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The interplay between T-cell states of differentiation, dysfunction, and treatment response in acute myeloid leukemia (AML) remains unclear. Here, we leveraged a multimodal approach encompassing high-dimensional flow cytometry and single-cell transcriptomics and found that early memory CD8+ T cells are associated with therapy response and exhibit a bifurcation into two distinct terminal end states. One state is enriched for markers of activation, whereas the other expresses NK-like and senescence markers. The skewed clonal differentiation trajectory towards CD8+ senescence was also a hallmark indicative of therapy resistance. We validated these findings by generating an AML CD8+ single-cell atlas integrating our data and other independent datasets. Finally, our analysis revealed that an imbalance between CD8+ early memory and senescent-like cells is linked to AML treatment refractoriness and poor survival. Our study provides crucial insights into the dynamics of CD8+ T-cell differentiation and advances our understanding of CD8+ T-cell dysfunction in AML.
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ABSTRACT: CD20 is an established therapeutic target in B-cell malignancies. The CD20 × CD3 bispecific antibody mosunetuzumab has significant efficacy in B-cell non-Hodgkin lymphomas (NHLs). Because target antigen loss is a recognized mechanism of resistance, we evaluated CD20 expression relative to clinical response in patients with relapsed and/or refractory NHL in the phase 1/2 GO29781 trial investigating mosunetuzumab monotherapy. CD20 was studied using immunohistochemistry (IHC), RNA sequencing, and whole-exome sequencing performed centrally in biopsy specimens collected before treatment at predose, during treatment, or upon progression. Before treatment, most patients exhibited a high proportion of tumor cells expressing CD20; however, in 16 of 293 patients (5.5%) the proportion was <10%. Analyses of paired biopsy specimens from patients on treatment revealed that CD20 levels were maintained in 29 of 30 patients (97%) vs at progression, where CD20 loss was observed in 11 of 32 patients (34%). Reduced transcription or acquisition of truncating mutations explained most but not all cases of CD20 loss. In vitro modeling confirmed the effects of CD20 variants identified in clinical samples on reduction of CD20 expression and missense mutations in the extracellular domain that could block mosunetuzumab binding. This study expands the knowledge about the occurrence of target antigen loss after anti-CD20 therapeutics to include CD20-targeting bispecific antibodies and elucidates mechanisms of reduced CD20 expression at disease progression that may be generalizable to other anti-CD20 targeting agents. These results also confirm the utility of readily available IHC staining for CD20 as a tool to inform clinical decisions. This trial was registered at www.ClinicalTrials.gov as #NCT02500407.
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Anticuerpos Biespecíficos , Antineoplásicos , Linfoma de Células B , Humanos , Antígenos CD20/genética , Recurrencia Local de Neoplasia/tratamiento farmacológico , Linfoma de Células B/tratamiento farmacológico , Linfoma de Células B/genética , Antineoplásicos/uso terapéuticoRESUMEN
Germinal center (GC) B cells feature repression of many gene enhancers to establish their characteristic transcriptome. Here we show that conditional deletion of Lsd1 in GCs significantly impaired GC formation, associated with failure to repress immune synapse genes linked to GC exit, which are also direct targets of the transcriptional repressor BCL6. We found that BCL6 directly binds LSD1 and recruits it primarily to intergenic and intronic enhancers. Conditional deletion of Lsd1 suppressed GC hyperplasia caused by constitutive expression of BCL6 and significantly delayed BCL6-driven lymphomagenesis. Administration of catalytic inhibitors of LSD1 had little effect on GC formation or GC-derived lymphoma cells. Using a CRISPR-Cas9 domain screen, we found instead that the LSD1 Tower domain was critical for dependence on LSD1 in GC-derived B cells. These results indicate an essential role for LSD1 in the humoral immune response, where it modulates enhancer function by forming repression complexes with BCL6.
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Linfocitos B/fisiología , Centro Germinal/patología , Histona Demetilasas/metabolismo , Linfoma/metabolismo , Proteínas Proto-Oncogénicas c-bcl-6/metabolismo , Animales , Sistemas CRISPR-Cas , Carcinogénesis , ADN Intergénico/genética , Centro Germinal/inmunología , Histona Demetilasas/genética , Hiperplasia , Sinapsis Inmunológicas/genética , Intrones/genética , Linfoma/genética , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Proteínas Proto-Oncogénicas c-bcl-6/genéticaRESUMEN
Synovial sarcoma is an aggressive cancer invariably associated with a chromosomal translocation involving genes encoding the SWI-SNF complex component SS18 and an SSX (SSX1 or SSX2) transcriptional repressor. Using functional genomics, we identify KDM2B, a histone demethylase and component of a non-canonical polycomb repressive complex 1 (PRC1.1), as selectively required for sustaining synovial sarcoma cell transformation. SS18-SSX1 physically interacts with PRC1.1 and co-associates with SWI/SNF and KDM2B complexes on unmethylated CpG islands. Via KDM2B, SS18-SSX1 binds and aberrantly activates expression of developmentally regulated genes otherwise targets of polycomb-mediated repression, which is restored upon KDM2B depletion, leading to irreversible mesenchymal differentiation. Thus, SS18-SSX1 deregulates developmental programs to drive transformation by hijacking a transcriptional repressive complex to aberrantly activate gene expression.
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Proteínas F-Box/metabolismo , Histona Demetilasas con Dominio de Jumonji/metabolismo , Proteínas de Neoplasias/metabolismo , Complejo Represivo Polycomb 1/metabolismo , Proteínas Proto-Oncogénicas/metabolismo , Proteínas Represoras/metabolismo , Sarcoma Sinovial/metabolismo , Núcleo Celular/metabolismo , Transformación Celular Neoplásica/genética , Expresión Génica/fisiología , Humanos , Proteínas de Neoplasias/genética , Proteínas de Fusión Oncogénica/genética , Proteínas Represoras/genética , Sarcoma Sinovial/genéticaRESUMEN
Although the BCL6 transcriptional repressor is frequently expressed in human follicular lymphomas (FL), its biological role in this disease remains unknown. Herein, we comprehensively identify the set of gene promoters directly targeted by BCL6 in primary human FLs. We noted that BCL6 binds and represses NOTCH2 and NOTCH pathway genes. Moreover, BCL6 and NOTCH2 pathway gene expression is inversely correlated in FL. Notably, BCL6 upregulation is associated with repression of NOTCH2 and its target genes in primary human and murine germinal center (GC) cells. Repression of NOTCH2 is an essential function of BCL6 in FL and GC B cells because inducible expression of Notch2 abrogated GC formation in mice and killed FL cells. Indeed, BCL6-targeting compounds or gene silencing leads to the induction of NOTCH2 activity and compromises survival of FL cells, whereas NOTCH2 depletion or pathway antagonists rescue FL cells from such effects. Moreover, BCL6 inhibitors induced NOTCH2 expression and suppressed growth of human FL xenografts in vivo and primary human FL specimens ex vivo These studies suggest that established FLs are thus dependent on BCL6 through its suppression of NOTCH2Significance: We show that human FLs are dependent on BCL6, and primary human FLs can be killed using specific BCL6 inhibitors. Integrative genomics and functional studies of BCL6 in primary FL cells point toward a novel mechanism whereby BCL6 repression of NOTCH2 drives the survival and growth of FL cells as well as GC B cells, which are the FL cell of origin. Cancer Discov; 7(5); 506-21. ©2017 AACR.This article is highlighted in the In This Issue feature, p. 443.
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Linfoma Folicular/patología , Proteínas Proto-Oncogénicas c-bcl-6/metabolismo , Receptor Notch2/metabolismo , Animales , Linfocitos B/metabolismo , Regulación Neoplásica de la Expresión Génica/fisiología , Centro Germinal/metabolismo , Xenoinjertos , Humanos , Linfoma Folicular/metabolismo , Ratones , Ratones SCIDRESUMEN
Somatic mutations in CREBBP occur frequently in B-cell lymphoma. Here, we show that loss of CREBBP facilitates the development of germinal center (GC)-derived lymphomas in mice. In both human and murine lymphomas, CREBBP loss-of-function resulted in focal depletion of enhancer H3K27 acetylation and aberrant transcriptional silencing of genes that regulate B-cell signaling and immune responses, including class II MHC. Mechanistically, CREBBP-regulated enhancers are counter-regulated by the BCL6 transcriptional repressor in a complex with SMRT and HDAC3, which we found to bind extensively to MHC class II loci. HDAC3 loss-of-function rescued repression of these enhancers and corresponding genes, including MHC class II, and more profoundly suppressed CREBBP-mutant lymphomas in vitro and in vivo Hence, CREBBP loss-of-function contributes to lymphomagenesis by enabling unopposed suppression of enhancers by BCL6/SMRT/HDAC3 complexes, suggesting HDAC3-targeted therapy as a precision approach for CREBBP-mutant lymphomas. SIGNIFICANCE: Our findings establish the tumor suppressor function of CREBBP in GC lymphomas in which CREBBP mutations disable acetylation and result in unopposed deacetylation by BCL6/SMRT/HDAC3 complexes at enhancers of B-cell signaling and immune response genes. Hence, inhibition of HDAC3 can restore the enhancer histone acetylation and may serve as a targeted therapy for CREBBP-mutant lymphomas. Cancer Discov; 7(1); 38-53. ©2016 AACR.See related commentary by Höpken, p. 14This article is highlighted in the In This Issue feature, p. 1.
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Proteína de Unión a CREB/genética , Centro Germinal/metabolismo , Histona Desacetilasas/genética , Linfoma de Células B Grandes Difuso/genética , Mutación , Acetilación , Animales , Proteína de Unión a CREB/metabolismo , Línea Celular Tumoral , Elementos de Facilitación Genéticos , Técnicas de Inactivación de Genes , Histona Desacetilasas/metabolismo , Histonas/metabolismo , Humanos , Linfoma de Células B Grandes Difuso/metabolismo , Ratones , Trasplante de Neoplasias , Co-Represor 2 de Receptor Nuclear/genética , Proteínas Proto-Oncogénicas c-bcl-6/genética , Transcripción GenéticaRESUMEN
Chronic lymphocytic leukemia (CLL) is an incurable leukemia of unknown etiology. Multiple studies suggest that the structure of the variable domains of the surface IGs on these cells, and signaling through them, play key roles in developing the disease. Hence, CLL appears to be driven by antigen-BCR interactions, and identifying the selecting antigens involved in this process is an important goal. We studied the antigen-binding characteristics of 23 CLL-derived, recombinantly-expressed IGs with 5 pathogenic bacteria, determining that CLL IGs differ in bacterial reactivity based on IGHV gene use, mutation status, and association with IGHD and IGHJ genes ("stereotypy"). Although most bacterial-reactive IGs followed the paradigm that IGHV-unmutated IGs were more auto-/poly-reactive, several did not. In addition, some CLL IGs were bacterial mono-reactive, and these displayed IGKV use biases. These findings are consistent with CLL B cells being driven into the leukemogenic process by bacterial as well as auto- antigens.
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Anticuerpos Antibacterianos/inmunología , Cadenas Pesadas de Inmunoglobulina/inmunología , Región Variable de Inmunoglobulina/inmunología , Lactobacillales/inmunología , Leucemia Linfocítica Crónica de Células B/inmunología , Anticuerpos Antibacterianos/genética , Antígenos Bacterianos/inmunología , Enterobacter cloacae/inmunología , Células HEK293 , Humanos , Cadenas Pesadas de Inmunoglobulina/genética , Región Variable de Inmunoglobulina/genética , Leucemia Linfocítica Crónica de Células B/genética , MutaciónRESUMEN
During the humoral immune response, B cells undergo a dramatic change in phenotype to enable antibody affinity maturation in germinal centers (GCs). Using genome-wide chromosomal conformation capture (Hi-C), we found that GC B cells undergo massive reorganization of the genomic architecture that encodes the GC B cell transcriptome. Coordinate expression of genes that specify the GC B cell phenotype-most prominently BCL6-was achieved through a multilayered chromatin reorganization process involving (1) increased promoter connectivity, (2) formation of enhancer networks, (3) 5' to 3' gene looping, and (4) merging of gene neighborhoods that share active epigenetic marks. BCL6 was an anchor point for the formation of GC-specific gene and enhancer loops on chromosome 3. Deletion of a GC-specific, highly interactive locus control region upstream of Bcl6 abrogated GC formation in mice. Thus, large-scale and multi-tiered genomic three-dimensional reorganization is required for coordinate expression of phenotype-driving gene sets that determine the unique characteristics of GC B cells.
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Afinidad de Anticuerpos/inmunología , Linfocitos B/inmunología , Genoma/inmunología , Centro Germinal/inmunología , Región de Control de Posición/inmunología , Animales , Formación de Anticuerpos/inmunología , Cromosomas Humanos Par 3/inmunología , Epigénesis Genética/inmunología , Humanos , Inmunidad Humoral/inmunología , Ratones , Regiones Promotoras Genéticas/inmunología , Proteínas Proto-Oncogénicas c-bcl-6/inmunologíaRESUMEN
Diffuse large B cell lymphomas (DLBCLs) arise from proliferating B cells transiting different stages of the germinal center reaction. In activated B cell DLBCLs (ABC-DLBCLs), a class of DLBCLs that respond poorly to current therapies, chromosomal translocations and amplification lead to constitutive expression of the B cell lymphoma 6 (BCL6) oncogene. The role of BCL6 in maintaining these lymphomas has not been investigated. Here, we designed small-molecule inhibitors that display higher affinity for BCL6 than its endogenous corepressor ligands to evaluate their therapeutic efficacy for targeting ABC-DLBCL. We used an in silico drug design functional-group mapping approach called SILCS to create a specific BCL6 inhibitor called FX1 that has 10-fold greater potency than endogenous corepressors and binds an essential region of the BCL6 lateral groove. FX1 disrupted formation of the BCL6 repression complex, reactivated BCL6 target genes, and mimicked the phenotype of mice engineered to express BCL6 with corepressor binding site mutations. Low doses of FX1 induced regression of established tumors in mice bearing DLBCL xenografts. Furthermore, FX1 suppressed ABC-DLBCL cells in vitro and in vivo, as well as primary human ABC-DLBCL specimens ex vivo. These findings indicate that ABC-DLBCL is a BCL6-dependent disease that can be targeted by rationally designed inhibitors that exceed the binding affinity of natural BCL6 ligands.
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Antineoplásicos/farmacología , Diseño de Fármacos , Regulación Neoplásica de la Expresión Génica , Linfoma de Células B Grandes Difuso/tratamiento farmacológico , Proteínas Proto-Oncogénicas c-bcl-6/antagonistas & inhibidores , Animales , Línea Celular Tumoral , Doxorrubicina/farmacología , Ensayos de Selección de Medicamentos Antitumorales , Células HEK293 , Humanos , Indoles/farmacología , Ligandos , Linfoma de Células B Grandes Difuso/patología , Espectroscopía de Resonancia Magnética , Masculino , Ratones , Ratones SCID , Trasplante de Neoplasias , Unión Proteica , Proteínas Proto-Oncogénicas c-bcl-6/metabolismo , Tiazolidinedionas/farmacología , Translocación GenéticaRESUMEN
The EZH2 histone methyltransferase mediates the humoral immune response and drives lymphomagenesis through formation of bivalent chromatin domains at critical germinal center (GC) B cell promoters. Herein we show that the actions of EZH2 in driving GC formation and lymphoma precursor lesions require site-specific binding by the BCL6 transcriptional repressor and the presence of a non-canonical PRC1-BCOR-CBX8 complex. The chromodomain protein CBX8 is induced in GC B cells, binds to H3K27me3 at bivalent promoters, and is required for stable association of the complex and the resulting histone modifications. 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 DLBCLs.
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Proteína Potenciadora del Homólogo Zeste 2/metabolismo , Centro Germinal/metabolismo , Linfoma de Células B Grandes Difuso/metabolismo , Complejo Represivo Polycomb 1/metabolismo , Proteínas Proto-Oncogénicas c-bcl-6/metabolismo , Proteínas Represoras/metabolismo , Animales , Centro Germinal/patología , Humanos , Linfoma de Células B Grandes Difuso/genética , Linfoma de Células B Grandes Difuso/patología , Ratones , Ratones Endogámicos C57BL , Ratones Transgénicos , Proteínas de Transporte de Membrana Mitocondrial , Proteínas del Grupo Polycomb/metabolismo , Regiones Promotoras Genéticas , Proteínas Proto-Oncogénicas/metabolismo , Transcripción GenéticaRESUMEN
The BCL6 oncogene plays a crucial role in sustaining diffuse large B-cell lymphomas (DLBCL) through transcriptional repression of key checkpoint genes. BCL6-targeted therapy kills lymphoma cells by releasing these checkpoints. However BCL6 also directly represses several DLBCL oncogenes such as BCL2 and BCL-XL that promote lymphoma survival. Herein we show that DLBCL cells that survive BCL6-targeted therapy induce a phenomenon of "oncogene-addiction switching" by reactivating BCL2-family dependent anti-apoptotic pathways. Thus, most DLBCL cells require concomitant inhibition of BCL6 and BCL2-family members for effective lymphoma killing. Moreover, in DLBCL cells initially resistant to BH3 mimetic drugs, BCL6 inhibition induces a newly developed reliance on anti-apoptotic BCL2-family members for survival that translates in acquired susceptibility to BH3 mimetic drugs ABT-737 and obatoclax. In germinal center B cell-like (GCB)-DLBCL cells, the proteasome inhibitor bortezomib and the NEDD inhibitor MLN4924 post-transcriptionally activated the BH3-only sensitizer NOXA thus counteracting the oncogenic switch to BCL2 induced by BCL6-targeting. Hence our study indicates that BCL6 inhibition induces an on-target feedback mechanism based on the activation of anti-apoptotic BH3 members. This oncogene-addition switching mechanism was harnessed to develop rational combinatorial therapies for GCB-DLBCL.
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Resistencia a Antineoplásicos/efectos de los fármacos , Linfoma de Células B Grandes Difuso/tratamiento farmacológico , Proteínas Proto-Oncogénicas c-bcl-2/metabolismo , Proteínas Proto-Oncogénicas c-bcl-6/antagonistas & inhibidores , Animales , Compuestos de Bifenilo/farmacología , Western Blotting , Proliferación Celular/efectos de los fármacos , Humanos , Indoles , Linfoma de Células B Grandes Difuso/enzimología , Linfoma de Células B Grandes Difuso/patología , Masculino , Ratones , Ratones Desnudos , Nitrofenoles/farmacología , Fragmentos de Péptidos/farmacología , Piperazinas/farmacología , Proteínas Proto-Oncogénicas/farmacología , Proteínas Proto-Oncogénicas c-bcl-2/antagonistas & inhibidores , Proteínas Proto-Oncogénicas c-bcl-6/genética , Proteínas Proto-Oncogénicas c-bcl-6/metabolismo , Pirroles/farmacología , ARN Interferente Pequeño/genética , Ratas , Ratas Sprague-Dawley , Sulfonamidas/farmacología , Células Tumorales Cultivadas , Ensayos Antitumor por Modelo de XenoinjertoRESUMEN
Follicular helper T cells (Tfh cells) are required for T cell help to B cells, and BCL6 is the defining transcription factor of Tfh cells. However, the functions of BCL6 in Tfh cells have largely remained unclear. Here we defined the BCL6 cistrome in primary human germinal center Tfh cells to assess mechanisms of BCL6 regulation of CD4 T cells, comparing and contrasting BCL6 function in T and B cells. BCL6 primarily acts as a repressor in Tfh cells, and BCL6 binding was associated with control of Tfh cell migration and repression of alternative cell fates. Interestingly, although some BCL6-bound genes possessed BCL6 DNA-binding motifs, many BCL6-bound loci were instead characterized by the presence of DNA motifs for AP1 or STAT. AP1 complexes are key positive downstream mediators of TCR signaling and external stimuli. We show that BCL6 can directly bind AP1, and BCL6 depends on AP1 for recruitment to BCL6-binding sites with AP1 motifs, suggesting that BCL6 subverts AP1 activity. These findings reveal that BCL6 has broad and multifaceted effects on Tfh biology and provide insight into how this master regulator mediates distinct cell context-dependent phenotypes.
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Diferenciación Celular/inmunología , Proteínas de Unión al ADN/inmunología , Linfocitos T Colaboradores-Inductores/inmunología , Secuencias de Aminoácidos , Linfocitos B/citología , Linfocitos B/inmunología , Sitios de Unión , Diferenciación Celular/genética , Proteínas de Unión al ADN/genética , Femenino , Humanos , Masculino , Proteínas Proto-Oncogénicas c-bcl-6 , Factores de Transcripción STAT/genética , Factores de Transcripción STAT/inmunología , Linfocitos T Colaboradores-Inductores/citología , Factor de Transcripción AP-1/genética , Factor de Transcripción AP-1/inmunologíaRESUMEN
B cell lymphoma 6 (BCL6) corepressor (BCOR) was discovered as a BCL6-interacting corepressor, but little is known about its other biological activities in normal B cell development and function. Previously, we found that interferon regulatory factor 8 (IRF8), also known as interferon consensus sequence-binding protein, directly targets a large number of genes in germinal center B cells including BCL6. In this study, we screened potential binding partners of IRF8 using a retrovirus-based protein complementation assay screen in a mouse pre-B cell line. We found that IRF8 interacts directly with BCOR and that the α-helical region of IRF8 and the BCL6 binding domain of BCOR are required for this interaction. In addition, IRF8 protein interacts directly with BCL6. Using an siRNA-mediated IRF8 knockdown mouse B cell lymphoma cell line, we showed that IRF8 represses Bcor and enhances Bcl6 transcription. Taken together, these data suggest that a complex comprising BCOR-BCL6-IRF8 modulates BCL6-associated transcriptional regulation of germinal center B cell function.
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Núcleo Celular/metabolismo , Proteínas de Unión al ADN/genética , Regulación de la Expresión Génica , Factores Reguladores del Interferón/genética , Linfocitos/metabolismo , Proteínas Represoras/genética , Animales , Línea Celular Tumoral , Núcleo Celular/genética , Proteínas de Unión al ADN/metabolismo , Genes Reporteros , Vectores Genéticos , Células HEK293 , Humanos , Factores Reguladores del Interferón/antagonistas & inhibidores , Factores Reguladores del Interferón/metabolismo , Luciferasas/genética , Luciferasas/metabolismo , Linfocitos/citología , Ratones , Unión Proteica , Mapeo de Interacción de Proteínas , Proteínas Proto-Oncogénicas c-bcl-6 , ARN Interferente Pequeño/genética , ARN Interferente Pequeño/metabolismo , Proteínas Represoras/metabolismo , Retroviridae/genética , Transducción de Señal , Transcripción GenéticaRESUMEN
To understand how the Bcl6 transcriptional repressor functions in the immune system, we disrupted its RD2 repression domain in mice. Bcl6RD2(MUT) mice exhibit a complete loss of germinal center (GC) formation but retain normal extrafollicular responses. Bcl6RD2(MUT) antigen-engaged B cells migrate to the interfollicular zone and interact with cognate T helper cells. However, these cells fail to complete early GC-commitment differentiation and coalesce as nascent GC aggregates. Bcl6 directly binds and represses trafficking receptors S1pr1 and Gpr183 by recruiting Hdac2 through the RD2 domain. Deregulation of these genes impairs B cell migration and may contribute to GC failure in Bcl6RD2(MUT) mice. The development of functional GC-TFH cells was partially impaired in Bcl6RD2(MUT) mice. In contrast to Bcl6(-/-) mice, Bcl6RD2(MUT) animals experience no inflammatory disease or macrophage deregulation. These results reveal an essential role for RD2 repression in early GC commitment and striking biochemical specificity in Bcl6 control of humoral and innate immune-cell phenotypes.
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Linfocitos B/metabolismo , Proteínas de Unión al ADN/metabolismo , Centro Germinal/citología , Animales , Linfocitos B/inmunología , Linfocitos B/fisiología , Movimiento Celular , Citocinas/genética , Citocinas/metabolismo , Proteínas de Unión al ADN/química , Centro Germinal/inmunología , Histona Desacetilasa 2/metabolismo , Activación de Linfocitos , Ratones , Mutación , Unión Proteica , Estructura Terciaria de Proteína , Proteínas Proto-Oncogénicas c-bcl-6 , Receptores Acoplados a Proteínas G/metabolismo , Receptores de Lisoesfingolípidos/metabolismo , Receptores de Esfingosina-1-Fosfato , Linfocitos T Colaboradores-Inductores/inmunología , Linfocitos T Colaboradores-Inductores/metabolismoRESUMEN
The B cell lymphoma 6 (BCL6) transcriptional repressor is a master regulator of the germinal center (GC) B cell program, required for their unique proliferative and stress tolerant phenotype. Most B cell lymphomas arise from GC B cells and are dependent on the continued or deregulated expression of BCL6 to maintain their survival. The actions of BCL6 in B cells involve formation of distinct chromatin modifying complexes that silence specific promoter and enhancer networks, respectively. The same biochemical mechanisms are maintained in malignant lymphoma cells. Targeted inhibition of these BCL6 functions has emerged as the basis for rational design of lymphoma therapies and combinatorial regimens. In this review, we summarize recent advances on BCL6 mechanisms of action and the deregulation of its target gene networks in lymphoma.
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Proteínas de Unión al ADN/metabolismo , Linfoma de Células B/genética , Supervivencia Celular , Proteínas de Unión al ADN/genética , Elementos de Facilitación Genéticos , Epigénesis Genética , Regulación de la Expresión Génica , Regulación Neoplásica de la Expresión Génica , Humanos , Sistema Inmunológico/fisiología , Linfoma de Células B/metabolismo , Linfoma de Células B/patología , Terapia Molecular Dirigida , Regiones Promotoras Genéticas , Proteínas Proto-Oncogénicas c-bcl-6RESUMEN
Memory is a hallmark of adaptive immunity, wherein lymphocytes mount a superior response to a previously encountered antigen. It has been speculated that epigenetic alterations in memory lymphocytes contribute to their functional distinction from their naive counterparts. However, the nature and extent of epigenetic alterations in memory compartments remain poorly characterized. Here we profile the DNA methylome and the transcriptome of B-lymphocyte subsets representing stages of the humoral immune response before and after antigen exposure in vivo from multiple humans. A significant percentage of activation-induced losses of DNA methylation mapped to transcription factor binding sites. An additional class of demethylated loci mapped to Alu elements across the genome and accompanied repression of DNA methyltransferase 3A. The activation-dependent DNA methylation changes were largely retained in the progeny of activated B cells, generating a similar epigenetic signature in downstream memory B cells and plasma cells with distinct transcriptional programs. These findings provide insights into the methylation dynamics of the genome during cellular differentiation in an immune response.
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Elementos Alu , Linfocitos B/inmunología , Metilación de ADN , Activación de Linfocitos/genética , Elementos Reguladores de la Transcripción/genética , Inmunidad Adaptativa/genética , Inmunidad Adaptativa/inmunología , Linfocitos B/metabolismo , Sitios de Unión/genética , Diferenciación Celular/genética , ADN (Citosina-5-)-Metiltransferasas/genética , ADN (Citosina-5-)-Metiltransferasas/metabolismo , ADN Metiltransferasa 3A , Epigénesis Genética , Perfilación de la Expresión Génica , Regulación de la Expresión Génica , Genoma Humano , Humanos , Memoria Inmunológica/genética , Células Plasmáticas/inmunología , Células Plasmáticas/metabolismo , Factores de Transcripción/genética , Factores de Transcripción/metabolismoRESUMEN
The BCL6 transcriptional repressor is required for the development of germinal center (GC) B cells and diffuse large B cell lymphomas (DLBCLs). Although BCL6 can recruit multiple corepressors, its transcriptional repression mechanism of action in normal and malignant B cells is unknown. We find that in B cells, BCL6 mostly functions through two independent mechanisms that are collectively essential to GC formation and DLBCL, both mediated through its N-terminal BTB domain. These are (1) the formation of a unique ternary BCOR-SMRT complex at promoters, with each corepressor binding to symmetrical sites on BCL6 homodimers linked to specific epigenetic chromatin features, and (2) the "toggling" of active enhancers to a poised but not erased conformation through SMRT-dependent H3K27 deacetylation, which is mediated by HDAC3 and opposed by p300 histone acetyltransferase. Dynamic toggling of enhancers provides a basis for B cells to undergo rapid transcriptional and phenotypic changes in response to signaling or environmental cues.