The role of phase II antioxidant enzymes in protecting memory T cells from spontaneous apoptosis in young and old mice

Aging is associated with a functional decline and change in the phenotypic distribution of T cell subsets. The free radical theory of aging is widely promoted as the mechanistic basis for cellular senescence, including the immune system. Although the exact molecular explanation for the role of oxidative stress in cellular senescence is unclear, there is a connection to altered mitochondrial function, both as a contributor and as a target of oxidative stress. In this study we demonstrate that splenic T lymphocytes from old C57BL/6 mice exhibit a significant decline in mitochondrial membrane potential (deltapsi(m)). However, despite this change, there is a lower rate of withdrawal apoptosis in the memory CD4+ and CD8+ T cells. To explain the survival of these long-lived cells against a background of increased oxidative stress, we demonstrate increased glutathione production and phase II enzyme expression, which combine to protect memory T cells against oxidative stress, mitochondrial dysfunction, and cell death. The accumulation of memory T cells with aging explains higher phase II enzyme expression in CD4+ and CD8+ T cells from old mice. Compared with wild-type mice, mice lacking the expression of NF-E2-related factor-2, the transcription factor that regulates phase II enzyme expression, had a significantly enhanced rate of apoptosis in the presence of an oxidative stress stimulus. NF-E2-related factor-2-deficient T cells exhibit a bigger decline in deltapsi(m) and increased reactive oxygen species production than cells from wild-type animals. Taken together, we suggest that phase II enzyme expression and the accompanying increase in intracellular thiol levels protect memory T cells from mitochondrial dysfunction and spontaneous apoptosis.

Combined effects of GSTP1 and MRP1 in melanoma drug resistance

Glutathione-S-transferase Pi1 (GSTP1) and multidrug resistance protein 1 (MRP1) are overexpressed in melanoma, a skin cancer notoriously resistant to all current modalities of cancer therapy. To investigate the involvement of these detoxifying enzymes in the drug resistance of melanoma, an inducible (Tet-On™ system) antisense (AS) RNA strategy was used to specifically inhibit GSTP1 expression in A375 cells, a human melanoma cell line expressing high levels of GSTP1 and MRP1. Stable transfectant clones were established and analysed for GSTP1 inhibition by AS RNA. The clone A375-ASPi1, presenting a specific 40% inhibition of GSTP1 expression in the presence of doxycycline, was selected. Lowering the GSTP1 level significantly increased (about 3.3-fold) the sensitivity of A375-ASPi1 cells to etoposide. Inhibitors of glutathione synthesis (BSO), GSTs (curcumin, ethacrynic acid), and also of MRPs (MK571, sulphinpyrazone) improved the sensitising effect of GSTP1 AS RNA. All these inhibitors had stronger sensitising effects in control cells expressing high GSTP1 level (A375-ASPi1 cells in the absence of doxycycline). In conclusion, GSTP1 can act in a combined fashion with MRP1 to protect melanoma cells from toxic effects of etoposide.

Ethnic group-related differences in CpG hypermethylation of the GSTP1 gene promoter among African-American, Caucasian and Asian patients with prostate cancer

The incidence and mortality of prostate cancer (PC) is approximately 2-fold higher among African-Americans as compared to Caucasians and very low in Asian. We hypothesize that inactivation of GSTP1 genes through CpG methylation plays a role in the pathogenesis of PC, and its ability to serve as a diagnostic marker that differs among ethnic groups. GSTP1 promoter hypermethylation and its correlation with clinico-pathological findings were evaluated in 291 PC (Asian = 170; African-American = 44; Caucasian = 77) and 172 benign prostate hypertrophy samples (BPH) (Asian = 96; African-American = 38; Caucasian = 38) using methylation-specific PCR. In PC cells, 5-aza-dC treatment increased expression of GSTP1 mRNA transcripts. The methylation of all CpG sites was found in 191 of 291 PC (65.6%), but only in 34 of 139 BPH (24.5%). The GSTP1 hypermethylation was significantly higher in PC as compared to BPH in each ethnic group (p < 0.0001). Logistic regression analysis (PC vs. BPH) showed that African-Americans had a higher hazard ratio (HR) (13.361) compared to Caucasians (3.829) and Asian (8.603). Chi-square analysis showed correlation of GSTP1 hypermethylation with pathological findings (pT categories and higher Gleason sum) in Asian PC (p < 0.0001) but not in African-Americans and Caucasian PC. Our results suggest that GSTP1 hypermethylation is a sensitive biomarker in African-Americans as compared to that in Caucasians or Asian, and that it strongly influences tumor progression in Asian PC. Ours is the first study investigating GSTP1 methylation differences in PC among African-American, Caucasian and Asian.

Elevated activity of an Epsilon class glutathione transferase confers DDT resistance in the dengue vector, Aedes aegypti

Glutathione transferases (GSTs) play a central role in the detoxification of xenobiotics such as insecticides and elevated GST expression is an important mechanism of insecticide resistance. In the mosquito, Anopheles gambiae, increased expression of an Epsilon class GST, GSTE2, confers resistance to DDT. We have identified eight GST genes in the dengue vector, Aedes aegypti. Four of these belong to the insect specific GST classes Delta and Epsilon and three are from the more ubiquitously distributed Theta and Sigma classes. The expression levels of the two Epsilon genes, a Theta GST and a previously identified Ae. aegypti GST [Grant and Hammock, 1992. Molecular and General Genetics 234, 169-176] were established for an insecticide susceptible and a resistant strain. We show that the putative ortholog of GSTe2 in Ae. aegypti (AaGSTe2) is over expressed in mosquitoes that are resistant to the insecticides DDT and permethrin. Characterisation of recombinant AaGSTE2-2 confirmed the role of this enzyme in DDT metabolism. In addition, unlike its Anopheles ortholog, AaGSTE2-2 also exhibited glutathione peroxidase activity.

Glutathione S-transferase hGSTM3 and ageing-associated neurodegeneration: relationship to Alzheimer's disease

Glutathione S-transferases (GSTs) are detoxification enzymes that can counter ageing-associated oxidative and chemical stresses. The transcript of a distinct subclass of human GSTs (hGSTM3) was shown by RNA blot analysis to be widely distributed in different regions of adult brain. HPLC profiles indicated that the hGSTM3 subunit was the second most abundant GST subunit in brain. Immunocytochemistry performed with hGSTM3-specific antisera, showed prominent staining of neuritic plaques, neurofibrillary tangles and microglia in sections of hippocampus obtained from patients with Alzheimer's disease. The staining pattern was distinct from that obtained with normal brains. Because hGSTM3 is rich in cysteine residues and readily undergoes S-glutathiolation reactions, deposition of this protein could originate from cross-links produced by oxidative stress.

The chemistry and biology of inhibitors and pro-drugs targeted to glutathione S-transferases

The cytosolic glutathione S-transferases are a family of structurally homologous enzymes with multiple functions, including xenobiotic detoxification, clearance of oxidative stress products, and modulation of cell proliferation and apoptosis signaling pathways. This wide-ranging functional repertoire leads to several possible therapeutic uses for isoform-specific GST inhibitors. These inhibitors may be used, in principle, to modulate tumor cell drug resistance, as sensitizers to therapeutically directed oxidative stress, to enhance cell proliferation and to augment anti-malarial drugs. With increasing knowledge of GST structural and function, rational design strategies and mechanism-based inhibitors have been exploited successfully. However, design of isoform specificity remains a significant challenge in GST inhibitor development. Strategies for further inhibitor design and their possible limitations, along with potential therapeutic uses, are summarized.

Glutathione transferases

This review describes the three mammalian glutathione transferase (GST) families, namely cytosolic, mitochondrial, and microsomal GST, the latter now designated MAPEG. Besides detoxifying electrophilic xenobiotics, such as chemical carcinogens, environmental pollutants, and antitumor agents, these transferases inactivate endogenous alpha,beta-unsaturated aldehydes, quinones, epoxides, and hydroperoxides formed as secondary metabolites during oxidative stress. These enzymes are also intimately involved in the biosynthesis of leukotrienes, prostaglandins, testosterone, and progesterone, as well as the degradation of tyrosine. Among their substrates, GSTs conjugate the signaling molecules 15-deoxy-delta(12,14)-prostaglandin J2 (15d-PGJ2) and 4-hydroxynonenal with glutathione, and consequently they antagonize expression of genes trans-activated by the peroxisome proliferator-activated receptor gamma (PPARgamma) and nuclear factor-erythroid 2 p45-related factor 2 (Nrf2). Through metabolism of 15d-PGJ2, GST may enhance gene expression driven by nuclear factor-kappaB (NF-kappaB). Cytosolic human GST exhibit genetic polymorphisms and this variation can increase susceptibility to carcinogenesis and inflammatory disease. Polymorphisms in human MAPEG are associated with alterations in lung function and increased risk of myocardial infarction and stroke. Targeted disruption of murine genes has demonstrated that cytosolic GST isoenzymes are broadly cytoprotective, whereas MAPEG proteins have proinflammatory activities. Furthermore, knockout of mouse GSTA4 and GSTZ1 leads to overexpression of transferases in the Alpha, Mu, and Pi classes, an observation suggesting they are part of an adaptive mechanism that responds to endogenous chemical cues such as 4-hydroxynonenal and tyrosine degradation products. Consistent with this hypothesis, the promoters of cytosolic GST and MAPEG genes contain antioxidant response elements through which they are transcriptionally activated during exposure to Michael reaction acceptors and oxidative stress.

Dynamics of glutathione conjugation and conjugate efflux in detoxification of the carcinogen, 4-nitroquinoline 1-oxide: contributions of glutathione, glutathione S-transferase, and MRP1

4-Nitroquinoline 1-oxide (NQO) is a reactive electrophile with potent cytotoxic as well as genotoxic activities. NQO forms a conjugate, QO-SG, with glutathione, which greatly reduces its chemical reactivity. Previous studies demonstrated that glutathione S-transferase (GST) P1a-1a and multidrug resistance protein (MRP) 1/2 act in synergy to confer resistance to both cyto- and genotoxicities of NQO, whereas protection afforded by GSTP1a-1a or MRP alone was much less. To better understand the role of glutathione, GSTP1a-1a, and MRP1 in NQO detoxification, we have characterized the kinetics and cofactor requirements of MRP1-mediated transport of QO-SG and NQO. Additionally, using recombinant GSTP1a-1a and physiological conditions, we have examined the enzymatic and nonenzymatic formation of QO-SG. Results show that MRP1 supports efficient transport of QO-SG with a K(m) of 9.5 microM and a V(max) comparable to other good MRP1 substrates. Glutathione or its S-methyl analogue enhanced the rate of (3)H-QO-SG transport, whereas QO-SG inhibited the rate of (3)H-glutathione transport. These data favor a mechanism for glutathione-enhanced, MRP1-mediated QO-SG transport that does not involve cotransport of glutathione. NQO was not transported by MRP1 either alone or in the presence of S-methyl glutathione. Transport of (3)H-NQO was observed in the presence of glutathione, but uptake into MRP1-containing vesicles was entirely attributable to its conjugate, QO-SG, formed nonenzymatically. While the nonenzymatic rate was readily measurable, enzyme catalysis was overwhelmingly dominant in the presence of GSTP1a-1a (rate enhancement factor, (k(cat)/K(m))/k(2), approximately 3 x 10(6)). We conclude that MRP1 supports detoxification of NQO via efficient, glutathione-stimulated efflux of QO-SG. While nonenzymatic QO-SG formation and MRP1-mediated conjugate efflux result in low-level protection from cyto- and genotoxicities, this protection is greatly enhanced by coexpression of GSTP1-1 with MRP1. This result emphasizes the quantitative importance of enzyme-catalyzed conjugate formation, a crucial determinant of high-level, MRP-dependent protection of cells from NQO toxicity.

Microsomal glutathione S-transferase 1 in the retinal pigment epithelium: protection against oxidative stress and a potential role in aging

High oxygen tension, exposure to light, and the biochemical events of vision generate significant oxidative stress in the retina and the retinal pigment epithelium (RPE). Understanding the mechanisms and basis of susceptibility to progressive retinal diseases involving oxidative damage such as age-related macular degeneration (AMD) remains a major challenge. Here microsomal glutathione S-transferase (MGST1) is shown to be a dominant, highly expressed enzyme in bovine and mouse RPE microsomes that displays significant reduction activity toward synthetic peroxides, oxidized RPE lipids, and oxidized retinoids. This enzymatic reduction activity (GPx) can be partially neutralized with a monoclonal anti-MGST1 antibody developed in this study. MGST1-transfected HEK293 cells exhibited greater viability (70 +/- 4% survival) compared with untransfected control cells (46 +/- 4% survival) when challenged with 20 microM H(2)O(2), and greater viability of MGST1-transfected cells following challenge with oxidized docosahexaenoic acid was also observed. Cultured ARPE19 cells transfected with silencing MGST1 siRNAs exhibited lower expression of MGST1 (12% and 26% of the controls) and significantly lower GPx activity (44 +/- 13%) and, thus, were more susceptible to oxidative damage. Immunoblotting revealed that the in vivo expression of MGST1 in mouse RPE decreases 3-4-fold with age, to trace levels in 18-month-old mice. GPx activity in the RPE was also found to be reduced in 12-month-old mice to approximately 67%. These results support an important protective function for MGST1 against oxidative insult in the RPE that decreases with age and suggest that this enzyme may play a role in the development of age-related diseases such as AMD.

Catalytic and structural contributions for glutathione-binding residues in a Delta class glutathione S-transferase

Glutathione S-transferases (GSTs) are dimeric proteins that play a major role in cellular detoxification. The GSTs in mosquito Anopheles dirus species B, an important malaria vector in South East Asia, are of interest because they can play an important role in insecticide resistance. In the present study, we characterized the Anopheles dirus (Ad)GST D3-3 which is an alternatively spliced product of the adgst1AS1 gene. The data from the crystal structure of GST D3-3 shows that Ile-52, Glu-64, Ser-65, Arg-66 and Met-101 interact directly with glutathione. To study the active-site function of these residues, alanine substitution site-directed mutagenesis was performed resulting in five mutants: I52A (Ile-52-->Ala), E64A, S65A, R66A and M101A. Interestingly, the E64A mutant was expressed in Escherichia coli in inclusion bodies, suggesting that this residue is involved with the tertiary structure or folding property of this enzyme. However, the I52A, S65A, R66A and M101A mutants were purified by glutathione affinity chromatography and the enzyme activity characterized. On the basis of steady-state kinetics, difference spectroscopy, unfolding and refolding studies, it was concluded that these residues: (1) contribute to the affinity of the GSH-binding site ('G-site') for GSH, (2) influence GSH thiol ionization, (3) participate in kcat regulation by affecting the rate-limiting step of the reaction, and in the case of Ile-52 and Arg-66, influenced structural integrity and/or folding of the enzyme. The structural perturbations from these mutants are probably transmitted to the hydrophobic-substrate-binding site ('H-site') through changes in active site topology or through effects on GSH orientation. Therefore these active site residues appear to contribute to various steps in the catalytic mechanism, as well as having an influence on the packing of the protein.

Expression of glutathione-S-transferase and its role in plant growth and development in vivo and shoot morphogenesis in vitro

The enzymes glutathione-S-transferases (GSTs, E.C.2.5.1.18) have been associated with detoxification of xenobiotics, limiting oxidative damage and other stress responses in plants. In this study, we report the isolation of a mustard gene, BjGSTF2, homologous to the phi class GSTs and changes in plant growth in vivo and shoot regeneration in vitro were related to GST expression. GST transcripts accumulated differentially in mustard organs, where transcript was most abundant in root. Tissues incubated at high temperature or in the presence of exogenous H2O2, HgCl2, 1-aminocyclopropane-1-carboxylate, salicylic acid and paraquat upregulated GST expression, whereas spermidine was inhibitory. To investigate the in vivo function of GST, transgenic Arabidopsis thalianaplants expressing sense (GST-S6), antisense (GST-A4) and double-stranded BjGSTF2 (GST-DS1) RNAs were generated. GST-S6 was shown to flower two days earlier and was relatively more tolerant to HgCl2 and paraquat, whereas GST-DS1 with least stress tolerance flowered one week later compared to WT and GST-A4. In shoot regeneration response, tissues originated from GST-S6 were highly regenerative, whereas no shoot regeneration was observed in GST-DS1 tissues after 30 days of culture. Results of this study provide the evidence showing that GST plays a role in plant growth and development in vivo and shoot regeneration in vitro.

Functional analysis and localisation of a delta-class glutathione S-transferase from Sarcoptes scabiei

The mite Sarcoptes scabiei causes sarcoptic mange, or scabies, a disease that affects both animals and humans worldwide. Our interest in S. scabiei led us to further characterise a glutathione S-transferase. This multifunctional enzyme is a target for vaccine and drug development in several parasitic diseases. The S. scabiei glutathione S-transferase open reading frame reported here is 684 nucleotides long and yields a protein with a predicted molecular mass of 26 kDa. Through phylogenetic analysis the enzyme was classified as a delta-class glutathione S-transferase, and our paper is the first to report that delta-class glutathione S-transferases occur in organisms other than insects. The recombinant S. scabiei glutathione S-transferase was expressed in Escherichia coli via three different constructs and purified for biochemical analysis. The S. scabiei glutathione S-transferase was active towards the substrate 1-chloro-2,4-dinitrobenzene, though the positioning of fusion partners influenced the kinetic activity of the enzyme. Polyclonal antibodies raised against S. scabiei glutathione S-transferase specifically localised the enzyme to the integument of the epidermis and cavities surrounding internal organs in adult parasites. However, some minor staining of parasite intestines was observed. No staining was seen in host tissues, nor could we detect any antibody response against S. scabiei glutathione S-transferase in sera from naturally S. scabiei infected dogs or pigs. Additionally, the polyclonal sera raised against recombinant S. scabiei glutathione S-transferase readily detected a protein from mites, corresponding to the predicted size of native glutathione S-transferase.

Polymorphisms in glutathione S-transferase omega-1 and AD, vascular dementia, and stroke

BACKGROUND

Glutathione S-transferase omega-1 (GSTO1) protects from oxidative stress, a risk factor for Alzheimer disease (AD), vascular dementia (VaD), and stroke. Polymorphisms in GSTO1 might influence the function of the protein and thus the risk of AD, VaD, and stroke.

METHODS

The GSTO1 gene was screened for variations. The effect of the detected polymorphisms on the risk of AD, VaD, and stroke was evaluated. CSF levels of cholesterol and plasma homocysteine levels were compared according to the GSTO1 genotype.

RESULTS

Two missense polymorphisms in exon 4 of GSTO1 (Ala140Asp and Glu155DeltaGlu) were detected and tested for their association with AD, VaD, and stroke. The Asp/Asp and Ala/Asp genotypes increased the risk of stroke (p = 0.003, OR = 2.1), and the Asp/Asp genotype increased the risk of VaD (p = 0.02, OR = 2.2). GSTO1 polymorphisms did not influence the risk of AD, but the Asp allele influenced the age at onset (p = 0.05). In nondemented probands CSF levels of cholesterol were increased in carriers of the Asp/Asp genotype (p = 0.004); however, in patients with manifest dementia the authors found decreased CSF levels of cholesterol in carriers of the Asp/Asp genotype (p = 0.028). Serum homocysteine levels in stroke patients were higher in carriers of at least one Asp allele (p = 0.011).

CONCLUSION

The GSTO1 Asp allele may be a genetic risk factor for cerebrovascular diseases, and might influence the course of Alzheimer disease, even though effects vary in different studies.

Nuclear glutathione S-transferase pi prevents apoptosis by reducing the oxidative stress-induced formation of exocyclic DNA products

We previously found that nuclear glutathione S-transferase pi (GSTpi) accumulates in cancer cells resistant to anticancer drugs, suggesting that it has a role in the acquisition of resistance to anticancer drugs. In the present study, the effect of oxidative stress on the nuclear translocation of GSTpi and its role in the protection of DNA from damage were investigated. In human colonic cancer HCT8 cells, the hydrogen peroxide (H(2)O(2))-induced increase in nuclear condensation, the population of sub-G(1) peak, and the number of TUNEL-positive cells were observed in cells pretreated with edible mushroom lectin, an inhibitor of the nuclear transport of GSTpi. The DNA damage and the formation of lipid peroxide were dependent on the dose of H(2)O(2) and the incubation time. Immunological analysis showed that H(2)O(2) induced the nuclear accumulation of GSTpi but not of glutathione peroxidase. Formation of the 7-(2-oxo-hepyl)-substituted 1,N(2)-etheno-2'-deoxyguanosine adduct by the reaction of 13-hydroperoxyoctadecadienoic acid (13-HPODE) with 2'-deoxyguanosine was inhibited by GSTpi in the presence of glutathione. The conjugation product of 4-oxo-2-nonenal, a lipid aldehyde of 13-HPODE, with GSH in the presence of GSTpi, was identified by LS/MS. These results suggested that nuclear GSTpi prevents H(2)O(2)-induced DNA damage by scavenging the formation of lipid-peroxide-modified DNA.

Using a residue clash map to functionally characterize protein recombination hybrids

In this article, we introduce a rapid, protein sequence database-driven approach to characterize all contacting residue pairs present in protein hybrids for inconsistency with protein family structural features. This approach is based on examining contacting residue pairs with different parental origins for different types of potentially unfavorable interactions (i.e. electrostatic repulsion, steric hindrance, cavity formation and hydrogen bond disruption). The identified clashing residue pairs between members of a protein family are then contrasted against functionally characterized hybrid libraries. Comparisons for five different protein recombination studies available in the literature: (i) glycinamide ribonucleotide transformylase (GART) from Escherichia coli (purN) and human (hGART), (ii) human Mu class glutathione S-transferase (GST) M1-1 and M2-2, (iii) beta-lactamase TEM-1 and PSE-4, (iv) catechol-2,3-oxygenase xylE and nahH, and (v) dioxygenases (toluene dioxygenase, tetrachlorobenzene dioxygenase and biphenyl dioxygenase) reveal that the patterns of identified clashing residue pairs are remarkably consistent with experimentally found patterns of functional crossover profiles. Specifically, we show that the proposed residue clash maps are on average 5.0 times more effective than randomly generated clashes and 1.6 times more effective than residue contact maps at explaining the observed crossover distributions among functional members of hybrid libraries. This suggests that residue clash maps can provide quantitative guidelines for the placement of crossovers in the design of protein recombination experiments.

Transcription factor Nrf2/MafK regulates rat placental glutathione S-transferase gene during hepatocarcinogenesis

The rat GST-P (placental glutathione S-transferase), a phase II detoxifying enzyme, is not expressed in normal liver cells, but is highly and specifically induced during early hepatocarcinogenesis as well as in hepatocellular carcinoma cells. Results of previous studies indicated that GST-P gene activation was mainly controlled by an enhancer element, GPE1 (GST-P enhancer 1), but the specific activation mechanism of the GST-P gene was not fully understood [Morimura, Suzuki, Hochi, Yuki, Nomura, Kitagawa, Nagatsu, Imagawa and Muramatsu (1993) Proc. Natl. Acad. Sci. U.S.A. 90, 2065-2068; Suzuki, Imagawa, Hirabayashi, Yuki, Hisatake, Nomura, Kitagawa and Muramatsu (1995) Cancer Res. 55, 2651-2655]. In the present study, we investigate the transcription factor Nrf2/MafK heterodimer (where Nrf2 stands for NF-E2 p45-related factor 2) as an activator of the GST-P gene through the action of GPE1 during hepatocarcinogenesis. Electrophoretic mobility-shift assay and footprinting analysis with wild-type GPE1 and GPE1 point mutants showed that the Nrf2/MafK heterodimer specifically bound GPE1. Reporter transfection assays indicated that Nrf2 strongly stimulated GST-P gene expression in mouse F9 embryonal carcinoma cells and H4IIE rat hepatoma cells. Northern-blot analysis indicated that GST-P and Nrf2 mRNA increased in parallel with development of precancerous lesions and hepatocellular carcinoma. Keap1 (Kelch-like ECH-associated protein 1), an inhibitory factor of Nrf2, decreased the activation of GPE1 by Nrf2 and this suppression was restored after treatment with electrophilic compounds. GST-P mRNA expression in H4IIE cells was induced by electrophilic compounds, as was the expression of mRNAs of other phase II detoxifying enzymes. Chromatin immunoprecipitation analyses showed that antibodies both against Nrf2 and against MafK precipitated GPE1 from the chromatin of the pre-neoplastic hepatocytes and rat hepatoma cells (H4IIE and dRLh84), but not from normal hepatocytes. These results indicate that the Nrf2/MafK heterodimer regulates GST-P gene expression during early hepatocarcinogenesis and in hepatoma cells.

[Overexpression of GST gene accelerates the growth of transgenic Arabidopsis under salt stress]

The Suaeda salsa glutathione s-transferase gene (GST) was inserted downstream of the 35S promoter in the plant expression vector pROK II and then was introduced into Arabidopsis thaliana by Agrobacterium tumefaciens through floral dip method. Transformants were selected for their ability to grow on medium containing kanamycin. The fact that the GST gene had been transferred into the Arabidopsis thaliana genome was confirmed by the PCR-Southern blotting analysis. After cultivation, independent homozygous transgenic lines were obtained after selection of T(3) progenies on MS medium containing kanamycin. The expression of the gene transferred into the Arabidopsis thaliana was confirmed by Northern blotting. During salt stress, analysis of total glutathione (both oxidized and reduced type) and biomass of transgenic and wild Arabidopsis. The biomass of transgenic lines (GT) was slightly but significantly greater than that of wild type line (WT), and levels of oxidized glutathione (GSSG) were significantly higher in transgenic lines than in wild type. Therefore, overexpression of GST can increase Arabidopsis growth under salt stress, and this effect can be caused by oxidation of the reduced glutathione (GSH ).

Dynamic evolution of the adenine nucleotide translocase interactome during chemotherapy-induced apoptosis

The mitochondrial permeability transition pore complex (PTPC) is involved in the control of the mitochondrial membrane permeabilization during apoptosis, necrosis and autophagy. Indeed, the adenine nucleotide translocator (ANT) and the voltage-dependent anion channel (VDAC), two major components of PTPC, are the targets of a variety of proapoptotic inducers. Using co-immunoprecipitation and proteomic analysis, we identified some of the interacting partners of ANT in several normal tissues and human cancer cell lines. During chemotherapy-induced apoptosis, some of these interactions were constant (e.g. ANT-VDAC), whereas others changed strongly concomitantly with the dissipation of the mitochondrial transmembrane potential and until nuclear degradation occurred (e.g. Bax, Bcl-2, subunits of the respiratory chain, a subunit of the phosphatase PP2A, phospholipase PLC beta 4 and IP3 receptor). In addition, a glutathione-S-transferase (GST) interacts with ANT in normal tissue, in colon carcinoma cells and in vitro. This interaction is lost during apoptosis induction, suggesting that GST behaves as an endogenous repressor of PTPC and ANT pore opening. Thus, ANT is connected to mitochondrial proteins as well as to proteins from other organelles such as the endoplasmic reticulum forming a dynamic polyprotein complex. Changes within this ANT interactome coordinate the lethal response of cells to apoptosis induction.

Mice deficient in glutathione transferase zeta/maleylacetoacetate isomerase exhibit a range of pathological changes and elevated expression of alpha, mu, and pi class glutathione transferases

Glutathione transferase zeta (GSTZ1-1) is the major enzyme that catalyzes the metabolism of alpha-halo acids such as dichloroacetic acid, a carcinogenic contaminant of chlorinated water. GSTZ1-1 is identical with maleylacetoacetate isomerase, which catalyzes the penultimate step in the catabolic pathways for phenylalanine and tyrosine. In this study we have deleted the Gstz1 gene in BALB/c mice and characterized their phenotype. Gstz1(-/-) mice do not have demonstrable activity with maleylacetone and alpha-halo acid substrates, and other GSTs do not compensate for the loss of this enzyme. When fed a standard diet, the GSTZ1-1-deficient mice showed enlarged liver and kidneys as well as splenic atrophy. Light and electron microscopic examination revealed multifocal hepatitis and ultrastructural changes in the kidney. The addition of 3% (w/v) phenylalanine to the drinking water was lethal for young mice (<28 days old) and caused liver necrosis, macrovesicular steatosis, splenic atrophy, and a significant loss of circulating leukocytes in older surviving mice. GSTZ1-1-deficient mice showed constitutive induction of alpha, mu, and pi class GSTs as well as NAD(P)H:quinone oxidoreductase 1. The overall response is consistent with the chronic accumulation of a toxic metabolite(s). We detected the accumulation of succinylacetone in the serum of deficient mice but cannot exclude the possibility that maleylacetoacetate and maleylacetone may also accumulate.

Differential Roles of Tau Class Glutathione S-Transferases in Oxidative Stress

The plant glutathione S-transferase BI-GST has been identified as a potent inhibitor of Bax lethality in yeast, a phenotype associated with oxidative stress and disruption of mitochondrial functions. Screening of a tomato two-hybrid library for BI-GST interacting proteins identified five homologous Tau class GSTs, which readily form heterodimers between them and BI-GST. All six LeGSTUs were found to be able to protect yeast cells from prooxidant-induced cell death. The efficiency of each LeGSTU was prooxidant-specific, indicating a different role for each LeGSTU in the oxidative stress-response mechanism. The prooxidant protective effect of all six proteins was suppressed in the absence of YAP1, a transcription factor that regulates hydroperoxide homeostasis in Saccharomyces cerevisiae, suggesting a role for the LeGSTUs in the context of the YAP1-dependent stress-responsive machinery. The different LeGSTUs exhibited varied substrate specificity and showed activity against oxidative stress by-products, indicating that their prooxidant protective function is likely related to the minimization of oxidative damage. Taken together, these results indicate that Tau class GSTs participate in a broad network of catalytic and regulatory functions involved in the oxidative stress response.

Transfection with 4-hydroxynonenal-metabolizing glutathione S-transferase isozymes leads to phenotypic transformation and immortalization of adherent cells

4-Hydroxy-2-trans-nonenal (4-HNE), one of the major end products of lipid peroxidation, has been shown to induce apoptosis in a variety of cell lines. It appears to modulate signaling processes in more than one way because it has been suggested to have a role in signaling for differentiation and proliferation. We show for the first time that incorporation of 4-HNE-metabolizing glutathione S-transferase (GST) isozyme, hGSTA4-4, into adherent cell lines HLE B-3 and CCL-75, by either cDNA transfection or microinjection of active enzyme, leads to their transformation. The dramatic phenotypic changes due to the incorporation of hGSTA4-4 include rounding of cells and anchorage-independent rapid proliferation of immortalized, rounded, and smaller cells. Incorporation of the inactive mutant of hGSTA4-4 (Y212F) in cells by either microinjection or transfection does not cause transformation, suggesting that the activity of hGSTA4-4 toward 4-HNE is required for transformation. This is further confirmed by the fact that mouse and Drosophila GST isozymes (mGSTA4-4 and DmGSTD1-1), which have high activity toward 4-HNE and subsequent depletion of 4-HNE, cause transformation whereas human GST isozymes hGSTP1-1 and hGSTA1-1, with minimal activity toward 4-HNE, do not cause transformation. In cells overexpressing active hGSTA4-4, expression of transforming growth factor beta1, cyclin-dependent kinase 2, protein kinase C betaII and extracellular signal regulated kinase is upregulated, whereas expression of p53 is downregulated. These studies suggest that alterations in 4-HNE homeostasis can profoundly affect cell-cycle signaling events.

Structural organization of the murine microsomal glutathione S-transferase gene (MGST1) from the 129/SvJ strain: identification of the promoter region and a comprehensive examination of tissue expression

The structure and regulation of the murine microsomal glutathione transferase gene (MGST1) from the 129/SvJ strain is described and demonstrates considerable difference in nucleotide sequence and consequently in restriction enzyme sites as compared to other mouse strains. A comparison of the amino acid sequence for MGST1 revealed one difference in exon 2 between the 129/SvJ strain (arginine at position 5) and the sequence previously reported for the Balb/c strain (lysine). The promoter region immediately upstream of the dominant first exon is functional, transcriptionally responds to oxidative stress, and is highly homologous to the human region. Oxidative stress also induced the production of endogenous MGST1 mRNA. The tissue-specific expression of MGST1 mRNA was studied, and as anticipated, was indeed highest in liver. There was, however, marked mRNA expression in several tissues not previously studied including smooth muscle, epidymus, ovaries, and endocrine glands in which the expression of various peroxidases is also very high (salivary and thyroid). Overall, there was a good agreement between the mRNA content detected and previous reports of MGST1 activity with the exception of brain tissue.

GlutathioneS-Transferase M1 and Multidrug Resistance Protein 1 Act in Synergy to Protect Melanoma Cells from Vincristine Effects

Previous studies have shown that glutathione S-transferases (GSTs) can operate in synergy with efflux transporters, multi-drug resistance proteins (MRPs), to confer resistance to several carcinogens, mutagens and anticancer drugs. To address the poorly documented role of the GSTM1 in cancer chemoresistance, we used CAL1 human melanoma cells expressing no endogenous GSTM1 and a high level of MRP1. Cells were transfected with an expression vector containing the GSTM1 cDNA, and different clones were selected expressing different levels of GSTM1 (RT-PCR, Western blot, and enzyme activity). Cells overexpressing GSTM1 displayed a 3- to 4-fold increase in resistance to anticancer drugs vincristine (VCR) and chlorambucil (CHB) in proliferation, cytotoxic, and clonogenic survival assays. Inhibitors of MRP1 (sulfinpyrazone, verapamil) and GST (dicumarol, curcumin) completely reversed the GSTM1-associated resistance to VCR, indicating that a MRP efflux function is necessary to potentiate GSTM1-mediated resistance to VCR. Conversely, MRP1 inhibitors had no effect on the sensitivity to CHB. Using immunofluorescence assay, GSTM1 was also shown to protect microtubule network integrity from VCR-induced inhibition of microtubule polymerization. In conclusion, these results show that GSTM1 alone is involved in melanoma resistance to CHB, whereas it can act in synergy with MRP1 to protect cells from toxic effects of VCR.

Physiological role of mGSTA4-4, a glutathione S-transferase metabolizing 4-hydroxynonenal: generation and analysis of mGsta4 null mouse

The lipid peroxidation product 4-hydroxynon-2-enal (4-HNE) is a strong electrophile that forms covalent adducts with proteins and, to a lesser extent, nucleic acids and phospholipids. The generation of 4-HNE appears to be an inevitable consequence of aerobic metabolism. The metabolism of 4-HNE is mainly, although not entirely, conjugative, and proceeds via Michael addition of glutathione to the double bond of 4-HNE. This reaction is catalyzed by specialized glutathione S-transferases (GSTs) exemplified by the murine mGSTA4-4. To study the (patho)physiological effects of 4-HNE in an intact organism, we disrupted the mGsta4 gene in the mouse. The resulting mGsta4 null mouse expressed no mGsta4 mRNA and no corresponding protein, had a reduced ability to conjugate 4-HNE, and had an increased steady-state level of this aldehyde in tissues. The residual conjugating activity for 4-HNE (23-64% depending on the tissue) is probably attributable to isoforms of glutathione S-transferases which have low catalytic efficiency for 4-HNE but are more abundant than mGSTA4-4, or are upregulated upon mGsta4 gene disruption. Mice homozygous for the disrupted mGsta4 allele were viable and appeared normal except for lower litter size, higher fat content in bones, and greater susceptibility to bacterial infection. The null mice had a significantly lower survival time than wild-type controls when chronically treated with relatively low doses of paraquat, a finding consistent with a role of mGSTA4-4 in the defense against oxidative stress. The mouse model should be useful for the study of degenerative conditions in which 4-HNE is postulated to be a contributing factor.