Development of a versatile platform for nuclear receptor screening using AlphaScreen.

The interaction between nuclear receptors (NRs) and their coactivators, a key step in transcription regulation, requires a short consensus sequence called the LXXLL motif found in the coactivators' structure. Using the AlphaScreen technology, the authors have taken advantage of this receptor-coactivator interaction to develop a highly sensitive assay to identify and characterize compounds modulating NR activity. Estrogen and retinoic acid receptors were chosen as models to demonstrate the versatility of the AlphaScreen technology: (1) the assay can be designed using different antibodies to capture either full-length receptors or receptor domains that have been tagged, (2) the assay can differentiate between ligands that act as agonists or antagonists because only agonists will allow recruitment of the coactivator sequence-derived peptide, and (3) the assay gives the opportunity to screen for antagonists targeting the ligand-binding site or the dimerization interface between the receptor and the coactivator. Titration of the receptor and biotinylated peptide indicates that AlphaScreen is highly sensitive, requiring nanomolar concentration of reagents. Competition isotherms performed with known receptor antagonists demonstrate that the assay is a useful tool to rank the antagonists according to their order of potency. Overall, the results presented here indicate that the versatility, sensitivity, robustness, and ease of execution of the AlphaScreen NR assay will allow for efficient screening of NR modulators.