NMD resulting from encephalomyocarditis virus IRES-directed translation initiation seems to be restricted to...

Area of Science:

• Molecular Biology
• Gene Regulation
• RNA Metabolism

Background:

• Nonsense-mediated mRNA decay (NMD) is a crucial cellular surveillance pathway that eliminates aberrant mRNAs with premature termination codons.
• In mammalian cells, NMD typically targets newly spliced mRNAs bound by the cap-binding protein complex CBP80/20 and exon junction complexes during the initial translation round.
• Internal ribosome entry site (IRES)-mediated translation offers an alternative to cap-dependent initiation, raising questions about its interaction with NMD.

Purpose of the Study:

• To investigate whether NMD triggered by encephalomyocarditis virus (EMCV) IRES-initiated translation targets CBP80/20-bound mRNA or the subsequently remodeled eIF4E-bound mRNA.
• To elucidate the specific binding partners of mRNA undergoing NMD when translation initiates via an EMCV IRES.

Main Methods:

• Utilized reporter constructs to study translation initiation via EMCV IRES.
• Employed techniques to assess mRNA binding to CBP80/20 and eIF4E.
• Quantified NMD activity under conditions of premature translation termination.

Main Results:

• NMD triggered by EMCV IRES initiation targets CBP80/20-bound mRNA.
• Evidence suggests that eIF4E-bound mRNA, formed after remodeling, is not a detectable target of NMD in this context.
• EMCV IRES-initiated translation involves a CBP80/20-associated pioneer translation round, which is essential for subsequent CBP80/20-dependent and Upf factor-dependent NMD.

Conclusions:

• NMD surveillance during IRES-mediated translation preferentially targets the initial CBP80/20-bound mRNA complex.
• This finding clarifies the substrate specificity of NMD in the context of alternative translation initiation pathways.
• The study highlights the role of the pioneer translation round and specific protein complexes in directing NMD activity.