MRNA Targeting to Endoplasmic Reticulum Precedes Ago Protein Interaction and MicroRNA (miRNA)-mediated Translation Repression in Mammalian Cells

Bahnisikha Barman,Suvendra N Bhattacharyya

doi:10.1074/jbc.c115.661868

Abstract

MicroRNA (miRNA) binds to the 3'-UTR of its target mRNAs to repress protein synthesis. Extensive research was done to understand the mechanism of miRNA-mediated repression in animal cells. Considering the progress in understanding the mechanism, information about the subcellular sites of miRNA-mediated repression is surprisingly limited. In this study, using an inducible expression system for an miRNA target message, we have delineated how a target mRNA passes through polysome association and Ago2 interaction steps on rough endoplasmic reticulum (ER) before the miRNA-mediated repression sets in. From this study, de novo formed target mRNA localization to the ER-bound polysomes manifested as the earliest event, which is followed by Ago2 micro-ribonucleoprotein binding, and translation repression of target message. Compartmentalization of this process to rough ER membrane ensures enrichment of miRNA-targeted messages and micro-ribonucleoprotein components on ER upon reaching a steady state.

Highlights

Polysome association of newly formed mRNA precedes Ago2 binding on endoplasmic reticulum (ER) membrane and its translation repression
MiRNA, Ago2, and target messages are enriched on endoplasmic reticulum (ER) in metazoan cells
De novo formed target mRNA localization to the ER-bound polysomes manifested as the earliest event, which is followed by Ago2 micro-ribonucleoprotein binding, and translation repression of target message

Summary

Introduction

Results: Polysome association of newly formed mRNA precedes Ago2 binding on ER membrane and its translation repression. De novo formed target mRNA localization to the ER-bound polysomes manifested as the earliest event, which is followed by Ago2 micro-ribonucleoprotein binding, and translation repression of target message. It becomes associated with the Argonaute proteins and miRNAs. Detail time course experiments have revealed that polysome localization of target messages followed by Ago2 miRNP binding on the ER membrane occurs before the miRNA-mediated translation repression sets in.

Results

Conclusion