Inactivation by Na+,K+-ATPase of cytosol glucocorticoid receptors from rat brain and liver

Summary We have examined the effect of Na⁺,K⁺-ATPase on ³H-triamcinolone acetonide binding capacity of cytosol glucocorticoid receptors from rat brain and liver. Preincubation of the brain or liver cytosol with Na⁺,K⁺-ATPase (10 units/ml) at 30 °C resulted in a rapid loss of specific ³H-triamcinolone acetonide binding, with a half-life of approximately 7 min. The ATPase effect could be prevented by the addition of 10^–5 M ouabain, or substantially reduced by the omission of Na⁺,K⁺ or Mg⁺². The cytosol receptor bound with ³H-triamcinolone acetonide was totally resistant to the inactivation by the ATPase. Since there is some evidence that ATP may bind to glucocorticoid receptor, our findings indicate that an ATP-receptor complex may be essential for steroid binding. The effects of the ATPase in the inactivation of the receptor are very similar to those of alkaline phosphatase reported by others. This raises doubts about the proposal based on the phosphatase inactivation that the cytosol glucocorticoid receptor may be phosphorylated.