Large isoform of hepatitis delta antigen activates serum response factor-associated transcription

Investigating the Genetic Diversity of Hepatitis Delta Virus in Hepatocellular Carcinoma (HCC): Impact on Viral Evolution and Oncogenesis in HCC

Hepatitis delta virus (HDV), an RNA virus with two forms of the delta antigen (HDAg), relies on hepatitis B virus (HBV) for envelope proteins essential for hepatocyte entry. Hepatocellular carcinoma (HCC) ranks third in global cancer deaths, yet HDV's involvement remains uncertain. Among 300 HBV-associated HCC serum samples from Taiwan's National Health Research Institutes, 2.7% (8/300) tested anti-HDV positive, with 62.7% (5/8) of these also HDV RNA positive. Genotyping revealed HDV-2 in one sample, HDV-4 in two, and two samples showed mixed HDV-2/HDV-4 infection with RNA recombination. A mixed-genotype infection revealed novel mutations at the polyadenylation signal, coinciding with the ochre termination codon for the L-HDAg. To delve deeper into the possible oncogenic properties of HDV-2, the predominant genotype in Taiwan, which was previously thought to be less associated with severe disease outcomes, an HDV-2 cDNA clone was isolated from HCC for study. It demonstrated a replication level reaching up to 74% of that observed for a widely used HDV-1 strain in transfected cultured cells. Surprisingly, both forms of HDV-2 HDAg promoted cell migration and invasion, affecting the rearrangement of actin cytoskeleton and the expression of epithelial-mesenchymal transition markers. In summary, this study underscores the prevalence of HDV-2, HDV-4, and their mixed infections in HCC, highlighting the genetic diversity in HCC as well as the potential role of both forms of the HDAg in HCC oncogenesis.

Hepatitis Delta Virus and Hepatocellular Carcinoma

The hepatitis D virus (HDV) is a compact, enveloped, circular RNA virus that relies on hepatitis B virus (HBV) envelope proteins to initiate a primary infection in hepatocytes, assemble, and secrete new virions. Globally, HDV infection affects an estimated 12 million to 72 million people, carrying a significantly elevated risk of developing cirrhosis, liver failure, and hepatocellular carcinoma (HCC) compared to an HBV mono-infection. Furthermore, HDV-associated HCC often manifests at a younger age and exhibits more aggressive characteristics. The intricate mechanisms driving the synergistic carcinogenicity of the HDV and HBV are not fully elucidated but are believed to involve chronic inflammation, immune dysregulation, and the direct oncogenic effects of the HDV. Indeed, recent data highlight that the molecular profile of HCC associated with HDV is unique and distinct from that of HBV-induced HCC. However, the question of whether the HDV is an oncogenic virus remains unanswered. In this review, we comprehensively examined several crucial aspects of the HDV, encompassing its epidemiology, molecular biology, immunology, and the associated risks of liver disease progression and HCC development.

Hepatocellular carcinoma: The virus or the liver?

Hepatocellular carcinoma (HCC) represents a major public health problem being one of the most common causes of cancer-related deaths worldwide. Hepatitis B (HBV) and C viruses have been classified as oncoviruses and are responsible for the majority of HCC cases, while the role of hepatitis D virus (HDV) in liver carcinogenesis has not been elucidated. HDV/HBV coinfection is related to more severe liver damage than HBV mono-infection and recent studies suggest that HDV/HBV patients are at increased risk of developing HCC compared to HBV mono-infected patients. HBV is known to promote hepatocarcinogenesis via DNA integration into host DNA, disruption of molecular pathways by regulatory HBV x (HBx) protein and excessive oxidative stress. Recently, several molecular mechanisms have been proposed to clarify the pathogenesis of HDV-related HCC including activation of signalling pathways by specific HDV antigens, epigenetic dysregulation and altered gene expression. Alongside, ongoing chronic inflammation and impaired immune responses have also been suggested to facilitate carcinogenesis. Finally, cellular senescence seems to play an important role in chronic viral infection and inflammation leading to hepatocarcinogenesis. In this review, we summarize the current literature on the impact of HDV in HCC development and discuss the potential interplay between HBV, HDV and neighbouring liver tissue in liver carcinogenesis.

[Modern views on the role of X gene of the hepatitis B virus (Hepadnaviridae: Orthohepadnavirus: Hepatitis B virus) in the pathogenesis of the infection it causes]

The review presents information on the role of hepatitis B virus (Hepadnaviridae: Orthohepadnavirus: Hepatitis B virus) (HBV) X gene and the protein it encodes (X protein) in the pathogenesis of viral hepatitis B. The evolution of HBV from primordial to the modern version of hepadnaviruses (Hepadnaviridae), is outlined as a process that began about 407 million years ago and continues to the present. The results of scientific works of foreign researchers on the variety of the influence of X protein on the infectious process and its role in the mechanisms of carcinogenesis are summarized. The differences in the effect of the X protein on the course of the disease in patients of different ethnic groups with regard to HBV genotypes are described. The significance of determining the genetic variability of X gene as a fundamental characteristic of the virus that has significance for the assessment of risks of hepatocellular carcinoma (HCC) spread among the population of the Russian Federation is discussed.

Adaptive Immune Responses, Immune Escape and Immune-Mediated Pathogenesis during HDV Infection

The hepatitis delta virus (HDV) is the smallest known human virus, yet it causes great harm to patients co-infected with hepatitis B virus (HBV). As a satellite virus of HBV, HDV requires the surface antigen of HBV (HBsAg) for sufficient viral packaging and spread. The special circumstance of co-infection, albeit only one partner depends on the other, raises many virological, immunological, and pathophysiological questions. In the last years, breakthroughs were made in understanding the adaptive immune response, in particular, virus-specific CD4+ and CD8+ T cells, in self-limited versus persistent HBV/HDV co-infection. Indeed, the mechanisms of CD8+ T cell failure in persistent HBV/HDV co-infection include viral escape and T cell exhaustion, and mimic those in other persistent human viral infections, such as hepatitis C virus (HCV), human immunodeficiency virus (HIV), and HBV mono-infection. However, compared to these larger viruses, the small HDV has perfectly adapted to evade recognition by CD8+ T cells restricted by common human leukocyte antigen (HLA) class I alleles. Furthermore, accelerated progression towards liver cirrhosis in persistent HBV/HDV co-infection was attributed to an increased immune-mediated pathology, either caused by innate pathways initiated by the interferon (IFN) system or triggered by misguided and dysfunctional T cells. These new insights into HDV-specific adaptive immunity will be discussed in this review and put into context with known well-described aspects in HBV, HCV, and HIV infections.

Hepatitis D Virus and Hepatocellular Carcinoma

Hepatitis D virus (HDV) is a small, defective RNA virus that depends on hepatitis B virus (HBV) for virion assembly and transmission. It replicates within the nucleus of hepatocytes and interacts with several cellular proteins. Chronic hepatitis D is a severe and progressive disease, leading to cirrhosis in up to 80% of cases. A high proportion of patients die of liver decompensation or hepatocellular carcinoma (HCC), but the lack of large prospective studies has made it difficult to precisely define the rate of these long-term complications. In particular, the question of whether HDV is an oncogenic virus has been a matter of debate. Studies conducted over the past decade provided evidence that HDV is associated with a significantly higher risk of developing HCC compared to HBV monoinfection. However, the mechanisms whereby HDV promotes liver cancer remain elusive. Recent data have demonstrated that the molecular profile of HCC-HDV is unique and distinct from that of HBV-HCC, with an enrichment of upregulated genes involved in cell-cycle/DNA replication, and DNA damage and repair, which point to genome instability as an important mechanism of HDV hepatocarcinogenesis. These data suggest that HBV and HDV promote carcinogenesis by distinct molecular mechanisms despite the obligatory dependence of HDV on HBV.

HDV Pathogenesis: Unravelling Ariadne's Thread

Hepatitis Delta virus (HDV) lies in between satellite viruses and viroids, as its unique molecular characteristics and life cycle cannot categorize it according to the standard taxonomy norms for viruses. Being a satellite virus of hepatitis B virus (HBV), HDV requires HBV envelope glycoproteins for its infection cycle and its transmission. HDV pathogenesis varies and depends on the mode of HDV and HBV infection; a simultaneous HDV and HBV infection will lead to an acute hepatitis that will resolve spontaneously in the majority of patients, whereas an HDV super-infection of a chronic HBV carrier will mainly result in the establishment of a chronic HDV infection that may progress towards cirrhosis, liver decompensation, and hepatocellular carcinoma (HCC). With this review, we aim to unravel Ariadne’s thread into the labyrinth of acute and chronic HDV infection pathogenesis and will provide insights into the complexity of this exciting topic by detailing the different players and mechanisms that shape the clinical outcome.

Innate immune recognition and modulation in hepatitis D virus infection

Hepatitis D virus (HDV) is a global health threat with more than 15 million humans affected. Current treatment options are largely unsatisfactory leaving chronically infected humans at high risk to develop liver cirrhosis and hepatocellular carcinoma. HDV is the only human satellite virus known. It encodes only two proteins, and requires Hepatitis B virus (HBV) envelope protein expression for productive virion release and spread of the infection. How HDV could evolve and why HBV was selected as a helper virus remains unknown. Since the discovery of Na⁺-taurocholate co-transporting polypeptide as the essential uptake receptor for HBV and HDV, we are beginning to understand the interactions of HDV and the immune system. While HBV is mostly regarded a stealth virus, that escapes innate immune recognition, HBV-HDV coinfection is characterized by a strong innate immune response. Cytoplasmic RNA sensor melanoma differentiation antigen 5 has been reported to recognize HDV RNA replication and activate innate immunity. Innate immunity, however, seems not to impair HDV replication while it inhibits HBV. In this review, we describe what is known up-to-date about the interplay between HBV as a helper and HDV’s immune evasion strategy and identify where additional research is required.

The oncogenic role of hepatitis delta virus in hepatocellular carcinoma

Hepatitis delta virus (HDV) is a small defective virus that needs hepatitis B virus (HBV) to replicate and propagate. HDV infection affects 20-40 million people worldwide and pegylated interferon (PegIFN) is the only recommended therapy. There is limited data on the contribution of HDV infection to HBV-related liver disease or liver cancer. Evidence from retrospective and cohort studies suggests that HBV/HDV coinfection accelerates progression to cirrhosis and is associated with an increased risk of hepatocellular carcinoma (HCC) development compared to HBV monoinfection. Although the life cycle of HDV is relatively well known, there is only ancillary information on the molecular mechanisms that can drive specific HDV-related oncogenesis. No thorough reports on the specific landscape of mutations or molecular classes of HDV-related HCC have been published. This information could be critical to better understand the uniqueness, if any, of HDV-related HCC and help identify novel targetable mutations. Herein, we review the evidence supporting an oncogenic role of HDV, the main reported mechanisms of HDV involvement and their impact on HCC development.

The hepatitis delta virus: Replication and pathogenesis

Hepatitis delta virus (HDV) is a defective virus and a satellite of the hepatitis B virus (HBV). Its RNA genome is unique among animal viruses, but it shares common features with some plant viroids, including a replication mechanism that uses a host RNA polymerase. In infected cells, HDV genome replication and formation of a nucleocapsid-like ribonucleoprotein (RNP) are independent of HBV. But the RNP cannot exit, and therefore propagate, in the absence of HBV, as the latter supplies the propagation mechanism, from coating the HDV RNP with the HBV envelope proteins for cell egress to delivery of the HDV virions to the human hepatocyte target. HDV is therefore an obligate satellite of HBV; it infects humans either concomitantly with HBV or after HBV infection. HDV affects an estimated 15 to 20 million individuals worldwide, and the clinical significance of HDV infection is more severe forms of viral hepatitis--acute or chronic--, and a higher risk of developing cirrhosis and hepatocellular carcinoma in comparison to HBV monoinfection. This review covers molecular aspects of HDV replication cycle, including its interaction with the helper HBV and the pathogenesis of infection in humans.

Hepatitis D virus infection, replication and cross-talk with the hepatitis B virus

Viral hepatitis remains a worldwide public health problem. The hepatitis D virus (HDV) must either coinfect or superinfect with the hepatitis B virus (HBV). HDV contains a small RNA genome (approximately 1.7 kb) with a single open reading frame (ORF) and requires HBV supplying surface antigens (HBsAgs) to assemble a new HDV virion. During HDV replication, two isoforms of a delta antigen, a small delta antigen (SDAg) and a large delta antigen (LDAg), are produced from the same ORF of the HDV genome. The SDAg is required for HDV replication, whereas the interaction of LDAg with HBsAgs is crucial for packaging of HDV RNA. Various clinical outcomes of HBV/HDV dual infection have been reported, but the molecular interaction between HBV and HDV is poorly understood, especially regarding how HBV and HDV compete with HBsAgs for assembling virions. In this paper, we review the role of endoplasmic reticulum stress induced by HBsAgs and the molecular pathway involved in their promotion of LDAg nuclear export. Because the nuclear sublocalization and export of LDAg is regulated by posttranslational modifications (PTMs), including acetylation, phosphorylation, and isoprenylation, we also summarize the relationship among HBsAg-induced endoplasmic reticulum stress signaling, LDAg PTMs, and nuclear export mechanisms in this review.

Large hepatitis delta antigen activates STAT-3 and NF-κB via oxidative stress

Hepatitis delta virus (HDV) coinfection or superinfection in hepatitis B virus (HBV)-infected patients results in a more aggressive liver disease, with more often fulminant forms and more rapid progression to cirrhosis and hepatocellular carcinoma. The mechanism(s) for this pejorative evolution remains unclear. To explore a specific HDV pathogenesis, we used a model of transient transfection of plasmids expressing the small (sHDAg or p24) or the large (LHDAg or p27) delta antigen in hepatocyte cell lines. We found that the production of reactive oxygen species was significantly higher in cells expressing p27. Consequently, p27 activated the signal transducer and activator of transcription-3 (STAT-3) and the nuclear factor kappa B (NF-κB) via the oxidative stress pathway. Moreover in the presence of antioxidants (PDTC, NAC) or calcium inhibitors (TMB-8, BAPTA-AM, Ruthenium Red), p27-induced activation of STAT-3 and NF-κB was dramatically reduced. Similarly, using a mutated form of p27, where the cysteine 211-isoprenylation residue was replaced by a serine, a significant reduction of STAT-3 and NF-κB activation was seen, suggesting the involvement of isoprenylation in this process. Additionally, we show that p27 is able to induce oxidative stress through activation of NADPH oxidase-4. These results provide insight into the mechanisms by which p27 can alter intracellular events relevant to HDV-related liver pathogenesis.

Multiple genomic sequences of hepatitis delta virus are associated with cDNA promoter activity and RNA double rolling-circle replication

To understand how DNA-dependent RNA polymerase II (pol II) recognizes hepatitis delta virus (HDV) RNA as a template, it is first necessary to identify the HDV sequence that acts as a promoter of pol II-initiated RNA synthesis. Therefore, we isolated the pol II-response element from HDV cDNA and examined the regulation by hepatitis delta antigens (HDAgs). Two HDV cDNA fragments containing bidirectional promoter activity were identified. One was located at nt 1582–1683 (transcription-promoter region 1, TR-P1) and the other at nt 1223–1363 (transcription-internal region 5, TR-I5). The promoter activities of these two regions were enhanced by HDAgs to differing degrees. Next, the role of these sequences in an HDV cDNA-free RNA replication system was characterized by site-directed mutagenesis. Our data showed that: (i) the AUG codon at the HDAg ORF of HDV RNA (nt 1599–1601) that mutates to UAG (amber stop codon) results in loss of dimeric but not monomeric HDV RNA synthesis. (ii) A 5 nt mutation of TR-P1 (P1-m5, nt 1670–1674) abolishes RNA replication completely. Two-nucleotide-mutated RNA (P1-m2, nt 1662–1663) is able to synthesize short RNAs but not monomeric HDV RNA. (iii) A mutation in 5 nt at the TR-I5 region (I5-m5, nt 1351–1355) also abolishes HDV replication. Mutants with 2 nt mutations (I5-m2, nt 1351–1352) or 3 nt mutations (I5-m3, nt 1353–1355) inhibit HDV dimeric but not monomeric RNA synthesis. Furthermore, large HDAg is expressed in cells transfected with I5-m3 and I5-m2 RNAs and that demonstrate the RNA-editing event in the monomeric HDV RNA. These results provide further understanding of the double rolling-circle mechanism in HDV RNA replication.

Interaction of host cellular proteins with components of the hepatitis delta virus

The hepatitis delta virus (HDV) is the smallest known RNA pathogen capable of propagation in the human host and causes substantial global morbidity and mortality. Due to its small size and limited protein coding capacity, HDV is exquisitely reliant upon host cellular proteins to facilitate its transcription and replication. Remarkably, HDV does not encode an RNA-dependent RNA polymerase which is traditionally required to catalyze RNA-templated RNA synthesis. Furthermore, HDV lacks enzymes responsible for post-transcriptional and -translational modification, processes which are integral to the HDV life cycle. This review summarizes the known HDV-interacting proteins and discusses their significance in HDV biology.

Hepatitis delta virus proteins repress hepatitis B virus enhancers and activate the alpha/beta interferon-inducible MxA gene

Co-infection and superinfection of hepatitis B virus (HBV) with hepatitis delta virus (HDV) leads to suppression of HBV replication both in patients and in animal and cellular models. The mechanisms behind this inhibition have not previously been explored fully. HBV replication is governed by four promoters and two enhancers, Enh1 and Enh2. Repression of these enhancers has been reported to be one of the main mechanisms of HBV inhibition. Moreover, in a previous study, it has been demonstrated that alpha interferon (IFN-alpha)-inducible MxA protein inhibits HBV replication. HDV encodes two proteins, p24 and p27. p27 was shown to activate several heterologous promoters, including HBV promoters. In an attempt to analyse the mechanisms of HBV inhibition by HDV, the question was raised whether HDV proteins could act directly by repressing HBV enhancers, and/or indirectly by activating the MxA gene. This issue was addressed in a co-transfection model in Huh-7 cells, using p24- or p27-expressing plasmids along with Enh1, Enh2, HBV and MxA promoter-luciferase constructs. Enh1 and Enh2 were strongly repressed, by 60 and 80 % and 40 and 60 %, by p24 and p27, respectively. In addition, p27 was responsible for threefold activation of the MxA promoter and potentiation of IFN-alpha on this promoter. MxA mRNA quantification and a virus yield reduction assay confirmed these results. In conclusion, this study shows that HDV proteins inhibit HBV replication by trans-repressing its enhancers and by trans-activating the IFN-alpha-inducible MxA gene.

Hepatitis delta virus epigenetically enhances clusterin expression via histone acetylation in human hepatocellular carcinoma cells

Both isoforms of the hepatitis delta antigen (HDAg) of hepatitis delta virus (HDV) are highly associated with virus proliferation and may act as co-activators of cellular gene expression. Human hepatocellular carcinoma (HCC) cell line Huh7, which stably expresses HDAgs, was differentially screened and the results showed that clusterin gene expression was enhanced. The mechanisms for HDAg-mediated clusterin gene upregulation were investigated. Expression of HDAgs was associated with enhanced histone H3 acetylation within the clusterin promoter in a chromatin immunoprecipitation assay. Transient transfection of HDAg-expressing plasmids into Huh7 cells also enhanced clusterin expression and histone acetylation. Furthermore, HDV replication was associated with histone hyperacetylation and clusterin induction. The effect of increased clusterin expression was determined by a chemosensitivity assay with adriamycin treatment. These data indicated that HDV-induced clusterin protein increases cell survival potential. Thus, it is possible that epigenetic regulation by HDV contributes to a pathological outcome of hepatitis D/hepatitis B viral hepatitis and HCC.

Transcription factor YY1 and its associated acetyltransferases CBP and p300 interact with hepatitis delta antigens and modulate hepatitis delta virus RNA replication

Hepatitis delta virus (HDV) is a pathogenic RNA virus with a plant viroid-like genome structure. HDV encodes two isoforms of delta antigen (HDAg), the small and large forms of HDAg (SHDAg and LHDAg), which are essential for HDV RNA replication and virion assembly, respectively. Replication of HDV RNA depends on host cellular transcription machinery, and the exact molecular mechanism for HDV RNA replication is still unclear. In this study, we demonstrated that both isoforms of HDAg interact with transcription factor YY1 (Yin Yang 1) in vivo and in vitro. Their interaction domains were identified as the middle region encompassing the RNA binding domain of HDAg and the middle GA/GK-rich region and the C-terminal zinc-finger region of YY1. Results of sucrose gradient centrifugation analysis indicated the cosedimentation of the majority of SHDAg and a portion of the LHDAg with YY1 and its associated acetyltransferases CBP (CREB-binding protein) and p300 as a large nuclear complex in vivo. Furthermore, exogenous expression of YY1 or CBP/p300 in HDV RNA replication system showed an enhancement of HDV RNA replication. Interestingly, the acetyltransferase activity of p300 is important for this enhancement. Moreover, SHDAg could be acetylated in vivo, and treatment with cellular deacetylase inhibitor elevated the replication of HDV RNA and acetylation of SHDAg. All together, our results reveal that HDAg interacts with cellular transcription factor YY1 and its associated acetyltransferases CBP and p300 in a large nuclear complex, which in turn modulates the replication of HDV RNA.

Large hepatitis delta antigen is a novel clathrin adaptor-like protein

Clathrin-mediated endocytosis is a common pathway for viral entry, but little is known about the direct association of viral protein with clathrin in the cytoplasm. In this study, a putative clathrin box known to be conserved in clathrin adaptors was identified at the C terminus of the large hepatitis delta antigen (HDAg-L). Similar to clathrin adaptors, HDAg-L directly interacted with the N terminus of the clathrin heavy chain through the clathrin box. HDAg-L is a nucleocytoplasmic shuttle protein important for the assembly of hepatitis delta virus (HDV). Here, we demonstrated that brefeldin A and wortmannin, inhibitors of clathrin-mediated exocytosis and endosomal trafficking, respectively, specifically blocked HDV assembly but had no effect on the assembly of the small surface antigen of hepatitis B virus. In addition, cytoplasm-localized HDAg-L inhibited the clathrin-mediated endocytosis of transferrin and the degradation of epidermal growth factor receptor. These results indicate that HDAg-L is a new clathrin adaptor-like protein, and it may be involved in the maturation and pathogenesis of HDV coinfection or superinfection with hepatitis B virus through interaction with clathrin.

DIPA, which can localize to the centrosome, associates with p78/MCRS1/MSP58 and acts as a repressor of gene transcription

DIPA (delta-interacting protein A) was initially identified as a protein that associates with the hepatitis delta antigen. In this study, we found that DIPA can associate with p78/MCRS/MSP58, a Forkhead-associated domain containing protein implicated in malignant transformation as well as in regulation of gene transcription and translation. We analyzed the interaction between DIPA and p78 by co-immunoprecipitation and identified the structural regions involved in the interaction. Consistent with the physical interaction, we found that DIPA is predominant co-localized with p78 to the nucleus. In addition, a fraction of DIPA can be detected on the centrosome. Furthermore, we demonstrate that DIPA can act as a repressor of gene transcription, an activity that appears to be enhanced by p78. Taken together, our results revealed a novel protein complex that plays a role in regulation of gene expression and cell proliferation. We propose that dysfunction of DIPA may contribute to malignant transformation by affecting the functions of p78.

HDV RNA replication: ancient relic or primer?

HDV replicates its circular RNA genome using a double rolling-circle mechanism and transcribes a hepatitis delta antigen-encodeing mRNA from the same RNA template during its life cycle. Both processes are carried out by RNA-dependent RNA synthesis despite the fact that HDV does not encode an RNA-dependent RNA polymerase (RdRP). Cellular RNA polymerase II has long been implicated in these processes. Recent findings, however, have shown that the syntheses of genomic and antigenomic RNA strands have different metabolic requirements, including sensitives to alpha-amanitin and the site of synthesis. Evidence is summarized here for the involvement of other cellular polymerases, probably pol I, in the synthesis of antigenomic RNA strand. The ability of mammalian cells to replicate HDV RNA implies that RNA-dependent RNA synthesis was preserved throughout evolution.

Hepatitis C virus core protein upregulates transforming growth factor-beta 1 transcription

The majority of persons with chronic hepatitis C virus (HCV) infection develop liver fibrosis. Transforming growth factor (TGF)-beta 1 plays a pivotal role in the pathogenesis of post-inflammatory liver scarring. To clarify the influence of HCV infection on liver fibrosis, a reporter assay was used to investigate the effect of viral proteins on TGF-beta 1 expression in human hepatoma cells. Of all HCV proteins investigated (core, E1/E2/p7, NS2, NS3, NS4A, NS4B, NS5A, and NS5B), only the core protein activated the TGF-beta 1 promoter and upregulated TGF-beta 1 expression measured by an RNase protection assay. Bases -376 to -331 bp in the promoter region of TGF-beta 1 are responsible for upregulation by HCV core protein, and the nuclear protein that binds to this region increased with the stimulation of HCV core protein. Blocking the mitogen-activated protein kinase pathway prevented upregulation of TGF-beta 1 by HCV core protein. The immunological response is supposed to be a major factor to cause the secretion of TGF-beta 1 from non-parenchymal cells, but the results suggest that the HCV core protein expression may upregulate directly TGF-beta 1 transcription in parenchymal cells and suggest a new paradigm for exacerbation of liver fibrosis by HCV infection.

In vivo antiviral efficacy of prenylation inhibitors against hepatitis delta virus

Hepatitis delta virus (HDV) can dramatically worsen liver disease in patients coinfected with hepatitis B virus (HBV). No effective medical therapy exists for HDV. The HDV envelope requires HBV surface antigen proteins provided by HBV. Once inside a cell, however, HDV can replicate its genome in the absence of any HBV gene products. In vitro, HDV virion assembly is critically dependent on prenyl lipid modification, or prenylation, of its nucleocapsid-like protein large delta antigen. To overcome limitations of current animal models and to test the hypothesis that pharmacologic prenylation inhibition can prevent the production of HDV virions in vivo, we established a convenient mouse-based model of HDV infection capable of yielding viremia. Such mice were then treated with the prenylation inhibitors FTI-277 and FTI-2153. Both agents were highly effective at clearing HDV viremia. As expected, HDV inhibition exhibited duration-of-treatment dependence. These results provide the first preclinical data supporting the in vivo efficacy of prenylation inhibition as a novel antiviral therapy with potential application to HDV and a wide variety of other viruses.

In vivo antiviral efficacy of prenylation inhibitors against hepatitis delta virus

Hepatitis delta virus (HDV) can dramatically worsen liver disease in patients coinfected with hepatitis B virus (HBV). No effective medical therapy exists for HDV. The HDV envelope requires HBV surface antigen proteins provided by HBV. Once inside a cell, however, HDV can replicate its genome in the absence of any HBV gene products. In vitro, HDV virion assembly is critically dependent on prenyl lipid modification, or prenylation, of its nucleocapsid-like protein large delta antigen. To overcome limitations of current animal models and to test the hypothesis that pharmacologic prenylation inhibition can prevent the production of HDV virions in vivo, we established a convenient mouse-based model of HDV infection capable of yielding viremia. Such mice were then treated with the prenylation inhibitors FTI-277 and FTI-2153. Both agents were highly effective at clearing HDV viremia. As expected, HDV inhibition exhibited duration-of-treatment dependence. These results provide the first preclinical data supporting the in vivo efficacy of prenylation inhibition as a novel antiviral therapy with potential application to HDV and a wide variety of other viruses.

In vivo antiviral efficacy of prenylation inhibitors against hepatitis delta virus

Hepatitis delta virus (HDV) can dramatically worsen liver disease in patients coinfected with hepatitis B virus (HBV). No effective medical therapy exists for HDV. The HDV envelope requires HBV surface antigen proteins provided by HBV. Once inside a cell, however, HDV can replicate its genome in the absence of any HBV gene products. In vitro, HDV virion assembly is critically dependent on prenyl lipid modification, or prenylation, of its nucleocapsid-like protein large delta antigen. To overcome limitations of current animal models and to test the hypothesis that pharmacologic prenylation inhibition can prevent the production of HDV virions in vivo, we established a convenient mouse-based model of HDV infection capable of yielding viremia. Such mice were then treated with the prenylation inhibitors FTI-277 and FTI-2153. Both agents were highly effective at clearing HDV viremia. As expected, HDV inhibition exhibited duration-of-treatment dependence. These results provide the first preclinical data supporting the in vivo efficacy of prenylation inhibition as a novel antiviral therapy with potential application to HDV and a wide variety of other viruses.

Large hepatitis delta antigen is phosphorylated at multiple sites and phosphorylation is associated with protein conformational change

Hepatitis delta antigen (HDAg) consists of two species, small HDAg (SHDAg) and large HDAg (LHDAg), which are identical in sequence with the exception that the large form contains an additional 19 amino acids at the C-terminus. Both HDAgs are nuclear phosphoproteins. However, LHDAg is hyperphosphorylated, i.e. it is at least 10 times more phosphorylated than SHDAg. To determine the phosphorylation site(s) of the LHDAg, we mutated all the conserved serine residues and expressed these mutant proteins using a recombinant baculovirus expression system. By labeling insect cells in vivo with (32)P-orthophosphate and immunoprecipitation, we showed that LHDAg is phosphorylated at multiple serine residues. Although LHDAg contains two additional serines at its 19-amino acid extension, mutations of these two amino acids did not affect the overall phosphorylation level. Most importantly, the phosphorylation level of middle domain-deleted LHDAg (M75del) was significantly higher than that of wild-type LHDAg. We conclude that phosphorylation of the LHDAg occurs at multiple sites and that hyperphosphorylation is associated with alteration of protein conformation.

Helicobacter pylori CagA protein activates serum response element-driven transcription independently of tyrosine phosphorylation

BACKGROUND & AIMS

Infection with Helicobacter pylori possessing the cag pathogenicity island (PAI) is associated with severe gastritis and gastric cancer. CagA protein, one of the products of cag PAI, is translocated into epithelial cells, where cytoskeletal rearrangements occur as a result of CagA tyrosine (Tyr) phosphorylation. Here we identify a new role for CagA protein as an activator of host cell signaling.

METHODS

We transfected CagA into epithelial cells and analyzed its effect on transcription by reporter assays. The mechanism of reporter activation was assessed by electrophoretic mobility shift assays (EMSA) and immunoblots. Responsible regions of CagA for reporter activation were determined by truncation and mutagenesis of cagA gene.

RESULTS

In HeLa cells, expression of CagA increased serum response element (SRE)-driven and serum response factor (SRF)-driven transcription by 40-fold and 3.3-fold, respectively, but did not affect nuclear factor kappaB- or AP-1-driven transcription. CagA-mediated SRE activation was also observed in gastric cell lines. Immunoblotting and EMSA revealed that transfection of CagA enhanced phosphorylation of and DNA binding by Elk1. Furthermore, involvement of Ras and MEK in CagA-mediated Elk1 phosphorylation was observed. SRE activation was dependent on several regions within the C-terminal portion of CagA (CagA(873-1002)), and independent of Tyr phosphorylation.

CONCLUSIONS

The C-terminal portion of CagA enhances SRE-driven transcription by activating an upstream signaling cascade without requiring CagA Tyr phosphorylation. This result suggests that translocated CagA regulates 2 distinct cellular responses: phosphorylation-dependent cytoskeletal rearrangement and phosphorylation-independent transcriptional activation.

Hepatitis C virus core protein inhibits apoptosis via enhanced Bcl-xL expression

Previous studies indicated that hepatitis C virus core protein influences cellular apoptosis. However, the precise mechanisms of the effects are not fully understood. Therefore, in this study, we examined the mechanisms of the effects on cell apoptosis by core protein, using transiently transfected and magnetically collected core-producing HepG2 cells. First, to elucidate the target site of core protein in the apoptotic pathway, we examined the activation of caspases after anti-Fas antibody stimulation. Core protein inhibited the apoptotic cascade downstream from caspase 8 and upstream from caspase 3. Next, to clarify more direct mechanisms of this effect, mRNA levels of several bcl-2-related genes were examined. An RNase protection assay showed that the mRNA of bcl-xl increased in the core-producing cells. We showed that this increase was mediated by the enhancement of bcl-x promoter activity by core protein through an extracellular-regulated kinase pathway. These results suggest that core protein inhibits apoptosis at the mitochondria level through augmentation of Bcl-x expression, resulting in an inhibition of caspase 3 activation.

Hepatitis C virus NS4A and NS4B proteins suppress translation in vivo

Many viruses can inhibit protein synthesis in their host cells by targeting translation ("translational shutoff"). There are few reports on the effects of hepatitis C virus (HCV) infection on protein synthesis, because of the lack of a reproducible tissue culture system for HCV. In this study, the influence of seven HCV proteins (core, NS2, NS3, NS4A, NS4B, NS5A, NS5B) on protein synthesis was examined using a reporter assay. In addition, it was determined whether the HCV proteins inhibit protein synthesis via transcription or translation using an RNase protection assay and the effect of HCV proteins on translation from the HCV internal ribosome entry site (IRES) was also examined using a bicistronic reporter. Of the seven HCV proteins, NS4A and NS4B proteins inhibited cellular protein synthesis by targeting the process of translation. They also inhibited translation from the HCV IRES. Moreover, NS4A protein, induced under the control of doxycycline, inhibited the proliferation of HeLa cells. In conclusion, HCV NS4A and NS4B proteins have an effect of translational inhibition. This novel function may be involved in HCV infection and help its survival in host cells.

Distinct mechanism of Helicobacter pylori-mediated NF-kappa B activation between gastric cancer cells and monocytic cells

NF-kappaB is a critical regulator of genes involved in inflammation. Gastric epithelial cells and macrophages are considered the main sources of pro-inflammatory cytokines. We investigated NF-kappaB activation by Helicobacter pylori in MKN45 gastric epithelial cells and THP-1 monocytic cells. Although, cag pathogenicity island (PAI)-positive H. pylori (wild type) activated NF-kappaB in both cells, isogenic mutant of cagE (DeltacagE) activated it only in THP-1 cells. Supernatant from the wild type culture could activate NF-kappaB in THP-1 cells but not in MKN45 cells. High density cDNA array analysis revealed that mRNA expression of NF-kappaB-regulated genes such as interleukin (IL)-8, tumor necrosis factor-alpha (TNFalpha), and IL-1beta was significantly up-regulated by the wild type in both cells, whereas it was up-regulated by DeltacagE only in THP-1 cells. Experiments using CD14-neutralizing antibody and IL-1 receptor-associated kinase (IRAK) assay showed that both wild type and DeltacagE H. pylori activated NF-kappaB through CD14 and IRAK in THP-1 cells but not in MKN45 cells. Macrophages from C3H/HeJ mice carrying point mutation in the Toll-like receptor 4 (TLR4) gene showed decreased NF-kappaB activation and TNFalpha secretion compared with C3H/HeN mouse macrophage when treated with H. pylori. In conclusion, H. pylori-induced NF-kappaB activation in epithelial cells is dependent on cag PAI and contact but does not involve CD14 and IRAK, whereas in macrophage/monocytic cells it is independent of cag PAI or contact but involves CD14 and TLR4.