Fig. 1.

Relative PXR reporter activity and firefly or Renilla luminescence with an PXR activator exhibiting low cytotoxicity. Idealized model (upper panels): a ① Cell proliferation remains at 100%, ② Relative PXR activity shows a sigmoidal concentration-dependent increase; b ① The firefly luminescence increases in a sigmoidal manner and ② reaches a maximum, resulting in a plateau of relative PXR activity given ③ the constant Renilla luminescence. Experimental data (lower panels): c Rifampicin effect on cell proliferation and relative PXR activity after 24 h drug exposure, normalized to untreated control. d Firefly and Renilla luminescence normalized to untreated control. Data shown are the mean ± SEM of three independent biological replicates with n = 4 (reporter data) or n = 8 (proliferation data) replicates for each concentration/replicate. Whenever data could not be fitted to a sigmoidal Emax model (four parameter-logistic equation; variable slope), data points are simply connected (here: rifampicin effect on proliferation or Renilla luminescence). Impact of drug treatments on firefly or Renilla values was evaluated by ANOVA with non-parametric Kruskal–Wallis test and Dunn’s test compared to untreated control. *P < 0.05; **P < 0.01; ***P < 0.001