Proteasomal degradation of core protein variants from chronic hepatitis B patients

Abstract

The accumulation of complex hepatitis B virus (HBV) variants with internal in-frame deletions in the C gene in immunosuppressed renal transplant recipients is associated with a severe course of the infection leading to end-stage liver disease (ESLD). A set of six HBV C genes with internal in-frame deletions corresponding to the pattern of HBV population in immunosuppressed patients has been expressed in two different eukaryotic cell lines. Synthesis and proteasomal degradation of HBV core (HBc) protein variants were compared with those of the wild-type HBc. In all cases, the steady-state level of internally deleted HBc proteins, predominantly with longer deletions, were considerably lower and turnover was significantly higher in comparison with those of the wild-type HBc, since all deletion variants were degraded rapidly via the proteasome pathway. Involvement and consequences of the proteasomal degradation machinery in the HBc protein turnover during HBV infection with complex HBV variants in the immunosuppressed patients are discussed.

Preparation by alkaline treatment and detailed characterisation of empty hepatitis B virus core particles for vaccine and gene therapy applications

“…Natural HBc molecules harbour only two lysine residues at positions 7 and 96 that are positioned on the external VLP surface at the base of the HBc spikes. Therefore, the CTD positive charge is ensured by the arginine, while the lysine residues play a specific role in HBc ubiquitination 65 . Although lysine never appears at the selected positions in naturally mutated HBc variants 6 17 , the incorporation of lysine residues at the fully conserved positions 75 and 79 and minimally variable positions 77 and 80 ( Fig.…”

Entecavir combined with furin inhibitor simultaneously reduces hepatitis B virus replication and e antigen secretion

“…In fact, cytosolic HBcAg and pre-HBe have been reported to be degraded in cellular ubiquitin-proteasome system [19–21]. However, the accumulation of truncated HBcAg by proteasome inhibitors [21] suggests that cytosolic HBcAg and pre-HBe are partially proteolyzed by some cellular proteases prior to proteasomal degradation.…”

“…In fact, cytosolic HBcAg and pre-HBe have been reported to be degraded in cellular ubiquitin-proteasome system [19–21]. However, the accumulation of truncated HBcAg by proteasome inhibitors [21] suggests that cytosolic HBcAg and pre-HBe are partially proteolyzed by some cellular proteases prior to proteasomal degradation. Cellular HBcAg existing as dimers in virion, nucleocapsids or capsids is usually resistant to proteases except for the protease-sensitive hinge (E 145 -D 153 , R 150 ) between the capsid assembly-competent and pregenomic RNA encapsidation-competent domains of HBcAg [22].…”

Design and Synthesis of Hepatitis B Virus (HBV) Capsid Assembly Modulators and Evaluation of Their Activity in Mammalian Cell Model

“…Previously, we developed and optimized the use of the recombinant alphavirus expression vector for HBc synthesis within 24 h [ 30 , 53 ], which cannot be achieved in HBV-producing cell cultures [ 32 ]. According to our protocol, there is a potential for the production of recombinant alphaviruses containing different HBV genotypes and HBc mutant variants, thus providing an opportunity to study the differences in the effects of capsid self-assembly inhibitors on different HBV genotypes and clinical mutants, allowing, to a large extent, individualized drug treatment testing.…”

“…Although capsid aggregates for Bay 41-4109 were not detected in BHK-21 cells, this does not mean that they do not occur. It was shown previously that non-assembled and defective HBc proteins in BHK-21 cells are rapidly degraded through the proteasomal pathway [ 53 ], this factor has no influence on in vitro capsid assembly experiments. The rate of degradation of the HBc aggregates may depend also on the amount and rate of aggregate formation or the nature of the aggregate structures themselves, suggesting different misdirecting assembly mechanisms compared with the reference compound Bay 41-4109.…”