Degradation of PKB/Akt protein by inhibition of the VEGF receptor/mTOR pathway in endothelial cells

Oncogene. 2004 Jun 3;23(26):4624-35. doi: 10.1038/sj.onc.1207596.

Abstract

An intact VEGF receptor/PI3K/PKB/Akt signaling cascade protects endothelial cells from apoptotic stress-stimuli and mediates the formation of new blood vessels in pathological conditions such as cancer. Therefore, downregulation of this signaling cascade is of clinical interest for antiangiogenic cancer therapy. In this report, we demonstrate that VEGF controls the protein stability of the serine-threonine kinase PKB/Akt via inhibition of PKB/Akt protein degradation. VEGF deprivation or blockage of the VEGF signal transduction cascade with the VEGF receptor tyrosine kinase inhibitor PTK787/ZK222584 resulted in a specific decrease of the PKB/Akt protein level and subsequent cellular restimulation with VEGF rescued its stability. Real-time quantitative RT-PCR analysis demonstrated that VEGF does not regulate PKB/Akt gene expression. On the other hand, broad range inhibitors of caspases and the proteasome complex prevented VEGF-dependent downregulation of the PKB/Akt protein level indicating that PKB/Akt protein stability is regulated by VEGF-controlled proteolysis. Inhibition of the VEGF receptor and PKB/Akt-downstream PIK-related mTOR-kinase by rapamycin also neutralized the VEGF-protective effect in an PKB/Akt gene expression-independent way but results in proteolysis-dependent reduction of PKB/Akt protein stability. These results demonstrate a novel regulatory mechanism of the activated VEGF receptor/mTOR-signal transduction pathway to control the protein stability of PKB/Akt and survival threshold in endothelial cells.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Caspase Inhibitors
  • Caspases / metabolism
  • Cell Death / genetics
  • Cell Survival / drug effects
  • Cell Survival / physiology
  • Cells, Cultured
  • Cysteine Endopeptidases / metabolism
  • Cysteine Proteinase Inhibitors / pharmacology
  • Endothelium, Vascular / cytology
  • Endothelium, Vascular / drug effects
  • Endothelium, Vascular / metabolism*
  • Enzyme Stability
  • Multienzyme Complexes / antagonists & inhibitors
  • Multienzyme Complexes / metabolism
  • Phthalazines / pharmacology
  • Proteasome Endopeptidase Complex
  • Protein Kinases / drug effects
  • Protein Kinases / metabolism*
  • Protein-Serine-Threonine Kinases*
  • Proto-Oncogene Proteins / drug effects
  • Proto-Oncogene Proteins / genetics
  • Proto-Oncogene Proteins / metabolism*
  • Proto-Oncogene Proteins c-akt
  • Pyridines / pharmacology
  • Receptors, Vascular Endothelial Growth Factor / metabolism*
  • Signal Transduction
  • Sirolimus / pharmacology
  • TOR Serine-Threonine Kinases
  • Vascular Endothelial Growth Factor A / genetics
  • Vascular Endothelial Growth Factor A / metabolism
  • Vascular Endothelial Growth Factor A / pharmacology

Substances

  • Caspase Inhibitors
  • Cysteine Proteinase Inhibitors
  • Multienzyme Complexes
  • Phthalazines
  • Proto-Oncogene Proteins
  • Pyridines
  • Vascular Endothelial Growth Factor A
  • vatalanib
  • Protein Kinases
  • TOR Serine-Threonine Kinases
  • Receptors, Vascular Endothelial Growth Factor
  • Protein-Serine-Threonine Kinases
  • Proto-Oncogene Proteins c-akt
  • Caspases
  • Cysteine Endopeptidases
  • Proteasome Endopeptidase Complex
  • Sirolimus