Role of spectrin signaling complex in angiogenesis

血管生成缺陷是50多种恶性、缺血性和炎症性疾病的基础。 虽然目前的血管内皮生长因子信号拮抗剂有广泛的治疗应用，但大多数 由于获得性耐药性和毒性，治疗无法提供长期疗效。克服这些障碍 因此，临床挑战需要解决血管内皮生长因子信号转导的一些关键方面，这些方面包括 非常不清楚。VEGFR2是血管生成的主要驱动力，因为它的膜运输 控制许多(如果不是大多数)血管内皮生长因子诱导的信号通路的特异性、持续时间和幅度。 但与VEGFR2酪氨酸磷酸化传递受体信号的分子基础不同，它如何 各种丝氨酸/苏氨酸激酶在时空上协调膜的运输和周转， 伴侣和泛素连接酶仍然知之甚少。事实上，尽管PKC很早就被认为是 作为VEGFR2降解的关键介质，PKC是否直接或间接促进VEGFR2的降解尚不清楚 丝氨酸/苏氨酸磷酸化诱导的周转。在这里，我们的工作通过以下方式支持一个令人兴奋的新机制 其中VEGFR2的稳定性是通过一种新型的膜信号复合体来调节的。在预赛中 研究发现，IV-SPECTIN是一种大的细胞膜骨架蛋白，其特征仅为 在神经系统和心脏中，是表达在血管内皮细胞(ECs)中起临界阴性作用的 血管生成的调节剂。新生小鼠和斑马鱼胚胎中的IV-SPECTIN功能障碍会导致虚弱 血管过度发芽的部分原因是异常高水平的血管内皮生长因子/血管内皮生长因子2信号，并显著 尖端细胞数量增加。我们的数据有力地表明，IV-SPECTIN作为一个重要的信号转导系统发挥作用 通过CaMKII直接诱导新的磷酸化来靶向降解VEGFR2的平台 丝氨酸/苏氨酸位点。根据我们的发现，我们假设IV-血影蛋白/CaMKII信号复合体 调节VEGFR2的磷酸化、膜转运和周转以抑制血管内皮生长因子信号和TIP 萌发血管形成过程中的细胞表型。提出了两个目的来检验这一假设：1)定义IV- 基于血影蛋白的血管内皮生长因子信号转导机制；2)建立IV的作用 内皮细胞尖端和柄细胞中的血影蛋白规范。总体而言，这些研究的结果将涉及 通过表征一种新的IV-光谱蛋白信号复合体，研究血管内皮生长因子受体信号传导中的关键问题 在失败的长期血管内皮生长因子相关治疗中确定新的血管靶点。

Defective angiogenesis underlies the pathogenesis of over 50 malignant, ischemic and inflammatory diseases. While current antagonists of VEGF signaling have a wide range of therapeutic applications, most of these treatments fail to provide long-term efficacy due to acquired resistance and toxicities. Overcoming these clinical challenges will therefore require addressing a number of critical aspects of VEGF signaling that are very much unclear. VEGFR2 is the principal driver of sprouting angiogenesis as its membrane trafficking controls the specificity, duration and amplitude of many, if not most, of the VEGF-induced signaling pathways. But unlike the molecular basis of VEGFR2 tyrosine phosphorylation that transduces receptor signaling, how its membrane trafficking and turnover are spatiotemporally coordinated by various serine/threonine kinases, chaperones and ubiquitin ligases remain poorly understood. In fact, although PKCs have been long recognized as key mediators of VEGFR2 degradation, it is still unclear whether PKCs directly or indirectly promote serine/threonine phosphorylation-induced turnover. Here our work supports an exciting new mechanism by which VEGFR2 stability is regulated through a novel membrane-based signaling complex. In preliminary studies, we discovered that IV-spectrin, a large membrane cytoskeletal scaffolding protein characterized only in the nervous system and heart, is expressed in vascular endothelial cells (ECs) to act as a critical negative regulator of angiogenesis. IV-spectrin dysfunction in newborn mice and zebrafish embryos produce debilitating hypersprouting vessels in part due to abnormally high levels of VEGF/VEGFR2 signaling and dramatically elevated number of tip cells. Our data strongly suggest that IV-spectrin functions as a crucial signaling platform by which VEGFR2 is targeted for degradation through direct CaMKII-induced phosphorylation of novel serine/threonine sites. Based on our findings, we hypothesize that the IV-spectrin/CaMKII signaling complex regulates VEGFR2 phosphorylation, membrane trafficking and turnover to suppress VEGF signaling and tip cell phenotype during sprouting angiogenesis. Two aims are proposed to test this hypothesis: 1) Define IV- spectrin-based mechanisms of VEGF signaling during sprouting angiogenesis; 2) Establish the role of IV- spectrin in endothelial tip and stalk cell specification. Collectively, results from these studies will address a crucial question in VEGFR signaling through the characterization of a novel IV-spectrin signaling complex, and identify new vascular targets in failed long-term VEGF-related therapies.