Mechanisms of Leukemogenesis in Down Syndrome

描述（申请人提供）：唐氏综合征（DS）儿童发生白血病的风险增加10-20倍，特别是急性巨核细胞白血病（AMKL）。虽然唐氏综合征中促进白血病的遗传病变在很大程度上尚未确定，但我们最近证明，来自每一个DS-AMKL患者的白血病细胞都在必需的造血转录因子基因GATA 1中存在突变。在每种情况下，突变都涉及GATA 1中的小插入或缺失，导致移码和在编码加塔-1的N-末端活化结构域的序列内引入提前终止密码子。这些突变阻止了50-kD全长加塔-1的合成，但不阻止进一步下游起始的40-kD同种型（称为加塔-1 s）的合成。在本申请中，我们建议研究GATA 1突变患者的白血病发生机制。此外，我们将寻求确定合作的因素，可能有助于21三体唐氏综合征AMKL。具体而言，我们计划：1）确定GATA 1突变在更多数量的DS-AMKL样品以及来自患有DS白血病前期（称为短暂性骨髓增生性疾病）的患者的DNA中的发生率和分布; 2）评估加塔-1的缺失与小鼠等同的21三体是否可以促进小鼠中的白血病发生，并且进一步，过表达加塔-1 s是否能促进加塔-1缺陷型巨核祖细胞的永生化;和3）通过产生将条件性地仅表达加塔的40-kD同种型的小鼠来开发DS-AMKL的小鼠模型。1，并将它们与小鼠DS的小鼠等同物进行繁殖。另外，我们还将这些新的GATA 1突变小鼠与BXH-2小鼠品系杂交，以鉴定与白血病中的GATA 1突变合作的基因。这些研究可能会增加我们对GATA 1突变如何促进唐氏综合征白血病的发生或进展的理解，也可能导致21号染色体上新的白血病基因的鉴定。

DESCRIPTION (provided by applicant): Children with Down syndrome (DS) have a 10-20 fold increased risk of developing leukemia, in particular acute megakaryoblastic leukemia (AMKL). While the genetic lesions that promote leukemia in Down syndrome have been largely undefined, we recently demonstrated that leukemic cells from every DS-AMKL patient examined harbor mutations in the essential hematopoietic transcription factor gene GATA1. In every instance, the mutation involved a small insertion or deletion in GATA1 that resulted in a frame-shift and the introduction of a premature stop codon within the sequences encoding the N-terminal activation domain of GATA-1. These mutations prevent the synthesis of the 50-kD full length GATA-1, but not of a 40-kD isoform initiated further downstream, termed GATA-1s. In this application, we propose to study the mechanism of leukemogenesis in patients with GATA1 mutations. Furthermore, we will seek to identify the cooperating factors that are likely contributed by trisomy 21 in Down syndrome AMKL. Specifically, we plan: 1) To determine the incidence and distribution of GATA1 mutations in a greater number of DS-AMKL samples as well as in DNA from patients with DS pre-leukemia, named Transient Myeloproliferative Disorder; 2) To assess whether loss of GATA-1 in conjunction with the mouse equivalent of trisomy 21 can promote leukemogenesis in mice, and further, whether overexpression of GATA-1s can promote immortalization of GATA-1-deficient megakaryocyte progenitors; and 3) To develop a mouse model of DS-AMKL by creating mice that will conditionally express only the 40-kD isoform of GATA-1 and breeding them to mice with the murine equivalent of DS. Separately, we will also cross these novel GATA1 mutant mice into the BXH-2 strain of mice to identify genes that cooperate with the GATA1 mutations in leukemia. These studies will likely increase our understanding of how GATA1 mutations contribute to the initiation or progression of leukemia in Down syndrome and may also lead to the identification of novel leukemia disease genes on chromosome 21.