RT-qPCR analysis of (A) CYP1A1 and (B) AhR mRNA expression following incubation of HepG2-C3A cells with 10 nM TCDD in the presence or not of 100 μM skatole for 2, 4, 8 or 24 h (n = 3). RT-qPCR analysis of CYP1A1, CYP1A2, CYP1B1 and AhR mRNA expression in PHHs treated for 8 (C) or 24 h (D) with TCDD in the presence or not of 100 μM skatole (n = 5). Results are expressed as the percentage of the induction observed with 10 nM TCDD. (E) CYP1A and actin protein expression in PHHs after incubation with 10 nM TCDD in the presence or not of 10, 50 or 100 μM skatole for 24 h (Donor #401). (F) Luciferase activity in HepG2-C3 cells transfected with pTXINV-XRE and incubated with TCDD alone or with skatole, in the presence or not of 3 μM CH223191 for 2, 4, 8 or 24 h (n = 3). * Significantly different from time-matched control cells (DMSO); # significantly different from time-matched TCDD treated cells (Student’s t–test; p < 0.01).