aPC/PAR1 confers endothelial anti-apoptotic activity via a discrete β-arrestin-2 mediated SphK1-S1PR1-Akt signaling axis
Endothelial dysfunction is associated with multiple vascular diseases and lacks effective treatments. Activated Protein C (aPC) is a promising biotherapeutic that signals via protease-activated receptor-1 (PAR1) to promote diverse cytoprotective responses, including endothelial barrier stabilization, anti-inflammatory and anti-apoptotic activities, which is facilitated by co-receptors. We showed that aPC-activated PAR1 signals preferentially via {beta}-arrestin-2 ({beta}-arr2) and dishevelled-2 (Dvl2) scaffolds rather than G proteins to enhance barrier protection. However, the mechanisms by which aPC/PAR1 promotes other cytoprotective responses are poorly understood. Here we define a novel {beta}-arr2-mediated sphingosine kinase-1 (SphK1)-sphingosine-1-phosphate receptor-1 (S1PR1)-Akt signaling axis that confers aPC/PAR1-mediated protection against cell death. We show that PAR1 and S1PR1 co-exist in caveolin-1-rich microdomains basally and aPC markedly increases S1PR1-caveolin-1 co-association. Moreover, aPC stimulates {beta}-arr2-dependent SphK1 activation independent of Dvl2, which is critical for S1PR1 transactivation. These studies reveal that different aPC/PAR1 cytoprotective responses are mediated by discrete {beta}-arr2-driven signaling pathways in caveolae.