Regulation of gene expression by nuclear hormone receptors. Pathological role of nuclear receptors in hormone dependent cancers
Steroid, retinoid and thyroid hormones are powerful regulators of gene expression and play a critical role in nearly every aspect of vertebrate development and adult physiology. The receptors for these hormones (nuclear hormone receptors) are ligand-activated transcription factors that bind to DNA and activate or repress transcription from specific genes. The primary goal of the research in my lab is to investigate the molecular mechanisms by which nuclear receptors regulate transcription. An emphasis of our work has been the identification and characterization of coregulatory factors (i.e. coactivators and corepressors) which specifically associate with nuclear receptors and play an essential role in mediating receptor transcriptional functions. Our work focuses on two areas:
(1) We recently identified a large multisubunit transcriptional coactivator complex termed TRAP/Mediator containing as many as 25 different subunits ranging in size from 20 to 240 kDa. The TRAP/Mediator complex serves to enhance hormone-dependent transcription by a broad range of nuclear receptors including the thyroid, prostanoi, androgen, estrogen and vitamin D3 receptors. Our studies currently focus on several major questions including: a) How does TRAP/Mediator functionally interface with other co-recruited chromatin remodeling/modifying complexes at hormone responsive promoters? b) What is the molecular mechanism of action of the individual TRAP subunits? c) What is the biochemical nature of the of the TRAP complex in terms of a multi-protein structures (subunit stoichiometry, step-wise complex assembly, specific protein-protein interactions)?
(2) Relative to the general study of nuclear receptors, we are examining the pathogenic role of estrogen and androgen receptors (ER and AR) in both normal and cancer (breast and prostate) cells. To facilitate these studies, we have generated stable cancer cell lines which over express epitope-tagged estrogen receptors (ER) or androgen receptors (AR). The epitope-tagging allows us to biochemically characterize AR and ER from cancer cells in culture and subsequently purify and identify their associated coregulatory factors. These studies address three major questions: a) What nuclear factors or coactivators are associated with the ER and AR and potentiate receptor function? b) What molecular mechanisms account for the differential effects of estrogen versus anti-estrogens (and androgen versus anti-androgens) on nuclear receptor function in different tissues? c) What specific coactivators are associated with ER and AR obtained from cells in late stages of tumor progression versus ER- and AR-associated proteins observed in normal cells?