title: Phosphorylation of CHOP (C/EBP Homologous Protein) by the AMP-Activated Protein Kinase Alpha 1 in Macrophages Promotes CHOP Degradation and Reduces Injury-Induced Neointimal Disruption In Vivo.
abstract: BACKGROUND
  Elevated levels of CHOP (C/EBP homologous protein), a member of the C/EBP transcription factor family, in advanced atherosclerotic plaques is reported to be associated with atherosclerotic plaque rupture in humans. However, the molecular mechanism by which CHOP accumulation occurs is poorly defined.
  
  
  OBJECTIVE
  The aim of this study was to investigate if (1) macrophage AMPK (AMP-activated protein kinase) regulates cellular CHOP accumulation and (2) whole-body Ampk deletion leads to neointimal disruption.
  
  
  RESULTS
  In isolated or cultured macrophages, Ampkα1 deletion markedly increased apoptosis and CHOP, whereas pharmacological activation of AMPK dramatically reduced CHOP protein level via promoting CHOP degradation by proteasome. In addition, cotransfection of Chop-specific siRNA, but not control siRNA, markedly reduced apoptosis in macrophages transfected with Ampkα1-specific siRNA. Mechanistically, AMPKα1 was found to coimmunoprecipitate with CHOP and phosphorylate CHOP at serine 30. Furthermore, serine 30 phosphorylation of CHOP triggered its ubiquitination and proteasomal degradation. In a mouse model of plaque stability, deletion of Ampkα1 but not Ampkα2 promoted injury-induced neointimal disruption. This was paralleled by increased CHOP expression and apoptosis in vivo. Finally, transfection of Chop-specific siRNA but not control siRNA reduced both CHOP level and injury-induced neointimal disruption in vivo.
  
  
  CONCLUSIONS
  Our results indicate that AMPKα1 mediates CHOP ubiquitination and proteasomal degradation in macrophages by promoting the phosphorylation of CHOP at serine 30. We conclude that AMPKα1 might be a valid therapeutic target in preventing atherosclerotic vulnerable plaque formation.
authors.affiliation: From the Center for Molecular and Translational Medicine, Georgia State University, Atlanta (X.D., Y.D., Z.L., M.-H.Z.); The Key Laboratory of Cardiovascular Remodeling and Function Research, Chinese Ministry of Education and Chinese Ministry of Health; and the State and Shandong Province Joint Key Laboratory of Translational Cardiovascular Medicine, Qilu Hospital of Shandong University, Jinan, China (W.Z.).
authors.forename: Xiaoyan
authors.initials: X
authors.lastname: Dai
authors.affiliation: From the Center for Molecular and Translational Medicine, Georgia State University, Atlanta (X.D., Y.D., Z.L., M.-H.Z.); The Key Laboratory of Cardiovascular Remodeling and Function Research, Chinese Ministry of Education and Chinese Ministry of Health; and the State and Shandong Province Joint Key Laboratory of Translational Cardiovascular Medicine, Qilu Hospital of Shandong University, Jinan, China (W.Z.).
authors.forename: Ye
authors.initials: Y
authors.lastname: Ding
authors.affiliation: From the Center for Molecular and Translational Medicine, Georgia State University, Atlanta (X.D., Y.D., Z.L., M.-H.Z.); The Key Laboratory of Cardiovascular Remodeling and Function Research, Chinese Ministry of Education and Chinese Ministry of Health; and the State and Shandong Province Joint Key Laboratory of Translational Cardiovascular Medicine, Qilu Hospital of Shandong University, Jinan, China (W.Z.).
authors.forename: Zhaoyu
authors.initials: Z
authors.lastname: Liu
authors.affiliation: From the Center for Molecular and Translational Medicine, Georgia State University, Atlanta (X.D., Y.D., Z.L., M.-H.Z.); The Key Laboratory of Cardiovascular Remodeling and Function Research, Chinese Ministry of Education and Chinese Ministry of Health; and the State and Shandong Province Joint Key Laboratory of Translational Cardiovascular Medicine, Qilu Hospital of Shandong University, Jinan, China (W.Z.).
authors.forename: Wencheng
authors.initials: W
authors.lastname: Zhang
authors.affiliation: From the Center for Molecular and Translational Medicine, Georgia State University, Atlanta (X.D., Y.D., Z.L., M.-H.Z.); The Key Laboratory of Cardiovascular Remodeling and Function Research, Chinese Ministry of Education and Chinese Ministry of Health; and the State and Shandong Province Joint Key Laboratory of Translational Cardiovascular Medicine, Qilu Hospital of Shandong University, Jinan, China (W.Z.). MZou@gsu.edu.
authors.forename: Ming-Hui
authors.initials: MH
authors.lastname: Zou
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D000818:Animals; D001057:Apolipoproteins E / Q000172:deficiency / Q000235:genetics; D017209:Apoptosis; D017536:Carotid Artery, Common / Q000473:pathology; D016893:Carotid Stenosis / Q000473:pathology; D002478:Cells, Cultured; D004195:Disease Models, Animal; D008264:Macrophages / Q000378:metabolism*; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D058426:Neointima; D010766:Phosphorylation; D010768:Phosphoserine; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D059748:Proteolysis; D034741:RNA, Small Interfering / Q000235:genetics / Q000627:therapeutic use; D051742:Transcription Factor CHOP / Q000235:genetics / Q000378:metabolism*
chemical_list: D001057:Apolipoproteins E; C497250:Ddit3 protein, mouse; D034741:RNA, Small Interfering; D051742:Transcription Factor CHOP; D010768:Phosphoserine; C548179:Prkaa1 protein, mouse; C534978:Prkaa2 protein, mouse; D055372:AMP-Activated Protein Kinases; D046988:Proteasome Endopeptidase Complex
keywords: AMPK; CHOP; apoptosis; degradation; macrophage; neointima; ubiquitination