The role of inhibitory receptors in leukemia development

描述（由申请人提供）：急性髓性白血病（AML）是成人最常见的急性白血病，其发病率随年龄增长而增加。少数患者通过目前的治疗治愈，尽管持续治疗，但大多数患者在5年内复发。具有无限自我更新能力的癌症干细胞（CSC）可能是肿瘤发生和复发所必需的。需要新的靶标来有效抑制CSC活性。最近，我们鉴定了免疫抑制受体，人白细胞免疫球蛋白（IG）样受体B2（LILRB 2）及其小鼠直系同源物配对的Ig样受体（PirB），作为血管生成素样蛋白（Angptl）的受体。先前的研究表明，几种Angptl促进癌症发展，而免疫抑制受体抑制免疫激活以支持癌症生长。我们的初步研究表明，LILRB 2水平在人类AML的M5亚型中显著升高。Angptl结合LILRB 2和PirB并诱导酪氨酸磷酸酶SHP-2和钙/钙调蛋白依赖性蛋白激酶4（CAMK 4）的活化。两种小鼠AML模型中PirB的缺乏导致白血病干细胞的分化增加和自我更新减少。一致地，在两种人白血病细胞系中LILRB 2的敲低在很大程度上阻断了异种移植小鼠中白血病的发展。这些结果表明LILRB 2和PirB支持白血病发展。因此，我们的研究揭示了经典的免疫抑制受体在维持癌症干细胞的干细胞性方面意想不到的功能意义。我们假设Angptl结合LILRB 2和PirB以抑制分化并通过激活SHP-2和CAMK 4促进自我更新。我们提出了三个目标来检验这一假设。在目的1中，我们将确定LILRB 2及其配体结合在调节原发性人AML-SC活性中的作用。在目的2中，我们将剖析AML-SC中Angptl受体启动的信号传导途径，使用功能获得和功能丧失方法来阐明SHP-2信号传导和CAMK 4信号传导在调节AML-SC的自我更新和分化中的功能意义。在目的3中，我们将研究Angptl受体介导的信号传导的下游靶标如何调节AML-SC活性。据我们所知，这是第一次研究这些“抑制性受体”在维持癌症干细胞和祖细胞的干细胞性中的分子机制。所提出的研究将确定Angptl受体在人AML中的功能意义，并鉴定控制AML-SC活性的Angptl受体介导的信号传导的分子决定因素。这可能会开辟一个新的研究前沿，研究抑制性受体在干细胞和癌症中的作用。此外，对配体-受体结合、信号传导事件和这一新发现的通路中的下游效应物的理解将直接指导人类AML新治疗策略的开发。

DESCRIPTION (provided by applicant): Acute myeloid leukemia (AML) is the most common acute leukemia affecting adults, and its incidence increases with age. The minority of patients are cured by current therapy and the majority relapse within 5 years despite continuous treatment. Cancer stem cells (CSCs), which have the capacity for indefinite self-renewal, may be essential for tumor initiation and relapse. New targets are needed to efficiently inhibit CSC activity. Most recently, we identified the immune inhibitory receptors, human leukocyte immunoglobulin (Ig)-like receptor B2 (LILRB2) and its mouse ortholog paired Ig-like receptor (PirB), as receptors for Angiopoietin-like proteins (Angptls). Previous studies showed that several Angptls promote cancer development, whereas immune inhibitory receptors suppress the immune activation to support cancer growth. Our preliminary research showed that LILRB2 level is significantly elevated in the M5 subtype of human AML. Angptls bind to LILRB2 and to PirB and induce activation of tyrosine phosphotase SHP-2 and calcium/calmodulin-dependent protein kinase 4 (CAMK4). A deficiency of PirB in two mouse AML models resulted in increased differentiation and decreased self-renewal of leukemia stem cells. Concordantly, the knockdown of LILRB2 in two human leukemia cell lines largely blocked leukemia development in xenografted mice. These results indicate that LILRB2 and PirB support leukemia development. Therefore, our study revealed unexpected functional significance of classical immune inhibitory receptors in the maintenance of stemness of cancer stem cells. We hypothesize that Angptls bind LILRB2 and PirB to inhibit differentiation and promote self-renewal through activating SHP-2 and CAMK4. We propose three aims to test this hypothesis. In Aim 1, we will determine the role of LILRB2 and its ligand binding in regulation of primary human AML-SC activity. In Aim 2, we will dissect the Angptl receptor initiated signaling pathway in AML-SCs, using gain-of-function and loss-of- function approaches to illuminate the functional significance of the SHP-2 signaling and CAMK4 signaling in regulation of self-renewal and differentiation of AML-SCs. In Aim 3, we will investigate how the downstream targets of the Angptl receptor-mediated signaling regulate AML-SC activity. To our knowledge, this is the first study of the molecular mechanism of these "inhibitory receptors" in the maintenance of stemness of cancer stem cells and progenitors. The proposed study will determine the functional significance of the Angptl receptor in human AML and identify the molecular determinants of the Angptl receptor-mediated signaling in control of AML-SC activity. It will likely open a new research front to study the role of inhibitory receptors in stem cells and cancer. Moreover, the understanding of the ligand-receptor binding, the signaling events, and the downstream effectors in this newly identified pathway will directly guide the development of new therapeutic strategies for human AML.