A conserved role for cytoplasmic poly(A)-binding protein 1 (PABPC1) in nonsense-mediated mRNA decay

Abstract

The nonsense-mediated mRNA decay (NMD) pathway degrades mRNAs with premature translation termination codons (PTCs). The mechanisms by which PTCs and natural stop codons are discriminated remain unclear. We show that the position of stops relative to the poly(A) tail (and thus of PABPC1) is a critical determinant for PTC definition in Drosophila melanogaster. Indeed, tethering of PABPC1 downstream of a PTC abolishes NMD. Conversely, natural stops trigger NMD when the length of the 3 0 UTR is increased. However, many endogenous transcripts with exceptionally long 3 0 UTRs escape NMD, suggesting that the increase in 3 0 UTR length has co-evolved with the acquisition of features that suppress NMD. We provide evidence for the existence of 3 0 UTRs conferring immunity to NMD. We also show that PABPC1 binding is sufficient for PTC recognition, regardless of cleavage or polyadenylation. The role of PABPC1 in NMD must go beyond that of providing positional information for PTC definition, because its depletion suppresses NMD under conditions in which translation efficiency is not affected. These findings reveal a conserved role for PABPC1 in mRNA surveillance.

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

“…Consistent with this model, the majority of yeast 39 UTRs are homogeneous in length and aberrant transcripts with exceptionally long 39 UTRs are substrates for NMD (Muhlrad and Parker 1999). In contrast, the requirement for a splicing-dependent signal seems to be a particular feature of mammalian NMD, and it is well established that EJCs play a pivotal role in the mechanism of PTC definition (Behm-Ansmant et al 2007). In addition, 39 UTRs in mammalian mRNAs are very heterogeneous in length and, thus far, there is no solid evidence of a critical 39 UTR length above which transcripts are targeted for NMD.…”

“…The resultant termination defect and associated NMD can be abolished by flanking the nonsense codon with a native 39 untranslated region (UTR) or by tethering the poly(A)-binding protein downstream from a PTC to mimic a normal 39 terminus (Amrani et al 2004(Amrani et al , 2006. The position of nonsense codons relative to the cytoplasmic poly(A)-binding protein 1 (PABPC1) is also a critical determinant for PTC definition in Drosophila melanogaster (Behm-Ansmant et al 2007). The existence of global differences among the mechanisms and pathways of NMD in yeast, Drosophila, and mammalian cells (Conti and Izaurralde 2005) raises the question of whether structural parameters of NMD such as context of the termination codon and proximity of the PABPC1 extend to mammalian systems.…”

BCR-ABLalternative splicing as a common mechanism for imatinib resistance: evidence from molecular dynamics simulations

“…Furthermore, premature translation termination of an mRNA is usually associated with poor mRNA stability (38,39); this alternatively expressed BCR-ABL transcript is no exception. We observed a significant reduction in the relative ratio of alternatively spliced to wild-type BCR-ABL mRNA when samples were not processed promptly (data not shown).…”

Autoregulation of the nonsense-mediated mRNA decay pathway in human cells

“…The experimental evidence from several different model organisms suggests, for example, that long 39 UTRs can elicit NMD (Muhlrad and Parker 1999;Amrani et al 2004;Kertesz et al 2006;Behm-Ansmant et al 2007;Longman et al 2007;Eberle et al 2008;Kerenyi et al 2008;Singh et al 2008;Hansen et al 2009;Kebaara and Atkin 2009). A greater distance between the TC and PABP would impede transmission of the PABP-mediated termination-stimulating signal to the ribosome stalled at the TC, thus tilting the balance from efficient termination and ribosome release toward NMD.…”

“…According to these new mechanistic working models, normal translation termination involves an interaction between poly(A) binding protein (PABP) and ribosome-bound eukaryotic release factor 3 (eRF3), which promotes fast polypeptide release, disassembly of the ribosomal subunits, and recycling of the ribosomal subunits to the start codon (Hoshino et al 1999;Amrani et al 2004;Behm-Ansmant et al 2007). When the ribosome reaches a TC located in a messenger ribonucleoprotein (mRNP) environment where it fails to receive the PABP-mediated termination-stimulating signal, the ribosome stalls for a prolonged period of time, allowing binding of UPF1, a key factor in NMD, to eRF3 (Singh et al 2008).…”