Modulators of the glucocorticoid receptor also regulate mineralocorticoid receptor function

Abstract

Modulators are proposed to be novel ether aminophosphoglycerides that stabilize unoccupied and occupied glucocorticoid receptor steroid binding and inhibit glucocorticoid receptor complex activation. Two isoforms, modulator 1 and modulator 2, have been purified from rat liver cytosol [Bodine, P.V., & Litwack, G. (1990) J. Biol. Chem. 265, 9544-9554]. Since the mineralocorticoid receptor is relatively resistant to activation, modulator's effect on rat distal colon mineralocorticoid receptor function was examined. Warming of unoccupied receptor decreased residual specific [3H]aldosterone binding by 86 +/- 2%. Both modulator isoforms completely prevented this destabilization with Km's of 2 +/- 1 microM modulator 1 and 24 +/- 5 microM modulator 2. Warming of occupied mineralocorticoid receptors decreased [3H]aldosterone binding by 56 +/- 3%. Modulator only partially stabilized occupied receptor binding with Km's of 10 +/- 2 microM modulator 1 and 68 +/- 8 microM modulator 2. Modulator inhibited receptor activation with Km's of 3 +/- 1 microM modulator 1 and 33 +/- 10 microM modulator 2. Double-reciprocal analysis showed linear kinetics, and mixing modulator isoforms together had additive effects on unoccupied and occupied receptor steroid binding stabilization and activation inhibition. Colon cytosol contained a low molecular weight, heat-stable factor(s) which inhibited receptor activation and stabilized occupied receptor steroid binding. Molybdate completely stabilized unoccupied mineralocorticoid receptor steroid binding and inhibited activation with half-maximal effects at 3-4 mM but only stabilized occupied receptor binding by approximately 40%. These data indicate that (i) apparent physiologic concentrations of modulator stabilize mineralocorticoid receptor steroid binding and inhibit receptor activation, (ii) an aldosterone-responsive tissue contains a modulator-like activity, and (iii) molybdate mimics the effects of modulator.(ABSTRACT TRUNCATED AT 250 WORDS)