Unveiling a Novel Mechanism of Oncovirus-Induced Carcinogenesis - ABSTRACT Seven well-established oncoviruses collectively contribute to approximately 12% of all human cancers. Chronic infection with the hepatitis B virus (HBV) alone is responsible for approximately 360,000 liver cancer cases per year worldwide. Unlike human papillomavirus (HPV), which promotes tumorigenesis through the provision of E6 and E7 oncogenes, the mechanisms underlying HBV-driven carcinogenesis remain incompletely understood. The integration of HBV sequences into the host genome is widely observed in HBV positive tumors, suggesting its oncogenic role. It is hypothesized that HBV integrations may directly alter the protein sequence or expression level of nearby genes and increase genome instability. We conducted long-read sequencing on HBV-positive tumors and cell lines to fully map HBV integrations. Surprisingly, we identified HBV integration-bridged chromosomal translocation events in all analyzed samples, indicating their frequent occurrence in HBV- positive tumors. These chromosomal structural variations may facilitate enhancer hijacking, bringing strong enhancers into proximity with oncogenes located in different chromosomes or topologically associating domains (TADs). Enhancer hijacking has been widely implicated in human cancer, but has not been connected to oncoviral integration. We propose that HBV integration-bridged chromosomal translocations lead to enhancer hijacking, contributing to the tumorigenesis of HBV-positive tumors. To test this hypothesis, we performed high-throughput chromosome conformation capture (HiC) on Tong and SNU761 cell lines to profile genome-wide DNA-DNA interactions. Our analysis revealed neo-TADs across HBV integration-bridged chromosomal translocations, affecting key cancer genes such as NRAS and ST3GAL1. In this study, we aim to validate these enhancer-hijacking events (Aim 1) and identify additional events in other cell lines (Aim 2). Our findings will unveil a novel mechanism of oncovirus-induced tumorigenesis. Furthermore, considering that agents disrupting enhancer function, such as BET and CDK inhibitors, have shown promising results in clinical trials for various cancers, our study may nominate these enhancer-targeting drugs for liver cancer treatment.
