Abstract
Topoisomerase (Topo) IIIalpha associates with BLM helicase, which is proposed to be important in the alternative lengthening of telomeres (ALT) pathway that allows telomere recombination in the absence of telomerase. Here, we show that human Topo IIIalpha colocalizes with telomeric proteins at ALT-associated promyelocytic bodies from ALT cells. In these cells, Topo IIIalpha immunoprecipitated with telomere binding protein (TRF) 2 and BLM and was shown to be associated with telomeric DNA by chromatin immunoprecipitation, suggesting that these proteins form a complex at telomere sequences. Topo IIIalpha depletion by small interfering RNA reduced ALT cell survival, but did not affect telomerase-positive cell lines. Moreover, repression of Topo IIIalpha expression in ALT cells reduced the levels of TRF2 and BLM proteins, provoked a strong increase in the formation of anaphase bridges, induced the degradation of the G-overhang signal, and resulted in the appearance of DNA damage at telomeres. In contrast, telomere maintenance and TRF2 levels were unaffected in telomerase-positive cells. We conclude that Topo IIIalpha is an important telomere-associated factor, essential for telomere maintenance and chromosome stability in ALT cells, and speculate on its potential mechanistic function.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Adenosine Triphosphatases / analysis
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Adenosine Triphosphatases / metabolism
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Anaphase
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Cell Line
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Cell Proliferation / drug effects
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Chromatin Immunoprecipitation
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Chromosomal Instability* / genetics
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DNA Helicases / analysis
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DNA Helicases / metabolism
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DNA Topoisomerases, Type I / analysis
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DNA Topoisomerases, Type I / genetics
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DNA Topoisomerases, Type I / metabolism*
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Humans
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Neoplasm Proteins / analysis
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Neoplasm Proteins / metabolism
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Nuclear Proteins / analysis
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Nuclear Proteins / metabolism
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Promyelocytic Leukemia Protein
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Protein Subunits / analysis
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Protein Subunits / metabolism
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RNA, Small Interfering / genetics
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RNA, Small Interfering / pharmacology
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RecQ Helicases
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Shelterin Complex
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Telomere / metabolism*
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Telomere / ultrastructure*
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Telomere-Binding Proteins / analysis
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Telomere-Binding Proteins / metabolism
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Telomeric Repeat Binding Protein 2 / analysis
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Telomeric Repeat Binding Protein 2 / metabolism
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Transcription Factors / analysis
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Transcription Factors / metabolism
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Tumor Suppressor Proteins / analysis
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Tumor Suppressor Proteins / metabolism
Substances
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Neoplasm Proteins
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Nuclear Proteins
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Promyelocytic Leukemia Protein
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Protein Subunits
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RNA, Small Interfering
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Shelterin Complex
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TERF2 protein, human
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Telomere-Binding Proteins
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Telomeric Repeat Binding Protein 2
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Transcription Factors
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Tumor Suppressor Proteins
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PML protein, human
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Adenosine Triphosphatases
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Bloom syndrome protein
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DNA Helicases
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RecQ Helicases
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DNA Topoisomerases, Type I