The chimeric E2A-HLF transcription factor abrogates p53-induced apoptosis in myeloid leukemia cells.
Leukemic lymphoblasts expressing the E2A-HLF oncoprotein possess wild-type p53 genes, but do not undergo apoptosis in response to DNA damage. Experimentally, E2A-HLF prevents apoptosis due to growth factor deprivation or gamma-irradiation in interleukin-3 (IL-3)-dependent murine pro-B cells. To directly test the chimeric protein's ability to abrogate p53-mediated cell death, we used mouse myeloid leukemia cells (M1p53tsval) that constitutively express a temperature-sensitive (ts) mutant p53 gene and undergo apoptosis when p53 assumes an active wild-type configuration. This effect is blocked by treatment with IL-6, which allows the cells to survive in culture despite wild-type p53 activation. We introduced E2A-HLF into M1p53tsval cells and found that they were resistant to p53-mediated apoptosis and that E2A-HLF effectively substituted for the survival functions of IL-6. The expression of p53-responsive genes such as p21 and Bax was upregulated normally, suggesting that E2A-HLF acts downstream of p53 to block execution of the p53-induced apoptotic program. NFIL3, a growth factor-regulated bZIP protein that binds to the same DNA-consensus site as E2A-HLF, delays apoptosis in IL-3-dependent pro-B cells deprived of growth factor. By contrast, in the present study, enforced expression of NFIL3 failed to protect M1p53tsval cells from p53-dependent apoptosis and actively antagonized the ability of IL-6 to rescue cells from that fate, consistent with its role as either a transcriptional repressor or activator, depending on the cell type in which it is expressed. We conclude that the E2A-HLF chimera abrogates p53-induced apoptosis in leukemic cells, possibly through the transcriptional modulation of cell death pathways that are activated by p53 in response to DNA damage.
Altura
R A
RA
Department of Experimental Oncology, St Jude Children's Research Hospital, Memphis, TN 38105-2794, USA.
Inukai
T
T
Ashmun
R A
RA
Zambetti
G P
GP
Roussel
M F
MF
Look
A T
AT
D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D050976:Basic-Leucine Zipper Transcription Factors; D001665:Binding Sites; D016384:Consensus Sequence; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000096:biosynthesis / Q000235:genetics; D004249:DNA Damage; D004273:DNA, Neoplasm / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000502:physiology*; D051790:G-Box Binding Factors; D015973:Gene Expression Regulation, Leukemic; D016158:Genes, p53; D015850:Interleukin-6 / Q000494:pharmacology; D007951:Leukemia, Myeloid / Q000473:pathology*; D051379:Mice; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors / Q000502:physiology*; D015514:Oncogene Proteins, Fusion / Q000502:physiology*; D011485:Protein Binding; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis / Q000235:genetics; D019253:Proto-Oncogene Proteins c-bcl-2; D011993:Recombinant Fusion Proteins / Q000502:physiology; D013696:Temperature; D014157:Transcription Factors / Q000502:physiology; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000037:antagonists & inhibitors* / Q000235:genetics; D051028:bcl-2-Associated X Protein
D050976:Basic-Leucine Zipper Transcription Factors; C494827:Bax protein, mouse; C493957:Cdkn1a protein, mouse; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D004273:DNA, Neoplasm; D004268:DNA-Binding Proteins; C489626:E2a-Hlf fusion protein, mouse; D051790:G-Box Binding Factors; D015850:Interleukin-6; D009363:Neoplasm Proteins; C497441:Nfil3 protein, mouse; D015514:Oncogene Proteins, Fusion; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; D016159:Tumor Suppressor Protein p53; D051028:bcl-2-Associated X Protein