Anti-HBV hairpin ribozyme-mediated cleavage of target RNA in vitro

Progress and Prospects of Anti-HBV Gene Therapy Development

Despite the availability of an effective vaccine against hepatitis B virus (HBV), chronic infection with the virus remains a major global health concern. Current drugs against HBV infection are limited by emergence of resistance and rarely achieve complete viral clearance. This has prompted vigorous research on developing better drugs against chronic HBV infection. Advances in understanding the life cycle of HBV and improvements in gene-disabling technologies have been impressive. This has led to development of better HBV infection models and discovery of new drug candidates. Ideally, a regimen against chronic HBV infection should completely eliminate all viral replicative intermediates, especially covalently closed circular DNA (cccDNA). For the past few decades, nucleic acid-based therapy has emerged as an attractive alternative that may result in complete clearance of HBV in infected patients. Several genetic anti-HBV strategies have been developed. The most studied approaches include the use of antisense oligonucleotides, ribozymes, RNA interference effectors and gene editing tools. This review will summarize recent developments and progress made in the use of gene therapy against HBV.

Intervention of geminiviral replication in yeast by ribozyme mediated downregulation of its Rep protein

Geminiviruses pose serious threat to many economically important crops such as mungbean, tomato, cotton, etc. To devise a specific antiviral strategy at the viral DNA replication level, a hammerhead ribozyme was directed against the mRNA of the replication initiator protein (Rep). Rep is the most important viral protein for the DNA replication of the Mungbean yellow mosaic India virus (MYMIV), a member of the Geminiviridae family. The ribozyme showed approximately 33% cleavage activity on synthetic rep transcript within 1h under in vitro conditions, whereas the mutant ribozyme, designed to lack the catalytic activity but target the same site, showed no cleavage. The in vivo efficiency of ribozyme was evaluated in Saccharomyces cerevisiae as it can act as a surrogate host for replication of the MYMIV-DNA and lacks RNAi machinery. In the presence of the ribozyme, growth of the yeast cells that are dependent on geminiviral replication was inhibited by 30% and cellular generation time was increased by 2h. The RT-PCR analysis showed a maximum of about 50% reduction in the rep mRNA level in presence of the ribozyme compared to its noncatalytic mutant control. About 65% decrease in geminiviral DNA replication was observed due to the downregulation of replication initiator protein by the ribozyme. These results raise the possibility of engineering resistance to geminiviruses employing the ribozyme approach.

Activity identification of ribozyme and U1 snRNA chimeric ribozyme against TGFbeta1 in cell-free system and in hepatic stellate cells

Transforming growth factorbeta1 (TGFbeta1) is known to be intimately involved in many cellular processes. To explore the mechanism of TGFbeta1 in these processes, the non-chimeric hammerhead ribozyme and U1 snRNA chimeric ribozyme against TGFbeta1 were designed to down-regulate TGFbeta1 expression. The activity of non-chimeric ribozyme and U1 snRNA chimeric ribozyme against TGFbeta1 in vitro and in activated hepatic stellate cells (HSCs) was detected. Cleavage reactions of both ribozymes in vitro demonstrated that non-chimeric ribozyme possessed better cleavage activity in vitro than U1 snRNA chimeric ribozyme. The further study showed U1 snRNA chimeric ribozyme inhibited TGFbeta1 expression more efficiently than non-chimeric ribozyme in transfected HSC cells. So it indicates that the U1 snRNA chimeric ribozyme provides an alternative approach for the research on the precise mechanism of TGFbeta1 in many cellular processes and a potential therapeutic candidate for TGFbeta1-related diseases.

Effect of ribozyme against transforming growth factorbeta1 on biological character of activated HSCs

Transforming growth factorbeta1 (TGFbeta1) is considered to be the principal contributor to liver fibrosis. So in this study the ribozymes against TGFbeta1 were designed. The in vitro cleavage activities of the ribozymes were assayed through incubation of (32)p-labeled target RNAs and (32)p-labeled ribozymes in different conditions. HSC-T6 cells were transfected with the eukaryotic constructs encoding ribozyme and disable ribozyme, then the stable cell clones were used to evaluate its antifibrotic characteristic through the effect of ribozyme on biological character of activated hepatic stellate cells (HSCs). The results demonstrated that two ribozymes (Rz803 and Rz1395) could cleave target RNAs into expected products effectively, Rz803 possessed better cleavage activity in vitro. Stable transfection of Rz803 into activated HSCs reduced TGFbeta1 expression in mRNA and protein level efficiently. The further studies demonstrated that Rz803 reduced deposition of collagen I, suppressed HSC proliferation, but had no effect on HSC activation in transfected HSC-T6 cells. Therefore, it indicated that Rz803 could reverse the character of activated HSCs by down-regulating TGFbeta1 expression efficiently and diminishing TGFbeta1 signaling underlying activation of hepatic stellate cells. As the consequence, it would provide a potential therapeutic approach for liver fibrosis.

Construction of hepatitis B virus X gene expression vector in eucaryotic cells and its transfection in HL-7702 cells

AIM: To establish a human hepatocyte cell line which can express hepatitis B virus (HBV) X gene.

METHODS: HBV X gene was obtained through PCR techn-ology. After A-tailing added, X gene was connected into vector PUCmT. Vector PUCmT-X and PcDNA3 were digested with EcoRI and HindIII. The fragments of X and PcDNA3 were connected to establish reconstituted plasmid PcDNA3-X. Then PcDNA3-X and PcDNA3 were transfected into HL-7702 cells by lipid-mediated transfection. After selected with G418, HL-7702/HBx cells were analysed by the reverse transcription-PCR to confirm the steady expression of X gene in HL-7702.

RESULTS: Reconstituted plasmid PcDNA3-X included the anticipated fragment of HBV X gene was proved by auto-sequencing assay. RT-PCR analysis showed that reconstituted plasmid PcDNA3-X could express the X protein efficiently in HL-7702 cells.

CONCLUSION: Hepatocyte can express HBV X gene, which is an ideal model to study the effect of HBV X gene on the development of hepatitis and hepatocelular carcinoma.

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Inhibition of HBV targeted ribonuclease enhanced by introduction of linker

AIM: To construct human eosinophil-derived neurotoxin(hEDN) and HBV core protein (HBVc) eukaryotic fusion expression vector with a linker (Gly₄Ser)₃ between them to optimize the molecule folding, which will be used to inhibit HBV replication in vitro.

METHODS: Previously constructed pcDNA3.1(-)/TR was used as a template. Linker sequence was synthesized and annealed to form dslinker, and cloned into pcDNA3.1(-)/TR to produce plasmid pcDNA3.1(-)/HBc-linker. Then the hEDN fragment was PCR amplified and inserted into pcDNA3.1(-)/HBc-linker to form pcDNA3.1(-)/TNL in which the effector molecule and the target molecule were separated by a linker sequence. pcDNA3.1(-)/TNL expression was identified by indirect immunofluorescence staining. Radioimmunoassay was used to analyse anti-HBV activity of pcDNA3.1(-)/TNL. Meanwhile, metabolism of cells was evaluated by MTT colorimetry.

RESULTS: hEDN and HBVc eukaryotic fusion expression vector with a linker (Gly4Ser)3 between them was successfully constructed. pcDNA3.1(-)/TNL was expressed in HepG2.2.15 cells efficiently. A significant decrease of HBsAg concentration from pcDNA3.1(-)/TNL transfectant was observed compared to pcDNA3.1(-)/TR (P = 0.036, P < 0.05). MTT assay suggested that there were no significant differences between groups (P = 0.08, P > 0.05).

CONCLUSION: Linker introduction enhances the inhibitory effect of HBV targeted ribonuclease significantly.

Anti-HBV effect of TAT- HBV targeted ribonuclease

AIM: To prepare and purify TAT-HBV targeted ribonuclease fusion protein, evaluate its transduction activity and investigate its effect on HBV replication in 2.2.15 cells.

METHODS: The prokaryotic expression vector pTAT containing TR gene was used in transforming E.coli BL21 (DE3) LysS and TR was expressed with the induction of IPTG. The TAT-TR fusion protein was purified using Ni-NTA-agrose and PD-10 desalting columns, and analyzed by SDS-PAGE. Transduction efficiency of TAT-TR was detected with immunofluorescence assay and the concentration of HBeAg in the supernatant of the 2.2.15 cells was determined via solid-phase radioimmunoassay (spRIA). MTT assay was used to detect the cytotoxicity of TAT-TR.

RESULTS: The SDS-PAGE showed that the TAT-TR fusion protein was purified successfully, and the purity of TAT-TR was 90%. The visualization of TAT-TR by immunofluorescence assay indicated its high efficiency in transducing 2.2.15 cells. RIA result suggests that TAT-TR could inhibit the replication of HBV effectively, it didn’t affect cell growth and had no cytotoxicity.

CONCLUSION: TAT-TR possesses a significant anti-HBV activity and the preparation of TAT-TR fusion protein has laid the foundation for the use of TR in the therapeutic trial of HBV infection.

Expression of HLA-I on HepG2 cells by hepatitis B virus nucleocapsid mutants

AIM

To study the expression of HLA-I/antigen peptide complex on HepG2 cells transfected with HBV (adr) wild type and nucleocapsid protein mutants.

METHODS

The site-directed mutation was performed to introduce nucleocapsid protein point mutations V60 and L97 into 1.2 copies of HBV genome plasmid p3.8 Ⅱ. After identification of DNA sequence and biological activities, the plasmid p3.8Ⅱ and mutant plasmid constructs were subcloned respectively into EB virus based vector EBO-plpp for stable expression. The vector constructed EBO-wild type, EBO-V60, and EBO-L97 were analyzed by restriction enzyme digestion and DNA sequenceing, then transfected into HepG2 cells via the liposome technique, respectively. HBV antigen in their culture supernatants was quantified by Abbott kits. The cells were stained with murine monoclonal antibody anti-HLA-ABC conjugated directly to FITC, and expression of HLA-I on their membrane was analyzed by flow-cytometry.

RESULTS

Restriction enzyme digestion of 3 vector constructs showed two bands similar to HBV 1.2 copies genome and EBO vector, respectively. Analysis of DNA sequence confirmed the mutated nucleotides of EBO-V60 and EBO-L97 (i.e nt2078 C→G, nt2189 A→C). The expression of HBeAg S/CO in culture supernatant of EBO-wild type was much higher than that of mutant EBO-V60 and EBO-L97, while the expression of HBsAg S/N in three constructs had similar level, indicating similar transfecting rate in this experiment. The expression of HLA-I on HepG2 cells transfected with EBO empty vector was at low level. Fluorescence intensity of HLA-I expression of transfected cells was elevated by EBO-wild type (18.2), while that of L97 was increased to 34.5 and V60 declined to 3.4.

CONCLUSION

HBV might enhance the expression of HLA-I/antigen peptide complex on HepG2 cells. Hot-spot mutations of HBV nucleocapsid protein L97 and V60 could influence the expression level of HLA-I on host cells.

Maxizyme-mediated specific inhibition on mutant-type p53 in vitro

AIM: To evaluate the specific inhibition of maxizyme directing against mutant-type p53 gene (mtp53) at codon 249 in exon 7 (AGG→AGT) in vitro.

METHODS: Two different monomers of anti-mtp53 maxizyme (maxizyme right MzR, maxizyme left MzL) and control mutant maxizyme (G⁵→A⁵) were designed by computer and cloned into vector pBSKU6 (pBSKU6MzR, pBSKU6MzL). After being sequenced, the restrictive endonuclease site in pBSKU6MzR was changed by PCR and then U6MzR was inserted into pBSKU6MzL, the recombinant vector was named pU6Mz and pU6asMz (mutant maxizyme). Mtp53 and wild-type p53 (wtp53) gene fragments were cloned into pGEM-T vector under the T7 promoter control. The ³²p-labeled mtp53 transcript was the target mRNA. Cold maxizyme transcripts were incubated with ³²p-labeled target RNA in vitro and radioautographed after denaturing polyacrylamide gel electrophoresis.

RESULTS: In cell-free systems, pU6Mz showed a specific cleavage activity against target mRNA at 37 °C and 25 mM MgCL₂. The cleavage efficiency of pU6Mz was 42%, while pU6asMz had no inhibitory effect. Wtp53 was not cleaved by pU6Mz either.

CONCLUSION: pU6Mz had a specific catalytic activity against mtp53 in cell-free system. These lay a good fundation for studying the effects of anti-mtp53 maxizyme in HCC cell lines. The results suggest that maxizyme may be a promising alternative approach for treating hepatocellular carcinoma containing mtp53.

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Construction of replication-deficient recombinant adenoviral vector carrying HBV S and C region gene by homologous recombination in bacteria and its expression in vitro

AIM

To construct recombinant adenoviral vector carrying HBV S and C region gene by homologous recombination in bacteria and to detect its expression in vitro.

METHODS

HBV pre-S2/S genes and pre-C/C genes were amplified by PCR and were cloned to adenoviral shuttle plasmid pAdTrack-CMV, respectively. Then the resultant pAd Track-CMV-HBs or pAdTrack-CMV-HBe was cotransfected into BJ5183 bacteria with the plasmid pAdeasy-1. The adenoviral plasmid carrying HBV S and C gene (pAd-HBs and pAd-HBe) was generated with homologous recombination in bacteria and the adenoviruses were produced in 293 cells. Both 293 and Vero cells were infected with adenoviruses and the expression of HBsAg and HBeAg was detected by RT-PCR and ELISA in vitro.

RESULTS

The titer of Ad-HBs and Ad-HBe adenoviruses was up to 5×10¹² pfu/L after proliferation in 293 cells. HBsAg and HBeAg were expressed efficiently in 293 and Vero cells after infection.

CONCLUSION

The recombinant adenoviruses expressing HBsAg or HBeAg were constructed successfully and can be used further in gene therapy of HBV.

Effect of expression of interferon-g gene in inhibition of growth of colon cancer cell

AIM: To investigate the effect of expression of interferon-γ(IFN-γ) in tumor cell and its inhibitory effect on the growth of tumor cell.

METHODS: pcDNA3-IFN-γ vector containing IFN- γ gene was constructed and transfected into LOVO, SW620, HCT116BG and Hela cell lines by lipofectamine, respectively. The expression of IFN-γ, CEA and HLA-DR in transfected cells were tested. Both the number of apoptosis of and the proportion of cell cycles of tumor cells were measured to investigate the anti-tumor effect of IFN-γ gene therapy.

RESULTS: LOVO and HCT116BG transfected cell lines had high expression of CEA, the average level of CEA was significantly increased from 26.02±6.76 to 38.85±7.07 mg/L (P < 0.05). However, there was no detectable increase in the supernatants of Hela, SW620 cell lines that naturally expressed little of CEA. Flow cytometry analysis showed that HLA-DR expression rate (11.67±7.20) was significantly higher than that prior gene transfection (3.91±3.61) (P < 0.01), and the IFN-γ gene transfer effectively induced the apoptosis of tumor cells, the proportion of DNA synthesis phase was deceased gradually after IFN-γ gene transfer, which indicated that the synthesis of DNA and growth of tumor cells were repressed.

CONCLUSION: IFN-γ gene therapy enhanced the expression of antigens on cell surface and thus induced powerful antitumor immunity. Repressing of synthesis of DNA, inducing the apoptosis of tumor cells and inhibiting the proliferation of tumor cells might be anti-tumor mechanisms of IFN-γ.

Intracellular immunization by hammerhead ribozyme against HCV

AIM: To evaluate the effect of hammerhead ribozyme 213 (Rz 213) against hepatitis C virus (HCV) infection.

METHODS: Rz213 cleaving 5'oncoding region (5'CR) of HCV was beforehand transfected in a human hepatic carcinoma cell (HHCC) line and selected for G418 resistance. Cells stably expressing Rz213 were retransfected with pCMVNCRluc containing 5扤CR-luc fusion genes by lipofectAMINE; luciferase activity in lysate of transfactant was measured in scintillation counter.

RESULTS: HHCC cells stably expressing Rz213 exhibited significant resistance to retransfection of targeting gene.

CONCLUSION: Stably transfected cells with Rz213 were selected and expressed in HHCC, and thus exerted the intracellular immunity against infection of HCV.

Effect of ribozymes on inhibiting expression of HBV mRNA in HepG2 cells

AIM: To study the activity of ribozymes with multiple cleavage sites and mutated ribozymes on expression of HBV mRNA in HepG2 cells.

METHODS: The triple ribozymes and two cis-ribozymes or two mutated ribozymes were inserted, respectively, into five kinds of eukaryotic plasmids, which were cotransfected into the HepG2 cells with p1.2Ⅱplasmid carring genome of adv-subtype HBV. Cleavage effect of ribozymes on HBeAg and HBcAg were detected by ELISA and laser confocal imaging technique.

RESULTS: The transfected HepG2 cells expressed the expected ribozyme and muta-ribozyme. Intracellular level of HBeAg was surpressed variably with variety of ribozymes. The ribozyme plasmid with tRNA promoter demonstrated the highest inhibitory rate at 81% for suppression HBeAg expression.

CONCLUSION: The ribozymes exert varied inhibitory effect on the expression of HBV in HepG2 cells depending on kinds of eukaryotic expressing plasmids.

Targeted ribonuclease can inhibit replication of hepatitis B virus

AIM: To study the effect of a novel targeted ribonuclease (TN), the fusion protein of HBVc and human eosinophil-derived neurotoxin (hEDN), on the HBV replication in vitro.

METHODS: The gene encoding the targeted ribonuclease was cloned into pcDNA3.1 (-) to form recombinant eukaryotic expression vector p/TN. Control plasmids, including p/hEDN, p/HBVc, and p/TNmut in which a Lys113→Arg mutation was introduced by sequential PCR to eliminate the ribonuclease activity of hEDN, were also constructed. Liposome-mediated transfection of 2.2.15 cells by p/TN, p/TNmut, p/hEDN, p/HBVc, and pcDNA3.1 (-), or mock transfection was performed. After that, RT-PCR was used to verify the transgene expression. Morphology of the transfected cells was observed and MTT assay was performed to detect the cytotoxicity of transgene expression. Concentration of HBsAg in the supernatant of the transfected cells was measured using solid-phase radioimmunoassay.

RESULTS: Transgenes were successfully expressed in 2.2.15 cells. No obvious cytotoxic effect of transgene expression on 2.2.15 cells was found. The HBsAg concentration in the p/TN transfected cells was reduced by 58% compared with that of mock transfected cells. No such an effect was found in all other controls.

CONCLUSION: The targeted ribonuclease can inhibit HBV replication in vitro while it has no cytotoxicity on host cells. The targeted ribonuclease may be used as a novel antiviral agent for human HBV infection.

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Investigation of HGV and TTV infection in sera and saliva from non-hepatitis patients with oral diseases

AIM: To determine the frequencies of HGV and TTV infections in serum and saliva samples of non-hepatitis patients with oral diseases in Hangzhou area, and to understand the correlation between detected results of HGV RNA and/or TTV DNA in sera and in saliva from the same patients.

METHODS: RT-nested PCR for HGV RNA detection and semi-nested PCR for TTV DNA detection were performed in the serum and saliva samples from 226 non-hepatitis patients with oral diseases, and nucleotide sequence analysis.

RESULTS: Twenty-seven (11.9%) and 21 (9.3%) of the 226 serum samples were only positive for HGV RNA and TTV DNA, respectively. 10 (4.4%) and 9 (3.9%) of the 226 saliva samples were only positive for HGV RNA and TTV DNA, respectively. And 7 (3.1%) of the serum samples and 2 (0.9%) of the saliva samples showed the positive amplification results for both HGV RNA and TTV DNA. 12 saliva samples from the 34 patients (35.3%) with HGV or HGV/TTV viremia and 11 saliva samples from the 28 patients (39.3%) with TTV or HGV/TTV viremia were HGV RNA detectable, respectively, including two patients positive for both HGV RNA and TTV DNA in serum and saliva samples. No saliva samples from the 226 patients were found to be HGV RNA or TTV DNA detectable while their serum samples were negative for HGV or TTV. Homologies of the nucleotide sequences of HGV and TTV amplification products from the serum and saliva samples of the two patients compared with the reported sequences were 88.65%-91.49% and 65.32%-66.67%, respectively. In comparison with the nucleotide sequences of amplification products between serum and from saliva sample from any one of the two patients, the homologies were 98.58% and 99.29% for HGV, and were 98.65% and 98.20% for TTV, respectively.

CONCLUSION: Relatively high carrying rates of HGV and/or TTV in the sera of non-hepatitis patients with oral diseases in Hangzhou area are demonstrated. Parts of the carriers are HGV and/or TTV positive in their saliva. The results of this study indicate that dentists may be one of the populations with high risk for HGV and/or TTV infection, and by way of saliva HGV and TTV may be transmitted among individuals.