The DDX6-4E-T interaction mediates translational repression and P-body assembly

Area of Science:

• Molecular Biology
• Gene Regulation
• RNA Biology

Background:

• 4E-Transporter (4E-T) is a nucleocytoplasmic shuttling protein that inhibits protein synthesis by binding eIF4E.
• 4E-T also represses translation independently of eIF4E and contributes to microRNA (miRNA)-mediated silencing.
• The precise mechanisms underlying 4E-T's diverse regulatory roles are not fully understood.

Purpose of the Study:

• To elucidate the mechanism of translational repression by 4E-T.
• To identify and characterize the interacting partners and binding sites of 4E-T.
• To investigate the role of 4E-T in miRNA-dependent gene silencing and P-body formation.

Main Methods:

• Mass spectrometry and western blotting to identify protein-protein interactions.
• Site-directed mutagenesis to delineate functional motifs.
• Functional assays to assess mRNA translation and P-body assembly.

Main Results:

• Identified novel interactions between 4E-T and its partners, including UNR-CNOT4 and unrip-LSM14A, forming a complex network.
• Deletion of UNR- and DDX6-binding motifs in 4E-T relieved mRNA repression, partly via the 4E-T-DDX6-CNOT1 axis.
• The DDX6-4E-T interaction was crucial for miRNA-dependent translational repression and de novo P-body assembly, linking these processes.

Conclusions:

• 4E-T nucleates a complex network of RNA-binding proteins, extending its known functions beyond eIF4E binding.
• The interaction between 4E-T, DDX6, and CNOT1 is critical for translational repression of 4E-T-bound mRNAs.
• 4E-T-mediated translational repression and P-body formation are coupled processes, highlighting 4E-T's central role in gene regulation during development and neurogenesis.