Receptor protein tyrosine phosphatase beta/zeta is a functional binding partner for vascular endothelial growth factor

Background: Receptor protein tyrosine phosphatase beta/zeta (RPTP beta/C) is a chondroitin sulphate (CS) transmembrane protein tyrosine phosphatase and is a receptor for pleiotrophin (PIN). RPTPW interacts with alpha(v)beta(3) on the cell surface and upon binding of PIN leads to c-Src dephosphorylation at 1yr530, beta 3 Tyr773 phosphorylation, cell surface nucleolin (NCL) localization arid stimulation of cell migration. c-Src-mediated beta 3 Tyr773 phosphorylation is also observed after vascular endothelial growth factor 165 (VEGF(165)) stimulation of endothelial cells and is essential for VEGF receptor type 2 (VEGFR2) alpha(v)beta(3) integrin association and subsequent signaling. In the present work, we studied whether RPTPW mediates angiogenic actions of VEGF. Methods: Human umbilical vein endothelial, human glioma U87MG and stably transfected Chinese hamster ovary cells expressing different beta(3) subunits were used. Protein protein interactions were studied by a combination of immunoprecipitation/Western blot, immunofluorescence and proximity ligation assays, properly quantified as needed. RPTP beta/C expression was down -regulated using small interference RNA technology. Migrat on assays were performed in 24 well microchemotaxis chambers, using uncoated polycarbonate membranes with 8 pm pores. Results: RPTP beta/C, mediates VEGF(165)-induced c-Src-dependent Tyr773 phosphorylation, which is required for VEGFR2-alpha(v)beta(3) interaction and the downstream activation of phosphatidylinositol 3-kinase (PI3K) and cell surface NCL localization. RPTPW directly interacts with VEGF(165), and this interaction is not affected by bevacizumab, while it is interrupted by both CS -E and PIN. Down regulation of RPTP beta/C by siRNA or administration of exogenous CS-E abolishes VEGF(165)-induced endothelial cell migration, while PIN inhibits the migratory effect of VEGF(165) to the levels of its own effect. Conclusions: These data identify RPTPM as a cell membrane binding partner for VEGF that regulates angiogenic functions of endothelial cells and suggest that it warrants further validation as a potential target for development of additive or alternative anti-VEGF therapies.