Deregulated E2F-1 blocks terminal differentiation and loss of leukemogenicity of M1 myeloblastic leukemia cells without abrogating induction of p15(INK4B) and p16(INK4A).
The transcription factor E2F-1 has been postulated to play a crucial role in the control of cell cycle progression because of its ability to be bound and regulated by the retinoblastoma gene product (pRb). Exogenous expression of E2F-1, under growth restrictive conditions, was shown to result in p53-dependent programmed cell death. The consequences of deregulated expression of E2F-1 on terminal differentiation of hematopoietic cells in the absence of E2F-1-mediated apoptosis, as well as mechanistic insights into how deregulated E2F-1 may affect terminal differentiation, have not been established. The autonomously proliferating M1 myeloblastic leukemia cell line, which is null for p53 expression and can be induced by interleukin-6 (IL-6) to undergo terminal macrophage differentiation with concomitant loss of leukemogenicity, provides a particularly attractive model system to address these issues. Deregulated and continued expression of E2F-1 blocked the IL-6-induced terminal differentiation program at an early blast stage, giving rise to immature cells, which continued to proliferate without undergoing apoptosis and retained their leukemogenic phenotype. Although E2F-1 blocked IL-6-mediated terminal differentiation and its associated growth arrest, it did not prevent the rapid induction of both p15(INK4B) and p16(INK4A), inhibition of cdk4 kinase activity, and subsequent hypophosphorylation of pRb. The results obtained imply that genetic alterations that both impair p53 function and deregulate E2F-1 expression may render hematopoietic cells refractory to the induction of differentiation and are, thereby, likely to play a major role in the progression of leukemias. (Blood. 2000;96:475-482)
Amanullah
A
A
Fels Institute for Cancer Research and Molecular Biology and Department of Biochemistry, Temple University School of Medicine, Philadelphia, PA 19140, USA.
Hoffman
B
B
Liebermann
D A
DA
D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D002352:Carrier Proteins / Q000096:biosynthesis*; D018797:Cell Cycle Proteins; D002454:Cell Differentiation / Q000187:drug effects*; D002455:Cell Division / Q000187:drug effects; D050762:Cyclin-Dependent Kinase Inhibitor p15; D019941:Cyclin-Dependent Kinase Inhibitor p16; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D005786:Gene Expression Regulation; D015850:Interleukin-6 / Q000494:pharmacology; D015470:Leukemia, Myeloid, Acute / Q000378:metabolism / Q000473:pathology*; D051379:Mice; D008819:Mice, Nude; D009368:Neoplasm Transplantation; D011994:Recombinant Proteins / Q000494:pharmacology; D056465:Retinoblastoma-Binding Protein 1; D050680:Transcription Factor DP1; D014157:Transcription Factors / Q000235:genetics / Q000494:pharmacology*; D014407:Tumor Cells, Cultured; D025521:Tumor Suppressor Proteins
C533431:Arid4a protein, mouse; D002352:Carrier Proteins; C493968:Cdkn2b protein, mouse; D018797:Cell Cycle Proteins; D050762:Cyclin-Dependent Kinase Inhibitor p15; D019941:Cyclin-Dependent Kinase Inhibitor p16; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; C493754:E2f1 protein, mouse; D015850:Interleukin-6; D011994:Recombinant Proteins; D056465:Retinoblastoma-Binding Protein 1; D050680:Transcription Factor DP1; D014157:Transcription Factors; D025521:Tumor Suppressor Proteins