Cross talk between paxillin and Rac is critical for mediation of barrier-protective effects by oxidized phospholipids

Birukova AA, Alekseeva E, Cokic I, Turner CE, Birukov KG. Cross talk between paxillin and Rac is critical for mediation of barrier-protective effects by oxidized phospholipids. Am J Physiol Lung Cell Mol Physiol 295: L593-L602, 2008. First published August 1, 2008; doi: 10.1152/ajplung.90257.2008.-We previously reported that the barrier-protective effects of oxidized 1-palmitoyl-2-arachidonoylsn-glycero-3-phosphocholine (OxPAPC) on pulmonary endothelial cells (ECs) delineate the role of Rac- and Cdc42-dependent mechanisms and described the involvement of the focal adhesion ( FA) protein paxillin in enhancement of the EC barrier upon OxPAPC challenge. This study examined a potential role of paxillin in the feedback mechanism of Rac regulation by FAs in OxPAPC-stimulated ECs. Our results demonstrate that OxPAPC induced Rac- dependent, Rho-independent peripheral accumulation of paxillin-containing FAs and time-dependent paxillin phosphorylation. Molecular inhibition of Rac decreased association of paxillin with the Rac- specific guanine nucleotide exchange factor beta-PIX. Molecular inhibition of paxillin also attenuated OxPAPC-induced enhancement of adherens junctions critical for the EC barrier-protective response, accumulation of vascular endothelial cadherin in the membrane fractions, and decreased activation of Rac and its effector p21-activated kinase (PAK1). Expression of paxillin with a mutated PAK1-dependent phosphorylation site (S273A) attenuated OxPAPC-induced PAK1 activation and the EC barrier-protective response. These results suggest that PAK1-specific paxillin phosphorylation at Ser273 is critically involved in the positive-feedback regulation of the Rac- PAK1 pathway and may contribute to sustained enhancement of the EC barrier caused by oxidized phospholipids.