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

Eukaryotic mRNAs with premature translation termination codons (PTCs) are recognized and degraded through a process termed nonsense-mediated mRNA decay (NMD). The evolutionary conservation of the core NMD factors UPF1, UPF2 and UPF3 implies a similar basic mechanism of PTC recognition in all eukaryotes. However, while PTC-containing mRNAs in yeast seem to be available to NMD at each round of translation, mammalian NMD has been reported to be restricted to cap-binding complex (CBC)-bound mRNAs during the pioneer round of translation. Here, we compared decay kinetics of two NMD reporter genes in mRNA fractions bound to either CBC or the eukaryotic initiation factor 4E (eIF4E) in human cells and demonstrate that NMD destabilizes eIF4E-bound transcripts as efficiently as those associated with CBC. These results corroborate an emerging unified model for NMD substrate recognition, according to which NMD can ensue at every aberrant translation termination event.