A defect in G-quadruplex binding disrupts AID chromatin localization
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ABSTRACT:
ORGANISM(S): Mus musculus
PROVIDER: GSE136959 | GEO | 2020/10/14
REPOSITORIES: GEO
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Project description:The activation induced cytosine deaminase (AID) mediates diversification of B cell immunoglobulin genes by the three distinct yet related processes of somatic hypermutation (SHM), class switch recombination (CSR), and gene conversion (GCV). SHM occurs in germinal center B cells, and the transcription factor Bcl6 is a key regulator of the germinal center B cell gene expression program, including expression of AID. To test the hypothesis that Bcl6 function is important for the process of SHM, we compared WT chicken DT40 B cells, which constitutively perform SHM/GCV, to their Bcl6-deficient counterparts. We found that Bcl6-deficient DT40 cells were unable to perform SHM and GCV despite enforced high level expression of AID and substantial levels of AID in the nucleus of the cells. To gain mechanistic insight into the GCV/SHM dependency on Bcl6, transcriptional features of a highly expressed SHM target gene were analyzed in Bcl6-sufficient and -deficient DT40 cells. No defect was observed in the accumulation of single stranded DNA in the target gene as a result of Bcl6 deficiency. In contrast, association of Spt5, an RNA polymerase II (Pol II) and AID binding factor, was strongly reduced at the target gene body relative to the transcription start site in Bcl6-deficient cells as compared to WT cells. However, partial reconstitution of Bcl6 function substantially reconstituted Spt5 association with the target gene body but did not restore detectable SHM. Our observations suggest that in the absence of Bcl6, Spt5 fails to associate efficiently with Pol II at SHM targets, perhaps precluding robust AID action on the SHM target DNA. Our data also suggest, however, that Spt5 binding is not sufficient for SHM of a target gene even in DT40 cells with strong expression of AID. Sequencing of the IgL V region and mutationally active GFP transgene in WT, Bcl6-/- Pax5R, and Bcl6-/- Pax5R Bcl6R chicken DT40 cells for evidence of AID dependent mutations. ChIP-seq proiles of RNA Pol II, Spt5, and pSer5 Pol II at a GFP transgene in WT, Bcl6-/- Pax5R, and Bcl6-/- Pax5R Bcl6R chicken DT40 cells.
2016-02-21 | E-GEOD-77141 | biostudies-arrayexpress
Project description:The activation induced cytosine deaminase (AID) mediates diversification of B cell immunoglobulin genes by the three distinct yet related processes of somatic hypermutation (SHM), class switch recombination (CSR), and gene conversion (GCV). SHM occurs in germinal center B cells, and the transcription factor Bcl6 is a key regulator of the germinal center B cell gene expression program, including expression of AID. To test the hypothesis that Bcl6 function is important for the process of SHM, we compared WT chicken DT40 B cells, which constitutively perform SHM/GCV, to their Bcl6-deficient counterparts. We found that Bcl6-deficient DT40 cells were unable to perform SHM and GCV despite enforced high level expression of AID and substantial levels of AID in the nucleus of the cells. To gain mechanistic insight into the GCV/SHM dependency on Bcl6, transcriptional features of a highly expressed SHM target gene were analyzed in Bcl6-sufficient and -deficient DT40 cells. No defect was observed in the accumulation of single stranded DNA in the target gene as a result of Bcl6 deficiency. In contrast, association of Spt5, an RNA polymerase II (Pol II) and AID binding factor, was strongly reduced at the target gene body relative to the transcription start site in Bcl6-deficient cells as compared to WT cells. However, partial reconstitution of Bcl6 function substantially reconstituted Spt5 association with the target gene body but did not restore detectable SHM. Our observations suggest that in the absence of Bcl6, Spt5 fails to associate efficiently with Pol II at SHM targets, perhaps precluding robust AID action on the SHM target DNA. Our data also suggest, however, that Spt5 binding is not sufficient for SHM of a target gene even in DT40 cells with strong expression of AID.
2016-02-21 | GSE77141 | GEO
Project description:After immunization or infection, activation-induced cytidine deaminase (AID) initiates diversification of immunoglobulin (Ig) genes in B cells, introducing mutations within the antigen binding V regions (somatic hypermutation, SHM) and double-strand DNA breaks (DSBs) into switch (S) regions, leading to antibody class switch recombination (CSR). Using a candidate approach, AID has been shown to initiate mutations at numerous non-Ig genes in B cells in Peyer’s patches. However, it is not known if during B cell activation, AID also induces DNA breaks at genes other than IgH genes, which would lead to genomic instability and malignancy. Using a non-biased genome-wide approach, we have identified hundreds of reproducible AID-dependent DSBs in mouse splenic B cells shortly after induction of CSR in culture. Most interestingly, AID induces DSBs at sites syntenic with sites of translocations, deletions, and amplifications found in human B cell lymphomas, including within the oncogene B cell lymphoma11a (bcl11a)/evi9. The AID-dependent DSBs are not restricted to transcribed regions, and they frequently occur within repeated sequence elements, including CA and non-CA repeats, and SINEs. Comparison of Nbs1 binding sites in wild-type vs. aid-/- splenic B cells induced to undergo CSR; aid-dependent Nbs1 sites correlated with gene transcription (RNA Pol2).
2011-01-21 | E-GEOD-24827 | biostudies-arrayexpress
Project description:Most human B cell lymphomas (B-NHL) are derived from germinal centers (GCs), the structure where B-cells undergo class switch recombination (CSR) and somatic hypermutation (SHM) and are selected for high-affinity antibody production. The pathogenesis of B-NHL is associated with distinct genetic lesions, including chromosomal translocations and aberrant somatic hypermutation, which appear to arise from mistakes occurring during CSR and SHM. To ascertain the role of CSR and SHM in lymphomagenesis, we crossed three oncogene-driven (MYC, BCL6, MYC/BCL6) mouse models of B cell lymphoma with mice lacking activation-induced cytidine deaminase (AID), the enzyme required for both processes. We show that AID deficiency prevents BCL6-dependent, GC-derived B-NHL, while it has no impact on the formation of MYC-driven, pre-GC lymphomas. Accordingly, abrogation of AID is associated with the disappearance of both CSR- and SHM-mediated structural alterations, including cMYC-IgH chromosomal translocations and aberrant SHM. These results demonstrate that AID is required for GC-derived lymphomagenesis, providing direct support to the notion that errors in AID-mediated antigen-receptor gene modification events represent major contributors to the pathogenesis of human B-NHL. Keywords: Phenotypic characterization of tumors developing in oncogene-driven mouse models of lymphomas
2007-11-01 | GSE9249 | GEO
Project description:Activation-induced cytidine deaminase (AID) initiates both somatic hypermutation (SHM) for antibody affinity maturation and DNA breakage for antibody class switch recombination (CSR) via transcription-dependent cytidine deamination of single stranded DNA targets. While largely specific for immunglobulin genes, AID also acts on a limited set of off-targets, generating oncogenic translocations and mutations that contribute to B cell lymphoma. How AID is recruited to off-targets has been a long-standing mystery. Based on deep GRO-Seq studies of mouse and human B lineage cells activated for CSR or SHM, we report that most robust AID off-target translocations occur within highly focal regions of target genes in which sense and antisense transcription converge. Moreover, we found that such AID-targeting "convergent" transcription arises from antisense transcription that emanates from Super-Enhancers within sense transcribed gene bodies. Our findings provide a mechanistic explanation for AID off-targeting to a small subset of mostly lineage-specific genes in activated B cells. We performed GRO-Seq and H3K27Ac ChIP-Seq with different B lineage cell types and MEF cells to find the signatures associated with AID targeting.
2014-12-04 | E-GEOD-62296 | biostudies-arrayexpress
Project description:Class switch recombination (CSR) and somatic hypermutation (SHM) are antibody gene diversification reactions occurring in mature B cells that are essential for protective humoral immunity. CSR and SHM are initiated following activation by the antigen, and are dependent on efficient induction of activation-induced cytidine deaminase (AID). Therefore, mature B cell viability and fitness are crucial to mount effective immune responses. Here, we identified PDGFA-associated protein 1 (Pdap1) as an essential regulator of cellular homeostasis in mature B cells. Pdap1 deficiency leads to sustained expression of the integrated stress response (ISR) effector activating transcription factor 4 (Atf4) and induction of the ISR transcriptional program, increased cell death, and defective AID expression. As a consequence, loss of Pdap1 reduces germinal center B cell formation and impairs CSR and SHM. Thus, Pdap1 protects mature B cells against chronic ISR activation, and ensures efficient antibody diversification by promoting their survival and optimal function.
2020-06-19 | GSE141876 | GEO
Project description:During germinal center (GC) reactions, activated B cells undergo clonal expansion and functional maturation to produce high-affinity antibodies, and differentiate into plasma and memory cells, accompanied with class-switching recombination (CSR) and somatic hypermutation (SHM). Activation-induced deaminase (AID) is responsible for both CSR and SHM in GC B cells. Transcriptional mechanisms underlying AID regulation and GC B cell reactions are still not well understood. Here, we show that expression of Ascl2 transcription factor is upregulated in GC B cells. Ectopic expression of Ascl2 promotes GC B cell development and enhances antibody production as well as affinity maturation. Conversely, deletion of Ascl2 in B cells impairs the germinal center response. Genome-wide analysis reveals that Ascl2 directly regulates GC B cell-related genes, including AID; ectopic expression of AID in Ascl2-deficient B cells rescues their antibody defects. Thus, Ascl2 regulates AID transcription and promotes germinal center B cell responses.
2021-03-30 | GSE169416 | GEO
Project description:Activation-induced cytidine deaminase (AID) initiates both somatic hypermutation (SHM) for antibody affinity maturation and DNA breakage for antibody class switch recombination (CSR) via transcription-dependent cytidine deamination of single stranded DNA targets. While largely specific for immunglobulin genes, AID also acts on a limited set of off-targets, generating oncogenic translocations and mutations that contribute to B cell lymphoma. How AID is recruited to off-targets has been a long-standing mystery. Based on deep GRO-Seq studies of mouse and human B lineage cells activated for CSR or SHM, we report that most robust AID off-target translocations occur within highly focal regions of target genes in which sense and antisense transcription converge. Moreover, we found that such AID-targeting "convergent" transcription arises from antisense transcription that emanates from Super-Enhancers within sense transcribed gene bodies. Our findings provide a mechanistic explanation for AID off-targeting to a small subset of mostly lineage-specific genes in activated B cells.
2014-12-04 | GSE62296 | GEO
Project description:Activation-induced cytidine deaminase (AID) is essential for class switch recombination (CSR) and somatic hypermutation (SHM). Its deregulated expression acts as a genomic mutator that can contribute to the development of various malignancies. During treatment with imatinib mesylate (IM), patients with chronic myeloid leukemia (CML) often develop hypogammaglobulinemia, the mechanism of which has not yet been clarified. Here, we provide evidence that CSR upon B cell activation is apparently inhibited by IM through downregulation of AID. Furthermore, expression of E2A, a key transcription factor for AID induction, was markedly suppressed by IM. These results elucidate not only the underlying mechanism of IM-induced hypogammaglobulinemia but also its potential efficacy as an AID suppressor.
2012-02-08 | GSE35559 | GEO
Project description:Activation-induced cytidine deaminase (AID) is essential for class switch recombination (CSR) and somatic hypermutation (SHM). Its deregulated expression acts as a genomic mutator that can contribute to the development of various malignancies. During treatment with imatinib mesylate (IM), patients with chronic myeloid leukemia (CML) often develop hypogammaglobulinemia, the mechanism of which has not yet been clarified. Here, we provide evidence that CSR upon B cell activation is apparently inhibited by IM through downregulation of AID. Furthermore, expression of E2A, a key transcription factor for AID induction, was markedly suppressed by IM. These results elucidate not only the underlying mechanism of IM-induced hypogammaglobulinemia but also its potential efficacy as an AID suppressor. We investigated that class switch recombination(CSR) upon B cell activation is apparently inhibited by imatinib mesylate(IM) through downregulation of activation-induced cytidine deaminase(AID). Furthermore, expression of E2A was markedly suppressed by IM. To elucidate the more detailed pathway, we performed the microarray analysis. Microarray analysis was performed on splenocytes cultured for 72 h in the presence or absence of 10 µM Imatinib. The mouse splenocytes were cultured for 72 h with or without 10 µM Imatinib (IM) in conditioning medium containing IL-4 and LPS. RNA from 1X10^6 splenocytes used for microarray analysis was isolated using the RNeasy Mini Kit (50) (Qiagen, Hilden, Germany). Gene expression microarray analysis was performed using one-color microarray-based gene-expression analysis (Agilent Technologies, Santa Clara, CA, USA) according to the manufacturer’s instructions. After scanning, expression values for the genes were determined using GeneSpringGX software.
2012-02-08 | E-GEOD-35559 | biostudies-arrayexpress