Eph receptor tyrosine kinases in tumor angiogenesis

描述（由申请人提供）：血管生成，即从现有血管系统中萌发新血管，是实体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。本研究旨在探讨Eph受体酪氨酸激酶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调节肿瘤新生血管形成的细胞表面分子。Eph受体和配体成员在胚胎血管发育中是必需的，但它们在出生后血管生成中的功能尚不清楚。我们的初步结果表明，ephrinA1配体和EphA2受体在两种类型的小鼠肿瘤和相关的血管系统中表达。在血管窗口实验中，一种可溶性EphA2受体阻断了胰岛肿瘤的新生血管形成，在RIP-Tag转基因小鼠中抑制血管生成性胰岛的形成，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机制，我们发现VEGF诱导内皮细胞ephrinA1表达和EphA2受体磷酸化，阻断EphA受体激活抑制VEGF，但不抑制fgf诱导的内皮细胞存活、迁移、发芽和角膜血管生成。综上所述，这些数据支持了一个假设，即EphA rtk及其配体ephrinA在肿瘤新生血管中起着关键作用，并且内皮细胞上的ephrinA木质素的作用至少在一定程度上是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VEGF诱导的内皮反应，(2)解剖血管生成中VEGF与EphA/ephrinA信号之间的相互作用机制，以及(3)使用RIP-Tag转基因肿瘤模型研究EphA受体激活对促进肿瘤生长和血管生成是否必要和充分。每一个特定的目标代表了一个不同的，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、细胞和全动物水平上的研究将对理解不同的血管生成因子如何协调促进肿瘤血管生成取得重大进展，并可能找到抑制肿瘤新生血管形成的新靶点。

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.