Expression of Hepatitis B Virus Core Antigen Gene Is Induced in Human Hepatoma Cells by Their Growth in Nude Mice

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Abstract
The human hepatoma cell line PLC/PRF/5 is persistently infected with hepatitis B virus. Cells cultured in vitro are known to produce the virus surface antigen but not the other structural virus proteins, the core and the e antigen. It is shown here that expression of the core antigen gene was inducible by growing the cells as a nude mouse tumor. The buoyant density in CsCl (1.31-1.32 g/ml) of core or e antigen produced in the tumors was very similar to that of virus core particles. Expression of the core antigen gene was shut off by culture in vitro of core or e antigen-producing nude mouse tumor cells and induced again by subsequent passage of cells in the nude mouse. The experimental system thus allows studies on the regulation of expression of the core antigen gene.