Trans-amplifying RNA expressing functional miRNA mediates target gene suppression and simultaneous transgene expression

Abstract

The co-delivery of microRNAs (miRNAs) and protein-coding RNA presents an opportunity for a combined approach to gene expression and gene regulation for therapeutic applications. Protein delivery is established using long mRNA, self-, and trans-amplifying RNA (taRNA), whereas miRNA delivery typically uses short synthetic oligonucleotides rather than incorporating it as a precursor into long RNA. Although miRNA delivery into the cell cytoplasm using long genomes of RNA viruses has been described, concerns have remained regarding low processing efficiency. However, miRNA precursors can be released from long cytoplasmic alphaviral RNA by a cytoplasmic fraction of Drosha. taRNA, a promising vector platform for infectious disease vaccination, uses a nonreplicating mRNA expressing an alphaviral replicase to amplify a protein-coding short transreplicon-RNA (STR) in trans. To investigate the possibility of simultaneously delivering protein expression and gene silencing, we tested whether a taRNA system can carry and release functional miRNA to target cells. Here, we show that mature miRNA is released from STRs and silences specific targets in a replication-dependent manner for several days without compromising the expression of STR-encoded proteins. Our findings suggest that incorporating miRNAs into the taRNA vector platform has the potential for gene regulation alongside the expression of therapeutic genes.

Graphical abstract

Abstract

Yıldız and colleagues exploit trans-amplifying RNA, a recently established RNA vaccine platform, to deliver functional miRNAs excised from the 3' UTR of protein-coding transreplicons. Target gene knockdown lasted for 96 h and protein expression remained unalterably high, suggesting co-delivery of therapeutic proteins and miRNA with taRNA whenever deemed beneficial.