转人肝刺激物质基因的肝癌细胞增殖状态研究

本文通过研究转染人肝刺激物质（hepatic stimulator substance,HSS）的肝癌细胞增殖状态,进一步探讨了该基因的生物功能。将人HSS基因导入BEL－7402肝癌细胞,用Northern和Southern杂交法证实该基因在靶细胞中有稳定表达。并通过测定细胞生长曲线、细胞S期比例和细胞MAPK活性,观察到转HSS基因BEL－7402细胞增殖发生了改变。实验结果提示,HSS表达的肝癌细胞DNA合成增加、增殖速度加快,可能与MAPK激活有关,HSS基因表达可促进细胞增殖。     

Chromosome remodeling related to hepatitis B virus replication in HepG2 cells

Hepatitis B Virus (HBV) covalently closed circular DNA (cccDNA) is the main replicative intermediate of HBV and is organized into minichromosomes by the interaction with histone and nonhistone proteins. The remodeling of HBV minichromosomes such as post-translational modifications of histone proteins plays an important role in regulating HBV replication. To determine whether other remodeling occurs in addition to acetylation of cccDNA-bound H3 histones in the presence of HBV replication, a cell culture replication model of HBV was used to assess the dynamic status of acetylation, phosphorylation, and methylation of cccDNA-bound H3 histones at various times after transient transfection of linear HBV DNA into human hepatoma, HepG2 cells. H3 histones bound to cccDNA were found to be phosphorylated, mono-methylated, and acetylated in HepG2 cells containing replicating HBV. The acetylation and methylation status of H3 histones bound to cccDNA paralleled HBV replication. Our results demonstrate that phosphorylation and methylation occur in the remodeling of HBV minichromosomes during HBV replication. The modifications of cccDNA-bound H3 histones were associated with the level of HBV replication. These findings suggest that alterations in the extent of minichromosome remodeling might be a potential target to inhibit HBV replication in the development of effective novel antiviral agents.     

Increased frequency of micronuclei in the lymphocytes of patients chronically infected with hepatitis B or hepatitis C virus

In this study, we analysed the frequency of micronuclei (MN), nucleoplasmic bridges (NPBs) and nuclear buds (NBUDs) and evaluated mutagen-induced sensitivity in the lymphocytes of patients chronically infected with hepatitis B virus (HBV) or hepatitis C virus (HCV). In total, 49 patients with chronic viral hepatitis (28 HBV-infected and 21 HCV-infected patients) and 33 healthy, non-infected blood donor controls were investigated. The frequencies (‰) of MN, NPBs and NBUDs in the controls were 4.41 ± 2.15, 1.15 ± 0.97 and 2.98 ± 1.31, respectively. The frequencies of MN and NPBs were significantly increased (p < 0.0001) in the patient group (7.01 ± 3.23 and 2.76 ± 2.08, respectively) compared with the control group. When considered separately, the HBV-infected patients (7.18 ± 3.57) and HCV-infected patients (3.27 ± 2.40) each had greater numbers of MN than did the controls (p < 0.0001). The HCV-infected patients displayed high numbers of NPBs (2.09 ± 1.33) and NBUDs (4.38 ± 3.28), but only the HBV-infected patients exhibited a significant difference (NPBs = 3.27 ± 2.40, p < 0.0001 and NBUDs = 4.71 ± 2.79, p = 0.03) in comparison with the controls. Similar results were obtained for males, but not for females, when all patients or the HBV-infected group was compared with the controls. The lymphocytes of the infected patients did not exhibit sensitivity to mutagen in comparison with the lymphocytes of the controls (p = 0.06). These results showed that the lymphocytes of patients who were chronically infected with HBV or HCV presented greater chromosomal instability.     

Conditional replication of duck hepatitis B virus in hepatoma cells

To facilitate investigations of replication and host cell interactions in the hepadnavirus system, we have developed cell lines permitting the conditional replication of duck hepatitis B virus (DHBV). With the help of this system, we devised conditions for core particle isolation that preserve replicase activity, which was not found in previous preparations. Investigations of the stability of viral DNA intermediates indicated that both encapsidated DNA and covalently closed circular DNA (cccDNA) were turned over independently of cell division. Moreover, we showed that alpha interferon reduced the accumulation of RNA-containing viral particles. The availability of a synchronized replication system will permit the biochemical analysis of individual steps of the viral replication cycle, including the mechanism and regulation of cccDNA formation.     

Vaccine against human hepatitis B virus prepared from antigen derived from human hepatoma cells in culture

Vaccine against human hepatitis B was prepared using antigen derived from hepatitis B carrier hepatoma cells grown in the interstices of a Diaflo hollow filter unit. Hepatitis B surface antigen (HBsAg) produced by these cells was purified by immune affinity chromatography, digestion with DNase and pepsin, and Sephadex G-150 separation. The Formalin-treated antigen was formulated in 20-micrograms dose on alum adjuvant with thimerosal added as a preservative. This cell culture vaccine was as potent as human plasma-derived vaccine as measured in a mouse potency assay. The vaccine proved safe in tests in chimpanzees and in human subjects who were in late stages of cancer of the central nervous system and who were receiving therapy for their condition. None of five subjects who received the vaccine developed untoward clinical reactions. Two of the subjects who received all three doses of vaccine developed antibody against HBsAg. Three persons, two given only the primary doses and one who was given all three doses but was lost to follow-up, demonstrated no response. The slow and relatively low antibody responses to the vaccine were similar to those in other immunosuppressed persons who were given vaccine of human plasma origin.     

Tryptophan and iodothyronine transport interactions in HepG2 human hepatoma cells

This study identifies interactions between transport of the aromatic amino acid l-tryptophan (Trp) and thyroid hormones (TH) in HepG2 human hepatoma cells. The major portion of Trp uptake in HepG2 cells occurs via the NEM-sensitive amino acid transport System L2 (consistent with hepatic LAT3 expression), with a smaller aromatic-AA selective System T (MCT10) component. LAT3 and MCT10 mRNA were both detected in HepG2 cells. Uptake of TH does not involve System L2, but a significant portion of T₃ uptake is mediated by System T, alongside a taurocholate-sensitive organic anion transporter. T₄ uptake into HepG2 cells appears to be mediated principally by organic anion/monocarboxylate transporters, with smaller contributions by System T and receptor-mediated endocytosis. TH–Trp transport interactions in liver cells centre on System T which, due to a perivenous localisation alongside deiodinase 1, may impact on hepatic T₃ generation and release.     

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.     

Rearrangement of the surface antigen gene of hepatitis B virus integrated in the human hepatoma cell lines.

The rearrangement of integrated HBV DNA sequences in three different hepatoma cell lines, huH-1, huH-2, KG-55-T from Japanese patients, were studied by blot hybridization using whole HBV genome or a HBsAg or HBcAg DNA as a probe. The characteristic existence of multiple integration sites of HBV DNA sequences in each HindIII-restricted hepatoma cell DNA was revealed by the HBV genome probe. Detection of the isolated HBsAg gene in the HindIII fragment indicates that the integration of HBV DNA was not always related to the maintenance of the whole viral genome, and that movement of the HBsAg gene to another location occurred by rearrangement. On the other hand, the presence of the HBV DNA sequence without the intact HBcAg gene was shown in some of the HindIII fragments, when the HBcAg gene, probe was used, but a HindIII fragment, containing only the HBcAg gene, was not detected so far. The absence of the intact HBcAg gene suggests that the viral genome may lose a part of the HBcAg gene in the process of integration. This is consistent with recent findings of Ogston et al. (1982) that in Woodchuck hepatocellular carcinoma viral sequences are extensively rearranged.     

Control of gene expression by the retinoic acid-related orphan receptor alpha in HepG2 human hepatoma cells

Retinoic acid-related Orphan Receptor alpha (RORα; NR1F1) is a widely distributed nuclear receptor involved in several (patho)physiological functions including lipid metabolism, inflammation, angiogenesis, and circadian rhythm. To better understand the role of this nuclear receptor in liver, we aimed at displaying genes controlled by RORα in liver cells by generating HepG2 human hepatoma cells stably over-expressing RORα. Genes whose expression was altered in these cells versus control cells were displayed using micro-arrays followed by qRT-PCR analysis. Expression of these genes was also altered in cells in which RORα was transiently over-expressed after adenoviral infection. A number of the genes found were involved in known pathways controlled by RORα, for instance LPA, NR1D2 and ADIPOQ in lipid metabolism, ADIPOQ and PLG in inflammation, PLG in fibrinolysis and NR1D2 and NR1D1 in circadian rhythm. This study also revealed that genes such as G6PC, involved in glucose homeostasis, and AGRP, involved in the control of body weight, are also controlled by RORα. Lastly, SPARC, involved in cell growth and adhesion, and associated with liver carcinogenesis, was up-regulated by RORα. SPARC was found to be a new putative RORα target gene since it possesses, in its promoter, a functional RORE as evidenced by EMSAs and transfection experiments. Most of the other genes that we found regulated by RORα also contained putative ROREs in their regulatory regions. Chromatin immunoprecipitation (ChIP) confirmed that the ROREs present in the SPARC, PLG, G6PC, NR1D2 and AGRP genes were occupied by RORα in HepG2 cells. Therefore these genes must now be considered as direct RORα targets. Our results open new routes on the roles of RORα in glucose metabolism and carcinogenesis within cells of hepatic origin.     

Rebound of hepatitis B virus replication in HepG2 cells after cessation of antiviral treatment

Treatment of patients with lamivudine (3TC) results in loss of detectable levels of hepatitis B virus (HBV) DNA from serum; however, the relapse rate, with regard to both reappearance of virus in the bloodstream and hepatic inflammation, is high when therapy is terminated. Although the rebound observed in patients has also been seen in animal hepadnavirus models, rebound has not been analyzed in an in vitro cell culture system. In this study, we used the HBV recombinant baculovirus/HepG2 system to measure the time course of antiviral agent-mediated loss of HBV replication as well as the time course and magnitude of HBV production after release from antiviral treatment. Because of the sensitivity of the system, it was possible to measure secreted virions, intracellular replicative intermediates, and nuclear non-protein-bound HBV DNA and separately analyze individual species of DNA, such as single-stranded HBV DNA compared to the double-stranded form and relaxed circular compared to covalently closed circular HBV DNA. We first determined that HBV replication in the HBV recombinant baculovirus/HepG2 system could proceed for at least 35 days, with a 30-day plateau level of replication, making it possible to study antiviral agent-mediated loss of HBV followed by rebound after cessation of drug treatment. All HBV DNA species decreased in a time-dependent fashion following antiviral treatment, but the magnitude of decline differed for each HBV DNA species, with the covalently closed circular form of HBV DNA being the most resistant to drug therapy. When drug treatment ceased, HBV DNA species reappeared with a pattern that recapitulated the initiation of replication, but with a different time course.     

Replicative intermediates of hepatitis B virus in HepG2 cells that produce infectious virions.

Clonal cells derived from HepG2 cells transfected with a plasmid containing hepatitis B virus (HBV) DNA secrete hepatitis B surface antigen particles, nucleocapsids, and virions (M. A. Sells, M.-L. Chen, and G. Acs, Proc. Natl. Acad. Sci. USA 84:1005-1009, 1987) which elicit acute hepatitis in chimpanzees (G. Acs, M. A. Sells, R. H. Purcell, P. Price, R. Engle, M. Shapiro, and H. Popper, Proc. Natl. Acad. Sci. USA 84:4641-4644, 1987). We report here the initial characterization of the viral nucleic acids produced in this culture system. Kinetic analyses of nuclear, cytoplasmic, and extracellular HBV DNAs were performed by Southern blotting with radiolabeled HBV strand-specific probes. The results from these analyses indicate that at the stationary cellular growth phase, there is a dramatic increase in the rate at which HBV DNA accumulates. Incomplete double- and single-stranded forms of the HBV genome were detected in the nuclear and cytoplasmic fractions as well as in the extracellular medium. In addition, the nuclear DNA apparently includes multiple complete copies of the HBV genome chromosomally integrated and full-length covalently closed circular HBV DNA. Multiple HBV-specific polyadenylated RNAs with lengths of 3.5, 2.5, and 2.1 kilobases were identified by Northern (RNA) blot analysis. S1 nuclease mapping and primer extension identified a single 3' end and multiple unique initiation sites corresponding to nucleotides just 5' to the pre-S1 region, as well as upstream and within the pre-S2 and precore regions. The nucleic acid profile obtained from these analyses is essentially a facsimile of that obtained by studying liver tissue from HBV-infected individuals.     

Elimination of apolipoprotein B48 formation in rat hepatoma cell lines transfected with mutant human apolipoprotein B cDNA constructs.

Rat hepatoma McA-RH7777 cell lines transfected with full-length human apolipoprotein (apo) B constructs produce mostly human apoB48 and only small amounts of apoB100, as a result of mRNA editing at codon 2153 (C to U conversion at nucleotide 6666). To abolish the formation of apoB48 and increase the yield of apoB100 and other forms of apoB longer than apoB48, site-specific mutations were introduced at or near the site of apoB mRNA editing. Among four mutations examined, only that in which codon 2153 was converted from CAA (Gln) to CTA (Leu) effectively precluded the formation of apoB48. In this mutant, a stop codon would not be generated even if the C to U conversion occurred. The three other mutations were introduced to disrupt the proposed stem-loop structure encompassing the editing site. Changes made in the third positions of five codons on the 5' side of the edited base or of four codons 3' of the edited base failed to eliminate the production of a protein with the approximate size of apoB48. A construct in which codon 2153 was changed from CAA to GAT (Asp) also failed to eliminate the production of a protein the size of apoB48. Analysis of the region between nucleotides 6200 and 6900 of the cDNA did not detect any prevalent alternate editing sites. Immunoblot analysis using polyclonal antibodies raised against synthetic peptides of human apoB100 indicated that the carboxyl terminus of the apoB48-like proteins probably resides between amino acid residues 2068 and 2129 of apoB100. These results provide some insight into the mechanism of apoB mRNA editing and will facilitate further studies on apoB-containing lipoproteins.     

Expression of the hepatitis B virus surface antigen gene by rat hepatocyte X mouse hepatoma hybrid cells

The expression of the S gene of hepatitis B virus has been studied in the somatic hybrid cells resulting from the fusion between rat hepatocytes in primary culture and cells of the mouse hepatoma line BWTG3, and in the parental line BWTG3. The DNA of the S gene inserted into the plasmids pAC Tk+ and pNY4 has been co-transfected into these cells with a plasmid DNA bearing a resistance gene to aminoglycoside. The level of expression of the S gene among the co-transfected resistant clones was estimated by radioimmunoassay. The results show that a high number of the co-transfected cellular hybrid clones express the S gene, whereas it is found, by contrast, that the S gene is poorly expressed in the mouse hepatoma cells. The level of expression of the S gene (as the amount of HBs Ag synthesized) is high in the hybrid clones and the synthesis of the HBs antigen is stable in time. These observations suggest for the first time in cell cultures in vitro, the role which is probably played by the normal hepatocyte genome in the expression of the S gene of HBV.     

Insulin suppresses hepatitis B surface antigen expression in human hepatoma cells

The human hepatoma Hep3B cells contain integrated hepatitis B viral genome and continually secret hepatitis B surface antigen (HBsAg). The production of HBsAg (but not alpha-fetoprotein) was suppressed by addition of low concentrations (0.1-1 nM) of insulin into serum-free medium. In addition, the suppression of HBsAg production by insulin was paralleled with the decrease in HBsAg mRNA abundance. Insulin also cause a rapid rate of disappearance of HBsAg mRNA (t 1/2, 2 h) in Hep3B cells. The Hep3B cells carry specific receptor with high affinity for insulin (Kd = 1.8 nM). The receptor showed an insulin-dependent protein tyrosine kinase activity. The half-maximal insulin concentration for the activation of the receptor kinase was about 5 nM. Only very high concentrations of insulin-like growth factor I and human proinsulin can compete for the insulin receptor binding and suppress HBsAg production, this suggests that insulin may act through its receptor binding to suppress HBsAg expression in human hepatoma Hep3B cells.