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

2004; Elsevier BV; Volume: 127; Issue: 5 Linguagem: Inglês

10.1053/j.gastro.2004.08.023

1528-0012

Eric Sérée, P.H. Villard, Jean‐Marc Pascussi, Thierry Pineau, Patrick Maurel, Quoc-Binh N'Guyen, Frédérique Fallone, P.M. Martin, Serge Champion, Bruno Lacarelle, J.-F. Savouret, Y. Barra,

Metabolism, Diabetes, and Cancer

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. 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. Cytochromes P450 (CYPs) are hemoproteins involved in the metabolism of some endogenous compounds (estradiol and fatty acids) and numerous xenobiotics. CYPs are the main enzymes involved in the bioactivation of environmental procarcinogens. CYP1A1 catalyzes the bioactivation of polycyclic aromatic hydrocarbons (PAHs) and arylamines. PAHs are ubiquitous compounds found in tobacco smoke, industrial workplaces, and food. Arylamines are pyrolysis derivatives of proteins. PAHs and arylamines are mainly involved in the etiology of smokers' lung cancers and colorectal cancers, respectively.1Guengerich F.P. Metabolism of chemical carcinogens.Carcinogenesis. 2000; 21: 345-351Crossref PubMed Scopus (212) Google Scholar, 2Ma J.Y. Yang H.M. Barger M.W. Siegel P.D. Zhong B.Z. Kriech A.J. Castranova V. Alteration of pulmonary cytochrome p-450 system effects of asphalt fume condensate exposure.J Toxicol Environ Health. 2002; 65: 1247-1260Crossref Scopus (21) Google Scholar Moreover, CYP1A1 overexpression was associated with predisposition to various human cancers.3Gonzalez F.J. Gelboin H.V. Role of human cytochromes P450 in the metabolic activation of chemical carcinogens and toxins.Drug Metab Rev. 1994; 26: 165-170Crossref PubMed Scopus (455) Google Scholar CYP1A1 is constitutively expressed in human enterocytes at relatively low levels. However, it should be remembered that its expression is highly enhanced after exposition to chemical inducers, and this modulates cellular susceptibility to procarcinogens. CYP1A1 gene expression is mainly regulated by the aryl hydrocarbon receptor (AhR), which is activated by a variety of xenobiotic compounds, including dioxins and PAHs,4Li W. Harper P. Tang B.K. Okey A. Regulation of cytochrome P450 enzymes by aryl hydrocarbon receptor in human cells CYP1A2 expression in the LS180 colon carcinoma cell line after treatment with 2,3,7,8-tetrachlorodibenzo-p-dioxin or 3-methylcholanthrene.Biochem Pharmacol. 1998; 56: 599-612Crossref PubMed Scopus (121) Google Scholar, 5Whithlock J.P. Induction of cytochrome P4501A1.Annu Rev Pharmacol Toxicol. 1999; 39: 103-125Crossref PubMed Scopus (1010) Google Scholar, 6Jones L.C. Whitlock J.P. Dioxin-inducible transactivation in a chromosomal setting. Analysis of the acidic domain of the Ah receptor.J Biol Chem. 2001; 276: 25037-25040Crossref PubMed Scopus (15) Google Scholar flavonoids, and indole and benzimidazole derivatives.7Quattrochi L.C. Tukey R.H. Nuclear uptake of the Ah dioxin receptor in response to omeprazole transcriptional activation of the human CYP1A1 gene.Mol Pharmacol. 1993; 43: 504-508PubMed Google Scholar, 8Daujat M. Charasse S. Fabre I. Lesca P. Joinaidi Y. Larroque C. Poellinger L. Maurel P. Induction of CYP1A1 gene by benzimidazole derivatives during Caco-2 cell differentiation. Evidence for an aryl-hydrocarbon receptor-mediated mechanism.Eur J Biochem. 1996; 237: 642-652Crossref PubMed Scopus (56) Google Scholar, 9Dzeletovic N. McGuire J. Daujat M. Tholander K. Ema M. Fujii-Kuriyama Y. Gbergman J. Maurel P. Pollinger L. Regulation of dioxin receptor function by omeprazole.J Biol Chem. 1997; 272: 12705-12713Crossref PubMed Scopus (72) Google Scholar The AhR is present in cytoplasm as an inactive form associated with 2 heat shock protein 90 and another protein, named aryl hydrocarbon receptor—interacting protein, involved in the stability of the complex AhR/heat shock protein 90. The ligand binding on AhR induces the dissociation of this complex and activates the receptor. After its activation, AhR is able to translocate in the nucleus, where it dimerizes with its partner, the AhR nuclear translocator. This new complex binds specifically to enhancer DNA sequences within the CYP1A1 promoter called xenobiotic responsive elements (XREs). Even though AhR plays a central role in CYP1A1 gene regulation, the activation of this transcription factor cannot always explain the observed CYP1A1 induction. For instance, carbaryl, which is not an AhR ligand, was found to induce CYP1A110Ledirac N. Delescluse C. de Sousa G. Pralavorio M. Lesca P. Amichot M. Berge J.B. Rahmani R. Carbaryl induces CYP1A1 gene expression in HepG2 and HaCaT cells but is not a ligand of the human hepatic Ah receptor.Toxicol Appl Pharmacol. 1997; 144: 177-182Crossref PubMed Scopus (69) Google Scholar by a mechanism not yet characterized. AhR excepted, the other transcription factor involved in CYP1A1 induction was the retinoic acid receptor, but the level of induction reached was relatively faint.11Vecchini F. Lenoir-Viale M.C. Cathelineau C. Magdalou J. Bernard B.A. Shroot B. Presence of a retinoid responsive element in the promoter region of the human cytochrome P4501A1 gene.Biochem Biophys Res Commun. 1994; 201: 1205-1212Crossref PubMed Scopus (65) Google Scholar It has been previously shown that induction of CYP1A1 activity can be obtained by cell culture agitation, with a level comparable to those obtained with exposure to 0.1 nmol/L 2,3,7,8-tetrachlorodibenzo-p-dioxine.12Mufti N. Shuler M. Possible role of arachidonic acid in stress-induced cytochrome P450IA1 activity.Biotechnol Prog. 1996; 12: 847-854Crossref PubMed Scopus (23) Google Scholar Increasing shear stress leads to an increase of arachidonic acid,13Nollert M.U. Hall E.R. Eskin S.G. McIntire L.V. The effect of shear stress on the uptake and metabolism of arachidonic acid by human endothelial cells.Biochem Biophys Acta. 1989; 1005: 72-80Crossref PubMed Scopus (54) Google Scholar, 14Nollert M.U. Eskin S.G. McIntire L.V. Shear stress increases inositol trisphosphate levels in human endothelial cells.Biochem Biophys Res Commun. 1990; 170: 281-287Crossref PubMed Scopus (185) Google Scholar and arachidonic acid metabolites are peroxisome proliferator—activated receptor (PPAR)-α ligands.15Hihi A.K. Michalik L. Wahli W. PPARs transcriptional effectors of fatty acids and their derivatives.Cell Mol Life Sci. 2002; 59: 790-798Crossref PubMed Scopus (274) Google Scholar Using arachidonic acid and different phospholipid metabolism inhibitors, Mufti and Shuler12Mufti N. Shuler M. Possible role of arachidonic acid in stress-induced cytochrome P450IA1 activity.Biotechnol Prog. 1996; 12: 847-854Crossref PubMed Scopus (23) Google Scholar showed that arachidonic acid and derivatives induce CYP1A1 gene activity and that cell stress induces phospholipase D, resulting in the formation of phosphatidic acid, which activates phospholipase A2, resulting in the release of arachidonic acid. The metabolism of arachidonic acid probably resulted in a metabolite that, by an as-yet-unknown mechanism, induced CYP1A1.12Mufti N. Shuler M. Possible role of arachidonic acid in stress-induced cytochrome P450IA1 activity.Biotechnol Prog. 1996; 12: 847-854Crossref PubMed Scopus (23) Google Scholar Moreover, it was shown that peroxisome proliferators, such as phthalates, can increase the DNA adducts induced by the bioactivation of benzo(a)pyrene, which is mainly catalyzed by CYP1A1.16Voskoboinik I. Ooi S.G. Drew R. Ahokas J.T. Peroxisome proliferators increase the formation of BPDE-DNA adducts in isolated rat hepatocytes.Toxicology. 1997; 122: 81-91Crossref PubMed Scopus (9) Google Scholar The mechanism involved in this increase of DNA adducts was not characterized. Therefore, phthalates seemed to be inducers of CYP1A1 activity. To date, it has been shown that some phthalate derivatives are potent agonist ligands of PPAR-α and, to a lesser extent, of PPAR-γ.17Lovekamp-Swan T. Jette A. Davis B. Dual activation of PPARalpha and PPARgamma by mono-(2-ethylhexyl) phthalate in rat ovarian granulosa cells.Mol Cell Endocrinol. 2003; 201: 133-141Crossref PubMed Scopus (164) Google Scholar We hypothesized that the potentiation of benzo(a)pyrene DNA adducts by phthalates could be related to CYP1A1 induction via the PPAR pathway. The aim of this study was to evaluate the effect of PPAR-α ligands, such as WY-14643 (a specific PPAR-α ligand), bezafibrate (BZF), clofibrate (CF), and mono(2-ethylhexyl)phthalate (MEHP), or specific PPAR-γ ligands, such as thiazolidinedione (TZD), on CYP1A1 expression in CaCo-2 cells. We showed that CYP1A1 is highly inducible by PPAR-α ligands. This induction specifically involves the transcription factor PPAR-α and requires 2 peroxisome proliferator response element (PPRE) sites located within the CYP1A1 promoter (positions −931/−919 and −531/−519). Our data characterize a new PPAR-α—mediated CYP1A1 regulation pathway. This may be the basis of carcinogenesis by many environmental compounds that act as PPAR-α ligands. 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). 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 with (1) PPAR-α agonists such as WY-14643 (10, 30, 100, 200, and 400 μmol/L), MEHP (100 μmol/L), CF (50 μmol/L), or BZF (50 μmol/L); (2) the PPAR-γ agonist 2,4-TZD (200 μmol/L); or (3) the AhR ligand 3-MC (1 μmol/L). In the same conditions, HepG2 cells, keratinocytes, and A549 cells were treated with WY-14643 200 μmol/L and 3-MC 1 μmol/L. 3-MC was used as the control CYP1A1 inducer. Total RNA was isolated from cells by using Nucleospin RNAII (Macherey Nagel, Hoerdt, France). One microgram of total RNA was reverse-transcribed in 30 μL by using GibcoBRL Moloney murine leukemia virus reverse transcriptase (Life Technologies, Cergy Pontoise, France) in its own buffer and random primers at 37°C for 1 hour. CYP1A1 messenger RNA (mRNA) expression normalized to β2-microglobulin expression was determined with the LightCycler System (Roche Diagnostics, Meylan, France) and the Faststart DNA master SYBRGreen I Kit (Roche Diagnostics). The primers for CYP1A1 and β2-microglobulin were as follows: CYP1A1-Sense, 5′-AAGAGGAGCTAGACACAGT-3′; CYP1A1-Antisense, 5′-GAAACCGTTCAGGTAGGA-3′; β2m-Sense, 5′-CCGACATTGAAGTTGACTTAC-3′; and β2m-Antisense, 5′-ATCTTCAAACCTCCATGATG-3′. Polymerase chain reaction (PCR) was performed with MgCl2 5 mmol/L, 0.25 μmol/L of each primer, and LightCycler FastStart DNA Master SYBR Green I mix in a total volume of 16 μL. Cycling conditions were as follows: 10 minutes of denaturation at 95°C followed by 45 cycles of 10 seconds of denaturation at 95°C, 8 seconds of primer annealing at 55°C, and 8 seconds of fragment elongation at 72°C. The melting curve was analyzed with the LightCycler software, and quantitation was performed with RelQuant software (Roche). Three independent experiments were realized at least in triplicate. CaCo-2 cells were either untreated or treated with different concentrations of WY-14643 (10, 30, 100, or 200 μmol/L). Ethoxyresorufin O-deethylase (EROD) activity, mainly supported by CYP1A1, was determined according to the method of Burke et al.,18Burke M.D. Thompson S. Elcombe C.R. Halpert J. Haaparanta T. Mayer R.T. Ethoxy-, pentoxy- and benzyloxyphenoxazones and homologues a series of substrates to distinguish between different induced cytochromes P450.Biochem Pharmacol. 1985; 34: 3337-3345Crossref PubMed Scopus (1341) Google Scholar which was slightly modified by Kennedy et al.19Kennedy S.W. Jones S.P. Bastien L.J. Efficient analysis of cytochrome P4501A catalytic activity, porphyrins, and total proteins in chicken embryo hepatocyte cultures with a fluorescence plate reader.Anal Biochem. 1995; 226: 362-370Crossref PubMed Scopus (104) Google Scholar The fluorescence of resorufin produced during the reaction was measured with a CYTOFLUOR multiwell plate reader series 400 (PerSeptive Biosystems, Framingham, MA) with 530-nm excitation and 590-nm emission wavelengths. Fluorescence values were converted to picomoles by using a calibration curve of resorufin fluorescence, and EROD activity was expressed as picomoles of resorufin per minute per milligram of total cellular protein. Sense and antisense oligonucleotides containing 2 CYP1A1 XRE sites were synthesized with the addition of HindIII and XbaI restriction sites at the 5′ and 3′ ends, respectively. After hybridization and their digestion by HindIII and XbaI, these 2 oligonucleotides were cloned in the corresponding sites of the pBLCAT2 vector containing a thymidine kinase promoter (TK). This construction was named XRE-TK-chloramphenicol acetyltransferase (CAT). The oligonucleotide sense used was 5′-CCGCCCAAGCTTCCTCCCCCCTCGCGTGACTGCGAGGGGAAGGAGGCGTGGCCACACGTCTAGACTAGCT-3′. The XRE sites are in bold, and the HindIII and XbaI restriction sites are underlined. The chimeric construction pRNH25c, containing the −1140/+80 region of the CYP1A1 gene driving CAT gene expression, was used. Cells in 6-well plates were transiently transfected with 1 μg of pRNH25c by using lipofectin (Life Technologies). The transfection was performed as specified by the supplier. Twenty-four hours after the end of the transfection, cells were treated for 48 hours with 200 μmol/L WY-14643 or 1 μmol/L 3-MC. CAT expression was then evaluated by the amount of CAT protein by using the CAT enzyme-linked immunosorbent assay System (Roche). A similar experiment was realized with a construct coding PPAR-α. Transfected cells with 1 μg of complementary DNA or untransfected cells were then either untreated or treated with 200 μmol/L WY-14643 for 48 hours. The CYP1A1 mRNA level was determined as described previously. Three independent experiments were realized at least in triplicate. The PPRE mutations of pRNH25c were introduced by using the QuickChange site-directed mutagenesis kit (Stratagene, France) to obtain pRNH25c(ΔPPRE1), pRNH25c(ΔPPRE2), and pRNH25c(ΔPPRE1+2). The sense and antisense primers were used for mutagenesis. The sense primers were as follows (the PPRE core is underlined, and bold letters represent mutated nucleotides compared with the wild-type sequence): wild-type 1, 5′-GGACGGGCCGCCTGACCTCTGCCCCCTAGAGGGATGTCG-3′; PPRE1 mut-sense, 5′-GGACGGGCCGCCTGACCTCGATCCCCTAGAGGGATGTCG-3′; wild-type 2, 5′-GGCCTTCCGGCCCCGTGACCTCAGGGCTGGGGTCGCAGC-3′; and PPRE2 mut-sense, 5′-GGCCTTCCGGCCCCGTGAATTCAGGGCTGGGGTCGCAGC-3′. The presence of the mutations was verified by DNA sequencing. Cells were transfected by pRNH25c, pRNH25c(ΔPPRE1), pRNH25c(ΔPPRE2), or pRNH25c(ΔPPRE1+2), and after a 48-hour treatment with WY-14643 (200 μmol/L), the CAT expression was evaluated as described previously. Electromobility shift assays were performed with PPAR-α and retinoid X receptor (RXR)-α prepared by in vitro translation by using a coupled transcription/translation system (Promega, Charbonnieres, France). Proteins were incubated for 20 minutes at room temperature with 50,000 counts per minute of T4 polynucleotide kinase—labeled oligonucleotides in 10 mmol/L Tris (pH 8.0), 100 mmol/L KCl, 10% glycerol, 1 mmol/L dithiothreitol, 1 μg poly(dI:dC), and 0.5 μg of salmon sperm. The mixture was then submitted to electrophoresis on a 4% polyacrylamide gel in 45 mmol/L Tris base, 45 mmol/L boric acid, and 1 mmol/L ethylenediaminetetraacetic acid. The following oligonucleotides were used either as radiolabeled probes or as competitors (the sense strand is shown, with the core sequence underlined and the mutation in bold): PPRE consensus, 5′-CCGCCAAGCTTGCTCCGCCAGGTCACAGGTCACTAG; CYP1A1-PPRE1, 5′-GGACGGGCCGCCTGACCTCTGCCCCCTAGAGGGATGTCG; CYP1A1-PPRE2, 5′-GGCCTTCCGGCCCCGTGACCTCAGGGCTGGGGTCGCAGC; CYP1A1-PPRE1 mutant, 5′-GGACGGGCCGCCTGACCTCGATCCCCTAGAGGGATGTCG; and CYP1A1-PPRE2 mutant, 5′-GGCCTTCCGGCCCCGTGAATTCAGGGCTGGGGTCGCAGC. Anti—PPAR-α antibody (Santa Cruz Biotechnology, Santa Cruz, CA) was used for the supershift assays. Autoradiography was performed by exposing the dried gel to Kodak X-AR film (Rochester, NY). Confluent CaCo-2 cells (100 mm culture dishes) were treated with or without WY-14643 200 μmol/L for 1 hour. Cells were then fixed with formaldehyde at 37°C for 15 minutes. The reaction was then stopped by the addition of 1 mL of 1 mol/L glycine and incubation for 15 minutes at room temperature. Cells were harvested and pooled. Soluble chromatin prepared with a chromatin immunoprecipitation assay kit (Upstate Biotechnology, Lake Placid, NY) was precleared for 1 hour with salmon sperm DNA/bovine serum albumin/Protein A—Sepharose. Precleared chromatin was then incubated for 16 hours with 10 μg of anti-human PPAR-α antibodies (N-19 from Santa Cruz Biotechnology or MIA-822 from Affinity BioReagents, Golden, CO) or 10 μg of control mouse immunoglobulin G antibody (Sigma). Immune complexes were collected with 50 μL of Protein G—Sepharose (Santa Cruz Biotechnology) supplemented with salmon sperm DNA (200 μg/mL) and bovine serum albumin (1 mg/mL) and purified according to the manufacturer's recommendations (Upstate Biotechnology). Purified DNA samples (phenol-chloroform-isoamyl alcohol and, further on, Qiagen columns) were used as templates for PCR performed for 40 cycles (Pfx Taq DNA polymerase; Invitrogen, Carlsbad, CA). Similarly purified DNA fragments from the chromatin extracts (input) were used as control (PCR performed for 30 cycles). Cycling conditions were as follows: 3 minutes of denaturation at 93°C followed by 30 or 40 cycles of 30 seconds of denaturation at 91°C, 30 seconds of primer annealing at 55°C, and 1 minute of elongation at 72°C. Primers used for proximal CYP1A1 PPREs containing promoter region amplification were 5′-GCCTCCGGTCCTTCACAC-3′ and 5′-CGCTACAGCCTACCAGGACT-3′ (−1000 to −413 upstream of the transcriptional start site), and primers used for the distal CYP1A1 promoter region (harboring no PPRE sites) were 5′-CACAACTTGCACTGCCCTTA-3′ and 5′-CCAACAGCTCATTGAGAACG-3′ (−4053 to −3780 upstream of the transcriptional start site). Statistical analysis was performed with the Newman—Keuls test. Data were considered statistically significant at P < .05. 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 CYP1A1-mediated induction was dose dependent and reached a plateau at 200 μmol/L (6-fold). The results presented in Figure 1B also show that CYP1A1 expression was induced after 200 μmol/L WY-14643 treatment of various human cell lines other than CaCo-2, including HepG2 (hepatoma), in a primary culture of human keratinocytes and A549 cells (lung adenocarcinoma). However, the CYP1A1 inductions obtained in these cells were lower than in CaCo-2 cells. EROD activity was analyzed after treatment of CaCo-2 cells with increasing concentrations of WY-14643 (10–200 μmol/L). The results, shown in Figure 2, indicate that the CYP1A1 EROD activity was dose-dependently induced by WY-14643 (10-fold at 200 μmol/L) and that the induction obtained with 200 μmol/L WY-14643 was similar to that obtained with 1 μmol/L 3-MC (12.6-fold). By means of CAT assay analysis, we investigated whether WY-14643, a potent PPAR-α ligand, was able to stimulate the XRE target sequences of AhR. Cells were treated either with 1 μmol/L 3-MC or with 200 μmol/L WY-14643 after transient transfection with an XRE-TK-CAT construct. Figure 3A shows that 3-MC, a classic AhR ligand, activated CAT expression 2.1-fold, whereas WY-14643 did not increase CYP1A1 gene expression via the AhR signaling pathway. To strengthen the implication of PPAR-α in CYP1A1 induction by WY-14643, PPAR-α—transfected CaCo-2 cells were treated with WY-14643. Figure 3B shows that PPAR-α transfection doubled CYP1A1 mRNA induction by 200 μmol/L WY-14643 (10-fold) as compared with cells receiving the reporter gene alone (6-fold). CYP1A1 promoter gene analysis with MatInspector (Genomatix Software GmbH, Munich, Germany)20Quandt K. Frech K. Karas H. Wingender E. Werner T. MatInd and MatInspector new fast and versatile tools for detection of consensus matches in nucleotide sequence data.Nucleic Acids Res. 1995; 23: 4878-4884Crossref PubMed Scopus (2436) Google Scholar showed that 2 putative PPRE sites are located within the promoter at positions −931/−919 (CYP1A1-PPRE1) and −531/−519 (CYP1A1-PPRE2), respectively. To confirm that PPAR-α ligands were able to induce CYP1A1 mRNA by activation of its promoter, we transfected CaCo-2 cells either with the pRNH25c construct containing the wild-type CYP1A1 promoter or with the pRNH25c construct, in which the PPRE1 (pRNH25c[ΔPPRE1]), PPRE2 (pRNH25c[ΔPPRE2]), or PPRE1+2 (pRNH25c[ΔPPRE1+2]) sequences were mutated. Cells were then treated with either 200 μmol/L WY-14643 or 1 μmol/L 3-MC for 48 hours. Figure 4 shows that WY-14643 and 3-MC efficiently induced the transactivation of the CYP1A1 wild-type promoter pRNH25c (2.4-fold with 200 μmol/L WY-14643 and 4.6-fold with 1 μmol/L 3-MC). The mutation of 1 of the 2 CYP1A1 PPRE sites led to a decrease of CYP1A1 promoter activation by WY-14643. Indeed, the induction of CAT expression was lower with the pRNH25cΔPPRE1 or pRNH25cΔPPRE2 constructs (1.6-fold and 1.4-fold, respectively) as compared with the pRNH25c construct (2.4-fold). When the 2 sites were mutated (pRNH25cΔPPRE1+2), the decrease of the WY-14643 effect was higher (1.1-fold at 200 μmol/L WY-14643). We first checked the binding of an in vitro—translated PPAR-α/RXR heterodimer to the 2 CYP1A1 putative PPRE sequences by gel shift assay (Figure 5). As expected, a specific retarded band was observed when PPAR-α and its partner RXR were incubated together with the target oligonucleotide (lanes 5 and 11), but not when these receptors were incubated separately (lanes 3, 4, 9, and 10). We confirmed that the shift obtained with CYP1A1-PPRE1 and -PPRE2 was the consequence of the binding of PPAR-α by using a specific PPAR-α antibody, which produced the supershift shown in lanes 6 and 12. In addition, the specific PPAR-α/RXR-α/PPRE complex was repressed in a dose-dependent manner when incubated in the presence of a 10-fold (Figure 6, lanes 7, 9, and 11) or 50-fold (lanes 6, 8, and 10) excess of unlabeled consensus PPRE or unlabeled CYP1A1-PPRE1 or CYP1A1-PPRE2 sequences. In the same conditions, a 50-fold excess of mutated PPRE1 or PPRE2 CYP1A1 sequences did not affect the binding of PPAR-α/RXR-α on the PPRE consensus core (Figure 6, lanes 12 and 13, respectively). A supershifted band appeared with a PPAR-α antibody (lane 14). These observations showed that the in vitro—translated heterodimer PPAR-α/RXR-α binds to the 2 PPRE1 and PPRE2 sites within the CYP1A1 gene promoter. To strengthen our demonstration, chromatin immunoprecipitation assay analysis was performed with CaCo-2 cells untreated or treated with 200 μmol/L WY-14643 for 1 hour. We showed (Figure 7) that the PPAR-α/RXR-α heterodimer binds to the PPRE sites located within the proximal CYP1A1 gene promoter. 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 was increased after 6 hours of treatment with other PPAR-α ligands (CF, BZF, and MEHP). The induction factors were lower than those observed with WY-14643, which is one of the most potent agonists of PPAR-α. These results confirmed that CYP1A1 is induced by different classes of PPAR-α ligands, including the fibrates and phthalates. In contrast, TZD led to a marked decrease of CYP1A1 transcription. Such an antagonist regulatory effect of these 2 transcription factors (PPAR-α and PPAR-γ) has already been described for some genes, such as vascular cell adhesion molecule-1.21Rival Y. Beneteau N. Taillandier T. Pezet M. Dupont-Passelaigue E. Patoiseau J.F. Junquero D. Colpaert F.C. Delhon A. PPARalpha and PPARdelta activators inhibit cytokine-induced nuclear translocation of NF-kappaB and expression of VCAM-1 in EAhy926 endothelial cells.Eur J Pharmacol. 2002; 4352: 143-151Crossref Scopus (162) Google Scholar, 22Marx N. Sukhova G.K. Collins T. Libby P. Plutzky J. PPARalpha activators inhibit cytokine-induced vascular cell adhesion molecule-1 expression in human endothelial cells.Circulation. 1999; 99: 3125-3131Crossref PubMed Scopus (558) Google Scholar However, the repressive effect of PPAR-γ on CYP1A1 expression remains to be clarified and is presently under investigation in our laboratory. Moreover, transfection of PPAR-α complementary DNA leads to a higher induction with WY-14643, thus strengthening the involvement in the CaCo-2 cell line of PPAR-α in CYP1A1 regulation. The CYP1A1 induction by PPAR-α was not restricted to CaCo-2 cells, because similar results were obtained with HepG2 hepatoma cells, A549 lung adenocarcinoma cells, and primary cultures of human keratinocytes. The effect of PPAR-α ligands on CYP1A1 induction seems to be a general phenomenon that is not restricted to colon cell lines. The induction of CYP1A1 mRNA by WY-14643 was associated with an increase of EROD activity. This induction of EROD activity was similar to that obtained with 1 μmol/L 3-MC. Therefore, PPAR-α agonists may increase the genotoxic effect of procarcinogens bioactivated by CYP1A1, such as PAH or arylamines. Such a phenomenon was previously described with 2 peroxisome proliferators, silvex and di(2-ethylhexyl)phthalate, which enhance benzo(a)pyrene-induced DNA adducts.16Voskoboinik I. Ooi S.G. Drew R. Ahokas J.T. Peroxisome proliferators increase the formation of BPDE-DNA adducts in isolated rat hepatocytes.Toxicology. 1997; 122: 81-91Crossref PubMed Scopus (9) Google Scholar To date, PPAR-α ligands belonging to the fibrates class have been widely used as hypolipidemic drugs and have never been implicated in human carcinogenesis, although they are well-known hepatocarcinogens in rodents. The lack of such a side effect in humans may be related to the poor expression of PPAR-α in liver. Our data suggest that exposure to environmental PPAR-α ligands, including fibrate and chemical compounds such as phthalates or chlorophenoxyacetic pesticides, may increase CYP1A1 extrahepatic expression. Therefore, cells harboring a higher CYP1A1 expression would have a greater susceptibility to the genotoxic effect of CYP1A1-bioactivated procancerogens. Because CYP1A1 is mainly regulated by the AhR, it was logical to assume that WY-14643 could have a direct or indirect action on this transcription factor. However, using the XRE-TK-CAT construct, we showed that WY-14643 failed to activate the XRE site, thus showing that CYP1A1 induction by PPAR-α ligand did not involve AhR. Sequence analysis of the CYP1A1 promoter showed the presence of 2 putative PPRE sites. Indeed, treatment with WY-14643 increased CAT expression when cells were transiently transfected with pRNH25c harboring the wild-type CYP1A1 promoter. The results obtained in Figure 4 clearly show that the mutation of 1 PPRE site (ΔPPRE1 or ΔPPRE2) reduces the CAT induction, whereas no induction occurs with pRNH25c(ΔPPRE1+2). Therefore, it seems that the 2 PPRE sites located within the promoter at positions −931/−919 (CYP1A1-PPRE1) and −531/−519 (CYP1A1-PPRE2) were necessary for the CYP1A1 induction by PPAR-α ligands. The direct role played by these 2 PPRE sites in the binding of PPAR transcription factor was evaluated first by electrophoretic mobility shift assay. We found that even if the 2 sites diverge from the canonical DR1 sequence, they are still able to bind PPAR-α with good efficiency. PPAR-α binding is no longer possible when mutations are introduced into these CYP1A1-PPRE sites. To show the in vivo relevance of these PPRE sites, we performed chromatin immunoprecipitation assay. We immunoprecipitated the human CYP1A1 gene promoter by using 2 different anti-human PPAR-α antibodies and showed that the PPAR-α/RXR-α heterodimer binds in vivo on the CYP1A1-PPRE sites. We actually showed that with or without WY-14643 treatment, PPAR-α/RXR-α bound to the PPRE sites within the CYP1A1 promoter. This binding without any treatment has already been shown in CaCo-2 cells for the carnitine palmitoyltransferase II gene.23Barrero M.J. Camarero N. Marrero P.F. Haro D. Control of human carnitine palmitoyltransferase II gene transcription by peroxisome proliferator-activated receptor through a partially conserved peroxisome proliferator-responsive element.Biochem J. 2003; 369: 721-729Crossref PubMed Scopus (64) Google Scholar Recently, with a chromatin immunoprecipitation assay performed on mouse liver extract, Ijpenberg et al.24Ijpenberg A. Tan N.S. Gelman L. Kersten S. Seydoux J. Xu J. Metzger D. Canaple L. Chambon P. Wahli W. Desvergne B. In vivo activation of PPAR target genes by RXR homodimers.EMBO J. 2004; 23: 2083-2091Crossref PubMed Scopus (171) Google Scholar did not observe any PPAR-α/RXR-α binding on the PPRE site of the malic enzyme gene in untreated mice but had to treat the animals with WY-14643 to visualize such a binding. Conversely, Jia et al.25Jia Y. Qi C. Kashireddi P. Surapureddi S. Zhu Y.J. Rao M.S. Le Roith D. Chambon P. Gonzalez F.J. Reddy J.K. Transcription coactivator PBP, the peroxisome proliferator-activated receptor (PPAR)-binding protein, is required for PPARalpha-regulated gene expression in liver.J Biol Chem. 2004; 279: 24427-24434Crossref PubMed Scopus (101) Google Scholar showed in mouse liver extract that PPAR-α/RXR-α was already bound to the PPRE site of the enoyl-CoA hydratase/L-3-hydroxyacyl-CoA dehydrogenase (L-bifunctional enzyme) gene. Mouse treatment with WY-14643 seemed to increase this binding, but it is generally accepted that chromatin immunoprecipitation assay technology is qualitative but not quantitative. To date, it has not been clearly documented whether, without any ligand, the PPAR-α/RXR-α heterodimer is unbound or bound to PPRE sites in an inactive conformation, as has been largely described for the retinoic acid receptor.26Bastien J. Rochette-Egly C. Nuclear retinoid receptors and the transcription of retinoid-target genes.Gene. 2004; 328: 1-16Crossref PubMed Scopus (628) Google Scholar It seems that the binding of PPAR-α/RXR-α on PPRE sites in the presence or absence of PPAR-α ligands is dependent on the nature of the tissue, the cell type, and the gene studied. The PPRE2 site seems to have an inverted orientation compared with a canonical consensus site, whereas the PPRE1 site displays a conventional orientation. Sequence alignment of the CYP1A1 promoter (Figure 8) from various species shows that PPRE1 and PPRE2 sites are highly conserved in human, rat, and mouse species. Rat and mouse harbor the same PPRE1 and PPRE2 sequences and differ from humans in that they show a unique base transition. It is interesting to note that the flanking regions are also conserved. Moreover, when sequence alignment was performed with a CYP1A1 promoter from fish species, such as Anguilla japonica or Microgadus tomcod, we were unable to localize any PPRE sites, whereas several XRE sites were located within these promoters (data not shown). PPAR orthologues have already been described in fish species. Therefore, the CYP1A1 regulation by PPAR-α occurred tardily in the evolution of species, contrary to the regulation of CYP1A1 by AhR. Until now, only CYP4A, involved in fatty acid biotransformation, was known to be induced by PPAR-α ligands within the CYP superfamily.27Aldridge T.C. Tugwood J.D. Green S. Identification and characterization of DNA elements implicated in the regulation of CYP4A1 transcription.Biochem J. 1995; 306: 473-479Crossref PubMed Scopus (182) Google Scholar Because CYP1A1, largely involved in procarcinogen activation, is also implicated in fatty acid metabolism,28Yamazaki H. Shimada T. Effects of arachidonic acid, prostaglandins, retinol, retinoic acid and cholecalciferol on xenobiotic oxidations catalysed by human cytochrome P450 enzymes.Xenobiotica. 1999; 29: 231-241Crossref PubMed Scopus (73) Google Scholar it was logical to find its expression regulated through PPAR-α. Moreover, the CYP1A1 modification level could have a physiological effect in terms of fatty acid metabolite levels. Until now, CYP1A1 was known to be expressed and induced by the transcription factor AhR. This is the first time that another strong CYP1A1 induction pathway apart from AhR has been described. We showed that CYP1A1 was highly induced by PPAR-α via 2 PPRE sites within the promoter. The up-regulation of CYP1A1 by PPAR-α ligands may be involved in human carcinogenesis, notably in colon, through an increase of CYP1A1-bioactivated procancerogens present in diet, such as arylamines. The authors thank R. Hines for the pRNH25c and Chacon Christine for her technical assistance.