The glucocorticoid receptor acts as an antirepressor in receptor-dependent in vitro transcription

Glucocorticoid-receptor-dependent and glucocorticoid-response-element-dependent in vitro transcription was established using a crude nuclear extract and purified glucocorticoid receptor from rat liver. The capacity of glucocorticoid receptor to stimulate in vitro transcription was only detectable when basal transcription, i.e. transcription in the absence of glucocorticoid receptor, had been repressed. Transcriptional repression was achieved either by adding purified histone H1, or by lowering the amount of DNA template relative to the amount of crude nuclear extract. Glucocorticoid receptor caused a 1.1 +/- 0.7-fold stimulation of transcription from the mouse-mammary-tumor-virus promoter when basal transcription was not repressed, and a 7.0 +/- 1.5-fold stimulation when basal transcription had been repressed by addition of histone H1. Similar results were obtained when using a minimal promoter consisting of two glucocorticoid-response elements and a TATA box. Our data suggest that glucocorticoid receptor stimulates in vitro transcription by an antirepression mechanism.