Fig. 7.

aPC-induced anti-apoptotic responses requires β-arr2 and Cav1. (A) EA.hy926 cells transfected with ns or β-arr2 siRNA were stimulated with 20 nM aPC for 4 h, treated with 20 ng/mL TNF-α for 20 h, and apoptosis determined. Data (mean ± SD, n = 5) were analyzed by two-way ANOVA (*P < 0.05). NS, not significant. (B) EA.hy926 cells transfected with ns or Cav1 siRNA were pretreated with aPC and then stimulated with TNF-α, as described above. Cell lysates were immunoblotted (IB) using caspase-3, Cav1, or β-tubulin antibodies. Data (±SD, n = 3) were analyzed by t test (*P < 0.05; ***P < 0.001). (C) Model of aPC/PAR1 transactivation of S1PR1 via β-arr2–mediated SphK1 activation. Activation of PAR1 by aPC bound to its coreceptor EPCR cleaves and activates PAR1, which promotes β-arr2–dependent SphK1 activation and transactivation of S1PR1, resulting in Akt activation and cell survival. SphK1 catalyzes phosphorylation of sphingosine to form S1P, a ligand for S1PR1. The aPC-PAR1-β-arr2–driven SphK1-S1PR1-Akt signaling axis is distinct from the β-arr2–mediated ERK1/2 signaling pathway.