Objective: To explore the antiviral efficacy of small interfering RNAs (siRNAs)/shRNA targeting preC/C of HBV in human hepatoma cells Huh-7 and HepG2.2.15 cells.
Methods: Three 21 nucleotide(nt) siRNAs for treating HBV preC/C gene were designed and synthesized according to the HBV genome in GenBank accession numbers (U95551); simultaneously, one 21-nt-long non-homologous siRNA was also designed randomly for negative control. They were cloned into vector pU6 for constructing shRNA-expressing plasmids pU6-C1, pU6-C2, pU6-C3 and control pU6-C4. To assess the function of siRNAs, a reporter gene system was constructed. The HBV preC/C gene was synthesized by PCR with pT-HBV1.3 as the template. The preC/C gene was then inserted into the enhanced green fluorescent protein expression vector (EGFP-N1) in order to construct the recombinant plasmid pEGFP-preC/C (E-C), which carries the EGFP reporter gene. The three shRNA-expressing plasmids-pU6-C1, pU6-C2, or pU6-C3-was each then cotransfected into Huh-7 cells along with either reporter gene expression vector E-C or the controls; or these three plasmids-pU6-C1, pU6-C2, or pU6-C3-was each cotransfected into HepG2.2.15 cells along with the controls. First, upon determination of the number of cells exhibiting EGFP expression in Huh-7cells as detected by an BH-2 fluorescence microscope and FACS-440 flow cytometry at different times after cotransfection, the investigators evaluated the inhibitory efficiency of the three shRNA-expressing plasmids by an EGFP reporter system in cultured cells. Subsequently, the expression amount of HBsAg and HBeAg in HepG2.2.15 cell supernatant at 24, 48, 72 and 96 h post-cotransfection was detected by enzyme-linked immunosorbent assay (ELISA). Immunofluorescence was used to detect the expression of HBsAg and HBcAg at 72 h post-cotransfection in HepG2.2.15 cells. The copy level of HBV mRNA transcripts cDNA in HepG2.2.15 cells was further investigated through quantitative real-time polymerase chain reaction (real-time PCR).
Results: In comparison with single plasmid transfection pEGFP-N1 or E-C, fluorescence microscope examination and flow cytometry detection at 48 hours after cotransfection indicated that the expression of the reporter gene EGFP in cotransfected group Huh-7 cell involving pU6-C1, pU6-C2 or pU6-C3 resulted in an 80% reduction in EGFP signal relative to the controls (P < 0.01). It was also found through immunofluorescence that the expression of HBsAg and HBcAg in HepG2.2.15 cells was reduced markedly (P < 0.01), that the copy level of HBV mRNA transcripts cDNA as detected at 48 hours after cotransfection by quantitative real-time PCR was reduced respectively by 73.9% ± 1.2% (P = 0.029), 48.2% ± 1.8% and 35.8% ± 1.4% (P = 0.037, 0.040) relative to the control, that it conformed with that detected by fluorescence microscope/flow cytometry, ELISA, and immunofluorescence (P < 0.01). Thereby further corroborating the antiviral efficacy of RNAi. The efficacy was obvious at 48 h, reaching a peak at 72 h.
Conclusion: For the first time it has been found that RNAi induced by siRNA/shRNA targeting HBV preC/C gene is effective and specific in inhibiting HBV replication and expression in human hepatoma cells Huh-7 and HepG2.2.15 cells. Our data suggest that RNAi may provide an effective, viable approach in gene therapy to treating major infectious diseases such as HBV/HCV/HIV infection.