Hepatitis B virus X protein affects S phase progression leading to chromosome segregation defects by binding to damaged DNA binding protein 1.

UNLABELLED: Chronic hepatitis B virus (HBV) infection is a leading cause of hepatocellular carcinoma (HCC), but its role in the transformation process remains unclear. HBV encodes a small protein, known as HBx, which is required for infection and has been implicated in hepatocarcinogenesis. Here we show that HBx induces lagging chromosomes during mitosis, which in turn leads to formation of aberrant mitotic spindles and multinucleated cells. These effects require the binding of HBx to UV-damaged DNA binding protein 1 (DDB1), a protein involved in DNA repair and cell cycle regulation, and are unexpectedly attributable to HBx interfering with S-phase progression and not directly with mitotic events. HBx also affects S-phase and induces lagging chromosomes when expressed from its natural viral context and, consequently, exhibits deleterious activities in dividing, but not quiescent, hepatoma cells. CONCLUSION: In addition to its reported role in promoting HBV replication, the binding of HBx to DDB1 may induce genetic instability in regenerating hepatocytes and thereby contribute to HCC development, thus making this HBV-host protein interaction an attractive target for new therapeutic intervention.

Interaction of hepatitis B viral oncoprotein with cellular target HBXIP dysregulates centrosome dynamics and mitotic spindle formation.

Hepatitis B virus infection is associated with hepatocellular carcinoma, claiming 1 million lives annually worldwide. To understand the carcinogenic mechanism of hepatitis B virus-encoded oncoprotein HBx, we explored the function of HBx interaction with its cellular target HBXIP. Previously, we demonstrated that viral HBx and cellular HBXIP control mitotic spindle formation, regulating centrosome splitting. By using various fragments of HBx, we determined that residues (137)CRHK(140) within HBx are necessary for binding HBXIP. Mutation of the (137)CRHK(140) motif in HBx abolished its ability to bind HBXIP and to dysregulate centrosome dynamics in HeLa and immortal diploid RPE-1 cells. Unlike wild-type HBx, which targets to centrosomes as determined by subcellular fractionation and immunofluorescence microscopy, HBx mutants failed to localize to centrosomes. Overexpression of viral HBx wild-type protein and knockdown of endogenous HBXIP altered centrosome assembly and induced modifications of pericentrin and centrin-2, two essential proteins required for centrosome formation and function, whereas HBXIP nonbinding mutants of HBx did not. Overexpression of HBXIP or fragments of HBXIP that bind HBx neutralized the effects of viral HBx on centrosome dynamics and spindle formation. These results suggest that HBXIP is a critical target of viral HBx for promoting genetic instability through formation of defective spindles and subsequent aberrant chromosome segregation.

Hepatitis B virus x protein induces perinuclear mitochondrial clustering in microtubule- and Dynein-dependent manners.

The hepatitis B virus (HBV) X protein (HBx) is thought to play a key role in HBV replication and the development of liver cancer. It became apparent that HBx induces mitochondrial clustering at the nuclear periphery, but the molecular basis for mitochondrial clustering is not understood. Since mitochondria move along the cytoskeleton as a cargo of motor proteins, we hypothesized that mitochondrial clustering induced by HBx occurs by an altered intracellular motility. Here, we demonstrated that the treatment of HBx-expressing cells with a microtubule-disrupting drug (nocodazole) abrogated mitochondrial clustering, while the removal of nocodazole restored clustering within 30 to 60 min, indicating that mitochondrial transport is occurring in a microtubule-dependent manner. The addition of a cytochalasin D-disrupting actin filament, however, did not measurably affect mitochondrial clustering. Mitochondrial clustering was further studied by observations of HBV-related hepatoma cells and HBV-replicating cells. Importantly, the abrogation of the dynein activity in HBx-expressing cells by microinjection of a neutralizing anti-dynein intermediate-chain antibody, dynamitin overexpression, or the addition of a dynein ATPase inhibitor significantly suppressed the mitochondrial clustering. In addition, HBx induced the activation of the p38 mitogen-activated protein kinase (MAPK) and inhibition of the p38 kinase activity by SB203580-attenuated HBx-induced mitochondrial clustering. Taken together, HBx activation of the p38 MAPK contributed to the increase in the microtubule-dependent dynein activity. The data suggest that HBx plays a novel regulatory role in subcellular transport systems, perhaps facilitating the process of maturation and/or assembly of progeny particles during HBV replication. Furthermore, mitochondrion aggregation induced by HBx may represent a cellular process that underlies disease progression during chronic viral infection.

cDNA microarray analysis of early gene expression profiles associated with hepatitis B virus X protein-mediated hepatocarcinogenesis.

Chronic hepatitis B virus (HBV) infection is one of the major causes of hepatocellular carcinoma. HBV encodes an oncogenic hepatitis B virus X protein (HBx), which can transactivate host cell transcriptional machinery and mediate cellular transformation. To disclose the early genetic response in HBx-mediated transformation process, we constructed a conditional HBx-expressing hepatocyte cell line, which allows us to compare the gene expression profiles under controllable HBx induction. A cDNA microarray containing more than 8700 mouse genes and ESTs was utilized to examine the gene expression profiles. We identified 260 candidate genes and 259 ESTs which have shown aberrant expression under HBx induction. Most of them are involved in signal transduction pathway, cell cycle control, metastasis, transcriptional regulation, immune response, and metabolism. These results provide additional insight into early cellular targets of HBx, which could give us a better understanding of the function of HBx and their progressive changes during HBx-mediated hepatocarcinogenesis.

Early molecular and genetic determinants of primary liver malignancy.

Although the overview above provides a partial molecular picture of the early stages of stepwise hepatocarcinogenesis. it should be emphasized that tumor and nontumor liver contain multiple changes, and that there is variability in their profile among different patients even within single studies. Variability in the number and types of genetic changes has also been observed geographically, and may be dependent upon the etiology of the tumor (viral, chemical or both). Interestingly, HBxAg inactivates tumor suppressors (such as p53 [by direct binding] and Rb [by stimulating its phosphorylation]) early in carcinogenesis that are mutated later during tumor progression. HBxAg also constitutively activates signal transduction pathways, such as those involving c-jun and ras, and activates oncogenes,such as c-nloc, that are otherwise activated by 3-catenin mutations. These findings suggest common molecular targets in hepatocarcinogenesis, despite different mechanisms of activation or inactivation. These observations need to be exploited in future drug discovery and in the development of new therapeutics. Heterogeneity in the mechanisms of tumor development, evidenced by the differences in the up- and down regulated genes reported in micro array analyses, as well as in the genetic loci that undergo mutation or LOH indifferent reports, has now been well documented. This suggests that there are multiple pathways to HCC, and that there is redundancy in the pathways that regulate cell growth and survival. These findings also reflect that,although hepatocarcinogenesis is multistep, the molecular changes that underpin histopathological changes in tumor development are likely to be different or only partially overlapping in individual tumors. Overall, the consequences of these changes suggest that the pathogenesis of HCC is accompanied by a progressive loss of differentiation, loss of normal cell adhesion, loss of the ECM, and constitutive activation of selected signal transduction pathways that promote cell growth and survival. Although mechanisms are important, attention also has to be paid to the target genes whose altered expression actually mediate the neoplastic phenotype. Other key avenues of work need to be explored. For example, it will be important to try to identify germline mutations in HBV-infected patients that are passed on to their children, resulting in the development of HCC in childhood. Clinical materials will also be important for the validation of new markers with diagnostic or prognostic potential. In this context, there is an urgent need to establish simple and low-cost tests based upon molecular changes that are hallmarks of HCC development. Identification of patients with early HCC will also significantly increase survival through its impact upon treatment. The discovery and validation of HCC markers may permit accurate staging of lesions, determine the proximity of such lesions to malignancy, and determine whether lesions with a particular genetic profile are still capable of remodeling through appropriate therapeutic intervention. The efficient reintroduction of the relevant tumor suppressors, or the inhibition of oncogene expression by siRNA, provide just some of the additional opportunities that will ultimately be useful in patient treatment. Together, these approaches will go far in reducing the very high morbidity and mortality associated with HCC.

Upregulated expression of a unique gene by hepatitis B x antigen promotes hepatocellular growth and tumorigenesis.

Hepatitis B x antigen (HB x Ag) is a trans-activating protein that may be involved in hepatocarcinogenesis, although few natural effectors of HB x Ag that participate in this process have been identified. To identify additional effectors, whole cell RNA isolated from HB x Ag-positive and HB x Ag-negative HepG2 cells were compared by polymerase chain reaction select cDNA subtraction, and one clone, upregulated gene, clone 11 (URG11), was chosen for further characterization. Elevated levels of URG11 mRNA and protein were observed in HB x Ag-positive compared to HB x Ag-negative HepG2 cells. Costaining was observed in infected liver (P < 0.01). URG11 stimulated cell growth in culture (P < 0.01), anchorage-independent growth in soft agar (P < 0.001), and accelerated tumor formation (P < 0.01), and yielded larger tumors (P < 0.02) in SCID mice injected subcutaneously with HepG2 cells. These data suggest that URG11 is a natural effector of HB x Ag that may promote the development of hepatocellular carcinoma.

Weak protein-protein interactions are sufficient to drive assembly of hepatitis B virus capsids.

Hepatitis B virus (HBV) is an enveloped DNA virus with a spherical capsid (or core). The capsid is constructed from 120 copies of the homodimeric capsid protein arranged with T = 4 icosahedral symmetry. We examined in vitro assembly of purified E. coli expressed HBV capsid protein. After equilibration, concentrations of capsid and dimer were evaluated by size exclusion chromatography. The extent of assembly increased as temperature and ionic strength increased. The concentration dependence of capsid assembly conformed to the equilibrium expression: K(capsid) = [capsid]/[dimer](120). Given the known geometry for HBV capsids and dimers, the per capsid assembly energy was partitioned into energy per subunit-subunit contact. We were able to make three major conclusions. (i) Weak interactions (from -2.9 kcal/mol at 21 degrees C in low salt to -4.4 kcal/mol at 37 degrees C in high salt) at each intersubunit contact result in a globally stable capsid; weak intersubunit interactions may be the basis for the phenomenon of capsid breathing. (ii) HBV assembly is characterized by positive enthalpy and entropy. The reaction is entropy-driven, consistent with the largely hydrophobic contacts found in the crystal structure. (iii) Increasing NaCl concentration increases the magnitude of free energy, enthalpy, and entropy, as if ionic strength were increasing the amount of hydrophobic surface buried by assembly. This last point leads us to suggest that salt acts by inducing a conformational change in the dimer from an assembly-inactive form to an assembly-active form. This model of conformational change linked to assembly is consistent with immunological differences between dimer and capsid.

Hepatitis B viral transactivator HBx alleviates p53-mediated repression of alpha-fetoprotein gene expression.

Chronic infection with hepatitis B virus (HBV) is associated with development of hepatocellular carcinoma (HCC). The exact mechanism by which chronic infection with HBV contributes to onset of HCC is unknown. However, previous studies have implicated the HBV transactivator protein, HBx, in progression of HCC through its ability to bind the human tumor suppressor protein, p53. In this study, we have examined the ability of HBx to modify p53 regulation of the HCC tumor marker gene, alpha-fetoprotein (AFP). By utilizing in vitro chromatin assembly of DNA templates prior to transcription analysis, we have demonstrated that HBx functionally disrupts p53-mediated repression of AFP transcription through protein-protein interaction. HBx modification of p53 gene regulation is both tissue-specific and dependent upon the p53 binding element. Our data suggest that the mechanism by which HBx alleviates p53 repression of AFP transcription is through an association with DNA-bound p53, resulting in a loss of p53 interaction with liver-specific transcriptional co-repressors.

Use of the hepatitis B virus recombinant baculovirus-HepG2 system to study the effects of (-)-beta-2',3'-dideoxy-3'-thiacytidine on replication of hepatitis B virus and accumulation of covalently closed circular DNA.

(-)-Beta-2',3'-Dideoxy-3'-thiacytidine (lamivudine [3TC]) is a nucleoside analog which effectively interferes with the replication of hepatitis B virus (HBV) DNA in vitro and in vivo. We have investigated the antiviral properties of 3TC in vitro in HepG2 cells infected with recombinant HBV baculovirus. Different types of information can be obtained with the HBV baculovirus-HepG2 system because (i) experiments can be carried out at various levels of HBV replication including levels significantly higher than those that can be obtained from conventional HBV-expressing cell lines, (ii) cultures can be manipulated and/or treated prior to or during the initiation of HBV expression, and (iii) high levels of HBV replication allow the rapid detection of HBV products including covalently closed circular (CCC) HBV DNA from low numbers of HepG2 cells. The treatment of HBV baculovirus-infected HepG2 cells with 3TC resulted in an inhibition of HBV replication, evidenced by reductions in the levels of both extracellular HBV DNA and intracellular replicative intermediates. The effect of 3TC on HBV replication was both dose and time dependent, and the reductions in extracellular HBV DNA that we observed agreed well with the previously reported efficacy of 3TC in vitro. As expected, levels of HBV transcripts and extracellular hepatitis B surface antigen and e antigen were not affected by 3TC. Importantly, the HBV baculovirus-HepG2 system made it possible to observe for the first time that CCC HBV DNA levels are lower in cells treated with 3TC than in control cells. We also observed that the treatment of HepG2 cells prior to HBV baculovirus infection resulted in a slight increase in the efficacy of 3TC compared to treatments starting 24 h postinfection. The treatment of HepG2 cells with the highest concentration of 3TC tested in this study (2 microM) prior to the initiation of HBV replication markedly inhibited the accumulation of CCC DNA, whereas treatment with the same concentration of 3TC at a time when CCC HBV DNA pools were established within the cells was considerably less effective. In addition, our results suggest that in HepG2 cells, non-protein-associated relaxed circular HBV DNA and particularly CCC HBV DNA are considerably more resistant to 3TC treatment than other forms of HBV DNA, including replicative intermediates and extracellular DNA. We conclude from these studies that the HBV baculovirus-HepG2 system has specific advantages for drug studies and can be used to complement other in vitro model systems currently used for testing antiviral compounds.

Differential immediate early gene expression in conditional hepatitis B virus pX-transforming versus nontransforming hepatocyte cell lines.

We report construction and characterization of tetracycline-controlled hepatitis B virus pX-expressing hepatocyte (AML12) cell lines. These cell lines were constructed in AML12 clonal isolates (clones 3 and 4), which express constitutively the tetracycline-controlled transactivator. Since pX is implicated in HCC, this immortalized hepatocyte model system was used to investigate the mechanism of pX in transformation. Clonal isolates of 3pX and 4pX lineages display conditional synthesis of pX mRNA and protein and a 2-fold increase in growth saturation density following tetracycline removal, implicating pX in monolayer overgrowth. Interestingly, only 3pX clones display pX-dependent anchorage independence. Clone 3 lineages express hepatocyte nuclear factor-1alpha and hepatocyte-specific marker genes; clone 4 lineages express hepatocyte nuclear factor-1beta and reduced levels of hepatocyte-specific marker genes, suggesting the importance of the differentiated hepatocyte in pX-mediated oncogenic transformation. Importantly, 3pX and 4pX lineages display differential expression of immediate early genes c-fos and ATF3. The pX-transforming 3pX lineage displays early, pX-dependent induction of ATF3 and prolonged induction of c-fos. The nontransforming 4pX cells display an absence of pX-dependent ATF3 induction and transient induction of c-fos. Our results support the direct link of pX expression to oncogenic transformation in 3pX lineage clones and underscore the advantage of this conditional cellular model system for studying mechanisms of pX-mediated oncogenesis.

p53-independent apoptotic effects of the hepatitis B virus HBx protein in vivo and in vitro.

The hepatitis B virus protein HBx is a promiscuous transactivator implicated in both cell growth and death and in the development of hepatocellular carcinoma. We recently reported that HBx can potentiate c-myc-induced liver oncogenesis in a transgenic model where low level expression of HBx induces no pathology. To assess if HBx could affect the hepatocyte turnover, we investigated the HBx-elicited apoptotic responses in transgenic livers and in primary hepatocyte cultures. Here we show that transgenic expression of HBx is associated with a twofold increase of spontaneous cell death in the mouse liver. The finding that apoptosis was enhanced to similar extents in HBx mice carrying homozygous p53 null mutations implied that functionally intact p53 was not required to transduce the death signal. A direct, dose-dependent apoptotic function of HBx was demonstrated in transient transfections of liver-derived cell lines. We further show that stable expression of HBx at low, presumably physiological levels in primary hepatocytes, induced cellular susceptibility to diverse apoptotic insults, including growth factor deprivation, treatment with anti-Fas antibodies or doxorubicine and oxidative stress. HBx expression, but not p53 status profoundly affected the commitment of cells to die upon apoptotic stimuli. These data strengthen the notion that HBX may contribute to HBV pathogenesis by enhancing apoptotic death in the chronically infected liver.

The hepatitis B virus X protein up-regulates tumor necrosis factor alpha gene expression in hepatocytes.

Human hepatocytes infected by hepatitis B virus (HBV) produce the proinflammatory cytokine, tumor necrosis factor (TNF-). In this study, we explored the mechanism of induction of TNF- synthesis by HBV. We found that the stable HBV-transfected hepatoma cell line, 2. 2.15, expressed high-molecular-weight (HMW) TNF- mRNAs, which were absent in the parent HepG2 cells. Treatment of 2.2.15 cells with interferon alfa (IFN-) and/or interleukin-1beta (IL-1beta) reduced both viral gene transcription and TNF- mRNA expression. Transient or stable transfection of hepatocyte-derived cell lines with HBV X protein (HBx) expression vectors induced the production of biologically active TNF-. In these cells, the HBx-induced TNF- was detected both as cell-associated and soluble forms. Luciferase gene-expression assays showed that the TNF- gene promoter contained target sequences for HBx trans-activation within the proximal region of the promoter. These results indicate that the hepatocyte TNF- synthesis induced by HBV is transcriptionally up-regulated by HBx. Thus, HBx may have a role in the induction of the intrahepatic inflammatory processes that take place during acute and chronic hepatitis B.

Hepatitis B virus X antigen in the pathogenesis of chronic infections and the development of hepatocellular carcinoma.

Chronic infection with hepatitis B virus is associated with a high incidence of liver diseases, including hepatocellular carcinoma. Hepatitis-B-virus-encoded X antigen (HBxAg) stimulates virus gene expression and replication, which may be important for the establishment and maintenance of the chronic carrier state. Integration of viral DNA encoding HBxAg during chronic infection results in increased X antigen expression. HBxAg overexpression may alter signal transduction pathways important for the regulation of cell growth during hepatocellular regeneration. The finding that HBxAg binds to and inactivates negative growth-regulatory molecules, such as the tumor suppressor p53, suggests additional ways that HBxAg may act in hepatocarcinogenesis. HBxAg may also stimulate the expression of positive growth regulators, such as insulin-like growth factor II and the insulin-like growth factor I receptor. The finding that HBxAg may compromise DNA repair and that it may effect the normal turnover of growth-regulatory molecules in the proteasome may also contribute to its carcinogenic properties. Hence, HBxAg may contribute to the pathogenesis of chronic infection and development of hepatocellular carcinoma in a variety of ways.

T cell recognition of hepatitis B and C viral antigens.

The outcome of hepatitis B and C heavily depends on the appropriate virus specific T cell response. Both CD8+ and CD4+ T lymphocytes do not recognize native viral proteins but processed peptides bound to MHC class I and class II, respectively. For therapeutical intervention aimed at T lymphocytes in chronic carriers as well as for the development of new vaccines, a precise identification of immunodominant epitopes, which can be recognized by a majority of patients, is necessary. Biological features of certain viral antigens have been partly characterized in animal models, but with the availability of modern molecular technology it is possible to extend these findings to the human system. The identification of anchor residues and motifs in peptides, which are essential for binding to certain MHC class I and class II molecules, allows the prediction of MHC allele-specific epitopes within viral proteins. By the use of synthetic peptides and vaccinia expression vectors, several epitopes for cytotoxic and helper T lymphocytes have been identified in HBV and HCV antigens. In HBV infection cytotoxic T lymphocytes recognize epitopes within the polymerase protein, the envelope protein and the nucleocapsid. In HCV cytotoxic epitopes have so far been identified within the nucleocapsid, E1, E2 and NS2. Since virus specific CD8+ T lymphocytes lyse virus infected cells in vitro and seem to play an important role for viral elimination in vivo, activation of virus specific effector cells may be achieved by immunizing chronically infected patients with the MHC-allele-specific peptides. Epitopes for CD4+ T lymphocytes have been demonstrated in the majority of HBV- and HCV-proteins. Different subsets of CD4+ T lymphocytes influence the course of infection by the production of lymphokines which either support antibody production by B cells or cellular antiviral effector mechanisms. In acute and chronic HBV infection the HBcAg/HBeAg-specific T cell response is closely correlated to viral elimination and the occurrence of anti-HBe- and anti-HBs antibodies. In HCV infection the CD4+ T cell response appears to be more heterogenous, and better functional characterization of the CD4+ response to immunodominant peptide epitopes in association with certain disease stages is required. Since T cell activation, the resulting effector functions and binding of the peptide to the HLA-molecule mainly depend on the peptide structure, viral mutations leading to amino acid changes may contribute to T cell non-responsiveness or an inappropriate T cell response.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of hepatitis B virus antigens on interferon-gamma production of peripheral blood mononuclear cells from hepatitis B virus carriers and healthy individuals.

BACKGROUND: Although the precise mechanisms of persistent infection by hepatitis B virus are not yet known, several lines of studies suggest that hepatitis B e antigen in sera might modulate the immune response of the host. The aim of this study was to clarify the effects of hepatitis B virus antigen on cytokine production of lymphocytes. METHODS: We studied the effects of recombinant hepatitis B core antigen and surface antigen on interferon-gamma production of phytohemagglutinin-stimulated peripheral blood mononuclear cells from hepatitis B virus carriers and healthy individuals. Hepatitis B core antigen used in this study shared the antigenic site responsible for hepatitis B core and e antigen. RESULTS: Although pre-incubation of peripheral blood mononuclear cells with hepatitis B core/e antigen followed by stimulation with phytohemagglutinin significantly reduced the production of interferon-gamma, pre-incubation with hepatitis B surface antigen did not affect them. CONCLUSIONS: These results indicate that hepatitis B core/e antigen has the ability to inhibit interferon-gamma production of lectin-stimulated peripheral blood mononuclear cells in vitro, suggesting that secretion of hepatitis B e antigen into sera might be how hepatitis B virus escapes the immuno-surveillance system of the host.

Seroprevalencia de marcadores de hepatis B y C en trabajadores del área de salud

Introducción : La vía percutánea es una de las más frecuentes y efectivas formas de contagio con los virus B y C. Por lo tanto los trabajadores del área tienen un riesgo importante de contagio. El presente estudio se realizó para evaluar la seroprevalencia de marcadores de infección con estos virus, y para medir la frecuencia

Effect of X protein on transactivation of hepatitis B virus promoters and on viral replication.

The X gene product of hepatitis B virus (HBV) transactivates a wide variety of promoters, including four promoters on the HBV genome (Rossner, 1992, J. Med. Virol. 36, 101-117). We compared their transactivation efficiencies and investigated whether the spatial organization of the promoters with respect to other cis-acting elements might influence their activities. Eight reporter plasmid constructs containing the bacterial chloramphenicol acetyltransferase (CAT) gene were designed such that four had the isolated HBV promoters linked to the CAT gene. In the other four, the CAT gene was inserted downstream to each of the four promoters retained in context in the HBV genome. Cells of the human hepatoblastoma line HepG2 were transfected with each one of these reporters together with an effector plasmid, pRSVX, which allowed expression of X protein. All of these promoters could be stimulated by X protein by approximately 2- to 3.5-fold irrespective of their spatial context in the HBV genome. Mutational analysis of in-frame ATG codons in the X gene provides evidence that transactivator product(s) are produced by internal initiation of translation. Transfection of HepG2 cells with HBV genomes bearing a stop mutation in the X gene at codon 118 resulted in poor production of all viral components. Their syntheses were restored upon transfection of the wild-type X gene.

Hepatitis B virus and hepatocellular carcinoma: a possible role for the viral transactivators.

Several epidemiological studies have demonstrated a link between chronic B virus infection and primary hepatocellular carcinoma (PHC). HBV DNA sequence integrations into the host cell genome have often been observed in hepatocarcinoma tissues. However, since only in a few cases of PHC the target of HBV-DNA insertion has been identified, alternative mechanisms for HBV-induced hepatocyte transformation have been investigated. Like many other DNA viruses, the hepatitis B virus bears a transactivational potential. Both full length and truncated versions of HBV X protein are able to influence the expression of cellular nuclear protooncogenes c-fos and c-myc. A second transcriptional activator is encoded by the PreS/S region of HBV, but its activity on viral and cellular genes become evident only after dislocations from its downstream sequences. Thus, HBV is able to influence infected cell growth and differentiation using both native proteins, newly generated truncated proteins and virus-cell fusion polypeptides.