Human Pumilio proteins recruit multiple deadenylases to efficiently repress messenger RNAs

Area of Science:

• Molecular Biology
• Gene Regulation
• RNA Biology

Background:

• PUF ( Pumilio) proteins are conserved eukaryotic RNA-binding proteins crucial for regulating mRNA, impacting processes like stem cell proliferation, fertility, and memory.
• While PUF proteins are known to repress protein expression from target mRNAs, the precise mechanisms, particularly in humans, remain incompletely understood.

Purpose of the Study:

• To elucidate the regulatory activities and mechanisms of action for human PUF proteins, PUM1 and PUM2.
• To investigate the role of deadenylases in PUF-mediated mRNA repression.

Main Methods:

• Development of functional assays to quantify sequence-specific repression by PUM1 and PUM2.
• In vitro interaction studies between purified PUM complexes and CCR4-NOT (CNOT) complex subunits.
• Experimental validation using dominant-negative mutants, RNA interference, and poly(A) tail manipulation to assess deadenylase involvement.

Main Results:

• Human PUM1 and PUM2 effectively inhibit translation and promote mRNA degradation.
• Purified PUM complexes associate with CCR4-NOT deadenylase subunits, and PUMs interact with CNOT deadenylase subunits in vitro.
• Deletions or depletion of CNOT7 and CNOT8 deadenylases, as well as the absence of a poly(A) tail, significantly impacted PUM repression, indicating both deadenylation-dependent and -independent mechanisms.

Conclusions:

• Human PUM proteins employ a conserved mechanism of repression by directly recruiting the CCR4-POP2-NOT deadenylase complex, leading to translational inhibition and mRNA degradation.
• PUM proteins exhibit dual modes of repression: one dependent on deadenylation and another independent of it, offering a nuanced understanding of their regulatory function.