The molecular basis of E2F-1/DP-1-induced S-phase entry and apoptosis.
The transcription factor E2F plays a critical role in the G1 to S transition. E2F is a heterodimer formed by members of the E2F and DP families of DNA-binding proteins. Ectopic expression of E2F-1, the first member of the E2F family identified, is sufficient to cause quiescent cells to enter S phase. Thus, the biological significance of the interaction of E2F-1 with its DP protein partner, DP-1, was unclear. Here, we report on the role of DP-1 in the mediation of E2F-induced S-phase entry and apoptosis. Cells inducible for DP-1, E2F-1, or both were established and characterized. Ectopic expression of DP-1 alone fails to promote cell cycle entry, even when the potent transactivation domain of human papillomavirus-VP16 is fused to the DNA-binding domain of DP-1. In contrast, coexpression of DP-1 and E2F-1 results in greater loss of G1 regulation and significantly more apoptosis than does E2F-1 alone. Using clones co-inducible for DP-1 and E2F-1, expression of potential target genes of E2F activity that may account for its ability to induce S-phase entry was also examined. Induction of E2F-1/DP-1 resulted in increased expression and activity of cyclins A and E, as well as CDK2, prior to S-phase entry. Cyclin D and CDK4, however, were not induced. Phosphorylation of the retinoblastoma protein is also increased following induction of E2F-1/DP-1, suggesting that E2F can feed-back on the retinoblastoma protein, presumably through activation of cyclin A- and/or E-associated kinase activity.
Shan
B
B
Center for Molecular Medicine/Institute of Biotechnology, University of Texas Health Science Center at San Antonio 78245, USA.
Farmer
A A
AA
Lee
W H
WH
D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D002352:Carrier Proteins; D018797:Cell Cycle Proteins / Q000502:physiology*; D002999:Clone Cells; D016213:Cyclins / Q000502:physiology; D004268:DNA-Binding Proteins / Q000502:physiology*; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D005786:Gene Expression Regulation / Q000502:physiology; D027383:Papillomaviridae / Q000235:genetics; D010766:Phosphorylation; D017434:Protein Structure, Tertiary; D051381:Rats; D056465:Retinoblastoma-Binding Protein 1; D016196:S Phase / Q000502:physiology*; D050680:Transcription Factor DP1; D014157:Transcription Factors / Q000096:biosynthesis / Q000502:physiology*; D015533:Transcriptional Activation
D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D016213:Cyclins; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; C493755:E2f1 protein, rat; D056465:Retinoblastoma-Binding Protein 1; D050680:Transcription Factor DP1; D014157:Transcription Factors