Histamine induces tyrosine phosphorylation of endothelial cell-to-cell adherens junctions

Endothelial adherens junctions (AJ) promote intercellular adhesion and may contribute to the control of vascular permeability. These structures are formed by a transmembrane and cell-specific adhesive protein, vascular endothelial (VE)-cadherin, which is linked by its cytoplasmic tail to intracellular proteins called catenins (alpha-catenin, beta-catenin, and plakoglobin) and to the actin cytoskeleton. Little is known about the functional regulation of AJ in endothelial cells. In this study, we analyzed the effect of histamine on AJ organization in cultured endothelial cells. We first observed that histamine induced detectable intercellular gaps only in loosely-confluent cells, whereas this effect was strongly reduced or absent in long-confluent cultures. Despite this difference, in vitro permeability was augmented by histamine in both conditions. In resting conditions, tyrosine phosphorylation of AJ components and permeability values were higher in recently-confluent cells as compared with long-confluent cells. Histamine did not affect the phosphorylation state of AJ in recently-confluent cells but strongly increased this parameter in long-confluent cultures. In addition, in long-confluent cells, histamine caused dissociation of VE-cadherin from the actin cytoskeleton measured by a decrease of the amount of the molecule in the detergent-insoluble fraction of the cell extracts. Dibutyryl cAMP was able to prevent the effect of histamine on both tyrosine phosphorylation of AJ components and on endothelial permeability. The effect of histamine was specific for VE-cadherin because the phosphorylation state of neural (N)-cadherin, the other major endothelial cadherin, was unchanged by this agent. Hence AJ components are a target of histamine activation cascade; we suggest that induction of tyrosine phosphorylation of VE-cadherin and catenins contributes to the histamine effect on permeability, even in absence of frank intercellular gaps and cell retraction.