Endotoxin induces endothelial barrier dysfunction through protein tyrosine phosphorylation

Bacterial lipopolysaccharide (LPS) induces actin reorganization, intercellular gap formation, and endothelial barrier dysfunction in vitro. We studied whether LPS-induced increments in C-14-labeled bovine serum albumin (BSA) flux across bovine pulmonary artery endothelial cell (EC) monolayers and actin depolymerization are mediated through protein tyrosine phosphorylation. Lysates from EC exposed to LPS derived from Escherichia coli 0111:B4 (100 ng/ml, 1 h) demonstrated increased tyrosine phosphorylation of the cytoskeletal protein paxillin. Protein tyrosine kinase inhibition, with either herbimycin A (1 mu M) or genistein (50 mu g/ml), protected against LPS-induced actin depolymerization, intercellular gap formation, and increments in [C-14]BSA flux. In contrast, inhibition of tyrosine phosphatases with sodium orthovanadate (2.5 mu M) or phenylarsine oxide (0.1 mu M) enhanced the LPS-induced increments in the G-actin pool and the transendothelial flux of [C-14]BSA compared with that seen after exposure to LPS alone. Our data indicate that the influence of LPS on EC actin organization and barrier function is mediated, in part, through a signaling pathway that is dependent on tyrosine phosphorylation.