The secreted Ly6/uPAR-related protein-1 suppresses neutrophil binding, chemotaxis, and transmigration through human umbilical vein endothelial cells

The secreted Ly-6/uPAR Related Protein-1 (SLURP1) is an immunomodulatory protein that promotes corneal immune- and angiogenic-privilege. Here, we have examined the influence of SLURP1 on neutrophil-vascular endothelial cell interactions using human umbilical vein endothelial cells (HUVEC) and differentiated neutrophil-like HL-60 (dHL-60) cells, or primary human neutrophils. SLURP1 blocked the tumor necrosis factor-alpha (TNF-α)-activated dHL-60 cells (i) binding to TNF-α-activated HUVEC with a concurrent reduction in endothelial cell adhesion molecule E-selectin, (ii) transmigration through TNF-α-activated confluent HUVEC monolayer by stabilizing VE-cadherin and β-catenin on endothelial cell cytoplasmic membranes, (iii) chemotaxis towards chemoattractant formyl Met-Leu-Phe (fMLP) coupled with their decreased polarization, and (iv) TNF-α-stimulated matrix metalloproteinase-9 (MMP9) expression and activity. SLURP1 also suppressed the primary human neutrophil chemotaxis, and interaction with HUVEC. Furthermore, SLURP1 suppressed fMLP-induced phosphorylation of protein kinase-B (AKT) in dHL-60 cells. Collectively, these results provide evidence that SLURP1 suppresses neutrophil (i) docking on HUVEC cells by decreasing endothelial cell adhesion molecule E-Selectin production, (ii) transmigration through HUVEC monolayer by stabilizing endothelial cell membrane localization of VE-cadherin and β-catenin complex and promoting their barrier function, and (iii) chemotaxis by modulating their polarization and TNF-α-stimulated MMP9 production.