General RNA-binding proteins have a function in poly(A)-binding protein-dependent translation

Area of Science:

• Molecular Biology
• Biochemistry
• Genetics

Background:

• The poly(A)-binding protein (PABP) interacts with eukaryotic translational initiation factor 4G (eIF4G) to promote mRNA circularization, thereby stimulating translation.
• The roles of general RNA-binding proteins in mRNA circularization and their impact on translation initiation have not been extensively studied.

Purpose of the Study:

• To investigate the function of the major mRNA ribonucleoprotein YB-1 in regulating the activity of the translation initiation factor 4F (eIF4F) complex by PABP.
• To elucidate the mechanism by which YB-1 influences PABP-mediated stimulation of translation.

Main Methods:

• Analysis of 80S ribosome initiation complex formation in cell extracts.
• Experiments using rabbit reticulocyte lysate to assess PABP-dependent translation.
• Investigation of eIF4E binding to the cap structure under various conditions, including YB-1 and PABP manipulation.

Main Results:

• YB-1 exacerbates PABP depletion-induced inhibition of 80S ribosome initiation complex formation.
• YB-1 renders translation in rabbit reticulocyte lysate dependent on PABP.
• YB-1 inhibits eIF4E cap-binding, while nonspecific RNA stimulates it.
• PABP more potently stimulates eIF4E cap-binding when previously downregulated by YB-1.
• Nonspecific RNA abrogates PABP stimulation of eIF4E binding.

Conclusions:

• YB-1 plays a pivotal role in regulating eIF4F activity by PABP.
• Competition between YB-1 and eIF4G for mRNA binding is essential for PABP to efficiently stimulate eIF4F activity.
• These findings reveal a novel mechanism for translational control involving RNA-binding proteins and mRNA circularization.