Receptor Phosphorylation Mediates Estradiol
- 1 January 2001
- journal article
- Published by Springer Nature in Endocrine
- Vol. 14 (2), 165-174
- https://doi.org/10.1385/endo:14:2:165
Abstract
Estrogen increases evoked norepinephrine release in the hypothalamus of female rodents, in part by reducing the ability of α2-adrenoceptors to act as negative feedback inhibitors of norepinephrine release. Estrogen enhancement of norepinephrine release in the hypothalamus correlates with decreased coupling of the α2-adrenoceptor to G protein. To determine the mechanism by which estrogen uncouples α2-adrenoceptors from G protein, we tested the hypothesis that estrogen increases α2-adrenoceptor phosphorylation. Short-term activation of endogenous serine/threonine phosphatases with protamine or treatment with exogenous phosphatase restored α2-adrenoceptor coupling to G protein to control levels in hypothalami from estrogen-exposed female rats. Additional experiments examined whether estrogen alters G protein-coupled receptor kinase expression or activity or serine/threonine phosphatase activity. These proteins are involved in G protein-coupled receptor phosphorylation, internalization, and recycling. Estrogen exposure reduced G protein-coupled receptor kinase mRNA, protein, and activity in the hypothalamus. Furthermore, estrogen treatment reduced serine/threonine phosphatase activity in the hypothalamus. Analysis of ligand binding in subcellular fraction demonstrated that estrogen decreases the fraction of internalized α2-adrenoceptors in the hypothalamus. Therefore, estrogen promotes norepinephrine release in the hypothalamus by stabilizing α2-adrenoceptor phosphorylation, uncoupling the receptor from G protein. Estrogen may stabilize α2-adrenoceptor phosphorylation by inhibiting receptor internalization and dephosphorylation.Keywords
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