This proposal addresses the understanding of basic mechanisms controlling liver-specific regulation of transcription that play a pivotal role in development and differentiation. The model used is the gene for apolipoprotein B (apo B100), the major protein constituent of low density lipoprotein (LDL), one of the most atherogenic components in the plasma. Knowledge of the molecular mechanisms that regulate apoB gene expression is clinically important because if the levels of apoB-100 are substantially reduced, the levels of LDL will also be lowered, reducing significantly the risks for coronary heart disease. Previous studies have identified the regulatory elements which are essential for expression of the apoB gene in liver. Of particular importance are the elements III and IV, which interact with the transcription factors HNF-4 and C/EBP, respectively. These elements play a central role in the apoB gene transcription, since substitution mutations that abolish binding of either HNF-4 or C/EBP to their cognate elements, dramatically decrease apoB gene transcription. HNF-4 and C/EBP activate apoB gene expression synergistically , however the molecular mechanism of this synergistic activation is not known.
The specific aims of this proposal are: 1) to identify the domains of HNF-4 that are involved in the transcriptional activation of the apoB gene, 2) to elucidate the molecular mechanisms that are involved in the synergistic activation of the apoB promoter by HNF-4 and C/EBP. The proposed experiments will provide significant new information regarding the structure and function of HNF-4, the molecular mechanisms of transcriptional activation by nuclear hormone receptors and the molecular nature of apoB gene expression.
