Interaction of cytosol fractions containing activated glucocorticoid-receptor complexes from rat liver and thymus with heterologous nuclei: effects on transcription.

Two rat liver cytosol fractions containing activated glucocorticoid-receptor complexes are able to stimulate the transcriptional activity of rat liver nuclei; the respective fractions from the cytosol of thymocytes inhibit the capacity of thymus nuclei for RNA synthesis. A similar inhibitory effect on thymus nuclei is exerted by the presence of rat liver cytosol fractions. Spot hybridization using a tyrosine aminotransferase (TAT) probe demonstrates that TAT gene expression is stimulated by the liver cytosol fractions acting on homologous nuclei whereas it is inhibited, in thymus nuclei, by the addition of thymus cytosol fractions. No effect on transcription is observed if the liver or thymus cytosol is heat activated in the presence of the glucocorticoid antagonist, cortexolone. Treatment of liver nuclei, previously subjected to the action of thymus cytosol fractions with the respective liver ones, restores transcriptional activity to control or higher levels. We conclude that rat thymocyte nuclei and cytosol contain transcriptional factors, which in the presence of the glucocorticoid-receptor complex, irrespective of its source, inhibit gene expression, whereas in the absence of such factors, the glucocorticoid-receptor complex positively regulates the respective genes.