Project description:ERCC6L2 is a recently characterized component in DNA damage repair. To investigate its function in chromosome translocation, we conducted a study using K562 and HEK293T cell lines. We introduced twinned DNA double-strand breaks (DSBs) or genome-wide DSBs into these cell lines via nucleofection and transfection, respectively. Subsequently, we employed high-throughput genome translocation sequencing (HTGTS) to capture the translocation events (i.e., ligation between "prey(s)" and "bait") and the rejoining events (i.e., direct repair within the "bait" locus) under different conditions, including with or without ERCC6L2 deletion. We quantified the number of translocation events by normalizing them to the number of rejoining events, denoted as TL. Interestingly, ERCC6L2 deletion led to an increase in TL, indicating a higher frequency of translocations.
Project description:Structurally complex genomic regions, such as centromeres, are inherently difficult to duplicate. The mechanism that underlies centromere inheritance is not well understood, and one of the key questions relates to the reassembly of centromeric chromatin following DNA replication. Here we define the SNF2 ATPase ERCC6L2 as a key regulator of this process. ERCC6L2 accumulates at centromeres and promotes efficient deposition of core centromeric factors. Our genomic analyses show that ERCC6L2 deficiency erodes centromeric chromatin, leading to unrestrained replication of centromeric DNA. We also establish that, beyond centromeres, ERCC6L2 facilitates replication at genomic repeats and non-canonical DNA structures. Notably, ERCC6L2 interacts with the major DNA replication factor PCNA through an atypical peptide, presented here as a co-crystal structure. Finally, we examine ERCC6L2 activities at DNA breaks, and show that it acts to restrict end resection independently of the 53BP1-REV7-Shieldin complex. Our observations allow us to propose a mechanistic model of ERCC6L2 activity, which reconciles its seemingly distinct functions in DNA repair and DNA replication. Together, these findings provide a new molecular context for studies linking ERCC6L2 to human disease.
Project description:Structurally complex genomic regions, such as centromeres, are inherently difficult to duplicate. The mechanism that underlies centromere inheritance is not well understood, and one of the key questions relates to the reassembly of centromeric chromatin following DNA replication. Here we define the SNF2 ATPase ERCC6L2 as a key regulator of this process. ERCC6L2 accumulates at centromeres and promotes efficient deposition of core centromeric factors. Our genomic analyses show that ERCC6L2 deficiency erodes centromeric chromatin, leading to unrestrained replication of centromeric DNA. We also establish that, beyond centromeres, ERCC6L2 facilitates replication at genomic repeats and non-canonical DNA structures. Notably, ERCC6L2 interacts with the major DNA replication factor PCNA through an atypical peptide, presented here as a co-crystal structure. Finally, we examine ERCC6L2 activities at DNA breaks, and show that it acts to restrict end resection independently of the 53BP1-REV7-Shieldin complex. Our observations allow us to propose a mechanistic model of ERCC6L2 activity, which reconciles its seemingly distinct functions in DNA repair and DNA replication. Together, these findings provide a new molecular context for studies linking ERCC6L2 to human disease.
Project description:Despite the inclusion of inherited myeloid malignancies as a separate entity in the WHO Classification, our understanding of the etiology of familial leukemia remains limited. ERCC6L2-deficiency is a rare, life-threatening inherited condition that gives rise to bone marrow failure (BMF), myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML) resulting from germline mutations in DNA repair factor ERCC6L2. Here we employ a lentiviral shRNA approach to functionally characterize the impact of ERCC6L2 loss on hematopoietic stem/progenitor cells (HSPCs) and mesenchymal stromal cells (MSCs). By combining cell culture assays and transcriptomic analysis of knockdown and ERCC6L2-mutated patient cells, we find that ERCC6L2-deficiency reduces HSPC clonogenic potential and delays erythropoiesis, while in MSCs it induces a significant lineage skewing, with increased osteogenesis and suppressed adipogenesis. Altogether, we demonstrate that ERCC6L2-deficiency impacts both hematopoietic and stromal compartments, and that our ex vivo model recapitulates patient phenotypes, providing a robust system to study germline mutations in hematological malignancies.
Project description:Two DNA repair pathways, non-homologous end joining (NHEJ) and alternative end joining (A-EJ), are involved in V(D)J recombination and chromosome translocation. Previous studies reported distinct repair mechanisms for chromosome translocation, with NHEJ predominantly involved in human and A-EJ in mice. NHEJ depends on DNA-PKcs, a critical partner in synapsis formation and downstream component activation. While DNA-PKcs inhibition promotes chromosome translocations harboring microhomologies in mice, its synonymous effect in human is not known. We find partial DNA-PKcs inhibition in human cell lines leads to increased genome-wide translocations composed mostly of direct joints, indicating the continued involvement of dampened NHEJ in these processes. In contrast, complete DNA-PKcs inhibition and genetic inhibition DNA-PKcs kinase domain substantially increased microhomology-mediated end joining (MMEJ), thus bridging the two different translocation mechanisms between human and mice. Similar to a previous study on Ku70 deletion, DNA-PKcs deletion in G1/G0-phase mouse pro-B cell lines, impair the recombination of RAG1/2-mediated DNA double-strand breaks (DSBs). This DNA-PKcs-deficient repair mechanism exhibited reduced V(D)J recombination efficiency, increased end resection, decreased polymerase-mediated insertions, loss of recombination fidelity and generated relatively higher rates of chromosome translocation as a consequence of dysregulated coding and signal end joining. Our study underscores DNA-PKcs in suppressing illegitimate chromosome rearrangement in both species.
Project description:Topoisomerase II-induced Chromosome Breakage and Translocation Is Determined by Chromosome Architecture and Transcriptional Activity
Project description:Topoisomerase II-induced Chromosome Breakage and Translocation Is Determined by Chromosome Architecture and Transcriptional Activity [HTGTS]
Project description:DNA-PKcs is a crucial component of the non-homologous end joining (NHEJ) repair machinery. To investigate its function in human cell lines, we conducted a study using K562 and HEK293T cell lines. We introduced twinned DNA double-strand breaks (DSBs) or genome-wide DSBs into these cell lines via nucleofection and transfection, respectively. Subsequently, we employed high-throughput genome translocation sequencing (HTGTS) to capture the translocation events (i.e., ligation between "prey(s)" and "bait") and the rejoining events (i.e., direct repair within the "bait" locus) under different conditions, including with or without DNA-PKcs inhibition or deletion. We quantified the number of translocation events by normalizing them to the number of rejoining events, denoted as TL. Interestingly, DNA-PKcs inhibition led to an increase in TL, indicating a higher frequency of translocations. However, it is important to note that chromosomal translocations still predominantly relied on NHEJ despite DNA-PKcs inhibition. Furthermore, we observed that DNA-PKcs deletion resulted in an elevated utilization of microhomology in translocation formation. Nevertheless, NHEJ remained the primary mechanism driving translocation events.These findings provide valuable insights into the role of DNA-PKcs in the repair pathways involved in translocation events in human cell lines. The utilization of HTGTS allowed us to comprehensively analyze the effects of DNA-PKcs inhibition and deletion, shedding light on the interplay between NHEJ and alternative repair mechanisms in translocation formation.