Bile acids are physiological ligands for a nuclear receptor

Bile acids are essential for the solubilization and transport of dietary li pids and are the major products of cholesterol catabolism. Results presente d here show that bile acids are physiological ligands for the farnesoid X r eceptor (FXR), an orphan nuclear receptor. When bound to bile acids, FXR re pressed transcription of the gene encoding cholesterol 7 alpha-hydroxylase, which is the rate-limiting enzyme in bile acid synthesis, and activated th e gene encoding intestinal bile acid-binding protein, which is a candidate bile acid transporter. These results demonstrate a mechanism by which bile acids transcriptionally regulate their biosynthesis and enterohepatic trans port.