Glutathione transferases

Chemical modification at subunit 1 of rat kidney Alpha class glutathione transferase with 2,3,5,6-tetrachloro-1,4-benzoquinone: Close structural connectivity between glutathione conjugation activity and non-substrate ligand binding

2, 3, 5, 6-Tetrachloro-1, 4-benzoquinone (TCBQ) is a metabolite of pentachlorophenol known to react with cysteines of glutathione transferases (GSTs). TCBQ treatment of rat kidney rGSTA1-2 and rGSTA1-1 abolishes 70-80% conjugation of glutathione (GSH) to 1-chloro-2, 4-dinitrobenzene and results in strongly correlated quenching of intrinsic fluorescence of Trp-20 (R>0.96). rGSTA2-2 is only inhibited by 25%. Approximately 70% (rGSTA1-1) and 60% (rGSTA1-2) conjugation activity is abolished at TCBQ: GST stoichiometries near 1:1. The inactivation follows a Kitz/Wilson model with K(D) of 4.77+/-2.5microM for TCBQ and k(3) for inactivation of 0.036+/-0.01min(-1). A single tryptic peptide labelled with TCBQ was isolated from kidney rGSTA1-2 containing Cys-17 which we identify as the site of modification. Treatment with more than stoichiometric amounts of TCBQ modified other residues but resulted in only modest further inhibition of catalysis. We interpret these findings in terms of localised steric effects on the relatively rigid alpha-helix 1 adjacent to the catalytic site of subunit 1 possibly affecting the Alpha class-specific alpha-helix 9 which acts as a "lid" on the hydrophobic part of the active site. Homology modelling of rGSTA1-1 modified at Cys-17 of one subunit revealed only modest structural perturbations in the second subunit and tends to exclude global structural effects.

Relationship between genotype and enzyme activity of glutathione S-transferases M1 and P1 in Chinese

Glutathione S-transferases (GSTs) are the major detoxifying Phase II enzyme for eliminating electrophilic compounds. Mutations in GSTM1, GSTP1 and GSTT1 in Caucasian and GSTA1 in Chinese have been found to reduce enzyme activity. However, data on the impact of common genetic polymorphisms of GSTM1 and GSTP1 on enzyme activity in Chinese is lacking. This study aimed to investigate the effect of common GSTP1 and GSTM1 polymorphisms on erythrocyte GST activity in healthy Chinese (n = 196). GSTM1 null mutation (GSTM1*0) was analyzed by a PCR-Multiplex procedure, whereas GSTP1 313A-->G polymorphism (resulting in Ile105Val at codon 105) was analyzed by PCR-restriction fragment length polymorphism (RFLP) analysis. Erythrocyte GST activity was measured using 1-chloro-2,4-dinitro-bezene (CDNB) as the model substrate. The frequency of GSTM1 null genotype was 54.3% and the frequency of GSTP1-Ile/Ile, -Ile/Val, and -Val/Val genotype was 60.7%, 35.2% and 4.1%, respectively, with a frequency of 21.7% for the 105 valine allele. Age, gender and smoking did not significantly affect the erythrocyte GST activities. The mean erythrocyte GST enzyme activity for GSTP1*-Ile/Val genotype group (3.53 +/- 0.63U/gHb) was significantly lower than that for subjects with GSTP1-Ile/Ile genotype (4.25 +/- 1.07U/gHb, P = 0.004), while subjects with the GSTP1-Val/Val genotype had the lowest enzyme activity (2.44 +/- 0.67U/gHb). In addition, the GST activity in carriers of GSTM1*0/GSTP1-Ile/Ile was significantly higher than that of subjects inherited GSTM1*0/GSTP1-Ile/Val or GSTM1*0/GSTP1-Val/Val. However, there is no association between GSTM1 null mutation and reduced enzyme activity. GSTP1 codon 105 mutation led to reduced erythrocyte GST activity in Chinese. A combined GSTP1 and GSTM1 null mutations also resulted in significantly reduced GST activity. Further studies are needed to explore the clinical implications of GSTM1 and GSTP1 polymorphisms.

Several glutathione S-transferase isozymes that protect against oxidative injury are expressed in human liver mitochondria

The mitochondrial environment is rich in reactive oxygen species (ROS) that may ultimately peroxidize membrane proteins and generate unsaturated aldehydes such as 4-hydroxy-2-nonenal (4HNE). We had previously demonstrated the presence of hGSTA4-4, an efficient catalyst of 4HNE detoxification, in human liver mitochondria to the exclusion of the cytosol. In the present study, GSH-affinity chromatography was used in conjunction with biochemical and proteomic analysis to determine the presence of additional cytosolic glutathione S-transferases (GSTs) in human hepatic mitochondria. HPLC-subunit analysis of GSH affinity-purified liver mitochondrial proteins indicated the presence of several potential mitochondrial GST isoforms. Electrospray ionization-mass spectrometry analysis of eluted mitochondrial GST subunits yielded molecular masses similar to those of hGSTP1, hGSTA1 and hGSTA2. Octagonal matrix-assisted laser desorption/ionization time of flight mass spectrometry and proteomics analysis using MS-FIT confirmed the presence of these three GST subunits in mitochondria, and HPLC analysis indicated that the relative contents of the mitochondrial GST subunits were hGSTA1>hGSTA2>hGSTP1. The mitochondrial localization of the alpha and pi class GST subunits was consistent with immunoblotting analysis of purified mitochondrial GST. Enzymatic studies using GSH-purified mitochondrial GST fractions demonstrated the presence of significant GST activity using the nonspecific GST substrate 1-chloro-2,4-dinitrobenzene (CDNB), as well as 4HNE, delta(5)-androstene-3,17-dione (ADI), and cumene hydroperoxide (CuOOH). Interestingly, the specific mitochondrial GST activities toward 4HNE, a highly toxic alpha,beta-unsaturated aldehyde produced during the breakdown of membrane lipids, exceeded that observed in liver cytosol. These observations are suggestive of a role of GST in protecting against mitochondrial injury during the secondary phase of oxidative stress, or modulation of 4HNE-mediated mitochondrial signaling pathways. However, other properties of mitochondrial GST, such as conjugation of environmental chemicals and binding of lipophilic non-substrate xenobiotics and endogenous compounds, remain to be investigated.

Structural and functional characterization of human microsomal prostaglandin E synthase-1 by computational modeling and site-directed mutagenesis

Microsomal prostaglandin (PG) E synthase-1 (mPGES-1) has recently been recognized as a novel, promising drug target for inflammation-related diseases. Functional and pathological studies on this enzyme further stimulate to understand its structure and the structure-function relationships. Using an approach of the combined structure prediction, molecular docking, site-directed mutagenesis, and enzymatic activity assay, we have developed the first three-dimensional (3D) model of the substrate-binding domain (SBD) of mPGES-1 and its binding with substrates prostaglandin H2 (PGH2) and glutathione (GSH). In light of the 3D model, key amino acid residues have been identified for the substrate binding and the obtained experimental activity data have confirmed the computationally determined substrate-enzyme binding mode. Both the computational and experimental results show that Y130 plays a vital role in the binding with PGH2 and, probably, in the catalytic reaction process. R110 and T114 interact intensively with the carboxyl tail of PGH2, whereas Q36 and Q134 only enhance the PGH2-binding affinity. The modeled binding structure indicates that substrate PGH2 interacts with GSH through hydrogen binding between the peroxy group of PGH2 and the -SH group of GSH. The -SH group of GSH is expected to attack the peroxy group of PGH2, initializing the catalytic reaction transforming PGH2 to prostaglandin E2 (PGE2). The overall agreement between the calculated and experimental results demonstrates that the predicted 3D model could be valuable in future rational design of potent inhibitors of mPGES-1 as the next-generation inflammation-related therapeutic.

Activation of coupled Ah receptor and Nrf2 gene batteries by dietary phytochemicals in relation to chemoprevention

The Ah receptor (AhR) is a ligand-activated transcription factor and member of the bHLH/PAS (basic helix-loop-helix/Per-Arnt-Sim) family of chemosensors and developmental regulators. It represents a multifunctional molecular switch involved in regulation of endo- and xenobiotic metabolism, in vascular development and in dioxin-mediated toxicities. Recently, the oxidative stress-protecting Nrf2 has been shown to be a downstream target of the AhR [Miao W, Hu L, Scrivens PJ, Batist G. Transcriptional regulation of NF-E2 p45-regulated factor (NRF2) expression by the aryl hydrocarbon receptor-xenobiotic response element signaling pathway. J Biol Chem 2005;280:20340-8]. This finding offers the possibility that distinct but partially overlapping AhR and Nrf2 gene batteries of Phase II xenobiotic-metabolizing enzymes can be synergistically activated by a number of phytochemicals, acting as selective or mixed activators of target genes. In addition, it is conceivable that AhR-mediated oxidative/electrophile stress may be attenuated by coupled Nrf2 activation. The commentary discusses potentials and limitations of (i) selective Nrf2 and of (ii) synergistic AhR plus Nrf2 activation by phytochemicals in efforts towards chemoprevention of cancer and degenerative diseases, and describes clinical trials providing the expectation that chemopreventive measures may favorably modulate unavoidable endo- and exogenous toxin exposures in high risk populations.

GLUTATHIONES-TRANSFERASE OMEGA 1 AND OMEGA 2 PHARMACOGENOMICS

Glutathione S-transferase omega 1 and omega 2 (GSTO1 and GSTO2) catalyze monomethyl arsenate reduction, the rate-limiting reaction in arsenic biotransformation. As a step toward pharmacogenomic studies of these phase II enzymes, we resequenced human GSTO1 and GSTO2 using DNA samples from four ethnic groups. We identified 31 and 66 polymorphisms in GSTO1 and GSTO2, respectively, with four nonsynonymous-coding single nucleotide polymorphisms (cSNPs) in each gene. There were striking variations among ethnic groups in polymorphism frequencies and types. Expression constructs were created for all eight nonsynonymous cSNPs, as well as a deletion of codon 155 in GSTO1, and those constructs were used to transfect COS-1 cells. Quantitative Western blot analysis, after correction for transfection efficiency, showed a reduction in protein level of greater than 50% for the GSTO1 Tyr32 variant allozyme compared with wild type (WT), whereas levels for the Asp140, Lys208, Val236, and codon 155 deletion variant constructs were similar to that of the WT. For GSTO2, the Tyr130 and Ile158 variant allozymes showed 50 and 84% reductions in levels of expression, respectively, compared with WT, whereas the Ile41 and Asp142 allozymes displayed levels similar to that of WT GSTO2. Rabbit reticulocyte lysate degradation studies showed that the GSTO1 Tyr32 and the GSTO2 Tyr130, Ile158, and Asp142/Ile158 variant allozymes were degraded more rapidly than were their respective WT allozymes. These observations raise the possibility of functionally significant pharmacogenomic variation in the expression and function of GSTO1 and GSTO2.

Drosophila models pioneer a new approach to drug discovery for Parkinson's disease

Despite the prevalence and severity of Parkinson's disease (PD), little is known about the molecular etiology of this disease, and preventative and disease-modifying therapies remain elusive. Recently, linkage studies have begun to identify single-gene mutations that are responsible for rare, heritable forms of PD, which offer an opportunity to gain insight into the molecular mechanisms of this disorder through the creation and analysis of appropriate animal models. One model system that is tractable for these studies is the fruit fly, Drosophila melanogaster. Analysis of several Drosophila models of PD has revealed some surprising insights into the pathogenesis of PD and begun to highlight potential treatment strategies.

Two-photon imaging of glutathione levels in intact brain indicates enhanced redox buffering in developing neurons and cells at the cerebrospinal fluid and blood-brain interface

Glutathione is the major cellular thiol present in mammalian cells and is critical for maintenance of redox homeostasis. However, current assay systems for glutathione lack application to intact animal tissues. To map the levels of glutathione in intact brain with cellular resolution (acute tissue slices and live animals), we have used two-photon imaging of monochlorobimane fluorescence, a selective enzyme-mediated marker for reduced glutathione. Previously, in vitro experiments using purified components and cultured glial cells attributed cellular monochlorobimane fluorescence to a glutathione S-transferase-dependent reaction with GSH. Our results indicate that cells at the cerebrospinal fluid or blood-brain interface, such as lateral ventricle ependymal cells (2.73 +/- 0.56 mm; glutathione), meningeal cells (1.45 +/- 0.09 mm), and astroglia (0.91 +/- 0.08 mm), contain high levels of glutathione. In comparison, layer II cortical neurons contained 20% (0.21 +/- 0.02 mm) the glutathione content of nearby astrocytes. Neuronal glutathione labeling increased 250% by the addition of the cell-permeable glutathione precursor N-acetylcysteine indicating that the monochlorobimane level or glutathione S-transferase activity within neurons was not limiting. Regional mapping showed that glutathione was highest in cells lining the lateral ventricles, specifically ependymal cells and the subventricular zone, suggesting a possible function for glutathione in oxidant homeostasis of developing neuronal progenitors. Consistently, developing neurons in the subgranular zone of dentate gyrus contained 3-fold more glutathione than older neurons found in the neighboring granular layer. In conclusion, mapping of glutathione levels in intact brain demonstrates a unique role for enhanced redox potential in developing neurons and cells at the cerebrospinal fluid and blood-brain interface.

T null and M null genotypes of the glutathione S-transferase gene are risk factor for CAD independent of smoking

Background

The association of the deletion in GSTT1 and GSTM1 genes with coronary artery disease (CAD) among smokers is controversial. In addition, no such investigation has previously been conducted among Arabs.

Methods

We genotyped 1054 CAD patients and 762 controls for GSTT1 and GSTM1 deletion by multiplex polymerase chain reaction. Both CAD and controls were Saudi Arabs.

Results

In the control group (n = 762), 82.3% had the T ^wild M ^wildgenotype, 9% had the T^wild M ^null, 2.4% had the T^null M ^wild and 6.3% had the T^null M ^null genotype. Among the CAD group (n = 1054), 29.5% had the T^wild M ^wild genotype, 26.6% (p < .001) had the T^wild M ^null, 8.3% (p < .001) had the T^null M ^wild and 35.6% (p < .001) had the T^null M ^null genotype, indicating a significant association of the T^wild M ^null, T^null M ^wild and T^null M ^null genotypes with CAD. Univariate analysis also showed that smoking, age, hypercholesterolemia and hypertriglyceridemia, diabetes mellitus, family history of CAD, hypertension and obesity are all associated with CAD, whereas gender and myocardial infarction are not. Binary logistic regression for smoking and genotypes indicated that only M ^null and T^nullare interacting with smoking. However, further subgroup analysis stratifying the data by smoking status suggested that genotype-smoking interactions have no effect on the development of CAD.

Conclusion

GSTT1 and GSTM1 null-genotypes are risk factor for CAD independent of genotype-smoking interaction.

Regulation of drug-metabolizing enzymes and transporters in inflammation

Inflammation and infection have long been known to downregulate the activity and expression of cytochrome P450 (CYP) enzymes involved in hepatic drug clearance. This can result in elevated plasma drug levels and increased adverse effects. Recent information on regulation of human CYP enzymes is presented, as are new developments in our understanding of the mechanisms of regulation. Experiments to study the effects of modulating CYP activities on the inflammatory response have yielded possible insights into the physiological consequences, if not the purpose, of the downregulation. Regulation of hepatic flavin monooxygenases, UDP-glucuronosyltransferases, sulfotransferases, glutathione S-transferases, as well as of hepatic transporters during the inflammatory response, exhibits similarities and differences with regulation of CYPs.

Acetaminophen metabolism does not contribute to gender difference in its hepatotoxicity in mouse

Gender is an important factor in pharmacokinetics and pharmacodynamics. In the current study, gender difference in acetaminophen (APAP)-induced hepatotoxicity has been examined. Male and female mice were injected with a toxic dose of APAP (500 mg/kg, ip). Female mice were resistant to the hepatotoxic effects of APAP, depicted by serum alanine aminotransferase and sorbital dehydrogenase activities and histological analysis. Basal hepatic reduced glutathione (GSH) levels were lower in females than in males, suggesting that basal GSH level may not be a factor in determining the gender difference of APAP hepatotoxicity. APAP metabolism was slower in females than males, revealed by lower levels of glucuronidation and sulfation and higher amounts of free APAP in the livers of female mice. Lower basal Cyp1a2 mRNA levels and lower expression of Cyp1a2 and Cyp3a11 mRNAs after APAP dosing were also observed in females compared with males. However, there was no gender difference in N-acetyl-p-benzoquinone imine covalent binding 2 h after APAP administration, suggesting similar APAP bioactivation between genders. Moreover, liver Gst pi mRNA levels were significantly lower in females than males. This finding is consistent with a previous report, which showed that Gst pi knockout mice are protected from APAP-induced liver toxicity. In conclusion, gender difference of APAP-induced hepatotoxicity is not likely due to APAP metabolism. Perhaps, it is in part due to gender-dependent Gst pi expression. However, the mechanism underlying the association between reduction in Gst pi expression and hepatoprotective effect against APAP toxicity remains to be further explored.

Phosphorylation of glutathione-S-transferase by protein kinase C-alpha implications for affinity-tag purification

Expression and purification of proteins as fusions with glutathione S-transferase (GST) is a standard and widely employed system. In more than 2,500 published studies, GST has been used to facilitate the purification of recombinant proteins, assess protein-protein interactions, and establish protein function. In this report, we provide evidence that GST can be phosphorylated in vitro by protein kinase C-alpha (PKC-alpha) at Ser-93. Therefore, since GST itself may be a target for a number of catalytic enzymes, failure to remove the GST tag from the recombinant protein may lead to inaccurate conclusions.

Structural basis for defects of Keap1 activity provoked by its point mutations in lung cancer

Nrf2 regulates the cellular oxidative stress response, whereas Keap1 represses Nrf2 through its molecular interaction. To elucidate the molecular mechanism of the Keap1 and Nrf2 interaction, we resolved the six-bladed beta propeller crystal structure of the Kelch/DGR and CTR domains of mouse Keap1 and revealed that extensive inter- and intrablade hydrogen bonds maintain the structural integrity and proper association of Keap1 with Nrf2. A peptide containing the ETGE motif of Nrf2 binds the beta propeller of Keap1 at the entrance of the central cavity on the bottom side via electrostatic interactions with conserved arginine residues. We found a somatic mutation and a gene variation in human lung cancer cells that change glycine to cysteine in the DGR domain, introducing local conformational changes that reduce Keap1's affinity for Nrf2. These results provide a structural basis for the loss of Keap1 function and gain of Nrf2 function.

Molecular Profiling of Hepatocellular Carcinoma in Mice with a Chronic Deficiency of HepaticS-Adenosylmethionine: Relevance in Human Liver Diseases

S-adenosylmethionine arises as a central molecule in the preservation of liver homeostasis as a chronic hepatic deficiency results in spontaneous development of steatohepatitis and hepatocellular carcinoma. In the present work, we have attempted a comprehensive analysis of proteins associated with hepatocarcinogenesis in MAT1A knock out mice using a combination of two-dimensional electrophoresis and mass spectrometry, to then apply the resulting information to identify hallmarks of human HCC. Our results suggest the existence of individual-specific factors that might condition the development of preneoplastic lesions. Proteomic analysis allowed the identification of 151 differential proteins in MAT1A-/- mice tumors. Among all differential proteins, 27 changed in at least 50% of the analyzed tumors, and some of these alterations were already detected months before the development of HCC in the KO liver. The expression level of genes coding for 13 of these proteins was markedly decreased in human HCC. Interestingly, seven of these genes were also found to be down-regulated in a pretumoral condition such as cirrhosis, while depletion of only one marker was assessed in less severe liver disorders.

Keap1 recruits Neh2 through binding to ETGE and DLG motifs: characterization of the two-site molecular recognition model

The expression of the phase 2 detoxification enzymes and antioxidant proteins is induced at the transcriptional level by Nrf2 and negatively regulated at the posttranslational level by Keap1 through protein-protein interactions with and subsequent proteolysis of Nrf2. We found that the Neh2 domain of Nrf2 is an intrinsically disordered but biologically active regulatory domain containing a 33-residue central alpha-helix followed by a mini antiparallel beta-sheet. Isothermal calorimetry analysis indicated that one Neh2 molecule interacts with two molecules of Keap1 via two binding sites, the stronger binding ETGE motif and the weaker binding DLG motif. Nuclear magnetic resonance titration study showed that these two motifs of the Neh2 domain bind to an overlapping site on the bottom surface of the beta-propeller structure of Keap1. In contrast, the central alpha-helix of the Neh2 domain does not have any observable affinity to Keap1, suggesting that this region may serve as a bridge connecting the two motifs for the association with the two beta-propeller structures of a dimer of Keap1. Based on these observations, we propose that Keap1 recruits Nrf2 by the ETGE motif and that the DLG motif of the Neh2 domain locks its lysine-rich central alpha-helix in a correct position to benefit ubiquitin signaling.

Evolutionarily conserved structural motifs in bacterial GST (glutathione S-transferase) are involved in protein folding and stability

The bacterium Proteus mirabilis expresses a cytosolic class beta glutathione S-transferase (PmGST B1-1) that is part of a family of multifunctional detoxication enzymes. Like other cytosolic GSTs, PmGST B1-1 possesses two local structural motifs, an N-capping box and a hydrophobic staple motif, both of which are located between amino acids 151 and 156. The N-capping box consists of a reciprocal hydrogen bonding interaction of Thr152 with Asp155, whereas the hydrophobic staple motif consists of a hydrophobic interaction between Phe151 and Ala156. By contrast with other GSTs, PmGST B1-1 displays distinct hydrogen bond interactions in the N-capping box. In mammalian GSTs these structural elements are critical for protein folding and stability. To investigate the role played by these two motifs in a distantly related organism on the evolutionary scale, site-directed mutagenesis was used to generate several mutants of both motifs in PmGST B1-1. All mutants were efficiently overexpressed and purified, but they were quite unstable, although at different levels, indicating that protein folding was significantly destabilized. The analysis of the T152A and D155G variants indicated that the N-capping box motif plays an important role in the stability and correct folding of the enzyme. The analysis of F151A and A156G mutants revealed that the hydrophobic staple motif influences the structural maintenance of the protein and is implicated in the folding process of PmGST B1-1. Finally, the replacement of Thr152 and Asp155, as well as Phe151 and Ala156 residues influences the catalytic efficiency of the enzyme.

An intersubunit lock-and-key 'clasp' motif in the dimer interface of Delta class glutathione transferase

Structural investigations of a GST (glutathione transferase), adGSTD4-4, from the malaria vector Anopheles dirus show a novel lock-and-key 'Clasp' motif in the dimer interface of the Delta class enzyme. This motif also appears to be highly conserved across several insect GST classes, but differs from a previously reported mammalian lock-and-key motif. The aromatic 'key' residue not only inserts into a hydrophobic pocket, the 'lock', of the neighbouring subunit, but also acts as part of the 'lock' for the other subunit 'key'. The 'key' residues from both subunits show aromatic ring stacking with each other in a pi-pi interaction, generating a 'Clasp' in the middle of the subunit interface. Enzyme catalytic and structural characterizations revealed that single amino acid replacements in this 'Clasp' motif impacted on catalytic efficiencies, substrate selectivity and stability. Substitutions to the 'key' residue create strong positive co-operativity for glutathione binding, with a Hill coefficient approaching 2. The lock-and-key motif in general and especially the 'Clasp' motif with the pi-pi interaction appear to play a pivotal role in subunit communication between active sites, as well as in stabilizing the quaternary structure. Evidence of allosteric effects suggests an important role for this particular intersubunit architecture in regulating catalytic activity through conformational transitions of subunits. The observation of co-operativity in the mutants also implies that glutathione ligand binding and dimerization are linked. Quaternary structural changes of all mutants suggest that subunit assembly or dimerization basically manipulates subunit communication.

eEF1B: At the dawn of the 21st century

Translational regulation of gene expression in eukaryotes can rapidly and accurately control cell activity in response to stimuli or when rapidly dividing. There is increasing evidence for a key role of the elongation step in this process. Elongation factor-1 (eEF1), which is responsible for aminoacyl-tRNA transfer on the ribosome, is comprised of two entities: a G-protein named eEF1A and a nucleotide exchange factor, eEF1B. The multifunctional nature of eEF1A, as well as its oncogenic potential, is currently the subject of a number of studies. Until recently, less work has been done on eEF1B. This review describes the macromolecular complexity of eEF1B, its multiple phosphorylation sites and numerous cellular partners, which lead us to suggest an essential role for the factor in the control of gene expression, particularly during the cell cycle.

The structural roles of a conserved small hydrophobic core in the active site and an ionic bridge in domain I of Delta class glutathione S-transferase

GSTs (glutathione S-transferases; E.C.2.5.1.18) are a supergene family of dimeric multifunctional enzymes that have a major role in detoxification pathways. Using a GST from the mosquito Anopheles dirus (adGSTD4-4), we have characterized the enzymatic and physical properties of Leu-6, Thr-31, Leu-33, Ala-35, Glu-37, Lys-40 and Glu-42. These residues generate two motifs located in the N-terminal domain (domain I) that are functionally conserved across GST classes. The aim of this study was to understand the function of these two motifs. The first motif is a small hydrophobic core in the G-site (glutathione-binding site) wall, and the second motif contains an ionic bridge at the N-terminus of the alpha2 helix and is also part of the G-site. The mutations in the small hydrophobic core appear to have structural effects, as shown by the thermal stability, refolding rate and intrinsic fluorescence differences. In the Delta class GST, interactions form an ionic bridge motif located at the beginning of the alpha2 helix. The data suggest that electrostatic interactions in the alpha2 helix are involved in alpha-helix stabilization, and disruption of this ionic bridge interaction changes the movement of the alpha2-helix region, thereby modulating the interaction of the enzyme with substrates. These results show that the small hydrophobic core and ionic bridge have a major impact on structural stabilization, as well as being required to maintain structural conformation of the enzyme. These structural effects are also transmitted to the active site to influence substrate binding and specificity. Therefore changes in the conformation of the G-site wall in the active site appear to be capable of exerting influences on the tertiary structural organization of the whole GST protein.

Glutathione S-transferase polymorphisms: cancer incidence and therapy

The super family of glutathione S-transferases (GSTs) is composed of multiple isozymes with significant evidence of functional polymorphic variation. Over the last three decades, data from cancer studies have linked aberrant expression of GST isozymes with the development and expression of resistance to a variety of chemicals, including cancer drugs. This review addresses how differences in the human GST isozyme expression patterns influence cancer susceptibility, prognosis and treatment. In addition to the well-characterized catalytic activity, recent evidence has shown that certain GST isozymes can regulate mitogen-activated protein kinases or can facilitate the addition of glutathione to cysteine residues in target proteins (S-glutathionylation). These multiple functionalities have contributed to the recent efforts to target GSTs with novel small molecule therapeutics. Presently, at least two drugs are in late-stage clinical testing. The evolving functions of GST and their divergent expression patterns in individuals make them an attractive target for drug discovery.

Effect of selenium-containing compounds on hepatic chemoprotective enzymes in mice

Selenite and organoselenium compounds have been examined at supranutritional levels for their ability to influence the activity and mRNA levels of chemoprotective enzymes in the livers of selenium-sufficient mice and the changes compared to those elicited by oltipraz. Compounds investigated included novel selenocysteine prodrugs that have previously been evaluated for their ability to reduce the tumorigenicity of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) in mice. Following seven daily doses (i.g.), all compounds except 2-methylselenazolidine-4(R)-carboxylic acid (MSCA) increased thioredoxin reductase activity (43-92%) but only for 2-oxoselenazolidine-4(R)-carboxylic acid (OSCA) was there an accompanying increase in mRNA. No compound enhanced glutathione peroxidase activity, although sodium selenite significantly elevated the mRNA of this enzyme. Oltipraz was an efficacious inducer of both thioredoxin reductase and glutathione peroxidase mRNAs. Sodium selenite, selenazolidine-4(R)-carboxylic acid (SCA), and OSCA elevated NAD(P)H-quinone oxidoreductase mRNA but only for OSCA was the elevation in mRNA accompanied by an increase in enzyme activity. L-Selenocystine significantly increased this activity without increasing mRNA levels. Sodium selenite, L-selenocystine, L-selenomethionine, and Se-methyl-L-selenocysteine all enhanced glutathione S-transferase activity. The increased activity with sodium selenite was accompanied by increases in mRNAs of Gst alpha, Gst mu and Gst pi classes, while for L-selenocystine and Se-methyl-L-selenocysteine, only an elevation in the mRNA for the Gst alpha class was observed. Gst alpha and Gst mu class mRNAs were elevated by OSCA without a significant elevation in enzyme activity. SCA and MSCA both elevated a Gst pi mRNA and MSCA elevated Gst mu in addition. By comparison, oltipraz only significantly elevated the mRNA of Gst mu, adding to the conclusion that across the entire study, no selenium compound appears to be acting purely through the antioxidant response typified by oltipraz. Despite their chemical similarity, the three cysteine prodrugs, SCA, MSCA, and OSCA, each produced its own unique pattern of effects on protective enzymes and none was identical to the pattern elicited by sodium selenite, L-selenocystine, L-selenomethionine, and Se-methyl-L-selenocysteine. The study also shows that after 7 days of administration, there was only occasional concordance between elevations in mRNA and enzyme activity for any selenium compound and for any protective enzyme, there was no response in common for all selenium compounds.

Antiglioma activity of 2,2':6',2"-terpyridineplatinum(II) complexes in a rat model--effects on cellular redox metabolism

The mammalian thioredoxin system, comprising the selenoenzyme thioredoxin reductase (TrxR) and the 12-kDa protein thioredoxin (Trx), is implicated in thiol-mediated antioxidant defense and redox regulatory processes including transcriptional control, DNA synthesis, and apoptosis. Cell proliferation supported by the thioredoxin system can be suppressed by TrxR inhibition. In this study, we assessed the effects of the potent hTrxR inhibitors 4-mercaptopyridine (4'-chloro-2,2':6',2"-terpyridine)platinum nitrate (I(23)2N) and 2-mercaptopyridine (4'-chloro-2,2':6',2"-terpyridine)platinum nitrate (I(25)2N) on glioblastoma in a rat model. These compounds show no or little cross-resistance with cisplatin and are thus of great clinical interest. Triple intravenous application of 25-35 mg/kg of the compounds led to a significant decrease of tumor growth as determined by magnetic resonance imaging. Metabolic as well as redox parameters in the blood of the animals were not altered. However, TrxR activity was significantly decreased in the tumor tissue, and redox parameters-including glutathione concentrations, total antioxidant status, and the activities of different antioxidant enzymes-showed tissue-specific variations. As indicated by different apoptotic markers, the antitumor activity of I(23)2N is not mediated by the induction of programmed cell death but rather by hTrxR inhibition and DNA intercalation leading to cell cycle arrest.

Crystallization and preliminary X-ray crystallographic analysis of a highly stable mutant V107A of glutathione transferase from Anopheles dirus in complex with glutathione

An engineered mutant V107A of the dimeric glutathione transferase enzyme from Anopheles dirus (adgstD4-4) was cocrystallized with glutathione substrate using the hanging-drop vapour-diffusion method. The crystal diffracted to 2.47 A resolution in space group P3(2)21 (unit-cell parameters a = b = 49.4, c = 272.4 A). Although the crystal morphology differed from that previously obtained for the wild-type enzyme, the crystal packing was the same. At 318 K, the engineered mutant showed an enzyme stability that was increased by about 32-fold, while possessing a similar catalytic function to the wild type. Structural determination will provide valuable understanding of the role of Val107. This residue is in the dimeric interface and appears to contribute towards enhancing the physical properties of the entire protein.

GSTP1 and GSTA1 polymorphisms interact with cruciferous vegetable intake in colorectal adenoma risk

The possible interplay between cruciferous vegetable consumption, functional genetic variations in glutathione S-transferases (GST) M1, T1, P1, and A1, and colorectal adenomas, was investigated in a Dutch case-control study. The GSTM1 and GSTT1 deletion polymorphisms, and the single nucleotide polymorphisms in GSTP1 (A313G) and in GSTA1 (C-69T) were assessed among 746 cases who developed colorectal adenomas and 698 endoscopy-based controls without any type of colorectal polyps. High and low cruciferous vegetable consumption was defined based on a median split in the control group. High consumption was slightly positively associated with colorectal adenomas [odds ratio (OR) 1.15; 95% confidence interval, 0.92-1.44]. For GSTP1, a positive association with higher cruciferous vegetable intake was only apparent in individuals with the low-activity GSTP1 genotype (GG genotype, OR 1.94; 95% confidence interval, 1.02-3.69). This interaction was more pronounced in men, with higher age and with higher meat intake. The GSTA1 polymorphism may have a modifying role as well: the OR for higher intake compared with lower intake was 1.57 (0.93-2.65) for individuals homozygous for the low expression variant (TT genotype). This seemed to be stronger with younger age and higher red meat intake. Cruciferous vegetable consumption and the combined GSTA1 and GSTP1 genotypes showed a statistically significant interaction (P = 0.034). The GSTM1 and GSTT1 genotypes did not seem to modify the association between cruciferous vegetable intake and colorectal adenomas. In conclusion, GSTP1 and GSTA1 genotypes might modulate the association between cruciferous vegetable intake and colorectal adenomas.

Changes in hepatic cytosolic glutathione S-transferase activity and expression of its class-P during prenatal and postnatal period in rats treated with aflatoxin B1

The effect of aflatoxin B1 (AFB1) on the expression of glutathione S-transferase-P (GST-P) which is the major isoform of GST in developmental stages has been investigated in rat liver during prenatal and postnatal stages. Following administration of AFB1 (0, 0.5, 1.0, 2.0, 3.0 or 4.0 mg/kg bw) injected I.P on day 8.5 of gestation the number of dead or reabsorbed fetuses and malformed embryos were recorded. Then the fetal livers were processed for measurement of total GST and GST-P activities, using 1-chloro-2,4-dinitrobenzene (CDNB) and ethacrynic acid (ETA) as substrates respectively. RT-PCR using rat GST-P specific primers was performed on mRNA extracted from livers. Besides, the effects of AFB1 on hepatic GST and GST-P were assessed in groups of suckling rats directly injected with the toxin. The results show that a single dose of AFB1 (1.0 or 2.0 mg/kg bw) caused approximately 50-60% depletion in fetal liver GST towards CDNB. Postnatal experiments revealed that liver GST (using CDNB as substrate) was significantly induced (approximately 40%) in suckling rats injected with a single dose of AFB1 (3.0 mg AFB1/kg) 24 h before killing. Liver GST-P expression was unaffected due to AFB1 exposures of rats before and after the birth. This finding was substantiated by western blotting and RT-PCR techniques. These data suggest that AFB1-related induction in rat liver total GST after birth may be implicated in protective mechanisms against AFB1. In contrast, inhibition of this enzyme in fetal liver following placental transfer of the carcinogen may explain high susceptibility of fetal cells to trans-plancental aflatoxins. Furthermore, lack of influence of AFB1 on GST-P expression in developmental stages can role out the involvement of this class of GST in AFB1 biotransformation.

The role of genetic polymorphisms in alcoholic liver disease

Chronic alcohol consumption is a major cause of liver cirrhosis which, however, develops in only a minority of heavy drinkers. Evidence from twin studies indicates that genetic factors account for at least 50% of individual susceptibility. The contribution of genetic factors to the development of diseases may be investigated either by means of animal experiments, through linkage studies in families of affected patients, or population based case-control studies. With regard to the latter, single nucleotide polymorphisms of genes involved in the degradation of alcohol, antioxidant defense, necroinflammation, and formation and degradation of extracellular matrix are attractive candidates for studying genotype-phenotype associations. However, many associations in early studies were found to be spurious and could not be confirmed in stringently designed investigations. Therefore, future genotype-phenotype studies in alcoholic liver disease should meet certain requirements in order to avoid pure chance observations due to a lack of power, false functional interpretation, and insufficient statistical evaluation.

Metabolism and transport of oxazaphosphorines and the clinical implications

The oxazaphosphorines including cyclophosphamide (CPA), ifosfamide (IFO), and trofosfamide represent an important group of therapeutic agents due to their substantial antitumor and immuno-modulating activity. CPA is widely used as an anticancer drug, an immunosuppressant, and for the mobilization of hematopoetic progenitor cells from the bone marrow into peripheral blood prior to bone marrow transplantation for aplastic anemia, leukemia, and other malignancies. New oxazaphosphorines derivatives have been developed in an attempt to improve selectivity and response with reduced toxicity. These derivatives include mafosfamide (NSC 345842), glufosfamide (D19575, beta-D-glucosylisophosphoramide mustard), NSC 612567 (aldophosphamide perhydrothiazine), and NSC 613060 (aldophosphamide thiazolidine). This review highlights the metabolism and transport of these oxazaphosphorines (mainly CPA and IFO, as these two oxazaphosphorine drugs are the most widely used alkylating agents) and the clinical implications. Both CPA and IFO are prodrugs that require activation by hepatic cytochrome P450 (CYP)-catalyzed 4-hydroxylation, yielding cytotoxic nitrogen mustards capable of reacting with DNA molecules to form crosslinks and lead to cell apoptosis and/or necrosis. Such prodrug activation can be enhanced within tumor cells by the CYP-based gene directed-enzyme prodrug therapy (GDEPT) approach. However, those newly synthesized oxazaphosphorine derivatives such as glufosfamide, NSC 612567 and NSC 613060, do not need hepatic activation. They are activated through other enzymatic and/or non-enzymatic pathways. For example, both NSC 612567 and NSC 613060 can be activated by plain phosphodiesterase (PDEs) in plasma and other tissues or by the high-affinity nuclear 3'-5' exonucleases associated with DNA polymerases, such as DNA polymerases and epsilon. The alternative CYP-catalyzed inactivation pathway by N-dechloroethylation generates the neurotoxic and nephrotoxic byproduct chloroacetaldehyde (CAA). Various aldehyde dehydrogenases (ALDHs) and glutathione S-transferases (GSTs) are involved in the detoxification of oxazaphosphorine metabolites. The metabolism of oxazaphosphorines is auto-inducible, with the activation of the orphan nuclear receptor pregnane X receptor (PXR) being the major mechanism. Oxazaphosphorine metabolism is affected by a number of factors associated with the drugs (e.g., dosage, route of administration, chirality, and drug combination) and patients (e.g., age, gender, renal and hepatic function). Several drug transporters, such as breast cancer resistance protein (BCRP), multidrug resistance associated proteins (MRP1, MRP2, and MRP4) are involved in the active uptake and efflux of parental oxazaphosphorines, their cytotoxic mustards and conjugates in hepatocytes and tumor cells. Oxazaphosphorine metabolism and transport have a major impact on pharmacokinetic variability, pharmacokinetic-pharmacodynamic relationship, toxicity, resistance, and drug interactions since the drug-metabolizing enzymes and drug transporters involved are key determinants of the pharmacokinetics and pharmacodynamics of oxazaphosphorines. A better understanding of the factors that affect the metabolism and transport of oxazaphosphorines is important for their optional use in cancer chemotherapy.

Cysteine S-conjugate beta-lyases

Cysteine S-conjugate beta-lyases are pyridoxal 5'-phosphate-containing enzymes that catalyze beta-elimination reactions with cysteine S-conjugates that possess an electron-withdrawing group attached at the sulfur. The end products of the beta-lyase reaction are pyruvate, ammonium and a sulfur-containing fragment. If the sulfur-containing fragment is reactive, the parent cysteine S-conjugate may be toxic, particularly to kidney mitochondria. Halogenated alkenes are examples of electrophiles that are bioactivated (toxified) by conversion to cysteine S-conjugates. These conjugates are converted by cysteine S-conjugate beta-lyases to thioacylating fragments. Several cysteine S-conjugates found in allium foods (garlic and onion) are beta-lyase substrates. This finding may account in part for the chemopreventive activity of allium products. This review (1) identifies enzymes that catalyze cysteine S-conjugate beta-lyase reactions, (2) suggests that toxicant channeling may contribute to halogenated cysteine S-conjugate-induced toxicity to mitochondria, and (3) proposes mechanisms that may contribute to the antiproliferative effects of sulfur-containing fragments eliminated from allium-derived cysteine S-conjugates.

Nomenclature for mammalian soluble glutathione transferases

The nomenclature for human soluble glutathione transferases (GSTs) is extended to include new members of the GST superfamily that have been discovered, sequenced, and shown to be expressed. The GST nomenclature is based on primary structure similarities and the division of GSTs into classes of more closely related sequences. The classes are designated by the names of the Greek letters: Alpha, Mu, Pi, etc., abbreviated in Roman capitals: A, M, P, and so on. (The Greek characters should not be used.) Class members are distinguished by Arabic numerals and the native dimeric protein structures are named according to their subunit composition (e.g., GST A1-2 is the enzyme composed of subunits 1 and 2 in the Alpha class). Soluble GSTs from other mammalian species can be classified in the same manner as the human enzymes, and this chapter presents the application of the nomenclature to the rat and mouse GSTs.

Characterization of the omega class of glutathione transferases

The Omega class of cytosolic glutathione transferases was initially recognized by bioinformatic analysis of human sequence databases, and orthologous sequences were subsequently discovered in mouse, rat, pig, Caenorhabditis elegans, Schistosoma mansoni, and Drosophila melanogaster. In humans and mice, two GSTO genes have been recognized and their genetic structures and expression patterns identified. In both species, GSTO1 mRNA is expressed in liver and heart as well as a range of other tissues. GSTO2 is expressed predominantly in the testis, although moderate levels of expression are seen in other tissues. Extensive immunohistochemistry of rat and human tissue sections has demonstrated cellular and subcellular specificity in the expression of GSTO1-1. The crystal structure of recombinant human GSTO1-1 has been determined, and it adopts the canonical GST fold. A cysteine residue in place of the catalytic tyrosine or serine residues found in other GSTs was shown to form a mixed disulfide with glutathione. Omega class GSTs have dehydroascorbate reductase and thioltransferase activities and also catalyze the reduction of monomethylarsonate, an intermediate in the pathway of arsenic biotransformation. Other diverse actions of human GSTO1-1 include modulation of ryanodine receptors and interaction with cytokine release inhibitory drugs. In addition, GSTO1 has been linked to the age at onset of both Alzheimer's and Parkinson's diseases. Several polymorphisms have been identified in the coding regions of the human GSTO1 and GSTO2 genes. Our laboratory has expressed recombinant human GSTO1-1 and GSTO2-2 proteins, as well as a number of polymorphic variants. The expression and purification of these proteins and determination of their enzymatic activity is described.

Acute lymphoblastic leukaemia: a model for the pharmacogenomics of cancer therapy

The use of combination chemotherapy to cure acute lymphoblastic leukaemia (ALL) in children emerged in the 1980s as a paradigm for curing any disseminated cancer, and many of the therapeutic principles were subsequently applied to the treatment of other disseminated human cancers. Similarly, elucidation of the pharmacogenomics of ALL and its translation into new chemotherapeutic approaches might serve as a model for optimizing the treatment of other human cancers. Germline polymorphisms and gene-expression patterns in ALL cells have been linked to the toxicity and efficacy of chemotherapy for ALL and are beginning to emerge as useful clinical diagnostics.

Low detoxification capacity in the ileal pouch mucosa of patients with ulcerative colitis

BACKGROUND

An ileal pouch-anal anastomosis has become the most widely accepted procedure for surgical treatment of patients with ulcerative colitis (UC). The primary function of the ileum within the pouch changes from absorption to storage. Malignancies have been described in the pouch mucosa. The detoxifying glutathione S-transferase (GST) enzymes are involved in the mucosal protection against toxins and carcinogens. Levels of GSTs are much higher in the ileum as compared with the colon. The adaptation of the ileal pouch mucosa into a more colon-like phenotype possibly influences the activity and levels of GST. This study compares the detoxification capacity of GST of the afferent ileal limb mucosa with the ileal pouch mucosa of patients with UC.

METHODS

Biopsies from normal-appearing mucosa from the ileal pouch and the ileal afferent limb were obtained from 18 patients with UC. GST isoforms were quantified by immunoblotting. GST activity was measured spectrophotometrically, and glutathione and cysteine levels were determined by high-performance liquid chromatography.

RESULTS

The GST activity and GSTA1+A2 levels were significantly lower in the pouch compared with the afferent ileal limb of patients with UC, whereas the GSTP1 levels were higher in the pouch. No differences were observed in the levels of GSTM1, GSTT1, glutathione, or cysteine.

CONCLUSIONS

The lower GST detoxification activity in the pouch mucosa of patients with UC may result in higher levels of toxins and carcinogens and thus partly contribute to the risk of developing malignancies in the pouch.

C/EBPα-dependent induction of glutathione S-transferase ζ/maleylacetoacetate isomerase (GSTζ/MAAI) expression during the differentiation of mouse fibroblasts into adipocytes

Western blot analysis of 3T3-L1 adipocyte proteins using an anti-C/EBPalpha antibody detected a 24kD polypeptide in addition to the expected 42 and 30kD isoforms of C/EBPalpha. Mass spectrometric sequencing of the protein following its purification by HPLC and preparative 2D gel electrophoresis identified it as glutathione S-transferase zeta/maleylacetoacetate isomerase (GSTzeta/MAAI). Expression of GSTzeta/MAAI mRNA and protein was induced during the terminal phase of adipogenesis in 3T3-L1 preadipocytes. Ectopic expression of PPARgamma2 in NIH-3T3 fibroblasts exposed to insulin and troglitazone-induced perilipin production, but was incapable of activating GSTzeta/MAAI unless C/EBPalpha was also expressed. Similarly, ectopic expression of C/EBPalpha in PPARgamma +/- or PPARgamma -/- MEFs demonstrated that the C/EBPalpha-dependent induction of GSTzeta/MAAI production was dependent on expression of endogenous PPARgamma. These data suggest a role for GSTzeta/MAAI in mature adipocytes that may be responsive to the thiazolidinedione class of insulin sensitizing PPARgamma ligands.

Molecular cloning and characterization of cDNA encoding a novel cytosolic glutathione transferase from Clonorchis sinensis

Glutathione transferases (GSTs) are a group of multifunction isoenzymes coded by many genes. A cDNA encoding a novel cytosolic GST enzyme was cloned from a Clonorchis sinensis (Cs) adult worm cDNA library by large-scale sequencing. This new cDNA contains 786 bp with a putative open reading frame of 212 amino acids. The deduced amino acid sequence exhibits 61% identity to C. sinensis cytosolic 28-kDa GST. Recombinant CsGST was overexpressed in Escherichia coli BL21(DE3) and was purified by Ni-NTA Agarose. Enzymatic assays showed that the recombinant CsGST had a high activity of 22.7 U mg(-1). The average K (m) of the CsGST for 1-chloro-2,4-dinitrobenzene is 111 microM. Cibacron blue F3GA and albendazole inhibited the CsGST activity with respective average IC(50) of 1.1 and 247.1 microM. It provides a model for the structure and physiological function analysis on CsGST. The nucleotide sequence reported in this paper has been submitted to the GenBank Database with accession number DQ179264.

Increased risk for treatment-related mortality after bone marrow transplantation in GSTM1-positive recipients

Treatment-related mortality (TRM) is a major obstacle to successful allogeneic hematopoietic stem cell transplantation (HSCT). A variety of drugs are used in allogeneic HSCT, and a genetic polymorphism in metabolic enzymes could affect the metabolism of drugs and potentially influence TRM. Here, we focused attention on GSTM1 and GSTT1 enzymes, which metabolize chemotherapeutic agents, chemical carcinogens and by-products of oxidative stress and are absent from more than 50% of some populations. To assess the significance of homozygous GSTM1 and GSTT1 gene deletion in HSCT, we analyzed DNA from 373 patients with hematological disease and their HLA-identical unrelated bone marrow donors using PCR. Homozygous GSTM1 and GSTT1 gene deletions were observed in 56 and 45% of patients, respectively, and 57 and 46% of donors, respectively. There was no significant association between GSTT1 polymorphism and any outcome. However, a GSTM1-positive genotype in recipients was significantly associated with higher TRM and lower survival. These results suggest that a GSTM1-null genotype in recipients protects against TRM after allogeneic HSCT. Further studies are needed to elucidate a mechanism of increased risk for TRM in GSTM1-positive recipients.

Molecular cloning and characterization of alpha-class glutathioneS-transferase gene from the liver of silver carp, bighead carp, and other major chinese freshwater fishes

Two full-length cDNAs encoding glutathione S-transferase (GST) were cloned and sequenced from the hepatopancreas of planktivorous silver carp (Hypophthalmichthys molitrix) and bighead carp (Aristichthys nobilis). The silver carp and bighead carp GST cDNA were 920 and 978 bp in length, respectively, and both contained an open reading frame that encoding 223 amino acids. Partial GST cDNA sequences were also obtained from the liver of grass carp (Ctenopharyngodon idellus), crucian carp (Carassius auratu), mud carp (Cirrhinus molitorella), and tilapia (Oreochromis nilotica). All these GSTs could be classified as alpha-class GSTs on the basis of their amino acid sequence identity with other species. The three-dimensional structure of the silver carp GST was predicted using a computer program, and was found to fit the classical two-domain GST structure. Using the genome walker method, a 875-bp 5'-flanking region of the silver carp GST gene was obtained, and several lipopolysaccharide (LPS) response elements were identified in the promoter region of the phytoplanktivorous fish GST gene, indicating that the GST gene expression of this fish might be regulated by LPS, released from the toxic blue-green algae producing microcystins. To compare the constitutive expression level of the liver GST gene among the six freshwater fishes with completely different tolerance to microcystins, beta-actin was used as control and the ratio GST/beta-actin mRNA (%) was determined as 130.7 +/- 6.6 (grass carp), 103.1 +/- 8.9 (bighead carp), 92.6 +/- 15.0 (crucian carp), 72.3 +/- 7.8 (mud carp), 58.8 +/- 11.5 (silver carp), and 33.6 +/- 13.7 (tilapia). The constitutive expression level of the liver GST gene clearly shows that all the six freshwater fishes had a negative relationship with their tolerance to microcystins: high-resistant fishes (phytoplanktivorous silver carp and tilapia) had the lowest tolerance to microcystins and the high-sensitive fish (herbivorous grass carp) had the highest tolerance to microcystins. Taken together with the reciprocal relationship of constitutive and inducible liver GST expression level in some of the tested fish species to microcystin exposure, a molecular mechanism for different microcystin detoxification abilities of the warm freshwater fishes was discussed.

Loss-of-function mutations in a glutathione S-transferase suppress the prune-Killer of prune lethal interaction

The prune gene of Drosophila melanogaster is predicted to encode a phosphodiesterase. Null alleles of prune are viable but cause an eye-color phenotype. The abnormal wing discs gene encodes a nucleoside diphosphate kinase. Killer of prune is a missense mutation in the abnormal wing discs gene. Although it has no phenotype by itself even when homozygous, Killer of prune when heterozygous causes lethality in the absence of prune gene function. A screen for suppressors of transgenic Killer of prune led to the recovery of three mutations, all of which are in the same gene. As heterozygotes these mutations are dominant suppressors of the prune-Killer of prune lethal interaction; as homozygotes these mutations cause early larval lethality and the absence of imaginal discs. These alleles are loss-of-function mutations in CG10065, a gene that is predicted to encode a protein with several zinc finger domains and glutathione S-transferase activity.

Electrophilic aromatic substituted luciferins as bioluminescent probes for glutathione S-transferase assays

New highly sensitive latent bioluminescent luciferin substrates were designed and synthesized for monitoring mammalian glutathione S-transferase (GST) and Schistosoma japonicum enzyme activities.

High levels of antioxidant enzymatic defence assure good protection against hypoxic stress in spontaneously diabetic rats

Recent data from literature report that reactive oxygen species (ROS) seem to play a crucial role in the etiology of both types I and II diabetes. This may render diabetic individuals more prone to oxidative injury when challenged with hypoxic stress. It is in fact well known that many diabetic complications cause ischaemic episodes, with a consequent reduction in oxygen supply to various tissues and organs. To check this hypothesis, in this work we tested type I diabetic individuals' antioxidant capability towards a hypoxic-mediated oxidative challenge. In particular, spontaneously diabetic and age-matched non-diabetic biobreeding (BB) Wistar rats were submitted to chronic normobaric hypoxia, and the response of antioxidant enzymes, as well as redox-sensitive transcription factor NF-kappaB and p53, were monitored. Results show that diabetic subjects present a dramatic enhancement in the major antioxidant enzymes activities, thus supporting the notion of diabetes-related changes in cellular redox status. This allows diabetic individuals to counteract hypoxia-mediated oxidative challenge better than the non-diabetic counterpart. Also the behaviour of both the redox-sensitive nuclear transcription factor NF-kappaB and p53 protein in response to hypoxic stimulation seems to support the hypothesis of a better ROS scavenging efficiency in diabetics under hypoxic conditions. In conclusion, high levels of antioxidant enzymatic defences in diabetic BB rats reflect a positive adaptive response able to assure an efficient protection not only against chronic, diabetes-mediated reactive oxygen species (ROS) overproduction, but also versus further oxidative damage.

Computational identification of key biological modules and transcription factors in acute lung injury

RATIONALE

Mechanical ventilation augments the acute lung injury (ALI) caused by bacterial products. The molecular pathogenesis of this synergistic interaction remains incompletely understood.

OBJECTIVE

We sought to develop a computational framework to systematically identify gene regulatory networks activated in ALI.

METHODS

We have developed a mouse model in which the combination of mechanical ventilation and intratracheal LPS produces significantly more injury to the lung than either insult alone. We used global gene ontology analysis to determine overrepresented biological modules and computational transcription factor analysis to identify putative regulatory factors involved in this model of ALI.

RESULTS

By integrating expression profiling with gene ontology and promoter analysis, we constructed a large-scale regulatory modular map of the important processes activated in ALI. This map assigned differentially expressed genes to highly overrepresented biological modules, including "defense response," "immune response," and "oxidoreductase activity." These modules were then systematically incorporated into a gene regulatory network that consisted of putative transcription factors, such as IFN-stimulated response element, IRF7, and Sp1, that may regulate critical processes involved in the pathogenesis of ALI.

CONCLUSIONS

We present a novel, unbiased, and powerful computational approach to investigate the synergistic effects of mechanical ventilation and LPS in promoting ALI. Our methodology is applicable to any expression profiling experiment involving eukaryotic organisms.

Glutathione S-transferase pi1 promotes tumorigenicity in HCT116 human colon cancer cells

GSTP1 is a member of the glutathione S-transferase enzyme superfamily, which catalyzes the conjugation of electrophiles with glutathione in the process of detoxification. GSTP1 is widely overexpressed in colorectal cancer, from aberrant crypt foci to advanced carcinomas. Increased expression of GSTP1 is associated with multidrug resistance and a worse clinical prognosis. However, GSTP1-null mice have an increased risk of tumor formation. Thus, the biological function of GSTP1 in colorectal cancer biology remains speculative. In an effort to gain further insights into the role of GSTP1 in tumorigenesis, we disrupted the GSTP1 gene in HCT116 human colorectal cancer cells using targeted homologous recombination. We find that loss of GSTP1 resulted in impaired clonogenic survival and proliferation. Specifically, under growth-limiting conditions, (a) GSTP1 protected HCT116 cells from oxidative stress and associated apoptosis and (b) promoted mitogen-activated protein kinase-extracellular signal-regulated kinase kinase/extracellular signal-regulated kinase-mediated G1-S cell cycle progression. In vivo, GSTP1 was critical for engraftment and growth of HCT116 tumor xenografts. These studies directly show that GSTP1 promotes clonogenic survival and proliferation in HCT116 human colon cancer cells.

Modulation of xenobiotic metabolising enzymes by anticarcinogens -- focus on glutathione S-transferases and their role as targets of dietary chemoprevention in colorectal carcinogenesis

There is evidence that consumption of certain dietary ingredients may favourably modulate biotransformation of carcinogens. Associated with this is the hypothesis that the risk for developing colorectal cancer could be reduced, since its incidence is related to diet. Two main groups of biotransformation enzymes metabolize carcinogens, namely Phase I enzymes, which convert hydrophobic compounds to more water-soluble moieties, and Phase II enzymes (e.g. glutathione S-transferases [GST]), which primarily catalyze conjugation reactions. The conjugation of electrophilic Phase I intermediates with glutathione, for instance, frequently results in detoxification. Several possible colon carcinogens may serve as substrates for GST isoenzymes that can have marked substrate specificity. The conjugated products could be less toxic/genotoxic if GSTs are induced, thereby reducing exposure. Thus, numerous studies have shown that the induction of GSTs by antioxidants enables experimental animals to tolerate exposure to carcinogens. One important mechanism of GST induction involves an antioxidant-responsive response element (ARE) and the transcription factor nuclear factor E2-related factor 2 (Nrf2), which is bound to the Kelch-like ECH associated protein 1 (Keap1) in the cytoplasm. Antioxidants may disrupt the Keap-Nrf2 complex, allowing Nrf2 to translocate to the nucleus and mediate expression of Phase II genes via interaction with the ARE. GSTs are also induced by butyrate, a product of gut flora-derived fermentation of plant foods, which may act via different mechanisms, e.g. by increasing histone acetylation. GSTs are expressed with high inter-individual variability in human colonocytes, which points to large differences in cellular susceptibility to xenobiotics. Enhancing expression of GSTs in human colon tissue could therefore contribute to reducing cancer risks. However, it has not been demonstrated in humans that this mechanism is associated with cancer prevention. In the future, it will be useful to determine GSTs during dietary intervention studies to enhance our understanding of this protective mechanism.

The 110kDa glutathione transferase of Yarrowia lipolytica is encoded by a homologue of the TEF3 gene from Saccharomyces cerevisiae: Cloning, expression, and homology modeling of the recombinant protein

The TEF4 gene of the non-saccharomyces yeast Yarrowia lipolytica encodes an EF1Bgamma protein with structural similarity to the glutathione transferases (GSTs). This 1203bp gene was cloned, over-expressed in Escherichia coli, and the recombinant protein characterized. DNA sequencing of the cloned gene agreed with the recently completed Y. lipolytica genome and showed 100% identity to a previously reported 30-residue N-terminal sequence for a 110kDa Y. lipolytica GST, except that it encoded two additional N-terminal residues (N-Met-Ser-). The recombinant protein (subunit M(r) 52kDa) was found not to possess GST activity with 1-chloro-2,4-dinitrobenzene. Partial tryptic digestion released two fragments of M(r) 22 and 18kDa, which we interpret as N- and C-terminal domains. Homology modeling confirmed that the N-terminal domain of Y. lipolytica TEF4 encodes a GST-like protein.

Glutathione transferases: new functions

Well known as detoxification enzymes, the glutathione transferases also function in prostaglandin and steroid hormone synthesis. New uses for the canonical glutathione transferase fold are becoming apparent; the bacterial stringent starvation protein SspA and the yeast prion protein Ure2p (both transcription factors) were found to adopt this fold, but their roles remain unclear. The intracellular chloride ion channel CLIC1 adopts the canonical glutathione transferase fold in its soluble form and appears to undergo radical structural modification as part of its membrane insertion process. The structures of rat and human mitochondrial glutathione transferases have been solved: they adopt a topology similar to that of bacterial disulfide bond isomerases, leading to the suggestion that they have evolved independently of the canonical enzymes. Recent structural studies of integral membrane glutathione S-transferases from microsomes have revealed common patterns of tertiary and quaternary structure.

Glutathione S-transferase M1 polymorphism and metabolism of sulforaphane from standard and high-glucosinolate broccoli

BACKGROUND

Broccoli consumption is associated with a reduction in the risk of cancer, particularly in persons with a functional glutathione S-transferase M1 allele, as opposed rotrose whose GSTM1 gene has been deleted. Sulforaphane, the major isothiocyanate derived from 4-methylsulfinylbutyl glucosinolate, is thought to be the main agent conferring protection.

OBJECTIVE

We compared sulforaphane metabolism in GSTM1-null and GSTM1-positive subjects after they consumed standard broccoli and high-glucosinolate broccoli (super broccoli).

DESIGN

Sixteen subjects were recruited into a randomized, 3-phase crossover dietary trial of standard broccoli, super broccoli, and water. Liquid chromatography linked to tandem mass spectrometry was used to quantify sulforaphane and its thiol conjugates in plasma and urine.

RESULTS

GSTM1-null subjects had slightly higher, but statistically significant, areas under the curve for sulforaphane metabolite concentrations in plasma, a greater rate of urinary excretion of sulforaphane metabolites during the first 6 h after broccoli consumption, and a higher percentage of sulforaphane excretion 24 h after ingestion than did GSTM1-positive subjects. Consumption of high-glucosinolate broccoli led to a 3-fold greater increase in the areas under the curve and maximum concentrations of sulforaphane metabolites in plasma, a greater rate of urinary excretion of sulforaphane metabolites during the first 6 h after consumption, and a lower percentage of sulforaphane excretion after its ingestion than did the consumption of standard broccoli.

CONCLUSIONS

GSTM1 genotypes have a significant effect on the metabolism of sulforaphane derived from standard or high-glucosinolate broccoli. It is possible that the difference in metabolism may explain the greater protection that GSTM1-positive persons gain from consuming broccoli. The potential consequences of consuming glucosinolate-enriched broccoli for GSTM1-null and -positive persons are discussed.

The galectin-3 gene promoter binding proteins in the liver of rats 48-h post-treatment with CCl4

The present study was undertaken to characterize structure-function relationships of the rat galectin-3 gene promoter especially focusing on the promoter binding proteins included in livers injured with CCl4. Transcription start site determination identified a 66-nucleotide-long exon 1 of this gene. Transient expression analysis using a reporter luciferase gene assigned a region between -161 and -15 to the proximal promoter within the 1-kb region flanking the 5'-end of exon 1. The rat galectin-3 gene promoter possesses a Runx2 binding site and inverted repeats of Sp1 binding motifs in separate regions downstream from -117 as structures resembling those of the mouse galectin-3 gene promoter. The -161/-118 region bound two different proteins. One is a novel protein, a rat version of Purbeta that binds to a guanine nucleotide pair at -145 and -144 to modulate constitutive galectin-3 gene transcription. Southwestern blot analysis using the -161/-118 ligand revealed a signal of a 50-kDa protein in liver nuclear extracts from rats 48-h post-treatment with CCl4, but not in those from Ac2F cells and normal rat livers. The inducible nature of this protein suggested its distinctive role in galectin-3 induction in a liver injured with CCl4. E-box and peroxisome proliferator response element-like motifs reside on separate DNA strands from -140 to -135. Contribution of this segment to the regulation of galectin-3 gene transcription under pathological conditions was suggested, since a DNA ligand with the two motifs simultaneously mutagenized at -136 and -137 was not bound by the 50-kDa protein.

Identification of the insulin signaling cascade in the regulation of alpha-class glutathione S-transferase expression in primary cultured rat hepatocytes

We reported previously that insulin elevated alpha-class glutathione S-transferase (GSTs) protein levels in primary cultured rat hepatocytes (Kim et al., 2003b). In contrast, glucagon down-regulated alpha- and pi-class GST expression, and mechanistic research implicated cAMP and protein kinase A in this process (Kim et al., 2003b). The present study examines the signaling pathways involved in the regulation of alpha-class GST in response to insulin in primary cultured rat hepatocytes. Protein levels of GSTA1/2 and GSTA3/5 and activity of GST toward 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole (NBD) were increased in an insulin concentration-dependent manner. Treatment of cells with the phosphatidylinositol 3-kinase (PI3K) inhibitors wortmannin and LY294002 [2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one] or rapamycin, an inhibitor of mammalian target of rapamycin and ribosomal p70 S6 kinase (p70S6K) phosphorylation, or with an adenovirus containing green fluorescent protein and a dominant-negative and kinase-dead Akt, effectively inhibited the insulin-mediated increase in alpha-class GST expression and GST activity toward NBD. In contrast, PD98059 (2'-amino-3'-methoxyflavone), an inhibitor of mitogen-activated protein kinase kinase, SP600125 (1,9-pyrazoloanthrone), an inhibitor of c-Jun N-terminal kinase, SB203580 [4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)1H-imadazole], an inhibitor of p38 mitogen-activated protein kinase, or bisindolylmaleimide, a broad spectrum inhibitor of protein kinase C, did not inhibit the insulin-mediated increase in alpha-class GST protein levels in hepatocytes. These results show that PI3K/Akt/p70S6K signaling is active in the insulin-mediated up-regulation of the antioxidant defense system and that low insulin levels, as encountered in diabetes, potentially increase the susceptibility of hepatocytes to xenobiotic-mediated and/or oxidative stress-mediated damage.