Expression of the X protein of hepatitis B virus in insect cells using recombinant baculoviruses

The impact of hepatitis B virus x protein and microRNAs in hepatocellular carcinoma: a comprehensive analysis

microRNAs (miRNAs) are evolutionarily conserved small non-coding RNAs, approximately 22 nucleotides (nts) in length, widely found in animals, plants, and viruses. Mature miRNAs control gene expression at a post-transcriptional level through blocking protein translation or inducing mRNA degradation. Many recent studies have shown that hepatitis B virus x protein (HBx), a viral protein with a crucial role in hepatogenesis, is associated with the regulation of miRNAs. This interaction impacts fundamental tumor processes, such as cell proliferation, differentiation, and apoptosis. In this review, we summarized the recent literature on the roles of HBx-regulated miRNAs in the pathogenesis of hepatocellular carcinoma.

The viral transactivator HBx protein exhibits a high potential for regulation via phosphorylation through an evolutionarily conserved mechanism

BACKGROUND

Hepatitis B virus (HBV) encodes an oncogenic factor, HBx, which is a multifunctional protein that can induce dysfunctional regulation of signaling pathways, transcription, and cell cycle progression, among other processes, through interactions with target host factors. The subcellular localization of HBx is both cytoplasmic and nuclear. This dynamic distribution of HBx could be essential to the multiple roles of the protein at different stages during HBV infection. Transactivational functions of HBx may be exerted both in the nucleus, via interaction with host DNA-binding proteins, and in the cytoplasm, via signaling pathways. Although there have been many studies describing different pathways altered by HBx, and its innumerable binding partners, the molecular mechanism that regulates its different roles has been difficult to elucidate.

METHODS

In the current study, we took a bioinformatics approach to investigate whether the viral protein HBx might be regulated via phosphorylation by an evolutionarily conserved mechanism.

RESULTS

We found that the phylogenetically conserved residues Ser25 and Ser41 (both within the negative regulatory domain), and Thr81 (in the transactivation domain) are predicted to be phosphorylated. By molecular 3D modeling of HBx, we further show these residues are all predicted to be exposed on the surface of the protein, making them easily accesible to these types of modifications. Furthermore, we have also identified Yin Yang sites that might have the potential to be phosphorylated and O-β-GlcNAc interplay at the same residues.

CONCLUSIONS

Thus, we propose that the different roles of HBx displayed in different subcellular locations might be regulated by an evolutionarily conserved mechanism of posttranslational modification, via phosphorylation.

Prognostic analysis in chronic hepatitis B patients: a retrospective study of 216 cases about Scheuer scores, in situ expression of viral antigens and tissue hepatitis B virus DNA levels

BACKGROUND

Most of the previous studies of patients with chronic hepatitis B virus (HBV) infection concentrated on serum samples. Liver biopsy specimens for HBV have not been systematically analyzed. This study was performed to analyze some histopathological indicators (Scheuer scores, the expression of HBV antigens in situ, HBV DNA quantification) in the biopsy samples and showed the relationship among them and the prognosis of chronic hepatitis.

METHODS

A total of 216 consecutive chronic HBV-infected patients were followed up by clinical and laboratory data and classified into two groups at first: carcinogenesis and non-carcinogenesis. The non-carcinogenesis also included two groups: cirrhosis and non-cirrhosis. The non-cirrhosis was still divided into fluctuation and normalization at last. Histological activity index was described by Scheuer scores. Two-step immunohistochemical staining showed the expression of viral antigens in situ. Tissue HBV DNA levels were determined by fluorescence quantitative real-time PCR.

RESULTS

Regression analysis revealed significant positive correlations between the expression of hepatitis B e antigen (HBeAg) and grading, as well as between hepatitis Bx (HBx) protein and grading or staging of Scheuer scores. Positive correlations between grading or staging and prognosis were statistically significant. The expressions of HBeAg and HBx protein were higher in patients with cirrhosis than those without cirrhosis. Scheuer score was the most important indicator of prognosis.

CONCLUSIONS

HBeAg and HBx protein can be used as indicators of hepatitis activity and their positive expressions increase the risk for cirrhosis remarkably. In addition to be a marker of liver damage, Scheuer score is the most reliable indicator of the prognosis.

Inhibition of tumorigenicity of the hepatitis B virus X gene in Chang liver cell line

The hepatitis B virus X gene, which encodes the HBx protein, has multiple functions and is involved in hepatocarcinogenesis. However, the exact role of HBx in hepatocarcinogenesis is still controversial. We have established an inducible (tet-off system) HBx-expressing cell line, Chang-HBx. Compared with the original of Chang liver cell line (ATCC CCL13), Chang-HBx grows faster in serum-containing medium but slower in serum-free medium. Chang-HBx colony formation in soft agar shows an anchorage-demanding character and its tumorigenicity potential in BALB/c nude mice were substantially inhibited. HBx also causes the induction of G1 phase arrest of cell growth in early infection of HBV and therefore plays a negative role in tumorigenicity. An excellent mice animal model for producing hepatoma was also provided in this study.

Characterization and gene cloning of monoclonal antibody specific for the hepatitis B virus X protein

The hepatis B virus X protein (HBx) has been thought to be implicated in the development of hepatocellular carcinoma. Although many functions of HBx have been reported, it is not clear which of HBx functions is important in hepatocellular carcinogenesis. To study HBx function, we produced a monoclonal anti-HBx Ab secreted by hybridoma cell clone H7 and mapped its epitope to a region of HBx between amino acids 29 and 48 by Western blot with truncated forms of HBx and by enzyme-linked immunoadsorbent assay (ELISA) with synthetic HBx peptides. The variable regions of H7 anti-HBx Ab were cloned by polymerase chain reaction using the degenerate-primers and by the 5' rapid amplification-cDNA end method. The sequence analyses revealed that the variable gene segments of the heavy and light chains are the members of mouse heavy chain variable gene 1 family and kappa light chain variable gene 2 family, respectively. In addition, J(H)2 or Jkappa4 gene segment at the end of the heavy-chain or light-chain variable region and DSP2.x gene segment in the CDR 3 of heavy chain were identified.

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.

Expression of hepatitis B virus X protein in HBV-infected human livers and hepatocellular carcinomas

Transactivation of cellular genes and functional inactivation of p53 by the hepatitis B virus (HBV) X gene-encoded protein (HBx) are proposed as alternative mechanisms for induction of hepatocellular carcinomas (HCCs) in chronic HBV infection. Using an immunohistochemical approach, we studied the expression of HBx in 39 explanted livers with HBV-associated disease. Because the data reported previously have been inconsistent, possibly due to the application of different antibodies, we compared results with 5 polyclonal and 6 monoclonal anti-HBx antibodies from five laboratories. Ten of the 11 antibodies reacted with recombinant HBx by Western blotting, but only 1 polyclonal and 2 monoclonal antibodies reacted specifically with HBx in tissue, and were thus suitable for immunohistochemistry. Three other polyclonal antibodies reacted with tissue components in addition to HBx. One polyclonal and 4 monoclonal antibodies did not recognize the HBx in the tissue. HBx was demonstrated in 16 of 30 (53.3%) cirrhotic livers and 10 of 18 (58.8%) HCCs by all specific antibodies. The expression of HBx, among three HBV antigens examined, was found to be preferentially maintained in HCC and the surrounding liver parenchyma, including focal or nodular preneoplastic lesions. However, the immunoreactivity was always limited to the cytoplasm of a small number of parenchymal and neoplastic cells. The role of X gene expression in HBV-associated human hepatocarcinogenesis remains to be established.

Transactivating function and expression of the x gene of hepatitis B virus

BACKGROUND/AIMS

The x gene of hepatitis B virus encodes a transactivating factor of 154 amino acids, termed HBx, which stimulates transcription of multiple viral and cellular genes. The transactivating function is probably associated with a tumorigenic potential of HBx, since x gene sequences, encoding functional HBx, have been repeatedly found integrated into the genome of liver carcinoma cells.

METHODS

To identify the transactivating domain of HBx, we constructed x gene plasmids encoding full length HBx or HBx fragments. We determined their transactivating function after cotransfection of cells, along with a plasmid that contains a reporter gene driven by the SV40 early promoter/enhancer region.

RESULTS

Our results demonstrate that a 95-amino acid fragment of HBx, encompassing amino acids 49 to 143, contains all the elements that are required for the transactivating function. Within this fragment a sequence element, encompassing amino acids 107 to 130, which contains a relatively high number of amino acids with charged side chains, appears to be crucial for the stimulation of gene expression. The influence of deletion mutations on x mRNA steady-state levels and HBx stability was examined. In essence, stable RNA and protein were produced if at least codons 1-82 or 70-154 were present in the deletion plasmids.

CONCLUSION

This finding strongly suggests that the deletion of functional domains between codons 49 and 143, but not an instability of RNA and/or protein, was critical for the loss of transactivation.

Primary structure and microtubule-interacting domain of the SP-H antigen: a mitotic MAP located at the spindle pole and characterized as a homologous protein to NuMA

Using a human autoantibody, SP-H, we identified a 200–230 kDa mitotic MAP in a variety of mammalian cell lines which shows affinity for the minus end of microtubules and also becomes associated with the spindle pole during mitosis. To examine the detailed structure and functional organization of the protein, the gene coding for the end-specific MAP was isolated and characterized by screening a human placenta lambda gt11 expression library using SP-H as a probe. Overlapping cDNA clones, which covered the entire length of the coding region of the SP-H antigen, were obtained. Polyclonal antibodies raised against fusion proteins generated from non-overlapping cDNA fragments stained the HeLa SP-H antigen in interphase and mitotic cells, and recognized a single 215 kDa band on immunoblots, as did the original SP-H antibody. Analysis of the nucleotide sequence revealed a 7,091 nucleotide sequence with an open reading frame of 6,345 nucleotides encoding a 2,115 amino acid polypeptide with a calculated molecular mass of 238,376 Da. The predicted amino acid sequence showed the protein to be composed of an alpha-helical domain, flanked by globular domains located at the amino and carboxy termini. The sequence contained five repeats of the hypothetical leucine zipper motif: one is in the N-terminal globular domain, and four are in the central alpha-helical stalk. Comparison with other sequences in the database shows that the SP-H antigen is identical to the NuMA protein reported by Yang et al. (1992) J. Cell Biol. 116, 1303–1317, but there are differences between the SP-H antigen and NuMA sequence reported by Compton et al. (1992) J. Cell Biol. 116, 1395–1408. cDNA inserts of the truncated SP-H antigen were expressed in both insect Sf9 cells and in cultured mammalian cells. The recombinant protein corresponding to the C-terminal half of the protein was restricted to the nucleus, whereas the N-terminal half of the protein was localized in the cytoplasm, suggesting the presence of a nuclear translocation signal(s) in the C-terminal domain. The C-terminal polypeptide expressed in mitotic COS cells was shown to specifically localize at the spindle pole. Microtubule-binding assays using in vitro transcribed/translated polypeptide products from different domains of the SP-H antigen further suggested that the SP-H antigen interacts with microtubules through the globular domain at the C-terminus.