ANGIOTENSINOGEN GENE ACTIVATION BY ANGIOTENSIN-II IS MEDIATED BY THE REL-A (NUCLEAR FACTOR-KAPPA-B P65) TRANSCRIPTION FACTOR - ONE MECHANISM FOR THE RENIN-ANGIOTENSIN SYSTEM POSITIVE FEEDBACK LOOP IN HEPATOCYTES

The renin-angiotensin system controls blood pressure through the enzym atic production of the vasopressor angiotensin II (All) from the angio tensinogen (AGT) precursor. Intravascular All production stimulates de novo synthesis of its precursor in a positive feedback loop through i ncreased gene expression. In this study, we investigate the effects of All on AGT gene expression. At nanomolar concentrations, All activate s transcription of the native AGT gene; this region is mapped to the A GT gene multihormone-inducible enhancer (-615 to -470). Within the mul tihormone-inducible enhancer, site-directed mutations of the acute-pha se response element (APRE) that interfere with nuclear factor-kappa B (NF-kappa B) transcription factor binding also abolish All responsiven ess. The APRE functions as a rapidly inducible All-inducible enhancer with peak reporter activity detected after a 4-h stimulation; this eff ect occurs only when the type 1 All receptor is expressed. All induces sequence-specific NF-kappa B binding to the APRE in HepG2 nuclear ext racts. Moreover, All infusions of primary rat hepatocyte cultures prod uces a rapid 4-fold increase in sequence-specific NF-kappa B binding t o the APRE. Antibodies against the transcriptional activator subunit, Rel A, quantitatively supershift the nucleoprotein complex, whereas an tibodies to other NF-kappa B members do not, demonstrating that Rel A APRE-binding activity is All-inducible. Transient overexpression of Re l A(1-551) activates the AGT multihormone-inducible enhancer. All-indu cible domains of Rel A were mapped by cotransfecting a chimeric GAL4-R el A fusion protein with a reporter gene containing GAL4-binding sites . GAL4-Rel A(1-551) was an All-inducible transactivator. Deletion of t he NH2-terminal 254 amino acids of Rel A produces a constitutive trans activator, indicating that Rel A is activated by All in a manner depen dent on its NH2 terminus. These studies define one mechanism for the r enin-angiotensin system positive feedback loop in hepatocytes.