Transcriptional inhibition of TCDD-mediated induction of cytochrome P450 1A1 and alteration of protein expression in a zebrafish hepatic cell line following the administration of TCDD and Cd2+

We studied the effects of Cd2+ on TCDD-mediated induction of the cytochrome P450 1A1 (cyp1a1) gene using a zebrafish liver cell line (ZFL). Our results showed that Cd2+ inhibited the TCDD-mediated induction of the cyp1a1 protein, enzyme activity, and mRNA expression level. Cd2+ also down-regulated levels of the aryl hydrocarbon receptor (ahr2) and the aryl hydrocarbon receptor nuclear translocator 2b (arnt2b) mRNAs. Compared with TCDD (3 nM) treatment alone, co-treatment with Cd2+ (0-30 μM) and TCDD (3 nM) significantly inhibited the activity of the luciferase reporter gene constructs harboring the distal promoter region (P-2626/-2009) of CYP1A1 and the synthetic 3XRE gene promoter. This indicates that Cd2+ decreased the level of TCDD-induced cyp1a1 through transcriptional inhibition. Proteomic analysis was also used to evaluate the effect of Cd2+ on TCDD-altered protein expression in ZFL cells. The identified proteins are mainly enzymes of the glycolysis pathway and proteasomes, and have anti-oxidative and anti-stress effects.