Cytoplasmic poly-adenosine binding proteins modulate susceptibility of mRNAs to Pumilio-mediated decay

Area of Science:

• Molecular Biology
• RNA Biology
• Gene Regulation

Background:

• Cytoplasmic messenger RNA (mRNA) fate is determined by translation and degradation.
• The 3' poly-adenosine (poly(A)) tail and poly(A)-binding proteins (PABPCs) are key regulators of mRNA stability.
• Sequence-specific RNA-binding factors, like Pumilio proteins (PUM1 and PUM2), modulate mRNA decay pathways.

Purpose of the Study:

• To investigate the mechanism by which human PUM1 and PUM2 repress target mRNAs through accelerated degradation.
• To elucidate the role of the poly(A) tail, deadenylases, and PABPCs in PUM-mediated mRNA repression.

Main Methods:

• Investigated PUM1/2 repression of target mRNAs in human cells.
• Assessed the requirement for deadenylases (CCR4-NOT) and PABPCs (PABPC1, PABPC4) in PUM repression.
• Examined the effect of varying PABPC concentrations on PUM activity and mRNA stability.

Main Results:

• PUM-mediated repression of mRNA degradation is dependent on the poly(A) tail, deadenylases (CCR4-NOT), and specific PABPCs (PABPC1, PABPC4).
• PUM proteins associate with and require PABPC1 and PABPC4 for efficient repression.
• Absence of PABPCs leads to general mRNA instability, bypassing PUM control.
• Increasing PABPC concentration inhibits PUM activity in a dose-dependent manner by stabilizing poly(A) tails.

Conclusions:

• PUM1/2 repression of mRNA degradation is modulated by PABPC abundance through a "Goldilocks principle", where PABPCs protect the poly(A) tail from deadenylation.
• This mechanism highlights the critical interplay between PABPCs, deadenylases, and RNA-binding proteins in fine-tuning mRNA stability.
• The findings suggest potential physiological relevance for this regulatory mechanism, given variations in PABPC levels across tissues and developmental stages.