Poster abstracts

Poster number 43 submitted by GeunYoung Sim

ISG20 converts AGO-associated microRNAs to tiny RNAs

GeunYoung Sim (The Ohio State University, Molecular, Cellular and Developmental Biology, Columbus, OH), Audrey Kehling, Mi Seul Park (The Ohio State University, Chemistry and Biochemistry, Columbus, OH), Jackson Secor, Huaqun Zhang (The Ohio State University, Chemistry and Biochemistry, Columbus, OH), Divyaa Bhagdikar, Ekram Abd El-Wahaband (The Ohio State University, Chemistry and Biochemistry, Columbus, OH), Kotaro Nakanishi (The Ohio State University, Molecular, Cellular and Developmental Biology, Columbus, OH, The Ohio State University, Chemistry and Biochemistry, Columbus, OH)

Abstract:
MicroRNAs (miRNAs), small non-coding RNAs post-transcriptionally regulate the gene expression, have been extensively studied. During the canonical miRNA biogenesis pathway, the precursor miRNA is processed by a Dicer, a molecular ruler, to generate the miRNA duplex with lengths ranging in 18-25 nucleotides (nt). However, tiny RNAs (TyRNAs) shorter than 18 nt also exist in plants and animals though they usually have been excluded for the RNA sequencing analysis due to technical difficulty. Moreover, the biogenesis pathway and biological functions of tyRNAs have not been elucidated yet.
Once miRNAs are loaded into the argonaute protein (AGO), they form RNA-induced silencing complexes, which can induce gene interference (RNAi). Among four human AGOs, only AGO2 and AGO3 share the same catalytic DEDH tetrad. Our group discovered AGO2 is activated by the full-length miRNA, while AGO3 is activated by 14-nt cleavage-inducing tyRNA (cityRNA), suggesting one possible biological function of tyRNAs1.
Interferon-Stimulated Gene 20 protein (ISG20), a 3’-5’ exoribonuclease, requires its 3’-5’ exonuclease activity for its antiviral activities2,3. However, ISG20 does not directly degrade viral RNA, but rather inhibits the translation of viral mRNAs, though its underlying mechanism remains unclear2,3. Here, we show that ISG20 trims AGO-associated miRNAs and generates 13-14 nt tyRNAs both in vitro and in cells. In addition, we find AGO3 loaded with miR-20a and let-7a shows higher target cleavage activity once it is incubated with ISG20, suggesting the slicer activity of AGO3 is activated by ISG20. Our study proposes the potential tyRNA biogenesis pathway. These findings will broaden current knowledge of small non-coding RNAs and present a new approach to connect the antiviral immune response with RNAi mediated by AGOs.

References:
1. Park, M. S., et al. (2020). Human Argonaute2 and Argonaute3 are catalytically activated by different lengths of guide RNA. Proc Natl Acad Sci U S A 117(46):28576-28578.

2. Wu, N., et al. (2019). The interferon stimulated gene 20 protein (ISG20) is an innate defense antiviral factor that discriminates self versus non-self translation. PLoS Pathog. 15(10):e1008093.

3. Weiss, C., et al. (2018). The Interferon-Induced Exonuclease ISG20 Exerts Antiviral Activity through Upregulation of Type I Interferon Response Proteins. mSphere. 3(5):e00209-18.

4. Nakanishi (2016). Anatomy of RISC: how do small RNAs and chaperones activate Argonaute proteins? WIREs RNA 7(5):637-60.

Keywords: Small RNAs, Argonautes, RNA silencing