E2F-1 transcriptional activity is a critical determinant of Mdm2 antagonist-induced apoptosis in human tumor cell lines

Oncogene. 2008 Sep 11;27(40):5303-14. doi: 10.1038/onc.2008.164. Epub 2008 Jun 2.


Nutlin-3 is a selective inhibitor of the p53-Mdm2 interaction, and inhibits growth in most tumor cells with wild-type p53. However, it only induces apoptosis in subsets of tumor cells. We report that the apoptotic response induced by Nutlin-3 correlates with its antitumor effects in xenograft models in athymic mice. We have investigated signals that sensitize cells to undergo apoptosis induced by Nutlin-3. We demonstrate that adenovirus E1A increases Nutlin-3-induced apoptosis through pRb inhibition in mouse embryonic fibroblast cells in a p53-dependent manner. Consistent with this, pRb depletion by siRNA transfection with Nutlin-3 synergistically increases apoptosis in HCT116 human colon cancer cells, which are insensitive to induction of apoptosis by Nutlin-3 alone. As pRb is a key negative regulator of E2F, we asked whether E2F transcriptional activity determines the apoptotic response of cancer cells to Nutlin-3. We demonstrate that transcriptional activity of E2F correlates with the apoptotic response to Nutlin-3 in various tumor cells and depletion of E2F-1 suppresses Nutlin-3-induced apoptosis in cells possessing high transcriptional activity of E2F, including retinoblastoma cells harboring mutated Rb with wild-type p53. Furthermore, we report that expression of the p53 homologue p73, a target of E2F-1, is markedly increased by Nutlin-3 in Rb-mutated tumor cells harboring wild-type p53. Depletion of p73 by siRNA transfection suppresses Nutlin-3-induced apoptosis in these cells. Taken together, our results demonstrate that E2F-1 transcriptional activity is a critical determinant of Mdm2 antagonist-induced apoptosis and p73 is important for E2F-1-mediated apoptosis induced by Nutlin-3, especially in tumor cells with mutated Rb. Furthermore, our results suggest that tumor cells, including Rb mutated cells, which harbor wild-type p53 and high E2F transcriptional activity, could be a good target for Mdm2 antagonist therapy.

MeSH terms

  • Animals
  • Apoptosis / physiology
  • Cell Cycle Proteins
  • Cell Proliferation
  • Cells, Cultured
  • E2F1 Transcription Factor / antagonists & inhibitors
  • E2F1 Transcription Factor / genetics*
  • E2F1 Transcription Factor / metabolism*
  • G1 Phase / physiology
  • Humans
  • Imidazoles / metabolism*
  • Male
  • Mice
  • Mice, Inbred BALB C
  • Mice, Inbred NOD
  • Mice, Nude
  • Mutation / genetics
  • Neoplasms / metabolism
  • Neoplasms / pathology*
  • Nuclear Proteins / genetics
  • Nuclear Proteins / metabolism
  • Piperazines / metabolism*
  • Promoter Regions, Genetic
  • Proto-Oncogene Proteins / genetics
  • Proto-Oncogene Proteins / metabolism
  • Proto-Oncogene Proteins c-mdm2 / antagonists & inhibitors
  • Proto-Oncogene Proteins c-mdm2 / genetics
  • Proto-Oncogene Proteins c-mdm2 / metabolism*
  • RNA, Small Interfering / pharmacology
  • Resting Phase, Cell Cycle / physiology
  • Retinoblastoma Protein / genetics
  • Retinoblastoma Protein / metabolism
  • Stereoisomerism
  • Transcription, Genetic
  • Transfection
  • Tumor Cells, Cultured
  • Tumor Suppressor Protein p53 / genetics
  • Tumor Suppressor Protein p53 / metabolism


  • Cell Cycle Proteins
  • E2F1 Transcription Factor
  • Imidazoles
  • MDM4 protein, human
  • Nuclear Proteins
  • Piperazines
  • Proto-Oncogene Proteins
  • RNA, Small Interfering
  • Retinoblastoma Protein
  • Tumor Suppressor Protein p53
  • nutlin 3
  • MDM2 protein, human
  • Proto-Oncogene Proteins c-mdm2