Endothelial phospholipase Cγ (PLCγ) is essential for vascular development; however, its role in healthy, mature, or pathological vessels is unexplored. Here, we show that PLCγ was prominently expressed in vessels of several human cancer forms, notably in renal cell carcinoma (RCC). High PLCγ expression in clear cell RCC correlated with angiogenic activity and poor prognosis, while low expression correlated with immune cell activation. PLCγ was induced downstream of vascular endothelial growth factor receptor 2 (VEGFR2) phosphosite Y1173 (pY1173). Heterozygous Vegfr2Y1173F/+ mice or mice lacking endothelial PLCγ (Plcg1iECKO) 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/PLCγ signaling induced Ca2+/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/PLCγ/eNOS/Src pathway was detected in both healthy and tumor vessels in Vegfr2Y1173F/+ mice, which displayed decreased activation of PLCγ and eNOS and suppressed vascular leakage. Thus, we believe that we have identified a clinically relevant endothelial PLCγ pathway downstream of VEGFR2 pY1173, which destabilizes the endothelial barrier and results in loss of antitumor immunity.
Keywords: Oncology; Signal transduction; Vascular Biology.