Bacterial lipopolysaccharide disrupts endothelial monolayer integrity and survival signaling events through caspase cleavage of adherens junction proteins

Bacterial lipopolysaccharide or endotoxin induces actin reorganization, increased paracellular permeability, and endothelial cell detachment from the underlying extracellular matrix in vitro. We studied the effect of endotoxin on transendothelial albumin flux and detachment of endothelial cells cultured on gelatin-impregnated filters. The endotoxin-induced changes in endothelial barrier function and detachment occurred at doses and times that were compatible with endotoxin-induced apoptosis. Since the actin cytoskeleton and cell-cell and cell-matrix adhesion all participate in the regulation of the paracellular pathway and cell-matrix interactions, we studied whether protein components of the actin-linked adherens junctions were modified in response to endotoxin. Components of cell-cell (beta- and gamma-catenin) and cell-matrix (focal adhesion kinase and p130(Cas)) adherens junctions were cleaved by caspases activated during apoptosis with dose and time requirements that paralleled those seen for barrier dysfunction and detachment. Cleavage of focal adhesion kinase led to its dissociation from the focal adhesion-associated signaling protein, paxillin, resulting in reduced paxillin tyrosine phosphorylation. Inhibition of caspase-mediated cleavage of these proteins protected against detachment but not opening of the paracellular pathway. Therefore, endotoxin-induced disruption of endothelial monolayer integrity and survival signaling events is mediated, in part, through caspase cleavage of adherens junction proteins.