Role of core protein mutations in the development of occult HBV infection.
Occult hepatitis B virus (HBV) infection (OBI) is associated with transfusion-transmitted HBV infection and hepatocellular carcinoma. Studies on OBI genesis concentrated on mutations in the S region and the regulatory elements. The role of mutations in the core region of OBIs remains unclear.Here, 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.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 overall comparison between intracellular or extracellular viral protein production related to individual Cp mutants was measured with Western blot, chemiluminescent microparticle immunoassay, immunofluorescent staining or immunohistochemical staining indicated that W62R mutation in Cp had a critical impact on reduction of HBcAg and HBeAg production during HBV replication, while its combined mutations with P50H or/and S74G played a limited role in influencing viral protein production in vivo.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.