title: Role of nuclear unphosphorylated STAT3 in angiotensin II type 1 receptor-induced cardiac hypertrophy.
abstract: OBJECTIVE
  Cardiac hypertrophy is a risk factor independent of blood pressure; however, the mechanisms that distinguish pathological remodelling due to local cues from pressure overload are unresolved. This study was aimed at discovering a novel gene expression mechanism in heart failure.
  
  
  RESULTS
  In angiotensin II type 1 receptor (AT1R) transgenic mice (TG), we found a significant increase of mRNA and total STAT3 (T-STAT3) protein, but not STAT3 phosphorylated at residues Y705 and S727. A net increase in nuclear accumulation of this unphosphorylated form of STAT3 (U-STAT3) correlated with the development of cardiac hypertrophy and dysfunction, which are associated with abnormal expression of osteopontin and regulator of G protein signalling 2 genes. Nuclear accumulation of U-STAT3 is induced by angiotensin II treatment in neonatal cardiac myocytes, fibroblasts, and AT1R-expressing human embryonic kidney 293 (HEK-AT1R) cells. Chromatin immunoprecipitation demonstrated that U-STAT3 binds to the target gene promoter, and siRNA-mediated knockdown of STAT3 expression significantly altered the expression of target genes in HEK-AT1R cells. T-STAT3 in TG mouse hearts and the phosphorylation-deficient Y705F mutant STAT3 in HEK-AT1R cells physically interacted with transcription co-activator p300.
  
  
  CONCLUSIONS
  Chronic activation of AT1R induces unregulated expression of the Stat3 gene, leading to nuclear accumulation of U-STAT3, which significantly correlated with progression of cardiac hypertrophy.
authors.affiliation: Department of Molecular Cardiology, Lerner Research Institute, Cleveland Clinic, Cleveland, OH 44195, USA.
authors.forename: Hong
authors.initials: H
authors.lastname: Yue
authors.forename: Wei
authors.initials: W
authors.lastname: Li
authors.forename: Russell
authors.initials: R
authors.lastname: Desnoyer
authors.forename: Sadashiva S
authors.initials: SS
authors.lastname: Karnik
mesh_terms: D000818:Animals; D006332:Cardiomegaly / Q000209:etiology* / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism*; D002478:Cells, Cultured; D005786:Gene Expression Regulation; D051379:Mice; D008810:Mice, Inbred C57BL; D032383:Myocytes, Cardiac / Q000378:metabolism*; D053244:Osteoprotegerin / Q000502:physiology; D010766:Phosphorylation; D020710:RGS Proteins / Q000502:physiology; D044140:Receptor, Angiotensin, Type 1 / Q000502:physiology*; D050796:STAT3 Transcription Factor / Q000235:genetics / Q000378:metabolism*; D050880:p300-CBP Transcription Factors / Q000502:physiology
chemical_list: D053244:Osteoprotegerin; D020710:RGS Proteins; D044140:Receptor, Angiotensin, Type 1; C105345:Rgs2 protein, mouse; D050796:STAT3 Transcription Factor; C494087:Stat3 protein, mouse; D050880:p300-CBP Transcription Factors
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