Reactive oxygen species-mediated homologous downregulation of angiotensin II type I receptor mRNA by angiotensin II

Recent studies suggest a crucial role of reactive oxygen species (ROS) for the signaling of angiotensin (Ang) II through Ang II type 1 receptor (AT₁-R). However, the role of ROS in the regulation of AT₁-R expression has not been explored. In this study, we examined the effect of an antioxidant on the homologous downregulation of AT₁-R by Ang Il. Ang II (10^-6 mol/L) decreased AT₁-R mRNA with a peak suppression at 6 hours of stimulation in rat aortic vascular smooth muscle cells. Preincubation of vascular smooth muscle cells with N-acetylcysteine (NAC), a potent antioxidant, almost completely inhibited the Ang II-induced downregulation of AT₁-R mRNA. The effect of NAC was due to stabilization of the AT₁-R mRNA that was destabilized by Ang II. The Ang II-induced AT₁-R mRNA downregulation was also blocked by PD98059, an extracellular signal-regulated protein kinase (ERK) kinase inhibitor. Ang II-induced ERK activation was inhibited by NAC as well as by PD98059. Exogenous H₂O₂ also suppressed AT₁-R mRNA. These results suggest that the production of ROS and the activation of ERK are critical for the downregulation of AT₁-R mRNA. The generation of ROS through stimulation of AT₁-R not only mediates signaling of Ang II but also may play a crucial role in the adaptation process of AT₁-R to the sustained stimulation of Ang II.