Promoter-targeted siRNAs Induce Gene Silencing of Simian Immunodeficiency Virus (SIV) Infection In Vitro

doi:doi:10.1038/sj.mt.6300380

Subject Category: Oligonucleotide Therapy

Molecular Therapy (2007); 16 3, 565–570. doi:10.1038/sj.mt.6300380

Promoter-targeted siRNAs Induce Gene Silencing of Simian Immunodeficiency Virus (SIV) Infection In Vitro

Heidi GW Lim^1,2, Kazuo Suzuki¹, David A Cooper^1,2 and Anthony D Kelleher^1,2

¹Centre for Immunology, Immunovirology Laboratory, St Vincent's Hospital, Darlinghurst, New South Wales, Australia
²National Centre in HIV Epidemiology and Clinical Research, University of New South Wales, Darlinghurst, New South Wales, Australia

Correspondence: Heidi GW Lim, Centre for Immunology, Immunovirology Laboratory, St.Vincent's Hospital, Corner of West and Boundary Streets, Darlinghurst, Sydney, New South Wales 2010, Australia. E-mail: h.lim@cfi.unsw.edu.au

Received 22 April 2007; Accepted 15 November 2007; Published online 29 January 2008.

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Abstract

RNA interference is a conserved process by which sequence-specific double-stranded RNA is converted into small interfering double-stranded RNAs (siRNAs) that can induce gene silencing via two pathways: post-transcriptional gene silencing and transcriptional gene silencing (TGS). We previously reported TGS of human immunodeficiency virus-1 (HIV-1) could be induced by siRNAs targeting regions within its 5'-long-terminal repeat (5'LTR) promoter region. Here we show that promoter-targeted siRNAs can also induce silencing of simian immunodeficiency virus (SIV) replication by similar mechanisms. Suppression of productive infection was achieved in two different cell lines: a CD4, CCR5, CXCR4 expressing HeLa cell line (MAGIC-5) and in a human lymphoid cell line (CEMx174). HpaII digestion demonstrated induction of methylation at a CpG site within the SIV promoter region following siRNA-induced suppression. Both 5-azacytidine (5-AzaC) and trichostatin A (TSA), inhibitors of DNA methyltransferases (DNMTs) and histone deacetylation, respectively, partially reversed the silencing effect. Furthermore, using chromatin immunoprecipitation (ChIP) assays we found enrichment in the region of the LTR of heterochromatin markers dimethylated histone 3 lysine 9 (H3K9) and trimethylated histone 3 lysine 27 (H3K27) in the siRNA silenced cultures. Together, these results strongly suggest certain siRNAs targeting the promoter region of SIV can effect viral silencing through the induction of epigenetic changes.