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In our previous study, chlorinated ethylenes (CEs) such as tetrachloroethylene (PCE), trichloroethylene (TCE) and 1,1-dichloroethylene (1,1-DCE) were found to suppress CYP1A1 activity in rats. In the present study, the effects of CEs on CYP1A1 activity, CYP1A1 mRNA expression and the binding of nuclear proteins to the xenobiotic response element (XRE) were investigated in rat hepatocytes and human hepatoma HepG2 cells. Unexpectedly, CYP1A1 activity was enhanced in the cells cultured in the presence of CEs, suggesting that the suppressive effect of CEs in vivo is indirect. Well consistent with the enhanced enzymatic activity, the expression of CYP1A1 mRNA was increased by all CEs. Furthermore, the induction by 3-methylchoranthrene (3-MC) was reversed in the presence of individual CEs, implying cross-talk between the induction mechanisms of PAHs and CEs. In a luciferase reporter assay of transcription under the control of 4 repeats of XRE, a 2.5-fold increase was induced in HepG2 cells by CEs in the case of 1,1-DCE-treatment, while a 11-fold increase was observed in the cells treated with 3-MC. In HepG2 cells transfected with plasmids expressing aryl hydrocarbon receptor (AhR) antisense mRNA, in which the AhR-expression level was reduced by approximately 40%, no increase in luciferase activity was observed following the CE-treatment, though a 15-fold induction was observed in the presence of 3-MC. As for the nuclear XRE-binding proteins in the presence of CEs analyzed with the gel mobility shift assay, the band-intensity peaked 3 hr after the PCE-, TCE- and 3-MC-treatments. The metabolic activation might be responsible for the 3-hr delay to attain the maximal band-intensity in the case of 1,1-DCE.

journal of health science

Possible Involvement of Chlorinated Ethylenes in Arylhydrocarbon Receptor-Related Induction of Cytochrome P4501A1 (CYP1A1) in Human Hepatoma HepG2 Cells