Abstract 5877: Regulation of Signal Transducer and Activator of Transcription 3 Signaling Pathway by AP-endonuclease 1 in Vascular Inflammation
Background: Signal transducer and activator of transcription-3 (STAT3) is a latent interleukin-6 (IL-6) inducible transcription factor that mediates hepatic and vascular inflammation including atherosclerosis (AS). Chronic vascular inflammation producing AS is associated with the presence of circulating hepatic acute phase reactants including C-reactive protein (CRP) and angiotensinogen (AGT). In this study we investigated the mechanism by which AP-endonuclease 1 (APE1/Ref-1), an essential multifunctional protein in DNA base excision repair process and a transcriptional co-factor, regulates the IL-6-STAT3 pathway.
Methods and Result: Here we showed that IL-6-induced endogenous STAT3 forms a nuclear complex with APE1 in a co-immunoprecipitation assay and that the NH2-terminal acetylation domain of STAT3 is required for APE1 binding. Ectopic expression of APE1 potentiated STAT3 mediated human AGT promoter activity whereas siRNA mediated silencing of APE1 resulted in reduced DNA binding activity of STAT3 in electrophoretic mobility shift assay. We observed that IL-6 inducible acute phase reactant protein (APP) expression (CRP and serum amyloid P) and MCP1 (Monocyte Chemotactic Protein-1) expression are inhibited by APE1 knockdown. Consistent with this, we also observed that activation of APP expression in APE1 heterozygous mice is reduced by lipopolysaccharide treatment as compared to wild type mice. Chromatin immunoprecipitation assays showed that STAT3-regulated Socs3 and γ-Fibrinogen (γ-FBG) promoters directly bind STAT3 and APE1 in IL-6 stimulated cells. Moreover, we observed that cells lacking APE1 expression did not form a stable enhanceosome on the endogenous γ-FBG promoter.
Conclusion: Taken together, our study provides a novel STAT3-APE1 interaction, required for stable chromatin association in IL-6-induced hepatic acute phase response.
This research has received full or partial funding support from the American Heart Association, South Central Affiliate (Arkansas, New Mexico, Oklahoma & Texas).