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Analysis of promoter binding by the E2F and pRB families in vivo: distinct E2F proteins mediate activation and
Y Takahashi1, J B Rayman, B D Dynlacht
1Harvard University, Department of Molecular and Cellular Biology, Cambridge, Massachusetts 02138, USA.
Abstract:
The E2F transcription factor plays a pivotal role in the timely activation of gene expression during mammalian cell cycle progression, whereas pRB and related proteins control cell growth in part through the ability to block the action of E2F. To identify physiologically important E2F-responsive promoters and to study their occupancy and histone acetylation state in vivo, we have taken advantage of a cross-linking approach in synchronized, living cells. We find that the pattern of E2F and pRB-related polypeptides recruited to these promoters changes in a strikingly dynamic fashion as cells progress from quiescence into G(1) and S phase: Repression of each promoter in quiescent cells is associated with recruitment of E2F-4 and p130 and low levels of histone acetylation, but by late G(1), these proteins are replaced largely by E2F-1 and E2F-3, in concert with acetylation of histones H3 and H4 and gene activation. These findings suggest that repression and activation of E2F-responsive genes may occur through distinct E2F heterodimers that direct the sequential recruitment of enzymes able to deacetylate and then acetylate core histones.
Insights
Cell cycle progression involves dynamic E2F transcription factor activity. Distinct E2F proteins and pRB family members regulate gene expression and histone acetylation during cell growth and division.
Area of Science:
- Molecular Biology
- Cell Biology
- Epigenetics
Background:
- E2F transcription factors are crucial for mammalian cell cycle gene expression.
- pRB proteins regulate cell growth by inhibiting E2F activity.
Purpose of the Study:
- To identify key E2F-responsive promoters.
- To investigate in vivo promoter occupancy and histone acetylation during the cell cycle.
Main Methods:
- Utilized a cross-linking approach in synchronized, living cells.
- Analyzed protein recruitment and histone acetylation patterns.
Main Results:
- Observed dynamic changes in E2F and pRB polypeptide recruitment during cell cycle progression (quiescence to G1/S phase).
- Quiescent cells showed E2F-4/p130 binding and low histone acetylation.
- Late G1 phase exhibited E2F-1/E2F-3 binding, H3/H4 acetylation, and gene activation.
Conclusions:
- Distinct E2F heterodimers mediate gene repression and activation.
- Sequential recruitment of enzymes for histone deacetylation and acetylation controls E2F-responsive genes.