RESUMO
The estrogen-related receptors (ERR alpha, ERR beta, and ERR gamma) form a family of orphan nuclear receptors that share significant amino acid identity with the estrogen receptors, but for which physiologic roles remain largely unknown. By using a peptide sensor assay, we have identified the stilbenes diethylstilbestrol (DES), tamoxifen (TAM), and 4-hydroxytamoxifen (4-OHT) as high-affinity ligands for ERR gamma. In direct binding assays, 4-OHT had a K(d) value of 35 nM, and both DES and TAM displaced radiolabeled 4-OHT with K(i) values of 870 nM. In cell-based assays, 4-OHT binding caused a dissociation of the complex between ERR gamma and the steroid receptor coactivator-1, and led to an inhibition of the constitutive transcriptional activity of ERR gamma. ERR alpha did not bind 4-OHT, but replacing a single amino acid predicted to be in the ERR alpha ligand-binding pocket with the corresponding ERR gamma residue allowed high-affinity 4-OHT binding. These results demonstrate the existence of high-affinity ligands for the ERR family of orphan receptors, and identify 4-OHT as a molecule that can regulate the transcriptional activity of ERR gamma.
Assuntos
Antagonistas de Estrogênios/metabolismo , Receptores de Estrogênio/metabolismo , Tamoxifeno/análogos & derivados , Tamoxifeno/metabolismo , Transativadores/metabolismo , Sequência de Aminoácidos , Animais , Linhagem Celular , Chlorocebus aethiops , Dietilestilbestrol/metabolismo , Receptor alfa de Estrogênio , Receptor beta de Estrogênio , Humanos , Dados de Sequência Molecular , Receptores de Estrogênio/genética , Proteínas Recombinantes de Fusão/genética , Proteínas Recombinantes de Fusão/metabolismo , Transativadores/genética , Ativação TranscricionalRESUMO
Bile acids are essential for the solubilization and transport of dietary lipids and are the major products of cholesterol catabolism. Results presented here show that bile acids are physiological ligands for the farnesoid X receptor (FXR), an orphan nuclear receptor. When bound to bile acids, FXR repressed transcription of the gene encoding cholesterol 7alpha-hydroxylase, which is the rate-limiting enzyme in bile acid synthesis, and activated the 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 transport.
