A small yeast RNA inhibits HCV IRES mediated translation and inhibits replication of poliovirus in vivo

Hepatitis C viral protein translation: mechanisms and implications in developing antivirals

Hepatitis C viral protein translation occurs in a cap-independent manner through the use of an internal ribosomal entry site (IRES) present within the viral 5'-untranslated region. The IRES is composed of highly conserved structural domains that directly recruit the 40S ribosomal subunit to the viral genomic RNA. This frees the virus from relying on a large number of translation initiation factors that are required for cap-dependent translation, conferring a selective advantage to the virus especially in times when the availability of such factors is low. Although the mechanism of translation initiation on the Hepatitis C virus (HCV) IRES is well established, modulation of the HCV IRES activity by both cellular and viral factors is not well understood. As the IRES is essential in the HCV life cycle and as such remains well conserved in an otherwise highly heterogenic virus, the process of HCV protein translation represents an attractive target in the development of novel antivirals. This review will focus on the mechanisms of HCV protein translation and how this process is postulated to be modulated by cis-acting viral factors, as well as trans-acting viral and cellular factors. Numerous therapeutic approaches investigated in targeting HCV protein translation for the development of novel antivirals will also be discussed.

A peptide from autoantigen La blocks poliovirus and hepatitis C virus cap-independent translation and reveals a single tyrosine critical for La RNA binding and translation stimulation

La, a 52-kDa autoantigen in patients with systemic lupus erythematosus, was one of the first cellular proteins identified to interact with viral internal ribosome entry site (IRES) elements and stimulate poliovirus (PV) and hepatitis C virus (HCV) IRES-mediated translation. Previous results from our laboratory have shown that a small, yeast RNA (IRNA) could selectively inhibit PV and HCV IRES-mediated translation by sequestering the La protein. Here we have identified an 18-amino-acid-long sequence from the N-terminal "La motif" which is required for efficient interaction of La with IRNA and viral 5' untranslated region (5'-UTR) elements. A synthetic peptide (called LAP, for La peptide) corresponding to this sequence (amino acids 11 to 28) of La was found to efficiently inhibit viral IRES-mediated translation in vitro. The LAP efficiently enters Huh-7 cells and preferentially inhibits HCV IRES-mediated translation programmed by a bicistronic RNA in vivo. The LAP does not bind RNA directly but appears to block La binding to IRNA and PV 5'-UTR. Competition UV cross-link and translation rescue experiments suggested that LAP inhibits IRES-mediated translation by interacting with proteins rather than RNA. Mutagenesis of LAP demonstrates that single amino acid changes in a highly conserved sequence within LAP are sufficient to eliminate the translation-inhibitory activity of LAP. When one of these mutations (Y23Q) is introduced into full-length La, the mutant protein is severely defective in interacting with the PV IRES element and consequently unable to stimulate IRES-mediated translation. However, the La protein with a mutation of the next tyrosine moiety (Y24Q) could still interact with PV 5'-UTR and stimulate viral IRES-mediated translation significantly. These results underscore the importance of the La N-terminal amino acids in RNA binding and viral RNA translation. The possible role of the LAP sequence in La-RNA binding and stimulation of viral IRES-mediated translation is discussed.

Lethiferous effects of a recombinant vector carrying thymidine kinase suicide gene on 2.2.15 cells via a self-modulating mechanism

AIM: To determine the lethiferous effects of a recombinant vector carrying thymidine kinase (TK) suicide gene on 2.2.15 cells and the possible self-modulating mechanism.

METHODS: A self-modulated expressive plasmid pcDNA3-SCITK was constructed by inserting the fragments carrying hepatitis B virus antisense-S (HBV-anti-S) gene, hepatitis C virus core (HCV-C) gene, internal ribosome entry site (IRES) element of HCV and TK gene into the eukaryotic vector pcDNA3, in which the expression of TK suicide gene was controlled by the HBV S gene transcription. 2.2.15 cells that carry the full HBV genome and stably express series of HBV antigen were transfected with pcDNA₃-SCITK or vector pcDNA₃-SCI which was used as the mock plasmid. The HepG2 cells transfected with pcDNA₃-SCITK were functioned as the negative control. All the transfected cells were incubated in DMEM medium supplemented with 10 μg/mL. of ganciclovir (GCV). The HBsAg levels in the supernatant of cell culture were detected by ELISA on the 1^st, 3^rd and 6^th day post-transfection. Meanwhile, the morphology of tranfected cells was recorded by the photograph and the survival cell ratio was assessed by the trypan blue exclusion test on the 6^th day post-transfection.

RESULTS: The structural accuracy of pcDNA₃-SCITK was confirmed by restriction endonuclease digestion, PCR with specific primers and DNA sequencing. The HBsAg levels in the supernatant of transfected 2.2.15 cell culture were significantly decreased on the 6^th day post-transfection as compared with that of the mock control (P < 0.05). The lethiferous effect of pcDNA₃-SCITK expression on 2.2.15 cells was initially noted on the 3^rd day after transfection and aggravated on the 6^th day post transfection, in which the majority of transfected 2.2.15 cells were observed shrunken, round in shape and even dead. With assessment by the trypan blue exclusion test, the survival cell ratio on the 6^th day post transfection was 95% in the negative control and only 11% in the experimental group.

CONCLUSION: The results indicate that suicide gene expression of pcDNA₃-SCITK can only respond to HBV-S gene transcription, which may be potentially useful in the treatment of HBV infection and its related liver malignancies.

Construction of the vector that harbors self-restricted system for hepatitis B virus clearance in gene therapy

AIM

To construct the vector that harbors self-restricted system for clearing hepatitis B virus, eliminating infected hepatic cells and inhibiting hepatitis B recurrence in gene therapy.

METHODS

After amplifying hepatitis C virus (HCV) internal ribosome entry sites (IRES) by reverse-transcription PCR (RT-PCR), the products were cloned into pcDNA3. A biscistronic vector was obtained. A part of sequence in HBV anti-surface gene and part of sequence in HCV core gene were cloned into the vector before IRES site in turn and thymidine kinase (TK) was also cloned into it following the IRES site. After determination by PCR and sequencing, we acquired the vector containing HBV anti-S, HCV-C gene, HCV IRES and thymidine kinase gene, which was named the vector pcDNA3-SCITK. The vectors were separately transfected into HepG2 cells and 2.2.15 cells and all the media contained ganciclovir.

RESULTS

The novel vector was transfected into 2.2.15 and hepG2 cells, the expressed protein could destroy the former, but had no effect on HepG2 cells if all the media contained ganciclovir. Apoptosis cells in the former accounted for 15 per cent of all cells by fluorescence (FACS) detection. There was obvious difference between the two types of cells (the later was only 6 per cent).

CONCLUSION

The function of genes that pcDNA3-SCITK carried with self-restricted system could be ego-controlled, and it might be used as gene therapy vector for HBV clearance if taking HBV S gene as target gene and TK gene as objective gene.