A new HDV mouse model identifies mitochondrial antiviral signaling protein (MAVS) as a key player in IFN-β induction

BACKGROUND & AIMS

Studying hepatitis delta virus (HDV) and developing new treatments is hampered by the limited availability of small animal models. Herein, a description of a robust mouse model of HDV infection that mimics several important characteristics of the human disease is presented.

METHODS

HDV and hepatitis B virus (HBV) replication competent genomes were delivered to the mouse liver using adeno-associated viruses (AAV; AAV-HDV and AAV-HBV). Viral load, antigen expression and genomes were quantified at different time points after AAV injection. Furthermore, liver pathology, genome editing, and the activation of the innate immune response were evaluated.

RESULTS

AAV-HDV infection initiated HDV replication in mouse hepatocytes. Genome editing was confirmed by the presence of small and large HDV antigens and sequencing. Viral replication was detected for 45days, even after the AAV-HDV vector had almost disappeared. In the presence of HBV, HDV infectious particles were detected in serum. Furthermore, as observed in patients, co-infection was associated with the reduction of HBV antigen expression and the onset of liver damage that included the alteration of genes involved in the development of liver pathologies. HDV replication induced a sustained type I interferon response, which was significantly reduced in immunodeficient mice and almost absent in mitochondrial antiviral signaling protein (MAVS)-deficient mice.

CONCLUSION

The animal model described here reproduces important characteristics of human HDV infection and provides a valuable tool for characterizing the viral infection and for developing new treatments. Furthermore, MAVS was identified as a main player in HDV detection and adaptive immunity was found to be involved in the amplification of the innate immune response. Lay summary: Co-infection with hepatitis B and D virus (HBV and HDV, respectively) often causes a more severe disease condition than HBV alone. Gaining more insight into HDV and developing new treatments is hampered by limited availability of adequate immune competent small animal models and new ones are needed. Here, a mouse model of HDV infection is described, which mimics several important characteristics of the human disease, such as the initiation and maintenance of replication in murine hepatocytes, genome editing and, in the presence of HBV, generation of infectious particles. Lastly, the involvement of an adaptive immunity and the intracellular signaling molecule MAVS in mounting a strong and lasting innate response was shown. Thus, our model serves as a useful tool for the investigation of HDV biology and new treatments.

5'-triphosphate-siRNA activates RIG-I-dependent type I interferon production and enhances inhibition of hepatitis B virus replication in HepG2.2.15 cells

Hepatitis B virus (HBV) infection often results in acute or chronic viral hepatitis and other liver diseases including cirrhosis and hepatocellular carcinoma. Current therapies for HBV usually have severe side effects and can cause development of drug-resistant mutants. An alternative and safe immunotherapeutic approach for HBV infection is urgently needed for effective anti-HBV therapy. In this study, we propose a new strategy for anti-HBV therapy that activates type-I interferon (IFN) antiviral innate immunity through stimulating pattern-recognition receptors with RNA interference (RNAi) using a 5'-end triphosphate-modified small interfering RNA (3p-siRNA). We designed and generated a 3p-siRNA targeting overlapping region of S gene and P gene of the HBV genome at the 5'-end of pregenomic HBV RNA. Our results demonstrated that 3p-siRNA induced a RIG-I-dependent antiviral type-I IFN response when transfected into HepG2.2.15 cells that support HBV replication. The 3p-siRNA significantly inhibited HBsAg and HBeAg secretion from HepG2.2.15 cells in a RIG-I-dependent manner, and the antiviral effect of 3p-siRNA was superior to that of siRNA. Furthermore, 3p-siRNA had more pronounced inhibition effects on the replication of HBV DNA and the transcription of mRNA than that of siRNA. Finally, 3p-siRNA displayed antiviral activity with long-term suppression of HBV replication. In conclusion, our findings suggest that 3p-siRNA could act as a powerful bifunctional antiviral molecule with potential for developing a promising therapeutic against chronic HBV infection.

[Immunosuppressant dexamethasone can significantly extend the expression of hepatitis B virus antigens in the HBV mouse model by hydrodynamic transfection method]

To develop a HBV infection mouse model by hydrodynamic-based transfection and further to optimize the method of development of HBV infection mouse model. We first developed a construct which contained inverted terminal repeat elements (ITR) of adeno-associated virus (AAV) and 1. 3 copies of HBV genome (ayw subtype). The pAAV-HBV1. 3 DNA was then injected hydrodynamically into the tail veins of C57BL/6 mice in 5 seconds. The virus load in serum and liver was assayed by ELISA and Real-time PCR. The expression of virus antigen and the pathologic changes of liver were analyzed by HE and immunohistochemical staining. Meanwhile, to develop HBV transfected immunosuppressied mouse, mice were injected intraperitoneally triple with 0.2 ml dexamethason (50 mg/kg) every two days before HBV transfection. The levels of HBsAg and HBeAg were assayed by ELISA. Our data showed: (1) HBsAg and HBeAg were positive (100%) in serum and liver of experimental normal mouse at day 10 after HBV transfection, and became negative at day 30 and day 60. Meanwhile the viral load in serum and liver in experimental group was significantly higher than that in control group at day 10, 30 and 60 after HBV transfection (P < 0.01, P < 0.05, respectively). (2) HBsAg and HBeAg in serum in immunosuppressed mouse model were positive until 60 days. In conclusion, a HBV infection mouse model was developed successfully by hydrodynamic-based transfection. By suppressing the immune status of mice injected with dexamethasone, the expression of HBV antigens was extended longer than that in normal adult mice. These models pave a way for HBV research and evaluation of HBV vaccine and drug development.

[Recombinant adenovirus-mediated expression of 1.2-copy hepatitis B virus DNA in three hepatocytes]

OBJECTIVE

To study hepatitis B virus (HBV) expression in 3 hepatocytes infected with recombinant adenovirus containing 1.2-copy HBV DNA.a

METHODS

A chicken hepatoma cell line and two human hepatocytes were infected by the recombinant adenovirus containing 1.2-copy HBV DNA at 25 pfu/cell. HBV-specific mRNA was detected by RT-PCR 3 days after the infection, and HBsAg and HBeAg were detected by ELISA and HBV DNA by real-time PCR daily after the infection.

RESULTS

HBV mRNA expression was detected in all the 3 cells after recombinant adenovirus infection, and the quantities of HBV DNA and HBV antigens in the culture supernatant increased with the passage of time.a

CONCLUSION

Infection with the recombinant adenovirus containing 1.2-copy HBV DNA can mediate HBV infection in the 3 cells in vitro.

[A construct competent to support the replication of hepatitis B virus of genotype B]

OBJECTIVE

To construct a vector that is competent to support the replication of hepatitis B virus (HBV) of genotype B.

METHODS

The HBV genome of genotype B was amplified by PCR and ligated into pBlueskript II KS(+) vector, the resulting plasmid was verified by enzyme digestion and DNA sequencing. After transfection of this plasmid into Huh7 cells, the HBsAg and HBeAg antigens in culture medium were quantified by ELISA, the transcripts and replication intermediates of HBV were detected by northern blot and southern blot respectively. On the other hand, the plasmid was hydrodynamically injected into BALB/cJ mice via tail vein. Then the HBV DNA in serum was quantified by real-time PCR, and HBcAg expression in liver tissue was detected by immunohistochemistry.

RESULTS

After transfection of the plasmid into Huh7 cells, the HBsAg and HBeAg antigens were detected in the culture medium, the transcripts and replication intermediates of HBV were detected in the cells. High titer of HBV DNA was detected in the serum of hydrodynamic-injected mice. Immunostaining indicated that HBcAg was expressed in hepatocytes of injected mice.

CONCLUSION

This construct is competent to support the replication of hepatitis B virus of genotype B.

[Increased expression of inducible nitric oxide synthase in chronic hepatitis B patients is correlated with histopathological grading and staging]

OBJECTIVE

To investigate the intrahepatic expression of inducible nitric oxide synthase (iNOS) in patients with chronic hepatitis B (CHB) and its relation to liver histopathology.

METHODS

The intensity and distribution of the immunohistochemical staining of intrahepatic iNOS were studied in the liver biopsy specimens obtained from 74 patients with CHB and statistical analyses were performed between intrahepatic iNOS and ALT, HbeAg, HBV DNA grading of liver inflammation and staging of fibrosis. Seven histologically normal liver sections were used as a control group.

RESULTS

Compared with the control group, the intrahepatic iNOS immunoexpression was significantly higher in patients with CHB (P < 0.05), iNOS immunoreactivity was observed mainly in hepatocytes showing a predominant cytoplasmic staining, with the positive liver cells distributed diffusely throughout the hepatic lobule. Immunopositive staining could also be detected in Kupffer cells, sinusoidal lining cells and vascular endothelial cells. Compared with patients with normal ALT, the hepatocellular iNOS immunoexpression was significantly higher in patients with elevated ALT (P < 0.05) and the iNOS immunoexpression was significantly correlated with the serum level of ALT (r=0.601, P=0.000). Statistical analysis also showed that the intrahepatic iNOS immunoexpression was positively correlated with the grading of liver inflammation and the staging of liver fibrosis (r=0.660, P=0.000; r=0.507, P=0.000). No significant correlation between iNOS and HBeAg and HBV DNA was detected. CONCLUSION The intrahepatic expression of iNOS is elevated in chronic hepatitis B patients and correlated well with the severity of the disease, which indicated that inducible nitric oxide synthase may have a critical role in the pathogenesis of chronic viral hepatitis B.

[Establishing a L02 cell model with whole HBV gene transfection and analyzing its expressions of HLA-A, B, C and MICA/B]

OBJECTIVE

To establish a cell model with HBV secretion by plasmid transfection with whole HBV genes into hepatic L02 cells, and to analyze the effect of HBV on the expression of HLA-A, B, C and MICA/B in L02 cells.

METHODS

The mock control plasmid was built by digesting pEcob6 plasmid with EcoR I at the HBV DNA site and ligating the fragment without HBV DNA. The L02 cells were transfected with pEcob6 or mock plasmid and pcDNA3 1-neo by liposome. The expressions of HBsAg, HBcAg/HBeAg and HBV DNA were detected by immunofluorescence assay, Abbott enzymoimmunoassay, or FQ-PCR. The expressions of HLA-A, B, C and MICA/B were determined by FACS and the differences in the two molecules were analyzed.

RESULTS

After the transfected cells were selected by G418, the HBsAg and HBeAg in the supernatant of L02-HBV cells were 24.78(S/N) and 4.117(S/N). The quantity of HBV DNA was 9.67 x 10(4) copies/ml, but in L02-mock and in L02 cells they were all negative. Under a confocal microscope HBsAg was brightly shown in the cytoplasm while HBcAg showed dimly in the cytoplasm or in the nuclei. By using FACS, the L02 and L02-mock cells showed some low expressions of HLA-A, B, C and a little expression of MICA/B, while the expression of the two molecules was higher in L02-HBV and the differences were significant (P < 0.05).

CONCLUSION

A cell model with the expression of HBV antigens and the secretion of HBV DNA was established by pEcob6 transfection into L02 cells, the transcription or replication of HBV gene might induce stronger expressions of HLA-A, B, C and MICA/B on hepatic cells. They might be related to the immune injuries of hepatic cells.

Expression profiling reveals dysregulation of cellular cytoskeletal genes in HBx-induced hepatocarcinogenesis

The molecular mechanisms underlying hepatitis B virus encoded HBx protein-mediated tumorigenesis are not fully understood. In order to gain a better view of the effects of HBx on transcriptional regulation and hepatocarcinogenesis, the expression profiles of liver and tumor tissues from 6- and 18-month-old p21-HBx transgenic and control mice were monitored using oligo microarrays. Data analysis demonstrated that 42 genes were deregulated in both 6- and 18-month-old HBx transgenic mouse tissues. Gene ontology assisted analysis classified these genes into functionally related clusters that encode proteins related to metabolism, signal transduction, transcription regulation and stress responses. Among them, cytoskeletal genes, including microtubule genes tubulinbeta2 (Tubb2), tubulinbeta3 (Tubb3) and tubulinbeta6 (Tubb6), intermediate filament genes periplakin, keratin 8 (K8) and keratin 18 (K18) and actingamma1 (Actg1), were closely clustered and upregulated in liver tissues. These results were validated by semi-quantitative RT-PCR in both mouse and human HCC tissues. The upregulation of K8 and K18 was only detected in p21-HBx but not p21-HBsAg liver tissues, suggesting that the global change in the expression of cellular cytoskeletal genes was correlated with the expression of HBx transgene. These findings propose for the first time that systemic dysregulation of cellular cytoskeletal genes is involved in HBx-induced hepatocarcinogenesis.

[Preventive and therapeutic effects of qiongyugao on hepatocellular carcinoma via inhibition of the expression of HBxAg in hepatic carcinoma cells]

AIM

To investigate the effects of qiongyugao on the expression of hepatitis B x antigen (HBxAg) in BALB/c-nu mice into which human hepatic carcinoma cells were transplanted, and to analyze its specific mechanism in prophylaxis and treatment of hepatocellular carcinoma.

METHODS

A nude mouse model with the transplantation of human hepatic carcinoma cells was established to observe the preventive and therapeutic effects of qiongyugao on the body weight and tumor weight of the mice. The expression of HBxAg in tumor and liver tissue wsa detected by immunohistochemical studies.

RESULTS

Compared with model control group, prophylaxis and treatment with qiongyugao increased the body weight, depressed the tumor weight and inhibited HBxAg expression. The same efficacy was showed in both qiongyugao prophylaxis group and cyclophosphamide treatment group.

CONCLUSION

Qiongyugao can slow down the growth of tumor and inhibit the expression of HBxAg, which may be an essential mechanism in prophylaxis and treatment of hepatocellular carcinoma.

Mechanisms of co-modified liver-targeting liposomes as gene delivery carriers based on cellular uptake and antigens inhibition effect

In order to deliver antisense oligonucleotides (asODN) into hepatocytes orientedly in the treatment of hepatitis B virus (HBV) infection, the liver-targeting cationic liposomes was developed as a gene carrier, which was co-modified with the ligand of the asialoglycoprotein receptor (ASGPR), beta-sitosterol-beta-d-glucoside (sito-G) and the nonionic surfactant, Brij 35. Flow cytometry (FCM) analysis and enzyme-linked immunosorbent assay (ELISA) showed that the asODN-encapsulating cationic liposomes exhibited high transfection efficiency and strong antigens inhibition effect in primary rat hepatocytes and HepG2.2.15 cells, respectively. With the help of several inhibitors acting on different steps during the targeting lipofection, the cellular uptake mechanisms of the co-modified liver-targeting cationic liposomes were investigated through antigens inhibition effect assay and confocal laser scanning microscopy (CLSM) analysis. The cellular uptake with high transfection efficiency seemed to involve both endocytosis and membrane fusion. The ligand sito-G was confirmed to be able to enhance ASGPR-mediated endocytosis, the nonionic surfactant Brij 35 seemed to be able to facilitate membrane fusion, and the co-modification resulted in the most efficient transfection but no enhanced cytotoxicity. These results suggested that the co-modified liver-targeting cationic liposomes would be a specific and effective carrier to transfer asODN into hepatocytes infected with HBV orientedly.

[Transfection and anti-HBV effect mediated by the hepatocytes-targeting cationic liposomes co-modified with beta-sitosterol-beta-D-glucoside and Brij 35]

AIM

To study the transfection and anti-hepatitis B virus (HBV) effect of the co-modified hepatocytes-targeting cationic liposomes encapsulating anti-HBV antisense oligonucleotides (asON) , and to investigate the transfection mechanisms of the liposomes.

METHODS

Dipalmitoylphosphatidylcholine (DPPC) and 3beta-[N-(N',N'-dimethylaminoethane)-carbamoyl] cholesterol (DC-Chol) were used as the lipids, beta-sitosterol-beta-D-glucoside (sito-G) and Brij 35 were used to modify the liposomes. Flow cytometry (FCM), fluorescence microscopy and enzyme-linked immunosorbent assay (ELISA) were utilized to evaluate the transfection improvement of the asON encapsulated in the liposomes in primary rat hepatocytes and the antigens inhibition activity in HepG 2.2.15 cells. The transfection mechanisms were evaluated based on the influence of wortmannin, nigericin, and asialofetuin on the antigens inhibition in HepG 2.2.15 cells by ELISA.

RESULTS

The co-modification with sito-G and Brij 35 significantly improved the transfection of the liposomes in primary rat hepatocytes and antigens inhibition effect in HepG 2.2.15 cells. Both transfection efficiency and antigens inhibition effect showed to be concentration-dependent with the asON-encapsulating liposomes. In fluorescence microscopy, the transfected cells showed strong fluorescence in primary rat hepatocytes, especially in the nuclei. Wortmannin, nigericin and asialofetuin decreased the antigens inhibition of the asON-encapsulating liposomes to different levels. Cationic liposomes modification with sito-G and Brij 35 could improve the transfection and antigens inhibition effect of the asON. The transfection mechanisms of the co-modified liposomes included endocytosis and membrane fusion. The ligand sito-G was confirmed to be able to enhance asialoglycoprotein receptor (ASGPR)-mediated endocytosis.

CONCLUSION

Co-modified hepatocytes-targeting cationic liposomes would be a specific and effective carrier to transfer asON into hepatocytes.

Inhibition of hepatitis B virus expression and replication by RNA interference in HepG2.2.15

AIM: To observe the inhibition of hepatitis B virus replication and expression by transfecting vector-based small interference RNA (siRNA) pGenesil-HBV X targeting HBV X gene region into HepG2.2.15 cells.

METHODS: pGenesil-HBV X was constructed and transfected into HepG2.2.15 cells via lipofection. HBV antigen secretion was determined 24, 48, and 72 h after transfection by time-resolved immunofluorometric assays (TRFIA). HBV replication was examined by fluorescence quantitative PCR, and the expression of cytoplasmic viral proteins was determined by immunohistochemistry.

RESULTS: The secretion of HBsAg and HBeAg into the supernatant was found to be inhibited by 28.5% and 32.2% (P < 0.01), and by 38.67% (P < 0.05) and 42.86% (P < 0.01) at 48 h and 72 h after pGenesil-HBV X transfection, respectively. Immunohistochemical staining for cytoplasmic HBsAg showed a similar decline in HepG2.2.15 cells 48 h after transfection. The number of HBV genomes within culture supernatants was also significantly decreased 48 h and 72 h post-transfection as quantified by fluorescence PCR (P < 0.05).

CONCLUSION: In HepG2.2.15 cells, HBV replication and expression is inhibited by vector-based siRNA pGenesil-HBV X targeting the HBV X coding region.

Inhibition of the replication of hepatitis B virus in vitro by emodin

BACKGROUND

Emodin (1, 3, 8-trihvdroxy-6-methylanthraquinone) is derived from herbal medicines and proved to have a strong antimicrobial activity. However, its anti-virus effects are less known. The aim of the present study was to investigate the effects of emodin, interferon alpha (IFNalpha), and lamivudine (3TC) on hepatitis B virus (HBV) in vitro.

MATERIAL/METHODS

The human hepatoma G2.2.15 cell line stably expresses hepatitis B virus particles in culture. The cells were exposed to different concentrations of emodin, IFNa, and lamivudine triphosphate, respectively. MTT (methyl thiazolyl tetrazolium) assay was used to evaluate the cytotoxicity of the drugs and real-time PCR was applied to quantify extracellular HBV DNA. HIBsAg and HBeAg were assessed by enzyme-linked immurnosorbent assay (ELISA).

RESULTS

The results showed that exposure of HepG2.2.15 cells to emodin resulted in a time- and concentration-dependent inhibition of HBV DNA replication and HBsAg secretion. After exposed to three different concentrations of emodin for 3, 6, and 9 days, the inhibition rates of extracellular HBV DNA, HBsAg, and HBeAg of each concentration decreased significantly (P < 0.05). After 9 days of treatment, the inhibition rates of extracellular HBV DNA of the different concentrations differed greatly (P < 0.001). IFNalpha and 3TC had similar inhibition results to HBV DNA replication to those previously found.

CONCLUSIONS

These findings suggest that mnodin may prove to be a new modality to treat hepatitis B infection.

Hepatitis B virus is inhibited by RNA interference in cell culture and in mice

BACKGROUND AND AIMS

For chronic hepatitis B virus (HBV) infection the effects of current therapies are limited. Recently, RNA interference (RNAi) of virus-specific genes has emerged as a potential antiviral mechanism. Here we studied the effects of HBV-specific 21-bp short hairpin RNAs (shRNAs) targeted to the surface antigen (HBsAg) region and the core antigen (HBcAg) region both in a cell culture system and in a mouse model for HBV replication.

METHODS

HBsAg and hepatitis B e antigen (HBeAg) in the media of the cells and in the sera of the mice were analyzed by time-resolved immunofluorometric assay, intracellular HBcAg by immunofluorescence assay, HBsAg and HBcAg in the livers of the mice by immunohistochemical assay, HBV DNA by fluorogenic quantitative polymerase chain reaction (FQ-PCR) and HBV mRNA by semi-quantitative reverse transcriptase PCR (RT-PCR).

RESULTS

Transfection with the shRNAs induced an RNAi response. Secreted HBsAg was reduced by >80% in cell culture and >90% in mouse serum, and HBeAg was also significantly inhibited. Immunofluorescence detection of intracellular HBcAg revealed 76% reduction. In the liver tissues by immunohistochemical detection, there were no HBsAg-positive cells and >70% reduction of HBcAg-positive cells for shRNA-1. And for shRNA-2 the detection of HBsAg and HBcAg also revealed substantial reduction. The shRNAs caused a significant inhibition in the levels of viral mRNA relative to the controls. HBV DNA was reduced by >40% for shRNA-1 and >60% for shRNA-2.

CONCLUSIONS

RNAi is capable of inhibiting HBV replication and expression in vitro and in vivo and thus may constitute a new therapeutic strategy for HBV infection.

Toll-like receptor 4 plays an anti-HBV role in a murine model of acute hepatitis B virus expression

AIM: Toll-like receptor 4 (TLR4) has been shown to be important for bacterial infection, especially to lipopolysaccharide signaling. Its possible role in HBV infection is studied in the present study.

MATERIALS AND METHODS: pHBV3.6 plasmid, containing full-length HBV genome was used in the murine model of acute HBV expression by hydrodynamics in vivo transfection. TLR4 normal or mutant mouse strain was compared to investigate the possible role of TLR4 in acute HBV expression.

RESULTS: After pHBV3.6 injection, the infiltrating leukocytes expressed TLR4 were observed nearby the HBsAg-expressing hepatocytes. The HBV antigenemia as well as the replication and transcription were higher in TLR4-mutant C3H/HeJ mice than in normal C3H/HeN mice. The HBV-specific immune responses were impaired in the liver or spleen of the C3H/HeJ mice. Their inducible nitric oxide synthase (iNOS) expression on the hepatic infiltrating cells was also impaired. When adoptively transferring splenocytes from C3H/HeN mice to C3H/HeJ mice, the HBV replication was inhibited to the level as that of C3H/HeN.

CONCLUSION: These results suggest that TLR4 plays an anti-HBV role in vivo through the induction of iNOS expression and HBV-specific immune responses after HBV expression.

Hepatitis B virus DNA replication is coordinated by core protein serine phosphorylation and HBx expression

The hepatitis B virus (HBV) core protein forms the capsid of viral particles and is essential for viral genome DNA replication and maturation. The C terminus of core protein contains three serines at positions 155, 162, and 170, phosphorylation of which is important for viral DNA replication. We demonstrate that the phosphorylation of these serines is stimulated by the viral HBx protein, a regulatory protein that activates signal transduction pathways and viral replication. HBx is therefore shown to stimulate HBV replication by increasing core serine phosphorylation. Mutational, biochemical, and mixing studies of C-terminal core serine mutants demonstrate that multiple serine phosphorylations occur on the same core protein. Mutation of individual core protein serines is shown to inhibit HBV replication at distinct stages corresponding to encapsidation of viral pregenomic RNA, reverse transcription, and restriction to synthesis of specific DNA replicative intermediates. We therefore demonstrate that a primary target of HBV replication that is regulated by HBx protein corresponds to increased phosphorylation of the viral core protein. We also demonstrate that core phosphorylation mediated by HBx promotes sequential progression of viral replication through the assembly of capsids primed for different stages of DNA synthesis.

HBx protein of hepatitis B virus (HBV) can form complex with mitochondrial HSP60 and HSP70

HBx, a transcriptional transactivating protein of hepatitis B virus (HBV), is required for viral infection and has been implicated in virus-mediated liver oncogenesis. However, the molecular mechanism for its influence on cell remains largely unknown. It was proved that HBx need the help of host cell proteins to exert its function by binding to them. During purifying of GSTX (fusion protein of GST and HBx) expressed in E. coli, we found that it can bind specifically with GrpE (HSP60) and DnaK (HSP70) of E. coli while GST cannot. Using GST pull-down, two-dimensional gel electrophoresis and mass spectrum, we found that GSTX can also bind to human mitochondrial HSP60 and HSP70, which are homologues of GrpE and DnaK. These interactions between HBx and mitochondrial HSP60 and HSP70 are supported by the result of co-immunoprecipitation experiment. It means that HBx can form complex with E. coli and human HSP60 and HSP70. The implication of HBx, HSP60 and HSP70 complex in molecular mechanism of virus infection is discussed.

Human hepatitis B virus X protein promotes cell proliferation and inhibits cell apoptosis through interacting with a serine protease Hepsin

The X protein of human hepatitis B virus (HBV) acts as an indirect transcriptional transactivator to regulate the expression of many viral and cellular genes as well as playing a critical role in the development of hepatocellular carcinoma. While the biological importance of HBx has been well established, the cellular and molecular bases of its function remain largely undefined. In this study, we isolated a new HBV field strain from a patient with chronic viral infection. The X protein encoded by this virus was used as a bait protein for screening a human liver cDNA library using a yeast two-hybrid system. Several cell proteins were identified as new HBx interacting partners, including a transmembrane serine protease, Hepsin. Direct interaction between HBx and Hepsin proteins was confirmed by in vitro and in vivo co-immunoprecipitation assays. HBx also co-localized with Hepsin in human cells as determined by confocal immunofluorescence microscopy. The interaction between HBx and Hepsin protein appeared to play a role in both promoting cell proliferation and blocking apoptosis in human liver tumor cell and normal liver cell lines. In addition, the complex of HBx and Hepsin promoted the expression of HBeAg in Hep G2.2.1.5 cells indicating that the association of these two proteins stimulated viral replication.

[Effect of p16 gene on carcinogenesis of hepatitis B virus related hepatocellular carcinoma]

OBJECTIVE

To investigate the relation between p16 gene expression and the carcinogenesis and progress of hepatitis B virus (HBV) related hepatocellular carcinoma (HCC).

METHODS

In 35 specimens of HCC tissue and the adjacent liver tissue, the integration of HBV X gene was detected by polymerase chain reaction (PCR) and Southern blot. The point mutation of exon-1alpha, 2 and 3 of p16 gene were detected by PCR-single strand conformation polymorphism (SSCP). The expression of p16 mRNA and p16 protein was detected by RT-PCR and Western blot.

RESULTS

The integration of X gene correlated with the expression loss of p16 mRNA and p16 protein in HCC (P < 0.05). The expression loss rates of p16 protein in HCC and adjacent tissues were 62.9% (22/35) and 40.0% (14/35) with significant difference (P < 0.05). The expression loss of p16 protein in HCC correlated with the differentiation degrees of HCC and the infiltration of tumor cells (P < 0.05).

CONCLUSION

The integration of X gene correlates with the expression loss of p16 protein. The alteration of p16 gene, playing an important role in all stages of hepatocarcinogenesis, correlates with the progress and invasion of hepatocellular carcinoma.

A plant signal peptide-hepatitis B surface antigen fusion protein with enhanced stability and immunogenicity expressed in plant cells

The use of transgenic plants to express orally immunogenic protein antigens is an emerging strategy for vaccine biomanufacturing and delivery. This concept has particular suitability for developing countries. One factor that has limited the development of this technology is the relatively modest levels of accumulation of some antigenic proteins in plant tissues. We used fusion protein design to improve expression of the hepatitis B surface antigen (HBsAg) by attempting to mimic the process of HBsAg targeting to the endoplasmic reticulum of human liver cells during hepatitis B virus infection. We created a gene encoding a recombinant HBsAg modified to contain a plant signal peptide fused to its amino terminus. The signal peptide from soybean vegetative storage protein vspA (VSP alpha S) directed endoplasmic reticulum targeting of HBsAg in plant cells, but was not cleaved and resulted in enhanced VSP alpha S-HBsAg fusion accumulation. This product was more stable and presented the protective "a" antigenic determinant to significantly higher levels than unmodified native HBsAg expressed in plant cells. It also showed a greater extent of intermolecular disulfide bond formation and formation of virus-like particles. Moreover, VSP alpha S-HBsAg stimulated higher levels of serum IgG than native HBsAg when injected into mice. We conclude that HBsAg tolerates a polypeptide fusion at the amino terminus and that VSP alpha S-HBsAg is an improved antigen for plant-based expression of a subunit vaccine for hepatitis B virus.

Changes in serum and histology of patients with chronic hepatitis B after interferon alpha-2b treatment

AIM: Chronic hepatitis B is a serious health problem. Interferon has long been used to treat Chronic hepatitis B. To evaluate the effects of interferon on chronic hepatitis B better, we designed the study to investigate the changes in sera and liver histology of patients with chronic hepatitis B after interferon alpha-2b treatment.

METHODS: Twenty-four patients with chronic hepatitis B were enrolled in this study. They all received interferon alpha-2b treatment as following: 3 million units, i.m. t.i.w., for 18 weeks. Sera of all patients were obtained respectively for evaluation of ALT, HBsAg, HBcAg, HBeAg, HBV DNA and TIMP-1 before and after interferon treatment, also a liver biopsy pre- and post-treatment was performed for comparison of HAI, HBsAg, HBcAg, HBeAg, TIMP-1 and activated HSC in the liver tissue.

RESULTS: Patients who had normalization of serum ALT and seroconversion of HBeAg and/or HBV DNA (blot hybridization) after treatment were defined as responders. The response rate in this study group was 37.5% (7/24). Compared to pretreatment, the serum HBV DNA and TIMP-1 decreased significantly (P < 0.05), so did the HAI, HBcAg, HBeAg, TIMP-1 and activated HSC (P < 0.05).

CONCLUSION: The significant decrease in HBV DNA in sera, the seroconversion of HBeAg, and the decrease of viral expression in liver indicated that interferon alpha-2b treatment can inhibit viral replication. The normalization of ALT in sera and the improvement of HAI in liver showed that interferon alpha-2b can improve the liver histology of patients with chronic hepatitis B. At the same time, interferon alpha-2b treatment can reduce the TIMP-1 in serum and liver and decrease the number of activated HSC, which may allievate or inhibit hepatic fibrosis. Although the response rate was unsatisfactory, interferon play a benefical role on patients with chronic hepatitis B in other respects. We still need further studies to improve the therapy effects.

Expression of hepatitis B virus X protein in transgenic mice

AIM: To establish a mice model harboring hepatitis B virus x gene (adr subtype) for studying the function of hepatitis B virus X protein, a transactivator of viral and cellular promoter/enhancer elements.

METHODS: Expression vector pcDNA3-HBx, containing CMV promoter and hepatitis B virus x gene open reading fragment, was constructed by recombination DNA technique. Hela cells were cultured in DMEM and transfected with pcDNA3-HBx or control pcDNA3 plasmids using FuGENE6 Transfection Reagent. Expression of pcDNA3-HBx vectors in the transfected Hela cells was confirmed by Western blotting. After restriction endonuclease digestion, the coding elements were microinjected into male pronuclei of mice zygotes. The pups were evaluated by multiplex polymerase chain reaction (PCR) at genomic DNA level. The x gene transgenic mice founders were confirmed at protein level by Western blotting, immunohistochemistry and immunogold transmission electron microscopy.

RESULTS: Expression vector pcDNA3-HBx was constructed by recombination DNA technique and identified right by restriction endonuclease digestion and DNA direct sequencing. With Western blotting, hepatitis X protein was detected in Hela cells transfected with pcDNA3-HBx plasmids, suggesting pcDNA3-HBx plasmids could express in eukaryotic cells. Following microinjection of coding sequence of pcDNA3-HBx, the embryos were transferred to oviducts of psedopregnant females. Four pups were born and survived. Two of them were verified to have the HBx gene integrated in their genomic DNA by multiplex PCR assay, and named C57-TgN (HBx)S MMU1 and C57-TgN (HB x) SMMU3 respectively. They expressed 17KD X protein in liver tissue by Western blotting assay. With the immunohistochemistry, X protein was detected mainly in hepatocytes cytoplasm of transgenic mice, which was furthermore confirmed by immunogold transmission electon microscopy.

CONCLUSION: We have constructed the expression vector pcDNA3-HBx that can be used to study the function of HBx gene in eukaryotic cells in vitro. We also established HBx gene (adr subtype) transgenic mice named C57-TgN (HBx) SMMU harboring HBx gene in their genome and express X protein in hepatocytes, Which might be a valuable animal system for studying the roles of HBx gene in hepatitis B virus life cycle and development of hepatocellular carcinoma in vivo.

Mechanisms for inhibition of hepatitis B virus gene expression and replication by hepatitis C virus core protein

We have demonstrated previously that the core protein of hepatitis C virus (HCV) exhibits suppression activity on gene expression and replication of hepatitis B virus (HBV). Here we further elucidated the suppression mechanism of HCV core protein. We demonstrated that HCV core protein retained the inhibitory effect on HBV gene expression and replication when expressed as part of the full length of HCV polyprotein. Based on the substitution mutational analysis, our results suggested that mutation introduced into the bipartite nuclear localization signal of the HCV core protein resulted in the cytoplasmic localization of core protein but did not affect its suppression ability on HBV gene expression. Mutational studies also indicated that almost all dibasic residue mutations within the N-terminal 101-amino acid segment of the HCV core protein (except Arg(39)-Arg(40)) impaired the suppression activity on HBV replication but not HBV gene expression. The integrity of Arg residues at positions 101, 113, 114, and 115 was found to be essential for both suppressive effects, whereas the Arg residue at position 104 was important only in the suppression of HBV gene expression. Moreover, our results indicated that the suppression on HBV gene expression was mediated through the direct interaction of HCV core protein with the trans-activator HBx protein, whereas the suppression of HBV replication involved the complex formation between HBV polymerase (pol) and the HCV core protein, resulting in the structural incompetence for the HBV pol to bind the package signal and consequently abolished the formation of the HBV virion. Altogether, this study suggests that these two suppression effects on HBV elicited by the HCV core protein likely depend on different structural context but not on nuclear localization of the core protein, and the two effects can be decoupled as revealed by its differential targets (HBx or HBV pol) on these two processes of the HBV life cycle.

The hepatitis B virus X protein promotes tumor cell invasion by inducing membrane-type matrix metalloproteinase-1 and cyclooxygenase-2 expression

Hepatocellular carcinoma is strongly associated with chronic infection by the hepatitis B virus (HBV) and has poor prognosis due to intrahepatic metastasis. HBx is often the only HBV protein detected in hepatic tumor cells; however, its contribution to tumor invasion and metastasis has not been established so far. In this work, we show that HBx enhances tumor cell invasion, both in vivo and in vitro. The increased invasive capacity induced by HBx is mediated by an upregulation of membrane-type 1 matrix metalloproteinase (MT1-MMP) expression, which in turn activates matrix metalloproteinase-2. Induction of both MT1-MMP expression and cell invasion by HBx is dependent on cyclooxygenase-2 (COX-2) activity. In addition, HBx upregulates the expression of COX-2, which is mediated by the transcriptional activation of the COX-2 gene promoter in a nuclear factor of activated T cell-dependent (NF-AT-dependent) manner. These results demonstrate the ability of HBx to promote tumor cell invasion by a mechanism involving the upregulation of MT1-MMP and COX-2 and provide new insights into the mechanism of action of this viral protein and its involvement in tumor metastasis and recurrence of hepatocellular carcinoma.

Hepatitis B virus X protein associated with UV-DDB1 induces cell death in the nucleus and is functionally antagonized by UV-DDB2

The hepatitis B virus X protein (HBx) is essential for viral infection and strongly interferes with cell growth and viability in culture. These activities involve interaction of HBx with the DDB1 subunit of UV-damaged DNA-binding factor UV-DDB. UV-DDB consists of DDB1 and a DDB2 subunit that mediates nuclear import and has recognized functions in DNA repair and E2F1-mediated transcription. Here we show that HBx retains DDB1-binding-dependent cytotoxic activities when engineered to accumulate in the nucleus but not when excluded from the nucleus. Nuclear localization of HBx does not require binding to DDB1 and remains unaffected by ectopically expressed UV-DDB subunits, indicating that HBx reaches the nuclear compartment independently of UV-DDB. Unexpectedly, HBx appears to largely exist in association with DDB1 and is in direct competition with DDB2 for binding to DDB1. Hence, HBx-mediated cell death can be relieved by increased levels of DDB2, an effect that is not observed with a naturally occurring mutant of DDB2 that lacks DDB1-binding activity. These findings indicate that HBx acts through a pathway that involves a DDB2-independent nuclear function of DDB1 and that this activity will depend on the relative concentration of DDB1 and DDB2 in cells.

NF-kappaB activation by hepatitis B virus X (HBx) protein shifts the cellular fate toward survival

In this paper, we examined the cellular effect of hepatitits B virus X (HBx) in ChangX-34 cells, inducible HBx-expressing cells. High expression of HBx protein in ChangX-34 cells resulted in approximately three-fold increase in DNA synthesis and did not show apoptotic changes. Expression of HBx in these cells was accompanied by the NF-kappaB-mediated transcription. Interestingly, inhibition of NF-kappaB activity either by treatment with sulfasalazine, a specific inhibitor of NF-kappaB, or by expressing IkappaBalpha super-repressor significantly increased cell death in ChangX-34 cells but had no influence on parental Chang cells. Thus, the activation of NF-kappaB in HBx-expressing cells may play a critical role in shifting the balance toward cell survival.

Clinicopathological significance of loss of heterozygosity on chromosome 13q in hepatocellular carcinoma

PURPOSE

Allelic loss is the most frequently genetic alteration found in hepatocellular carcinoma (HCC). Previous genome-wide studies have indicated that chromosome 13q is one of the most frequently affected chromosomes. However, reports on detailed deletion mapping as well as detailed clinicopathological correlation are scanty.

EXPERIMENTAL DESIGN

We performed high-density allelotyping on chromosome 13q in HCC from 60 patients and investigated the correlation between allelic losses on chromosome 13q and the clinicopathological features.

RESULTS

Allelic loss at one or more of the 29 microsatellite markers was found in 28 (47%) of the 60 HCCs. Allelic losses were more frequently found in tumors with larger size or in tumors at more advanced tumor stages (P = 0.015 and 0.012, respectively). These two clinicopathological features were also significantly associated with the accumulation of allelic losses in terms of fractional allelic loss index (P = 0.028 and 0.018, respectively). In addition, subchromosomal regions located at 13q12.3-14.1 and 13q32 were found to be significantly associated with advanced tumor stages and larger tumor size, respectively (P = 0.008 and 0.007).

CONCLUSIONS

The overall findings suggested that allelic losses on 13q might play an important role in contributing to a more aggressive tumor behavior. Putative tumor suppressor genes might be harbored at 13q12.3-14.1 and 13q32, and inactivation of these genes via allelic losses might enhance tumor progression in HCC.

Expression of p57(KIP2) in hepatocellular carcinoma: relationship between tumor differentiation and patient survival

Cyclins, cyclin-dependent kinases (CDK), and CDK inhibitors (CKI) are frequently altered in neoplasm. p57(KIP2) is a member of the KIP (kinase inhibitory protein) family of CKI and is a potential tumor suppressor gene. p27(KIP1) is the most extensively studied KIP family member with respect to the clinical significance in human neoplasms. However, the clinical significance of p57(KIP2) expression in patients with human cancers, including hepatocellular carcinoma (HCC), remains unknown. This study examined whether p57(KIP2) expression has any impact on clinical behavior of HCC including prognosis. We examined an expression of p57(KIP2) by immunohistochemistry in 101 cases of various liver diseases, including 59 HCC. The p57(KIP2) expression in HCC was analyzed in association with the pathohistologic stage, differentiation, proliferating cell nuclear antigen (PCNA) expression status and several histopathologic factors of possible prognostic value, and patient survival. Immunohistochemical analysis revealed the frequent loss of p57(KIP2) in HCC, especially in moderately and poorly differentiated HCC. By Kaplan-Meier analysis, overall survival was significantly correlated with p57(KIP2) expression and PCNA, and multivariate analysis showed p57(KIP2) was an independent prognostic factor. When the status of p57(KIP2) and PCNA were combined, cases positive for p57(KIP2) and with a low expression of PCNA had a significantly better prognosis than those negative for p57KIP2 and/or with a high expression of PCNA. These data indicate that loss of p57(KIP2) is a frequent event in HCC, especially in poorly differentiated HCC, suggesting that p57(KIP2) might play a role in the differentiation of HCC. In addition, p57(KIP2) expression status is an independent prognostic factor for patients with HCC, and the loss of p57(KIP2) is correlated with poor prognosis. New therapeutic options might be provided by the combination of the loss of p57(KIP2) and expression of PCNA.

Identification of hepatitis B virus-specific CTL epitopes presented by HLA-A*2402, the most common HLA class I allele in East Asia

BACKGROUND/AIMS

The aim of this study was to identify and characterize hepatitis B virus (HBV)-specific cytotoxic T lymphocytes (CTL) epitopes presented by human leukocyte antigen (HLA)-A*2402, most common HLA class I allele in East Asia.

METHODS

HLA-A*2402-restricted CTL epitopes were identified by reverse immunogenetics. Immunogenecity of these epitopes was investigated using peripheral blood mononuclear cell (PBMC) from HLA-A24+ patients with acute hepatitis B.

RESULTS

An HLA-A*2402 stabilization assay demonstrated that 36 of 63 HBV peptides carrying HLA-A*2402 anchor residues have high- and medium-HLA-A*2402 binding affinity. Two (C117-125 and P756-764) of the 36 peptides induced peptide-specific CTLs. CTL clones and lines specific for these peptides killed HBV recombinant vaccinia virus-infected target cells expressing HLA-A*2402, indicating that these two peptides are CTL epitopes presented by HLA-A*2402. These two peptides were able to induce specific CTLs in 7 and 11 of 12 HLA-A24+ patients with acute hepatitis B, respectively.

CONCLUSIONS

We identified two immunodominant CTL epitopes restricted by HLA-A*2402. Because HLA-A*2402 is the most common allele in East Asia, a region in which there are approximately 200 million HBV carriers, these epitopes will be useful for analysis of CTL responses in patients from East Asia.

A novel cytotoxic T-cell epitope presented by HLA-A24 molecule in hepatitis C virus infection

BACKGROUND/AIMS

It has been suggested that cytotoxic T lymphocytes (CTL) have crucial roles for the hepatocellular damage in hepatitis C virus (HCV) infection. A series of CTL epitopes located in the HCV protein have been identified. However, no CTL epitopes restricted by HLA-A24, a common HLA allele in humans, has been identified.

METHODS

Peripheral blood and liver infiltrating mononuclear cells from the patients with hepatitis C virus infection and healthy controls were stimulated with a series of peptides containing HLA-A24 binding motifs located in HCV protein.

RESULTS

An immunodominant HLA-A24 restricted CTL epitope (A24-4; AYSQQTRGL, amino acids 1031-1039) presented by HLA-A24 molecule was identified using a series of synthetic peptides containing the HLA-A24 binding motifs. The CTL activity against this peptide was induced both in peripheral blood and liver infiltrating mononuclear cells from HLA-A24-positive chronic hepatitis C patients, not from HLA-A24-negative patients and HLA-A24-positive healthy controls. CTL activity was blocked by anti-HLA-A24 and anti-CD8 antibodies, not by anti-CD4 antibody. Furthermore, the A24-4-specific CTL recognized the HCV gene transfected target cells.

CONCLUSIONS

Because this peptide is presented by a common HLA class I molecule, it might be useful for protection against hepatocellular damage and vaccine development in large population of the HCV-infected patients.

The hepatitis B virus-X protein activates a phosphatidylinositol 3-kinase-dependent survival signaling cascade

The hepatitis B virus-X (HBx) protein is known as a multifunctional protein that not only coactivates transcription of viral and cellular genes but coordinates the balance between proliferation and programmed cell death, by inducing or blocking apoptosis. In this study the role of the HBx protein in activation of phosphatidylinositol 3-kinase (PI3K) was investigated as a possible cause of anti-apoptosis in liver cells. HBx relieved serum deprivation-induced and pro-apoptic stimuli-induced apoptosis in Chang liver (CHL) cells. Treatment with 1-d-3-deoxy-3-fluoro-myo-inositol, an antagonist to PI3K, which blocks the formation of 3'-phosphorylated phosphatidyl inositol in CHL cells transformed by HBx (CHL-X) but not normal Chang liver (CHL) cells, showed a marked loss of viability with evidence of apoptosis. Similarly, treatment with wortmannin, an inhibitor of PI3K, stimulated apoptosis in HBx-transformed CHL cells but not in normal cells, confirming that HBx blocks apoptosis through the PI3K pathway. The serine 47 threonine kinase, Akt, one of the downstream effectors of PI3K-dependent survival signaling was 2-fold higher in HBx-transformed CHL (CHL-X) cells than CHL cells. Phosphorylation of Akt at serine 473 and Bad at serine 136 were induced by HBx, which were specifically blocked by wortmannin and dominant negative mutants of Akt and Bad, respectively. We also demonstrated that HBx inhibits caspase 3 activity and HBx down-regulation of caspase 3 activity was blocked by the PI3K inhibitor. Regions required for PI3K phosphorylation on the HBx protein overlap with the known transactivation domains. HBx blocks apoptosis induced by serum withdrawal in CHL cells in a p53-independent manner. The results indicate that, unlike other DNA tumor viruses that block apoptosis by inactivating p53, the hepatitis B virus achieves protection from apoptotic death through a HBx-PI3K-Akt-Bad pathway and by inactivating caspase 3 activity that is at least partially p53-independent in liver cells. Moreover, these data suggest that modulation of the PI3K activity may represent a potential therapeutic strategy to counteract the occurrence of apoptosis in human hepatocellular carcinoma.

Expression of deletion mutants of the hepatitis B virus protein HBx in E. coli and characterization of their RNA binding activities

The hepatitis B virus protein HBx has been implicated in the development of liver cancer. It has been shown that the HBx protein is able to bind to single-stranded DNA in a specific manner. This DNA binding activity might be relevant for HBx oncogene character. To study the HBx interaction with nucleic acids in more detail we expressed full-length HBx as well as several N- and C-terminally truncated HBx proteins as 6xHis and GST-fusions in E. coli. Using a gel shift assay, we were able to demonstrate that all of the truncated HBx proteins have the ability to bind to an AU-rich RNA. The affinity of GST-HBx #3 (residues 80-142) was an order of magnitude higher than that of GST-HBx #2 (residues 5-79), indicating that a high affinity RNA binding site is located in HBx C-terminal half. AUF1 is the protein ligand that binds to AU-rich RNA regions present in certain proto-oncogene mRNAs and causes their rapid degradation. By a competitive binding experiment of AUF1 and HBx to the AU-rich RNA oligonucleotide, we show that HBx is able to displace AUF1 from its binding site on the RNA oligonucleotide. This new aspect of HBx function is discussed in the context of cellular transformation.

Chemotherapeutic drug, adriamycin, restores the function of p53 protein in hepatitis B virus X (HBx) protein-expressing liver cells

Hepatitis B virus X (HBx) protein implicated in the development of liver cancer may inhibit the function of p53 tumor suppressor protein through cytoplasmic retention of p53 protein. Here, we attempt to investigate whether the functional inhibition of p53 protein by HBx protein is reversible. First, we provide the evidence for the association of endogenous p53 protein with HBx by co-immunoprecipitation in stable Chang cells that express HBx protein in an inducible manner (ChangX-34). By immunofluorescence microscopy, the major location of p53 protein of ChangX-34 cells was confirmed at the nuclear periphery as well as in the cytoplasm where HBx protein is mainly expressed. Surprisingly, anticancer drug, adriamycin induces the nuclear translocation of p53 protein sequestered in the cytoplasm. This change is accompanied by the restoration of p53 activity, which results in increased transcriptional activity at the p53-responsive DNA elements as well as increase of p21WAF1 mRNA expression. Further, we observed the induction of cell death and G1 arrest in these cells upon adriamycin treatment regardless of HBx expression. Together, we demonstrate that functional inhibition of p53 protein through its cytoplasmic retention by HBx protein is reversible. These results may be extended into other tumors of which p53 activity is modulated by viral oncoproteins.

Activation of the insulin-like growth factor II transcription by aflatoxin B1 induced p53 mutant 249 is caused by activation of transcription complexes; implications for a gain-of-function during the formation of hepatocellular carcinoma

Aflatoxin B1 (AFB1) induced mutation of the p53 gene at codon 249 (p53mt249) is critical during the formation of hepatocellular carcinoma (HCC) following hepatitis B virus (HBV) infection. p53mt249 markedly increases insulin-like growth factor II (IGF-II) transcription largely from promoter 4, accumulating the fetal form of IGF-II. Modulation of the transcription factor binding to IGF-II P4 by wild-type p53 and p53mt249 was identified. Wild-type p53 inhibited binding of transcription factors Sp1 and TBP on the P4 promoter, while p53mt249 enhanced the formation of transcriptional complexes through enhanced DNA-protein (Sp1 or TBP) and protein-protein (Sp1 and TBP) interactions. p53mt249 stimulates transcription factor Sp1 phosphorylation which might be a cause of increased transcription factor binding on the P4 promoter while wild-type p53 does not. Transfection of hepatocytes with p53mt249 impaired induction of apoptosis by the HBV-X protein and TNF-alpha. Therefore, the blocking of apoptosis through enhanced production of IGF-II should provide a favorable opportunity for the selection of transformed hepatocytes. These results explain the molecular basis for the genesis of HCC by p53mt249 which was found to be induced by a potent mutagen, AFB1.

Structural and functional characterization of interaction between hepatitis B virus X protein and the proteasome complex

Hepatitis B virus (HBV) has a unique fourth open reading frame coding for a 16.5-kDa protein known as hepatitis B virus X protein (HBX). The importance of HBX in the life cycle of HBV has been well established, but the underlying molecular function of HBX remains controversial. We previously identified a proteasome subunit PSMA7 that interacts specifically with HBX in the Saccharomyces cerevisiae two-hybrid system. Here we demonstrate that PSMC1, an ATPase-like subunit of the 19 S proteasome component, also interacts with HBX and PSMA7. Analysis of the interacting domains among PSMA7, PSMC1, and HBX by deletion and site-directed mutagenesis suggested a mutually competitive structural relationship among these polypeptides. The competitive nature of these interactions is further demonstrated using a modified yeast two-hybrid dissociator system. The crucial HBX sequences involved in interaction with PSMA7 and PSMC1 are important for its function as a transcriptional coactivator. HBX, while functioning as a coactivator of AP-1 and acidic activator VP-16 in mammalian cells, had no effect on the transactivation function of their functional orthologs GCN4 and Gal4 in yeast. Overexpression of PSMC1 seemed to suppress the expression of various reporters in mammalian cells; this effect, however, was overcome by coexpression of HBX. In addition, HBX expression inhibited the cellular turnover of c-Jun and ubiquitin-Arg-beta-galactosidase, two well known substrates of the ubiquitin-proteasome pathway. Thus, interaction of HBX with the proteasome complex in metazoan cells may underlie the functional basis of proteasome as a cellular target of HBX.

Epstein-Barr virus encoded nuclear protein EBNA-3 binds XAP-2, a protein associated with Hepatitis B virus X antigen

EBNA-3 (also called EBNA-3A) is one of the EBV encoded nuclear antigens that are necessary for B-cell transformation. EBNA-3 is known to target RBPs, nuclear proteins that also interacts with EBNA-2, EBNA-4 and EBNA-6. In order to identify additional EBNA-3 targets, an EBV-transformed human lymphocyte cDNA library was screened in the yeast two-hybrid system with N-terminus truncated EBNA-3 that cannot interact with RBP-Jkappa. A clone, encoding Xap-2 protein, a cellular partner of Hepatitis B virus X-antigen was isolated. This protein is also known as the p38 subunit of the aryl hydrocarbon receptor complex (ARA9). The specific binding to EBNA-3 was confirmed by showing that the GST-Xap-2 precipitated EBNA-3 from CV1 cells that were infected with recombinant vaccinia virus expressing EBNA-3. Deletion of the C-terminus of Xap-2 eliminated the binding. Fusion with green fluorescent protein showed that Xap-2 is preferentially cytoplasmic but translocates to the nucleus upon expression of EBNA-3.

Galectin-3 expression is induced in cirrhotic liver and hepatocellular carcinoma

Galectins are a family of beta-galactoside-binding animal lectins. In particular, a widely studied member galectin-3, previously designated as epsilonBP, CBP35, Mac-2, L-29 and L-34, has been associated with assorted processes such as cell growth, tumor transformation and metastasis. Galectin-3 is expressed in various tissues and organs but is significantly absent in normal hepatocytes. However, evaluation of patient liver biopsies for galectin-3 expression resulted in the finding that hepatocellular carcinoma (HCC) frequently expressed significant levels of this lectin (76% immunohistochemically positive). Further investigation revealed that galectin-3 expression in HCC is independent of whether the patient had prior hepatitis B virus infection: 14 of 18 HCC cases from HBV- patients, and 5 of 7 cases from HBV patients demonstrated positive galectin-3 immunohistochemistry. However, co-transfection studies using a galectin-3 promoter construct and an HBV-X protein (HBV-X) expression vector demonstrated that galectin-3 expression can occur through transactivation of the lectin promoter by HBV-X. Based on presently known properties of this lectin, it is possible that deregulated expression of galectin-3 can result in tumor transformation and invasiveness, or confer propensity for tumor cell survival. In addition, galectin-3 was abundantly expressed in cirrhotic liver in peripheral distribution within regenerating nodules. Such galectin-3 expression in rapidly proliferating hepatocytes in cirrhotic liver may be a result of the high mitotic index. Alternatively, it is possible that proliferating cells expressing galectin-3 are in the process of being transformed, thus indicating an early neoplastic event.

Galectin-3 expression is induced in cirrhotic liver and hepatocellular carcinoma

Galectins are a family of beta-galactoside-binding animal lectins. In particular, a widely studied member galectin-3, previously designated as epsilonBP, CBP35, Mac-2, L-29 and L-34, has been associated with assorted processes such as cell growth, tumor transformation and metastasis. Galectin-3 is expressed in various tissues and organs but is significantly absent in normal hepatocytes. However, evaluation of patient liver biopsies for galectin-3 expression resulted in the finding that hepatocellular carcinoma (HCC) frequently expressed significant levels of this lectin (76% immunohistochemically positive). Further investigation revealed that galectin-3 expression in HCC is independent of whether the patient had prior hepatitis B virus infection: 14 of 18 HCC cases from HBV- patients, and 5 of 7 cases from HBV patients demonstrated positive galectin-3 immunohistochemistry. However, co-transfection studies using a galectin-3 promoter construct and an HBV-X protein (HBV-X) expression vector demonstrated that galectin-3 expression can occur through transactivation of the lectin promoter by HBV-X. Based on presently known properties of this lectin, it is possible that deregulated expression of galectin-3 can result in tumor transformation and invasiveness, or confer propensity for tumor cell survival. In addition, galectin-3 was abundantly expressed in cirrhotic liver in peripheral distribution within regenerating nodules. Such galectin-3 expression in rapidly proliferating hepatocytes in cirrhotic liver may be a result of the high mitotic index. Alternatively, it is possible that proliferating cells expressing galectin-3 are in the process of being transformed, thus indicating an early neoplastic event.

The hepatitis B pX protein promotes dimerization and DNA binding of cellular basic region/leucine zipper proteins by targeting the conserved basic region

The hepatitis B virus pX protein is a potent transcriptional activator of viral and cellular genes whose mechanism of action is poorly understood. Here we show that pX dramatically stimulates in vitro DNA binding of a variety of cellular proteins that contain basic region/leucine zipper (bZIP) DNA binding domains. The basis for increased DNA binding is a direct interaction between pX and the conserved bZIP basic region, which promotes bZIP dimerization and the increased concentration of the bZIP homodimer then drives the DNA binding reaction. Unexpectedly, we found that the DNA binding specificity of various pX-bZIP complexes differs from one another and from that of the bZIP itself. Thus, through recognition of the conserved basic region, pX promotes dimerization, increases DNA binding, and alters DNA recognition. These properties of pX are remarkably similar to those of the human T-cell lymphotrophic virus type I Tax protein. Although Tax and pX are not homologous, we show that the regions of the two proteins that stimulate bZIP binding contain apparent metal binding sites. Finally, consistent with this in vitro activity, we provide evidence that both Tax and pX activate transcription in vivo, at least in part, by facilitating occupancy of bZIPs on target promoters.

The proapoptotic effect of hepatitis B virus HBx protein correlates with its transactivation activity in stably transfected cell lines

The role of hepatitis B virus HBx protein in the carcinogenesis associated with chronic viral infection remains ill-defined. Indeed, pleiotropic effects have been ascribed to HBx: in addition to its well-documented ability to indirectly stimulate transcription, the protein has been reported to affect cell growth, signal transduction, DNA repair and apoptosis. In this work, we generated Chang (CCL-13)-derived cell lines constitutively expressing wild type or mutant HBx, as a model of HBx-host cell interaction closer to the chronic infection setting, than the classically used transient expression systems. We document the potentiation by HBx of the apoptotic cell death pathway in the recipient cells. This effect is unlikely to rely on p53 activity since the protein is functionally inactivated in CCL-13. In addition, antioxidants and cyclosporin A failed to reduce the apoptotic response back to the normal level, suggesting that production of reactive oxygen species and calcineurin activation are not directly involved in the proapoptotic effect of HBx. In contrast, our data show that transactivation and stimulation of apoptosis are tightly linked HBx activities. Finally, expression of transactivation-active protein did not result in detectable change in the pattern of MAP kinases phosphorylation nor did it affect the ability of the host cell to repair in vitro irradiated plasmid DNA.

Human hepatitis B virus X protein augments the DNA binding of nuclear factor for IL-6 through its basic-leucine zipper domain

The X gene product of human hepatitis B virus, HBx, transactivates the expression of viral and cellular genes through a wide variety of cis elements, including the nuclear factor for IL-6 (NF-IL6) binding sites, although HBx does not appear to bind DNA directly. We previously reported that HBx transactivated the interleukin 8 promoter through NF-kappaB binding site and C/EBP-like binding site (NF-IL6 binding site). In this study, the interactions were examined between NF-IL6 and HBx using recombinant proteins. In a DNA-protein binding assay, the formation of a specific complex between NF-IL6 and a DNA probe harboring an NF-IL6 binding site was increased by the addition of either the full or the C-terminal 104 amino acids of HBx. A direct protein-protein binding assay (far-Western blot) revealed the direct interaction between the C-terminal 104 amino acids of HBx and the basic region-leucine zipper domain of NF-IL6. These results indicate that HBx alters the DNA-binding affinity of NF-IL6 through the direct interaction between the C-terminal domain of HBx and the basic region-leucine zipper domain of NF-IL6.

Hepatitis B x antigen and p53 in the development of hepatocellular carcinoma

Hepatitis B virus (HBV) is one of the major etiological agents responsible for the appearance of chronic liver diseases, including hepatocellular carcinoma (HCC). There is increasing evidence that the HBV excoded x antigen (HBxAg) is involved in one or more steps that contribute to multistep hepatocarcinogenesis. Recent work has now defined one of these steps as the physical binding and functional inactivation of the tumor suppressor protein, p53, by HBxAg. The centrality of p53 to genomic stability, cell cycle arrest, induction of apoptosis, and in senescence related pathways, suggests that its disruption by HBxAg will result in genomic instability, loss of cell cycle control, a lower apoptotic rate, and an extension in the life span of HBV-infected cells. It is proposed that HBxAg/p53 complex formation represents one of several steps whereby HBV contributes to the development of HCC.

Interaction of hepatitis B viral X protein and CCAAT/ enhancer-binding protein alpha synergistically activates the hepatitis B viral enhancer II/pregenomic promoter

The hepatitis B viral X protein (HBx) is known to exert its transactivation activity by the interaction with several cellular transcription factors. Here we report the interaction of HBx and CCAAT/enhancer-binding protein alpha (C/EBPalpha) and their effects on the enhancer/promoters of hepatitis B virus (HBV). A chloramphenicol acetyltransferase assay showed that the cotransfection of HBx and C/EBPalpha strongly activated the enhancer II/pregenomic promoter of HBV in a synergistic manner. This effect was also observed in the heterologous expression system with promoters of SV40 and herpes simplex virus thymidine kinase genes. Serial deletion analysis of the enhancer II/pregenomic promoter identified the responsible region (nucleotides 1639-1679), in which two C/EBP-binding sites are located. An in vitro interaction assay and electrophoretic mobility shift assay showed that HBx augmented the DNA binding activity of C/EBPalpha by direct interaction with it, and its basic leucine zipper domain was responsible for the interaction with HBx. Domain analysis of HBx showed that the central region (amino acids 78-103) was necessary for direct interaction with C/EBPalpha. However, the complete form of HBx was necessary for the synergistic activation of the HBV pregenomic promoter. These results suggest that the interaction of HBx and C/EBPalpha enhances the transcription of the HBV pregenomic promoter for the effective life cycle of HBV in hepatocytes.

Compensatory apoptosis in preneoplastic liver of a transgenic mouse model for viral hepatocarcinogenesis

The HBx protein of hepatitis B virus has been shown to induce hepatocellular carcinoma in transgenic mice as direct evidence for its involvement in hepatocarcinogenesis. In these transgenic mice, however, it is not clear why hepatocytes do not acquire a neoplastic phenotype by 13 months old despite the continuous growth stimulation by the HBx protein from 2 months old. In this study, we show that the accelerated proliferation of hepatocytes is counterbalanced by apoptosis, which maintains liver homeostasis. A decrease in the extent of apoptosis seems to precede the emergence of neoplasia in the transgenic mouse liver. The disappearance or block of apoptotic signals, which may be the result of additional genetic or epigenetic aberrations, may result in the preneoplastic hepatocytes becoming neoplastic.

Cloning, bacterial synthesis, and characterization of immunoglobulin variable regions of a monoclonal antibody specific for the hepatitis B virus X protein

The nucleotide (nt) sequences encoding the variable regions of the heavy (H) and light (L) chains were determined for a murine monoclonal antibody, 12/231/93, which is specific for a linear epitope located between amino acids 90 and 102 of the hepatitis B virus (HBV) X protein (HBx). The variable (V) regions of the H and L chains were shown to belong to the mouse H chain subgroup II (C) and kappa L chain group III, respectively. The cloned variable region sequences were used for the production of a Fab fragment in Escherichia coli, which had binding activity for membrane immobilized recombinant HBx. These gene sequences may be useful for the study of HBx function in cells that will support HBV replication.

Cytosol is the prime compartment of hepatitis B virus X protein where it colocalizes with the proteasome

The hepatitis B virus X protein plays an important role in the regulation of viral genome expression and has also been implicated in the development of liver cancer associated with chronic viral infection. Several effects have been attributed to X but their biological relevance remains elusive. One of the confusing issues has been so far the uncertainty concerning its cellular location. To gain insight into the mechanism(s) how X exerts its effects, we have analysed its subcellular distribution and its dependency on the cell cycle. We used two complementary approaches namely, immunolocalization using a cell line stably expressing X, and characterization of the dynamics of X location in living cells by means of the reporter gene GFP. Our data clearly define the cytosol as the prime location of X, irrespectively of the cell cycle and show in addition the close attachment of a fraction of X to the nuclear membrane. However, X does not associate with any cytoplasmic vesicles and organelles so far tested. In contrast, our study provides strong evidence for the codistribution of X with the cytosolic fraction of proteasomes. In pulse-chase experiments, X decayed with a half-life of less than 30 min and proteasome-inhibitors did not modify its turnover, suggesting that X colocalization with the proteasome does not simply point to its degradation pathway. The proteolytic processing of the p105 precursor of the p50 subunit of the NF-kappaB transcription factor, which has been shown to be proteasome-dependent, is markedly slow down in the presence of X. These findings suggest that X modulates the processing rate of p105 by acting presumably at the level of the proteasome. Thus, targeting of proteasomes by X might be one of the pathways employed by this viral protein to subvert cellular functions.

Cloning and characterization of a novel hepatitis B virus x binding protein that inhibits viral replication

The hepatitis B virus and the mammalian hepadnavirus genomes encode for a short open reading frame called x. Expression of the protein product (HBx) appears necessary for establishment of natural infection. However, in vitro studies have suggested a multifunctional role for HBx as an indirect transcriptional transactivator of a variety of different viral and cellular promoters. Indeed, HBx has no known direct DNA binding properties but may interact with transcription factors as well as activate intracellular signaling pathways associated with cell growth. To further address the possible functional role of HBx in the life cycle of hepatitis B virus, we performed an analysis using the yeast two-hybrid system to screen a cDNA library derived from a hepatocellular carcinoma cell line with a HBx fusion bait in an attempt to identify cellular partners that may bind to and alter the biologic properties of HBx. A HBx-interacting protein that specifically complexes with the carboxy terminus of wild-type HBx was identified and designated XIP. This 9.6-kDa protein is capable of binding to HBx in vitro, and transient and stable expression in hepatocellular carcinoma cells abolishes the transactivation properties of HBx on luciferase constructs driven by AP-1 and endogenous hepatitis B virus enhancer/promoter elements. Investigation of the role of XIP in hepatitis B virus replication in differentiated hepatocellular carcinoma cells revealed that XIP expression reduces wild-type hepatitis B virus replication to levels observed following transfection with an HBx-minus virus. In contrast, the replication levels of the duck hepatitis B virus, a hepadnavirus that lacks the x open reading frame, were unchanged in the context of XIP expression. We propose that one of the physiologic functions of the cellular protein XIP is to negatively regulate HBx activity and thus to alter the replication life cycle of the virus.