Phospholipase Cϵ Modulates Rap1 activity and the endothelial barrier

Abstract

The phosphoinositide-specific phospholipase C, PLCϵ, is a unique signaling protein with known roles in regulating cardiac myocyte growth, astrocyte inflammatory signaling, and tumor formation. PLCϵ is also expressed in endothelial cells, however its role in endothelial regulation is not fully established. We show that endothelial cells of multiple origins, including human pulmonary artery (HPAEC), human umbilical vein (HUVEC), and immortalized brain microvascular (hCMEC/D3) endothelial cells, express PLCϵ. Knockdown of PLCϵ in arterial endothelial monolayers decreased the effectiveness of the endothelial barrier. Concomitantly, RhoA activity and stress fiber formation were increased. PLCϵ-deficient arterial endothelial cells also exhibited decreased Rap1-GTP levels, which could be restored by activation of the Rap1 GEF, Epac, to rescue the increase in monolayer leak. Reintroduction of PLCϵ rescued monolayer leak with both the CDC25 GEF domain and the lipase domain of PLCϵ required to fully activate Rap1 and to rescue endothelial barrier function. Finally, we demonstrate that the barrier promoting effects PLCϵ are dependent on Rap1 signaling through the Rap1 effector, KRIT1, which we have previously shown is vital for maintaining endothelial barrier stability. Thus we have described a novel role for PLCϵ PIP2 hydrolytic and Rap GEF activities in arterial endothelial cells, where PLCϵ-dependent activation of Rap1/KRIT1 signaling promotes endothelial barrier stability.