Gastroenterology

Gastroenterology

Volume 127, Issue 5, November 2004, Pages 1436-1445
Gastroenterology

Basic-alimentary tract
Evidence for a new human CYP1A1 regulation pathway involving PPAR-α and 2 PPRE sites

https://doi.org/10.1053/j.gastro.2004.08.023Get rights and content

Background & Aims: Cytochrome P450 1A1 catalyzes the degradation of endobiotics (estradiol, fatty acids, and so on) and the bioactivation of numerous environmental procarcinogens, such as arylamines and polycyclic aromatic hydrocarbons, that are found in food. Several peroxisome proliferators and arachidonic acid derivatives enhance cytochrome P450 1A1 activity, but the mechanisms involved remain unknown. The aim of this work was to study the role of peroxisome proliferator—activated receptors in cytochrome P450 1A1 gene induction. Methods: The role of peroxisome proliferator—activated receptor transcription factors in cytochrome P450 1A1 induction was assessed by means of enzymatic activities, quantitative real-time polymerase chain reaction, gene reporter assays, mutagenesis, and electrophoretic mobility shift assay. Results: We show that peroxisome proliferator—activated receptor-α agonists (WY-14643, bezafibrate, clofibrate, and phthalate) induce human cytochrome P450 1A1 gene expression, whereas 2,4-thiazolidinedione, a specific peroxisome proliferator—activated receptor-γ agonist, represses it. The induction of cytochrome P450 1A1 transcripts by WY-14643 was associated with a marked increase of ethoxyresorufin O-deethylase activity (10-fold at 200 μmol/L). Transfection of peroxisome proliferator—activated receptor-α complementary DNA enhanced cytochrome P450 1A1 messenger RNA induction by WY-14643, although WY-14643 failed to activate xenobiotic responsive element sequences. Two peroxisome proliferator response element sites were located at positions −931/−919 and −531/−519 of the cytochrome P450 1A1 promoter. Their inactivation by directed mutagenesis suppressed the inductive effect of WY-14643 on cytochrome P450 1A1 promoter activation. Electrophoretic mobility shift assay and chromatin immunoprecipitation assay experiments showed that the 2 cytochrome P450 1A1 peroxisome proliferator response element sites bind the peroxisome proliferator—activated receptor-α/retinoid X receptor-α heterodimer. Conclusions: We describe here a new cytochrome P450 1A1 induction pathway involving peroxisome proliferator—activated receptor-α and 2 peroxisome proliferator response element sites, indicating that peroxisome proliferator—activated receptor-α ligands, which are common environmental compounds, may be involved in carcinogenesis.

Section snippets

Chemicals

WY-14643 was purchased from VWR (Fontenay-sous-Bois, France); 2,4-TZD, 3-methylcholanthrene (3-MC), CF, BZF, and dimethyl sulfoxide were purchased from Sigma (France); and MEHP was purchased from TCI Europe (Antwerp, Belgium).

Cell culture and treatments

Human colic adenocarcinoma CaCo-2, hepatoma HepG2, and adenocarcinoma A549 cells and the primoculture of human keratinocytes were used. As soon as the CaCo-2 cells reached confluence, the culture medium was changed, and 24 hours later, they were further treated for 6 hours

Induction of the cytochrome P450 1A1 gene by peroxisome proliferator—activated receptor ligands

CaCo-2 cells were treated for 6 hours with increasing concentrations of WY-14643 (10–400 μmol/L), 50 μmol/L BZF, 50 μmol/L CF, 100 μmol/L MEHP, 200 μmol/L TZD, or 1 μmol/L 3-MC. CYP1A1 mRNA was then evaluated by quantitative real-time PCR analysis. The results presented in Figure 1A show that TZD does not increase and even decreases CYP1A1 gene expression. In contrast, CYP1A1 mRNA levels increased after treatment with the PPAR-α ligands, such as WY-14643, BZF, CF, or MEHP. The WY-14643

Discussion

We characterized a new CYP1A1 regulation pathway that involves the binding of PPAR-α transcription factor on 2 PPRE sequences located within the 5′ untranslated region of the CYP1A1 gene. The effects of agonists of PPAR-α (WY-14643, CF, BZF, and MEHP) and PPAR-γ (TZD) on CYP1A1 mRNA expression levels were evaluated in the CaCo-2 cell line by real-time quantitative real-time PCR analysis. WY-14643 induced CYP1A1 mRNA in a dose-dependent manner up to 6-fold from 200 μmol/L. Similarly, CYP1A1 mRNA

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      The K19 promoter is led to development and differentiation of the GI trace epithelium in both adults and embryos [76]. The Cytochrome P450 CYP1A1 gene, as a hemoprotein involved in the metabolism and synthesis of lipids, is expressed in a wide range of mouse and human tissues, which its overexpression is related to different cancer development [77]. A tissue-specific aryl hydrocarbon (Ah) receptor has been located downstream of the CYP1A1 gene to regulate its expression [70,78].

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    This work was a part of a multicentric study under the authority of Dr. A. Sasco (International Agency for Research on Cancer/Institut National de la Santé et de la Recherche Médicale [INSERM]) and was partly funded by Ligue Nationale contre le Cancer, Comité du Rhône, Association de Recherche sur le Cancer (research project 3410), and INSERM (Action Thématique Concertée Environnement et Santé, Grant ASE 02048SSP).

    1

    E.S. and P.-H.V. contributed equally to this work.

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