Abstract 2396: Widespread occurrence of extrachromosomal microDNAs in normal and cancerous vertebrate tissues and cell lines

Abstract

Abstract MicroDNAs are small (<400 base pairs in length) single- or double-stranded extrachromosomal circular DNAs that are derived by excision from tens of thousands of sites within the mammalian genome. Thus far, microDNAs have been detected in several mouse tissues, mouse and human cell lines, and both normal and malignant cells. Here, we examine the properties of microDNAs across ten tissue types (brain, heart, lung, liver, thymus, spleen, kidney, skeletal muscle, testis and sperm) from normal adult mice, chicken cell lines and human cancer cell lines. We observed microDNAs in all tissue types, originating from thousands of unique genomic loci. As was previously described, these microDNAs are small circles (100 to 400 base pairs), possess a high GC content and are enriched in genic regions. Hot spots of microDNA generation were noted across all tissue types and correlate with high gene density and GC content. Previously, we suggested that the release of microDNAs leaves behind microdeletions within the source genomic loci, resulting in somatically mosaic cells. Our results confirm this possibility by demonstrating that microDNAs are universally present across cell and tissue types in vertebrates. Interestingly, we found altered distribution patterns in the human cancer cell lines. In addition, short (2-15 bp) direct repeats that usually flank the genomic loci yielding microDNAs lead us to hypothesize that DNA damage repair pathways may be involved in microDNA generation. A survey of microDNAs in cell lines defective in proteins required for many DNA repair pathways revealed that the homologous recombination and non-homologous end joining pathways are dispensable for microDNA formation. However, deletion of two proteins, MSH3 and AID, resulted in a significant increase of microDNA originating from CpG islands. These observations combined with those in the cancer cell lines suggest that perturbation of normal cellular processes can alter the generation of microDNA. Citation Format: Laura Dillon, Pankaj Kumar, Yoshiyuki Shibata, Anindya Dutta. Widespread occurrence of extrachromosomal microDNAs in normal and cancerous vertebrate tissues and cell lines. [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 2396. doi:10.1158/1538-7445.AM2014-2396