Strategies for silencing human disease using RNA interference

Strategies for silencing human disease using
RNA interference

As shown in the pathway at the bottom left, cytoplasmic double-stranded RNAs (dsRNAs) are processed by a complex consisting of Dicer, TAR RNA-binding protein (TRBP) and protein activator of protein kinase PKR (PACT) into small interfering RNAs (siRNAs), which are loaded into Argonaute 2 (AGO2) and the RNA-induced silencing complex (RISC). The siRNA guide strand recognizes target sites to direct mRNA cleavage, which is carried out by the catalytic domain of AGO2. siRNAs complementary to promoter regions direct transcriptional gene silencing in the nucleus through chromatin changes involving histone methylation (top left); the precise molecular details of this pathway in mammalian cells are currently unclear. As shown in the pathway on the right, endogenously encoded primary microRNA transcripts (pri-miRNAs) are transcribed by RNA polymerase II (Pol II) and initially processed by Drosha–DGCR8 (DiGeorge syndrome critical region gene 8) to generate precursor miRNAs (pre-miRNAs). These precursors are exported to the cytoplasm by exportin 5 and subsequently bind to the Dicer–TRBP–PACT complex, which processes the pre-miRNA for loading into AGO2 and RISC. The mature miRNA recognizes target sites in the 3' untranslated region (3' UTR) of mRNAs to direct translational inhibition and mRNA degradation in processing (P)-bodies that contain the decapping enzymes DCP1 and DCP2. H3K9, histone 3 lysine 9; H3K27, histone 3 lysine 27; m⁷G, 7-methylguanylate; ORF, open reading frame.