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Rapid Estrogenic Regulation of Extracellular Signal- Regulated Kinase 1/2 Signaling in Cerebellar Granule Cells Involves a G Protein- and Protein Kinase A-Dependent Mechanism and Intracellular Activation of Protein Phosphatase 2A

Department of Pharmacology and Cell Biophysics, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267

Address all correspondence and requests for reprints to: Scott M. Belcher, Ph.D., Department of Pharmacology and Cell Biophysics, University of Cincinnati College of Medicine, 231 Albert Sabin Way, P.O. Box 670575, Cincinnati, Ohio 45267-0575. E-mail: scott.belcher{at}uc.edu.

In neonatal rat cerebellar neurons, 17ß-estradiol (E₂) rapidly stimulates ERK1/2 phosphorylation through a membrane-associated receptor. Here the mechanism of rapid E₂-induced ERK1/2 signaling in primary cultured granule cells was investigated in more detail. The results of these studies show that E₂ and ICI182,780, a steroidal antagonist of estrogen receptor transactivation, rapidly increased ERK signaling with a time course similar to the transient activation induced by epidermal growth factor (EGF). However, EGF receptor (EGFR) autophosphorylation was not increased by E₂, and blockade of EGFR tyrosine kinase activity did not abrogate the rapid actions of E₂. The involvement of Src-tyrosine kinase activity was demonstrated by detection of increased c-Src phosphorylation in response to E₂ and by blockade of E₂-induced ERK1/2 activation by inhibition of Src-family tyrosine kinase activity. Inhibition of Gi signaling or protein kinase A (PKA) activity blocked the ability of ICI182,780 to rapidly stimulate ERK signaling. Under those conditions, E₂ treatment induced a rapid and transient suppression of basal ERK1/2 phosphorylation. Protein phosphatase 2A (PP2A) activity was rapidly increased by E₂ but not by E₂ covalently linked to BSA. Rapid E₂-induced increases in PP2A activity were insensitive to pertussis toxin. The presented evidence indicates that the rapid effects of estrogens on ERK signaling in cerebellar granule cells are induced through a novel G protein-coupled receptor mechanism that requires PKA and Src-kinase activity to link E₂ to the ERK/MAPK signaling module. Along with stimulating ERK signaling, E₂ rapidly activates PP2A via an independent signaling mechanism that may serve as a cell-specific regulator of signal duration.

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