Eph receptor tyrosine kinases in tumor angiogenesis

描述(申请人提供)：血管生成，即从现有的血管系统中萌发新的血管，是实体肿瘤进展和转移的关键步骤。我们研究的长期目标是剖析肿瘤血管生成的分子机制。这项拟议的研究的目的是调查受体酪氨酸激酶Eph家族如何调节肿瘤中新血管的生长。受体酪氨酸激酶是一类主要的调节肿瘤新生血管的细胞表面分子。Eph受体和配体是胚胎血管发育所必需的成员，但它们在出生后血管生成中的功能尚不清楚。我们的初步结果显示，在两种类型的小鼠肿瘤和相关的血管系统中都有EparinA1配体和EphA2受体的表达。可溶性EphA2受体在血管窗实验中消除胰岛肿瘤新生血管，抑制RIP-Tag转基因小鼠血管生成胰岛的形成，并在体内抑制4T1乳腺癌的生长和血管生成。为了分析EphA受体介导的血管生成的机制，我们发现，VEGF诱导内皮细胞EphA1表达和EphA2受体的磷酸化，阻断EphA受体的激活可以抑制VEGF-，但不能抑制成纤维细胞生长因子诱导的内皮细胞的存活、迁移、发芽和角膜血管生成。综上所述，这些数据支持一种假说，即EphA RTK及其配体ePhinA在肿瘤新生血管中发挥关键作用，ePhinA木质素对血管内皮细胞的作用至少部分是VEGF诱导的血管生成所必需的。为了验证这一假设，我们将(1)确定EphA2受体的激活是否介导了VEGF诱导的血管内皮细胞反应，(2)剖析了血管生成中EphA/EphA信号相互作用的机制，(3)利用RIP-Tag转基因肿瘤模型研究EphA受体激活是否是促进体内肿瘤生长和血管生成的必要条件和充分条件。这些特定的目标中的每一个都代表了一种不同但互补的方法来理解Eph受体酪氨酸激酶在肿瘤血管生成中的作用。这些在分子、细胞和整个动物水平上的研究将在理解不同的血管生成因子如何协调促进肿瘤血管生成方面取得重大进展，并可能发现抑制肿瘤新生血管的新靶点。

DESCRIPTION (provided by applicant): Angiogenesis, the sprouting of new blood vessels from existing vasculature, is a critical step in the progression and metastasis of solid tumors. The long-term goal of our research is to dissect the molecular mechanisms of tumor angiogenesis. The purpose of the proposed research is to investigate how the Eph family of receptor tyrosine kinases regulate the growth of new blood vessels in tumors. Receptor tyrosine kinases represent a major class of cell-surface molecules that regulate tumor neovascularization. Members of Eph receptors and ligands are required in embryonic vascular development, yet their functions in postnatal angiogenesis remains unclear. Our preliminary results now show that ephrinA1 ligand and EphA2 receptor are expressed in two types of murine tumors and associated vasculature. A soluble EphA2 receptor abrogates islet tumor neovascularization in a vascular window assay, inhibits the formation of angiogenic islets in RIP-Tag transgenic mice, and suppresses 4T1 breast cancer growth and angiogenesis in vivo. To dissect the mechanisms of EphA receptor-mediated angiogenesis, we found that VEGF induces ephrinA1 expression and phosphorylation of EphA2 receptor in endothelial cells, and blocking EphA receptor activation inhibits VEGF-, but not FGF-induced endothelial cell survival, migration, sprouting, and corneal angiogenesis. Taken together, these data support a hypothesis that EphA RTKs and their ligands, ephrinAs, play a critical role in tumor neovascularization, and actions of ephrinA lignads on endothelial cells are required, at least in part, for VEGF-induced angiogenesis. To test this hypothesis, we will (1) determine whether activation of EphA2 receptor mediates VEGF-induced endothelial responses, (2) dissect the mechanisms of interactions between VEGF and the EphA/ephrinA signaling in angiogenesis, and (3) investigate whether EphA receptor activation is necessary and sufficient to promote tumor growth and angiogenesis in vivo using RIP-Tag transgenic tumor model. Each of these specific aims represents a different, but complementary, approach to understand the role of Eph receptor tyrosine kinases in tumor angiogenesis. These studies at the molecular, cellular, and whole animal level will make significant advances to the understanding of how different angiogenic factors are coordinated to promote tumor angiogenesis, and may identify novel targets to inhibit neovascularization in cancer.