Inhibition of porcine reproductive and respiratory syndrome virus replication in vitro using DNA-based short antisense oligonucleotides

BACKGROUND

Porcine reproductive and respiratory syndrome (PRRS) is caused by porcine reproductive and respiratory syndrome virus (PRRSV) and is an economically important disease in swine-producing areas. The objective of this study was to screen for effective antisense oligonucleotides (AS-ONs) which could inhibit PRRSV replication in MARC-145 cells and in pulmonary alveolar macrophages (PAM).

RESULTS

Nine short AS-ON sequences against the well-conserved regions of PRRSV (5'-UTR, NSP9, ORF5 and ORF7) were selected. When MARC-145 cells or PAM were infected with PRRSV followed by transfection with AS-ONs, four AS-ON sequences targeting 5'-UTR, ORF5 or NSP9 were found to be the most effective oligonucleotides in decreasing the cytopathic effect (CPE) induced by PRRSV infection. Quantitative PCR and indirect immunofluorescence staining confirmed that ORF7 levels were significantly reduced both at RNA and protein levels. The PRRSV titration data furthermore indicated that transfection with AS-ON YN8 could reduce the PRRSV titer by 1000-fold compared with controls.

CONCLUSION

The results presented here indicate that DNA-based antisense oligonucleotides can effectively inhibit PRRSV replication in MARC-145 cells and in PAM. Furthermore, comparing with the reported hit rates (approximately 10-30 %), we achieved a higher success rate (44 %). The strategy we took to design the antisense sequences might be applied to select AS-ONs that more efficiently reduce the expression of target genes.

Therapeutic regulation of gene expression in the inner ear using RNA interference

Targeting and downregulating specific genes with antisense and decoy oligonucleotides, ribozymes or RNA interference (RNAi) offer the theoretical potential of altering a disease phenotype. Here we review the molecular mechanism behind the in vivo application of RNAi-mediated gene silencing, focusing on its application to the inner ear. RNAi is a physiological phenomenon in which small, double-stranded RNA molecules (small interfering RNA, siRNA) reduce expression of homologous genes. Notable for its exquisite sequence specificity, it is ideally applied to diseases caused by a gain-of-function mechanism of action. Types of deafness in which gain-of-function mutations are observed include DFNA2 (KCNQ4), DFNA3 (GJB2) and DFNA5 (DFNA5). Several strategies can be used to deliver siRNA into the inner ear, including cationic liposomes, adeno-associated and lentiviral vectors, and adenoviral vectors. Transduction efficiency with cationic liposomes is low and the effect is transient; with adeno-associated and lentiviral vectors, long-term transfection is possible using a small hairpin RNA expression cassette.

Antisense delivery and protein knockdown within the intact central nervous system

The ability to down regulate the expression of a specific protein within the intact central nervous system (CNS) is highly desirable from both a research and therapeutic perspective. Antisense has the potential to do this. However, problems of invasive antisense delivery methods and short half life of remain problematic. We overcome this by using Pluronic gel to provide a sustained delivery antisense oligodeoxynucleotides (ODN's) to the intact central nervous system and achieving rapid penetration throughout the spinal cord in 2-3 hours and significant knockdown of our target protein connexin 43 (Cx43) in 4-8 hours (recovering at 48-72 hours). Interestingly CY3-siRNA probes could not be detected penetrating the intact CNS and no knockdown the Cx43 was found. This approach with conventional ODNs could provide a faster and cheaper alternative to knockout mice in the investigation of the functions of specific proteins within the CNS and may also have therapeutic implications for drug discovery and development.

Down-regulation of E-cadherin by antisense oligonucleotide enhances basement membrane invasion of pancreatic carcinoma cells

Pancreatic carcinoma shows a marked invasiveness around tissues lymph node and/or hematogenous metastases resulting in poor prognoses of the patients. We examined on whether E-cadherin is associated with these malignant behaviors of pancreatic carcinoma cells using a human pancreatic adenocarcinoma cell line, JHP-1. Immunohistochemically, E-cadherin expression of JHP-1 cells was remarkably inhibited by treatment with E-cadherin antisense oligonucleotide. By invasion-MTT assay, JHP-1 cells treated with E-cadherin antisense oligonucleotide showed a significant increase of invasiveness compared to those treated with the control oligonucleotide (P < 0.001), whereas the proliferation of JHP-1 cells was not affected by the presence of either E-cadherin antisense or control oligonucleotide. Thus, down-regulation of E-cadherin of pancreatic carcinoma cells induced the invasiveness into the basement membrane. These results suggest that the reduction in E-cadherin expression plays a key role not only in detachment of cell-cell adhesion but also in invasion and metastasis of pancreatic carcinoma cells.