Quantitative Dissection of Steroid Receptor Function

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DESCRIPTION (provided by applicant): The long-term goal of this research is to determine the mechanisms responsible for higher eukaryotic gene regulation. As a model system we are studying the five members of the steroid receptor family of ligand-activated transcription factors. These proteins - the estrogen receptor, progesterone receptor, glucocorticoid receptor, androgen receptor and mineralocorticoid receptor - are structurally similar. However, the basis by which each receptor executes its unique gene regulatory functions is unclear, particularly so when in the presence of its remaining family members. Our research indicates that a) different steroid receptors exhibit variable energetics of inter-site cooperativity when binding to an identical promoter; and b) the energetics of cooperativity exhibited by a steroid receptor can vary at different promoters. We therefore hypothesize that the extent to which a gene is activated by a particular steroid receptor correlates with the energetics of receptor cooperativity when assembling at the promoter of that gene. Differences in cooperative binding energetics will thus dictate the degree of successful promoter occupancy by each steroid receptor, and thus the extent of receptor-specific gene regulation. In Aim 1, we will determine the microscopic binding energetics for steroid receptor assembly at the mouse mammary tumor virus (MMTV) promoter. We will resolve the DNA- independent self-association properties of each receptor using analytical ultracentrifugation, and we will determine the intrinsic and cooperative binding free energies for receptor assembly at the promoter using quantitative DNase footprint titration. In Aim 2, we will characterize androgen receptor transcriptional activation mutants identified in prostate carcinomas. We will examine their self-association properties using analytical ultracentrifugation, and we will dissect the microstate binding energetics of these mutants to the MMTV promoter using footprint titrations. In Aim 3, we will correlate the binding energetics of the receptors with their promoter occupancy and transcriptional activation ability within the cell. Cellular occupancy at the promoter will be determined by chromatin immunoprecipitation (ChIP) assays, and the extent of mRNA production will be determined by quantitative RT-PCR.