Topoisomerase IIIalpha is required for normal proliferation and telomere stability in alternative lengthening of telomeres.
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.
Temime-Smaali
Nassima
N
Laboratoire d'Onco-Pharmacologie, JE 2428, UFR de Pharmacie, Université de Reims Champagne-Ardenne, Reims, France.
Guittat
Lionel
L
Wenner
Thomas
T
Bayart
Emilie
E
Douarre
Céline
C
Gomez
Dennis
D
Giraud-Panis
Marie-Josèphe
MJ
Londono-Vallejo
Arturo
A
Gilson
Eric
E
Amor-Guéret
Mounira
M
Riou
Jean-François
JF
D000251:Adenosine Triphosphatases / Q000032:analysis / Q000378:metabolism; D000705:Anaphase; D002460:Cell Line; D049109:Cell Proliferation / Q000187:drug effects; D047369:Chromatin Immunoprecipitation; D043171:Chromosomal Instability / Q000235:genetics; D004265:DNA Helicases / Q000032:analysis / Q000378:metabolism; D004264:DNA Topoisomerases, Type I / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D009363:Neoplasm Proteins / Q000032:analysis / Q000378:metabolism; D009687:Nuclear Proteins / Q000032:analysis / Q000378:metabolism; D000071156:Promyelocytic Leukemia Protein; D021122:Protein Subunits / Q000032:analysis / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics / Q000494:pharmacology; D053484:RecQ Helicases; D000089804:Shelterin Complex; D016615:Telomere / Q000378:metabolism* / Q000648:ultrastructure*; D034501:Telomere-Binding Proteins / Q000032:analysis / Q000378:metabolism; D035341:Telomeric Repeat Binding Protein 2 / Q000032:analysis / Q000378:metabolism; D014157:Transcription Factors / Q000032:analysis / Q000378:metabolism; D025521:Tumor Suppressor Proteins / Q000032:analysis / Q000378:metabolism
D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D000071156:Promyelocytic Leukemia Protein; D021122:Protein Subunits; D034741:RNA, Small Interfering; D000089804:Shelterin Complex; C504753:TERF2 protein, human; D034501:Telomere-Binding Proteins; D035341:Telomeric Repeat Binding Protein 2; D014157:Transcription Factors; D025521:Tumor Suppressor Proteins; C070576:PML protein, human; D000251:Adenosine Triphosphatases; C097151:Bloom syndrome protein; D004265:DNA Helicases; D053484:RecQ Helicases; D004264:DNA Topoisomerases, Type I