Targeting Microenvironmental Signals in Myeloid Malignancies

摘要 已知干细胞与其周围微环境的相互作用对于正常的细胞发育和分化是必不可少的。 造血干细胞（HSC）是造血干细胞的一个重要组成部分，它可以促进造血干细胞的发育，并维持自我更新的成体干细胞，如造血干细胞（HSC）。 由于癌症经常劫持发展信号，因此很可能是利基驱动的信号， 维持造血干细胞还影响造血干细胞突变引起的白血病的生长， 在一些实施方案中，白血病细胞是造血祖细胞，例如急性髓性白血病（AML）和慢性髓性白血病（bcCML）的母细胞危象。尽管 尽管最近的治疗进展，约75%的AML患者仍然死于这种疾病，突出了需要更好地 了解疾病进展的机制。虽然许多工作都集中在白血病细胞的内在 由于微环境的调节作用，人们对微环境在疾病建立和传播中的作用知之甚少。我们 总体目标是确定白血病-小生境相互作用对髓系白血病发生的作用。以支持 我们的工作表明，AML与微环境的粘附相互作用， 内皮细胞对于维持治疗抗性白血病干细胞（LSC）至关重要。由于骨祖细胞 在白血病骨髓中扩增，这些骨祖细胞也可能产生支持癌症的细胞。 微环境作为识别促进白血病发生的小生境驱动信号的替代方法，我们确定 LSC上表达的细胞表面抗原可以作为这些信号的受体，使用我们最近的体内 全基因组CRISPR筛选。我们筛选出的140个细胞表面基因包括那些已知的 促进白血病生长（例如，Cd 47，Cd 157）和白血病进展的新调节剂。关注信号 可能是癌症特异性的，我们选择了一个新的细胞表面调节子的子集，其表达高出2倍， 在我们新的RNA-seq数据集中，与正常HSC相比，人类bcCML LSC中的细胞数。其中，牛磺酸转运蛋白 SLC 6A 6（TauT）是特别感兴趣的，因为其高表达与AML中的不良预后相关 （TCGA）。使用TauT-/-小鼠，我们发现TauT的遗传缺失显著损害体内白血病生长， 与TauT+/+相比。我们关键的初步数据表明，合成非必需氨基酸的酶 牛磺酸随着骨髓基质细胞的成骨分化而上调， 环境保护基于我们的初步研究显示，骨祖细胞合成牛磺酸， LSC TauT表达对AML中肿瘤生长和骨祖细胞扩增的影响，我们假设 骨祖细胞通过分泌牛磺酸维持LSC并支持白血病进展。我们现在将测试TauT 表达对于小鼠疾病模型中的疾病进展以及对于 原发性人类白血病我们还将确定骨祖细胞是否形成支持性微环境， 分泌牛磺酸导致白血病恶化总的来说，这些研究将确定牛磺酸的作用， 髓系白血病进展中的骨髓成骨细胞龛从长远来看，这项工作可能会导致 开发针对支持癌细胞的微环境信号的新疗法。

ABSTRACT Interactions of stem cells with their surrounding microenvironment are known to be essential for both normal development, and for sustaining self-renewing adult stem cells, such as the hematopoietic stem cells (HSCs). Since cancers often hijack developmental signals for their progression, it is likely that niche-driven signals that sustain HSCs also influence the growth of leukemias arising from mutations in HSCs and early hematopoietic progenitors, such as acute myeloid leukemia (AML) and blast crisis chronic myeloid leukemia (bcCML). Despite recent advances in treatment, ~75% of AML patients still succumb to the disease, highlighting the need to better understand mechanisms of disease progression. While much work has focused on leukemia cell-intrinsic regulators, the role of the microenvironment in disease establishment and propagation is poorly understood. Our overall goal is to define the role of leukemia-niche interactions on myeloid leukemogenesis. In support of a functional role of the niche in disease progression, our work has shown that adhesive interaction of AML with endothelial cells is critical to maintain the therapy-resistant leukemia stem cells (LSCs). Since osteoprogenitors expand in the leukemic bone marrow, it is possible that these osteoprogenitors also create a cancer-supporting microenvironment. As an alternate to identifying niche-driven signals promoting leukemogenesis, we determined cell surface antigens expressed on LSCs that can act as receptors for these signals using our recent in vivo genome-wide CRISPR screen. The 140 cell surface genes identified by our screen included those known to promote leukemia growth (e.g., Cd47, Cd157) and novel regulators of leukemia progression. To focus on signals likely to be cancer-specific, we selected a subset of novel cell-surface regulators with 2-fold higher expression in human bcCML LSCs compared to normal HSCs in our new RNA-seq dataset. Of these, the taurine transporter SLC6A6 (TauT) is of particular interest since its high expression is associated with poor prognosis in AML (TCGA). Using TauT-/- mice, we find that genetic loss of TauT significantly impairs leukemia growth in vivo as compared to TauT+/+. Our key preliminary data show that enzymes for synthesis of the non-essential amino acid taurine are upregulated with osteolineage differentiation of bone marrow stromal cells, and taurine is secreted in the environment. Based on our pilot studies showing taurine synthesis by osteoprogenitors, a requirement for LSC TauT expression for cancer growth, and expansion of osteoprogenitors in AML, we hypothesize that osteoprogenitors sustain LSCs and support leukemia progression by secreting taurine. We will now test if TauT expression is essential for disease progression in mouse models of disease, as well as for the propagation of primary human leukemias. We will also determine if osteoprogenitors form a supportive microenvironment for leukemia progression by secreting taurine. Collectively, these studies will establish the role of taurine from the bone marrow osteolineage niche in myeloid leukemia progression. In the long term this work may lead to development of new therapies targeting microenvironmental signals supporting cancer cells.