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E2F1 identified by promoter and biochemical analysis as a central target of glioblastoma cell‐cycle arrest in response to ras inhibition
Author(s) -
Blum Roy,
Nakdimon Itay,
Goldberg Liat,
Elkon Ran,
Shamir Ron,
Rechavi Gideon,
Kloog Yoel
Publication year - 2006
Publication title -
international journal of cancer
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.475
H-Index - 234
eISSN - 1097-0215
pISSN - 0020-7136
DOI - 10.1002/ijc.21735
Subject(s) - e2f1 , downregulation and upregulation , transcription factor , e2f , cell cycle , biology , cell growth , cancer research , retinoblastoma protein , cell cycle checkpoint , microbiology and biotechnology , cyclin d1 , chemistry , cell , biochemistry , gene
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‐1α, 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‐1α represents 2 distinct arms of the antioncogenic effect of Ras inhibitors in glioblastoma. © 2006 Wiley‐Liss, Inc.