Abstract C52: Induction of homologous recombination by DNA nicks

Abstract

Abstract Homologous recombination (HR) is a major mechanism of DNA repair, such that mutations in HR genes are associated with tumor susceptibility. We have used a recently adapted system for genome engineering to study HR mechanisms in mammalian cells. Clustered regularly-interspaced short palindromic repeats (CRISPR) are prokaryotic adaptive immune systems that specifically cleave nucleic acids of invading pathogens. The effector phase of CRISPR system in Staphylococcus pyogenes consists of two main components, the endonuclease Cas9 and RNA strands that dictate the recognition sequence cleaved by Cas9. The activity of Cas9 resides in 2 nucleolytic domains, HNH-like and RuvC1-like, such that mutating the active site of either of these domains turns Cas9 into a DNA nicking enzyme. Here we applied the commonly used DR-GFP HR reporter to investigate the repair of both DNA double-strand breaks (DSBs) and nicks induced by Cas9 in human cells. We show that a DSB, introduced by wild-type (wt) Cas9 and a guide RNA (gRNA) directed to the I-SceI site of the DR-GFP reporter, induces HR at levels similar to the I-SceI endonuclease, demonstrating the robustness of the system and confirming the potential of the CRISPR system as a genome engineering tool. Cas9 with mutations in either of the nucleolytic domains also stimulates HR, albeit at much lower levels, suggesting that a nick can also be repaired by HR. Stimulation of HR by DNA nicks is not reduced by PARP inhibition and has the same genetic requirements as DSB-induced HR. Given that SSBs are induced by endogenous DNA metabolic processes as well as by many anti-cancer treatments, our results may advance the understanding of mechanisms responsible for repair of these abundant DNA lesions. Citation Format: Lianne E.M. Vriend, Przemek M. Krawczyk, Maria Jasin. Induction of homologous recombination by DNA nicks. [abstract]. In: Proceedings of the Third AACR International Conference on Frontiers in Basic Cancer Research; Sep 18-22, 2013; National Harbor, MD. Philadelphia (PA): AACR; Cancer Res 2013;73(19 Suppl):Abstract nr C52.