Xenobiotic-inducible expression of murine glutathione S-transferase Ya subunit gene is controlled by an electrophile-responsive element.
Glutathione S-transferase (GST) Ya subunit gene expression is induced in mammalian tissues by two types of chemical agents: (i) planar aromatic compounds (e.g., 3-methylcholanthrene, beta-naphthoflavone, and 2,3,7,8-tetrachlorodibenzo-p- dioxin) and (ii) electrophiles (e.g., trans-4-phenyl-3-buten-2-one and dimethyl fumarate) or compounds easily oxidized to electrophiles (e.g., tert-butylhydroquinone). To study the mechanism of this induction, we have introduced deletions in the 5' flanking region of a mouse GST Ya subunit gene, fused it to the coding sequence for chloramphenicol acetyltransferase (CAT) activity, and transfected the Ya-CAT genes for expression into hepatoma cells. We show that a single cis-regulatory element, between nucleotides -754 and -713 from the start of transcription, is responsible for the induction by both planar aromatic and electrophilic compounds. Using murine hepatoma cell mutants defective in either the Ah-encoded aryl hydrocarbon receptor (BPrc1 mutant) or in cytochrome P1-450 gene (c1 mutant), we show that induction by planar aromatic but not by electrophilic inducers requires a functional Ah receptor and cytochrome P1-450 activity. From this it is concluded that Ya gene activation by planar aromatic compounds involves metabolism of these inducers by the phase I xenobiotic-metabolizing cytochrome P1-450 system into electrophilic compounds, which is consistent with a recently proposed model [Prochaska, H. J. & Talalay, P. (1988) Cancer Res. 48, 4776-4782]. Therefore, the regulatory sequence of the Ya gene should be considered an electrophile-responsive element (EpRE) activated exclusively by inducers containing an electrophilic center. An EpRE-containing 41-bp oligonucleotide ligated at the -187 site of the Ya gene promoter confers upon it an increase in basal activity and xenobiotic inducibility. The basal activity augments with the number of EpRE copies. DNase I protection patterns show the protection of the EpRE domain by a nuclear factor(s) that becomes more abundant upon exposure of Hepa 1c1c7 cells to tert-butylhydroquinone.
Friling
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Department of Biochemistry, Weizmann Institute of Science, Rehovot, Israel.
Bensimon
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A
Tichauer
Y
Y
Daniel
V
V
D000818:Animals; D001483:Base Sequence; D006528:Carcinoma, Hepatocellular; D002460:Cell Line; D015500:Chloramphenicol O-Acetyltransferase / Q000096:biosynthesis / Q000235:genetics; D004273:DNA, Neoplasm / Q000235:genetics; D015870:Gene Expression / Q000187:drug effects*; D005796:Genes; D005982:Glutathione Transferase / Q000096:biosynthesis / Q000235:genetics*; D006801:Humans; D008113:Liver Neoplasms; D008114:Liver Neoplasms, Experimental; D046911:Macromolecular Substances; D051379:Mice; D008969:Molecular Sequence Data; D015345:Oligonucleotide Probes; D011083:Polycyclic Compounds / Q000494:pharmacology; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D015183:Restriction Mapping; D014158:Transcription, Genetic; D014162:Transfection; D015262:Xenobiotics / Q000494:pharmacology*
D004273:DNA, Neoplasm; D046911:Macromolecular Substances; D015345:Oligonucleotide Probes; D011083:Polycyclic Compounds; D011993:Recombinant Fusion Proteins; D015262:Xenobiotics; D015500:Chloramphenicol O-Acetyltransferase; D005982:Glutathione Transferase