Epac/Rap1‐regulated deactivation of PAF‐induced hyperpermeability is independent of eNOS activation

Abstract

Platelet‐activating factor (PAF) increases endothelial permeability via phosphorylation and translocation of endothelial nitric oxide synthase (eNOS) and nitric oxide (NO) production. PAF‐induced hyperpermeability is partly attenuated through Epac/Rap1 pathway. We tested the hypothesis that activation of Epac/Rap1 inhibits PAF‐induced phosphorylation and localization of eNOS. We activated Epac/Rap1 specifically with 8CPT (8‐(4‐chlorophenylthio)‐2′‐O‐methyladenose‐3′,5′‐cyclic monophosphate) in human dermal microvascular endothelial cells (HMVEC). 8CPT activated eNOS‐S1177 phosphorylation and dephosphorylation of eNOS on T495, starting as early as 30”, achieving peak at 1′, and returned to the basal level at 10′; a time‐course that is similar to PAF stimulation. 8CPT applied after PAF did not attenuate eNOSS1177 phosphorylation or dephosphorylation on T495. Furthermore, 8CPT increased NO production in dose‐dependent manner. Interestingly, our immunofluorescence microscopy studies revealed that 8CPT inhibited PAF‐induced eNOS internalization. Our data suggest that Epac/Rap1 reverses PAF‐induced hyperpermeability by limiting eNOS to the cell plasma membrane while allowing eNOS phosphorylation and NO production. (Supported by NIH grants HL070634 and HL088479).