p21-Activated kinase mediates rapid estradiol-negative feedback actions in the reproductive axis

Abstract

Nonclassical estrogen receptor α (ERα) signaling can mediate E2negative feedback actions in the reproductive axis; however, downstream pathways conveying these effects remain unclear. These studies tested the hypothesis that p21-activated kinase 1 (PAK1), a serine/threonine kinase rapidly activated by E2in nonneural cells, functions as a downstream node for E2signaling pathways in cells of the preoptic area, and it may thereby mediate E2negative feedback effects. Treatment of ovariectomized (OVX) rats with estradiol benzoate (EB) caused rapid and transient induction of phosphorylated PAK1 immunoreactivity in the medial preoptic nucleus (MPN) but not the arcuate nucleus. To determine whether rapid induction of PAK phosphorylation by E2is mediated by nonclassical [estrogen response element (ERE)-independent] ERα signaling, we used female ERα null (ERα−/−) mice possessing an ER knock-in mutation (E207A/G208A; AA), in which the mutant ERα is incapable of binding DNA and can signal only through membrane-initiated or ERE-independent genotropic pathways (ERα−/AAmice). After 1-h EB treatment, the number of pPAK1-immunoreactive cells in the MPN was increased in both wild-type (ERα+/+) and ERα−/AAmice but was unchanged in ERα−/−mice. Serum luteinizing hormone (LH) was likewise suppressed within 1 h after EB treatment in ERα+/+and ERα−/AAbut not ERα−/ −mice. In OVX rats, 5-min intracerebroventricular infusion of a PAK inhibitor peptide but not control peptide blocked rapid EB suppression of LH secretion. Taken together, our findings implicate PAK1 activation subsequent to nonclassical ERα signaling as an important component of the negative feedback actions of E2in the brain.