MULTIPLE CCAAT BINDING-PROTEINS REGULATE THE EXPRESSION OF THE ANGIOTENSINOGEN GENE

Angiotensinogen is a serum glycoprotein which is primarily synthesized in the liver and converted into the octapeptide hormone angiotensin-I I in circulation. Transient transfection studies have identified a cis -acting DNA element located between 115 and 145 bp upstream from the t ranscriptional initiation site in the promoter of the rat angiotensino gen gene which is involved in the regulation of its transcription. Thi s region of the promoter has sequence homology with NF-1/CCAT, C/EBP, and CP1 binding sites. We show here by DNase-I footprint and gel shift assay in presence of recombinant transcription factors and their anti bodies that NF-1/CAAT and C/EBP like transcription factors bind to thi s region of the promoter. Our DNase footprint assay with recombinant N F-1/CAAT has also identified another NF-1 binding site between -180 an d -190. Since our previous studies have identified a NF-1 site in the proximal promoter region and two C/EBP binding sites in the distal pro moter region of the angiotensinogen gene, our data suggests that multi ple CAAT binding factors regulate the expression of the angiotensinoge n gene in liver cells. In accordance with these results, we show that cotransfection of mammalian expression vectors containing NF-1/CAAT or C/EBP coding sequence increases the promoter activity of the angioten sinogen gene in human hepatoma cells.