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DNA damage-induced phosphorylation of CtIP at a conserved ATM/ATR site promotes lymphomagenesis in NHEJ/p53-double deficient mice

ABSTRACT: Human lymphoid malignancies are often characterized by oncogenic translocations involving the antigen receptor gene loci. CtIP is a DNA end-resection factor that has been widely implicated in alternative end-joining (A-EJ) mediated chromosomal translocations in reporters. The ATM and ATR kinases phosphorylate CtIP at T859 (T855 in mouse) and other sites to promote DNA end-resection. Using two classical non-homologous end-joining (cNHEJ) and Tp53-double deficient mouse models, we identified a role of CtIP T855 phosphorylation in the neonatal development of Xrcc4-/-Tp53-/- mice and the IgH-Myc translocation driven lymphomagenesis in DNA-PKcs-/-Tp53-/- mice. Mechanistically, we found that CtIP T855 phosphorylation is important for the progression of DNA end-resection, while dispensable for hairpin opening and inter-sister DNA break ligation. Moreover, we found that CtIP-T855 phosphorylation supports the proliferation of Myc-driven lymphoma cells by promoting the transition from ATM-mediated to ATR-mediated G2/M cell cycle checkpoint. Correspondingly, the CtIP-T855A mutation delays splenomegaly in l-Myc mice. Collectively, our findings suggest that DNA damage-induced CtIP phosphorylation has a checkpoint function during lymphomagenesis independent of its role in A-EJ-mediated chromosomal translocation

ORGANISM(S): Mus musculus

PROVIDER: GSE174496 | GEO | 2021/12/31

REPOSITORIES: GEO

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CtIP-mediated DNA resection is dispensable for IgH class switch recombination by alternative end-joining

Project description:To generate antibodies with different effector functions, B cells undergo Immunoglobulin class switch recombination (CSR). The ligation step of CSR is usually mediated by the classical non-homologous end-joining (cNHEJ) pathway. In cNHEJ-deficient cells, a remarkable ~25% CSR can be achieved by the alternative end-joining (A-EJ) pathway that preferentially uses microhomology (MH) at the junctions. While A-EJ mediated repair of endonuclease generated breaks requires DNA end-resection, we show that CtIP-mediated DNA end-resection is dispensable for A-EJ-mediated CSR using cNHEJ-deficient B cells. High-throughput sequencing analyses revealed that loss of ATM/ATR phosphorylation of CtIP at T855 or ATM kinase inhibition suppress resection without altering the MH-pattern of the A-EJ-mediated switch junctions. Moreover, we found that ATM kinase promotes Alt-EJ mediated CSR by suppressing inter-chromosomal translocations independent of end-resection. Finally, temperol analyses reveal that MHs are enriched in early internal deletions even in cNHEJ-proficient B cells. Thus, we propose that repetitive IgH switch regions represent favoriate substrates for MH-mediated end-joining contributing to the robustness and resection-indepndence of A-EJ-mediated CSR.

2020-09-18 | GSE156392 | GEO

CtIP is essential for early B cell proliferation and development in mice

Project description:B cell development requires efficient proliferation and successful assembly and modifications of the immunoglobulin gene products. CtIP is an essential gene implicated in end-resection and DNA repair. Here we show that CtIP is essential for early B cell development, while dispensable in naïve B cells. CtIP loss is well-tolerated in G1 arrested B cells and during V(D)J recombination. But, in proliferating B cells, CtIP loss leads to a progressive cell death characterized by ATM hyper-activation, G2/M arrest, genomic instability, and 53BP1 nuclear body formation, indicating that the essential role of CtIP during proliferation underscores its stage-specific requirement in B cells. B cell proliferation requires phosphorylation of CtIP at T847 presumably by CDK, but not its interaction with CtBP, Rb, nor its nuclease activity. CtIP phosphorylation by ATM/ATR at T859 (T855 in mice) promotes end-resection in G1 arrested cells, but dispensable for B cell development and class switch recombination, suggesting distinct roles for T859 and T847 phosphorylation in B cell development.

2019-05-12 | GSE129850 | GEO

CTCF cooperates with CtIP to drive homologous recombination repair of double-strand breaks

Project description:The pleiotropic CCCTC-binding factor (CTCF) plays a role in homologous recombination (HR) repair of DNA double-strand breaks (DSBs). However, the precise mechanistic role of CTCF in HR remains largely unclear. Here, we show that CTCF engages in DNA end resection, which is the initial, crucial step in HR, through its interactions with MRE11 and CtIP. Depletion of CTCF profoundly impairs HR and attenuates CtIP recruitment at DSBs. CTCF physically interacts with MRE11 and CtIP and promotes CtIP recruitment to sites of DNA damage. Subsequently, CTCF facilitates DNA end resection to allow HR, in conjunction with MRE11-CtIP. Notably, the zinc finger domain of CTCF binds to both MRE11 and CtIP and enables proficient CtIP recruitment, DNA end resection, and HR. The N-terminus of CTCF is able to bind to only MRE11 and its C-terminus is incapable of binding to MRE11 and CtIP, thereby resulting in compromised CtIP recruitment, DSB resection, and HR. Overall, this suggests an important function of CTCF in DNA end resection through the recruitment of CtIP at DSBs. Collectively, our findings identify a critical role of CTCF at the first control point in selecting the HR repair pathway

2019-11-12 | PXD014441 | Pride

DNA-PKcs Suppresses Illegitimate Chromosome Rearrangements

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.

2023-12-30 | GSE249453 | GEO

DNA-PK Promotes DNA End Resection at DNA Double Strand Breaks in G0 cells [ChIP-Seq]

Project description:DNA double-strand break (DSB) repair by homologous recombination is confined to the S and G2 phases of the cell cycle partly due to 53BP1 antagonizing DNA end resection in G1 phase and non-cycling quiescent (G0) cells where DSBs must be repaired by non-homologous end joining (NHEJ). Unexpectedly, we uncovered extensive MRE11- and CtIP-dependent DNA end resection at DSBs in G0 mammalian cells. A whole genome CRISPR/Cas9 screen revealed the DNA-dependent kinase (DNA-PK) complex as a key factor in promoting DNA end resection in G0 cells. In agreement, depletion of FBXL12, which promotes ubiquitylation and removal of the KU70/KU80 subunits of DNA-PK from DSBs, promotes even more extensive resection in G0 cells. In contrast, a requirement for DNA-PK in promoting DNA end resection in cycling cells at the G1 or G2 phase cells was not observed. Our findings establish that DNA-PK uniquely promotes DNA end resection in G0, but not in G1 or G2 phase cells, and has important implications for DNA DSB repair in quiescent cells.

2022-05-16 | GSE186086 | GEO

DNA-PK Promotes DNA End Resection at DNA Double Strand Breaks in G0 cells [END-seq]

2022-05-16 | GSE186085 | GEO

ATM Inhibition Exploits Checkpoint Defects and ATM-Dependent Double Strand Break Repair in TP53-Mutant Glioblastoma

Project description:Determining the balance between DNA double strand break repair (DSBR) pathways is essential for understanding treatment response in cancer. We report a novel method for simultaneously measuring non-homologous end joining (NHEJ), homologous recombination (HR), and microhomology-mediated end joining (MMEJ). This approach revealed enhanced MMEJ and HR in glioblastoma (GBM) xenograft models with acquired temozolomide (TMZ) resistance. Knockdown of proteins in either pathway enhanced killing by TMZ, and a targeted screen identified pharmacological-grade dual HR/MMEJ inhibitors, including AZD1390, an ATM kinase inhibitor. AZD1390 suppressed DSB end resection, blocked phosphorylation of end protection proteins in response to DNA damage, and potentiated TMZ in treatment-naïve and treatment-resistant models. TP53-mutant GBMs were most susceptible to AZD1390 in combination with DNA-damaging agents due to elevated ATM-dependent HR/MMEJ, preferential activation of these pathways in response to DNA damage, and a defective G2/M checkpoint, which caused these GBMs to enter mitosis despite unrepaired DNA damage, leading to cell death via apoptosis. This report establishes ATM-dependent HR and MMEJ as targetable resistance mechanisms in TP53-mutant GBM and establishes an approach for simultaneously measuring multiple DSBR pathways in treatment selection and oncology research.

2024-03-08 | PXD047837 | Pride

CtIP-mediated DNA resection is dispensable for IgH class switch recombination by alternative end-joining

Project description:CtIP-mediated DNA resection is dispensable for IgH class switch recombination by alternative end-joining

| PRJNA657760 | ENA

Ku70 and Ligase IV deficiencies reveal distinct alternative end-joining outcomes in G1-arrested progenitor B cells

Project description:Classical nonhomologous end-joining (C-NHEJ) repairs DNA double-stranded breaks (DSBs) throughout interphase but is thought to predominate in G1-phase when homologous recombination is unavailable. Complexes containing the Ku70/80 ("Ku") and XRCC4/Ligase IV (Lig4) core C-NHEJ factors are required, respectively, for sensing and joining DSBs. While such factors are exclusively required for joining RAG1/2-initiated DSBs during V(D)J recombination in G1-phase lymphocyte progenitors, cycling cells deficient for core C-NHEJ factors join chromosomal DSBs by alternative end-joining (A-EJ) pathways. Restriction of V(D)J recombination to C-NHEJ has been attributed to RAG-mediated exclusion of A-EJ; however, it remains unclear whether A-EJ is similarly excluded from more general DSBs in G1. Here, we report that Ku actively and robustly suppresses A-EJ of RAG1/2 and two classes of engineered endonuclease-mediated DSBs in G1-arrested progenitor B cell lines. Thus, while targeted DSBs remain as free broken ends in Lig4-deficient G1-arrested progenitor B cells, deletion of Ku70 in Lig4-deficient cells restores DSB rejoining and translocation to levels observed in Ku70-deficient counterparts. Correspondingly, while V(D)J recombination is abrogated in Ligase4-deficient lines, V(D)J-like joining occurs in Ku70-deficient and Ku70/Lig4 double-deficient lines through a translocation-based A-EJ mechanism. We conclude that in G1, Lig4-deficient progenitor B cells are functionally end-joining deficient due to a near complete Ku-dependent block in A-EJ. Thus, the differential impacts of Ku deficiency versus XRCC4/Ligase IV deficiency on V(D)J recombination, severity of neuronal apoptosis, and embryonic development, including Ku-deficiency rescuing Lig4-deficient embryonic lethality, may be explained by Ku-mediated inhibition of A-EJ in the G1 cell cycle phase.

2021-05-08 | GSE162453 | GEO

The impact of DNA-PKcs in V(D)J recombination of mouse IgK antigen locus

Project description:DNA-PKcs is a critical component of the non-homologous end joining (NHEJ) pathway, playing a role in the re-ligation of DNA double-strand breaks (DSBs) generated by RAG1/2 during V(D)J recombination in antigen loci. When NHEJ is deficient, DSBs can be repaired through alternative end joining (A-EJ). In this study, we investigated the consequences of DNA-PKcs deletion on V-J recombination at the IgK antigen locus. Our results reveal that DNA-PKcs deletion leads to inefficient V-J recombination, exhibiting phenotypes such as reduced efficiency, increased end resection, and decreased micro-insertions in the repair pattern. These findings are consistent with previously reported functions of Ku70, another key player in NHEJ. However, unlike Ku70, additional deletion of DNA-PKcs does not restore the efficiency of repair in the absence of Lig4. Instead, it reduces both end resection and microhomology-mediated repair. These observations highlight the context-dependent role of DNA-PKcs in end processing. The presence or absence of Lig4 appears to influence the function of DNA-PKcs, further emphasizing the intricate interplay between repair factors in the DNA damage response. Overall, our findings provide insights into the distinct functions of DNA-PKcs and Ku70 in V(D)J recombination and underscore the complex regulatory mechanisms underlying repair efficiency in different genetic backgrounds.

2023-09-01 | GSE232924 | GEO

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