Abstract 2492: DNA polymerase beta participates in DNA end-joining

DNA double strand breaks (DSBs) are one of the most deleterious lesions. If left unrepaired, DSBs lead to genomic instability and carcinogenesis. The cells combat DSBs by two classical pathways that include homologous recombination (HR) which requires the sister chromatid for sequence homology, and non-homologous end-joining (NHEJ), wherein the two DNA ends are re-joined. Recently a back-up NHEJ pathway has been reported and is referred non-canonical NHEJ which has been given many names, such as alternative NHEJ or microhomology-mediated end joining (MMEJ). The enzymatic mechanisms of non-canonical NHEJ are not well defined. NHEJ requires processing enzymes including nucleases and polymerases, although the roles of these enzymes in the pathway are poorly understood. Recent studies have implicated a role for DNA polymerase theta (Pol θ), an A-family polymerase is essential for non-canonical NHEJ pathway. Emerging evidence indicates X-family polymerases, mammalian DNA polymerases lambda (λ) and mu (μ) and yeast Pol 4 promote DNA end-joining. Our laboratory has recently provided evidence for a role for DNA polymerase beta (Pol β), another X-family polymerase, in V(D)J recombination, a process that requires end-joining. Here, using a recently developed fluorescence based assay that monitors non-canonical NHEJ and HR, we provide evidence that Pol β plays a role in the non-canonical NHEJ process. DNA sequencing at the break point junctions revealed Pol β-depleted cells have fewer small deletions than control cells, but significantly greater numbers of insertions and large deletions. We further demonstrate that Pol β-depleted cells have increased sensitivity to DNA damaging agents that induce double-strand breaks and that there is persistent accumulation of DSBs in these cells. In combination, our results suggest that Pol β is critical for double-strand break repair. Citation Format: Sreerupa Ray, Michelle DeVeaux, Gregory Breuer, Ranjit Bindra, Daniel Zelterman, Joann Sweasy. DNA polymerase beta participates in DNA end-joining [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2492. doi:10.1158/1538-7445.AM2017-2492