Studies On The Mechanisms Of Enhanced Replicative Efficiency Of Hepatitis B Virus

Hepatitis B virus (HBV) infection has a broad clinical manifestations including asymptomatic carrier, acute hepatitis, chronic hepatitis, which may lead to cirrhosis and hepatocellular carcinoma. In the past decade , studies showed that aside from host immue responses, the biological characteristics of HBV strains also contributed to the pathogenesis of HBV infection. Enhanced replication could display enhanced virulence of HBV strains. In this study, naturally occurring HBV strains were used to study the mechanisms of enhanced replicative efficiency. This study not only would help for deep understanding the pathogenesis of HBV, but also could be informative for development of new anti-HBV therapeutic drugs.The first part of this study was based on two HBV strains with different replicative efficiency, which were isolated separately from the sera of two patients with chronic hepatitis. Strategies to generate chimeric genome by polymerase chain reaction and site-directed mutagenesis were employed for characterization of the functional domain responsible for different replication competence between these two HBV strains. Results showed that a single amino acid substitution from serine to proline in position 652 within the RT region of polymerase gene was responsible for such striking difference between these two HBV strains. Moreover, three dimensional analysis of RT region of HBV polymerase showed that amino acid substitution from proline to serine in position 652 could impair the polymerase activity. Therefore, the 652 amino acid in the polymerase protein is a newly identified functional site associated with enhanced replication. This finding can be used to develop new anti-HBV therapeutics drugs. In the second part of this study, full-length HBV genomes were collected from hepatocellular carcinoma (HCC) tissues to study their replicative efficiency. When isolates were collected from a patient who was an HBsAg positive asymptomatic carrier who developed HCC in four years, it was showed that full-length HBV isolated from the liver tissues of HCC patients exhibited higher replicative competence than those from the sera samples. In addition, it was also showed that 2.2Kb splicing variants of HBV in liver tissues could enhance the repliation of its full-length counterpart. Both enhanced replication of full-length HBV and the 2.2Kb splicing variants might contribute to the persistence of HBV infection which could be one of the factors involved in the high incidence of hepatocellular carcinoma in China.