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Multiple members of the E2F transcription factor family are the products of oncogenes
1Dana-Farber Cancer Institute, Boston, MA.
Abstract:
The retinoblastoma gene product (pRB) is a known tumor suppressor, capable of arresting growth in mid-to-late G1. Part of its growth suppression action arises from interaction(s) with one or more members of the E2F family of transcription factors. These proteins most likely contribute to progression from G0 to S phase in mammalian cells, and pRB binding most likely inhibits aspects of their suspected growth-promoting function. Given their growth-stimulating potential, we asked whether one or more E2F alleles can function as oncogenes. Uncloned pools of NIH 3T3 cells producing the pRB binding target E2F-1, E2F-2, or E2F-3 grew in semisolid medium. In addition, they grew to much higher saturation density than controls. From the study of cells producing selected E2F-1 mutant species, it appears that E2F DNA-binding function contributes to, and pRB/E2F binding suppresses, soft-agar growth. Thus, three E2F family members can act as oncogene products, suggesting that part of the normal role of pRB is to down-modulate this potential activity.
Insights
The retinoblastoma gene product (pRB) suppresses tumors by inhibiting E2F transcription factors. Three E2F members (E2F-1, E2F-2, E2F-3) can act as oncogenes, promoting cell growth.
Area of Science:
- Molecular Biology
- Cell Cycle Regulation
- Oncogenesis
Background:
- The retinoblastoma gene product (pRB) is a crucial tumor suppressor that halts cell cycle progression.
- pRB interacts with E2F transcription factors, which are implicated in cell cycle progression from G0 to S phase.
- E2F proteins are suspected to possess growth-promoting functions that are normally inhibited by pRB.
Purpose of the Study:
- To investigate whether E2F transcription factors can function as oncogenes.
- To determine if specific E2F family members (E2F-1, E2F-2, E2F-3) exhibit oncogenic properties.
- To elucidate the role of pRB binding and E2F DNA-binding in oncogenic transformation.
Main Methods:
- NIH 3T3 cells were engineered to produce E2F-1, E2F-2, or E2F-3.
- Cell growth in semisolid medium (soft agar) and saturation density were assessed.
- Mutant E2F-1 species were studied to analyze the contribution of DNA-binding and pRB interaction.
Main Results:
- NIH 3T3 cells expressing E2F-1, E2F-2, or E2F-3 demonstrated growth in soft agar.
- These cells also exhibited significantly higher saturation density compared to control cells.
- E2F DNA-binding activity was found to contribute to soft-agar growth, while pRB binding suppressed it.
Conclusions:
- Three members of the E2F family (E2F-1, E2F-2, E2F-3) possess oncogenic potential.
- The tumor suppressor pRB likely functions, in part, by down-modulating the oncogenic activity of E2F proteins.
- Understanding these interactions is key to comprehending tumor suppression and oncogenesis.