Identification of Regulatory Cofactors Interacting with Glucocorticoid Receptor
Supervisor: Professor Rick Nicholson
CRH is a hypothalamically-derived hormone that orchestrates a series of neural and endocrine adaptations known as the "stress response". A challenge to homeostasis by any stressor initiates the release of CRH from the hypothalamus, which in turn results in release of adrenocortiotropin hormone (ACTH) from the pituitary into general circulation. ACTH then acts on the adrenal cortex resulting in release of glucocorticoids, a steroid hormone, into the blood. Glucocorticoids act in a negative feedback fashion to terminate the release of CRH from the hypothalamus. CRH has also been identified in many tissues outside the hypothalamus; in particular, in the placenta during human pregnancy. Placental production of CRH has been linked to the length of gestation in humans and several groups, including ours, have reported that increased CRH concentrations in maternal blood are associated with preterm delivery.
Glucocorticoids mediate inhibition of CRH gene expression in the hypothalamus, whereas these steroid hormones stimulate the expression of CRH in the placenta. In vitro assays have identified 3 regions of the promoter that can bind GR but we have shown that these sites are not involved in the glucocorticoid-mediated stimulation of CRH gene expression in the placenta. Indeed, we have shown that glucocorticoids stimulate CRH gene expression in the placenta through the cAMP Regulatory Element (CRE), presumably through protein-protein interactions with proteins that bind at the CRE. Other studies have shown one of the regions of the CRH promoter that can bind GR in vitro is responsible for negative regulation by glucocorticoids in cAMP stimulated AtT20 cells (a hypothalamic cell model). Surprisingly, in the absence of this negative regulatory region the CRH promoter is stimulated by glucocorticoids in AtT20 cells in a manner similar to that seen in placenta cells.
This Research Project will involve the use of RNAi techniques in addition to the study of protein-protein interactions between GR and other transcription factors, and the identification of these factors through several techniques.