E2F-1 and E2F-3 are functionally distinct in their ability to promote myeloid cell cycle progression and block granulocyte differentiation.
Interleukin 3 (IL-3)-dependent 32D.3 myeloid cells are an attractive model system for the analysis of hematopoietic cell growth, differentiation, and apoptosis. In these cells, E2F-3, E2F-4, and DP-1 are regulated by both IL-3 and granulocyte colony-stimulating factor (G-CSF), whereas E2F-1 was expressed at low levels and was not regulated by either cytokine. E2F-2 and E2F-5 were not detectable. To examine phenotypes associated with the loss of normal cell cycle regulation by pRb, we established E2F-1- and E2F-3-overexpressing cell lines. In contrast to E2F-1, E2F-3 overexpression did not accelerate apoptosis or promote S-phase entry in the absence of IL-3, demonstrating that they are not functionally redundant. In addition, when cells were cultured in G-CSF to stimulate granulocytic differentiation, E2F-1 overexpression overrode survival functions provided by G-CSF and serum and induced apoptosis. In contrast, cells overexpressing E2F-3 exhibited normal granulocytic differentiation. Bcl-2 coexpression blocked E2F-1-induced apoptosis in the presence of G-CSF. However, these cells were blocked in the granulocytic differentiation program at the metamyelocyte stage and remained dependent on G-CSF for continuous culture. Cells overexpressing both E2F-1 and Bcl-2 exhibited slowed but continuous cell cycling in the absence of IL-3 until they eventually succumbed to apoptosis. Therefore, E2F-1, but not E2F-3, can temporally replace the requirement for growth factors to promote cell cycle progression, and in terminally differentiating cells, this leads to a block in differentiation and induction of apoptosis.
Strom
D K
DK
Department of Biochemistry and the Vanderbilt Cancer Center, Vanderbilt University School of Medicine, Nashville, Tennessee 37232, USA.
Cleveland
J L
JL
Chellappan
S
S
Nip
J
J
Hiebert
S W
SW
D017209:Apoptosis; D002352:Carrier Proteins; D002453:Cell Cycle; D018797:Cell Cycle Proteins; D002454:Cell Differentiation; D002460:Cell Line; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D050703:E2F2 Transcription Factor; D050699:E2F3 Transcription Factor; D050704:E2F4 Transcription Factor; D050700:E2F5 Transcription Factor; D005786:Gene Expression Regulation / Q000187:drug effects; D016179:Granulocyte Colony-Stimulating Factor / Q000494:pharmacology; D006098:Granulocytes / Q000166:cytology* / Q000378:metabolism; D006801:Humans; D007377:Interleukin-3 / Q000494:pharmacology; D056465:Retinoblastoma-Binding Protein 1; D050680:Transcription Factor DP1; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014407:Tumor Cells, Cultured
D002352:Carrier Proteins; D018797:Cell Cycle Proteins; 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; C098319:E2F3 protein, human; D050704:E2F4 Transcription Factor; C493762:E2F4 protein, human; D050700:E2F5 Transcription Factor; D007377:Interleukin-3; D056465:Retinoblastoma-Binding Protein 1; C493735:TFDP1 protein, human; D050680:Transcription Factor DP1; D014157:Transcription Factors; D016179:Granulocyte Colony-Stimulating Factor