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: 33.12). 11/2011; 147(5):1080-91. DOI: 10.1016/j.cell.2011.10.020
Source: PubMed

ABSTRACT 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.

  • Source
    • "As a result of this knockdown, mature let-7 family miRNAs accumulated , as measured by RT-PCR, relative to transfection of a nontarget (siNT) control (Figure S3C). Also of note, siRNAs against both homologs were necessary to observe an induction of the let-7 family members, demonstrating their known semiredundant roles in let-7 maturation (Nam et al., 2011). "
    [Show abstract] [Hide abstract]
    ABSTRACT: It is clear that neural differentiation from human pluripotent stem cells generates cells that are developmentally immature. Here, we show that the let-7 plays a functional role in the developmental decision making of human neural progenitors, controlling whether these cells make neurons or glia. Through gain- and loss-of-function studies on both tissue and pluripotent derived cells, our data show that let-7 specifically regulates decision making in this context by regulation of a key chromatin-associated protein, HMGA2. Furthermore, we provide evidence that the let-7/HMGA2 circuit acts on HES5, a NOTCH effector and well-established node that regulates fate decisions in the nervous system. These data link the let-7 circuit to NOTCH signaling and suggest that this interaction serves to regulate human developmental progression.
    Stem Cell Reports 10/2014; 3(5). DOI:10.1016/j.stemcr.2014.08.015 · 5.64 Impact Factor
  • Source
    • "While Lin28B represses let-7 processing in the nucleus to prevent the formation of the precursor form from the primary let-7, Lin28A also blocks cytoplasmic processing of let-7 [6]. It has recently been shown in mouse that deletion of the Lin28 linker domain alters the protein’s three-dimensional structure and is sufficient to disrupt sequestration of the precursor form of let-7 (pre-let-7) [14]. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Understanding the control of stem cell (SC) differentiation is important to comprehend developmental processes as well as to develop clinical applications. Lin28 is a conserved molecule that is involved in SC maintenance and differentiation by regulating let-7 miRNA maturation. However, little is known about the in vivo function of Lin28. Here, we report critical roles for lin-28 during oogenesis. We found that let-7 maturation was increased in lin-28 null mutant fly ovaries. We showed that lin-28 null mutant female flies displayed reduced fecundity, due to defects in egg chamber formation. More specifically, we demonstrated that in mutant ovaries, the egg chambers fuse during early oogenesis resulting in abnormal late egg chambers. We also showed that this phenotype is the combined result of impaired germline SC differentiation and follicle SC differentiation. We suggest a model in which these multiple oogenesis defects result from a misregulation of the ecdysone signaling network, through the fine-tuning of Abrupt and Fasciclin2 expression. Our results give a better understanding of the evolutionarily conserved role of lin-28 on GSC maintenance and differentiation.
    PLoS ONE 06/2014; 9(6):e101141. DOI:10.1371/journal.pone.0101141 · 3.23 Impact Factor
  • Source
    • "For example, Gln29 can recognize all four bases by a simple adjustment of its side-chain position and orientation. Alternative side-chain conformations have also been suggested to contribute to the degenerate recognition of polypyrimidine tracts by U2AF65 (45), the recognition of multiple RNA targets by the specific fem-3 binding factor (FBF) protein of the PUMILIO/FBF (PUF) family (46) or three different RNA targets by Lin28 (47). Very recently, the X-ray crystal structures of Pot1pC in complex with its cognate and several non-cognate ssDNA ligands have nicely demonstrated that changes in nucleic acid and protein structure (such as rotation of bases or protein side-chains) allows for alternative H-bond networks or stacking interactions and thus for the accommodation of several different DNA sequences by the same protein with thermodynamic equivalence (48). "
    [Show abstract] [Hide abstract]
    ABSTRACT: The carbon storage regulator/regulator of secondary metabolism (Csr/Rsm) type of small non-coding RNAs (sRNAs) is widespread throughout bacteria and acts by sequestering the global translation repressor protein CsrA/RsmE from the ribosome binding site of a subset of mRNAs. Although we have previously described the molecular basis of a high affinity RNA target bound to RsmE, it remains unknown how other lower affinity targets are recognized by the same protein. Here, we have determined the nuclear magnetic resonance solution structures of five separate GGA binding motifs of the sRNA RsmZ of Pseudomonas fluorescens in complex with RsmE. The structures explain how the variation of sequence and structural context of the GGA binding motifs modulate the binding affinity for RsmE by five orders of magnitude (∼10 nM to ∼3 mM, Kd). Furthermore, we see that conformational adaptation of protein side-chains and RNA enable recognition of different RNA sequences by the same protein contributing to binding affinity without conferring specificity. Overall, our findings illustrate how the variability in the Csr/Rsm protein-RNA recognition allows a fine-tuning of the competition between mRNAs and sRNAs for the CsrA/RsmE protein.
    Nucleic Acids Research 02/2014; 42(8). DOI:10.1093/nar/gku141 · 9.11 Impact Factor
Show more