Hypoxic regulation of vascular endothelial growth factor through the induction of phosphatidylinositol 3-kinase/Rho/ROCK and c-Myc

J Biol Chem. 2006 May 19;281(20):13957-63. doi: 10.1074/jbc.M511763200. Epub 2006 Mar 16.

Abstract

The induction of vascular endothelial growth factor (VEGF) is an essential feature of tumor angiogenesis. Hypoxia is a potent stimulator of VEGF expression, and hypoxia-inducible factor-1 (HIF-1) is considered to be critical for this induction. However, we have previously demonstrated that induction of VEGF by hypoxia was preserved when HIF-1alpha was silenced. We sought to better define the molecular basis of this HIF-1-independent regulation. In colon cancer cells, hypoxia stimulated multiple K-ras effector pathways including phosphatidylinositol 3-kinase. VEGF promoter deletion studies identified a novel promoter region between -418 and -223 bp that was responsive to hypoxia in a PI3K/Rho/ROCK-dependent manner. Electrophoretic mobility shift assays identified a fragment between -300 and -251 bp that demonstrated a unique shift only in hypoxic conditions. Inhibition of PI3K or ROCK blocked the formation of this complex. A binding site for c-Myc, a target of ROCK, was identified at -271 bp. A role for c-Myc in the hypoxic induction of VEGF was demonstrated by site-directed mutagenesis of the VEGF promoter and silencing of c-Myc by small interfering RNA. Collectively, these findings suggest an alternative mechanism for the hypoxic induction of VEGF in colon cancer that does not depend upon HIF-1alpha but instead requires the activation of PI3K/Rho/ROCK and c-Myc.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Base Sequence
  • Colonic Neoplasms / metabolism
  • Gene Expression Regulation, Neoplastic*
  • Humans
  • Hypoxia*
  • Intracellular Signaling Peptides and Proteins
  • Models, Biological
  • Molecular Sequence Data
  • Phosphatidylinositol 3-Kinases / metabolism*
  • Promoter Regions, Genetic
  • Protein Serine-Threonine Kinases / metabolism*
  • Proto-Oncogene Proteins c-myc / metabolism*
  • Vascular Endothelial Growth Factor A / genetics
  • Vascular Endothelial Growth Factor A / metabolism*
  • rho-Associated Kinases

Substances

  • Intracellular Signaling Peptides and Proteins
  • Proto-Oncogene Proteins c-myc
  • Vascular Endothelial Growth Factor A
  • Protein Serine-Threonine Kinases
  • rho-Associated Kinases