Ribosome rescue factor PELOTA modulates translation start site choice for C/EBPα protein isoforms.

Area of Science:

• Molecular Biology
• Cell Biology
• Genetics

Background:

• Alternative translation initiation generates distinct protein isoforms from a single mRNA.
• CCAAT/enhancer-binding protein α (C/EBPα) isoforms, produced from alternative start sites, have opposing roles in myeloid cell development.
• The regulation of C/EBPα isoform choice is influenced by transcript features like upstream open reading frames (uORFs) but remains incompletely understood.

Purpose of the Study:

• To identify molecular factors regulating C/EBPα isoform selection.
• To elucidate the mechanisms controlling the balance between C/EBPα isoforms.
• To understand the implications for hematopoiesis and leukemogenesis.

Main Methods:

• Utilized a quantitative two-color fluorescent reporter system to monitor C/EBPα isoform expression.
• Performed a CRISPR interference (CRISPRi) screen to identify regulatory factors.
• Investigated the role of the ribosome rescue factor PELOTA (PELO) and the mechanistic target of rapamycin (mTOR) kinase.

Main Results:

• The CRISPRi screen identified PELOTA as a key regulator of C/EBPα isoform choice.
• PELOTA promotes the expression of the longer C/EBPα isoform.
• PELOTA acts by directly removing stalled ribosomes and indirectly via mTOR signaling.

Conclusions:

• PELOTA plays a critical role in regulating C/EBPα isoform production.
• This study highlights the connection between ribosome rescue, translation reinitiation, and the control of key developmental transcription factors.
• Findings have implications for understanding normal hematopoiesis and the development of leukemia.