MECHANISMS INVOLVED IN THE REGULATION OF STEROID-RECEPTOR LEVELS

The turnover of steroid receptors comprises: synthesis in the cytoplasm, translocation into the cell nucleus and degradation at a still unknown site. From studies on the oestradiol/receptor system, the following conclusions can be drawn. 1. The in-vivo uptake of oestradiol by target cell nuclei is receptordependent. Steroid and receptor are translocated from the cytoplasm in a 1:1 ratio. A recycling of receptor is undetectable after pulse administration of oestradiol. Receptor replenishment in the cytoplasm is accomplished by synthesis. 2. The nuclear uptake of receptor-in contrast-proceeds also in the absence of oestradiol. Both forms of receptor, monomer and activated" dimer are present in oestrogen-free nuclei. 3. Oestradiol enhances the "nucleotropy" and the turnover rate of receptor. 4. Oestrogenicity and antioestrogenicity are apparently linked to effects exerted on the "nucleotropy" of receptor and its ability to interact with the relevant nuclear structures. © 1979."