-Catenin plays an important role in the regulation of vascular endothelial cell-cell adhesions and barrier function by linking the VE-cadherin junction complex to the cytoskeleton. The purpose of this study was to evaluate the effect of -catenin and VE-cadherin interactions on endothelial permeability during inflammatory stimulation by histamine. We first assessed the ability of a -catenin-binding polypeptide known as Inhibitor of -catenin and T-cell factor (ICAT) to compete -catenin binding to VE-cadherin in vitro. We then over-expressed recombinant FLAG-ICAT in human umbilical vein endothelial cells (HUVEC) to study its impact on endothelial barrier function controlled by cell-cell adhesions. The binding of -catenin to VE-cadherin was quantified before and after stimulation with histamine, along with measurements of the transendothelial electrical resistance (TER) and apparent permeability to albumin (Pa) under the same conditions. The results showed that ICAT bound to -catenin and competitively inhibited binding of the VE-cadherin cytoplasmic domain to -catenin in a concentration-dependent manner. Overexpression of FLAG-ICAT in endothelial cell monolayers did not affect their basal permeability properties, as indicated by unaltered TER and Pa; however, the magnitude and duration of histamine-induced decrease in TER were significantly augmented. Likewise, the increase in Pa in the presence of histamine was exacerbated. Overexpression of FLAG-ICAT also significantly decreased the level of -catenin-associated VE-cadherin following histamine stimulation. Taken together, the data suggest that inflammatory agents like histamine cause a transient and reversible disruption of binding between -catenin and VE-cadherin, during which endothelial permeability is elevated.