Abstract
The oncoprotein MDM2 binds and inactivates p53. MDM2 also binds to the tumor suppressor pRB, as well as E2F-1. E2F-1 is a transcription factor that regulates S phase entry and has been shown to cause apoptosis in some cell types when overexpressed. To investigate the effect of adenovirus-mediated E2F-1 overexpression, MDM2-overexpressing tumor cell lines were treated by mock infection, infection with an adenoviral vector expressing beta galactosidase, or E2F-1 (Ad5CMV-E2F-1). Western blot analysis confirmed significant overexpression of E2F-1 in Ad5CMV-E2F-1-infected cells. E2F-1 overexpression resulted in marked growth inhibition and rapid loss of cell viability. Ad5CMV-E2F-1 infection resulted in early S phase entry, followed by apoptotic cell death. E2F-1 overexpression was associated with a marked decrease in MDM2 levels and no evidence of increased Bax levels, whereas p53 and Bcl-2 levels remained undetectable. Cleavage of poly-ADP-ribose polymerase and caspase 3/CPP32 implicated activation of the caspase cascade in E2F-1-mediated apoptosis. These results indicate that adenovirus-mediated E2F-1 overexpression in MDM2-overexpressing tumor cells results in decreased MDM2 expression and widespread apoptosis. Because MDM2-overexpressing tumors are often resistant to p53 gene therapy, adenovirus-mediated E2F-1 gene therapy may be a promising alternative strategy.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Adenoviridae / genetics*
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Animals
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Apoptosis*
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Blotting, Western
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Carrier Proteins*
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Caspase 3
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Caspases / metabolism
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Cell Cycle / genetics
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Cell Cycle Proteins*
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Cell Division / genetics
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Cell Line
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Cell Survival / genetics
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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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Gene Expression
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Gene Transfer Techniques
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Humans
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Mice
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Neoplasms, Experimental / genetics
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Neoplasms, Experimental / metabolism*
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Neoplasms, Experimental / pathology
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Nuclear Proteins*
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Proto-Oncogene Proteins / biosynthesis*
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Proto-Oncogene Proteins / metabolism
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Proto-Oncogene Proteins c-bcl-2 / metabolism
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Proto-Oncogene Proteins c-mdm2
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Retinoblastoma-Binding Protein 1
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Transcription Factor DP1
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Transcription Factors / biosynthesis
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Transcription Factors / genetics*
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Tumor Suppressor Protein p53 / biosynthesis
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bcl-2-Associated X Protein
Substances
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Arid4a protein, mouse
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BAX protein, human
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Bax protein, mouse
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Carrier Proteins
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Cell Cycle Proteins
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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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E2f1 protein, mouse
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Nuclear Proteins
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Proto-Oncogene Proteins
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Proto-Oncogene Proteins c-bcl-2
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Retinoblastoma-Binding Protein 1
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Transcription Factor DP1
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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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MDM2 protein, human
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Mdm2 protein, mouse
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Proto-Oncogene Proteins c-mdm2
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CASP3 protein, human
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Casp3 protein, mouse
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Caspase 3
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Caspases