title: Inhibition of mir-21, which is up-regulated during MYCN knockdown-mediated differentiation, does not prevent differentiation of neuroblastoma cells.
abstract: BACKGROUND
  Neuroblastoma is a malignant childhood tumour arising from precursor cells of the sympathetic nervous system. Genomic amplification of the MYCN oncogene is associated with dismal prognosis. For this group of high-risk tumours, the induction of tumour cell differentiation is part of current treatment protocols. MicroRNAs (miRNAs) are small non-coding RNA molecules that effectively reduce the translation of target mRNAs. MiRNAs play an important role in cell proliferation, apoptosis, differentiation and cancer. In this study, we investigated the role of N-myc on miRNA expression in MYCN-amplified neuroblastoma. We performed a miRNA profiling study on SK-N-BE (2) cells, and determined differentially expressed miRNAs during differentiation initiated by MYCN knockdown, using anti-MYCN short-hairpin RNA (shRNA) technology.
  
  
  RESULTS
  Microarray analyses revealed 23 miRNAs differentially expressed during the MYCN knockdown-mediated neuronal differentiation of MNA neuroblastoma cells. The expression changes were bidirectional, with 11 and 12 miRNAs being up- and down-regulated, respectively. Among the down-regulated miRNAs, we found several members of the mir-17 family of miRNAs. Mir-21, an established oncomir in a variety of cancer types, became strongly up-regulated upon MYCN knockdown and the subsequent differentiation. Neither overexpression of mir-21 in the high-MYCN neuroblastoma cells, nor repression of increased mir-21 levels during MYCN knockdown-mediated differentiation had any significant effects on cell differentiation or proliferation.
  
  
  CONCLUSIONS
  We describe a subset of miRNAs that were altered during the N-myc deprived differentiation of MYCN-amplified neuroblastoma cells. In this context, N-myc acts as both an activator and suppressor of miRNA expression. Mir-21 was up-regulated during cell differentiation, but inhibition of mir-21 did not prevent this process. We were unable to establish a role for this miRNA during differentiation and proliferation of the two neuroblastoma cell lines used in this study.
authors.affiliation: Department of Paediatrics, University Hospital of North-Norway, 9038 Tromsø, Norway. jochen.buechner@unn.no
authors.forename: Jochen
authors.initials: J
authors.lastname: Buechner
authors.forename: Jørn R
authors.initials: JR
authors.lastname: Henriksen
authors.forename: Bjørn Helge
authors.initials: BH
authors.lastname: Haug
authors.forename: Ellen
authors.initials: E
authors.lastname: Tømte
authors.forename: Trond
authors.initials: T
authors.lastname: Flaegstad
authors.forename: Christer
authors.initials: C
authors.lastname: Einvik
mesh_terms: D015153:Blotting, Western; D002454:Cell Differentiation / Q000235:genetics*; D045744:Cell Line, Tumor; D005434:Flow Cytometry; D005455:Fluorescent Antibody Technique; D055785:Gene Knockdown Techniques; D016259:Genes, myc; D006801:Humans; D035683:MicroRNAs / Q000235:genetics / Q000502:physiology*; D046228:Microarray Analysis; D000071447:N-Myc Proto-Oncogene Protein; D009447:Neuroblastoma / Q000235:genetics* / Q000473:pathology*; D009687:Nuclear Proteins / Q000172:deficiency / Q000235:genetics*; D015513:Oncogene Proteins / Q000172:deficiency / Q000235:genetics*; D034741:RNA, Small Interfering / Q000032:analysis / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: C524940:MIRN21 microRNA, human; C459801:MYCN protein, human; D035683:MicroRNAs; D000071447:N-Myc Proto-Oncogene Protein; D009687:Nuclear Proteins; D015513:Oncogene Proteins; D034741:RNA, Small Interfering