Chromosomal translocations in human cells are generated by canonical nonhomologous end-joining.

Breakpoint junctions of the chromosomal translocations that occur in human cancers display hallmarks of nonhomologous end-joining (NHEJ). In mouse cells, translocations are suppressed by canonical NHEJ (c-NHEJ) components, which include DNA ligase IV (LIG4), and instead arise from alternative NHEJ (alt-NHEJ). Here we used designer nucleases (ZFNs, TALENs, and CRISPR/Cas9) to introduce DSBs on two chromosomes to study translocation joining mechanisms in human cells. Remarkably, translocations were altered in cells deficient for LIG4 or its interacting protein XRCC4. Translocation junctions had significantly longer deletions and more microhomology, indicative of alt-NHEJ. Thus, unlike mouse cells, translocations in human cells are generated by c-NHEJ. Human cancer translocations induced by paired Cas9 nicks also showed a dependence on c-NHEJ, despite having distinct joining characteristics. These results demonstrate an unexpected and striking species-specific difference for common genomic rearrangements associated with tumorigenesis.

Ghezraoui H ，Piganeau M ，Renouf B ，Renaud JB ，Sallmyr A ，Ruis B ，Oh S ，Tomkinson AE ，Hendrickson EA ，Giovannangeli C ，Jasin M ，Brunet E ... -  《-》

DNA ligase III promotes alternative nonhomologous end-joining during chromosomal translocation formation.

Simsek D ，Brunet E ，Wong SY ，Katyal S ，Gao Y ，McKinnon PJ ，Lou J ，Zhang L ，Li J ，Rebar EJ ，Gregory PD ，Holmes MC ，Jasin M ... -  《PLoS Genetics》

Alternative end-joining is suppressed by the canonical NHEJ component Xrcc4-ligase IV during chromosomal translocation formation.

Simsek D ，Jasin M 《-》

Marked contribution of alternative end-joining to chromosome-translocation-formation by stochastically induced DNA double-strand-breaks in G2-phase human cells.

Ionizing radiation (IR) induces double strand breaks (DSBs) in cellular DNA, which if not repaired correctly can cause chromosome translocations leading to cell death or cancer. Incorrect joining of DNA ends generating chromosome translocations can be catalyzed either by the dominant DNA-PKcs-dependent, classical non-homologous end-joining (c-NHEJ), or by an alternative end-joining (alt-EJ) process, functioning as backup to abrogated c-NHEJ, or homologous recombination repair. Alt-EJ operates with slower kinetics as compared to c-NHEJ and generates larger alterations at the junctions; it is also considered crucial to chromosome translocation-formation. A recent report posits that this view only holds for rodent cells and that in human cells c-NHEJ is the main mechanism of chromosome translocation formation. Since this report uses designer nucleases that induce DSBs with unique characteristics in specific genomic locations and PCR to detect translocations, we revisit the issue using stochastically distributed DSBs induced in the human genome by IR during the G2-phase of the cell cycle. For visualization and analysis of chromosome translocations, which manifest as chromatid translocations in cells irradiated in G2, we employ classical cytogenetics. In wild-type cells, we observe a significant contribution of alt-EJ to translocation formation, as demonstrated by a yield-reduction after treatment with inhibitors of Parp, or of DNA ligases 1 and 3 (Lig1, Lig3). Notably, a nearly fourfold increase in translocation formation is seen in c-NHEJ mutants with defects in DNA ligase 4 (Lig4) that remain largely sensitive to inhibitors of Parp, and of Lig1/Lig3. We conclude that similar to rodent cells, chromosome translocation formation from randomly induced DSBs in human cells largely relies on alt-EJ. We discuss DSB localization in the genome, characteristics of the DSB and the cell cycle as potential causes of the divergent results generated with IR and designer nucleases.

Soni A ，Siemann M ，Pantelias GE ，Iliakis G ... -  《-》

Alternative end-joining catalyzes robust IgH locus deletions and translocations in the combined absence of ligase 4 and Ku70.

Boboila C ，Jankovic M ，Yan CT ，Wang JH ，Wesemann DR ，Zhang T ，Fazeli A ，Feldman L ，Nussenzweig A ，Nussenzweig M ，Alt FW ... -  《-》