Rat ovary glucocorticoid receptor: identification and characterization

A soluble, thermolabile protein with characteristics typical of glucocorticoid receptors has been identified in the ovaries of estrogen-stimulated hypophysectomized immature rats. After the incubation of 3H- dexamethasone with ovarian cytosol, fractionation on a Sephadex G-200 column reveals a peak of radioactivity which elutes at the void volume. This peak, which represents saturable 3H-dexamethasone binding, disappears following heating (4 degrees C X 15 min) or treatment of the cytosol with pronase. Scatchard analysis of the 3H-dexamethasone binding to cytosol shows it to be high affinity (Kd=5.1 nM) and saturable, with 327 fmol binding sites/mg cytosol protein. Binding site number rises linearly with increasing cytosol protein concentrations. The relative abilities of various steroids to inhibit 3H-dexamethasone binding are: triamcinolone acetonide greater than or equal to dexamethasone greater than cortisol = progesterone greater than dihydro-testosterone greater than estradiol. This binding protein sediments at 9 S on a sucrose gradient, has a mean Stokes radius of 105 A on gel exclusion chromatography, and has a calculated molecular weight of 388,000 daltons and a frictional ratio of 2.1. 3H-Dexamethasone is not metabolized and does not bind specifically to serum. We have identified a protein in the rat ovary with characteristics of a glucocorticoid receptor and propose that this protein may be responsible for mediating direct effects of glucocorticoids on the ovary.