Role of KMT2D Gene Inactivation in B cell Non Hodgkin Lymphoma

研究综述 弥漫性大B细胞淋巴瘤（DLBCL）和滤泡性淋巴瘤（FL）是两种最常见的淋巴瘤。 成熟B细胞淋巴瘤的形式，一起占所有诊断的70%以上。这两种疾病仍然是 重大临床挑战，因为大量患者人群在以下治疗后未实现持久缓解 传统的治疗策略。确定肿瘤的分子机制 启动和维持，并可能容易受到有针对性的治疗干预，代表了一项研究 为了提高我们治愈这些疾病的能力。 导致KMT 2D甲基转移酶失活的体细胞突变是最常见的 FL（80%的病例）和DLBCL（~30%的病例）中的遗传性病变，表明表观遗传学的重要作用 这些癌症发病机制的扰动（Pasqualucci等人，Nature Genetics 2011; Morin等人， Nature 2011）。事实上，体内KMT 2D的条件性失活导致生发中心（GC）的扩增。 B细胞，FL和DLBCL的正常对应物，并与BCL 2失调合作，以增加FL和DLBCL的表达。 肿瘤发生率重现人FL/DLBCL的表型和遗传特征，从而 将KMT 2D确定为真正的肿瘤抑制基因（Zhang等，Nature Medicine 2015; Ortega- Molina等人，Nature Medicine 2015）。然而，单独的KMT 2D的GC特异性缺失不足以 驱动肿瘤形成，表明需要额外的合作事件。我们观察到KMT 2D 突变通常与CREBBP/EP 300乙酰转移酶的改变有关，在60%的 KMT 2D突变的FL和约25%的KMT 2D突变的新发DLBCL。这两种改变都代表了 淋巴瘤（Pasqualucci等，Cell Reports 2014）。此外，CREBBP乙酰化KMT 2D蛋白， 最后，这两种蛋白质的染色质结合模式在GC特异性超- 增强子（Zhang等人，Nature Medicine 2015和Cancer Discovery 2017）。这些数据表明，KMT 2D 和CREBBP在B细胞淋巴瘤发生中通过协调调节共同和特异性程序而协同作用。 在这些结果的基础上，本项目的总体目标将是阐明 正常和转化的GC B细胞中的KMT 2D和CREBBP，具有三个特定目的： 在正常GC B细胞中由这两种蛋白协同或组合调节的转录程序， 并在伴有失活突变的B细胞淋巴瘤中被破坏，以及CREBBB介导的 ii）研究KMT 2D/CREBBP增强子结合在促进乙酰化对KMT 2D功能的影响中的作用; 染色体易位和异常体细胞超突变;和iii）检查 联合KMT 2D/CREBBP缺陷在体内淋巴瘤起始中的作用。我们预计， 这些研究将影响我们目前对这些疾病发病机制的理解， 新的见解的机制启动肿瘤转化和其具体的治疗靶向。 PHS 398/2590（Rev.06/09）

RESEARCH SUMMARY Diffuse large B-cell lymphoma (DLBCL) and follicular lymphoma (FL) represent the two most common forms of mature B-cell lymphoma, together accounting for over 70% of all diagnoses. Both diseases remain a significant clinical challenge, as a significant patient population does not achieve durable remissions following conventional therapeutic strategies. The identification of molecular mechanisms that are responsible for tumor initiation and maintenance, and could be vulnerable to targeted therapeutic intervention, represents a research imperative in order to advance our ability to cure these diseases. Somatic mutations leading to inactivation of the KMT2D methyltransferase emerged as the most common genetic lesion in FL (80% of cases) and DLBCL (~30% of cases), suggesting a prominent role for epigenetic perturbations in the pathogenesis of these cancers (Pasqualucci et al., Nature Genetics 2011; Morin et al., Nature 2011). Indeed, conditional inactivation of KMT2D in vivo leads to the expansion of germinal center (GC) B cells, the normal counterpart of FL and DLBCL, and cooperates with BCL2 deregulation to increase the incidence of tumors recapitulating phenotypic and genetic features of the human FL/DLBCL, thereby establishing KMT2D as a bona fide tumor suppressor gene (Zhang et al., Nature Medicine 2015; Ortega- Molina et al., Nature Medicine 2015). However, GC-specific deletion of KMT2D individually was insufficient to drive tumor formation, suggesting the requirement of additional cooperating events. We observed that KMT2D mutations are frequently associated with alterations in the CREBBP/EP300 acetyltransferases, found in 60% of KMT2D-mutated FL and ~25% of KMT2D-mutated de novo DLBCL. Both alterations represent early lesions in lymphomagensis (Pasqualucci et al, Cell Reports 2014). Moreover, CREBBP acetylates the KMT2D protein in vivo; finally, the chromatin-binding pattern of these two proteins significantly overlaps at GC-specific super- enhancers (Zhang et al., Nature Medicine 2015 and Cancer Discovery 2017). These data suggest that KMT2D and CREBBP cooperate in B cell lymphomagenesis by coordinately regulating common and specific programs. Building on these results, the general goal of this project will be to elucidate the cooperative role of KMT2D and CREBBP in normal and transformed GC B cells, with three Specific Aims: i) identify the transcriptional program coordinately or combinatorially regulated by these two proteins in normal GC B cells, and disrupted in B cell lymphomas with concurrent inactivating mutations, and the role of CREBBP-mediated acetylation on KMT2D function; ii) investigate the role of KMT2D/CREBBP enhancer binding in favoring chromosomal translocations and aberrant somatic hypermutation; and iii) examine the synergistic role of combined KMT2D/CREBBP deficiency in lymphoma initiation in vivo. We anticipate that the results obtained from these studies will impact our current understanding of the pathogenesis of these diseases, by providing new insights on the mechanisms initiating neoplastic transformation and on their specific therapeutic targeting. PHS 398/2590 (Rev. 06/09) Page Continuation Format Page