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Rewiring Cancer Drivers to Activate Apoptosis

ABSTRACT: Genes that drive the proliferation, survival, invasion and metastasis of malignant cells have been identified for manyhuman cancers. Independent studies have identified cell death pathways that eliminate cells by an altruistic form of suicide. The coexistence of the cell death pathways with the driver mutations suggest that the cancer driver could be reprogrammedto activate cell death. We have invented a new class of molecules: TCIPs (Transcriptional/EpigeneticChemical 20Inducers of Proximity) that recruit the cancer driver, or a downstream transcription factor,to the promoters of cell death genesmthereby activating their expression. To develop this concept, we have focused on diffuse largeB cell lymphoma(DLBCL),in which BCL6 is amplified or mutated. BCL6 binds to the promoters of cell death genes and epigenetically suppresses their expression. We produced the first TCIPs by chemically linking BCL6 inhibitors with small molecule binders to transcriptional activators. Several of these molecules robustly kill DLBCL at single-digit nanomolar concentrations, including chemotherapy-resistant, TP53-mutant lines. The dominant gain-of-function approach provided by TCIPs allows access to therapeutic space unreachable to conventional small molecule inhibitors or degraders, RNAi,or CRISPR(i). TCIPs are relatively non-toxic to normal cells and selective in malignant cells, reflecting their need for coincident expression of both target proteins for effective killing. The later attribute should allow highly personalized treatment. The general TCIP concept has applications in elimination of senescent cells, enhancing expression of therapeutic genes, treatment of diseases produced by haploinsufficiency,and activation of immunogens for immunotherapy.

ORGANISM(S): Mus musculus Homo sapiens

PROVIDER: GSE211282 | GEO | 2023/05/03

REPOSITORIES: GEO

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CD137 (4-1BB) ligand mediates CD4 T-cell immuno-surveillance of pre- lymphoma B cells in a lymphoma-prone mouse model

Project description:Aberrant expression of the proto-oncogene BCL6 is a driver of tumorigenesis in diffuse large B cell lymphoma (DLBCL). Mice overexpressing BCL6 from the B cell-specific immunoglobulin heavy chain μ intron promoter (Iμ-Bcl6 Tg/+ ) develop B cell lymphomas with features typical of human DLBCL. B cell lymphoma development in these mice is tightly controlled by T cells; however, the mechanisms of this immune surveillance are poorly understood. Here we show that CD4 T cells contribute to the control of lymphoproliferative disease in lymphoma-prone Iμ-Bcl6 Tg/+ mice. Furthermore, we reveal that this CD4 T-cell immuno-surveillance requires signaling by the co-stimulatory molecule, CD137 ligand (CD137L; also known as 4-1BBL), which promotes the transition of pre malignant B cells with an activated phenotype into the germinal center stage, preventing their hazardous accumulation. Thus, CD137L-mediated CD4 T cell immuno-surveillance adds another layer of protection against B-cell malignancy to that provided by CD8 T-cell cytotoxicity.

2023-01-04 | GSE196100 | GEO

BCL6 repression of EP300 provides a basis for rational combinatorial therapy in diffuse large B cell lymphomas.

Project description:The BCL6 transcriptional repressor is a critical oncogene in diffuse large B-cell lymphomas (DLBCL). The specific BCL6 inhibitor RI-BPI potently kills DLBCL cells. We find that RI-BPI induces a particular gene expression signature in DLBCL. In order to identify classes of drugs that might synergize with RIBPI we examined the connectivity of this signature and found a strong association with HDAC and Hsp90 inhibitors. This was explained by the discovery that BCL6 directly represses the p300 lysine acetyltransferase and its co-factor BAT3. RI-BPI induced expression of p300 and BAT3, and p300 acetyltransferase activity, resulting in acetylation of p300 targets like p53 and Hsp90. As a consequence, RI-BPI could attenuate Hsp90 chaperone function, similar to the effect of Hsp90 and HDAC inhibitors. Induction of p300 and BAT3 was required for the anti-lymphoma effects of RI-BPI since specific blockade of either protein rescued DLBCL cells from the BCL6 inhibitor. RI-BPI synergistically killed DLBCL cells in combination with HDAC inhibitors (SAHA, TSA and VPA) and Hsp90 inhibitors (17-DMAG and PUH71). The combination of RI-BPI and SAHA, or RI-BPI and PU-H71 potently suppressed or even eradicated human DLBCL in mice. BCL6 repression of EP300 thus provides a basis for rational targeted combinatorial therapy for patients with DLBCL. Direct comparison of gene expression levels in DLBCL cell lines after 24hs of treatment with either a Bcl6 inhibitor peptide or control peptide

2010-09-21 | E-GEOD-24236 | biostudies-arrayexpress

Inducible knock-out of BCL6 in lymphoma cells results in tumor stasis

Project description:Diffuse large B-cell lymphoma (DLBCL) is the most common type of non-Hodgkin lymphomas worldwide and is characterized by a high diversity of genetic and molecular alterations. Chromosomal translocations and mutations leading to deregulated expression of the transcriptional repressor BCL6 occur in a significant fraction of DLBCL patients. An oncogenic role of BCL6 in the initiation of DLBCL has been shown as the constitutive expression of BCL6 in mice recapitulates the pathogenesis of human DLBCL. However, the role of BCL6 in tumor maintenance remains poorly investigated due to the absence of suitable genetic models and limitations of pharmacological inhibitors. Here, we have utilized tetracycline-inducible CRISPR/Cas9 mutagenesis to study the consequences of BCL6 deletion in established DLBCL models in culture and in vivo. We show that BCL6 knock-out in SU-DHL-4 cells in vitro results in an anti-proliferative response 4-7 days after Cas9 induction that was characterized by cell cycle (G1) arrest. Conditional BCL6 deletion in established DLBCL tumors in vivo induced a significant tumor growth inhibition with initial tumor stasis followed by slow tumor growth kinetics. Our findings support a role of BCL6 in the maintenance of lymphoma growth and showcase the utility of inducible CRISPR/Cas9 systems for probing oncogene addiction.

2020-03-23 | GSE127266 | GEO

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

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

Therapeutic targeting of GCB- and ABC-DLBCL by rationally designed BCL6 inhibitor

Project description:Rationale: The BCL6 oncogene is constitutively activated by chromosomal translocations and amplification in ABC-DLBCLs, a class of DLBCLs that respond poorly to current therapies. Yet the role of BCL6 in maintaining these lymphomas has not been investigated. BCL6 mediates its effects by recruiting corepressors to an extended groove motif. Development of effective BCL6 inhibitors requires compounds exceeding the binding affinity of these corepressors. Objectives: To design small molecule inhibitors with superior potency vs. endogenous BCL6 ligands for unmet putative therapeutic needs such as targeting ABC-DLBCL. Findings: We used an in silico drug design functional-group mapping approach called SILCS to create a specific BCL6 inhibitor with 10-fold greater potency than endogenous corepressors. The compound, called FX1, binds in such a way as to occupy an essential region of the BCL6 lateral groove. FX1 disrupts BCL6 repression complex formation, reactivates BCL6 target genes, and mimics the phenotype of mice engineered to express BCL6 with lateral groove mutations. This compound eradicated established DLBCLs xenografts at low doses. Most strikingly, FX1 suppressed ABC-DLBCL cells as well as primary human ABC-DLBCL specimens ex vivo. Conclusions: ABC-DLBCL is a BCL6 dependent disease that can be targeted by novel inhibitors able to exceed the binding affinity of natural BCL6 ligands.

2016-10-12 | GSE80351 | GEO

BCL6 repression of EP300 provides a basis for rational combinatorial therapy in diffuse large B cell lymphomas.

2010-09-21 | GSE24236 | GEO

Global expression analysis of DLBCL cell lines with LITAF over-expression or silencing

Project description:The multifunctional protein lipopolysaccharide-induced TNFalpha factor (LITAF) induces the secretion of inflammatory cytokines in monocytes and regulates protein degradation in neural cells. In B-cell lymphomas, LITAF is frequently inactivated by epigenetic mechanisms, but beyond these data little is known about its regulation and function. Immunohistochemical and gene expression profiling analyses of normal and malignant B-cells revealed that LITAF and BCL6 exhibited opposite expression patterns. Accordingly, chromatin immunoprecipitation and luciferase experiments showed that LITAF is transcriptionally repressed by BCL6 in germinal center (GC) lymphocytes and in B-cell lymphoma cells. Gain- and-loss-of-function assays demonstrated that LITAF does not exert any of its previous roles. Conversely, LITAF co-localized with autophagosomes in B-cells whereby activated autophagic responses, which were abrogated upon LITAF silencing. Therefore, BCL6-mediated transcriptional repression of LITAF may contribute to an appropriate GC reaction by suppressing autophagy in GC lymphocytes, whereas constitutive repression of autophagic responses may promote B-cell lymphoma development. Analysis of global gene expression in the diffuse large B-cell lymphoma (DLBCL) cell lines KARPAS-231 and VAL treated with a specific siRNA for LITAF or a scrambled control, and analysis of global gene expression in the DLBCL cell lines RL and SC-1 stably transfected with a tetracycline-inducible LITAF expression vector in the presence or absence of 4 mg/ml doxycycline in the culture medium. The over-expression experiments were performed in duplicate and the silencing experiments in triplicate, resulting in a total of 20 microarrays.

2012-11-10 | E-GEOD-42174 | biostudies-arrayexpress

ChIP-on-chip of BCL6

Project description:Identification BCL6 target genes in primary germinal center cells and DLBCL cell lines by ChIP-on-chip

2009-03-14 | GSE15179 | GEO

Patterns of oncogene co-expression at single-cell resolution influence clinical outcome in Diffuse Large B-Cell Lymphoma.

Project description:Intratumor heterogeneity (ITH) in oncogene expression is common in cancer, but it is not known if oncogenes exert combinatorial effects at the single cell level to influence clinical outcome. We address this question using quantitative spectral imaging to simultaneously measure the cellular co-expression of the oncogenes MYC, BCL2 and BCL6 in clinically annotated cohorts of Diffuse Large B-Cell Lymphoma (DLBCL). Unlike in non-malignant lymphoid tissue, where the co-expression of these oncogenes is spatially constrained, DLBCL samples show multiple permutations of oncogenic co-expression at the single cell level. Oncogene co-expression follows clustered and non-random spatial distribution, and is typically stable across different regions of a tumour. Interestingly, we noted that the extent of cells with the unique oncogene combination MYC+BCL2+BCL6- (M+2+6-) associates consistently with patient survival across three independent DLBCL cohorts. We then show that the fraction of M+2+6- co-expressing cells can be inferred from quantitative single oncogene data, as the overall frequencies of co-expression of these oncogenes are stochastic. Predicted values of M+2+6- cellular co-expression frequency from immunohistochemistry of MYC/BCL2/BCL6 (n=316) and multiple independent gene expression datasets (n=2522; 8 cohorts) consistently correlate with survival after R-CHOP chemotherapy, offering a novel strategy for identification of high-risk DLBCL. Finally, we use comparative RNAseq analysis of patient-derived M+2+6+ and M+2+6- B-cells to identify cyclin D2 as a potential BCL6-repressed mediator of the aggressive behavior of M+2+6- population. Overall, our work demonstrates that patterns of oncogene co-expression analyzed at single-cell resolution are clinically relevant, with implications for both diagnostics and target discovery in other cancer types.

2022-05-23 | GSE203446 | GEO

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