Phosphorylation Alters Oestrogen Receptor -Mediated Transcription in Neurones

Nuclear steroid hormone receptors are ubiquitously expressed transcription factors whose activity can be altered by post-translational modifications, such as phosphorylation. The consequences of post-translational modifications have been described for several members of the nuclear steroid hormone receptor superfamily; however, little is known about the effects of oestrogen receptor (ER) phosphorylation in the brain. Moreover, to our knowledge, the presence of phosphorylated ER has not been detected in the brain of any species to date. Oestrogen receptor is highly expressed in several regions of the brain and invitro studies have demonstrated that it can be phosphorylated at two serine residues (S87 and S105) in the N-terminal AF-1 region. The present study aimed to determine whether phosphorylated ER is detectable in the hippocampus of aged female rats, as well as the functional consequences of ER S87 and S105 phosphorylation on transcriptional activity in neuronal cells. First, we used a novel PhosTag approach to detect phosphorylated forms of ER in the dorsal hippocampus of aged female rats. The data obtained demonstrated abundant forms of phosphorylated ER in the dorsal hippocampus, suggesting that this post-translational modification might be an important regulator of ER function. To assess the functional consequences of ER phosphorylation in neuronal cells, we created phospho-mimetic (S87E, S105E) and phospho-null (S87A, S105A) ER receptors that were transiently transfected in a hippocampal-derived cell line. Collectively, our results showed that phosphorylation of S87 and S105 altered both ligand-independent and ligand-dependent ER transcriptional regulation. Overall, these data demonstrate that phosphorylated forms of ER are present in the brain of aged female rats and that phosphorylation of ER could differentially alter ER-mediated gene expression.