Functional characterization of a new enzymatic activity of the miRNase XRN 2 from Caenorhabditis elegans

Abstract

Ribonucleic acid (RNA) molecules play a central role in every pivotal process in the cell, and ribonucleases (RNases) are critical for their biogenesis, processing, and degradation. Therefore, RNases are indispensable for cellular RNA homeostasis. MicroRNAs (miRNAs) are endogenous, small non-coding RNAs that extensively regulate gene expression in eukaryotes. Any alteration in their expression profiles, as well as their steady-state levels, may lead to several pathological conditions, notably neurological disorders and cancer. Therefore, regulation of the levels of these regulators is of utmost importance. While the events leading to the biogenesis of a mature, functional miRNA are well lineated, little is known about the turnover pathways responsible for the maintenance of the functional levels of these RNAs. Recent research in Caenorhabditis elegans (C. elegans), identified and characterized a multiprotein miRNA turnover complex, miRNasome-1. This biological machine is composed of four subunits (XRN-2, PAXT-1, NOL-58, B0024.11/ miRNasome-1.4), and it displays a dual mode of action on the substrate miRNAs in in vitro assays. The researchers also reported a previously unknown endoribonuclease activity of the fundamentally important enzyme, XRN-2, and surprisingly, this activity was found to be much more efficacious on the miRNAs than the previously known exoribonuclease activity. It was shown that miRNasome-1 residing XRN-2 s activity and specificity is governed by two of the newly identified members. The RNA-binding receptor component of the complex, NOL-58, was not only found to be crucial for worm development but also conferred in vivo substrate specificity to the complex, which corroborated with that of the complex s activity, in vitro. The researchers demonstrated that miRNasome-1 residing XRN-2 cleaves the substrate through an endoribonucleolytic mode at low substrate concentrations, in the absence of ATP. In the presence of ATP, miRNasome-1...