Molecular Basis for Interaction of let-7 MicroRNAs with Lin28

Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA.
Cell (Impact Factor: 32.24). 11/2011; 147(5):1080-91. DOI: 10.1016/j.cell.2011.10.020
Source: PubMed


MicroRNAs (miRNAs) are small noncoding RNA molecules that regulate gene expression. Among these, members of the let-7 miRNA family control many cell-fate determination genes to influence pluripotency, differentiation, and transformation. Lin28 is a specific, posttranscriptional inhibitor of let-7 biogenesis. We report crystal structures of mouse Lin28 in complex with sequences from let-7d, let-7-f1, and let-7 g precursors. The two folded domains of Lin28 recognize two distinct regions of the RNA and are sufficient for inhibition of let-7 in vivo. We also show by NMR spectroscopy that the linker connecting the two folded domains is flexible, accommodating Lin28 binding to diverse let-7 family members. Protein-RNA complex formation imposes specific conformations on both components that could affect downstream recognition by other processing factors. Our data provide a molecular explanation for Lin28 specificity and a model for how it regulates let-7.


Available from: James J Chou, Mar 11, 2015

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Article: Molecular Basis for Interaction of let-7 MicroRNAs with Lin28

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    • "There are two paralogs of LIN28, LIN28A, and LIN28B, both containing a cold shock domain (CSD) and CCHC-zinc finger RNA-binding domain. They regulate let-7 miRNA levels by CSD binding to the NGN- GAYNNN (N = any base and Y = pyrimidine) sequence on the terminal loop of let-7 and CCHC-zinc finger binding to the GGAG sequence on the same terminal loop [26]. The linker between the CSD and the CCHC-zinc finger allows for binding of all twelve let-7 miRNA family members. "
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    ABSTRACT: Epithelial ovarian cancer is the most aggressive and deadly form of ovarian cancer and is the most lethal gynecological malignancy worldwide; therefore, efforts to elucidate the molecular factors that lead to epithelial ovarian cancer are essential to better understand this disease. Recent studies reveal that tumor cells release cell-secreted vesicles called exosomes and these exosomes can transfer RNAs and miRNAs to distant sites, leading to cell transformation and tumor development. The RNA-binding protein LIN28 is a known marker of stem cells and when expressed in cancer, it is associated with poor tumor outcome. We hypothesized that high LIN28 expressing ovarian cancer cells secrete exosomes that can be taken up by nontumor cells and cause changes in gene expression and cell behavior associated with tumor development. IGROV1 cells were found to contain high LIN28A and secrete exosomes that were taken up by HEK293 cells. Moreover, exposure to these IGROV1 secreted exosomes led to significant increases in genes involved in Epithelial-to-Mesenchymal Transition (EMT), induced HEK293 cell invasion and migration. These changes were not observed with exosomes secreted by OV420 cells, which contain no detectable amounts of LIN28A or LIN28B. No evidence was found of LIN28A transfer from IGROV1 exosomes to HEK293 cells.
    11/2015; 2015(5):1-13. DOI:10.1155/2015/701390
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    • "These functions of let-7 miRNAs primarily are accomplished in differentiated cells where they are expressed abundantly. Let-7 pri-and pre-miRNAs harbor a typical hairpin structure with a stem containing the let-7-5p miRNA sequence base paired extensively with the partially complementary let- 7-3p miRNA sequence, connected by a so-called terminal loop region of variable lengths and structures among different let-7 family members, a region referred to as pre-element (preE) (Nam et al., 2011). Let-7 preE serves as a platform to recruit RNA-binding proteins, such as LIN28, KHSRP (also known as KSRP), hnRNPA1, and TRIM25, in order to posttranscriptionally regulate let-7 biogenesis (Heo et al., 2008; Michlewski and Cá ceres, 2010; Newman et al., 2008; Rybak et al., 2008; Trabucchi et al., 2009; Viswanathan et al., 2008; Zhang et al., 2015). "
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    ABSTRACT: Let-7 microRNAs (miRNAs) are critical regulators of animal development, stem cell differentiation, glucose metabolism, and tumorigenesis. Mammalian genomes contain 12 let-7 isoforms that suppress expression of a common set of target mRNAs. LIN28 proteins selectively block let-7 biogenesis in undifferentiated cells and in cancer. The current model for coordinate let-7 repression involves the LIN28 cold-shock domain (CSD) binding the terminal loop and the two CCHC-type zinc fingers recognizing a GGAG sequence motif in precursor let-7 (pre-let-7) RNAs. Here, we perform a systematic analysis of all let-7 miRNAs and find that a single let-7 family member, human let-7a-3 (and its murine ortholog let-7c-2), escapes LIN28-mediated regulation. Mechanistically, we find that the pre-let-7c-2 loop precludes LIN28A binding and regulation. These findings refine the current model of let-7 regulation by LIN28 proteins and have important implications for understanding the LIN28/let-7 axis in development and disease.
    Cell Reports 10/2015; 13(2):1-7. DOI:10.1016/j.celrep.2015.08.086 · 8.36 Impact Factor
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    • "Mono-uridylation by TUT7/4/2 restores the optimal 2-nt 3 0 overhang of group II pre-miRNAs resulting in efficient Dicer processing (Heo et al, 2012). Between the two contrasting roles that TUTs play in miRNA biogenesis, Lin28-dependent oligo-uridylation by TUT4/7 has been intensively characterized via biochemical and structural studies (Heo et al, 2008, 2009; Hagan et al, 2009; Nam et al, 2011; Yeom et al, 2011; Loughlin et al, 2012; Mayr et al, 2012; Thornton et al, 2012), whereas mechanism of monouridylation has been largely unknown. "
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    ABSTRACT: Terminal uridylyl transferases (TUTs) function as integral regulators of microRNA (miRNA) biogenesis. Using biochemistry, single-molecule, and deep sequencing techniques, we here investigate the mechanism by which human TUT7 (also known as ZCCHC6) recognizes and uridylates precursor miRNAs (pre-miRNAs) in the absence of Lin28. We find that the overhang of a pre-miRNA is the key structural element that is recognized by TUT7 and its paralogues, TUT4 (ZCCHC11) and TUT2 (GLD2/PAPD4). For group II pre-miRNAs, which have a 1-nt 3′ overhang, TUT7 restores the canonical end structure (2-nt 3′ overhang) through mono-uridylation, thereby promoting miRNA biogenesis. For pre-miRNAs where the 3′ end is further recessed into the stem (as in 3′ trimmed pre-miRNAs), TUT7 generates an oligo-U tail that leads to degradation. In contrast to Lin28-stimulated oligo-uridylation, which is processive, a distributive mode is employed by TUT7 for both mono- and oligo-uridylation in the absence of Lin28. The overhang length dictates the frequency (but not duration) of the TUT7-RNA interaction, thus explaining how TUT7 differentiates pre-miRNA species with different overhangs. Our study reveals dual roles and mechanisms of uridylation in repair and removal of defective pre-miRNAs.
    The EMBO Journal 05/2015; 34(13). DOI:10.15252/embj.201590931 · 10.43 Impact Factor
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