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E2F-1:DP-1 induces p53 and overrides survival factors to trigger apoptosis
S W Hiebert1, G Packham, D K Strom
1Department of Tumor Cell Biology, St. Jude Children's Research Hospital, Memphis, Tennessee 38105, USA.
Abstract:
The E2F DNA binding activity consists of a heterodimer between E2F and DP family proteins, and these interactions are required for association of E2F proteins with pRb and the pRb-related proteins p107 and p130, which modulate E2F transcriptional activities. E2F-1 expression is sufficient to release fibroblasts from G0 and induce entry into S phase, yet it also initiates apoptosis. To investigate the mechanisms of E2F-induced apoptosis, we utilized interleukin-3 (IL-3)-dependent 32D.3 myeloid cells, a model of hematopoietic progenitor programmed cell death. In the absence of IL-3, E2F-1 alone was sufficient to induce apoptosis, and p53 levels were diminished. DP-1 alone was not sufficient to induce cell cycle progression or alter rates of death following IL-3 withdrawal. However, overexpression of both E2F-1 and DP-1 led to the rapid death of cells even in the presence of survival factors. In the presence of IL-3, levels of endogenous wild-type p53 increased in response to E2F-1, and coexpression of DP-1 further augmented p53 levels. These results provide evidence that E2F is a functional link between the tumor suppressors p53 and pRb. However, induction of p53 alone was not sufficient to trigger apoptosis, suggesting that the ability of E2F to override survival factors involves additional effectors.
Insights
E2F proteins regulate cell cycle and apoptosis. Overexpressing E2F-1 and DP-1 induces rapid cell death, linking E2F to tumor suppressors p53 and pRb.
Area of Science:
- Molecular Biology
- Cell Biology
- Cancer Research
Background:
- E2F and DP proteins form heterodimers, regulating gene transcription and interacting with retinoblastoma tumor suppressors (pRb, p107, p130).
- E2F-1 expression drives cell cycle entry but also triggers apoptosis.
- Understanding E2F-mediated apoptosis is crucial for cancer research.
Purpose of the Study:
- To investigate the mechanisms underlying E2F-induced apoptosis.
- To determine the roles of E2F-1 and DP-1 in cell death pathways.
- To explore the relationship between E2F, p53, and pRb in apoptosis.
Main Methods:
- Utilized interleukin-3 (IL-3)-dependent 32D.3 myeloid cells as a model for hematopoietic progenitor cell death.
- Manipulated the expression of E2F-1 and DP-1 to assess their effects on cell cycle progression and apoptosis.
- Measured p53 levels in response to E2F-1 and DP-1 overexpression.
Main Results:
- E2F-1 alone induced apoptosis in IL-3-deprived cells, with diminished p53 levels.
- DP-1 alone did not affect cell cycle or survival.
- Coexpression of E2F-1 and DP-1 caused rapid cell death, even with survival factors present.
- E2F-1 increased endogenous p53 levels in IL-3-treated cells, further augmented by DP-1 coexpression.
Conclusions:
- E2F acts as a functional link between the tumor suppressors p53 and pRb.
- E2F-induced apoptosis overrides survival signals through mechanisms beyond p53 induction alone.
- E2F-1 and DP-1 cooperate to induce cell death, highlighting their complex role in cell fate determination.