Molybdate inhibition of glucocorticoid receptor inactivation and transformation

The inactivation of glucocorticoid receptors that occurs when cytosol is heated at 25 degrees C is blocked reversibly by molybdate and slowed by some other phosphatase inhibitors such as fluoride and glucose 1-phosphate. Molybdate is also capable of preventing nonenzymatic inactivation of unbound receptors caused by exposure to salt or precipitation with ammonium sulfate at 0 degrees C. Inactivation of unbound receptors caused by Sephadex G-50 gel filtration is prevented by all three inhibitors. Both molybdate and tungstate block temperature-dependent transformation of glucocorticoid.receptor complexes to the DNA-binding state, where fluoride and glucose 1-phosphate have no effect. Transformation brought about at 0 degrees C by salt, ammonium sulfate precipitation, or gel filtration is also blocked by both molybdate and tungstate. Tungstate differs from molybdate in that it has little or no effect on receptor inactivation. Fluoride and glucose 1-phosphate do not inhibit transformation. These observations support the proposal that molybdate and tungstate are interacting through a reversible association with the glucocorticoid receptor itself. We propose that they may act by forming a complex with a phosphate moiety on the receptor.