Superoxide increases angiotensin II AT1 receptor function in human kidney‐2 cells

The redox‐sensitive Sp family transcription factor has been linked to the regulation of angiotensin II type 1 receptor (AT1R). However, the exact mechanism of AT1R regulation in renal cells is poorly understood. We tested the specificity of reactive oxygen species (ROS), superoxide vs. hydrogen peroxide (H(2)O(2)), and the specific role of Sp3 transcription factor, if any, in the regulation of AT1R in human kidney cells (HK2 cells). Superoxide dismutase (SOD) inhibitor diethyldithiocarbamate (DETC), but not H(2)O(2) treatment, increased fluorescence levels of superoxide probe dihydroethidium (DHE). H(2)O(2,) but not DETC, treatment increased the fluorescence of the H(2)O(2)‐sensitive probe dichloro‐dihydro‐fluorescein (DCFH). These data suggest that SOD inhibition by DETC increases the superoxide but not H(2)O(2) and exogenously added H(2)O(2) is not converted to superoxide in renal cells. Furthermore, DETC, but not H(2)O(2), treatment increased nuclear accumulation of Sp3, which was attenuated with the superoxide dismutase (SOD)‐mimetic tempol. DETC treatment also increased AT1R mRNA and protein levels that were attenuated with tempol, whereas H(2)O(2) did not have any effects on AT1R mRNA. Moreover, Sp3 overexpression increased, while Sp3 depletion by siRNA decreased, protein levels of AT1R. In addition, Sp3 siRNA in the presence of DETC decreased AT1R protein expression. Furthermore, DETC treatment increased the levels of cell surface AT1R as measured by biotinylation and immunofluorescence studies. Angiotensin II increased PKC activity in vehicle‐treated cells that further increased in DETC‐treated cells, which was attenuated by AT1R blocker candesartan and SOD‐mimetic tempol. Taken together, our results suggest that superoxide, but not H(2)O(2), via Sp3 up‐regulates AT1R expression and function in the renal cells.