Precore-mediated inhibition of hepatitis B virus progeny DNA synthesis

HBV PreC interacts with SUV39H1 to induce viral replication by blocking the proteasomal degradation of viral polymerase

Hepatitis B e antigen (HBeAg) seropositivity during the natural history of chronic hepatitis B (CHB) is known to coincide with significant increases in serum and intrahepatic HBV DNA levels. However, the precise underlying mechanism remains unclear. In this study, we found that PreC (HBeAg precursor) genetic ablation leads to reduced viral replication both in vitro and in vivo. Furthermore, PreC impedes the proteasomal degradation of HBV polymerase, promoting viral replication. We discovered that PreC interacts with SUV39H1, a histone methyltransferase, resulting in a reduction in the expression of Cdt2, an adaptor protein of CRL4 E3 ligase targeting HBV polymerase. SUV39H1 induces H3K9 trimethylation of the Cdt2 promoter in a PreC-induced manner. CRISPR-mediated knockout of endogenous SUV39H1 or pharmaceutical inhibition of SUV39H1 decreases HBV loads in the mouse liver. Additionally, genetic depletion of Cdt2 in the mouse liver abrogates PreC-related HBV replication. Interestingly, a negative correlation of intrahepatic Cdt2 with serum HBeAg and HBV DNA load was observed in CHB patient samples. Our study thus sheds light on the mechanistic role of PreC in inducing HBV replication and identifies potential therapeutic targets for HBV treatment.

Vitamin D signaling inhibits HBV activity by directly targeting the HBV core promoter

Clinical and epidemiological studies support a role for vitamin D in suppressing hepatitis B virus (HBV). This antiviral role of vitamin D is widely attributed to vitamin D receptor (VDR)/retinoid X receptor-mediated regulation of host immunomodulatory genes through vitamin D response elements (VDREs) in their promoters. Here, we investigated the ability of calcitriol (1α,25-dihydroxyvitamin D3, metabolically activated vitamin D) to directly regulate HBV activity through this signaling pathway. We observed that calcitriol selectively inhibited only the HBV core promoter without affecting the HBV-PreS1, HBV-PreS2/S, or HBx promoters. We then identified a VDRE cluster in the HBV core promoter that is highly conserved across most HBV genotypes. Disruption of this VDRE cluster abrogated calcitriol-mediated suppression of the HBV core promoter. Furthermore, we showed that VDR interacts directly with the VDRE cluster in the HBV core promoter independent of retinoid X receptor. This demonstrates that calcitriol inhibits HBV core promoter activity through a noncanonical calcitriol-activated VDR pathway. Finally, we observed that calcitriol suppressed expression of the canonical HBV core promoter transcripts, pregenomic RNA, and precore RNA in multiple HBV cell culture models. In addition, calcitriol inhibited the secretion of hepatitis B "e" antigen and hepatitis B surface antigen (HBV-encoded proteins linked to poor disease prognosis), without affecting virion secretion. Our findings identify VDR as a novel regulator of HBV core promoter activity and also explain at least in part the correlation of vitamin D levels to HBV activity observed in clinical studies. Furthermore, this study has implications on the potential use of vitamin D along with anti-HBV therapies, and lays the groundwork for studies on vitamin D-mediated regulation of viruses through VDREs in virus promoters.

In vitro expression of precore proteins of hepatitis B virus subgenotype A1 is affected by HBcAg, and can affect HBsAg secretion

HBeAg, a non-particulate protein of hepatitis B virus (HBV), is translated from the precore/core region as a precursor, which is post-translationally modified. Subgenotype A1 of HBV, which is a risk factor for hepatocellular carcinoma (HCC), has unique molecular characteristics in the basic core promoter/precore regions. Carriers of A1 exhibit early HBeAg loss. We sought to further characterize the precore proteins of A1 in vitro. HuH-7 cells were transfected with subgenomic constructs expressing individual precore proteins. Western blot analysis using DAKO anti-core antibody showed the expected sizes and a 1 kDa larger band for P22, P20 and P17. Using confocal microscopy, a cytoplasmic accumulation of HBeAg and precursors was observed with P25-expressing plasmid, whereas P22 localized both in the cytoplasm and nucleus. P20 and P17, which lack the carboxy end of P22 showed strong nuclear accumulation, implicating a nuclear localization signal in the N-terminal 10 amino acids. G1862T, unique to subgenotype A1, is frequently found in HBV from HCC patients. P25 with G1862T showed delayed and reduced HBeAg expression/secretion. Knock-out of core in the replication competent clones led to precore protein accumulation in the cytoplasm/perinuclear region, and decreased HBeAg secretion. Knock-out of precore proteins increased HBsAg secretion but intracellular HBsAg expression was unaffected. Over-expression of precore proteins in trans led to decreased HBsAg expression and secretion. Intracellular trafficking of HBV A1 precore proteins was followed. This was unaffected by the CMV promoter and different cell types. In the viral context, precore protein expression was affected by absence of core, and affected HBsAg expression, suggesting an interrelationship between precore proteins, HBcAg and HBsAg. This modulatory role of HBeAg and its precursors may be important in viral persistence and ultimate development of HCC.

Transcriptome analysis of hepatoma cells transfected with Basal Core Promoter (BCP) and Pre-Core (PC) mutant hepatitis B virus full genome construct

Infections with Basal Core Promoter (BCP) (A1762T/G1764A) and Pre-Core (PC) (G1896A) hepatitis B virus HBeAg mutants are associated with severe liver injury. We analysed host cell responses in HepG2/C3A, hepatoma cells transfected with infectious clones developed from genotype D wild type (WT) and BCP/PC mutant (MT) viruses isolated from an acute resolved and an acute liver failure hepatitis B case respectively. Cells transfected with MT virus construct showed ~55 % apoptosis and with WT ~30 % apoptosis at 72 h. To determine possible roles of HBe and HBx proteins in apoptosis, we cloned these genes and co-transfected cells with WT+HBe/HBx or MT+HBe/HBx constructs. Co-expression of HBe protein improved cell viability significantly in both WT and MT virus constructs, indicating an important role of HBe in protecting cells. RNA sequencing analysis carried out at 12 and 72 h post-transfection with WT virus construct showed enrichment of innate/adaptive immune response-activating signal transduction, cell survival and amino acid/nucleic acid biosynthetic pathways at 12 and 72 h. By contrast, MT virus construct showed enrichment in host defence pathways and some biosynthetic pathways at the early time point (12 h), and inflammatory response, secretary granule, regulation of membrane potential and stress response regulatory pathways at the late time point (72 h). There was a significant down-regulation of genes involved in endoplasmic reticulum and mitochondrial functions and metabolism with MT construct and this possibly led to induction of apoptosis in cells. Considering rapid apoptotic changes in cells transfected with MT construct, it can be speculated that HBeAg plays a crucial role in cell survival. It enhances induction of metabolic and synthetic pathways and facilitates management of cellular stress that is induced due to hepatitis B virus infection/replication.

Mechanisms of Hepatitis B Virus-Induced Hepatocarcinogenesis

Hepatitis B virus (HBV) is a major cause of hepatocellular carcinoma (HCC). There are approximately 250 million people in the world that are chronically infected by this virus, resulting in nearly 1 million deaths every year. Many of these patients die from severe liver diseases, including HCC. HBV may induce HCC through the induction of chronic liver inflammation, which can cause oxidative stress and DNA damage. However, many studies also indicated that HBV could induce HCC via the alteration of hepatocellular physiology that may involve genetic and epigenetic changes of the host DNA, the alteration of cellular signaling pathways, and the inhibition of DNA repair mechanisms. This alteration of cellular physiology can lead to the accumulation of DNA damages and the promotion of cell cycles and predispose hepatocytes to oncogenic transformation.

Biological features of hepatitis B virus strains associated with fulminant hepatitis

Accumulating evidence suggests that hepatitis B virus (HBV) biological features may influence the course and clinical manifestations of infection and possibly the development of fulminant hepatitis (FH). Since HBV is not a cytocidal virus, virus-induced liver damage results from an interplay between the virus replication and the host's defense. Therefore, viral factors contributing to enhanced replication, induction of a stronger immune attack or apoptosis of hepatocytes could be crucial in development of FH. Numerous mutations in basal core promoter, pre-C, C and S regions of the HBV genome contribute to development of FH by different mechanisms, including enhanced viral replication, the loss of a decoy for immune response, unbalanced expression of viral proteins and retention of unprocessed cytotoxic proteins in hepatocytes.

Immune-Escape Hepatitis B Virus Mutations Associated with Viral Reactivation upon Immunosuppression

Hepatitis B virus (HBV) reactivation occurs as a major complication of immunosuppressive therapy among persons who have recovered from acute hepatitis and those who have controlled chronic infection. Recent literature data emphasize the presence of a high degree of S gene variability in HBV isolates from patients who developed reactivation. In reactivated HBV, the most frequently detected mutations belong to the second loop of “a” determinant in HBsAg. These mutations were identified to be immune escape and responsible for vaccine- and diagnostic-escape phenomena. Their emergence clearly provides survival in the presence of a developed humoral immune response and is often associated with impaired serological diagnosis of HBV reactivation. The knowledge of their existence and roles can elucidate the process of reactivation and strongly highlights the importance of HBV DNA detection in monitoring all patients with a history of HBV infection who are undergoing immunosuppression. This review discusses the possible influence of the most frequently found immune-escape mutations on HBV reactivation.

Mechanisms of Hepatitis B Virus Persistence

Hepatitis B virus (HBV) chronically infects 250 million people worldwide, resulting in nearly one million deaths annually. Studies in recent years have significantly improved our knowledge on the mechanisms of HBV persistence. HBV uses multiple pathways to harness host innate immunity to enhance its replication. It can also take advantage of the developing immune system and the not-yet-stabilized gut microbiota of young children to facilitate its persistence, and use maternal viral e antigen to educate immunity of the offspring to support its persistence after vertical transmission. The knowledge gained from these recent studies paves the way for the development of new therapies for the treatment of chronic HBV infection, which has so far been very challenging.

Maternal-Derived Hepatitis B Virus e Antigen Alters Macrophage Function in Offspring to Drive Viral Persistence after Vertical Transmission

In contrast to horizontal transmission of hepatitis B virus (HBV) between adults, which often leads to self-limited acute infection, vertical transmission of HBV from mother to child often leads to chronic infection. However, the mechanisms linking vertical transmission with chronic infection are not known. We developed a mouse model to study the effect of maternal HBV infection on HBV persistence in offspring and found that HBV carried by the mother impaired CD8(+) T cell responses to HBV in her offspring, resulting in HBV persistence. This impairment of CD8(+) T cell responses was mediated by hepatic macrophages, which were predisposed by maternal HBV e antigen (HBeAg) to support HBV persistence by upregulation of inhibitory ligand PD-L1 and altered polarization upon restimulation with HBeAg. Depletion of hepatic macrophages led to CD8(+) T cell activation and HBV clearance in the offspring, raising the possibility of targeting macrophages to treat chronic HBV patients.

Conserved aromatic residues of the hepatitis B virus Precore propeptide are involved in a switch between distinct dimeric conformations and essential in the formation of heterocapsids

The Hepatitis B virus Precore protein, present in the secretory pathway as the HBeAg precursor, can associate in the cytoplasm with the Core protein to form heterocapsids, likely to favor viral persistence. Core and Precore proteins share their primary sequence except for ten additional aminoacids at the N-terminus of Precore. To address the role of this propeptide sequence in the formation of Precore heterocapsids, we designed a Precore mutant in which the two propeptide tryptophans are replaced by glycines. This mutant retains the properties of the wild-type Precore, notably cell trafficking and ability to interact with Core. However, it is not incorporated into heterocapsids and forms stable dimers distinct from the labile HBe dimers and the presumably Core-like dimers assembled into heterocapsids. Our data highlights the essential role of Precore׳s propeptide in switching between different conformations for different functions and pinpoint the propeptide Tryptophan residues as central in these properties.

Hepatitis B e antigen-suppressing mutations enhance the replication efficiency of adefovir-resistant hepatitis B virus strains

Hepatitis B e antigen (HBeAg) negative hepatitis B virus (HBV) infections caused by precore (PC) or basal core promoter (BCP) mutations are associated with disease progression and complications. PC or BCP mutations may enhance the replication capacity of distinct drug-resistance-associated polymerase mutations, but their effect on adefovir-resistant HBV mutants is unclear. Importantly, BCP mutations were an independent risk factor for virological breakthrough in lamivudine-resistant patients treated with adefovir. We aimed at addressing the functional consequences of PC and BCP mutations on the replication and drug susceptibility of adefovir-resistant HBV mutants. Therefore, HBV constructs with wild type (WT) or adefovir-resistant rtN236T, rtA181V and rtA181T mutations, with or without concomitant PC or BCP mutations, were analysed in vitro using molecular assays. The adefovir-resistant polymerase mutations rtN236T, rtA181V and rtA181T showed a drastically reduced viral replication compared with WT. Interestingly, additional PC or BCP mutations enhanced the reduced replication efficacy of adefovir-resistant constructs and restored HBV replication to WT level. HBV rtA181T mutants displayed abolished hepatitis B surface antigen (HBsAg) secretion, owing to a sW172* stop codon in the overlapping envelope gene. All rtN236T- or rtA181V/T-containing constructs, regardless of concomitant PC or BCP mutations, were resistant to adefovir, but remained susceptible to telbivudine, entecavir and tenofovir. In conclusion, adefovir drug resistance mutations reduced viral replication, which can be significantly increased by additional HBeAg-suppressing PC or BCP mutations. Because increased HBV replication in HBeAg-negative patients has been associated with an unfavourable clinical course, close monitoring appears indispensable during adefovir treatment in HBeAg-negative patients.

Hepatitis B precore protein: pathogenic potential and therapeutic promise

Hepatitis B virus (HBV), a small and economically packaged double-stranded DNA virus, represents an enormous global health care burden. In spite of an effective vaccine, HBV is endemic in many countries. Chronic hepatitis B (CHB) results in the development of significant clinical outcomes such as liver disease and hepatocellular carcinoma (HCC), which are associated with high mortality rates. HBV is a non-cytopathic virus, with the host's immune response responsible for the associated liver damage. Indeed, HBV appears to be a master of manipulating and modulating the immune response to achieve persistent and chronic infection. The HBV precore protein or hepatitis B e antigen (HBeAg) is a key viral protein involved in these processes, for instance though the down-regulation of the innate immune response. The development of new therapies that target viral proteins, such as HBeAg, which regulates of the immune system, may offer a new wave of potential therapeutics to circumvent progression to CHB and liver disease.

The inhibitors of nucleotide biosynthesis leflunomide, FK778, and mycophenolic acid activate hepatitis B virus replication in vitro

The inhibitors of pyrimidine synthesis, leflunomide and FK778, have been reported to exert broad antiviral effects, in addition to their immunosuppressive activities. Their possible therapeutic benefit for transplantation medicine is currently discussed, because they also block the replication of human cytomegalovirus and human polyomavirus BK, which both cause important complications in transplant recipients. Here, we show that leflunomide and FK778 strongly enhance hepatitis B virus (HBV) replication in vitro. This activity is shared by mycophenolic acid (MPA), an inhibitor of purine biosynthesis. Stimulation of HBV replication by these agents was linked to their inhibitory effects on de novo nucleotide biosynthesis because it could be efficiently counteracted by external nucleoside supply. Mechanistically, we found that mitogen-activated protein kinase p38 played a key role for the enhancement of HBV replication by leflunomide, FK778, and MPA. All three HBV-activating compounds increased p38 phosphorylation, in contrast to the HBV inhibitors, telbivudine and cyclosporine A. Moreover, silencing of p38 expression through RNA interference efficiently counteracted the stimulatory effect of leflunomide, FK778, and MPA on HBV replication.

CONCLUSION

Our data indicate that, in contrast to their reported inhibitory effects on other viruses, both leflunomide and FK778 can augment HBV replication. Treatment with leflunomide, FK778, or MPA may bear the risk to enhance HBV replication in infected patients.

Antiviral resistance mutations potentiate HBV surface antigen-induced transcription of hfgl2 prothrombinase gene

Antiviral resistance mutations in the hepatitis B virus (HBV) polymerase (pol) gene have been demonstrated to play an important role in the progression of liver disease and the development of hepatocellular carcinoma. The HBV pol gene overlaps the S gene encoding surface antigen (HBsAg). Previous studies from our laboratory have shown that HBV core protein (HBc) and X protein (HBx), but not HBV S protein (HBs), promote hfgl2 prothrombinase transcription. To investigate whether the nucleotide (nucleoside)-induced resistant mutations of HBs potentiate transcription of hfgl2 prothrombinase gene, we generated two mutant HB expression constructs harboring rtM204V/sI195M or rtM204I/sW196L mutations. Two mutant expression plasmids were co-transfected with hfgl2 promoter luciferase-reporter plasmids and β-galactosidase plasmid in CHO cells and HepG2 cells, respectively. Luciferase assay showed that the rtM204I/V mutant HBs could activate the transcription of hfgl2 promoter compared with the wild type HBs. Site-directed mutagenesis and further experiment (co-transfection) demonstrated that transcription factor Ets translocated to its cognate cis-element in the hfgl2 promoter. The results show that mutated HBs caused by antiviral drug resistance induce transcription of the hfgl2 gene dependent on the transcription factor Ets.

The hepatitis B e antigen suppresses IL-1β-mediated NF-κB activation in hepatocytes

Previous clinical studies have demonstrated an association between the hepatitis B e antigen and Toll-like receptor (TLR) expression and signalling. Therefore, the aim of this study was to develop an in vitro assay to measure the effect of hepatitis B virus proteins, including the precore protein, on signalling mediated by members of the Toll-like/interleukin 1 (TIR) superfamily, by measuring NF-κB promoter activity. The basal level of NF-κB reporter activity was measured in three hepatocyte cell lines (Huh7, HepG2 and PH5CH8) and one kidney cell line (HEK293) using a luciferase assay. All cell lines were virtually refractory to stimulation with lipopolysaccharide; however, PH5CH8 cells had a robust activation of NF-κB in response to IL-1β stimulation, with ∼ 40-fold higher activation than the unstimulated control, a higher degree of activation than that observed in either Huh7 and HepG2, or HEK293 and HEK293-TLR2 cells. In PH5CH8 cells transfected with pCI expression constructs and stimulated with IL-1β, we showed that the precursor form of the precore protein, p25, inhibits NF-κB activation by up to 30% and the cytosolic form, p22, inhibits NF-κB activation by 70%. The core protein, p21, which shares significant homology with the precore protein except for a 10-amino acid extension at the N-terminus, had no effect on NF-κB activation. We hypothesize that the inhibition of IL-1β-mediated NF-κB activation by the precore protein may be a mechanism that allows the virus to persist, suggesting a role for the pool of precore protein that remains intracellular.

The YMDD and rtA194T mutations result in decreased replication capacity in wild-type HBV as well as in HBV with precore and basal core promoter mutations

BACKGROUND

A recent study indicated that addition of the hepatitis B e antigen (HBeAg) precore (PC) or basal core promoter (BCP) mutations to wild-type HBV offset the reduced replication of the HBV polymerase rtA194T±rtL180M+rtM204V mutations. rtA194T was reportedly associated with tenofovir resistance. We investigated these findings in genotype D HBV, where both PC and BCP naturally occur in vivo.

METHODS

A plasmid containing a wild-type 1.3 genome length genotype D HBV laboratory strain was used as a parent for PC, BCP, rtA194T±rtL180M+rtM204V, rtL180M+rtM204V and rtM204I mutants. Viral replication was evaluated by Southern blot analysis of intracellular HBV core DNA following transient transfection of HepG2 cells. Drug susceptibility was evaluated by quantitative PCR of intracellular HBV DNA.

RESULTS

PC and BCP mutations each increased HBV DNA replication by approximately 200% over wild-type. rtA194T reduced replication by <40%, whereas rtL180M+rtM204V, rtL180M+rtA194T+rtM204V or rtM204I each reduced by >75% from their respective wild-type, PC or BCP genome backbone (P<0.05). The enhanced replication by PC or BCP offset the reduction by rtA194T; however, the other reverse transcriptase (RT) mutations in PC or BCP backbones remained significantly lower than wild-type (P<0.05). Regardless of the backbone, rtA194T±rtL180M+rtM204V remained susceptible to tenofovir in vitro. rtA194T alone remained susceptible to lamivudine, while rtL180M+rtM204V and rtL180M+rtA194T+rtM204V were resistant.

CONCLUSIONS

PC or BCP mutations increased HBV DNA replication, offset the decreased replication by rtA194T alone, but they did not fully rescue the impaired replication conferred by other RT mutations as compared with wild-type. rtA194T±rtL180M+rtM204V did not confer tenofovir resistance.

Case-control study for the identification of virological factors associated with fulminant hepatitis B

BACKGROUND

Host and viral factors can promote the development of fulminant hepatitis B (FHB), but there have been no case-control studies for figuring out virological parameters that can distinguish FHB.

METHODS

In a case-control study, virological factors associated with the development of FHB were sought in 50 patients with FH developed by transient hepatitis B virus (HBV) infection (FH-T) and 50 with acute self-limited hepatitis B (AHB) who were matched for sex and age. In addition, 12 patients with FH developed by acute exacerbation (AE) of asymptomatic HBV carrier (ASC) (FH-C) were also compared with 12 patients without FH by AE of chronic hepatitis B (AE-C).

RESULTS

Higher HBV DNA levels, subgenotype B1/Bj, A1762T/G1764A, G1896A, G1899A and A2339G mutation were significantly more frequent (P < 0.05), while hepatitis B e-antigen was less frequent in the FH-T patients than AHB. In multivariate analysis, G1896A mutation (odds ratio [OR], 13.53; 95% confidence interval [CI], 2.75-66.64), serum HBV DNA more than 5.23 log copies/mL (OR, 5.14; 95% CI, 1.10-24.15) and total bilirubin more than 10.35 mg/mL (OR, 7.81; 95% CI, 1.77-34.51) were independently associated with a fulminant outcome by transient HBV infection. On the other hand, in comparison with the patients between FH-C and AE-C groups, there was no significant difference of virological factors associated with the development of FHB.

CONCLUSION

A number of virological factors have been defined that may distinguish FH-T from AHB in a case-control study. The pathogenic mechanism of FHB between transient HBV infection and AE of ASC would be different.

The rtA194T polymerase mutation impacts viral replication and susceptibility to tenofovir in hepatitis B e antigen-positive and hepatitis B e antigen-negative hepatitis B virus strains

Tenofovir is a new effective treatment option for patients with chronic hepatitis B, but could be potentially hampered by mutations in the hepatitis B virus (HBV) polymerase conferring drug resistance. Drug resistance may occur preferentially if long-term administration is required, for example, in patients with hepatitis B e antigen (HBeAg)-negative HBV infection bearing precore (PC) and basal core promoter (BCP) mutations. The rtA194T polymerase mutation has been found in HBV/HIV coinfected patients during tenofovir treatment and may be associated with tenofovir resistance. We generated replication-competent HBV constructs harboring rtA194T alone or in addition to lamivudine (LAM) resistance (rt180M + rtM204V), PC mutations, and BCP mutations and assessed their replicative capacity after transient transfection in human hepatoma cells. The rtA194T polymerase mutation alone or in conjunction with LAM resistance reduced the replication efficiency as compared with wild-type (WT) HBV. In contrast, combination of rtA194T (+/- LAM resistance) with HBeAg-negative PC or BCP mutants increased the replication capacity of the drug-resistant polymerase mutants, thereby restoring the viral replication to similar levels as WT clones. Clones harboring rtA194T showed partial resistance to tenofovir in vitro and also to LAM but remained susceptible to telbivudine and entecavir.

CONCLUSION

The rtA194T polymerase mutation is associated with partial tenofovir drug resistance and negatively impacts replication competence of HBV constructs. Viral replication, however, can be restored to WT levels, if these polymerase mutations occur together with precore or basic core promoter substitutions as found in HBeAg-negative hepatitis B. Patients with HBeAg-negative chronic HBV infection may therefore be at particular risk when developing drug resistance to tenofovir. Telbivudine or entecavir should be considered as effective alternative treatment options for these patients.

The hepatitis B virus precore protein is retrotransported from endoplasmic reticulum (ER) to cytosol through the ER-associated degradation pathway

The hepatitis B virus precore protein is closely related to the nucleocapsid core protein but is processed distinctly in the cell and plays a different role in the viral cycle. Precore is addressed to the endoplasmic reticulum (ER) through a signal peptide, and the form present in the ER is the P22 protein. P22 is then cleaved in its C-terminal part to be secreted as HBe antigen. In addition, a cytosolic form of 22 kDa less characterized has been observed. Precore gene was shown to be implicated in viral persistence, but until now, the actual protein species involved has not been determined. Our work focuses on the cytosolic form of precore. Using human cells expressing precore and a convenient fractionation assay, we demonstrated that the cytosolic form is identical to the ER form and retrotransported in the cytoplasm through the ER-associated degradation pathway. This cellular machinery translocates misfolded proteins to the cytoplasm, where they are ubiquitinated on lysine residues and degraded by proteasome. We showed that precore escapes proteasome due to its low lysine content and accumulates in the cytosol. The role of this retrotransport was investigated. In the presence of precore, we found a specific redistribution of the Grp78/BiP chaperone protein to cytosol and demonstrated a specific interaction between precore and Grp78/BiP. Altogether, these data support the idea that the hepatitis B virus develops a strategy to take advantage of the ER-associated degradation pathway, allowing distinct subcellular localization and probably distinct roles for the viral precore protein.

Molecular testing in the diagnosis and management of chronic hepatitis B

Hepatitis B virus (HBV) is an enveloped virus with a small (3.2-kb) partially double-stranded DNA genome that causes acute and chronic infections. The impact of these infections on public health worldwide is enormous, with an estimated prevalence of 2 billion acute infections and 360 million chronic infections globally. This review focuses on chronic hepatitis B and the molecular assays used in its diagnosis and management. Background information, including that about features of the hepatitis B virion, viral replication, and epidemiology of infection, that is important for understanding chronic hepatitis B and molecular diagnostic tests for HBV is provided. To facilitate an understanding of the utility of molecular testing for chronic hepatitis B, the four stages of chronic hepatitis B infection that are currently recognized, as well as an additional entity, occult hepatitis B, that can be diagnosed only by sensitive nucleic acid amplification methods, are reviewed in detail, including available therapeutic agents. The molecular diagnostic content focuses on tests for HBV DNA quantification, genotyping, and mutation detection (including precore/core promoter and antiviral resistance mutations). The discussion of these tests encompasses their current utility and performance characteristics, drawing from current clinical guidelines and other studies from the literature. In recognition of the continual evolution of this field, the final section describes emerging molecular markers with future diagnostic potential.

Pathogenesis of hepatitis B virus infection

Infection with hepatitis B virus (HBV) leads to a wide spectrum of clinical presentations ranging from an asymptomatic carrier state to self-limited acute or fulminant hepatitis to chronic hepatitis with progression to cirrhosis and hepatocellular carcinoma. Infection with HBV is one of the most common viral diseases affecting man. Both viral factors as well as the host immune response have been implicated in the pathogenesis and clinical outcome of HBV infection. In this review, we will discuss the impact of virus-host interactions for the pathogenesis of HBV infection and liver disease. These interactions include the relevance of naturally occurring viral variants for clinical disease, the role of virus-induced apoptosis for HBV-induced liver cell injury and the impact of antiviral immune responses for outcome of infection.

Infectious source factors affecting the severity of sexually transmitted acute hepatitis due to hepatitis B virus genotype C

OBJECTIVE

The aim of this study was to identify clinical features and virological aspects of infectious sources that are related to the severity of sexually transmitted acute hepatitis B virus (HBV) infection in patients, especially in cases of genotype C.

METHODS

Nineteen patients with acute HBV infection, 10 classified with severe acute hepatitis (SH) (prothrombin time; PT <40%) and 9 with typical acute hepatitis (AH) (PT >40%), and their infectious sources (all were sexual partners) were studied. Infectious source factors were analyzed in relation to the severity of hepatitis in the patients' partners.

RESULTS

The nucleotide homology of HBV-DNA between each pair was >/=98.9%. Sixteen were infected with HBV genotype C. Among the 16 infectious sources, age, numbers with elevated alanine aminotransferase (ALT, 7/9 vs. 1/7), anti-HBe positivity (8/9 vs. 1/7) and core promoter mutations at nt 1762 (7/9 vs. 1/7), nt 1764 (8/9 vs. 1/7) and precore mutation at nt 1896 (8/9 vs. 1/7) were significantly higher in the sources of SH than in those of AH.

CONCLUSION

Higher age, elevated ALT, anti-HBe positivity and core promoter/precore mutations were possible risk factors for an infectious source of the severe form of sexually transmitted acute hepatitis due to HBV genotype C.

High level of hepatitis B virus DNA after HBeAg-to-anti-HBe seroconversion is related to coexistence of mutations in its precore and basal core promoter

AIM: G1896A mutation in precore or A1762T/G1764A mutations in basal core promoter are suspected to be responsible for patients with detectable level of HBV DNA in serum after seroconversion from HBeAg to anti-HBe. However, G1896A variant has impaired, while A1762T/G1764A variant may have intact replication ability. They themselves or their coexistence status may play different roles in such meaningless seroconversion. For these reasons, the significances of these two types of mutations were comparatively investigated in this study.

METHODS: One hundred and sixty-five sera with positive anti-HBe and HBV DNA were collected from different patients. Mutations of G1896A and A1762T/G1764A among these serum samples were detected using competitively differentiated PCR. HBV DNA was demonstrated using real-time quantitative PCR.

RESULTS: G1896A and/or A1762T/G1764A mutations were detected in 89.1% (147/165) out of patients with detectable HBV DNA in serum after HBeAg-to-anti-HBe seroconversion. The positive rate of G1896A variants was significantly higher than that of A1762T/G1764A mutations (77.6% vs 50.3%, χ² = 26.61, P<0.01). The coexistence positive rate of these two types of mutations was 38.8% (64/165). Coexistence mutations were found in 77.1% (64/83) out of sera with A1762T/G1764A mutations, and in 50.0% (64/128) out of sera with G1896A mutation. Compared with variants with G1896A mutation only, the coexistence mutations were predominant in patients with high level of serum HBV DNA, and related to higher total bilirubin, lower serum albumin and progressive liver diseases.

CONCLUSION: The coexistence of G1896A mutation and A1762T/G1764A mutations is very common, and responsible for the major cases with high level of HBV DNA in serum and progressive liver diseases after HBeAg-to-anti-HBe seroconversion. This coexistence mutation variant may have higher pathogenicity and replication ability.

An application of gene comparative image for predicting the effect on replication ratio by HBV virus gene missense mutation

Hepatitis B viruses (HBVs) show instantaneous and high-ratio mutations when they are replicated, some sorts of which significantly affect the efficiency of virus replication through enhancing or depressing the viral replication, while others have no influence at all. The mechanism of gene expression is closely correlated with its gene sequence. With the rapid increase in the number of newly found sequences entering into data banks, it is highly desirable to develop an automated method for simulating the gene regulating function. The establishment of such a predictor will no doubt expedite the process of prioritizing genes and proteins identified by genomics efforts as potential molecular targets for drug design. Based on the power of cellular automata (CA) in treating complex systems with simple rules, a novel method to present HBV gene image has been introduced. The results show that the images thus obtained can very efficiently simulate the effects of the gene missense mutation on the virus replication. It is anticipated that CA may also serve as a useful vehicle for many other studies on complicated biological systems.

Cellular response to conditional expression of the hepatitis B virus precore and core proteins in cultured hepatoma (Huh-7) cells

BACKGROUND

The expression of the hepatitis Be antigen (HBeAg) is one of several strategies used by hepatitis B virus (HBV) to ensure persistence. The HBeAg may function as a toleragen in utero and has been shown to regulate the host's immune response.

AIM

The aim of this study was to examine the effect of the HBV precore and core protein on cellular gene expression in the hepatoma cell line Huh-7.

STUDY DESIGN

Huh-7 cells with tight regulated expression of the HBV core or precore protein were produced using the Tet-Off tetracycline gene expression system. Changes in cellular gene expression in response to core/precore expression compared to Huh-7 cells not expressing the proteins were determined using a commercial high-density oligonucleotide array (Affymetrix Hu95A GeneChip) containing probes for 12,626 full-length human genes.

RESULTS

Analysis of differential mRNA gene expression profiles at 7 days post precore and core expression revealed 45 and 5 genes, respectively, with mRNA changes greater than three-fold. The most striking feature was in Huh-7 cells expressing the precore protein in which 43/45 genes were downregulated 3-11-fold. These included genes that encoded products that regulate transcription/DNA binding proteins, cell surface receptors, cell-cycle/nucleic acid biosynthesis and intracellular signalling and trafficking. The only known gene, which was upregulated encoded a cytoskeletal protein. For the core cell line, 4/5 genes were downregulated 3-15-fold upon core induction and included genes that encoded products that affect intermediary metabolism, cell surface receptors and intracellular signalling. The one gene, which was upregulated was a cytokine gene.

CONCLUSION

The results of this study show that HBV precore protein has a much greater effect on cellular gene expression in comparison to the core protein, suggesting that core and precore proteins may have diverse effects on cellular functions and equally different roles in modulating HBV pathogenesis.

The precore mutation is associated with severity of liver damage in Brazilian patients with chronic hepatitis B

BACKGROUND

The clinical relevance of the G1896A precore mutation in chronic hepatitis B is still poorly understood.

OBJECTIVES

To assess the frequency of G1896A precore mutation in Brazilian patients with chronic hepatitis B, as well as its relation to the viral genotype, serum HBV-DNA levels and liver damage.

STUDY DESIGN

Fifty chronic hepatitis B patients (29 HBeAg-negative and 21 HBeAg-positive) were studied. HBV-DNA was quantified by the Amplicor HBV Monitor test and precore region and S gene were amplified and submitted to automatic sequencing. The histological activity index (HAI), degrees of hepatic fibrosis and distribution of core antigen (HBcAg) in hepatocytes were determined.

RESULTS

Precore mutation occurred in 1/21 (4.8%) HBeAg-positive patients and in 17/29 (58.6%) HBeAg-negative (p < 0.0001). Genotype D was identified in 56.5%, genotype A in 41.3%, and genotype F in 2.2%. The frequency of genotypes D and A, as well as serum levels of ALT and HBV-DNA were similar in patients infected with wild type and with precore mutant. Patients infected with precore mutant presented a higher frequency of moderate/severe HAI (p: 0.03) and moderate/severe fibrosis and cirrhosis (p: 0.03) than those infected with wild type. There was no association between G1896A mutation and cytoplasmic expression of HBcAg.

CONCLUSIONS

Precore mutation was frequent among Brazilian subjects with chronic hepatitis B and its presence was associated with greater severity of liver disease.

Comparative study of genotype B and C hepatitis B virus-induced chronic hepatitis in relation to the basic core promoter and precore mutations

BACKGROUND

The clinicopathological profiles and outcome of chronic hepatitis B can differ by hepatitis B virus (HBV) genotypes. In Japan, genotype B and C are two major HBV genotypes. The basic core promoter and precore mutations are other known viral factors for disease activity, although the relationship between HBV genotypes and these mutations is not fully understood.

METHODS

The HBV genotypes in 90 patients with chronic hepatitis B were determined using an ELISA. Obtained data were correlated with clinicopathological parameters, basic core promoter, precore and the nucleotide 1858 mutations of the HBV genome.

RESULTS

Among 90 cases, 20 (22.2%) had genotype B and 70 (77.8%) had genotype C HBV. Genotype B patients were older than genotype C patients (44.0 +/- 13.9 vs 34.7 +/- 11.0 P = 0.0022). The HBeAg was more prevalent in genotype C than B patients (P = 0.0008) while anti-HBe was more common in genotype B than C patients (P = 0.0002). Serum aspartate aspartate aminotransferase/alanine aminotransferase levels (B: 220.7 +/- 612.8/257.0 +/- 498.0 IU/L vs C: 111.3 +/- 122.8/201.6 +/- 229.4 IU/L, P = 0.16/0.48) and HBV viral loads in blood (B: 6.1 +/- 3.1 log genome equivalent [LGE]/mL vs C: 6.7 +/- 2.3 LGE/mL, P = 0.42) were equivalent. The seroconversion from HBeAg to anti-HBe occurred significantly earlier in genotype B than C patients (62 +/- 53 months vs 136 +/- 54 months, P = 0.0028) during the mean observation period of 149 +/- 82 months even under various therapeutic modalities. The categories III and IV of the histological activity index in genotype C were higher (III: P < 0.005, IV: P < 0.05, n = 68) than that in B patients whereas category II was higher in genotype B than C patients (P < 0.05). The double mutation (1762T/1764A) in the basic core promoter was more frequently found in genotype C than in B HBV (P = 0.0068), whereas the precore mutation (1896A) was more common in genotype B than C HBV (P = 0.0233). The incidence of 1858C that was complementary to the precore mutation site in the stem-loop structure in, was equally rare in both genotype B and C HBV.

CONCLUSIONS

Genotype B patients were older, had earlier HBeAg seroconversion and exhibited more severe lobular necroinflammation, less portal inflammation and fibrosis than genotype C patients. This genotypic difference is related to the basic core promoter and precore mutations irrespective of 1858C. (c) 2004 Blackwell Publishing Asia Pty Ltd.

Basal core promoter and precore mutations in the hepatitis B virus genome enhance replication efficacy of Lamivudine-resistant mutants

During chronic hepatitis B virus (HBV) infection, mutations in the precore (PC) or basal core promoter (BCP) region affecting HBV e antigen (HBeAg) expression occur commonly and represent the predominant virus species in patients with HBeAg-negative chronic hepatitis B. The PC mutation (G1896A+C1858T) creates a translational stop codon resulting in absent HBeAg expression, whereas BCP mutations (A1762T/G1764A) reduce HBeAg expression by transcriptional mechanisms. Treatment of chronic HBV infection with lamivudine (LMV) often selects drug-resistant strains with single (rtM204I) or double (rtL180M+rtM204V) point mutations in the YMDD motif of HBV reverse transcriptase. We cloned replication-competent HBV vectors (genotype A, adw2) combining mutations in the core (wild type [wt], PC, and BCP) and polymerase gene (wt, rtM204I, and rtL180M/M204V) and analyzed virus replication and drug sensitivity in vitro. Resistance to LMV (rtM204I/rtL180M+rtM204V) was accompanied by a reduced replication efficacy as evidenced by reduced pregenomic RNA, encapsidated progeny DNA, polymerase activity, and virion release. PC mutations alone did not alter virus replication but restored replication efficacy of the LMV-resistant mutants without affecting drug resistance. BCP mutants had higher replication capacities than did the wt, also in combination with LMV resistance mutations. All nine HBV constructs showed similar sensitivities to adefovir. In conclusion, BCP-PC mutations directly impact the replication capacity of LMV-resistant mutants. PC mutations compensated for replication inefficiency of LMV-resistant mutants, whereas BCP mutations increased viral replication levels to above the wt baseline values, even in LMV-resistant mutants, without affecting drug sensitivity in vitro. Adefovir may be an effective treatment when combinations of core and polymerase mutations occur.

Complete hepatitis B virus genome analysis in HBsAg positive mothers and their infants with fulminant hepatitis B

Background

After perinatal transmission of hepatitis B virus, infants of anti-HBe positive HBsAg carrier mothers may develop fulminant hepatitis B. Previously it has been suggested, that fulminant hepatitis B in adults was associated with specific mutations in the HBV-genome. The aim of this study was to investigate, whether specific viral variants are associated with fulminant hepatitis B in young infants.

Methods

The complete HBV-genomes of five mothers and their infants with fulminant hepatitis were isolated from the sera, amplified and directly sequenced.

Results

Between 6 and 43 base pair exchanges between the HBV genomes of the infants and their mothers were identified. The mutations spread over the entire virus genome. Nucleotide exchanges in the basic core promotor and precore region were identified in all cases. A heterogeneous virus population was detected in four mothers.

Conclusions

Many new mutations were proved to emerge during fulminant hepatitis B in infants, who had been perinatally infected. HBeAg negative variants were the predominant population in all children, whereas these mutants could only be detected as subpopulations in four mothers. The data suggest that the selection of a specific HBeAg negative viral strain may be associated with the development of fulminant hepatitis B in children.

In vitro and in vivo interactions between the hepatitis B virus protein P22 and the cellular protein gC1qR

gC1qR, a mitochondrial matrix protein, was identified as the main cellular partner of the hepatitis B virus P22 protein. We demonstrated by immunofluorescence studies that some P22 molecules were colocalized with the endogenous gC1qR in both the cytoplasm and the nucleus but never in the mitochondria. We also showed that the last 34 amino acids of P22 were involved in the association with gC1qR.

Antivirals interacting with hepatitis B virus core protein and core mutations may misdirect capsid assembly in a similar fashion

Recently, heteroarylpyrimidines (HAP) have been identified as potent inhibitors of capsid maturation. Here we discuss the HAP mode of action comparing the aggregation phenotype of wild-type and mutant core proteins with the respective phenotype imposed by HAP or other agents interacting with core protein. Pertinent tests include core fusion protein-mediated transactivation in a two-hybrid system and capsid formation. The finding that transactivation appeared to be unaffected by HAP, or by mutations preventing assembly, is surprising and raises the question for the structure of the interacting hybrid core proteins: Are they monomers, dimers or even oligomers? A direct activity of core fusion monomers is not excluded but considered to be highly unlikely due to rapid homodimerisation. A role of core fusion dimers in transactivation would indicate distinct interactions with a differential sensitivity to HAP. Regarding significance of data gained in two-hybrid systems, caution is necessary, since the site of transactivation is the nucleus, whereas the real site of the core protein interactions during replication is the cytoplasm. Apparently, HAP leave the monomer-monomer interface of HBV core protein unaffected but prevent capsid maturation by interacting with a region known to be crucial for dimer multimerisation and formation of stable capsids. It is suggested to use antivirals as tools for the elucidation of early steps in genome replication and capsid assembly. A frame for this could be the hypothesis that the virus uses soluble core protein, namely intracellular maturation intermediates of HbeAg for a core targeted self-restriction of replication.

Core promoter/pre-core mutations are associated with lamivudine-induced HBeAg loss in chronic hepatitis B with genotype C

BACKGROUND/AIMS

To clarify the factors associated with the efficacy of lamivudine.

METHODS

Variables including basic core promoter (BCP) and pre-core (PreC) mutations were evaluated in 60 chronic hepatitis B e antigen (HBeAg)-positive patients with genotype C. Thirty patients were treated with lamivudine and the remaining 30 patients were age- and sex-matched controls.

RESULTS

Severe fibrosis was significantly more frequent in patients with the BCP-mutant/PreC-wild (MW) and BCP-mutant/PreC-mutant (MM) patterns compared to BCP-wild/PreC-wild (WW) pattern (P=0.02). The cumulative rates of HBeAg loss at 6, 12 and 18 months were significantly higher in the lamivudine group (14.2, 36.3, and 60.9%) compared with the control group (17.6, 17.6, and 24.5%, P=0.03), and was especially pronounced in patients with the MW pattern (P=0.04). The rate of lamivudine-related HBeAg loss was significantly lower in patients with the WW pattern (P=0.03). Factors correlating with HBeAg loss were histological fibrosis and activity, hepatitis B virus-DNA levels, BCP/PreC mutation and lamivudine therapy. Multivariate analysis revealed BCP/PreC mutations and fibrosis were independent factors for HBeAg loss.

CONCLUSIONS

With specific reference to the genotype C, we found earlier HBeAg loss was expected in patients carrying MM and MW patterns, while the efficacy of lamivudine was limited in patients with the WW pattern.

Exploring the biological basis of hepatitis B e antigen in hepatitis B virus infection

The function of the hepatitis B e antigen (HBeAg) is largely unknown because it is not required for viral assembly, replication, or infection. In this report we chronicle clinical and experimental studies in an attempt to understand the role of HBeAg in natural infection. These studies largely have focused on clinical-pathologic features of HBeAg-negative variants in acute and chronic HBV infection, mutational analysis in animal models of hepadnavirus infection, and the use of transgenic murine models. The clinical and experimental data suggest that serum HBeAg may serve an immunoregulatory role in natural infection. To the contrary, cytosolic HBeAg serves as a target for the inflammatory immune response. These dual roles of the HBeAg and its ability to activate or tolerize T cells show the complexity of the interactions between the HBeAg and the host during HBV infection.

Regulation of hepatitis B virus replication by the ras-mitogen-activated protein kinase signaling pathway

The replication of hepatitis B virus (HBV) can be regulated by a variety of factors, including hormones, growth factors, and cytokines. However, the molecular mechanisms of these regulations are largely unknown. Ras is a small GTPase that responds to many of these external stimuli. In this study, we investigated the possible effect of Ras on the replication of HBV. Our results indicated that activated Ras could suppress the replication of HBV in both Huh7 and HepG2 cells. This suppression was independent of the X protein and most likely occurred at the transcriptional level. Deletion-mapping analysis of the HBV core promoter and its upstream ENI and ENII enhancers revealed multiple elements responsive to activated Ras. This suppression of HBV replication by activated Ras was apparently mediated by the mitogen-activated protein (MAP) kinase pathway, as it was accompanied by activation of ERK1/2 and abolished by the MEK1/2 inhibitor U0126. Our results thus indicate that external stimuli may suppress HBV replication through the Ras-MAP kinase pathway.

Inhibition of hepatitis B virus replication by drug-induced depletion of nucleocapsids

Chronic hepatitis B virus (HBV) infection is a major cause of liver disease. Only interferon-alpha and the nucleosidic inhibitors of the viral polymerase, 3TC and adefovir, are approved for therapy. However, these therapies are limited by the side effects of interferon and the substantial resistance of the virus to nucleosidic inhibitors. Potent new antiviral compounds suitable for monotherapy or combination therapy are highly desired. We describe non-nucleosidic inhibitors of HBV nucleocapsid maturation that possess in vitro and in vivo antiviral activity. These inhibitors have potential for future therapeutic regimens to combat chronic HBV infection.

Distinct modes of regulation of transcription of hepatitis B virus by the nuclear receptors HNF4alpha and COUP-TF1

To study the effects of the nuclear receptors (NRs) HNF4alpha and COUP-TF1 on the life cycle of hepatitis B virus (HBV), the human hepatoma cell line Huh7 was transiently cotransfected with plasmids containing the HBV genome and encoding these two NRs. Overexpression of HNF4alpha and COUP-TF1 led to a 9-fold increase and a 7- to 10-fold decrease, respectively, in viral DNA synthesis. These two NRs also exhibited distinct modes of regulation of viral transcription. Overexpression of HNF4alpha led to a more-than-10-fold increase in synthesis of the pregenomic RNA but to only a 2- to 3-fold increase in synthesis of the pre-C and S RNAs. Moreover, the NR response element within the pre-C promoter, NRRE(preC,) played the major role in activation of pregenomic RNA synthesis by HNF4alpha. On the other hand, overexpression of COUP-TF1 led to an over-10-fold repression of synthesis of both pre-C and pregenomic RNAs mediated through either NRRE(preC) or NRRE(enhI). HNF4alpha and COUP-TF1 antagonized each other's effects on synthesis of pregenomic RNA and viral DNA when they were co-overexpressed. A naturally occurring HBV variant which allows for binding by HNF4alpha but not COUP-TF1 in its NRRE(preC) exhibited significantly higher levels of synthesis of pregenomic RNA and viral DNA than wild-type HBV in coexpression experiments. Last, deletion analysis revealed that non-NRRE sequences located within both the C and pre-S1 regions are also essential for maximum activation of the pregenomic promoter by HNF4alpha but not for repression by COUP-TF1. Thus, HNF4alpha and COUP-TF1 function through different mechanisms to regulate expression of the HBV genes.

Complete genome sequence of hepatitis B virus (HBV) from a patient with fulminant hepatitis without precore and core promoter mutations: comparison with HBV from a patient with acute hepatitis infected from the same infectious source

BACKGROUND/AIMS

There is a paucity of information regarding hepatitis B virus (HBV) from patients with fulminant hepatitis (FH) without precore (pre-C, nt 1896) and core promoter (CP, nt 1762, 1764) mutations.

METHODS

Pre-C and CP mutations were studied in eight patients with FH and 26 patients with acute hepatitis (AH) due to HBV. One patient with FH (FH1) was infected with HBV without these mutations. Interestingly, the sera of the infectious source (IS1) and of a patient with AH (AH1) infected from IS1 were available. Complete HBV genomes from these three patients were analyzed.

RESULTS

These mutations were found in seven of eight FH and five of 26 AH (P<0.01). HBV from FH1, IS1 and AH1 belonged to genotype D. Nucleotide difference between FH1 and AH1 was six of 3182 bases (nt 493, 998, 1173, 2928, 3067, and 3078). Two and five substitutions of deduced amino acid sequences were found in the pre-S1 and polymerase regions, respectively. The same nucleotide substitutions at nt 493, 1173, 2928 and 3067 were found in several patients with FH in our laboratory or GenBank.

CONCLUSIONS

These six nucleotide substitutions of HBV DNA could be candidates of mutations relating to FH.

Effect of the G1896A precore mutation on drug sensitivity and replication yield of lamivudine-resistant HBV in vitro

Hepatitis B e antigen (HBeAg) negative chronic hepatitis B (CHB) is frequently caused by a mutation (G1896A) in the hepatitis B virus (HBV) precore (PC) reading frame that creates a stop codon, causing premature termination of the PC protein. During lamivudine treatment, drug resistance develops at a similar rate in HBeAg positive and HBeAg negative CHB. Lamivudine-resistant HBV mutants have been shown to replicate inefficiently in vitro in the absence of PC mutations, but it is unknown whether the presence of PC mutations affects replication efficiency or antiviral sensitivity. This study utilized the recombinant HBV baculovirus system to address these issues. HBV baculoviruses encoding the G1896A PC stop codon mutation were generated in wild-type (WT) and lamivudine-resistant (rtM204I and rtL180M + rtM204V) backgrounds, resulting in a panel of 6 related recombinant baculoviruses. In vitro assays were performed to compare the sensitivities of the PC mutant viruses with lamivudine and adefovir and to compare relative replication yields. The PC mutation did not significantly affect sensitivities to either adefovir or lamivudine. WT HBV and PC mutant HBV showed similar replication yields, whereas the replication yields of the lamivudine-resistant mutants were greatly reduced in HBeAg positive HBVs, confirming previous observations. However, the presence of the PC mutation was found to compensate for the replication deficiency in each of the lamivudine-resistant mutants, increasing the replication yields of each virus. In conclusion, the PC stop codon mutation appears to increase the replication efficacy of lamivudine-resistant virus but does not affect in vitro drug sensitivity.

Peptide aptamers targeting the hepatitis B virus core protein: a new class of molecules with antiviral activity

A substantial proportion of the worldwide liver cancer incidence is associated with chronic hepatitis B virus (HBV) infection. The therapeutic management of HBV infections is still problematic and novel antiviral strategies are urgently required. Using the peptide aptamer screening system, we aimed to isolate new molecules, which can block viral replication by interfering with capsid formation. Eight peptide aptamers were isolated from a randomized expression library, which specifically bound to the HBV core protein under intracellular conditions. One of them, named C1-1, efficiently inhibited viral capsid formation and, consequently, HBV replication and virion production. Hence, C1-1 is a novel model compound for inhibiting HBV replication by blocking capsid formation and provides a new basis for the development of therapeutic molecules with specific antiviral potential against HBV infections.

Drug discovery and development of antiviral agents for the treatment of chronic hepatitis B virus infection

A safe and effective vaccine for hepatitis B virus (HBV) has been available for nearly twenty years and currently campaigns to provide universal vaccination in developing countries are underway. Nevertheless, chronic HBV infection remains a leading cause of chronic hepatitis worldwide and there is a strong need for safe and effective antiviral therapies. Attempts to identify and develop antiviral agents to treat chronic HBV infection remains focused on nucleoside analogs such as 3TC (lamivudine), adefovir dipivoxil, (bis-POMPMEA), and others. However, advances in our understanding of the molecular biology of HBV and the development of new assays for HBV polymerase activity, such as the reconstitution of active HBV polymerase in vitro, should facilitate large screening efforts for non-nucleoside reverse transcriptase inhibitors. Recent advances have furthered our understanding of clinical resistance to lamivudine, have provided new approaches to treatment, and have offered new perspectives on the major challenges to the identification and development of antiviral agents for chronic HBV infection. Here, in an update to our previous review article that appeared in this series [59a], we focus on recent advances that have occurred in the areas of virus structure and replication, in vitro viral polymerase assays, cell culture systems, and animal models.

Immune escape by hepatitis B viruses

Hepatitis B viruses are DNA viruses characterized by their very small genome size and their unique replication via reverse transcription. The circular genome has been efficiently exploited, thereby limiting genome variation, and leaves no space for genes in addition to those essentially needed during the viral live cycle. Hepatitis B viruses are prototype non-cytopathic viruses causing persistent infection. Human hepatitis B virus (HBV), as well as the closely related animal viruses, most frequently are transmitted vertically from mothers to their offspring. Because infection usually persists for many years, if not lifelong, hepatitis B viruses need efficient mechanisms to hide from the immune response of the host. To escape the immune response, they exploit different strategies. Firstly, they use their structural and non-structural proteins multiplely. One of the purposes is to alter the immune response. Secondly, they replicate by establishing a pool of stable extrachromosomal transcription templates, which allow the virus to react sensitively to changes in its microenvironment by up- or downregulating gene expression. Thirdly, hepatitis B viruses replicate in the liver which is an immunopriviledged site.

Molecular pathogenesis of viral hepatitis

The global burden of chronic liver disease caused by persistent infection with hepatitis B and C viruses has meant the urgent development of therapeutic strategies designed to control active replication and therefore prevent subsequent clinical sequelae. Advances in these therapeutic strategies are now clearly happening, mainly as a consequence of a better understanding of the viral life cycle and the unique pathogenesis of each disease. Further progress should continue as further insights into the virus-cell relationship are derived, which will sharpen attention on specific viral targets as well as shift and enhance host cytokine responses.

Emergence of the precore mutant late in chronic hepatitis B infection correlates with the severity of liver injury and mutations in the core region

OBJECTIVE

The reason that precore negative mutants (e-minus DNA) gradually become predominant in some patients during chronic hepatitis B virus infection is not clear. Theoretically, as long as both e-plus and e-minus DNA share the same epitopes in the core region, HBcAg-specific cytotoxic T lymphocytes (CTLs) cannot distinguish between the target peptides expressed by e-plus and e-minus DNA. Therefore, e-minus DNA may be accompanied by additional mutations in the core region, which may affect cytotoxic T lymphocyte recognition. To examine this possibility, the sequences of the precore and the entire core region of the hepatitis B virus genome were analyzed from paired serum samples in CH-B patients who experienced HBeAg to anti-HBe seroconversion (SC).

METHODS

Patients were divided into two groups. Group A patients (n = 17) genome-converted to e-minus DNA in the precore region, which abolished HBeAg secretion within 3-4 yr after SC. Group B patients (n = 16) retained precore wild-type DNA for more than 3-4 yr after SC. To investigate the impact of the emergence of precore mutant type DNA on liver injury, alanine aminotransferase (ALT) levels were also examined.

RESULTS

ALT flares were more severe among patients in group A than in group B. The average mean ALT level during the HBeAg negative phase of chronic infection was 54 +/- 38 in group A and 28 +/- 24 in group B. The average maximal ALT level during the HBeAg negative phase was 235 +/- 249 in group A and 83 +/- 106 in group B. Furthermore, all 17 patients in group A developed new core mutants during genome conversion. The average number of mutations in the core gene was 0.9 +/- 1.2 before genome conversion (e-plus DNA dominant phase) and increased to 2.8 +/- 1.3 for the 3-4 yr during genome conversion (e-minus DNA dominant phase). In contrast, only 56% (nine of 16) of patients in group B developed new core mutations after the loss of HBeAg. The average number of mutations in the core gene was 1.8 +/- 1.3 before SC (HBeAg-positive and e-plus DNA dominant phase), and decreased to 1.1 +/- 1.1 for 3-4 yr after seroconversion (anti-HBe-positive and e-plus DNA dominant phase).

CONCLUSIONS

These data indicate that the emergence of a predominant precore negative genotype late in chronic hepatitis B virus infection is associated with the selection of additional mutations in the core gene, as well as with liver injury.

H-2(d) mice born to and reared by HBeAg-transgenic mothers do not develop T cell tolerance toward the hepatitis B virus core gene products

The function of the secretory core gene product (HBeAg) of the human hepatitis B virus (HBV) is unknown. It has been proposed that this protein may be passed from the mother to her offspring at the perinatal stage where it might induce immune tolerance. In a previous study we have shown that the murine placenta presents an efficient barrier for the HBe protein and that H-2(b) mice born to HBeAg-positive transgenic mothers do not develop tolerance of specific cytotoxic T cells. In the present work we demonstrate that transgenic mice expressing high serum levels of HBeAg secrete only small amounts of this protein into their milk and excrete minute amounts of the viral gene product in their urine. Furthermore, it is shown that nontransgenic H-2(d) mice born to and reared by HBeAg-positive mothers exhibit a reactivity of HBc/eAg-specific CD4(+) Th cells and CD8(+) cytotoxic T cells comparable to that of normal isogenic control mice. In accordance with this observation the humoral immune responses directed against the HBeAg were comparable between these two groups of animals. This finding indicates that H-2(d) mice potentially exposed to small amounts of maternal HBeAg transferred by the transplacental, lactogenic, or renal route do not develop tolerance toward the HBV core gene products. These data challenge the hypothesis that a potential function of the HBeAg may be to operate as a tolerogen at the perinatal developmental stage.

The enhancer I core region contributes to the replication level of hepatitis B virus in vivo and in vitro

Chronic hepatitis B virus (HBV) infection can lead to liver cirrhosis and hepatocellular carcinoma. Long-term interaction of the immune system with the virus results in the selection of escape mutants and viral persistence. In this work we characterize mutations in the enhancer I region isolated prior to liver transplantation from the HBV genomes of 10 patients with chronic HBV infection. The HBV-genomes were sequenced, and the enhancer I region was cloned into luciferase reporter constructs to determine the transcriptional activity. Functional studies were performed by transfecting HBV replication-competent plasmids into hepatoma cells. Analyses of the replication fitness of the mutant strains were conducted by biochemical analysis. In all HBV genomes the enhancer I region was mutated. Most of these mutations resulted in decreased transcriptional activity. The strongest effects were detectable in strains with mutations in the hepatocyte nuclear factor 3 and 4 (HNF3 and HNF4) binding sites of the enhancer I core domain. Replication-competent HBV constructs containing these mutations demonstrated up to 10-fold-reduced levels of virus replication. Before liver transplantation, when the mutant strains were detected in the patients' sera, low HBV DNA levels were found. After transplantation and reinfection with a wild-type virus, the levels of replication were up to 240-fold higher. Our results show that mutations in the enhancer I region of HBV have a major impact on HBV replication. These mutations may also determine the switch from high to low levels of viral replication which is frequently observed during chronic HBV infection.

Mutations of the core promoter and response to interferon treatment in chronic replicative hepatitis B

In chronic replicative hepatitis B the significance of mutations in the basic core promoter (BCP), core upstream regulatory sequences (CURS) and negative regulatory element (NRE) for response to interferon (IFN) is unknown. A sequence analysis of the NRE, CURS, BCP, and precore region was performed from sera of 96 patients with chronic replicative hepatitis B (64 hepatitis B e antigen [HBeAg]-positive patients and 32 HBeAg-negative patients) treated with alfa-IFN (IFN-alpha). The overall sustained response (SR) rate to IFN was 30% with no significant difference between HBeAg-positive and HBeAg-negative patients. IFN responsiveness correlated to hepatitis B virus (HBV)-DNA levels, hepatitis B surface antigen (HBsAg) levels, the number of mutations in the complete BCP, especially nucleotide (nt) region 1753 to 1766 and mutations at nt 1762 and 1764. In HBeAg-positive hepatitis, SR to IFN was associated with a high number of mutations in the BCP (P <.04) and nucleotide region 1753 to 1766 (P <.015) as well as mutations at nucleotide 1764 (P <.007). In HBeAg-negative hepatitis, SR to IFN correlated with a low number of mutations in the BCP (P <.04) and nucleotide region 1753 to 1766 (P <.02) and a wild-type sequence at nt 1764 (P <.003). Prediction of IFN response was possible on the basis of nt 1764 in 77% of HBeAg-positive patients and 78% of HBeAg-negative patients. IFN response did not correlate with the occurrence of the 1896 mutation, mutations in the CURS or NRE, disease duration, ethnic origin of the patient, alanine transaminase (ALT) levels and HBV genotype. Our data suggest that HBV genome mutations located within the BCP are determinants of a response to IFN therapy.

Immune escape by hepatitis B viruses

Hepatitis B viruses are DNA viruses characterized by their very small genome size and their unique replication via reverse transcription. The circular genome has been efficiently exploited, thereby limiting genome variation, and leaves no space for genes in addition to those essentially needed during the viral live cycle. Hepatitis B viruses are prototype non-cytopathic viruses causing persistent infection. Human hepatitis B virus (HBV), as well as the closely related animal viruses, most frequently are transmitted vertically from mothers to their offspring. Because infection usually persists for many years, if not lifelong, hepatitis B viruses need efficient mechanisms to hide from the immune response of the host. To escape the immune response, they exploit different strategies. Firstly, they use their structural and non-structural proteins multiplely. One of the purposes is to alter the immune response. Secondly, they replicate by establishing a pool of stable extrachromosomal transcription templates, which allow the virus to react sensitively to changes in its microenvironment by up- or downregulating gene expression. Thirdly, hepatitis B viruses replicate in the liver which is an immunopriviledged site.