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Thrombin upregulates the angiopoietin–Tie2 Axis: endothelial protein C receptor occupancy prevents the thrombin mobilization of angiopoietin 2 and P‐selectin from Weibel–Palade bodies
Author(s) -
BAE J.S.,
REZAIE A. R.
Publication year - 2010
Publication title -
journal of thrombosis and haemostasis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.947
H-Index - 178
eISSN - 1538-7836
pISSN - 1538-7933
DOI - 10.1111/j.1538-7836.2010.03812.x
Subject(s) - angiopoietin receptor , angiopoietin 2 , thrombin , angiopoietin , p selectin , receptor , microbiology and biotechnology , chemistry , biology , cancer research , platelet activation , biochemistry , immunology , platelet , vegf receptors , vascular endothelial growth factor
Summary. Background: Activated protein C (APC) in complex with endothelial protein C receptor (EPCR) can reverse the barrier‐disruptive and cytotoxic effects of proinflammatory cytokines by cleaving protease‐activated receptor 1 (PAR‐1). Recently, it was reported that the PAR‐1‐dependent vascular barrier‐protective effect of APC is mediated through transactivation of the angiopoietin (Ang)–Tie2 signaling pathway. The antagonist of this pathway, Ang2, is stored in Weibel–Palade bodies within endothelial cells. Objectives: To determine whether the occupancy of EPCR by its ligand can switch the PAR‐1‐dependent signaling specificity of thrombin through the Ang–Tie2 axis. Methods: We activated endothelial cells with thrombin before and after treating them with the catalytically inactive Ser195→Ala substitution mutant of protein C. The expression levels of Ang1, Ang2 and Tie2 in response to thrombin were measured by both an enzyme‐linked immunosorbent assay and a cell permeability assay in the absence and presence of small interfering RNA and a blocking antibody to Tie2. Results: Thrombin upregulated the expression of both Ang1 and Tie2 but downregulated the expression of Ang2 when EPCR was occupied by its ligand. The Ang1–Tie2‐dependent protective effect of thrombin was initiated through protein C inhibiting the rapid mobilization of Ang2 from Weibel–Palade bodies. Interestingly, the protein C mutant also inhibited the thrombin mobilization of P‐selectin. Conclusions: These results suggest a physiologic role for the low concentration of thrombin in maintaining the integrity of the EPCR‐containing vasculature through the PAR‐1‐dependent inhibition of Ang2 and P‐selectin release from Weibel–Palade bodies.