Highlights
- •Amino acid (aa) substitutions in the core protein (Cp) of occult HBV infection (OBI) strains were identified.
- •An OBI mutant strain (SZA) carrying 9 aa substitutions in Cp was characterised in vitro (cells) and in vivo (mice).
- •The functional impact of individual aa substitutions in pHBV1.3-SZA Cp replicons was assessed in vitro and in vivo.
- •The Cp W62R mutation significantly reduced HBV protein production.
- •The Cp W62R and its combination mutations might contribute to the occurrence of OBI.
Background & Aims
Occult HBV infection (OBI) is associated with transfusion-transmitted HBV infection
and hepatocellular carcinoma. Studies on OBI genesis have concentrated on mutations
in the S region and the regulatory elements. Herein, we aimed to determine the role
of mutations in the core region on OBIs.
Methods
An OBI strain (SZA) carrying 9 amino acid (aa) substitutions in the core protein/capsid
(Cp) was selected by sequence alignment and Western blot analysis from 26 genotype
B OBI samples to extensively explore the impact of Cp mutations on viral antigen production
in vitro and in vivo.
Results
A large panel of 30 Cp replicons were generated by a replication-competent pHBV1.3
carrying SZA or wild-type (WT) Cp in a 1.3-fold over-length of HBV genome, in which
the various Cp mutants were individually introduced by repairing site mutations of
SZA-Cp or creating site mutations of WT-Cp by site-directed mutagenesis. The expression
of HBcAg, HBeAg, and HBsAg and viral RNA was quantified from individual SZA and WT
Cp mutant replicons in transfected Huh7 cells or infected mice, respectively. An analysis
of the effect of Cp mutants on intracellular or extracellular viral protein production
indicated that the W62R mutation in Cp had a critical impact on the reduction of HBcAg
and HBeAg production during HBV replication, whereas P50H and/or S74G mutations played
a limited role in influencing viral protein production in vivo.
Conclusions
W62R and its combination mutations in HBV Cp might massively affect HBcAg and HBeAg
production during viral replication, which, in turn, might contribute to the occurrence
of OBI.
Lay summary
Occult hepatitis B virus infections (OBIs) have been found to be associated with amino
acid mutations in the S region of the HBV, but the role of mutations in the core protein
(Cp) remains unclear. In this study, an OBI strain (SZA) carrying 9 amino acid substitutions
in Cp has been examined comprehensively in vitro and in vivo. The W62R mutation in Cp majorly reduces HBcAg and HBeAg production during HBV replication,
potentially contributing to the occurrence of OBI.
Graphical abstract
Graphical Abstract
Keywords
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Article info
Publication history
Published online: January 13, 2021
Accepted:
December 14,
2020
Received in revised form:
November 4,
2020
Received:
July 13,
2020
Footnotes
Author names in bold designate shared co-first authorship
Identification
Copyright
© 2021 European Association for the Study of the Liver. Published by Elsevier B.V. All rights reserved.
