Angiotensin II Induces Nuclear Factor (NF)-κB1 Isoforms to Bind the Angiotensinogen Gene Acute-Phase Response Element: A Stimulus-Specific Pathway for NF-κB Activation

Abstract

The vasopressor angiotensin II (AII) activates tran-scriptional expression of its precursor, angio-tensinogen. This biological "positive feedback loop" occurs through an angiotensin receptor-coupled pathway that activates a multihormone-responsive enhancer of the angiotensinogen promoter , termed the acute-phase response element (APRE). Previously, we showed that the APRE is a cytokine [tumor necrosis factor-(TNF)]-induc-ible enhancer by binding the heterodimeric nuclear factor-B (NF-B) complex Rel A•NF-B1. Here, we compare the mechanism for NF-B activation by the AII agonist, Sar 1 AII, with TNF in HepG2 hepatocytes. Although Sar 1 AII and TNF both rapidly activate APRE-driven transcription within 3 h of treatment, the pattern of inducible NF-B binding activity in electrophoretic mobility shift assay is distinct. In contrast to the TNF mechanism, which strongly induces Rel A•NF-B1 binding, Sar 1 AII selectively activates a heterogenous pattern of NF-B1 binding. Using a two-step microaffinity DNA binding assay, we observe that Sar 1 AII recruits 50-, 56-, and 96-kDa NF-B1 isoforms to bind the APRE. Binding of all three NF-B1 isoforms occurs independently of changes in their nuclear abundance or proteolysis of cytoplasmic IB inhibitors. Phorbol ester-sensitive protein kinase C (PKC) iso-forms are required because PKC down-regulation completely blocks AII-inducible transcription and inducible NF-B1 binding. We conclude that AII stimulates the NF-B transcription factor pathway by activating latent DNA-binding activity of NF-B subunits through a phorbol ester-sensitive (PKC-dependent) mechanism. (Molecular Endocrinology