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这两种正常的 发育和维持自我更新的成体干细胞，如造血干细胞(HSC)。 由于癌症经常劫持其进展的发育信号，很可能是生态位驱动的信号 持续的HSCs也影响由HSCs突变和早期造血引起的白血病的生长 祖细胞，如急性髓系白血病(AML)和急变型慢性髓系白血病(BcCML)。尽管 在最近的治疗进展中，~75%的AML患者仍然死于这种疾病，突显出需要更好地 了解疾病发展的机制。虽然许多工作都集中在白血病细胞固有的方面 作为管理者，人们对微环境在疾病建立和传播中的作用知之甚少。我们的 总体目标是确定白血病-小生境相互作用在髓系白血病发生中的作用。为了支持一个 小生境在疾病进展中的功能作用，我们的工作表明AML与 内皮细胞是维持耐药白血病干细胞(LSCs)的关键。因为骨祖细胞 在白血病的骨髓中扩张，有可能这些骨祖细胞也会产生支持癌症的 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案，我们确定 利用我们最近的活体实验，在LSCs上表达的细胞表面抗原可以作为这些信号的受体 全基因组CRISPR屏幕。我们的筛选鉴定出的140个细胞表面基因包括那些已知的 促进白血病生长(如CD47、CD157)和白血病进展的新调节因子。把注意力集中在信号上 可能是癌症特异性的，我们选择了一组新的细胞表面调节因子，它们的表达水平高出2倍 在我们新的RNA-SEQ数据集中，将人类bcCML LSCs与正常HSCs进行比较。其中，牛磺酸转运蛋白 SLC6A6(TRAUT)的高表达与急性髓系白血病预后不良有关，因此备受关注 (TCGA)。使用Taut-/-小鼠，我们发现Taut的基因缺失显著损害了体内白血病的生长，因为 与Taut+/+相比。我们的主要初步数据显示，合成非必需氨基酸的酶 随着骨髓基质细胞的骨线样分化，牛磺酸被上调，牛磺酸被分泌到 环境。根据我们的初步研究显示，骨祖细胞合成牛磺酸需要 LSC在AML中过度表达对肿瘤生长和骨祖细胞的扩张，我们假设 骨祖细胞通过分泌牛磺酸维持LSCs和支持白血病进展。我们现在要测试一下是否拉紧 在疾病的小鼠模型中，表达对于疾病的进展以及对病毒的繁殖是必不可少的 人类原发白血病。我们还将确定骨祖细胞是否形成了支持 白血病是通过分泌牛磺酸而进展的。总的来说，这些研究将确定牛磺酸在体内的作用 髓系白血病进展过程中的骨髓骨线生态位。从长远来看，这项工作可能会导致 针对支持癌细胞的微环境信号的新疗法的开发。

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.