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Unbound E2F modulates TGF-beta1-induced apoptosis in HuH-7 cells
Guangsheng Fan1, Xiaoming Ma, Betsy T Kren
1Department of Medicine, University of Minnesota Medical School, Minneapolis, MN 55455, USA.
Journal of Cell Science
|July 16, 2002
Summary
Transforming growth factor-beta1 (TGF-beta1) induces apoptosis in HuH-7 cells by increasing transcription factor E2F activity, which is partially blocked by pRb. Preapoptotic changes are reversible, with cells re-entering the cell cycle upon TGF-beta1 removal.
Area of Science:
- Cell Biology
- Molecular Biology
- Cancer Research
Background:
- The retinoblastoma protein (pRb) targets E2F transcription factors, crucial for cell cycle progression from G1 to S phase.
- Transforming growth factor-beta1 (TGF-beta1) is known to arrest cells in G1 and induce apoptosis in HuH-7 cells.
Purpose of the Study:
- To investigate the downstream effects of TGF-beta1-induced apoptosis.
- To elucidate the roles of pRb and E2F in TGF-beta1-mediated apoptosis and cell cycle arrest.
Main Methods:
- Cell cycle analysis (G1/S phase arrest).
- E2F DNA-binding activity assays.
- Reporter construct transcription assays.
- Western blotting for E2F and pRb levels.
- Gel-shift assays to identify E2F complexes.
Main Results:
- TGF-beta1 treatment arrested over 90% of HuH-7 cells in G1 phase.
- A significant increase in E2F DNA-binding activity and transcription was observed.
- Overexpression of pRb partially inhibited the increased E2F activity.
- TGF-beta1 induced apoptosis in both G1 and S phases, irrespective of E2F activity.
- Removal of TGF-beta1 allowed cells to re-enter the cell cycle, with 33% undergoing apoptosis within 72 hours.
Conclusions:
- TGF-beta1-induced apoptosis in HuH-7 cells is linked to increased E2F transcription factor activity.
- pRb plays a partial inhibitory role in TGF-beta1-induced E2F activation.
- The preapoptotic state induced by TGF-beta1 is reversible, allowing cell cycle re-entry.