Characterization of a promoter for gamma-glutamyl transpeptidase activated in rat liver in response to aflatoxin B1 and ethoxyquin.
gamma-Glutamyl transpeptidase (GGT) is normally absent from adult rat hepatocytes but is induced by a range of xenobiotics, including carcinogens and chemoprotective agents. As many as six mRNA species for this enzyme have been described in both rat and mouse, with various degrees of tissue specificity. These originate from one gene and have separate promoters within alternative 5' untranslated sequences. By using a cDNA-derived sequence specific for GGT mRNA III to screen a rat genomic library, a clone that contains the promoter region for this mRNA was isolated and characterized. The transcriptional start site lay some 3.5 kb upstream from that already characterized for mRNA II in rat kidney. Luciferase activity was obtained after transfection of rat hepatoma-derived cell lines with constructs containing the putative promoter III fused to a luc reporter. Although this promoter lacks a TATA box, a sequence close to the start site that binds the transcription factor TFIID in vitro was identified. By using PCR techniques, mRNA III (homologous to both mouse III and IV) and an mRNA (IV) with homology to VI in mouse were found in ethoxyquin- and aflatoxin B1-treated rat liver and kidney as well as in a hepatoma-derived cell line. No evidence was found for a product homologous to mRNA from promoter V described in the mouse.
Griffiths
S A
SA
MRC Toxicology Unit, University of Leicester, United Kingdom.
Good
V M
VM
Gordon
L A
LA
Hudson
E A
EA
Barrett
M C
MC
Munks
R J
RJ
Manson
M M
MM
D016604:Aflatoxin B1 / Q000494:pharmacology*; D000818:Animals; D001483:Base Sequence; D002273:Carcinogens / Q000494:pharmacology*; D002874:Chromosome Mapping; D017931:DNA Primers; D004789:Enzyme Activation; D005015:Ethoxyquin / Q000494:pharmacology*; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects*; D008099:Liver / Q000187:drug effects / Q000201:enzymology* / Q000502:physiology; D051379:Mice; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction / Q000379:methods; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D014158:Transcription, Genetic; D014162:Transfection; D005723:gamma-Glutamyltransferase / Q000235:genetics* / Q000378:metabolism
D002273:Carcinogens; D017931:DNA Primers; D012333:RNA, Messenger; D016604:Aflatoxin B1; D005015:Ethoxyquin; D005723:gamma-Glutamyltransferase