A non‐GPCR dependent role for P‐Rex1 in endothelial cells

Maintenance of vascular endothelial integrity is of great importance to homeostasis of vital organ functions. The small GTPase Rac is one of the key signaling mediators for vascular endothelial functions, but how Rac activation is regulated under various pathophysiological conditions remains incompletely understood. Using gene deletion and knockdown approaches, we investigated the potential role of the phosphoinositide‐ and G protein βγ subunits‐regulated guanine nucleotide exchange factor P‐Rex1 in TNF‐α induced lung vascular injury. P‐Rex1, previously found in neutrophils and neurons, is also expressed in endothelial cells. In cultured human lung microvascular endothelial cells (HLMVECs), small interference (si) RNA‐mediated knockdown of P‐Rex1 markedly attenuated the loss of TNF‐α induced transendothelial electrical resistance (TER), intercellular gap formation, Rac activation and reactive oxygen species (ROS) production, compared to cells receiving scrambled siRNA. TNF‐α stimulated P‐Rex1 membrane translocation and the resulting Rac activation is dependent on PI3K. Both, in vivo and in vitro , absence of P‐Rex1 resulted in significantly less neutrophil transendothelial migration. Moreover, endothelial P‐Rex1 plays a predominant role over neutrophil P‐Rex1 in this process. These results demonstrate a pivotal role of endothelial P‐Rex1 in TNF‐α signaling, making it a therapeutic target in the control of vascular permeability and neutrophil infiltration to inflammatory tissues. (Research supported by NIH grant HL077806)