Control of gene expression by glucocorticoid hormones

Glucocorticoids control the expression of a small number of transcriptionally active genes by increasing or decreasing mRNA concentration. Either effect can result from a transcriptional or a post-transcriptional mechanism. Induction of mouse mammary tumour virus RNA results from a stimulation of transcription initiation and depends on the presence of defined regions in proviral DNA. These regions bind the glucocorticoid receptor and behave functionally as proto-enhancers. Glucocorticoid-inducible genes can retain their sensitivity to the hormone after transfer to a heterologous cell by transfection techniques. Non-inducible genes can become inducible when linked to the promoter region of an inducible gene. The mechanisms by which the receptor-steroid complex stimulates or inhibits transcription or influences mRNA stability are unknown. Receptor binding to nucleic acids appears to be a necessary but not sufficient condition. It is likely that the receptor also interacts with chromatin proteins. This might lead to a catalytic modification of these proteins, resulting in a modulation of gene expression. Development of glucocorticoid-sensitive, biochemically defined, cell-free transcription systems should provide a tool to delineate the molecular determinants of this essential regulatory mechanism.