EIF4A2 drives repression of translation at initiation by Ccr4-Not through purine-rich motifs in the 5\u2032UTR

Ania Wilczynska,Tobias Schmidt,Sara Zanivan,Hedda A Meijer,Benjamin R Hawley,Martin Bushell,Kelvin Cain,Kelly Hodge,Rebekah Jukes-Jones,Claudia Langlais,Sarah L Gillen,Jack D Godfrey,Wei-Ting Lu,Kari Kopra,John Le Quesne

doi:10.1186/s13059-019-1857-2

Abstract

BackgroundRegulation of the mRNA life cycle is central to gene expression control and determination of cell fate. miRNAs represent a critical mRNA regulatory mechanism, but despite decades of research, their mode of action is still not fully understood.ResultsHere, we show that eIF4A2 is a major effector of the repressive miRNA pathway functioning via the Ccr4-Not complex. We demonstrate that while DDX6 interacts with Ccr4-Not, its effects in the mechanism are not as pronounced. Through its interaction with the Ccr4-Not complex, eIF4A2 represses mRNAs at translation initiation. We show evidence that native eIF4A2 has similar RNA selectivity to chemically inhibited eIF4A1. eIF4A2 exerts its repressive effect by binding purine-rich motifs which are enriched in the 5′UTR of target mRNAs directly upstream of the AUG start codon.ConclusionsOur data support a model whereby purine motifs towards the 3′ end of the 5′UTR are associated with increased ribosome occupancy and possible uORF activation upon eIF4A2 binding.

Highlights

Two mRNA-binding complexes—eIF4F and Ccr4-Not— play fundamental roles in directing the cytosolic fate of mRNAs at the level of translation as well as mRNA turnover
EIF4A2 represses translation of miRNA targets at initiation via CNOT1 Since eIF4A2 had been previously implicated in miRNAmediated repression [11], it interacts with the Ccr4-Not complex, and eIF4A2-regulated mRNAs were involved in the miRNA pathway, we further investigated its role in the miRNA silencing mechanism
We have shown that eIF4A2 interacts with the Ccr4-Not complex, but there is ample evidence for DDX6 playing a role in imposing miRNA-mediated repression via the Ccr4-Not complex [4, 11, 17, 34, 35], which is the principal effector of translational repression and mRNA degradation induced by miRNAs [60]

Summary

Introduction

Two mRNA-binding complexes—eIF4F and Ccr4-Not— play fundamental roles in directing the cytosolic fate of mRNAs at the level of translation as well as mRNA turnover. The eIF4F complex, consisting of the cap binding protein eIF4E, the regulatory scaffold protein eIF4G, and the DEAD-box RNA helicase eIF4A, is recruited to the 5′-cap structure of mRNAs and is required for translation [1]. Translational repression, which is the required first step of miRNA-mediated silencing [11], can be induced by the Ccr4-Not complex independently of its deadenylation and degradation activities [12,13,14,15]. The Ccr4-Not complex defines mRNA fate and sculpts the translational landscape of the cell [16] well beyond miRNA-mediated repression by binding to mRNAs via its many partner RNA-binding proteins which recognize a number of regulatory sequence motifs. Regulation of the mRNA life cycle is central to gene expression control and determination of cell fate. miRNAs represent a critical mRNA regulatory mechanism, but despite decades of research, their mode of action is still not fully understood

Methods

Results

Discussion

Conclusion