Pre-S mutations of hepatitis B virus affect genome replication and expression of surface antigens

The N-Terminus Makes the Difference: Impact of Genotype-Specific Disparities in the N-Terminal Part of The Hepatitis B Virus Large Surface Protein on Morphogenesis of Viral and Subviral Particles

The N-terminus of the hepatitis B virus (HBV) large surface protein (LHB) differs with respect to genotypes. Compared to the amino terminus of genotype (Gt)D, in GtA, GtB and GtC, an additional identical 11 amino acids (aa) are found, while GtE and GtG share another similar 10 aa. Variants of GtB and GtC affecting this N-terminal part are associated with hepatoma formation. Deletion of these amino-terminal 11 aa in GtA reduces the amount of LHBs and changes subcellular accumulation (GtA-like pattern) to a dispersed distribution (GtD-like pattern). Vice versa, the fusion of the GtA-derived N-terminal 11 aa to GtD causes a GtA-like phenotype. However, insertion of the corresponding GtE-derived 10 aa to GtD has no effect. Deletion of these 11aa decreases filament size while neither the number of released viral genomes nor virion size and infectivity are affected. A negative regulatory element (aa 2–8) and a dominant positive regulatory element (aa 9–11) affecting the amount of LHBs were identified. The fusion of this motif to eGFP revealed that the effect on protein amount and subcellular distribution is not restricted to LHBs. These data identify a novel region in the N-terminus of LHBs affecting the amount and subcellular distribution of LHBs and identify release-promoting and -inhibiting aa residues within this motive.

Analysis of clinical characteristics and S gene sequences in chronic asymptomatic HBV carriers with low-level HBsAg

BACKGROUND

During the natural hepatitis B virus (HBV) infection process, some infected subjects are characterized by a sustained low serum HBV surface antigen (HBsAg) expression level. Most members in this population are chronic asymptomatic HBV carriers (ASCs). To elucidate the mechanism underlying low-level HBsAg expression in ASCs, we sequenced the HBV S gene in these patients to reveal specific sequence characteristics.

METHODS

Overall, 1308 cases of chronic ASCs were grouped according to their HBsAg serum expression levels (10 IU/mL). The clinical characteristics of the population were analysed in detail. The HBV S gene was sequenced from 276 ASC cases with low-level HBsAg expression. Additionally, 100 of 1032 ASC cases with high-level HBsAg expression were randomly selected for HBV S gene sequencing based on age matching according to the low-level HBsAg group. A comparative analysis was conducted with the HBV S gene sequences from ASCs with low HBsAg expression and the HBV reference S gene sequences from ASCs with high HBsAg expression.

RESULTS

The population with low-level HBsAg expression displayed the following primary clinical characteristics: mostly chronic asymptomatic HBV carriers, older age (mean age 55.09 years), HBsAg/anti-HBe/anti-HBc (core) positivity as the main serological pattern (97.1%), low HBV DNA replication (1.32 ± 1.60 log₁₀ IU/mL), a low HBV-DNA positive rate (45.65%) and primarily genotype B (82.54%) and serotype adw (84.13%). The comparative analysis of the HBV S gene sequences from ASCs with low-level HBsAg showed significant mutations (including co-mutations) on both sides of the main hydrophilic region (MHR).

CONCLUSION

Significant mutations in multiple regions and at multiple sites (including co-mutations) on both sides of the MHR may be one cause of the low HBsAg expression level in this population.

Sequence analysis of the Pre-S gene in chronic asymptomatic HBV carriers with low-level HBsAg

In a hepatitis B virus (HBV)-infected population, persistently low expression levels of serum HBV serum antigen (HBsAg) are present, particularly in chronic asymptomatic HBV carriers (ASCs). The present study sequenced the HBV Pre-S gene, and aimed to elucidate its features in ASCs with low HBsAg expression compared with in the established HBV Pre-S reference gene sequences from ASCs with high HBsAg expression. A total of 1,308 ASCs were grouped according to HBsAg serum levels (cut-off value, 10 IU/ml), and clinical characteristics were analyzed in detail. The HBV Pre-S gene was sequenced in 276 ASCs with low-level HBsAg; in addition, 100 of the remaining 1,032 ASCs with high-level HBsAg were randomly selected for HBV Pre-S gene sequencing on the basis of age matching with the low-level HBsAg group. Comparative analysis of the gene sequences from these groups was subsequently conducted. The major clinical features of the population with low-level HBsAg were as follows: Most were ASCs with chronic HBV infection; 97.1% were HBsAg/anti-HBe/anti-HBc-positive; 82.54% carried the B genotype; and 84.13% displayed the adw serotype. The results indicated that there were novel and meaningful mutations, including co-mutations, at numerous loci and sites in the Pre-S gene, as well as deletion mutations in the Pre-S2 gene. These mutations in the Pre-S1 and Pre-S2 gene frag ments accounted for 65.38% (68/104) of the 104 B genotype cases in the low-level HBsAg group and 90.91% (20/22) of the 22 C genotype cases in the low-level HBsAg group, respectively. In conclusion, Pre-S gene mutations may be associated with HBV replication defects, which may be the cause of the observed low expression levels of HBsAg.

Different pre-S deletion patterns and their association with hepatitis B virus genotypes

AIM

To investigate the associations of different types of pre-S deletions with hepatitis B virus (HBV) genotypes.

METHODS

The sequences of the pre-S region, basal core promoter (BCP) mutation, and precore (PC) mutation were examined through direct DNA sequencing or clonal analysis and sequencing in 273 HBV carriers, namely 55 asymptomatic carriers, 55 carriers with chronic hepatitis (CH), 55 with liver cirrhosis (LC), 53 with liver cirrhotic hepatocellular carcinoma (LC-HCC), and 55 with noncirrhotic HCC. A total of 126 HBV carriers (46.2%) harbored pre-S deletions. The DNA sequences of pre-S deletion mutants from 43 age-matched genotype B (HBV/B)-infected carriers and 43 age-matched genotype C (HBV/C)-infected carriers were further examined, aligned, and compared.

RESULTS

No significant difference was observed in the mean age distribution (P = 0.464), male sex (P = 0.805), viral load (P = 0.635), or BCP mutation (P = 0.117) between the HBV/B and HBV/C groups. However, the rate of PC mutation was significantly higher in the HBV/B-infected carriers than in the HBV/C-infected carriers (P = 0.003). Both genotypes exhibited a high rate of deletion in the C-terminal half of the pre-S1 region and N-terminus of the pre-S2 region (86.0% and 79.1% in the HBV/B group; 69.8% and 72.1% in the HBV/C group, respectively). Epitope mapping showed that deletion in several epitope sites was frequent in both genotypes, particularly pS1-BT and pS2-B2. Conversely, the rate of pS2-B1 deletion was significantly higher in the HBV/B group (72.1% vs 37.2%, P = 0.002), and the rate of pS2-T deletion was significantly higher in the HBV/C group (48.8% vs 25.6%, P = 0.044). Functional mapping showed that the rate of deletion in three functional sites (the nucleocapsid binding site, start codon of M, and site for viral secretion) located in the N-terminus of the pre-S2 region was significantly higher in the HBV/B group (P < 0.05). One type of N-terminus pre-S1 deletion mutant with deletion of the start codon of the L protein was frequently observed in the HBV/C group (20.9% vs 9.3%, P = 0.228), particularly in the LC patients (42.9% vs 12.5%). Different patterns of pre-S deletions were also found between the HBV/B and HBV/C groups according to different clinical outcomes. In CH patients, deletion in the site for polymerized human serum albumin was more frequent in the HBV/B group (88.9% vs 36.4%, P = 0.028). In the LC-HCC patients, the rate of deletion in the pre-S2 region was significantly higher in the HBV/B group than in the HBV/C group (P < 0.05).

CONCLUSION

HBV/B- and HBV/C-infected carriers exhibit different patterns of pre-S deletion, which may be associated with the progression of liver diseases.

Different pre-S deletion patterns and their association with hepatitis B virus genotypes

AIM

To investigate the associations of different types of pre-S deletions with hepatitis B virus (HBV) genotypes.

METHODS

The sequences of the pre-S region, basal core promoter (BCP) mutation, and precore (PC) mutation were examined through direct DNA sequencing or clonal analysis and sequencing in 273 HBV carriers, namely 55 asymptomatic carriers, 55 carriers with chronic hepatitis (CH), 55 with liver cirrhosis (LC), 53 with liver cirrhotic hepatocellular carcinoma (LC-HCC), and 55 with noncirrhotic HCC. A total of 126 HBV carriers (46.2%) harbored pre-S deletions. The DNA sequences of pre-S deletion mutants from 43 age-matched genotype B (HBV/B)-infected carriers and 43 age-matched genotype C (HBV/C)-infected carriers were further examined, aligned, and compared.

RESULTS

No significant difference was observed in the mean age distribution (P = 0.464), male sex (P = 0.805), viral load (P = 0.635), or BCP mutation (P = 0.117) between the HBV/B and HBV/C groups. However, the rate of PC mutation was significantly higher in the HBV/B-infected carriers than in the HBV/C-infected carriers (P = 0.003). Both genotypes exhibited a high rate of deletion in the C-terminal half of the pre-S1 region and N-terminus of the pre-S2 region (86.0% and 79.1% in the HBV/B group; 69.8% and 72.1% in the HBV/C group, respectively). Epitope mapping showed that deletion in several epitope sites was frequent in both genotypes, particularly pS1-BT and pS2-B2. Conversely, the rate of pS2-B1 deletion was significantly higher in the HBV/B group (72.1% vs 37.2%, P = 0.002), and the rate of pS2-T deletion was significantly higher in the HBV/C group (48.8% vs 25.6%, P = 0.044). Functional mapping showed that the rate of deletion in three functional sites (the nucleocapsid binding site, start codon of M, and site for viral secretion) located in the N-terminus of the pre-S2 region was significantly higher in the HBV/B group (P < 0.05). One type of N-terminus pre-S1 deletion mutant with deletion of the start codon of the L protein was frequently observed in the HBV/C group (20.9% vs 9.3%, P = 0.228), particularly in the LC patients (42.9% vs 12.5%). Different patterns of pre-S deletions were also found between the HBV/B and HBV/C groups according to different clinical outcomes. In CH patients, deletion in the site for polymerized human serum albumin was more frequent in the HBV/B group (88.9% vs 36.4%, P = 0.028). In the LC-HCC patients, the rate of deletion in the pre-S2 region was significantly higher in the HBV/B group than in the HBV/C group (P < 0.05).

CONCLUSION

HBV/B- and HBV/C-infected carriers exhibit different patterns of pre-S deletion, which may be associated with the progression of liver diseases.

Characterization of Novel Hepatitis B Virus PreS/S-Gene Mutations in a Patient with Occult Hepatitis B Virus Infection

Objective

The impact of hepatitis B virus (HBV) preS/S-gene mutations on occult HBV infection (OBI) is not fully understood. This study characterized multiple novel HBV preS/S-gene mutants obtained from an OBI patient.

Methods

PreS/S-gene mutants were analyzed by clonal sequencing. Viral replication and expression were analyzed by transfecting HBV genomic recombinants into HepG2 cells.

Results

Twenty-one preS/S-gene mutants were cloned from four sequential serum samples, including 13 mutants that were not previously documented: (1) sI/T126V+sG145R; (2) preS1 nt 3014−3198 deletion; (3) preS1 nt 3046−3177 deletion; (4) preS1 nt 3046−3177 deletion+s115−116 “INGTST” insertion; (5) preS1 nt 3046−3177 deletion+s115−116 “INGTST” insertion+sG145R; (6) preS1 nt 3115−3123 deletion+sQ129N; (7) preS1 nt 3115−3123 deletion+s126−127 “RPCMNCTI” insertion; (8) s115−116 “INGTST” insertion; (9) s115−116 “INGTST” insertion+sG145R; (10) s126−127 “RPCMNCTI” insertion; (11) preS1 nt 2848−2862 deletion+preS2 initiation codon M→I; (12) s122−123 “KSTGLCK” insertion+sQ129N; and (13) preS2 initiation codon M→I+s131−133TSM→NST. The proportion of preS1 nt 3046−3177 deletion and preS2 initiation codon M→I+s131−133TSM→NST mutants increased in the viral pool with prolonged disease. The 13 novel OBI-related mutants showed a 51.2−99.9% decrease in HBsAg levels compared with that of the wild type. Additional N-glycosylation-associated mutations, sQ129N and s131−133TSM→NST, but not s126−127 “RPCMNCTI,” greatly attenuated anti-HBs binding to HBsAg. Compared with the wild type, replication and surface antigen promoter II activity of the preS1 nt 3046−3177 deletion mutant decreased by 43.3% and 97.0%, respectively.

Conclusion

PreS/S-gene mutations may play coordinated roles in the presentation of OBI and might be associated with disease progression. This has implications for HBV diagnosis and vaccine improvement.

Characterization of hepatitis B virus surface antigen variability and impact on HBs antigen clearance under nucleos(t)ide analogue therapy

For hepatitis B virus (HBV)-related chronic infection under treatment by nucleos(t)ide analogues (NUCs), HBsAg clearance is the ultimate therapeutic goal but very infrequent. We investigated how HBV envelope protein variability could lead to differential HBsAg clearance on NUCs. For 12 HBV genotype D patients receiving NUCs, six resolvers (HBsAg clearance) were compared to six matched nonresolvers (HBsAg persistence). PreS/S amino acid (aa) sequences were analysed with bioinformatics to predict HBV envelope antigenicity and aa covariance. To enrich our analyses on very rare resolvers, these were compared with other HBV genotype D strains in three characterized clinical cohorts including common chronically infected patients. The sT125M+sP127T combination was observed in four nonresolvers of six, corroborated by aa covariance analysis, associated with a lower predicted antigenicity than sT125T+sP127P. Concordant features within this HBV key functional domain, at positions 125 and 127, were reported from two of the three comparative cohorts. In our hands, a lower ELISA reactivity of HBV-vaccinated mice sera was observed against the sT125M mutant. In the S gene, 56 aa changes in minor variants were detected in non-resolvers, mainly in the major hydrophilic region, vs 28 aa changes in resolvers. Molecular features in patients showing HBsAg persistence on NUCs argue in favour of a different aa pattern in the HBV S gene compared to those showing HBsAg clearance. In nonresolvers, a decrease in HBs 'a' determinant antigenicity and more frequent mutations in the S gene suggest a role for the HBV envelope characteristics in HBsAg persistence.