Modulation of Hepatitis B Virus Secretion by Naturally Occurring Mutations in the S Gene

Abstract

Alteration in hepatitis B virus (HBV) secretion efficiency may have pathological consequences. Naturally occurring mutations that regulate virion secretion have not been defined. We recently identified HBV genomes displaying high (4B), substantially reduced (3.4), or negative (4C) virion secretion. In the present study, the underlying mutations were mapped. A T552C point mutation in the 4B genome was responsible for its enhanced virion secretion, whereas a G510A mutation in 3.4 and G660C in 4C impaired virus secretion. The three point mutations generate M133T, G119E, and R169P substitutions in the S domains of viral envelope proteins, respectively, without modifying the coding capacity of the overlapping polymerase gene. The mutated residues are predicted to lie in the luminal side of the endoplasmic reticulum (ER) or to be embedded in the ER membrane and thus are not involved in contact with core particles during envelopment. Of the two mutations inhibitory of virion secretion, G510A greatly reduced small envelope protein (hepatitis B surface antigen [HBsAg]) levels both inside cells and in culture medium, whereas G660C specifically abolished HBsAg secretion. Surprisingly, a T484G mutation in the 4B genome, generating an I110M substitution in the S domain, could also reduce HBsAg secretion and block virion secretion. However, its inhibitory effect was suppressed in the 4B genome by the T552C mutation, the enhancer of virion secretion. T552C can also override the inhibitory G510A mutation, but not the G660C mutation. These findings suggest a hierarchy in the regulation of virion secretion and a close link between defective virion secretion and impaired HBsAg formation or secretion.

Selection of a Multiple Drug-Resistant Hepatitis B Virus Strain in a Liver-Transplanted Patient

“…101 to 163 of the S protein, including the "a" determinant (a.a. 124-147) which is the major target of neutralizing anti-HBs antibodies, due to its exposition at the surface of viral particles 23 . Surprisingly, sequencing of the S gene revealed on the baseline sample the presence of mutations in the immunodominant loop for many clones.…”

Frequency of hepatitis B virus ‘a’ determinant variants in unselected Spanish chronic carriers

“…Mutant HBV strains displaying amino-acid substitutions in the region known as the 'a' determinant of HBsAg can modify the antigenicity of the protein and may impair virion secretion and HBsAg formation [Chen et al, 2003;Shizuma et al, 2003;Khan et al, 2004], as well as the detection of the antigen by the routine diagnostic tests (Table I) [Wallace et al, 1994;Carman, 1997;Carman et al, 1997;Ireland et al, 2000;Hou et al, 2001;Allain, 2004]. Such mutants have also been reported in association with escape from vaccineinduced immunity [Oon et al, 1995;Carman, 1997;Ho et al, 1998;Chong-Jin et al, 1999;He et al, 2001;Lee et al, 2001;Seddigh-Tonekaboni et al, 2001] and with failures of therapy with specific immunoglobulin in newborns from carrier women and in liver-transplant recipients [Harrison et al, 1994;Oon et al, 1996Oon et al, , 2002Brind et al, 1997;Carman, 1997;Ngui et al, 1997;Protzer-Knolle et al, 1998;Santantonio et al, 1999;Roznovsky et al, 2000;Liu et al, 2002].…”

Point Mutations Upstream of Hepatitis B Virus Core Gene Affect DNA Replication at the Step of Core Protein Expression

“…Mutant constructs generated for this study are based on clone N4, which is a chimera between two naturally occurring core promoter mutants of the European subgroup of genotype A. Specifically, it contains the backbone of clone 3.4 with a 0.8-kb AvrIIEcoRV fragment derived from clone 4B (11,20). This construct maintains high replication capacity and efficient HBeAg expression as well as robust expression of HBsAg (hepatitis B surface antigen, viral envelope proteins) and secretion of virus particles.…”