Hepatitis B virus X protein partially substitutes for E1A transcriptional function during adenovirus infection

Lack of an in vitro culture system for human hepatitis B virus has hampered the ability to address fundamental questions regarding the viral life cycle and the effect of viral gene products during productive infection. To study the activity of HBV X protein (HBx) in the context of a viral infectious cycle, we provided HBx in trans during adenovirus infection of liver-derived cells. In hepatoma cells infected with adenovirus mutants deficient in expression of various E1A products, HBx was able to partially substitute for the transcriptional activation function of E1A. HBx also activated adenovirus replication, but to a lesser extent than the activation of transcription. Adenovirus genes transcribed by either RNA polymerase II or RNA polymerase III were activated by HBx during infection. These results suggest that HBx and E1A activate transcription by a similar mechanism and that this viral infection system will be useful for characterization of the functional activities of HBx.