Cancer Letters

Cancer Letters

Volume 209, Issue 2, 25 June 2004, Pages 155-163
Cancer Letters

Mini review
Regulatory mechanism of glutathione S-transferase P-form during chemical hepatocarcinogenesis: old wine in a new bottle

https://doi.org/10.1016/j.canlet.2004.01.003Get rights and content

Abstract

The expression of glutathione S-transferase P-form (GST-P) is markedly up-regulated in the initial phase of chemical hepatocarcinogenesis. It is unlikely that a specific genetic change is associated with this common response to a variety of carcinogens. Here, we describe how GST-P gene expression is induced by carcinogenic treatment, focusing on the changes in the network of liver-enriched transcription factors, including CCAAT/enhancer-binding proteins. Although the balance of positive and negative transcription factors regulates the expression of the GST-P gene, additional factors such as the altered regulation of growth control may certainly be necessary for these cells to develop into preneoplastic foci. Furthermore, our genetic analyses on the tumor susceptibility of (F344 x DRH)F2 rats support the hypothesis that the formation of GST-P-positive lesions is required but is not directly associated with final malignant transformation.

Introduction

The rat glutathione S-transferase P-form (GST-P) has been found to be dramatically up-regulated in its expression in preneoplastic and neoplastic cells [1], [2] and is widely used as a specific marker in the basic analysis of chemical carcinogenesis [3]. However, the mechanism by which the expression of GST-P is induced in the rat liver during carcinogenic treatment has remained to be solved. The aim of this review is to highlight recent advances in our understanding of how GST-P gene expression is regulated during the early stages of hepatocarcinogenesis by chemical carcinogens and to obtain a hint as to why GST-P gene expression is the end point marker in most cases of chemical carcinogenesis [4].

Although GST-P expression has been routinely employed as a preneoplastic marker during chemical hepatocarcinogenesis in rats, it must be noted that there is no induction of the GST-P gene in preneoplastic foci and hepatoma by nongenotoxic proliferators such as clofibrate [5]. On the contrary, adult rat brain [6] and adult male mouse liver [7] constitutively expressed GST-P at significant levels without any tumor formation. Human hepatocellular carcinomas do not consistently overexpress GST P-form, but it is found in cholangiocarcinoma, presumably reflecting the tissue of origin [8]. Therefore, it is unlikely that GST-P expression is essentially associated with the transformation of hepatocytes among these species.

To distinguish between the two alternative possibilities in the liver, that is, either the GST-P gene is coactivated with a closely located transforming gene by a cis mechanism or it is activated in trans by a common trans-acting factor, Moriyama et al. carried out carcinogenesis experiments using transgenic rats harboring the chloramphenycol acetyltransferase (CAT) reporter gene ligated to the upstream regulatory sequence of the rat GST-P gene [9]. Although different lines of transgenic rats had multiple copies of the CAT gene, immunohistochemical staining demonstrated the co-expression of CAT with endogenous GST-P-positive foci, indicating clearly that the GST-P gene is activated position independently by a trans-mechanism [9].

Section snippets

GPEI as an enhancer element for GST-P gene expression

As with the expression of most eukaryotic genes, GST-P gene expression depends on at least two regulatory elements: a promoter and a far-upstream enhancer. GST-P enhancer I (GPEI) located at āˆ’2.5 kb, consists of imperfect TPA (12-o-tetradecanoyl-phorbol-13-acetate) responsive element (TRE)-like sequences that are palindromically oriented [10]. The AP-1 DNA-binding site, or TRE, contains the sequence 5ā€²-TGACTCA-3ā€² which shares some homology with the core consensus ARE (antioxidant responsive

Changes in regulatory network of transcription factors during carcinogenesis

In the 5ā€²-flanking region of the rat GST-P gene, the negative regulatory elements located around 400 bp upstream from the cap site are also significant, and these elements would aid the repressive mechanism of the GST-P gene in normal rat liver [23]. One of the binding factors, a member of the CCAAT/enhancer binding protein (C/EBP) family, binds to GST-P silencer-1 (GPS-1). The ratio of C/EBP alpha to C/EBP-beta is an important factor for GST-P silencer activity and a decrease in the ratio

Possible participation of CCAAT/enhancer-binding proteins(C/EBPs)

At least six members of C/EBP family have been isolated and characterized to date (C/EBP-alpha-C/EBP-zeta), particularly in hepatocytes, adipocytes and hematopoietic cells [32]. The expression of C/EBPs is regulated at multiple levels under several physiological and pathological conditions through the actions of a variety of factors, including hormones, mitogens, cytokines, nutrients and certain toxins.

C/EBP-alpha is expressed at high levels in terminally differentiated cells and the expression

Specific genetic change is not necessary for GST-P expression

To return to our hypothesis, the induction of GST-P gene expression during the early stages of chemical hepatocarcinogenesis is not necessarily associated with the mutation of any specific gene(s), but could be caused similarly by a variety of hepatocarcinogens with different chemical structures and also by different protocols. Randomly occurring mutations, if any exist, may be incidental to the early stage of carcinogenesis.

Possible explanation is as follows: metabolically activated

Genetic analysis of GST-P gene expression in carcinogen-resistant DRH rats

A final question is whether the formation of GST-P-positive foci is a prerequisite for the development of hepatocellular carcinoma (HCC). Genetic linkage analysis was carried out on the GST-P-positive foci in the livers of (F344 x DRH)F2 rats at early (7 weeks) and later (20 weeks) stage in the development of HCC with 3ā€²-Me-DAB administration. Our previous study showed that the size of GST-P-positive foci in the livers of carcinogen-resistant DRH rats at 7 weeks of 3ā€²-Me-DAB administration was

Acknowledgements

We are grateful to Dr Masaharu Sakai (Hokkaido University, School of Medicine) for helpful discussion and Ms Junko Iuchi for preparing this manuscript.

References (60)

  • H.C Pitot et al.

    The stages of initiation and promotion in hepatocarcinogenesis

    Biochim. Biophys. Acta

    (1980)
  • M Schwarz et al.

    Heterogeneity of enzyme-altered foci in rat liver

    Toxicol. Lett.

    (1989)
  • A Denda et al.

    Genetic properties for the suppression of development of putative preneoplastic glutathione S-transferase placental form-positive foci in the liver of carcinogen-resistant DRH strain rats

    Cancer Lett.

    (1999)
  • H.E VanGijssel et al.

    Loss of nuclear p53 protein in preneoplastic rat hepatocytes is accompanied by Mdm2 and Bcl-2 overexpression and by defective response to DNA damage in vivo

    Hepatology

    (2000)
  • K Satoh et al.

    Purification, induction, and distribution of placental glutathione S-transferase: a new marker enzyme for preneoplastic cells in rat chemical hepatocarcinogenesis

    Proc. Natl Acad. Sci. USA

    (1984)
  • K Sato

    Glutathione S-transferases as markers of preneoplasia and neoplasia

    Adv. Cancer Res.

    (1984)
  • N Ito et al.

    A medium-term rat liver bioassay for rapid in vivo detection of carcinogenic potential of chemicals

    Cancer Sci.

    (2003)
  • M.S Rao et al.

    Analysis of peroxisome proliferators-induced preneoplastic and neoplastic lesions of rat liver for placental form of glutathione S-transferase and gamma-glutamyltranspeptidase

    Cancer Res.

    (1986)
  • M Abramovitz et al.

    Developmental regulation of glutathione S-transferase

    Xenobiotics

    (1988)
  • P.C Hayes et al.

    Glutathione S-transferases in human liver cancer

    Gut

    (1991)
  • S Moriyama et al.

    Trans-activation of glutathione S-transferase P gene during chemical hepatocarcinogenesis of the rat

    Proc. Natl Acad. Sci. USA

    (1993)
  • M Sakai et al.

    Multiple regulatory elements and phorbol 12-o-tetradecanoate 13-acetate

    Proc. Natl Acad. Sci. USA

    (1988)
  • J.D Hayes et al.

    The glutathione S-transferase superfamily: regulation of GST and the contribution of the isozyme to cancer prevention and drug resistance

    Crit. Rev. Biochem. Mol. Biol.

    (1995)
  • A Okuda et al.

    Functional cooperativity between two TPA responsive elements in undifferentiated F9 embryonic stem cells

    Eur. Mol. Biol. Org. J.

    (1990)
  • M.B Diccianni et al.

    The dyad palindromic glutathione transferase P enhancer binds multiple factors including AP1

    Nucleic Acids Res.

    (1992)
  • M Sakai et al.

    Suppression of rat glutathione transferase P expression by peroxisome proliferators: interaction between Jun and peroxisome proliferators-activated receptor alpha

    Cancer Res.

    (1995)
  • S.H Kang et al.

    Combining chromatin immunoprecipitation and DNA footprinting: a novel method to analyze protein-DNA interaction in vivo

    Nucleic Acids Res.

    (2002)
  • T.K Bammler et al.

    Isolation and characterization of two mouse Pi-class glutathione S-transferase genes

    Biochem. J.

    (1994)
  • M.K Kwak et al.

    Role of transcription factor Nrf2 in the induction of hepatic phase 2 and antioxidative enzymes in vivo by the cancer chemoprotective agent, 3H-1, 2-dimethione-3-thione

    Mol. Med.

    (2001)
  • K Kawamoto et al.

    Cyclopentenone prostaglandins as potential inducers of phase II detoxification enzymes

    J. Biol. Chem.

    (2000)
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