Effect of the aging process on the gender and phenobarbital dependent expression of glutathione S-transferase subunits in brown Norway rat liver

The effect of age, gender and phenobarbital treatment on the hepatic cytosolic glutathione S-transferase subunit composition was studied in Brown Norway rats. Affinity chromatography followed by reversed phase HPLC was used in order to separate the various glutathione S-transferase subunits. Corresponding steady-state mRNA levels were measured by Northern Blot analysis using cDNA clones hybridizing to mRNA encoding glutathione S-transferase subunits 1/2, 3/4 and 7, respectively. In all the age groups studied (15, 25, 53, 99, 112 and 136 weeks) the total amount of glutathione S-transferase protein was in untreated rats significantly higher in males (132 micrograms/mg cytosolic protein) than in females (91 micrograms/mg cytosolic protein) and significant gender dependent differences in the subunit composition were demonstrated. Aging seemed to be of minor importance in untreated as well as in phenobarbital treated rats. Under control conditions, the subunit composition of male rats between 15 and 136 weeks old consisted of 28, 12, 11 and 49% of subunits 1, 2, 3 and 4 respectively and of female animals of the same age groups of 38, 26, 7 and 30%, respectively. In all the age groups studied phenobarbital administration (45 mg/kg body weight, i.p., once a day for 7 days) doubled total glutathione S-transferase protein in both genders and affected the subunit composition in a significant way, emphasizing the already existing differences between genders. Subunits 1, 2 and 3, especially, were increased in male rats in comparison to females resulting in the observation that levels of glutathione S-transferase subunits studied became higher in males than in their female counterparts. The HPLC results were confirmed by steady-state mRNA analysis. In untreated rats, higher levels of mRNA encoding glutathione S-transferase subunits 1/2 and 3/4 were present in male than in female livers. Phenobarbital treatment increased mRNA levels in both genders. Subunit 7 was never detected. These effects were demonstrated in both young and old rats.

Cloning of a mu-class glutathione S-transferase complementary DNA and characterization of its glucocorticoid inducibility in a smooth muscle tumor cell line

A cDNA (designated hGSTYBX) encompassing the complete coding sequence of a hamster mu-class glutathione S-transferase (GST) subunit was cloned from a lambda ZAP library constructed with mRNA isolated from triamcinolone acetonide-treated smooth muscle tumor cells (DDT1 MF-2). Analysis of its nucleotide and deduced amino acid sequences demonstrated highest homology to the rat mu-class GST YB2 subunit. In proliferating subconfluent cells, in which constitutive expression of hGSTYBX mRNA was undetectable, glucocorticoid treatment induced hGSTYBX expression after a time lag of 3 h, and maximal induction occurred at 10 h. Nuclear run-on analysis showed that glucocorticoid induction resulted at least in part from an increased rate of transcription. Simultaneous treatment with glucocorticoid and cycloheximide prevented glucocorticoid induction, but had little effect on basal expression in confluent cells. In contrast, cycloheximide treatment 3 h after glucocorticoid treatment resulted in nearly full induction. These results taken together suggest that hGSTYBX induction may be a secondary glucocorticoid response.

Evidence for a glycoconjugate form of glutathione S-transferase pI

The anionic form of glutathione S-transferase from human (GST pi) and rat (GST Yp) sources has been shown to exist in multiple forms which have similar molecular weights but different isoelectric points (pIs). Treatment with endoglycosidase H caused the acidic forms of GST Yp to be converted to proteins with more basic pIs as compared to the untreated control mixtures, suggesting that an N-linked mannose moiety containing acidic residues had been removed. Inability to detect these carbohydrates by techniques requiring unsubstituted vicinal hydroxyls further suggested acidic substitutions on the sugar moiety. GST pi/Yp carbohydrate modifications were also identified by differential staining procedures. These data represent the first indication that glycosylation of GST can occur. Additionally, this may offer an explanation for the often seen microheterogeneity within a class of GST isozymes.

Cloning, expression, and characterization of a class-mu glutathione transferase from human muscle, the product of the GST4 locus

A class-mu glutathione transferase cDNA clone, GTHMUS, was isolated from human myoblasts and its sequence was determined. The sequence predicts a protein of molecular weight 25,599 whose 24 amino-terminal residues are identical to those of the class-mu isoenzyme expressed from the GST4 locus. The GTHMUS cDNA shares 93.7% nucleotide sequence identity with a human liver cDNA clone, GTH411, that is encoded at the GST1 locus. Comparison of the liver and muscle cDNA sequences shows two regions of remarkable sequence conservation: a 140-nucleotide region in the 5' coding portion of the molecule that has a single silent nucleotide substitution, and a 550-nucleotide region, including the entire 3' noncoding region, that has only three nucleotide substitutions or deletions. This sequence conservation suggests that gene conversion has occurred between the human GST1 and GST4 glutathione transferase gene loci. The human muscle and liver glutathione transferase clones GTHMUS and GTH411 have been expressed in Escherichia coli. The kinetic mechanism of the muscle enzyme was examined in product inhibition studies. The inhibition patterns are best modeled by a steady-state ordered bi-bi reaction mechanism. Glutathione is the first substrate bound and chloride ion is the first product released. Chloride ion inhibits the muscle enzyme.

The initial-rate kinetics of mouse glutathione S-transferase YfYf. Evidence for an allosteric site for ethacrynic acid

Mouse glutathione S-transferase GST YfYf (an orthologue of GST P or 7-7 in the rat and of GST pi in the human) was found to have a subunit Mr of 24,500 and cross-reacted with anti-(rat GST YfYf). N-Terminal analysis showed a close similarity to the rat, human and bovine orthologues. On isoelectric focusing the native enzyme had a pI of 8.3 and a pI of 7.3 in the presence of urea. Initial-rate studies with 1-chloro-2,4-dinitrobenzene (CDNB) and GSH as substrates and inhibition studies with the product of the enzyme-catalysed conjugation of CDNB and GSH, S-(2,4-dinitrophenyl)glutathione, indicated a rapid-equilibrium random mechanism for the enzyme. The diuretic drug ethacrynic acid was found to be simultaneously a competitive inhibitor and an uncompetitive activator of the enzyme (with CDNB as the substrate whose concentration was varied). By using a computer simulation program (EKPLOT) a model was developed that would explain the experimental data. It is proposed that ethacrynic acid can compete with CDNB at the active site but simultaneously bind to an allosteric site on the enzyme, causing an elevation in the Vmax. for the conjugation of CDNB and GSH. The implications of such an activation mechanism for an enzyme potentially conjugating a range of xenobiotic compounds are discussed.

The contribution of the C-terminal sequence to the catalytic activity of GST2, a human alpha-class glutathione transferase

A plasmid vector was constructed that encodes the expression in Escherichia coli of a truncated form of GST2, a human Alpha-class glutathione transferase. The truncated enzyme, GST2del210, has 12 residues deleted from the C-terminus and has the last two residues of the new C-terminal mutated from aspartic acid and glutamic acid to histidine and glycine respectively. GST2del210 has substantially diminished specific activity with either 1-chloro-2,4-dinitrobenzene or cumene hydroperoxide as substrate. The affinity of the truncated enzyme for a GSH-agarose matrix was also diminished, but sufficient interaction remained to enable affinity purification. Inhibition of GST2del210 by bromosulphophthalein was not altered. In contrast, this truncated form was not inhibited by S-pentylglutathione, a competitive inhibitor of the wild-type GST2 isoenzyme. The results show that the C-terminal segment of the Alpha-class glutathione transferases may form a component of the hydrophobic substrate-binding site. In contrast, this region appears not to be directly involved in GSH binding and is not absolutely essential for catalytic activity.

Class pi glutathione S-transferase from pig lung. Purification, biochemical characterization, primary structure and crystallization

A cytosolic glutathione S-transferase from pig lung was purified 210-fold to apparent homogeneity. The enzyme was classified as a class pi isoenzyme on the basis of its physical and chemical properties. It is homodimeric with a subunit Mr of 23,500, has a pI of 7.2, and shows a high specific activity towards ethacrynic acid. The glutathione analogues, S-hexylglutathione and glutathione sulfonate, were strong reversible inhibitors. The enzyme's primary structure, established entirely by protein chemical methods, consists of 203 amino acids and is highly similar (82-84% residue identity) to the rat and human class pi isoenzymes. Furthermore, there was no evidence of microheterogeneity or post-translational modifications. Each subunit contains a highly reactive cysteine residue, the modification of which leads to enzyme inactivation. None of the cysteine residues in the pig enzyme appear to form intramolecular disulfide bonds. Singel crystals of the glutathione-S-transferase-glutathione-sulfonate complex were obtained by the hanging-drop method of vapour diffusion from poly(ethylene glycol) 4000 solutions. The crystals belong to the orthorhombic space group P212121 with unit cell dimensions of a = 10.125 nm, b = 8.253 nm and c = 5.428 nm and diffract to better than 0.22 nm.

Characterization of glutathione transferase from Gammarus italicus

1. By using affinity chromatography and chromatofocusing analysis at least two major glutathione transferases, named GST II and GST III can be isolated from Gammarus italicus. 2. GST II has an isoelectric point at pH 5.0 and is composed of two subunits with an apparent molecular mass of 28 KDa. 3. GST III which has an isoelectric point at pH 4.6 was found to be an heterodimer of 27 KDa and 28 KDa. 4. The 28 KDa subunit cross-reacted in immunoblotting analysis with antisera raised against pi class GST, whereas none of the antisera raised against alpha, mu and pi class GSTs cross-reacted with the 27 KDa subunit.

The major glutathione S-transferase in salmonid fish livers is homologous to the mammalian pi-class GST

1. The hepatic glutathione S-transferase (GST) isoenzymes were isolated and characterized from salmon, sea trout and rainbow trout. 2. In all three species the predominant GST expressed comprised subunits of Mr 24,800. These subunits each co-migrated with the rat pi-class Yf polypeptide during SDS/polyacrylamide gel electrophoresis. 3. Western blotting experiments demonstrated immunochemical cross-reactivity between the major salmonid and the rat pi-class GSTs. 4. The salmon GST of subunit Mr 24,800 was digested with cyanogen bromide and the peptides, once purified by reverse-phase HPLC, were subjected to automated amino acid sequencing. 5. Over the region sequenced, the salmon GST possessed about 65% homology with the rat and human pi-class GST.

The isolation and characterization of the major glutathione S-transferase from the squid Loligo vulgaris

1. The major glutathione S-transferase (GST) from the common squid Loligo vulgaris has been purified and shown to be a homodimer of subunit molecular mass 24,000 and pI 6.8. 2. It has high activity towards 1-chloro-2,4-dinitrobenzene, p-nitrobenzyl chloride, 4-hydroxynon-2-enal and linoleic acid hydroperoxide, low activity with 1,2-dichloro-4-nitrobenzene and no activity with ethacrynic acid, trans-4-phenyl-3-buten-2-one and 1,2-epoxy-3-(p-nitrophenoxy)propane. 3. The L. vulgaris GST did not cross-react with any of the available polyclonal antibodies raised against mammalian GSTs. 4. Forty amino acids of its N-terminal sequence have been determined. 5. Its activities and primary structure are compared with related proteins from other species.

Partial purification and isoelectric focusing patterns of the buffalo (Bubalus bubalis) and the Kedah-Kelantan cattle (Bos indicus) glutathione transferases

1. Glutathione transferases from the liver, lung and kidney tissues of the buffalo (Bubalus bubalis) and the Kedah-Kelantan cattle (Bos indicus) were partially purified by ammonium sulphate precipitation and Sephadex G-75 gel filtration. 2. Liver tissue contains the highest enzyme activity when compared to the lung and kidney tissues. 3. The activity in cattle is higher than that in the buffalo. 4. Isoelectric focusing separates the activities into the acidic, near neutral and basic fractions. 5. The focused patterns are different for each of the tissues and in each of the species investigated.

Hybrid formation of rabbit and rat hepatic glutathione S-transferases

1. A reconstitution experiment resulted in the formation of new proteins between limited combinations of rat and rabbit hepatic glutathione S-transferases: AA(subunit composition: YcYc) and R3b(Y3Y3), Lig(YaYa) and R3b(Y3Y3), and A(Yb1Yb1) and R2(Y2Y2). 2. It was demonstrated that the new protein formed between R2 and A had the subunit composition of Y2Yb1, suggesting a hybrid of rabbit (R2) and rat isozyme (A). 3. This hybrid protein showed intermediate spec. acts between those of R2 and A when either 1-chloro-2,4-dinitrobenzene (CDNB) or 1,2-dichloro-4-nitrobenzene (DCNB) was employed as the substrate.

Effect of protein-free diet on activities and subunits of glutathione S-transferase in livers of young and aged female rats

Female Fischer-344 rats of different ages (8 and 25 months old) were fed a protein-free diet (PFD) for 7 days and refed a normal diet (ND) (23% protein) thereafter. Rats were killed immediately after the PFD was stopped (day 0) and at different time intervals during refeeding of a ND. Four subunits (1,2,3 and 4) and activities of glutathione S-transferases (GSTs) toward five different substrates, [styrene oxide (STOX), 1,2-dichloro-4-nitrobenzene (DCNB), 1-chloro-2,4-dinitro benzene (CDNB), sulfobromophthalein (BSP) and benzalacetone (PBO)] were determined. There were no significant differences between young and old rats in the liver enzyme activities before the PFD. The PFD caused significant decreases in activities for three substrates (DCNB, BSP and STOX) in both age groups, with no significant differences between young and old rats a day 0. During recovery from the PFD, activities for the three substrates exceeded basal levels in young rats but at different time intervals (STOX, day 2; BSP, day 5; DCNB, day 9), while enzyme values in old rats tended to return slowly to basal values with no "overshoot." Concentrations of subunits 3 and 4 in young rat livers that were depressed by the PFD did not recover until day 9 of the ND, while subunits 2 and especially 1 increased during the ND refeeding, overshooting the basal levels. In contrast, in old rat livers the only change was a reduction of subunit 1 by the PFD and its gradual recovery during ND refeeding. These results demonstrate that our previous observation of overshooting of enzyme activities in mice is reproducible in rats but with certain substrate specificities. Furthermore, changes in subunit concentrations caused by aging and a PFD are more complex than what was predicted from changes in enzyme activities of GSTs.

Synthesis and use of an isoform-specific affinity matrix in the purification of glutathione S-transferases from the housefly, Musca domestica (L.)

Glutathione may be linked to an agarose matrix which has been activated by treatment with epichlorhydrin. The resulting resin displayed group selectivity for the glutathione S-transferases of the housefly Musca domestica (L). The isoenzymes of low isoelectric point, which have little activity with substrates other than 1-chloro-2,4-dinitrobenzene, bound strongly to this matrix and were eluted with 10 mM glutathione at pH 7.4. On the other hand, the group of isoenzymes of higher isoelectric point, showing activity with other substrates such as 3,4-dichloronitrobenzene, did not bind. These isoenzymes did bind to a sulfobromophthalein-glutathione conjugate immobilized on agarose and could be eluted with 5 mM sulfobromophthalein at pH 7.4. The immobilized glutathione resin bound rat liver glutathione S-transferase subunits from all three molecular weight classes.

Influence of hormones and drugs on glutathione-S-transferase levels in primary culture of adult rat hepatocytes

GST activities against 1-Chloro-2,4-dinitrobenzene (CDNB) and 1,2-dichloro-4-nitrobenzene (DCNB) were measured in isolated and cultured adult rat hepatocytes. Within 24 h in culture, both GST activities decreased to about 70% and either stabilized at this level (CDNB) or recovered (DCNB) to the initial level. Use of hyaluronidase in addition to collagenase during the isolation of the cells strongly reduced both activities and its stimulation by various drugs for up to 168 h. The hormones insulin, glucagon, triiodothyronine, estradiol, testosterone, and progesterone did not affect GST activity, while dexamethasone showed some interference. In the presence of dexamethasone the activity against CDNB was mainly stimulated by the combination of methylcholanthrene (MC) and phenobarbital (PB) to about 260% within 168 h. The activity against DCNB was stimulated predominantly by MC alone reaching 170% after 168 h. Quantification of the GST subunits Ya, Yb1 and Yp by an ELISA technique revealed a strong decrease of Ya, a transient increase of Yb1 after 24 h followed by a moderate decrease, and a stable low level of the transformation marker Yp during cultivation. The level of Ya was markedly induced by PB, particularly in combination with MC. The level of Yb1 was equally induced by MC or PB with no synergistic effect. Yp was not affected by these drugs. None of the hormones affected the level of these GST subunits. These results indicate that the physiological type of regulation of the GSTs is maintained during primary culture and no signs of dedifferentiation or transformation are observed. Furthermore, they demonstrate that the interaction of drugs and hormones and their inducing potential can be efficiently studied in the cultured hepatocytes.

Evidence for identifying fatty acids in rat liver glutathione S-transferase and its possible involvement in the secondary structure

A rat liver glutathione S-transferase isozyme (GST 3-3) has been purified to apparent electrophoretic homogeneity by procedures including Sephadex G-100, S-hexylglutathione-linked Sepharose, and CM-cellulose column chromatographies. The present study provides evidence for the existence of endogenous fatty acids in the purified GST 3-3 by gas-liquid chromatographic and mass-spectrometric analyses. The liver GST isozyme associated long chain fatty acids such as 14:0, 16:0, 18:0, and 18:1 and the molar ratio of fatty acids to the protein was estimated to be around 3.2. When the enzyme preparation was freed of fatty acids by a mild delipidization technique using Lipidex, the GST activity was significantly decreased. Computer analysis of the circular dichroism spectra revealed that rat liver GST 3-3 contained approximately 49% alpha-helix and 24% random coil. By delipidizing, the enzyme's alpha-helix was decreased to 4% and the random coil was in turn increased to 62%. The enzymatic and structural properties of the delipidized enzyme, however, could be restored to nearly the original levels by recombining with the fatty acids. These findings suggest that weakly bound fatty acids are responsible for the functional capacity of the GST by virtue of changing the protein conformation.

Identification of rat liver glutathione S-transferase Yb subunits by partial N-terminal sequencing after electroblotting of proteins onto a polyvinylidene difluoride membrane from an analytical isoelectric focusing gel

Rat liver glutathione S-transferases were partially purified using S-hexyl glutathione affinity chromatography, followed by native isoelectric focusing employing a pH 7-11 or pH 3-10 gradient. Proteins were excised and eluted from the gel for determination of subunit composition using sodium dodecyl sulfate-polyacrylamide gel electrophoresis. In separate experiments, isoelectric focusing gels were equilibrated with a sodium dodecyl sulfate-containing buffer at high pH, and proteins on the gel were electroblotted onto a polyvinylidene difluoride membrane, utilizing graphite plates as electrodes. The membrane-bound proteins were visualized by Coomassie Brilliant Blue staining. The protein bands were then excised from the membrane and inserted into a gas phase sequenator for direct sequencing. N-Terminal sequences thus determined were compared with published cDNA sequences. The isoelectric points (pIs) and positions on the isoelectric focusing gel of Yb1Yb1, Yb1Yb2 and Yb2Yb2 subunits were determined. We have also located on the pH 3-10 focusing gel an N-terminal blocked glutathione S-transferase which has a molecular weight similar to Yb subunits.

Sex differences in the subunits of glutathione-S-transferase isoenzyme from rat and human kidney

Glutathione-S-transferase (GST) isoenzymes were purified from cytosolic preparations from kidneys of male and female rats and kidney cortical specimens from 2 male and 1 female human subjects. GST isoenzyme expression was analyzed by SDS-PAGE, measurement of catalytic activities with specific substrates and determination of their subunits by ELISA and Western blotting using specific antibodies. GST from female rat kidneys showed a preponderance of subunits 3 and 4; levels of these isoenzymes were 3-4 times greater in females than in males. Levels of subunits 1 and 2 were 1.5-2 times greater in the male rat kidneys. Additional minor bands at 24 and 22 kD were observed in GST preparations from both male and female rat kidneys while a band at 25.3 kD was observed only in the male rat kidney. These bands did not react with antibodies to GST 1-1, GST 2-2 or GST 3-4. Both male and female human kidney samples contained GST isoenzymes comparable to the near-neutral (25-5 kD) and basic forms (25 kD) of GSTs found in human liver. In addition a 28-kD band was present in GST preparations from both male and female human kidneys. Additional bands at 29 and 25.2 kD were present only in male human kidneys. Both the kidney cytosol and the total GSTs prepared from female rats shared 2- to 4-fold greater activity with 1,2-dichloro-4-nitrobenzene, ethacrynic acid and trans-4-phenyl-3-buten-2-one than those from males. The measurement of specific subunit amounts by ELISA were in agreement with these results.(ABSTRACT TRUNCATED AT 250 WORDS)