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Evidence for replicative repair of DNA double-strand breaks leading to oncogenic translocation and gene amplification.

Difilippantonio MJ, Petersen S, Chen HT, Johnson R, Jasin M, Kanaar R, Ried T, Nussenzweig A - J. Exp. Med. (2002)

Bottom Line: Subsequent DNA repair events juxtaposing IgH and c-myc are mediated by a break-induced replication pathway.Cycles of breakage-fusion-bridge result in amplification of IgH/c-myc while chromosome stabilization occurs through telomere capture.Thus, mice deficient in NHEJ provide excellent models to study the etiology of unbalanced translocations and amplification events during tumorigenesis.

View Article: PubMed Central - PubMed

Affiliation: Genetics Branch, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA. difilipm@mail.nih.gov

ABSTRACT
Nonreciprocal translocations and gene amplifications are commonly found in human tumors. Although little is known about the mechanisms leading to such aberrations, tissue culture models predict that they can arise from DNA breakage, followed by cycles of chromatid fusion, asymmetric mitotic breakage, and replication. Mice deficient in both a nonhomologous end joining (NHEJ) DNA repair protein and the p53 tumor suppressor develop lymphomas at an early age harboring amplification of an IgH/c-myc fusion. Here we report that these chromosomal rearrangements are initiated by a recombination activating gene (RAG)-induced DNA cleavage. Subsequent DNA repair events juxtaposing IgH and c-myc are mediated by a break-induced replication pathway. Cycles of breakage-fusion-bridge result in amplification of IgH/c-myc while chromosome stabilization occurs through telomere capture. Thus, mice deficient in NHEJ provide excellent models to study the etiology of unbalanced translocations and amplification events during tumorigenesis.

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Two types of rearrangement scenarios observed in pro-B cell lymphomas from Ku−/−p53−/− and Ku−/−p53−/−Rad54−/− mice. In scenarios A and B, the IgH locus on mouse chromosome 12 and the c-myc locus on mouse chromosome 15 are brought into close proximity with each other. The top panel contains chromosomes hybridized with chromosome 12 (red) and 15 (green) specific painting probes. Chromosomes 12 (n12) and 15 (n15) illustrate the normal locations of the probes used in the FISH analysis. In scenario A, der(12)a results from translocation of chromosome 15 (distal to c-myc [pink]), including the subtelomeric region (15T - red), to chromosome 12. Copying of the IgH Cα locus (IgH - green) from chromosome 12 to chromosome 15 results in der(15)a. In scenario B, both homologues of chromosome 15 usually appear to be intact, whereas copying of the c-myc oncogene to chromosome 12 results in der(12)b. The extrachromosomal material at the end of the der(12)b is explained in Fig. 5.
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fig1: Two types of rearrangement scenarios observed in pro-B cell lymphomas from Ku−/−p53−/− and Ku−/−p53−/−Rad54−/− mice. In scenarios A and B, the IgH locus on mouse chromosome 12 and the c-myc locus on mouse chromosome 15 are brought into close proximity with each other. The top panel contains chromosomes hybridized with chromosome 12 (red) and 15 (green) specific painting probes. Chromosomes 12 (n12) and 15 (n15) illustrate the normal locations of the probes used in the FISH analysis. In scenario A, der(12)a results from translocation of chromosome 15 (distal to c-myc [pink]), including the subtelomeric region (15T - red), to chromosome 12. Copying of the IgH Cα locus (IgH - green) from chromosome 12 to chromosome 15 results in der(15)a. In scenario B, both homologues of chromosome 15 usually appear to be intact, whereas copying of the c-myc oncogene to chromosome 12 results in der(12)b. The extrachromosomal material at the end of the der(12)b is explained in Fig. 5.

Mentions: Using a combination of whole-chromosome painting probes, a chromosome 15-specific subtelomeric probe, and probes for c-myc, IgH Cα, and IgH Cμ, we found two distinct types of configurations that juxtaposed IgH and c-myc in the pro-B cell lymphomas. Although we describe results for IgH Cα, identical results were obtained using BAC clones containing the most JH-proximal constant region (IgH Cμ). In the first configuration there is an exchange of material between chromosomes 12 and 15 resulting in the formation of two derivative chromosomes, der(12)a and der(15)a (Fig. 1 ; scenario A). IgH Cα was found near c-myc on the der(15)a and both genes were coamplified as determined by FISH and Southern blot analysis (reference 4, Table I, and data not shown). A single copy of the IgH Cα region, however, remained on der (12)a, indicating that a portion of chromosome 12 had been copied (not simply translocated) to der(15)a. Additionally, the region of chromosome 15 telomeric of c-myc was translocated to the der(12)a and was therefore absent from der(15)a. In fact, the subtelomeric region of chromosome 15, as indicated by hybridization with a region-specific BAC clone (15T), was found on the normal 15 [n15] as well as on the der(12)a (Fig. 1; scenario A). It should be noted that 15T is absent from the der(15)a. Scenario A–type rearrangements were found in 66% of the tumors analyzed. The alternative rearrangement pathway (Fig. 1; scenario B), was used by the remainder of the tumors. In these tumors c-myc and IgH Cα were coamplified on the derivative 12 [der(12)b] and no IgH Cα signal was detectable on chromosome 15. In fact, both copies of chromosome 15 appeared normal and hybridized with the c-myc and 15T BAC clones, while der(12)b did not contain any 15T sequences. In summary, in one class of tumors, IgH Cα was copied and amplified together with c-myc on the der(15)a (scenario A), whereas in the other class (scenario B) the c-myc oncogene was copied and amplified together with IgH Cα on der(12)b. These unbalanced rearrangements and amplifications are much more complex than the reciprocal translocations that juxtapose c-myc and IgH in human Burkitt's lymphoma and mouse plasmacytomas (29) but resemble the gene amplifications typically seen in solid tumors (30) and multiple myelomas (31).


Evidence for replicative repair of DNA double-strand breaks leading to oncogenic translocation and gene amplification.

Difilippantonio MJ, Petersen S, Chen HT, Johnson R, Jasin M, Kanaar R, Ried T, Nussenzweig A - J. Exp. Med. (2002)

Two types of rearrangement scenarios observed in pro-B cell lymphomas from Ku−/−p53−/− and Ku−/−p53−/−Rad54−/− mice. In scenarios A and B, the IgH locus on mouse chromosome 12 and the c-myc locus on mouse chromosome 15 are brought into close proximity with each other. The top panel contains chromosomes hybridized with chromosome 12 (red) and 15 (green) specific painting probes. Chromosomes 12 (n12) and 15 (n15) illustrate the normal locations of the probes used in the FISH analysis. In scenario A, der(12)a results from translocation of chromosome 15 (distal to c-myc [pink]), including the subtelomeric region (15T - red), to chromosome 12. Copying of the IgH Cα locus (IgH - green) from chromosome 12 to chromosome 15 results in der(15)a. In scenario B, both homologues of chromosome 15 usually appear to be intact, whereas copying of the c-myc oncogene to chromosome 12 results in der(12)b. The extrachromosomal material at the end of the der(12)b is explained in Fig. 5.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2196056&req=5

fig1: Two types of rearrangement scenarios observed in pro-B cell lymphomas from Ku−/−p53−/− and Ku−/−p53−/−Rad54−/− mice. In scenarios A and B, the IgH locus on mouse chromosome 12 and the c-myc locus on mouse chromosome 15 are brought into close proximity with each other. The top panel contains chromosomes hybridized with chromosome 12 (red) and 15 (green) specific painting probes. Chromosomes 12 (n12) and 15 (n15) illustrate the normal locations of the probes used in the FISH analysis. In scenario A, der(12)a results from translocation of chromosome 15 (distal to c-myc [pink]), including the subtelomeric region (15T - red), to chromosome 12. Copying of the IgH Cα locus (IgH - green) from chromosome 12 to chromosome 15 results in der(15)a. In scenario B, both homologues of chromosome 15 usually appear to be intact, whereas copying of the c-myc oncogene to chromosome 12 results in der(12)b. The extrachromosomal material at the end of the der(12)b is explained in Fig. 5.
Mentions: Using a combination of whole-chromosome painting probes, a chromosome 15-specific subtelomeric probe, and probes for c-myc, IgH Cα, and IgH Cμ, we found two distinct types of configurations that juxtaposed IgH and c-myc in the pro-B cell lymphomas. Although we describe results for IgH Cα, identical results were obtained using BAC clones containing the most JH-proximal constant region (IgH Cμ). In the first configuration there is an exchange of material between chromosomes 12 and 15 resulting in the formation of two derivative chromosomes, der(12)a and der(15)a (Fig. 1 ; scenario A). IgH Cα was found near c-myc on the der(15)a and both genes were coamplified as determined by FISH and Southern blot analysis (reference 4, Table I, and data not shown). A single copy of the IgH Cα region, however, remained on der (12)a, indicating that a portion of chromosome 12 had been copied (not simply translocated) to der(15)a. Additionally, the region of chromosome 15 telomeric of c-myc was translocated to the der(12)a and was therefore absent from der(15)a. In fact, the subtelomeric region of chromosome 15, as indicated by hybridization with a region-specific BAC clone (15T), was found on the normal 15 [n15] as well as on the der(12)a (Fig. 1; scenario A). It should be noted that 15T is absent from the der(15)a. Scenario A–type rearrangements were found in 66% of the tumors analyzed. The alternative rearrangement pathway (Fig. 1; scenario B), was used by the remainder of the tumors. In these tumors c-myc and IgH Cα were coamplified on the derivative 12 [der(12)b] and no IgH Cα signal was detectable on chromosome 15. In fact, both copies of chromosome 15 appeared normal and hybridized with the c-myc and 15T BAC clones, while der(12)b did not contain any 15T sequences. In summary, in one class of tumors, IgH Cα was copied and amplified together with c-myc on the der(15)a (scenario A), whereas in the other class (scenario B) the c-myc oncogene was copied and amplified together with IgH Cα on der(12)b. These unbalanced rearrangements and amplifications are much more complex than the reciprocal translocations that juxtapose c-myc and IgH in human Burkitt's lymphoma and mouse plasmacytomas (29) but resemble the gene amplifications typically seen in solid tumors (30) and multiple myelomas (31).

Bottom Line: Subsequent DNA repair events juxtaposing IgH and c-myc are mediated by a break-induced replication pathway.Cycles of breakage-fusion-bridge result in amplification of IgH/c-myc while chromosome stabilization occurs through telomere capture.Thus, mice deficient in NHEJ provide excellent models to study the etiology of unbalanced translocations and amplification events during tumorigenesis.

View Article: PubMed Central - PubMed

Affiliation: Genetics Branch, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA. difilipm@mail.nih.gov

ABSTRACT
Nonreciprocal translocations and gene amplifications are commonly found in human tumors. Although little is known about the mechanisms leading to such aberrations, tissue culture models predict that they can arise from DNA breakage, followed by cycles of chromatid fusion, asymmetric mitotic breakage, and replication. Mice deficient in both a nonhomologous end joining (NHEJ) DNA repair protein and the p53 tumor suppressor develop lymphomas at an early age harboring amplification of an IgH/c-myc fusion. Here we report that these chromosomal rearrangements are initiated by a recombination activating gene (RAG)-induced DNA cleavage. Subsequent DNA repair events juxtaposing IgH and c-myc are mediated by a break-induced replication pathway. Cycles of breakage-fusion-bridge result in amplification of IgH/c-myc while chromosome stabilization occurs through telomere capture. Thus, mice deficient in NHEJ provide excellent models to study the etiology of unbalanced translocations and amplification events during tumorigenesis.

Show MeSH
Related in: MedlinePlus