title: TGF-β1 downregulates AT1 receptor expression via PKC-δ-mediated Sp1 dissociation from KLF4 and Smad-mediated PPAR-γ association with KLF4.
abstract: OBJECTIVE
  Cardiovascular effects of angiotensin II are primarily mediated via the angiotensin II type 1 receptor (AT1R). Krüppel-like factor 4 (KLF4), a transcription factor that binds to the transforming growth factor (TGF)-β control element (TCE), regulates a variety of receptor expression in vascular smooth muscle cells. In the present study, we investigated the mechanisms of TGF-β-mediated KLF4 regulation of AT1R expression.
  
  
  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-β1 signaling, Sp1 is dissociated from the KLF4-Sp1 complex through PKC-δ-mediated KLF4 phosphorylation at Thr401, downregulating AT1R expression. Simultaneously, TGF-β1 facilitates KLF4-PPAR-γ 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.
  
  
  CONCLUSIONS
  KLF4 functions as a protein platform that is able to bind to the TCE of the AT1R promoter. On activation of TGF-β signaling, KLF4 mediates Sp1 dissociation from, and PPAR-γ association with, the AT1R promoter, leading to downregulation of AT1R expression in VSMCs.
authors.affiliation: Department of Biochemistry and Molecular Biology, Key Laboratory of Neural and Vascular Biology, Ministry of Education, Hebei Medical University, Shijiazhuang, China.
authors.forename: Xin-hua
authors.initials: XH
authors.lastname: Zhang
authors.forename: Bin
authors.initials: B
authors.lastname: Zheng
authors.forename: Chun
authors.initials: C
authors.lastname: Gu
authors.forename: Jian-ran
authors.initials: JR
authors.lastname: Fu
authors.forename: Jin-kun
authors.initials: JK
authors.lastname: Wen
mesh_terms: D000818:Animals; D001665:Binding Sites; D049109:Cell Proliferation; D047369:Chromatin Immunoprecipitation; D015536:Down-Regulation; D017930:Genes, Reporter; D057809:HEK293 Cells; D006801:Humans; D047468:Immunoprecipitation; D000090062:Kruppel-Like Factor 4; D051741:Kruppel-Like Transcription Factors / Q000235:genetics / Q000378:metabolism*; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000201:enzymology*; D032389:Myocytes, Smooth Muscle / Q000201:enzymology*; D047495:PPAR gamma / Q000378:metabolism*; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D051745:Protein Kinase C-delta / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D044140:Receptor, Angiotensin, Type 1 / Q000235:genetics / Q000378:metabolism*; D012694:Serine; D051785:Smad Proteins / Q000378:metabolism*; D016329:Sp1 Transcription Factor / Q000235:genetics / Q000378:metabolism*; D013997:Time Factors; D015533:Transcriptional Activation; D014162:Transfection; D053773:Transforming Growth Factor beta1 / Q000378:metabolism*
chemical_list: C544065:AGTR1 protein, human; C000715467:KLF4 protein, human; C000715469:Klf4 protein, rat; D000090062:Kruppel-Like Factor 4; D051741:Kruppel-Like Transcription Factors; D047495:PPAR gamma; D012333:RNA, Messenger; D044140:Receptor, Angiotensin, Type 1; D051785:Smad Proteins; D016329:Sp1 Transcription Factor; D053773:Transforming Growth Factor beta1; D012694:Serine; C497260:Prkcd protein, rat; C497258:PRKCD protein, human; D051745:Protein Kinase C-delta