Phosphatidylinositol 3-kinase and glycogen synthase kinase 3 regulate estrogen receptor-mediated transcription in neuronal cells.
In addition to 17beta-estradiol binding, estrogen receptor (ER) transcriptional activity could be controlled by intracellular kinase signaling pathways activated by growth factors. In this report we present evidence suggesting that glycogen synthase kinase 3 (GSK3), an effector kinase of the phosphatidylinositol 3-kinase (PI3K) pathway, may affect ERalpha activity in N2a neuroblastoma cells. LiCl, sodium valproate, and SB415286, three inhibitors of GSK3, dose-dependently blocked ERalpha-mediated transcription. In contrast, overexpression of wild-type GSK3, but not of a mutant inactive form, increased ER-dependent gene expression. Pharmacological or genetic inhibition of the PI3K/Akt pathway, whose activity is inversely correlated with that of GSK3, increased ERalpha-mediated transcription, and this effect was blocked by GSK3 inhibitors. As in other cell types, IGF-I increased ERalpha activity in absence of estradiol by a mechanism independent of PI3K. In contrast, IGF-I decreased ERalpha activity in the presence of estradiol, and this effect was mediated by PI3K. We also observed a regulated interaction between beta-catenin, one of the main GSK3 nuclear targets, and ERalpha. Transfection with a nondegradable mutant of beta-catenin blocked the increase in ERalpha transcriptional activity induced by the PI3K inhibitor wortmannin, suggesting a role for beta-catenin in estrogen signaling. In addition, we investigated the regulation of ER protein levels as a potential mechanism for its regulation by the PI3K/GSK3 pathway; GSK3 blockade increased ERalpha protein stability, whereas PI3K inhibition decreased it. In summary, our findings suggest that ER-dependent gene expression in N2a cells is controlled by the PI3K/Akt/GSK3 signaling pathway.
Mendez
Pablo
P
Instituto Cajal, Cajero Superior de Investigaciones, E-28002 Madrid, Spain.
Garcia-Segura
Luis Miguel
LM
D045744:Cell Line, Tumor; D047628:Estrogen Receptor alpha / Q000502:physiology*; D038362:Glycogen Synthase Kinase 3 / Q000502:physiology*; D006801:Humans; D009474:Neurons / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology*; D051057:Proto-Oncogene Proteins c-akt / Q000502:physiology; D015398:Signal Transduction; D014158:Transcription, Genetic; D051176:beta Catenin / Q000502:physiology
D047628:Estrogen Receptor alpha; D051176:beta Catenin; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D038362:Glycogen Synthase Kinase 3