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 thesetreatments fail to provide long-term efficacy due to acquired resistance and toxicities. Overcoming theseclinical challenges will therefore require addressing a number of critical aspects of VEGF signaling that arevery much unclear. VEGFR2 is the principal driver of sprouting angiogenesis as its membrane traffickingcontrols 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 itsmembrane trafficking and turnover are spatiotemporally coordinated by various serine/threonine kinaseschaperones and ubiquitin ligases remain poorly understood. In fact although PKCs have been long recognizedas key mediators of VEGFR2 degradation it is still unclear whether PKCs directly or indirectly promoteserine/threonine phosphorylation-induced turnover. Here our work supports an exciting new mechanism bywhich VEGFR2 stability is regulated through a novel membrane-based signaling complex. In preliminarystudies we discovered that IV-spectrin a large membrane cytoskeletal scaffolding protein characterized onlyin the nervous system and heart is expressed in vascular endothelial cells (ECs) to act as a critical negativeregulator of angiogenesis. IV-spectrin dysfunction in newborn mice and zebrafish embryos produce debilitatinghypersprouting vessels in part due to abnormally high levels of VEGF/VEGFR2 signaling and dramaticallyelevated number of tip cells. Our data strongly suggest that IV-spectrin functions as a crucial signalingplatform by which VEGFR2 is targeted for degradation through direct CaMKII-induced phosphorylation of novelserine/threonine sites. Based on our findings we hypothesize that the IV-spectrin/CaMKII signaling complexregulates VEGFR2 phosphorylation membrane trafficking and turnover to suppress VEGF signaling and tipcell 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 acrucial question in VEGFR signaling through the characterization of a novel IV-spectrin signaling complex andidentify new vascular targets in failed long-term VEGF-related therapies.