IRF8 and lymphomagenesis

大规模并行测序的出现突显了癌症的遗传复杂性，并揭示了 几个未知基因在恶性转化过程中的推定作用。这些 进展还表明，有必要对新发现的突变基因进行系统检查，以确定 它们是否真的与癌症的发病机制有关，或者仅仅是与 观察到的表型。弥漫性大B细胞淋巴瘤(DLBCL)是 成人，只有约60%的病例可以治愈。这一临床挑战与疾病的复杂性有关 遗传学，包括表观遗传修饰物的破坏，NF-κB途径的结构性激活，以及 解除对B细胞相关转录因子的调控。后者可以通过染色体易位产生， 基因组扩增/缺失和体细胞突变。最近，我们开发了一种针对IGH的 捕获/测序策略和发现包括并列在内的DLBCL新的异常基因融合 IRF8(干扰素调节因子8)到免疫球蛋白基因座，t(14；16)(q32；q24)，一个典型的转录模式 B细胞淋巴瘤中的因子去调节。独立地，IRF8被发现在大约10%的细胞中发生体细胞突变 DLBCL活组织检查。有趣的是，近50%的IRF8突变DLBCL也在KMT2D、a 组蛋白甲基转移酶失活时可增强其他基因的淋巴生成潜能 损伤。IRF8是干扰素转录因子家族的成员，在生发中心表达 (GC)它直接影响GC反应的几个关键调节因子的表达，包括BCL6， AICDA和PRDM1。这项提议的中心目标是检验IRF8是真正的 DLBCL中的癌基因，可通过染色体易位和体细胞突变来解除调控。至 提出这一概念，我们发现IRF8在DLBCL细胞系中的异位表达促进了 以BCL6和AICDA诱导、PRDM1抑制和耐药为特征的淋巴瘤谱 到细胞凋亡。此外，我们生成了初步数据，以表明在 DLBCL都是函数增益。最后，我们建立了B细胞限制性转基因表达IRF8的小鼠。 基于我们的初步数据，以及这种新的动物模型的可用性，我们建议解决 以下是特定的目的：1)确定IRF8淋巴癌的发生机制 人DLBCL中发现的IgH/IRF8融合；2)体内表征 致癌基因IRF8和肿瘤抑制基因Kmt2d；3)定义了体细胞的功能后果 DLBCL中发现IRF8突变。当这个项目完成时，我们将展示IRF8作为一个 与KMT2D Lost协同发展为DLBCL的癌基因。我们还希望机械地 把IRF8的S淋巴癌与bcl6、aicda和prdm1基因的解除调控联系起来。

The advent of massive parallel sequencing highlighted the genetic complexity of cancer, and unveiled the putative contribution of several unsuspected genes to the process of malignant transformation. These advances also indicated a need for the systematic examination of newly-found mutant genes as to determine whether they truly contribute to cancer pathogenesis, or simply represent innocuous variants irrelevant to the observed phenotype. Diffuse large B cell lymphoma (DLBCL), the most common lymphoid malignancy in adults, is curable in only ~60% of cases. This clinical challenge is associated with the disease’s complex genetics, which include disruption of epigenetic modifiers, constitutive activation of the NF-κB pathway, and deregulation of B cell relevant transcription factors. The latter, can derive from chromosomal translocation, genomic amplification/deletions and somatic mutations. Recently, we developed an IGH-targeted capture/sequencing strategy and discovered novel aberrant gene fusions in DLBCL including the juxtaposing of IRF8 (interferon regulatory factor 8) to the IGH locus, t(14;16)(q32;q24), a prototypical model of transcription factor deregulation in B cell lymphomas. Independently, IRF8 was found to be somatically mutated in ~10% of DLBCL biopsies. Interestingly, close to 50% of the IRF8-mutant DLBCLs also have mutations in KMT2D, a histone methyltransferase that when inactivated enhances the lymphomagenic potential of other genetic lesions. IRF8, a member of the interferon family of transcription factors, is expressed in the germinal center (GC) where it directly influences the expression of several key regulators of the GC reaction, including BCL6, AICDA and PRDM1. The central objective of this proposal is to test the hypothesis that IRF8 is a bona fide oncogene in DLBCL, which can be deregulated by chromosomal translocation and somatic mutations. To advance this concept, we found that ectopic expression of IRF8 in DLBCL cell lines promotes a lymphomagenic profile characterized by induction of BCL6 and AICDA, suppression of PRDM1 and resistance to apoptosis. In addition, we generated preliminary data to show that the missense IRF8 mutants found in DLBCL are all gain-of-function. Lastly, we created a mouse with B cell restricted transgenic expression of Irf8. Building on our preliminary data, and on the availability of this novel animal model, we propose to address the following specific aims: 1) Determine the mechanism for Irf8 lymphomagenesis in a mouse model that mimics the IGH/IRF8 fusion found in human DLBCL; 2) Characterize in vivo the pro-lymphoma cooperation between the oncogenic Irf8 and the tumor suppressor Kmt2d; 3) Define the functional consequences of the somatic IRF8 mutations found in DLBCL. When this project is completed, we will show that IRF8 functions as an oncogene that cooperates with KMT2D loss for the development of DLBCL. We also expect to mechanistically link IRF8’s lymphomagenesis to the deregulation of BCL6, AICDA and PRDM1.