Identification of the hepatitis B virus factor that inhibits expression of the beta interferon gene

The parapoxvirus Orf virus inhibits IFN-β expression induced by dsRNA

Orf virus (ORFV) is the type species of the Parapoxvirus genus that belongs to the Poxviridae family. Type I interferons (IFN) are critical in the host defence against viruses. They induce hundreds of interferon stimulated genes (ISGs) many of which have an antiviral role. The ability of ORFV to modulate type I IFN production was undertaken to investigate whether ORFV could inhibit IFN-β expression via dsRNA dependant signalling pathways. HEK293 cells are known to lack DNA pattern-recognition receptors and Toll-like receptors however, they do express the cytosolic dsRNA receptors RIG-I and MDA5. HEK293 cells were shown to produce high levels of IFN-β when cells were stimulated with poly(I:C) and this was shown to be predominantly via RIG-I-dependant signalling as confirmed by siRNA knock-down of RIG-I. Further we showed that HEK293 cells are permissive for ORFV and caused potent inhibition of IFN-β transcription when cells were stimulated with poly(I:C) post-viral infection. Studies using heat inactivated ORFV suggested that de novo synthesis of early genes was required. In addition our findings showed that the ORFV encoded factor ORF020, that is known to bind dsRNA, is involved in antagonising IFN expression. Overall, this study has shown for first time the ability of ORFV to counteract type I IFN expression by antagonising dsRNA-activated RIG-I signalling.

Virus-Induced Tumorigenesis and IFN System

Oncogenic viruses favor the development of tumors in mammals by persistent infection and specific cellular pathways modifications by deregulating cell proliferation and inhibiting apoptosis. They counteract the cellular antiviral defense through viral proteins as well as specific cellular effectors involved in virus-induced tumorigenesis. Type I interferons (IFNs) are a family of cytokines critical not only for viral interference but also for their broad range of properties that go beyond the antiviral action. In fact, they can inhibit cell proliferation and modulate differentiation, apoptosis, and migration. However, their principal role is to regulate the development and activity of most effector cells of the innate and adaptive immune responses. Various are the mechanisms by which IFNs exert their effects on immune cells. They can act directly, through IFN receptor triggering, or indirectly by the induction of chemokines, the secretion of further cytokines, or by the stimulation of cells useful for the activation of particular immune cells. All the properties of IFNs are crucial in the host defense against viruses and bacteria, as well as in the immune surveillance against tumors. IFNs may be affected by and, in turn, affect signaling pathways to mediate anti-proliferative and antiviral responses in virus-induced tumorigenic context. New data on cellular and viral microRNAs (miRNAs) machinery, as well as cellular communication and microenvironment modification via classical secretion mechanisms and extracellular vesicles-mediated delivery are reported. Recent research is reviewed on the tumorigenesis induced by specific viruses with RNA or DNA genome, belonging to different families (i.e., HPV, HTLV-1, MCPyV, JCPyV, Herpesviruses, HBV, HCV) and the IFN system involvement.

Peculiarities in the designations of hepatitis B virus genes, their products, and their antigenic specificities: a potential source of misunderstandings

The nomenclature of the hepatitis B virus (HBV) genes and their products has developed stepwise, occasionally in an erratic way, creating many misunderstandings, especially among those who do not know the structure of HBV and its genome in detail. One of the most frequent misunderstandings, even presented in leading journals, is the designation of HBV “e”-antigen as envelope or early antigen. Another problem area are the so-called “pre” regions in the HBV genome present upstream of both the core and the surface genes of HBV, inadvertently suggesting that they may be a part of corresponding precursor proteins. Misnomers and misclassifications are frequent in defining the subgenotypes and serological subtypes of HBV. Even the well-established terminology for HBV surface (HBs) or HBV core (HBc) antigen deviates from the conventional virological nomenclature for viral envelopes or capsid proteins/antigens, respectively. Another matter of undesirable variability between publications is the numbering of the nucleotides and the graphical representation of genomic maps. This editorial briefly explains how the nomenclature evolved, what it really means, and suggests how it could be adapted to today’s knowledge.

Interferon signaling during Hepatitis B Virus (HBV) infection and HBV-associated hepatocellular carcinoma

Chronic Hepatitis B Virus (HBV) infection is linked to hepatocellular carcinoma (HCC) pathogenesis. The World Health Organization estimates that globally 257 million people are chronic HBV carriers at risk of developing liver cancer. Current therapies for prevention and treatment of HCC are inadequate. Although interferon-based treatment strategies hold great promise for combating chronic infection and HCC, many patients do not respond to the IFN-based drugs for reasons not completely understood. Interferon signaling plays key roles in activation of innate and adaptive immunity. However, HBV has evolved various mechanisms to suppress IFN signaling. In this review, we present the basics about HBV infection and interferon signaling. Next, we discuss mechanisms through which HBV downregulates the function -activity and transcription- of the transcription factor STAT1 during acute and chronic infection. STAT1 is activated in response to all types (I/II/III) of interferon signaling and is essential in mediating all types (I/II/III) of interferon responses. Lastly, we discuss emerging evidence from different human cancers linking loss of interferon signaling to aggressive cancer and cancer stem cells. Whether the same occurs during HBV-associated hepatocarcinogenesis is discussed and currently under investigation.

Current progress in the development of therapeutic vaccines for chronic hepatitis B virus infection

Chronic hepatitis B is still a major public health issue despite the successful prophylactic vaccination attempts. Chronicity of hepatitis B virus (HBV) is mainly due to its ability to debilitate host's immune system. Therefore, major measures have been taken to stop this process and help patients with chronic hepatitis B infection recover from their illness. While satisfactory results have been achieved using preventive HBV vaccines, a reliable and effective therapeutic treatment is still in need of extensive studies. Current treatments for chronic hepatitis B include direct antiviral agents and nucleoside/nucleotide analogs, which are not always effective and are also costly. In addition, due to the fact that chronic HBV is responsible for debilitation of the immune system, studies have focused on developing therapeutic vaccines to help host's immune system recover and limit the infection. Several approaches including but not restricted to recombinant peptide-based, DNA-based, viral vector-based, and cell-based approaches are currently in use to develop therapeutic vaccines against the chronic form of HBV infection. In the current review, the authors will first discuss the role of the immune system in chronic hepatitis B infection and will then focus on latest advancements in therapeutic vaccination of HBV especially the clinical trials that have been carried out so far.

Mechanism of inhibiting type I interferon induction by hepatitis B virus X protein

Hepatitis B virus (HBV) is regarded as a stealth virus, invading and replicating efficiently in human liver undetected by host innate antiviral immunity. Here, we show that type I interferon (IFN) induction but not its downstream signaling is blocked by HBV replication in HepG2.2.15 cells. This effect may be partially due to HBV X protein (HBx), which impairs IFNβ promoter activation by both Sendai virus (SeV) and components implicated in signaling by viral sensors. As a deubiquitinating enzyme (DUB), HBx cleaves Lys63-linked polyubiquitin chains from many proteins except TANK-binding kinase 1 (TBK1). It binds and deconjugates retinoic acid-inducible gene I (RIG I) and TNF receptor-associated factor 3 (TRAF3), causing their dissociation from the downstream adaptor CARDIF or TBK1 kinase. In addition to RIG I and TRAF3, HBx also interacts with CARDIF, TRIF, NEMO, TBK1, inhibitor of kappa light polypeptide gene enhancer in B-cells, kinase epsilon (IKKi) and interferon regulatory factor 3 (IRF3). Our data indicate that multiple points of signaling pathways can be targeted by HBx to negatively regulate production of type I IFN.

Hepatitis B virus core protein with hot-spot mutations inhibit MxA gene transcription but has no effect on inhibition of virus replication by interferon α

It has been reported that hepatitis B virus (HBV) core protein (HBc) can inhibit the transcription of human interferon-induced MxA gene. In this study, we investigated whether HBc protein mutations at hot spots (L60V, S87G and I97L) could still inhibit MxA transcription and the potential significance of this inhibition in virus replication in vitro. Our data indicated that the IFN-induced MxA mRNA expression level and MxA promoter activity was significantly down-regulated by mutant protein of HBc(I97L), compared to WT and the other two mutated HBc proteins(L60V or S87G). However, in Huh7 cells stably expressing WT or the mutated HBc proteins (L60V, S87G or I97L), IFN-α could inhibit the extra- and intracellular HBV DNA level and HBsAg secretion to a similar level compared to that in cells transfected with control plasmids. In conclusion, HBc protein with I97L mutation may play an especial role in suppressing the transcription of MxA gene. Moreover, the inhibitory effect on MxA gene transcription by the WT or mutated HBc proteins (L60V, S87G and I97L) has no impact on inhibition of HBV replication by IFN-α in Huh7 cells. The clinical significance of the inhibitory effect of MxA gene transcription by HBc protein requires further study.

Innate antiviral immune responses to hepatitis B virus

Hepatitis B virus (HBV) is a major cause of acute and chronic hepatitis in humans. As HBV itself is currently viewed as a non-cytopathic virus, the liver pathology associated with hepatitis B is mainly thought to be due to immune responses directed against HBV antigens. The outcome of HBV infection is the result of complex interactions between replicating HBV and the immune system. While the role of the adaptive immune response in the resolution of HBV infection is well understood, the contribution of innate immune mechanisms remains to be clearly defined. The innate immune system represents the first line of defense against viral infection, but its role has been difficult to analyze in humans due to late diagnosis of HBV infection. In this review, we discuss recent advances in the field of innate immunity to HBV infection.

Control of hepatitis B virus replication by innate response of HepaRG cells

Hepatitis B virus (HBV) is currently viewed as a stealth virus that does not elicit innate immunity in vivo. This assumption has not yet been challenged in vitro because of the lack of a relevant cell culture system. The HepaRG cell line, which is physiologically closer to differentiated hepatocytes and permissive to HBV infection, has opened new perspectives in this respect.HBV baculoviruses were used to initiate an HBV replication in both HepG2 and HepaRG cells. To monitor HBV replication, the synthesis of encapsidated DNA, and secretion of hepatitis B surface antigen (HBsAg), was respectively analyzed by southern blot and enzyme-linked immunosorbent assay. The induction of a type I interferon (IFN) response was monitored by targeted quantitative reverse transcription polymerase chain reaction (qRT-PCR), low-density arrays, and functional assays. The invalidation of type I IFN response was obtained by either antibody neutralization or RNA interference. We demonstrate that HBV elicits a strong and specific innate antiviral response that results in a noncytopathic clearance of HBV DNA in HepaRG cells. Challenge experiment showed that transduction with Bac-HBV-WT, but not with control baculoviruses, leads to this antiviral response in HepaRG cells, whereas no antiviral response is observed in HepG2 cells. Cellular gene expression analyses showed that IFN-beta and other IFN-stimulated genes were up-regulated in HepG2 and HepaRG cells, but not in cells transduced by control baculoviruses. Interestingly, a rescue of viral replication was observed when IFN-beta action was neutralized by antibodies or RNA interference of type I IFN receptor.

CONCLUSION

Our data suggest that a strong HBV replication is able to elicit a type I IFN response in HepaRG-transduced cells.

Induction of a striking systemic cytokine cascade prior to peak viremia in acute human immunodeficiency virus type 1 infection, in contrast to more modest and delayed responses in acute hepatitis B and C virus infections

Characterization of the immune responses induced in the initial stages of human immunodeficiency virus type 1 (HIV-1) infection is of critical importance for an understanding of early viral pathogenesis and prophylactic vaccine design. Here, we used sequential plasma samples collected during the eclipse and exponential viral expansion phases from subjects acquiring HIV-1 (or, for comparison, hepatitis B virus [HBV]or hepatitis C virus [HCV]) to determine the nature and kinetics of the earliest systemic elevations in cytokine and chemokine levels in each infection. Plasma viremia was quantitated over time, and levels of 30 cytokines and chemokines were measured using Luminex-based multiplex assays and enzyme-linked immunosorbent assays. The increase in plasma viremia in acute HIV-1 infection was found to be associated with elevations in plasma levels of multiple cytokines and chemokines, including rapid and transient elevations in alpha interferon (IFN-alpha) and interleukin-15 (IL-15) levels; a large increase in inducible protein 10 (IP-10) levels; rapid and more-sustained increases in tumor necrosis factor alpha and monocyte chemotactic protein 1 levels; more slowly initiated elevations in levels of additional proinflammatory factors including IL-6, IL-8, IL-18, and IFN-gamma; and a late-peaking increase in levels of the immunoregulatory cytokine IL-10. Notably, there was comparatively little perturbation in plasma cytokine levels during the same phase of HBV infection and a delayed response of more intermediate magnitude in acute HCV infection, indicating that the rapid activation of a striking systemic cytokine cascade is not a prerequisite for viral clearance (which occurs in a majority of HBV-infected individuals). The intense early cytokine storm in acute HIV-1 infection may have immunopathological consequences, promoting immune activation, viral replication, and CD4(+) T-cell loss.

Hepatitis B virus core protein inhibits TRAIL-induced apoptosis of hepatocytes by blocking DR5 expression

Hepatitis B virus (HBV) causes chronic hepatitis in hundreds of millions of people worldwide, which can eventually lead to hepatocellular carcinoma (HCC). The molecular mechanisms underlying HBV persistence are not well understood. TRAIL, the TNF-related apoptosis-inducing ligand, has recently been implicated in hepatocyte death during HBV infection. We report here that the HBV core protein (HBc) is a potent inhibitor of TRAIL-induced apoptosis. Overexpressing HBc significantly decreased TRAIL-induced apoptosis of human hepatoma cells, whereas knocking-down HBc expression in hepatoma cells transfected with HBV genome enhanced it. When present in the same cell, HBc blocked the pro-apoptotic effect of the HBV X protein (HBx). The resistance of HBc-expressing cells to TRAIL-induced apoptosis was associated with a significant reduction in death receptor 5 (DR5) expression. Upon transfection, HBc significantly repressed the promoter activity of the human DR5 gene. Importantly, HBc gene transfer inhibited hepatocyte death in a mouse model of HBV-induced hepatitis; and in patients with chronic hepatitis, DR5 expression in the liver was significantly reduced. These results indicate that HBc may prevent hepatocytes from TRAIL-induced apoptosis by blocking DR5 expression, which in turn contributes to the development of chronic hepatitis and HCC. They also call into question the potential side effects of HBc-based vaccines.

Interferons and viruses: an interplay between induction, signalling, antiviral responses and virus countermeasures

The interferon (IFN) system is an extremely powerful antiviral response that is capable of controlling most, if not all, virus infections in the absence of adaptive immunity. However, viruses can still replicate and cause disease in vivo, because they have some strategy for at least partially circumventing the IFN response. We reviewed this topic in 2000 [Goodbourn, S., Didcock, L. & Randall, R. E. (2000). J Gen Virol 81, 2341-2364] but, since then, a great deal has been discovered about the molecular mechanisms of the IFN response and how different viruses circumvent it. This information is of fundamental interest, but may also have practical application in the design and manufacture of attenuated virus vaccines and the development of novel antiviral drugs. In the first part of this review, we describe how viruses activate the IFN system, how IFNs induce transcription of their target genes and the mechanism of action of IFN-induced proteins with antiviral action. In the second part, we describe how viruses circumvent the IFN response. Here, we reflect upon possible consequences for both the virus and host of the different strategies that viruses have evolved and discuss whether certain viruses have exploited the IFN response to modulate their life cycle (e.g. to establish and maintain persistent/latent infections), whether perturbation of the IFN response by persistent infections can lead to chronic disease, and the importance of the IFN system as a species barrier to virus infections. Lastly, we briefly describe applied aspects that arise from an increase in our knowledge in this area, including vaccine design and manufacture, the development of novel antiviral drugs and the use of IFN-sensitive oncolytic viruses in the treatment of cancer.

TLR3 signaling in a hepatoma cell line is skewed towards apoptosis

Toll-like receptors (TLRs) recognize pathogen-associated molecular patterns (PAMPS) leading to the activation of the innate immune response and subsequently to the shaping of the adaptive immune response. Of the known human TLRs, TLR3, 7, 8, and 9 were shown to recognize nucleic acid ligands. TLR3 signaling is induced by double-stranded (ds)RNA, a molecular signature of viruses, and is mediated by the TRIF (TIR domain-containing adaptor-inducing IFNbeta) adaptor molecule. Thus, TLR3 plays an important role in the host response to viral infections. The liver is constantly exposed to a large variety of foreign substances, including pathogens such as HBV (hepatitis B virus) and HCV (hepatitis C virus), which frequently establish persistent liver infections. In this work, we investigated the expression and signaling pathway of TLR3 in different hepatoma cell lines. We show that hepatocyte lineage cells express relatively low levels of TLR3 mRNA. TLR3 signaling in HEK293 cells (human embryonic kidney cells) activated NF-kappaB and IRF3 (interferon regulatory factor 3) and induced IFNbeta (interferon beta) promoter expression, which are known to lead to pro-inflammatory cytokine secretion. In Huh7 cells, there was only a short-term IRF3 activation, and a very low level of IFNbeta expression. In HepG2 cells on the other hand, while no induction of pro-inflammatory factors was observed, signaling by TLR3 was skewed towards the induction of apoptosis. These results indicate preferential induction of the apoptotic pathway over the cytokine induction pathway by TLR3 signaling in hepatocellular carcinoma cells with potential implications for therapeutic strategies.

Human MxA protein participates to the interferon-related inhibition of hepatitis B virus replication in female transgenic mice

BACKGROUND/AIMS

The interferon (IFN) inducible MxA protein is endowed with antiviral activity against a broad range of RNA viruses. In a previous in vitro study, we demonstrated that MxA inhibits hepatitis B virus (HBV) replication, arguing that the antiviral activity of MxA is not restricted to RNA viruses but also includes a DNA virus. The aim of the present study was to further demonstrate in vivo the antiviral action of MxA against HBV.

METHODS

We generated HBV and HBV/MxA transgenic mice lacking a functional IFN-alpha/beta receptor and thus constituting a good model to evaluate MxA-induced virus resistance. HBV proteins expression, viral load and HBV replication were compared in HBV and HBV/MxA mice.

RESULTS

An MxA-dependent moderate inhibitory effect on HBV expression was only observed in female HBV/MxA mice, in which MxA downregulates (i) viral HBeAg and capsid protein expression, (ii) viremia and (iii) HBV replication by decreasing the synthesis of HBV DNA replicative intermediates. Furthermore, these effects were not associated with changes to steady-state levels of HBV RNAs.

CONCLUSIONS

Our results show that in vivo, MxA is able per se to reduce HBV expression by a post-transcriptional mechanism, and thus participates in the antiviral activity of IFN-alpha against HBV.

Distinct poly(I-C) and virus-activated signaling pathways leading to interferon-beta production in hepatocytes

Innate cellular antiviral defenses are likely to influence the outcome of infections by many human viruses, including hepatitis B and C viruses, agents that frequently establish persistent infection leading to chronic hepatitis, cirrhosis, and liver cancer. However, little is known of the pathways by which hepatocytes, the cell type within which these hepatitis agents replicate, sense infection, and initiate protective responses. We show that cultured hepatoma cells, including Huh7 cells, do not activate the interferon (IFN)-beta promoter in response to extracellular poly(I-C). In contrast, the addition of poly(I-C) to culture media activates the IFN-beta promoter and results in robust expression of IFN-stimulated genes (ISG) in PH5CH8 cells, which are derived from non-neoplastic hepatocytes transformed with large T antigen. Small interfering RNA knockdown of TLR3 or its adaptor, Toll-interleukin-1 receptor domain-containing adaptor inducing IFN-beta (TRIF), blocked extracellular poly(I-C) signaling in PH5CH8 cells, whereas poly(I-C) responsiveness could be conferred on Huh7 hepatoma cells by ectopic expression of Toll-like receptor 3 (TLR3). In contrast to poly(I-C), both cell types signal the presence of Sendai virus infection through a TLR3-independent intracellular pathway requiring expression of retinoic acid-inducible gene I (RIG-I), a putative cellular RNA helicase. Silencing of RIG-I expression impaired only the response to Sendai virus and not extracellular poly(I-C). We conclude that hepatocytes contain two distinct antiviral signaling pathways leading to expression of type I IFNs, one dependent upon TLR3 and the other dependent on RIG-I, with little cross-talk between these pathways.

Porcine reproductive and respiratory syndrome virus field isolates differ in in vitro interferon phenotypes

Type I interferons (IFN-α and -β) play an important role in the innate host defense against viral infection by inducing antiviral responses. In addition to direct antiviral activities, type I IFN serves as an important link between the innate and adaptive immune response through multiple mechanisms. Therefore, the outcome of a viral infection can be affected by IFN induction and the IFN sensitivity of a virus. North American porcine reproductive and respiratory syndrome virus (PRRSV) field isolates were studied with regard to IFN-α sensitivity and induction in order to understand the role of type I IFN in PRRSV pathogenesis. PRRSV isolates were differentially sensitive to porcine recombinant IFN-α (rIFN-α) and varied in their ability to induce IFN-α in porcine alveolar macrophages (PAM) cultures as measured by a porcine IFN-α specific ELISA on cell culture supernatants. Fifty-two plaques were purified from three PRRSV isolates (numbers 3, 7, and 12) and tested for IFN sensitivity and IFN induction. Plaque-derived populations were composed of heterogeneous populations in terms of IFN-inducing capacity and sensitivity to rIFN-α. When macrophages infected with isolates 3, 7, or 12 were treated with polycytidylic acid (polyI:C), IFN-α production was enhanced. Cells infected with isolate 3 and treated with polyI:C showed the most consistent and strongest enhancement of IFN-α production. It was demonstrated that the relatively low concentrations of IFN-α produced by isolate 3 contributed to the enhanced IFN-α synthesis in response to polyI:C. Isolates 7 and 12 significantly suppressed the enhanced IFN-α production by isolate 3 in polyI:C treated cells. To determine if suppression was at the level of IFN-α transcription, quantitative RT-PCR was performed for IFN-α mRNA and compared to GAPDH and cyclophilin mRNA quantification. However, the relative number of IFN-α transcript copies did not correlate with IFN-α protein levels, suggesting a post-transcriptional mechanism of suppression. In summary, these results demonstrate that PRRSV field isolates differ both in IFN-α sensitivity and induction. Furthermore, a PRRSV field isolate strongly enhance polyI:C-induced IFN-α production in PAM cultures and this priming effect was suppressed by other PRRSV isolates.

Specific Inhibition of Type I Interferon Signal Transduction by Respiratory Syncytial Virus

Respiratory viruses often express mechanisms to resist host antiviral systems, but the biochemical basis for evasion of interferon effects by respiratory syncytial virus (RSV) is poorly defined. In this study, we identified RSV effects on interferon (IFN)-dependent signal transduction and gene expression in human airway epithelial cells. Initial experiments demonstrated inhibition of antiviral gene expression induced by IFN-alpha and IFN-beta, but not IFN-gamma, in epithelial cells infected with RSV. Selective viral effects on type I IFN-dependent signaling were confirmed when we observed impaired type I, but not type II, IFN-induced activation of the transcription factor Stat1 in RSV-infected cells. RSV infection of airway epithelial cells resulted in decreased Stat2 expression and function with preservation of upstream signaling events, providing a molecular mechanism for viral inhibition of the type I IFN JAK-STAT pathway. Furthermore, nonspecific pharmacologic inhibition of proteasome function in RSV-infected cells restored Stat2 levels and IFN-dependent activation of Stat1. The results indicate that RSV acts on epithelial cells in the airway to directly modulate the type I IFN JAK-STAT pathway, and this effect is likely mediated though proteasome-dependent degradation of Stat2. Decreased antiviral gene expression in RSV-infected airway epithelial cells may allow RSV replication and establishment of a productive viral infection through subversion of IFN-dependent immunity.

Persistent infection and suppression of host response by alphaviruses

Alphaviruses cause chronic noncytopathic infection in mosquito cells and develop a highly cytopathic infection in a wide variety of cells of vertebrate origin. Upon infection, alphaviruses modify cellular processes to meet the virus needs for propagation. Downregulation of translation and transcription caused by viral infection appears to reduce interferon (IFN) and cytokine gene expression and allows more efficient dissemination of infection. Alphaviruses with mutations in nonstructural protein nsP2 can become less cytopathic and capable of persisting in some vertebrate cell lines for a number of passages. nsP2 likely functions as an important regulator of virus-host cell interactions and plays a significant role in suppressing the antiviral response. Mammalian cells having no defects in type I IFN system react to replication of the nsP2 viral mutants by more efficient activation of IFN and IFN-dependent genes and are capable of eliminating established alphavirus infection. Blocking of IFN-alpha/beta signaling makes mouse fibroblasts unable to stop replication of Sindbis virus (SINV) with mutated nsP2 and leads to persistent infection. Downregulation of transcription and translation during alphavirus infection are quite independent events, and both probably are involved in inhibition of the antiviral response.

Hepatitis B virus downregulates the human interferon-inducible MxA promoter through direct interaction of precore/core proteins

The human MxA protein is an interferon (IFN)-inducible GTPase with proven antiviral activity against diverse viruses. IFN responsiveness is impaired in chronic hepatitis B virus (HBV) infection. Accordingly, initial experiments showed that, in contrast to parental HepG2 cells, when HepG2-derived 2.2.15 liver cells carrying the HBV genome were treated with IFN, they could not synthesize the MxA protein. Furthermore, MxA expression was reduced in HepG2 cells transiently transfected with the HBV genome. To assess whether HBV-encoded precore/core (preC/C) proteins interact with the IFN-signalling pathway, HepG2, Chang and HeLa cells were transfected with preC/C expression plasmids; the levels of signal transducers remained unaffected. Next, full-length and deletion mutants fused to the CAT reporter gene were tested to investigate whether MxA inhibition occurs at the promoter level. In co-transfection experiments, IFN-induced CAT activity was inhibited by preC/C expression in a dose-dependent manner. Analysis of deletion mutants showed that the region affected by the preC/C proteins comprises IFN-stimulated response elements 2 and 3, upstream of the putative start codon of the MxA promoter. In addition, HBV preC/C proteins interacted directly with the MxA promoter, as shown by electrophoretic mobility shift assays. These results demonstrate a mechanism that HBV probably uses to downregulate an element of the IFN-induced host antiviral responses, which accounts for the impairment observed in HBV-infected patients.

Hepatitis B viral core protein activates the hepatitis B viral enhancer II/pregenomic promoter through the nuclear factor kappaB binding site

We here demonstrated that the hepatitis B viral (HBV) core protein (HBc) functions as a transcriptional activator on the pregenomic promoter of HBV. Detailed analyses on the HBV pregenomic promoter by serial deletion, mutation, and heterologous promoter system showed that the site responsible for activation was the nuclear factor kappaB (NF-kappaB) binding site (GGGACGTACT, nucleotides 1408-1417) upstream of the enhancer II/pregenomic promoter. The electrophoretic mobility shift assay using the HBc-transfected HepG2 nuclear extracts showed that the HBc enhanced the NF-kappaB DNA-binding ability. These results suggest that the HBc functions as a positive regulator, which may enhance viral replication in hepatocytes.

Transcriptional repression of the human p53 gene by hepatitis B viral core protein (HBc) in human liver cells

Hepatitis B virus (HBV) is a causative agent of chronic and acute hepatitis, and is associated with the development of hepatocellular carcinoma (HCC). We demonstrate here that the Hepatitis B viral core protein (HBc) functions as a repressor on the promoter activity of the human p53 gene. The functional analyses of the promoter of the p53 gene by serial deletion, site-directed mutagenesis, and the heterologous promoter system revealed that the promoter activity was repressed through the E2F1-binding site (nucleotides -28 to -8) by HBc. An electrophoretic mobility shift assay (EMSA) showed that the HBc reduced the DNA-binding ability of E2F1 to the binding site of the p53 promoter. The interaction of HBc with E2F1 was also observed by glutathione S-transferase (GST) fusion protein binding assay. Furthermore, HBc represses the expression of the p53 gene in the human liver cell line HepG2. Finally, HBc and HBx synergistically repress both the promoter activity and the expression of the p53 gene in HepG2 cells. These results, together with our previous study, strongly suggest that HBc, like HBx, represses the expression of the human p53 tumor suppressor gene.

Cytokine gene polymorphisms in patients infected with hepatitis B virus

OBJECTIVE

Cytokines play a key role in the regulation of the immune response. The maximal capacity of cytokine production varies among individuals and correlates with the polymorphism in the cytokine gene promoters. The aim of this study was to characterize gene polymorphism in patients with chronic hepatitis B virus (HBV) infection and to determine the different patterns in patient subgroups.

METHODS

The study population consisted of 77 patients with chronic HBV infection (23 low-level HBV replicative carriers, 23 compensated high-level HBV replicative carriers, 21 decompensated liver transplant candidates, and 10 patients with documented hepatocellular carcinoma). The genetic profile of five cytokines was analyzed by polymerase chain reaction-sequence-specific primer (SSP), and subjects were genotyped as high or low producers of tumor necrosis factor-alpha and interleukin (IL)-6, and as high, intermediate, or low producers of transforming growth factor-beta(1), interferon (IFN)-gamma, and IL-10 based on single nucleotide substitutions. The control group included 10 healthy individuals who recovered from HBV infection and 48 healthy controls.

RESULTS

A highly statistically significant difference in the distribution of the IFN-gamma gene polymorphism (at position +879) was observed between patients with chronic HBV infection and controls. The majority of the patients (65.2%) exhibited the potential to produce low levels of IFN-gamma (A/A genotype) compared with 37.5% of the control group (p = 0.003). Healthy individuals who recovered from HBV infection had a similar distribution of IFN-gamma gene polymorphism as the healthy controls. No statistically significant difference in IFN-gamma production was found between patients with low- and high-level HBV replication and between compensated and decompensated patients. There was also no statistically significant difference in the genetic ability to produce tumor necrosis factor-alpha (at position -308), IL-6 (at position -174), IL-10 (at position -1082, -819, and -592), and transforming growth factor-beta(1) (at position +10 and +25).

CONCLUSION

These findings suggest an association between the genetic ability to produce low levels of IFN-gamma and the susceptibility to develop chronic HBV infection.

Roles of nonstructural protein nsP2 and Alpha/Beta interferons in determining the outcome of Sindbis virus infection

Alphaviruses productively infect a variety of vertebrate and insect cell lines. In vertebrate cells, Sindbis virus redirects cellular processes to meet the needs of virus propagation. At the same time, cells respond to virus replication by downregulating virus growth and preventing dissemination of the infection. The balance between these two mechanisms determines the outcome of infection at the cellular and organismal levels. In this report, we demonstrate that a viral nonstructural protein, nsP2, is a significant regulator of Sindbis virus-host cell interactions. This protein not only is a component of the replicative enzyme complex required for replication and transcription of viral RNAs but also plays a role in suppressing the antiviral response in Sindbis virus-infected cells. nsP2 most likely acts by decreasing interferon (IFN) production and minimizing virus visibility. Infection of murine cells with Sindbis virus expressing a mutant nsP2 leads to higher levels of IFN secretion and the activation of 170 cellular genes that are induced by IFN and/or virus replication. Secreted IFN protects naive cells against Sindbis virus infection and also stops viral replication in productively infected cells. Mutations in nsP2 can also attenuate Sindbis virus cytopathogenicity. Such mutants can persist in mammalian cells with defects in the alpha/beta IFN (IFN-alpha/beta) system or when IFN activity is neutralized by anti-IFN-alpha/beta antibodies. These findings provide new insight into the alphavirus-host cell interaction and have implications for the development of improved alphavirus expression systems with better antigen-presenting potential.

Mechanisms of inhibition of the host interferon alpha/beta-mediated antiviral responses by viruses

Complex multicellular organisms have evolved sophisticated mechanisms to prevent and control infection by pathogens. Among these mechanisms, the type I interferon or interferon alpha/beta system represents one of the first lines of defense against viral infections. Typically, viral infection induces the synthesis and secretion of interferon alpha/beta by the infected cell, which in turn activates signaling pathways leading to an antiviral state. As a counter measure, many viruses have developed intriguing mechanisms to evade the interferon alpha/beta system of the host. In this review, we will summarize recent research developments in this interesting field of virus-host cell interactions.

Control or persistence of hepatitis B virus: the critical role of initial host-virus interactions

Following infection with hepatitis B virus (HBV), the period before symptomatic disease is now recognized as a time of dynamic interaction between virus and host. Recent work has shown that this period is the phase of infection during which maximal changes in virus replication and the activation of critical components of the immune system occurs. This suggests that the different outcomes following exposure might be determined during the early phase of infection, before the onset of clinical disease. The hypothesis that small differences in the dynamic relationship between host and virus, such as in the kinetics of HBV replication, may influence the final outcome of infection, will be discussed.

Viruses and interferons

The interferon system is the first line of defense against viral infection in mammals. This system is designed to block the spread of virus infection in the body, sometimes at the expense of accelerating the death of the infected cells. As expected of potent cytokines, in addition to their antiviral effects, interferons have profound effects on many aspects of cell physiology. All these actions of interferons are mediated by hundreds of interferon-induced proteins that are usually not synthesized in resting cells. Interferons induce their synthesis by activating the Jak-STAT pathways, a paradigm of cell signaling used by many cytokines and growth factors. Surprisingly, some of the same genes can also be induced directly by viruses and double-stranded RNA, a common viral by-product. Some of the interferon-induced proteins have novel biochemical properties and some are inactive as such but can be activated by double-stranded RNA produced during virus infection. Finally, almost all viruses have evolved mechanisms to evade the interferon system by partially blocking interferon synthesis or interferon action. Thus, in nature interferons and viruses maintain an equilibrium that allows regulated viral replication.

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.

Inhibition of hepatitis B virus replication by the interferon-inducible MxA protein

Human MxA is an alpha/beta interferon-inducible intracytoplasmic protein that mediates antiviral activity against several RNA viruses. We had previously shown that overexpression of the hepatitis B virus (HBV) capsid led to selective downregulation of MxA gene expression, suggesting a mechanism by which the virus escapes from the host defense system (O. Rosmorduc, H. Sirma, P. Soussan, E. Gordien, P. Lebon, M. Horisberger, C. Brechot and D. Kremsdorf, J. Gen. Virol. 80:1253-1262, 1999). In the present study, we investigated the antiviral activity of MxA protein against HBV. MxA-expressing HuH7 clones were established and transiently transfected with HBV, and viral replication was then studied. Viral protein secretion was profoundly reduced in MxA-expressing clones by 80% for HBV surface antigen (HBsAg) and 70% for HBV e antigen (HBeAg). The levels of intracytoplasmic HBsAg and HBeAg were reduced by about 80 and 50% in the two MxA-positive clones tested. A nearly complete disappearance of HBV DNA replicative intermediates was observed in MxA-expressing clones. Although the expression of total viral RNAs was not modified, two- to fourfold reductions in HBV cytoplasmic RNAs were found in MxA-expressing clones. This suggests the inhibition of HBV replication at a posttranscriptional level. Indeed, using the well-characterized posttranscriptional regulation element (PRE) reporter system, we were able to demonstrate a marked reduction (three- to eightfold) in the nucleocytoplasmic export of unspliced RNA in MxA-expressing clones. In addition, MxA protein did not interact with HBV nucleocapsid or interfere with HBV nucleocapsid formation. Our results show an antiviral effect of MxA protein on a DNA virus for the first time. MxA protein acts, at least in part, by inhibiting the nucleocytoplasmic export of viral mRNA via the PRE sequence.

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.

Virus interception of cytokine-regulated pathways

Cytokines regulate host antiviral, immune and antitumor responses. Viruses combat the host-imposed inhibitory pathways to survive and spread the infection. Some viruses have evolved molecules that override apoptotic programs to promote cell survival until virus assembly is complete, persistence is established or cellular transformation occurs.

Expression of interferon alpha/beta receptor in the liver of chronic hepatitis C patients

Interferon (IFN) demonstrates antiviral activity by binding to receptors on the cell surface. Expression of the IFN receptor in hepatocytes may be directly associated with a hepatitis C virus (HCV) infection and the response to IFN therapy. A competitive PCR method was developed to measure IFN alpha/beta (alphabeta) receptor mRNA in liver samples obtained by needle biopsy. Thirty-one patients with chronic hepatitis C (21 without cirrhosis, 10 with cirrhosis) and six normal subjects were used. Eighteen of the 21 patients without cirrhosis received the IFN therapy. Competitive PCR was carried out using IFN alphabeta receptor gene-specific primers and a specific competitor. Expression of the receptor was detected in all liver samples. There was no association between the expression level and serum alanine aminotransferase level, serum (2'-5') oligo (A) synthetase level, amount of serum HCV RNA, or HCV genotype. The expression level in patients with chronic hepatitis was significantly higher than that in normal livers (P < 0.05) and in cirrhotic livers (P< 0.01). Seven of the 18 patients treated with IFN demonstrated a sustained response to IFN (sustained responders), and the remaining 11 did not (nonsustained responders). The expression level of IFN alphabeta receptor mRNA in the sustained responders was significantly higher than that in the nonsustained responders (P< 0.01). Thus, the expression of IFN alphabeta receptor mRNA may be one of the host factors influencing the response to IFN therapy.

Pathogen interactions with cytokines and host defence: an overview

This review summarises some of the immune evasion tactics adopted by pathogens. They include the antagonism of immune function through the use of homologues of cytokine receptors, expression of viral proteins which interact with cytokine signal transduction and expression of cytokine mimics and host proteins that influence the Type I or II cytokine responses. Some of the viral defense molecules that interfere with the functions of cytokines include the EBV protein BCRF1 (viral IL-10) which blocks synthesis of cytokines such as IFN-gamma, viral IL-17 and IL-8 receptor encoded by the herpesvirus saimiri genome and chemokine receptor homologues of Epstein-Barr virus, herpesvirus saimiri and cytomegalovirus. These immunomodulatory tactics function to protect the host from the lethal inflammatory effects as well as inhibit the local inflammatory response elicited to kill the foreign pathogen. Other strategies include the alterations in cytokine expression such as demonstrated with the hepatitis B virus (HBV) core protein and terminal protein which can inhibit interferon-beta gene expression, the interactions of the hepatitis C virus core protein to lymphotoxin-beta receptor and the effects of the interferon signal transduction pathway by adenovirus EIA oncogene and HBV by reducing levels or activity of the cytosolic latent transcriptional factors (STATS). Immune evasive strategies of helminth parasites related to cytokine activities will also be briefly discussed.

Analysis of hepatitis B virus populations in an interferon-alpha-treated patient reveals predominant mutations in the C-gene and changing e-antigenicity

It is largely unknown whether hepatitis B virus (HBV) sequence variation during chronic infection hampers HBV immune recognition or the antiviral effect of cytokines on HBV production. Here we have analyzed which region of the HBV genome changes most drastically during an interferon-alpha (IFNalpha)-stimulated immune response. In addition, we have investigated whether the mutations affect viral replication, gene expression, and immune recognition of the mutant viral proteins. The study was performed with full-length HBV genomes taken longitudinally from a patient who transiently cleared HBV and seroconverted to anti-HBe during a long-term IFNalpha treatment. We found a replacement of the predominant virus population during IFNalpha therapy The virus populations differed mainly by a cluster of nucleotide changes in the C-gene and a pre-S2 deletion. Most of the newly emerging mutations localized within core/HBe B-cell epitopes, changed HBe antigenicity toward mono- and polyclonal antibodies, and also influenced the reactivity of the anti-HBc/e antibodies of the patient. All genomes tested expressed less HBeAg than wild-type HBV, while replication and IFNalpha susceptibility were similar. These data indicate that IFNalpha therapy can lead to the emergence of HBV variants with mutations mainly affecting recognition of the core/HBe proteins by antibodies. Taken together, the type of core/HBe-specific B-cell immune response, the sequence of the corresponding epitopes, and the HBe expression level appear to contribute to the decision on viral clearance or persistence.

A tumor necrosis factor-alpha (TNF-alpha) promoter polymorphism is associated with chronic hepatitis B infection

Cytokines such as TNF-alpha and interferon gamma (IFN-gamma) are important for the elimination of infected hepatocytes during acute hepatitis B virus (HBV) infection. Two G versus A transitions in the TNF-alpha promoter region at positions -308 and -238 possibly influence TNF-alpha expression. We investigated these TNF-alpha polymorphisms in 71 patients with chronic HBV infection, in 32 subjects that had spontaneously recovered from acute HBV infection, and in 99 healthy controls. The -238 A promoter variant was present in 18 (25%) of 71 patients with chronic HBV infection compared with two (6%) of 32 subjects with acute infection (P<0.04), and seven (7%) of 99 controls (P<0.003). By contrast, the prevalence of the variant at position -308 was similar in all investigated groups. The observed differences could not be explained by linkage disequilibrium to HLA-B or -DRB1* alleles. These findings suggest an association between the TNF-alpha promoter polymorphism at position -238 and the development of chronic HBV infection. This promoter variant appears to be linked to defective viral clearance.

Tumor necrosis factor alpha promoter polymorphism at position -238 is associated with chronic active hepatitis C infection

Tumor necrosis factor alpha (TNF-alpha) is involved in the pathogenesis of chronic hepatitis C virus infection. The gene for TNF-alpha is encoded in the major histocompatibility locus (MHC). Two polymorphisms at positions -308 and -238 in the TNF-alpha promoter region might influence TNF-alpha expression. These promoter polymorphisms have been linked previously to a number of infectious diseases. TNF-alpha promoter polymorphisms at positions -238 and -308 were studied by DNA sequencing and sequence-specific oligonucleotide hybridization in 82 individuals with chronic hepatitis C and 99 control subjects. Subjects had been HLA class I and class II typed in a previous study. The frequency of the TNF238.2 promoter allele was significantly higher in the hepatitis C group (18.7%) compared to the controls (3.5%; P < 0.0001; pcorr < 0.009). No significant differences in the frequency of the TNF308.2 allele were observed between patients and controls. The increased frequency of the TNF238.2 allele could not be explained by linkage disequilibrium to HLA-B or -DR genes. These findings show an association between the TNF238.2 promoter variant and chronic active hepatitis C. They suggest that this polymorphism or a linked gene may be a host factor contributing to the development of chronic active hepatitis C.

Evidence for a deficiency of interferon response in mononuclear cells from hepatitis C viremic patients

BACKGROUND/AIMS

The pathophysiology of chronic hepatitis C and the mechanisms of resistance to interferon alpha are poorly understood. The aim of this work was to assess the influence of HCV infection and the viral genotype on lymphocyte production of 2',5' oligo-adenylate synthetase activity and monocyte production of TNF alpha and IL1 beta.

METHODS

Mononuclear cells from 50 consecutive patients were studied after 6 months of interferon treatment. Patients with persistent viremia (PCR-positive, elevated ALT, n = 39) were compared with the PCR-negative patients with normal ALT activity (n = 11) of similar age and sex ratio.

RESULTS

Cells from the viremic patients showed lower basal and stimulated 2',5' oligo-adenylate synthetase activity, and a lower in vitro response capacity to human recombinant interferon. In contrast, no difference was observed in basal and stimulated TNF alpha or IL1 beta production between the two groups. In the PCR-positive patients the viral genotype had no significant influence on the response of mononuclear cells to interferon or endotoxin.

CONCLUSIONS

These results show that the presence of HCV in blood is associated with an elective defect in interferon system activation, independently of the viral genotype.

Diagnosis and treatment of hepatic disease in patients with HIV

Liver involvement with opportunistic infections and neoplasms is a well-recognized component of AIDS, affecting most patients. The cause of hepatic disease in these patients may be divided into hepatitis, granulomatous disease, mass lesions, vascular lesions, hepatotoxic drugs, and nonspecific findings. With a rational approach, most patients with AIDS and liver disease can be diagnosed and treated in a cost-effective manner with low morbidity.

Biology and therapeutic uses of myeloid hematopoietic growth factors and interferons

Recent advances in basic science and clinical trials have demonstrated that IFNs and myeloid hematopoietins play crucial roles in host defense against pathogens and immune surveillance. Here we have reviewed the biologic functions of GM-CSF, G-CSF, IFN-alpha and IFN-gamma. For patients with neutropenia resulting from cytotoxic chemotherapy, bone marrow transplantation, congenital agranulocytosis and cyclic neutropenia, therapeutic uses of GM-CSF and G-CSF were reviewed. Application of these growth factors to patient management represents a major contribution of biotechnology to a difficult area of therapeutics in febrile, neutropenic patients. Because IFN-alpha plays crucial roles in antiviral responses, its clinical applications in hepatitis B and C, human papilloma virus, HIV infection and malignancy were discussed. The use of IFN-gamma in bacterial prophylaxis in patients with chronic granulomatous disease was also presented. Advances in clinical applications of IFNs and hematopoietic growth factors serve as a paradigm for further development to investigate the use of other important cytokines in modern therapeutics.

Hepatitis B virus immunopathology

Approximately 5% of the world population is infected by the hepatitis B virus (HBV) which causes a necroinflammatory liver disease of variable duration and severity. Chronically infected patients with active liver disease carry a high risk of developing cirrhosis and hepatocellular carcinoma. The immune response to HBV-encoded antigens is responsible both for viral clearance and for disease pathogenesis during this infection. While the humoral antibody response to viral envelope antigens contributes to the clearance of circulating virus particles, the cellular immune response to the envelope, nucleocapsid and polymerase antigens eliminates infected cells. The class I- and class II-restricted T cell responses to the virus are vigorous, polyclonal and multispecific in acutely infected patients who successfully clear the virus, and they are relatively weak and more narrowly focussed in chronically infected patients who do not. The pathogenetic and antiviral potential of the cytotoxic T lymphocyte (CTL) response to HBV have been demonstrated by the induction of a severe necroinflammatory liver disease following the adoptive transfer of HBV surface antigen-specific CTL into HBV transgenic mice, and by the noncytolytic suppression of viral gene expression and replication in the same animals by a post-transcriptional mechanism mediated by interferon-gamma, tumor necrosis factor-alpha and interleukin-2. The dominant cause of viral persistence during HBV infection is the development of a weak antiviral immune response to the viral antigens. While neonatal tolerance probably plays an important role in viral persistence in patients infected at birth, the basis for poor responsiveness in adult onset infection is not well understood and requires further analysis. Viral evasion by epitope inactivation and T cell receptor antagonism may contribute to the worsening of viral persistence in the setting of an ineffective immune response, as can the incomplete down-regulation of viral gene expression and the infection of immunologically privileged tissues. Chronic liver cell injury and the attendant inflammatory and regenerative responses create the mutagenic and mitogenic stimuli for the development of DNA damage that can cause hepatocellular carcinoma. Elucidation of the immunological and virological basis for HBV persistence may yield immunotherapeutic and antiviral strategies to terminate chronic HBV infection and reduce the risk of its life-threatening sequellae.

Resistance of lymphocytic choriomeningitis virus to alpha/beta interferon and to gamma interferon

The susceptibility to alpha/beta interferon (IFN-alpha/beta) or to gamma interferon (IFN-gamma) of various lymphocytic choriomeningitis virus (LCMV) strains was evaluated in C57BL/6 mice and in various cell lines. Anti-IFN-gamma treatment in vivo revealed that the LCMV strains Armstrong, Aggressive, and WE were most susceptible to IFN-gamma whereas Traub, Cl 13-Armstrong, and Docile were resistant. The same pattern of susceptibility to recombinant IFN-gamma was observed in vitro. In vivo treatment with anti-IFN-alpha/beta showed a sizeable increase in replication of Aggressive, Armstrong, and WE; effects were less pronounced for Docile, Cl 13-Armstrong, or Traub. Correspondingly, WE, Armstrong, and Aggressive were all relatively sensitive to purified IFN-alpha/beta in vitro, and Cl 13-Armstrong, Docile, and Traub were more resistant. Overall, there was a good correlation between the capacity of LCMV strains to establish a persistent infection in adult immunocompetent mice and their relative resistance to IFN-gamma and IFN-alpha/beta.

Cell cycle regulation of nuclear localization of hepatitis B virus core protein

The hepatitis B virus (HBV) core protein has been found in the nucleus, the cytoplasm, or both of HBV-infected hepatocytes. However, the mechanism that regulates the subcellular localization of the HBV core protein is still unclear. In this report, we demonstrate that nuclear localization of the HBV core protein is cell cycle-regulated in two different cell lines. The amount of the core protein in the nucleus was increased during the G1 phase, reduced to an undetectable level during the S phase, and increased again when the cells were confluent and ceased to grow. Thus, the nuclear localization of the core protein during HBV infection can be at least partially attributed to liver injury and regeneration, which cause the hepatocytes to enter cell cycles. Based on the observation that the cytoplasmic core protein was phosphorylated and the nuclear core protein was not, we speculate that nuclear localization of the HBV core protein is negatively regulated by phosphorylation during the cell cycle.