Chemical inhibition of eIF4A3 abolishes UPF1 recruitment onto mRNA encoding NMD factors and restores their expression

Nonsense-Mediated mRNA Decay (NMD) is a key control mechanism of RNA quality widely described to target mRNA harbouring Premature Termination Codon (PTC). However, recent studies suggested the existence of non-canonical pathways which remain unresolved. One of these alternative pathways suggested that specific mRNA could be targeted through their 3′ UTR (Untranslated Region), which contain various elements involved in mRNA stability regulation. This study focused on 3′UTR of mRNA encoding NMD factors, on which we observed an enrichment of binding sites for UPF1 and eIF4A3 proteins, two important NMD factors. Using GFP reporter constructs containing the 3′UTR of these NMD mRNA fused to the GFP cDNA, we showed that GFP expression was significantly increased upon eIF4A3 inhibition, suggesting mRNA level stabilization. Furthermore, co-immunoprecipitation targeting UPF1 revealed that its interaction with mRNA encoding NMD factors was disrupted when cells were previously treated with the eIF4A3 inhibitor. We therefore propose that eIF4A3 might be necessary to recruit UPF1 and trigger the degradation of these transcripts through a non-canonical 3′UTR-dependent mechanism.