Glutathione S-transferases

Uranium(VI) Complexes of Glutathione Disulfide Forming in Aqueous Solution

The interactions between glutathione disulfide, GSSG, the redox partner and dimer of the intracellular detoxification agent glutathione, GSH, and hexavalent uranium, U(VI), were extensively studied by solution NMR (in D₂O), complemented by time-resolved laser-induced fluorescence and IR spectroscopies. As expected for the hard Lewis acid U(VI), coordination facilitates by the ligands' O-donor carboxyl groups. However, owing to the adjacent cationic α-amino group, the glutamyl-COO reveal monodentate binding, while the COO of the glycyl residues show bidentate coordination. The log K value for the reaction UO₂²⁺ + H₃GSSG^- → UO₂(H₃GSSG)⁺ (pH 3, 0.1 M NaClO₄) was determined for the first time, being 4.81 ± 0.08; extrapolation to infinite dilution gave log K^⊖ = 5.24 ± 0.08. U(VI) and GSSG form precipitates in the whole pD range studied (2-8), showing least solubility for 4 < pD < 6.5. Thus, particularly GSSG, hereby representing also other peptides and small proteins, affects the mobility of U(VI), strongly depending on the speciation of either component.

Mechanism of glutathione transferase P1-1-catalyzed activation of the prodrug canfosfamide (TLK286, TELCYTA)

Canfosfamide (TLK286, TELCYTA) is a prodrug that upon activation by glutathione transferase P1-1 (GST P1-1) yields an anticancer alkylating agent and a glutathione derivative. The rationale underlying the use of TLK286 in chemotherapy is that tumor cells overexpressing GST P1-1 will be locally exposed to the released alkylating agent with limited collateral toxicity to the surrounding normal tissues. TLK286 has demonstrated clinical effects in phase II and III clinical trials for the treatment of malignancies, such as ovarian cancer, nonsmall cell lung cancer, and breast cancer, as a single agent and in combination with other chemotherapeutic agents. In spite of these promising results, the detailed mechanism of GST P1-1 activation of the prodrug has not been elucidated. Here, we propose a mechanism for the TLK286 activation by GST P1-1 on the basis of density functional theory (DFT) and on potential of mean force (PMF) calculations. A catalytic water molecule is instrumental to the activation by forming a network of intermolecular interactions between the active-site Tyr7 hydroxyl and the sulfone and COO(-) groups of TLK286. The results obtained are consistent with the available experimental kinetic data and provide an atomistic understanding of the TLK286 activation mechanism.

Genetic damage, but limited evidence of oxidative stress markers in diethyl maleate-induced glutathione depleted mouse lymphoma L5178Y (TK(+/-)) cell cultures

Depletion of glutathione (GSH) in cells exposed to certain xenobiotics has been proposed to result in oxidative stress, which could lead to damage of cellular macromolecules such as proteins, lipids, and DNA. Diethyl maleate (DEM) is known to conjugate with GSH and rapidly lower cellular GSH levels. The objective of this study was to investigate the influence of DEM-induced GSH depletion on various genotoxicity and gene expression end points in mouse lymphoma L5178Y (TK(+/-)) cell cultures. Cells were exposed to DEM for 4 h at concentrations of 0, 6.7, 13.5, 26.9, 53.8, 107.6, 215.3, and 430.6 µg/mL (0.039-2.5 mM). Genotoxicity was evaluated by examining the induction of in vitro micronuclei (20 h post-treatment) and DNA strand breaks as measured by comet (immediately following treatment), and correlating these observations to cellular GSH levels. In the current study, GSH was decreased more than 50% at the lowest test concentration (6.7 µg/mL) and more than 95% at ≥ 107.6 µg/mL. A significant increase in micronuclei and DNA strand breaks was observed at concentrations of ≥ 26.9 µg/mL. Gene expression of seven apoptosis and oxidative-stress related genes showed significant alterations in only three genes only at the highest test concentration. Quantifiable levels of 8-OH-dG (≥ 2 adducts per 1 × 10(8) NT) were not detected at any treatment concentration. These results demonstrate an association between DEM-induced genotoxicity and GSH depletion in mouse lymphoma L5178Y (TK(+/-)) cells, but not with other oxidative markers.

First molluscan theta-class Glutathione S-Transferase: identification, cloning, characterization and transcriptional analysis post immune challenges

Glutathione S-Transferases (GSTs) are multifunctional cytosolic isoenzymes, distinctly known as phase II detoxification enzymes. GSTs play a significant role in cellular defense against toxicity and have been identified in nearly all organisms studied to date, from bacteria to mammals. In this study, we have identified a full-length cDNA of the theta class GST from Ruditapes philippinarum (RpGSTθ), an important commercial edible molluscan species. RpGSTθ was cloned and the recombinant protein expressed, in order to study its biochemical characteristics and determine its physiological activities. The cDNA comprised an ORF of 693 bp, encoding 231 amino acids with a predicted molecular mass of 27 kDa and an isoelectric point of 8.2. Sequence analysis revealed that RpGSTθ possessed characteristic conserved domains of the GST_N family, Class Theta subfamily (PSSM: cd03050) and GST_C_family Super family (PSSM: cl02776). Phylogenetic analysis showed that RpGSTθ evolutionarily linked with other theta class homologues. The recombinant protein was expressed in Escherichia coli BL21(DE3) cells and the purified enzyme showed high activity with GST substrates like CDNB and 4-NBC. Glutathione dependent peroxidase activity of GST, investigated with cumene hydroperoxide as substrate affirmed the antioxidant property of rRpGSTθ. By quantitative PCR, RpGSTθ was found to be ubiquitously expressed in all tissues examined, with the highest levels occurring in gills, mantle, and hemocytes. Since GSTs may act as detoxification enzymes to mediate immune defense, the effects of pathogen associated molecular pattern, lipopolysaccharide and intact Vibrio tapetis bacteria challenge on RpGSTθ gene transcription were studied. Furthermore, the RpGSTθ expression changes induced by immune challenges were similar to those of the antioxidant defense enzyme manganese superoxide dismutase (RpMnSOD). To our knowledge, RpGSTθ is the first molluscan theta class GST reported, and its immune-related role in Manila clam may provide insights into potential therapeutic targets for protecting this important aquaculture species.

GSTP1 Ile105Val Polymorphism in Serbian Patients with Pancreatic Diseases

The aim of the current preliminary case-control study was to identify glutathione S-transferase P1 (GSTP1) Ile105Val allele and genotype frequency and to evaluate its impact on susceptibility to pancreatic diseases in a Serbian population. This study has encompassed 157 patients with three major types of chronic pancreatic pathology: 47 with pancreatic cancer, 50 with chronic pancreatitis and 60 with type 2 diabetes mellitus, as well as 107 healthy individuals. The presence of GSTP1 Ile105Val polymorphism was analyzed using a PCR-RFLP method. Allele 105Val was less frequent in patients with pancreatic cancer (24.5%) and chronic pancreatitis (24.0%) and slightly more frequent in patients with type 2 diabetes mellitus (31.7%) in comparison to healthy individuals (29.9%), but the differences were not statistically significant. Distribution of Ile105Val polymorphism genotypes differed between the analyzed groups, but differences were also not statistically significant. There are only a few studies regarding the role of GSTP1 Ile105Val polymorphism in pancreatic diseases and their results are inconsistent. The significance of GSTP1 Ile105Val polymorphism for pancreatic pathology remains unclear and further studies are needed in order to elucidate its role in pancreatic diseases.

Glutathione S-transferase P1 Ile105Val polymorphism and colorectal cancer risk: a meta-analysis and HuGE review

Colorectal cancer is the third most common form of cancer and the fourth most frequent cause of cancer deaths worldwide. Its development is influenced by both environmental and genetic factors. The glutathione S-transferase P1 gene (GSTP1) is a particularly attractive candidate for colorectal cancer susceptibility because it codes the enzyme involved in the metabolism of environmental carcinogens such as polycyclic aromatic hydrocarbons (PAHs). However, epidemiologic findings have been inconsistent. To investigate a putative association of GSTP1 Ile105Val polymorphism with the risk of colorectal cancer, we performed a meta-analysis and HuGE review of 16 published case-control studies (involving a total of 4386 colorectal cancer patients and 7127 controls). We used odds ratios (ORs) with 95% confidence intervals (CIs) to assess the strength of the association. Overall, the comparison of Val versus Ile allele showed no differential susceptibility to colorectal cancer (OR=0.98, 95% CI: 0.92-1.04). A protective effect was found in recessive, with an OR of 0.86 (95% CI: 0.76-0.98). Whereas no significant association was observed in either dominant or codominant model. In stratified subgroup analysis, no effect of Val allele was seen in subjects of Caucasian and Asian descent, and in healthy and hospital controls. In conclusion, the meta-analysis suggests that the GSTP1 Ile105Val polymorphism is unlikely to increase considerably the risk of sporadic colorectal cancer, and it should be confirmed in further studies.

Ile105Val GSTP1 polymorphism and susceptibility to colorectal carcinoma in Bulgarian population

BACKGROUND AND AIMS

Etiologically, the sporadic colorectal cancer (CRC) is a complex and multifactorial disease that is linked to both exogenic and endogenic factors. Accumulating evidence indicates that susceptibility to cancers, including CRC, is mediated by genetically determined differences in the effectiveness of detoxification of potential carcinogens. A member of the glutathione-S-transferase (GST) family, GSTP1, is an important candidate for involvement in susceptibility to carcinogen-associated CRC. An A-->G transition in exon 5 of the GSTP1 gene resulting in Ile(105)Val amino acid substitution has been identified. This change leads to alteration in catalytic efficiency of variant enzyme. The aim of the current study was to evaluate the influence of Ile(105)Val GSTP1 polymorphism on susceptibility to CRC.

MATERIALS AND METHODS

The GSTP1 genotyping was conducted in a case-control study of 80 ethnic Bulgarian CRC patients and 126 unaffected controls using polymerase chain reaction restriction fragment length polymorphism method.

RESULTS

A statistically significant case-control difference in genotype frequencies was observed: 0.69 vs 0.54 for Ile/Ile, 0.22 vs 0.39 for Ile/Val, and 0.09 vs 0.07 for Val/Val (p = 0.049). The odds ratio (OR) for Val/Val was close to 1 (0.96, 95%CI: 0.35-2.66, p = 0.942), whereas the OR for Ile/Val was significantly lower, 0.45 (95%CI: 0.24-0.86, p = 0.016), compared to the referent Ile/Ile genotype. Although a prevalence of the GSTP1 variant allele-containing genotypes (Ile/Val or Val/Val) was found in controls than in patients (OR = 0.53, 95%CI: 0.30-0.96, p = 0.035), the allele frequencies did not show significant difference between cases and controls (p = 0.127).

CONCLUSIONS

Based on the obtained protective effect of Ile/Val GSTP1 genotype, we could suggest that Ile(105)Val GSTP1 polymorphism may play some role in susceptibility to CRC.

Expression-Based Discovery of Variation in the Human Glutathione S-Transferase M3 Promoter and Functional Analysis in a Glioma Cell Line Using Allele-Specific Chromatin Immunoprecipitation

Discovery and functional evaluation of biologically significant regulatory single nucleotide polymorphisms (SNP) in carcinogen metabolism genes is a difficult challenge because the phenotypic consequences may be both transient and subtle. We have used a gene expression screening approach to identify a functional regulatory SNP in glutathione S-transferase M3 (GSTM3). Anttila et al. proposed that variation in GSTM3 expression was affected by exposure to cigarette smoke and inheritance of the GSTM1-null genotype. To investigate the mechanism of GSTM3 expression was affected by exposure to cigarette smoke and inheritance of the GSTM1-null genotype. To investigate the mechanism of GSTM3 expression variation, we measured GSTM3 expression in lymphoblast cells from a human Centre d'Etude du Polymorphisme Humain family and observed a low expression phenotype. Promoter sequencing revealed two novel GSTM3 promoter SNPs: A/C and A/G SNPs, 63 and 783 bp upstream of the codon 1 start site, respectively. In this pedigree, the two children homozygous for the −63C/C genotype had 8-fold lower GSTM3 expression relative to the two children with the −63A/A genotype, with no association between A−783G SNP and GSTM3 expression. Further evaluation using genotyped glioma cell lines and with luciferase reporter constructs showed that the −63C allele was associated with lower GSTM3 expression (P &lt; 0.0001 and P &lt; 0.003). RNA pol II chromatin immunoprecipitation was combined with quantitative probed-based allelic discrimination genotyping to provide direct evidence of a 9-fold reduced RNA pol II binding capacity for the −63C allele. These results show that the GSTM3 −63C allele strongly affects gene expression in human cell lines and suggests that individuals who carry the low expression allele may be deficient in glutathione transferase catalyzed biological functions.

Increased resistance to nitrogen mustards and antifolates following in vitro selection of murine fibroblasts and primary hematopoietic cells transduced with a bicistronic retroviral vector expressing the rat glutathione S-transferase A3 and a mutant dihydrofolate reductase

We have constructed a retroviral bicistronic vector, MFG/GID, that transduces the expression of both the A3 isoform of the rat glutathione S-transferase (GST A3), and the tyr-22 variant of the human dihydrofolate reductase (DHFR(L22Y)). Transduction of murine 3T3 fibroblasts with this vector increased their in vitro resistance to chlorambucil (1.8-fold) and trimetrexate (TMTX) (748-fold). TMTX selection of a mixed population of 20% GID-transduced NIH 3T3 cells and 80% control cells resulted in a marked increase in the GST peroxidase activity associated with the GST A3 isoform (17.7-fold). MFG/GID-transduced primary clonogenic murine hematopoietic progenitor cells were likewise more resistant to TMTX and chlorambucil than control beta-gal-transduced cells. Selecting GID-transduced hematopoietic cells with a combination of TMTX and a nucleoside transport inhibitor resulted in a marked increase in resistance upon re-exposure to TMTX (99% survival). Similarly, GID-transduced hematopoietic cells selected with TMTX were more resistant to chlorambucil, with 40% survival at a drug concentration that killed practically all control cells. These results suggest that antifolate-mediated selection of MFG/GID-transduced hematopoietic cells could be used as a mean to enrich the population of transduced cells prior to or following transplantation, thus potentially conferring in vivo chemoprotection to nitrogen mustards and antifolates.

Glutathione S-transferase and drug sensitivity in malignant glioma

Malignant gliomas are largely resistant to current approaches of adjuvant chemotherapy. Gluthatione S-transferases (GST) have been attributed a role in the resistance of cancer cells, e.g., to nitrosoureas. Here, we assessed the expression levels of GST-pi and GST-mu RNA and protein as well as total GST activity in a panel of 12 human glioma cell lines and correlated these data with p53 status, BCL-2 family protein expression and drug sensitivity in these cells. Neither GST protein levels nor GST activity correlated with genetic or functional p53 status or with the expression of various BCL-2 family proteins. No evidence for GST-mediated protection from chemotherapeutic drugs became apparent. In contrast, high levels of GST-pi protein, probably the major source of GST activity in glioma cells, and of total GST activity correlated with enhanced sensitivity to vincristine-induced clonogenic cell death. Expression of GST-pi in human glioblastomas in vivo was confirmed by immunohistochemistry. Neither total, nor cytoplasmic or nuclear, GST-pi immunoreactivity correlated with the response to adjuvant radiotherapy or radiochemotherapy. A comparative analysis of primary and recurrent tumors showed that GST expression was not enhanced by radiochemotherapy in vivo. We conclude that GST does not account for the differential chemosensitivity of glioma cell lines in vitro and does not accumulate in glioma subpopulations that form recurrent tumors after radiochemotherapy in vivo.

Genetic pathways in colorectal and other cancers

Cells from cancers show aberrant behaviour such as unrestrained growth, invasion into adjacent tissue and metastasis. All these features of cancer cell behaviour can be explained in terms of genetic changes and the functional impact of these changes. In this review, colorectal cancer (CRC) is examined as a classical example of multistep carcinogenesis. First there is an overview which shows that cancers develop by a process of somatic evolution. This gives rise to preferred genetic pathways of tumorigenesis. The factors which may influence the development and ultimate choice of genetic pathways are then examined. Next, CRC is studied as a specific disease and the putative genetic pathways are described. The mutations that comprise these pathways and the possible functional sequelae of these are explored. The review concludes with a look at those avenues which may further elucidate the natural history of CRC and lead to improved therapy.

Genetic pathways in colorectal and other cancers

Cells from cancers show aberrant behaviour such as unrestrained growth, invasion into adjacent tissue and metastasis. All these features of cancer cell behaviour can be explained in terms of genetic changes and the functional impact of these changes. In this review, colorectal cancer (CRC) is examined as a classical example of multistep carcinogenesis. First there is an overview which shows that cancers develop by a process of somatic evolution. This gives rise to preferred genetic pathways of tumorigenesis. The factors which may influence the development and ultimate choice of genetic pathways are then examined. Next, CRC is studied as a specific disease and the putative genetic pathways are described. The mutations that comprise these pathways and the possible functional sequelae of these are explored. The review concludes with a look at those avenues which may further elucidate the natural history of CRC and lead to improved therapy.

Different expression of glutathione S-transferase alpha, mu and pi in childhood acute lymphoblastic and myeloid leukaemia

Expression of three major classes of glutathione S-transferases (GSTs), i.e. alpha, mu and pi class, P-glycoprotein (P-gp) and multidrug resistance-associated protein (MRP) were studied in childhood acute lymphoblastic leukaemia (ALL), acute myeloid leukaemia (AML) and normal peripheral blood lymphocytes by flow cytometry. In vitro cytotoxicity of 4-hydroxy-ifosfamide (IFOS), daunorubicin (DNR) and prednisolone (PRED) was assessed by the MTT assay. Expression of alpha, mu and pi class GST did not significantly differ between leukaemic cells from 100 initial and 14 unrelated relapse ALL patients (GSTalpha P=026; GSTmu P=O009; GSTpi P=0.13). The expression of GSTalpha (1.4-fold, P=0.0004), GSTpi (13-fold, P = 0001) and to a lesser extent also GSTmu (1.1-fold, P=0.03) was higher in ALL compared with normal peripheral blood lymphocytes. Expression of GSTmu and GST7pi was significantly higher in 18 AML compared with 100 ALL patients at initial diagnosis (respectively 1.3-fold, P=0.0005 and 2-fold, P<0.0001). In contrast, GSTalpha was median 2-fold lower expressed in the AML samples (P< 0.0001). Expression levels of alpha, mu and pi class GSTs were not related to the degree of resistance to IFOS, DNR and PRED nor to immunophenotype, white blood cell count or age at presentation of childhood ALL. One exception was a remarkably low expression of GSTalpha in IFOS-sensitive samples compared with a heterogenous expression in IFOS-resistant samples (P= 0.02). Expression of GSTpi, but not of GSTalpha or GSTmu, weakly correlated with the expression of MRP (Rs 0.36, P = 0.002, n = 74) but not with P-gp. However, a high expression of both GSTpi and MRP was not associated with in vitro resistance to IFOS, DNR or PRED. The present data suggest that expression of GSTs is not linked to the degree of resistance to IFOS, DNR and PRED or clinical risk factors in childhood ALL. Whether the high expression of GSTmu and GSTpi in AML cells contributes to the relative resistance to IFOS, DNR and PRED compared with ALL samples (P < or = 0.0001) warrants further study.