Characterization of Hepatitis B Precore/Core-Related Antigens
Xupeng Hong 1 , Laurie Luckenbaugh 1 , Megan Mendenhall 1 , Renae Walsh 2 , Liza Cabuang 2 , Sally Soppe 2 , Peter Revill 2 , Dara Burdette 3 , Becket Feierbach 3 , William Delaney 3 , Jianming Hu 4
Affiliations
Affiliations
1
Department of Microbiology and Immunology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania, USA.
2
Victorian Infectious Diseases Reference Laboratory, Royal Melbourne Hospital at the Peter Doherty Institute for Infection and Immunity, Melbourne, Australia.
3
Gilead Sciences, Inc., Foster City, California, USA.
4
Department of Microbiology and Immunology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania, USA [email protected].
PMID: 33148795 DOI: 10.1128/JVI.01695-20
Abstract
Current therapies rarely cure chronic hepatitis B virus (HBV) infection due to the persistence of the viral episome, the covalently closed circular DNA (cccDNA), in hepatocytes. The hepatitis B core-related antigen (HBcrAg), a mixture of the viral precore/core gene products, has emerged as one potential marker to monitor the levels and activities of intrahepatic cccDNA. Here, a comprehensive characterization of precore/core gene products revealed that HBcrAg components included the classical hepatitis B core antigen (HBc) and e antigen (HBeAg), and additionally, the precore-related antigen, PreC, retaining the N-terminal signal peptide. Both HBeAg and PreC antigens displayed heterogeneous proteolytic processing at their C-terminus resulting in multiple species, which varied with viral genotypes. HBeAg was the predominant form of HBcrAg in HBeAg-positive patients. Positive correlations were found between HBcrAg and PreC, between HBcrAg and HBeAg, and between PreC and HBeAg, but not between HBcrAg and HBc. Serum HBeAg and PreC shared similar buoyant density and size distributions, and both displayed density and size heterogeneity. HBc, but not HBeAg or PreC antigens, was found as the main component of capsids in DNA-containing or empty virions. Neither HBeAg nor PreC proteins were able to form capsids in cells or in vitro under physiological conditions. In conclusion, our study provides important new quantitative information on levels of each component of precore/core gene products as well as their biochemical and biophysical characteristics, implying that each component may have distinct functions and applications in reflecting intrahepatic viral activities.IMPORTANCE Chronic hepatitis B virus (HBV) infection afflicts approximately 257 million people, who are at high risk of progressing to chronic liver diseases, including cirrhosis, fibrosis, and hepatocellular carcinoma. Current therapies rarely achieve cure of HBV due to the persistence of HBV episome, covalently closed circular DNA (cccDNA), in the nucleus of infected hepatocytes. Peripheral markers of cccDNA levels and transcriptional activities are urgently required to guide antiviral therapy and drug development. Serum hepatitis B core-related antigen (HBcrAg) is one such emerging peripheral marker. We have herein characterized the components of HBcrAg in HBV infected patients as well as in cell cultures. Our results provide important new quantitative information on levels of each HBcrAg component, as well as their biochemical and biophysical characteristics. Our findings further suggest that each HBcrAg component may have distinct functions and applications in reflecting intrahepatic viral activities.