High Quality Content by WIKIPEDIA articles! Estrogen receptor refers to a group of receptors that are activated by the hormone 17 -estradiol (estrogen). Two types of estrogen receptor exist: ER which is a member of the nuclear hormone family of intracellular receptors and the estrogen G protein coupled receptor GPR30 (GPER), which is a G-protein coupled receptor. This article refers to the nuclear hormone receptor ER. The main function of the estrogen receptor is as a DNA binding transcription factor that regulates gene expression. However, the estrogen receptor has additional functions independent of DNA binding.