BACKGROUND AND OBJECTIVE: Coagulation is intrinsically tied to inflammation, and both proinflammatory and anti-inflammatory responses are modulated by coagulation protease signaling through protease-activated receptor-1 (PAR1). Activated factor X (FXa) can elicit cellular signaling through PAR1, but little is known about the role of cofactors in this pathway. Endothelial protein C receptor (EPCR) supports PAR1 signaling by the protein C pathway, and in the present study we tested whether EPCR mediates surface recruitment and signaling of FXa.
METHODS AND RESULTS: Here, we show that FXa binds to overexpressed as well as native endothelial EPCR. PAR1 cleavage by FXa as analyzed with conformation-sensitive antibodies and a tagged PAR1 reporter construct was strongly enhanced if EPCR was available. Anti-EPCR failed to affect the tissue factor-dependent activation of FX, but high concentrations of FXa decreased EPCR-dependent protein C activation. Most importantly, the FXa-mediated induction of Erk1/2 activation, expression of the transcript for connective tissue growth factor and barrier protection in endothelial cells required binding to EPCR.
CONCLUSIONS: Our results demonstrate that EPCR plays an unexpected role in supporting cell surface recruitment, PAR1 activation, and signaling by FXa.