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

The vasopressor angiotensin II (AII) activates transcriptional expression of its precursor, angiotensinogen. 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-alpha (TNF alpha)]-inducible enhancer by binding the heterodimeric nuclear factor-kappa B (NF-kappa B) complex Rel A . NF-kappa B1. Here, we compare the mechanism for NF-kappa B activation by the All agonist, Sar(1) All, with TNF alpha in HepG2 hepatocytes. Although Sar(1) All and TNF alpha both rapidly activate APRE-driven transcription within 3 h of treatment, the pattern of inducible NF-kappa B binding activity in electrophoretic mobility shift assay is distinct. In contrast to the TNF alpha mechanism, which strongly induces Rel A . NF-kappa B1 binding, Sar(1) All selectively activates a heterogenous pattern of NF-kappa B1 binding. Using a two-step microaffinity DNA binding assay, we observe that Sar(1) All recruits 50-, 56-, and 96-kDa NF-kappa B1 isoforms to bind the APRE. Binding of all three NF-kappa B1 isoforms occurs independently of changes in their nuclear abundance or proteolysis of cytoplasmic I kappa B inhibitors. Phorbol ester-sensitive protein kinase C (PKC) isoforms are required because PKC down-regulation completely blocks AII-inducible transcription and inducible NF-kappa B1 binding. We conclude that All stimulates the NF-kappa B transcription factor pathway by activating latent DNA-binding activity of NF-kappa B subunits through a phorbol ester-sensitive (PKC-dependent) mechanism.