Immunological and sequence interrelationships between multiple human liver and rat glutathione S-transferases

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

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

Structural organization of the microsomal glutathione S-transferase gene (MGST1) on chromosome 12p13.1-13.2. Identification of the correct promoter region and demonstration of transcriptional regulation in response to oxidative stress

The structure and regulation of the microsomal glutathione S-transferase gene (MGST1) are considerably more complex than originally perceived to be. The MGST1 gene has two alternative first exons and is located in the 12p13.1-13.2 region. Two other potential first exons were determined to be nonfunctional. The region between the functional first exons cannot direct transcription. Thus, one common promoter element directing transcription exists, and RNA splicing occurs such that only one of the first exons (containing only untranslated mRNA) is incorporated into each mRNA species with common downstream exons. MGST1 expression and regulation are therefore similar to those of other hepatic xenobiotic handling enzymes, which also produce mRNA species differing only in the 5'-untranslated regions to yield identical proteins. MGST1 was previously considered a "housekeeping" gene, as non-oxidant inducers had little effect on activity. However, the promoter region immediately upstream of the dominant first exon transcriptionally responds to oxidative stress. In this respect, MGST1 is similar to glutathione peroxidases that also transcriptionally respond to oxidative stress. The discovery that MGST1 utilizes alternative first exon splicing eliminates a problem with the first description of MGST1 cDNA in that it appeared that MGST1 expression was in violation of the ribosomal scanning model. The identification that the first exon originally noted is in fact a minor alternative first exon far downstream of the primary first exon eliminates this conundrum.

The 30 kDa protein co-purified with chick liver glutathione S-transferases is a carbonyl reductase

An unidentified 30 kDa protein was co-purified with chick liver glutathione S-transferases from S-hexylglutathione affinity column. The protein was isolated to apparent homogeneity with chromatofocusing. The molecular mass of the protein was determined to be 30 277 +/- 3 dalton by mass spectrometry. The protein was digested with Achromobacter proteinase I. Amino-acid sequence analyses of the resulting peptides show a high degree of identity with those of human carbonyl reductase. The protein is active with menadione as substrate. Thus, it is identified as chick liver carbonyl reductase.

Brain and testis selective expression of the glutathione S-transferase Yb3 subunit is governed by tandem direct repeat octamer motifs in the 5'-flanking region of its gene

To gain insight into mechanisms of cell type-specific transcription of class mu-glutathione S-transferase genes, the gene encoding the Yb3 subunit was cloned. Yb3 subunits are selectively expressed at high levels in rat brain and testis but not in liver or kidney. The Yb3 subunit gene spans over 6 kb and consists of 8 exons and 7 introns and a sequence consisting of tandem direct repeat consensus octamer DNA binding motifs separated by a 6 base pair (bp) spacer was identified in its 5'-flanking region. Gel shift assays with a 40 bp segment of DNA containing the two consensus octamer sequences, revealed the presence of specific binding proteins in nuclear extracts of rat brain, testis and C6 glioma cells. DNA binding activity was greatly reduced in liver, kidney and HTC cells. Reporter vectors carrying segments of the 5'-flanking region of the Yb3 subunit gene fused to a luciferase gene were introduced into C6 glioma cells which express high levels of Yb3 subunits, and into HTC cells which do not. The plasmids consisting of the Yb3 gene promoter up to, but not including, the octamer motifs did not support luciferase transcription in the C6 glioma cells, but larger fragments that included the octamer repeat sequences, effectively directed transcription in the C6 glioma cells. With mutated octameric sequences transcriptional activity was greatly reduced, and none of the same Yb3 constructs directed substantial luciferase transcription in the HTC cells. The results show that octamer motifs in the 5'-flanking region of the Yb3 subunit gene are functional and are the principal cis-acting elements that account for its discrete cell type-selective expression. This gene is one of the few known targets for octamer DNA binding transcription factors in brain.

Immunological comparison of cytosolic glutathione S-transferases between rat and two strains of houseflies

Five different antisera, which include three antisera raised against rat liver glutathione S-transferases (GST), one antiserum raised against human pi GST, and one antiserum raised against housefly GST1, were used to examine their cross-reactivity with different classes of GST subunits isolated from rat liver and the housefly. Two classes of rat liver GSTs, alpha and mu, were isolated from rat liver and two classes of housefly GSTs, GST1 and GST2, were isolated from both CSMA and Cornell-R strains. Antiserum against GST 3-3 was the most reactive antiserum and reacted not only with the mu class of GSTs but also with the GST1 class from both CSMA and Cornell-R strains. Antiserum against human pi GST and antiserum against housefly GST1 had weak immunological reactivity toward the GST1 class from both strains of housefly. Antiserum against GST 4-4 and antiserum against GST 1-1 had no immunological reactivity toward any class of GSTs from housefly. None of the five antisera had any immunological cross-reactivity toward subunit 2 of the alpha class of rat GST and the GST2 class of housefly GSTs from both strains.

Glutathione S-transferases: gene structure and regulation of expression

The current knowledge about the structure of GST genes and the molecular mechanisms involved in regulation of their expression are reviewed. Information derived from the study of rat and mouse GST Alpha-class, Ya genes, and a rat GST Pi-class gene seems to indicate that a single cis-regulatory element, composed of two adjacent AP-1-like binding sites in the 5'-flanking region of these GST genes, is responsible for their basal and xenobiotic-inducible activity. The identification of Fos/Jun (AP-1) complex as the trans-acting factor that binds to this element and mediates the basal and inducible expression of GST genes offers a basis for an understanding of the molecular processes involved in GST regulation. The induction of expression of Fos and Jun transcriptional regulatory proteins by a variety of extracellular stimuli is known to mediate the activation of target genes via the AP-1 binding sites. The modulation of the AP-1 activity may account for the changes induced by growth factors, hormones, chemical carcinogens, transforming oncogenes, and cellular stress-inducing agents in the pattern of GST expression. Recent observations implying reactive oxygen as the transduction signal that mediates activation of c-fos and c-jun genes are presently considered to provide an explanation for the induction of GST gene expression by chemical agents of diverse structure. The possibility that these agents may all induce conditions of oxidative stress by various pathways to activate expression of GST genes that are regulated by the AP-1 complex is discussed.

Isolation and characterization of a human glutathione S-transferase Ha1 subunit gene

We have isolated and characterized a human liver glutathione S-transferase Ha1 subunit gene. The gene spans approximately 12 kilobases and comprises seven exons separated by six introns. The transcription initiation site has been determined by primer extension analysis. A TATA box is located 26 nucleotides upstream from the transcription initiation site, an adenine residue. RNA blot analysis reveals that the gene is expressed at significantly higher levels in human liver than in HepG2 cells. The isolation and characterization of a human glutathione S-transferase Ha1 subunit gene should facilitate a detailed analysis of its transcriptional regulation.

The human Hb (mu) class glutathione S-transferases are encoded by a dispersed gene family

The human glutathione S-transferases are products of a gene superfamily which consists of at least four gene families. The various glutathione S-transferase genes are located on different human chromosomes, and new gene(s) are still being added to the gene superfamily. We have characterized a cDNA in pGTH4 encoding human glutathione S-transferase subunit 4 (GST mu) and mapped its gene (or a homologous family member) on chromosome 1 at p31 by in situ hybridization. Genomic Southern analysis with the 3' noncoding region of the cDNA revealed at least four human DNA fragments with highly homologous sequences. Using a panel of DNAs from mouse-human somatic cell hybrids in genomic DNA hybridization we show that the Hb (or B) genes of human glutathione S-transferases are on three separate chromosomes: 1, 6, and 13. Therefore, the glutathione S-transferase B gene family, which encodes the Hb (mu) class subunits, is a dispersed gene family. The GST mu (psi) gene, whose expression is polymorphic in the human population, is probably located on chromosome 13. We propose that the GST mu (psi) gene was created by a transposition or recombination event during evolution. The null phenotype may have resulted from a lack of DNA transposition just as much as from the deletion of an inserted gene.

Purification and characterization of glutathione S-transferases from rat pancreas

Glutathione S-transferases (GSTs) of rat pancreas have been characterized and their interrelationship with fatty acid ethyl ester synthase (FAEES) has been studied. Seven GST isozymes with pI values of 9.2, 8.15, 7.8, 7.0, 6.3, 5.9 and 5.4 have been isolated and designated as rat pancreas GST suffixed by their pI values. Structural, immunological and kinetic properties of these isozymes indicated that GST 9.2 belonged to the alpha class, GST 7.8, 7.0, 6.3 and 5.9 belonged to the mu class, whereas GST 8.15 and 5.4 belong to pi class. The N-terminal sequences and pI values of the mu class isozymes suggested that rat GST subunits 3, 4 and 6 may be expressed in pancreas. N-Terminal sequences of both the pi class isozymes, GST 8.15 and 5.4, were similar to that of GST-P, but there were significant differences in the substrate specificities of these two enzymes. Results of peptide finger print studies also indicated minor structural differences between these two isozymes. None of the GST isozymes of rat pancreas expressed FAEES activity. Rat pancreas had a significant amount of FAEES activity, but it segregated independently during the purification of GST indicating that these two activities are expressed by different proteins and are not related as suggested previously.

The Drosophila glutathione S-transferase 1-1 is encoded by an intronless gene at 87B

The Drosophila glutathione S-transferase 1-1 is a dimer of a 209 amino acid subunit, designated DmGST1. DmGST1 is encoded by a member of a multigene family. Sequence analysis of a genomic clone for GST1 revealed that it is encoded by an intronless gene. We designate this gene and its other family members the GST D genes in the glutathione S-transferase gene superfamily. The Drosophila GST D genes are mapped by in situ hybridization to chromosome 3R at 87B of the polytene chromosome, which is flanked by the two clusters of hsp70 genes at 87A7 and 87C1. Cytogenetic data in the literature indicated that a puff occurred in this region under heat shock. We report that the glutathione S-transferase activity in Kco cells as determined by conjugation with 1-chloro-2,4-dinitrobenzene is elevated slightly to two-fold under heat shock. The implication of this finding is discussed.

Development and characterisation of a cyclophosphamide resistant variant of the BNML rat model for acute myelocytic leukaemia

A cyclophosphamide resistant subline (BNML/CPR) was developed in vivo in the BN rat acute myelocytic leukaemia (BNML) model. Full resistance was achieved after in vivo exposure of leukaemic animals to cyclophosphamide with, in total, 15 intraperitoneal injections of 100 mg/kg. The CPR line was cross-resistant to ifosfamide, but less so to mafosfamide. Continuous transplantation of the BNML/CPR line without a cyclophosphamide selection pressure resulted in the emergence of a subline (BNML/CPR greater than S) whose sensitivity to cyclophosphamide was similar to that of the parent BNML/S line. Both in the BNML parent line and in the BNML/CPR greater than S line, a 2p+ marker chromosome was present, whereas a 2p+q+ marker chromosome was characteristic for the BNML/CPR line. The mechanism of cyclophosphamide resistance can now be investigated in the BNML model at the DNA, at the mRNA and at the protein level.

Immunodetection with a monoclonal antibody of glutathione S-transferase mu in patients with and without carcinomas

Several monoclonal antibodies against human liver glutathione S-transferase mu were developed. One of these monoclonal antibodies, called GST-3H4 was further characterized and used in this study. In hepatic tissue, after immunoblotting, GST-3H4 strains a 27 kDa protein with a pI value of 6.2. GST-3H4 recognizes other human class-mu glutathione S-transferases, but does not detect acidic or basic glutathione S-transferases. By immunodetection with this monoclonal antibody, glutathione S-transferase mu can be demonstrated in human breast, stomach, liver, small and large intestine, mononuclear blood cells, kidney and placenta. A 100% correlation is found in the distribution of glutathione S-transferase mu when different tissues or mononuclear blood cells from the same individuals are investigated. In 62.5% of the mononuclear blood cells from controls, glutathione S-transferase mu is present. In patients with polyposis coli, breast cancer or colon cancer a similar distribution is found. Therefore no important role for glutathione S-transferase mu deficiencies in the aetiology of these diseases is suggested.

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.

Amino acid substitutions in the human glutathione S-transferases confer different specificities in the prostaglandin endoperoxide conversion pathway

The human glutathione S-transferases 1-1 and 2-2, which differ from each other by 11 amino acids, have different catalytic activities against cumene hydroperoxide and t-butyl hydroperoxide. Using prostaglandin H2 as the peroxide substrate, we found that GSH S-transferase 1-1 catalyzed the transformation of prostaglandin H2 to prostaglandin F2 alpha and E2 at a 4:1 ratio whereas GSH S-transferase 2-2 produced primarily prostaglandin D2 and F2 alpha at a 4:1 ratio. Our results indicate that GSH S-transferases catalyze the reduction and isomerization of prostaglandin H2 endoperoxide in vitro. We suggest that the amino acid substitutions between these two isozymes may be responsible for the difference in catalytic specificities. We propose that these isozymes are important reagents for the biosynthesis of various prostaglandins.

Purification and biochemical characterization of the rabbit pulmonary glutathione S-transferase: stereoselectivity and activity toward pyrene 4,5-oxide

Two homodimeric isozymes, glutathione S-transferase (GST) 25 kDa and GST 27 kDa, in equal proportion comprise the majority (greater than 75%) of the pulmonary cytosolic GST of untreated rabbits. The subunits of GST 25 kDa and GST 27 kDa are distinguishable by electrophoretic mobility (25 and 27 kDa, respectively), apparent isoelectric points (pI 7.4 and pI 9.1, respectively), and immunoreactivity. Immunoblots indicated that these subunits may be minor components in hepatic cytosol. The pulmonary isozymes could not be distinguished by their activities toward chloro-2,4-dinitrobenzene (CDNB) or activity and stereoselectivity toward pyrene 4,5-oxide (PyO). The purified GST fractions represented less than or equal to 16% of the PyO activity for pulmonary cytosol. The stereoselectivity of the cytosolic GST for the pro-S-configured oxirane carbon of PyO was not maintained in the purified preparations which were virtually nonstereoselective. Immunoprecipitation of pulmonary cytosolic GST with anti-GST 27 kDa and anti-GST 25 kDa indicated that at least 84 and 60% of the activity toward CDNB and PyO, respectively, is mediated by the two isozymes. The specific PyO activities of GST 27 kDa, GST 25 kDa, and the rabbit hepatic preparations (approximately 0.2 unit/mg) were similar to that of hepatic GST purified from horse, cow, and pig, and to human placental GST pi (0.02-0.5 unit/mg) but one-tenth that of rat hepatic GST or human hepatic GST mu. However, the activity of the hepatic cytosol from rat and human was similar to that of rabbit. Thus, some GST isozymes may be particularly susceptible to modulation of activity/stereoselectivity that can be discerned with arene oxide substrates such as PyO.

Purification and characterization of five forms of glutathione transferase from human uterus

Five glutathione transferase (GST) forms were purified from human uterus by glutathione-affinity chromatography followed by chromatofocusing, and their structural, kinetic and immunological properties were investigated. Upon SDS/polyacrylamide slab gel electrophoresis all forms resulted composed of two subunits of identical molecular size. GST V (pI 4.5) is a dimer of 23-kDa subunits. GST I (pI 6.8) and GST IV (pI 4.9) are dimers of 24-kDa subunits whereas GST II (pI 6.1) and GST III (pI 5.5) are dimers of 26.5-kDa subunits. GST V accounts for about 85-90% of the activity whereas the other isoenzymes are present in trace quantities. On the basis of the molecular mass of the subunits, amino acid composition, substrate specificities, sensitivities to inhibitors, CD spectra and immunological studies, GST V appeared very similar to transferase pi. Structural and immunological studies provide evidence that GST IV is closely related to the less 'basic' transferase (GST pI 8.5) of human skin. Extensive similarities have been found between GST II and GST III. The comparison includes amino acid compositions, subunits molecular size and immunological properties. The two enzymes, however, are kinetically distinguishable. The data presented also indicate that GST II and GST III are related to transferase mu and to transferase psi of human liver. Even though GST I has a subunit molecular mass identical to GST IV, several lines of evidence, including catalytic and immunological properties, indicate that they are different from each other. GST I seems not to be related to any of known human transferases, suggesting that it may be specific for the uterus.

Purification and characterization of glutathione S-transferases in human kidney

Four glutathione S-transferase (GST, EC 2.5.1.18) forms were purified from human kidney by S-hexylglutathione affinity chromatography followed by chromatofocusing using a fast protein liquid chromatography system. These forms were demonstrated to be identical with GSTs I, II, IV, V(pi) in human liver previously characterized by us, by SDS-polyacrylamide slab gel electrophoresis, two-dimensional gel electrophoresis and double immunodiffusion. GST III (mu) was not detected in any of 5 specimens examined. GST-pi was a major form in the kidney. The activity was 30-40% of the total activity in kidney cytosol and the protein amount was approximately 140 micrograms/g of tissue; 0.27% of the total cytosol protein amount. In many organs including the placenta, GST-pi is present at levels similar to that in the kidney but low in the liver (34 micrograms/g).

The basic glutathione S-transferases from human livers are products of separate genes

We have characterized a second cDNA sequence, pGTH2, for the human liver glutathione S-transferases Ha subunits. It is 95% homologous base-for-base to the Ha subunit 1 cDNA, pGTH1, except for its longer 3' noncoding sequences. Our results indicate that the multiple basic human liver glutathione S-transferases are products of separate genes. The proposal [Kamisaka, K., Habig, W. H., Ketley, J. N., Arias, I. M., and Jakoby, W. B. (1975) Eur. J. Biochem. 60, 153-161] that deamidation may be a physiologically important process for generating glutathione S-transferases isozyme multiplicity can be all but ruled out.

Isolation of a human liver ligandin cDNA clone and demonstration of sequence homology at ligandin loci in rats and humans

Using a monospecific antibody to the major cytosolic glutathione-S-transferase of human liver, we have isolated a cDNA clone from a human liver cDNA expression vector library in lambda gt11. The clone cross-hybridizes with a rat liver ligandin (glutathione-S-transferase 1-2) cDNA probe. The clone has an insert of 1.25 kb, a size sufficient to code for the 23 kilodalton subunit of human GST. Digestion of the insert with Hinf I produced three fragments (0.8 kb, 0.4 kb and 0.1 kb). A similar pattern of multiple bands was observed when rat liver GST1-2 cDNA probe was used for Southern blot analysis of Pst digests of rat and human genomic DNAs. These data suggest that these two functionally similar proteins exhibit sequence homology between their respective cDNAs and at ligandin loci, in spite of the lack of immuno-crossreactivity between them.

Human liver glutathione S-transferases: complete primary sequence of an Ha subunit cDNA

Multiple human liver GSH S-transferases (GST) with overlapping substrate specificities may be essential to their multiple roles in xenobiotics metabolism, drug biotransformation, and protection against peroxidative damage. Human liver GSTs are composed of at least two classes of subunits, Ha (Mr = 26,000) and Hb (Mr = 27,500). Immunological cross-reactivity and nucleic acid hybridization studies revealed a close relationship between the human Ha subunit and rat Ya, Yc subunits and their cDNAs. We have determined the nucleotide sequence of the Ha subunit 1 cDNA, pGTH1. The alignments of its coding sequence with the rat Ya and Yc cDNAs indicate that they are approximately 80% identical base-for-base without any deletion or insertion. Regions of sequence homology (greater than 50%) have also been found between pGTH1 and a corn GST cDNA and rat GST cDNAs of the Yb and Yp subunits. Among the 62 highly conserved amino acid residues of the rat GST supergene family, 56 of them are preserved in the Ha subunit 1 coding sequences. Comparison of amino-acid replacement mutations in these coding sequences revealed that the percentage divergence between the rat Ya and Yc genes is more than that between the Ha and Ya or Ha and Yc genes.