Role of CREBBP missense mutations in lymphomagenesis

研究综述 非霍奇金淋巴瘤是美国癌症的第五大原因。其中，扩散大 B细胞淋巴瘤（DLBCL）和滤泡性淋巴瘤（FL）代表两种最常见的形式， 占诊断的60%以上。尽管在治疗这些疾病方面取得了显著进展， 在多达40%的DLBCL患者中死亡率仍然很高，而FL，尽管被认为是一种惰性疾病， 在晚期是无法治愈的，通常会转化为高度侵袭性的恶性肿瘤。复发和 转化与维持“创始者”突变子集的常见突变祖细胞有关 存在于诊断性显性肿瘤克隆中。因此，提高了对生物学的共同认识， 前体和识别可能易受靶向治疗干预的机制， 因此，这是一个优先事项，以提高我们治愈这些疾病的能力。 抑制CREBBP乙酰转移酶的体细胞突变，包括截短和HAT结构域 错义突变是FL（70%的病例）和DLBCL中第二常见的遗传变异 (40%的病例属于最近确定的EZB/C3基因亚群），揭示了EZB/C3基因的突出作用。 GC衍生淋巴瘤发病机制中的表观遗传畸变（Pasqualucci等，Nature 2011; Morin et 例如，Nature 2011）。CREBBP突变代表了肿瘤系统发育进化过程中的早期事件， 在获得额外的致癌病变之前，通过共同的突变前体获得（Pasqualucci 等人，Cell Reports 2014; Okosun等人，Nature Genetics 2014）。事实上，减少剂量的CREBBP协同 与BCL 2去调节，以增强类人FL/DLBCL的发展。虽然截短突变具有 尽管错义突变已经被广泛研究，但其作用仍在很大程度上未被探索。这是一个重大的差距 当考虑到错义突变占FL中CREBBP改变的绝大多数时， 与截短突变不同，这些等位基因表达，表明它们可以干扰 与其他乙酰转移酶或转录复合物的募集的补偿机制。在 与这一假设一致，我们和其他人的初步数据表明，热点CREBBP错义 与CREBBP缺陷细胞中观察到的那些相比，HAT突变诱导明显的变化。 基于这些结果，本项目的总体目标是阐明CREBBP错义的影响 (vs截短）突变对体内前体GC B细胞恶性转化的影响，具有三种特异性 目的：i）研究最常见的R1446 H突变宿主点在GC应答中的体内作用， 淋巴瘤发生; ii）识别由错义与非错义基因调控的共享与独特的转录程序， GC B细胞前体中的截短突变; iii）研究CREBBP突变在重编程中的作用 GC微环境我们预计，这些研究的结果将提供新的见解 启动肿瘤转化的机制及其特异性治疗靶向。

RESEARCH SUMMARY Non-Hodgkin lymphomas are the 5th leading cause of cancer in the United States. Among them, diffuse large B-cell lymphoma (DLBCL) and follicular lymphoma (FL) represent the two most common forms, together accounting for over 60% of diagnoses. Despite remarkable advances in the treatment of these diseases, mortality remains high in as many as 40% of DLBCL patients, and FL, although regarded as an indolent disease, is incurable in advanced stages, often transforming into a highly aggressive malignancy. Relapse and transformation are linked to common mutated progenitor cells that maintain a subset of “founder” mutations present in the diagnostic dominant tumor clone. Therefore, improved understanding of the biology of the common precursor and the identification of mechanisms that could be vulnerable to targeted therapeutic intervention are therefore a priority in order to advance our ability to cure these diseases. Somatic mutations that inactivate the CREBBP acetyltransferase, including truncating and HAT domain missense mutations, emerged as the second most common genetic alteration in FL (70% of cases) and DLBCL (40% of cases belonging to the recently identified EZB/C3 genetic subset), revealing a prominent role for epigenetic aberrations in the pathogenesis of GC-derived lymphomas (Pasqualucci et al., Nature 2011; Morin et al., Nature 2011). CREBBP mutations represent early events during the tumor phylogenetic evolution, which are acquired by the common mutated precursor prior to the acquisition of additional oncogenic lesions (Pasqualucci et al, Cell Reports 2014; Okosun et al., Nature Genetics 2014). Indeed, reduced dosage of CREBBP synergizes with BCL2 deregulation to enhance the development of human-like FL/DLBCL. While truncating mutations have been extensively studied, the role of missense mutations remains largely unexplored. This is a significant gap when considering that missense mutations account for the overwhelming majority of CREBBP alterations in FL, and that different from truncating mutations, these alleles are expressed, suggesting that they could interfere with compensatory mechanisms by other acetyltransferases or the recruitment of transcription complexes. In line with this hypothesis, preliminary data from us and others have shown that the hotspot CREBBP missense HAT mutation induces distinct changes compared to those observed in CREBBP-deficient cells. Building on these results, the general goal of this project is to elucidate the impact of CREBBP missense (vs truncating) mutations on the malignant transformation of the precursor GC B cell in vivo, with three Specific Aims: i) investigate the in vivo role of the most common R1446H mutational hostspot in GC responses and lymphomagenesis; ii) identify the shared vs unique transcriptional programs dysregulated by missense vs truncating mutations in the GC B cell precursor; iii) investigate the role of CREBBP mutations in reprogramming the GC microenvironment. We anticipate that the results obtained from these studies will provide new insights on the mechanisms initiating neoplastic transformation and on their specific therapeutic targeting.