Regulation of estrogen receptor α-mediated transcription by a direct interaction with protein phosphatase 2A

Abstract

Estrogen receptor α (ERα) mediates the effects of estrogen by altering gene expression following hormone binding. It has recently been shown that kinase-mediated phosphorylation of ERα also transcriptionally activates the receptor in the absence of estrogen. We now report that ERα-dependent gene expression also is regulated by protein phosphatase 2A (PP2A). ERα co-immunoprecipitates with enzymatically active PP2A. ERα binds directly to the catalytic subunit of PP2A, which dephosphorylates serine 118 of the receptor. Amino acids 176-182 in the A/B domain of ERα are required for the interaction between PP2A and the receptor. Phosphatase inhibition disrupts the ERα-PP2A complex and induces formation of an ERα-activated mitogen-activated protein kinase complex, phosphorylation of ERα on serine 118, and transcriptional activation. These findings demonstrate that estrogen receptors exist in complexes with phosphatases as well as kinases. We propose a new model of ligand-independent activation of estrogen receptors in which the level of phosphorylation of ERα, and hence its transcriptional activation, is determined by the net effect of these counterregulatory pathways.