HCC-derived SNU cell lines as model systems to study HBV life cycle

Human SNU cell lines derived from hepatocellular carcinomas associated with chronic hepatitis B virus (HBV) infection were examined. The analysis of intracellular RNA and DNA markers of HBV replication and examination of HBV RNA reads coverage of selected regions on HBV-related RNAs and polyadenylation positions within HBV sequence using RNA-sequencing suggested absence of HBV replication in SNU-423, SNU-368 SNU-398, SNU-182, SNU-449, SNU-475, SNU-354, SNU-739 and SNU-387 cells, while SNU-761 and SNU-886 still could maintain residual HBV replication. The undetectable intracellular HBV core antigen (HBcAg) and absence of significant levels of secreted core-associated and virion-associated HBV DNA confirmed the absence or profound suppression of HBV replication in parental SNU cell lines. Various 5'-human-HBV-3' and 5'-HBV-human-3' RNAs transcribed from integrated HBV DNA were found in most of SNU cell lines. The 5'-HBV-human-3' junctions suggested that several SNU cell lines could generate 5'-HBV-human-3' RNAs encoding HBV envelope proteins. The known and novel spliced HBV RNAs were detected in SNU-886, SNU-739, SNU-387, SNU-761, and SNU-354 cells. At least some of them were generated independently of HBV replication. All SNU cell lines could not support efficient HBV replication after transfection with the vector initiating efficient HBV replication in Huh7 cells. This was reflected by three distinct accumulation patterns of HBV replication markers, undetectable intracellular HBcAg, and by the lack of considerable levels of secreted core-bound and virion-associated HBV DNA. Overall, SNU cell lines represent valuable model systems for detailed analysis of integrant-transcribed HBV RNAs, spliced HBV RNAs, and mechanisms of suppression of HBV genome replication.