Spatiotemporal Uncoupling of MicroRNA-Mediated Translational Repression and Target RNA Degradation Controls MicroRNP Recycling in Mammalian Cells

Abstract

miRNA-mediated repression control expression of more than half of protein coding genes in metazoan animals. Translation repression is associated with target mRNA degradation initiated by decapping and deadenylation of the repressed mRNAs. Earlier evidence suggest Endoplasmic Reticulum (ER) as the site where miRNPs interact with their targets before the translation repression sets in but the subcellular location of subsequent degradation of miRNA-repressed messages is largely unidentified. Here, we explore the subcellular distribution of essential components of degradation machineries of miRNA-targeted mRNAs. We have noted that interaction of target mRNAs with AGO2 protein on ER precedes the relocalization of repressed messages to Multivesicular Bodies (MVBs). The repressed messages subsequently get deadenylated, lose their interaction with AGO2 and also become decapped. Blocking maturation of endosomes to late endosome and MVBs by targeting the endosomal protein HRS, uncouples miRNA-mediated translation repression from target RNA degradation. HRS is also targeted by the intracellular parasite Leishmania donovani (Ld) that curtails HRS level in infected cells to prevent uncoupling of mRNA-AGO2 interaction, prevent degradation of translationally repressed messages and thus stop recycling of miRNPs pre-engaged in repression.