Steroid hormone receptors: interaction with deoxyribonucleic acid and transcription factors

Gene regulation by steroid hormones is mediated by binding of the hormone ligand to the corresponding receptor that triggers a complex set of interactions of the hormone receptors with each other, with DNA in chromatin, and with a variety of other proteins. In this review we attempt to summarize what is known about these interactions using as the main example the regulation of mouse mammary tumor virus transcription by glucocorticoids and progestins. We describe in some detail the interaction of monomers and homodimers of the steroid receptors with their recognition sequences, and the molecular mechanism used to discriminate between the responsive elements for glucocorticoids/progestins and estrogens. We then review the interactions between homologous and heterologous hormone receptors on complex hormone regulatory regions, before devoting some attention to the synergistic and inhibitory interactions of hormone receptors with other transcription factors. Finally we briefly summarize some of the possible mechanisms that modulate the molecular interactions of hormone receptors. In addition to ligand binding, these include receptor phosphorylation, changes in DNA topology, and the organization of DNA in nucleosomes. From this overview we draw the tentative conclusion that the specificity of the hormonal response in different cells results from a combination of developmental restrictions both in the accessibility of genomic sequence and in the repertoire of regulatory proteins present in each particular cell. In addition, the array of regulatory sequences in DNA and chromatin determines the precise nature of macromolecular interactions of the receptors that are modulated by their degree of phosphorylation.