Abstract
E2F-1 is capable of promoting both cell cycle progression and apoptosis. The latter is important for suppressing untoward expansion of proliferating cells. In this study, we investigated its underlying mechanisms. E2F-1-induced apoptosis was accompanied by caspase-9 activation and inhibited by a specific inhibitor of caspase-9 in K562 sublines overexpressing E2F-1. E2F-1 enhanced the expression of Apaf-1 without the cytosolic accumulation of cytochrome c. Apaf-1-deficient melanoma cell lines were resistant to E2F-1, indicating that Apaf-1 is an essential element of E2F-1-mediated apoptosis. Finally, we isolated the promoter region of the Apaf-1 gene and found a putative binding site for E2F. A chromatin immunoprecipitation assay revealed that E2F-1 bound to Apaf-1 promoter upon E2F-1 overexpression, suggesting that Apaf-1 is under transcriptional regulation of E2F-1. These data demonstrate a novel mechanism of apoptosis in which an increase in Apaf-1 levels results in direct activation of caspase-9 without mitochondrial damage, leading to the initiation of a caspase cascade.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Apoptosis*
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Apoptotic Protease-Activating Factor 1
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Base Sequence
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Binding Sites
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Blotting, Northern
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Caspase 3
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Caspase 6
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Caspase 9
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Caspases / metabolism
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Cell Cycle Proteins*
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Cell Line
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Chromatin / metabolism
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CpG Islands
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Cytosol / metabolism
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DNA-Binding Proteins*
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E2F Transcription Factors
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E2F1 Transcription Factor
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Enzyme Activation
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Flow Cytometry
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Gene Expression Regulation
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Humans
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Immunoblotting
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K562 Cells
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Membrane Potentials
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Microscopy, Confocal
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Microscopy, Fluorescence
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Mitochondria / metabolism
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Molecular Sequence Data
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Plasmids / metabolism
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Precipitin Tests
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Promoter Regions, Genetic
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Protein Binding
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Proteins / metabolism*
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Proteins / physiology*
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Proto-Oncogene Proteins / metabolism
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Proto-Oncogene Proteins c-bcl-2*
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Time Factors
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Transcription Factors / metabolism*
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Transcription, Genetic
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Transfection
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Tumor Cells, Cultured
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Tumor Suppressor Protein p53 / metabolism
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Up-Regulation
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bcl-2-Associated X Protein
Substances
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APAF1 protein, human
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Apoptotic Protease-Activating Factor 1
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Cell Cycle Proteins
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Chromatin
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DNA-Binding Proteins
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E2F Transcription Factors
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E2F1 Transcription Factor
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E2F1 protein, human
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Proteins
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Proto-Oncogene Proteins
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Proto-Oncogene Proteins c-bcl-2
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Transcription Factors
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Tumor Suppressor Protein p53
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bcl-2-Associated X Protein
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CASP3 protein, human
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CASP6 protein, human
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CASP9 protein, human
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Caspase 3
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Caspase 6
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Caspase 9
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Caspases