CDC25A phosphatase is a target of E2F and is required for efficient E2F-induced S phase.
Functional inactivation of the pRB pathway is a very frequent event in human cancer, resulting in deregulated activity of the E2F transcription factors. To understand the functional role of the E2Fs in cell proliferation, we have developed cell lines expressing E2F-1, E2F-2, and E2F-3 fused to the estrogen receptor ligand binding domain (ER). In this study, we demonstrated that activation of all three E2Fs could relieve the mitogen requirement for entry into S phase in Rat1 fibroblasts and that E2F activity leads to a shortening of the G(0)-G(1) phase of the cell cycle by 6 to 7 h. In contrast to the current assumption that E2F-1 is the only E2F capable of inducing apoptosis, we showed that deregulated E2F-2 and E2F-3 activities also result in apoptosis. Using the ERE2F-expressing cell lines, we demonstrated that several genes containing E2F DNA binding sites are efficiently induced by the E2Fs in the absence of protein synthesis. Furthermore, CDC25A is defined as a novel E2F target whose expression can be directly regulated by E2F-1. Data showing that CDC25A is an essential target for E2F-1, since its activity is required for efficient induction of S phase by E2F-1, are provided. Finally, our results show that expression of two E2F target genes, namely CDC25A and cyclin E, is sufficient to induce entry into S phase in quiescent fibroblasts. Taken together, our results provide an important step in defining how E2F activity leads to deregulated proliferation.
Vigo
E
E
Department of Experimental Oncology, European Institute of Oncology, 20141 Milan, Italy.
Müller
H
H
Prosperini
E
E
Hateboer
G
G
Cartwright
P
P
Moroni
M C
MC
Helin
K
K
D000818:Animals; D017209:Apoptosis; D001483:Base Sequence; D001665:Binding Sites; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D002455:Cell Division; D002460:Cell Line; D019927:Cyclin E / Q000378:metabolism; D017931:DNA Primers / Q000235:genetics; D018076:DNA, Complementary / Q000235:genetics; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D050703:E2F2 Transcription Factor; D050699:E2F3 Transcription Factor; D018390:Gene Targeting; D006801:Humans; D008954:Models, Biological; D008969:Molecular Sequence Data; D017027:Protein Tyrosine Phosphatases / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D016160:Retinoblastoma Protein / Q000378:metabolism; D056465:Retinoblastoma-Binding Protein 1; D016196:S Phase / Q000502:physiology*; D050680:Transcription Factor DP1; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D020687:cdc25 Phosphatases
D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D019927:Cyclin E; D017931:DNA Primers; D018076:DNA, Complementary; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; C493753:E2F1 protein, human; D050703:E2F2 Transcription Factor; C493761:E2F2 protein, human; D050699:E2F3 Transcription Factor; C493755:E2f1 protein, rat; D011993:Recombinant Fusion Proteins; D016160:Retinoblastoma Protein; D056465:Retinoblastoma-Binding Protein 1; D050680:Transcription Factor DP1; D014157:Transcription Factors; C517004:CDC25A protein, human; C517007:Cdc25a protein, rat; D017027:Protein Tyrosine Phosphatases; D020687:cdc25 Phosphatases