Nuclease-independent functions of RAG1 direct distinct DNA damage responses in B cells
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ABSTRACT:
SUBMITTER: Ms. Rachel Johnston
PROVIDER: S-SCDT-10_15252-EMBR_202255429 | biostudies-other |
REPOSITORIES: biostudies-other
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Project description:The RAG recombinase (RAG1/2) plays an essential role in adaptive immunity by mediating V(D)J recombination in developing lymphocytes. In contrast, aberrant RAG1/2 activity promotes lymphocyte malignancies by causing chromosomal translocations and DNA deletions at cancer genes. RAG1/2 can also induce genomic DNA insertions by transposition and trans-V(D)J recombination, but only few such putative events have been documented in vivo. We used next-generation sequencing techniques to examine chromosomal rearrangements in primary murine B cells and discovered that RAG1/2 causes aberrant insertions by releasing cleaved antibody gene fragments that subsequently reintegrate into DNA breaks induced on a heterologous chromosome. We confirmed that RAG1/2 also mobilizes genomic DNA into independent physiological breaks by identifying similar insertions in human lymphoma and leukemia. Our findings reveal a novel RAG1/2-mediated insertion pathway distinct from DNA transposition and trans-V(D)J recombination that destabilizes the genome and shares features with reported oncogenic DNA insertions.
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Project description:Defects in meiotic recombination in many organisms result in arrest because of activation of a meiotic checkpoint(s). The proximal defect that triggers this checkpoint in mammalian germ cells is not understood, but it has been suggested to involve either the presence of DNA damage in the form of unrepaired recombination intermediates or defects in homologous chromosome pairing and synapsis independent of DNA damage per se. To distinguish between these possibilities in the female germ line, we compared mouse oocyte development in a mutant that fails to form the double-strand breaks (DSBs) that initiate meiotic recombination (Spo11-/-) to mutants with defects in processing DSBs when they are formed (Dmc1-/- and Msh5-/-), and we examined the epistasis relationships between these mutations. Absence of DSB formation caused a partial defect in follicle formation, whereas defects in DSB repair caused earlier and more severe meiotic arrest, which could be suppressed by eliminating DSB formation. Therefore, our analysis reveals that there are both DNA-damage-dependent and -independent responses to recombination errors in mammalian oocytes. By using these findings as a paradigm, we also examined oocyte loss in mutants lacking the DNA-damage checkpoint kinase ATM. The absence of ATM caused defects in folliculogenesis that were similar to those in Dmc1 mutants and that could be suppressed by Spo11 mutation, implying that oocyte death in Atm-deficient animals is a response to defective DSB repair.
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Project description:In budding yeast four mitotic cyclins (Clb1-4) cooperate in a partially redundant manner to bring about M-phase specific events, including the apical isotropic switch that ends polarized bud growth initiated at bud emergence. How exactly this morphogenetic transition is regulated by mitotic CDKs remains poorly understood. We have taken advantage of the isotropic bud growth that prevails in cells responding to DNA damage to unravel the contribution of mitotic cyclins in this cellular context. We find that clb2?, in contrast to the other mitotic cyclin mutants, inappropriately respond to the presence of DNA damage. This aberrant response is characterized by a Cdc42- and Bni1-dependent but Cln-independent resumption of polarized bud growth after a brief period of actin depolarization. Biochemical and genetic evidence is presented that formally excludes the possibility of indirect effects due for instance to unrestrained APC activity, untimely mitotic exit or Swe1-mediated CDK inhibition. Importantly, our data demonstrate that in order to maintain the characteristic dumbbell arrest phenotype upon checkpoint activation Clb2 needs to be efficiently exported into the cytoplasm. We propose that the inhibition of mitotic cyclin destruction by the DNA damage checkpoint pathway leads to a buildup of Clb2 in the cytoplasm where this cyclin can stabilize the apical isotropic switch throughout a G 2/M checkpoint arrest. Our study also unveils an essential role of nuclear Clb2 in both survival and adaptation to the DNA damage checkpoint, illustrating a spatially distinct dual function of this mitotic cyclin in the response to DNA damage.
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Project description:The cellular response to DNA double-strand breaks involves direct activation of ataxia telangiectasia mutated (ATM) and indirect activation of ataxia telangiectasia and Rad3 related (ATR) in an ATM/Mre11/cell-cycle-dependent manner. Here, we report that the crucial checkpoint signalling proteins-p53, structural maintainance of chromosomes 1 (SMC1), p53 binding protein 1 (53BP1), checkpoint kinase (Chk)1 and Chk2-are phosphorylated rapidly by ATR in an ATM/Mre11/cell-cycle-independent manner, albeit at low levels. We observed the sequential recruitment of replication protein A (RPA) and ATR to the sites of DNA damage in ATM-deficient cells, which provides a mechanistic basis for the observed phosphorylations. The recruitment of ATR and consequent phosphorylations do not require Mre11 but are dependent on Exo1. We show that these low levels of phosphorylation are biologically important, as ATM-deficient cells enforce an early G2/M checkpoint that is ATR-dependent. ATR is also essential for the late G2 accumulation that is peculiar to irradiated ATM-deficient cells. Interestingly, phosphorylation of KRAB associated protein 1 (KAP-1), a protein involved in chromatin remodelling, is mediated by DNA-dependent protein kinase catalytic subunit (DNA-PKcs) in a spatio-temporal manner in addition to ATM. We posit that ATM substrates involved in cell-cycle checkpoint signalling can be minimally phosphorylated independently by ATR, while a small subset of proteins involved in chromatin remodelling are phosphorylated by DNA-PKcs in addition to ATM.
| S-EPMC2711839 | biostudies-literature
Project description:In response to cellular genome breaks, MRE11/RAD50/NBS1 (MRN) activates a global ATM DNA damage response (DDR) that prevents cellular replication. Here, we show that MRN-ATM also has critical functions in defending the cell against DNA viruses. We reveal temporally distinct responses to adenovirus genomes: a critical MRN-ATM DDR that must be inactivated by E1B-55K/E4-ORF3 viral oncoproteins and a global MRN-independent ATM DDR to viral nuclear domains that does not impact viral replication. We show that MRN binds to adenovirus genomes and activates a localized ATM response that specifically prevents viral DNA replication. In contrast to chromosomal breaks, ATM activation is not amplified by H2AX across megabases of chromatin to induce global signaling and replicative arrest. Thus, ?H2AX foci discriminate "self" and "non-self" genomes and determine whether a localized anti-viral or global ATM response is appropriate. This provides an elegant mechanism to neutralize viral genomes without jeopardizing cellular viability.
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Project description:The nucleolus contains multiple copies of ribosomal (r)DNA, which indicate sites of frequent replication stress and suggest the existence of a mechanism to prevent replication stress-related rDNA instability and the possibility that such a mechanism contributes to the whole genomic stability against replication stress. We have previously reported that nucleolin, a major nucleolar protein, is involved in ionizing radiation-induced DNA damage responses (DDRs) such as ataxia telangiectasia mutated (ATM)-dependent cell cycle checkpoints and homologous recombination (HR) repair. Here, we investigated the role of nucleolin in DDR due to replication stress. The results indicate that following replication stress, nucleolin interacted with the histone γH2AX, proliferating cell nuclear antigen (PCNA), and replication protein A (RPA)32, suggesting that it may be recruited to DNA damage sites on the replication fork. Furthermore, the knockdown of nucleolin by siRNA reduced the activation of ATM and RAD3-related (ATR) kinase and the formation of RAD51 and RPA32 foci after replication stress due to UV or camptothecin exposure, whereas nucleolin overexpression augmented ATR-dependent phosphorylation and RAD51 and RPA accumulation on chromatin. Moreover, these overexpressing cells seemed to increase repair activity and resistance to replication stress. Our results indicate that nucleolin plays an important role in replication stress-induced DDRs such as ATR activation and HR repair. Given that nucleolin overexpression is often observed in many types of cancer cells, our findings suggest that nucleolin is involved in the regulation of resistance to replication stress that may otherwise lead to tumorigenesis and it could be a possible target for chemotherapy and radiotherapy.
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Project description:BACKGROUND:Arsenic sulfide was found to have potential anti-cancer activities, especially in gastric cancer. However, the underlying mechanism need to be further explored. This study was aimed to investigate the mechanism of arsenic compounds on gastric cancer. METHODS:Gastric cancer cell lines were infected with lentiviral vector carrying shNFATc3 and/or treated with arsenic sulfide. MTT assay were performed to assess cell growth. Flow cytometer assays were used to detect cell cycle and reactive oxygen species (ROS) level of gastric cancer cells. Western blot was carried out to detect nuclear factor of activated T-cells, cytoplasmic 3 (NFATc3), cell cycle markers, DNA damage pathway protein expression as well as other protein expression in gastric cancer cell lines. The expression of recombination activating gene 1 (RAG1) in gastric cancer cell lines was determined by RNA-sequencing analyses and Real-Time qPCR. The effect of NFATc3 on RAG1 were determined by CHIP-qPCR assay. The effect of arsenic sulfide on AGS cells was evaluated in vivo. RESULTS:We show that arsenic sulfide as well as knockdown of NFATc3 resulted in increased double-strand DNA damage in gastric cancer cells by increasing the expression of RAG1, an endonuclease essential for immunoglobulin V(D) J recombination. Overexpression of NFATc3 blocked the expression of RAG1 expression and DNA damage induced by arsenic sulfide. Arsenic sulfide induced cellular oxidative stress to redistribute NFATc3, thereby inhibiting its transcriptional function, which can be reversed by N-acetyl-L-cysteine (NAC). We show that NFATc3 targets the promoter of RAG1 for transcriptional inhibition. We further showed that NFATc3 upregulation and RAG1 downregulation significantly associated with poor prognosis in patients with gastric cancer. Our in vivo experiments further confirmed that arsenic sulfide exerted cytotoxic activity against gastric cancer cells through inhibiting NFATc3 to activate RAG1 pathway. CONCLUSION:These results demonstrate that arsenic sulfide targets NFATc3 to induce double strand DNA break (DSB) for cell killing through activating RAG1 expression. Our results link arsenic compound to the regulation of DNA damage control and RAG1 expression as a mechanism for its cytotoxic effect.
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Project description:The molecular basis for p53-mediated tumor suppression remains unclear. Here, to elucidate mechanisms of p53 tumor suppression, we use knockin mice expressing an allelic series of p53 transcriptional activation mutants. Microarray analysis reveals that one mutant, p53(25,26), is severely compromised for transactivation of most p53 target genes, and, moreover, p53(25,26) cannot induce G(1)-arrest or apoptosis in response to acute DNA damage. Surprisingly, p53(25,26) retains robust activity in senescence and tumor suppression, indicating that efficient transactivation of the majority of known p53 targets is dispensable for these pathways. In contrast, the transactivation-dead p53(25,26,53,54) mutant cannot induce senescence or inhibit tumorigenesis, like p53 nullizygosity. Thus, p53 transactivation is essential for tumor suppression but, intriguingly, in association with a small set of novel p53 target genes. Together, our studies distinguish the p53 transcriptional programs involved in acute DNA-damage responses and tumor suppression-a critical goal for designing therapeutics that block p53-dependent side effects of chemotherapy without compromising p53 tumor suppression.
| S-EPMC3259909 | biostudies-literature
Project description:p53 is critical in regulating the differentiation of ES and induced pluripotent stem (iPS) cells. Here, we report a whole-genome study of p53-mediated DNA damage signaling in mouse ES cells. Systems analyses reveal that binding of p53 at the promoter region significantly correlates with gene activation but not with repression. Unexpectedly, we identify a regulatory mode for p53-mediated repression through interfering with distal enhancer activity. Importantly, many ES cell-enriched core transcription factors are p53-repressed genes. Further analyses demonstrate that p53-repressed genes are functionally associated with ES/iPS cell status while p53-activated genes are linked to differentiation. p53-activated genes and -repressed genes also display distinguishable features of expression levels and epigenetic markers. Upon DNA damage, p53 regulates the self-renewal and pluripotency of ES cells. Together, these results support a model where, in response to DNA damage, p53 affects the status of ES cells through activating differentiation-associated genes and repressing ES cell-enriched genes.
| S-EPMC3327774 | biostudies-literature
Project description:Cells have evolved a robust and highly regulated DNA damage response to preserve their genomic integrity. Although increasing evidence highlights the relevance of RNA regulation, our understanding of its impact on a fully efficient DNA damage response remains limited. Here, through a targeted CRISPR-knockout screen, we identify RNA binding proteins and modifiers that participate in the p53 response. Among the top hits, we find the m6A reader YTHDC1 as a master regulator of p53 expression. YTHDC1 binds to the transcription start sites of TP53 and other genes involved in the DNA damage response, promoting their transcriptional elongation. YTHDC1 deficiency also causes the retention of introns and therefore aberrant protein production of key DNA damage factors. While YTHDC1-mediated intron retention requires m6A, TP53 transcriptional pause-release is promoted by YTHDC1 independently of m6A. Depletion of YTHDC1 causes genomic instability and aberrant cancer cell proliferation mediated by genes regulated by YTHDC1. Our results uncover YTHDC1 as an orchestrator of the DNA damage response through distinct mechanisms of co-transcriptional mRNA regulation.
| S-SCDT-10_1038-S44318-024-00153-X | biostudies-other