Retinoid and thyroid hormone receptors: ligand-regulated transcription factors as proto-oncogenes.

The retroviral v-erb A locus is derived from a cellular gene, c-erb A, encoding a thyroid hormone receptor. The v-erb A and c-erb A proteins are, in turn, members of a larger family of structurally and functionally interrelated polypeptides that includes the steroid, retinoic acid, and vitamin D3 receptors. These nuclear hormone receptors act by binding to specific sites on the cell genome and, in response to cognate hormone, modulating the transcription of adjacent 'target' genes. The expression, properties, and mechanisms of action of the thyroid hormone receptors (c-erb A proteins) and the closely related retinoic acid receptors are discussed.