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Publication : An RNA-binding Protein, Lin28, Recognizes and Remodels G-quartets in the MicroRNAs (miRNAs) and mRNAs It Regulates.

First Author  O'Day E Year  2015
Journal  J Biol Chem Volume  290
Issue  29 Pages  17909-22
PubMed ID  26045559 Mgi Jnum  J:235236
Mgi Id  MGI:5795796 Doi  10.1074/jbc.M115.665521
Citation  O'Day E, et al. (2015) An RNA-binding Protein, Lin28, Recognizes and Remodels G-quartets in the MicroRNAs (miRNAs) and mRNAs It Regulates. J Biol Chem 290(29):17909-22
abstractText  Lin28 is an evolutionarily conserved RNA-binding protein that inhibits processing of pre-let-7 microRNAs (miRNAs) and regulates translation of mRNAs that control developmental timing, pluripotency, metabolism, and tumorigenesis. The RNA features that mediate Lin28 binding to the terminal loops of let-7 pre-miRNAs and to Lin28-responsive elements (LREs) in mRNAs are not well defined. Here we show that Lin28 target datasets are enriched for RNA sequences predicted to contain stable planar structures of 4 guanines known as G-quartets (G4s). The imino NMR spectra of pre-let-7 loops and LREs contain resonances characteristic of G4 hydrogen bonds. These sequences bind to a G4-binding fluorescent dye, N-methyl-mesoporphyrin IX (NMM). Mutations and truncations in the RNA sequence that prevent G4 formation also prevent Lin28 binding. The addition of Lin28 to a pre-let-7 loop or an LRE reduces G4 resonance intensity and NMM binding, suggesting that Lin28 may function to remodel G4s. Further, we show that NMM inhibits Lin28 binding. Incubation of a human embryonal carcinoma cell line with NMM reduces its stem cell traits. In particular it increases mature let-7 levels, decreases OCT4, HMGA1, CCNB1, CDK4, and Lin28A protein, decreases sphere formation, and inhibits colony formation. Our results suggest a previously unknown structural feature of Lin28 targets and a new strategy for manipulating Lin28 function.
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