Rat ovary glucocorticoid receptor: Identification and characterization |
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Authors: | James R Schreiber Kevin Nakamura Gregory F Erickson |
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Institution: | Department of Reproductive Medicine, M-025 University of California, San Diego La Jolla, California 92093 USA |
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Abstract: | A soluble, thermolabile protein with characteristics typical of glucocorticoid receptors has been identified in the ovaries of estrogenstimulated 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 ° C × 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 ≥ dexamethasone > cortisol = progesterone > dihydrotestosterone > estradiol. This binding protein sediments at 9 S on a sucrose gradient, has a mean Stokes radius of 105 Å 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. |
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