eIF4E-bound mRNPs are substrates for nonsense-mediated mRNA decay in mammalian cells

Area of Science:

• Molecular Biology
• Genetics
• Cell Biology

Background:

• Nonsense-mediated mRNA decay (NMD) is a conserved surveillance pathway that eliminates eukaryotic messenger RNAs (mRNAs) containing premature translation termination codons (PTCs).
• Core NMD factors UPF1, UPF2, and UPF3 are evolutionarily conserved, suggesting a fundamental mechanism for PTC recognition across eukaryotes.
• Mammalian NMD has been thought to primarily act on transcripts bound by the cap-binding complex (CBC) during the pioneer round of translation, unlike in yeast where NMD appears to occur at each translation round.

Purpose of the Study:

• To investigate the role of eukaryotic initiation factor 4E (eIF4E) in NMD-mediated mRNA decay.
• To compare the decay kinetics of NMD reporter genes bound to CBC versus eIF4E in human cells.
• To evaluate the validity of a unified model for NMD substrate recognition.

Main Methods:

• Utilized NMD reporter genes to assess mRNA decay rates.
• Fractionated mRNA based on binding to either CBC or eIF4E in human cells.
• Compared the destabilization efficiency of NMD on eIF4E-bound versus CBC-bound transcripts.

Main Results:

• Nonsense-mediated mRNA decay (NMD) destabilizes transcripts bound to eukaryotic initiation factor 4E (eIF4E) with similar efficiency as those bound to the cap-binding complex (CBC).
• Decay kinetics analysis revealed no significant difference in NMD targeting between eIF4E- and CBC-bound NMD reporter genes.
• These findings challenge the notion of NMD being exclusively restricted to the pioneer round of translation or CBC-bound mRNAs.

Conclusions:

• NMD can effectively target and degrade mRNAs regardless of whether they are bound by CBC or eIF4E.
• The results support an emerging unified model where NMD can occur at any aberrant translation termination event.
• This broadens the understanding of mRNA surveillance mechanisms in human cells and their regulation.