Characterization of specific glucocorticoid receptor in the Syrian hamster testis

Abstract

Cytosols of whole testicular homogenates from the Syrian golden hamster contained specific binding sites for [3H]triamcinolone acetonide that exhibited limited capacity and high affinity binding characteristic of glucocorticoid receptors in other target tissues. The receptor complex sedimented as an 8.6S binder in low salt 5-20% linear sucrose gradients and as 6.2S and 4.0S moieties in 0.15M and 0.4 M KCl, respectively. The Ka at equilibrium was 3.1-3.3 X 10(9) M-1 at 4 C in intact and adrenalectomized males. The testicular glucocorticoid binder was vulnerable to proteolytic degradation while being completely resistant to the action of RNase and DNase. In addition the binding protein exhibited the usual steroid specificities for type I glucocorticoid receptor: triamcinolone acetonide greater than dexamethasone greater than cortisol greater than corticosterone greater than progesterone greater than aldosterone greater than prednisone greater than 5 alpha-dihydrotestosterone greater than diethylstilbestrol. Unexpectedly, 17 beta-estradiol competed for receptor binding to the same extent as prednisone. A 3.2 S nuclear receptor was extracted from purified testicular nuclei after incubation of whole suspensions in culture media containing 5 nm radiolabeled triamcinolone acetonide at 32 C. Although the glucocorticoid receptor concentrations in prepubertal, adrenalectomized, and hypophysectomized animals were markedly higher in the testis compared to the concentration in the normal adult hamster (52 +/- 4 fmol/mg cytosol protein), the greatest total amount of receptor per testis was found in the mature intact animal. Moreover, under the conditions studied, the concentration of glucocorticoid receptor substantially exceeded the levels of either androgen or estrogen receptor when determined simultaneously. In contrast, no measurable cytoplasmic [3H]triamcinolone acetonide binding was detected in adjacent urogenital organs such as the epididymis and seminal vesicle. It is therefore unlikely that the testicular glucocorticoid receptor is associated with the spermatid or present as a secretory product in the seminiferous tubule lumen.