Cyclic AMP Potentiates Vascular Endothelial Cadherin-Mediated Cell-Cell Contact To Enhance Endothelial Barrier Function through an Epac-Rap1 Signaling Pathway

Abstract

Cyclic AMP (cAMP) is a well-known intracellular signaling molecule improving barrier function in vascular endothelial cells. Here, we delineate a novel cAMP-triggered signal that regulates the barrier function. We found that cAMP-elevating reagents, prostacyclin and forskolin, decreased cell permeability and enhanced vascular endothelial (VE) cadherin-dependent cell adhesion. Although the decreased permeability and the increased VE-cadherin-mediated adhesion by prostacyclin and forskolin were insensitive to a specific inhibitor for cAMP-dependent protein kinase, these effects were mimicked by 8-(4-chlorophenylthio)-2-O-methyladenosine-3, 5-cyclic monophosphate, a specific activator for Epac, which is a novel cAMP-dependent guanine nucleotide exchange factor for Rap1. Thus, we investigated the effect of Rap1 on permeability and the VE-cadherin-mediated cell adhesion by expressing either constitutive active Rap1 or Rap1GAPII. Activation of Rap1 resulted in a decrease in permeability and enhancement of VE-cadherin-dependent cell adhesion, whereas inactivation of Rap1 had the counter effect. Furthermore, prostacyclin and forskolin induced cortical actin rearrangement in a Rap1-dependent manner. In conclusion, cAMP-Epac-Rap1 signaling promotes decreased cell permeability by enhancing VE-cadherin-mediated adhesion lined by the rearranged cortical actin.

Prostaglandins PGE2 and PGI2 promote endothelial barrier enhancement via PKA- and Epac1/Rap1-dependent Rac activation

“…Prostaglandins represent another important group of lipid mediators with barrier-protective potential towards vascular endothelium [6,7]. However, the role of PGs and their receptors in inflammation is not well understood.…”

“…Recent reports described a novel mechanism of cAMP-dependent regulation of Rac pathway via cAMP-dependent nucleotide exchange factor Epac, which activates small GTPase Rap1 [7,37]. We examined a role of Epac/Rap1 mechanism in the PG-induced activation of Rac pathway.…”

“…Stable PGI 2 analogs beraprost and iloprost currently widely used as treatment of pulmonary hypertension, showed potent anti-inflammatory and endothelium-dependent anti-edemagenic effects in several models of acute lung injury [4,5]. PGE 2 has been also shown to regulate endothelial permeability in vivo and in vitro [6,7]. However, molecular mechanisms of pulmonary endothelial barrier protection by prostaglandins remain largely unexplored.…”

“…Rap1 is a member of Ras family of small GTPases. Activated Rap1 may function in diverse processes, including integrinmediated cell adhesion [35], cadherin-mediated cell junction formation and regulation of endothelial barrier [7,36]. Rap1 activation induces localization of Rac-specific GEFs Tiam1 and Vav2 to the membrane areas at the cell periphery [35,37], which causes local activation of small GTPase Rac.…”

“…Rap1 activation induces localization of Rac-specific GEFs Tiam1 and Vav2 to the membrane areas at the cell periphery [35,37], which causes local activation of small GTPase Rac. In turn, activated Rac stimulates effector signaling kinase PAK1 as well as cytoskeletal and cell contact-associated downstream effectors and induces rearrangements of actin cytoskeleton, focal adhesions and adherens junctions, which determine increased EC monolayer barrier properties [7,10,13,38,39].…”