Gas1 is induced by VE-cadherin and vascular endothelial growth factor and inhibits endothelial cell apoptosis.

The junctional membrane protein vascular endothelial (VE)-cadherin mediates contact inhibition of growth and inhibits apoptosis of endothelial cells. In this article we show that VE-cadherin induces expression of growth arrest-specific 1 (Gas1), an integral membrane protein up-regulated in nonproliferating cells. By comparing syngenic endothelial cell lines, we found that Gas1 mRNA was increased by 3-fold in VE-cadherin-positive cells in comparison to VE-cadherin-null cells. Ectopic expression of Gas1 in endothelial or 293 cells strongly reduced apoptosis without affecting cell growth. Addition of vascular endothelial growth factor (VEGF) also up-regulated Gas1 and this effect was augmented more so in confluent nonproliferating cells than in sparse cultures. VE-cadherin-blocking antibody partially inhibited VEGF-induced Gas1, suggesting that VE-cadherin clustering is required for an optimal response to this stimulus. Inhibition of phosphoinositole-3-OH kinase (PI3-kinase) pathway by Wortmannin prevented Gas1 synthesis and the antiapoptotic effect of VEGF, but, in cells ectopically expressing Gas1, Wortmannin was ineffective. Furthermore, inhibition of Gas1 expression by short interfering RNA (siRNA) both in vitro and in allantois organ cultures made endothelial cells refractory to the antiapoptotic effect of VEGF. Overall these data indicate that Gas1 induction by VE-cadherin and VEGF in endothelial cells requires activation of PI3-kinase. Gas1 expression positively correlates with inhibition of endothelial cell apoptosis and may contribute to the integrity of resting endothelium.

VE-cadherin regulates endothelial actin activating Rac and increasing membrane association of Tiam.

Previously published reports support the concept that, besides promoting homotypic intercellular adhesion, cadherins may transfer intracellular signals. However, the signaling pathways triggered by cadherin clustering and their biological significance are still poorly understood. We report herein that transfection of VE-cadherin (VEC) cDNA in VEC null endothelial cells induces actin rearrangement and increases the number of vinculin positive adhesion plaques. VEC expression augments the level of active Rac but decreases active Rho. Microinjection of a dominant negative Rac mutant altered stress fiber organization, whereas inhibition of Rho was ineffective. VEC expression increased protein and mRNA levels of the Rac-specific guanosine exchange factor Tiam-1 and induced its localization at intercellular junctions. In addition, in the presence of VEC, the amounts of Tiam, Rac, and the Rac effector PAK as well as the level of PAK phosphorylation were found increased in the membrane/cytoskeletal fraction. These observations are consistent with a role of VEC in localizing Rac and its signaling partners in the same membrane compartment, facilitating their reciprocal interaction. Through this mechanism VEC may influence the constitutive organization of the actin cytoskeleton.