E2F1 identified by promoter and biochemical analysis as a central target of glioblastoma cell-cycle arrest in response to Ras inhibition

Int J Cancer. 2006 Aug 1;119(3):527-38. doi: 10.1002/ijc.21735.


Active Ras contributes to the malignant phenotype of glioblastoma multiforme. Recent studies showed that the Ras inhibitor farnesyl thiosalicylic acid downregulates the transcription factor hypoxia-inducible factor-1alpha, causing shutdown of glycolysis in U87 glioblastoma cells. Farnesyl thiosalicylic acid also inhibited the growth of U87 cells. The way in which Ras inhibition affects U87 cell proliferation was not clear. Here we applied a computational method in which gene expression profile clustering is combined with promoter sequence analysis to obtain global dissection of the transcriptional response to farnesyl thiosalicylic acid in U87 cells. The analysis revealed a prominent Ras-dependent cell-cycle arrest response, in which a major component is highly enriched for the binding-site signature of the transcription factor E2F1. Electrophoretic mobility shift assays together with E2F-luciferase reporter assays showed that E2F1 was inactivated by the Ras inhibitor. Inhibition of Ras by farnesyl thiosalicylic acid promoted proteasomal degradation of cyclin D1, with a concomitant decrease in phosphorylated retinoblastoma protein accompanied by downregulation of E2F1 and decreased expression of key E2F1-regulated genes critical for cell-cycle progression. U87 cell growth arrest induced by farnesyl thiosalicylic acid was overridden by constitutive expression of E2F1. Thus, downregulation of E2F1 and of hypoxia-inducible factor-1alpha represents 2 distinct arms of the antioncogenic effect of Ras inhibitors in glioblastoma.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cell Cycle / drug effects*
  • Cell Line, Tumor
  • Cell Survival / drug effects
  • Cyclin D1 / metabolism
  • Dose-Response Relationship, Drug
  • E2F1 Transcription Factor / genetics*
  • E2F1 Transcription Factor / metabolism
  • Electrophoretic Mobility Shift Assay
  • Enzyme Inhibitors / pharmacology
  • Farnesol / analogs & derivatives*
  • Farnesol / pharmacology
  • Gene Expression Profiling
  • Gene Expression Regulation, Neoplastic / drug effects
  • Glioblastoma / genetics
  • Glioblastoma / metabolism
  • Glioblastoma / pathology
  • Green Fluorescent Proteins / genetics
  • Green Fluorescent Proteins / metabolism
  • Humans
  • Immunoblotting
  • Immunohistochemistry
  • Luciferases / genetics
  • Luciferases / metabolism
  • Phosphorylation / drug effects
  • Promoter Regions, Genetic / genetics*
  • Proteasome Endopeptidase Complex / metabolism
  • Recombinant Fusion Proteins / genetics
  • Recombinant Fusion Proteins / metabolism
  • Retinoblastoma Protein / metabolism
  • Salicylates / pharmacology*
  • ras Proteins / antagonists & inhibitors
  • ras Proteins / genetics*
  • ras Proteins / metabolism


  • E2F1 Transcription Factor
  • E2F1 protein, human
  • Enzyme Inhibitors
  • Recombinant Fusion Proteins
  • Retinoblastoma Protein
  • Salicylates
  • farnesylthiosalicylic acid
  • Cyclin D1
  • Green Fluorescent Proteins
  • Farnesol
  • Luciferases
  • Proteasome Endopeptidase Complex
  • ras Proteins