Recurrent integration of domestic cat hepatitis B virus DNA near feline CCNE1 supports an oncogenic role in hepatocellular carcinoma in cats

Hepatitis B virus (HBV) is the major cause of hepatocellular carcinoma (HCC) in humans. Domestic cat hepatitis B virus (DCHBV) naturally infects cats worldwide, but the oncogenic potential of this hepadnavirus is unclear. We investigated whether DCHBV contributes to feline HCC. Feline liver biopsies diagnosed with HCC (cases) and lymphocytic cholangitis (controls) were tested for DCHBV DNA by PCR. DCHBV-positive HCCs were further characterised by in situ hybridisation (ISH), whole-genome sequencing (WGS) and phylogenetic analysis. Targeted capture sequencing was used to identify and map viral DNA integrations. DCHBV DNA was detected in 17/71 (23.9 %) HCCs versus 0/88 controls (P < 0.001). ISH confirmed hepatocyte-specific viral localization. Phylogenetic analysis placed six viruses in genotype A, and a seventh divergent virus in genotype B virus. Virus-host chimeric sequences, consistent with integration sites, were identified in 11/16 PCR-positive HCCs. Eight of the 11 integration sites were independently confirmed with WGS. Viral termini in integrated DCHBV sequences corresponded to double-stranded linear DNA, the substrate for HBV integration. Five unique DCHBV integrations fell within, or were adjacent to, the promoter of the feline homologue of proto-oncogene CCNE1, a recurrent target for HBV integration in human HCC. Our findings reveal a compelling association between DCHBV detection and HCC in cats. Critically, virus integration in DCHBV-associated HCC is described for the first time, supporting that, like HBV, DCHBV can promote hepatocarcinogenesis by insertional mutagenesis. Clarification of fundamental DCHBV virology in vitro, and the consequences of natural infection could advance disease-prevention strategies for feline and human patients.