Abstract

Estrogen receptor (ER) biology reflects the actions of estrogens through the two receptors, ERa and ERß, although little is known regarding the preference for formation of ER homo- vs. heterodimers, and how this is affected by the level of ligand occupancy and preferential ligand affinity for one of the ER subtypes. In this report, we use a split optical reporter-protein complementation system to demonstrate the physical interaction between ERa and ERß in response to different ER ligands in cells and, for the first time, by in vivo imaging in living animals. The genetically encoded reporter vectors constructed with the ligand-binding domains of ERa and ERß, fused to split firefly or Renilla luciferase (Fluc or hRluc) fragments, were used for this study. This molecular proteomic technique was used to detect ERa/ERa or ERß/ERß homodimerization, or ERa/ERß heterodimerization induced by ER subtype-selective and nonselective ligands, and selective ER modulators (SERM), as well as in dimers in which one mutant monomer was unable to bind estradiol. The SERM-bound ERa and ERß form the strongest dimers, and subtype-preferential homodimerization was seen with ERa-selective ligands (methyl piperidino pyrazole/propyl pyrazole triol) and the ERß-selective ligands (diarylpropionitrile/tetrahydrochrysene/genistein). We also demonstrated that a single ligand-bound monomer can form homo- or heterodimers with an apo-monomer. Xenografts of human embryonic kidney 293T cells imaged in living mice by bioluminescence showed real-time ligand induction of ERa/ERß heterodimerization and reversal of dimerization upon ligand withdrawal. The results from this study demonstrate the value of the split luciferase-based complementation system for studying ER-subtype interactions in cells and for evaluating them in living animals by noninvasive imaging. They also probe what combinations of ERa and ERß dimers might be the mediators of the effects of different types of ER ligands given at different doses.

View details for DOI 10.1210/me.2011-1145

View details for PubMedID 22052998