Phosphorylation of Purified Estradiol-Liganded Estrogen Receptor by Casein Kinase II Increases Estrogen Response Element Binding but Does Not Alter Ligand Stability

The estrogen receptor is a ligand-activated transcription factor that binds to specific DNA sequences, estrogen response elements. Recent studies have characterized the location of tyrosine and serine residues in the estrogen receptor that are phosphorylated either by purified protein kinases in vitro or in response to ligand and DNA binding in vivo. Here we examined how phosphorylation of purified bovine uterine estrogen receptor in vitro by casein kinase II impacts estrogen receptor-estrogen response element binding and 17 beta-estradiol ligand binding stability. Our results show that phosphorylation doubles estrogen receptor-estrogen response element binding, but does not affect estradiol binding stability. These finding suggest that phosphorylation by casein kinase II on serine residues within the A/B domain results in intramolecular interactions affecting the DNA binding domain but not the ligand binding domain of the estrogen receptor.