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-α (TNFα)]- inducible enhancer by binding the heterodimeric nuclear factor-κB (NF-κB) complex Rel A•NF-κB1. Here, we compare the mechanism for NF-κB activation by the All agonist, Sar1 All, with TNFα in HepG2 hepatocytes. Although Sar1 All and TNFα both rapidly activate APRE-driven transcription within 3 h of treatment, the pattern of inducible NF-κB binding activity in electrophoretic mobility shift assay is distinct. In contrast to the TNFα mechanism, which strongly induces Rel A•NF-κB1 binding, Sar1 All selectively activates a heterogenous pattern of NF-κB1 binding. Using a two-step microaffinity DNA binding assay, we observe that Sar1 All recruits 50-, 56-, and 96-kDa NF-κB1 isoforms to bind the APRE. Binding of all three NF-κB1 isoforms occurs independently of changes in their nuclear abundance or proteolysis of cytoplasmic IκB inhibitors. Phorbol ester-sensitive protein kinase C (PKC) isoforms are required because PKC down-regulation completely blocks All-inducible transcription and inducible NF-κB1 binding. We conclude that All stimulates the NF-κB transcription factor pathway by activating latent DNA-binding activity of NF-κB subunits through a phorbol ester-sensitive (PKC-dependent) mechanism.
ASJC Scopus subject areas
- Molecular Biology