Abstract
Cytotoxicity of the topoisomerase II (topoII) poison etoposide has been ascribed to the persistent covalent trapping of topoII in DNA cleavage complexes that become lethal as cells replicate their DNA. However, short term etoposide treatment also leads to subsequent cell death, suggesting that the lesions that lead to cytotoxicity arise rapidly and prior to the onset DNA replication. In the present study 1h treatment with 25muM etoposide was highly toxic and initiated a double-stranded DNA damage response as reflected by the recruitment of ATM, MDC1 and DNA-PKcs to gammaH2AX foci. While most DNA breaks were rapidly repaired upon withdrawal of the etoposide treatment, the repair machinery remained engaged in foci for at least 24h following withdrawal. TopoII siRNA ablation showed the etoposide toxicity and gammaH2AX response to correlate with the inability of the cell to correct topoIIalpha-initiated DNA damage. gammaH2AX induction was resistant to the inhibition of DNA replication and transcription, but was increased by pre-treatment with the histone deacetylase inhibitor trichostatin A. These results link the lethality of etoposide to the generation of persistent topoIIalpha-dependent DNA defects within topologically open chromatin domains.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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ATP Binding Cassette Transporter, Subfamily B, Member 1 / metabolism
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Antigens, Neoplasm / immunology*
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Antigens, Neoplasm / metabolism
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Antigens, Neoplasm / pharmacology
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Antineoplastic Agents, Phytogenic / therapeutic use*
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Apoptosis / drug effects
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Cell Cycle Proteins / drug effects
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Cell Cycle Proteins / metabolism
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Cell Survival / drug effects
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Cell Survival / physiology
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DNA / drug effects
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DNA Breaks, Double-Stranded / drug effects
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DNA Damage / drug effects*
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DNA Damage / genetics
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DNA Repair / drug effects
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DNA Repair / genetics*
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DNA Replication / drug effects
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DNA Topoisomerases, Type II / metabolism
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DNA Topoisomerases, Type II / pharmacology*
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DNA-Binding Proteins / metabolism
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DNA-Binding Proteins / pharmacology*
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Drug Resistance, Neoplasm / drug effects
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Drug Resistance, Neoplasm / genetics
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Etoposide
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Flow Cytometry
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G2 Phase / drug effects
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G2 Phase / genetics
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Humans
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K562 Cells
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Promoter Regions, Genetic / drug effects
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Promoter Regions, Genetic / genetics
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Tumor Suppressor Proteins
Substances
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ATP Binding Cassette Transporter, Subfamily B, Member 1
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Antigens, Neoplasm
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Antineoplastic Agents, Phytogenic
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Cell Cycle Proteins
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DNA-Binding Proteins
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Tumor Suppressor Proteins
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Etoposide
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DNA
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DNA Topoisomerases, Type II