IGF/IGF1R signaling in hematopoiesis and leukemogenesis

描述（由申请人提供）：胰岛素样生长因子/胰岛素样生长因子1受体（IGF/IGF 1 R）信号传导在调节细胞生长、增殖和凋亡中起关键作用。IGFs（IGF 1和IGF 2）和IGF 1 R通常参与人类癌症，包括白血病。然而，很少有人知道这一途径在正常造血的作用，以及如何激活白血病的发生。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及其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细胞白血病（DS-AMKL）和相关的白血病前期条件称为短暂性白血病（DS-TL）被用作模型来研究这一点。DS-AMKL是一种独特的儿科白血病，其特征为胎儿来源的三联体、21三体和造血转录因子GATA 1的体细胞突变（导致产生称为GATA 1的GATA 1的较短变体）。通过分析GATA 1 s敲入小鼠和人DS-TL/DS-AMKL细胞，发现GATA 1 s导致胎儿巨核细胞祖细胞（MP）过度增殖，但不导致其成年对应物。胎儿MP的增殖和存活高度依赖于IGF/IGF 1 R信号，而成人MP则不是。GATA 1 s突变的胎儿MP和白血病细胞对IGF/IGF 1 R信号的抑制和激活都非常敏感。基于这些初步数据，假设GATA 1可能作为“制动器”来限制IGF/IGF 1 R信号传导（“引擎”）刺激的胎儿MP增殖，可能是通过抑制E2 F靶基因，而GATA 1 s在此功能中有缺陷。其他假设包括：过度活跃的IGF/IGF 1 R信号传导可能与体内GATA 1合作启动DS-TL/DS-AMKL;胎儿和成人造血可能对IGF/IGF 1 R信号传导有不同的要求，某些类型的白血病利用这一特征来驱动其恶性转化。提出了三个具体目标来测试这些：（1）确定GATA 1控制IGF/IGF 1 R信号传导的靶基因（例如，E2 F靶点，包括Myc）;（2）在体外和体内测试组成型活性IGF/IGF 1 R信号是否与GATA 1协同作用以增强胎儿MP的自我更新增殖。这将使用转基因方法在小鼠胎肝细胞中异位表达IGF 2来完成;（3）通过在造血的不同阶段条件性敲除Igf 1 r，建立并比较IGF/IGF 1 R信号传导在胎儿与成人阶段造血中的体内作用。预计这些研究将显著增强我们对IGF/IGF 1 R信号在血液发育中的作用的理解，以及其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.