Effect of CYP1A1 siRNA on CYP1A1 mRNA (A), CYP1B1 mRNA (B), and CYP1A1/1B1 enzymatic activity (C) in DMSO- and TCDD-treated HAECs. (A–C). Total RNA was isolated 48 h after transfection of HAECs with control siRNA or CYP1A1 siRNA and 24 h after exposure to DMSO or 1 nM TCDD (n=3). CYP1A1 and CYP1B1 RNA expression was determined by real-time PCR. Results were normalized to 18s rRNA and expressed relative to DMSO control (n=3). (C) CYP1A1/1B1 enzymatic activity was determined 48 h after transfection of HAECs with control siRNA or CYP1A1 siRNA and 24 h after exposure to DMSO or 1 nM TCDD. CYP1A1/1B1 enzymatic activity, normalized to DNA content, was determined by P450Glow assay (Promega) (n=8). All results are expressed as mean ± SEM. *p < 0.05, compared to respective DMSO control. #p < 0.05, compared to respective control siRNA.