Replication and gene expression of hepatitis B virus in a transgenic mouse that contains the complete viral genome

Conversion of hepatitis B virus relaxed circular to covalently closed circular DNA is supported in murine cells

Background & Aims

HBV has a narrow host restriction, with humans and chimpanzees representing the only known natural hosts. The molecular correlates of resistance in species that are commonly used in biomedical research, such as mice, are currently incompletely understood. Expression of human NTCP (hNTCP) in mouse hepatocytes enables HBV entry, but subsequently covalently closed circular (cccDNA) does not form in most murine cells. It is unknown if this blockade in cccDNA formation is due to deficiency in repair of relaxed circular DNA (rcDNA) to cccDNA.

Methods

Here, we deployed both in vivo and in vitro virological and biochemical approaches to investigate if murine cells contain a complete set of repair factors capable of converting HBV rcDNA to cccDNA.

Results

We demonstrate that HBV cccDNA does form in murine cell culture or in mice when recombinant rcDNA without a protein adduct is directly introduced into cells. We further show that the murine orthologues of core components in DNA lagging strand synthesis, required for the repair of rcDNA to cccDNA in human cells, can support this crucial step in the HBV life cycle. It is worth noting that recombinant HBV rcDNA substrates, either without a protein adduct or containing neutravidin to mimic HBV polymerase, were used in our study; it remains unclear if the HBV polymerase removal processes are the same in mouse and human cells.

Conclusions

Collectively, our data suggest that the HBV life cycle is blocked post entry and likely before the repair stage in mouse cells, which yields critical insights that will aid in the construction of a mouse model with inbred susceptibility to HBV infection.

Lay summary

Hepatitis B virus (HBV) is only known to infect humans and chimpanzees in nature. Mouse models are often used in modeling disease pathogenesis and preclinical research to assess the efficacy and safety of interventions before they are then tested in human participants. However, because mice are not susceptible to HBV infection it is difficult to accurately model human infection (and test potential treatments) in mouse models. Herein, we have shown that mice are able to perform a key step in the HBV life cycle, tightening the net around the possible reason why HBV can not efficiently infect and replicate in mice.

Animal models for the study of human hepatitis B and D virus infection: New insights and progress

Hepatitis B virus (HBV) is a member of the Hepadnaviridae family and infects hepatocytes, leading to liver pathology in acutely and chronically infected individuals. Co-infection with Hepatitis D virus (HDV), which requires the surface proteins of HBV to replicate, can exacerbate this disease progression. Thus, the >250 million people living with chronic HBV infection, including 13 million co-infected with HDV, would significantly benefit from an effective and affordable curative treatment. Animal models are crucial to the development of innovative disease therapies, a paradigm repeated again and again throughout the fields of immunology, neurology, reproduction, and development. Unfortunately, HBV has a highly-restricted species tropism, infecting limited species including humans, chimpanzees, and treeshrews. The first experimentally controlled studies of HBV infection were following inoculation of human volunteers in 1942, which identified the transmissibility of hepatitis through serum transfer and led to the hypothesis that the etiological agent was viral. Subsequent research in chimpanzees (Desmyter et al., 1971; Lichter, 1969) and later in other species, such as the treeshrews (Walter et al., 1996; Yan et al., 1996), further confirmed the viral origin of hepatitis B. Shortly thereafter, HBV-like viral infections were identified in woodchucks (Summers et al., 1978; Werner et al., 1979) and ducks, and much of our understanding of HBV replication can be attributed to these important models. However, with the exodus of chimpanzees from research and the limited reagents and historical data for treeshrews and other understudied species, there remains an urgent need to identify physiologically relevant models of chronic HBV infection. While large strides have been made in generating such models, particularly over the past two decades, there is still no available model that faithfully recapitulates the immunity and pathogenesis of HBV infection. Here, we discuss recent advancements in the generation of murine and non-human primate (NHP) models of HBV/HDV infection.

The Regulation of HBV Transcription and Replication

Hepatitis B virus (HBV) is a major human pathogen lacking a reliable curative therapy. Current therapeutics target the viral reverse transcriptase/DNA polymerase to inhibit viral replication but generally fail to resolve chronic HBV infections. Due to the limited coding potential of the HBV genome, alternative approaches for the treatment of chronic infections are desperately needed. An alternative approach to the development of antiviral therapeutics is to target cellular gene products that are critical to the viral life cycle. As transcription of the viral genome is an essential step in the viral life cycle, the selective inhibition of viral RNA synthesis is a possible approach for the development of additional therapeutic modalities that might be used in combination with currently available therapies. To address this possibility, a molecular understanding of the relationship between viral transcription and replication is required. The first step is to identify the transcription factors that are the most critical in controlling the levels of HBV RNA synthesis and to determine their in vivo role in viral biosynthesis. Mapping studies in cell culture utilizing reporter gene constructs permitted the identification of both ubiquitous and liver-enriched transcription factors capable of modulating transcription from the four HBV promoters. However, it was challenging to determine their relative importance for viral biosynthesis in the available human hepatoma replication systems. This technical limitation was addressed, in part, by the development of non-hepatoma HBV replication systems where viral biosynthesis was dependent on complementation with exogenously expressed transcription factors. These systems revealed the importance of specific nuclear receptors and hepatocyte nuclear factor 3 (HNF3)/forkhead box A (FoxA) transcription factors for HBV biosynthesis. Furthermore, using the HBV transgenic mouse model of chronic viral infection, the importance of various nuclear receptors and FoxA isoforms could be established in vivo. The availability of this combination of systems now permits a rational approach toward the development of selective host transcription factor inhibitors. This might permit the development of a new class of therapeutics to aid in the treatment and resolution of chronic HBV infections, which currently affects approximately 1 in 30 individuals worldwide and kills up to a million people annually.

In Vivo Model Systems for Hepatitis B Virus Research

Hepatitis B virus (HBV) affects more than 257 million people globally, resulting in progressively worsening liver disease, manifesting as fibrosis, cirrhosis, and hepatocellular carcinoma. The exceptionally narrow species tropism of HBV restricts its natural hosts to humans and non-human primates, including chimpanzees, gorillas, gibbons, and orangutans. The unavailability of completely immunocompetent small-animal models has contributed to the lack of curative therapeutic interventions. Even though surrogates allow the study of closely related viruses, their host genetic backgrounds, immune responses, and molecular virology differ from those of HBV. Various different models, based on either pure murine or xenotransplantation systems, have been introduced over the past years, often making the choice of the optimal model for any given question challenging. Here, we offer a concise review of in vivo model systems employed to study HBV infection and steps in the HBV life cycle or pathogenesis.

Proportion of transcriptionally active DNA virus integrants: a meta-analysis

Oncoviruses are collectively responsible for over 1,000,000 new cases of cancer per year; some can integrate into the host's chromosomes. The present work was aimed at assessing the proportion of transcriptionally active viral integrants through a systematic review of the scientific publications present on the MedLine database. From the articles screened, 628 viral integrants overall were retrieved, of which 530.84 were transcriptionally active (84.53%); among the clinical samples, 264 of 323 integrants were active (81.73%). The causes for the silencing were not addressed in the articles analyzed. These findings might highlight a possible risk factor for the insurgence of cancer since some oncovirus integrants could be reactivated by stimuli of disparate nature. Further studies should address such possibility.

Immune therapy for hepatitis B

Although several antiviral drugs are now available for treatment of patients with chronic hepatitis B (CHB), sustained off-treatment clinical responses and containment of CHB-related complications are not achieved in majority of CHB patients by antiviral therapy. In addition, use of these drugs is endowed with substantial long term risk of viral resistance and drug toxicity. The infinite treatment regimens of antiviral drugs for CHB patients are also costly and usually unbearable by most patients of developing and resource-constrained countries. Taken together, there is a pressing need to develop new and innovative therapeutic approaches for CHB patients. Immune therapy seems to be an alternate therapeutic approach for CHB patients because impaired or distorted or diminished immune responses have been detected in most of these patients. Also, investigators have shown that restoration or induction of proper types of immune responses may have therapeutic implications in CHB. Various immunomodulatory agents have been used to treat patients with CHB around the world and the outcomes of these clinical trials show that the properties of immune modulators and nature and designing of immune therapeutic regimens seem to be highly relevant in the context of treatment of CHB patients. In this review, the general properties and specific features of immune therapy for CHB have been discussed for developing the guidelines of effective regimens of immune therapy for CHB.

Hepatocarcinogenesis associated with hepatitis B, delta and C viruses

Globally, over half a billion people are persistently infected with hepatitis B (HBV) and/or hepatitis C viruses. Chronic HBV and HCV infection frequently lead to fibrosis, cirrhosis and hepatocellular carcinoma (HCC). Co-infections with hepatitis delta virus (HDV), a subviral satellite requiring HBV for its propagation, accelerates the progression of liver disease toward HCC. The mechanisms by which these viruses cause malignant transformation, culminating in HCC, remain incompletely understood, partially due to the lack of adequate experimental models for dissecting these complex disease processes in vivo.

Determinants of hepatitis B and delta virus host tropism

Hepatitis B virus (HBV) infections are a global health problem afflicting approximately 360 million patients. Of these individuals, 15-20 million are co-infected with hepatitis delta virus (HDV). Progress toward curative therapies has been impeded by the highly restricted host tropism of HBV, which is limited to productive infections in humans and chimpanzees. Here, we will discuss different approaches that have been taken to study HBV and HDV infections in vivo. The development of transgenic and humanized mice has lead to deeper insights into HBV pathogenesis. An improved understanding of the determinants governing HBV and HDV species tropism will aid in the construction of a small animal model with inheritable susceptible to HBV/HDV.

Modeling hepatitis B virus infection, immunopathology and therapy in mice

Despite the availability of a preventive vaccine, chronic hepatitis B virus (HBV) infection-induced liver diseases continue to be a major global public health problem. HBV naturally infects only humans and chimpanzees. This narrow host range has hindered our ability to study the characteristics of the virus and how it interacts with its host. It is thus important to establish small animal models to study HBV infection, persistence, clearance and the immunopathogenesis of chronic hepatitis B. In this review, we briefly summarize currently available animal models for HBV research, then focus on mouse models, especially the recently developed humanized mice that can support HBV infection and immunopathogenesis in vivo. This article is part of a symposium in Antiviral Research on "From the discovery of the Australia antigen to the development of new curative therapies for hepatitis B: an unfinished story."

Novel Woodchuck Hepatitis Virus (WHV) transgene mouse models show sex-dependent WHV replicative activity and development of spontaneous immune responses to WHV proteins

The woodchuck model is an informative model for studies on hepadnaviral infection. In this study, woodchuck hepatitis virus (WHV) transgenic (Tg) mouse models based on C57BL/6 mice were established to study the pathogenesis associated with hepadnaviral infection. Two lineages of WHV Tg mice, harboring the WHV wild-type genome (lineage 1217) and a mutated WHV genome lacking surface antigen (lineage 1281), were generated. WHV replication intermediates were detected by Southern blotting. DNA vaccines against WHV proteins were applied by intramuscular injection. WHV-specific immune responses were analyzed by flow cytometry and enzyme-linked immunosorbent assays (ELISAs). The presence of WHV transgenes resulted in liver-specific but sex- and age-dependent WHV replication in Tg mice. Pathological changes in the liver, including hepatocellular dysplasia, were observed in aged Tg mice, suggesting that the presence of WHV transgenes may lead to liver diseases. Interestingly, Tg mice of lineage 1281 spontaneously developed T- and B-cell responses to WHV core protein (WHcAg). DNA vaccination induced specific immune responses to WHV proteins in WHV Tg mice, indicating a tolerance break. The magnitude of the induced WHcAg-specific immune responses was dependent on the effectiveness of different DNA vaccines and was associated with a decrease in WHV loads in mice. In conclusion, sex- and age-dependent viral replication, development of autoimmune responses to viral antigens, pathological changes in the liver in WHV Tg mice, and the possibility of breaking immune tolerance to WHV transgenes will allow future studies on pathogenesis related to hepadnaviral infection and therapeutic vaccines.

[Reverse genetics of Hepatitis B virus]

A global expansion of Hepatitis B virus (HBV) infection continues still now, and it poses a still big problem. Since the Australia antigen was discovered, HBV research has been continued by various methods, such as clinical medicine and epidemiology. However, the simple and efficient infection experimental systems (in vitro and in vivo) have not been established, because the host range of HBV is narrow. Therefore, the techniques of reverse genetics have contributed to HBV research greatly. We have established the HBV clones of various genotypes from the chronic hepatitis B patients, and have analyzed using the techniques of reverse genetics. Based on our results, it has become clear gradually how HBV pathogenesis related to the genotypes. In this paper, we would like to introduce the outline of research analyzed by reverse genetics about HBV.

Use of RNA interference to modulate liver adenoma development in a murine model transgenic for hepatitis B virus

Chronic hepatitis B virus (HBV) infection is closely related to the development of severe liver complications, including hepatocellular carcinoma. In previous studies, we reported that in vivo long-term HBV suppression in transgenic mice can be achieved without apparent toxicity by short hairpin RNA sequentially delivered using adeno-associated viral (AAV) vectors of different serotypes. Our goal herein was to address the clinical utility of this delivery system and, in particular, to determine whether RNA interference (RNAi) and its ability to induce long-term HBV suppression will modulate the development of HBV-associated liver pathology. As a model system, we used a unique HBV transgenic mouse model, containing a 1.3 times over length of the HBV genome, on the ICR mouse background. These transgenic mice produce high serum HBV titers comparable with human chronic HBV patients, and, importantly, manifest characteristic HBV-associated pathology, including progressive hepatocellular injury and the development of hepatocellular adenoma. Using this system, we injected animals with AAV vectors expressing either HBV-specific or a control luciferase-specific short hairpin RNA and followed animals for a total of 18 months. We report herein that AAV-mediated RNAi therapy profoundly inhibits HBV replication and gene expression, with a significant reduction in hepatic regeneration, liver enzymes and, importantly, the appearance of liver adenomas. Indeed, the therapeutic effect of RNAi correlated with the reduction in HBV titers. Our data demonstrate that appropriately designed RNAi therapy has the potential to prevent formation of HBV-associated hepatocellular adenoma.

Assembly and export determine the intracellular distribution of hepatitis B virus core protein subunits

Little is known about the parameters and factors that determine the intracellular distribution of the hepatitis B virus core protein (HBc). In order to study HBc in living cells, HBc was tagged with green fluorescent protein (GFP). Being assembly-incompetent, the GFP-fusion protein was distributed equally throughout the cell. Mutational inactivation of known serine-phosphorylation sites within the C-terminal region led to predominantly intranuclear localization. Phosphorylation of these targets, presumably by an SR domain protein kinase, resulted in a predominantly cytoplasmic localization, which suggests active cytoplasmic export or retention. The phosphoserine itself, and not its negative charge, appears essential for the underlying mechanism. In addition, the arginine-rich, protamine-like domain surrounding these phosphorylation sites does not function as the dominant nuclear-localization signal, as had been assumed previously, because neither deleting nor altering these sequences led to a change in intracellular HBc subunit distribution. Restoring the capability of the fusion protein to form capsids by co-assembly with assembly-competent, sterically uncompromised HBc subunits provided a second assay that gave insight into the effects resulting from capsid formation. Assembly was found to be the dominant factor in the cytoplasmic retention of the GFP-HBc fusion protein. Furthermore, the stability of these empty capsids was influenced by the cell-cycle inhibitor nocodazole. Thus, the intracellular distribution of HBc is dominated by cytoplasmic assembly, which is supported by the active nuclear export of HBc subunits, and modulated during the cell cycle by the instability of capsids.

Stable transmission and expression of the hepatitis B virus total genome in hybrid transgenic mice until F10 generation

The aim of the present study was the generation of transgenic mice carrying the complete Hepatitis B Virus (HBV) genome and investigation of the presence of Hepatitis B surface antigen (HBsAg) expression through successive generations. Transgenic mice were generated by microinjecting HBV genome into fertilized eggs. Integration and expression of HBsAg in transgenic mice were analyzed by genomic DNA PCR, Southern and slot blots and enzyme-linked immunosorbent assay (ELISA). Expression was also confirmed by Western blotting and RT-PCR. Histological changes in liver tissue of transgenic mice were examined by HE staining. The HBV genome was transmitted to the F10 generation and the presence of HBV X gene transcripts was confirmed by RT-PCR analysis using liver cDNAs from the F10 generation mice. During an observation period of 2.5 years, mice were sacrificed and their organs subjected to histopathological examination. In the liver, slight histopathologic alterations were observed but none of these lineages had any hepatocellular carcinoma (HCC). HBV DNA can be stably transmitted and expressed in the transgenic mice until F10 generation. However, although we showed the presence of X gene transcripts in liver tissues of F10 generation mice by RT-PCR in these animals, long-term expression of the HBV complete genome and expression of X protein in hepatocytes did not cause neoplasia during the life span and HCC. These transgenic mice should be useful for detailed studies of the replication and expression of HBV and for physiological studies of HBV genome.

Animal models for the study of HBV replication and its variants

Enormous progresses in hepatitis B virus research have been made through the identification of avian and mammalian HBV related viruses, which offer ample opportunities for studies in naturally occurring hosts. However, none of these natural hosts belongs to the commonly used laboratory animals, and the development of various mouse strains carrying HBV transgenes offered unique opportunities to investigate some mechanisms of viral pathogenesis. Furthermore, the need to perform infection studies in a system harbouring HBV-permissive hepatocytes has lately led researchers to create new challenging human mouse chimera models of HBV infection. In this review, we will overview the type of animal models currently available in hepadnavirus research.

Hepatocyte-like cells transdifferentiated from a pancreatic origin can support replication of hepatitis B virus

Recently, a rat pancreatic cell line (AR42J-B13) was shown to transdifferentiate to hepatocyte-like cells upon induction with dexamethasone (Dex). The aim of this study is to determine whether transdifferentiated hepatocytes can indeed function like bona fide liver cells and support replication of hepatotropic hepatitis B virus (HBV). We stably transfected AR42J-B13 cells with HBV DNA and examined the expression of hepatocyte markers and viral activities in control and transdifferentiated cells. A full spectrum of HBV replicative intermediates, including covalently closed circular DNA (cccDNA) and Dane particles, were detected only after induction with Dex and oncostatin M. Strikingly, the small envelope protein and RNA of HBV were increased by 40- to 100-fold upon induction. When HBV RNAs were examined by primer extension analysis, novel core- and precore-specific transcripts were induced by Dex which initiated at nucleotide (nt) 1820 and nt 1789, respectively. Most surprisingly, another species of core-specific RNA, which initiates at nt 1825, is always present at almost equal intensity before and after Dex treatment, a result consistent with Northern blot analysis. The fact that HBV core protein is dramatically produced only after transdifferentiation suggests the possibility of both transcriptional and translational regulation of HBV core antigen in HBV-transfected AR42J-B13 cells. Upon withdrawal of Dex, HBV replication and gene expression decreased rapidly-less than 50% of the cccDNA remained detectable in 1.5 days. Our studies demonstrate that the transdifferentiated AR42J-B13 cells can function like bona fide hepatocytes. This system offers a new opportunity for basic research of virus-host interactions and pancreatic transdifferentiation.

Existence and significance of hepatitis B virus DNA in kidneys of IgA nephropathy

AIM

To investigate the existence and significance of hepatitis B virus (HBV) DNA in the pathogenesis of IgA nephropathy (IgAN).

METHODS

Fifty cases of IgAN with HBV antigenaemia and/or hepatitis B virus antigens (HBAg, or HBsAg, HBcAg) detected by immunohistochemistry in renal tissues were enrolled in our study. The distribution and localization of HBV DNA were observed using in situ hybridization. Southern blot analysis was performed to reveal the state of renal HBV DNA.

RESULTS

Among the 50 patients with IgAN, HBs antigenemia was detected in 17 patients (34%). HBAg in renal tissues was detected in 48 patients (96%), the positive rate of HBAg, HBsAg, and HBcAg was 82% (41/50), 58% (29/50), and 42% (21/50) in glomeruli, respectively; and was 94% (47/50), 56% (28/50) and 78% (39/50) in tubular epithelia, respectively. Positive HBV DNA was detected in 72% (36/50) and 82% (41/50) cases in tubular epithelia and glomeruli respectively by in situ hybridization, and the positive signals were localized in the nuclei of tubular epithelial cells and glomerular mesangial cells as well as infiltrated interstitial lymphocytes. Moreover, 68% (34/50) cases were proved to be HBV DNA positive by Southern blot analysis, and all were the integrated form.

CONCLUSION

HBV infection might play an important role in occurrence and progress of IgAN. In addition to humoral immune damages mediated by HBAg-HBAb immune complex, renal tissues of some IgAN are directly infected with HBV and express HBAg in situ, and the cellular mechanism mediated by HBV originating from renal cells in situ may also be involved in the pathogenesis of IgAN.

Cell culture and animal models of viral hepatitis. Part I: hepatitis B

Despite the existence of a preventative vaccine, HBV represents a substantial threat to public health, suggesting the need for research to develop new treatments to combat the disease. The authors review the available in vitro and in vivo models, including recently developed transgenic and chimeric mouse models.

Role of hepatitis B virus infection in pathogenesis of IgA nephropathy

AIM: To investigate the role of hepatitis B virus (HBV) in the pathogenesis of IgA nephropathy (IgAN).

METHODS: HBV antigens (HBAg, or HBsAg, HBcAg, and HBeAg) in renal tissues with IgAN were detected by immunohistochemical technique. The distribution and localization of HBV DNA were observed by using in situ hybridization. Southern blot analysis was performed to reveal the state of renal HBV DNA.

RESULTS: Among 100 patients with IgAN, HBs antigenemia was detected in 18 patients (18.00%). HBAg in renal tissues was detected in 31 patients (31.00%), the positive rate of HBAg, HBsAg and HBcAg was 64.52% (20/31), 32.26% (10/31), 32.26% (10/31), respectively in glomeruli. HBcAg was also found in tubular epithelia and interstitia, which was 45.16% (14/31) and 6.45% (2/31), respectively. Five out of six cases with positive HBV DNA by in situ hybridization were proved to be HBV DNA positive by Southern blot analysis, and all were of the integrated form. Eight specimens were demonstrated to be HBV DNA positive by in situ hybridization, which was localized in the nuclei of tubular epithelial cells and glomerular mesangial cells as well as in infiltrated interstitial lymphocytes.

CONCLUSION: There is a relationship between HBV infection and IgAN. In addition to the humoral immune damage mediated by HBAg-HBAb immune complex, the cellular mechanism mediated by HBV originating from renal cells in situ may be also involved in the pathogenesis of IgAN.

Transgenic mouse models of hepatitis B virus-associated hepatocellular carcinoma

The multi-factorial and multi-step nature of cancer development makes analysis difficult in cell culture and non-genetic animal models. Recent progress in technology has allowed the development of several transgenic animal models addressing various aspects of liver diseases caused by hepatitis B virus in human patients. The experimental data from these studies in vivo highlight the importance of HBV gene products that alone or in conjunction with other host cellular protein(s) can deregulate the cell cycle control checkpoints in the hepatocytes of transgenic mice leading to the development of hepatocellular carcinoma. Moreover, these models are extremely useful in analysing and ascertaining the stages of malignant transformation linked to multiple genetic and non-genetic events of cancer development and in developing novel strategies of intervention.

Transcriptional and posttranscriptional control of hepatitis B virus gene expression

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

Hepatocarcinogenesis in hepatitis viral infection: lessons from transgenic mouse studies

Over the past decade, genetically engineered mouse models have been used for studies of the mechanisms underlying human diseases. One advantage of these models is that the targeted protein executes its function in normal cells in their natural tissue microenvironments. Transgenic mouse models for human viral hepatitis have also been established and have provided new insights into the pathogenesis of hepatitis and hepatocellular carcinoma (HCC). In the search for the mechanism of hepatocarcinogenesis in hepatitis viral infection, two viral proteins, the core protein of hepatitis C virus (HCV) and the HBx protein of hepatitis B virus (HBV), have been shown to possess oncogenic potential through transgenic mouse studies, indicating the direct involvement of the hepatitis viruses in hepatocarcinogenesis. The presence of the hepatitis C virus core or HBx protein, which has an oncogenic potential, may allow some of the steps in multistep hepatocarcinogenesis to be skipped. This may explain the very high frequency of HCC in patients with HCV or HBV infection.

A short N-proximal region in the large envelope protein harbors a determinant that contributes to the species specificity of human hepatitis B virus

Infection by hepatitis B virus (HBV) is mainly restricted to humans. This species specificity is likely determined at the early phase of the viral life cycle. Since the envelope proteins are the first viral factors to interact with the cell, they represent attractive candidates for controlling the HBV host range. To investigate this assumption, we took advantage of the recent discovery of a second virus belonging to the primate Orthohepadnavirus genus, the woolly monkey HBV (WMHBV). A recombinant plasmid was constructed for the expression of all WMHBV envelope proteins. In additional constructs, N-terminal sequences of the WMHBV large envelope protein were substituted for their homologous HBV counterparts. All wild-type and chimeric WMHBV surface proteins were properly synthesized by transfected human hepatoma cells, and they were competent to replace the original HBV proteins for the production of complete viral particles. The resulting pseudotyped virions were evaluated for their infectious capacity on human hepatocytes in primary culture. Virions pseudotyped with wild-type WMHBV envelope proteins showed a significant loss of infectivity. By contrast, infectivity was completely restored when the first 30 residues of the large protein originated from HBV. Analysis of smaller substitutions within this domain limited the most important region to a stretch of only nine amino acids. Reciprocally, replacement of this motif by WMHBV residues in the context of the HBV L protein significantly reduced infectivity of HBV. Hence this short region of the L protein contributes to the host range of HBV.

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

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

New animal models of hepatitis B and C

The narrow host range of infection and lack of suitable tissue culture systems for the propagation of hepatitis B and C viruses are limitations that have prevented a more thorough understanding of persistent infection and the pathogenesis of chronic liver disease. With hepatitis B virus (HBV), this lack of knowledge has been partially overcome by the discovery and characterization of HBV-like viruses in wild animals. With hepatitis C virus (HCV), related flaviviruses have been used as surrogate systems for such studies. Other laboratories have developed transgenic mice that express virus gene products and/or support virus replication. Some HBV transgenic mouse models develop fulminant hepatitis, acute hepatitis, or chronic liver disease after adoptive transfer, and others spontaneously develop hepatocellular carcinoma (HCC), as in human infections. Among HCV transgenic mice, most develop no disease, but acute hepatitis has been observed in one model, and HCC in another. Although mice are not susceptible to HBV and HCV, their ability to replicate these viruses and to develop liver diseases characteristic of human infections provides new opportunities to study pathogenesis and develop novel therapeutics.

Signals for bidirectional nucleocytoplasmic transport in the duck hepatitis B virus capsid protein

Hepadnavirus genome replication involves cytoplasmic and nuclear stages, requiring balanced targeting of cytoplasmic nucleocapsids to the nuclear compartment. In this study, we analyze the signals determining capsid compartmentalization in the duck hepatitis B virus (DHBV) animal model, as this system also allows us to study hepadnavirus infection of cultured primary hepatocytes. Using fusions to the green fluorescent protein as a functional assay, we have identified a nuclear localization signal (NLS) that mediates nuclear pore association of the DHBV nucleocapsid and nuclear import of DHBV core protein (DHBc)-derived polypeptides. The DHBc NLS mapped is unique. It bears homology to repetitive NLS elements previously identified near the carboxy terminus of the capsid protein of hepatitis B virus, the human prototype of the hepadnavirus family, but it maps to a more internal position. In further contrast to the hepatitis B virus core protein NLS, the DHBc NLS is not positioned near phosphorylation target sites that are generally assumed to modulate nucleocytoplasmic transport. In functional assays with a knockout mutant, the DHBc NLS was found to be essential for nuclear pore association of the nucleocapsid. The NLS was found to be also essential for virus production from the full-length DHBV genome in transfected cells and from hepatocytes infected with transcomplemented mutant virus. Finally, the DHBc additionally displayed activity indicative of a nuclear export signal, presumably counterbalancing NLS function in the productive state of the infected cell and thereby preventing nucleoplasmic accumulation of nucleocapsids.

Animal models of hepadnavirus-associated hepatocellular carcinoma

Animal models of hepatitis B virus infection have been valuable for determining the mechanisms of hepadnavirus replication, for studies of pathogenesis, and for investigations of viral hepatocarcinogenesis. The woodchuck model also seems to be useful in the discovery and development of antiviral drugs to treat HBV infection and for testing new forms of immunotherapy. In particular, the woodchuck seems to be ideal for studying the effect of antiviral treatment and immunotherapy on the outcome of hepadnavirus infection and on survival. The median life expectancy of experimentally infected, chronic WHV carriers is approximately 29 months, and almost all develop HCC. New types of prophylaxis or therapy can be evaluated under controlled experimental conditions, in a relevant animal model, and within a reasonable time frame.

Enhanced replication contributes to enrichment of hepatitis B virus with a deletion in the core gene

Accumulation in immunosuppressed patients of hepatitis B virus (HBV) with a deletion in the C gene is associated with severe liver disease. The aim of this study was to determine the phenotype of such genomes in vitro. Four C gene fragments with different types of deletions were inserted in the context of a wild-type genome and tested by transfection into HuH7 cells. The deletions did not influence mRNA and surface protein levels. Truncated C gene translation products were expressed only from variants with in-frame deletions, whereas full-length polymerase was expressed from all variants at a similar or higher level than in wild-type virus. None of the variants was competent for autonomous replication; however, they produced 2- to 4.5-fold more progeny DNA than wild-type HBV when sufficiently complemented with wild-type core protein. Similarly, when variant and wild-type DNA were cotransfected in different ratios, the variants produced 2- to 5-fold more progeny DNA relative to the wild-type; this enrichment required the expression of the viral polymerase in cis. The mechanism of enrichment depended on the percentage of variant in the transfected DNA mixture. When the transfected DNA contained a small percentage of variant, enhanced replication of the variant accompanied by no or little suppression of wild-type replication was seen. Accordingly, overall production of progeny virus was slightly increased. At a high percentage of variant DNA, replication of both variant and wild-type decreased, probably due to a shortage of wild-type core protein. In conclusion, emergence of C gene deletion variants in vivo may be due to enhanced replication mediated at the level of encapsidation or reverse transcription. If the variants constitute a small part of the ccc DNA, they can be fully trans-complemented by wild-type virus which may increase the overall virus production.

Hepatitis B virus in hepatocarcinogenesis

Hepatitis B virus (HBV) is an important etiologic agent of chronic hepatitis, cirrhosis, and hepatocellular carcinoma (HCC). Although the mechanism whereby HBV causes HCC is not fully understood, it is likely that there are many relevant molecular pathways that contribute to the development of HBV-associated HCC. This review provides an overview of some of these proposed pathways and their relative importance. It also raises questions on basic and translational research that will signficantly contribute to the better understanding of underlying mechanisms, prevention, and treatment of this tumor type.

Hepatitis B virus transgenic mouse model of chronic liver disease

A model for hepatitis B virus-associated chronic liver disease has been made using cloned hepatitis B virus DNA as a transgene in a severe combined immunodeficient host. These mice consistently support virus gene expression and replication. After adoptive transfer of unprimed, syngeneic splenocytes, these mice cleared virus from liver and serum, and developed chronic liver disease. This model will permit identification of the host and virus contributions to chronic liver disease in the absence of tolerance.

Altered expression of hepatic carcinogen metabolizing enzymes with liver injury in HBV transgenic mouse lineages expressing various amounts of hepatitis B surface antigen

AIMS/BACKGROUND

The objective of this work was to evaluate the possible modulation of carcinogen metabolizing enzymes in relation to chronic infection by hepatitis B virus (HBV). This was to test whether enzyme level is altered in association with HBV gene expression per se or only when that expression was associated with an induction of liver injury.

METHODS

For this purpose, we studied four different HBV transgenic mouse lineages (23.3, 45.2, 50.4 and 107.5) that express the transgene encoding for the large envelope protein (HBsAg) at different levels. These lineages exhibit an associated liver injury which progresses with age and is positively correlated with the degree of accumulation of HBsAg in the hepatocytes. The modulation of levels of cytochrome P450 (1a, 2a-5, 2b, 2c, 3A4 and 2E1) and glutathione S-transferases (GST alpha and pi) involved in carcinogen metabolism was examined by immunohistochemistry in these lineages.

RESULTS

While we observed an increase in staining intensity of P450s 1-a and 2a-5 in lineages expressing cytopathic amounts of HBsAg (lineages 50.4 and 45.2), we only observed minor changes or no changes at all for the other lineages (23.3 and 107.5). Staining with antibodies to cytosolic pi class GST demonstrated an increase in older mice, although no major alterations were observed for GST alpha.

CONCLUSIONS

These results suggest that liver cell injury induced by accumulation of HBV antigens can result in the induction of some carcinogen metabolizing enzymes and this may be one mechanism of chemical-viral interaction in hepatocarcinogenesis.

Transcriptional repression of human hepatitis B virus genes by a bZIP family member, E4BP4

Box alpha is an essential element of both the upstream regulatory sequence of the core promoter and the second enhancer, which positively regulate the transcription of human hepatitis B virus (HBV) genes. In this paper, we describe the cloning and characterization of a box alpha binding protein, E4BP4. E4BP4 is a bZIP type of transcription factor. Overexpression of E4BP4 represses the stimulating activity of box alpha in the upstream regulatory sequence of the core promoter and the second enhancer in differentiated human hepatoma cell lines. E4BP4 can also suppress the transcription of HBV genes and the production of HBV virions in a transient-transfection system that mimics the viral infection in vivo. Expression of an E4BP4 antisense transcript can, instead, elevate the transcription of the core promoter. A low abundance of E4BP4 protein and mRNA in differentiated human hepatoma cell lines is detected, and E4BP4 is not a major component of box alpha binding proteins in untransfected differentiated human hepatoma cell lines. C/EBPalpha and C/EBPbeta, in contrast, are major components of the box alpha binding activity present in nuclear extracts. E4BP4 has a stronger binding affinity towards box alpha than the endogenous box alpha binding activity present in nuclear extracts. Structure and function analysis of E4BP4 reveals that DNA binding activity is sufficient to confer the negative regulatory function of E4BP4. These results indicate that binding site occlusion is the mechanism whereby E4BP4 suppresses transcription in HBV.

Transfection of a rat hepatoma cell line with a construct expressing human liver annexin V confers susceptibility to hepatitis B virus infection

Previously, we have found that human liver annexin V (hA-V; in earlier reports referred as Endonexin II) is a specific hepatitis B surface antigen (HBsAg) binding protein. In this study, we demonstrate that transfection of rat hepatoma FTO 2B cells, a cell line that is not infectable by hepatitis B virus (HBV) and does not express hA-V, with a construct containing the hA-V gene, resulted in hA-V expressing cells susceptible to HBV infection. After in vitro infection, transfected FTO cells (assigned as FTO 9.1 cells) expressing hA-V in cultures were shown to contain HBV-precore/core, X mRNAs, and covalently closed circular (ccc) DNA as detected by polymerase chain reaction (PCR). The presence of HBV ccc and replicative intermediate DNA was also demonstrated by Southern blot hybridization assay. HBV DNA secreted in the culture medium was also evident as determined by quantitative branched DNA (bDNA) assay. HBsAg and hepatitis B core antigen (HBcAg) could also be detected by an immunocytochemical method in 10% to 15% of the cells at day 3 and day 5 after infection. Infectivity of in vitro-propagated HBV was demonstrated by infection of the naive FTO 9.1 cells with the culture supernatant from HBV-carrier cultures. In contrast to primary cultures of human hepatocytes and FTO 9.1 cells, primary rat and mouse hepatocytes, as well as rat hepatoma cell lines that do not express hA-V, are not susceptible to HBV infection. These findings suggest that hA-V plays a key role in the initial step of HBV infection and that the species-specific susceptibility to HBV infection and replication in hepatocytes is associated with the expression of hA-V.

How do animal DNA viruses get to the nucleus?

Genome and pre-genome replication in all animal DNA viruses except poxviruses occurs in the cell nucleus (Table 1). In order to reproduce, an infecting virion enters the cell and traverses through the cytoplasm toward the nucleus. Using the cell's own nuclear import machinery, the viral genome then enters the nucleus through the nuclear pore complex. Targeting of the infecting virion or viral genome to the multiplication site is therefore an essential process in productive viral infection as well as in latent infection and transformation. Yet little is known about how infecting genomes of animal DNA viruses reach the nucleus in order to reproduce. Moreover, this nuclear locus for viral multiplication is remarkable in that the sizes and composition of the infectious particles vary enormously. In this article, we discuss virion structure, life cycle to reproduce infectious particles, viral protein's nuclear import signal, and viral genome nuclear targeting.

The identification and development of antiviral agents for the treatment of chronic hepatitis B virus infection

Hepatitis B virus (HBV) is the leading cause of chronic hepatitis throughout the world. Notwithstanding the availability of a safe and effective vaccine, the world prevalence of HBV has not declined significantly, thus resulting in the need for a selective antiviral agent. HBV is a small, partially double-stranded DNA virus which replicates through an RNA intermediate. Most efforts to develop anti-HBV agents have been targeted to the viral DNA polymerase which possesses reverse transcriptase activity. Currently, the most promising anti-HBV agents are nucleoside analogs which interfere with viral DNA replication. Although earlier nucleoside analogs such as vidarabine (ara-A) and fialuridine (FIAU) have displayed unacceptable toxicities, newer analogs such as lamivudine (3TC), bis-POM PMEA (GS-840), lobucavir, and BMS-200,475 have demonstrated clinical utility. In particular, the use of lamivudine has generated considerable interest in the development of other L-enantiomeric nucleoside analogs for use against HBV. Here, we provide an overview of HBV structure and replication strategy and discuss the use of cell culture systems, in vitro viral polymerase systems, and animal models to identify and evaluate anti-HBV agents. We also discuss the various classes of nucleoside analogs in terms of structure, mechanism of action, status in clinical development, ability to select for resistant HBV variants, and use in combination therapies. Finally, we present a discussion of novel antiviral approaches, including antisense and gene therapy, and address the various challenges to successful anti-HBV chemotherapeutic intervention.

Differential regulation of the pre-C and pregenomic promoters of human hepatitis B virus by members of the nuclear receptor superfamily

Synthesis of the pre-C and pregenomic RNAs of human hepatitis B virus (HBV) is directed by two overlapping yet separate promoters (X. Yu and J. E. Mertz, J. Virol. 70:8719-8726, 1996). Previously, we reported the identification of a binding site for the nuclear receptor hepatocyte nuclear factor 4 (HNF4) spanning the TATA box-like sequence of the pre-C promoter. This HNF4-binding site consists of an imperfect direct repeat of the consensus half-site sequence 5'-AGGTCA-3' separated by one nucleotide; i.e., it is a DR1 hormone response element (HRE). We show here that other receptors, including chicken ovalbumin upstream promoter transcription factor 1 (COUP-TF1), human testicular receptor 2 (TR2), and peroxisome proliferator-activated receptors (PPARs) as heterodimers with retinoid X receptors (RXRs), can also specifically bind this DR1 HRE. Synthesis of the pre-C and pregenomic RNAs was affected both in transfected hepatoma cells and in a cell-free transcription system by the binding of factors to this DR1 HRE. Interestingly, whereas some members of the hormone receptor superfamily differentially repressed synthesis of the pre-C RNA (e.g., HNF4 and TR2) or activated synthesis of the pregenomic RNA (e.g., PPARgamma-RXRalpha), other members (e.g., COUP-TF1) coordinately repressed synthesis of both the pre-C and pregenomic RNAs. Thus, HBV likely regulates its expression and replication in part via this DR1 HRE. These findings indicate that appropriate ligands to nuclear receptors may be useful in the treatment of HBV infection.

Members of the nuclear receptor superfamily regulate transcription from the hepatitis B virus nucleocapsid promoter

The role of members of the nuclear receptor superfamily of transcription factors in regulating hepatitis B virus (HBV) transcription was investigated. Hepatocyte nuclear factor 4 (HNF4), the retinoid X receptor (RXR), and the peroxisome proliferator-activated receptor (PPAR) were examined for their capacity to modulate the level of transcriptional activity from the four HBV promoters by transient-transfection analysis in the dedifferentiated hepatoma cell line, HepG2.1. It was found that the nucleocapsid and large surface antigen promoters were transactivated in the presence of HNF4 whereas the enhancer I/X gene, nucleocapsid, and large surface antigen promoters were transactivated in the presence of RXR and PPAR. Characterization of the nuclear receptors interacting with the nucleocapsid promoter region demonstrated that HNF4 is the primary transcription factor binding to the regulatory region spanning nucleotides -127 to -102 whereas HNF4, RXR-PPAR heterodimers, COUPTF1, and ARP1 bind the regulatory region spanning nucleotides -34 to -7. Transcriptional transactivation from the nucleocapsid promoter by HNF4 appears to be mediated through the two HNF4 binding sites in the promoter, whereas modulation of the level of transcription from the nucleocapsid promoter by RXR-PPAR appears to be regulated by the regulatory sequence element spanning nucleotides -34 to -7 and the HBV enhancer 1 region. These observations indicate that HBV transcription, and pregenomic RNA synthesis in particular, is regulated by ligand-dependent nuclear receptors. Agonists and antagonists capable of regulating the activity of these nuclear receptors may permit the modulation of HBV transcription and consequently replication during viral infection.

Long-term expression of the hepatitis B virus core-e- and X-proteins does not cause pathologic changes in transgenic mice

BACKGROUND/AIMS

Chronic infections with the human hepatitis B virus can result in liver cirrhosis and primary hepatocellular carcinoma. The reasons for these long-term effects are unclear. The aim of this study was to generate transgenic mice expressing the HBV X- and c/e-gene under authentic and foreign promoter control and to test whether the respective gene products can cause pathologic effects during the lifespan of a mouse. Moreover, the temporal and the tissue-specific regulation of the crucial HBV c/e-gene promoter was analyzed.

METHODS

Eight transgenic mouse lines were generated. Four contained the c/e- and X-gene and two contained only the X-gene under authentic promoter control. Two lines expressed only the X-gene under control of the rat insulin promoter/enhancer. Gene expression was tested by protein and mRNA analyses. During an observation period of 2 years, mice were sacrificed and organs subjected to histologic examination. Mice expressing the X-gene in pancreatic beta cells were tested for the development of diabetes.

RESULTS

In the liver, slight histopathologic alterations but no neoplastic changes could be observed in mice expressing the X-gene. Activity of the c/e-gene promoter/enhancer was age dependent and was not restricted to hepatocytes.

CONCLUSION

No evidence was obtained that long-term expression of the HBV c/e- and X-gene products can cause neoplasia during the lifespan of a mouse.

Detection of hepatitis B virus DNA and RNA in kidneys of HBV related glomerulonephritis

Glomerular deposition of hepatitis B virus (HBV) antigens are observed in chronic HBsAg carriers with different glomerulonephritides yet the etiologic role of HBV remains uncertain. We examined the paraffin section of kidney biopsies from 40 chronic HBsAg carriers with membranous nephropathy (MGN), mesangiocapillary glomerulonephritis (MCGN) or IgA nephropathy (IgAN) for HBV DNA and HBV RNA using in situ hybridization (ISH). Glomerular HBV antigens were present in all biopsies by immunofluorescence. HBsAg or HBcAg mRNA was also studied in RNA extracted from frozen renal tissue using a two-step polymerase chain reaction (PCR) following reverse transcription (RT). HBcAg DNA was not easily detected with ISH alone, but was readily found in 31 biopsies (78%) following PCR. HBV DNA was detected mainly in the cytoplasm of proximal tubular epithelia but not in glomerular cells. HBsAg and/or HBcAg mRNA were detected by RT-PCR in extracted RNA from 13 biopsies (33%). The PCR findings were further confirmed by (a) Southern blot hybridization using a cloned HBV probe and (b) absence of PCR product following treating RNA with RNase or omitting the RT. It is plausible that HBV DNA in renal tubules represents endocytosis of HBV DNA in the urinary filtrate and the HBV RNA extracted from kidney biopsies could derive from infiltrating cells bearing HBV RNA. Hence, ISH with specific HBV core gene RNA probe was performed subsequently. HBcAg RNA, localized in the nuclei and cytoplasm of glomerular and tubular cells, was detected in 56%, 20%, and 36% of renal biopsies in chronic HBsAg carriers with MGN, MCGN, and IgAN, respectively. Our findings indicate the presence of viral transcription in glomerular cells and renal tubular epithelia, supporting an etiological role of HBV in some chronic HBsAg carriers who develop coexisting glomerulonephritides.

Cell type-specific mechanisms regulate hepatitis B virus transgene expression in liver and other organs

Intracellular expression of hepatitis B virus (HBV) was analysed in transgenic HBV mouse lines designated G7 and G26, the former lacking hepatitis B surface antigen (HBsAg) promoters. HBsAg mRNA expression was greater in the G26 line than in the G7 line, although in situ hybridization showed a qualitatively similar expression pattern in specific cell types. HBsAg mRNA was most abundant in hepatocytes, followed in magnitude by proximal renal tubular epithelial cells, pancreatic acinar cells, and epithelial cells of the gastric, small intestinal, and bronchiolar mucosae. In biliary epithelial cells, brain, spleen, large intestine, testis, heart, and skeletal muscle, HBsAg mRNA was undetectable. In cell transfection assays, the HBV enhancer/preS1 promoter efficiently expressed a luciferase reporter with appropriate upregulation by HNF-3 alpha and C/EBP alpha transcription factors in hepatocyte-derived cells but not in non-parenchymal epithelial liver cells or fibroblasts. These results suggest that cell-type specificity of HBV expression is regulated by interactions between viral elements and cellular transactivators. Variable expression of G7 and G26 HBV transgenes in epithelial cells combined with differences in transgene expression in similar sets of cells suggests at least two levels of regulation: one directing cell specificity of HBV expression and the other governing quantitative expression of HBV mRNA.

Promoters for synthesis of the pre-C and pregenomic mRNAs of human hepatitis B virus are genetically distinct and differentially regulated

Two similar, yet functionally distinct genomic RNAs are transcribed from the DNA genome of the human hepatitis B virus. The pre-C RNAs encode the precore protein which is proteolytically processed to yield e antigen. The pregenomic RNAs encode both the nucleocapsid protein and reverse transcriptase and serve as the templates for viral DNA replication. To determine whether synthesis of these two RNAs is directed from a single or a closely spaced pair of promoters, we introduced point and insertion mutations into the basal elements of the promoter that directs their synthesis. Transcription from these mutants was examined both in cell-free transcription systems derived from hepatoma (HepG2) and nonliver (HeLa) cell lines and by transient transfection of hepatoma cell lines (Huh7 and HepG2). The data from these experiments indicated that synthesis of the pre-C and pregenomic RNAs is directed by two distinct promoters and that the basal elements of these two promoters partially overlap, yet are genetically separable, with each consisting of its own transcriptional initiator and a TATA box-like sequence situated approximately 25 to 30 bp upstream of its sites of initiation. A 15-bp insertion was found to be sufficient to physically separate these two promoters. Furthermore, these two promoters can be differentially regulated, with the transcriptional activator Sp1 specifically activating transcription from the pregenomic promoter and the hepatocyte nuclear factor 4 specifically repressing transcription from the pre-C promoter. Thus, we conclude that the promoters used in synthesis of the pre-C and pregenomic mRNAs are genetically distinct and separately regulated.