The alpha1B adrenergic receptor (alpha1BAR) is a G-protein-coupled receptor that plays an important role in the control of cardiovascular homeostasis and metabolic processes in the liver, and recent studies have shown differential regulation of the transcription of the alpha1BAR gene in heart and liver under a variety of conditions. Dr. Gao will test the hypothesis that this differential regulation may be due to the tissue specific modulation of the action of the same transcription factor or to the interaction of the gene with different, tissue-specific transcription factors. Nuclear factor 1 (NF1) activates transcription driven by the dominant P2 promoter of the alpha1BAR gene in Hep3B cells and primary hepatocytes, but inhibits it in DDT1MF-2 cells. This duality may be due to modulation of the activity of NF1 by cell-specific cofactors. These cofactors will be identified by using the yeast two-hybrid system. The tissue distribution of NF1 parallels the relative abundance of the 2.7-kb alpha1BAR mRNA species, except for the heart, which expresses high levels of alpha1BAR and its 2.7 kb mRNA but little, if any, NFl. This suggests that transcription of the alpha1BAR gene in heart involves factor(s) other than NF1. Indeed, DNase I footprinting and DNA gel mobility shift analyses showed that the region -721 to -723 within the P2 promoter binds a new, previously unidentified transcription factor, called HF, in heart. This factor will be further characterized, purified by DNA affinity chromatography and cloned, if necessary. The role of this factor in transcription control will be identified by mutational and transfection analyses. Identification of the cell type-specific cofactors involved in modulating function of NF1 and the cardiac-specific transcription factors involved in the transcription of alpha1BAR gene in heart will shed light on the molecular mechanisms involved in the tissue specific regulation of alpha1BAR gene expression.
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