Interactions between MAP kinase and oestrogen receptor in human breast cancer

This study confirms that ligand-mediated phosphorylation is associated with rapid nuclear localisation of ERα, due to oestrogen binding. ERα is phosphorylated at serine 118 in a ligand-independent manner. Preventing nuclear translocation of pMAPK reduced the levels of ligand-independent, but not ligand-dependent phosphorylation of ERα. Co-stimulation with both oestrogen and heregulin suggested that heregulin mediated signalling determines the subcellular localisation of ERα. Activation of ERα by direct phosphorylation may result in its rapid deactivation due to degradation or nuclear export.