Subcellular distribution and selectivity of the protein-binding component of the recognition system for sex-hormone-binding protein-estradiol complex in human decidual endometrium.

In order to assess the subcellular distribution of the protein-binding component of the recognition system for sex-hormone-binding protein-estradiol complex (Strel'chyonok, O.A., Avvakumov, G.V. and Survilo, L.I. (1984) Biochim. Biophys. Acta 802, 459-466), plasma membranes and other subcellular fractions were prepared from homogenate of human decidual endometrium (8-12 weeks of pregnancy). Specific binding of 125I-labeled sex-hormone-binding protein complexed with estradiol was found preferentially in the plasma membrane fraction. The protein-binding component of the recognition system was found to specifically bind sex-hormone-binding protein complexed with estrogens (estradiol, estriol, estrone, with close affinities) but not with androgens (testosterone and 5 alpha-dihydrotestosterone). Specific membrane binding of 125I-labeled sex-hormone-binding protein complexed with 17 alpha-pregna-2,4-dien-20-yn-[2,3-d]isoxazol-17-ol (danazol) was also detected. This allowed us to suggest a putative mechanism for the danazol pharmacological action on endometrium which involves the interaction of the steroid-protein complex with the plasma membrane of endometrial cells. It is proposed that sex-hormone-binding protein takes part in the guided transport of steroids into endometrial cells.