Isolation of a promoter region in mouse cytochrome P450 3A (Cyp3A16) gene and its transcriptional control

Dynamic patterns of histone methylation are associated with ontogenic expression of the Cyp3a genes during mouse liver maturation

Human cytochrome P450 3A (CYP3A) members are major drug-metabolizing enzymes in the liver. Two genes, CYP3A4 and CYP3A7, exhibit a developmental switch in gene expression during liver maturation. CYP3A4 is mainly expressed in adults, whereas CYP3A7 is dominantly expressed during the fetal and neonatal stages. Their ontogenic expression results in developmentally related changes in the capacity to metabolize endogenous and exogenous compounds. Thus, it is desirable to understand the mechanisms controlling the developmental switch. Mice also exhibit a developmental switch between Cyp3a16 (neonatal isoform) and Cyp3a11 (adult isoform) and may serve as a model to study the mechanisms controlling the developmental switch. Because the epigenetic code (e.g., DNA methylation and histone modifications) is implicated in regulating gene expression and cellular differentiation during development, the current study determined the status of DNA methylation, histone-3-lysine-4 dimethylation (H3K4me2) and histone-3-lysine-27 trimethylation (H3K27me3) around the mouse Cyp3a locus at various developmental ages from prenatal, through neonatal, to young adult. DNA was not hypermethylated in the Cyp3a locus at any age. However, increases in Cyp3a16 expression in neonatal livers and Cyp3a11 in adult livers were associated with increases of H3K4me2. Suppression of Cyp3a16 expression in adult livers coincided with decreases of H3K4me2 and increases of H3K27me3 around Cyp3a16. In conclusion, histone modifications of H3K4me2 and H3K27me3 are dynamically changed in a locus-specific manner along the Cyp3a locus. Developmental switch between Cyp3a11 and Cyp3a16 gene expression seems to be due to dynamic changes of histone modifications during postnatal liver maturation.

Novel transcriptional regulation of the human CYP3A7 gene by Sp1 and Sp3 through nuclear factor kappa B-like element

Human CYP3A7 and CYP3A4 are expressed in fetal and adult livers, respectively, although the 5'-flanking regions of the two genes show 90% homology. The purpose of this study was to clarify the mechanism(s) responsible for the transcriptional regulation of the CYP3A7 gene in human hepatoma HepG2 cells that showed fetal phenotypes. Transfection studies using a series of the CYP3A7 or CYP3A4 promoter-luciferase chimeric genes identified a nuclear factor kappaB (NF-kappaB)-like element between nucleotides -2326 and -2297 that conferred the transcriptional activation of the CYP3A7 gene. A 1-base pair mismatch within the corresponding region of the CYP3A4 gene was sufficient for a differential enhancer activity. A gel shift assay using nuclear extracts from HepG2 cells showed that Sp1 and Sp3 bound to the NF-kappaB-like element of the CYP3A7 but not CYP3A4 gene. Specific activation of the CYP3A7 promoter by Sp1 and Sp3 was confirmed by a co-transfection of the p3A7NF-kappaB or p3A4NF-kappaB reporter gene with Sp1 or Sp3 expression plasmid into Drosophila cells, which lacked endogenous Sp family. Additionally, introduction of mutations into binding sites for hepatocyte nuclear factor 3beta, upstream stimulatory factor 1, and a basic transcription element in the proximal promoter attenuated luciferase activity to 20% of the level seen with the intact CYP3A7 promoter. Thus, we conclude that the expression of the CYP3A7 gene in HepG2 cells is cooperatively regulated by Sp1, Sp3, hepatocyte nuclear factor 3beta, and upstream stimulatory factor 1.

Studies on transcriptional regulation of Cyp3a16 gene in mouse livers by application of direct DNA injection method

CYP3A16 is expressed in the mouse liver specifically during a fetal and puberty life. Functional regions responsible for the transcriptional regulation of the Cyp3a16 gene were identified by an in vivo direct DNA injection into mouse livers followed by a luciferase assay. The results of the deletion analysis of a 5'-flanking sequence suggested the existence of an adult-specific repressor(s) interacting with the Cyp3a16 gene. In addition, a positive regulatory element was assumed to be present in a region from -146 to -56 of the Cyp3a16 gene. A hepatocyte nuclear factor 4 (HNF-4)-binding consensus sequence was found in this region. In fact, HNF-4alpha bound to this sequence as evidenced by a gel mobility shift assay. The role of the HNF-4-binding sequence was further examined by an introduction of mutations in this sequence. The introduction of the mutations resulted in a reduced activity of a luciferase in the assay. These results obtained by an application of the direct DNA injection method suggest that the HNF-4alpha activates the transcription of the Cyp3a16 gene in vivo.

Short-term treatment with alcohols causes hepatic steatosis and enhances acetaminophen hepatotoxicity in Cyp2e1(-/-) mice

CYP2E1 has been reported to have an essential role in alcohol-mediated increases in hepatic steatosis and acetaminophen hepatotoxicity. We found that pretreatment of Cyp2e1(-/-) mice with ethanol plus isopentanol, the predominant alcohols in alcoholic beverages, for 7 days resulted in micro- and macrovesicular steatosis in the livers of all mice, as well as a dramatic increase in acetaminophen hepatotoxicity. In Cyp2e1(-/-) mice administered up to 600 mg acetaminophen/kg alone and euthanized 7 h later, there was no increase in serum levels of ALT. In Cyp2e1(-/-) mice pretreated with ethanol and isopentanol, subsequent exposure to 400 or 600 mg acetaminophen/kg resulted in centrilobular necrosis in all mice with maximal elevation in serum levels of ALT. Acetaminophen-mediated liver damage was similar in males and females. Hepatic microsomal levels of APAP activation in untreated females were similar to those in males treated with the alcohols. However, the females, like the males, required pretreatment with the alcohols in order to increase APAP hepatotoxicity. These findings suggest that, in the Cyp2e1(-/-) mice, the alcohol-mediated increase in acetaminophen hepatotoxicity involves the contribution of other factors, in addition to induction of CYP(s) that activate acetaminophen. Alternatively, CYP-mediated activation of acetaminophen measured in vitro may not reflect the actual activity in vivo. Our findings that a 7-day treatment with ethanol and isopentanol causes extensive hepatic steatosis and increases acetaminophen hepatotoxicity in Cyp2e(-/-) mice indicate that CYP2E1 is not essential for either response.

Hepatocyte nuclear factor 4-mediated activation of rat CYP3A1 gene and its modes of modulation by apolipoprotein AI regulatory protein I and v-ErbA-related protein 3

CYP3A1 gene (P450/6betaB) encodes testosterone 6beta-hydroxylase (EC 1.14.14.1) in rats. The promoter region of CYP3A1 gene contains three binding sites for nuclear factors: 6betaB-A (-105 to -86), 6betaB-B (-139 to -118), and 6betaB-C (-164 to -145). The 6betaB-A site shows a high degree of similarity to a consensus sequence of the binding site of hepatocyte nuclear factor 4 (HNF-4) and also to the 6betaA-A site on the rat CYP3A2 gene promoter region. Our previous study suggested an involvement of the 6betaA-A site in the basal transactivation of CYP3A2 gene using HepG2 cells. In the present study, transactivation through the 6betaB-A and 6betaA-A sites of CYP3A1 and CYP3A2 genes has directly been shown by coexpression of HNF-4 and CYP3A1 or CYP3A2 promoter-reporter fused genes. Similar experiments further showed that nuclear factor binding at the 6betaB-B site hampered HNF-4-mediated transactivation of CYP3A1 gene. Recombinant apolipoprotein AI regulatory protein I (ARP-1) and v-ErbA-related protein 3 (EAR-3) are shown to suppress HNF-4-mediated activation at the 6betaB-B site without competition of HNF-4.

The gut-enriched Krüppel-like factor suppresses the activity of the CYP1A1 promoter in an Sp1-dependent fashion

The gut-enriched Krüppel-like factor (GKLF) is a newly identified zinc finger-containing transcription factor. Recent studies indicate that GKLF binds to a core DNA sequence of 5'-(G/A)(G/A)GG(C/T)G(C/T)-3', which is found in an endogenous cis element, the basic transcription element (BTE) of the cytochrome P-450IA1 (CYP1A1) promoter. The present study characterizes the ability of GKLF to regulate CYP1A1 expression. By electrophoretic mobility gel shift assay (EMSA) and methylation interference assay, GKLF was found to bind BTE in a manner similar to several other transcription factors known to interact with BTE including Sp1 and BTEB. Cotransfection studies in Chinese hamster ovary cells showed that GKLF inhibited the CYP1A1 promoter in a dose- and BTE-dependent manner. The same experiments also revealed that BTE was responsible for a significant portion of the CYP1A1 promoter activity. EMSA of nuclear extracts from Chinese hamster ovary cells showed that Sp1 and Sp3 were two major proteins that interacted with BTE. Additional cotransfection studies showed that GKLF inhibited Sp1-mediated activation of the CYP1A1 promoter. In contrast, GKLF enhanced Sp3-dependent suppression of the same promoter. Moreover, the ability of GKLF to inhibit Sp1-dependent transactivation was in part due to physical interaction of the two proteins. These findings indicate that GKLF is a negative regulator of the CYP1A1 promoter in a BTE-dependent fashion and that this inhibitory effect is in part mediated by physical interaction with Sp1.