Schematic representation of cis -acting elements involved in the transcriptional regulation of the GST Ya subunit gene. cis -acting regulatory elements identified in the 5 ́-flanking region of the GST Ya subunit gene promoter, HNF1 (nucleotides -860 to - 850) and HFN4 (nucleotides -775 to -755); GRE (nucleotides -1609 to -1595) (Adapted from 3). 

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... S-conjugate formation, translocation of the glutathione S-conjugates or the corresponding cysteine S-conjugates to the kidney and renal activation by cysteine conjugate β -lyase (21). In the kidney, cysteine S-conjugates are taken up by amino acid transport systems and undergo β -lyase-catalyzed metabolism. β -lyases a pyridoxal phosphate-dependent enzyme catalyzes β -elimination reactions of cysteine S-conjugates to yield ammonia, pyruvate and -chlorovinyl- or fluoroalkylthiolates as products. In cancer chemotherapy, the ability of GSTs to produce reactive metabolites has been exploited to target tumors that over express particular transferases (24), such as the latent cytotoxic drug TER286 (now called TLK286) (25) and the prodrug PABA/NO (O2-[2,4-dinitro-5-(N-methyl-N-4-carboxyphenylamino)phenyl] 1-N,N-dimethylamino)diazen-1-ium-1,2-diolate) (26). The process of aerobic respiration can lead to the production of reactive oxygen species (super oxide anion O 2 − , hydrogen peroxide H 2 O 2 , and the hydroxyl radical • HO) (27). Free radicals primarily arise through oxidative phosphorylation, although 5-lipoxygenase-, cyclooxygenase-, cytochrome P450-, and xanthene oxidase–catalyzed reactions are also a source. Such species are scavenged by the catalytic activities of superoxide dismutase, catalase, and GPx and nonenzymatically by α -tocopherol, ascorbic acid, GSH, and bilirubin. Despite these antioxidant defenses, reactive oxygen species inflict damage on membrane lipid, DNA, protein, and carbohydrate. The GSTs both soluble and MAPEG supergene families have the capacity to reduce these and another compounds (Table 3), because they also display GPx activity, and thus protect from oxidative damage (13), for example, they can detoxify downstream products of oxidative damage such as the reactive aldehydes, 4-hydroxynonenal and acrolein (9). The GSTZ has been identified as the maleylacetoacetate isomerase that catalyzes the penultimate step in the catabolism of phenylalanine and tyrosine (7), where phenylalanine is degraded to acetoacetate and fumaric acid. The five intermediates are tyrosine, 4-hydroxyphenylpyruvate, homogentisate, aleyacetoacetate and fumarylacetoacetate. Mammal GSTs are involved in the intracellular transport of a variety of endogenous metabolites, drugs, and hormones. Particularly, GSTs are glucocorticoid-binding proteins and, thereby, may influence transport, metabolism, and action of steroids. The GSTs also participate in the intracellular binding and transport of a broad range of other lipophilic compounds including bilirubin, glucocorticoids and thyroid hormones. It has been demonstrated that testosterone and progesterone have the ability to bind GSTs with moderate affinity. Thus, GSTs could play a key role in the physiological action of these hormones (29). The metabolic pathways of steroid hormone biosynthesis leading to compounds such as testosterone and progesterone start with cholesterol and proceed in multiple steps involving oxidation and isomerization reactions that are mediated by GSTA3-3 (Figure 3) (28). The GSTA3-3 is expressed in steroidogenic tissues like testis, ovary, adrenal gland, and placenta. The GSTA1-1 is a major hepatic enzyme (2-3% of the total cytosolic protein) and is also found in significant amounts in kidney and testis. In human gonads, GSTA have been immunohistochemically identified in cells involved in hormone production, i.e. testicular interstitial Leydig cells and ovarian cells of the Graffian follicle and corpus luteum as well as cells in the reticular layer of the adrenal cortex. This selective tissue expression provides support for a role of GSTs in steroid hormone biosynthesis (28). On the other hand, GSTs contribute to the biosynthesis of pharmacologically important metabolites of arachidonic acid (7). Membrane-associated GSTs and related proteins have been linked to the metabolism of eicosanoids such as leukotrienes and prostaglandins, however, several of the soluble enzymes such as GSTA2-2, GSTM2-2, and GSTM3-3 also display activity of physiological relevance with prostaglandins (28). The regulation of cytosolic GSTs is subjected to a complex set of endogenous parameters. These include development, sex and tissue specific factors, as well as a large number of xenobiotics, inducing agents such as PAHs, phenolic antioxidants, Michael acceptors, reactive oxygen species, isothiocyanates, trivalents arsenicals, barbiturates and synthetic glucocorticoids (6). Eaton and Bammler (30), describe that the majority of the GSTs are regulated by glucocorticoid-response elements (GRE), xenobiotic response elements (XRE), and antioxidant-response elements (ARE) (Figure 3). Thus, induction of GSTs by dexamethasone, 3-methyl-chloranthene, dioxins, hydroxyanisole (BHA), butylated hidroxytoluene (BHT), and oltipraz has been described (31). Okuda et al. (32) characterized the rat P (Yp) gene; it contains 7 exons and 6 introns and spans approximately 3 kilobase pairs (Figure 4). Cowell et al. (33) and Morrow et al. (34) had characterized the human GSTM gene. Analysis of the human GSTT promoter revealed four putative transcription regulatory motifs. These sequences included a TATA box, 29 base pairs upstream from the start of transcription, two Spl recognition sequences (GGGCGG) at nucleotides -46 to -41 and -56 to -51 and an AP-1 recognition sequence (TGACTCA) at nucleotide position -69 to -63. Comparison of the human GSTM gene with the homologous rat gene disclosed extensive conservation of genomic organization between the two species (3). Functional AP-1 and SP1 response elements have also been identified in the 5 ́regulatory region of human GSTP1 gene. Post-transcriptional mechanisms such as mRNA stability are also involved in regulating human GSTP1-1 protein levels (35). Also, the expression of human GSTP1 may be influenced by the methylation status of a CpG island in the regulatory region of the gene (36). Also, the cytosolic GSTs and GSH synthesis is up-regulated by electrophiles through the Nrf2 transcription factor via the cis-acting ARE (indeed, also called electrophile response element) (13). Thimmulappa et al. (37), found several Nrf2- dependent genes coding for isozymes of GSTs, including GSTM and GSTA. The regulation of GSTM1 can be activated by electrophiles that react with cysteine 49, it was initially suggested to be particularly reactive (13). The notion that Nrf2 mediates basal expression of GSTs by endogenous thiol-active endobiotics is supported by the fact that in null mice of this transcription factor the normal homeostatic levels of many A, M, and P transferases are reduced (37). Variation in GSTs alleles is very common in the population and will presumably make a significant contribution to inter-individual differences in drug metabolism. Although cytosolic GST enzymes have a key position in biological detoxification processes, two of the most relevant human isoenzymes, GSTT1-1 and GSTM1-1, are genetically deleted (non-functional alleles GSTT1*0 and GSTM1*0) (38) in a high percentage of the human population with major ethnic differences. GSTT1-1 is highly conserved during evolution. There are three alleles in GSTM1 locus: GSTM1*A, GSTM1*B and GSTM1*0, this last allele corresponds to a gene deletion and homozygotes express no protein (Table 4) (39). GSTM1*A and GSTM1*B differ by one base in exon 7, the catalytic properties of the enzymes encoded by these alleles are similar. The genetic polymorphisms of the GSTP1 were describe in 1997 by Ali- Osman et al. (40), the wild type genotype is known as GSTP1*A, there are three alleles of GSTP1 (Table 4) with not known effects. The first hints about the existence of a polymorphic glutathione S- transferase Theta came from Peter et al. (41) demonstrating that erythrocytes from only 60% of individuals (“conjugators”) catalyze the conjugation of methyl chloride with glutathione while remaining 40% (“non-conjugators”) lack this activity. There are two genes in GST Theta family –GSTT1 and GSTT2- are located on chromosome 22 and are separated by about 50 kb. Like GSTM1, the GSTT1 locus has a deleted express no protein (42). More recently, Alexandrie et al. (43) found a novel functional polymorphism in the GSTT1 gene. Sequencing of GSTT1 cDNA revealed a single nucleotide substitution, 310A>C, that altered the amino acid residue 104 from threonine to proline (T104P). Modeling studies of GSTT1 have suggested that residue 104 is located in the middle of α -helix 4. Introduction of a α -helix-disrupting proline most likely distorts the conformation of the protein. Individuals that lacked GSTT1 activity and carried the variant allele, tentatively denoted GSTT1*B, had no detectable GSTT1 immunoreactive protein. Pemble et al. (42) showed that the GSTT1 gene was absent around 38% of the population. The presence or absence of the gene was coincident with the conjugator (GSTT1+) and nonconjugator (GSTT1-) phenotypes, respectively. Genotoxic effects such as induction of sister chromatid exchanges (SCE) after exposure of human blood to methyl bromide and other agents in vitro were found to be more pronounced in nonconjugators. Even the background levels of SCE were higher in the nonconjugator phenotype (44). In this aspect, we realized some experiments in human lymphocytes in vitro exposed to different concentrations of DCM; we found that high conjugators had more SCE that the low conjugators (Figure 5), showing that GSTT1 could be a susceptibility factor when humans are environmentally or occupationally exposed to dihalomethanes (45). The genetic frequency of these polymorphic proteins (GSTM1 and GSTT1) is variable between ethnic groups (Table 5). GSTM1 is inherited as autosomal dominant and between 40 and 60% of most populations express GSTM1. GSTT1-1 is also polymorphic in humans, with 20% of Caucasians and 80% of Asians lacking the enzyme. Recently we have detected that the frequency of the null allele for GSTT1 in ...