Vascular Endothelial Growth Factor in Hematopoiesis in Cancer

描述（由申请人提供）：血管内皮生长因子（VEGF）是一种由大多数人实体瘤产生的促血管生成因子，是造血的重要调节因子。VEGF信号传导对早期造血发育至关重要。然而，最近的数据，包括我们的，揭示了VEGF作为免疫细胞分化的抑制剂的作用，对树突状细胞（DC）和T细胞具有深远的影响。我们做了一个重要的观察，VEGF对DC的抑制作用的实质部分是由酪氨酸激酶非依赖性机制介导的。我们的初步数据强烈暗示VEGF受体1（VEGFR1）在这个过程中。确定VEGF的免疫抑制作用的具体机制对于开发针对癌症免疫校正的有效治疗策略至关重要。本课题的目的是研究该系统中抑制性信号转导的机制和功能元件。大多数VEGF配体或受体的扰动的胚胎致死性使得造血作用的遗传研究更加困难。因此，我们已经开发了在体外系统中，基因修饰的小鼠胚胎干细胞（ES）可以分化为DC。我们将使用小鼠ES细胞敲除各种受体，并转导特定的受体突变体，以确定每个受体，它们的子域和信号伴侣在这一过程中的作用。我们的动物骨髓移植研究旨在阐明体内DC功能障碍中每个VEGF受体及其酪氨酸激酶的相对贡献。我们假设VEGFR1是DC失调的主要介质，通过酪氨酸激酶依赖性机制转导其抑制性信号传导的实质部分，包括胞膜结构域、异源二聚体的形成或内化。我们将通过以下具体目的来测试这一点：1）表征VEGFR1非酪氨酸激酶亚结构域在体外DC分化和造血中的作用。2)确定VEGFR1酪氨酸磷酸化依赖性信号在体外DC缺陷中的作用。3)评估每种VEGF受体在介导VEGF对体内DC发育的影响中的信号传导作用。了解造血细胞中VEGF信号传导的机制和作用将导致对正常和病理性造血的更深入了解，以及旨在改善免疫功能和与癌症和免疫治疗高度临床相关的潜在治疗干预。

DESCRIPTION (provided by applicant): Vascular Endothelial Growth Factor (VEGF), a pro-angiogenic factor produced by most human solid tumors is important modulator of hematopoiesis. VEGF signaling is crucial for early hematopoietic development. However, recent data including ours, revealed the role of VEGF as inhibitor of immune cell differentiation with profound effect on dendritic (DC) and T cells. We made an important observation that substantial part of VEGF inhibitory effect on DCs is mediated by tyrosine kinase-independent mechanism. Our preliminary data strongly implicate VEGF receptor 1 (VEGFR1) in this process. Identifying specific mechanisms of immunosuppressive effects of VEGF would be essential for the development of efficient therapeutic strategies aimed at immune correction in cancer. The goal of the proposed project is to investigate the mechanism and functional elements of inhibitory signal transduction in this system. The embryonic lethality of most perturbations of VEGF ligand or receptors makes genetic studies of hematopoietic effects more difficult. We have therefore developed in vitro system where genetically modified murine embryonic stem (ES) cells can be differentiated into DCs. We will use murine ES cells knocked out for various receptors and transduced with specific receptor mutants to determine the role of each receptor, their subdomains and signaling partners in this process. Our animal bone marrow transplant studies are designed to elucidate relative contribution of each VEGF receptor and their tyrosine kinases in DC dysfunction in vivo. We hypothesize that VEGFR1 being a major mediator of DC dysregulation transduces substantial part of its inhibitory signaling by mechanism other then tyrosine kinase-dependent, involving juxtamembrane domain, formation of heterodimers, or internalization. We will test this by the following specific aims: 1) Characterize the roles of VEGFR1 non-tyrosine kinase subdomains on DC differentiation and hematopoiesis in vitro. 2) Determine the role of VEGFR1 tyrosine phosphorylation dependent signaling in DC defects in vitro. 3) Assess the role of signaling by each VEGF receptors in mediating VEGF effects on DC development in vivo. Understanding the mechanism and effects of VEGF signaling in hematopoietic cells will lead to greater insight into normal and pathological hematopoiesis, and potential therapeutic interventions aimed at improvement of immune function and highly clinically relevant to cancer and immunotherapy.