Abstract 751: Acetylated APE1 is a Repressor in Calcium-Mediated Downregulation of the Human Renin Gene
The mammalian AP-endonuclease (APE1/Ref-1) plays a central role in the repair of most genomic damage induced by endogenous and reactive oxygen species. APE1 also has two functions in transcriptional regulation: indirectly as a redox activator of several transcription factors and directly as a trans-acting factor by binding to a negative calcium response element (nCaRE). Chronic hypertension in APE1 heterozygous (APE1+/−) mice implicates APE1 in blood pressure homeostasis in which renin plays a key role via its angiotensinogen- processing activity. [Ca2+]i -dependent repression of the human renin gene is mediated by APE1/Ref-1 that binds to nCaRE-B in the human renin promoter. This study was aimed to test the hypothesis that acetylated APE1 (AcAPE1), rather than unmodified APE1 acts as a repressor in [Ca 2+]i -mediated downregulation of human renin gene and observed elevated blood pressure in APE1+/− mice is due to enhanced renin expression. SiRNA-mediated downregulation of the APE1 level in renin-producing mouse As4.1 cells significantly increased (2.5 ± 0.3-fold) the renin mRNA as determined by quantitative RT-PCR. Repression of both human and mouse renin promoter-dependent luciferase activity by ectopic overexpression of WT APE1 but not its nonacetyable mutant in a reporter expression assay suggests that acetylation of APE1 plays a critical role in repression of the renin gene. Western blot analysis with AcAPE1-specific antibody showed that increased [Ca 2+]i enhances (2-fold) the AcAPE1 level. Coimmunoprecipitation analysis showed that APE1 stably interacts with histone deacetylase1 which could be responsible for its repressor activity. Quantitative determination of plasma renin activity by the radioimmunoassay of angiotensin I (ANG I) showed that APE1+/− mice have significantly increased [WT (n=9), 9.86 ± 1.5 ng ANGI/ml/h; APE1+/− (n=9), 20.45 ± 2.9 ng ANGI/ml/h; p<0.05] plasma renin activity which is consistent with the higher level of renin mRNA in their kidneys. In conclusion, AcAPE1 acts as a repressor in [Ca 2+]i -mediated downregulation of renin gene and APE1+/− mice have enhanced renin expression. Hence we have uncovered a novel physiological role of APE1acetylation in regulating renin expression and thus maintaining blood pressure.