Fig. 2. Suggested functional modifications of endothelial AJs under in vitro conditions that increase endothelial permeability. (A) Under resting conditions, VE-cadherin clusters at junctions in zipper-like structures; p120, β-catenin (βcat) and plakoglobin (plako) bind directly to VE-cadherin, whereas -catenin (cat) binds indirectly through its association with β-catenin or plakoglobin. (B) Phosphorylation (P) of tyrosine residues of VE-cadherin, β-catenin, plakoglobin and p120 reduces AJ strength. The VE-cadherin complex might become partially disorganized without any evidence of cell retraction. Phosphorylation of VE-cadherin at Ser665 has also been reported. This process is thought to mediate VE-cadherin internalization and increase vascular permeability (see also Fig. 3). (C) Several permeability-increasing agents, or inflammatory conditions or lytic enzymes, can cause intercellular gaps. The phenomenon is mediated by actomyosin, which links to the cadherin complex and induces cell retraction. (D) Antibodies that block VE-cadherin bind to its adhesive domain and inhibit clustering. The effect of such antibodies can last for several hours in vivo and can induce a dramatic increase in permeability.