Serum induces a transcriptional activation of CYP1A1 gene in HepG2 independently of the AhR pathway

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.

Dietary lipids affect human ethanol-inducible CYP2E1 gene expression in vivo in mononuclear cells

We tested the hypothesis that dietary cholesterol modulate human ethanol-inducible CYP2E1 expression in vivo in circulating mononuclear cells. Healthy volunteers (n= 10) were submitted to a low fat low cholesterol diet for 4 days (day 0-day 3, LFLC). Cholesterol (595 +/- 56 mg/day) was then reintroduced for 7 days (day 4-day 10, LFHC). In the same time, controls subjects (n=7) did not change their habitual daily diet. CYP2E1 mRNA levels, evaluated in mononuclear cells, decreased in experimental subjects during both LFLC and LFHC from 100% to 53 +/- 5%, (p<0.001) with a main decrease during LFLC period (100% to 71 +/- 16%, p=0.05). Immunoreactive CYP2E1 showed a similar pattern and decreased from 100 to 62 +/- 12% during the trial (p<0.05). No significant change occured in control subjects. Between day 0 and day 11, changes in CYP2E1 mRNA correlated positively with plasma cholesterol (r2=0.67, p<0.001) and HDL cholesterol concentrations (r2=0.61, p<0.001). In contrast, no correlation was found between plasma fatty acids concentrations and CYP2E1 expression. The present results suggest that lipid factors regulate CYP2E1 expression, in vivo, in human mononuclear cells. In particular, plasma cholesterol concentrations may play an important role in this regulation.

Opposite effects of antimicrotubule agents on c-myc oncogene expression depending on the cell lines used

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.

Induction of CYP1A1 by serum independent of AhR pathway

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.

Hypomethylation and hypoexpression of human CYP2E1 gene in lung tumors

We have demonstrated the presence of CYP2E1 protein in a catalytically active form in lung tumors, differences being observed between the tumors and normal tissues from the same patients. Indeed, a higher microsomal CYP2E1 N-nitrosodimethylamine (NDMA) demethylase activity was present in normal tissues compared to tumors and was accompanied by corresponding change in CYP2E1 protein concentration, as shown by Western blot analysis. The catalytic activity among tumors differed from that among normal tissues with statistical significance of p < 0.01. CYP2E1 mRNA was present in lung tumors and less expressed compared to normal tissues from the same individuals. In order to understand the regulation of CYP2E1 gene expression, we studied the methylation status of the CYP2E1 gene in human lung tumors and normal tissues from the same patients and observed that a hypomethylation was associated with a hypoexpression of the CYP2E1 gene in lung tumors.

Tissue-specific expression and methylation of the human CYP2E1 gene

The level and number of CYP2E1 gene transcripts were investigated by northern blot analysis in various human adult tissues including liver, lung, placenta, skin and neurinoma. Three transcripts of 1.8, 2.6 and 4 Kb were expressed in a tissue-specific manner. The origin of the various transcripts was studied and showed that both 4 and 2.6 Kb mRNAs contained sequences from the 3' non-translated region of the gene and that the 4 Kb also contained region localized in the 5' non-translated region. Furthermore, it clearly appeared that a catalytically active CYP2E1 enzyme (as proved by NDMA demethylase activity) was only detected in tissues expressing the 1.8 Kb. The human CYP2E1 was also identified through immunohistochemical techniques. Finally, we observed a relation between the hypomethylation of the human CYP2E1 gene and the hypoexpression of the corresponding protein.

Effect of cigarette smoke on hepatic and pulmonary cytochromes P450 in mouse: evidence for CYP2E1 induction in lung

Pulmonary and liver microsomes of male NMRI mice were used to study the inductive effect of cigarette smoke on various cytochrome P450 isoforms implicated in precarcinogen and premutagen bioactivation. The enzymatic activities catalyzed by CYP1A1, CYP2B, CYP2C, CYP2D, CYP2E1 and CYP3A were induced in liver microsomes. Immunoquantification of lung and liver CYP1A1, 2E1 and 3A demonstrated that 1) CYP1A1 was induced in lung and liver, 2) CYP3A subfamily was induced in liver and not detected in lung, 3) CYP2E1 was slightly induced in liver whereas its pulmonary expression was more largely increased (6.8 fold) than CYP1A1 (2.0 fold). This latter data suggests that CYP2E1, which is known to be expressed in human lung, could actively participate in pulmonary carcinogenesis induced by cigarette smoke.