Plasma Membrane Is the Primary Site of Localization of the Nonactivated Estrogen Receptor in the Goat Uterus: Hormone Binding Causes Receptor Internalization

Evidence is presented to show that the cellular site of localization of the goat uterine nonactivated estrogen receptor (naER) is the plasma membrane. Exposure of purified plasma membrane preparations to estradiol (20 nM) causes dissociation of the receptor from the membrane into the medium. This receptor movement takes place in the presence of diethylstilbestrol while testosterone, progesterone, dexamethasone, and tamoxifen do not facilitate the dissociation of the naER from the plasma membrane. Further, tamoxifen inhibits the estradiol-mediated dissociation of the naER from the plasma membrane. The naER is a glycoprotein and is also a tyrosine kinase. The tyrosine kinase activity is inhibited in the presence of estrogens while tamoxifen reverses this estrogen-dependent inhibition.