Abstract 3168: Tumor cells express genome-derived DNA in the cytosol

Abstract Type I interferons (IFNs) are secreted by infected cells in response to the recognition of nucleic acids. DNA damage and the ensuing DNA damage response also induce the expression of IFNs by poorly understood mechanisms. Here we show the presence of extramitochondrial single-stranded (ss) and double-stranded (ds) DNA in the cytosol of mouse and human tumor cells. The DNA only partially co-localized with autophagosomes, stress granules or lysosomes, but a majority was associated with mitochondria. Genotoxic agents increased the amount of DNA in the cytosol of tumor cells with low levels of constitutive cytosolic DNA. Cloning of ssDNA and dsDNA present in the cytosol of mouse tumor cells showed that at least some of the cytosolic DNA is derived from unique genomic loci. Cloned cytosolic DNA sequences often contained genomic retroelements. In silico analysis of the cloned DNA indicated that cytosolic DNA is predicted to form putative triplex DNA structures. Overexpression of Rnaseh1, which degrades intermolecular triplex structures called R-loops, reduced the levels of cytosolic ssDNA and dsDNA, while overexpression of Trex1, the major 3’-5’ DNA exonuclease, decreased the amount of cytosolic ssDNA but not dsDNA. Upregulation of IFNs in response to genotoxic agents was impaired in cells expressing Rnaseh1 or Trex1. In summary, we provide evidence that DNA damage in tumor cells induces the accumulation of genomic DNA in the cytosol and the production of type I IFNs in many tumor cells, which may contribute to immunosurveillance of cancers. Citation Format: Yu J. Shen, Nina Le Bert, Christine XE Koo, Ho SW Samantha, Ken J. Ishii, David H. Raulet, Stephan Gasser. Tumor cells express genome-derived DNA in the cytosol. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3168. doi:10.1158/1538-7445.AM2014-3168