduced the formation of free oxygen radical species leading to almost complete normalization of growth retardation and embryonic dysmorphogenesis. These results indicate that the GSHdependent protection system has a central role against oxidative stress in embryos cultured under hyperglycemia and that GSH depletion in embryonic cells during the critical periods of organogenesis plays a role in hyperglycemia-induced embryopathy.

17β-Estradiol Protects against Oxidative Stress-induced Cell Death through the Glutathione/Glutaredoxin-dependent Redox Regulation of Akt in Myocardiac H9c2 Cells

The GSH/glutaredoxin (GRX) system is involved in the redox regulation of certain enzyme activities, and this system protects cells from H2O2-induced apoptosis by regulating the redox state of Akt (Murata, H., Ihara, Y., Nakamura, H., Yodoi, J., Sumikawa, K., and Kondo, T. (2003) J. Biol. Chem. 278, 50226–50233). Estrogens, such as 17β-estradiol (E2), play an important role in development, growth, and differentiation and appear to have protective effects on oxidative stress mediated by estrogen receptor α (ERα). However, the role of the ERβ-mediated pathway in this cytoprotection and the involvement of E2 in the redox regulation are not well understood. In the present study, we demonstrated that E2 protected cardiac H9c2 cells, expressing ERβ from H2O2-induced apoptosis concomitant with an increase in the activity of Akt. E2 induced the expression of glutaredoxin (GRX) as well as γ-glutamylcysteine synthetase, a rate-limiting enzyme for the synthesis of GSH. Inhibitors for both γ-glutamylcysteine synthetase and GRX and ICI182,780, a specific inhibitor of ERs, abolished the protective effect of E2 on cell survival as well as the activity of Akt, suggesting that ERβ is involved in the cytoprotection and redox regulation by E2. Transcription of the GRX gene was enhanced by E2. The promoter activity of GRX was up-regulated by an ERβ-dependent element. These results suggest that the GRX/GSH system is involved in the cytoprotective and genomic effects of E2 on the redox state of Akt, a pathway that is mediated, at least in part, by ERβ. This mechanism may also play an antiapoptotic role in cancer cells during carcinogenesis or chemotherapy.

Nuclear Factor Kappa B Dependent Induction of Gamma Glutamylcysteine Synthetase by Ionizing Radiation in T98G Human Glioblastoma Cells

Glioblastoma is one of the most malignant of all neoplasms, and often shows resistance to chemotherapy and radiation therapy. Ionizing radiation activates transcriptional factors, such as nuclear factor kappa-B (NF-kappa B). Previously we found that glutathione (GSH) synthesis is induced by cytokines mediated by NF-kappa B (Urata et al. J. Biol. Chem., 1996). Here, we present direct evidence that NF-kappa B activated by ionizing radiation induces the expression of gamma-glutamylcysteine synthetase (gamma-GCS), the rate limiting enzyme of GSH synthesis, using T98G human glioblastoma cells. T98G cells have approximately 14-times the level of intracellular GSH of NB9 cells, radiation-sensitive neuroblastoma cells. In T98G cells, 30-Gy of ionizing radiation was required for the activation of NF-kappa B on an electrophoretic mobility shift assay and the induction of gamma-GCS mRNA on Northern blots and a nuclear run-on assay. However, when T98G cells were treated with buthionine sulfoximine, 3-Gy of ionizing radiation stimulated the DNA-binding activity of NF-kappa B and the expression of gamma-GCS. We constructed chimeric genes containing various regions of gamma-GCS promoter gene and the coding region for Luciferase. T98G cells transiently transfected with a plasmid containing the gamma-GCS promoter-luciferase construct showed increased luciferase activity when treated with ionizing radiation. The luciferase activity stimulated by ionizing radiation was found in the gamma-GCS promoter containing the NF-kappa B binding site, whereas not in that containing its mutated site. These results suggest that GSH synthesis is upregulated by ionizing radiation mediated by NF-kappa B and a high concentration of GSH in T98G cells causes downregulation of the NF-kappa B-DNA binding activity in response to ionizing radiation. The irresponsiveness of the intracellular signal transduction cascade to irradiation may be a factor in the resistance of T98G cells to radiation therapy.

Doxorubicin-induced DNA intercalation and scavenging by nuclear glutathione S-transferase π

Glutathione S‐transferase (GST) functions in xenobiotic biotransformation and drug metabolism. Increased expression of GSTπ, an isozyme of GST, has been found in cancer cells resistant to doxo‐rubicin hydrochloride (DOX) or cis‐diamminedichloro‐platinum (II) (CDDP), and this increase was believed to be correlated with drug resistance of cancer cells. GST is mainly expressed in the cytoplasm;GSTπ in the nucleus has been reported in cancer cells, but the meaning of this result is not known. Here, we studied changes in the amount of nuclear GSTπ after exposure of cancer cells to anticancer drugs, and role of the nuclear GSTπ in drug resistance. We found nuclear GSTπ in cancer cells resistant to DOX, and the amount of nuclear GSTπ was enhanced by treatment of the cancer cells with DOX or CDDP. We also found that a mushroom lectin, an inhibitor of nuclear transport, inhibited the nuclear transfer of GSTπ, suggesting the existence of a specific transport system for the nuclear transfer of GSTπ. Nuclear GSTπ protected DNA against damage by anticancer drugs. These results suggest a possible role of GSTπ in the acquisition of resistance to anticancer drugs by cancer cells.—Goto, S., Ihara, Y., Urata, Y., Izumi, S., Abe, K., Koji, T., Kondo, T. Doxorubicin‐induced DNA intercalation and scavenging by nuclear glutathione S‐transferase π. FASEB J. 15, 2702–2714 (2001)

Mitochondrial dysfunction, a probable cause of persistent oxidative stress after exposure to ionizing radiation

Several recent studies have suggested that the reactive oxygen species (ROS) generated from mitochondria contribute to genomic instability after exposure of the cells to ionizing radiation, but the mechanism of this process is not yet fully understood. We examined the hypothesis that irradiation induces mitochondrial dysfunction to cause persistent oxidative stress, which contributes to genomic instability. After the exposure of cells to 5 Gy gamma-ray irradiation, we found that the irradiation induced the following changes in a clear pattern of time courses. First, a robust increase of intracellular ROS levels occurred within minutes, but the intracellular ROS disappeared within 30 min. Then the mitochondrial dysfunction was detected at 12 h after irradiation, as indicated by the decreased activity of NADH dehydrogenase (Complex I), the most important enzyme in regulating the release of ROS from the mitochondrial electron transport chain (ETC). Finally, a significant increase of ROS levels in the mitochondria and the oxidation of mitochondrial DNA were observed in cells at 24 h or later after irradiation. Although further experiments are required, results in this study support the hypothesis that mitochondrial dysfunction causes persistent oxidative stress that may contribute to promote radiation-induced genomic instability.

Pirfenidone inhibits TGF-β1-induced over-expression of collagen type I and heat shock protein 47 in A549 cells

BackgroundPirfenidone is a novel anti-fibrotic and anti-inflammatory agent that inhibits the progression of fibrosis in animal models and in patients with idiopathic pulmonary fibrosis (IPF). We previously showed that pirfenidone inhibits the over-expression of collagen type I and of heat shock protein (HSP) 47, a collagen-specific molecular chaperone, in human lung fibroblasts stimulated with transforming growth factor (TGF)-β1 in vitro. The increased numbers of HSP47-positive type II pneumocytes as well as fibroblasts were also diminished by pirfenidone in an animal model of pulmonary fibrosis induced by bleomycin. The present study evaluates the effects of pirfenidone on collagen type I and HSP47 expression in the human alveolar epithelial cell line, A549 cells in vitro.MethodsThe expression of collagen type I, HSP47 and E-cadherin mRNAs in A549 cells stimulated with TGF-β1 was evaluated by Northern blotting or real-time PCR. The expression of collagen type I, HSP47 and fibronectin proteins was assessed by immunocytochemical staining.ResultsTGF-β1 stimulated collagen type I and HSP47 mRNA and protein expression in A549 cells, and pirfenidone significantly inhibited this process. Pirfenidone also inhibited over-expression of the fibroblast phenotypic marker fibronectin in A549 cells induced by TGF-β1.ConclusionWe concluded that the anti-fibrotic effects of pirfenidone might be mediated not only through the direct inhibition of collagen type I expression but also through the inhibition of HSP47 expression in alveolar epithelial cells, which results in reduced collagen synthesis in lung fibrosis. Furthermore, pirfenidone might partially inhibit the epithelial-mesenchymal transition.

Glutaredoxin Modulates Platelet-derived Growth Factor-dependent Cell Signaling by Regulating the Redox Status of Low Molecular Weight Protein-tyrosine Phosphatase

Glutaredoxin (GRX) is a glutathione-disulfide oxidoreductase involved in various cellular functions, including the redox-dependent regulation of certain integral proteins. Here we demonstrated that overexpression of GRX suppressed the proliferation of myocardiac H9c2 cells treated with platelet-derived growth factor (PDGF)-BB. After stimulation with PDGF-BB, the phosphorylation of PDGF receptor (PDGFR) β was suppressed in GRX gene-transfected cells, compared with controls. Conversely, the phosphorylation was enhanced by depletion of GRX by RNA interference. In this study we focused on the role of low molecular weight protein-tyrosine phosphatase (LMW-PTP) in the dephosphorylation of PDGFRβ via a redox-dependent mechanism. We found that depletion of LMW-PTP using RNA interference enhanced the PDGF-BB-induced phosphorylation of PDGFRβ, indicating that LMW-PTP works for PDGFRβ. The enhancement of the phosphorylation of PDGFRβ was well correlated with inactivation of LMW-PTP by cellular peroxide generated in the cells stimulated with PDGF-BB. In vitro, with hydrogen peroxide treatment, LMW-PTP showed decreased activity with the concomitant formation of dithiothreitol-reducible oligomers. GRX protected LMW-PTP from hydrogen peroxide-induced oxidation and inactivation in concert with glutathione, NADPH, and glutathione disulfide reductase. This strongly suggests that retention of activity of LMW-PTP by enhanced GRX expression suppresses the proliferation of cells treated with PDGF-BB via enhanced dephosphorylation of PDGFRβ. Thus, GRX plays an important role in PDGF-BB-dependent cell proliferation by regulating the redox state of LMW-PTP.

Regulation of γ-glutamycysteine synthetase expression in response to oxidative stress

Glutathione (GSH) is synthesized by the activity of two ATP-requiring GSH synthesizing enzymes. Gammaglutamylcysteine synthetase (γ-GCS) is the rate limiting enzyme for the GSH synthesis. γ-GCS is a heterodimer of heavy, catalytic subunit and light, regulatory subunit and responsive to many stresses, such as heat shock, oxidative stress or cytokines. To know the regulation of the expression of γ-GCS gene, in the present study, we show evidences that γ-GCS heavy subunit is upregulated by oxidative stress by ionizing radiation and TNF-α mediated by nuclear factor-κB (NF-κB), and impairment of the expression of γ-GCS by TNF-α in diabetic condition. Furthermore we describe the importance of GSH in the regulation of NF-κB subunits.

Glutathione S-transferase pi localizes in mitochondria and protects against oxidative stress.

Glutathione S-transferases (GSTs) are multifunctional enzymes involved in the protection of cellular components against anti-cancer drugs or peroxidative stress. Previously we found that GST pi, an isoform of the GSTs, is transported into the nucleus. In the present study, we found that GST pi is present in mitochondria as well as in the cytosol and nucleus in mammalian cell lines. A construct comprising the 84 amino acid residues in the amino-terminal region of GST pi and green fluorescent protein was detected in the mitochondria. The mutation of arginine to alanine at positions 12, 14, 19, 71, and 75 in full-length GST pi completely abrogated the ability to distribute in the mitochondria, suggesting that arginine, a positively charged residue, is required for the mitochondrial transport of GST pi. Chemicals generating reactive oxygen species, such as rotenone and antimycin A, decreased cell viability and reduced mitochondrial membrane potential. The overexpression of GST pi diminished these changes. GST pi-targeting siRNA abolished the protective effect of GST pi on the mitochondria under oxidative stress. The findings indicate that the peptide signal is conducive to the mitochondrial localization of GST pi under steady-state conditions without alternative splicing or posttranslational modifications such as proteolysis, suggesting that GST pi protects mitochondria against oxidative stress.