Agonist-dependent phosphorylation and nuclear dephosphorylation of glucocorticoid receptors in intact cells

Phosphorylation and dephosphorylation has been suggested to influence the function of glucocorticoid receptors, but evidence for hormone-dependent changes in the phosphorylation state under physiological conditions is lacking. Here we show that in intact WEHI-7 mouse thymoma cells, labeled for 18-20 h with [32P]orthophosphate and [35S]methionine, glucocorticoids rapidly increase the average number of phosphates on the steroid-binding protein approximately from three to five. This stimulation is agonist-dependent since the antiglucocorticoid RU 486 (17 beta-hydroxy-11 beta,4-dimethylaminophenyl-17 alpha-propynyl estra-4,9-diene-3-one) has no effect by itself and blocks the cortisol-induced phosphorylation. Furthermore, the salt-unextractable nuclear bound receptors lose at least two phosphates compared to cytosolic and nuclear extractable forms. These results show for the first time that these hormone-dependent transcription regulators undergo agonist-induced phosphorylation and dephosphorylation which may affect their activity.