Trim25 Is an RNA-Specific Activator of Lin28a/TuT4-Mediated Uridylation

Area of Science:

• Molecular Biology
• RNA Biology
• Epigenetics

Background:

• Lin28a is a key RNA-binding protein regulating pluripotency and cancer.
• Lin28a facilitates TuT4-mediated uridylation of pre-let-7, impacting its processing and degradation.
• The specificity of Lin28a-mediated uridylation for pre-let-7 over other pre-miRNAs remained unexplained.

Purpose of the Study:

• To identify cofactors that confer specificity to Lin28a-mediated pre-let-7 uridylation.
• To elucidate the mechanism by which Lin28a selectively targets pre-let-7 for uridylation.
• To understand how protein-modifying enzymes can influence ribonucleoprotein complex function.

Main Methods:

• RNA pull-down assays coupled with quantitative mass spectrometry to identify interacting proteins.
• Biochemical assays to assess the uridylation activity of Lin28a, TuT4, and Trim25.
• RNA-binding studies to determine the interaction sites of Trim25 on pre-let-7.

Main Results:

• The E3 ligase Trim25 was identified as an RNA-specific cofactor for Lin28a/TuT4-mediated uridylation.
• Trim25 binds to the conserved terminal loop (CTL) of pre-let-7.
• Trim25 activates TuT4, enhancing Lin28a-mediated uridylation of pre-let-7.

Conclusions:

• Trim25 acts as a crucial cofactor, conferring substrate specificity to the Lin28a/TuT4 uridylation complex.
• Trim25's interaction with the pre-let-7 CTL is essential for its cofactor activity.
• This study reveals a novel mechanism where protein-modifying enzymes guide the function of canonical RNA-binding complexes, adding a layer of regulatory specificity.