title: c-Myc Represses Tumor-Suppressive microRNAs, let-7a, miR-16 and miR-29b, and Induces Cyclin D2-Mediated Cell Proliferation in Ewing's Sarcoma Cell Line.
abstract: Myc oncogenic transcription factor is known to inhibit tumor suppressive microRNAs (miRNAs), resulting in greater expression of their target protein related to cell cycle, invasion or anti-apoptotic factors in human cancer cells. To explore possible oncogenic factors in Ewing's sarcoma (ES), we conducted microarray-based approach to profile the changes in the expression of miRNAs and its downstream mRNAs in five ES cell lines and human mesenchymal stem cells (hMSCs). Three miRNAs, let-7a, miR-16 and miR-29b were significantly down-regulated, whereas c-Myc and cyclin D2 (CCND2) were significantly up-regulated in all tested ES cells compared with hMSCs. To verify that let-7a, miR-16 and miR-29b were the targets of c-Myc in ES cell lines, we transfected siRNA against c-Myc and confirmed the coordinate up-regulation of let-7a, miR-16 and miR-29b through the repression of c-Myc. The ES cells transfected with c-Myc-siRNA and let-7a, miR-16 and miR-29b exhibited the inhibition of the cell cycle progression. The increased expression of let-7a, miR-16 and miR-29b resulted in the reduction of CCND2 protein expression. We also demonstrated that c-Myc-siRNA treatment of ES cells was associated with the decreased expression of CCND2 as a down-stream of three miRNAs. Furthermore, the introduction of let-7a, miR-16 and miR-29b in ES cells could inhibit the c-Myc-mediated up-regulation of CCND2 resulted in the prevention of cell cycle progression. In addition, the transfection of let-7a, miR-16 and miR-29b in ES cells suppressed tumor growth ex vivo treatment. These findings suggests that the up-regulation of c-Myc inhibited the expression of let-7a, miR-16 and miR-29b subsequently induced CCND2 expression in ES cells. The present study might identify a novel oncogenic axis that c-Myc regulates the expression of CCND2 via let-7a, miR-16 and miR-29b, leading to the development new therapeutic targets for ES.
authors.affiliation: Department of Orthopaedic Surgery, Faculty of Medicine, Oita University, Oita, Japan.
authors.forename: Masanori
authors.initials: M
authors.lastname: Kawano
authors.affiliation: Department of Orthopaedic Surgery, Faculty of Medicine, Oita University, Oita, Japan.
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Tanaka
authors.affiliation: Department of Orthopaedic Surgery, Faculty of Medicine, Oita University, Oita, Japan.
authors.forename: Ichiro
authors.initials: I
authors.lastname: Itonaga
authors.affiliation: Department of Orthopaedic Surgery, Faculty of Medicine, Oita University, Oita, Japan.
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Iwasaki
authors.affiliation: Department of Orthopaedic Surgery, Faculty of Medicine, Oita University, Oita, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Tsumura
mesh_terms: D000818:Animals; D002453:Cell Cycle / Q000235:genetics; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000235:genetics*; D056742:Cyclin D2 / Q000235:genetics*; D015536:Down-Regulation / Q000235:genetics; D015972:Gene Expression Regulation, Neoplastic / Q000235:genetics; D016147:Genes, Tumor Suppressor / Q000502:physiology*; D006801:Humans; D059630:Mesenchymal Stem Cells / Q000473:pathology; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D035683:MicroRNAs / Q000235:genetics*; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics; D012512:Sarcoma, Ewing / Q000235:genetics* / Q000473:pathology*; D015854:Up-Regulation / Q000235:genetics
chemical_list: D056742:Cyclin D2; D035683:MicroRNAs; D016271:Proto-Oncogene Proteins c-myc; D012333:RNA, Messenger; D034741:RNA, Small Interfering