Normalization of tumor vasculature by R-Ras

描述(申请人提供)：由于长期的血管生成微环境，肿瘤中新形成的血管不能成熟为完全功能的血管。这些血管的功能受损阻碍了药物的输送，从而降低了抗肿瘤治疗的效果。与肿瘤相关的过度血管通透性也允许肿瘤细胞侵入循环，促进转移扩散。因此，控制肿瘤血管成熟度的能力提供了潜在的治疗机会。这项研究的长期目标是了解血管成熟的分子基础。我们最近的研究揭示了小GTP酶R-RAS在肿瘤中建立成熟的、有功能的血管中的重要作用。因此，R-RAS促进肿瘤血管的正常化。现在，这项研究的重要新目标是确定R-RAS介导的血管调节的分子途径，以便寻找新的分子靶点来控制肿瘤血管，从而达到治疗的目的。R-RAS通过调节VE-钙粘附素增强血管完整性。我们最近的研究还表明，R-RAS通过抑制血管内皮细胞生长因子受体2的内化来抑制血管内皮细胞中的血管内皮细胞生长因子信号转导。此外，R-RAS不仅促进内皮细胞-周细胞的结合，而且通过转化生长因子-β和Jagged1介导的Notch信号通路促进两种细胞之间的细胞间信号转导。这些途径促进内皮细胞静止和壁细胞分化；因此，它们对血管成熟很重要。基于这些观察，我们提出了一个假设，即R-RAS协调这些途径，将新生肿瘤血管形成从血管生成萌芽/分支过程重定向到成熟过程。在这项研究中，我们将探讨R-RAS通路在肿瘤血管形成过程中的意义和确切作用。在目标1中，我们将利用不同的培养/共培养系统进行一系列的体外实验，鉴定和表征介导R-RAS对内皮细胞和周细胞影响的关键信号通路。在目标2中，我们将在不同的动物模型中验证目标1的发现，以确定这些机制在建立功能性肿瘤血管中的作用。这些研究将为血管正常化现象的分子基础及其在肿瘤恶性和治疗中的意义提供重要的见解。

DESCRIPTION (provided by applicant): Newly formed blood vessels fail to mature into fully functional vessels in tumors due to the chronically angiogenic microenvironment. The functional impairment of these vessels hampers drug delivery, thereby diminishing the efficacy of antitumor therapies. Excessive vessel permeability associated with tumors also allows tumor cell invasion into the circulation facilitating metastatic spreading. Therefore, the ability to conrol vessel maturity in tumors provides a potential therapeutic opportunity. The long-term goal of this study is to understand the molecular basis for vascular maturation. Our recent studies uncovered an essential role of the small GTPase R-Ras in establishment of mature, functional blood vessels in tumors. Thus, R-Ras promotes normalization of the tumor vasculature. Now, the important new objective of this investigation is to determine the molecular pathway for R-Ras-mediated vessel regulation so that new molecular targets may be identified for controlling the tumor vasculature for therapeutic advantage. R-Ras enhances vascular integrity through regulation of VE-cadherin. Our recent studies also show that R-Ras attenuates VEGF signaling in endothelial cells by inhibiting VEGFR2 internalization upon VEGF stimulation. Furthermore, R-Ras not only promotes endothelial cell-pericyte association but also facilitates intercellular signaling between the two cell types via TGF-beta and Jagged1-mediated Notch signaling. These pathways promote endothelial cell quiescence and mural cell differentiation; therefore, they are important for vessel maturation. Based on these observations, we propose a hypothesis that R-Ras orchestrates these pathways to redirect nascent tumor vessel formation from an angiogenic sprouting/branching process to a maturation process. In this proposal, we will investigate the significance and precise roles of the R-Ras pathways during tumor vascularization. In Aim 1, we will identify and characterize the key signaling pathways mediating the R-Ras effects on endothelial cells and pericytes in a series of in vitro experiments using various culture/coculture systems. In Aim 2, we will validate the findings from Aim 1 in various animal models to determine the role of these mechanisms during the establishment of functional tumor vessels. The proposed studies will provide an important insight into the molecular basis for the vascular normalization phenomenon and its implications in tumor malignancy and therapies.