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Loss of p53 but not ARF Accelerates Medulloblastoma in Mice Heterozygous for patched¹

Departments of Developmental Neurobiology [C. W., D. E. E., T. C.] and Hematology/Oncology [C. W.], St. Jude Children’s Research Hospital, Memphis, Tennessee 38105

	ABSTRACT

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Brain malignancies represent the most common solid tumors in children, and they are responsible for significant mortality and morbidity. The molecular basis of the most common malignant pediatric brain tumor, medulloblastoma, is poorly understood. Mutations in several genes including the human homologue of the Drosophila segment polarity gene, patched (PTCH), the adenomatous polyposis coli gene (APC), ß-catenin, and p53 have been reported in subsets of hereditary and sporadic medulloblastoma. Inactivation of one Ptc allele in mice results in a 14% incidence of medulloblastoma. Here, we report a dramatic increase in the incidence (>95%) and accelerated development (prior to 12 weeks of age) of medulloblastoma in mice heterozygous for Ptc that lack p53. The acceleration of tumorigenesis in Ptc^+/- mice is specific for loss of p53, because no change in tumor incidence was observed in Ptc^+/- mice carrying a mutation in APC (Min^+/-) or in Ptc^+/- mice deficient in p19^ARF. Thus, there is a specific interaction between p53 loss and heterozygosity of Ptc that results in medulloblastoma. This may be a consequence of increased genomic instability associated with loss of p53 function that may enhance the rate of acquisition of secondary mutations. Ptc^+/-p53^-/- mice provide a useful model for investigation of the molecular bases of medulloblastoma and for evaluation of the efficacy of therapeutic intervention strategies in a spontaneously arising endogenous brain tumor.

	Introduction

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Medulloblastoma arises from the primitive neuroectoderm in the posterior fossa of children generally between the ages of 3 and 9. The tumors are derived from cerebellar granule precursor cells that undergo a dramatic proliferative expansion during the early phases of postnatal brain development. Several gene mutations have been described in medulloblastoma, although they occur in small subsets of tumors (1) . A low frequency of mutations in patched (PTCH; Ref. 2 ), p53 (3) , the adenomatous polyposis coli (APC) gene (4) , and ß-catenin (5 , 6) have been reported in subsets of sporadic medulloblastoma. In addition, brain tumors, including medulloblastoma, have been reported to occur more frequently in patients carrying germ-line mutations in PTCH, APC, or p53 (7, 8, 9) . In the case of heterozygous loss of PTCH, which is associated with Gorlin syndrome, also known as basal cell nevus syndrome (OMIM 109400), the incidence of medulloblastoma increases from 2 per million to 4 per hundred in children <18 years of age (10 , 11) . Thus, it is likely that there are several unknown prevalent mutations in these tumors that contribute to disease progression.

Progress in understanding the etiology of medulloblastoma has been hampered by the lack of an appropriate animal model. Recently, a mouse strain was generated in which Ptc was mutated by targeted disruption (12 , 13) . Homozygous deletion of Ptc results in embryonic lethality, whereas mice heterozygous for Ptc exhibit several features of Gorlin syndrome, including an increased propensity to develop tumors in the brain and soft tissues. Histological analysis of the brain tumors showed that they closely resemble human medulloblastoma (12 , 14) . However, only 14% of mice heterozygous for Ptc develop medulloblastoma over a period of 10 months, indicating that it is likely that additional genetic lesions are required for oncogenic transformation.

Ptc functions as a component of the receptor complex that transduces a signal from Hedgehog (Hh) through a complex pathway that was first described in Drosophila (7) . The interaction of Shh, the mammalian orthologue of Hh, with Ptc relieves suppression of smoothened (Smo), resulting in increased transcription of Gli1 and other target genes (7) . During cerebellar development, Shh, produced by Purkinje cells, functions as a mitogen to stimulate proliferation of granule cell precursors (15) . Ptc does not function as a classic tumor suppressor gene in medulloblastomas in Ptc^+/- mice because the normal allele is not lost, and it continues to be expressed in tumors (14 , 15) .

p53 functions as a transcription factor that transduces signals elicited by physiological stress and DNA damage to regulate cell proliferation and apoptosis. Abrogation of p53 function attenuates both of these responses (17) . The mouse tumor suppressor gene p19^ARF (p14^ARF in humans) is the product of an alternative reading frame encoded by the INK4a-ARF locus. ARF functions as a sensor of normal proliferative signals upstream of p53 by interfering with Mdm2, a negative regulator of p53 function (18) . Thus, loss of p19^ARF diminishes p53 activity and promotes tumor formation (19) . Mice deficient in p53 do not develop brain tumors, although they are predisposed to develop tumors in several other tissues by 5 months of age (20 , 21) . Approximately 10% of ARF-null mice develop glial tumors by 6 months of age (19) .

To address the possible involvement of tumor suppressor genes in medulloblastoma and to accelerate the incidence of these tumors, we crossed Ptc^+/- mice with mice carrying mutations in other tumor suppressor genes. We selected APC because it regulates the levels of ß-catenin, which functions in the Wnt signaling pathway (22) . Humans with brain tumor-polyposis, or Turcot’s syndrome, carry germ-line mutations in APC, and they have an increased incidence of tumors arising in colon and brain (8) . In addition, mutations in ß-catenin have been reported in spontaneous medulloblastoma, albeit at a low frequency (5 , 6) . We also crossed the Ptc^+/- mice with mice carrying inactivating mutations in two major tumor suppressor genes that are defective in more than half of all human cancer, p53 and ARF (18) . These genes serve critical functions in the regulation of cell proliferation, apoptosis, and response to DNA damage (18 , 23) .

	Materials and Methods

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Animals.
The Ptc^+/- mice used in this study were generated and maintained on a mixed C57Bl/6 x 129Sv background, as described previously (14) , and crossed with mice carrying targeted disruptions in p53, APC (C57BL/6J-Min^+/-; Jackson Laboratories, Bar Harbor, ME), and ARF (19) to generate the following cohorts of mice: Ptc^+/-p53^+/+ (n = 440), Ptc^+/-p53^+/- (n = 68), Ptc^+/-p53^-/- mice (n = 40), Ptc^+/-ARF^-/- (n = 40), and Ptc^+/-Min^+/- (n = 16). Cohorts of mice were observed for tumor formation for a minimum of 6 months after birth. All mice were observed daily for signs of increased intracranial pressure and for evidence of enlarged occipital prominence three times weekly for at least 24 weeks. Animals were euthanized when they were moribund according to NIH-approved institutional guidelines or when they showed signs of increased intracranial pressure or when extracranial tumors were evident. Brains were removed from the surrounding calvarium, and tumor tissue was carefully separated from surrounding brain parenchyma under a dissecting microscope. In every mouse, the presence of tumor was confirmed by gross examination of the brain. If the mouse was not available for examination or if no tumor was detected, the cause of death was attributed to "unknown causes." Fresh tissue was snap frozen and stored at -80°C for later extraction of RNA, DNA, and protein. For histochemical analyses, animals were deeply anesthetized and perfused transcardially with 4% paraformaldehyde in 0.1 M PBS and processed for immunohistochemical analyses as described previously (14) .

RNA Isolation and Northern Analysis.
Total cellular RNA was isolated from 11 mouse medulloblastomas using Trizol (Ambion, Inc., Austin, TX) according to the manufacturer’s directions. Five to 10 µg of total RNA were electrophoresed on a 0.8% agarose-formaldehyde gel, transferred to a nitrocellulose filter (Hybond N+; Amersham Pharmacia; Buckinghamshire, United Kingdom), and hybridized under stringent conditions (18 h at 68°C in 5x SSPE, 50% formamide, 5x Denhardt’s solution, 1% SDS, and 0.1 mg/ml denatured salmon sperm DNA) with a ³²P-labeled RNA probe. Filters were washed (twice x 20 min in 0.1 SSC, 0.1% SDS at 68°C) and exposed to MR film (Eastman Kodak) for 12–72 h at -80°C. Control and tumor tissues were analyzed by hybridization with ³²P-labeled RNA probes specific for mouse Ptc (12) , Gli1 (mouse EST clone 38654), and mdm2.

Immunoblot Analysis.
Protein extracts were prepared by Dounce homogenization of 80–100 mg of snap-frozen tumor or normal tissue as described (14) . Extracts were clarified by microcentrifugation at 14,000 rpm for 30 min. Protein lysates (200 µg) from medulloblastomas arising in Ptc^+/- mice (tumor nos. 185, 199, 241, 448, 530, and 574), mouse leukemia cells known to express mutated (CR246) or wild-type P53 (CR205), medulloblastoma from a Ptc^+/-p53^-/- mouse (1138), and normal adult mouse brain were separated on 10% polyacrylamide gels and transferred to nitrocellulose membranes. The membranes were incubated with anti-p53 antiserum (Ab7; Oncogene; 1:5000), followed by donkey antisheep IgG-horseradish peroxidase (Chemicon; 1:2500) diluted in 5% evaporated milk powder in 1% TBST [50 mM Tris-Cl, 0.15 M NaCl (pH 8.0) with 1% Tween]. The signal was detected by enhanced chemiluminescence. The membranes were stripped and incubated with antibodies directed against Ref-1 and ß-tubulin to control for protein loading and transfer efficiency.

RT-PCR.⁴ %Two-step RT-PCR was carried out to maximize uniformity of PCR templates for all reactions. cDNA was derived in 20-µl volumes with random hexamers, oligo dT, and gene-specific priming using SuperScript reverse transcriptase (Life Technologies, Inc., Rockville, MD). The reverse transcriptase first-strand cDNA synthesis reactions were carried out using 3 µg of total RNA prepared from adult C57BL/6 mouse cerebellum and from seven tumor samples (tumor nos. 185,199, 241, 448, 530, 574, and 646) according to the manufacturer’s directions. Gene-specific oligonucleotides corresponding to sequences within the open reading frame of p53 were synthesized, and PCR amplification of overlapping regions was performed to generate templates for nucleotide sequencing. Sequence analysis of PCR products generated from both the sense and antisense strands of p53 were analyzed from two separate cDNA templates and from multiple PCR reactions.

Nucleotide Sequencing.
Sequencing reactions were performed by the Hartwell Center for Biotechnology at St. Jude Children’s Research Hospital on template DNA using rhodamine or dRhodamine dye terminator cycle sequencing ready reaction kits with AmpliTaq DNA polymerase FS (Perkin-Elmer Applied Biosystems, Inc., Foster City, CA) and synthetic oligonucleotides complementary to regions covering the entire open reading frame of p53. Samples were electrophoresed, detected, and analyzed on PE/ABI model 373, model 37 Stretch, or model 377 DNA sequencers (Perkin-Elmer Applied Biosystems, Inc.). Sequence analysis was performed using Sequencher (Gene Codes Corp., Ann Arbor, MI) software.

	Results and Discussion

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The Loss of p53 Dramatically Accelerated the Age of Onset and the Incidence of Medulloblastoma in Ptc^+/- Mice.
Tumors were apparent as early as 4 weeks, and all of the Ptc^+/-p53^-/- mice developed either brain tumors or died from unknown causes prior to 12 weeks of age (Fig. 1) . Within this Ptc^+/-p53^-/- cohort, 95% of mice were confirmed by gross and histological analysis to have tumors in the posterior fossa. In 5% of the mice, no brain tumor was apparent by gross examination at the time of death. A very low incidence of extracranial soft tissue sarcomas were noted to arise at similar frequencies in all cohorts of Ptc^+/- mice. There was no acceleration in the incidence or time of onset of the extracranial tumors (soft tissue sarcomas, basal cell carcinomas, and lymphomas) described in Ptc^+/- (7 , 14) and p53^-/- mice (21) . This may reflect the fact that the mice became moribund with medulloblastoma prior to the time when they would develop these other tumors, which usually occur after 5 months of age (21) . In contrast, no significant change in the age of onset or the incidence of tumors was observed in Ptc^+/-p53^+/- mice (Fig. 1) . Thus, complete loss of p53 synergizes with haploinsufficiency of Ptc to produce a very high frequency of medulloblastoma in young mice.

View larger version (21K): [in this window] [in a new window] [Download PPT slide]   Fig. 1. Medulloblastoma incidence is increased and age of tumor onset is decreased in Ptc+/- mice lacking a normal p53 gene. Greater than 95% of Ptc+/-p53-/- mice spontaneously developed tumors in the posterior fossa between 10 and 12 weeks of age, compared with a 14% incidence of tumors in Ptc+/- mice by 10 months of age. A small percentage (3%) of the Ptc+/-p53-/- mice died within the first 3–4 weeks of life, with no tumor detected by gross examination of the brain. All Ptc+/-p53-/- mice died by 12 weeks of age. Brains were removed and examined for the presence of tumor. No significant acceleration in tumorigenesis was noted in Ptc+/-p53+/-, Ptc+/-ARF-/-, or in Ptc+/-Min+/- mice.

View larger version (67K): [in this window] [in a new window] [Download PPT slide]   Fig. 2. Analysis of mRNA expression of medulloblastomas arising in Ptc+/- and Ptc+/-p53-/- mice. A, persistent expression of Ptc and Gli1 mRNA in tumors arising in Ptc+/-p53-/- mice. Total RNA was prepared from the following tumors and control tissues: postnatal day 7 C57BL/6 mouse brain (P7 brain), C57BL/6 adult cerebellum (Ptc+/+p53+/+), non-tumor-bearing adult Ptc+/- cerebellum (Ptc+/-p53+/+), nontumor-bearing adult p53-/- cerebellum (Ptc+/+p53-/-), tumor from one Ptc+/- mouse (199), and tumors from 10 Ptc+/-p53-/- mice. Three transcripts (5, 8, and 12.5 kb) were detected with the Ptc probe. The major 8-kb Ptc transcript was decreased in all tumors examined compared with control tissues, whereas the 5- and 12.5-kb transcripts were expressed more robustly in tumors than in control tissues. A single Gli1 mRNA transcript of 4 kb was detected in all tumors from Ptc+/- as well as from Ptc+/-p53+/+ mice at higher levels than those in control tissues. B, increased expression of wild-type p53 mRNA in tumors from Ptc+/-p53+/+ mice. Northern analysis of total RNA prepared from medulloblastoma and control brain tissues revealed increased expression of p53 mRNA and no increase in mdm2 mRNA in tumor tissues.

p53 Loss Is Not Required for Medulloblastoma Formation in Ptc^+/- Mice.
The dramatic acceleration of medulloblastoma formation in Ptc^+/-p53^-/- mice prompted us to investigate the status of p53 in tumors arising in Ptc^+/- mice in which there is no germ-line mutation of p53. Interestingly, these tumors contained high levels of p53 mRNA compared with control tissues. In contrast, there was no consistent difference in Mdm2 mRNA levels between normal and tumor tissues (Fig. 2B) . The Mdm2 gene product acts to repress p53 activity, and amplification of Mdm2 inactivates p53 in a subset of astrocytomas (25 , 26) . Wild-type p53 protein has a short half-life, and it is not readily detected in populations of nonproliferating cells unless it has been stabilized by mutation (23) . Therefore, we performed immunoblotting analysis to look for evidence of p53 inactivation in tumors from Ptc^+/- mice. As shown in Fig. 3 , despite the increase in p53 mRNA, p53 protein was present at significantly lower levels in medulloblastomas from Ptc^+/- mice, compared with those observed in a mouse lymphoma with a E254G substitution mutation in p53 (CR246). However, expression of p53 protein and mRNA were higher in the tumors than in control brain tissue, which contains relatively few proliferating cells (Figs. 2A and 3) . Nucleotide sequence analysis of p53 revealed no mutations in any of the seven tumor mRNAs examined. Thus, although germ-line loss of p53 accelerates tumorigenesis in Ptc^+/- mice, mutation of p53 is not required for medulloblastoma formation. This contrasts with a report of increased medulloblastoma formation in mice carrying homozygous mutations in both the retinoblastoma (Rb) and p53 genes. In this mouse model, brain tumors were not detected in mice in which only one of these genes was disrupted (27) .

View larger version (49K): [in this window] [in a new window] [Download PPT slide]   Fig. 3. p53 expression in medulloblastomas arising in Ptc+/-p53+/+ mice. Immunoblot analysis of protein extracts from medulloblastomas arising in Ptc+/- mice revealed very low levels of p53 expression in the medulloblastoma tissues compared with a murine B-cell leukemia (CR246) that expresses mutated p53 (E251G). In contrast, p53 expression was much lower in B-cell leukemia cells lacking p53 mutations (CR205). p53 protein was not detected in control tissues (normal brain and medulloblastoma arising in Ptc+/-p53-/- mice). Sequence analysis of RT-PCR products amplified from these tumors revealed no mutations in p53.

Loss of p53 leads to accumulation of cytogenetic abnormalities (23 , 30) . Indeed, we observed a much higher incidence of random chromosome loss in tumors from Ptc^+/-p53^-/- mice compared with those from Ptc^+/-p53^+/+ mice. In p53^+/- mice, there may be an insufficient number of cell generations to lose the remaining p53 allele and to acquire other genetic changes. Additionally, no acceleration in tumorigenesis was noted in Ptc^+/-ARF^-/- mice. This may be because ARF does not increase genomic instability, and therefore, the tumor precursor cells may be less prone to sustain DNA damage than cells deficient in p53. It is likely that the genomic instability associated with complete loss of p53 function accelerates the mutation rate in granule cell precursors. This may synergize with the effects of reduced Ptc expression in these mice to increase the incidence of medulloblastoma.

Survivors of pediatric brain tumors have significant morbidity as a direct consequence of the therapy required to eradicate tumor cells from the developing brain of a child. Genetic mutations have been detected only in small subsets of medulloblastoma, and the molecular basis of the majority of these tumors remains to be elucidated. The high frequency and rapid onset of tumors in Ptc^+/-p53^-/- mice provide a useful model to investigate other molecules that influence the balance between proliferation and cell death in the nervous system.

	ACKNOWLEDGMENTS

 
We thank M. Scott and L. Goodrich for the Ptc^+/- mice and Ptc plasmids (617 and M2-3); G. Zambetti for mdm2 plasmid; C. Sherr for the ARF^-/- mice; S. Mathew and J. Dalton for karyotype analysis; M. Connelly for assistance with tumor cell culture; and C. Eischen for mouse lymphoma cell lysates.

	FOOTNOTES

 
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 in part by NIH Cancer Center Support CORE Grant P30 CA 21765, the American Lebanese Syrian Associated Charities, the Pediatric Brain Tumor Foundation of the United States (to C. W.), National Cancer Institute Training Grant T32-CA70089 for Physician-Scientists (to C. W.), and an American Cancer Society Postdoctoral Fellowship (to D. E.).

² Present address: Lexicon Genetics, Inc., 4000 Research Forest Drive, The Woodlands, TX 77381.

³ To whom requests for reprints should be addressed, at Developmental Neurobiology, St. Jude’s Childrens’ Research Hospital, 332 North Lauderdale Street, Memphis, TN 38105-2794. Phone: (901) 495-2255; Fax: (901) 495-2270; E-mail: fos1{at}aol.com

⁴ The abbreviation used is: RT-PCR, reversed transcription-PCR.

Received 10/25/00. Accepted 11/29/00.

	REFERENCES

Top ABSTRACT Introduction Materials and Methods Results and Discussion REFERENCES

 

1. World Health Organization Classification of Tumors. Pathology and Genetics of Tumors of the Nervous System, pp. 129–140. Lyon, France: IARC Press, 2000.
2. Raffel C., Jenkins R. B., Frederick L., Hebrink D., Alderete B., Fults D. W., James C. D. Sporadic medulloblastomas contain PTCH mutations. Cancer Res., 57: 842-845, 1997.[Abstract/Free Full Text]
3. Cogen P. H., McDonald J. D. Tumor suppressor genes and medulloblastoma. J. Neuro-Oncol., 29: 103-112, 1996.[Medline]
4. Huang H., Mahler-Araujo B. M., Sankila A., Chimelli L., Yonekawa Y., Kleihues P., Ohgaki H. APC mutations in sporadic medulloblastomas. Am. J. Pathol., 156: 433-437, 2000.[Abstract/Free Full Text]
5. Zurawel R. H., Chiappa S. A., Allen C., Raffel C. Sporadic medulloblastomas contain oncogenic ß-catenin mutations. Cancer Res., 58: 896-899, 1998.[Abstract/Free Full Text]
6. Eberhart C. G., Tihan T., Burger P. C. Nuclear localization and mutation of ß-catenin in medulloblastomas. J. Neuropathol. Exp. Neurol., 59: 333-337, 2000.[Medline]
7. Goodrich L. V., Scott M. P. Hedgehog and patched in neural development and disease. Neuron, 21: 1243-1257, 1998.[Medline]
8. Paraf F., Jothy S., Van Meir E. G. Brain tumor-polyposis syndrome: two genetic diseases?. J. Clin. Oncol., 15: 2744-2758, 1997.[Abstract/Free Full Text]
9. Kleihues P., Schauble B., zur Hausen A., Esteve J., Ohgaki H. Tumors associated with p53 germline mutations: a synopsis of 91 families. Am. J. Pathol., 150: 1-13, 1997.[Abstract]
10. CBTRUS 1997 Annual Report. Published by the Central Brain Tumor Registry of the United States, 1998.
11. Kimonis V. E., Goldstein A. M., Pastakia B., Yang M. L., Kase R., DiGiovanna J. J., Bale A. E., Bale S. J. Clinical manifestations in 105 persons with nevoid basal cell carcinoma syndrome. Am. J. Med. Genet., 69: 299-308, 1997.[Medline]
12. Goodrich L. V., Milenkovic L., Higgins K. M., Scott M. P. Altered neural cell fates and medulloblastoma in mouse patched mutants. Science (Washington DC), 277: 1109-1113, 1997.[Abstract/Free Full Text]
13. Hahn H., Wojnowski L., Zimmer A. M., Hall J., Miller G., Zimmer A. Rhabdomyosarcomas and radiation hypersensitivity in a mouse model of Gorlin syndrome. Nat. Med., 4: 619-622, 1998.[Medline]
14. Wetmore C., Eberhart D. E., Curran T. The normal patched allele is expressed in medulloblastomas from mice with heterozygous germ-line mutation of patched.. Cancer Res., 60: 2239-2246, 2000.[Abstract/Free Full Text]
15. Zurawel, R. H., Allen, C., Wechsler-Reya, R., Scott, M. P., and Raffel, C. Evidence that haploinsufficiency of Ptch leads to medulloblastoma in mice. Genes Chromosomes Cancer, 28: 77–81.
16. Wechsler-Reya R. J., Scott M. P. Control of neuronal precursor proliferation in the cerebellum by Sonic Hedgehog. Neuron, 22: 103-114, 1999.[Medline]
17. Giaccia A. J., Kastan M. B. The complexity of p53 modulation: emerging patterns from divergent signals. Genes Dev., 12: 2973-2983, 1998.[Free Full Text]
18. Sherr C. J. Tumor surveillance via the ARF-p53 pathway. Genes Dev., 12: 2984-2991, 1998.[Free Full Text]
19. Kamijo T., Bodner S., van de Kamp E., Randle D. H., Sherr C. J. Tumor spectrum in ARF-deficient mice. Cancer Res., 59: 2217-2222, 1999.[Abstract/Free Full Text]
20. Donehower L. A. The p53-deficient mouse: a model for basic and applied cancer studies. Semin. Cancer Biol., 7: 269-278, 1996.[Medline]
21. Macleod K. F., Jacks T. Insights into cancer from transgenic mouse models. J. Pathol., 187: 43-60, 1999.[Medline]
22. Barth A. I., Nathke I. S., Nelson W. J. Cadherins, catenins and APC protein: interplay between cytoskeletal complexes and signaling pathways. Curr. Opin. Cell Biol., 9: 683-690, 1997.[Medline]
23. Levine A. J. p53, the cellular gatekeeper for growth and division. Cell, 88: 323-331, 1997.[Medline]
24. Gottlieb T. M., Oren M. p53 plays a regulatory role in differentiation and apoptosis of central nervous system-associated cells. Mol. Cell. Biol., 16: 5178-5185, 1996.[Abstract]
25. Reifenberger G., Liu L., Ichimura K., Schmidt E. E., Collins V. P. Amplification and overexpression of the MDM2 gene in a subset of human malignant gliomas without p53 mutations. Cancer Res., 53: 2736-2739, 1993.[Abstract/Free Full Text]
26. Fulci G., Van Meir E. G. p53 and the CNS: tumors and developmental abnormalities. Mol. Neurobiol., 19: 61-77, 1999.[Medline]
27. Marino S., Vooijs M., van Der Gulden H., Jonkers J., Berns A. Induction of medulloblastomas in p53-null mutant mice by somatic inactivation of Rb in the external granular layer cells of the cerebellum. Genes Dev., 14: 994-1004, 2000.[Abstract/Free Full Text]
28. Goldowitz D., Hamre K. The cells and molecules that make a cerebellum. Trends Neurosci., 21: 375-382, 1998.[Medline]
29. Sidman R. L., Rakic P. Neuronal migration, with special reference to developing human brain: a review. Brain Res., 62: 1-35, 1973.[Medline]
30. Harvey M., Sands A. T., Weiss R. S., Hegi M. E., Wiseman R. W., Pantazis P., Giovanella B. C., Tainsky M. A., Bradley A., Donehower L. A. In vitro growth characteristics of embryo fibroblasts isolated from p53-deficient mice. Oncogene, 8: 2457-2467, 1993.[Medline]

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				Y. Lee, H. L. Miller, H. R. Russell, K. Boyd, T. Curran, and P. J. McKinnon Patched2 modulates tumorigenesis in patched1 heterozygous mice. Cancer Res., July 15, 2006; 66(14): 6964 - 6971. [Abstract] [Full Text] [PDF]

				O. Shakhova, C. Leung, E. van Montfort, A. Berns, and S. Marino Lack of Rb and p53 Delays Cerebellar Development and Predisposes to Large Cell Anaplastic Medulloblastoma through Amplification of N-Myc and Ptch2. Cancer Res., May 15, 2006; 66(10): 5190 - 5200. [Abstract] [Full Text] [PDF]

				C. T. Yan, D. Kaushal, M. Murphy, Y. Zhang, A. Datta, C. Chen, B. Monroe, G. Mostoslavsky, K. Coakley, Y. Gao, et al. XRCC4 suppresses medulloblastomas with recurrent translocations in p53-deficient mice PNAS, May 9, 2006; 103(19): 7378 - 7383. [Abstract] [Full Text] [PDF]

				K. Sasai, J. T. Romer, Y. Lee, D. Finkelstein, C. Fuller, P. J. McKinnon, and T. Curran Shh pathway activity is down-regulated in cultured medulloblastoma cells: implications for preclinical studies. Cancer Res., April 15, 2006; 66(8): 4215 - 4222. [Abstract] [Full Text] [PDF]

				F. Mendrzyk, B. Radlwimmer, S. Joos, F. Kokocinski, A. Benner, D. E. Stange, K. Neben, H. Fiegler, N. P. Carter, G. Reifenberger, et al. Genomic and Protein Expression Profiling Identifies CDK6 As Novel Independent Prognostic Marker in Medulloblastoma J. Clin. Oncol., December 1, 2005; 23(34): 8853 - 8862. [Abstract] [Full Text] [PDF]

				T. Uziel, F. Zindy, S. Xie, Y. Lee, A. Forget, S. Magdaleno, J. E. Rehg, C. Calabrese, D. Solecki, C. G. Eberhart, et al. The tumor suppressors Ink4c and p53 collaborate independently with Patched to suppress medulloblastoma formation Genes & Dev., November 15, 2005; 19(22): 2656 - 2667. [Abstract] [Full Text] [PDF]

				J. Romer and T. Curran Targeting Medulloblastoma: Small-Molecule Inhibitors of the Sonic Hedgehog Pathway as Potential Cancer Therapeutics Cancer Res., June 15, 2005; 65(12): 4975 - 4978. [Abstract] [Full Text] [PDF]

				T. G. Oliver, T. A. Read, J. D. Kessler, A. Mehmeti, J. F. Wells, T. T. T. Huynh, S. M. Lin, and R. J. Wechsler-Reya Loss of patched and disruption of granule cell development in a pre-neoplastic stage of medulloblastoma Development, May 15, 2005; 132(10): 2425 - 2439. [Abstract] [Full Text] [PDF]

				G. N. Fuller, X. Su, R. E. Price, Z. R. Cohen, F. F. Lang, R. Sawaya, and S. Majumder Many human medulloblastoma tumors overexpress repressor element-1 silencing transcription (REST)/neuron-restrictive silencer factor, which can be functionally countered by REST-VP16 Mol. Cancer Ther., March 1, 2005; 4(3): 343 - 349. [Abstract] [Full Text] [PDF]

				A. R. Hallahan, J. I. Pritchard, S. Hansen, M. Benson, J. Stoeck, B. A. Hatton, T. L. Russell, R. G. Ellenbogen, I. D. Bernstein, P. A. Beachy, et al. The SmoA1 Mouse Model Reveals That Notch Signaling Is Critical for the Growth and Survival of Sonic Hedgehog-Induced Medulloblastomas Cancer Res., November 1, 2004; 64(21): 7794 - 7800. [Abstract] [Full Text] [PDF]

				L. Di Marcotullio, E. Ferretti, E. De Smaele, B. Argenti, C. Mincione, F. Zazzeroni, R. Gallo, L. Masuelli, M. Napolitano, M. Maroder, et al. RENKCTD11 is a suppressor of Hedgehog signaling and is deleted in human medulloblastoma PNAS, July 20, 2004; 101(29): 10833 - 10838. [Abstract] [Full Text] [PDF]

				M A Dyer Mouse models of childhood cancer of the nervous system J. Clin. Pathol., June 1, 2004; 57(6): 561 - 576. [Abstract] [Full Text] [PDF]

				F. Zindy, L. M. Nilsson, L. Nguyen, C. Meunier, R. J. Smeyne, J. E. Rehg, C. Eberhart, C. J. Sherr, and M. F. Roussel Hemangiosarcomas, Medulloblastomas, and Other Tumors in Ink4c/p53-null Mice Cancer Res., September 1, 2003; 63(17): 5420 - 5427. [Abstract] [Full Text] [PDF]

				Y. Lee, H. L. Miller, P. Jensen, R. Hernan, M. Connelly, C. Wetmore, F. Zindy, M. F. Roussel, T. Curran, R. J. Gilbertson, et al. A Molecular Fingerprint for Medulloblastoma Cancer Res., September 1, 2003; 63(17): 5428 - 5437. [Abstract] [Full Text] [PDF]

				W. Q. Yang, D. Senger, H. Muzik, Z. Q. Shi, D. Johnson, P. M. A. Brasher, N. B. Rewcastle, M. Hamilton, J. Rutka, J. Wolff, et al. Reovirus Prolongs Survival and Reduces the Frequency of Spinal and Leptomeningeal Metastases from Medulloblastoma Cancer Res., June 15, 2003; 63(12): 3162 - 3172. [Abstract] [Full Text] [PDF]

				L. Li, M. C. Connelly, C. Wetmore, T. Curran, and J. I. Morgan Mouse Embryos Cloned from Brain Tumors Cancer Res., June 1, 2003; 63(11): 2733 - 2736. [Abstract] [Full Text] [PDF]

				D. H. Gutmann, S. J. Baker, M. Giovannini, J. Garbow, and W. Weiss Mouse Models of Human Cancer Consortium Symposium on Nervous System Tumors Cancer Res., June 1, 2003; 63(11): 3001 - 3004. [Abstract] [Full Text] [PDF]

				T. J. MacDonald, B. R. Rood, M. R. Santi, G. Vezina, K. Bingaman, P. H. Cogen, and R. J. Packer Advances in the Diagnosis, Molecular Genetics, and Treatment of Pediatric Embryonal CNS Tumors Oncologist, April 1, 2003; 8(2): 174 - 186. [Abstract] [Full Text] [PDF]

				C. G. Eberhart Medulloblastoma in Mice Lacking p53 and PARP: All Roads Lead To Gli Am. J. Pathol., January 1, 2003; 162(1): 7 - 10. [Full Text] [PDF]

				W.-M. Tong, H. Ohgaki, H. Huang, C. Granier, P. Kleihues, and Z.-Q. Wang Null Mutation of DNA Strand Break-Binding Molecule Poly(ADP-ribose) Polymerase Causes Medulloblastomas in p53-/- Mice Am. J. Pathol., January 1, 2003; 162(1): 343 - 352. [Abstract] [Full Text] [PDF]

				K. Y. Tsai, D. MacPherson, D. A. Rubinson, A. Yu. Nikitin, R. Bronson, K. L. Mercer, D. Crowley, and T. Jacks ARF mutation accelerates pituitary tumor development in Rb+/- mice PNAS, December 24, 2002; 99(26): 16865 - 16870. [Abstract] [Full Text] [PDF]

				P. J. Houghton, P. C. Adamson, S. Blaney, H. A. Fine, R. Gorlick, M. Haber, L. Helman, S. Hirschfeld, M. G. Hollingshead, M. A. Israel, et al. Testing of New Agents in Childhood Cancer Preclinical Models: Meeting Summary Clin. Cancer Res., December 1, 2002; 8(12): 3646 - 3657. [Abstract] [Full Text] [PDF]

				H. L. Weiner, R. Bakst, M. S. Hurlbert, J. Ruggiero, E. Ahn, W. S. Lee, D. Stephen, D. Zagzag, A. L. Joyner, and D. H. Turnbull Induction of Medulloblastomas in Mice by Sonic Hedgehog, Independent of Gli1 Cancer Res., November 15, 2002; 62(22): 6385 - 6389. [Abstract] [Full Text] [PDF]

				D. M. Berman, S. S. Karhadkar, A. R. Hallahan, J. I. Pritchard, C. G. Eberhart, D. N. Watkins, J. K. Chen, M. K. Cooper, J. Taipale, J. M. Olson, et al. Medulloblastoma Growth Inhibition by Hedgehog Pathway Blockade Science, August 30, 2002; 297(5586): 1559 - 1561. [Abstract] [Full Text] [PDF]

				H. A. Fine Polyomavirus and Medulloblastoma: A Smoking Gun or Guilt By Association? J Natl Cancer Inst, February 20, 2002; 94(4): 240 - 241. [Full Text] [PDF]

				D. Tolbert, X. Lu, C. Yin, M. Tantama, and T. Van Dyke p19ARF Is Dispensable for Oncogenic Stress-Induced p53-Mediated Apoptosis and Tumor Suppression In Vivo Mol. Cell. Biol., January 1, 2002; 22(1): 370 - 377. [Abstract] [Full Text] [PDF]

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