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Cooperative transcriptional repression by BCL6 and BACH2 in germinal center B-cell differentiation

ABSTRACT: The transcriptional repressors BCL6 and BACH2 are crucial regulators of germinal center (GC) B-cell fate, and are known to interact and repress transcription of PRDM1, a key driver of plasma cell differentiation. How these factors cooperate is not fully understood. Herein we show that while GC formation is only minimally impaired in Bcl6+/- or Bach2+/- mice, double heterozygous Bcl6+/-Bach2+/- mice exhibit profound reduction in GC formation. Splenic B-cells from Bcl6+/- Bach2+/- mice display accelerated plasmacytic differentiation and high expression of key plasma cell genes such as Prdm1, Xbp1 and CD138. ChIP-seq revealed that in B-cells BACH2 is mostly bound to genes together with its heterodimer partner MAFK. The BACH2-MAFK complex binds to sets of genes known to be involved in the GC response, 60% of which are also targets of BCL6. Approximately 30% of BACH2 peaks overlap with BCL6 including cis-regulatory sequences of the PRDM1 gene. BCL6 also modulates BACH2 protein stability and their protein levels are positively correlated in GC B-cells. Therefore, BCL6 and BACH2 cooperate to orchestrate gene expression patterning in GC B cells through both transcriptional and biochemical mechanisms, which collectively determine the proper initiation and timing of terminal differentiation. ChIP-seq using P18 antibodies in OCI-Ly7 cells

ORGANISM(S): Homo sapiens

SUBMITTER: Huimin Geng

PROVIDER: E-GEOD-47784 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Cooperative transcriptional repression by BCL6 and BACH2 in germinal center B-cell differentiation

Project description:The transcriptional repressors BCL6 and BACH2 are crucial regulators of germinal center (GC) B-cell fate, and are known to interact and repress transcription of PRDM1, a key driver of plasma cell differentiation. How these factors cooperate is not fully understood. Herein we show that while GC formation is only minimally impaired in Bcl6+/- or Bach2+/- mice, double heterozygous Bcl6+/-Bach2+/- mice exhibit profound reduction in GC formation. Splenic B-cells from Bcl6+/- Bach2+/- mice display accelerated plasmacytic differentiation and high expression of key plasma cell genes such as Prdm1, Xbp1 and CD138. ChIP-seq revealed that in B-cells BACH2 is mostly bound to genes together with its heterodimer partner MAFK. The BACH2-MAFK complex binds to sets of genes known to be involved in the GC response, 60% of which are also targets of BCL6. Approximately 30% of BACH2 peaks overlap with BCL6 including cis-regulatory sequences of the PRDM1 gene. BCL6 also modulates BACH2 protein stability and their protein levels are positively correlated in GC B-cells. Therefore, BCL6 and BACH2 cooperate to orchestrate gene expression patterning in GC B cells through both transcriptional and biochemical mechanisms, which collectively determine the proper initiation and timing of terminal differentiation.

2013-11-17 | GSE47784 | GEO

BACH2 mediates negative selection and p53-dependent tumor suppression at the pre-B cell receptor checkpoint.

Project description:The B cell-specific BACH2 transcription factor is required for affinity maturation of mature B cells. Here, we show that Bach2 mediates negative selection at the pre-B cell receptor checkpoint and functions as a critical safeguard against leukemogenesis. Bach2-mediated activation of p53 is required for stringent elimination of pre-B cells that failed to productively rearrange immunoglobulin VH-DJH gene segments, and thus lack pre-B cell receptor expression. Upon productive VH-DJH gene rearrangement, pre-B cell receptor signaling ends negative selection through BCL6-mediated repression of p53. In patients with pre-B acute lymphoblastic leukemia, Bach2-mediated checkpoint control is frequently compromised and low levels of Bach2 expression represent a strong independent predictor of poor clinical outcome. Bach2+/+ pre-B cells resist leukemic transformation by Myc through Bach2-dependent upregulation of p53. Upon transformation with Myc, Bach2-/- pre-B cells fail to upregulate p53, form large colonies and initiate fatal leukemia in transplant recipient mice. ChIP-seq and gene expression analyses revealed that BACH2 competes with BCL6 for promoter binding and reverses BCL6-mediated repression of p53 and multiple other checkpoint control genes. These findings identify Bach2 as a key activator of p53 in pre-B cells, which is critical to maintain stringency of the pre-B cell receptor checkpoint and an important barrier against leukemic transformation. ChIP-seq using BACH2 and BCL6 antibodies in OCI-Ly7 cells

2013-06-27 | E-GEOD-44420 | biostudies-arrayexpress

A biochemical basis for toggling enhancers from the active to poised state in B cells

Project description:BCL6 is crucial for B-cell activation and lymphomagenesis. We used integrative genomics to explore BCL6 mechanism in normal and malignant B-cells. Surprisingly, BCL6 assembled distinct complexes at enhancers vs. promoters. At enhancers BCL6 preferentially recruited SMRT, which mediated H3K27 deacetylation through HDAC3, antagonized p300 activity and repressed transcription, but without decommissioning enhancers. This provides a biochemical basis for toggling enhancers from the active to poised state. Virtually all SMRT was bound with BCL6 suggesting that in B-cells BCL6 uniquely sequesters SMRT from other factors. In promoters BCL6 preferentially recruited BCOR, but most potently repressed promoters where it formed a distinctive ternary complex with SMRT and BCOR. Promoter repression was associated with decreased H3K36me3, H3K79me2 and Pol II elongation, linking BCL6 to transcriptional pausing. We identified the binding patterns of BCL6, SMRT, NCOR and BCOR corepressors in normal germinal center B cells and a DLBCL cell line (OCI-Ly1) using ChIP-seq. Additionally we treated lymphoma cells with siRNA against BCL6 and a non-targeted siRNA (NT control) and performed RNA-seq to identify the genes bound and repressed by BCL6. RNA-seq experiments were performed at 24h and 48h after siRNA treatments. Additional biological triplicate RNA-seq experiments were performed at 48h after BCL6 knockdown. Furthermore, a series of histone mark ChIP-seq and RNA polymerase ChIP-seq (total, Ser5-P and Ser2-P) were preformed to capture the chromatin states associated with the formation of BCL6 corepressor complexes.

2013-08-05 | E-GEOD-29282 | biostudies-arrayexpress

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Effect of Bach2 overexpression in BCL6+/+ and -/- BCR-ABL1 transformed pre-B cells

Project description:The aim was to investigate how BCL6 genotype affects Bach2 dependent gene expression changes. We compared gene expression profiles of BCL6+/+ and BCL6-/- BCR-ABL1 transformed pre-B cells after inducible overexpression of Bach2.

2013-07-11 | E-GEOD-41042 | biostudies-arrayexpress

EZH2 and BCL6 cooperate to assemble CBX8-BCOR Polycomb complex to repress bivalent promoters, mediate germinal center formation and promote lymphomagenesis [ChIP-seq]

Project description:The EZH2 histone methyltransferase mediates the humoral immune response and drives lymphomagenesis through de novo formation of bivalent chromatin domains at critical germinal center (GC) B cell promoters. Herein we show that the actions EZH2 in driving GC formation and lymphoma precursor lesions are dependent on the presence of the BCL6 transcriptional repressor, both of which are in turn dependent on the presence of non-canonical PRC1-BCOR complex. BCL6-BCOR complexes assemble preferentially at bivalent promoters in an H3K27me3-dependent manner. We observe specific induction of the CBX8 chromodomain protein in GC B cells. CBX8 binds to H3K27me3 at bivalent promoters and is required for stable association of BCOR complex and its histone modifications. CBX8 loss of function in B cells phenocopies loss of EZH2 and H3K27me3. Moreover, oncogenic BCL6 and EZH2 cooperate to accelerate diffuse large B cell lymphoma (DLBCL) development and combinatorial targeting of these repressors results in enhanced anti-lymphoma activity in vitro, in vivo and in primary human DLBCLs. KDM2B ChIP-sequencing of OCI-Ly1 cells

2016-07-20 | E-GEOD-81623 | biostudies-arrayexpress

EZH2 and BCL6 cooperate to assemble CBX8-BCOR Polycomb complex to repress bivalent promoters, mediate germinal center formation and promote lymphomagenesis [RNA-seq]

Project description:EZH2 mediates the humoral immune response and drives lymphomagenesis through de novo formation of bivalent chromatin domains and critical germinal center (GC) B cell promoters. We show that such formation is dependent on the presense of BCL6 and the presence of non-canonical PRC1-BCOR complex. We observe that BCL6 and EZH2 cooperate to accelerate diffuse large B cell lymphoma (DLBCL) development and combinatorial targeting of these repressors results in enhanced anti-lymphoma activity in vitro, in vivo, and in primary human DLBCLs. DLBCL cell lines treated with BCL6 inhibitor 79-6.1085

2016-07-20 | E-GEOD-73109 | biostudies-arrayexpress

The forkhead transcription factor FOXP1 profile in B-cells and B-cell lymphoma cell lines

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2015-05-19 | E-GEOD-69009 | biostudies-arrayexpress

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2013-12-16 | E-GEOD-50721 | biostudies-arrayexpress

Whole genome mapping of STAT3 binding sites in the two major subtypes of diffuse large B cell lymphoma

Project description:The goal of this study is to identify the effect of the transcription factor STAT3 in the two major subtypes of diffuse large B cell lymphoma (DLBCL). STAT3 is a signal transducer that, when dysregulated, becomes a powerful oncogene found in many human cancers, including DLBCL. DLBCL is the most common form of non-Hodgkin’s lymphoma and has two major subtypes: germinal center B-cell-like (GCB) and activated B-cell-like (ABC). When compared to the GCB form, ABC lymphomas respond much more poorly to current therapies and often exhibit overexpression or overactivation of STAT3. To investigate how STAT3 might contribute to this aggressive phenotype, we have used ChIP-Seq to identify STAT3 binding sites in 8 DLBCL cell lines (4 GCB subtype, 4 ABC) that are derived from patient tumors. 10,337 distinct STAT3 binding regions are occupied in at least two of the eight cell lines. One third (n = 3524) are differentially bound by STAT3 between the two subtypes (FDR < 0.05). More BRs are strongly bound in ABC than in GCB: 44% of differentially bound BRs (n = 1550) show more STAT3 binding in GCB, while 56% (n = 1974) are more strongly bound in ABC. Identification and comparison of STAT3 transcription factor binding sites in 8 cell lines that represent the 2 subtypes of DLBCL. 4 cell lines are subtyped as ABC and 4 are subtyped as GCB. 2-9 replicates and 1 input control are present for each cell line. (Cell line OCI-Ly19 was not included in the final analysis because RNA-Seq showed that its gene expression clustered in between the subtypes, probably due to its EBV+ status. However, its peak calls were used in intermediate steps of the analysis pipeline. Its sequencing runs have been included for completeness.)

2013-12-16 | E-GEOD-50723 | biostudies-arrayexpress

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