How T cells trigger the dissociation of the endothelial receptor phosphatase VE-PTP from VE-cadherin

Abstract

Key Points• The endothelial leukocyte receptor VCAM-1 triggers opening of endothelial junctions via dissociation of VE-PTP from VE-cadherin.• VCAM-1 and VEGF signaling use a similar signaling pathway to trigger the dissociation of VE-PTP from VE-cadherin.The vascular endothelial (VE) receptor protein tyrosine phosphatase (VE-PTP) associates with VE-cadherin and supports endothelial cell contact integrity. This complex is rapidly dissociated by adhesion of leukocytes to endothelial cells or by vascular endothelial growth factor. We have shown recently that this dissociation is indeed required for the opening of endothelial cell contacts during leukocyte extravasation in vivo. The leukocyte receptor and signaling mechanism that stimulates VE-cadherin/VE-PTP dissociation are unknown. Here, we identify vascular cell adhesion molecule 1 as the relevant receptor for lymphocytes in this process. As signaling steps downstream of this receptor, we determined the activation of Rac1, the generation of reactive oxygen species by nicotinamide adenine dinucleotide phosphate oxidase and the activation of the redox-sensitive tyrosine kinase Pyk2 as essential for VE-cadherin/VE-PTP dissociation. These signaling steps are also required for the dissociation induced by VE growth factor. Searching for the molecular mechanism of complex dissociation, we found that a model substrate of VE-PTP represented by a tyrosine-phosphorylated peptide of Tie-2 dissociates VE-PTP from VE-cadherin when introduced with the help of a Tat peptide. We suggest that lymphocyte binding to vascular cell adhesion molecule 1 triggers a signaling process that enables a VE-PTP substrate to dissociate VE-PTP from VEcadherin, thereby facilitating efficient transmigration. (Blood. 2013;122(14):2512-2522) IntroductionDuring inflammation, leukocytes extravasating from the blood into tissues have to migrate through the blood vessel wall. This is achieved by first binding to various cytokine-induced adhesion receptors on endothelial cells followed by inducing openings in the endothelial barrier.1 Although these openings can be transcellular, the vast majority of leukocytes use a paracellular route through endothelial junctions, as was documented in vitro 2 and more recently in vivo. 3,4 Vascular endothelial (VE)-cadherin is a junctional adhesion molecule that is of vital importance for the integrity of endothelial cell junctions. 5,6 Blocking of VE-cadherin adhesion by antibodies is sufficient to destabilize endothelial junctions in vivo and to increase leukocyte extravasation. 7,8 Furthermore, replacing the VE-cadherinb-catenin-a-catenin complex by a VE-cadherin-a-catenin fusion protein in knock-in mice stabilizes endothelial junctions efficiently and strongly inhibits leukocyte extravasation in various tissues. 4 This highlights the importance of regulating VE-cadherin function during leukocyte extravasation. It has been shown that tyrosine phosphorylation of VE-cadherin correlates with destabilization of endothelial junctions 9-11 and participates in vitro in the...

HIF2α signaling inhibits adherens junctional disruption in acute lung injury

“…It has also been reported that VE-PTP regulates the activity of the endothelial VEGF receptor VEGFR2 via the TIE2 receptor (38), which in turn could affect endothelial barrier function, since VEGF signaling increased vascular permeability (23). Further, since the dissociation of VE-PTP and VEcadherin is redox dependent (39) and HIF2α favors a reduced redox state (40), HIF2α activation in the endothelium may contribute to enhanced barrier function through suppression of ROS signaling. This reduced redox state may be a reflection of metabolic shifts induced by hypoxia or HIF2α signaling such as enhanced glycolytic activity, which we did not study but which may have contributed to the endothelial barrier-enhancing effects of hypoxia and HIF2α activation.…”

Focal adhesion kinase-related nonkinase (FRNK) negatively regulates IL-4-mediated inflammation

“…Despite blocking .85% of FAK protein expression and completely blocking FAK phosphorylation, downregulation of FAK had no effect on GATA6, VCAM-1 or CCL26 expression. Pyk2 is functionally related to FAK, expressed in endothelial cells, and can also be regulated by FRNK (Govindarajan et al, 2000;Schaller, 2010;Vockel and Vestweber, 2013). When we examined the effect of Pyk2 knockdown alone or in conjunction with FAK in this model Fig.…”

“…Blots in B and D are representative of four independent experiments. Schaller, 2010;Vockel and Vestweber, 2013). For this reason, we examined Pyk2 in our model system.…”

Leukocytes talking to VE-cadherin

“…1 A n excellent summary of their findings is contained in their figure 7D 1 : when a lymphocyte's a4b1 integrin binds endothelial vascular adhesion molecule (VCAM)-1, this causes activation of the small GTPase Rac1. Rac1 in turn activates the endothelial nicotinamide adenine dinucleotide phosphate oxidase (NOX complex), which produces superoxide and hydrogen peroxide, also known as reactive oxygen species (ROS).…”