ncing of Thrombospondin-1 Is Critical for Myc-Induced

Downlo hanisms by which c-Myc (Myc) amplification confers aggressive medulloblastoma phenotypes are poorned. Here, we show using orthotopic models that high Myc expression promotes cell migration/invasion duces metastatic tumors, which recapitulate aggressive histologic features of Myc-amplified primary medulloblastoma. Using ChIP-chip analysis, we identified cell migration and adhesion genes, including THBS1, ING4, PVRL3, and PPAP2B, as Myc-bound loci in medulloblastoma cells. Expression of Tsp-1 was consistently and robustly diminished in medulloblastoma cell lines and primary human tumors with yc expression (n = 101, P = 0.032). Strikingly, stable Tsp-1 expression significantly attenuated in vitro ormation and invasive/migratory properties of high Myc-expressing medulloblastoma cells without g cell proliferation, whereas RNA interference–mediated Myc knockdown was consistently accompay increased Tsp-1 levels and reduced cell migration and invasion in medulloblastoma cells. Chromatin noprecipitation (ChIP) assays revealed colocalization of Myc and obligate partner Max and correlated ished RNA polymerase II occupancy (∼3-fold decrease, P < 0.01) with increased Myc binding at a core promoter. Reporter gene and/or gel shift assays confirmed direct repression of Tsp-1 transcription by nd also identified JPO2, a Myc interactor associated with metastatic medulloblastoma, as a cofactor in ediated Tsp-1 repression. These findings indicate the Myc-regulatory network targets Tsp-1 via multiple Myc-m mechanisms in medulloblastoma transformation, and highlight a novel critical role for Tsp-1 in Myc-mediated aggressive medulloblastoma phenotypes. Cancer Res; 70(20); 8199–210. ©2010 AACR.