Mammalian polymerase θ promotes alternative NHEJ and suppresses recombination

• Published in: Nature (London) Vol. 518; no. 7538; pp. 254 - 257
• Main Authors: Mateos-Gomez, Pedro A., Gong, Fade, Nair, Nidhi, Miller, Kyle M., Lazzerini-Denchi, Eros, Sfeir, Agnel
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 12-02-2015; Nature Publishing Group
• Subjects: 13; 13/106; 631/337/103/560; 631/337/1427/2122; 631/337/1427/2191; 631/337/151; Animals; Base Sequence; Cell Death - genetics; Cell Line; Chromosome Aberrations; Chromosomes, Mammalian - genetics; Chromosomes, Mammalian - metabolism; DNA Breaks, Double-Stranded; DNA End-Joining Repair; DNA Polymerase theta; DNA polymerases; DNA-Directed DNA Polymerase - deficiency; DNA-Directed DNA Polymerase - metabolism; Genes, BRCA1; Genes, BRCA2; Genetic recombination; HeLa Cells; Humanities and Social Sciences; Humans; letter; Mice; multidisciplinary; Physiological aspects; Poly (ADP-Ribose) Polymerase-1; Poly(ADP-ribose) Polymerases - genetics; Poly(ADP-ribose) Polymerases - metabolism; Protein research; Rad51 Recombinase - metabolism; Recombination, Genetic - genetics; Recombinational DNA Repair - genetics; Science; Telomere - genetics; Telomere - metabolism; Translocation, Genetic - genetics
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature14157

Next-generation sequencing technology is used to show that the error-prone polymerase θ (Polθ) is needed to promote alternative non-homologous end joining at telomeres, and during chromosomal translocations, while counteracting homologous recombination; inhibition of Polθ represents a potential therapeutic strategy for tumours that have mutations in homology-directed repair genes.
Polθ involved in alternative DNA repair
The error-prone non-homologous end joining (NHEJ) DNA repair pathway is used as an alternative when the error-free homologous recombination pathway is compromised, or is the pathway of choice in some cellular contexts, such as in the immune system. After broken ends are paired via microhomology, NHEJ depends on DNA synthesis, but the identity of the polymerase involved was unclear. Two studies, from the laboratories of Agnel Sfeir and Alan D'Andrea, now implicate the mammalian
POLQ
gene, encoding the error-prone polymerase Polθ, in this process. Sfeir and colleagues show that upon telomere deprotection, Polθ is needed to prevent alternative end joining at telomeres, and chromosomal translations at non-telomeric sequences. D'Andrea and colleagues focus on the role of Polθ in cancer cells, and show that in a homologous-recombination-deficient background, the absence of Polθ results in a synthetic lethality, suggesting a possible therapeutic approach.
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 fusions
1
,
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.