[Endocrine signaling system mediated by nuclear receptors].

Nuclear receptors act as ligand-dependent DNA-binding transcription factors that transduce specific hormonal signals to modulate pattern of gene expression. Their unique modular structure defines the superfamily of intracellular signal mediators which include receptors for steroids, thyroid hormones, and several lipophilic vitamins as well as a large number of orphan receptors. Almost 50 distinct genes have been identified in the human genome, and their products can be classified into 5 different subfamilies based upon structural similarity, the mode of DNA binding, and evolutionary conservation. Recent advances in understanding the nuclear receptor system have uncovered complex yet well-organized regulatory networks of these signal transducers at the level of receptor dimerization, target gene recognition, and cofactor interaction.