Distinctive structure of the human GSTM3 gene-inverted orientation relative to the mu class glutathione transferase gene cluster

The Polymorphisms of Genes Encoding Catalytic Antioxidant Proteins Modulate the Susceptibility and Progression of Testicular Germ Cell Tumor

Simple Summary

Testicular cancer is the most common malignancy in the population of young and reproductively active men. The risk factors for its occurrence are not fully elucidated. Undescended testicle remains the main risk factor; however, more precise molecular studies associate genetic variations with susceptibility to testicular tumor development and progression. In this study, we found that specific variations in genes encoding antioxidant defense proteins confer risks of testicular cancer development and progression and, therefore, helps to identify subjects at higher risk, as well as those requiring additional diagnostics and more intensive forms of treatment.

Abstract

The simultaneous analysis of redox biomarkers and polymorphisms encoding for regulatory and catalytic antioxidant proteins was performed in order to evaluate their potential role in the development of testicular germ cell tumor (GCT), as well as the progression of the disease. NRF2 (rs6721961), GSTM3 (rs1332018), SOD2 (rs4880) and GPX3 (rs8177412) polymorphisms were assessed in 88 patients with testicular GCT (52 with seminoma) and 88 age-matched controls. The plasma levels of 8-hydroxy-2′-deoxyguanosine (8-OHdG), thiol groups and the plasma activity of glutathione peroxidase were measured. A significant association between variant GPX3*TC+CC genotype and risk of overall testicular GCT, as well as seminoma development, was found. Moreover, carriers of variant SOD2*TT genotype were at almost 3-fold increased risk of seminoma development. Interestingly, combined SOD2*TT/GPX3*TC+CC genotype conferred a 7-fold higher risk for testicular GCT development. Finally, variant GSTM3*AC+CC genotype was associated with a higher risk for the development of advanced diseased. The presence of assessed genetic variants was not associated with significantly higher levels of redox biomarkers in both testicular GCT patients, as well as in those diagnosed with seminoma. In conclusion, the polymorphic expression of certain antioxidant enzymes might affect susceptibility toward testicular GCT development, as well as the progression of the disease.

GSTP1 and GSTM3 Variant Alleles Affect Susceptibility and Severity of COVID-19

Based on the premise that oxidative stress plays an important role in severe acute respiratory syndrome coronavirus (SARS-CoV-2) infection, we speculated that variations in the antioxidant activities of different members of the glutathione S-transferase family of enzymes might modulate individual susceptibility towards development of clinical manifestations in COVID-19. The distribution of polymorphisms in cytosolic glutathione S-transferases GSTA1, GSTM1, GSTM3, GSTP1 (rs1695 and rs1138272), and GSTT1 were assessed in 207 COVID-19 patients and 252 matched healthy individuals, emphasizing their individual and cumulative effect in disease development and severity. GST polymorphisms were determined by appropriate PCR methods. Among six GST polymorphisms analyzed in this study, GSTP1 rs1695 and GSTM3 were found to be associated with COVID-19. Indeed, the data obtained showed that individuals carrying variant GSTP1-Val allele exhibit lower odds of COVID-19 development (p = 0.002), contrary to carriers of variant GSTM3-CC genotype which have higher odds for COVID-19 (p = 0.024). Moreover, combined GSTP1 (rs1138272 and rs1695) and GSTM3 genotype exhibited cumulative risk regarding both COVID-19 occurrence and COVID-19 severity (p = 0.001 and p = 0.025, respectively). Further studies are needed to clarify the exact roles of specific glutathione S-transferases once the SARS-CoV-2 infection is initiated in the host cell.

GSTM3 Function and Polymorphism in Cancer: Emerging but Promising

Cancer is a major cause of human mortality; however, the molecular mechanisms and proteomic biomarkers that cause tumor progression in malignant tumors are either unknown or only partially revealed. Glutathione S-transferases mu3 (GSTM3), which belongs to a family of xenobiotic detoxifying phase II enzymes, is associated with carcinogen detoxification and the metabolism of exogenous electrophilic substances. It has been reported that GSTM3 has different polymorphisms in various tumor cells and regulates tumorigenesis, cell invasion, metastasis, chemoresistance, and oxidative stress. Deep research into the regulatory mechanisms involved in disorders of GSTM3 expression and the function of GSTM3 in different cancers may facilitate improvements in cancer prevention and targeted therapy. The combination of GSTM3 with other family members can regulate the carcinogenesis and susceptibility to different cancers in humans. GSTM3 also regulates the reactive oxygen species (ROS) and participates in oxidative stress-mediated pathology. Here, we provide a general introduction to GSTM3 in order to better understand the role of GSTM3 in cancer.

Prediction, mapping and validation of tick glutathione S-transferase B-cell epitopes

In search of ways to address the increasing incidence of global acaricide resistance, tick control through vaccination is regarded as a sustainable alternative approach. Recently, a novel cocktail antigen tick-vaccine was developed based on the recombinant glutathione S-transferase (rGST) anti-sera cross-reaction to glutathione S-transferases of Rhipicephalus appendiculatus (GST-Ra), Amblyomma variegatum (GST-Av), Haemaphysalis longicornis (GST-Hl), Rhipicephalus decoloratus (GST-Rd) and Rhipicephalus microplus (GST-Rm). Therefore, the current study aimed to predict the shared B-cell epitopes within the GST sequences of these tick species. Prediction of B-cell epitopes and proteasomal cleavage sites were performed using immunoinformatics algorithms. The conserved epitopes predicted within the sequences were mapped on the homodimers of the respective tick GSTs, and the corresponding peptides were independently used for rabbit immunization experiments. Based on the dot blot assay, the immunogenicity of the peptides and their potential to be recognized by corresponding rGST anti-sera raised by rabbit immunization in a previous work were investigated. This study revealed that the predicted conserved B-cell epitopes within the five tick GST sequences were localized on the surface of the respective GST homodimers. The epitopes of GST-Ra, GST-Rd, GST-Av, and GST-Hl were also shown to contain a seven residue-long peptide sequence with no proteasomal cleavage sites, whereas proteasomal digestion of GST-Rm was predicted to yield a 4-residue fragment. Given that a few proteasomal cleavage sites were found within the conserved epitope sequences of the four GSTs, the sequences could also contain a T-cell epitope. Finally, the peptide and rGST anti-sera reacted against the corresponding peptide, confirming their immunogenicity. These data support the claim that the rGSTs, used in the previous study, contain conserved B-cell epitopes, which elucidates why the rGST anti-sera cross-reacted to non-homologous tick GSTs. Taken together, the data suggest that the B-cell epitopes predicted in this study could be useful for constituting epitope-based GST tick vaccines.

Glutathione transferases, regulators of cellular metabolism and physiology

BACKGROUND

The cytosolic glutathione transferases (GSTs) comprise a super family of proteins that can be categorized into multiple classes with a mixture of highly specific and overlapping functions.

SCOPE OF REVIEW

The review covers the genetics, structure and function of the human cytosolic GSTs with particular attention to their emerging roles in cellular metabolism.

MAJOR CONCLUSIONS

All the catalytically active GSTs contribute to the glutathione conjugation or glutathione dependant-biotransformation of xenobiotics and many catalyze glutathione peroxidase or thiol transferase reactions. GSTs also catalyze glutathione dependent isomerization reactions required for the synthesis of several prostaglandins and steroid hormones and the catabolism of tyrosine. An increasing body of work has implicated several GSTs in the regulation of cell signaling pathways mediated by stress-activated kinases like Jun N-terminal kinase. In addition, some members of the cytosolic GST family have been shown to form ion channels in intracellular membranes and to modulate ryanodine receptor Ca(2+) channels in skeletal and cardiac muscle.

GENERAL SIGNIFICANCE

In addition to their well established roles in the conjugation and biotransformation of xenobiotics, GSTs have emerged as significant regulators of pathways determining cell proliferation and survival and as regulators of ryanodine receptors that are essential for muscle function. This article is part of a Special Issue entitled Cellular functions of glutathione.

Proteomic analysis of gastric cancer and immunoblot validation of potential biomarkers

AIM: To search for and validate differentially expressed proteins in patients with gastric adenocarcinoma.

METHODS: We used two-dimensional gel electrophoresis and mass spectrometry to search for differentially expressed proteins in patients with gastric adenocarcinoma. A set of proteins was validated with immunoblotting.

RESULTS: We identified 30 different proteins involved in various biological processes: metabolism, development, death, response to stress, cell cycle, cell communication, transport, and cell motility. Eight proteins were chosen for further validation by immunoblotting. Our results show that gastrokine-1, 39S ribosomal protein L12 (mitochondrial precursor), plasma cell-induced resident endoplasmic reticulum protein, and glutathione S-transferase mu 3 were significantly underexpressed in gastric adenocarcinoma relative to adjacent non-tumor tissue samples. On the other hand, septin-2, ubiquitin-conjugating enzyme E2 N, and transaldolase were significantly overexpressed. Translationally controlled tumor protein was shown to be differentially expressed only in patients with cancer of the gastric cardia/esophageal border.

CONCLUSION: This work presents a set of possible diagnostic biomarkers, validated for the first time. It might contribute to the efforts of understanding gastric cancer carcinogenesis.

BMD values and GSTM3 gene polymorphisms in combination with GSTT1/GSTM1 genes: a genetic association study in Slovenian elderly

BACKGROUND

Much research suggests that oxidative stress is associated with osteoporosis development. Glutathione S-transferases mu3 (GSTM3) are an important group of detoxifying enzymes that eliminate oxidative stress-related products.

OBJECTIVES

To examine the associations of functional GSTM3 gene polymorphisms (Val224Ile and insdelAGG), their haplotypes and, in combination with GSTT1-null and GSTM1-null polymorphisms, with bone mineral density (BMD) measured at femoral neck (_fn), lumbar spine (_ls) and total hip (_th) and biochemical bone turnover markers in 593 Slovenian elderly women and 119 Slovenian elderly men.

METHODS

GSTM3, GSTT1-null and GSTM1-null gene polymorphisms using sizing denaturing high-performance liquid chromatography, triplex PCR method or real-time PCR; BMD_fn, BMD_ls, BMD_th values using dual energy X-ray absorptiometry, and plasma osteocalcin, serum bone alkaline phosphatase and free soluble tumor necrosis factor (ligand) superfamily, member 11 (sRANKL) concentrations using a solid-phase, two-site chemiluminescent enzyme-labeled immunometric assay, radioimmunoassay or enzyme immunoassay were determined. Statistical analysis was performed using one-way and two-way ANCOVA with adjustment for potential confounders (age, height and weight).

RESULTS

The (borderline) significant differences in BMD_th and BMD_fn values between genotype subgroups of Val224Ile polymorphism of GSTM3 gene (p = 0.057 and 0.053, respectively) with the lowest BMD values among heterozygotes and between 224Ile-insAGG haplotype subgroups (p = 0.048 and 0.019, respectively) were found. Significant differences of BMD_fn between the 224Ile-delAGG haplotype subgroups were observed (p = 0.012). Association of 224Val-insAGG with BMD_fn was of borderline significance (p = 0.062).

CONCLUSION

The results of our study demonstrate the genetic association between detoxifying enzyme GSTM3 and BMD variation, suggesting that the Val224Ile polymorphism and 224Ile-insAGG haplotype could be used for further evaluation of the impact of GSTs gene polymorphisms on osteoporosis, using larger cohorts in searching for osteoporosis risk markers.

Genetic variants in GSTM3 gene within GSTM4-GSTM2-GSTM1-GSTM5-GSTM3 cluster influence breast cancer susceptibility depending on GSTM1

Mu class of Glutathione-S-transferase (GSTM) genes arrange in a tandem on chromosome 1p13.3. The relationship between genetic variants in the GSTM1-5 gene cluster and breast cancer is still ambiguous. In the present study, 17 tagging single-nucleotide polymorphisms (SNPs) covering the GSTMs cluster were originally selected and 11 validated SNPs were used for genotyping 921 cases and 711 controls. The association analyses were performed according to the absence or presence of GSTM1. In the GSTM1-/- group, the allele frequency of one SNP in GSTM3 was significantly different between cases and controls (P = 2.0 x 10(-4), corrected P = 0.001), with odds ratio of 1.75 (95% confidence interval, 1.26-2.44). The observed association in the GSTM1-/- group was successfully replicated in an independent population set (familial/early-onset breast cancer cases, n = 267; community-based controls, n = 667). The combined P values were robust (10(-6)) and the false positive report probability (FPRP) values were low. In contrast, no susceptibility allele/haplotype was identified when the GSTM1 gene was present. Based on epidemiological observations, we further identified two genetic variants in the GSTM3 locus accounting for differential expression of GSTM3 in normal breast tissues by such means as altering binding of RNA-pol-II. Protective genotypes were correlated with higher GSTM3 expression levels. In conclusion, SNPs/haplotypes in the GSTM3 gene within the GSTMs gene cluster are likely to contribute to breast cancer risk when the GSTM1 is absent. We infer that GSTM3 catalyzing ability in normal breast tissue might protect against breast carcinogenesis.

The proximal promoter governs germ cell-specific expression of the mouse glutathione transferase mGstm5 gene

To explain the tissue-selective expression patterns of a distinct subclass of glutathione S-transferase (GST), transgenic mice expressing EGFP under control of a 2 kb promoter sequence in the 5'-flanking region of the mGstm5 gene were produced. The intent of the study was to establish whether the promoter itself or whether posttranscriptional mechanisms, particularly at the levels of mRNA translation and stability or protein targeting, based on unique properties of mGSTM5, determine the restricted expression pattern. Indeed, the transgene expression was limited to testis as the reporter was not detected in somatic tissues such as brain, kidney or liver, indicating that the mGstm5 proximal promoter is sufficient to target testis-specific expression of the gene. EGFP expression was also more restricted vis-a-vis the natural mGstm5 gene and exclusively found in germ but not in somatic cells. Real-time quantitative PCR (qPCR) data were consistent with alternate transcription start sites in which the promoter region of the natural mGstm5 gene in somatic cells is part of exon 1 of the germ cell transcript. Thus, the primary transcription start site for mGstm5 is upstream of a TATA box in testis and downstream of this motif in somatic cells. The 5' flanking sequence of the mGstm5 gene imparts germ cell-specific transcription.

Glutathione S-transferase variants and hypertension

OBJECTIVES

Glutathione S-transferases are involved in defences against oxidative stress. We have recently demonstrated reduced expression of glutathione S-transferase mu type 1 (Gstm1) in a rat model of hypertension. Here, we examine the association between GSTM variants and hypertension in human.

METHODS

We screened 83 patients with hypertension and 46 controls for single nucleotide polymorphisms in GSTM genes by TaqMan single nucleotide polymorphism genotyping assays and DNA sequencing. We then genotyped 753 trios from the Medical Research Council British Genetics of Hypertension Study transmission disequilibrium test cohort for 10 single nucleotide polymorphisms and the GSTM1 deletion and examined renal GSTM expression in a cohort of 27 hypertensive and 18 normotensive subjects. Finally, we attempted to replicate our findings in 1675 cases and 1654 controls from the Medical Research Council British Genetics of Hypertension Study case-control cohort.

RESULTS

We identified two major linkage disequilibrium blocks including GSTM4/GSTM2 and GSTM5/GSTM3 separated by the GSTM1 gene. In the British Genetics of Hypertension transmission disequilibrium test resource, a single nucleotide polymorphism in the 3' region of GSTM5 (rs11807) was found to be associated with hypertension (P = 0.01) with the T-allele being over-transmitted to hypertensive offspring. GSTM5 mRNA expression was found to be reduced in kidney tissue of subjects homozygous for the T-allele of rs11807 as compared to C-allele homozygous and CT heterozygous subjects (P = 0.02). Nevertheless, rs11807 was not associated with hypertension in the British Genetics of Hypertension case-control cohort (P = 0.61).

CONCLUSION

Our studies do not provide an evidence of an association of GSTM gene variants with hypertension in humans. They, however, illustrate the essential role of replication of initial results in a second cohort.

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.

Estradiol metabolites as isoform-specific inhibitors of human glutathione S-transferases

Numerous studies have suggested that the lifetime dose of unopposed estrogen is a significant risk factor for breast and uterine cancer. Estradiol (E2) plays a putative role as a tumor promoter through interaction with estrogen receptors but can also be metabolized to redox active and/or mutagenic semiquinones and quinones. Similarly, equine estrogens (components of certain hormone replacement therapy preparations) are converted to quinone metabolites. The use of hormone replacement therapy has also been associated with increased breast and endometrial cancer risk. Recently, metabolites of certain equine estrogens have been shown to inhibit human glutathione S-transferases (hGSTs). Since E2 and equine estrogens share similarities in other biological interactions, we have investigated the inhibitory capacity of endogenously formed E2 metabolites toward various hGSTs. The quinone metabolite of 2-hydroxy-17-beta-estradiol (2-OH-E2) was synthesized, and inhibition of hGST-mediated biotransformation of model substrates was assessed. Inhibition of purified recombinant hGSTM1-1 and hGSTA1-1 occurred in a concentration-dependent manner with IC50-values of approximately 250 and 350 nM, respectively. hGSTs M2-2, P1-1 and T1-1 were significantly less sensitive to inhibition. Specific glutathione-conjugates of the estrogen quinone also potently inhibited hGSTM1-1 and hGSTA1-1. Mass spectrometry data indicate that the inhibition was not mediated via covalent adduction. Although we have demonstrated hGST inhibition via E2 metabolites, our findings indicate that the isoform specificity and potency of GST inhibition by endogenous E2 metabolites is different than that of equine estrogen metabolites.

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

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

Glutathione S-transferase genotypes and cancer risk

Over 500 studies have examined the association of genetic variants of glutathione S-transferases with various malignancies yielding inconsistent results. The genotyping was based on PCR assays that identified the GSTM1 and GSTT1 null (-/-) genotypes but did not distinguish homozygous wild-type +/+ and heterozygous +/- individuals. Complete GSTM1 and GSTT1 genotyping can be accomplished by recently developed assays [Cancer Res. 64 (2004) 1233-1236; Pharmacogenetics 10 (2000) 557-565] that allow the definition of +/+, +/-, and -/- genotypes by separate identification of the respective GSTM1 and GSTT1 wild-type and null alleles. Application of the new GSTM1 assay to a breast cancer case-control study revealed that the relative risk of breast cancer for the +/+ genotype compared to the -/- genotype was 2.83 (95% confidence interval 1.45-5.59; P=0.002), suggesting a protective effect of the GSTM1 deletion [Cancer Res. 64 (2004) 1233-1236]. Regardless of the explanation for the association between the +/+ genotype and increased breast cancer risk, these results warrant application of true GSTM1 and GSTT1 genotyping to additional or previously analyzed groups with breast cancer or other malignancies.

Organ distribution and kinetics of Glutathione transferase from African river prawn, Macrobrachium vollenhovenii (Herklots)

The distribution of glutathione transferase (GST) in the major organs of African river prawn (Macrobrachium vollenhovenii) was studied. All the organs studied had GST activity. The specific activity of the extract from the hepatopancreas was highest while that from the muscle lowest. Purified GST from the hepatopancreas which could conjugate glutathione (GSH) with only 1-chloro-2,4-dinitrobenzene (CDNB) and 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole (NBDCl) among some electrophilic substrates tested, had a K(m)(NBDCl) of 2.2+/-0.12 mmol l(-1) while the K(m)CDNB was 2.03+/-0.29 mmol l(-1). Chloride ion, a product of the enzymatic reaction readily inhibited the conjugation of CDNB with GSH with an I50 of 0.12 mmol l(-1), whereas chloride ion up to 0.6 mol l(-1) had no inhibitory effect on the conjugation of GSH with NBDCl. However, nitrite inhibited the two reactions but the K(i) for the conjugation of NBDCl was lower than the K(i) for the conjugation of CDNB. The enzyme had an optimum temperature of 40 degrees C and an activation energy of 35.1 kJ/mol. The overall results show that M. vollenhovenii GST (mvGST) uses different mechanisms for different electrophilic substrates. The high K(m) of mvGST for the electrophilic substrates may be a special physiological adaptation for effective xenobiotic detoxication.

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 < 0.0001 and P < 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.

Phylogenies of Glutathione Transferase Families

The best known glutathione transferase family, with its class-alpha, -mu, -pi, -omega, -sigma, -theta, and -zeta subdivisions, is only one of four, or perhaps five, ancient protein families that conjugate glutathione or use a glutathione intermediate: (1) the cytoplasmic family, (2) the mitochondrial (kappa) family, (3) the microsomal (MAPEG) family, which may actually be two separate families, and (4) the fosphomycin/glyoxalase family. Although the cytoplasmic family is perhaps the most diverse, all four of these families have homologs in both prokaryotes and eukaryotes; it is striking that at least three, and perhaps as many as five, different protein folds capable of binding and positioning glutathione for a nucleophilic attack emerged more than 2 billion years ago. This chapter presents phylogenies for the four (or five) glutathione transferase families, focusing on the statistical evidence for homology (and non-homology).

A Subclass of Mu Glutathione S‐Transferases Selectively Expressed in Testis and Brain

A subclass of glutathione S-transferases (GSTs), exemplified by the human hGSTM3 and rodent GSTM5 subunits, has properties that distinguish it from other Mu class GSTs. Thus, they originate from single copy genes that are in an inverted order and, apart from the coding regions, share little sequence homology relative to the others in the Mu cluster. The genes for this M3/M5 subgroup encode for proteins that are in many ways unique, including their extended lengths with key amino acid substitutions. The M3/M5 subclass is selectively expressed in testis and brain and could function differently from the other GSTs.

Molecular epidemiology of sporadic breast cancer. The role of polymorphic genes involved in oestrogen biosynthesis and metabolism

The major known risk factors for female breast cancer are associated with prolonged exposure to increased levels of oestrogen. The predominant theory relates to effects of oestrogen on cell growth. Enhanced cell proliferation, induced either by endogenous or exogenous oestrogens, increases the number of cell divisions and thereby the possibility for mutation. However, current evidence also supports a role for oxidative metabolites, in particular catechol oestrogens, in the initiation of breast cancer. As observed in drug and chemical metabolism, there is considerable interindividual variability (polymorphism) in the conjugation pathways of both oestrogen and catechol oestrogens. These person-to-person differences, which are attributed to polymorphisms in the genes encoding for the respective enzymes, might define subpopulations of women with higher lifetime exposure to hormone-dependent growth promotion, or to cellular damage from particular oestrogens and/or oestrogen metabolites. Such variation could explain a portion of the cancer susceptibility associated with reproductive effects and hormone exposure. In this paper the potential role of polymorphic genes encoding for enzymes involved in oestrogen biosynthesis (CYP17, CYP19, and 17beta-HSD) and conversion of the oestrogen metabolites and their by-products (COMT, CYP1A1, CYP1B1, GSTM1, GSTM3, GSTP1, GSTT1 and MnSOD) in modulating individual susceptibility to breast cancer are reviewed. Although some of these low-penetrance genes appeared as good candidates for risk factors in the etiology of sporadic breast cancer, better designed and considerably larger studies than the majority of the studies conducted so far are evidently needed before any firm conclusions can be drawn.

Identification of residues in glutathione transferase capable of driving functional diversification in evolution. A novel approach to protein redesign

Evolution of protein function can be driven by positive selection of advantageous nonsynonymous codon mutations that arise following gene duplication. By observing the presence and degree of site-specific positive selection for change between divergent paralogs, residue positions responsible for functional changes can be identified. We applied this analysis to genes encoding Mu class glutathione transferases, which differ widely in substrate specificities. Approximately 3% of the amino acid residue positions, both near to and distant from the active site, are under statistically significant positive selection for change. Relevant human glutathione transferase (GST) M1-1 and GST M2-2 codons were mutated. A chemically conservative threonine to serine mutation in GST M2-2 elicited a 1,000-fold increase in specific activity with the GST M1-1-specific substrate trans-stilbene oxide and a 30-fold increase with the alternative epoxide substrates styrene oxide and nitrophenyl glycidol. The reverse mutation in GST M1-1 resulted in reciprocal decreases in activity. Thus, identification of hypervariable codon positions can be a powerful aid in the redesign of protein function, lessening the requirement for extensive mutagenesis or structural knowledge and sometimes suggesting mutations that would otherwise be considered functionally conservative.

Mu class glutathione S-transferase mRNA isoform expression in acute lymphoblastic leukaemia

Glutathione S-transferases (GSTs) are implicated in cytotoxic drug resistance in leukaemia. In a previous study, expression of mu class GST (GSTM) was associated with poor prognosis in childhood acute lymphoblastic leukaemia (ALL), however, that study did not differentiate between individual GSTM isoforms. This study, therefore, investigated individual GSTM isoform expression in ALL blasts at the mRNA level. Leukaemic blasts from 21 children with ALL were studied. Interindividual variation in the pattern of GSTM mRNA isoform expression was demonstrated. GSTM2 transcript was expressed in all patients in contradistinction to GSTM5, which was not detected in any sample. GSTM3 and GSTM4 expression varied between individuals, with GSTM3 expressed in 62% and GSTM4 in 24% of patients. Lymphoblast expression of GSTM3 was positively related to good prognosis whereas expression of GSTM4 was not related to clinical outcome in this small cohort. No relationship was demonstrated with established indicators of prognosis, including sex, age, immunophenotype and presenting white cell count. The results suggest that expression of GSTM3 may play a role in determining prognosis in childhood ALL and could provide more information for accurate stratification of treatment. Further studies are required to determine whether there is a causal relationship between GSTM3 expression and clinical outcome.

Rat glutathione S-transferase M4-4: an isoenzyme with unique structural features including a redox-reactive cysteine-115 residue that forms mixed disulphides with glutathione

Although the existence of the rat glutathione S-transferase (GST) M4 (rGSTM4) gene has been known for some time, the corresponding protein has not as yet been purified from tissue. A recombinant rGSTM4-4 was thus expressed in Escherichia coli from a chemically synthesized rGSTM4 gene. The catalytic efficiency (k(cat)/K(m)) of rGSTM4-4 for the 1-chloro-2,4-dinitrobenzene (CDNB) conjugation reaction was 50-180-fold less than that of the well-characterized homologous rGSTM1-1, and the pH optimum for the same reaction was 8.5 for rGSTM4-4 as opposed to 6.5 for rGSTM1-1. Molecular-modelling studies predict that key substitutions in the helix alpha4 region of rGSTM4-4 account for this pK(a) difference. A notable structural feature of rGSTM4-4 is the Cys-115 residue in place of the Tyr-115 of other Mu-class GSTs. The thiol group of Cys-115 is redox-reactive and readily forms a mixed disulphide even with GSH; the S-glutathiolated form of the enzyme is catalytically active. A mutated rGSTM4-4 (C115Y) had 6-10-fold greater catalytic efficiency than the wild-type rGSTM4-4. Trp-45, a conserved residue among Mu-class GSTs, is essential in rGSTM4-4 for both enzyme activity and binding to glutathione affinity matrices. Antibodies directed against either the unique C-terminal undecapeptide or tridecapeptide of rGSTM4 reacted with rat and mouse liver GSTs to reveal an orthologous mouse GSTM4-4 present at low basal levels but which is inducible in mouse liver. This subclass of rodent Mu GSTs with redox-active Cys-115 residues could have specialized physiological functions in response to oxidative stress.

Glutathione S-transferase polymorphisms and their biological consequences

Two supergene families encode proteins with glutathione S-transferase (GST) activity: the family of soluble enzymes comprises at least 16 genes; the separate family of microsomal enzymes comprises at least 6 genes. These two GST families are believed to exert a critical role in cellular protection against oxidative stress and toxic foreign chemicals. They detoxify a variety of electrophilic compounds, including oxidized lipid, DNA and catechol products generated by reactive oxygen species-induced damage to intracellular molecules. An increasing number of GST genes are being recognized as polymorphic. Certain alleles, particularly those that confer impaired catalytic activity (e.g. GSTM1(*)0, GSTT1(*)0), may be associated with increased sensitivity to toxic compounds. GST polymorphisms may be disease modifying; for example, in subgroups of patients with basal cell carcinoma or bronchial hyper-responsiveness, certain GST appear to exert a statistically significant and biologically relevant impact on disease susceptibility.

An asparagine-phenylalanine substitution accounts for catalytic differences between hGSTM3-3 and other human class mu glutathione S-transferases

The hGSTM3 subunit, which is preferentially expressed in germ-line cells, has the greatest sequence divergence among the human mu class glutathione S-transferases. To determine a structural basis for the catalytic differences between hGSTM3-3 and other mu class enzymes, chimeric proteins were designed by modular interchange of the divergent C-terminal domains of hGSTM3 and hGSTM5 subunits. Replacement of 24 residues of the C-terminal segment of either subunit produced chimeric enzymes with catalytic properties that reflected those of the wild-type enzyme from which the C-terminus had been derived. Deletion of the tripeptide C-terminal extension found only in the hGSTM3 subunit had no effect on catalysis. The crystal structure determined for a ligand-free hGSTM3 subunit indicates that an Asn212 residue of the C-terminal domain is near a hydrophobic cluster of side chains formed in part by Ile13, Leu16, Leu114, Ile115, Tyr119, Ile211, and Trp218. Accordingly, a series of point mutations were introduced into the hGSTM3 subunit, and it was indeed determined that a Y119F mutation considerably enhanced the turnover rate of the enzyme for nucleophilic aromatic substitution reactions. A more striking effect was observed for a double mutant (Y119F/N212F) which had a k(cat)/K(m)(CDNB) value of 7.6 x 10(5) s(-)(1) M(-)(1) as compared to 4.9 x 10(3) s(-)(1) M(-)(1) for the wild-type hGSTM3-3 enzyme. The presence of a polar Asn212 in place of a Phe residue found in the cognate position of other mu class glutathione S-transferases, therefore, has a marked influence on catalysis by hGSTM3-3.