Use of homogeneous time-resolved fluorescence energy transfer in the measurement of nuclear receptor activation

Nuclear receptors (NRs) are a superfamily of ligand-dependent transcription factors that mediate the effects of hormones and other endogenous ligands to regulate the expression of specific genes. NRs are clearly important targets for drug discovery. Ligand-dependent protein-protein interactions between NRs and NR coactivators (NRCoAs) are a critical step in regulation of transcription. Homogeneous time-resolved fluorescence (HTRF) energy transfer technology is sensitive, homogeneous, and nonradioactive. These characteristics make this approach attractive for developing high-throughput screening assays. The long-lived nature of the fluorescence of europium cryptate combined with a time delay in reading facilitates the homogeneous nature of the assay. Importantly, the introduction of lanthanides (with R0 values as great as 90 A in HTRF) make HTRF amenable to be used for protein-protein interactions. In this article we review, using peroxisome proliferator-activated receptor (PPAR)gamma as a model system, a novel approach for characterizing the ligand-dependent interaction between NR and NRCoA using HTRF technology and its potential uses in small-molecule screening, profiling selectivity of NR-NRCoA paired interactions, and profiling NR ligands as agonists versus partial agonists or antagonists.