title: The QKI-5 and QKI-6 RNA binding proteins regulate the expression of microRNA 7 in glial cells.
abstract: The quaking (qkI) gene encodes 3 major alternatively spliced isoforms that contain unique sequences at their C termini dictating their cellular localization. QKI-5 is predominantly nuclear, whereas QKI-6 is distributed throughout the cell and QKI-7 is cytoplasmic. The QKI isoforms are sequence-specific RNA binding proteins expressed mainly in glial cells modulating RNA splicing, export, and stability. Herein, we identify a new role for the QKI proteins in the regulation of microRNA (miRNA) processing. We observed that small interfering RNA (siRNA)-mediated QKI depletion of U343 glioblastoma cells leads to a robust increase in miR-7 expression. The processing from primary to mature miR-7 was inhibited in the presence QKI-5 and QKI-6 but not QKI-7, suggesting that the nuclear localization plays an important role in the regulation of miR-7 expression. The primary miR-7-1 was bound by the QKI isoforms in a QKI response element (QRE)-specific manner. We observed that the pri-miR-7-1 RNA was tightly bound to Drosha in the presence of the QKI isoforms, and this association was not observed in siRNA-mediated QKI or Drosha-depleted U343 glioblastoma cells. Moreover, the presence of the QKI isoforms led to an increase presence of pri-miR-7 in nuclear foci, suggesting that pri-miR-7-1 is retained in the nucleus by the QKI isoforms. miR-7 is known to target the epidermal growth factor (EGF) receptor (EGFR) 3' untranslated region (3'-UTR), and indeed, QKI-deficient U343 cells had reduced EGFR expression and decreased ERK activation in response to EGF. Elevated levels of miR-7 are associated with cell cycle arrest, and it was observed that QKI-deficient U343 that harbor elevated levels of miR-7 exhibited defects in cell proliferation that were partially rescued by the addition of a miR-7 inhibitor. These findings suggest that the QKI isoforms regulate glial cell function and proliferation by regulating the processing of certain miRNAs.
authors: Bloomfield Center for Research on Aging, Lady Davis Institute for Medical Research and Departments of Oncology and Medicine, McGill University, Montreal, Quebec, Canada.
authors: Yunling
authors: Y
authors: Wang
authors: Gillian
authors: G
authors: Vogel
authors: Zhenbao
authors: Z
authors: Yu
authors: Stéphane
authors: S
authors: Richard
mesh_terms: D048708:Cell Growth Processes / Q000502:physiology; D002460:Cell Line; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism; D004815:Epidermal Growth Factor / Q000235:genetics / Q000378:metabolism; D066246:ErbB Receptors / Q000235:genetics / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D020935:MAP Kinase Signaling System / Q000235:genetics; D035683:MicroRNAs / Q000096:biosynthesis / Q000235:genetics*; D009457:Neuroglia / Q000378:metabolism / Q000502:physiology*; D011485:Protein Binding; D020033:Protein Isoforms; D016601:RNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism*; D043244:Ribonuclease III / Q000235:genetics / Q000378:metabolism
chemical_list: D004815:Epidermal Growth Factor; D066246:ErbB Receptors; D035683:MicroRNAs; D020033:Protein Isoforms; D016601:RNA-Binding Proteins; D043244:Ribonuclease III; C549242:MIRN7-1 microRNA, human; C490832:QKI protein, human; C512478:EGFR protein, human; C517918:DROSHA protein, human