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Exogenous E2F expression is growth inhibitory before, during, and after cellular transformation
1Department of Oncology, McArdle Laboratory for Cancer Research, University of Wisconsin Medical School, Madison 53706, USA.
Abstract:
To gain insight into the tumor suppressor properties of E2F1, we investigated growth inhibition by the E2F family of transcription factors using a tissue culture model system. We first show that exogenous E2F expression causes an 80% decrease in NIH3T3 colony formation and activated c-Ha-Ras-mediated focus formation. Inhibition of Ras-mediated transformation was dependent upon E2F DNA binding activity but did not require amino- or carboxy-terminal E2F1 protein interaction domains. Because E2F upregulation has been suggested to be associated with a neoplastic phenotype, it was possible that increased E2F activity would not be inhibitory to previously transformed cells. However, we found that exogenous E2F was also inhibitory to growth of NIH3T3 cells previously transformed by Ras or Neu. Further characterization revealed that exogenous E2F expression is inhibitory at very early times after transfection, causing dramatic losses in transfected cell populations. Interestingly, those few cells which do establish appear to be unaffected by the overexpressed E2F. Therefore, we propose that increased E2F activity may only be tolerated in a subset of cells which have acquired specific alterations that are dominant over E2F-mediated growth inhibition.
Insights
E2F1 transcription factor expression significantly inhibits NIH3T3 cell growth and transformation. However, some cells with specific alterations can overcome this E2F1-mediated growth inhibition.
Area of Science:
- Molecular Biology
- Cell Biology
- Cancer Research
Background:
- The E2F family of transcription factors plays a crucial role in cell cycle regulation.
- Upregulation of E2F has been linked to neoplastic phenotypes, but its role as a tumor suppressor is under investigation.
Purpose of the Study:
- To investigate the tumor suppressor properties of E2F1.
- To determine the effect of exogenous E2F expression on cell growth and transformation in NIH3T3 cells.
Main Methods:
- Utilized a tissue culture model system (NIH3T3 cells).
- Assessed colony formation and focus formation assays.
- Investigated the role of E2F DNA binding activity and protein interaction domains.
Main Results:
- Exogenous E2F expression led to an 80% decrease in NIH3T3 colony formation and inhibited Ras-mediated focus formation.
- E2F's inhibitory effect was dependent on DNA binding but not specific protein domains.
- Exogenous E2F also inhibited the growth of pre-transformed NIH3T3 cells (Ras or Neu).
- Early transfection resulted in significant cell population loss, with a subset of cells eventually unaffected.
Conclusions:
- E2F1 exhibits tumor suppressor properties by inhibiting cell growth and transformation.
- Cells that acquire dominant alterations can evade E2F-mediated growth inhibition.
- Increased E2F activity may only be tolerated in cells with specific, dominant genetic changes.