Mechanisms of Leukemogenic Transformation by MLL-CALM

描述(申请人提供)：涉及染色体11q23的混合血统白血病(MLL)基因的染色体重排在白血病中常见。虽然已经确定了40多个MLL易位伙伴基因，但MLL融合伙伴蛋白导致白血病的确切机制仍不清楚。我们最近在一例急性髓系白血病(AML)婴儿中发现了一种新的11号染色体倒位，该倒位将MLL与网状蛋白组装淋巴白血病(Calm)基因并列在11q14上。Calm最初被确定为AF10的易位伙伴-本身是MLL伙伴-在急性白血病和淋巴瘤中。Calm蛋白直接与胞内蛋白和膜脂相互作用，在细胞内吞和胞内囊泡运输中起关键作用。最近，小鼠Calm基因的突变被证明是导致Fill小鼠表型的原因，Fill小鼠在造血和铁代谢方面存在显著异常。在血液系统恶性肿瘤中，作为两个不同基因的易位伙伴，CAMAL参与了正常的造血功能，提示正常CAMAL功能的紊乱有助于白血病的发生。这项建议的总体目标是研究MLL-Calm融合蛋白在白血病发生中的生物学作用。我们推测，MLL-Calm易位通过扰乱Calm和MLL的正常功能而参与了髓系白血病的发展。为了开始了解MLL-Calm蛋白参与AML发病的机制，我们的首要目标是确定MLL-Calm蛋白的表达是否会导致体外转化和体内白血病。我们将利用小鼠造血祖细胞转化实验，在体外严格证明MLL-Calm的表达导致转化，并在体内建立MLL-Calm依赖的小鼠白血病模型。此外，为了更真实地模拟MLL-Calm白血病的表型，我们将准备一只MLL-Calm转基因小鼠。最后，我们将在FIT1来源的造血祖细胞的背景下研究白血病的发生。我们的第二个总体目标是确定参与MLL-Calm依赖的转换的机制。在这些研究中，我们将重点研究三种特定的机制-二聚化、转录调节和内吞作用-在MLL-Calm-和Calm-AF10依赖的转化中的作用。对CAMAL功能所获得的见解可能适用于大量具有CAMPAL-AF10易位的白血病和淋巴瘤，在更广泛的意义上，将有助于我们对正常CAMPE生物学的理解。

DESCRIPTION (provided by applicant): Chromosomal rearrangements involving the Mixed Lineage Leukemia (MLL) gene at chromosome 11q23 are frequently seen in leukemias. Although more than 40 translocation partner genes have been identified for MLL, the precise mechanisms by which MLL-fusion partner proteins lead to leukemia remain unclear. We recently identified a novel chromosome 11 inversion in an infant with acute myeloid leukemia (AML) that juxtaposed MLL to the Clathrin Assembly Lymphoid Myeloid Leukemia (CALM) gene at 11q14. CALM was first identified as a translocation partner for AF10 - itself an MLL partner - in acute leukemias and lymphomas. The CALM protein directly interacts with clathrin and membrane lipids, and plays a key role in endocytosis and intracellular vesicle trafficking. Recently, mutations in the murine calm gene have been shown to account for the phenotype of the fill mouse, which has significant abnormalities in hematopoiesis and iron metabolism. The involvement of CALM as a translocation partner for two distinct genes in hematopoietic malignancies, together with its involvement in normal hematopoiesis, suggests that perturbation of normal CALM function contributes to the development of leukemia. The overall objective of this proposal is to study the biology of the MLL-CALM fusion protein in leukemogenesis. We hypothesize that the MLL-CALM translocation contributes to the development of myeloid leukemia by perturbing the normal function of both CALM and MLL. To begin to understand mechanisms by which the MLL-CALM protein is involved in the pathogenesis of AML, our first aim is to determine whether MLL-CALM expression results in transformation in vitro and leukemia in vivo. We will use the murine hematopoietic progenitor transformation assay to rigorously demonstrate that MLL-CALM expression results in transformation in vitro, and establish in vivo murine models of MLL-CALM-dependent leukemia. In addition, to more faithfully mimic the MLL-CALM leukemia phenotype, we will prepare an mll-CALM transgenic mouse. Finally, we will examine leukemogenesis in the context of fit1 -derived hematopoietic precursors. Our second overall aim is to identify mechanisms involved in MLL-CALM-dependent transformation. In these studies, we will focus on the role of three specific mechanisms - dimerization, transcriptional regulation and endocytosis - in MLL-CALM- and CALM-AF10-dependent transformation. Insights gained regarding CALM function may be generalizable to the large number of leukemias and lymphomas with CALM-AF10 translocations, and, in a broader sense, will contribute to our understanding of normal CALM biology.