Related Experiment Videos
Precore-mediated inhibition of hepatitis B virus progeny DNA synthesis
C Lamberts1, M Nassal, I Velhagen
1Angewandte Tumorvirologie, Deutsches Krebsforschungszentrum, Heidelberg, Germany.
Abstract:
The capacities to induce the synthesis of hepatitis B virus (HBV) unit-length DNA were compared for two HBV DNAs with an overall sequence diversity of about 10%. They had been cloned from serum (DNA2) and from a hepatocellular carcinoma (DNA4), respectively. As a major difference, DNA4 carries a translational stop signal preventing the synthesis of precore protein. Progeny DNA yields obtained after transfection with respective pregenome transcription units allocated DNA2 to a low-replicator and DNA4 to a high-replicator phenotype. Cotransfection of DNA2 interfered with progeny DNA synthesis induced by DNA4. By mutual exchange of restriction fragments, the region on the viral genome responsible for the differing replicator phenotypes was confined to a sequence comprising the 3'-terminal part of the X gene, core promoter, encapsidation signal epsilon, precore/core gene, and 5'-terminal part of the pol gene. Point mutations in DNA2 abolishing proper expression of the precore gene strongly enhanced the yield of progeny DNA, whereas cotransfection of a precore expression plasmid with DNA4 or with the mutated DNA2 substantially lowered the amount of progeny DNA. Hence, precore expression acts as an inhibitory principle for HBV replication. The same stop mutation as in DNA4 has been found to arise frequently in virus carriers. Loss of precore expression and concomitant conversion to a more severe hepatitis, as observed in the course of a chronic infection, thus can be explained by a relaxation of replication-level control.
Insights
Hepatitis B virus (HBV) replication is inhibited by precore protein expression. Loss of this expression, common in chronic infections, leads to increased viral DNA synthesis and potentially more severe hepatitis.
Area of Science:
- Virology
- Molecular Biology
- Hepatology
Background:
- Hepatitis B virus (HBV) replication is a complex process.
- Understanding the regulatory mechanisms of HBV DNA synthesis is crucial for managing chronic infections.
Purpose of the Study:
- To compare the replication capacities of two distinct HBV DNA sequences.
- To identify the viral genomic regions responsible for differential replication phenotypes.
- To elucidate the role of precore protein expression in regulating HBV replication.
Main Methods:
- Cloning and transfection of HBV DNA from serum and hepatocellular carcinoma.
- Comparative analysis of progeny DNA yields after transfection.
- Site-directed mutagenesis and cotransfection experiments to map regulatory regions.
- Analysis of precore protein expression effects on HBV replication.
Main Results:
- HBV DNA from hepatocellular carcinoma (DNA4) exhibited a higher replicator phenotype than HBV DNA from serum (DNA2).
- A specific genomic region, including the precore/core gene, was identified as responsible for differing replication phenotypes.
- Abolishing precore protein expression significantly enhanced HBV DNA yield, while precore expression inhibited replication.
Conclusions:
- Precore protein expression acts as a negative regulator of HBV replication.
- Loss of precore expression, due to mutations frequently observed in chronic carriers, can lead to uncontrolled viral replication.
- This mechanism explains the increased viral load and potential progression to severe hepatitis in chronic HBV infections.