The alternative non-homologous end-joining (NHEJ) machinery facilitates several genomic rearrangements, some of which can lead to cellular transformation. This error-prone repair pathway is triggered upon telomere de-protection to promote the formation of deleterious chromosome end-to-end fusions1,2,3. Using next-generation sequencing technology, here we show that repair by alternative NHEJ yields non-TTAGGG nucleotide insertions at fusion breakpoints of dysfunctional telomeres. Investigating the enzymatic activity responsible for the random insertions enabled us to identify polymerase theta (Polθ; encoded by Polq in mice) as a crucial alternative NHEJ factor in mammalian cells. Polq inhibition suppresses alternative NHEJ at dysfunctional telomeres, and hinders chromosomal translocations at non-telomeric loci. In addition, we found that loss of Polq in mice results in increased rates of homology-directed repair, evident by recombination of dysfunctional telomeres and accumulation of RAD51 at double-stranded breaks. Lastly, we show that depletion of Polθ has a synergistic effect on cell survival in the absence of BRCA genes, suggesting that the inhibition of this mutagenic polymerase represents a valid therapeutic avenue for tumours carrying mutations in homology-directed repair genes.
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Sequence has been deposited with the BioProject database under accession PRJNA269507.
We thank T. de Lange, R. Greenberg, J. Shay, N. Shima, C. Cazaux and R. Wood for providing key reagents for this study. We are grateful to M. Ji, L. Walton Masters, A. Phillips, A. Pinzaru, F. Yeung, P. Tonzi and J. Wong for technical assistance. We thank S. Kabir and F. Lottersberger for critical reading of the manuscript. This work was supported by a grant from the Breast Cancer Alliance (A.S.), V-foundation (A.S.), Department of Defense Breast Cancer Research Program BC134020 (P.A.M.-G.), Pew-Stewart Scholars Award (A.S.), Pew Scholars Award (E.L.-D.), Novartis Advanced Discovery Institute (E.L.-D.), and a grant from the National Institutes of Health (NIH) AG038677 (E.L.-D.). The A.S. laboratory was supported by start-up funds from the Helen L. and Martin S. Kimmel Center for Stem Cell Biology. The K.M.M. laboratory was supported in part by start-up funds from the University of Texas at Austin and from the Cancer Prevention Research Institute of Texas (CPRIT, R116). K.M.M. is a CPRIT scholar.
Extended data figures
This file contains Supplementary Data including sequence analysis of telomere fusions using illumina technology and C‐NHEJ junction sequences.
About this article
Cellular and Molecular Life Sciences (2018)