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Coupled protein quality control during nonsense-mediated mRNA decay
Alison J Inglis1, Alina Guna1,2, Ángel Gálvez-Merchán1
1Division of Biology and Biological Engineering, California Institute of Technology, 1200 E. California Blvd, Pasadena, CA 91125, USA.
Abstract:
Translation of mRNAs containing premature termination codons (PTCs) results in truncated protein products with deleterious effects. Nonsense-mediated decay (NMD) is a surveillance pathway responsible for detecting PTC containing transcripts. Although the molecular mechanisms governing mRNA degradation have been extensively studied, the fate of the nascent protein product remains largely uncharacterized. Here, we use a fluorescent reporter system in mammalian cells to reveal a selective degradation pathway specifically targeting the protein product of an NMD mRNA. We show that this process is post-translational and dependent on the ubiquitin proteasome system. To systematically uncover factors involved in NMD-linked protein quality control, we conducted genome-wide flow cytometry-based screens. Our screens recovered known NMD factors but suggested that protein degradation did not depend on the canonical ribosome-quality control (RQC) pathway. A subsequent arrayed screen demonstrated that protein and mRNA branches of NMD rely on a shared recognition event. Our results establish the existence of a targeted pathway for nascent protein degradation from PTC containing mRNAs, and provide a reference for the field to identify and characterize required factors.
Insights
Nonsense-mediated decay (NMD) degrades faulty mRNAs. This study reveals a new pathway that also targets the truncated proteins produced from these mRNAs for degradation via the ubiquitin proteasome system.
Area of Science:
- Molecular Biology
- Cell Biology
- Genetics
Background:
- Translation of messenger RNAs (mRNAs) with premature termination codons (PTCs) produces truncated proteins, which can be harmful.
- Nonsense-mediated decay (NMD) is a crucial cellular surveillance pathway that eliminates these PTC-containing mRNAs.
- The fate of the nascent truncated proteins generated from NMD targets has remained largely unknown.
Purpose of the Study:
- To investigate the degradation pathway of nascent proteins produced from NMD target mRNAs.
- To identify factors involved in the quality control of proteins linked to NMD.
- To determine if protein degradation relies on known pathways like the ribosome-quality control (RQC) pathway.
Main Methods:
- Utilized a fluorescent reporter system in mammalian cells to track protein products of NMD mRNAs.
- Employed genome-wide flow cytometry-based screens to identify factors involved in NMD-linked protein quality control.
- Conducted arrayed screens to compare mRNA and protein degradation pathways in NMD.
Main Results:
- Discovered a selective, post-translational degradation pathway for proteins arising from NMD mRNAs, dependent on the ubiquitin proteasome system.
- Genome-wide screens identified known NMD factors and indicated that protein degradation is independent of the canonical ribosome-quality control (RQC) pathway.
- Demonstrated that both the protein and mRNA branches of NMD share a common recognition event.
Conclusions:
- Established a targeted degradation pathway for nascent proteins from PTC-containing mRNAs.
- Provided a foundation for identifying and characterizing factors involved in NMD-linked protein quality control.
- Highlighted the coordinated action of mRNA and protein surveillance in cellular quality control mechanisms.
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