title: Silencing of thrombospondin-1 is critical for myc-induced metastatic phenotypes in medulloblastoma.
abstract: Mechanisms by which c-Myc (Myc) amplification confers aggressive medulloblastoma phenotypes are poorly defined. Here, we show using orthotopic models that high Myc expression promotes cell migration/invasion and induces metastatic tumors, which recapitulate aggressive histologic features of Myc-amplified primary human medulloblastoma. Using ChIP-chip analysis, we identified cell migration and adhesion genes, including Tsp-1/THBS1, ING4, PVRL3, and PPAP2B, as Myc-bound loci in medulloblastoma cells. Expression of Tsp-1 was most consistently and robustly diminished in medulloblastoma cell lines and primary human tumors with high Myc expression (n = 101, P = 0.032). Strikingly, stable Tsp-1 expression significantly attenuated in vitro transformation and invasive/migratory properties of high Myc-expressing medulloblastoma cells without altering cell proliferation, whereas RNA interference-mediated Myc knockdown was consistently accompanied by increased Tsp-1 levels and reduced cell migration and invasion in medulloblastoma cells. Chromatin immunoprecipitation (ChIP) assays revealed colocalization of Myc and obligate partner Max and correlated diminished RNA polymerase II occupancy (∼3-fold decrease, P < 0.01) with increased Myc binding at a core Tsp-1 promoter. Reporter gene and/or gel shift assays confirmed direct repression of Tsp-1 transcription by Myc and also identified JPO2, a Myc interactor associated with metastatic medulloblastoma, as a cofactor in Myc-mediated Tsp-1 repression. These findings indicate the Myc-regulatory network targets Tsp-1 via multiple mechanisms in medulloblastoma transformation, and highlight a novel critical role for Tsp-1 in Myc-mediated aggressive medulloblastoma phenotypes.
authors.affiliation: Sonia and Arthur Labatt Brain Tumor Research Centre, Hospital for Sick Children, University Avenue, Toronto, Ontario, Canada M5G 1X8.
authors.forename: Limei
authors.initials: L
authors.lastname: Zhou
authors.forename: Daniel
authors.initials: D
authors.lastname: Picard
authors.forename: Young-Shin
authors.initials: YS
authors.lastname: Ra
authors.forename: Meihua
authors.initials: M
authors.lastname: Li
authors.forename: Paul A
authors.initials: PA
authors.lastname: Northcott
authors.forename: Yaqi
authors.initials: Y
authors.lastname: Hu
authors.forename: Duncan
authors.initials: D
authors.lastname: Stearns
authors.forename: Cynthia
authors.initials: C
authors.lastname: Hawkins
authors.forename: Michael D
authors.initials: MD
authors.lastname: Taylor
authors.forename: James
authors.initials: J
authors.lastname: Rutka
authors.forename: Sandy D
authors.initials: SD
authors.lastname: Der
authors.forename: Annie
authors.initials: A
authors.lastname: Huang
mesh_terms: D002448:Cell Adhesion; D002455:Cell Division; D045744:Cell Line, Tumor; D002465:Cell Movement; D002528:Cerebellar Neoplasms / Q000235:genetics* / Q000473:pathology; D020868:Gene Silencing; D017930:Genes, Reporter; D016259:Genes, myc; D006801:Humans; D008527:Medulloblastoma / Q000235:genetics* / Q000473:pathology; D009361:Neoplasm Invasiveness; D009362:Neoplasm Metastasis / Q000235:genetics*; D020411:Oligonucleotide Array Sequence Analysis / Q000379:methods; D011401:Promoter Regions, Genetic; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics / Q000378:metabolism; D034622:RNA Interference; D012334:RNA, Neoplasm / Q000235:genetics / Q000302:isolation & purification; D019700:Thrombospondin 1 / Q000172:deficiency / Q000235:genetics*
chemical_list: D016271:Proto-Oncogene Proteins c-myc; D012334:RNA, Neoplasm; D019700:Thrombospondin 1