Glycogen Synthase Kinase-3 Interacts with and Phosphorylates Estrogen Receptor α and Is Involved in the Regulation of Receptor Activity

Senad Medunjanin, Alexander Hermani, Barbara De Servi, Jean Grisouard, Gabriele Rincke, Doris Mayer
2005 Journal of Biological Chemistry  
Like other steroid hormone receptors, estrogen receptor-␣ (ER␣) is a substrate for protein kinases, and phosphorylation has profound effects on the function and activity of this receptor. A number of different kinases have been implicated in ER␣ regulation. In this report we show by mutational analysis and in vitro kinase assays that ER␣ is a substrate for glycogen synthase kinase-3 (GSK-3) in vitro and is phosphorylated on two sites, the Ser-102, -104, and -106 motif and Ser-118, both located
more » ... n the N-terminal transcription activation function (AF-1) domain. GSK-3 forms a complex with ER␣ in vivo as demonstrated by co-immunoprecipitation from cell lysates. The GSK-3 inhibitor lithium chloride was used to determine the role of GSK-3 in phosphorylation of Ser-102, -104, and -106 and Ser-118 in vivo and to explore the role of these serines in the regulation of ER␣ function. Treatment of cells with lithium chloride resulted in dephosphorylation of Ser-104 and -106 and Ser-118, which suggests these serine residues as targets for GSK-3 in vivo. Our results further suggest that ER␣ phosphorylation by GSK-3 stabilizes ER␣ under resting conditions and modulates ER␣ transcriptional activity upon ligand binding. Inhibition and constitutive activation of GSK-3, both, resulted in inhibition of ER␣ transcriptional activity, indicating a function of active as well as inactive GSK-3 in ER␣ regulation. These findings uncover a novel mechanism for the regulation of ER␣-mediated estrogen signaling controlled by a dual action of GSK-3. Estrogen receptor-␣ (ER␣) 3 is a member of the nuclear receptor superfamily of transcription factors, which are activated by small lipidsoluble molecules including steroid hormones (1). Nuclear receptors are characterized by a conserved structural and functional organization and play essential roles in development, differentiation, and metabolism by controlling the expression of specific networks of genes (2, 3). Based on sequence homology and other approaches, the estrogen receptor protein can be divided into six functionally and physically independent domains, nominated A to F (1, 2), that encode sequences required for DNA binding (region C), nuclear localization (region D), and ligand binding (region E). Ligand binding results in conformational change of
doi:10.1074/jbc.m506758200 pmid:16076840 fatcat:jr5pm4kzm5htdk3pmdxlnglc2e