Activation of human Argonaute3 (AGO3) using cityRNAs
MicroRNAs (miRNAs) are small non-coding RNAs that control gene expression post-transcriptionally. Their sequences differ, but their lengths fall within a range of ~20-23 nucleotides because the precursor miRNAs are processed by Dicer. Dicer cleaves long double-stranded RNA (dsRNA) molecules into short double stranded fragments and acts as a molecular ruler that generates size-specific miRNA duplexes. The dsRNA is then separated into two single-stranded RNAs – the passenger strand and the guide strand. The duplexes are loaded into Argonaute (AGO); the passenger strand is ejected while the guide strand and the AGO form the RNA-induced silencing complex (RISC). Argonaute proteins are the active part of RISC, cleaving the target mRNA strand complementary to their bound siRNA. In humans, Argonaute2 (AGO2) has been known as the only slicer while Argonaute3 (AGO3) was beleived to barely cleave RNAs.
Researchers at The Ohio State University, led by Dr. Kotaro Nakanishi, have discovered new intrinsic slicing activity of AGO3. Specifically, they found that 14-nucleotide 3′ end-shortened variants of let-7a, miR-27a, and specific miR-17-92 families make AGO3 an extremely competent slicer and increase target cleavage by up to 82-fold. These shorter ~14-15 nucleotide guide RNAs, named cleavage-inducing tiny guide RNAs (cityRNAs), conversely lower the activity of AGO2, demonstrating that AGO2 and AGO3 have different optimum guide RNA lengths for target cleavage. This discovery represents a substantive departure from the status quo of RNAi. Importantly, this novel finding opens the opportunity for AGO3 specific activation using cityRNAs in disease-specific settings, which is the subject of further investigation.
- Provisional Patent Application Filed