Virus persistence in chronic hepatitis B patients is due to the sustaining level of covalently closed circular DNA (cccDNA) within the nuclei of infected hepatocytes. In this study, we used a modified 1.3-fold hepatitis B virus (HBV) genome, with a BclI genetic marker embedded in the redundancy region, to examine the transcriptional activity of cccDNA and the effect of the HBx protein on transcriptional regulation. After harvesting total RNA from transfected cells or stable lines, we specifically identified and monitored the transcripts from cccDNA by using reverse transcription-PCR (RT-PCR) combined with the restriction enzyme digestion method. In this approach, we have found that (i) RT-PCR combined with detection of the BclI marker is a highly specific method for distinguishing cccDNA-derived transcripts from the original integrated viral genome, (ii) the transcriptional ability of cccDNA was less efficient than that from the integrated viral genome, and (iii) the transcriptional activity of cccDNA was significantly regulated by the HBx protein, a potential transcription activator. In conclusion, we provided a tool with which to elucidate the transcriptional regulation of cccDNA and clarified the transcriptional regulation mechanism of HBx on cccDNA. The results obtained may be helpful in the development of a clinical intervention for patients with chronic HBV infections.
