RESUMEN
The most aggressive B cell lymphomas frequently manifest extranodal distribution and carry somatic mutations in the poorly characterized gene TBL1XR1. Here, we show that TBL1XR1 mutations skew the humoral immune response toward generating abnormal immature memory B cells (MB), while impairing plasma cell differentiation. At the molecular level, TBL1XR1 mutants co-opt SMRT/HDAC3 repressor complexes toward binding the MB cell transcription factor (TF) BACH2 at the expense of the germinal center (GC) TF BCL6, leading to pre-memory transcriptional reprogramming and cell-fate bias. Upon antigen recall, TBL1XR1 mutant MB cells fail to differentiate into plasma cells and instead preferentially reenter new GC reactions, providing evidence for a cyclic reentry lymphomagenesis mechanism. Ultimately, TBL1XR1 alterations lead to a striking extranodal immunoblastic lymphoma phenotype that mimics the human disease. Both human and murine lymphomas feature expanded MB-like cell populations, consistent with a MB-cell origin and delineating an unforeseen pathway for malignant transformation of the immune system.
Asunto(s)
Memoria Inmunológica/fisiología , Linfoma de Células B Grandes Difuso/patología , Proteínas Nucleares/genética , Células Precursoras de Linfocitos B/inmunología , Receptores Citoplasmáticos y Nucleares/genética , Proteínas Represoras/genética , Animales , Factores de Transcripción con Cremalleras de Leucina de Carácter Básico/genética , Factores de Transcripción con Cremalleras de Leucina de Carácter Básico/metabolismo , Cromatina/química , Cromatina/metabolismo , Centro Germinal/citología , Centro Germinal/inmunología , Centro Germinal/metabolismo , Histona Desacetilasas/metabolismo , Humanos , Linfoma de Células B Grandes Difuso/inmunología , Linfoma de Células B Grandes Difuso/metabolismo , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Mutagénesis Sitio-Dirigida , Proteínas Nucleares/química , Proteínas Nucleares/metabolismo , Co-Represor 2 de Receptor Nuclear/química , Co-Represor 2 de Receptor Nuclear/metabolismo , Células Precursoras de Linfocitos B/citología , Células Precursoras de Linfocitos B/metabolismo , Unión Proteica , Proteínas Proto-Oncogénicas c-bcl-6/antagonistas & inhibidores , Proteínas Proto-Oncogénicas c-bcl-6/genética , Proteínas Proto-Oncogénicas c-bcl-6/metabolismo , Interferencia de ARN , ARN Interferente Pequeño/metabolismo , Receptores Citoplasmáticos y Nucleares/química , Receptores Citoplasmáticos y Nucleares/metabolismo , Proteínas Represoras/química , Proteínas Represoras/metabolismo , Transcripción GenéticaRESUMEN
During the germinal center (GC) reaction, B cells undergo extensive redistribution of cohesin complex and three-dimensional reorganization of their genomes. Yet, the significance of cohesin and architectural programming in the humoral immune response is unknown. Herein we report that homozygous deletion of Smc3, encoding the cohesin ATPase subunit, abrogated GC formation, while, in marked contrast, Smc3 haploinsufficiency resulted in GC hyperplasia, skewing of GC polarity and impaired plasma cell (PC) differentiation. Genome-wide chromosomal conformation and transcriptional profiling revealed defects in GC B cell terminal differentiation programs controlled by the lymphoma epigenetic tumor suppressors Tet2 and Kmt2d and failure of Smc3-haploinsufficient GC B cells to switch from B cell- to PC-defining transcription factors. Smc3 haploinsufficiency preferentially impaired the connectivity of enhancer elements controlling various lymphoma tumor suppressor genes, and, accordingly, Smc3 haploinsufficiency accelerated lymphomagenesis in mice with constitutive Bcl6 expression. Collectively, our data indicate a dose-dependent function for cohesin in humoral immunity to facilitate the B cell to PC phenotypic switch while restricting malignant transformation.
Asunto(s)
Linfocitos B/metabolismo , Proteínas de Ciclo Celular/deficiencia , Proteínas de Ciclo Celular/genética , Transformación Celular Neoplásica/genética , Proteoglicanos Tipo Condroitín Sulfato/genética , Proteínas Cromosómicas no Histona/deficiencia , Proteínas Cromosómicas no Histona/genética , Dosificación de Gen , Centro Germinal/metabolismo , Inmunidad Humoral , Linfoma de Células B/genética , Animales , Linfocitos B/inmunología , Linfocitos B/patología , Proteínas de Ciclo Celular/metabolismo , Diferenciación Celular , Proliferación Celular , Transformación Celular Neoplásica/inmunología , Transformación Celular Neoplásica/metabolismo , Transformación Celular Neoplásica/patología , Células Cultivadas , Proteoglicanos Tipo Condroitín Sulfato/deficiencia , Proteoglicanos Tipo Condroitín Sulfato/metabolismo , Proteínas Cromosómicas no Histona/metabolismo , Proteínas de Unión al ADN/genética , Proteínas de Unión al ADN/metabolismo , Dioxigenasas , Eliminación de Gen , Regulación Neoplásica de la Expresión Génica , Centro Germinal/inmunología , Centro Germinal/patología , Haploinsuficiencia , N-Metiltransferasa de Histona-Lisina/genética , N-Metiltransferasa de Histona-Lisina/metabolismo , Humanos , Linfoma de Células B/inmunología , Linfoma de Células B/metabolismo , Linfoma de Células B/patología , Linfoma de Células B Grandes Difuso/genética , Linfoma de Células B Grandes Difuso/inmunología , Linfoma de Células B Grandes Difuso/metabolismo , Linfoma de Células B Grandes Difuso/patología , Ratones Endogámicos C57BL , Ratones Noqueados , Proteína de la Leucemia Mieloide-Linfoide/genética , Proteína de la Leucemia Mieloide-Linfoide/metabolismo , Proteínas Proto-Oncogénicas/genética , Proteínas Proto-Oncogénicas/metabolismo , Transducción de Señal , CohesinasRESUMEN
Cell fate transitions are accompanied by global transcriptional, epigenetic and topological changes driven by transcription factors, as is exemplified by reprogramming somatic cells to pluripotent stem cells through the expression of OCT4, KLF4, SOX2 and cMYC. How transcription factors orchestrate the complex molecular changes around their target gene loci remains incompletely understood. Here, using KLF4 as a paradigm, we provide a transcription-factor-centric view of chromatin reorganization and its association with three-dimensional enhancer rewiring and transcriptional changes during the reprogramming of mouse embryonic fibroblasts to pluripotent stem cells. Inducible depletion of KLF factors in PSCs caused a genome-wide decrease in enhancer connectivity, whereas disruption of individual KLF4 binding sites within pluripotent-stem-cell-specific enhancers was sufficient to impair enhancer-promoter contacts and reduce the expression of associated genes. Our study provides an integrative view of the complex activities of a lineage-specifying transcription factor and offers novel insights into the nature of the molecular events that follow transcription factor binding.
Asunto(s)
Reprogramación Celular/genética , Ensamble y Desensamble de Cromatina/genética , Elementos de Facilitación Genéticos , Factores de Transcripción de Tipo Kruppel/metabolismo , Células Madre Embrionarias de Ratones/metabolismo , Animales , Células Cultivadas , Femenino , Células HEK293 , Humanos , Factor 4 Similar a Kruppel , Masculino , Ratones , Células Madre Pluripotentes/metabolismoRESUMEN
During mitosis, transcription is halted and many chromatin features are lost, posing a challenge for the continuity of cell identity, particularly in fast cycling stem cells, which constantly balance self-renewal with differentiation. Here we show that, in pluripotent stem cells, certain histone marks and stem cell regulators remain associated with specific genomic regions of mitotic chromatin, a phenomenon known as mitotic bookmarking. Enhancers of stem cell-related genes are bookmarked by both H3K27ac and the master regulators OCT4, SOX2, and KLF4, while promoters of housekeeping genes retain high levels of mitotic H3K27ac in a cell-type invariant manner. Temporal degradation of OCT4 during mitotic exit compromises its ability both to maintain and induce pluripotency, suggesting that its regulatory function partly depends on its bookmarking activity. Together, our data document a widespread yet specific bookmarking by histone modifications and transcription factors promoting faithful and efficient propagation of stemness after cell division.