The ligand occupancy of endothelial protein C receptor switches the protease-activated receptor 1-dependent signaling specificity of thrombin from a permeability-enhancing to a barrier-protective response in endothelial cells

Abstract

Recent studies have indicated that activated protein C (APC) may exert its cytoprotective and anti-inflammatory activities through the endothelial protein C receptor (EPCR)-dependent cleavage of protease-activated receptor 1 (PAR-1) on vascular endothelial cells. Noting that (1) the activation of protein C on endothelial cells requires thrombin, (2) relative to APC, thrombin cleaves PAR-1 with approximately 3 to 4 orders of magnitude higher catalytic efficiency, and (3) PAR-1 is a target for the proinflammatory activity of thrombin, it is not understood how APC can elicit a protective signaling response through the cleavage of PAR-1 when thrombin is present. In this study, we demonstrate that EPCR is associated with caveolin-1 in lipid rafts of endothelial cells and that its occupancy by the gamma-carboxyglutamic acid (Gla) domain of protein C/APC leads to its dissociation from caveolin-1 and recruitment of PAR-1 to a protective signaling pathway through coupling of PAR-1 to the pertussis toxin-sensitive G(i)-protein. Thus, when EPCR is bound by protein C, the PAR-1 cleavage-dependent protective signaling responses in endothelial cells can be mediated by either thrombin or APC. These results provide a new paradigm for understanding how PAR-1 and EPCR participate in protective signaling events in endothelial cells.

Emerging roles of serine proteinases in tissue turnover in arthritis

“…These observations are dependent on APC binding to its specific receptor, endothelial protein C receptor (EPCR), although this receptor does not signal. The proposed mechanism involves APC binding to EPCR, activating PAR-1, and transactivating the epidermal growth factor receptor (46,50,51). Cleavage of PAR-1 by APC bound to EPCR within a lipid raft activates Gi and subsequent antiinflammatory signals.…”

“…Cleavage of PAR-1 by APC bound to EPCR within a lipid raft activates Gi and subsequent antiinflammatory signals. When PAR-1 is activated outside the lipid raft by other serine proteinases, signaling via Gq and/or G12/13 occurs, leading to proinflammatory signals (50).…”

Factor VIIa Interaction With Tissue Factor and Endothelial Cell Protein C Receptor on Cell Surfaces

“…EPCR-FVIIa complexes neither activate FX (31) nor induce cell signaling through activation of PAR1 or PAR2 (31,36). FVIIa binding to EPCR has no influence on the formation of TF-FVIIa complexes on activated endothelial cells (31).…”

Factor VIIa binding to endothelial cell protein C receptor

“…Recent studies of Bae et al [18] also suggested that FVIIa binding to EPCR does not induce cell signaling since FVIIa failed to prevent enhanced cell permeability induced by thrombin. However, these studies alone do not completely rule out a role for EPCR-FVIIa in cell signaling.…”