Characterization of cytoplasmic progesterone receptors in rat granulosa cells. Evidence for nuclear translocation

Abstract

The granulosa cells from immature rats possess binding components for progestins. The physicochemical properties were determined. By sucrose gradient centrifugation, binding of [3H]R-5020 [promegestone] was observed in the 7S and 4S region of the gradient. Isoelectric focusing, however, revealed only 1 binding component (pH 5.9). The component was of protein nature and was destroyed by heating the cytosol fraction to 37.degree. C for 30 min. Scatchard analysis of the data showed 1 single binding component with high affinity (Kd .apprx. 1.5 .times. 10-9 mol/l). The binding capacity was 50 f[femto]mol/mg protein in unprimed animals and 193 fmol/mg protein in animals treated with estrogen. Studies on the steroid specificity revealed that R-5020 had the highest affinity for the receptors, followed by progesterone and the synthetic progestin, cyproterone acetate, Corticosterone, estradiol-17.beta. and testosterone had low affinty, whereas cortisol had no significant affinity for the receptor. The cytoplasmic receptors translocated to the nucleus after administration of unlabeled progesterone to the animals. The presence of cytoplasmic and nuclear progestin receptors, strongly indicates that progesterone may have a direct effect on granulosa cell function.