Target-Directed miRNA Degradation: Mechanisms and Significance.

MicroRNAs are small noncoding RNAs that regulate gene expression within cells through the translational repression or degradation of targeted mRNA. miRNAs undergo a multiphase synthesis that includes conformational changes mediated by Drosha, Dicer, and Argonaute to integrate mature miRNA into the RNA-induced silencing complex to target messenger (m)RNA. miRNAs have been characterized through their transcription and biogenesis; however, the mechanism regarding miRNA turnover is less comprehensible because of the stability of each miRNA. Target-directed miRNA degradation (TDMD) is dependent on the stability of miRNAs, which modulates the decay rate of miRNAs. This mechanism is initiated through target RNAs' engagement with miRNAs via the 3' end complements, which induces Argonaute rearrangement. These rearrangements of Argonaute can be induced through tailing and trimming, with one of the central initiators being the ZSWIM8 E3 ubiquitin ligase. Tailing and trimming are often associated with TDMD, and the mechanistic role is context-dependent. This mechanism provides a regulation process in which mRNA is actively repressed and silenced by the miRNA. The significance of TDMD lies in its role in post-transcriptional regulation of miRNA expression, its implications for therapeutic treatments, and its association with various diseases.