Sequence-specific potent induction of IFN-α by short interfering RNA in plasmacytoid dendritic cells through TLR7

Speaker: 羅志文                    Date: 04/27/2005;13:10-14:00

Commentator: 楊倍昌 老師          Place: Room 601

Abstract:

    RNA interference (RNAi), which is gene silencing specifically by double-strand RNA molecules (dsRNAs), is a power tool for gene function research and gene-specific therapy. However, in mammalian cells, long dsRNAs can trigger non-specific and global gene suppression which results from production of interferons and activation of dsRNA-activated protein kinase, 2’-5’-oligoadenylate synthetase/RNase L, as well as toll-like receptor 3.¹ Short interfering RNA (siRNA), a 21-23-nucleotide dsRNA with two nucleotide 3’ overhangs, is a kind of RNAi which is shown to avoid inducing non-specific responses and efficiently silence target gene expression in mammalian cells.² In this paper, the authors attempted to silence toll-like receptor 9 (TLR9) gene expression by siRNA in human plasmacytoid dendritic cells (PDCs), which can produce large amounts of interfrons in response to virus infection. While their designed siRNA efficiently silenced TLR9 expression in HEK293 cells without inducing any interferon production, the siRNA induced IFN-α production in PDCs. By studying in vitro PDC cultures, they found that this IFN-α production response was sequence-specific and defined the 9-base motif (GUCCUUCAA) in the sense strand of their siRNA responsible for this phenomenon. They also showed that locked nucleic acid modification of the sense and antisense strands can modulate the silencing and immunological activities of the siRNA. Furthermore, for in vivo stimulation, they injected mice intravenously with the siRNA complexed with cationic liposomes and then found systemic levels of IFN-α arising and immune cell activation. Finally, the authors confirm the sequence-specific induction of IFN-α by siRNA in PDCs is toll-like receptor 7 (TLR7)-dependent because of no IFN-α production in in vitro stimulating TLR7-deficient mouse bone marrow cultures and no responses in in vivostimulating TLR7-deficient mice. These results show that TLR7 can be activated to induce immune responses through specific RNA sequences, and these RNA sequences, which should termed immunostimulatory RNA (isRNA), may be tools in vitro and promising drugs in vivo.³

References:

1.      Wang Q, Carmichael GG.. Effects of length and location on the cellular response to double-stranded RNA. Microbiol Mol Biol Rev. 68:432-52, 2004

2.      Elbashir SM. et al. Duplexes of 21-nucleotide RNAs mediate RNA interference in cultured mammalian cells. Nature. 411:494-8, 2001

3.      Hornung V. et al. Sequence-specific potent induction of IFN-alpha by short interfering RNA in plasmacytoid dendritic cells through TLR7. Nat Med. 11:263-70, 2005