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Dissecting the functions of SMG5, SMG7, and PNRC2 in nonsense-mediated mRNA decay of human cells

Type of publication Peer-reviewed
Publikationsform Original article (peer-reviewed)
Author Nicholson Pamela, Gkratsou Asimina, Josi Christoph, Colombo Martino, Mühlemann Oliver,
Project Quality control of gene expression: towards understanding mechanism and physiological role of nonsense-mediated mRNA decay (NMD)
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Original article (peer-reviewed)

Journal RNA
Volume (Issue) 24(4)
Page(s) 557 - 573
Title of proceedings RNA
DOI 10.1261/rna.063719.117

Open Access

URL http://muehlemann.dcb.unibe.ch/publications.html
Type of Open Access Repository (Green Open Access)

Abstract

The term "nonsense-mediated mRNA decay" (NMD) originally described the degradation of mRNAs with premature translation-termination codons (PTCs), but its meaning has recently been extended to be a translation-dependent post-transcriptional regulator of gene expression affecting 3%-10% of all mRNAs. The degradation of NMD target mRNAs involves both exonucleolytic and endonucleolytic pathways in mammalian cells. While the latter is mediated by the endonuclease SMG6, the former pathway has been reported to require a complex of SMG5-SMG7 or SMG5-PNRC2 binding to UPF1. However, the existence, dominance, and mechanistic details of these exonucleolytic pathways are divisive. Therefore, we have investigated the possible exonucleolytic modes of mRNA decay in NMD by examining the roles of UPF1, SMG5, SMG7, and PNRC2 using a combination of functional assays and interaction mapping. Confirming previous work, we detected an interaction between SMG5 and SMG7 and also a functional need for this complex in NMD. In contrast, we found no evidence for the existence of a physical or functional interaction between SMG5 and PNRC2. Instead, we show that UPF1 interacts with PNRC2 and that it triggers 5'-3' exonucleolytic decay of reporter transcripts in tethering assays. PNRC2 interacts mainly with decapping factors and its knockdown does not affect the RNA levels of NMD reporters. We conclude that PNRC2 is probably an important mRNA decapping factor but that it does not appear to be required for NMD.
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