Influence of PGC1α overexpression on the PXR-dependent suppression of reporter gene transcription by PPARα in COS-1 cells. (A) COS-1 cells were transfected with p3A4-pGL3, expression plasmids for hPXR and/or PGC1α (50 ng) as indicated, and phRL-SV40, and treated with vehicle (Veh; 0.1% DMSO) or 10 μM rifampicin (Rif) for 24 h. (B) COS-1 cells were transfected with a reporter plasmid containing the −250 to +42 of human HMGCS2, expression plasmids for hPXR (1 or 10 ng), hPPARα (10 ng) and PGC1α as indicated, and phRL-SV40, and treated with vehicle (0.1% DMSO), 100 µM bezafibrate (BZF), and/or 10 µM rifampicin for 24 h. Relative reporter activity was determined. Data are shown as the mean ± S.D. (n = 4).