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Selective destabilization of polypeptides synthesized from NMD-targeted transcripts

Vincent Chu1,2, Qing Feng1, Yang Lim3

  • 1Department of Cell Biology, Harvard Medical School, Blavatnik Institute, Boston, MA 02115.

Molecular Biology of the Cell
|September 29, 2021
PubMed

Insights

Termination of protein synthesis at premature termination codons (PTCs) selectively destabilizes polypeptides in mammalian cells. This polypeptide degradation is linked to nonsense-mediated decay (NMD) pathway activation.

Area of Science:

  • Molecular Biology
  • Cell Biology
  • Genetics

Background:

  • Nonsense-mediated decay (NMD) is a crucial mRNA surveillance pathway.
  • NMD degrades messenger RNAs (mRNAs) with premature termination codons (PTCs) to prevent the synthesis of truncated proteins.
  • The fate of polypeptides synthesized during NMD activation remains poorly understood.

Purpose of the Study:

  • To investigate the impact of premature termination codon recognition on polypeptide stability in mammalian cells.
  • To elucidate the relationship between polypeptide degradation and NMD pathway activation.

Main Methods:

  • Utilized reporter systems to compare polypeptide synthesis from normal and PTC-containing mRNAs.
  • Employed proteasome inhibition to assess the role of proteasomal degradation.
  • Depleted key NMD factors (UPF1) and inhibited related kinases (SMG1) to study their involvement.

Main Results:

  • Termination of protein synthesis at a PTC selectively destabilizes nascent polypeptides.
  • Proteasome inhibition transiently rescues PTC-terminated polypeptide levels but disrupts mRNA homeostasis.
  • Depletion of UPF1 or SMG1 alleviates PTC-terminated polypeptide destabilization, but inhibiting SMG1 kinase activity does not.

Conclusions:

  • Polypeptide degradation is intrinsically linked to premature termination codon recognition in mammalian cells.
  • The findings provide a framework for understanding the mechanisms connecting NMD activation and protein degradation.

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