Angiopoietin-1 induces Kruppel-like factor 2 expression through a phosphoinositide 3-kinase/AKT-dependent activation of myocyte enhancer factor 2

J Biol Chem. 2009 Feb 27;284(9):5592-601. doi: 10.1074/jbc.M806928200. Epub 2008 Dec 23.


Angiopoietin-1 (Ang1) regulates both vascular quiescence and angiogenesis through the receptor tyrosine kinase Tie2. We and another group have recently shown that Ang1 and Tie2 form distinct signaling complexes at cell-cell and cell-matrix contacts and further demonstrated that the former selectively induces expression of Krüppel-like factor 2 (KLF2), a transcription factor involved in vascular quiescence. Here, we investigated the mechanism of how Ang1/Tie2 signal induces KLF2 expression to clarify the role of KLF2 in Ang1/Tie2 signal-mediated vascular quiescence. Ang1 stimulated KLF2 promoter-driven reporter gene expression in endothelial cells, whereas it failed when a myocyte enhancer factor 2 (MEF2)-binding site of KLF2 promoter was mutated. Depletion of MEF2 by siRNAs abolished Ang1-induced KLF2 expression, indicating the requirement of MEF2 in KLF2 induction by Ang1. Constitutive active phosphoinositide 3-kinase (PI3K) and AKT increased the MEF2-dependent reporter gene expression by enhancing its transcriptional activity and stimulated the KLF2 promoter activity cooperatively with MEF2. Consistently, inhibition of either PI3K or AKT and depletion of AKT abrogated Ang1-induced KLF2 expression. In addition, we confirmed the dispensability of extracellular signal-regulated kinase 5 (ERK5) for Ang1-induced KLF2 expression. Furthermore, depletion of KLF2 resulted in the loss of the inhibitory effect of Ang1 on vascular endothelial growth factor (VEGF)-mediated expression of vascular cell adhesion molecule-1 in endothelial cells and VEGF-mediated monocyte adhesion to endothelial cells. Collectively, these findings indicate that Ang1/Tie2 signal stimulates transcriptional activity of MEF2 through a PI3K/AKT pathway to induce KLF2 expression, which may counteract VEGF-mediated inflammatory responses.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenoviridae / genetics
  • Angiopoietin-1 / physiology*
  • Cell Adhesion / physiology
  • Cells, Cultured
  • Endothelium, Vascular / cytology
  • Endothelium, Vascular / metabolism
  • Humans
  • Kruppel-Like Transcription Factors / genetics*
  • Kruppel-Like Transcription Factors / metabolism
  • MEF2 Transcription Factors
  • Mitogen-Activated Protein Kinase 1 / metabolism
  • Mitogen-Activated Protein Kinase 3 / metabolism
  • Mitogen-Activated Protein Kinase 7 / metabolism
  • Monocytes / cytology
  • Monocytes / metabolism
  • Myogenic Regulatory Factors / metabolism*
  • Phosphatidylinositol 3-Kinases / metabolism*
  • Phosphoinositide-3 Kinase Inhibitors
  • Proto-Oncogene Proteins c-akt / antagonists & inhibitors
  • Proto-Oncogene Proteins c-akt / metabolism*
  • RNA, Messenger / genetics
  • RNA, Messenger / metabolism
  • RNA, Small Interfering / pharmacology
  • Reverse Transcriptase Polymerase Chain Reaction
  • Signal Transduction
  • Subcellular Fractions
  • Umbilical Veins / cytology
  • Umbilical Veins / metabolism
  • Vascular Cell Adhesion Molecule-1 / metabolism
  • Vascular Endothelial Growth Factor A / metabolism


  • Angiopoietin-1
  • KLF2 protein, human
  • Kruppel-Like Transcription Factors
  • MEF2 Transcription Factors
  • Myogenic Regulatory Factors
  • Phosphoinositide-3 Kinase Inhibitors
  • RNA, Messenger
  • RNA, Small Interfering
  • VEGFA protein, human
  • Vascular Cell Adhesion Molecule-1
  • Vascular Endothelial Growth Factor A
  • Proto-Oncogene Proteins c-akt
  • Mitogen-Activated Protein Kinase 1
  • Mitogen-Activated Protein Kinase 3
  • Mitogen-Activated Protein Kinase 7