The nuclear bile acid receptor FXR (farnesoid X receptor) is one of the key factors that suppress bile acid biosynthesis in the liver. PGC-1α [PPARγ (peroxisome-proliferator-activated receptor γ) co-activator-1α] is known to control energy homoeostasis in adipose tissue, skeletal muscle and liver. We performed cell-based reporter assays using the expression system of a GAL4–FXR chimaera, the ligand-binding domain of FXR fused to the DNA-binding domain of yeast GAL4, to find the co-activators for FXR. We found that the transcriptional activation of a reporter plasmid by a GAL4–FXR chimaera was strongly enhanced by PGC-1α, in a ligand-dependent manner. Transcriptional activation of the SHP (small heterodimer partner) gene by the FXR–RXRα (retinoid X receptor α) heterodimer was also enhanced by PGC-1α in the presence of CDCA (chenodeoxycholic acid). Co-immunoprecipitation and pull-down studies using glutathione S-transferase–PGC-1α fusion proteins revealed that the ligand-binding domain of FXR binds PGC-1α in a ligand-influenced manner both in vivo and in vitro. Furthermore, our studies revealed that SHP represses its own transcription, and the addition of excess amounts of PGC-1α can overcome the inhibitory effect of SHP. These observations indicate that PGC-1α mediates the ligand-dependent activation of FXR and transcription of SHP gene.
Recognition of LXXLL by Ligand Binding Domain of the Farnesoid X Receptor in Molecular Dynamics Simulation.
