Induction of nuclear translocation of constitutive androstane receptor by peroxisome proliferator-activated receptor α synthetic ligands in mouse liver

Peroxisome proliferators activate nuclear receptor peroxisome proliferator-activated receptor α (PPARα) and enhance the transcription of several genes in liver. We report here that synthetic PPARα ligands Wy-14,643, ciprofibrate, clofibrate, and others induce the nuclear translocation of constitutive androstane receptor (CAR) in mouse liver cells in vivo. Adenoviral-enhanced green fluorescent protein-CAR expression demonstrated that PPARα synthetic ligands drive CAR into the hepatocyte nucleus in a PPARα- and PPARβ-independent manner. This translocation is dependent on the transcription coactivator PPAR-binding protein but independent of coactivators PRIP and SRC-1. PPARα ligand-induced nuclear translocation of CAR is not associated with induction of Cyp2b10 mRNA in mouse liver. PPARα ligands interfered with coactivator recruitment to the CAR ligand binding domain and reduced the constitutive transactivation of CAR. Both Wy-14,643 and ciprofibrate occupied the ligand binding pocket of CAR and adapted a binding mode similar to that of the CAR inverse agonist androstenol. These observations, therefore, provide information for the first time to indicate that PPARα ligands not only serve as PPARα agonists but possibly act as CAR antagonists.