| Περίληψη: | Background: Receptor protein tyrosine phosphatase beta/zeta (RPTPβ/ζ) is a chondroitin sulphate (CS) transmembrane
protein tyrosine phosphatase and is a receptor for pleiotrophin (PTN). RPTPβ/ζ interacts with ανβ3 on the cell surface and
upon binding of PTN leads to c-Src dephosphorylation at Tyr530, β3 Tyr773 phosphorylation, cell surface nucleolin
(NCL) localization and stimulation of cell migration. c-Src-mediated β3 Tyr773 phosphorylation is also observed
after vascular endothelial growth factor 165 (VEGF165) stimulation of endothelial cells and is essential for VEGF
receptor type 2 (VEGFR2) - ανβ3 integrin association and subsequent signaling. In the present work, we studied
whether RPTPβ/ζ mediates angiogenic actions of VEGF.
Methods: Human umbilical vein endothelial, human glioma U87MG and stably transfected Chinese hamster
ovary cells expressing different β3 subunits were used. Protein-protein interactions were studied by a combination
of immunoprecipitation/Western blot, immunofluorescence and proximity ligation assays, properly quantified as
needed. RPTPβ/ζ expression was down-regulated using small interference RNA technology. Migration assays were
performed in 24-well microchemotaxis chambers, using uncoated polycarbonate membranes with 8 μm pores.
Results: RPTPβ/ζ mediates VEGF165-induced c-Src-dependent β3 Tyr773 phosphorylation, which is required for
VEGFR2-ανβ3 interaction and the downstream activation of phosphatidylinositol 3-kinase (PI3K) and cell surface NCL
localization. RPTPβ/ζ directly interacts with VEGF165, and this interaction is not affected by bevacizumab, while it
is interrupted by both CS-E and PTN. Down-regulation of RPTPβ/ζ by siRNA or administration of exogenous CS-E
abolishes VEGF165-induced endothelial cell migration, while PTN inhibits the migratory effect of VEGF165 to the
levels of its own effect.
Conclusions: These data identify RPTPβ/ζ 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.
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