The Biology of Perlecan in Cancer and Angiogenesis

描述（申请人提供）：肿瘤的进展和转移在一定程度上是由增殖的微血管驱动的，微血管为生长的癌细胞提供氧气和营养。血管生成血管作为血管生态位发挥指向性作用，提供旁分泌和血管分泌调节模式，包括各种生长因子和细胞外基质成分的分泌和加工，从而双向影响肿瘤和内皮细胞。Perlecan是一种由内皮细胞分泌的主要硫酸肝素蛋白多糖，是血管生物学和肿瘤血管生成的复杂调节剂。Perlecan展示了一个清晰的功能二分法。亲本蛋白聚糖通过n端硫酸肝素链作为FGF2和VEGFA的共受体，促进血管生成。相反，perlecan的c端部分，称为内源性排斥素，是抗血管生成的。我们最近发现，内源性排斥素与¿2¿1整合素和VEGFR2都具有高亲和力。这种双受体结合诱导两种受体的共内化和物理下调，激活SHP-1和VEGFA转录的衰减。这些发现为抗血管生成蛋白的活性提供了新的范例，并从机制上解释了内皮细胞的内源性排斥素的特异性，内皮细胞是唯一同时表达¿2¿1整合素和VEGFR2的细胞。我们的长期目标是通过研究内源性排斥素及其各种LG模块与VEGFR2外域的结合模式来扩展这些观察结果，并解读这种两种主要血管生成受体的天然拮抗剂所诱发的下游信号通路。具体来说，我们计划：b[1]研究内源性排斥素及其LG模块与VEGFR2外域结合的精确模式。在生长肿瘤的内皮细胞中，内皮排斥素和perlecan分别有条件地过表达或消融，从而产生新的小鼠肿瘤发生模型。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，并通过内皮细胞特异性基因靶向，通过明确的功能增益和功能损失实验，确定其作为抗血管生成因子的体内作用。

DESCRIPTION (provided by applicant): Tumor progression and metastasis are in part driven by proliferating microvessels that provide oxygen and nutrients to the growing cancer cells. Angiogenic vessels exert an instructive role as a vascular niche by providing paracrine and angiocrine modes of regulation which include secretion and processing of various growth factors and extracellular matrix constituents that in turn influence tumor and endothelial cells in a bidirectional way. Perlecan, a major heparan sulfate proteoglycan secreted by endothelial cells, is a complex regulator of vascular biology and tumor angiogenesis. Perlecan shows a clear functional dichotomy. The parent proteoglycan is pro-angiogenic by acting as a co-receptor for FGF2 and VEGFA via the N-terminal heparin sulfate chains. In contrast, the C-terminal portion of perlecan, named endorepellin, is anti-angiogenic. We have recently discovered that endorepellin binds with high affinity to both ¿2¿1 integrin and VEGFR2. This dual receptor binding induces co-internalization and physical downregulation of both receptors, activation of SHP-1 and attenuation of VEGFA transcription. These findings provide a new paradigm for the activity of an anti-angiogenic protein and mechanistically explain the specificity of endorepellin for endothelial cells, the only cells that simultaneously express both ¿2¿1 integrin and VEGFR2. Our long-term objectives are to expand these observations by investigating the binding mode of endorepellin and its various LG modules to the ectodomain of VEGFR2, and decipher the downstream signaling pathway evoked by this natural antagonist of two major angiogenic receptors. Specifically we plan to: [1] Investigate the precise mode through which endorepellin and its LG modules bind to the ectodomain of VEGFR2. [2] Decipher the downstream signaling pathways evoked by endorepellin on vascular endothelial cells, and [3] Generate novel mouse models of tumorigenesis where endorepellin and perlecan are conditionally overexpressed or ablated, respectively, in the endothelia of growing tumors. 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 gain- and loss-of-function experiments through endothelial cell-specific gene targeting.