Human genes for glutathione S-transferases

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.

Cellular resistance to a nitric oxide releasing glutathione S-transferase P-activated prodrug, PABA/NO

PABA/NO is a diazeniumdiolate selectively activated by glutathione S-transferase P (GSTP) to release nitric oxide (NO) and is a potent inducer of protein S-glutathionylation, a redox-sensitive post-translational modification of cysteine residues. Using a procedure that incrementally increased exposure of cells to PABA/NO, an acquired drug resistant human promyelocytic leukemia HL60 cell line (HL60(PABA)) that exhibited 1.9-fold resistance to the drug (IC(50) 15 μM vs ~8 μM for wild-type) was created. HL60(PABA) cells had a decreased growth rate attributable to altered cellular differentiation, as measured by increased expression of CD11b; decreased expression of CD14; decreased nuclear to cytoplasmic ratios and a condensation of nuclear chromatin. This was accompanied by alterations in both plasma and mitochondrial membrane potentials. Both GSTP expression and nitric oxide release were reduced two-fold, while increased expression levels of genes involved in the unfolded protein response (UPR) were evident in HL60(PABA) cells. Wild type cells treated with PABA/NO had increased levels of protein S-glutathionylation and JNK activation, while JNK was constitutively active in HL60(PABA) cells and these cells had reduced levels of S-glutathionylation. By removing PABA/NO from the growth medium, HL60(PABA) cells reverted to sensitivity within 21 days suggesting that resistance was not genetically stable. Mechanistically, PABA/NO resistance is mediated through reduced levels of GSTP resulting in reduced NO release and its subsequent alterations in cellular response to nitrosative stress.

An Interethnic Comparison of Polymorphisms of the Genes Encoding Drug-Metabolizing Enzymes and Drug Transporters: Experience in Singapore

Much of the interindividual variability in drug response is attributable to the presence of single nucleotide polymorphisms (SNPs) in genes encoding drug-metabolizing enzymes and drug transporters. In recent years, we have investigated the polymorphisms in a number of genes encoding phase I and II drug-metabolizing enzymes including CYPIA1, CYP3A4, CYP3A5, GSTM1, NAT2, UGT1A1, and TPMT and drug transporter (MDR1) in three distinct Asian populations in Singapore, namely the Chinese, Malays, and Indians. Significant differences in the frequencies of common alleles encoding these proteins have been observed among these three ethnic groups. For example, the frequency of the variant A2455G polymorphism of CYP1A1 was 28% in Chinese and 31% in Malays, but only 18% in Indians. CYP3A4*4 was detected in two of 110 Chinese subjects, but absent in Indians and Malays. Many Chinese and Malays (61-63%) were homozygous for the GSTM1*0 null genotype compared with 33% of Indians. The frequency of the UGTIA1*28 allele was highest in the Indian population (35%) compared to similar frequencies that were found in the Chinese (16%) and Malay (19%) populations. More importantly, our experience over the years has shown that the pharmacogenetics of these drug-metabolizing enzymes and MDR1 in the Asian populations are different from these in the Caucasian and African populations. For example, the CYP3A4*1B allele, which contains an A-290G substitution in the promoter region of CYP3A4, is absent in all three Asian populations of Singapore studied, but occurs in more than 54% of Africans and 5% of Caucasians. There were no difference in genotype and allelic variant frequencies in exon 12 of MDR1 between the Chinese, Malay, and Indian populations. When compared with other ethnic groups, the distribution of the wild-type C allele in exon 12 in the Malays (34.2%) and Indians (32.8%) was relatively high and similar to the Japanese (38.55%) and Caucasians (41%) but different from African-Americans (15%). The frequency of wild-type TT genotype in Asians (43.5% to 52.1%) and Japanese (61.5%) was much higher than those found in Caucasians (13.3%). All the proteins we studied represent the primary hepatic or extrahepatic enzymes, and their polymorphic expression may be implicated in disease risk and the disposition of drugs or endogenous substances. As such, dose requirements of certain drugs may not be optimal for Asian populations, and a second look at the factors responsible for this difference is necessary.

Lipoamide protects retinal pigment epithelial cells from oxidative stress and mitochondrial dysfunction

alpha-Lipoic acid (LA) has been widely studied as an agent for preventing and treating various diseases associated with oxidative disruption of mitochondrial functions. To investigate a related mitochondrial antioxidant, we compared the effects of lipoamide (LM), the neutral amide of LA, with LA for measures of oxidative damage and mitochondrial dysfunction in a human retinal pigment epithelial (RPE) cell line. Acrolein, a major component of cigarette smoke and a product of lipid peroxidation, was used to induce oxidative mitochondrial damage in RPE cells. Overall, using comparable concentrations, LM was more effective than LA at preventing acrolein-induced mitochondrial dysfunction and oxidative stress. Relative to LA, LM improved ATP levels, membrane potentials, and activities of mitochondrial complexes I, II, and V and dehydrogenases that had been decreased by acrolein exposure. LM reduced acrolein-induced oxidant generation, calcium levels, protein oxidation, and DNA damage to a greater degree than LA. And, total antioxidant capacity, glutathione content, glutathione S-transferase, and superoxide dismutase activities and expression of nuclear factor-E2-related factor 2 were increased by LM relative to LA. These results suggest that LM is a more potent mitochondrial-protective agent and antioxidant than LA in protecting RPE from oxidative damage.

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.

A comparison of glutathione S-transferase mutant frequencies in healthy Han and Uygur Chinese

OBJECTIVE

This study was to compare the frequencies of genetic polymorphisms of GSTM1, GSTT1, and GSTP1 in Uygur Chinese with those in Han Chinese.

METHODS

GSTM1 and GSTT1 polymorphisms were analyzed by a PCR-Multiplex procedure, whereas GSTP1 polymorphism was analyzed by PCR-RFLP.

RESULTS

The frequency of GSTM1 null genotype in Han Chinese (56.1%) was similar to that in Uygur Chinese (53.2%) (P = 0.592), whilst the frequency of GSTT1 null genotype in Han Chinese (50.0%) was significantly (P < 0.05) higher than that of Uygur Chinese (26.6%). GSTP1 had a genotype distribution of 60.7% I/I, 35.2% I/V and 4.1% V/V in Han Chinese, and 51.3% I/I, 40.2% I/V and 8.4% V/V in Uygur Chinese.

CONCLUSION

There is marked ethnic difference in the mutant frequencies of GSTT1 and GSTP1, but not GSTM1, between Uygur and Han Chinese.

Rapid determination of common mutations in glutathione S-transferase gene by PCR-based methods in healthy Chinese

BACKGROUND

The glutathione S-transferase (GST) superfamily comprises multiple isozymes with compelling evidence of functional polymorphisms in various ethnic groups. All these mutations, in particular those in class mu, pi and theta GST, are likely to contribute to interindividual differences in responses to xenobiotics including response to chemotherapy and associated with altered disease. The frequency of common GST mutations in Uygur Chinese is unknown. We investigated the common mutations of GSTM1, GSTT1, and GSTP1 in Uygur (N=154) Chinese and compare with Han Chinese (N=196).

METHOD

GSTM1 and GSTT1 polymorphisms were analyzed by multiplexed PCR, and GSTP1 polymorphism was detected by PCR-based restriction fragment length polymorphism (RFLP) analysis.

RESULTS

GSTM1 null genotype was found in 53.2% Uygur Chinese, which was close to that in Han Chinese (56.1%) (P=0.592). A significantly lower frequency (P<0.05) of GSTT1 null genotype in Uygur Chinese (26.6%) was observed compared with Han Chinese (50.0%). Uygur Chinese exhibited a GSTP1 genotype distribution of 51.3% I/I, 40.2% I/V and 8.4% V/V, which was different from that in Han Chinese (60.7% I/I, 35.2% I/V and 4.1% V/V).

CONCLUSIONS

There is marked ethnic difference in the frequency of common GSTT1 and GSTP1 mutation, but not GSTM1 mutation, between Uygur and Han Chinese.

Polymorphism of human mu class glutathione transferases

OBJECTIVES AND METHODS

A combined database mining approach was used to detect polymorphisms in the mu class glutathione-S-transferase (GST) genes. Although a large number of potential polymorphisms were detected in the five genes that comprise the Mu class GSTs using sequence alignment programs and by searching single nucleotide polymorphism databases, the majority were not validated or detected in three major ethnic populations (African, Southern Chinese and Australian European).

RESULTS

Two new polymorphisms were detected and characterized in the GSTM3 gene. A rare pG147W substitution was detected only in the Southern Chinese subjects. A more common pV224I substitution was found in each of the ethnic groups studied, and significant differences in allele frequencies were observed between each group. These two polymorphisms can combine to form four distinct haplotypes (GSTM3A [p.G147;V224], GSTM3C [p.G147;I224], GSTM3D [p.W147;V224], GSTM3E [p.W147;I224]). The four isoforms were expressed in Escherichia coli and characterized enzymatically with several substrates including 1-chloro-2,4-dinitrobenzene (CDNB), cumene hydroperoxide and t-nonenal. GSTM3-3 containing the variant p.W147 residue tended to show diminished specific activity and catalytic efficiency with CDNB. In contrast, GSTM3-3 containing the variant p.I224 residue tended to show increased specific activity and catalytic efficiency with CDNB. Interactions between the different p.147 and p.224 residues were also observed, with the GSTM3C isoform exhibiting the greatest activity with each substrate, and GSTM3E the lowest.

CONCLUSION

These functional polymorphisms may play a significant role in modulating the ability of GSTM3-3 to metabolize substrates such as the chemotherapeutic agent 1,3-bis(2-chloroethyl)-1-nitrosourea.

Cancer drugs, genetic variation and the glutathione-S-transferase gene family

The glutathione-S-transferase (GST) super family comprises multiple isozymes (Alpha, Mu, Pi, Omega, Theta, and Zeta) with compelling evidence of functional polymorphic variation. Over the last two decades, a significant body of data has accumulated linking aberrant expression of GST isozymes with the development and expression of resistance to cancer drugs. Clinical correlation studies show that genetic differences within the human GST isozymes may play a role in cancer susceptibility and treatment. The initial confusion was presented by the fact that not all drugs used to select for resistance were substrates for thioether bond catalysis by GSTs. However, recent evidence that certain GST isozymes possess the capacity to regulate mitogen activated protein kinases presents an alternative explanation. This dual functionality has contributed to the recent efforts to target GSTs with novel small molecule therapeutics. While the ultimate success of these attempts remains to be shown, at least one drug is in late-stage clinical testing. In addition, the concept of designing new drugs that might interfere with protein:protein interactions between GSTs and regulatory kinases provides a novel approach to identify new targets in the search for cancer therapeutics.

Genetic polymorphisms and metabolism of endocrine disruptors in cancer susceptibility

Epidemiological studies have estimated that approximately 80% of all cancers are related to environmental factors. Individual cancer susceptibility can be the result of several host factors, including differences in metabolism, DNA repair, altered expression of tumor suppressor genes and proto-oncogenes, and nutritional status. Xenobiotic metabolism is the principal mechanism for maintaining homeostasis during the body's exposure to xenobiotics. The balance of xenobiotic absorption and elimination rates in metabolism can be important in the prevention of DNA damage by chemical carcinogens. Thus the ability to metabolize and eliminate xenobiotics can be considered one of the body's first protective mechanisms. Variability in individual metabolism has been related to the enzymatic polymorphisms involved in activation and detoxification of chemical carcinogens. This paper is a contemporary literature review on genetic polymorphisms involved in the metabolism of endocrine disruptors potentially related to cancer development.

Mantle-cell lymphoma

During the past decade, mantle-cell lymphoma has been established as a new disease entity. The normal counterparts of the cells forming this malignant lymphoma are found in the mantle zone of the lymph node, a thin layer surrounding the germinal follicles. These cells have small to medium-sized nuclei, are commonly indented or cleaved, and stain positively with CD5, CD20, cyclin D1, and FMC7 antibodies. Because of its morphological appearance and a resemblance to other low-grade lymphomas, many of which grow slowly, this lymphoma was initially thought to be an indolent tumour, but its natural course was not thoroughly investigated until the 1990s, when the BCL1 oncogene was identified as a marker for this disease. Mantle-cell lymphoma is a discrete entity, unrelated to small lymphocytic or small-cleaved-cell lymphomas.

Glutathione S-transferase M1 (GSTM1) polymorphism in two Brazilian populations

The distribution of GSTM1 phenotype frequencies was studied in two Brazilian samples composed of healthy and unrelated blood donors of both sexes ranging in age from 18 to 61 years. The first sample consisted of 658 individuals from Rio de Janeiro, and the second included 179 individuals from Brasília. The GSTM1 phenotypes were detected using PCR reactions and subsequent digestion by the restriction enzyme HaeII. The GSTM1 null phenotype frequency was 46% and 49% for Rio de Janeiro and Brasília samples, respectively. The GSTM1 phenotype distributions were not in agreement with Hardy-Weinberg equilibrium in either sample, chi²1 = 11.49 (P < 0.001) for Rio de Janeiro and chi²1 = 6.77 (P < 0.01) for Brasília. This deviation from Hardy-Weinberg equilibrium may be due to factors such as selection, errors in the phenotype determination or incomplete panmixia of the Brazilian population, whose main racial components are Caucasians, Africans and Indians.

Differential expression of a cDNA clone in human liver versus hepatic cancer--highly homologous to aryl-dialkyl-phosphatase

We applied the technique of mRNA differential display to normal liver tissue and hepatoma cell line Hep3B. One of the isolated cDNA clones was expressed in human normal liver tissue but not in the human hepatocarcinoma cell line. Northern Blot analysis confirmed that high level of mRNA was expressed in human normal liver tissue but the level was decreased in non-cancerous liver tissue from hepatoma patients. Low level or no expression was observed in human hepatoma tissue. One of these transcripts was about 1.8 kb in length. Southern Blot analysis showed that it was a single copy gene. We obtained a full length cDNA clone of 2,395 bp by screening human liver 5'-stretch plus cDNA library. Nucleotide sequence indicated that this clone was highly homologous to aryl-dialkyl-phosphatase and possessed two polymorphic sites. Aryl-dialkyl-phosphatase which has a prominent role in the metabolism of several toxic, synthetic compounds, may be potentially related to human hepatocarcinoma susceptibility. The biological significance of its differential expression in normal versus malignant tissue is discussed.

Gene deficiency of glutathione S-transferase mu isoform associated with susceptibility to lung cancer in a Chinese population

Increased lung cancer risk associated with genetic polymorphism of glutathione S-transferase (GST, EC 2.5.1.18) isozyme mu was examined in a Chinese population. A significantly higher proportion in lung cancer patients showed GST mu deficiency compared with control group (71.0% vs. 51.1%, P < 0.005). Although the susceptibility to lung cancer showing gene deletion for GST mu isoform in non-smoking group is not significantly different from that in smoking group, a great number of individuals with gene deletion was found among cancer patients who are less than 50 years old. The pathology of lung tumors related to that lack of class mu isoform which occurred most frequently in patients with small cell carcinomas. Thus, present data further support that sensitivity to chemical toxins and pulmonary carcinogens may be affected by GST mu isoform polymorphism.

Glutathione S-transferase expression in malignant mesothelioma and non-neoplastic mesothelium: an immunohistochemical study

Expression of the glutathione S-transferase (GST) subclasses alpha, mu and pi was investigated immunohistochemically in 20 normal or hyperplastic mesothelium and in 57 malignant mesothelioma cases. These results were correlated with survival and also with P-170 glycoprotein expression. Nearly all the non-neoplastic mesothelium cases were positive for GST alpha and pi. About half of the non-neoplastic cases were positive for mu. Twenty-nine (51%) malignant mesotheliomas were positive for at least one of the GST species; 21 (37%) showed immunoreactivity for alpha, 18 (31.5%) for mu and 21 (37%) for pi. A total of 54 mesothelioma cases displayed immunoreactivity for the P-170 glycoprotein. For GST pi and GST mu, a statistical significance between expression and increased survival was found (respectively P = 0.012 and 0.024) while for GST alpha no significance was found. The results of this study demonstrate that expression of GST pi correlates positively with increased survival in malignant mesothelioma. It is also concluded that, in mesothelioma, GST and P-170 glycoprotein may contribute to the resistance to cytotoxic drugs frequently observed in these tumours. No correlation between GST and P-170 expression was demonstrated.

Glutathione S-transferase-M1 'null' genotype and alcohol-induced disorders of human spermatogenesis

The association between alcohol-induced disorders of human spermatogenesis and glutathione S-transferase-M1 genotype was investigated in an autopsy study comprising 271 subjects, including interviews with relatives or close acquaintances on the alcohol consumption of the deceased. Of the 50 moderate drinking men (reported mean daily alcohol consumption < 40 g), 21 (42.0%) had normal spermatogenesis, whereas 24 men (48.0%) had partial, and five (10.0%) complete arrest of spermatogenesis. Of the 21 men with normal spermatogenesis, nine (42.9%) had GST M1 'null' genotype, while this genotype was found in 13 (44.8%) of the 29 men with partial or complete spermatogenic arrest. Of 212 heavy-drinking men (reported mean daily alcohol consumption > 80 g), only 45 (21.2%) had normal spermatogenesis, whereas 77 (36.3%) had partial spermatogenic arrest. Complete arrest of spermatogenesis was found in 81 men (38.2%) and nine men had Sertoli-cell-only syndrome (4.2%). Of the 45 heavy drinkers with normal spermatogenesis, 27 (60%) men had GST M1 'null' genotype (OR 2.7 with 95% confidence intervals: 1.0-4.0, when compared to those with disorders of spermatogenesis). The frequency of GST M1 'null' genotype in heavy drinkers with normal spermatogenesis also differed from that of corresponding moderate drinkers, whereas the frequency of GST M1 'null' genotype in heavy drinkers with disorders of spermatogenesis was similar to moderate drinkers with or without disorders of spermatogenesis. The finding that > 20% of men in the heavy-drinking group had normal spermatogenesis suggests individual variations in sensitivity to alcohol-induced disorders of this process. Heavy drinkers with GST M1 'null' genotype were slightly less prone to develop disorders of spermatogenesis. Thus, the GST M1 locus may be associated with susceptibility to develop alcohol-induced disorders of spermatogenesis.

Proportion of the GSTM1 0/0 genotype in some Slavic populations and its correlation with cystic fibrosis and some multifactorial diseases

A homozygous gene deletion at the glutathione S-transferase M1 (GSTM1) locus of genomic DNA from blood spots was studied by PCR in the group of Slavic populations from the north-western and central-eastern regions of European Russia and in patients with lung cancer (LC), other tumors (OT), endometriosis (E), alcoholic cirrhosis (AC), cystic fibrosis (CF) and chronic bronchitis (CB). The frequencies of the GSTM1 0/0 genotype were 38.8% and 67.5% for both population groups, respectively. The proportion of the GSTM1 gene deletion genotype was estimated as significantly increased in LC (81%), OT (65%), E (81%), AC (77.3%), and in CB (73.6%) patients with symptoms of CB confirmed by X-ray but not in CB patients without X-ray evidence of disease (40.9%). A definite preponderance of GSTM1-0 homozygotes (51.1%) has been registered in CF patients of the pancreatic sufficient group with clear-cut pulmonological manifestations but not in those of the pancreatic insufficient group with predominantly intestinal or mixed clinical symptoms (41.2% and 37.5%, respectively). Earlier clinical manifestations and death before the age of 5 years are typical for GSTM1-deleted CF patients. These data support the notion that GSTM1 deletion should be considered as a convenient genetic marker for the early detection of groups at higher risk of many diseases caused by environmental and genetic factors, where manifestation depends on the lack of detoxification. High levels of GSTM1 0/0 genotypes in E patients favor the substantial contribution of certain environmental toxins in the pathogenesis of this widespread disease.

Human leukocyte glutathione S-transferase isozyme (class mu) and susceptibility to smoking-related cancers

Glutathione S-transferase isozyme class mu from human leukocytes has been shown to be dominantly inherited and can be determined by activity measurement directed toward the substrate trans-stilbene oxide. The activity distribution of leukocyte glutathione S-transferase class mu was determined from control healthy nonsmokers, smokers, and smoking-related cancer patients. In a control healthy nonsmoker population, 54% (n = 50) of the subjects showed high levels of glutathione S-transferase class mu activity. In patients with cancers known to be related to smoking, 46% (n = 50) showed higher levels of glutathione S-transferase class mu. Noncancer smokers matched for age and smoking history with cancer patients showed an increased likelihood of having glutathione S-transferase (GST) class mu activity (76%). These results suggest that GST mu may be a cancer susceptibility marker in the case of smokers. In rats, benzo[a]pyrene (1 mg/kg, ip) administration daily for 3 d produced a significant increase in liver glutathione S-transferase class mu. Although these induction studies in experimental animals may not be relevant to humans, there is a possibility that, as in rats, this enzyme may be inducible in humans by polycyclic aromatic hydrocarbons.

Immunohistochemical demonstration of epithelial glutathione S-transferase isoenzymes in normal, benign, premalignant and malignant human oral mucosa

The expression and localization of glutathione S-transferase (GST) isoenzymes in the epithelium of normal oral mucosa (n = 9), overlying reactive fibrous hyperplasia (n = 9), and of potentially malignant [leukoplakia (n = 25), submucous fibrosis (n = 12), verrucous hyperplasia (n = 16)] and malignant [squamous cell carcinoma (n = 36), verrucous carcinoma (n = 13)] oral lesions were examined immunohistochemically using polyclonal antibodies raised against GST isoenzymes (alpha, mu and pi) with the standard avidin-biotin-peroxidase complex (ABC) method. GST alpha, mu and pi were almost completely absent in the epithelium of normal oral mucosa and overlying benign fibrous tissues. GST alpha staining was cytoplasmic and focally positive, while GST mu staining was similar to but weaker than that seen for GST alpha. GST pi showed both cytoplasmic and nuclear staining and was expressed in 60% of leukoplakias with mild dysplasia (n = 15), 80% of leukoplakias with moderate to severe dysplasia (n = 10). 75% of submucous fibrosis samples (n = 12), 75% of verrucous hyperplasias (n = 16), 77% of verrucous carcinomas (n = 13), 81% of well-differentiated squamous cell carcinomas (n = 26) and 70% of moderate- to poorly-differentiated squamous cell carcinomas (n = 10). In addition, GST pi expression was independent of the state of differentiation of oral cancers. Since GST pi was significantly over-expressed in the oral premalignant and malignant lesions, the kinetics of GST pi-positive cells and the value of GST pi as a tumor marker in oral carcinogenesis need further investigation.

Frequency of glutathione-S-transferase 1 gene deletion and its possible correlation with cataract formation

This experiment was conducted to investigate the possible association between an increased frequency of glutathione-S-transferase (GST)1 gene deletion and the presence of cataracts in elderly patients. Genomic DNA was isolated from blood samples obtained from 138 elderly patients who had undergone cataract surgery, and from 62 random blood donors. All subjects lived in the same geographic area (Ibaraki Prefecture, Japan). The DNA sequences among three different exon ranges (exons 3-5, exons 4-5 and exons 5-6) of the GST1 gene were amplified by the polymerase chain reaction (PCR) technique to determine if GST1 gene deletion occurred. Cataract patients had a significantly higher frequency of GST1 gene deletion than random controls did (P < 0.001, odds ratio = 2.91, 1.56-5.44; 95% of confidence interval). Mean age of cataract patients lacking GST1 gene was significantly younger (n = 101, mean age = 70.4, s.d. = 10.2) than that of patients possessing the GST1 gene (n = 37, mean age = 75.0, s.d. = 8.7) (P < 0.02). These results show that the deletion of the GST1 gene may be one of determinants of genetic susceptibility to cataractgenic agents.

Genetic differences in drug disposition

Genetic polymorphisms of drug metabolizing enzymes are well recognized. This review presents molecular mechanisms, ontogeny and clinical implications of genetically determined intersubject variation in some of these enzymes. Included are the polymorphic enzymes N-acetyl transferase, cytochromes P4502D6 and 2C, which have been well described in humans. Information regarding other Phase I and Phase II polymorphic pathways, such as glutathione and methyl conjugation and alcohol and acetaldehyde oxidation continues to increase and are also discussed. Genetic factors effecting enzyme activity are frequently important determinants of the disposition of drugs and their efficacy and toxicity. In addition, associations between genetic differences in these enzymes and susceptibility to carcinogens and teratogens have been reported. Ultimately, the application of knowledge regarding these genetic factors of enzyme activity may guide medical therapy and minimize xenobiotic-induced disease.

Similar toxic effect of 1,3-bis(2-chloroethyl)-1-nitrosourea on lymphocytes from human subjects differing in the expression of glutathione transferase M1-1

Sixteen healthy donors were investigated for the presence or absence of glutathione transferase (GST) M1-1 in lymphocytes by immunodetection with polyclonal antibodies against human GST M1-1. Nine out of 16 individuals (56%) were categorized as GST M1-1 positive. Phytohaemagglutinin stimulated lymphocytes from GST M1-1 positive and negative donors were treated with 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) and compared regarding inhibition of [3H]thymidine incorporation as a measure of cytotoxicity. No significant differences in the effect of BCNU were observed between the two groups, indicating that GST M1-1 is not an important resistance factor for BCNU.

Human glutathione S-transferases

1. Multiple forms of glutathione S-transferase (GST) isoenzymes present in human tissues are dimers of subunits belonging to three distinct gene families namely alpha, mu and pi. Only the subunits within each class hybridize to give active dimers. 2. These subunits are differentially expressed in a tissue-specific manner and the composition of glutathione S-transferases in various tissues differs significantly. 3. Minor GST subunits not belonging to these three classes are also present in some tissues. 4. An ortholog of rat GST 8-8 and mouse mGSTA4-4 is selectively expressed in some human tissues including bladder, brain, heart, liver, and pancreas. This isoenzyme designated as GST 5.8 expresses several fold higher activity towards 4-hydroxy-2,3-trans-nonenal as compared to the routinely used substrate 1-chloro-2,4-dinitrobenzene.

Antioxidant systems and erythrocyte life-span in mammals

1. Erythrocyte antioxidant systems--superoxide dismutase (SOD), catalase (CAT), reduced glutathione (GSH), glutathione peroxidase (GSH-Px), glutathione S-transferase (GST) and glutathione reductase (GR)--were discussed in relation to life-spans in some mammalian species. 2. The erythrocyte life-span of different mammals was found to be correlated with the levels of SOD, GSH-Px and GSH. 3. Data reviewed indicates that the erythrocyte life-span of each species is governed by both the oxygen radical formation and the efficiency of intrinsic antioxidant systems.

Deduced amino acid sequence, gene structure and chromosomal location of a novel human class Mu glutathione S-transferase, GSTM4

The Mu-Class glutathione S-transferases (GSTs) are subject to marked inter-individual variation in man, owing to the fact that 40-50% of the population fail to express M1 subunits. Mu-Class GST from two lymphoblastoid cell lines (expressing M1 subunits and the other 'nulled' for M1) have been studied. Both cell lines were found to express a Mu-Class GST that has not been described previously. The cDNA encoding this novel transferase, designated 'GSTM4' has been isolated and the enzyme shown to be comprised of 218 amino acids (including the initiator methionine residue) with an M(r) of approx. 25.5 kDa. Molecular cloning demonstrated that the lymphoblastoid cell line which expressed GSTM1 possessed the b allelic variant (i.e. that with an asparagine residue at position 173). The genes for GSTM4 and GSTM1b have been cloned and found to contain seven introns and eight exons. The coding region of the GSTM4 gene, including the seven introns, encompasses 5.0 kb, whereas the same region of GSTM1b is 5.5 kb; the difference in the size of the two genes is due to the length of intron 7. DNA sequencing allowed a GSTM4-gene-specific oligo-primer to be designed which has been utilized in a PCR-based assay to determine that the GSTM4 gene is located on chromosome 1.

The CYP1A1 gene and cancer susceptibility

A close correlation between cigarette smoking associated lung cancer incidence and an Msp I restriction fragment length polymorphism (RFLP) of the human P-450 1A1 (CYP1A1) gene was found in a Japanese population in terms of genotype frequency and cigarette dose. A Val/Ile codon difference in the primary structure of the CYP1A1 protein (Val-, Ile-type) was in linkage disequilibrium with the Msp I RFLP. A synergistic increase in susceptibility to lung cancer was found when combining genotyping of CYP1A1 and the Mu-class of glutathione S-transferase (GST1). Interindividual variability in the genetic make-up of carcinogen metabolizing enzymes may thus be a key host factor to explain the differences in susceptibility to chemical carcinogenesis among individuals.

Human glutathione S-transferase mu (GST mu) deficiency as a marker for the susceptibility to bladder and larynx cancer among smokers

The isoenzyme mu of glutathione S-transferase (GST mu) is dominantly inherited and the prevalence of this isoenzyme in the population is about 60%. An increased risk of lung cancer has been previously shown among smokers lacking GST mu in (Seidegard J., Pero R.W., Miller D.G., Beattie E.J. (1986) Carcinogenesis, 7, 751-753). The frequency of the phenotypes of this isoenzyme in bladder cancer patients (n = 75), in larynx cancer patients (n = 78) and healthy controls matched for age and smoking history is reported here. A significantly higher proportion of smokers in the control group had measurable GST mu compared with bladder cancer patients (54.6% vs. 33.3%, P < 0.01) and also compared to larynx cancer patients (55.1% vs. 33.3%, P < 0.01). Odds ratio analysis indicates that smokers with this polymorphic variant have an approximately 2-fold greater risk of developing these cancers.

The human Pi class glutathione transferase sequence at 12q13-q14 is a reverse-transcribed pseudogene

A previous in situ hybridization study with a Pi class glutathione S-transferase cDNA probe revealed the presence of hybridizing sequences on the long arms of chromosomes 11 and 12. Since the GSTP1 gene is known to be on chromosome 11 and since it is thought that chromosomes 11 and 12 arose from an ancient tetraploidization event, it was of interest to determine if the gene on chromosome 12 encoded a closely related Pi class glutathione S-transferase isoenzyme. This gene has now been cloned and sequenced. The results are surprising and indicate that the gene is a partial reverse-transcribed pseudogene that has been inserted into the genome at 12q by chance and has not resulted from the prior tetraploidization of the human genome.

Detection of GST1 gene deletion by the polymerase chain reaction and its possible correlation with stomach cancer in Japanese

A homozygous gene deletion at the GST1 locus of genomic DNA isolated from peripheral blood was investigated for its relationship with several types of cancer using the polymerase chain reaction (PCR) technique. DNA samples were prepared from blood obtained from 128 healthy blood donors and 150 patients with cancer or chronic hepatitis. PCR primers were prepared based on the human cDNA sequence and the intron/exon sequences of the rat Yb2 gene. The amplified sequence between exons 5 and 6 including intron 5 showed very clearly the presence of absence of the GST1 gene, after electrophoresis in a 2% agarose gel. Segregation of the presence and absence of PCR product from samples of twins and their parents indicated that presence involves homozygous or heterozygous normal GST1 genotypes while absence involves only homozygous gene deletion. The patients with stomach cancer had a significantly higher frequency of gene deletion than did the healthy controls (P < 0.005). Thus, GST1 deletion may be a possible genetic marker for early detection of a group at high risk of stomach cancer.

High susceptibility to lung cancer analyzed in terms of combined genotypes of P450IA1 and Mu-class glutathione S-transferase genes

Lung cancer is closely associated with cigarette smoking. Aromatic hydrocarbons in smoke, including benzo[a]pyrene, first require metabolic activation by Phase I enzymes, cytochrome P450, to their ultimate forms, and these activated forms are then subjected to detoxification by Phase II enzymes, especially glutathione S-transferases. Thus, genetically determined susceptibility to lung cancer may depend on the metabolic balance between Phase I and Phase II enzymes. In this study, we identified individuals genetically at high risk of lung cancer in terms of polymorphisms of the P450IA1 gene and GST1 gene. The relative risk of individuals with a combination of the genotypes of both a homozygous rare allele of the P450IA1 gene and the nulled GST1 gene was remarkably high at 5.8 for lung cancer and 9.1 for squamous cell carcinoma compared with other combinations of genotypes.

Glutathione transferases and cancer

The glutathione transferases, a family of multifunctional proteins, catalyze the glutathione conjugation reaction with electrophilic compounds biotransformed from xenobiotics, including carcinogens. In preneoplastic cells as well as neoplastic cells, specific molecular forms of glutathione transferase are known to be expressed and have been known to participate in the mechanisms of their resistance to drugs. In this article, following a brief description of recently identified molecular forms, we review new findings regarding the respective molecular forms involved in carcinogenesis and anticancer drug resistance, with particular emphasis on Pi class forms in preneoplastic tissues. The rat Pi class form, GST-P (GST 7-7), is strongly expressed not only in hepatic foci and hepatomas, but also in initiated cells that occur at the very early stages of chemical hepatocarcinogenesis, and is regarded as one of the most reliable markers for preneoplastic lesions in the rat liver. 12-O-Tetradecanoylphorbol-13-acetate (TPA)-responsive element-like sequences have been identified in upstream regions of the GST-P gene, and oncogene products c-jun and c-fos are suggested to activate the gene. The Pi-class forms possess unique enzymatic properties, including broad substrate specificity, glutathione peroxidase activity toward lipid hydroperoxides, low sensitivity to organic anion inhibitors, and high sensitivity to active oxygen species. The possible functions of Pi class glutathione transferases in neoplastic tissues and drug-resistant cells are discussed.

Characterization of a novel glutathione S-transferase isoenzyme from mouse lung and liver having structural similarity to rat glutathione S-transferase 8-8

In mouse lung, glutathione S-transferase (GST, EC 2.5.1.18) isoenzymes belonging to the three major known classes, Alpha, Mu and Pi, have been previously characterized, along with an isoenzyme (pI 5.7) that could not be identified with the Alpha, Mu or Pi classes of GSTs. In the present studies we have demonstrated that this isoenzyme is also expressed in liver. Its structural, kinetic, and immunological properties have been determined and compared with those of the three classes of GSTs. GST 5.7 has a subunit molecular mass of 23 kDa, which is intermediate between that of the previously characterized Alpha (25 kDa) and Pi (22.5 kDa) class GST subunits of mouse lung. Comparison of peptide maps of GST 5.7 with those representative of Alpha, Mu and Pi class GST isoenzymes of mouse lung showed that it had a distinct peptide fragmentation pattern. Kinetic and immunological properties of GST 5.7 were also distinct from other mouse GST isoenzymes belonging to the Alpha, Mu or Pi classes. N-Terminal amino-acid-sequence analysis of a 6 kDa fragment generated by CNBr digestion of mouse lung GST 5.7 revealed a 15-residue sequence that was distinct from sequences of known Alpha, Mu and Pi class mouse GSTs. The sequence, however, matched with the sequence of rat GST 8-8 between amino acid residues 106 and 120 with a 73% identity. The 6 kDa and 12 kDa fragments generated by CNBr digestion of mouse liver GST 5.7 also gave sequences which matched with those of rat GST 8-8 between positions 106 and 120 and 167 and 186, with a high degree of identity. These studies suggest that mouse GST 5.7 structurally corresponds to rat GST 8-8 and belongs to the Alpha class.

Purification and characterization of human muscle glutathione S-transferases: evidence that glutathione S-transferase zeta corresponds to a locus distinct from GST1, GST2, and GST3

Human muscle glutathione S-transferase isozyme, GST zeta (pI 5.2) has been purified by three different methods using immunoaffinity chromatography, DEAE cellulose chromatography, and isoelectric focusing. GST zeta prepared by any of the three methods does not recognize antibodies raised against the alpha, mu, or pi class glutathione S-transferases of human tissues. GST zeta has a blocked N-terminus and its peptide fingerprints also indicate it to be distinct from the alpha, mu, or pi class isozymes. As compared to GSTs of alpha, mu, and pi classes, GST zeta displays higher activities toward t-stilbene oxide and Leukotriene A4 methyl ester. GST zeta also expresses GSH-peroxidase activity toward hydrogen peroxide. The Kms of GST zeta for CDNB and GSH were comparable to those reported for other human GSTs but its Vmax for CDNB, 7620 mol/mol/min, was found to be considerably higher than that reported for other human GSTs. The kinetics of inhibition of GST zeta by hematin, bile acids, and other inhibitors also indicate that it was distinct from the three classes of GST isozymes. These studies suggest that GST zeta corresponds to a locus distinct from GST1, GST2, and GST3 and probably corresponds to the GST4 locus as suggested previously by Laisney et al. (1984, Human Genet. 68, 221-227). The results of peptide fingerprints and kinetic analysis indicate that as compared to the pi and alpha class isozymes, GST zeta has more structural and functional similarities with the mu class isozymes. Besides GST zeta several other GST isozymes belonging to pi and mu class have also been characterized in muscle. The pi class GST isozymes of muscle have considerable charge heterogeneity among them despite identical N-terminal sequences.

Variation in the expression of Mu-class glutathione S-transferase isoenzymes from human skeletal muscle. Evidence for the existence of heterodimers

The cytosolic glutathione S-transferases (GST) from human skeletal muscle were purified by a combination of affinity chromatography and anion-exchange chromatography followed by either chromatofocusing or hydroxyapatite chromatography. Pi-class and Mu-class GST, but not Alpha-class GST, were isolated from muscle. In addition to a Pi-class GST subunit, which exists as a homodimer, this tissue also contains a total of three distinct neutral-type Mu-class GST subunits, which hybridize to form homodimers or heterodimers. The neutral-type subunits are referred to as N1-N3 and are defined by the decreasing isoelectric points of the homodimers; GST N1N1, N2N2 and N3N3 have estimated pI values of 6.1, 5.3 and less than 5.0 respectively. SDS/PAGE showed that N1, N2 and N3 have Mr values of 26,700, 26,000 and 26,300 respectively. The N1, N2 and N3 subunits are catalytically distinct, with N1 possessing a high activity for trans-4-phenylbut-3-en-2-one and N2 having high activity with 1,2-dichloro-4-nitrobenzene. In skeletal muscle the expression of the N1 subunit, but not of N2 and N3 subunits, was found to differ from specimen to specimen. The N1 subunit was absent from about 50% of samples examined, and the purification results from two different specimens are presented to illustrate this inter-individual variation. Skeletal muscle from one individual (M1), which did not express N1, contained only GST N2N2, N2N3 and pi, whereas the second sample examined (M2) contained GST N1N2, N2N2 and N2N3 as well as GST pi. N-Terminal amino acid sequence analysis supported the electrophoretic evidence that the N2 subunit in GST N1N2, N2N2 and N2N3 represents the same polypeptide. The peptides obtained from CNBr digests of N2 were subjected separately to automated amino acid sequencing, and the results indicate that N2 is distinct but closely related to the protein encoded by the human Mu-class cDNA clone GTH4 [DeJong, Chang, Whang-Peng, Knutsen & Tu (1988) Nucleic Acids Res. 16, 8541-8554]. GST N2N2 is probably identical with GST 4 [Board, Suzuki & Shaw (1988) Biochim. Biophys. Acta 953, 214-217], as over the 24 N-terminal residues of GST 4 there is complete identity between the two enzymes. Our data suggest that the GST 1 and GST 4 loci are part of the same multi-gene family.

Human glutathione S-transferases: radioimmunoassay studies on the expression of alpha-, mu- and pi-class isoenzymes in developing lung and kidney

The developmental expression of the alpha-, mu- and pi-class glutathione S-transferases has been defined in human lung and kidney using radioimmunoassay, immunohistochemistry and column chromatography. Expression of alpha-class enzymes increased significantly after about 40 weeks gestation in kidney but not lung, while expression of mu isoenzymes was continuous throughout development in both tissues. Expression of the pi isoenzyme fell during in utero ontogeny in lung, the pattern of down-regulation being similar to that previously observed in liver. There was no change in the expression of this isoenzyme in kidney. Comparison of the expression of the glutathione S-transferases in developing lung, kidney and liver shows some common patterns of expression suggesting these genes are under similar regulatory control.

Glutathione transferase isoenzymes from human prostate

By using affinity-chromatography and isoelectric-focusing techniques, several forms of glutathione transferase (GSTs) were resolved from human prostate cytosol. All the three major classes of GST, i.e. Alpha, Mu and Pi, are present in human prostate. However, large inter-individual variation in the qualitative and quantitative expression of different isoenzymes resulted in the samples investigated. The most abundant group of prostate isoenzymes showed acid (pI 4.3-4.7) behaviour and were classified as Pi class GSTs on the basis of their immunological and structural properties. Immunohistochemical staining of Pi class GSTs was prevalently distributed in the epithelial cells surrounding the alveolar lumen. Class Mu GSTs are also expressed, although in small amounts and in a limited number of samples, by human prostate. The major cationic isoenzyme purified from prostate, GST-9.6; (pI 9.6; apparent subunit molecular mass of 28 kDa), appears to be different from the cationic GST alpha-epsilon forms isolated from human liver and kidney as evidenced by its structural, kinetical and immunological properties. This enzyme, which accounts for about 20-30% (on protein basis) of total amount of GSTs, is expressed by only 40% of samples. GST-9.6 has the ability to cross-react in immunoblotting analysis with antisera raised against rat liver GST 2-2, rather than with antisera raised against members of human Alpha, Mu and Pi class GSTs. Although prostate GST-9.6 shows close relationship with the human skin GST pI 9.9, it does not correspond to any other known human GST.

Glutathione S-transferase (placental) as a marker of transformation in the human cervix uteri: an immunohistochemical study

Using an indirect immunohistochemical technique on paraffin sections, employing a polyclonal antibody to the acidic (placental) form of glutathione-S-transferase (GST), we have evaluated cytoplasmic and nuclear staining in a series of 67 cervical biopsies including normal non neoplastic tissue, immature squamous metaplasia, all grades of cervical intraepithelial neoplasia (CIN) and invasive carcinomas of keratinising and non-keratinising types. No differences in cytoplasmic staining between the varied lesions studied were seen. However, there were marked differences in nuclear staining. While normal non-neoplastic stratified squamous epithelium showed weak staining of the lower one-third of the epithelium only, in immature squamous metaplasia and in all grades of CIN there was intense nuclear staining in all layers of the epithelium. Invasive carcinomas showed generally less intense nuclear staining than CIN lesions. Endocervical cell nuclei also showed intense nuclear staining. These findings indicate that GST is of limited use as a marker of transformation in the human cervix uteri.

Placental glutathione-S-transferase-pi mRNA is abundantly expressed in human skin

Four overlapping cDNA clones were isolated from a lambda gt11 human placenta cDNA library using purified human IgG antibody, from a patient with bullous pemphigoid. The sequence was homologous to human placenta glutathione-S-transferase-pi (GST-pi). Using the placenta clone, epidermal cDNA clones were isolated from a human keratinocyte library. Expression of GST-pi mRNA in human skin, cultured keratinocytes and fibroblasts, and disorders of squamous hyperplasia was demonstrated by Northern blotting and in situ hybridization. Human epidermal and placental cDNA clones hybridized to the same genomic DNA fragments. Hybridization of placental cDNA to interspecific somatic cell hybrids showed retention of chromosome 11, confirming the assignment of GST 3 to the long arm of chromosome 11 by molecular means. Anti-GST-pi antibody did not give a basement membrane zone pattern, although some normal and BP sera contained antibodies to GST-pi. Human skin expresses glutathione-S-transferase-pi, which belongs to an enzyme family important for detoxification and carcinogenesis.

Glutathione S-transferase and P-glycoprotein in multidrug resistant Chinese hamster cells

Glutathione S-transferases (GSTs) have been reported to be elevated in some forms of hepatic carcinogenesis, in multidrug resistant (MDR) cells exhibiting elevated P-glycoprotein, and in cells resistant to alkylating agents independent of the MDR phenotype. The reported elevation of GST in association with the MDR phenotype and the overexpression of P-glycoprotein along with induction of GST in hepatic carcinogenesis suggest a correlation in the two mechanisms of cellular detoxification. To evaluate this hypothesis we examined the expression of GSTs in an MDR Chinese hamster fibroblast cell line overexpressing P-glycoprotein. We were unable to demonstrate concordant elevation of GST in these MDR cells. We conclude that GST expression is independent of P-glycoprotein expression in MDR Chinese hamster fibroblasts. The overexpression of GSTs in certain cells may provide an alternative mechanism for the development of drug resistance, either in association with or independent of P-glycoprotein overexpression, but is not essential for the MDR phenotype.

Characterization of a novel alpha-class anionic glutathione S-transferase isozyme from human liver

A novel, alpha-class glutathione S-transferase (GST) isozyme has been isolated from human liver using glutathione (GSH) affinity chromatography, DEAE-cellulose ion-exchange chromatography, and immunoaffinity chromatography. The isozyme is a dimer of approximately 25,000 Mr with blocked N termini. Structural, kinetic, and immunological properties of this enzyme indicate that it belongs to the alpha class of GSTs. Noticeable differences between the properties of this enzyme and the other alpha-class GSTs of human liver are its anionic nature (pI 5.0), GSH peroxidase activity toward hydrogen peroxide, and relatively higher GSH conjugating activities toward CDNB and epoxide substrates as compared to other alpha-class GSTs. Results of these studies indicate that anionic GST omega characterized previously (Y. C. Awasthi, D. D. Dao, and R. P. Saneto, 1980, Biochem. J. 191, 1-10) from human liver is a mixture of GST pi and a novel alpha-class GST. We have, therefore, reassigned the name GST omega to this new alpha-class anionic GST of human liver.

Genetic heterogeneity of the human glutathione transferases: a complex of gene families

The glutathione transferases (GSTs) are involved in the metabolism of a wide range of compounds of both exogenous and endogenous origin. There is evidence that deficiency of GST may increase sensitivity to certain environmentally derived carcinogens. In contrast, elevated expression has been implicated in resistance to therapeutic drugs. The GSTs are the products of several gene families. This review summarizes the present knowledge of the genetic interrelationships between the various isoenzymes, their deficiencies and the physical locations of their genes.

The development expression of alpha-, mu- and pi-class glutathione S-transferases in human liver

The developmental expression of the alpha, mu and pi class glutathione S-transferases has been defined in human liver using radioimmunoassay and immunohistochemistry. Expression of alpha and mu class isoenzymes increased significantly at birth, while that of the pi isoenzyme declined during the first trimester. Mu-class isoenzymes (GST1 1, GST1 2, GST1 2-1) were expressed in hepatocytes but not in other liver cell types.

Glutathione transferase isoenzymes from human testis

By using affinity chromatography and isoelectric focusing techniques, several forms of glutathione transferase (GSTs) were resolved from human testis obtained from patients operated on for malignant diseases. Large interindividual variations in the expression of different isoenzymes resulted in the samples investigated. Five out of six samples analysed expressed GST-4.4 that resulted in being structurally and immunologically identical to GST-pi (class Pi). All the cationic GSTs of human testis, except for GST-8.36, GST-9.1 and GST-10.1, are homodimers of 24,500 Mr subunit and cross reacted with antisera raised against class Alpha GST. Some of the forms isolated (GST-3.8, GST-8.36, GST-9.1 and GST-10.1) can not apparently be related to any of GSTs so far characterized in other human tissues. Upon SDS/polyacrylamide gel electrophoresis, GST-8.36 and GST-9.1 appeared to be heterodimers of 24,500 and 26,500 Mr subunits and were found only in the testis seminoma suggesting that they might be tumour specific isoenzymes. GST-3.8 appeared to be formed by heterodimers of 23,000 and 26,500 Mr subunits whereas, GST-10.1 was found to be dimers of 22,000 and 24,500 Mr subunits. In addition, the results of immunohistochemical studies with antisera raised against both class Pi and Alpha GSTs are reported.