The HBV-producing cell line HepG2-4A5: a new in vitro system for studying the regulation of HBV replication and for screening anti-hepatitis B virus drugs.

All tissue culture systems for propagating HBV employed so far make use of tandemly arranged HBV genomes usually under the control of strong foreign promoters. Thus these systems are helpful for virus production but are of limited value in the investigation of the regulation of HBV replication or of the extent to which the expression of viral genes might be influenced by cellular signal transduction pathways. To overcome this barrier we established an HBV-producing cell line (HepG2-4A5) by stably transfecting HepG2 cells with a replication-competent, terminally redundant HBV plasmid (pSPT1.2 xHBV) that contains each of the four major HBV-ORFs only once and exclusively under the control of their own regulatory elements. HepG2-4A5 cells contain a single, nonrearranged, chromosomally integrated, replication-competent HBV genome. In the cytoplasm of HepG2-4A5 cells, all typical viral mRNAs were detectable, but no other viral transcripts were found. Furthermore, all viral gene products are synthesized in a balanced ratio, as close as possible to that found in an in vivo infection. Dane-like particles released from HepG2-4A5 cells were indistinguishable from virions synthesized in vivo, by all physical (electron microscopy, buoyant density) and biochemical (endogenous polymerase reaction, immunogenic behaviour) criteria. Because of the autologous genome organization in this system, the HepG2-4A5 cell line allows studies on the function of the HBV gene products with respect to their involvement in regulating HBV replication under conditions imitating as closely as possible the situation in vivo. Furthermore, this cell line might be a helpful tool in screening antiviral drugs and in studying their effect on regulating HBV replication.