Mechanisms of Leukemogenesis in Down Syndrome

描述(申请人提供)：唐氏综合征(DS)儿童患白血病的风险增加10-20倍，特别是急性巨核细胞白血病(AMKL)。虽然在唐氏综合征中促进白血病的遗传损害在很大程度上尚未确定，但我们最近证明，来自每一位DS-AMKL患者的白血病细胞在基本的造血转录因子基因GATA1中都存在突变。在每一种情况下，突变都涉及GATA1的一个小的插入或缺失，导致帧移位，并在编码GATA-1的N端激活结构域的序列中引入提前终止密码子。这些突变阻止了50kD全长GATA-1的合成，但不阻止下游启动的40kD异构体的合成，称为GATA-1S。在这个应用中，我们建议研究GATA1突变患者的白血病发生机制。此外，我们将寻求确定在唐氏综合征AMKL中可能由21三体引起的协同因素。具体地说，我们计划：1)确定GATA1突变在更多DS-AMKL样本中的发生率和分布，以及DS前白血病患者DNA中GATA1突变的发生率和分布；2)评估GATA-1的缺失与小鼠等同于21三体的基因缺失是否能促进小鼠白血病的发生，以及进一步评估GATA-1的过表达是否能促进GATA-1缺乏的巨核祖细胞的永生化；以及3)建立有条件地只表达40kD GATA-1亚型的小鼠并将它们培育成等效于DS的小鼠。另外，我们还将把这些新的GATA1突变小鼠杂交到BXH-2品系小鼠中，以识别与白血病中GATA1突变协同作用的基因。这些研究可能会增加我们对GATA1突变如何在唐氏综合征白血病的发生和发展中起作用的理解，并可能导致在21号染色体上发现新的白血病疾病基因。

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.