Role of Polycomb-mediated epigenetic regulation in diffuse large B cell lymphoma

Polycomb 介导的表观遗传调控在弥漫性大 B 细胞淋巴瘤中的作用

• 批准号: 8258674
• 负责人: ANN J FEENEY
• 金额: $ 33.16万
• 依托单位: SCRIPPS RESEARCH INSTITUTE, THE
• 依托单位国家: 美国
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-02-01 至 2014-01-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/8258674
• 关键词: Accounting; Affect; Affinity; Alleles; B cell differentiation; B-Lymphocyte Subsets; B-Lymphocytes; Binding; Biological; Catalytic Domain; Cell Line; ChIP-seq; Complex; DNA; DNA Methylation; Development; Disease; Drosophila genus; Epigenetic Process; Follicular Lymphoma; Frequencies; Gene Expression; Gene Expression Profile; Gene Silencing; Gene Targeting; Genes; Genetic Transcription; Genotype; Histones; Homologous Gene; Human; Lymphoma; Lymphomagenesis; Lysine; Malignant - descriptor; Malignant Neoplasms; Mediating; Memory B-Lymphocyte; Methylation; Methyltransferase; Modification; Molecular Profiling; Molecular Target; Mutate; Mutation; Non-Hodgkin' s Lymphoma; PRC1 Protein; Pathogenesis; Pathway interactions; Pattern; Polycomb; Post-Translational Protein Processing; Proteins; Recruitment Activity; Regulation; Regulator Genes; Repression; Rest; Role; Sampling; Staging; Structure of germinal center of lymph node; Tonsil; Tumor Suppressor Genes; Tumor Suppressor Proteins; Ubiquitination; Ursidae Family; cancer type; cell type; functional group; histone methyltransferase; insight; large cell Diffuse non-Hodgkin' s lymphoma; mutant; neoplastic cell; novel; paralogous gene; uH2A; ubiquitin-protein ligase

DESCRIPTION (provided by applicant): It has become increasingly clear that the pathogenesis of many forms of cancer have a significant epigenetic component. Many cancer types are characterized by gene inactivation, and genes can be silenced through epigenetic mechanisms such as DNA methylation and/or the acquisition of repressive histone 3 modifications such as the methylation of lysines 27 or 9. Methylation of H3K27 is catalyzed by the Polycomb protein Ezh2, the catalytic component of Polycomb Repressive Complex 2 (PRC2). Recently, a specific mutation in the catalytic site of Ezh2 that hyperactivates its H3K27me3 methyltransferase activity while eliminating its ability to monomethylate H3K27 been detected with high frequency in one specific subtype of cancer: the germinal center (GC) B cell subtype of diffuse large B cell lymphoma (GCB-DLBCL). This hyperactive Ezh2 mutation is not present in any other types of lymphomas examined, suggesting that it may be uniquely relevant for GCB- DLBCL lymphomagenesis. Ezh2 transcription is repressed in naove B cells, but it is upregulated in GC B cells. We hypothesize that Ezh2 expression is normally increased at this stage to repress a specific subset of genes that must be downregulated to allow the differentiation of a naove B cell into a GC B cell, and of a GC B cell into a post-GC B cell. Once Ezh2 methylates H3K27, H3K27me3 can be recognized by the Polycomb Repressive Complex 1 (PRC1). The catalytic component of this repressive PRC1 complex is Ring1b, which monoubiquitinates H2A on lysine 119 (uH2A), leading to further repression. However, H2AK119 can be ubiquitinylated by other complexes also. Furthermore, unlike Drosophila PRC1, the basic 4 components in mammalian PRC1 have many alternative paralogs, resulting in a variety of different PRC1 complexes with different affinities for H3K27me3. Very little is known about the biological consequences of PRC1 complexes having different compositions, although it is known that the 4 mammalian paralogs of the histone binding subunit have varying affinities for H3K27me3. We hypothesize that a direct downstream consequence of more H3K27me3 in a subset of GCB-DLBCL may be that there will be more PCR1 recruitment and/or recruitment of different PRC1 complexes. This could result in more uH2A and/or more DNA methylation on some genes. Consequently, these genes are likely to display the most dysregulation. This project will characterize the Polycomb-mediated epigenetic changes that take place in normal human B cells as they differentiate into GC B cells, then into post-GC memory B cells. We will perform ChIP-seq to identify PRC1 components binding to H3K27me3, and compare this to the expression profile and DNA methylation profile to determine which genes are normally repressed in a Polycomb-mediated manner. We will analyze a large set of GC-DLBCL, will determine the epigenetic profile of lymphomas that bear or do not bear the Ezh2 mutation, and will relate this to their gene expression profile. These studies will provide insight into the dysregulation of genes in GCB- DLBCL, and will also provide novel information on the normal epigenetic mechanisms by which genes are repressed in a Polycomb-dependent manner during the late steps of B lymphocyte differentiation. PUBLIC HEALTH RELEVANCE: Diffuse large B cell lymphoma (DLBCL) is an aggressive disease that accounts for 40% of all non- Hodgkins lymphomas, and the GCB subset has been described to have a unique mutation in the histone methyltransferase, Ezh2. Finding genes that are specifically misregulated due to the Ezh2 mutation, and understanding the downstream consequences of bearing this mutant Ezh2, will be a major step forward in pinpointing key molecular targets that may be involved in the pathogenesis of GCB-DLBCL. The novel information we will gain regarding the various mechanisms of Polycomb- mediated repression in normal germinal center B cells, the cell type that undergoes the malignant transformation to GCB-DLBCL, will be essential to understand the misregulation that occurs in lymphomagenesis.

描述（由申请人提供）：越来越清楚的是，多种癌症的发病机制都具有重要的表观遗传成分。许多癌症类型的特征是基因失活，并且可以通过表观遗传机制使基因沉默，例如 DNA 甲基化和/或获得抑制性组蛋白 3 修饰（例如赖氨酸 27 或 9 的甲基化）。H3K27 的甲基化由 Polycomb 蛋白催化Ezh2，Polycomb 抑制复合物 2 (PRC2) 的催化成分。最近，在一种特定的癌症亚型：弥漫性大 B 细胞的生发中心 (GC) B 细胞亚型中，高频率地检测到 Ezh2 催化位点的特定突变，该突变过度激活其 H3K27me3 甲基转移酶活性，同时消除其单甲基化 H3K27 的能力淋巴瘤（GCB-DLBCL）。这种高度活跃的 Ezh2 突变在检查的任何其他类型的淋巴瘤中都不存在，表明它可能与 GCB-DLBCL 淋巴瘤发生具有独特的相关性。 Ezh2 转录在 naove B 细胞中受到抑制，但在 GC B 细胞中上调。我们假设 Ezh2 表达通常在此阶段增加，以抑制必须下调的特定基因子集，以允许幼稚 B 细胞分化为 GC B 细胞，以及 GC B 细胞分化为 GC B 细胞。一旦 Ezh2 甲基化 H3K27，H3K27me3 即可被 Polycomb 抑制复合物 1 (PRC1) 识别。这种抑制性 PRC1 复合物的催化成分是 Ring1b，它使赖氨酸 119 (uH2A) 上的 H2A 单泛素化，从而导致进一步的抑制。然而，H2AK119 也可以被其他复合物泛素化。此外，与果蝇 PRC1 不同，哺乳动物 PRC1 的基本 4 个成分具有许多替代旁系同源物，从而产生各种不同的 PRC1 复合物，对 H3K27me3 具有不同的亲和力。尽管已知组蛋白结合亚基的 4 个哺乳动物旁系同源物对 H3K27me3 具有不同的亲和力，但对于具有不同组成的 PRC1 复合物的生物学后果知之甚少。我们假设 GCB-DLBCL 子集中更多 H3K27me3 的直接下游后果可能是会有更多的 PCR1 募集和/或不同 PRC1 复合物的募集。这可能会导致某些基因上出现更多的 uH2A 和/或更多的 DNA 甲基化。因此，这些基因可能表现出最严重的失调。该项目将表征正常人 B 细胞分化为 GC B 细胞，然后分化为 GC 后记忆 B 细胞时，Polycomb 介导的表观遗传变化。我们将进行 ChIP-seq 来鉴定与 H3K27me3 结合的 PRC1 成分，并将其与表达谱和 DNA 甲基化谱进行比较，以确定哪些基因通常以 Polycomb 介导的方式受到抑制。我们将分析大量 GC-DLBCL，确定携带或不携带 Ezh2 突变的淋巴瘤的表观遗传谱，并将其与其基因表达谱联系起来。这些研究将深入了解 GCB-DLBCL 中基因的失调，还将提供有关正常表观遗传机制的新信息，在 B 淋巴细胞分化的后期步骤中，基因以 Polycomb 依赖性方式受到抑制。 公共健康相关性：弥漫性大 B 细胞淋巴瘤 (DLBCL) 是一种侵袭性疾病，占所有非霍奇金淋巴瘤的 40%，GCB 亚群已被描述为在组蛋白甲基转移酶 Ezh2 中具有独特的突变。寻找因 Ezh2 突变而特异性失调的基因，并了解携带该突变 Ezh2 的下游后果，将是在查明可能参与 GCB-DLBCL 发病机制的关键分子靶点方面迈出的重要一步。我们将获得有关正常生发中心 B 细胞（经历恶性转化为 GCB-DLBCL 的细胞类型）中 Polycomb 介导的抑制的各种机制的新信息，对于理解淋巴瘤发生中发生的失调至关重要。