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。IGFs(IGF1和IGF2)和IGF1R通常与包括白血病在内的人类癌症有关。然而，人们对该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特定细胞类型的信号通路和癌基因的相互作用，这形成了开发新的、更有效的靶向癌症治疗和癌症预防的基础。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疾病称为一过性白血病(DS-TL)被用作研究这一问题的模型。DS-AMKL是一种独特的儿童白血病，其特征是胎儿起源的三体，21三体，以及造血转录因子GATA1的体细胞突变(导致产生GATA1的较短变体，称为GATA1)。通过对GATA1基因敲打小鼠和人DS-TL/DS-AMKL细胞的分析，发现GATA1基因可导致胎儿巨核系祖细胞(MPS)的过度增殖，但对其成体巨核系祖细胞无明显影响。胎儿MPS的增殖和存活高度依赖于IGF/IGF1R信号，而成年MPS则不是。GATA1突变的胎儿MPS和白血病细胞对IGF/IGF1R信号的抑制和激活都高度敏感。根据这些初步数据，推测GATA1可能通过抑制E2F靶基因来抑制IGF/IGF1R信号(“引擎”)刺激的胎儿MPS的增殖，而GATA1在这一功能上是有缺陷的。其他假设包括：过度激活的IGF/IGF1R信号可能在体内与GATA1协同启动DS-TL/DS-AMKL；胎儿和成人造血可能对IGF/IGF1R信号有不同的要求，某些类型的白血病利用这一特征来驱动其恶性转化。GATA1调控胎儿巨核细胞中IGF/IGF1R信号的靶基因(如E2F靶点，包括Myc)的分子机制；(2)在体外和体内检测IGF/IGF1R信号是否与GATA1协同促进胎儿MPS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IGF2；(3)通过有条件地敲除不同造血阶段的Igf1r，建立并比较IGF/IGF1R信号在胎儿和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/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上下文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.