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Endothelial phospholipase C[gamma] (PLC[gamma]) is essential for vascular development; however, its role in healthy, mature, or pathological vessels is unexplored. Here, we show that PLC[gamma] was prominently expressed in vessels of several human cancer forms, notably in renal cell carcinoma (RCC). High PLC[gamma] expression in clear cell RCC correlated with angiogenic activity and poor prognosis, while low expression correlated with immune cell activation. PLC[gamma] was induced downstream of vascular endothelial growth factor receptor 2 (VEGFR2) phosphosite Y1173 (pY1173). Heterozygous [Vegfr2.sup.Y1173F/+] mice or mice lacking endothelial PLC[gamma] ([Plcg1.sup.iECKO]) exhibited a stabilized endothelial barrier and diminished vascular leakage. Barrier stabilization was accompanied by decreased expression of immunosuppressive cytokines, reduced infiltration of B cells, helper T cells and regulatory T cells, and improved response to chemo- and immunotherapy. Mechanistically, pY1173/PLC[gamma] signaling induced [Ca.sup.2+]/protein kinase C-dependent activation of endothelial nitric oxide synthase (eNOS), required for tyrosine nitration and activation of Src. Src-induced phosphorylation of VE-cadherin at Y685 was accompanied by disintegration of endothelial junctions. This pY1173/PLC[gamma]/eNOS/Src pathway was detected in both healthy and tumor vessels in [Vegfr2.sup.Y1173F/+] mice, which displayed decreased activation of PLC[gamma] and eNOS and suppressed vascular leakage. Thus, we believe that we have identified a clinically relevant endothelial PLC[gamma] pathway downstream of VEGFR2 pY1173, which destabilizes the endothelial barrier and results in loss of antitumor immunity., Introduction Growth of solid cancers is accompanied by hypoxia-driven formation of abnormal blood vessels with a defective endothelial barrier, often due to chronic exposure to endothelial cell ligands such as [...]

Tumor angiogenesis occurs through regulation of genes that orchestrate endothelial sprouting and vessel maturation, including deposition of a vessel-associated extracellular matrix. CD93 is a transmembrane receptor that is upregulated in tumor vessels in many cancers, including high-grade glioma. Here, we demonstrate that CD93 regulates [[beta].sub.1] integrin signaling and organization of fibronectin fibrillogenesis during tumor vascularization. In endothelial cells and mouse retina, CD93 was found to be expressed in endothelial filopodia and to promote filopodia formation. The CD93 localization to endothelial filopodia was stabilized by interaction with multimerin-2 (MMRN2), which inhibited its proteolytic cleavage. The CD93- MMRN2 complex was required for activation of [[beta].sub.1] integrin, phosphorylation of focal adhesion kinase (FAK), and fibronectin fibrillogenesis in endothelial cells. Consequently, tumor vessels in gliomas implanted orthotopically in CD93-deficient mice showed diminished activation of [[beta].sub.1] integrin and lacked organization of fibronectin into fibrillar structures. These findings demonstrate a key role of CD93 in vascular maturation and organization of the extracellular matrix in tumors, identifying it as a potential target for therapy., Introduction Gliomas are common brain tumors that occur as ependymomas, oligodendrogliomas, and astrocytomas of WHO grades I-IV (1). Glioblastoma (WHO grade IV), the most malignant and common form of glioma, [...]