RESUMO
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.
Assuntos
Linfócitos B/metabolismo , Proteínas de Ciclo Celular/deficiência , Proteínas de Ciclo Celular/genética , Transformação Celular Neoplásica/genética , Proteoglicanas de Sulfatos de Condroitina/genética , Proteínas Cromossômicas não Histona/deficiência , Proteínas Cromossômicas não Histona/genética , Dosagem de Genes , Centro Germinativo/metabolismo , Imunidade Humoral , Linfoma de Células B/genética , Animais , Linfócitos B/imunologia , Linfócitos B/patologia , Proteínas de Ciclo Celular/metabolismo , Diferenciação Celular , Proliferação de Células , Transformação Celular Neoplásica/imunologia , Transformação Celular Neoplásica/metabolismo , Transformação Celular Neoplásica/patologia , Células Cultivadas , Proteoglicanas de Sulfatos de Condroitina/deficiência , Proteoglicanas de Sulfatos de Condroitina/metabolismo , Proteínas Cromossômicas não Histona/metabolismo , Proteínas de Ligação a DNA/genética , Proteínas de Ligação a DNA/metabolismo , Dioxigenases , Deleção de Genes , Regulação Neoplásica da Expressão Gênica , Centro Germinativo/imunologia , Centro Germinativo/patologia , Haploinsuficiência , Histona-Lisina N-Metiltransferase/genética , Histona-Lisina N-Metiltransferase/metabolismo , Humanos , Linfoma de Células B/imunologia , Linfoma de Células B/metabolismo , Linfoma de Células B/patologia , Linfoma Difuso de Grandes Células B/genética , Linfoma Difuso de Grandes Células B/imunologia , Linfoma Difuso de Grandes Células B/metabolismo , Linfoma Difuso de Grandes Células B/patologia , Camundongos Endogâmicos C57BL , Camundongos Knockout , Proteína de Leucina Linfoide-Mieloide/genética , Proteína de Leucina Linfoide-Mieloide/metabolismo , Proteínas Proto-Oncogênicas/genética , Proteínas Proto-Oncogênicas/metabolismo , Transdução de Sinais , CoesinasRESUMO
The EZH2 histone methyltransferase is required for B cells to form germinal centers (GC). Here we show that EZH2 mediates GC formation through repression of cyclin-dependent kinase inhibitor CDKN1A (p21Cip1). Deletion of Cdkn1a rescues the GC reaction in Ezh2 -/- mice. Using a 3D B cell follicular organoid system that mimics the GC reaction, we show that depletion of EZH2 suppresses G1 to S phase transition of GC B cells in a Cdkn1a-dependent manner. GC B cells of Cdkn1a -/- Ezh2 -/- mice have high levels of phospho-Rb, indicating that loss of Cdkn1a enables progression of cell cycle. Moreover, the transcription factor E2F1 induces EZH2 during the GC reaction. E2f1 -/- mice manifest impaired GC responses, which is rescued by restoring EZH2 expression, thus defining a positive feedback loop in which EZH2 controls GC B cell proliferation by suppressing CDKN1A, enabling cell cycle progression with a concomitant phosphorylation of Rb and release of E2F1.The histone methyltransferase EZH2 silences genes by generating H3K27me3 marks. Here the authors use a 3D GC organoid and show EZH2 mediates germinal centre (GC) formation through epigenetic silencing of CDKN1A and release of cell cycle checkpoints.
