Human hepatitis B virus X protein induces apoptosis in HepG2 cells: Role of BH3 domain

Interference of Apoptosis by Hepatitis B Virus

Hepatitis B virus (HBV) causes liver diseases that have been a consistent problem for human health, leading to more than one million deaths every year worldwide. A large proportion of hepatocellular carcinoma (HCC) cases across the world are closely associated with chronic HBV infection. Apoptosis is a programmed cell death and is frequently altered in cancer development. HBV infection interferes with the apoptosis signaling to promote HCC progression and viral proliferation. The HBV-mediated alteration of apoptosis is achieved via interference with cellular signaling pathways and regulation of epigenetics. HBV X protein (HBX) plays a major role in the interference of apoptosis. There are conflicting reports on the HBV interference of apoptosis with the majority showing inhibition of and the rest reporting induction of apoptosis. In this review, we described recent studies on the mechanisms of the HBV interference with the apoptosis signaling during the virus infection and provided perspective.

Wild type HBx and truncated HBx: Pleiotropic regulators driving sequential genetic and epigenetic steps of hepatocarcinogenesis and progression of HBV-associated neoplasms

Hepatitis B virus (HBV) is one of the causative agents of hepatocellular carcinoma. The molecular mechanisms of tumorigenesis are complex. One of the host factors involved is apparently the long-lasting inflammatory reaction which accompanies chronic HBV infection. Although HBV lacks a typical viral oncogene, the HBx gene encoding a pleiotropic regulatory protein emerged as a major player in liver carcinogenesis. Here we review the tumorigenic functions of HBx with an emphasis on wild type and truncated HBx variants, and their role in the transcriptional dysregulation and epigenetic reprogramming of the host cell genome. We suggest that HBx acquired by the HBV genome during evolution acts like a cellular proto-onc gene that is activated by deletion during hepatocarcinogenesis. The resulting viral oncogene (v-onc gene) codes for a truncated HBx protein that facilitates tumor progression. Copyright © 2015 John Wiley & Sons, Ltd.

The characteristic changes in hepatitis B virus x region for hepatocellular carcinoma: a comprehensive analysis based on global data

OBJECTIVES

Mutations in hepatitis B virus (HBV) X region (HBx) play important roles in hepatocarcinogenesis while the results remain controversial. We sought to clarify potential hepatocellular carcinoma (HCC)-characteristic mutations in HBx from HBV genotype C-infected patients and the distribution of those mutations in different disease phases and genotypes.

METHODS

HBx sequences downloaded from an online global HBV database were screened and then classified into Non-HCC or HCC group by diagnosis information. Patients' data of patient age, gender, country or area, and viral genotype were also extracted. Logistic regression was performed to evaluate the effects of mutations on HCC risk.

RESULTS

1) Full length HBx sequences (HCC: 161; Non-HCC: 954) originated from 1115 human sera across 29 countries/areas were extracted from the downloaded 5956 HBx sequences. Genotype C occupied 40.6% of Non-HCC (387/954) and 89.4% of HCC (144/161). 2) Sixteen nucleotide positions showed significantly different distributions between genotype C HCC and Non-HCC groups. 3) Logistic regression showed that mutations A1383C (OR: 2.32, 95% CI: 1.34-4.01), R1479C/T (OR: 1.96, 95% CI: 1.05-3.64; OR: 5.15, 95% CI: 2.53-10.48), C1485T (OR: 2.40, 95% CI: 1.41-4.08), C1631T (OR: 4.09, 95% CI: 1.41-11.85), C1653T (OR: 2.58, 95% CI: 1.59-4.19), G1719T (OR: 2.11, 95% CI: 1.19-3.73), and T1800C (OR: 23.59, 95% CI: 2.25-247.65) were independent risk factors for genotype C HBV-related HCC, presenting different trends among individual disease phases. 4) Several genotype C HCC risk mutations pre-existed, even as major types, in early disease phases with other genotypes.

CONCLUSIONS

Mutations associated with HCC risk were mainly located in HBx transactivation domain, viral promoter, protein/miRNA binding sites, and the area for immune epitopes. Furthermore, the signatures of these mutations were unique to disease phases leading to HCC, suggesting molecular counteractions between the virus and host during hepatocarcinogenesis.

Viruses as modulators of mitochondrial functions

Mitochondria are multifunctional organelles with diverse roles including energy production and distribution, apoptosis, eliciting host immune response, and causing diseases and aging. Mitochondria-mediated immune responses might be an evolutionary adaptation by which mitochondria might have prevented the entry of invading microorganisms thus establishing them as an integral part of the cell. This makes them a target for all the invading pathogens including viruses. Viruses either induce or inhibit various mitochondrial processes in a highly specific manner so that they can replicate and produce progeny. Some viruses encode the Bcl2 homologues to counter the proapoptotic functions of the cellular and mitochondrial proteins. Others modulate the permeability transition pore and either prevent or induce the release of the apoptotic proteins from the mitochondria. Viruses like Herpes simplex virus 1 deplete the host mitochondrial DNA and some, like human immunodeficiency virus, hijack the host mitochondrial proteins to function fully inside the host cell. All these processes involve the participation of cellular proteins, mitochondrial proteins, and virus specific proteins. This review will summarize the strategies employed by viruses to utilize cellular mitochondria for successful multiplication and production of progeny virus.

Hepatitis B virus X protein disrupts stress fiber formation and triggers apoptosis

Cytoskeletal proteins are key participants in the cellular progression to apoptosis. In a previous study we injected nude mice with CCL13-HBx cells and identified in contrast to non-HBx transfected cells a differentially phosphorylated myosin light chain (p-MLC) by two-dimensional PAGE and mass spectrometry of the tumor material. To investigate the role of HBx in myosin light chain kinase (MLCK) signaling pathways, we analyzed the key molecules, p-MLC and MLCK, by western blotting. Immunofluorescence staining analysis showed that HBx disrupted stress fiber formation and that focal adhesion kinase (FAK) and integrin-linked kinase (ILK) were regulated by HBx-mediated phosphatase and tensin homolog (PTEN). We also used pharmacological inhibitors to explore the correlation between cytoskeletal rearrangements and HBx-mediated cell apoptosis via an MLCK and a PTEN-dependent pathway. The results showed that both ML9 and bvp restored the effects caused by HBx induction. Our findings suggest that HBx disrupts stress fiber formation and triggers apoptosis via an MLCK and a PTEN-dependent pathway.

Hepatitis B virus X protein targets the Bcl-2 protein CED-9 to induce intracellular Ca2+ increase and cell death in Caenorhabditis elegans

HBx is a multifunctional hepatitis B virus (HBV) protein that is crucial for HBV infection and pathogenesis and a contributing cause of hepatocyte carcinogenesis. However, the host targets and mechanisms of action of HBx are poorly characterized. We show here that expression of HBx in Caenorhabditis elegans induces both necrotic and apoptotic cell death, mimicking an early event of liver infection by HBV. Genetic and biochemical analyses indicate that HBx interacts directly with the B-cell lymphoma 2 (Bcl-2) homolog CED-9 (cell death abnormal) through a Bcl-2 homology 3 (BH3)-like motif to trigger both cytosolic Ca(2+) increase and cell death. Importantly, Bcl-2 can substitute for CED-9 in mediating HBx-induced cell killing in C. elegans, suggesting that CED-9 and Bcl-2 are conserved cellular targets of HBx. A genetic suppressor screen of HBx-induced cell death has produced many mutations, including mutations in key regulators from both apoptosis and necrosis pathways, indicating that this screen can identify new apoptosis and necrosis genes. Our results suggest that C. elegans could serve as an animal model for identifying crucial host factors and signaling pathways of HBx and aid in development of strategies to treat HBV-induced liver disorders.

Hepatitis B virus X protein targets the Bcl-2 protein CED-9 to induce intracellular Ca2+ increase and cell death in Caenorhabditis elegans

HBx is a multifunctional hepatitis B virus (HBV) protein that is crucial for HBV infection and pathogenesis and a contributing cause of hepatocyte carcinogenesis. However, the host targets and mechanisms of action of HBx are poorly characterized. We show here that expression of HBx in Caenorhabditis elegans induces both necrotic and apoptotic cell death, mimicking an early event of liver infection by HBV. Genetic and biochemical analyses indicate that HBx interacts directly with the B-cell lymphoma 2 (Bcl-2) homolog CED-9 (cell death abnormal) through a Bcl-2 homology 3 (BH3)-like motif to trigger both cytosolic Ca(2+) increase and cell death. Importantly, Bcl-2 can substitute for CED-9 in mediating HBx-induced cell killing in C. elegans, suggesting that CED-9 and Bcl-2 are conserved cellular targets of HBx. A genetic suppressor screen of HBx-induced cell death has produced many mutations, including mutations in key regulators from both apoptosis and necrosis pathways, indicating that this screen can identify new apoptosis and necrosis genes. Our results suggest that C. elegans could serve as an animal model for identifying crucial host factors and signaling pathways of HBx and aid in development of strategies to treat HBV-induced liver disorders.

Autophagy and apoptosis-related genes in chronic liver disease and hepatocellular carcinoma

Background

Dysregulation of autophagy is important in the pathogenesis of many diseases, including cancer. Several aspects of the biological role of autophagy are however still unclear and the relationship between apoptosis and autophagy, particularly in the liver has yet to be thoroughly explored. In this study we evaluated the expression of Beclin 1 (one of the main autophagocytic agents, which bridges autophagy, apoptosis and both differentiation), and both pro- (Bad, Bax) and anti-apoptotic (Bcl-2, Bcl-xL) factors in liver samples from patients with different stages of liver disease.

Methods

The study concerned 93 patients from 49 cases of chronic hepatitis (CH) (30 HCV and 19 HBV-related), 13 of cirrhosis (CIRR) (10 HCV and 3 HBV-related), 21 of hepatocellular carcinoma (both HCC and peritumoral tissues [PHCC]), and 10 controls (CONTR). Real-time PCR and Western blotting were used to measure mRNA and protein expression levels.

Results

Beclin 1 mRNA levels were lower in HCC than in CH (P = 0.010) or CIRR (P = 0.011), and so were the Bcl-xL transcripts (P < 0.0001). Bad mRNA levels were higher in CH and CIRR than in CONTR, while Bax transcripts were increased in all tissues (P = 0.036). PHCC expressed the highest Bcl-2 mRNA levels. HBV-related CH tissues showed significantly higher Bcl-xL and Bad mRNA levels than HCV-related CH (P = 0.003 and P = 0.016, respectively).

Conclusions

High Beclin 1, Bcl-xL and Bad levels in CH and CIRR tissues suggest an interaction between autophagy and apoptosis in the early and intermediate stages of viral hepatitis. In HCC these processes seem to be downregulated, probably enabling the survival and growth of neoplastic hepatocytes.

The binding of hepatitis B virus X protein to glioma-associated oncogene homologue 1 and its biological characterization in vitro

Hepatitis B virus (HBV) X protein (HBx) is a 17-kDa transcriptional coactivator that plays a significant role in the regulation of genes involved in inflammation and cell survival. It has been known to be involved in the development of liver cancer and alteration of the cellular HBx level may influence the pathogenesis of HBV-induced liver diseases. The transcription factor GLI1, a member of the glioma-associated oncogene homologue (GLI) subfamily of Krüppel-like zinc finger proteins is involved in signal transduction within the hedgehog (Hh) signaling pathway, which is involved in the development of many human malignancies. GLI activation is important for cell proliferation and anti-apoptosis in various cancers. To investigate whether the transcriptional coactivator HBx binds to the zinc finger transcription factor GLI1, recombinant HBx and GLI1 were isolated. Expression and purification of the HBx and GLI1 proteins were successfully performed in Escherichia coli. The binding of HBx to GLI1 was detected by surface plasmon resonance spectroscopy (BIAcore), fluorescence measurement, and a His-tagged pull-down experiment. After measuring the fluorescence emission spectra of purified HBx and GLI1, it was found that the interaction of these proteins is accompanied by significant conformational changes in one or both. This study provides important clues for the structural identification of signal transduction pathways involving the HBx and GLI1 proteins.

Hepatitis B virus X protein enhances cisplatin-induced hepatotoxicity via a mechanism involving degradation of Mcl-1

Hepatitis B virus X protein (HBx) is implicated in the pathogenesis of hepatitis B virus (HBV)-associated liver diseases. However, whether HBx has the ability to disturb the susceptibility of hepatocytes to common chemotherapeutic agents remains incompletely understood. Here we demonstrate that HBx enhances cisplatin-induced hepatotoxicity by a mechanism involving degradation of Mcl-1, an antiapoptotic member of the Bcl-2 family. Ectopic expression of HBx sensitized hepatocytes to cisplatin-induced apoptosis, which was accompanied by a marked downregulation of Mcl-1 but not of Bcl-2 or Bcl-xL. Overexpression of Mcl-1 prevented HBx-induced proapoptotic and proinflammatory effects during cisplatin treatment both in vitro and in vivo. HBx-induced dysregulation of Mcl-1 resulted mainly from posttranslational degradation rather than transcription repression. Moreover, a caspase-3 inhibitor effectively abrogated HBx-enhanced Mcl-1 degradation and cell death. Importantly, antioxidants blocked activation of caspase-3 and acceleration of Mcl-1 loss, as well as cell death, in HBx-expressing hepatocytes upon cisplatin exposure in vitro and in vivo. Collectively, these data implicate oxidative stress-dependent caspase-3-mediated degradation of Mcl-1 as a mechanism contributing to HBx-mediated sensitization of cisplatin-induced hepatotoxicity. A combination of cisplatin and antioxidants might provide more advantage than cisplatin alone in the treatment of cancer patients with chronic HBV infection.

[Pro-apoptotic function of hepatitis B virus X protein]

Infection of hepatitis B virus (HBV) is a main cause of liver diseases including hepatitis, cirrhosis and hepatocellular carcinoma (HCC). Among the HBV-encoded proteins, the HBV X protein (HBx) has been suspected to be strongly involved in HBV-associated liver pathogenesis. HBx, a virally encoded multifunctional regulator, has been shown to induce apoptosis, anti-apoptosis, proliferation, and transformation of cells depending on the cell lines, model systems used, assay protocols, and research groups. Among the several activities of HBx, the pro-apoptotic function of HBx will be discussed in this review. Given that the disruption of apoptosis pathway by HBx contributes to the liver pathogenesis, a better understanding of the molecular interference in the cellular pro-apoptotic networks by HBx will provide useful clues for the intervention in HBV-mediated liver diseases.

Hepatitis B virus X gene is implicated in liver carcinogenesis

Hepatitis B virus (HBV) is a small hepatotropic and highly species-specific enveloped DNA virus. The carcinogenicity of this virus has become focused on the X gene and its coded X protein. The X protein itself is unable to bind to DNA directly, but works as a potent transcriptional activator through multiple cis-acting elements and mediates several signal transduction cascades. Two regions of the X protein, aa.61-69 and aa.105-140, are found essential for the viral replication and expression as well. These functions interacting with transcription factors and signaling cascades are acting cooperatively to cause cell proliferation. Furthermore, the association of X protein with mitochondria causes loss of the mitochondrial membrane potential and subsequently causes cell death, the function of which is attributed to the aa.68-104 region of X protein. As a result, the X protein has two independent proliferative and cell death-promoting activities. Liver cancer has been shown to result from a series of mutations in specific oncogenes and tumor suppressor genes. In a recent study, X protein stimulates ROS generation in the mitochondria due to collapse of the membrane potential and increases the mutation frequency, that evokes malignant transformation. Inflammation as a result of HBV infection is concerned to cause DNA damage. In the past 10years, the possibility that several viral proteins directly engaged in the DNA damage has increased to some extent. From an evolutionary viewpoint, it is noteworthy that several arrangement proteins have been found in viruses. Thus, there is some clue that a small amount of X protein acts as an arrangement protein for HBV replication dependent upon cellular DNA damage due to generated ROS as an amplified signal.

Hepatitis B virus X protein sensitizes cells to starvation-induced autophagy via up-regulation of beclin 1 expression

Human beclin 1 is the first identified mammalian gene to induce autophagy. It is commonly expressed at reduced levels in breast tumors; however, it is overexpressed in hepatitis B virus (HBV)-infected cancerous liver tissues. To expose the possible mechanism and biological significance of this up-regulation of beclin 1, we investigated the regulation of beclin 1 expression by HBV x protein (HBx) in hepatic or hepatoma cell lines. Here, we showed that enforced expression of HBx by transfection technology results in the up-regulation of the endogenous messenger RNA (mRNA) and protein levels of Beclin 1 in the tested cells. Using a luciferase- reporter assay, we demonstrated that HBx transactivates beclin 1 promoter activity in a dose-dependent manner. The promoter region of the beclin 1 gene identified in this study is located at nt -277/+197 and has the maximum transcriptional activity. HBx-mediated up-regulation of beclin 1 expression might be direct, that is, via its promoter. Furthermore, the cells that transiently or stably expressed HBx showed an enhanced accumulation of vacuoles carrying the autophagy marker LC3 as compared with the control cells, which was induced by nutrient starvation, indicating HBx-enhanced autophagy. Moreover, this enhanced autophagy occurred in HepG2.2.15 cells that replicate HBV and in cells transfected with HBV genomic DNA, suggesting that HBV infection also causes increased levels of autophagy under starvation conditions. Treatment of cells with beclin 1 small interfering RNA (siRNA) blocked HBx-enhanced autophagy, demonstrating that the function of HBx in influencing autophagy is Beclin 1 dependent.

CONCLUSION

Our findings suggest a novel function of HBx in increasing autophagy through the up-regulation of beclin1 expression, and this may provide an important mechanism in HBV-infected hepatocytes growing under nutrient-deficient conditions.

HBx genotype D represses GSTP1 expression and increases the oxidative level and apoptosis in HepG2 cells

Epigenetics has been implicated in human cancer development. Epigenetic factors include HBx protein, which is able to induce hypermethylation and suppresses tumor suppressor genes. One of such tumor suppressor genes, GSTP1, shows reduced expression in many human cancers. Hypermethylation of GSTP1 is the most studied mechanism of its silence. In the present study, we reported that GSTP1 expression was completely depleted in HBV integrated HepG2.2.15 cells due to the hypermethylation in its promoter region. And it was HBx, especially HBx genotype D, that played the key role in repressing GSTP1 expression. Further functional studies like ROS assay and apoptosis detection were also used to confirm this repression. Our findings should facilitate the understanding of HBV and their influences on the epigenetic modulations for epigenetic tumorigenesis during HBV-mediated hepatocellular carcinogenesis.

Association of human APOBEC3 cytidine deaminases with the generation of hepatitis virus B x antigen mutants and hepatocellular carcinoma

Human APOBEC3 (apolipoprotein B mRNA editing enzyme, catalytic polypeptide 3) cytidine deaminases have been shown to be potent inhibitors of diverse retroviruses including Vif-deficient human immunodeficiency virus 1 (HIV-1), hepatitis virus B (HBV), adeno-associated virus, and endogenous retroelements. Despite the fact that these enzymes are known to be potential DNA mutators and to target retroviral DNA for cytidine deamination, the pathological effects of their deregulated expression in human diseases are not yet clear. Mutants of the viral HBx protein have been implicated in the carcinogenesis of hepatocellular carcinoma (HCC); however, little is known about how or why such mutants are generated in the human liver. Here, we report that a number of APOBEC3 deaminases preferentially edit the HBx region of HBV DNA and generate C-terminally truncated HBx mutants. Our functional studies indicated that APOBEC3-mediated HBx mutants, especially the C-terminally truncated mutants, cause a gain of function that enhances the colony-forming ability and proliferative capacity of neoplastic cells. Furthermore, we detected G-to-A hypermutation-mediated HBx mutants in preneoplastic liver tissues of selected patients with active chronic HBV infections. We also observed that the APOBEC3B (A3B) cytidine deaminase was widely up-regulated in HCC tumor tissues; it also promoted the growth of neoplastic human HepG2 liver cells and up-regulated heat shock transcription factor1 (HSF1) expression.

CONCLUSION

These findings suggest that some of the APOBEC3 deaminases play a role in the carcinogenesis of HCC through the generation of HBx mutants, providing preneoplastic and neoplastic hepatocytes with a selective clonal growth advantage. Deregulated expression of A3B in liver tissues may also have the potential to promote genetic instability and tumorigenesis.

Cellular apoptosis induced by replication of hepatitis B virus: possible link between viral genotype and clinical outcome

HBV remains one of the major pathogens of liver diseases but the outcomes as inflammation, cirrhosis and cancer of the liver are greatly related to different viral genotypes. The aim of this study was to assess the pro-apoptotic effect of HBSP from three HBV genotypes on liver derived cells. HepG2 cells were applied in our system and transfected by HBV genotype A, B, and C. Cells were observed under phase contrast microscope, stained by apoptosis marker and analyzed by flow cytometre. HBSP expression was detected by western blot assay. BH3 sequences were aligned and analyzed by Vector NTI. HBV genotypes A, B, and C transfected cells displayed evidence of cell death which was further proved as apoptosis. Natural expression of a pro-apoptotic protein HBSP was detected during genomes transfection. The different apoptotic effects were correlated to the HBSP expression from each genome. Alignment and analysis of the BH3 domains from the three genomes revealed slight variance which might also contribute to the result. Our results suggested that variant HBSP expression and BH3 sequence of HBV genotypes may be involved in differential apoptotic effect in transfected cells. Detailed analysis of the role of HBV genotypes in cellular apoptotic process should provide molecular information on the reported clinical outcome of infection by different HBV genotypes.

Hepatitis B virus X protein induces apoptosis and cell cycle deregulation through interfering with DNA repair and checkpoint responses

AIM

To investigate the effects of hepatitis B virus X (HBx) gene on apoptosis and cell cycle in hepatocyte line HL-7702 and to discuss the possible mechanisms in the pathway.

METHODS

The recombinant plasmid pcDNA3-X and vector pcDNA3 were transfected into HL-7702 cells and selected by G418 to construct two new cell lines, which were named HL-7702-HBx and HL-7702-con, respectively. Reverse transcription polymerase chain reaction (RT-PCR) and western blot analysis were used to confirm that HBx gene was expressed steadily in the HL-7702-HBx cells. Then apoptosis and cell cycle of the two cells were detected by DNA ladder, flow cytometric analysis, and electronic microscope observation. Apoptosis and cell cycle gene expressions in the two cells were subsequently evaluated by using gene arrays. Some of results were further confirmed by real-time PCR and western blot analysis.

RESULTS

RT-PCR and the western blot analysis showed that HL-7702-HBx expressed the HBx gene steadily. Comparedwith the HL-7702-con cells, there was increased apoptosis and accumulation of the S phase in the HL-7702-HBx cells. The gene array analysis indicated that some DNA repair genes (XRCC1, DDB1, etc.) and DNA damage checkpoint-related genes (Cdc47, RAD17, etc.) played roles in the HBx-mediated imbalance of apoptosis and cell cycle. Both cDNA array analysis and real-time RT-PCR showed that mRNA of XRCC1, Cdc47 and RAD17 were upregulated by HBx. Unexpectedly, the western blot analysis revealed that HBx inhibited their protein expression.

CONCLUSION

The expression of HBx in HL-7702 cells promoted apoptosis and accumulation of the S phase through the inhibition of DNA repair and checkpoints via post-transcriptional mechanisms.

The HBSP gene is expressed during HBV replication, and its coded BH3-containing spliced viral protein induces apoptosis in HepG2 cells

The mechanisms of liver injury in hepatitis B virus (HBV) infection are defined to be due not to the direct cytopathic effects of viruses, but to the host immune response to viral proteins expressed by infected hepatocytes. We showed here that transfection of mammalian cells with a replicative HBV genome causes extensive cytopathic effects, leading to the death of infected cells. While either necrosis or apoptosis or both may contribute to the death of infected cells, results from flow cytometry suggest that apoptosis plays a major role in HBV-induced cell death. Data mining of the four HBV protein sequences reveals the presence of a Bcl-2 homology domain 3 (BH3) in HBSP, a spliced viral protein previously shown to be able to induce apoptosis and associated with HBV pathogenesis. HBSP is expressed at early stage of our cell-based HBV replication. When transfected into HepG2 cells, HBSP causes apoptosis in a caspase dependent manner. Taken together, our results suggested a direct involvement of HBV viral proteins in cellular apoptosis, which may contribute to liver pathogenesis.

Adhesion contact kinetics of HepG2 cells during Hepatitis B virus replication: Involvement of SH3-binding motif in HBX

It has been shown that Hepatitis B virus (HBV) replication directly alters the expression of key cytoskeleton-associated proteins which play key roles in mechanochemical signal transduction. Nevertheless, little is known on the correlation between HBV replication and the subsequent adhesion mechanism of HBV-replicating cells. In this study, it is demonstrated that the lag time of adhesion contact evolution of HepG2 cells with HBV replication is significantly increased by two times compared to that of normal HepG2 cell on collagen coated substrate. During the initial 20 min of cell seeding, only diffuse forms of vinculin was detected in HBV replicating cells while vinculin-associated focal complexes were found in normal and control cells. Similar delay in cell adhesion in HBV-replicating cells was observed in cells transfected with HBX, the smallest HBV protein, suggesting its involvement in this cellular process. In addition, a proline rich region found in many SH3 binding proteins was identified in HBX. HBX was found to interact with the focal adhesion protein, vinexin-beta, through the SH3 binding. Furthermore, HepG2 cells with HBV replication showed evidence of cell rounding up, possibly resulting from cytoskeletal reorganizations associated with interaction between HBX and vinexin-beta. Taken together, our results suggest that HBX is involved in the cytoskeletal reorganization in response to HBV replication.