ABSTRACT
CYP1A1 is largely implicated in carcinogenesis. To date, it is known that this gene is induced by xenobiotics such as polycyclic aromatic hydrocarbons. In this study, we evaluated the effect of serum in the regulation of CYP1A1 gene expression. CYP1A1 mRNA level is induced 1) in HepG2 and HT29-D4 cells by 3-methylcholanthrene 2) only in HepG2 after treatment by serum. The CYP1A1 mRNA induction in HepG2 is the consequence at least in part of a transcriptional activation as was demonstrated by evaluation of the hnRNA level. HepG2 cells were transfected by a plasmid containing the 7.5 Kb of the CYP1A1 promoter and the CAT reporter gene. No CAT stimulation was observed after serum treatment. These results demonstrated that CYP1A1 is induced at a transcriptional level by a physiological compound contained in serum independently of the Ah receptor and the 7.5 Kb promoter region.
Subject(s)
Blood , Carcinoma, Hepatocellular/metabolism , Cytochrome P-450 CYP1A1/genetics , Liver Neoplasms/metabolism , Receptors, Aryl Hydrocarbon/metabolism , Serum Albumin, Bovine/pharmacology , Tumor Cells, Cultured/metabolism , Adenocarcinoma/metabolism , Animals , Cattle , Chloramphenicol O-Acetyltransferase/genetics , Colonic Neoplasms/metabolism , Cytochrome P-450 CYP1A1/biosynthesis , Genes, Reporter , Humans , Methylcholanthrene/pharmacology , RNA, Heterogeneous Nuclear/analysis , RNA, Messenger/metabolism , RNA, Neoplasm/analysis , Reverse Transcriptase Polymerase Chain Reaction , Transcription, Genetic , Transfection , Tumor Cells, Cultured/drug effectsABSTRACT
We investigated the expression of c-myc in HT29-D4, HBL100 and Caco-2 cells treated with microtubule stabilising (paclitaxel) or depolymerising agents (vinblastine, nocodazole). After induction by epidermal growth factor (EGF), c-myc expression decreased in HT29-D4 cells treated with all the antimicrotubule agents. In HBL100 and Caco-2, when microtubules were stabilised with paclitaxel, c-myc expression also decreased. In contrast, its expression increased after treatment with depolymerising agents. In both cell lines, we also observed that depolymerising agents alone induced c-myc expression whilst paclitaxel had no effect. This mRNA induction was confirmed at the protein level. In HT29-D4, no variation of c-myc expression was observed. Then, we showed that the increase of mRNA level was due to activation of gene transcription. These results indicate that modulation of c-myc expression varied depending on the cell lines used and the type of antimicrotubule agents. This work provides a potential link between the microtubular network and c-myc gene expression.
Subject(s)
Adenocarcinoma/drug therapy , Colonic Neoplasms/drug therapy , Genes, myc/genetics , Microtubules/drug effects , Proto-Oncogene Proteins c-myc/metabolism , Blotting, Western , Caco-2 Cells/metabolism , Flow Cytometry , Gene Expression Regulation, Neoplastic/drug effects , HT29 Cells/metabolism , Humans , Polymerase Chain Reaction/methods , RNA, Messenger/metabolism , Reverse Transcriptase Polymerase Chain ReactionABSTRACT
CYP1A1 is implicated in the bioactivation of procarcinogens such as polycyclic aromatic hydrocarbons. To date, no physiological compounds have been described as inducers of this gene. In this study, we have examined the role of serum in the regulation of CYP1A1 gene expression. After treatment of CaCo-2 cells with fetal bovine serum, CYP1A1 mRNA level increased to the same extent as that observed after 3-methylcholanthrene induction. The same effect was obtained after treatment with adult bovine or human serum. Evaluation of hnRNA level performed on CaCo-2 cells indicates that CYP1A1 induction by serum acts at least in part through transcriptional activation. Promoter region containing the XRE (1.56 kb) was tested in the CAT assay. No stimulation of this reporter gene was detected after serum treatment. These results demonstrate for the first time that physiological compound(s) contained in serum induces CYP1A1 gene expression by transcriptional activation independent of the AhR pathway.
Subject(s)
Cytochrome P-450 CYP1A1/genetics , Receptors, Aryl Hydrocarbon/metabolism , Adult , Animals , Base Sequence , Caco-2 Cells , Cattle , Chloramphenicol O-Acetyltransferase/genetics , Culture Media , Cytochrome P-450 CYP1A1/biosynthesis , DNA Primers/genetics , Enzyme Induction , Gene Expression Regulation, Enzymologic/drug effects , Genes, Reporter , Humans , Methylcholanthrene/pharmacology , RNA, Messenger/genetics , RNA, Messenger/metabolism , Transcriptional Activation/drug effectsABSTRACT
A strong overlap exists between gp170 and CYP3A substrates and inducers. In order to investigate a putative coregulation of MDR and CYPA gene expression, we measured their transcripts in human liver and after dexamethasone treatment in HepG2 cells or in different mouse tissues. In human liver, we observed no correlation between MDR1 and CYP3A4 expression, whereas these genes were coinduced by dexamethasone in HepG2 cells. In mouse liver treated with dexamethasone, mdr1b and Cyp3a were induced (5- and 2-fold, respectively). In adrenals, the main expressing gp170 tissue, Cyp3a, was increased while mdr1b was repressed (-51%). The expression of mdr1b increased in heart, brain, and colon and decreased in lung and kidney but Cyp3a was not detectable. In conclusion, human hepatic CYP3A4 and MDR1 are not corregulated but are coinducible. In vivo murine mdr1b and Cyp3a are coregulated by dexamethasone in liver and inversely regulated in adrenals.
