A splice variant of estrogen receptor beta missing exon 3 displays altered subnuclear localization and capacity for transcriptional activation

There are two separate estrogen receptors (ERs), ERalpha and ERbeta. The ERbeta gene is variably spliced, and in some cases variant expression is high. Besides the full-length ERbeta (equivalent to ERbeta1), splice variants can encode proteins bearing an insert within the ligand-binding domain (beta2), a deletion of exon 3 (ERbeta1delta3) disrupting the DNA-binding domain, or both (ERbeta2delta3). Here we examine the intracellular localization and transcriptional properties of each of the ERbeta splice variants heterologously expressed in cultured cells. In accordance with ERalpha, ERbeta1 and ERbeta2 are both distributed in a reticular pattern within the nucleus after exposure to ligand. In contrast, ERbeta1delta3 and ERbeta2delta3 localize to discrete spots within the nucleus in the presence of ER agonists. In the presence of ER antagonists, the delta3 variants are distributed diffusely within the nucleus. We also show that the spots are stable nuclear structures to which the delta3 variants localize in a ligand-dependent manner. Coactivator proteins of ER colocalize with delta3 variants in the spots in the presence of agonists. The delta3 variants of ERbeta can activate luciferase reporter constructs containing an activator protein complex-1 site, but not an estrogen response element (ERE). These data suggest that without an intact DNA-binding domain, ERbeta is functionally altered, allowing localization to discrete nuclear spots and activation from activator protein-1-containing reporter genes.