RESUMO
Notch signaling is a key developmental pathway that is subject to frequent genetic and epigenetic perturbations in many different human tumors. Here we investigate whether long noncoding RNA (lncRNA) genes, in addition to mRNAs, are key downstream targets of oncogenic Notch1 in human T cell acute lymphoblastic leukemia (T-ALL). By integrating transcriptome profiles with chromatin state maps, we have uncovered many previously unreported T-ALL-specific lncRNA genes, a fraction of which are directly controlled by the Notch1/Rpbjκ activator complex. Finally we have shown that one specific Notch-regulated lncRNA, LUNAR1, is required for efficient T-ALL growth in vitro and in vivo due to its ability to enhance IGF1R mRNA expression and sustain IGF1 signaling. These results confirm that lncRNAs are important downstream targets of the Notch signaling pathway, and additionally they are key regulators of the oncogenic state in T-ALL.
Assuntos
Leucemia-Linfoma Linfoblástico de Células T Precursoras/genética , Leucemia-Linfoma Linfoblástico de Células T Precursoras/metabolismo , RNA Longo não Codificante/análise , Receptor Notch1/metabolismo , Estudo de Associação Genômica Ampla , Humanos , Leucemia-Linfoma Linfoblástico de Células T Precursoras/patologia , RNA Longo não Codificante/genética , Transdução de Sinais , Timo/patologiaRESUMO
Inactivating mutations of the CREBBP and EP300 acetyltransferases are among the most common genetic alterations in diffuse large B cell lymphoma (DLBCL) and follicular lymphoma (FL). Here, we examined the relationship between these two enzymes in germinal center (GC) B cells, the normal counterpart of FL and DLBCL, and in lymphomagenesis by using conditional GC-directed deletion mouse models targeting Crebbp or Ep300. We found that CREBBP and EP300 modulate common as well as distinct transcriptional programs implicated in separate anatomic and functional GC compartments. Consistently, deletion of Ep300 but not Crebbp impaired the fitness of GC B cells in vivo. Combined loss of Crebbp and Ep300 completely abrogated GC formation, suggesting that these proteins partially compensate for each other through common transcriptional targets. This synthetic lethal interaction was retained in CREBBP-mutant DLBCL cells and could be pharmacologically targeted with selective small molecule inhibitors of CREBBP and EP300 function. These data provide proof-of-principle for the clinical development of EP300-specific inhibitors in FL and DLBCL.
Assuntos
Linfócitos B/fisiologia , Proteína de Ligação a CREB/genética , Proteína p300 Associada a E1A/genética , Epigênese Genética/genética , Centro Germinativo/fisiologia , Linfoma Folicular/etiologia , Linfoma Difuso de Grandes Células B/genética , Acetiltransferases/genética , Animais , Linhagem Celular , Células HEK293 , Humanos , Camundongos , Camundongos Endogâmicos C57BL , Deleção de Sequência/genética , Transcrição Gênica/genéticaRESUMO
Diffuse large B cell lymphoma (DLBCL) is the most common B cell non-Hodgkin lymphoma and remains incurable in around 40% of patients. Efforts to sequence the coding genome identified several genes and pathways that are altered in this disease, including potential therapeutic targets1-5. However, the non-coding genome of DLBCL remains largely unexplored. Here we show that active super-enhancers are highly and specifically hypermutated in 92% of samples from individuals with DLBCL, display signatures of activation-induced cytidine deaminase activity, and are linked to genes that encode B cell developmental regulators and oncogenes. As evidence of oncogenic relevance, we show that the hypermutated super-enhancers linked to the BCL6, BCL2 and CXCR4 proto-oncogenes prevent the binding and transcriptional downregulation of the corresponding target gene by transcriptional repressors, including BLIMP1 (targeting BCL6) and the steroid receptor NR3C1 (targeting BCL2 and CXCR4). Genetic correction of selected mutations restored repressor DNA binding, downregulated target gene expression and led to the counter-selection of cells containing corrected alleles, indicating an oncogenic dependency on the super-enhancer mutations. This pervasive super-enhancer mutational mechanism reveals a major set of genetic lesions deregulating gene expression, which expands the involvement of known oncogenes in DLBCL pathogenesis and identifies new deregulated gene targets of therapeutic relevance.
Assuntos
Elementos Facilitadores Genéticos , Regulação Neoplásica da Expressão Gênica , Linfoma Difuso de Grandes Células B , Mutação , Oncogenes , Regulação para Baixo , Elementos Facilitadores Genéticos/genética , Humanos , Linfoma Difuso de Grandes Células B/genética , Linfoma Difuso de Grandes Células B/metabolismo , Oncogenes/genética , Fator 1 de Ligação ao Domínio I Regulador Positivo/metabolismo , Proteínas Proto-Oncogênicas c-bcl-2/genética , Proteínas Proto-Oncogênicas c-bcl-6/genética , Receptores CXCR4/genética , Receptores de Glucocorticoides/metabolismo , Proteínas Repressoras/metabolismoRESUMO
Heterozygous inactivating mutations of the KMT2D methyltransferase and the CREBBP acetyltransferase are among the most common genetic alterations in B cell lymphoma and co-occur in 40 to 60% of follicular lymphoma (FL) and 30% of EZB/C3 diffuse large B cell lymphoma (DLBCL) cases, suggesting they may be coselected. Here, we show that combined germinal center (GC)-specific haploinsufficiency of Crebbp and Kmt2d synergizes in vivo to promote the expansion of abnormally polarized GCs, a common preneoplastic event. These enzymes form a biochemical complex on select enhancers/superenhancers that are critical for the delivery of immune signals in the GC light zone and are only corrupted upon dual Crebbp/Kmt2d loss, both in mouse GC B cells and in human DLBCL. Moreover, CREBBP directly acetylates KMT2D in GC-derived B cells, and, consistently, its inactivation by FL/DLBCL-associated mutations abrogates its ability to catalyze KMT2D acetylation. Genetic and pharmacologic loss of CREBBP and the consequent decrease in KMT2D acetylation lead to reduced levels of H3K4me1, supporting a role for this posttranslational modification in modulating KMT2D activity. Our data identify a direct biochemical and functional interaction between CREBBP and KMT2D in the GC, with implications for their role as tumor suppressors in FL/DLBCL and for the development of precision medicine approaches targeting enhancer defects induced by their combined loss.
Assuntos
Linfoma Folicular , Linfoma Difuso de Grandes Células B , Animais , Humanos , Camundongos , Acetilação , Linfócitos B/metabolismo , Proteína de Ligação a CREB/genética , Proteína de Ligação a CREB/metabolismo , Centro Germinativo , Linfoma Folicular/genética , Linfoma Folicular/metabolismo , Linfoma Folicular/patologia , Linfoma Difuso de Grandes Células B/patologia , Mutação , Processamento de Proteína Pós-TraducionalRESUMO
MEF2B encodes a transcriptional activator and is mutated in â¼11% of diffuse large B cell lymphomas (DLBCLs) and â¼12% of follicular lymphomas (FLs). Here we found that MEF2B directly activated the transcription of the proto-oncogene BCL6 in normal germinal-center (GC) B cells and was required for DLBCL proliferation. Mutation of MEF2B resulted in enhanced transcriptional activity of MEF2B either through disruption of its interaction with the corepressor CABIN1 or by rendering it insensitive to inhibitory signaling events mediated by phosphorylation and sumoylation. Consequently, the transcriptional activity of Bcl-6 was deregulated in DLBCLs with MEF2B mutations. Thus, somatic mutations of MEF2B may contribute to lymphomagenesis by deregulating BCL6 expression, and MEF2B may represent an alternative target for blocking Bcl-6 activity in DLBCLs.
Assuntos
Regulação Neoplásica da Expressão Gênica , Linfoma Difuso de Grandes Células B/genética , Proteínas de Domínio MADS/genética , Mutação , Fatores de Regulação Miogênica/genética , Proteínas Proto-Oncogênicas c-bcl-6/genética , Proteínas Adaptadoras de Transdução de Sinal/química , Proteínas Adaptadoras de Transdução de Sinal/genética , Proteínas Adaptadoras de Transdução de Sinal/metabolismo , Sequência de Aminoácidos , Substituição de Aminoácidos , Animais , Linfócitos B/metabolismo , Linfócitos B/patologia , Ciclo Celular/genética , Proliferação de Células , Análise por Conglomerados , Biologia Computacional , Proteínas Quinases Dependentes de AMP Cíclico/genética , Proteínas Quinases Dependentes de AMP Cíclico/metabolismo , Perfilação da Expressão Gênica , Centro Germinativo/metabolismo , Centro Germinativo/patologia , Humanos , Linfoma Folicular/genética , Linfoma Folicular/metabolismo , Linfoma Difuso de Grandes Células B/metabolismo , Proteínas de Domínio MADS/química , Proteínas de Domínio MADS/metabolismo , Fatores de Transcrição MEF2 , Camundongos , Simulação de Acoplamento Molecular , Fatores de Regulação Miogênica/química , Fatores de Regulação Miogênica/metabolismo , Ligação Proteica , Conformação Proteica , Proto-Oncogene Mas , Sumoilação/genética , Transcrição GênicaRESUMO
After antigenic challenge, B cells enter the dark zone (DZ) of germinal centers (GCs) to proliferate and hypermutate their immunoglobulin genes. Mutants with greater affinity for the antigen are positively selected in the light zone (LZ) to either differentiate into plasma and memory cells or reenter the DZ. The molecular circuits that govern positive selection in the GC are not known. We show here that the GC reaction required biphasic regulation of expression of the cell-cycle regulator c-Myc that involved its transient induction during early GC commitment, its repression by Bcl-6 in DZ B cells and its reinduction in B cells selected for reentry into the DZ. Inhibition of c-Myc in vivo led to GC collapse, which indicated an essential role for c-Myc in GCs. Our results have implications for the mechanism of GC selection and the role of c-Myc in lymphomagenesis.
Assuntos
Linfócitos B/metabolismo , Genes myc/imunologia , Centro Germinativo/metabolismo , Proteínas Proto-Oncogênicas c-bcl-6/genética , Animais , Antígenos CD/genética , Antígenos CD/imunologia , Linfócitos B/imunologia , Linfócitos B/patologia , Ciclo Celular/genética , Ciclo Celular/imunologia , Movimento Celular , Proliferação de Células , Transformação Celular Neoplásica/genética , Transformação Celular Neoplásica/imunologia , Regulação da Expressão Gênica , Genes Reporter , Centro Germinativo/imunologia , Centro Germinativo/patologia , Proteínas de Fluorescência Verde , Linfoma/genética , Linfoma/metabolismo , Linfoma/patologia , Camundongos , Camundongos Transgênicos , Proteínas Proto-Oncogênicas c-bcl-6/imunologia , Receptores de Antígenos de Linfócitos B/genética , Receptores de Antígenos de Linfócitos B/imunologia , Transdução de Sinais , Linfócitos T/imunologia , Linfócitos T/metabolismo , Linfócitos T/patologiaRESUMO
The pathways regulating formation of the germinal center (GC) dark zone (DZ) and light zone (LZ) are unknown. In this study we show that FOXO1 transcription factor expression was restricted to the GC DZ and was required for DZ formation, since its absence in mice led to the loss of DZ gene programs and the formation of LZ-only GCs. FOXO1-negative GC B cells displayed normal somatic hypermutation but defective affinity maturation and class switch recombination. The function of FOXO1 in sustaining the DZ program involved the trans-activation of the chemokine receptor CXCR4, and cooperation with the BCL6 transcription factor in the trans-repression of genes involved in immune activation, DNA repair, and plasma cell differentiation. These results also have implications for the role of FOXO1 in lymphomagenesis because they suggest that constitutive FOXO1 activity might be required for the oncogenic activity of deregulated BCL6 expression.
Assuntos
Linfócitos B/imunologia , Diferenciação Celular/imunologia , Fatores de Transcrição Forkhead/imunologia , Centro Germinativo/imunologia , Animais , Linfócitos B/citologia , Imunoprecipitação da Cromatina , Citometria de Fluxo , Imunofluorescência , Proteína Forkhead Box O1 , Centro Germinativo/citologia , Humanos , Switching de Imunoglobulina/imunologia , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Reação em Cadeia da Polimerase , Hipermutação Somática de Imunoglobulina/imunologiaRESUMO
Fifty percent of diffuse large B cell lymphoma (DLBCL) cases lack cell-surface expression of the class I major histocompatibility complex (MHC-I), thus escaping recognition by cytotoxic T cells. Here we show that, across B cell lymphomas, loss of MHC-I, but not MHC-II, is preferentially restricted to DLBCL. To identify the involved mechanisms, we performed whole exome and targeted HLA deep-sequencing in 74 DLBCL samples, and found somatic inactivation of B2M and the HLA-I loci in 80% (34 of 42) of MHC-INEG tumors. Furthermore, 70% (22 of 32) of MHC-IPOS DLBCLs harbored monoallelic HLA-I genetic alterations (MHC-IPOS/mono), indicating allele-specific inactivation. MHC-INEG and MHC-IPOS/mono cases harbored significantly higher mutational burden and inferred neoantigen load, suggesting potential coselection of HLA-I loss and sustained neoantigen production. Notably, the analysis of >500,000 individuals across different cancer types revealed common germline HLA-I homozygosity, preferentially in DLBCL. In mice, germinal-center B cells lacking HLA-I expression did not progress to lymphoma and were counterselected in the context of oncogene-driven lymphomagenesis, suggesting that additional events are needed to license immune evasion. These results suggest a multistep process of HLA-I loss in DLBCL development including both germline and somatic events, and have direct implications for the pathogenesis and immunotherapeutic targeting of this disease.
Assuntos
Transformação Celular Neoplásica/genética , Antígenos de Histocompatibilidade Classe I/genética , Linfoma Difuso de Grandes Células B/genética , Linhagem Celular Tumoral , Citidina Desaminase , Inativação Gênica , Humanos , Linfoma Difuso de Grandes Células B/imunologia , Proteínas Proto-Oncogênicas c-bcl-6/genética , Microglobulina beta-2/genéticaRESUMO
CtIP is a DNA end resection factor widely implicated in alternative end-joining (A-EJ)-mediated translocations in cell-based reporter systems. To address the physiological role of CtIP, an essential gene, in translocation-mediated lymphomagenesis, we introduced the T855A mutation at murine CtIP to nonhomologous end-joining and Tp53 double-deficient mice that routinely succumbed to lymphomas carrying A-EJ-mediated IgH-Myc translocations. T855 of CtIP is phosphorylated by ATM or ATR kinases upon DNA damage to promote end resection. Here, we reported that the T855A mutation of CtIP compromised the neonatal development of Xrcc4-/-Tp53-/- mice and the IgH-Myc translocation-driven lymphomagenesis in DNA-PKcs-/-Tp53-/- mice. Mechanistically, the T855A mutation limits DNA end resection length without affecting hairpin opening, translocation frequency, or fork stability. Meanwhile, after radiation, CtIP-T855A mutant cells showed a consistent decreased Chk1 phosphorylation and defects in the G2/M cell cycle checkpoint. Consistent with the role of T855A mutation in lymphomagenesis beyond translocation, the CtIP-T855A mutation also delays splenomegaly in λ-Myc mice. Collectively, our study revealed a role of CtIP-T855 phosphorylation in lymphomagenesis beyond A-EJ-mediated chromosomal translocation.
Assuntos
Proteínas de Transporte/genética , Proteínas de Ciclo Celular/genética , Dano ao DNA/genética , Linfoma/genética , Linfoma/patologia , Fosforilação/genética , Animais , Proteínas Mutadas de Ataxia Telangiectasia/genética , Pontos de Checagem da Fase G2 do Ciclo Celular/genética , Camundongos , Mutação/genética , Translocação Genética/genéticaRESUMO
To repurpose compounds for diffuse large B cell lymphoma (DLBCL), we screened a library of drugs and other targeted compounds approved by the US Food and Drug Administration on 9 cell lines and validated the results on a panel of 32 genetically characterized DLBCL cell lines. Dasatinib, a multikinase inhibitor, was effective against 50% of DLBCL cell lines, as well as against in vivo xenografts. Dasatinib was more broadly active than the Bruton kinase inhibitor ibrutinib and overcame ibrutinib resistance. Tumors exhibiting dasatinib resistance were commonly characterized by activation of the PI3K pathway and loss of PTEN expression as a specific biomarker. PI3K suppression by mTORC2 inhibition synergized with dasatinib and abolished resistance in vitro and in vivo. These results provide a proof of concept for the repurposing approach in DLBCL, and point to dasatinib as an attractive strategy for further clinical development in lymphomas.
Assuntos
Dasatinibe/farmacologia , Resistencia a Medicamentos Antineoplásicos/efeitos dos fármacos , Linfoma Difuso de Grandes Células B , Adenina/análogos & derivados , Animais , Linhagem Celular Tumoral , Humanos , Linfoma Difuso de Grandes Células B/tratamento farmacológico , Linfoma Difuso de Grandes Células B/metabolismo , Linfoma Difuso de Grandes Células B/patologia , Alvo Mecanístico do Complexo 2 de Rapamicina/metabolismo , Camundongos , PTEN Fosfo-Hidrolase/metabolismo , Fosfatidilinositol 3-Quinases/metabolismo , Piperidinas , Estudo de Prova de Conceito , Pirazóis/farmacologia , Pirimidinas/farmacologia , Ensaios Antitumorais Modelo de XenoenxertoRESUMO
Diffuse large B-cell lymphoma (DLBCL), the most frequent subtype of lymphoid malignancy, remains a significant clinical challenge, as â¼30% of patients are not cured. Over the past decade, remarkable progress has been made in the understanding of the pathogenesis of this disease, spurred by the implementation of powerful genomic technologies that enabled the definition of its genetic and epigenetic landscape. These studies have uncovered a multitude of genomic alterations that contribute to the initiation and maintenance of the tumor clone by disrupting biological functions known to be critical for the normal biology of its cells of origin, germinal center B cells. The identified alterations involve epigenetic remodeling, block of differentiation, escape from immune surveillance, and the constitutive activation of several signal transduction pathways. This wealth of new information offers unique opportunities for the development of improved diagnostic and prognostic tools that could help guide the clinical management of DLBCL patients. Furthermore, a number of the mutated genes identified are potentially actionable targets that are currently being explored for the development of novel therapeutic strategies. This review summarizes current knowledge of the most common genetic alterations associated with DLBCL in relation to their functional impact on the malignant transformation process, and discusses their clinical implications for mechanism-based therapeutics.
Assuntos
Linfócitos B/metabolismo , Predisposição Genética para Doença , Variação Genética , Linfoma Difuso de Grandes Células B/genética , Animais , Linfócitos B/patologia , Transformação Celular Neoplásica/genética , Transformação Celular Neoplásica/metabolismo , Estudos de Associação Genética , Humanos , Linfoma Difuso de Grandes Células B/diagnóstico , Linfoma Difuso de Grandes Células B/metabolismo , Mutação , PrognósticoRESUMO
Activating mutations of NOTCH1 (a well-known oncogene in T-cell acute lymphoblastic leukemia) are present in â¼4-13% of chronic lymphocytic leukemia (CLL) cases, where they are associated with disease progression and chemorefractoriness. However, the specific role of NOTCH1 in leukemogenesis remains to be established. Here, we report that the active intracellular portion of NOTCH1 (ICN1) is detectable in â¼50% of peripheral blood CLL cases lacking gene mutations. We identify a "NOTCH1 gene-expression signature" in CLL cells, and show that this signature is significantly enriched in primary CLL cases expressing ICN1, independent of NOTCH1 mutation. NOTCH1 target genes include key regulators of B-cell proliferation, survival, and signal transduction. In particular, we show that NOTCH1 transactivates MYC via binding to B-cell-specific regulatory elements, thus implicating this oncogene in CLL development. These results significantly extend the role of NOTCH1 in CLL pathogenesis, and have direct implications for specific therapeutic targeting.
Assuntos
Linfócitos B/fisiologia , Leucemia Linfocítica Crônica de Células B/genética , Receptor Notch1/genética , Linfócitos B/patologia , Proliferação de Células/genética , Regulação Leucêmica da Expressão Gênica , Genes myc , Humanos , Mutação , Receptor Notch1/sangueRESUMO
The BCL6 proto-oncogene encodes a transcriptional repressor that is required for the germinal center (GC) reaction and is implicated in lymphomagenesis. BCL6 protein stability is regulated by F-box protein 11 (FBXO11)-mediated ubiquitination and degradation, which is impaired in â¼6% of diffuse large B-cell lymphomas that carry inactivating genetic alterations targeting the FBXO11 gene. In order to investigate the role of FBXO11 in vivo, we analyzed GC-specific FBXO11 knockout mice. FBXO11 reduction or loss led to an increased number of GC B cells, to an altered ratio of GC dark zone to light zone cells, and to higher levels of BCL6 protein in GC B cells. B-cell receptor-mediated degradation of BCL6 was reduced in the absence of FBXO11, suggesting that FBXO11 contributes to the physiologic downregulation of BCL6 at the end of the GC reaction. Finally, FBXO11 inactivation was associated with the development of lymphoproliferative disorders in mice.
Assuntos
Proteínas F-Box/genética , Inativação Gênica , Centro Germinativo/metabolismo , Centro Germinativo/patologia , Transtornos Linfoproliferativos/metabolismo , Transtornos Linfoproliferativos/patologia , Animais , Linfócitos B/metabolismo , Linhagem Celular Tumoral , Regulação para Baixo , Proteínas F-Box/metabolismo , Deleção de Genes , Marcação de Genes , Humanos , Imunoglobulina M/metabolismo , Contagem de Linfócitos , Camundongos , Especificidade de Órgãos , Proto-Oncogene Mas , Proteínas Proto-Oncogênicas c-bcl-6/metabolismoRESUMO
Diffuse large B-cell lymphoma (DLBCL) is one of the most common and aggressive types of B-cell lymphoma. Deregulation of proto-oncogene expression after a translocation, most notably to the immunoglobulin heavy-chain locus (IGH), is one of the hallmarks of DLBCL. Using whole-genome sequencing analysis, we have identified the PD-L1/PD-L2 locus as a recurrent translocation partner for IGH in DLBCL. PIM1 and TP63 were also identified as novel translocation partners for PD-L1/PD-L2 Fluorescence in situ hybridization was furthermore used to rapidly screen an expanded DLBCL cohort. Collectively, a subset of samples was found to be affected by gains (12%), amplifications (3%), and translocations (4%) of the PD-L1/PD-L2 locus. RNA sequencing data coupled with immunohistochemistry revealed that these cytogenetic alterations correlated with increased expression of PD-L1 but not of PD-L2 Moreover, cytogenetic alterations affecting the PD-L1/PD-L2 locus were more frequently observed in the non-germinal center B cell-like (non-GCB) subtype of DLBCL. These findings demonstrate the genetic basis of PD-L1 overexpression in DLBCL and suggest that treatments targeting the PD-1-PD-L1/PD-L2 axis might benefit DLBCL patients, especially those belonging to the more aggressive non-GCB subtype.
Assuntos
Antígeno B7-H1/genética , Linfoma Difuso de Grandes Células B/genética , Linfócitos B/metabolismo , Estudos de Coortes , Análise Citogenética , Variações do Número de Cópias de DNA , Amplificação de Genes , Perfilação da Expressão Gênica , Regulação Neoplásica da Expressão Gênica , Genes de Cadeia Pesada de Imunoglobulina , Estudo de Associação Genômica Ampla , Centro Germinativo/metabolismo , Centro Germinativo/patologia , Sequenciamento de Nucleotídeos em Larga Escala , Humanos , Linfoma Difuso de Grandes Células B/patologia , Proto-Oncogene Mas , Translocação Genética , Regulação para Cima/genéticaRESUMO
The full set of microRNAs (miRNAs) in the human genome is not known. Because presently known miRNAs have been identified by virtue of their abundant expression in a few cell types, many tissue-specific miRNAs remain unrevealed. To understand the role of miRNAs in B cell function and lymphomagenesis, we generated short-RNA libraries from normal human B cells at different stages of development (naive, germinal center, memory) and from a Burkitt lymphoma cell line. A combination of cloning and computational analysis identified 178 miRNAs (miRNome) expressed in normal and/or transformed B cell libraries. Most notably, the B cell miRNome included 75 miRNAs which to our knowledge have not been previously reported and of which 66 have been validated by RNA blot and/or RT-PCR analyses. Numerous miRNAs were expressed in a stage- or transformation-specific fashion in B cells, suggesting specific functional or pathologic roles. These results provide a resource for studying the role of miRNAs in B cell development, immune function, and lymphomagenesis.
Assuntos
Subpopulações de Linfócitos B/imunologia , MicroRNAs/fisiologia , Animais , Linhagem Celular Tumoral , Cães , Evolução Molecular , Regulação da Expressão Gênica , Haplorrinos , Humanos , Camundongos , MicroRNAs/análise , MicroRNAs/genética , Análise de Sequência com Séries de Oligonucleotídeos , Tonsila Palatina/metabolismo , RatosRESUMO
B-cell non-Hodgkin's lymphoma comprises biologically and clinically distinct diseases the pathogenesis of which is associated with genetic lesions affecting oncogenes and tumour-suppressor genes. We report here that the two most common types--follicular lymphoma and diffuse large B-cell lymphoma--harbour frequent structural alterations inactivating CREBBP and, more rarely, EP300, two highly related histone and non-histone acetyltransferases (HATs) that act as transcriptional co-activators in multiple signalling pathways. Overall, about 39% of diffuse large B-cell lymphoma and 41% of follicular lymphoma cases display genomic deletions and/or somatic mutations that remove or inactivate the HAT coding domain of these two genes. These lesions usually affect one allele, suggesting that reduction in HAT dosage is important for lymphomagenesis. We demonstrate specific defects in acetylation-mediated inactivation of the BCL6 oncoprotein and activation of the p53 tumour suppressor. These results identify CREBBP/EP300 mutations as a major pathogenetic mechanism shared by common forms of B-cell non-Hodgkin's lymphoma, with direct implications for the use of drugs targeting acetylation/deacetylation mechanisms.
Assuntos
Acetiltransferases/genética , Acetiltransferases/metabolismo , Proteína de Ligação a CREB/genética , Proteína p300 Associada a E1A/genética , Linfoma de Células B/enzimologia , Linfoma de Células B/genética , Mutação/genética , Acetilcoenzima A/metabolismo , Acetilação , Acetiltransferases/química , Acetiltransferases/deficiência , Animais , Sequência de Bases , Proteína de Ligação a CREB/química , Proteína de Ligação a CREB/deficiência , Proteína de Ligação a CREB/metabolismo , Células Cultivadas , Proteínas de Ligação a DNA/metabolismo , Proteína p300 Associada a E1A/química , Proteína p300 Associada a E1A/deficiência , Proteína p300 Associada a E1A/metabolismo , Regulação Neoplásica da Expressão Gênica , Células HEK293 , Histona Acetiltransferases/química , Histona Acetiltransferases/deficiência , Histona Acetiltransferases/genética , Histona Acetiltransferases/metabolismo , Humanos , Linfoma de Células B/patologia , Linfoma Folicular/enzimologia , Linfoma Folicular/genética , Linfoma Folicular/patologia , Linfoma Difuso de Grandes Células B/enzimologia , Linfoma Difuso de Grandes Células B/genética , Linfoma Difuso de Grandes Células B/patologia , Camundongos , Mutação de Sentido Incorreto/genética , Polimorfismo de Nucleotídeo Único/genética , Ligação Proteica , Estrutura Terciária de Proteína/genética , Proteínas Proto-Oncogênicas c-bcl-6 , Recidiva , Deleção de Sequência/genética , Proteína Supressora de Tumor p53/metabolismoRESUMO
Burkitt lymphoma (BL) is a highly aggressive B-cell non-Hodgkin lymphoma (B-NHL), which originates from germinal center (GC) B cells and harbors translocations deregulating v-myc avian myelocytomatosis viral oncogene homolog (MYC). A comparative analysis of microRNAs expressed in normal and malignant GC B cells identified microRNA 28 (miR-28) as significantly down-regulated in BL, as well as in other GC-derived B-NHL. We show that reexpression of miR-28 impairs cell proliferation and clonogenic properties of BL cells by modulating several targets including MAD2 mitotic arrest deficient-like 1, MAD2L1, a component of the spindle checkpoint whose down-regulation is essential in mediating miR-28-induced proliferation arrest, and BCL2-associated athanogene, BAG1, an activator of the ERK pathway. We identify the oncogene MYC as a negative regulator of miR-28 expression, suggesting that its deregulation by chromosomal translocation in BL leads to miR-28 suppression. In addition, we show that miR-28 can inhibit MYC-induced transformation by directly targeting genes up-regulated by MYC. Overall, our data suggest that miR-28 acts as a tumor suppressor in BL and that its repression by MYC contributes to B-cell lymphomagenesis.
Assuntos
Proliferação de Células , Linfoma de Células B/genética , Linfoma de Células B/patologia , MicroRNAs/fisiologia , Proteínas Adaptadoras de Transdução de Sinal/metabolismo , Linfócitos B/fisiologia , Linfoma de Burkitt/genética , Linfoma de Burkitt/patologia , Linfoma de Burkitt/fisiopatologia , Carcinogênese , Proteínas de Ciclo Celular/metabolismo , Linhagem Celular Tumoral , Transformação Celular Neoplásica/genética , Proteínas de Ligação a DNA/metabolismo , Regulação para Baixo/fisiologia , Regulação Neoplásica da Expressão Gênica/fisiologia , Genes myc/fisiologia , Centro Germinativo , Humanos , Linfoma de Células B/fisiopatologia , Sistema de Sinalização das MAP Quinases/fisiologia , Proteínas Nucleares/metabolismo , Processamento Pós-Transcricional do RNA/fisiologia , Fatores de Transcrição/metabolismo , TranscriptomaRESUMO
Fludarabine refractoriness (FR) represents an unsolved clinical problem of chronic lymphocytic leukemia (CLL) management. Although next-generation sequencing studies have led to the identification of a number of genes frequently mutated in FR-CLL, a comprehensive evaluation of the FR-CLL genome has not been reported. Toward this end, we studied 10 FR-CLLs by combining whole-exome sequencing and copy number aberration (CNA) analysis, which showed an average of 16.3 somatic mutations and 4 CNAs per sample. Screening of recurrently mutated genes in 48 additional FR-CLLs revealed that ~70% of FR-CLLs carry ≥1 mutation in genes previously associated with CLL clinical course, including TP53 (27.5%), NOTCH1 (24.1%), SF3B1 (18.9%), and BIRC3 (15.5%). In addition, this analysis showed that 10.3% of FR-CLL cases display mutations of the FAT1 gene, which encodes for a cadherin-like protein that negatively regulates Wnt signaling, consistent with a tumor suppressor role. The frequency of FAT1-mutated cases was significantly higher in FR-CLL than in unselected CLLs at diagnosis (10.3% vs 1.1%, P = .004), suggesting a role in the development of a high-risk phenotype. These findings have general implications for the mechanisms leading to FR and point to Wnt signaling as a potential therapeutic target in FR-CLL.