Changes in the structure of the ligand or substitutions to AF2 residues in the estrogen receptor make independent contributions to coactivator sensitivity by SRC-1

Abstract

The estrogen receptor (ER) is a ligand-inducible transcription factor which depends, in part, upon the C-terminal activation function (AF2) in order to regulate the expression of target genes. AF2 residues fold into an amphipathic α-helix on helix 12 of the ER, with hydrophobic and acidic faces. It is believed that AF2 mediates the gene regulatory activities of ligand-activated ER by interacting with coactivator proteins. We have analyzed the contribution of acidic AF2 residues to the process of ER coactivation by the steroid receptor coactivator, SRC-1. In HeLa cells, SRC-1 coexpression was found to restore transcriptional potency to otherwise inert complexes of wild type ER and 4-hydroxyestratrien-17 β-ol. SRC-1 coexpression also enhanced transcriptional activity of reporter genes induced by an ER mutant with neutral replacements to acidic AF2 residues, in response to E2 or 4-hydroxyestratrien-17 β-ol. By contrast, ER complexes from ICI164,384-treated HeLa cells were both transcriptionally inactive and coactivator insensitive. It is concluded that changes to the structure of the ligand or substitutions to acidic residues in the AF2 region of the receptor contribute independently to the control of coactivator sensitivity in ER.