Proximity of the poly(A)-binding protein to a premature termination codon inhibits mammalian nonsense-mediated mRNA decay

Abstract

mRNA surveillance pathways selectively clear defective mRNAs from the cell. As such, these pathways serve as important modifiers of genetic disorders. Nonsense-mediated decay (NMD), the most intensively studied surveillance pathway, recognizes mRNAs with premature termination codons (PTCs). In mammalian systems the location of a PTC more than 50 nucleotides 59 to the terminal exon-exon junction is a critical determinant of NMD. However, mRNAs with nonsense codons that fulfill this requirement but are located very early in the open reading frame can effectively evade NMD. The unexpected resistance of such mRNAs with AUG-proximal PTCs to accelerated decay suggests that important determinants of NMD remain to be identified. Here, we report that an NMD-sensitive mRNA can be stabilized by artificially tethering the cytoplasmic poly(A) binding protein 1, PABPC1, at a PTC-proximal position. Remarkably, the data further suggest that NMD of an mRNA with an AUG-proximal PTC can also be repressed by PABPC1, which might be brought into proximity with the PTC during cap-dependent translation and 43S scanning. These results reveal a novel parameter of NMD in mammalian cells that can account for the stability of mRNAs with AUG-proximal PTCs. These findings serve to expand current mechanistic models of NMD and mRNA translation.

Estrogen receptor β exon 3-deleted mouse: The importance of non-ERE pathways in ERβ signaling

“…Ribosomal subunits do not efficiently dissociate from the translated mRNA when stalling at a premature stop codon if it is not closely followed by a poly(A) signal. Indeed, proper translation termination depends on a stimulating signal from the poly(A) binding protein and therefore only occurs when the stop codon is in spatial proximity of the poly(A) tail region (26)(27)(28). For that reason, we speculate that the transcription machinery can read through the two stop codons (TAA followed by TGA) in the case of the manipulated ERβ gene.…”

Identification of hundreds of novel UPF1 target transcripts by direct determination of whole transcriptome stability

“…61,62 In addition, recent studies put forward a general and evolutionarily conserved mechanism in which the distance between the termination codon and the poly(A) tail is a determinant of NMD-mediated RNA degradation: the 'unified 3' model'. 35,53,63,64 This model proposes that the key trigger for NMD is an inefficient termination event caused by the failure of PABP to interact with the terminating ribosome. This model can explain the previous observation in which EJC-independent degradation is performed in nonsense mRNA having a long 3' UTR.…”

Structural insights into nonsense-mediated mRNA decay (NMD) by electron microscopy

“…Work over the years has provided significant insights into the molecular mechanisms of aberrant mRNA detection in the NMD pathway [1,[3][4][5][6][7]. NMD requires translating ribosomes and a signal downstream of the stop codon to define the context of translation termination as physiological or aberrant.…”

“…Despite intensive research, we do not fully understanding the molecular basis of this 50-55 nucleotide rule. According to current models, a large complex bridging the ribosome and an EJC, and containing the three UP-Frameshift proteins, UPF1, UPF2 and UPF3, assembles only when a downstream EJC comes into proximity of a ribosome that has terminated prematurely ( Figure 1a) [1,[3][4][5][6][7]17]. UPF1 is an RNA helicase that associates with ribosomes by interacting with eukaryotic release factors (eRFs) eRF1 and eRF3.…”