INITIAL INTRACELLULAR EVENTS OF STEROID HORMONE ACTION

这个项目的目标是定义初始的，细胞内的

The objective of this project is to define the initial, intracellular events of glucocorticoid hormone action and steroid hormone action in general. Such studies are of particular current relevance since steroid hormone receptors are arguably the best understood regulators of eukaryotic gene transcription. The first step of steroid binding to the intracellular receptor is followed by activation of the receptor-steroid complex to a DNA/nuclear-binding species that then associates with those nuclear acceptor sites involved in the regulation of transcription of selected genes in specific cells. We have concentrated on the nuclear localization of glucocorticoid receptors and how these nuclear receptors influence gene transcription. Glucocorticoid receptors are predominantly cytoplasmic in the absence of steroid and several lines of evidence suggest that microtubules may be intimately involved in the relocalization of steroid-bound glucocorticoid receptors from the cytoplasm to the nucleus. However, this hypothesis is now discredited by our finding that microtubule disruption with micromolar concentrations of colchicine had no effect on nuclear translocation as assayed by the induction of a transiently transfected reporter gene by endogenous receptors. The mechanism of how the nuclear receptor-steroid complexes regulate gene transcription is becoming increasingly complicated with the discovery of new DNA elements and trans-acting factors. We had previously reported that glucocorticoid induction of the tyrosine aminotransferase (TAT) gene involves a novel cis-acting element, called a glucocorticoid modulatory element (GME). We now find that two apparently novel proteins of 88 and 67 kDa bind to this GME in a manner that correlates with the expression of GME activity. Another new, cis-acting element of the TAT gene has now been defined that can block the effects of the GME. These new elements and binding proteins offer additional mechanisms for modifying glucocorticoid regulated gene expression. Collectively, our findings contribute to our long term goal of defining the action of steroid hormones at a molecular level and of understanding their role in human physiology.