IRF8 and lymphomagenesis

大规模平行测序的出现突出了癌症的遗传复杂性，并揭示了癌症的遗传复杂性。 几个未被怀疑的基因对恶性转化过程的假定贡献。这些 这些进展也表明，需要对新发现的突变基因进行系统的检查，以确定 它们是否真的有助于癌症发病机制，或者仅仅代表与癌症无关的无害变体。 观察表型。弥漫性大B细胞淋巴瘤（DLBCL）是美国最常见的淋巴系统恶性肿瘤， 成年人，只有约60%的病例可以治愈。这种临床挑战与疾病的复杂性有关， 遗传学，包括表观遗传修饰剂的破坏，NF-κ B途径的组成性激活，以及 B细胞相关转录因子的失调。后者可能来自染色体易位， 基因组扩增/缺失和体细胞突变。最近，我们开发了一种IGH靶向 捕获/测序策略，并在DLBCL中发现了新的异常基因融合， IRF8（干扰素调节因子8）的IGH基因座，t（14; 16）（q32; q24），转录的原型模型 B细胞淋巴瘤中因子失调。独立地，发现IRF8在约10%的人中发生体细胞突变。 DLBCL活检。有趣的是，接近50%的IRF8突变DLBCL也具有KMT2D突变， 组蛋白甲基转移酶，当失活时，可增强其他遗传因子的淋巴瘤发生潜力， 病变IRF8是干扰素家族转录因子的一员，在生发中心表达 (GC)其中它直接影响GC反应的几个关键调节因子的表达，包括BCL 6， AICDA和PRDM1。本提案的中心目标是检验IRF8是善意的假设。 DLBCL中的癌基因，其可通过染色体易位和体细胞突变而失调。到 提出这一概念后，我们发现IRF8在DLBCL细胞系中的异位表达促进了DLBCL细胞的增殖。 以BCL 6和AICDA诱导、PRDM 1抑制和耐药性为特征的淋巴瘤发生谱 到凋亡。此外，我们产生的初步数据表明，在大肠杆菌中发现的IRF8错义突变体， DLBCL都是功能获得性的。最后，我们创建了具有Irf 8的B细胞限制性转基因表达的小鼠。 基于我们的初步数据，以及这种新型动物模型的可用性，我们建议解决 1）确定在小鼠模型中Irf8淋巴瘤发生的机制， 在人DLBCL中发现的IGH/IRF8融合; 2）在体内表征人DLBCL与IGH/IRF8之间的促淋巴瘤协同作用。 致癌的Irf8和肿瘤抑制因子Kmt2d; 3）定义体细胞的功能后果， 在DLBCL中发现IRF8突变。当这个项目完成后，我们将展示IRF8的功能， 在DLBCL的发展中与KMT2D缺失协同作用的癌基因。我们还希望机械地 将IRF8的淋巴瘤发生与BCL 6、AICDA和PRDM 1的失调联系起来。

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.