scholarly journals Hepatitis B Virus X Protein Is both a Substrate and a Potential Inhibitor of the Proteasome Complex

1999 ◽  
Vol 73 (9) ◽  
pp. 7231-7240 ◽  
Author(s):  
Zongyi Hu ◽  
Zhensheng Zhang ◽  
Edward Doo ◽  
Olivier Coux ◽  
Alfred L. Goldberg ◽  
...  
Keyword(s):  
Hepatitis B Virus ◽  
Hepatitis B ◽  
Gradient Centrifugation ◽  
Proteasome Inhibitors ◽  
Hbv Infection ◽  
26S Proteasome ◽  
Viral Gene ◽  
X Protein ◽  
B Virus

ABSTRACT The hepatitis B virus X protein (HBX) is essential for the establishment of HBV infection in vivo and exerts a pleiotropic effect on diverse cellular functions. The yeast two-hybrid system had indicated that HBX could interact with two subunits of the 26S proteasome. Here we demonstrate an association in vivo of HBX with the 26S proteasome complex by coimmunoprecipitation and colocalization upon sucrose gradient centrifugation. Expression of HBX in HepG2 cells caused a modest decrease in the proteasome’s chymotrypsin- and trypsin-like activities and in hydrolysis of ubiquitinated lysozyme, suggesting that HBX functions as an inhibitor of proteasome. In these cells, HBX is degraded with a half-life of 30 min. Proteasome inhibitors retarded this rapid degradation and caused a marked increase in the level of HBX and an accumulation of HBX in polyubiquitinated form. Thus, the low intracellular level of HBX is due to rapid proteolysis by the ubiquitin-proteasome pathway. Surprisingly, the proteasome inhibitors blocked the transactivation by HBX, and this effect was not a result of a squelching phenomenon due to HBX accumulation. Therefore, proteasome function is possibly required for the transactivation function of HBX. The inhibition of protein breakdown by proteasomes may account for the multiple actions of HBX and may be an important feature of HBV infection, possibly in helping stabilize viral gene products and suppressing antigen presentation.

scholarly journals Upregulation of MicroRNA-146a by Hepatitis B Virus X Protein Contributes to Hepatitis Development by Downregulating Complement Factor H

mBio ◽  
2015 ◽  
Vol 6 (2) ◽  
Author(s):  
Jun-Feng Li ◽  
Xiao-Peng Dai ◽  
Wei Zhang ◽  
Shi-Hui Sun ◽  
Yang Zeng ◽  
...  
Keyword(s):  
Innate Immunity ◽  
Hepatitis B Virus ◽  
Hepatitis B ◽  
Complement Activation ◽  
Factor H ◽  
Hbv Infection ◽  
Complement Factor ◽  
Liver Inflammation ◽  
X Protein ◽  
B Virus

ABSTRACT Hepatic injuries in hepatitis B virus (HBV) patients are caused by immune responses of the host. In our previous study, microRNA-146a (miR-146a), an innate immunity-related miRNA, and complement factor H (CFH), an important negative regulator of the alternative pathway of complement activation, were differentially expressed in HBV-expressing and HBV-free hepatocytes. Here, the roles of these factors in HBV-related liver inflammation were analyzed in detail. The expression levels of miR-146a and CFH in HBV-expressing hepatocytes were assessed via analyses of hepatocyte cell lines, transgenic mice, adenovirus-infected mice, and HBV-positive human liver samples. The expression level of miR-146a was upregulated in HBV-expressing Huh-7 hepatocytes, HBV-expressing mice, and patients with HBV infection. Further results demonstrated that the HBV X protein (HBx) was responsible for its effects on miR-146a expression through NF-κB-mediated enhancement of miR-146a promoter activity. HBV/HBx also downregulated the expression of CFH mRNA in hepatocyte cell lines and the livers of humans and transgenic mice. Furthermore, overexpression and inhibition of miR-146a in Huh-7 cells downregulated and upregulated CFH mRNA levels, respectively. Luciferase reporter assays demonstrated that miR-146a downregulated CFH mRNA expression in hepatocytes via 3′-untranslated-region (UTR) pairing. The overall effect of this process in vivo is to promote liver inflammation. These results demonstrate that the HBx–miR-146a–CFH–complement activation regulation pathway might play an important role in the immunopathogenesis of chronic HBV infection. These findings have important implications for understanding the immunopathogenesis of chronic hepatitis B and developing effective therapeutic interventions. IMPORTANCE Hepatitis B virus (HBV) remains an important pathogen and can cause severe liver diseases, including hepatitis, liver cirrhosis, and hepatocellular carcinoma. Although HBV was found in 1966, the molecular mechanisms of pathogenesis are still poorly understood. In the present study, we found that the HBV X protein (HBx) promoted the expression of miR-146a, an innate immunity-related miRNA, through the NF-κB signal pathway and that increasingly expressed miR-146a downregulated its target complement factor H (CFH), an important negative regulator of the complement alternative pathway, leading to the promotion of liver inflammation. We demonstrated that the HBx–miR-146a–CFH–complement activation regulation pathway is potentially an important mechanism of immunopathogenesis caused by chronic HBV infection. Our data provide a novel molecular mechanism of HBV pathogenesis and thus help to understand the correlations between the complement system, an important part of innate immunity, and HBV-associated disease. These findings will also be important to identify potential therapeutic targets for HBV infection.

Characterization of the immune response to the hepatitis B virus X protein in acute and chronic HBV infection

1989 ◽  
Vol 9 ◽  
pp. S182
Author(s):  
M. Levrero ◽  
A. Franco ◽  
E. De Marzio ◽  
C. Balsano ◽  
M.L. Avantaggiati ◽  
...  
Keyword(s):  
Immune Response ◽  
Hepatitis B Virus ◽  
Hepatitis B ◽  
Hbv Infection ◽  
X Protein ◽  
Chronic Hbv Infection ◽  
B Virus ◽  
Chronic Hbv

452 IN VIVO INHIBITORY EFFECTS OF HEPATITIS B VIRUS X PROTEIN ON LIVER REGENERATION THROUGH A IL-6 DEPENDENT MECHANISM

2012 ◽  
Vol 56 ◽  
pp. S179
Author(s):  
I. Quétier ◽  
N. Brezillon ◽  
H. Massinet ◽  
S. Berissi ◽  
P. Soussan ◽  
...  
Keyword(s):  
Hepatitis B Virus ◽  
Hepatitis B ◽  
Liver Regeneration ◽  
Inhibitory Effects ◽  
X Protein ◽  
B Virus ◽  
Dependent Mechanism

scholarly journals Role and Functional Domain of Hepatitis B Virus X Protein in Regulating HBV Transcription and Replication in Vitro and in Vivo

Viruses ◽  
2013 ◽  
Vol 5 (5) ◽  
pp. 1261-1271 ◽  
Author(s):  
Dao-Yin Gong ◽  
En-Qiang Chen ◽  
Fei-Jun Huang ◽  
Xiao-Hua Leng ◽  
Xing Cheng ◽  
...  
Keyword(s):  
Hepatitis B Virus ◽  
Hepatitis B ◽  
Functional Domain ◽  
X Protein ◽  
B Virus ◽  
Transcription And Replication

scholarly journals Expression of Hepatitis B Virus X Protein Does Not Alter the Accumulation of Spontaneous Mutations in Transgenic Mice

2000 ◽  
Vol 74 (11) ◽  
pp. 5266-5272 ◽  
Author(s):  
Charles R. Madden ◽  
Milton J. Finegold ◽  
Betty L. Slagle
Keyword(s):  
Dna Repair ◽  
Hepatitis B Virus ◽  
Hepatitis B ◽  
Transgenic Mice ◽  
Spontaneous Mutations ◽  
Environmental Carcinogens ◽  
X Protein ◽  
B Virus ◽  
The Impact

ABSTRACT Chronic infection with hepatitis B virus (HBV) is one of the major etiological factors in the development of human hepatocellular carcinoma. Transgenic mice that express the HBV X protein (HBx) have previously been shown to be more sensitive to the effects of hepatocarcinogens, although the mechanism for this cofactor role remains unknown. The ability of HBx to inhibit DNA repair in transiently transfected cell lines suggests one possible pathway. In the present study, primary hepatocytes isolated from transgenic mice that possess the HBV X gene under the control of the human α-1-antitrypsin regulatory region (ATX mice) were found to be deficient in their ability to conduct unscheduled DNA synthesis in response to UV-induced DNA damage. In order to measure the impact of HBx expression on DNA repair in vivo, double-transgenic mice that express HBx and possess a bacteriophage lambda transgene were sacrificed at 30, 90, and 240 days of age. Mutation frequency was determined for high-molecular-weight liver DNA of ATX and control mice by functional analysis of the lambda transgene. Expression of HBx did not significantly increase the accumulation of spontaneous mutations. These results are consistent with previous studies of HBx transgenic mice in which no effect of HBx on liver histology was apparent. This new animal model provides a powerful system in which to investigate the in vivo cooperation between HBx expression and environmental carcinogens.

scholarly journals NEDD4 Induces K48-Linked Degradative Ubiquitination of Hepatitis B Virus X Protein and Inhibits HBV-Associated HCC Progression

2021 ◽  
Vol 11 ◽  
Author(s):  
Tao Wan ◽  
Zhao Lei ◽  
Biao Tu ◽  
Tianyin Wang ◽  
Jiale Wang ◽  
...  
Keyword(s):  
Hepatitis B Virus ◽  
Hepatitis B ◽  
Progression Free Survival ◽  
Suppressive Effect ◽  
Hbv Infection ◽  
Migration And Invasion ◽  
Dependent Manner ◽  
X Protein ◽  
B Virus ◽  
Gene 4

Neural precursor cell expressed developmentally downregulated gene 4 (NEDD4) plays two opposite roles in carcinogenesis. It has been reported that NEDD4 inhibits hepatocellular carcinoma (HCC) progression; however, little is known about its potential function and molecular mechanism in HCC in the context of hepatitis B virus (HBV) infection. In this study, we analyzed NEDD4 expression in 199 HCC specimens with or without HBV infection and observed that NEDD4 expression was unrelated to HBV exposure in HCC tumor tissue but that high NEDD4 expression conferred better overall survival (OS) and progression-free survival (PFS) than low NEDD4 expression in patients with HBV-associated HCC. Upregulation of NEDD4 inhibited proliferation, migration and invasion in HBV-related HCC cell lines. We demonstrated that NEDD4 interacts with HBV X protein (HBx) and that HBx upregulation could reverse the suppression of proliferation and mobility induced by NEDD4 overexpression. Furthermore, we confirmed that NEDD4 induced the degradation of HBx in a ubiquitin/proteasome-dependent manner via K48-linked ubiquitination. Our findings suggest that NEDD4 exerts a tumor-suppressive effect in HBV-associated HCC by acting as an E3 ubiquitin ligase for HBx degradation and provide new insights into the function of NEDD4.

scholarly journals Immunogenicity and Tolerogenicity of Hepatitis B Virus Structural and Nonstructural Proteins: Implications for Immunotherapy of Persistent Viral Infections

2002 ◽  
Vol 76 (17) ◽  
pp. 8609-8620 ◽  
Author(s):  
Kazuhiro Kakimi ◽  
Masanori Isogawa ◽  
JoSan Chung ◽  
Alessandro Sette ◽  
Francis V. Chisari
Keyword(s):  
Hepatitis B Virus ◽  
Hepatitis B ◽  
Viral Infections ◽  
Cytotoxic T Lymphocyte ◽  
T Cell Response ◽  
Hbv Infection ◽  
Peripheral Tolerance ◽  
Specific Ctls ◽  
B Virus

ABSTRACT Persistent hepatitis B virus (HBV) infection is characterized by a weak and narrowly focused CD8+ T-cell response to HBV that is thought to reflect the induction of central and/or peripheral tolerance to HBV proteins in neonatal and adult onset infections, respectively. Immunotherapeutic strategies that overcome tolerance and boost these suboptimal responses may lead to viral clearance in chronically infected individuals. The present study was performed to compare the relative immunogenicities and tolerogenicities of HBV structural (envelope [ENV]) and nonstructural (polymerase [POL]) proteins at the CD8+ cytotoxic T lymphocyte (CTL) level in transgenic mice that replicate HBV in the liver and secrete infectious virus into the blood, thus representing an excellent model of persistent HBV infection. Interestingly, the mice were tolerant to the ENV but not to the POL proteins at the CTL level. Furthermore, the POL-specific CTLs had no impact on HBV replication or liver function in vivo, even though they were readily induced and reached the liver after DNA immunization, reflecting their relatively low avidity and the low level at which the POL protein is expressed by the hepatocyte. Collectively, these results suggest that the factors that make POL less tolerogenic also make POL-specific CTLs relatively inefficient effector cells when they reach the target organ. Immunotherapeutic strategies to control HBV infection by inducing virus-specific CTL responses in chronically infected subjects should be evaluated in light of this observation.

scholarly journals Evaluation of Single and Combination Therapies with Tenofovir Disoproxil Fumarate and EmtricitabineIn Vitroand in a Robust Mouse Model Supporting High Levels of Hepatitis B Virus Replication

2012 ◽  
Vol 56 (12) ◽  
pp. 6186-6191 ◽  
Author(s):  
Raymond F. Schinazi ◽  
Leda Bassit ◽  
Marcia M. Clayton ◽  
Bill Sun ◽  
James J. Kohler ◽  
...  
Keyword(s):  
Hepatitis B Virus ◽  
Hepatitis B ◽  
Combination Therapy ◽  
Virus Replication ◽  
Tenofovir Disoproxil Fumarate ◽  
Hbv Infection ◽  
Experimental Drugs ◽  
Chronic Hepatitis B Virus ◽  
B Virus

ABSTRACTNext-generation therapies for chronic hepatitis B virus (HBV) infection will involve combinations of established and/or experimental drugs. The current study investigated thein vitroandin vivoefficacy of tenofovir disoproxil fumarate (TDF) and/or emtricitabine [(−)-FTC] alone and in combination therapy for HBV infection utilizing the HepAD38 system (human hepatoblastoma cells transfected with HBV). Cellular pharmacology studies demonstrated increased levels of (−)-FTC triphosphate with coincubation of increasing concentrations of TDF, while (−)-FTC had no effect on intracellular tenofovir (TFV) diphosphate levels. Quantification of extracellular HBV by real-time PCR from hepatocytes demonstrated the anti-HBV activity with TDF, (−)-FTC, and their combination. Combination of (−)-FTC with TDF or TFV (ratio, 1:1) had a weighted average combination index of 0.7 for both combination sets, indicating synergistic antiviral effects. No cytotoxic effects were observed with any regimens. Using anin vivomurine model which develops robust HBV viremia in nude mice subcutaneously injected with HepAD38 cells, TDF (33 to 300 mg/kg of body weight/day) suppressed virus replication for up to 10 days posttreatment. At 300 mg/kg/day, (−)-FTC strongly suppressed virus titers to up to 14 days posttreatment. Combination therapy (33 mg/kg/day each drug) sustained suppression of virus titer/ml serum (<1 log10unit from pretreatment levels) at 14 days posttreatment, while single-drug treatments yielded virus titers 1.5 to 2 log units above the initial virus titers. There was no difference in mean alanine aminotransferase values or mean wet tumor weights for any of the groups, suggesting a lack of drug toxicity. TDF–(−)-FTC combination therapy provides more effective HBV suppression than therapy with each drug alone.

scholarly journals Enhancement of Hepatitis B Virus Replication by Its X Protein in Transgenic Mice

2002 ◽  
Vol 76 (5) ◽  
pp. 2579-2584 ◽  
Author(s):  
Zhenming Xu ◽  
T. S. Benedict Yen ◽  
Lanying Wu ◽  
Charles R. Madden ◽  
Wenjie Tan ◽  
...  
Keyword(s):  
Hepatitis B Virus ◽  
Hepatitis B ◽  
Transgenic Mice ◽  
Viral Gene Expression ◽  
Viral Gene ◽  
X Protein ◽  
Multifunctional Protein ◽  
Hbv Replication ◽  
B Virus

ABSTRACT Hepatitis B virus (HBV) X gene encodes a multifunctional protein that can regulate cellular signaling pathways, interact with cellular transcription factors, and induce hepatocellular oncogenesis. In spite of its diverse activities, the precise role of the X protein in the viral life cycle of HBV remains unclear. To investigate this question, we have produced transgenic mice that carry either the wild-type HBV genome or a mutated HBV genome incapable of expressing the 16.5-kDa X protein. Our results indicate that while the X protein is not absolutely essential for HBV replication or its maturation in transgenic mice, it can enhance viral replication, apparently by activating viral gene expression. These results demonstrate a transactivation role of the X protein in HBV replication in transgenic mice.

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