Protein kinase activity associated with the purified rat hepatic glucocorticoid receptor.

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Abstract
The MW 94,000 steroid binding component of rat hepatic glucocorticoid receptor 5000-fold undergoes Ca-stimulated phosphorylation in vitro by [.gamma.-32P]ATP. Exogenous histones can be phosphorylated by this preparation without Ca. Calmodulin did not stimulate phosphorylation of the glucocorticoid receptor beyond that obtained with Ca alone. Although the specific calmodulin inhibitor calmidazolium had no effect, trifluoperazine and chlorpromazine, nonspecific calmodulin inhibitors, abolished the Ca-dependent phosphorylation of receptor. EGTA [ethylene glycol bis (.beta.-aminoethyl ether)N,N,N'',N''-tetracetic acid] blocks the effect of Ca; Mg cannot substitute for Ca. Cyclic nucleotides (cAMP or cGMP) do not stimulate phosphorylation of the receptor in the absence of Ca. Phosphorylation of the glucocorticoid receptor is steroid dependent. Triamcinolone acetonide elicited activation and phosphorylation of receptor in the presence of Ca, whereas the antagonists progesterone, cortexolone and .beta.-lapachone did not. Sodium molybdate, which blocks the thermal activation step, inhibits phosphorylation of the receptor. The activated form of the glucocorticoid receptor is required for phosphorylation to occur. The ATP analogs 8-azido-ATP or fluorosulfonylbenzoyl adenosine, inhibit phosphorylation of the MW 94,000 component, implying the presence of an ATP binding site inherent to the receptor.