TGF-β1 Downregulates AT1 Receptor Expression via PKC-δ-Mediated Sp1 Dissociation From KLF4 and Smad-Mediated PPAR-γ Association With KLF4

Objective-Cardiovascular effects of angiotensin II are primarily mediated via the angiotensin II type 1 receptor (AT1R). Kruppel-like factor 4 (KLF4), a transcription factor that binds to the transforming growth factor (TGF)-beta control element (TCE), regulates a variety of receptor expression in vascular smooth muscle cells. In the present study, we investigated the mechanisms of TGF-beta-mediated KLF4 regulation of AT1R expression. Methods and Results-Coimmunoprecipitation, chromatin immunoprecipitation, and luciferase assays were performed, with the results suggesting that Sp1 forms a complex with KLF4 bound to the TCE of the AT1R promoter and cooperatively activates AT1R transcription in vascular smooth muscle cells under basal conditions. On activation of TGF-beta 1 signaling, Sp1 is dissociated from the KLF4-Sp1 complex through PKC-delta-mediated KLF4 phosphorylation at Thr401, downregulating AT1R expression. Simultaneously, TGF-beta 1 facilitates KLF4-PPAR-gamma complex formation and its binding to the TCE of the AT1R promoter through Smad-mediated KLF4 phosphorylation at Ser470, subsequently leading to inhibition of AT1R transcription. Conclusion-KLF4 functions as a protein platform that is able to bind to the TCE of the AT1R promoter. On activation of TGF-beta signaling, KLF4 mediates Sp1 dissociation from, and PPAR-gamma association with, the AT1R promoter, leading to downregulation of AT1R expression in VSMCs. (Arterioscler Thromb Vasc Biol. 2012; 32: 1015-1023.)