Abstract 1415: SAN1: a novel senataxin associated nuclease required for the repair of interstrand crosslinks
Authors: Andrews Alex , Macara Ian 
Published: July 2017

Abstract
The DNA damage response (DDR) is a set of complex signaling pathways capable of sensing DNA damage, and activating a large number of enzymes involved in the remodeling and repair of the genome. Mutations in the genes involved in the DDR lead to DNA damage, genomic instability, and various cancers. One particularly dangerous type of DNA damage that can occur is an interstrand crosslink (ICL). ICLs can lead to the development of double strand breaks through the blockage of DNA replication and transcription. Although ICLs can arise endogenously from molecules such as aldehydes, most commonly they are induced from chemotherapeutic drugs such as Cisplatin and Mitomycin C (MMC). These drugs are commonly used in the treatment of breast and ovarian cancers. A better understanding of which proteins are involved in the repair of ICLs is critical for understanding resistance, toxicity, and response in patients treated with ICL inducing agents. The repair of ICLs requires the coordination of several DNA repair pathways including the Fanconi Anemia pathway, homologous recombination (HR), and nucleotide excision repair (NER). The Fanconi Anemia pathway is essential for the repair of these lesions as it is responsible for the recognition of the ICL lesion, as well as the recruitment of several nucleases responsible for unhooking and removal the cross-linked nucleotides. Recently, we identified an uncharacterized 5’ nuclease that interacts with the RNA/DNA helicase Senataxin, which we have named senataxin-associated nuclease 1 (SAN1). Senataxin has been shown to act on R loops, RNA/DNA hybrids that are a source of endogenous DNA damage. Deletion of the SAN1 gene in HeLa cells or in mouse embryonic fibroblasts leads to the sensitization of cells to Cisplatin and Mitomycin C (MMC), but not to ionizing radiation that induces double strand breaks. Importantly, the defect in ICL repair can be restored using WT SAN1 but not with a mutant that is catalytically inactive. Treatment of SAN1 -/- HeLa cells with MMC also leads to radial chromosome formation, a characteristic of cells deficient in ICL repair. Additionally, SAN1 partially colocalizes with Fancd2 MMC induced foci, and treatment with MMC results in increased DNA damage and R loops in SAN1-/- cells. In conclusion, this study highlights the discovery of a novel nuclease involved in the repair ICLs, a process critical for understanding resistance and response to chemotherapies such as Cisplatin and MMC. Future work is aimed at determining the specific step of ICL repair that SAN1 participates in, how and when during repair SAN1 is recruited to ICL sites, and which other DNA repair proteins SAN1 functions with.
Citation Format: Alex Andrews, Ian Macara. SAN1: a novel senataxin associated nuclease required for the repair of interstrand crosslinks [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 1415. doi:10.1158/1538-7445.AM2017-1415