The Biology of Perlecan in Cancer and Angiogenesis

描述（由申请人提供）：抗血管生成疗法基于一个简单而优雅的理论：通过切断肿瘤的血液供应来根除肿瘤。基质生物学领域的一个新兴概念是，几种硫酸肝素蛋白聚糖（如perlecan）不仅在发育和组织稳态过程中作为结构成分，而且在肿瘤血管生成过程中也是关键的信号分子。我们已经发现，perlecan蛋白核心的c端片段，命名为“内源性排斥素”，以表明其抗内皮活性，是一种强大的血管生成抑制剂。我们进一步发现了内源性排斥素的功能受体a2¿1整合素，并在体外和体内证明了重组内源性排斥素可以阻断内皮细胞迁移、胶原诱导的毛细血管形态发生和血管生长。最近的研究结果表明，内驱素在体内靶向肿瘤血管系统，并减少小鼠原位肿瘤异种移植物和同基因肿瘤的生长。尽管证据越来越多，但内源性驱避素的确切作用方式尚未完全确定。我们的长期目标是扩大我们的初步观察，更深入地研究内源性排斥素的作用机制，确定受这种强大蛋白质作用影响的新基因，并系统地测试其体内抗血管生成活性。具体而言，我们计划：[1]揭示内源性排斥素与a2¿1整合素I结构域结合的精确机制及其结构要求；[2]确定内源性排斥素在内皮细胞内内化、胞内命运和下游信号传导的精确机制；[3]利用具有或缺乏内源性排斥素功能受体的动物肿瘤模型，建立其体内抗血管生成活性。总的来说，预期的结果应该产生一个连贯和统一的内源性排斥素的作用模式，确定参与其信号通路的新靶标蛋白，这些靶标蛋白可能是抗血管生成治疗的潜在新靶标，并通过基因靶向明确的功能丧失实验确定其作为抗血管生成因子的体内作用。更好地了解内源性排斥素的生物学不仅有利于癌症研究，也有利于血管生成起关键作用的其他领域的研究。只有当我们加深对血管生成的理解并发现调节这一关键生物过程的新化合物时，控制癌症的抗血管生成方法才能最终成功。这一建议的重点是了解一种新发现的抗血管生成蛋白的确切作用机制。靶向已建立的肿瘤血管系统代表了一种替代的和潜在的重要治疗癌症的方式。

DESCRIPTION (provided by applicant): Anti-angiogenic therapy is based on a simple, elegant theory: eradicate tumors by depriving them of their blood supply. An emerging concept in the field of matrix biology is that several heparan sulfate proteoglycans such as perlecan act not only as structural constituents during development and in tissue homeostasis, but also as key signaling molecules in tumor angiogenesis. We have discovered that the C-terminal fragment of perlecan protein core, named "endorepellin" to signify its anti-endothelial activity, is a powerful angiogenesis inhibitor. We have further discovered the functional receptor for endorepellin, namely the a2¿1 integrin, and shown that recombinant endorepellin blocks endothelial cell migration, collagen-induced capillary morphogenesis, and growth of blood vessels in Matrigel in vitro and in vivo. More recent results have demonstrated that endorepellin targets tumor vasculature in vivo and reduces the growth of orthotopic tumor xenografts and syngeneic tumors in mice. In spite of this accumulating evidence, the precise mode of action of endorepellin is not fully established. Our long-term objectives are to expand our initial observations and investigate in more depth the mechanism of action of endorepellin, identify novel genes affected by the action of this powerful protein, and systematically test its in vivo anti-angiogenic activity. Specifically, we plan to: [1] Decipher the precise mechanism of binding of endorepellin on the I domain of the a2¿1 integrin and its structural requirements, [2] Determine the precise mechanism of internalization, intracellular fate and downstream signaling of endorepellin in endothelial cells, and [3] Establish its in vivo anti-angiogenic activity by utilizing animal tumor models possessing or lacking the endorepellin functional receptor. Collectively, the expected results should generate a coherent and unified mode of action for endorepellin, identify new target proteins involved in its signaling pathway which could be potential novel targets for anti-angiogenesis therapy, and establish its in vivo role as an anti-angiogenic factor using unambiguous loss-of-function experiments through gene targeting. A better understanding of the biology of endorepellin would benefit research not only in cancer but also in other fields where angiogenesis plays a key role. The anti-angiogenic approach to controlling cancer can eventually succeed only if we deepen our understanding of angiogenesis and discover new compounds that modulate this key biological process. This proposal is focused on understanding the precise mechanism of action of a newly-discovered anti-angiogenic protein named endorepellin. Targeting the established tumor vasculature represents an alternate and potentially important therapeutic modality against cancer.