Transcriptional silencing by the BCL6 oncoprotein

描述（申请人提供）：BCL6是弥漫性大b细胞淋巴瘤（DLBCL）中最常见的癌基因。在正常发育中，BCL6是b细胞进入分化的生发中心阶段和经历免疫球蛋白亲和成熟所必需的。从机制的角度来看，BCL6是btb -锌指蛋白家族的转录抑制因子。BCL6通过募集辅抑制蛋白来抑制靶基因介导其生物学效应。在最初的五年里，这项研究为BCL6的转录和生物学作用提供了新的见解。一些亮点包括发现BCL6通过直接抑制ATR基因来减弱正常和恶性b细胞中的DNA损伤感知，BCL6可以通过生化分隔具有不同生物学功能的靶基因，使它们可以通过环境刺激独立地发出信号，以及SMRT， N-CoR和BCoR协同抑制因子募集到BCL6 BTB结构域是抑制关键检查点基因和DLBCL细胞存活所必需的。后一种观察结果促使我们开发了一种BCL6抑制剂药物（按照最初提案的目标1和3），目前正在进入临床试验阶段。目前的版本将建立在这些线索的基础上，更深入地探索正常和恶性b细胞中转录编程的机制基础。具体来说，我们假设BCL6通过不同的生化机制控制许多不同的生物学途径，其中一些途径在正常和恶性b细胞之间存在差异。我们预测BCL6可以通过将组蛋白修饰的特定组合单独引入启动子或与相关转录因子结合，或通过物理运输不同的基因到b细胞细胞核中离散的转录抑制域，从而将基因区隔化。我们将结合先进的基因组学工具来探索这些问题。最后，我们预测BCL6通过不同的辅抑制因子调控的许多功能不同的转录程序在维持恶性淋巴瘤表型的各个方面发挥重要作用。我们将通过系统地消耗这些共抑制因子，并在体外和体内研究对淋巴瘤细胞的生物学影响，来探索它们的贡献。基因表达谱将用于识别与辅抑制因子功能丧失相关的特征。我们将把这些特征提交到连接图谱中，以确定模拟每个辅抑制因子耗竭的药物，并将研究它们作为抗淋巴瘤药物的潜在用途。

DESCRIPTION (provided by applicant): BCL6 is the most commonly involved oncogene in diffuse large B-cell lymphomas (DLBCL). In normal development BCL6 is required for B-cells to enter the germinal center stage of differentiation and undergo immunoglobulin affinity maturation. From the mechanistic standpoint BCL6 is a transcriptional repressor of the BTB-Zinc finger family of proteins. BCL6 represses target genes to mediate its biological effects through recruitment of corepressor proteins. In its initial five years this proposal revealed new insights into the transcriptional and biological actions of BCL6. Some highlights include the discovery that BCL6 attenuates DNA damage sensing in normal and malignant B-cells by directly repressing the ATR gene, that BCL6 can biochemically compartmentalize target genes with distinct biological functions so that they can be signaled to independently by environmental stimuli, and that recruitment of the SMRT, N-CoR and BCoR corepressors to the BCL6 BTB domain is required for repression of key checkpoint genes and the survival of DLBCL cells. This latter observation led us to develop a BCL6 inhibitor drug (as per Aim 1 and 3 of the original proposal) that is now in the process of moving to clinical trials. The current version of this proposal will build on some of these leads to more profoundly explore the mechanistic basis of transcriptional programming in normal and malignant B-cells. Specifically, we hypothesize that BCL6 controls many different biological pathways, several of which vary between normal and malignant B-cells, through biochemically distinct mechanisms. We predict that BCL6 can compartmentalize genes by either introducing a specific combination of histone modifications into their promoters alone or in combination with allied transcription factors, or by physically transporting different genes to discrete transcriptional repressor domains in the nuclei of B-cells. We will use a combination of advanced genomics tools to explore these questions. Finally we predict that many of these functionally distinct transcriptional programs regulated by BCL6 through different corepressors play important roles in maintaining various facets of the malignant lymphoma phenotype. We will explore their contribution by systematically depleting these corepressors and studying the biological impact on lymphoma cells in vitro and in vivo. Gene expression profiling will be used to identify the signatures associated with corepressor loss of function. We will submit these signatures to connectivity mapping in order to identify drugs that mimic depletion of each corepressor and will study their potential use as anti-lymphoma agents. PUBLIC HEALTH RELEVANCE: BCL6 is the most commonly involved oncogene in B-cell lymphomas. This proposal explores basic transcriptional mechanisms that mediate the phenotype of diffuse large Bcell lymphomas, and of normal B- cells undergoing immunoglobulin affinity maturation. The focus is translational, with an eye towards harnessing basic observations to improve diagnostic and therapeutic options for lymphoma patients. Along these lines, over the past five years this research led to the development of a rationally designed BCL6 inhibitor drug which is now being translated for use in clinical trials. In its next phase the proposal will expand upon the scientific theme of characterizing and therapeutically targeting transcriptional mechanisms in lymphoma cells, and using the information to learn as well about the normal immune system.