[CANCER RESEARCH 63, 5428 –5437, September 1, 2003] A Molecular Fingerprint for Medulloblastoma 1 Youngsoo Lee, Heather L. Miller, Patricia Jensen, Roberto Hernan, Michele Connelly, Cynthia Wetmore, Frederique Zindy, Martine F. Roussel, Tom Curran, Richard J. Gilbertson, and Peter J. McKinnon 2 Departments of Genetics and Tumor Cell Biology [Y. L., H. L. M., F. Z., M. R., P. J. M.] and Developmental Neurobiology [P. J., R. H., M. C., T. C., R. G.], Saint Jude Children’s Research Hospital, Memphis, Tennessee 38105, and Division of Pediatric Hematology/Oncology, Mayo Clinic, Rochester, Minnesota 55905 [C. W.] ABSTRACT Medulloblastoma is the most common malignant pediatric brain tumor. In mice, Ptc1 haploinsufficiency and disruption of DNA repair (DNA ligase IV inactivation) or cell cycle regulation (Kip1, Ink4d, or Ink4c inactivation), in conjunction with p53 dysfunction, predispose to medul- loblastoma. To identify genes important for this tumor, we evaluated gene expression profiles in medulloblastomas from these mice. Unexpectedly, medulloblastoma expression profiles were very similar among tumors and also to those of developing cerebellum. However, 21 genes were specifi- cally up-regulated in medulloblastoma, including sFrp1, Ptc2, and Math1, members of signaling pathways that regulate cerebellar development. Coordinated deregulation of these same genes also occurred in a large subset of human medulloblastomas. These data identify a group of genes that is central to medulloblastoma tumorigenesis. INTRODUCTION Medulloblastoma, a highly invasive brain tumor that arises in the cerebellum, is the most common malignant pediatric brain tumor. Histopathologically, this disease is characterized by sheets of small round blue cells that are punctuated by frequent mitoses, apoptosis, and regions of divergent differentiation (1). Although the cell of origin for medulloblastoma is unknown, granule cell-precursor cells in the external germinal layer of the developing cerebellum are likely can- didates (2). The treatment of medulloblastoma includes surgery, neuraxis radiation, and systemic chemotherapy that together cure only 60% of patients. Attempts to further reduce the morbidity and mor- tality associated with medulloblastoma have been restricted by the toxicity of conventional treatments and the infiltrative nature of the disease. Therefore, the availability of medulloblastoma model systems that can provide greater understanding of the molecular abnormalities that cause this tumor will be important for developing new strategies and approaches to treatment. Signaling pathways that regulate normal cerebellar development such as the SHH 3 and WNT pathways have been linked to medullo- blastoma tumorigenesis (2, 3). SHH and WNT proteins compose two families of secreted molecules that are required for cell growth and fate determination in many tissues including the nervous system (4 –7). Germ-line mutation of PTC1, the receptor for SHH, is respon- sible for Gorlin syndrome, a familial cancer predisposition syndrome with a high incidence of medulloblastoma (8). Mutation of PTC1 also occurs in sporadic medulloblastoma, and germ-line and somatic mu- tations of Suppressor of Fused, a downstream negative regulator of the SHH pathway, were reported recently in children with medulloblas- toma (9). Up-regulation of SHH target genes, such as the transcription factor GLI1, also occur in medulloblastoma (2, 10). Similar to Gorlin syndrome, Ptc1 haploinsufficiency in the mouse can lead to medul- loblastoma, underscoring the direct relationship between SHH/PTC1 signaling and medulloblastoma (11–13). The WNT pathway regulates -catenin, a key transcriptional acti- vator, via a multimeric protein complex that includes the APC tumor suppressor protein, GSK-3 (a serine-threonine kinase), and Axin (5, 14, 15). WNTs bind to the Frizzled family of receptors and inhibit GSK-3-mediated phosphorylation and degradation of -catenin. This enables translocation of -catenin to the nucleus, where it acti- vates the T-cell factor/lymphoid enhancer factor transcriptional com- plex, thereby up-regulating target genes that include cyclin D1 and c-MYC (16). Deletion and/or mutations in APC, AXIN1, or -catenin have been reported in sporadic medulloblastoma, and germ-line mu- tation of APC predisposes to medulloblastoma in Turcot’s syndrome (17–21). Recent studies suggest a strong interrelationship between SHH and WNT signaling, with the phosphorylation status of GSK-3 acting as a signaling nexus between the two pathways (7, 22). Thus, during development the SHH and WNT pathways act as important tumor suppressor pathways in the cerebellum. Defects in DNA repair, or defective responses to DNA damage, predispose to cancer (23). For example, mismatch repair defects are associated with colorectal cancer (24), whereas leukemia or lym- phoma occurs in human syndromes associated with deficiencies in the response to DNA double-strand breaks, such as ataxia-telangiectasia and Nijmegen breakage syndrome (23). Recent evidence indicates that brain tumors may also arise in association with defects in the DNA damage response. In this regard, mice with DNA ligase IV or Parp1 deficiency have a high incidence of medulloblastoma (25, 26). DNA damage responses are also important in other pathways linked to medulloblastoma; Ptc1 +/- mice are hypersensitive to ionizing radia- tion, and the incidence of medulloblastoma in these mice is dramat- ically increased after ionizing radiation (27–29). Thus, genotoxic stress may feature in the etiology of medulloblastoma. Mouse models that recapitulate human disease have provided an enormous benefit toward molecular understanding of tumor biology. However, only recently have a number of mouse models of medul- loblastoma become available (13, 25, 26, 30, 31). The defined genet- ics coupled with the ready accessibility of tissues, even at early developmental stages, are major advantages of mouse models. In this study, we have used a number of different mouse models for medul- loblastoma to identify genes that may be important for the genesis of medulloblastoma. We identified a cohort of genes selectively up- regulated in all of the mouse medulloblastomas examined, as well as in a large subset of human medulloblastomas, thus providing new molecular insights into this tumor. MATERIALS AND METHODS Animal Tissue. Lig4 -/- p53 -/- , Ptc1 +/- , and Ptc1 +/- p53 -/- mice have been described previously (13, 25, 30). Ink4d -/- Kip1 +/- p53 -/- and Ink4d +/+ Kip1 -/- p53 -/- animals were obtained by intercrossing of Ink4d +/- Kip1 +/- p53 -/- animals, and Ink4c -/- p53 -/- and Ink4d +/- Ink4c -/- p53 -/- animals were from intercrossing of Ink4d +/- Ink4c +/- p53 -/- animals (32–34). All Received 5/2/03; revised 6/12/03; accepted 6/17/03. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. 1 Supported by NIH Grants CA-096832, NS-37956, NS-39867, and CA-21765 and by a grant from the American Lebanese and Syrian Associated Charities of Saint Jude Children’s Research Hospital. Supplemental data are available on the AACR Web site. 2 To whom requests for reprints should be addressed, at Genetics, 332 North Lauder- dale Street, Memphis, TN 38105. Phone: (901) 495-2700; Fax: (901) 526-2907; E-mail: peter.mckinnon@stjude.org. 3 The abbreviations used are: SHH, sonic hedgehog; WNT, wingless; PTC/Ptc, Patched; sFRP/sFrp, secreted Frizzled-related protein; APC, adenomatous polyposis coli; GSK-3, glycogen synthase kinase-3; WT, wild type; P5 and P7, postnatal days 5 and 7, respectively; EGL, external germinal layer. 5428 Research. on February 2, 2016. © 2003 American Association for Cancer cancerres.aacrjournals.org Downloaded from