Translational repression of NMD targets by GIGYF2 and EIF4E2.

Boris Zinshteyn,Syed Usman Enam,Rachel Green,Niladri K Sinha,Benjamin Koleske,Niels Henrik Gehring

doi:10.1371/journal.pgen.1009813

Abstract

Translation of messenger RNAs (mRNAs) with premature termination codons produces truncated proteins with potentially deleterious effects. This is prevented by nonsense-mediated mRNA decay (NMD) of these mRNAs. NMD is triggered by ribosomes terminating upstream of a splice site marked by an exon-junction complex (EJC), but also acts on many mRNAs lacking a splice junction after their termination codon. We developed a genome-wide CRISPR flow cytometry screen to identify regulators of mRNAs with premature termination codons in K562 cells. This screen recovered essentially all core NMD factors and suggested a role for EJC factors in degradation of PTCs without downstream splicing. Among the strongest hits were the translational repressors GIGYF2 and EIF4E2. GIGYF2 and EIF4E2 mediate translational repression but not mRNA decay of a subset of NMD targets and interact with NMD factors genetically and physically. Our results suggest a model wherein recognition of a stop codon as premature can lead to its translational repression through GIGYF2 and EIF4E2.

Highlights

Translation of messenger RNAs with premature translation termination codons (PTCs) produces truncated peptides with potentially toxic dominant-negative effects [1,2]
Many disease-causing mutations result in premature stop codons, and current research suggests that differences between stop codons could be exploited for clinical therapy
We have carried out a genetic screen to identify factors that regulate the production of protein from an messenger RNA with a premature stop codon

Summary

Introduction

Translation of messenger RNAs (mRNAs) with premature translation termination codons (PTCs) produces truncated peptides with potentially toxic dominant-negative effects [1,2]. The universal eukaryotic NMD factors (UPF1, UPF2, UPF3), which play the major role in PTC detection, were identified genetically as suppressors of frameshift mutations in S. cerevisiae [14,15,16], or as suppressors of multiple unrelated mutations in C. elegans [17,18]. The latter studies identified the kinase SMG1, which phosphorylates UPF1, and additional NMD factors SMG5-7, which directly facilitate mRNA decay. More recent studies used targeted reporter assays coupled with RNAi or CRISPR to identify additional NMD factors in C. elegans and human cells [26,27,28,29,30], finding connections between NMD and ribosome recycling, splicing, and other processes

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Conclusion