title: Tumor-suppressive microRNA-22 inhibits the transcription of E-box-containing c-Myc target genes by silencing c-Myc binding protein.
abstract: Oncogenic c-Myc has been described to modulate the expression of a subset of microRNAs (miRNAs), which include miR-22; however, the mechanism through which a miRNA controls c-Myc activity remains unclear. Here we report a novel anti-c-Myc function mediated by miR-22. Ectopically expressed miR-22 inhibited cell proliferation and anchorage-independent growth of human cancer cell lines. Microarray screening and western analyses revealed that miR-22 repressed the c-Myc-binding protein MYCBP, a positive regulator of c-Myc. Consistent with this, reporter assays showed that miR-22-mediated MYCBP gene suppression largely depends on the conserved miR-22 target site within the MYCBP 3'-untranslational region (3'UTR), implying that MYCBP mRNA is a direct miR-22 target. Depletion of MYCBP using small interfering RNA (siRNA) recapitulated the miR-22-induced anti-growth effect on tumor cells, whereas ectopically expressed MYCBP rescued cells from the growth suppression mediated by miR-22. Moreover, repression of MYCBP by miR-22 downregulated a panel of E-box-containing c-Myc target genes. Our results suggest that miR-22 acts as a tumor suppressor through direct repression of MYCBP expression and subsequent reduction of oncogenic c-Myc activities. As c-Myc inhibits the expression of miR-22, we propose a novel positive feedback loop formed by oncogenic c-Myc to accelerate cell proliferation by suppressing miR-22, a potent inhibitor of MYCBP.
authors.affiliation: Institute of Molecular Medicine, Peking University, Beijing, China.
authors.forename: J
authors.initials: J
authors.lastname: Xiong
authors.forename: Q
authors.initials: Q
authors.lastname: Du
authors.forename: Z
authors.initials: Z
authors.lastname: Liang
mesh_terms: D020413:3' Untranslated Regions / Q000235:genetics; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D017124:Conserved Sequence; D004268:DNA-Binding Proteins / Q000172:deficiency* / Q000235:genetics*; D025461:Feedback, Physiological; D015972:Gene Expression Regulation, Neoplastic / Q000235:genetics; D020868:Gene Silencing; D006801:Humans; D035683:MicroRNAs / Q000235:genetics*; D009369:Neoplasms / Q000235:genetics* / Q000473:pathology; D016271:Proto-Oncogene Proteins c-myc / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics; D014157:Transcription Factors / Q000172:deficiency* / Q000235:genetics*; D014158:Transcription, Genetic / Q000235:genetics*
chemical_list: D020413:3' Untranslated Regions; D004268:DNA-Binding Proteins; C548375:MIRN22 microRNA, human; C489427:MYC protein, human; C116115:MYCBP protein, human; D035683:MicroRNAs; D016271:Proto-Oncogene Proteins c-myc; D012333:RNA, Messenger; D014157:Transcription Factors