DNA-PK and the TRF2 iDDR inhibit MRN-initiated resection at leading-end telomeres.

Logan R Myler, Beatrice Toia, Cara K Vaughan, Kaori Takai, Andreea M Matei, Peng Wu, Tanya T Paull, Titia de Lange, Francisca Lottersberger

Nature structural & molecular biology 2023 Sep

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Telomeres replicated by leading-strand synthesis lack the 3' overhang required for telomere protection. Surprisingly, resection of these blunt telomeres is initiated by the telomere-specific 5' exonuclease Apollo rather than the Mre11-Rad50-Nbs1 (MRN) complex, the nuclease that acts at DNA breaks. Without Apollo, leading-end telomeres undergo fusion, which, as demonstrated here, is mediated by alternative end joining. Here, we show that DNA-PK and TRF2 coordinate the repression of MRN at blunt mouse telomeres. DNA-PK represses an MRN-dependent long-range resection, while the endonuclease activity of MRN-CtIP, which could cleave DNA-PK off of blunt telomere ends, is inhibited in vitro and in vivo by the iDDR of TRF2. AlphaFold-Multimer predicts a conserved association of the iDDR with Rad50, potentially interfering with CtIP binding and MRN endonuclease activation. We propose that repression of MRN-mediated resection is a conserved aspect of telomere maintenance and represents an ancient feature of DNA-PK and the iDDR. © 2023. The Author(s).

Citation

Logan R Myler, Beatrice Toia, Cara K Vaughan, Kaori Takai, Andreea M Matei, Peng Wu, Tanya T Paull, Titia de Lange, Francisca Lottersberger. DNA-PK and the TRF2 iDDR inhibit MRN-initiated resection at leading-end telomeres. Nature structural & molecular biology. 2023 Sep;30(9):1346-1356