Regulation of rat glutathione S-transferase A5 by cancer chemopreventive agents: mechanisms of inducible resistance to aflatoxin B1

J. D. Hayes (Lead / Corresponding author), D. J. Pulford, E. M. Ellis, R. McLeod, R. F. James, J. Seidegård, E. Mosialou, B. Jernström, G. E. Neal

Research output: Contribution to journalReview article

75 Citations (Scopus)

Abstract

The rat can be protected against aflatoxin B1 (AFB1) hepatocarcinogenesis by being fed on a diet containing the synthetic antioxidant ethoxyquin. Evidence suggests that chemoprotection against AFB1 is due to increased detoxification of the mycotoxin by one or more inducible drug-metabolising enzymes. The glutathione S-transferase (GST) isoenzymes in rat liver that contribute to ethoxyquin-induced chemoprotection against AFB1 have been identified by protein purification. This approach resulted in the isolation of several heterodimeric class alpha GST, all of which contained the A5 subunit and possessed at least 50-fold greater activity towards AFB1-8,9-epoxide than previously studied transferases. Molecular cloning and heterologous expression of rat GSTA5-5 has led to the demonstration that it exhibits substantially greater activity for AFB1-8,9-epoxide than other rat transferases. The A5 homodimer can also catalyse the conjugation of glutathione with other epoxides, such as trans-stilbene oxide and 1,2-epoxy-3-(4'-nitrophenoxy)propane, and possesses high catalytic activity for the reactive aldehyde 4-hydroxynonenal. Western blotting has shown that the A5 subunit is not only induced by ethoxyquin but that it is also induced by other cancer chemopreventive agents, such as butylated hydroxyanisole, oltipraz, benzyl isothiocyanate, indole-3-carbinol and coumarin. In addition to GSTA5, we have identified a novel aflatoxin-aldehyde reductase (AFAR) that is similarly induced by ethoxyquin. However, immunoblotting has shown that GSTA5 and AFAR are not always co-ordinately regulated by chemoprotectors. In order to gain a better understanding of the mechanisms responsible for the induction of GSTA5 protein, the GSTA5 gene has been cloned. It was isolated on two overlapping bacteriophage lambda clones and found to be approximately 12 kb in length. The transcriptional start site of GSTA5 has been identified 228 bp upstream from the ATG translational initiation codon. Computer-assisted analysis of the upstream sequence has indicated the presence of a putative antioxidant responsive element (located between -421 and -429 bp) which may be responsible for the induction of GSTA5 by chemopreventive agents.

Original languageEnglish
Pages (from-to)51-67
Number of pages17
JournalChemico-Biological Interactions
Volume111-112
DOIs
Publication statusPublished - 24 Apr 1998

Fingerprint

Ethoxyquin
Aflatoxin B1
Rats
Aldehyde Reductase
Aflatoxins
Transferases
Neoplasms
Antioxidants
Butylated Hydroxyanisole
Bacteriophage lambda
Formulated Food
Propane
Detoxification
Bacteriophages
Initiator Codon
Mycotoxins
Cloning
Epoxy Compounds
Molecular Cloning
Nutrition

Keywords

  • Aflatoxin B1/pharmacokinetics
  • Aldehyde Reductase/biosynthesis
  • Amino Acid Sequence
  • Animals
  • Antioxidants/metabolism
  • Base Sequence
  • Biotransformation
  • Cloning, Molecular
  • DNA/genetics
  • Drug Resistance
  • Enzyme Induction/drug effects
  • Ethoxyquin/pharmacology
  • Glutathione Transferase/chemistry
  • Inactivation, Metabolic
  • Liver Neoplasms, Experimental/chemically induced
  • Molecular Sequence Data
  • Oxidative Stress
  • Protein Conformation
  • Rats

Cite this

Hayes, J. D. ; Pulford, D. J. ; Ellis, E. M. ; McLeod, R. ; James, R. F. ; Seidegård, J. ; Mosialou, E. ; Jernström, B. ; Neal, G. E. / Regulation of rat glutathione S-transferase A5 by cancer chemopreventive agents : mechanisms of inducible resistance to aflatoxin B1. In: Chemico-Biological Interactions. 1998 ; Vol. 111-112. pp. 51-67.
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abstract = "The rat can be protected against aflatoxin B1 (AFB1) hepatocarcinogenesis by being fed on a diet containing the synthetic antioxidant ethoxyquin. Evidence suggests that chemoprotection against AFB1 is due to increased detoxification of the mycotoxin by one or more inducible drug-metabolising enzymes. The glutathione S-transferase (GST) isoenzymes in rat liver that contribute to ethoxyquin-induced chemoprotection against AFB1 have been identified by protein purification. This approach resulted in the isolation of several heterodimeric class alpha GST, all of which contained the A5 subunit and possessed at least 50-fold greater activity towards AFB1-8,9-epoxide than previously studied transferases. Molecular cloning and heterologous expression of rat GSTA5-5 has led to the demonstration that it exhibits substantially greater activity for AFB1-8,9-epoxide than other rat transferases. The A5 homodimer can also catalyse the conjugation of glutathione with other epoxides, such as trans-stilbene oxide and 1,2-epoxy-3-(4'-nitrophenoxy)propane, and possesses high catalytic activity for the reactive aldehyde 4-hydroxynonenal. Western blotting has shown that the A5 subunit is not only induced by ethoxyquin but that it is also induced by other cancer chemopreventive agents, such as butylated hydroxyanisole, oltipraz, benzyl isothiocyanate, indole-3-carbinol and coumarin. In addition to GSTA5, we have identified a novel aflatoxin-aldehyde reductase (AFAR) that is similarly induced by ethoxyquin. However, immunoblotting has shown that GSTA5 and AFAR are not always co-ordinately regulated by chemoprotectors. In order to gain a better understanding of the mechanisms responsible for the induction of GSTA5 protein, the GSTA5 gene has been cloned. It was isolated on two overlapping bacteriophage lambda clones and found to be approximately 12 kb in length. The transcriptional start site of GSTA5 has been identified 228 bp upstream from the ATG translational initiation codon. Computer-assisted analysis of the upstream sequence has indicated the presence of a putative antioxidant responsive element (located between -421 and -429 bp) which may be responsible for the induction of GSTA5 by chemopreventive agents.",
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Regulation of rat glutathione S-transferase A5 by cancer chemopreventive agents : mechanisms of inducible resistance to aflatoxin B1. / Hayes, J. D. (Lead / Corresponding author); Pulford, D. J.; Ellis, E. M.; McLeod, R.; James, R. F.; Seidegård, J.; Mosialou, E.; Jernström, B.; Neal, G. E.

In: Chemico-Biological Interactions, Vol. 111-112, 24.04.1998, p. 51-67.

Research output: Contribution to journalReview article

TY - JOUR

T1 - Regulation of rat glutathione S-transferase A5 by cancer chemopreventive agents

T2 - mechanisms of inducible resistance to aflatoxin B1

AU - Hayes, J. D.

AU - Pulford, D. J.

AU - Ellis, E. M.

AU - McLeod, R.

AU - James, R. F.

AU - Seidegård, J.

AU - Mosialou, E.

AU - Jernström, B.

AU - Neal, G. E.

PY - 1998/4/24

Y1 - 1998/4/24

N2 - The rat can be protected against aflatoxin B1 (AFB1) hepatocarcinogenesis by being fed on a diet containing the synthetic antioxidant ethoxyquin. Evidence suggests that chemoprotection against AFB1 is due to increased detoxification of the mycotoxin by one or more inducible drug-metabolising enzymes. The glutathione S-transferase (GST) isoenzymes in rat liver that contribute to ethoxyquin-induced chemoprotection against AFB1 have been identified by protein purification. This approach resulted in the isolation of several heterodimeric class alpha GST, all of which contained the A5 subunit and possessed at least 50-fold greater activity towards AFB1-8,9-epoxide than previously studied transferases. Molecular cloning and heterologous expression of rat GSTA5-5 has led to the demonstration that it exhibits substantially greater activity for AFB1-8,9-epoxide than other rat transferases. The A5 homodimer can also catalyse the conjugation of glutathione with other epoxides, such as trans-stilbene oxide and 1,2-epoxy-3-(4'-nitrophenoxy)propane, and possesses high catalytic activity for the reactive aldehyde 4-hydroxynonenal. Western blotting has shown that the A5 subunit is not only induced by ethoxyquin but that it is also induced by other cancer chemopreventive agents, such as butylated hydroxyanisole, oltipraz, benzyl isothiocyanate, indole-3-carbinol and coumarin. In addition to GSTA5, we have identified a novel aflatoxin-aldehyde reductase (AFAR) that is similarly induced by ethoxyquin. However, immunoblotting has shown that GSTA5 and AFAR are not always co-ordinately regulated by chemoprotectors. In order to gain a better understanding of the mechanisms responsible for the induction of GSTA5 protein, the GSTA5 gene has been cloned. It was isolated on two overlapping bacteriophage lambda clones and found to be approximately 12 kb in length. The transcriptional start site of GSTA5 has been identified 228 bp upstream from the ATG translational initiation codon. Computer-assisted analysis of the upstream sequence has indicated the presence of a putative antioxidant responsive element (located between -421 and -429 bp) which may be responsible for the induction of GSTA5 by chemopreventive agents.

AB - The rat can be protected against aflatoxin B1 (AFB1) hepatocarcinogenesis by being fed on a diet containing the synthetic antioxidant ethoxyquin. Evidence suggests that chemoprotection against AFB1 is due to increased detoxification of the mycotoxin by one or more inducible drug-metabolising enzymes. The glutathione S-transferase (GST) isoenzymes in rat liver that contribute to ethoxyquin-induced chemoprotection against AFB1 have been identified by protein purification. This approach resulted in the isolation of several heterodimeric class alpha GST, all of which contained the A5 subunit and possessed at least 50-fold greater activity towards AFB1-8,9-epoxide than previously studied transferases. Molecular cloning and heterologous expression of rat GSTA5-5 has led to the demonstration that it exhibits substantially greater activity for AFB1-8,9-epoxide than other rat transferases. The A5 homodimer can also catalyse the conjugation of glutathione with other epoxides, such as trans-stilbene oxide and 1,2-epoxy-3-(4'-nitrophenoxy)propane, and possesses high catalytic activity for the reactive aldehyde 4-hydroxynonenal. Western blotting has shown that the A5 subunit is not only induced by ethoxyquin but that it is also induced by other cancer chemopreventive agents, such as butylated hydroxyanisole, oltipraz, benzyl isothiocyanate, indole-3-carbinol and coumarin. In addition to GSTA5, we have identified a novel aflatoxin-aldehyde reductase (AFAR) that is similarly induced by ethoxyquin. However, immunoblotting has shown that GSTA5 and AFAR are not always co-ordinately regulated by chemoprotectors. In order to gain a better understanding of the mechanisms responsible for the induction of GSTA5 protein, the GSTA5 gene has been cloned. It was isolated on two overlapping bacteriophage lambda clones and found to be approximately 12 kb in length. The transcriptional start site of GSTA5 has been identified 228 bp upstream from the ATG translational initiation codon. Computer-assisted analysis of the upstream sequence has indicated the presence of a putative antioxidant responsive element (located between -421 and -429 bp) which may be responsible for the induction of GSTA5 by chemopreventive agents.

KW - Aflatoxin B1/pharmacokinetics

KW - Aldehyde Reductase/biosynthesis

KW - Amino Acid Sequence

KW - Animals

KW - Antioxidants/metabolism

KW - Base Sequence

KW - Biotransformation

KW - Cloning, Molecular

KW - DNA/genetics

KW - Drug Resistance

KW - Enzyme Induction/drug effects

KW - Ethoxyquin/pharmacology

KW - Glutathione Transferase/chemistry

KW - Inactivation, Metabolic

KW - Liver Neoplasms, Experimental/chemically induced

KW - Molecular Sequence Data

KW - Oxidative Stress

KW - Protein Conformation

KW - Rats

U2 - 10.1016/S0009-2797(97)00151-8

DO - 10.1016/S0009-2797(97)00151-8

M3 - Review article

C2 - 9679543

VL - 111-112

SP - 51

EP - 67

JO - Chemico-Biological Interactions

JF - Chemico-Biological Interactions

SN - 0009-2797

ER -