Vascular Endothelial Growth Factor in Hematopoiesis in Cancer

描述（申请人提供）：血管内皮生长因子（VEGF）是大多数人类实体肿瘤产生的促血管生成因子，是重要的造血调节剂。VEGF信号对早期造血发育至关重要。然而，包括我们在内的最近数据显示，VEGF作为免疫细胞分化抑制剂的作用对树突状（DC）和T细胞有深远的影响。我们发现VEGF对DCs的抑制作用有很大一部分是通过不依赖酪氨酸激酶的机制介导的。我们的初步数据强烈暗示VEGF受体1 （VEGFR1）参与了这一过程。确定VEGF免疫抑制作用的具体机制对于开发针对癌症免疫纠正的有效治疗策略至关重要。该项目的目标是研究该系统中抑制性信号转导的机制和功能要素。VEGF配体或受体的大多数扰动的胚胎致死性使得造血作用的遗传学研究更加困难。因此，我们开发了一种体外系统，可以将转基因小鼠胚胎干细胞（ES）分化为DCs。我们将使用敲除各种受体的小鼠胚胎干细胞，并用特定受体突变体进行转导，以确定每种受体、它们的亚结构域和信号伙伴在这一过程中的作用。我们的动物骨髓移植研究旨在阐明每种VEGF受体及其酪氨酸激酶在体内DC功能障碍中的相对贡献。我们假设VEGFR1作为DC失调的主要介质，通过酪氨酸激酶依赖以外的机制，包括近膜结构域、异源二聚体的形成或内化，传导其抑制信号的大部分。我们将通过以下具体目标来验证这一点：1)表征VEGFR1非酪氨酸激酶亚域在体外DC分化和造血中的作用。2)确定VEGFR1酪氨酸磷酸化依赖信号在体外DC缺陷中的作用。3)评估各VEGF受体的信号在体内介导VEGF对DC发育的作用。了解造血细胞中VEGF信号传导的机制和作用，将有助于更好地了解正常和病理造血，以及潜在的治疗干预措施，旨在改善免疫功能，与癌症和免疫治疗具有高度的临床相关性。

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.