title: Structural gene products of the Ah locus. Transcriptional regulation of cytochrome P1-450 and P3-450 mRNA levels by 3-methylcholanthrene.
abstract: Mouse liver cytochromes P1-450 and P3-450 represent those forms of polycylic hydrocarbon-induced P-450 most closely associated with induced aryl hydrocarbon (benzo[a] pyrene) hydroxylase and acetanilide 4-hydroxylase activity, respectively. These two proteins are controlled by the Ah receptor: C57BL/6N mice possess the high-affinity receptor; DBA/2N mice, the poor-affinity receptor. 3-Methylcholanthrene at the highest dose technically possible induces both proteins in C57BL/6N but not DBA/2N mice, whereas sufficiently high doses of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) induce both proteins in both inbred mouse strains. Plasmids containing DNA complementary to P1-450 and P3-450 mRNA, respectively, were used in an in vitro nuclear transcription assay to determine the mechanism of the induction response. In C57BL/6N mice, transcriptional rates of the P1-450 and P3-450 genes increase dramatically as early as 3 hr after 3-methylcholanthrene treatment and at 12 hr reach maximal levels of 20- and 15-fold, respectively, above control values. In contrast, no increase in either gene is found in 3-methylcholanthrene-treated DBA/2N mice. Following TCDD administration, both P1-450 and P3-450 gene transcription rates are elevated in DBA/2N mice. There is a 3- to 6-hr lag period between the early onset of enhanced transcription rates and the later rise in P1-450 and P3-450 mRNA. Basal and induced levels of P3-450 mRNA are about 5-fold greater than those of P1-450 mRNA. These data confirm that the 3-methylcholanthrene and TCDD induction responses, governed by the Ah receptor, are mediated principally through an increase in specific gene transcription.
mesh_terms: D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases / Q000235:genetics*; D001579:Benzopyrene Hydroxylase / Q000235:genetics*; D002467:Cell Nucleus / Q000378:metabolism; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics*; D005260:Female; D005796:Genes / Q000187:drug effects*; D007527:Isoenzymes / Q000235:genetics*; D007700:Kinetics; D008099:Liver / Q000187:drug effects / Q000201:enzymology*; D008297:Male; D008748:Methylcholanthrene / Q000494:pharmacology*; D051379:Mice; D008815:Mice, Inbred Strains; D000072317:Polychlorinated Dibenzodioxins / Q000494:pharmacology; D012333:RNA, Messenger / Q000235:genetics*; D014158:Transcription, Genetic / Q000187:drug effects*
chemical_list: D007527:Isoenzymes; D000072317:Polychlorinated Dibenzodioxins; D012333:RNA, Messenger; D008748:Methylcholanthrene; D003577:Cytochrome P-450 Enzyme System; D001579:Benzopyrene Hydroxylase; D001189:Aryl Hydrocarbon Hydroxylases