Sequence of a Chicken Phenobarbital-Inducible Cytochrome P450 cDNA: Regulation of Two P450 mRNAs Transcribed from Different Genes

Abstract

The nucleic acid and derived amino acid sequences of a chicken phenobarbital-inducible cytochrome P450 cDNA clone, pCHP7, are presented. The amino acid sequence shares 92% identity with that of a previously characterized chicken cytochrome P450 cDNA clone, pCHP3. The two clones, pCHP7 and pCHP3, represent two distinct mRNAs of 2.2 and 3.5 kb and appear to be transcribed from separate cytochrome P450 genes. Sequence comparisons with P450s from mammalian species indicate that the chicken P450s are most closely related to the IIC subfamily. According to the cytochrome P450 nomenclature (Nebert et al., 1989), the chicken P450 gene encoding the 3.5-kb mRNA is termed P450IIF1 and the P450 gene encoding the 2.2-kb mRNA is designated P450IIF2. When chick embryos were treated with 2-allyl-2-isopropylacetamide, the levels of the 3.5- and 2.2-kb P450 mRNAs in liver were elevated maximally by about 100-fold, while phenobarbital treatment resulted in a maximal increase of about 50-fold. These increases in mRNA levels were accompanied by a less than sixfold increase in the corresponding gene transcription rates. The results indicate that the increase in the amount of these two mRNAs is due to both transcriptional activation of the P450 genes and to a marked post-transcriptional mechanism. By contrast, the drug-induced hepatic mRNA levels for 5-aminolevulinate synthase, the rate-controlling enzyme of the heme biosynthetic pathway, could be accounted for predominantly by activation of gene transcription. A close correlation was observed between the time courses of hepatic mRNA accumulation for cytochrome P450 and 5-aminolevulilnate synthase following drug treatment of chick embryos. In adult hens it was demonstrated that a tissue-specific drug induction of cytochrome P450 mRNAs occurred with levels being substantially elevated in the liver, kidney, and small intestine. The mRNA for 5-aminolevulinate synthase was also drug-induced in the same tissue-specific fashion. The results are compatible with the gene for 5-aminolevulinate synthase being activated in response to an increased cytochrome P450 heme requirement.

Induction of Cyp1a and Cyp2-Mediated Arachidonic Acid Epoxygenation and Suppression of 20-Hydroxyeicosatetraenoic Acid by Imidazole Derivatives Including the Aromatase Inhibitor Vorozole

“…Albendazole and TCDD failed to increase CYP2H1 mRNA. In other experiments, results essentially identical to those for CYP2H1 were found for CYP2H2, which has 92% homology to CYP2H1 (Hansen et al, 1989) (data not shown).…”

“…In prior work using the chick embryo model, we found that TCDD and ␤-NF induce CYP1A-dependent AA epoxygenation via the transcriptional enhancement of CYP1A5, the chick ortholog of mammalian CYP1A2 (Gilday et al, 1996) and PB by induction of CYP2H, the chick ortholog of mammalian CYP2B (Hansen et al, 1989;Nakai et al, 1992). CYP1A4, the chick ortholog of mammalian CYP1A1, is virtually inactive in AA epoxygenation (Nakai et al, 1992;Rifkind et al, 1994).…”

Les récepteurs nucléaires CAR et PXR contrôlent l’induction des cytochromes P450 par le phénobarbital

“…Les premières études moléculaires ex vivo ont démon-tré que le phénobarbital induit une augmentation des transcrits des gènes CYP2B1, CY2B2 et CYP2C6 dans les cellules d'hépatome de rat, et CYP2H1 dans les hépato-cytes de poulet [19,20]. Cette induction est inhibée par l'α-amanitine dans les cellules d'hépatome de rat, suggérant une régulation de nature transcriptionnelle [21], comme in vivo [22].…”

Evidence That the Coactivator CBP/p300 Is Important for Phenobarbital-Induced but Not Basal Expression of theCYP2H1Gene

“…The synthesis of specific cytochrome P450 enzymes can be selectively induced by their own substrates after the interaction of ligand-receptor complexes with upstream enhancer sequences in these genes (Kliewer et al, 1999;Waxman, 1999;Honkakoski and Negishi, 2000). Phenobarbital is a prototype inducer that markedly increases the expression of CYP2 genes in mammals (Waxman and Azaroff, 1992;Waxman, 1999;Honkakoski and Negishi, 2000) and chicken (Mattschoss et al, 1986;Hansen et al, 1989;Dogra et al, 1998). In recent years, a great deal of information has been obtained regarding the molecular mechanism of phenobarbital-mediated induction of cyp2b10, CYP2B1, and CYP2H1 genes (Dogra et al, 1999;Honkakoski and Negishi, 2000;Handschin et al, 2001;Kim et al, 2001).…”