In the hepatocyte, numerous genes are regulated by glucocorticoid hormones. Even though these genes are expressed in the liver and they all contain glucocorticoid response elements (GREs), their patterns of transcriptional response vary considerably. For example, some genes rapidly respond to glucocorticoid while others display a lag. In addition, cycloheximide abolishes the response to glucocorticoid in some, but not all genes. Thus, glucocorticoid regulation of transcription in hepatocytes may involve several different mechanisms, including interactions between the glucocorticoid receptor and several types of novel accessory factors which modulate the glucocorticoid response in a gene or a cell-specific fashion. Carbamyl phosphate synthetase-1 (CPS-- 1), is an example of a gene which shows a lag in its induction by glucocorticoid and whose induction is blocked by cycloheximide. These observations are consistent with the existence of accessory factors which modulate the glucocorticoid induction of CPS-1. Precedence for the existence of such factors has been demonstrated for the PEPCK gene, which displays almost identical glucocorticoid induction kinetics as CPS-1. The hypothesis that modulation of glucocorticoid regulation of the CPS-1 gene in hepatocytes requires one or more accessory factors, in addition to the glucocorticoid receptor, will be tested.
The specific aims are to: 1. Localize the Glucocorticoid Responsive Unit(s) (GRU) for the CPS-1 gene. 2. Examine the CPS-1 response to glucocorticoid in primary hepatocytes compared to H411E hepatoma cells to determine if malignant transformation alters the pattern of accessory factors. 3. Define and test the minimum GRE activity within the GRU. 4. Analyze the functional and biochemical interrelationships between accessory factors and the glucocorticoid receptor. 5. Characterize, isolate and clone the accessory factors. The identity of these accessory factors and their mechanism of interaction with the glucocorticoid receptor and transcriptional machinery is an exciting area for new investigation which could lead to a better understanding of steroid hormone regulation of gene expression. These studies have far reaching implications, possibly expanding our understanding of developmental or tissue-specific regulation of gene expression, mechanisms involving the role of glucocorticoid in sepsis or inflammation, and regulation of cellular growth at a more general level, including growth and benign or malignant tumor formation.
