title: Trim25 Is an RNA-Specific Activator  of Lin28a/TuT4-Mediated Uridylation.
abstract: RNA binding proteins have thousands of cellular RNA targets and often exhibit opposite or passive molecular functions. Lin28a is a conserved RNA binding protein involved in pluripotency and tumorigenesis that was previously shown to trigger TuT4-mediated pre-let-7 uridylation, inhibiting its processing and targeting it for degradation. Surprisingly, despite binding to other pre-microRNAs (pre-miRNAs), only pre-let-7 is efficiently uridylated by TuT4. Thus, we hypothesized the existence of substrate-specific cofactors that stimulate Lin28a-mediated pre-let-7 uridylation or restrict its functionality on non-let-7 pre-miRNAs. Through RNA pull-downs coupled with quantitative mass spectrometry, we identified the E3 ligase Trim25 as an RNA-specific cofactor for Lin28a/TuT4-mediated uridylation. We show that Trim25 binds to the conserved terminal loop (CTL) of pre-let-7 and activates TuT4, allowing for more efficient Lin28a-mediated uridylation. These findings reveal that protein-modifying enzymes, only recently shown to bind RNA, can guide the function of canonical ribonucleoprotein (RNP) complexes in cis, thereby providing an additional level of specificity.
authors.forename: Nila Roy
authors.initials: NR
authors.lastname: Choudhury
authors.forename: Jakub S
authors.initials: JS
authors.lastname: Nowak
authors.forename: Juan
authors.initials: J
authors.lastname: Zuo
authors.forename: Juri
authors.initials: J
authors.lastname: Rappsilber
authors.forename: Steven H
authors.initials: SH
authors.lastname: Spoel
authors.forename: Gracjan
authors.initials: G
authors.lastname: Michlewski
mesh_terms: D000818:Animals; D001483:Base Sequence; D006367:HeLa Cells; D006801:Humans; D007553:Isotope Labeling; D013058:Mass Spectrometry; D051379:Mice; D035683:MicroRNAs / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D009690:Nucleic Acid Conformation; D059372:Nucleotide Motifs / Q000235:genetics; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D011485:Protein Binding; D012323:RNA Processing, Post-Transcriptional / Q000235:genetics; D016601:RNA-Binding Proteins / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism*; D000070584:Tripartite Motif Proteins; D044764:Ubiquitin-Activating Enzymes / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism*; D014529:Uridine / Q000378:metabolism*
chemical_list: C516326:LIN28B protein, human; D035683:MicroRNAs; D016601:RNA-Binding Proteins; D014157:Transcription Factors; D000070584:Tripartite Motif Proteins; C487931:mirnlet7 microRNA, human; C084523:TRIM25 protein, human; D044767:Ubiquitin-Protein Ligases; D046988:Proteasome Endopeptidase Complex; D044764:Ubiquitin-Activating Enzymes; D014529:Uridine