Cytokine-sensitive replication of hepatitis B virus in immortalized mouse hepatocyte cultures

Lambda and alpha interferons inhibit hepatitis B virus replication through a common molecular mechanism but with different in vivo activities

The type III interferons (IFN-lambda1, 2, and 3) induce an antiviral response similar to IFN-alpha/beta, but mediate their activity through a unique receptor. We found that like IFN-alpha/beta, IFN-lambda prevents the assembly of HBV capsids, demonstrating convergence of the two signaling pathways through a single antiviral mechanism. In contrast to IFN-lambda, the structurally related cytokine interleukin (IL)-22 only minimally reduced HBV replication. The transcriptional program activated by IL-22 displayed little similarity to that induced by IFN-lambda, but instead resembled the response elicited by IL-6. We also found that murine IFN-lambda2 had only weak antiviral activity against HBV in the liver of transgenic mice, and that human IFN-lambda2 activity in serum correlated with the sensitivity of the cytokine to proteases. These results demonstrate that the IFN-alpha/beta and IFN-lambda anti-HBV responses operate through a single molecular mechanism, and support the notion that IFN-lambda plays a local, rather than systemic, role in antiviral immunity.

Differential effects of interferon and lamivudine on serum HBV RNA inhibition in patients with chronic hepatitis B

BACKGROUND

Lamivudine and interferon have been widely used for the treatment of patients with chronic HBV infection. Serum HBV RNA is detected during lamivudine therapy as a consequence of interrupted reverse transcription and because RNA replicative intermediates are unaffected by the drug. In this study, we aimed to determine the detectability of serum HBV RNA during sequential combination therapy of interferon and lamivudine.

METHODS

HBV DNA and RNA in serum samples were quantified by reverse transcription of HBV nucleic acid extract and real-time PCR. Samples were analysed every 2 weeks to 3 months from three groups of patients: 10 male patients treated with nucleoside analogue monotherapy for 44-48 weeks (5 with lamivudine and 5 with entecavir), 6 males on sequential interferon and lamivudine combination therapy, and 3 males on lamivudine monotherapy for 20-24 weeks.

RESULTS

HBV RNA was not detectable in any patients before treatment, but became detectable in 15 during antiviral treatment. Among the three groups, pre-treatment HBV DNA (8.1 +/-2.4 versus 7.7 +/-1.4 versus 5.1 +/-0.3 log(10) copies/ml; P=0.06), treatment and follow-up durations (45.5 +/-2.0 versus 49.7 +/-5.6 versus 48.7 +/-6.4 weeks; P=0.32) were comparable. HBV RNA was detectable at the end of treatment or follow-up in all patients with monotherapy, but in none of those with sequential combination therapy (100% versus 0%; P<0.001).

CONCLUSIONS

Compared with lamivudine therapy with detectable serum HBV RNA in patients with chronic HBV infection, interferon treatment might reduce HBV DNA replication through the inhibition of HBV RNA replicative intermediates, resulting in the loss of serum HBV RNA.

Proteomic analysis reveals a major role for contact inhibition in the terminal differentiation of hepatocytes

BACKGROUND & AIMS

Hepatocytes are considered an exception of the paradigmatic inverse correlation between cell proliferation and terminal differentiation. In fact, hepatic vital functions are guaranteed by proliferating parenchymal cells during liver regeneration. However, a fine molecular characterization of the relationship between proliferation and differentiation in hepatocytes has been hampered by the lack of reliable in vivo or in vitro models.

METHODS

The hepatocyte terminal differentiation program was characterized in the immortalized, untransformed and differentiated hepatocytic cell line MMH, using several techniques. Particularly, two-dimensional difference gel electrophoresis combined to tandem mass spectrometry proteomic approach was used. Cell cycle and cell adhesion properties of MMH have been altered using either myc-overexpression and MEK1/2 inhibition or a constitutive active beta-catenin mutant, respectively.

RESULTS

The hepatocyte terminal differentiation program is stimulated by the exit from the cell cycle induced by cell-cell contact. Comparative proteomic analysis of proliferating versus quiescent hepatocytes validated the importance of contact inhibition, identifying 68 differently expressed gene products, representing 49 unique proteins. Notably, enzymes involved in important liver functions such as detoxification processes, lipid metabolism, iron and vitamin A storage and secretion, anti-inflammatory response and exocytosis were found significantly up-regulated in quiescent hepatocytes. Finally, we found that: (i) cell cycle arrest induced by MEK1/2 inhibition is not sufficient to induce hepatic product expression; (ii) constitutive activation of beta-catenin counteracts the contact inhibition-induced terminal differentiation.

CONCLUSION

The hepatocyte terminal differentiation program requires a quiescent state maintained by cell-cell contact through the E-cadherin/beta-catenin pathway, rather than the inhibition of proliferation.

Not interferon, but interleukin-6 controls early gene expression in hepatitis B virus infection

With about 350 million virus carriers, hepatitis B virus (HBV) infection remains a major health problem. HBV is a noncytopathic virus causing persistent infection, but it is still unknown whether host recognition of HBV may activate an innate immune response. We describe that upon infection of primary human liver cells, HBV is recognized by nonparenchymal cells of the liver, mainly by liver macrophages (Kupffer cells), although they are not infected. Within 3 hours, this recognition leads to the activation of nuclear factor kappa B (NF-kappaB) and subsequently to the release of interleukin-6 (IL-6) and other proinflammatory cytokines (IL-8, TNF-alpha, IL-1beta), but does not induce an interferon response. The activation of proinflammatory cytokines, however, is transient, and even inhibits responsiveness toward a subsequent challenge. IL-6 released by Kupffer cells after activation of NF-kappaB controls HBV gene expression and replication in hepatocytes at the level of transcription shortly after infection. Upon binding to its receptor complex, IL-6 activates the mitogen-activated protein kinases exogenous signal-regulated kinase 1/2, and c-jun N-terminal kinase, which inhibit expression of hepatocyte nuclear factor (HNF) 1alpha and HNF 4alpha, two transcription factors essential for HBV gene expression and replication.

CONCLUSION

Our results demonstrate recognition of HBV patterns by nonparenchymal liver cells, which results in IL-6-mediated control of HBV infection at the transcriptional level. Thus, IL-6 ensures early control of the virus, limiting activation of the adaptive immune response and preventing death of the HBV-infected hepatocyte. This pattern recognition may be essential for a virus, which infects a new host with only a few virions. Our data also indicate that therapeutic neutralization of IL-6 for treatment of certain diseases may represent a risk if the patient is HBV-infected.

Host immunity influences disease progression and antiviral efficacy in humans infected with hepatitis B virus

Hepatitis B virus (HBV) infection can lead to several severe liver diseases, including hepatitis, cirrhosis and hepatocellular carcinoma, although the underlying mechanisms responsible for the clinical outcome have not been well characterized. In this review, we retrospectively examine the history of immunological responses to HBV infection and summarize the current understanding of innate and adaptive immunity in the context of HBV-associated liver disease. Recent data indicate that the interaction between HBV and the host immune response not only substantially drives disease progression, but also significantly influences antiviral efficacy in HBV-infected individuals. Advances in the field have provided insight into the immunopathology of HBV infection. Based on the characteristics of host immune responses in patients with HBV infection, a 'climbing slope hypothesis' is proposed to suggest that therapeutic strategies aimed at modulating the immune activity of the host may represent a complementary approach to antiviral drug treatment for the management of chronically HBV-infected patients.

Incidence and nature of infectious disease in patients treated with anti-TNF agents

Tumor necrosis factor alpha (TNF-alpha) inhibitors offer a targeted therapeutic strategy that contrasts with the nonspecific immunosuppressive agents traditionally used to treat most inflammatory diseases. These biologic agents have had a significant impact in ameliorating the signs and symptoms of inflammatory rheumatoid disease and improving patient function. From the onset of clinical trials, a central concern of cytokine blockade has been a potential increase in susceptibility to infections. Not surprisingly, a variety of infections have been reported in association with the use of TNF-alpha inhibitor agents. In particular, there is evidence suggesting an increased rate of granulomatous infections in patients treated with monoclonal TNF-alpha inhibitors. This review provides the incidence and nature of infections in patients treated with TNF-alpha inhibitor agents and reminds the clinician of the required vigilance in monitoring patients.

Highly efficient antiviral CD8+ T-cell induction by peptides coupled to the surfaces of liposomes

In previous studies, we have demonstrated that liposomes with differential lipid components display differential adjuvant effects when antigens (Ags) are chemically coupled to their surfaces. When ovalbumin was coupled to liposomes made by using unsaturated fatty acids, it was found to be presented not only to CD4(+) T cells but also to CD8(+) T cells and induced cytotoxic T lymphocytes (CTLs) which effectively eradicated the tumor from mice. In this study, we coupled liposomes to immunodominant CTL epitope peptides derived from lymphocytic choriomeningitis virus (LCMV) and evaluated its potency as an antiviral vaccine. The intramuscular immunization of mice with the peptide-liposome conjugates along with CpG resulted in the efficient induction of antiviral CD8(+) T-cell responses which conferred complete protection against not only LCMV Armstrong but also a highly virulent mutant strain, clone 13, that establishes persistent infections in immunocompetent mice. The intranasal vaccination induced mucosal immunity effective enough to protect mice from the virus challenge via the same route. Complete protection was achieved in mice even when the Ag dose was reduced to as low as 280 ng of liposomal peptide. This form of vaccination with a single CTL epitope induced Ag-specific memory CD8(+) T cells in the absence of CD4(+) T-cell help, which could be shown by the complete protection of CD4-knockout mice in 10 weeks as well as by the analysis of recall responses. Thus, surface-linked liposomal peptide might have a potential advantage for the induction of antiviral immunity.

Functional dissection of an IFN-alpha/beta receptor 1 promoter variant that confers higher risk to chronic hepatitis B virus infection

BACKGROUND/AIMS

We previously demonstrated that two linked single nucleotide polymorphisms (SNPs) at -408 and -3 of type I interferon receptor 1 (IFNAR1) promoter are associated with susceptibility to chronic HBV infection. We aimed to elucidate the mechanism by which -3 and/or -408 C/T SNPs had such profound effects.

METHODS

A functional SNP in IFNAR1 promoter was defined by reporter gene assay, mutational analysis, flow cytometry analysis and gel shift assay. The nuclear protein binding to the essential polymorphic site was identified and its effect on transcriptional regulation of IFNAR1 was further demonstrated in a series of ex vivo and in vivo experiments.

RESULTS

We found C>T change at the -3 locus reduced the transcriptional activity of IFNAR1 promoter. High mobility group B protein 1 (HMGB1) and PARP-1 were co-recruited to the IFNAR1 promoter to regulate its transcription. We demonstrated HMGB1-binding affinity to IFNAR1 promoter was reduced in the -3T variant. Additionally, PARP-1, a cofactor for IFNAR1 transcription activation, was significantly suppressed by HBV.

CONCLUSION

Upon HBV infection, decreased binding affinity of HMGB1 to the IFNAR1 promoter -3T variant is aggravated by the suppressed PARP-1 expression caused by HBV, resulting in a further attenuated IFNAR1 expression. This compromises the antiviral and immuno-regulatory effects of IFN-alpha/beta, which may in turn affect the clinical outcome of HBV infection.

Hepatitis B virus suppresses toll-like receptor-mediated innate immune responses in murine parenchymal and nonparenchymal liver cells

We have previously shown that Toll-like receptor (TLR)-activated murine nonparenchymal liver cells [(NPC); Kupffer cells (KC), liver sinusoidal endothelial cells (LSEC)] can suppress hepatitis B virus (HBV) replication. Therefore, the aim of this study was to investigate whether HBV has the ability to counteract the TLR-mediated control of its replication. Freshly purified murine hepatocytes and NPCs obtained from C57BL6 mice were stimulated by TLR 1-9 ligands in the presence or absence of hepatitis B surface antigen (HBsAg), hepatitis B e antigen (HBeAg), HBV virions, or supernatants from HBV-producing HBV-Met cells, and HBV replication was suppressed by anti- hepatitis B virus X protein (HBx) small interfering RNA (siRNA) in HBV-Met cells. Supernatants were collected and tested for antiviral cytokines by viral protection assay. HBV gene expression and replication was analyzed by southern blot. RNA and proteins were analyzed by quantitative reverse transcription polymerase chain reaction (RT-PCR) or western blot and enzyme-linked immunosorbent assay, respectively. Pretreatment of hepatocytes and NPCs with HBV-Met cells supernatants, HBsAg, HBeAg, or HBV virions almost completely abrogated TLR-induced antiviral activity, which correlated with suppression of interferon beta (IFN-beta) production and subsequent interferon-stimulated gene induction as well as suppressed activation of interferon regulatory factor 3 (IRF-3), nuclear factor kappa B (NF-kappaB), and extracellular signal-regulated kinase (ERK) 1/2. In HBV-infected HBV-Met cells, TLR stimulation did not induce antiviral cytokines in contrast to primary hepatocytes. TLR-stimulated expression of proinflammatory cytokines [tumor necrosis factor alpha (TNF-alpha), interleukin-6 (IL-6)], and activation of IRF-3 was suppressed after up-regulation of HBV replication in HBV-Met cells. Accordingly, suppression of HBV replication by siRNA led to activation or expression of proinflammatory transcription factors and cytokines.

CONCLUSION

Our data indicate that HBV can suppress the TLR-induced antiviral activity of liver cells. This has major implications for the interaction between HBV and the immune system.

Increased apoptosis in HepG2.2.15 cells with hepatitis B virus expression by synergistic induction of interferon-gamma and tumour necrosis factor-alpha

BACKGROUND

Interferon-gamma (IFN-gamma) and tumour necrosis factor-alpha (TNF-alpha) were thought to be important immune mediators in host defence against hepatitis B virus (HBV) infection.

AIMS

To examine the synergistic effect of IFN-gamma and TNF-alpha on HBV-expressing HepG2.2.15 cells and its potential mechanisms.

METHODS

Cell viability was quantitatively measured by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide assay. Cell morphology was captured using light microscopy. The typical DNA ladder test was performed using agarose gel electrophoresis. HBsAg and HBeAg titre changes were quantified by the enzyme-linked immunosorbent assay method. Gene expression was analysed using cDNA macroarrays.

RESULTS

Interferon-gamma (1000 U/ml) alone or combined with TNF-alpha (5 ng/ml) treatment resulted in apoptosis in HepG2.2.15 cells, but no significant apoptosis in the parent non-virus expressing HepG2 cells. IFN-gamma- and TNF-alpha-mediated apoptosis was reduced by lamivudine treatment in HepG2.2.15 cells. IFN-gamma combined with TNF-alpha reduced the titre of hepatitis B surface antigen and hepatitis B e antigen in the HepG2.2.15 cell line. For apoptosis-related gene changes, IFN regulatory factor 1 (IRF-1) (12.2-fold), c-myc (V00568 4.7-fold, L00058 2.4-fold) and caspase 7 (2.3-fold) genes were upregulated in the combination treatment group.

CONCLUSION

Interferon-gamma and TNF-alpha play a role in the cell death of HBV-expressing HepG2.2.15 cells. Expression of HBV leads to IFN-gamma- and TNF-alpha-mediated apoptosis in the cells. Increased IRF-1, c-myc and caspase 7 gene expression may be responsible for the synergistic induction of apoptosis by IFN-gamma and TNF-alpha.

Hepatitis B virus replication and release are independent of core lysine ubiquitination

Ubiquitin conjugation to lysine residues regulates a variety of protein functions, including endosomal trafficking and degradation. While ubiquitin plays an important role in the release of many viruses, the requirement for direct ubiquitin conjugation to viral structural proteins is less well understood. Some viral structural proteins require ubiquitin ligase activity, but not ubiquitin conjugation, for efficient release. Recent evidence has shown that, like other viruses, hepatitis B virus (HBV) requires a ubiquitin ligase for release from the infected cell. The HBV core protein contains two lysine residues (K7 and K96), and K96 has been suggested to function as a potential ubiquitin acceptor site based on the fact that previous studies have shown that mutation of this amino acid to alanine blocks HBV release. We therefore reexamined the potential connection between core lysine ubiquitination and HBV replication, protein trafficking, and virion release. In contrast to alanine substitution, we found that mutation of K96 to arginine, which compared to alanine is more conserved but also cannot mediate ubiquitin conjugation, does not affect either virus replication or virion release. We also found that the core lysine mutants display wild-type sensitivity to the antiviral activity of interferon, which demonstrates that ubiquitination of core lysines does not mediate the interferon-induced disruption of HBV capsids. However, mutation of K96 to arginine alters the nuclear-cytoplasmic distribution of core, leading to an accumulation in the nucleolus. In summary, these studies demonstrate that although ubiquitin may regulate the HBV replication cycle, these mechanisms function independently of direct lysine ubiquitination of core protein.

ERK5/MAPK is activated by TGFbeta in hepatocytes and required for the GSK-3beta-mediated Snail protein stabilization

Extracellular signal-regulated protein kinase 5 (ERK5) is a mitogen-activated protein kinase, specifically activated by MEK5, and involved in the regulation of many cellular functions including proliferation, survival, differentiation and apoptosis. MEK5/ERK5 module is an important element of different signal transduction pathways. The aim of this study was to investigate whether ERK5 participates to the signalling of the multifunctional cytokine TGFbeta, known to play an important role in the regulation of hepatic growth. Here, we reported that ERK5 is phosphorylated and activated by TGFbeta in hepatocytes, with a rapid and sustained kinetic, through a Src-dependent pathway. Moreover, we demonstrated that ERK5 participates to the TGFbeta-induced Snail protein regulation being required for its stabilization. We also found that the functional inactivation of ERK5 impedes the TGFbeta-mediated glycogen synthase kinase-3beta inactivation suggesting this as mechanism responsible for ERK5-mediated Snail stabilization. Thus, results presented in this study uncovered for the first time a role for ERK5 in the TGFbeta-induced cellular responses.

APOBEC3-independent interferon-induced viral clearance in hepatitis B virus transgenic mice

Interferon (IFN) has been part of the standard treatment of chronic hepatitis B infection for more than 2 decades, yet the mechanism of action of this antiviral remains poorly understood. It was recently observed that members of the human APOBEC family of cytidine deaminases endowed with anti-hepatitis B virus (HBV) activity are upregulated by type I and II IFNs. However, we demonstrated that, in tissue culture, these cellular enzymes are not essential effectors of the anti-HBV action of these cytokines. Here, we show that murine APOBEC3 (muA3) can also block HBV replication. While expressed at low levels in the mouse liver at baseline, muA3 is upregulated upon IFN induction. However, in HBV-transgenic muA3 knockout mice, IFN induction blocked HBV DNA production as efficiently as in control HBV-transgenic muA3-competent animals. We conclude that APOBEC3 is not an essential mediator of the IFN-mediated inhibition of HBV in vivo.

APOBEC and iNOS are not the main intracellular effectors of IFN-gamma-mediated inactivation of Hepatitis B virus replication

BACKGROUND/AIM

Interferon-gamma (IFN-gamma) produced by activated T-cells is the principle mediator of non-cytolytic Hepatitis B virus (HBV) inactivation; however the intracellular pathways responsible are poorly defined. We investigated the role of IFN-gamma-inducible nitric oxide synthase (iNOS) and APOBEC3 (A3) enzyme family in the inhibition of HBV replication by IFN-gamma.

METHODS

Hepatoma-cell lines transfected with HBV DNA were treated with IFN-gamma. Viral replication, iNOS and A3 mRNAs were quantitated by TaqManPCR and the direct nitric oxide (NO) effect on HBV replication was investigated using an NO-donor. A3G antiviral activity was verified by co-transfection with its inhibitor, human immunodeficiency virus (HIV)-associated virion infectivity factor (Vif).

RESULTS

IFN-gamma caused a dose-dependent reduction (>50%) of HBV DNA in the absence of cytotoxicity. Although iNOS mRNA increased 45-fold in IFN-gamma treated cells, NO2- was not detectable in supernatants and the use of an NO-donor did not inhibit HBV replication. A3 enzyme mRNAs varied between cells and were >10-fold higher in lymphocytes than in liver tissue. IFN-gamma up-regulated A3G mRNA by three-fold, associated with significant HBV DNA decrease. However, A3G degradation by Vif did not abolish the antiviral effect of IFN-gamma against HBV.

CONCLUSIONS

IFN-gamma inhibits HBV replication and up-regulates both iNOS and A3G. However, other pathways appear to have a greater role in IFN-gamma-induced HBV inactivation in the liver.

Immunobiology and pathogenesis of viral hepatitis

Among the many viruses that are known to infect the human liver, hepatitis B virus (HBV) and hepatitis C virus (HCV) are unique because of their prodigious capacity to cause persistent infection, cirrhosis, and liver cancer. HBV and HCV are noncytopathic viruses and, thus, immunologically mediated events play an important role in the pathogenesis and outcome of these infections. The adaptive immune response mediates virtually all of the liver disease associated with viral hepatitis. However, it is becoming increasingly clear that antigen-nonspecific inflammatory cells exacerbate cytotoxic T lymphocyte (CTL)-induced immunopathology and that platelets enhance the accumulation of CTLs in the liver. Chronic hepatitis is characterized by an inefficient T cell response unable to completely clear HBV or HCV from the liver, which consequently sustains continuous cycles of low-level cell destruction. Over long periods of time, recurrent immune-mediated liver damage contributes to the development of cirrhosis and hepatocellular carcinoma.

Toll-like receptor-mediated control of HBV replication by nonparenchymal liver cells in mice

Hepatitis B virus (HBV) infection is one of the most frequent causes of chronic liver disease worldwide. Because recent studies have suggested that Toll-like receptor (TLR)-based therapies may be a promising approach in the treatment of HBV infection, we studied the role of the local innate immune system of the liver as a possible mediator of this effect. Murine nonparenchymal cells, including Kupffer cells (KCs) and sinusoidal endothelial cells (LSECs), were isolated from C57/BL6 wild-type or MyD88(-/-) mice and stimulated by agonists of TLR1 to TLR9. Supernatants were harvested and assayed for their antiviral activity against HBV in HBV-Met cells. No direct antiviral effect of TLR agonists could be observed. In controls (myeloid dendritic cells), TLR1, TLR3, TLR4, TLR7, and TLR9 activation lead to production of antiviral cytokines. By contrast, only supernatants from TLR3-stimulated and TLR4-stimulated KCs and TLR3-stimulated LSECs from wild-type mice were able to potently suppress HBV replication as assessed via Southern blotting. Similar results were found with cells from MyD88(-/-) mice, indicating that the effect was independent of this signaling pathway. Cellular HBV RNA and hepatitis B surface antigen or hepatitis B e antigen levels in supernatants remained unchanged. Using neutralizing antibodies, we demonstrated that the TLR3-mediated effect but not the TLR4-mediated effect is mediated exclusively through interferon-beta.

CONCLUSION

Our data indicate that the innate immune system of the liver can control HBV replication after activation by TLR agonists. This has implications for the development of TLR-based therapeutic approaches against HBV.

The immunology of hepatitis B

The hepatitis B virus (HBV) is an enveloped, hepatotrophic, oncogenic hepadnavirus that is noncytopathic for hepatocytes. HBV infection results in a variety of outcomes that are determined by the quality, quantity, and kinetics of the host innate and adaptive immune responses. Whether HBV infection is cleared or persists as a progressive or nonprogressive liver disease is determined by both viral and host factors. Replicative intermediates can persist in the liver under immunologic control after resolution of acute or chronic hepatitis B, conferring a risk for reactivation following a course of immunosuppression or chemotherapy.

Transforming growth factor-beta1 suppresses hepatitis B virus replication primarily through transcriptional inhibition of pregenomic RNA

Transforming growth factor-beta1 (TGF-beta1) is a pleiotropic cytokine with pivotal roles in the regulation of cellular functions and immune responses. In this study, we found that TGF-beta1 was able to effectively suppress hepatitis B virus (HBV) replication. In the presence of TGF-beta1, the level of viral replicative intermediates was dramatically decreased, both in actively dividing cells and in confluent cells. At the same time, the levels of viral transcripts, core protein, and nucleocapsid were significantly diminished by TGF-beta1 treatment. Interestingly, the inhibitory activity of TGF-beta1 was associated with preferential reduction of the level of pregenomic RNA compared with pre-C mRNA. Further analysis indicated that TGF-beta1 might exert its antiviral effect primarily through reducing expression of the HBV core protein by transcriptional regulation instead of posttranscriptional modification.

CONCLUSION

TGF-beta1 may play a dual role in HBV infection, in the suppression of immune responses against viral infection and in the direct inhibition of viral replication, resulting in minimization of liver damage in patients with chronic hepatitis.

Induction of antiviral cytidine deaminases does not explain the inhibition of hepatitis B virus replication by interferons

Interferons (IFNs) play a major role in the control of hepatitis B virus (HBV), whether as endogenous cytokines limiting the spread of the virus during the acute phase of the infection or as drugs for the treatment of its chronic phase. However, the mechanism by which IFNs inhibit HBV replication has so far remained elusive. Here, we show that type I and II IFN treatment of human hepatocytes induces the production of APOBEC3G (A3G) and, to a lesser extent, that of APOBEC3F (A3F) and APOBEC3B (A3B) but not that of two other cytidine deaminases also endowed with anti-HBV activity, activation-induced cytidine deaminase (AID), and APOBEC1. Most importantly, we reveal that blocking A3B, A3F, and A3G by combining RNA interference and the virion infectivity factor (Vif) protein of human immunodeficiency virus does not abrogate the inhibitory effect of IFNs on HBV. We conclude that these cytidine deaminases are not essential effectors of IFN in its action against this pathogen.

Regulation of hepatitis B virus replication by the phosphatidylinositol 3-kinase-akt signal transduction pathway

The phosphatidylinositol 3-kinase (PI3K)-protein kinase B (Akt) signaling pathway is one of the major oncogenic pathways and is activated in many types of human cancers, including hepatocellular carcinoma. It can also be activated by the hepatitis C virus (HCV) nonstructural 5A (NS5A) protein. In the present study, we set out to determine the regulatory effects of this pathway on the replication of hepatitis B virus (HBV). Our results demonstrate that the expression of a constitutively active Akt1 profoundly inhibited HBV RNA transcription and consequently reduced HBV DNA replication in HepG2 cells. This suppression of HBV gene transcription was apparently mediated by the activation of mTOR, as it was abolished by the mTOR inhibitor rapamycin. Moreover, treatment of HBV-expressing HepG2.2.15 cells with inhibitors of PI3K, Akt, and mTOR increased the transcription of 3.5-kb and 2.4-kb viral RNA as well as the replication of HBV DNA. This observation implies that the basal level activation of this pathway in HepG2 cells regulated HBV replication. Consistent with previous reports showing that the HCV NS5A protein could bind to the p85 subunit of PI3K and activate the PI3K-Akt signal transduction pathway, our results showed that expression of this protein could inhibit HBV RNA transcription and reduce HBV DNA replication in HepG2 cells. Taken together, our results suggest that the activation of the PI3K-Akt pathway during liver oncogenesis may be at least partially responsible for the elimination of HBV replication from tumor cells and may also provide an explanation for the observed suppression of HBV replication by HCV coinfection.

Unique antiviral mechanism discovered in anti-hepatitis B virus research with a natural product analogue

Helioxanthin is a natural product that inhibits the replication of a number of viruses. We found that a previously undescribed helioxanthin analogue, 8-1, exhibited potent anti-hepatitis B virus (HBV) activity with little cytotoxicity. 8-1 suppressed both HBV RNA and protein expression, as well as DNA replication of both wild-type and 3TC-resistant virus. Time-course analyses revealed that RNA expression was blocked first after treatment with 8-1, followed by viral proteins, and then DNA. 8-1 inhibited the activity of all HBV promoters by decreasing the binding of hepatocyte nuclear factor 4 (HNF-4), HNF-3, and fetoprotein factor to the precore/core promoter enhancer II region. The amount of HNF-4 and HNF-3 was decreased posttranscriptionally by 8-1 in HBV-producing cells, but not in HBV-negative cells. Therefore, 8-1 suppresses HBV replication by posttranscriptional down-regulation of critical transcription factors in HBV-producing cells, thus diminishing HBV promoter activity and blocking viral gene expression and replication. This mechanism is unique and different from other anti-HBV compounds previously described.

PD-1:PD-L1 interactions contribute to the functional suppression of virus-specific CD8+ T lymphocytes in the liver

Mechanisms contributing to the development of chronic viral infections, including chronic hepatitis B virus (HBV) infections, are not well understood. We have shown recently that production of IFN-gamma, an important antiviral cytokine, by HBV-specific CTLs is rapidly induced when they enter the liver of HBV transgenic mice, and then rapidly suppressed, despite the continued presence of Ag. Suppression of IFN-gamma production by the CTLs coincides with the up-regulation of programmed cell death (PD)-1, a cell surface signaling molecule known to inhibit T cell function. To determine whether PD-1 plays a role in the functional suppression of IFN-gamma secretion by CTLs, we treated HBV transgenic mice with blocking Abs specific for PD ligand (PD-L)1, the most widely expressed PD-1 ligand, and adoptively transferred HBV-specific CTLs. Treatment with anti-PD-L1 Abs resulted in a delay in the suppression of IFN-gamma-producing CTLs and a concomitant increase in the absolute number of IFN-gamma-producing CTLs in the liver. These results indicate that PD-1:PD-L1 interactions contribute to the suppression of IFN-gamma secretion observed following Ag recognition in the liver. Blockade of inhibitory pathways such as PD-1:PD-L1 may reverse viral persistence and chronic infection in cases in which the CTL response is suppressed by this mechanism.

Polymorphisms of type I interferon receptor 1 promoter and their effects on chronic hepatitis B virus infection

BACKGROUND/AIMS

Exposure to HBV leads to a distinct clinical course which is partially pertained to host genetic variability. We aimed to study polymorphisms of type I interferon receptor 1 (IFNAR1) promoter and their potential effects on chronic HBV infection.

METHODS

Polymorphisms of IFNAR1 promoter were identified in 320 chronic hepatitis B patients, 148 spontaneously recovered individuals, 148 healthy Chinese donors and 114 Caucasians. Their functional capability in driving reporter gene expression was analyzed.

RESULTS

Four polymorphic alleles were identified at loci -568, -408, -77 and -3. Association analysis revealed that carriers of alleles -568G, -408C and their related haplotype I were less susceptible to chronic HBV infection whereas those of alleles -568C, -408T and related haplotype III were significantly associated with higher risk to chronic hepatitis B (P<0.01). In a reporter-driven system, the promoter variants with alleles -408C and -3C could drive higher expression of the reporter gene than those with alleles -408T and -3T (P<0.01). Interestingly, an allele with 9 GT repeats at -77 that was rarely found in Chinese but prevalent in Caucasian exhibited the highest transcriptional ability.

CONCLUSIONS

Our results showed that polymorphisms of IFNAR1 promoter may affect, at least in part, the outcomes of HBV infection.

Interferon-α response in chronic hepatitis B-transfected HepG2.2.15 cells is partially restored by lamivudine treatment

AIM: To characterize the IFN-response and its modul-ation by the antiviral compound lamivudine in HBV-transfected HepG2.2.15 cells.

METHODS: HepG2.2.15 and HepG2 cells were stimulated with various concentrations of IFN-α2a in the presence or absence of lamivudine. Then, total RNA was extracted and analysed by customised cDNA arrays and northern blot for interferon-inducible genes (ISGs). In addition, cellular proteins were extracted for EMSA and western blot. HBV replication was assessed by southern blot or ELISAs for HBsAg and HBeAg.

RESULTS: Two genes (MxA, Cig5) with completely abolished and 4 genes (IFITM1, -2, -3, and 6-16) with partially reduced IFN-responses were identified in HepG2.2.15 cells. In 2 genes (IFITM1, 6-16), the response to IFN-α could be restored by treatment with lamivudine. This effect could not be explained by a direct modulation of the Jak/Stat signalling pathway since EMSA and western blot experiments revealed no suppression of Stat1 activation and ISGF3 formation after stimulation with IFN-α in HepG2.2.15 compared to HepG2 cells.

CONCLUSION: These results are consistent with the assumption that chronic hepatitis B may specifically modulate the cellular response to IFN by a selective blockage of some ISGs. Antiviral treatment with lamivudine may partially restore ISG expression by reducing HBV gene expression and replication.

Quantitative analysis of HBV cccDNA from clinical specimens: correlation with clinical and virological response during antiviral therapy

Attempts to investigate changes in various forms of intrahepatic hepatitis B virus (HBV) DNA during antiviral therapy have been hampered by limitations in technologies and scarcity of adequate tissue for analysis. We used a sensitive, specific assay to detect and quantitate covalently closed circular DNA (cccDNA) from total intrahepatic HBV DNA in clinical liver specimens. Total HBV DNA and cccDNA from 21 needle-biopsy specimens were quantified, with levels ranging from 0.1 to 9.8 copies/cell and 0.3 to 491.0 copies/cell, respectively. Then, we performed the same determinations on baseline and week-52 liver needle-biopsy specimens from eight patients enrolled in a clinical trial and evaluated the association between intrahepatic HBV DNA levels and serological and virological endpoints. In most patients, levels of intrahepatic HBV DNA, including cccDNA, decreased over the 52-week study, regardless of therapy or serological outcome. Higher ratios of cccDNA to total HBV DNA were detected at week 52 than at baseline indicating a shift in predominance of nonreplicating virus in posttreatment specimens. In patients who achieved treatment-related or spontaneous hepatitis B e antigen (HBeAg) responses, including those harbouring tyrosine-methionine-aspartate-aspartate-mutant HBV, levels of intrahepatic and serum HBV DNA suppression were greater than those in patients without HBeAg responses. In conclusion, this pilot study of intrahepatic HBV replicative forms in patients with chronic hepatitis B indicated that total intrahepatic and, specifically, cccDNA levels are not static but change as a reflection of serological and virological events.

Production of infectious hepatitis C virus by well-differentiated, growth-arrested human hepatoma-derived cells

Dimethyl sulfoxide (DMSO) has been shown to induce the differentiation of primary hepatocytes in vitro. When actively dividing poorly differentiated human hepatoma-derived (Huh7) cells were cultured in the presence of 1% DMSO, cells became cytologically differentiated and transitioned into a nondividing state, characterized by the induction of hepatocyte-specific genes. Moreover, these cells were highly permissive for acute hepatitis C virus (HCV) infection, and persistent long term infection of these cultures could also be achieved. As HCV naturally replicates in highly differentiated nondividing human hepatocytes, this system may more accurately mimic the conditions under which HCV replicates in vivo than previous models using poorly differentiated rapidly dividing hepatoma cells.

Effect of seasonal variation on the clinical course of chronic hepatitis B

BACKGROUND

Seasonal variation in immunity has been found in healthy individuals and in association with some diseases. It is still unknown whether seasonal variation affects the clinical course of chronic hepatitis B. Our aim in this study was to explore the effect of seasonal variation on the clinical course of chronic hepatitis B.

METHODS

The flare and remission time of chronic hepatitis B were observed in patients with hepatitis B virus (HBV) infection. All patients enrolled were followed up at least every 3 months for a mean follow-up time of 24.0 (range, 12-60) months. Seasonal decomposition was employed to analyze the relationship between seasonal variation and flares, remission, and hepatitis B e antigen (HBeAg) seroconversion in chronic hepatitis B patients during follow-up.

RESULTS

A total of 2238 patients were observed in our study. Flare and HBeAg seroconversion were seldom seen in 1076 patients (48.08%) with alanine aminotransferase (ALT) levels of less than 2.0 x upper limit of normal (ULN) during follow-up (mean, 36 months). The remaining 1162 patients (51.92%) (766, HBeAg positive; 387 anti-HBeAg positive; 9 negative for both HBeAg and anti-HBeAg) with ALT levels >or=2.0 x ULN were followed longitudinally for 12 months to judge flare, remission, and HBeAg seroconversion. Flare, remission, and HBeAg seroconversion in patients with ALT levels >or=2.0 x ULN showed clear seasonal patterns (P < 0.001), with high peaks during spring, summer, and summer, respectively. An autocorrelation correlogram showed that flares, remission, and HBeAg seroconversion occurred with distinct periodicity in winter, spring, summer, and autumn.

CONCLUSIONS

Seasonal variation might affect the clinical course of chronic hepatitis B. The role of seasonal triggering factors should be further investigated.

Replication of a hepatitis C virus replicon clone in mouse cells

BACKGROUND

Hepatitis C Virus (HCV) is a significant public health burden and small animal models are needed to study the pathology and immunobiology of the virus. In effort to develop experimental HCV mouse models, we screened a panel of HCV replicons to identify clones capable of replicating in mouse hepatocytes.

RESULTS

We report the establishment of stable HCV replication in mouse hepatocyte and fibroblast cell lines using replicons derived from the JFH-1 genotype 2a consensus sequence. Viral RNA replication efficiency in mouse cells was comparable to that observed in human Huh-7 replicon cells, with negative-strand HCV RNA and the viral NS5A protein being readily detected by Northern and Western Blot analysis, respectively. Although HCV replication was established in the absence of adaptive mutations that might otherwise compromise the in vitro infectivity of the JFH-1 clone, no infectious virus was detected when the culture medium from full length HCV RNA replicating mouse cells was titrated on Huh-7 cells, suggesting that the mouse cells were unable to support production of infectious progeny viral particles. Consistent with an additional block in viral entry, infectious JFH-1 particles produced in Huh-7 cells were not able to establish detectable HCV RNA replication in naïve mouse cells.

CONCLUSION

Thus, this report expands the repertoire of HCV replication systems and possibly represents a step toward developing mouse models of HCV replication, but it also highlights that other species restrictions might continue to make the development of a purely murine HCV infectious model challenging.

Role of macrophage migration inhibitory factor in hepatitis B virus-specific cytotoxic-T-lymphocyte-induced liver injury

Macrophage migration inhibitory factor (MIF) plays a pivotal role in the development of various inflammatory diseases. Here, we found that anti-mouse MIF antibody treatment reduced liver injury and inflammatory cell infiltration into the liver after injection of antigen-specific cytotoxic T lymphocytes into hepatitis B virus transgenic mice.

Immune system and hepatitis B virus infection

The immune system plays an important role in determining the outcome of hepatitis B virus (HBV) infection. This is because recovery from of acute HBV infection is associated with a clear division in the profile of adaptive immune response. Multispecific antiviral CD4 and CD8 responses with a type 1 cytokine production can be observed in patients who recover from acute HBV infection. On the other hand, those who develop chronic infection tend to have a weak virus specific T cell response. Therapeutic strategies aimed at correcting this defective T cell reactivity could represent a complementary approach to the cure of chronic HBV infection.

Blockade of neutrophil elastase attenuates severe liver injury in hepatitis B transgenic mice

Serine proteinases produced by polymorphonuclear neutrophils play important roles in neutrophil-mediated tissue injury at inflammatory sites. Although neutrophil recruitment to the liver has been shown to be involved in the exacerbation of liver inflammation, the function of neutrophil elastase (NE) in liver injury remains unclear. Here, we found that administration of an NE inhibitor (NEI) reduced serum alanine aminotransferase (sALT) activity and inflammatory cell infiltration into the liver from 8 to 24 h after injection of antigen-specific cytotoxic T lymphocytes (CTLs) into hepatitis B virus transgenic mice. Furthermore, the NEI treatment reduced the expressions of inflammatory cytokines and chemokines in the liver and tumor necrosis factor alpha production by macrophages. In addition, the NEI treatment suppressed the mRNA expressions of CC chemokine ligand 3 (CCL-3), CCL-4, and macrophage inflammatory protein 2 (MIP-2) in neutrophils in the liver at 8 h after the CTL injection. In support of these results, we confirmed that administration of anti-CCL-3, anti-CCL-4, and anti-MIP-2 monoclonal antibodies suppressed sALT activity and leukocyte migration into the liver. In conclusion, the present results suggest that NE contributes to the early step of the inflammatory cascade in acute viral hepatitis and that NEIs may have potential as therapeutic drugs against acute severe viral hepatitis.

A vesicular stomatitis virus recombinant expressing granulocyte-macrophage colony-stimulating factor induces enhanced T-cell responses and is highly attenuated for replication in animals

Live attenuated vectors based on recombinant vesicular stomatitis viruses (rVSVs) expressing foreign antigens are highly effective vaccines in animal models. In this study, we report that an rVSV (VSV-GMCSF1) expressing high levels of murine granulocyte-macrophage colony-stimulating factor (GM-CSF) from the first position in the viral genome is highly attenuated in terms of viral dissemination and pathogenesis after intranasal delivery to mice. However, this highly attenuated virus generated antibody and T-cell responses equivalent to those induced by a control virus expressing enhanced green fluorescent protein (EGFP) from the first position (VSV-EGFP1). The better containment and clearance of VSV-GMCSF1 may be due to enhanced recruitment of macrophages to the site of infection but is not explained by a greater induction of interferons. The primary CD8 T-cell and neutralizing antibody responses to VSV-GMCSF1 were equivalent to those generated by VSV-EGFP1, while the CD8 T-cell memory and recall responses to the vector were enhanced in mice infected with VSV-GMCSF1. It is likely that the GM-CSF produced by immunization with this virus results in an enhanced recruitment of antigen-presenting cells, leading to better acute and long-term T-cell responses. This recruitment appears to cancel out any negative effect of viral attenuation on immunogenicity.

Cellular cIAP2 gene expression associated with anti-HBV activity of TNF-alpha in hepatoblastoma cells

Hepatitis B virus (HBV)-specific cytotoxic T lymphocytes (CTLs) can abolish HBV gene expression and replication through a noncytopathic mechanism mediated by tumor necrosis factor-alpha (TNF-alpha). However, the molecular mechanisms of TNF-alpha antiviral activity are not completely understood. To examine TNF-alpha-induced cellular responses and identify genes involved in anti-HBV activity, cDNA microarrays dotted with 14, 112 human genes were used to examine the transcriptional changes in HepG2 after treatment with TNF-alpha for 6 h. The results showed that many genes related to ligands and receptors, signal transduction including the TNF-alpha signaling pathway, mitochondrial and ribosomal proteins, and transcription regulation were induced by TNF-alpha. Interestingly, the TNF-alpha-inducible gene cIAP2 was found to inhibit HBV protein synthesis, viral replication, and transcription. Taken together, our results revealed the global effects of TNF-alpha treatment on hepatocellular gene expression. The antiviral genes identified by microarray could be developed as potential new anti-HBV drugs or for other novel therapies.

Interferon prevents formation of replication-competent hepatitis B virus RNA-containing nucleocapsids

We have previously shown that IFN-beta inhibits hepatitis B virus (HBV) replication by noncytolytic mechanisms that either destabilize pregenomic (pg)RNA-containing capsids or prevent their assembly. Using immortalized murine hepatocyte cell lines stably transfected with a doxycycline (dox)-inducible HBV replication system, we now show that replication-competent pgRNA-containing capsids are not produced when the cells are pretreated with IFN-beta before HBV expression is induced with dox. Furthermore, the turnover rate of preformed HBV RNA-containing capsids is not changed in the presence of IFN-beta or IFN-gamma under conditions in which further pgRNA synthesis is inhibited by dox removal. In summary, these results demonstrate that types 1 and 2 IFN activate hepatocellular mechanism(s) that prevent the formation of replication-competent HBV capsids and, thereby, inhibit HBV replication.

Toll-like receptor signaling inhibits hepatitis B virus replication in vivo

Toll-like receptors (TLR) play a key role in innate immunity. To examine the ability of diverse TLRs to modulate hepatitis B virus (HBV) replication, HBV transgenic mice received a single intravenous injection of ligands specific for TLR2, TLR3, TLR4, TLR5, TLR7, and TLR9. All of the ligands except for TLR2 inhibited HBV replication in the liver noncytopathically within 24 h in a alpha/beta interferon-dependent manner. The ability of these TLR ligands to induce antiviral cytokines at the site of HBV replication suggests that TLR activation could represent a powerful and novel therapeutic strategy for the treatment of chronic HBV infection.

Lambda interferon inhibits hepatitis B and C virus replication

Lambda interferon (IFN-lambda) induces an intracellular IFN-alpha/beta-like antiviral response through a receptor complex distinct from the IFN-alpha/beta receptor. We therefore determined the ability of IFN-lambda to inhibit hepatitis B virus (HBV) and hepatitis C virus (HCV) replication. IFN-lambda inhibits HBV replication in a differentiated murine hepatocyte cell line with kinetics and efficiency similar to IFN-alpha/beta and does not require the expression of IFN-alpha/beta or IFN-gamma. Furthermore, IFN-lambda blocked the replication of a subgenomic and a full-length genomic HCV replicon in human hepatocyte Huh7 cells. These results suggest the possibility that IFN-lambda may be therapeutically useful in the treatment of chronic HBV or HCV infection.

Biomedicines to reduce inflammation but not viral load in chronic HCV--what's the sense?

Although cytokines and cytotoxic T lymphocytes (CTL) are among the predominant mechanisms of host defense against viral pathogens, they can induce an inflammatory response that often leads to tissue injury. Hepatitis C virus (HCV) infection, a major cause of liver-related disease, results in the induction of proinflammatory cytokines, such as tumor necrosis factor-alpha (TNF-alpha), and CTL activity, followed by liver injury. Although inflammation facilitates the wound healing process, chronic persistence over several decades results in scar accumulation, fibrosis and often cirrhosis. This review summarizes biological data implicating a cause-and-effect relationship between TNF-alpha levels and the progression of fibrosis in chronic HCV infections, in contrast to the role of TNF-alpha in hepatitis B virus infections. Furthermore, an overview of therapeutic approaches to halting the inflammatory cascade in individuals with chronic HCV, including the use of agents to reduce the level of TNF-alpha, is presented.

Clearance of hepatitis B virus from the liver of transgenic mice by short hairpin RNAs

Hepatitis B virus (HBV) causes acute and chronic hepatitis and hepatocellular carcinoma. Although a preventive vaccine is available, the therapeutic options for chronically infected patients are limited. It has been shown that RNA interference can prevent HBV gene expression and replication in vivo when HBV expression vectors are delivered simultaneously with small interfering RNA (siRNA) or siRNA expression constructs. However, the therapeutic potential of siRNAs to interrupt ongoing HBV replication in vivo has not been established. Here, we show that expression of HBV-specific siRNAs in the liver of HBV transgenic mice by recombinant adenoviruses can suppress preexisting HBV gene expression and replication to almost undetectable levels for at least 26 days. These results demonstrate that efficiently delivered siRNAs should be able to silence HBV in chronically infected patients.

Adenovirus-based gene therapy during clevudine treatment of woodchucks chronically infected with woodchuck hepatitis virus

Interferon-alpha (IFN-alpha) is a potent suppressor of hepatitis B virus (HBV) replication in the HBV-transgenic mouse, depleting virus replication intermediates from infected hepatocytes via pathways mediated by interferon-gamma (IFN-gamma) and tumor necrosis factor alpha (TNF-alpha). It has also been hypothesized that cytokines induce curing of infected hepatocytes via non-cytolytic pathways during resolution of transient hepadnavirus infections. We have therefore evaluated therapy of chronic woodchuck hepatitis virus (WHV) infections using treatment with the nucleoside analog clevudine [L-FMAU; 1-(2-fluoro-5-methyl-b-L-arabinofuranosyl) uracil] and therapy with adenovirus vectors expressing INF-gamma, TNF-alpha, and beta-galactosidase. Before their use in vivo, expression of IFN-gamma and TNF-alpha from the adenovirus vectors was evaluated in vitro. Conditioned media from adenovirus-infected WC-3 cells was shown to inhibit WHV replication in baculovirus-transduced cells. Adenovirus super-infection of the liver in woodchucks led to declines in the percentage of hepatocytes with detectable core antigen and nucleic acids, and in levels of covalently closed circular DNA (cccDNA) and total WHV DNA, but a major long-term benefit of adenovirus super-infection during clevudine treatment was not demonstrated. Moreover, the effect took at least 2 weeks to develop suggesting that the declines in the percentage of WHV-infected cells, ccc, and total WHV DNA resulted from induction of the adaptive immune response by the adenovirus super-infection, and only indirectly from the expression of cytokines by the vectors.

Murine hepatocyte cell lines promote expansion and differentiation of NK cells from stem cell precursors

While fetal liver is a major hematopoietic organ, normal adult liver provides a suitable microenvironment for a variety of immune cells and, in several pathological conditions, may become a site of extramedullary hematopoiesis. The direct influence of hepatocytes on hematopoietic cell differentiation is poorly understood. We have previously reported that the Met murine hepatocyte (MMH) untransformed hepatocytic lines retain several morphological and functional features of hepatocytes in vivo and are able to support the survival, self-renewal, and differentiation of hematopoietic precursors in a cell-cell contact system. Here we report the effects of soluble factors released by MMH lines on bone marrow-derived cells. Lymphohematopoietic cells were cultured in two different cell contact-free systems: transwell inserts on MMH feeder layers, and MMH conditioned medium (MMH-CM). Both culture systems were able to promote a substantial expansion of bone marrow-derived cells and their differentiation to natural killer (NK) cells that express the NK1.1 and U5A2-13 markers. Purified hematopoietic stem cells (Sca-1+Lin-), either plated as a bulk population or as single cells, were also able to differentiate into NK cells, when cultured in MMH-CM; thus, soluble factors secreted by MMH lines promote the expansion and differentiation of NK precursor cells. MMH-CM-derived NK cells are functionally active; stimulation by interleukin (IL)-12 together with IL-18 was required to induce interferon-gamma (IFNgamma) expression and to enhance their cytotoxic activity. In conclusion, our findings may imply a direct role of hepatocytes in NK cell development, and the system we have used may provide a tool for studying the molecular mechanisms of NK cell differentiation.

Signal transduction pathways that inhibit hepatitis B virus replication

The replication of hepatitis B virus (HBV) in hepatocytes is strongly inhibited in response to IFN-alpha/beta and IFN-gamma. Although it has been previously demonstrated that IFN-alpha/beta eliminates HBV RNA-containing capsids from the cell in a proteasome-dependent manner, the precise cellular pathway that mediates this antiviral effect has not been identified. Because IFN-induced signal transduction involves kinase-mediated activation of gene expression, we used an immortalized hepatocyte cell line that replicates HBV in an IFN-sensitive manner to investigate the role of cellular kinase activity and the cellular transcription and translation machinery in the antiviral effect. Our results indicate that Janus kinase activity is required for the antiviral effect of IFN against HBV, but that phosphatidylinositol 3-kinase, cyclin-dependent kinase, mitogen-activated protein kinase, and NF-kappaB activity are not. Additionally, we found that inhibitors of cellular transcription and translation completely abolish the antiviral effect, which also appears to require cellular kinase activity downstream of signal transduction and gene expression. Collectively, these results identify IFN-regulated pathways that interrupt the HBV replication cycle by eliminating viral RNA-containing capsids from the cell, and they provide direction for discovery of the terminal effector molecules that ultimately mediate this antiviral effect.

IL-4 suppresses the expression and the replication of hepatitis B virus in the hepatocellular carcinoma cell line Hep3B

IL-4 has been known as a Th2 cytokine and can act on B cells, T cells, and monocytes. In this study we demonstrate that IL-4Rs are expressed on human hepatocellular carcinoma (HCC) cells. We found that IL-4 suppresses hepatitis B surface Ag (HBsAg) mRNA and HBsAg production in the Hep3B cell line, which contains an integrated hepatitis B virus (HBV) genome and constitutively secretes HBsAg. When Hep3B cells are further transfected with the plasmid pHBV3.6 that contains >1 U of HBV genome, IL-4 could suppress the production of all HBV RNA and secreted HBsAg and hepatitis B virus e Ag. Furthermore, an endogenous DNA polymerase activity assay shows a decrease in HBV DNA after IL-4 treatment. Using luciferase reporter assays we have demonstrated that IL-4 could suppress the activity of the surface promoter II and the core promotor (CP). To delineate how IL-4 suppressed the transcription of HBV genes, we have examined the effect of IL-4 on the expression of transcription factors that are known to bind to the core upstream regulatory sequence, which colocalizes with enhancer II of the HBV genome. Our results demonstrate that IL-4 suppresses the expression of C/EBPalpha. Furthermore, overexpression of C/EBPalpha blocked 43 and 30% of the IL-4-mediated suppression of CP activity and IL-4-induced suppression of pregenomic RNA, respectively. Finally, we have demonstrated that mutations affecting the C/EBPalpha-binding sites on core upstream regulatory sequence/enhancer II completely abolish the IL-4-mediated suppression of CP activity. Thus, down-regulation of C/EBPalpha may be involved in the anti-HBV effect of IL-4 in Hep3B cells.

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.

Viruses and the TNF-related cytokines, an evolving battle

Tumor necrosis factor (TNF)-related cytokines are critical effector molecules in the immune response to viral pathogens. Engagement of the TNF receptors by their cognate ligands activates apoptotic and non-apoptotic signaling pathways, both of which can mediate antiviral activity. In response, viruses have evolved mechanisms to inhibit signaling by some cytokines of the TNF superfamily. These strategies are largely unique to each class of virus, but are similar in that they all target key regulatory checkpoints of the TNF pathway. In recent years, studies directed towards dissecting the mechanisms of TNF signaling and the viral retort have led to several significant discoveries, and form the basis for this review.

Hepatitis C virus RNA replication is resistant to tumour necrosis factor-alpha

It was demonstrated using self-replicating hepatitis C virus (HCV) RNAs that both types of interferons (IFNs) (in particular IFN-alpha and IFN-gamma) are potent inhibitors of HCV replication in Huh-7 cells. Because IFN-gamma and tumour necrosis factor (TNF)-alpha trigger a partially overlapping set of antiviral defence mechanisms, it is tempting to speculate that TNF-alpha also inhibits HCV replication. However, this study shows that TNF-alpha does not affect HCV protein and RNA synthesis, nor does it synergistically enhance the inhibitory effect of IFN-gamma. Taken together, these results demonstrate that HCV replication in Huh-7 cells is highly resistant to TNF-alpha. It is, therefore, unlikely that the increased production of TNF-alpha, which is seen in many hepatitis C patients, contributes to HCV clearance by inducing antiviral defence mechanisms in infected hepatocytes.

Tumor necrosis factor alpha inhibition of hepatitis B virus replication involves disruption of capsid Integrity through activation of NF-kappaB

Chronic infection by hepatitis B virus results from an inability to clear the virus, which is associated with liver disease and liver cancer. Tumor necrosis factor alpha (TNF-alpha) is associated with noncytopathic clearance of hepatitis B virus in animal models. Here we demonstrate that the nuclear factor kappaB (NF-kappaB) signaling pathway is a central mediator of inhibition of hepatitis B virus by TNF-alpha and we describe the molecular mechanism. TNF-alpha is shown to suppress hepatitis B virus DNA replication without cell killing by disrupting the formation or stability of cytoplasmic viral capsids through a pathway requiring the NF-kappaB-activating inhibitor of kappaB kinase complex IKK-alpha/beta and active transcription factor NF-kappaB. Hepatitis B virus replication could also be inhibited and viral capsid formation could be disrupted in the absence of TNF-alpha solely by overexpression of IKK-alpha/beta or strong activation of NF-kappaB. In contrast, inhibition of NF-kappaB signaling stimulated viral replication, demonstrating that HBV replication is both positively and negatively regulated by the level of activity of the NF-kappaB pathway. Studies are presented that exclude the possibility that HBV inhibition by NF-kappaB is carried out by secondary production of gamma interferon or alpha/beta interferon. These results identify a novel mechanism for noncytopathic suppression of hepatitis B virus replication that is mediated by the NF-kappaB signaling pathway and activated by TNF-alpha.

Transcriptional and posttranscriptional control of hepatitis B virus gene expression

Hepatitis B virus (HBV) infects humans and certain nonhuman primates. Viral clearance and acute disease are associated with a strong, polyclonal, multispecific cytotoxic T lymphocyte response. Infiltrating T cells, as well as other activated inflammatory cells, produce cytokines that can regulate hepatocellular gene expression. Using an HBV transgenic mouse model, our laboratory has previously demonstrated that adoptive transfer of HBV-specific cytotoxic T lymphocytes or injection of IL-2 can noncytopathically inhibit HBV gene expression by a posttranscriptional IFN-gamma- and/or tumor necrosis factor alpha-dependent mechanism. Here, we report that HBV gene expression can also be controlled at the posttranscriptional level during persistent lymphocytic choriomeningitis virus infection. In contrast, it is controlled at the transcriptional level during acute murine cytomegalovirus infection or after repetitive polyinosinic-polycytidylic acid injection. Finally, we show that transcriptional inhibition of HBV is associated with changes in liver-specific gene expression. These results elucidate pathways that regulate the viral life cycle and suggest additional approaches for the treatment of chronic HBV infection.