IGF/IGF1R signaling in hematopoiesis and leukemogenesis

描述（申请人提供）：胰岛素样生长因子/胰岛素样生长因子1受体（IGF/IGF1R）信号在调节细胞生长、增殖和凋亡中起关键作用。igf （IGF1和IGF2）和IGF1R通常与包括白血病在内的人类癌症有关。然而，对于这一途径在正常造血中的作用以及它的激活如何促进白血病的发生，人们知之甚少。癌症的发展高度依赖于细胞环境，这是由受影响细胞的内在遗传程序和它们对微环境刺激的反应决定的。该项目的长期目标是了解信号通路和癌基因的细胞类型特异性相互作用，这为开发新的和更有效的靶向癌症治疗和癌症预防奠定了基础。唐氏综合征急性巨核母细胞白血病（DS- amkl）和相关的白血病前期疾病短暂性白血病（DS- TL）作为模型来研究这一点。DS-AMKL是一种独特的儿童白血病，其特征是胎儿起源、21三体和造血转录因子GATA1的体细胞突变（导致GATA1的较短变体GATA1s的产生）。通过分析小鼠和人DS-TL/DS-AMKL细胞中的Gata1s敲入，发现Gata1s可导致胎儿巨核细胞祖细胞（MPs）的过度增殖，而不导致成年巨核细胞祖细胞（MPs）的过度增殖。胎儿MPs高度依赖IGF/IGF1R信号来增殖和存活，而成年MPs则不依赖。GATA1s突变的胎儿MPs和白血病细胞都对IGF/IGF1R信号的抑制和激活高度敏感。基于这些初步数据，我们假设GATA1可能作为一个“刹车”来限制IGF/IGF1R信号（“引擎”）刺激的胎儿MPs增殖，可能是通过抑制E2F靶基因，而GATA1在这个功能上是有缺陷的。其他假设包括：体内过度活跃的IGF/IGF1R信号可能与GATA1s协同启动DS-TL/DS-AMKL；胎儿和成人造血可能对IGF/IGF1R信号有不同的需求，某些类型的白血病利用这一特征来驱动其恶性转化。研究人员提出了三个具体目标：(1)确定GATA1控制胎儿巨核细胞中IGF/IGF1R信号靶基因（如E2F靶基因，包括Myc）的分子机制；(2)在体外和体内检测组成型活性IGF/IGF1R信号是否与GATA1s协同促进胎儿MPs的自我更新增殖。这将通过转基因方法在小鼠胎儿肝细胞中异位表达IGF2来完成；(3)通过在不同造血阶段有条件地敲除IGF1R，建立并比较IGF/IGF1R信号在胎儿和成人造血阶段的体内作用。预计这些研究将显著增强我们对IGF/IGF1R信号在血液发育中的作用的理解，以及它的激活如何以细胞环境依赖的方式促进白血病。

DESCRIPTION (provided by applicant): Insulin-like Growth Factor/Insulin-like Growth Factor 1 Receptor (IGF/IGF1R) signaling plays critical roles in regulating cell growth, proliferation and apoptosis. Both IGFs (IGF1 and IGF2) and IGF1R are commonly involved in human cancers, including leukemia. However, little is known about the role of this pathway in normal hematopoiesis and how its activation contributes to leukemogenesis. Cancer development is highly dependent on cellular context, which is determined by intrinsic genetic programs in the affected cells and by their responses to microenvironment stimuli. The long-term objective of this project is to understand the cell type-specific interplay of signaling pathways and oncogenes, which forms the basis for developing novel and more effective targeted cancer therapies and for cancer prevention. Down syndrome acute megakaryoblastic leukemia (DS-AMKL) and a related preleukemic condition called transient leukemia (DS- TL) are used as a model to study this. DS-AMKL is a unique pediatric leukemia characterized by the triad of fetal origin, trisomy 21, and somatic mutations in the hematopoietic transcription factor, GATA1 (leading to production of a shorter variant of GATA1 called GATA1s). By analyzing Gata1s knockin mice and human DS-TL/DS-AMKL cells, it was found that GATA1s leads to hyperproliferation of fetal megakaryocytic progenitors (MPs), but not their adult counterparts. Fetal MPs are highly dependent on IGF/IGF1R signaling for their proliferation and survival, whereas adult MPs are not. GATA1s mutant fetal MPs and leukemic cells are both hypersensitive to inhibition and activation of IGF/IGF1R signaling. Based on these preliminary data, it is hypothesized that GATA1 may serve as a "brake" to restrict the IGF/IGF1R signaling ("engine")-stimulated proliferation of fetal MPs, likely through repression of E2F target genes, whereas GATA1s is defective in this function. Additional hypotheses include: overactive IGF/IGF1R signaling may cooperate with GATA1s in vivo to initiate DS-TL/DS-AMKL; and fetal and adult hematopoiesis may have different requirements for IGF/IGF1R signaling, a feature capitalized upon by certain types of leukemia to drive their malignant transformation. Three specific aims are proposed to test these: (1) To determine the molecular mechanism by which GATA1 controls target genes of IGF/IGF1R signaling (e.g., E2F targets, including Myc) in fetal megakaryocytes; (2) To test whether constitutively active IGF/IGF1R signaling cooperates with GATA1s in vitro and in vivo to enhance the self-renewal proliferation of fetal MPs. This will be done using transgenic approaches to ectopically express IGF2 in mouse fetal liver cells; (3) To establish and to compare the in vivo role of IGF/IGF1R signaling in fetal versus adult stage hematopoiesis, by conditionally knocking out Igf1r at different stages of hematopoiesis. It is expected that these studies will significantly enhance our understanding of the role of IGF/IGF1R signaling in blood development, and of how its activation contributes to leukemia in a cellular context-dependent manner.