TRF2/RAP1 and DNA-PK mediate a double protection against joining at telomeric ends.
DNA-dependent protein kinase (DNA-PK) is a double-strand breaks repair complex, the subunits of which (KU and DNA-PKcs) are paradoxically present at mammalian telomeres. Telomere fusion has been reported in cells lacking these proteins, raising two questions: how is DNA-PK prevented from initiating classical ligase IV (LIG4)-dependent non-homologous end-joining (C-NHEJ) at telomeres and how is the backup end-joining (EJ) activity (B-NHEJ) that operates at telomeres under conditions of C-NHEJ deficiency controlled? To address these questions, we have investigated EJ using plasmid substrates bearing double-stranded telomeric tracks and human cell extracts with variable C-NHEJ or B-NHEJ activity. We found that (1) TRF2/RAP1 prevents C-NHEJ-mediated end fusion at the initial DNA-PK end binding and activation step and (2) DNA-PK counteracts a potent LIG4-independent EJ mechanism. Thus, telomeres are protected against EJ by a lock with two bolts. These results account for observations with mammalian models and underline the importance of alternative non-classical EJ pathways for telomere fusions in cells.
Bombarde
Oriane
O
Institut de Pharmacologie et de Biologie Structurale, Toulouse, France.
Boby
Céline
C
Gomez
Dennis
D
Frit
Philippe
P
Giraud-Panis
Marie-Josèphe
MJ
Gilson
Eric
E
Salles
Bernard
B
Calsou
Patrick
P
D004247:DNA / Q000378:metabolism; D000072481:DNA Ligase ATP; D011088:DNA Ligases / Q000378:metabolism; D004260:DNA Repair; D051747:DNA-Activated Protein Kinase / Q000378:metabolism*; D042822:Genomic Instability; D006367:HeLa Cells; D006801:Humans; D000089804:Shelterin Complex; D016615:Telomere / Q000378:metabolism*; D034501:Telomere-Binding Proteins / Q000378:metabolism*; D035341:Telomeric Repeat Binding Protein 2 / Q000378:metabolism*
C000607893:LIG4 protein, human; D000089804:Shelterin Complex; C504753:TERF2 protein, human; C440809:TERF2IP protein, human; D034501:Telomere-Binding Proteins; D035341:Telomeric Repeat Binding Protein 2; D004247:DNA; D051747:DNA-Activated Protein Kinase; D011088:DNA Ligases; D000072481:DNA Ligase ATP
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