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Recurrent genomic alterations characterize medulloblastoma arising from DNA double-strand break repair deficiency - PubMed

  • ️Thu Jan 01 2009

Recurrent genomic alterations characterize medulloblastoma arising from DNA double-strand break repair deficiency

Pierre-Olivier Frappart et al. Proc Natl Acad Sci U S A. 2009.

Abstract

Inactivation of homologous recombination (HR) or nonhomologous end-joining (NHEJ) predisposes to a spectrum of tumor types. Here, we inactivated DNA double-strand break repair (DSBR) proteins, DNA Ligase IV (Lig4), Xrcc2, and Brca2, or combined Lig4/Xrcc2 during neural development using Nestin-cre. In all cases, inactivation of these repair factors, together with p53 loss, led to rapid medulloblastoma formation. Genomic analysis of these tumors showed recurring chromosome 13 alterations via chromosomal loss or translocations involving regions containing Ptch1. Sequence analysis of the remaining Ptch1 allele showed a variety of inactivating mutations in all tumors analyzed, highlighting the critical tumor suppressor function of this hedgehog-signaling regulator. We also observed genomic amplification or up-regulation of either N-Myc or cyclin D2 in all medulloblastomas. Additionally, chromosome 19, which contains Pten, was also selectively deleted in medulloblastoma arising after disruption of HR. Thus, our data highlight the preeminence of Ptch1 as a tumor suppressor in cerebellar granule cells and reveal other genomic events central to the genesis of medulloblastoma.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.
Fig. 1.

p53 deficiency induces medulloblastoma formation in Lig4Nes-Cre and Xrcc2Nes-Cre mice. (A) Survival curves of Lig4/p53-deficient mice. Lig4Nes-Cre (n = 42), Lig4Nes-Cre, p53+/− (n = 19), and Lig4Nes-Cre; p53−/− (n = 23) mice were monitored over a period of 32 weeks for survival and medulloblastoma development. The lifespan of Lig4Nes-Cre;p53−/− mice was significantly shorter compared with the Lig4Nes-Cre and Lig4Nes-Cre; p53+/− cohort (P < 0.0001). (B) Survival curves of Xrcc2/p53-deficient mice. Xrcc2Nes-Cre (n = 23), Xrcc2Nes-Cre, p53+/− (n = 11), and Xrcc2Nes-Cre, p53−/− (n = 33) are shown. The lifespan of Xrcc2Nes-Cre, p53−/− mice was significantly shorter compared with the Xrcc2Nes-Cre, p53+/− and Xrcc2Nes-Cre (P < 0.0001). (C) Survival curves of Ligase4/Xrcc2/p53-deficient mice. Lig4,Xrcc2Nes-Cre (n = 20), Lig4,Xrcc2Nes-Cre, p53+/− (n = 8), Lig4,Xrcc2Nes-Cre, p53−/− (n = 3). The survival curves are statistically significantly different (P < 0.0001). (D) Representative aCGH analysis of chr11 of Brca2 and Lig4,Xrcc2-deficient medulloblastoma associated with p53 heterozygosity. (E) Summary of aCGH results detecting hemizygous deletions of chr11 in medulloblastomas of Brca2Nes-Cre and Lig4/Xrcc2Nes-Cre. Each column represents a single tumor. Red indicates that the chromosome exhibited genomic loss; regional genomic changes were determined by using a normalized log2 ratio of ±0.2 as a cutoff.

Fig. 2.
Fig. 2.

Ptch1 is lost in DSBR-deficient medulloblastomas. (A) Representative aCGH analysis of chr13 of Brca2, Lig4, Xrcc2-deficient medulloblastomas in p53 mutant backgrounds. (B) Summary of aCGH results detecting deletions of chr13 in the medulloblastomas. Each column represents a single tumor, and each line represents 1 chromosome. Each red square indicates that the chromosome exhibited genomic loss. (C) Representative FISH analysis of chr13 showing either deletion or translocation. (D) Sequence analysis of Ptch1 mRNA from Lig4, Xrcc2, and Brca2-deficient medulloblastoma.

Fig. 3.
Fig. 3.

Genomic analysis of chromosomes 6, 12, and 19 in medulloblastomas. (A) Representative aCGH of chromosomes 6, 12, and 19 in medulloblastomas examined. (B) Representative complete SKY analysis of Brca2Nes-Cre, p53−/− showing a large number of double minutes, indicated by a white box. (C) FISH analysis for N-Myc amplification in medulloblastoma (Magnification: 1,000×). (D) Representative SKY of chr19 showing either deletion or translocation. (E) Summary of the genomic rearrangements of N-Myc, cylin D2, Sufu, and Pten in the medulloblastomas. Each column represents a single tumor, and each line represents 1 chromosome. Each red square indicates that the chromosome exhibited genomic loss, whereas each green square indicates a region of genomic amplification.

Fig. 4.
Fig. 4.

Pten pathway disruption in Brca2-deficient medulloblastoma. Shown are representative medulloblastoma sections showing loss of expression of Pten and up-regulation of levels of phospho-Ser-473 of Akt (p-Akt) and phospho-serine 235 and 236 of S6 (p-S6) in Brca2Nes-Cre;p53−/−-deficient medulloblastoma. Asterisks denote tumor tissue. (Scale bar: Upper, 0.1 mm; Lower, 0.05 mm.)

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