Extrachromosomal circular DNA promotes inflammation and hepatocellular carcinoma development

Two decades after the initial report on increased micronuclei in human chronic liver disease (CLD) and hepatocellular carcinoma (HCC), their role in HCC development is still poorly understood. Here, we show that micronuclei in hepatocytes trigger a hepatic immune response and promote HCC development via an increased level of extrachromosomal circular DNA (eccDNA). Livers of a CLD model (Mcl1$^{Δhep}$ mice) show increased micronuclei and eccDNA levels. Circular sequencing confirms higher eccDNA levels in micronuclei compared to primary nuclei. The nuclei-segregated DNA fiber (NuSeF) assay we developed demonstrates that micronuclei are more susceptible to replication stress, exhibiting increased replication fork slowing. Comparing different murine liver disease models reveals that high eccDNA correlates with an increased tumor incidence. eccDNA is a strong immunostimulant and promotes a cross-talk between hepatocytes and immune cells through the cGAS-STING pathway. Deletion of Sting1 in Mcl1$^{Δhep}$ mice reduces immune cell chemotaxis and tumor incidence. Our findings suggest that eccDNA from micronuclei mediates inflammation-driven liver carcinogenesis in CLD.