Howard Hughes Medical Institute, Program in Cellular and Molecular Medicine, Boston Children's Hospital, and Department of Genetics, Harvard Medical School, Boston, MA 02115.
Howard Hughes Medical Institute, Program in Cellular and Molecular Medicine, Boston Children's Hospital, and Department of Genetics, Harvard Medical School, Boston, MA 02115
Proc Natl Acad Sci U S A. 2014 Jul 15;111(28):10269-74. doi: 10.1073/pnas.1410112111. Epub 2014 Jun 30.
Mature IgM(+) B-cell lymphomas that arise in certain ataxia telangiectasia-mutated (ATM)-deficient compound mutant mice harbor translocations that fuse V(D)J recombination-initiated IgH double-strand breaks (DSBs) on chromosome 12 to sequences downstream of c-myc on chromosome 15, generating dicentric chromosomes and c-myc amplification via a breakage-fusion-bridge mechanism. As V(D)J recombination DSBs occur in developing progenitor B cells in the bone marrow, we sought to elucidate a mechanism by which such DSBs contribute to oncogenic translocations/amplifications in mature B cells. For this purpose, we applied high-throughput genome-wide translocation sequencing to study the fate of introduced c-myc DSBs in splenic IgM(+) B cells stimulated for activation-induced cytidine deaminase (AID)-dependent IgH class switch recombination (CSR). We found frequent translocations of c-myc DSBs to AID-initiated DSBs in IgH switch regions in wild-type and ATM-deficient B cells. However, c-myc also translocated frequently to newly generated DSBs within a 35-Mb region downstream of IgH in ATM-deficient, but not wild-type, CSR-activated B cells. Moreover, we found such DSBs and translocations in activated B cells that did not express AID or undergo CSR. Our findings indicate that ATM deficiency leads to formation of chromosome 12 dicentrics via recombination-activating gene-initiated IgH DSBs in progenitor B cells and that these dicentrics can be propagated developmentally into mature B cells where they generate new DSBs downstream of IgH via breakage-fusion-bridge cycles. We propose that dicentrics formed by joining V(D)J recombination-associated IgH DSBs to DSBs downstream of c-myc in ATM-deficient B lineage cells similarly contribute to c-myc amplification and mature B-cell lymphomas.
在某些共济失调毛细血管扩张症突变（ATM）缺陷的复合突变小鼠中出现的成熟 IgM(+) B 细胞淋巴瘤，其特征是易位融合了染色体 12 上 V(D)J 重组起始的 IgH 双链断裂（DSB）与染色体 15 上 c-myc 下游的序列，从而产生双着丝粒染色体和 c-myc 扩增，通过断裂-融合-桥机制。由于 V(D)J 重组 DSB 发生在骨髓中发育中的祖 B 细胞中，我们试图阐明这种 DSB 如何导致成熟 B 细胞中的致癌易位/扩增。为此，我们应用高通量全基因组易位测序来研究在诱导激活诱导的胞嘧啶脱氨酶（AID）依赖性 IgH 类别转换重组（CSR）刺激下引入的 c-myc DSB 在脾 IgM(+) B 细胞中的命运。我们发现野生型和 ATM 缺陷型 B 细胞中，c-myc DSB 频繁易位到 AID 起始的 IgH 开关区域中的 DSB。然而，在 ATM 缺陷但非野生型 CSR 激活的 B 细胞中，c-myc 也频繁易位到 IgH 下游 35Mb 区域内新生成的 DSB。此外，我们在未表达 AID 或未经历 CSR 的激活 B 细胞中发现了这种 DSB 和易位。我们的研究结果表明，ATM 缺陷导致重组激活基因起始的 IgH DSB 在祖 B 细胞中形成染色体 12 双着丝粒，这些双着丝粒可以在发育过程中传递到成熟 B 细胞中，在成熟 B 细胞中通过断裂-融合-桥循环在 IgH 下游产生新的 DSB。我们提出，在 ATM 缺陷的 B 细胞谱系细胞中，通过连接 V(D)J 重组相关的 IgH DSB 与 c-myc 下游的 DSB 形成的双着丝粒同样有助于 c-myc 扩增和成熟 B 细胞淋巴瘤。
