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

Area of Science:

• Molecular Biology
• Genetics
• RNA Biology

Background:

• The nonsense-mediated mRNA decay (NMD) pathway is crucial for degrading aberrant mRNAs containing premature translation termination codons (PTCs).
• The precise mechanisms differentiating PTCs from natural stop codons remain incompletely understood.
• Understanding this discrimination is vital for comprehending gene expression regulation and preventing disease-associated mRNA variants.

Purpose of the Study:

• To elucidate the molecular determinants governing the discrimination between premature stop codons (PTCs) and natural stop codons in mRNA decay.
• To investigate the role of poly(A)-binding protein 1 (PABPC1) and 3' untranslated region (3' UTR) length in NMD pathway regulation.
• To identify features within 3' UTRs that confer resistance to NMD.

Main Methods:

• Utilized Drosophila melanogaster as a model organism to study NMD mechanisms.
• Investigated the impact of PABPC1 tethering and 3' UTR length manipulation on NMD efficiency.
• Analyzed endogenous transcripts with long 3' UTRs to identify NMD-evading features.

Main Results:

• Demonstrated that the position of a stop codon relative to the poly(A) tail, and thus PABPC1 binding, is a critical factor in PTC recognition.
• Showed that PABPC1 tethering downstream of a PTC inhibits NMD, while increased 3' UTR length can promote NMD for natural stops.
• Identified 3' UTRs that confer immunity to NMD and confirmed PABPC1 binding is sufficient for PTC recognition, independent of cleavage or polyadenylation status.
• Observed that PABPC1 depletion suppresses NMD even when translation efficiency is unaffected, suggesting a broader role in mRNA surveillance.

Conclusions:

• The position of PABPC1, influenced by stop codon proximity to the poly(A) tail, is a key determinant for distinguishing PTCs from natural stop codons.
• Long 3' UTRs can evolve features that confer resistance to NMD, highlighting a co-evolutionary mechanism.
• PABPC1 plays a fundamental and conserved role in mRNA surveillance, extending beyond simple positional information for PTC definition.