Pre-B cell receptor signaling in acute lymphoblastic leukemia

描述（由申请人提供）：急性淋巴细胞白血病中的前B细胞受体信号传导。人骨髓中的B细胞前体注定要死亡，除非它们通过来自成功组装的前B细胞受体的存活信号被拯救。由于这个原因，前B细胞受体信号传导链组分的缺陷导致人类早期B细胞发育的严重阻断。同样，B细胞谱系急性淋巴细胞白血病（ALL）细胞在B细胞发育的早期阶段被阻滞。在这个提议中，我们检验了B细胞系ALL的发育停滞主要反映异常的前B细胞受体功能的假设。B细胞系ALL是迄今为止儿童中最常见的恶性肿瘤，在成人中也很常见。尽管在过去四十年中取得了重大进展，但细胞毒性治疗策略最近达到了一个平台，儿童治愈率为80%，成人为55%。细胞毒性药物治疗后复发、初始耐药性和剂量限制性毒性是当前治疗方法中最常见的并发症。出于这个原因，除了细胞毒性药物治疗外，途径特异性治疗策略似乎有望进一步改善ALL患者的治疗选择。在对148例前B细胞衍生的人类ALL的初步研究中，我们发现携带E2 A-PBX 1-或MYC-基因重排的ALL细胞与正常前B细胞一样，高度选择表达功能性前B细胞受体。与此形成鲜明对比的是，几乎在所有情况下，具有其他细胞遗传学异常（例如BCR-ABL 1-或MLL-AF 4）的ALL细胞都缺乏功能性前B细胞受体的表达。在一项原理验证实验中，我们研究了BCR-ABL 1转基因小鼠中前B细胞进行性白血病转化过程中前B细胞受体的功能：有趣的是，来自前B细胞受体和致癌BCR-ABL 1激酶的信号是相互排斥的，只有不能表达功能性前B细胞受体的“受损”前B细胞才允许BCR-ABL 1转化。与具有BCR-ABL 1-或MLL-AF 4-融合基因的ALL细胞相反，前B细胞受体信号传导在E2 A-PBX 1-或MYC-转化的ALL中是活跃的，因为这些细胞在响应前B细胞受体接合时表现出强烈的Ca 2+信号。基于这些发现，我们假设ALL可以根据前B细胞受体信号传导是否能够（I型）或抑制（II型）白血病生长而分为两组。研究原发性人ALL异种移植物和I型和II型ALL的转基因小鼠模型，我们在目的1中提出建立两个亚组中前B细胞受体信号传导的特征性关键差异。在目标2中，我们建议确定I型ALL中前B细胞受体依赖性生存信号传导的要求作为药理学抑制的潜在靶点。相反，我们在目标3中提出阐明II型ALL中前B细胞受体失活的机制以及功能性前B细胞受体信号传导如何诱导II型ALL细胞的凋亡。鉴于前B细胞受体信号在ALL的这个亚组中有效地抑制白血病生长，我们在目标3中的目标是干扰这些失活机制，以恢复II型ALL细胞中的前B细胞受体依赖性凋亡信号。提出的I型和II型ALL之间的区分类似于成熟B细胞淋巴瘤的分类，其中亚组可以基于B细胞受体表达的存在（即非霍奇金淋巴瘤）和不存在（即霍奇金淋巴瘤）来区分。该提案的中心目标是确定前B细胞受体信号传导在ALL恶性转化和克隆演变过程中的作用，并针对其信号级联的单个组分，以开发ALL的新途径特异性治疗方法。

DESCRIPTION (provided by applicant): Pre-B cell receptor signaling in acute lymphoblastic leukemia. B cell precursors in human bone marrow are destined to die unless they are rescued through survival signals from a successfully assembled pre-B cell receptor. For this reason, defects in components of the pre-B cell receptor signaling chain cause a severe block of early B cell development in humans. Likewise, B cell lineage acute lymphoblastic leukemia (ALL) cells are arrested at early stages of B cell development. In this proposal, we test the hypothesis that the developmental arrest in B cell lineage ALL predominantly reflects aberrant pre-B cell receptor function. B cell lineage ALL represents by far the most frequent malignancy in children and is also common in adults. Despite significant advances over the past four decades, cytotoxic treatment strategies have recently reached a plateau with cure rates at 80 percent for children and 55 percent for adults. Relapse after cytotoxic drug treatment, initial drug-resistance and dose-limiting toxicity are among the most frequent complications of current therapy approaches. For this reason, pathway-specific treatment strategies in addition to cytotoxic drug treatment seem promising to further improve therapy options for ALL patients. In preliminary studies for this proposal on 148 cases of pre-B cell-derived human ALL, we found that ALL cells carrying an E2A-PBX1- or MYC- gene rearrangement are -like normal pre-B cells- highly selected for the expression of a functional pre-B cell receptor. In striking contrast, ALL cells with other cytogenetic abnormalities (e.g. BCR-ABL1- or MLL-AF4) lack expression of a functional pre-B cell receptor in virtually all cases. In a proof-of-principle experiment, we studied pre-B cell receptor function during progressive leukemic transformation of pre-B cells in BCR-ABL1-transgenic mice: Interestingly, signaling from the pre-B cell receptor and the oncogenic BCR-ABL1 kinase are mutually exclusive and only "crippled" pre-B cells that fail to express a functional pre-B cell receptor are permissive to transformation by BCR-ABL1. As opposed to ALL cells with BCR-ABL1- or MLL-AF4-fusion gene, pre-B cell receptor signaling is active in E2A-PBX1- or MYC-transformed ALL, because these cells exhibit a vigorous Ca2+ signal in response to pre-B cell receptor engagement. Based on these findings, we hypothesize that ALL can be subdivided into two groups based on whether pre-B cell receptor signaling enables (Type I) or suppresses (Type II) leukemic growth. Studying primary human ALL xenografts and transgenic mouse models for Type I and Type II ALL, we propose in Aim 1 to establish characteristic key differences of pre-B cell receptor signaling in the two subgroups. In Aim 2, we propose to identify the requirements for pre-B cell receptor-dependent survival signaling in Type I ALL as potential targets for pharmacological inhibition. Conversely, we propose in Aim 3 to elucidate the mechanisms of pre-B cell receptor-inactivation in Type II ALL and how functional pre-B cell receptor signaling induces apoptosis in Type II ALL cells. Given that pre-B cell receptor signaling in this subgroup of ALL effectively suppresses leukemic growth, our goal in Aim 3 is to interfere with these inactivation mechanisms to restore pre-B cell receptor-dependent apoptosis-signaling in Type II ALL cells. The proposed discrimination between Type I and Type II ALL resembles the classification of mature B cell lymphoma, in which subgroups can be distinguished based on the presence (i.e. Non-Hodgkin's lymphoma) and absence (i.e. Hodgkin's lymphoma) of B cell receptor expression. The central goal of this proposal is to establish the role of pre-B cell receptor signaling during malignant transformation and clonal evolution of ALL and to target individual components of its signaling cascade for the development of novel pathway-specific therapy approaches for ALL.