Summary
The protein C (PC) system conveys beneficial anticoagulant and cytoprotective effects
in numerous in vivo disease models. The endothelial protein C receptor (EPCR) plays a central role in
these pathways as cofactor for PC activation and by enhancing activated protein C
(APC)-mediated protease-activated receptor (PAR) activation. During inflammatory disease,
expression of EPCR on cell membranes is often diminished thereby limiting PC activation
and APC’s effects on cells. Here a caveolae-targeting glycosylphosphatidylinositol
(GPI)-anchored EPCR (EPCR-GPI) was engineered to restore EPCR’s bioavailability via
“cell painting.” The painting efficiency of EPCR-GPI on EPCR-depleted endothelial
cells was time- and dose-dependent. The EPCR-GPI bioavailability after painting was
long lasting since EPCR surface levels reached 400 % of wild-type cells after 2 hours
and remained > 200 % for 24 hours. EPCR-GPI painting conveyed APC binding to EPCR-depleted
endothelial cells where EPCR was lost due to shedding or shRNA. EPCR painting normalised
PC activation on EPCR-depleted cells indicating that EPCR-GPI is functional active
on painted cells. Caveolin-1 lipid rafts were enriched in EPCR after painting due
to the GPI-anchor targeting caveolae. Accordingly, EPCR painting supported PAR1 and
PAR3 cleavage by APC and augmented PAR1-dependent Akt phosphorylation by APC. Thus,
EPCR-GPI painting achieved physiological relevant surface levels on endothelial cells,
restored APC binding to EPCR-depleted cells, supported PC activation, and enhanced
APC-mediated PAR cleavage and cytoprotective signalling. Therefore, EPCRGPI provides
a novel tool to restore the bioavailability and functionality of EPCR on EPCR- depleted
and -deficient cells.
Keywords
Endothelial protein C receptor - glycosylphosphatidylinositol anchors - protease-activated
receptors - protein C - vascular endothelium