Engineered extrachromosomal circular DNAs promote tumorigenesis (WGS)

Focal gene amplifications are among the most common cancer-associated mutations, but their evolution and contribution to tumorigenesis have proven challenging to recapitulate in primary cells and model organisms. Here we describe a general strategy to engineer large (>1 Mbp) focal amplifications mediated by extrachromosomal circular DNAs (ecDNAs) in a spatiotemporally controlled manner in cells and in genetically engineered mice. By coupling ecDNA formation with expression of selectable markers, we track the dynamics of ecDNA-containing cells under physiological conditions and in the presence of specific selective pressures. We also apply this approach to generate mice harboring Cre-inducible Myc- and Mdm2-containing ecDNAs analogous to those occurring in human cancers. We show that the engineered ecDNAs spontaneously accumulate in primary cells derived from these animals, promoting their proliferation, immortalization, and transformation. Finally, we demonstrate the ability of Mdm2-containing ecDNAs to promote tumor formation in an autochthonous mouse model of hepatocellular carcinoma. Control cells or cells harboring engineered ecDNAs were analyzed by shallow whole genome sequencing.