Mammalian class theta GST and differential susceptibility to carcinogens: a review

https://doi.org/10.1016/S1383-5742(00)00050-8Get rights and content

Abstract

Glutathione S-transferases (GSTs) are an important part of the cellular detoxification system and, perhaps, evolved to protect cells against reactive oxygen metabolites. Theta is considered the most ancient among the GSTs and theta-like GSTs are found in mammals, fish, insects, plants, unicellular algae, and bacteria. It is thought that an ancestral theta-gene underwent an early duplication before the divergence of fungi and animals and further duplications generated the variety of the other classes of GSTs (alpha, mu, phi, etc.). The comparison of the aminoacidic homologies among mammals suggests that a duplication of an ancient GST theta occurred before the speciation of mammals and resulted in the subunits GSTT1 and GSTT2. The ancestral GST theta has a dehalogenase activity towards several halogenated compounds, such as the dichloromethane. In fact, some aerobic and anaerobic methylotrophic bacteria can use these molecules as the sole carbon and energy source. The mammalian GST theta cannot sustain the growth of bacteria but still retains the dehalogenating activity. Therefore, although mammalian GST theta behaves as a scavenger towards electrophiles, such as epoxides, it acts also as metabolic activator for halogenated compounds, producing a variety of intermediates potentially dangerous for DNA and cells. For example, mice exposed to dichloromethane show a dose-dependent incidence of cancer via the GSTT1-1 pathway. Because GSTT1-1 is polymorphic in humans, with about 20% of Caucasians and 80% of Asians lacking the enzyme, the relationship between the phenotype and the incidence of cancer has been investigated extensively in order to detect GSTT1-1-associated differential susceptibility towards endogenous or exogenous carcinogens. The lack of the enzyme is related to a slightly increased risk of cancer of the bladder, gastro-intestinal tract, and for tobacco-related tumors (lung or oral cavity). More pronounced risks were found in males with the GSTT1-null genotype for brain diseases and skin basal cell carcinomas not related to sunlight exposures. Moreover, there was an increased risk of kidney and liver tumors in humans with the GSTT1-1 positive genotype following exposures to halogenated solvents. Interestingly, the liver and kidney are two organs that express the highest level of GST theta in the human body. Thus, the GSTT1-1 genotype is suspected to confer decreased or increased risk of cancer in relation to the source of exposure; in vitro studies, mostly conducted on metabolites of butadiene, confirm the protective action of GSTT1-1, whereas, thus far, experimental studies prove that the increasing risk is limited.

Introduction

The glutathione S-transferases (GSTs) are known to catalyze the conjugation of glutathione (GSH) with different species of electrophilic compounds. GSTs are an important part of the cellular detoxification system and, perhaps, evolved to protect cells against reactive oxygen metabolites. These proteins are found in all eukaryotic and prokaryotic systems, in the cytoplasm, in the microsomes and in mitochondria [1], [2]. The soluble GSTs exist as dimeric proteins of approximately 25 kDa, and the sequences and the known three-dimensional (3D) structures suggest that these proteins share a common ancestry, though the precise details of their evolution remain obscure. They are expressed at high levels in mammalian liver constituting up to 4% of the total soluble proteins [3], and at least seven distinct classes of soluble GSTs have been identified thus far: alpha (α), mu (μ), pi (π), sigma (σ), theta (θ), kappa (κ), and zeta (ζ). This classification is in accordance with the substrate specificity, chemical affinity, structure, aminoacid sequence and kinetic behavior of the enzyme.

Many excellent reviews have been published on GSTs. The present review focuses on the theta class. In comparison to other classes, the theta class has been discovered quite recently, due to the inability of GSH affinity matrices to retain the enzyme and the easy loss of activity during the purification steps [4]. Theta is one of the most interesting GSTs in terms of evolution, biochemistry, polymorphic allelism in humans, ethnical differences, and influence on human cancer risks. The theta class is so far one of the best characterized GSTs with regard to its role in the processes occurring between exposure to mutagens and the induction of DNA damage leading to mutations and cancer. These features of the GST theta class are reviewed in the present paper.

Section snippets

Nomenclature

Several different nomenclatures have been adopted during the years as new GSTs were discovered. For example, the subunit of the murine GST theta used to be called “Yrs”, whereas “GST 12” and “GST 5” were two GSTs theta found in the rat. Because soluble GSTs are formed by two identical subunits, the active forms of those GST theta enzymes were called GST Yrs–Yrs, GST 5–5, or GST 12–12 [4], [5], [6], [7]. A heterodimeric form composed by the subunits Yrs and Yrs′, was also reported in the

Chromosomal location

Human GSTT1 and GSTT2 genes were colocalized, by cell–cell hybridization, in the same chromosomic region on human chromosome 22 and, by in situ hybridization, to the subband 22q11.2 [11], [12]. The absence of other regions of hybridization suggested that there are no closely related sequences scattered throughout the genome or that, if there are, they must be clustered nearby [11]. The syntheny of GSTT1 and GSTT2 genes is conserved in the mouse. The mGSTT1 gene was found, by in situ

Description

In humans, glutathione-dependent conjugation of halomethanes, such as DCM, is dimorphic, with “conjugator” and “non-conjugator” phenotypes [60]. These phenotypes are due to a genetic polymorphism occurring in the human GSTT1 gene [19]. The polymorphism consists of a deletion of the whole gene or part of it, resulting in the lack of active GSTT1-1 enzyme, easily detectable with PCR-based assays or with hybridization-based methods [61], [62]. The genotype with the homozygous deletion of the GSTT1

Expression in different tissues

The class theta is highly expressed in human adult liver but not in the fetal liver [79], [80]. It is expressed in erythrocytes, lung, kidney, brain, skeletal muscles, heart, small intestine, and spleen [15], [80], as well as in the colon mucosal cytosol [9]. In comparison to other GSTs, such as mu and phi, the activity of GST theta in lymphocytes is undetectable [15]. Studies on humans, rats and mice show a similar pattern of tissue expression, with the highest levels in liver, and the lowest

Substrates for GST theta

Among the known substrates processed by GST theta, dichloromethane (DCM) is one of the most thoroughly studied [4]. The fact that mammalian GST theta can efficiently metabolize DCM, producing formaldehyde without consuming GSH, is a reminiscence of its ancestor DCM-dehalogenase, as discussed earlier. The pathway of reaction involving GSTT1-1, GSH, and DCM is reported in detail in Fig. 7. DCM attracted the attention of researchers because it is a very effective carcinogen in mice, but not in

Association between GSTT1 polymorphism and specific diseases

As the presence of the GSTT1 gene might modulate the biological effects of genotoxicants, the GSTT1 polymorphism is suspected to affect the risk of cancer in humans, in relation to the source of exposure. In fact, it is known that increased expression of GSTT1 in rats fed with GSTT1-inducers is able to prevent some cancers, other types of cancer are increased, depending on the carcinogen employed [85]. Moreover, simulated calculations of the incidence of cancer for subjects exposed to DCM

Conclusions

In spite of the relatively recent discovery of the GSTT1-polymorphism, several studies have provided evidence to suggest that individuals lacking the GSTT1-1 enzyme might be at an increased risk of cancer of different organs, whereas evidence that GSTT1-1 positive individuals have an increased risk of cancer to exposure to halogenated compounds are rather limited. Since the GSTT1-null genotype is highly associated with BCC of the skin (not related to UV-light exposure) and with brain tumors, it

Acknowledgments

S. Landi acknowledges the support of a Research Associate Award from the National Research Council, US National Academy of Sciences. This manuscript was reviewed by the National Health and Environmental Protection Agency, and approved for publication. Approval does not signify that the contents necessarily reflect the views and policies of the agency, or the mention of trade names or commercial products constitute endorsement or recommendation for use.

References (240)

  • A. Hiratsuka et al.

    Guinea pig liver Mu-class glutathione S-transferase M1-2 cross-reacts with antibodies to both rat Mu- and theta-class glutathione S-transferases

    Arch. Biochem. Biophys.

    (1998)
  • S. Liu et al.

    Contribution of tyrosine 6 to the catalytic mechanism of isoenzyme 3-3 of glutathione S-transferase

    J. Biol. Chem.

    (1992)
  • A.M. Caccuri et al.

    Catalytic mechanism and role of hydroxyl residues in the active site of theta class glutathione S-transferases. Investigation of Ser-9 and Tyr-113 in a glutathione S-transferase from the Australian sheep blowfly, Lucilia cuprina

    J. Biol. Chem.

    (1997)
  • S. Ouwerkerk-Mahadevan et al.

    Inhibition of glutathione conjugation in the rat in vivo by analogues of glutathione conjugates

    Chem. Biol. Interact.

    (1998)
  • K. Zemzoumi et al.

    Cloning of a Leishmania major gene encoding for an antigen with extensive homology to ribosomal protein S3a

    Gene

    (1999)
  • R. Kodym et al.

    The cloning and characterization of a new stress response protein. A mammalian member of a family of theta class glutathione S-transferase-like proteins

    J. Biol. Chem.

    (1999)
  • T. Hiltonen et al.

    A cDNA coding for glutathione S-transferase from the unicellular green algae Coccomyxa s.p

    Gene

    (1996)
  • K.S. Lin et al.

    Anionic glutathione S-transferases in shrimp eyes

    Comp. Biochem. Physiol.

    (1993)
  • E. Egaas et al.

    The separation and identification of glutathione S-transferase subunits from Orthosia gothica

    Insect, Biochem. Mol. Biol.

    (1995)
  • M.F. Lopez et al.

    A glutathione S-transferase (GST) isozyme from broccoli with significant sequence homology to the mammalian theta-class of GSTs

    Biochim. Biophys. Acta

    (1994)
  • F.A. Blocki et al.

    Reaction of rat liver glutathione S-transferases and bacterial dichloromethane dehalogenase with dihalomethanes

    J. Biol. Chem.

    (1994)
  • S.Z. Abdel-Rahman et al.

    A multiplex PCR procedure for polymorphic analysis of GSTM1 and GSTT1genes in population studies

    Cancer Lett.

    (1996)
  • C. Bruhn et al.

    Concordance between enzyme activity and genotype of glutathione S-transferase theta (GSTT1)

    Biochem. Pharmacol.

    (1998)
  • J.P. Bogaards et al.

    Interindividual differences in the in vitro conjugation of mthylene chloride with glutathione S-transferase in 22 human liver samples

    Biochem. Pharmacol.

    (1993)
  • M.P. Chamberlain et al.

    Investigations of the pathways of toxicity of methyl iodide in the rat nasal cavity

    Toxicology

    (1998)
  • J.J. Bogaards et al.

    Conjugation of isoprene monoepoxides with glutathione, catalyzed by alpha, mu, pi and theta-class glutathione S-transferases of rat and man

    Chem. Biol. Interact.

    (1999)
  • E.M.M. van Lieshout et al.

    Non-steroidal anti-inflammatory drugs enhance glutathione S-transferase theta levels in rat colon

    Biochim. Biophys. Acta

    (1998)
  • M. Casanova et al.

    Dichloromethane metabolism to formaldehyde and reaction of formaldehyde with nucleic acids in hepatocytes of rodents and humans with and without glutathione S-transferase T1 and M1 genes

    Fundam. Appl. Toxicol.

    (1997)
  • A. Hiratsuka et al.

    Subunit Ya-specific glutathione peroxidase activity toward cholesterol 7-hydroperoxides of glutathione S-transferases in cytosols from rat liver and skin

    J. Biol. Chem.

    (1997)
  • S.E. Pemble et al.

    Glutathione S-transferase class Kappa: characterization by the cloning ofrat mitochondrial GST and identification of a human homologue

    Biochem. J.

    (1996)
  • D.L. Eaton et al.

    Concise review of the glutathione S-transferase and their significance to toxicology

    Toxicol. Sci.

    (1999)
  • D.J. Meyer et al.

    Theta, a new class of glutathione transferases purified from rat and man

    Biochem. J.

    (1991)
  • J.M. Harris et al.

    A novel glutathione transferase (13–13) isolated from the matrix of rat liver mitochondria having structural similarity to class theta enzymes

    Biochem. J.

    (1991)
  • A.J. Hussey et al.

    Characterization of a human class-Theta glutathione S-transferase with activity towards 1-menaphthyl sulphate

    Biochem. J.

    (1992)
  • D. Lin et al.

    Effects of human and rat glutathione S-transferases on the covalent DNA binding of the N-acetoxy derivatives of heterocyclic amine carcinogens in vitro: a possible mechanism of organ specificity in their carcinogenesis

    Cancer Res.

    (1994)
  • P. Jemth et al.

    Heterologous expression, purification and characterization of rat class theta glutathione transferase T2-2

    Biochem. J.

    (1996)
  • A. Whittington et al.

    Gene structure, expression and chromosomal localization of murine theta class glutathione transferase mGSTT1-1

    Biochem. J.

    (1999)
  • M. Coggan et al.

    Structure and organization of the human theta-class glutathione S-transferase and d-dopachrome tautomerase gene complex

    Biochem. J.

    (1998)
  • E. Juronen et al.

    Purification, characterization and tissue distribution of human class theta glutathione S-transferase T1-1

    Biochem. Mol. Biol. Int.

    (1996)
  • T. Leisinger et al.

    Microbes, enzymes and genes involved in dichloromethane utilization

    Biodegradation

    (1994)
  • S.E. Pemble et al.

    An evolutionary perspective on glutathione transferases inferred from class-theta glutathione transferase cDNA sequences

    Biochem. J.

    (1992)
  • S. Pemble et al.

    Human glutathione S-transferase theta (GSTT1): cDNA cloning and the characterization of a genetic polymorphism

    Biochem. J.

    (1994)
  • G.W. Mainwaring et al.

    The distribution of theta-class glutathione S-transferases in the liver and lung of mouse, rat and human

    Biochem. J.

    (1996)
  • C.D. Hsiao et al.

    Aminoacid sequencing, molecular cloning and modelling of the chick liver class-theta glutathione S-transferase CL1

    Biochem. J.

    (1995)
  • J.U. Flanagan et al.

    A homology model for the human theta-class glutathione transferase T1-1

    Proteins

    (1998)
  • K.L. Tan et al.

    Mutagenesis of the active site of the human Theta-class glutathione transferase GSTT2-2: catalysis with different substrates involves different residues

    Biochem. J.

    (1996)
  • J.U. Flanagan et al.

    Mutagenic analysis of conserved arginine residues in and around the novel sulfate binding pocket of the human Theta class glutathione transferase T2-2

    Protein Sci.

    (1999)
  • M.C. Wilce et al.

    Crystal structure of a theta-class glutathione transferase

    EMBO J.

    (1995)
  • P.G. Board et al.

    Evidence for an essential serine residue in the active site of the Theta class glutathione transferases

    Biochem. J.

    (1995)
  • G. Chelvanayagam et al.

    Homology model for the human GSTT2 Theta class glutathione transferase

    Proteins

    (1997)
  • Cited by (424)

    • Metabolic pathways in sporadic colorectal carcinogenesis: A new proposal

      2021, Medical Hypotheses
      Citation Excerpt :

      Individuals homozygous for this deletion are thought to be at increased risk for CRC [99] because of a lower capacity to detoxify possible carcinogens. It was demonstrated that 20% of Caucasians carries this genotype [100]. The GSTT1 polymorphism was significant in breast cancer and for CRC risk in Caucasians [80,101].

    • Effects of glutathione S-transferase M1 and T1 deletions on Parkinson's disease risk among a North African population

      2021, Revue Neurologique
      Citation Excerpt :

      Numerous studies have attempted to link the GSTM1 null genotype, which leads to a lack of functional protein, with an increased susceptibility to several diseases such as cancer, cardiovascular diseases, schizophrenia, epilepsy, AD and PD [8,9,13,19–23]. The GSTT1 null genotype has also been, reported to be associated with PD [23,24] and to be related to a slightly increased risk of bladder cancer, gastrointestinal tract, tobacco-related tumors (lung or oral cavity) [25] and cardiovascular diseases [26]. A significant association between the null mutation in GSTM1 and GSTT1 and the risk of PD was found, respectively, in a Chilean [11], North Indian [12] and Caucasian populations [13].

    View all citing articles on Scopus
    View full text