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Gene expression analysis of B cell lymphomas from representative IµHABcl6, IµHABcl6 Ung-/- Msh2-/-, and IµHABcl6 Msh2-/- mouse models.

ABSTRACT: Somatic hypermutation (SHM) and class switch recombination (CSR) of immunoglobulin (Ig) genes are genomic modification events that occur in germinal center (GC) B cells and are initiated through deamination of cytidine to uracil by activation induced cytidine deaminase (AID). Resulting uracil-guanine (U-G) mismatches are subsequently processed by low-fidelity base-excision (BER) and mismatch repair (MMR) pathways to yield mutations and DNA strand lesions. Although off-target AID activity also contributes to oncogenic point mutations and chromosome translocations associated with B cell lymphomas, the role of downstream AID-associated DNA repair pathways in the pathogenesis of these lymphomas is unknown. Here, we show that simultaneous BER and MMR deficiency causes genomic instability and a shorter latency to the development of a BCL6-driven GC B cell lymphoma. In contrast, loss of BER alone is highly protective against B cell transformation while loss of MMR fosters the development of a variety of malignancies. These findings lend insight into a complex interplay between AID-associated BER and MMR pathways that produces a net protective effect against GC B cell lymphomagenesis.

ORGANISM(S): Mus musculus

PROVIDER: GSE48304 | GEO | 2015/12/08

SECONDARY ACCESSION(S): PRJNA209628

REPOSITORIES: GEO

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Gene expression analysis of B cell lymphomas from representative IÂµHABcl6, IÂµHABcl6 Ung-/- Msh2-/-, and IÂµHABcl6 Msh2-/- mouse models.

Project description:Somatic hypermutation (SHM) and class switch recombination (CSR) of immunoglobulin (Ig) genes are genomic modification events that occur in germinal center (GC) B cells and are initiated through deamination of cytidine to uracil by activation induced cytidine deaminase (AID). Resulting uracil-guanine (U-G) mismatches are subsequently processed by low-fidelity base-excision (BER) and mismatch repair (MMR) pathways to yield mutations and DNA strand lesions. Although off-target AID activity also contributes to oncogenic point mutations and chromosome translocations associated with B cell lymphomas, the role of downstream AID-associated DNA repair pathways in the pathogenesis of these lymphomas is unknown. Here, we show that simultaneous BER and MMR deficiency causes genomic instability and a shorter latency to the development of a BCL6-driven GC B cell lymphoma. In contrast, loss of BER alone is highly protective against B cell transformation while loss of MMR fosters the development of a variety of malignancies. These findings lend insight into a complex interplay between AID-associated BER and MMR pathways that produces a net protective effect against GC B cell lymphomagenesis. Representative B cell lymphomas from 3 IÂµHABcl6, 6 IÂµHABcl6 Ung-/- Msh2-/-, and 5 IÂµHABcl6 Msh2-/- mice were analyzed in this study. Total RNA was extracted from frozen tumor cells and processed according to Illumina standard protocols.

2015-12-08 | E-GEOD-48304 | biostudies-arrayexpress

A broad atlas of somatic hypermutation allows prediction of activation-induced deaminase targets.

Project description:Activation Induced Deaminase (AID) initiates somatic hypermutation (SHM) and class switch recombination (CSR) in germinal center (GC) B cells through the deamination of deoxycytidine residues (dC) into deoxyuridines (dU) in immunoglobulin (Ig) genes. Although AID has a strong preference for Ig genes, it can also target other genomic regions, giving rise to mutations or chromosomal translocations. Thus, understanding the specificity of AID has major implications for oncogenic transformation. However, approaching AID specificity has proved extremely challenging because AID deamination events occur at low frequencies. Here we have sequenced at very high depth >1500 genomic regions from GC B cells and identified 275 genes targeted by AID, including 30 of the previously known 35 AID targets. This has enabled for the first time to define the molecular features predictive of AID target specificity genome-wide. Furthermore, we identify the most highly mutated hotspot for AID activity described to date. We also find that Base Excision Repair (BER) and Mismatch Repair (MMR) systems, which are responsible for the resolution of AID deaminations, back-up each other to faithfully repair AID-induced lesions. Finally, our data establishes a novel link between AID mutagenic activity and malignant transformation.

2018-01-19 | GSE102944 | GEO

Gene expression analysis of B-NHL from λMYC, λMYC/IµHABCL6, λMYC/AIDKO and λMYC/IµHABCL6/AIDKO mouse models

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

Gene expression profile for BL2 and BL2 AID-/- cell lines

Project description:AID (activation-induced cytidine deaminase) is expressed at low levels in many tissue types but is most highly expressed in germinal center B cells where it deaminates cytidine to uracil during somatic hypermutation and class switch recombination of the immunoglobulin genes. In addition to this critical role in immune diversification, aberrant targeting of AID contributes to oncogenic point mutations and chromosome translocations associated with B cell malignancies. Thus, to explore a role for AID in DNA demethylation in B cell lymphoma, we performed genome-wide gene expression profiling in BL2 and AID-deficient (AID-/-) BL2 cell lines (Burkitt lymphoma that can be induced to express high levels of AID).

2016-10-01 | GSE85964 | GEO

DNA methylation profile for BL2 and BL2 AID-/- cell lines

Project description:AID (activation-induced cytidine deaminase) is expressed at low levels in many tissue types but is most highly expressed in germinal center B cells where it deaminates cytidine to uracil during somatic hypermutation and class switch recombination of the immunoglobulin genes. In addition to this critical role in immune diversification, aberrant targeting of AID contributes to oncogenic point mutations and chromosome translocations associated with B cell malignancies. Thus, to explore a role for AID in DNA demethylation in B cell lymphoma, we performed genome-wide methylation profiling in BL2 and AID-deficient (AID-/-) BL2 cell lines (Burkitt lymphoma that can be induced to express high levels of AID).

2016-11-01 | GSE81215 | GEO

Loss of Caenorhabditis elegans UNG-1 uracil-DNA glycosylase affects apoptosis in response to DNA damaging agents.

Project description:The nematode Caenorhabditis elegans has been used extensively to study responses to DNA damage. In contrast, little is known about DNA repair in this organism. C. elegans is unusual in that it encodes few DNA glycosylases and the uracil-DNA glycosylase (UDG) encoded by the ung-1 gene is the only known UDG. C. elegans could therefore become a valuable model organism for studies of the genetic interaction networks involving base excision repair (BER). As a first step towards characterization of BER in C. elegans, we show that the UNG-1 protein is an active uracil-DNA glycosylase. We demonstrate that an ung-1 mutant has reduced ability to repair uracil-containing DNA but that an alternative Ugi-inhibited activity is present in ung-1 nuclear extracts. Finally, we demonstrate that ung-1 mutants show altered levels of apoptotic cell corpses formed in response to DNA damaging agents. Increased apoptosis in the ung-1 mutant in response to ionizing radiation (IR) suggests that UNG-1 contributes to repair of IR-induced DNA base damage in vivo. Following treatment with paraquat however, the apoptotic corpse-formation was reduced. Gene expression profiling suggests that this phenotype is a consequence of compensatory transcriptomic shifts that modulate oxidative stress responses in the mutant and not an effect of reduced DNA damage signaling.

2010-05-26 | GSE21467 | GEO

Loss of Caenorhabditis elegans UNG-1 uracil-DNA glycosylase affects apoptosis in response to DNA damaging agents.

2010-06-08 | E-GEOD-21467 | biostudies-arrayexpress

Expression data from control and Mbd4 KO CH12 cells that were activated with CIT for 24 hours.

Project description:AID-dependent U/G mismatches in S DNA are converted by BER and MMR DNA pathways into double-stranded breaks that are required for optimal CSR in activated B cells. Deficits in MMR proteins, MSH2, MLH1, and PMS2 result in lower CSR frequencies that are coupled with impaired DSB formation. MBD4 interacts with MLH1 and has been postulated to coordinate mismatch repair of U/G. Deletions of Mbd4 targeting the 5' end of the gene in mice do not affect CSR . However, Mbd4 transcription is complex, with the propensity to create alternative transcripts, including residual transcription leading to to truncated protein expression that complicates ananlysis in these mice. We describe a novel function of MBD4 housed in the C-terminus that is critical for DSB formation, which shares several characteristics with MMR . We conclude that the 3' end of the Mbd4 gene positively contributes to CSR and likely intersects the MMR pathway. 2 independent samples for each control and Mbd4 KO group

2013-12-19 | E-GEOD-51559 | biostudies-arrayexpress

UNG shapes the specifity of AID-induced somatic hypermutation in B cells

Project description:Secondary diversification of antibodies through somatic hypermutation (SHM) and class switch recombination (CSR) is a critical component of the immune response. Activation-induced deaminase (AID) initiates both processes by deaminating cytosine residues in immunoglobulin genes. The resulting U:G mismatch can be processed by alternative pathways to give rise to a mutation (SHM) or a DNA double-strand break (CSR). Central to this processing is the activity of uracil-N-glycosylase (UNG), an enzyme normally involved in error-free base excision repair. We used next generation sequencing to analyze the contribution of UNG to the resolution of AID-induced lesions. Loss- and gain-of-function experiments showed that UNG activity can promote both error-prone and high fidelity repair of U:G lesions. Unexpectedly, the balance between these alternative outcomes was influenced by the sequence context of the deaminated cytosine, with individual hotspots exhibiting higher susceptibility to UNG-triggered error-free or error-prone resolution. These results reveal UNG as a new molecular layer that shapes the specificity of AID-induced mutations and may provide new insights into the role of AID in cancer development. Next Generation Sequencing analysis of mutations introduced by AID in activated B lymphocytes from WT and UNG-/- mice (n=4). Activated B cells from AID-/- mice (n=2) were used as negative controls.

2012-07-04 | E-GEOD-39114 | biostudies-arrayexpress

UNG shapes the specifity of AID-induced somatic hypermutation in B cells

2012-07-05 | GSE39114 | GEO

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