The programmed -1 ribosomal frameshifting (-1 PRF) utilized by eukaryotic RNA viruses plays a crucial role for the controlled, limited synthesis of viral RNA replicase polyproteins required for genome replication. The viral RNA replicase polyproteins of severe acute respiratory syndrome coronavirus (SARS-CoV) are encoded by the two overlapping open reading frames 1a and 1b, which are connected by a -1 PRF signal. We evaluated the antiviral effects of antisense peptide nucleic acids (PNAs) targeting a highly conserved RNA sequence on the - PRF signal. The ribosomal frameshifting was inhibited by the PNA, which bound sequence-specifically a pseudoknot structure in the -1 PRF signal, in cell lines as assessed using a dual luciferase-based reporter plasmid containing the -1 PRF signal. Treatment of cells, which were transfected with a SARS-CoV-replicon expressing firefly luciferase, with the PNA fused to a cell-penetrating peptide (CPP) resulted in suppression of the replication of the SARS-CoV replicon, with a 50% inhibitory concentration of 4.4. μM. There was no induction of type I interferon responses by PNA treatment, suggesting that the effect of PNA is not due to innate immune responses. Our results demonstrate that -1 PRF, critical for SARS-CoV viral replication, can be inhibited by CPP-PNA, providing an effective antisense strategy for blocking -1 PRF signals.
Bibliographical noteFunding Information:
We thank Dr. John Hiscott (McGill University, Montreal, Quebec, Canada) for providing the IFNβ-pGL3 luciferase reporter and a vector expressing an active form of IRF, and Dr. Naoya Sakamoto (Tokyo Medical and Dental University, Tokyo, Japan) for providing the pRep-Feo plasmid. This work was supported by a grant from the Seoul R&BD Program (Grant 10580 ) and a grant from Translation Research Center for Protein Function Control funded by the National Research Foundation of Korea ( NRF-2009-0092959 ). D.G.A., W.L., and J.K.C. were supported in part by the BK21 program of the Korean Ministry of Education, Science, and Technology.
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