GAS6 Inhibits Granulocyte Adhesion to Endothelial Cells

Abstract

GAS6 is a ligand for the tyrosine kinase receptors Rse, Axl, and Mer, but its function is poorly understood. Previous studies reported that both GAS6 and Axl are expressed by vascular endothelial cells (EC), which play a key role in leukocyte extravasation into tissues during inflammation through adhesive interactions with these cells. The aim of this work was to evaluate the GAS6 effect on the adhesive function of EC. Treatment of EC with GAS6 significantly inhibited adhesion of polymorphonuclear cells (PMN) induced by phorbol 12-myristate 13-acetate (PMA), platelet-activating factor (PAF), thrombin, interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α), but not that induced by FMLP and IL-8. GAS6 did not affect adhesion to resting EC. Titration experiments showed that high concentrations of GAS6 were needed to inhibit PMN adhesion and that inhibition was dose-dependent at the concentration range of 0.1 to 1 μg/mL. One possibility was that high concentrations were needed to overwhelm the effect of endogenous GAS6 produced by EC. In line with this possibility, treatment of resting EC with soluble Axl significantly potentiated PMN adhesion. Analysis of localization of GAS6 by confocal microscopy and cytofluorimetric analysis showed that it is concentrated along the plasma membrane in resting EC and treatment with PAF induces depletion and/or redistribution of the molecule. These data suggest that GAS6 functions as a physiologic antiinflammatory agent produced by resting EC and depleted when proinflammatory stimuli turn on the proadhesive machinery of EC.

Cholesteryl butyrate solid lipid nanoparticles inhibit adhesion of human neutrophils to endothelial cells

“…The effects of sodium butyrate and chol‐but SLN on PMN adhesion to HUVEC were evaluated by coincubating both cell types for 10 min with each compound (10 −8 –10 −5 M ) in the presence of 10 −7 M FMLP, which mimics bacterial chemotaxin and activates the PMN adhesive machinery. The 10 −7 M dose of FMLP had previously been found to induce maximal adhesion of PMNs (Avanzi et al ., 1998) (351±25% of control adhesion). Chol‐but SLN strikingly inhibited adhesion in a dose‐dependent manner with a maximal inhibition of 71±7% ( P <0.001 versus sodium butyrate) at about 10 −5 M and an IC 50 at 2.5±0.5 × 10 −7 M .…”

Gas 6 promotes Axl-mediated survival in pulmonary endothelial cells

“…Gas 6 is expressed in pulmonary endothelial cells in culture and in whole lung. Previous investigations identified the ligand Gas 6 in many cells and organs, but particularly high levels were identified in HUVEC and bovine aortic endothelial cells and in human and murine lungs (2,24,37). We examined Gas 6 expression in endothelial cells isolated from human pulmonary artery and tested whether our human cDNA Gas 6 probe also hybridizes to murine Gas 6.…”

“…Gas 6, the product of the growth arrest-specific gene 6, is a soluble factor implicated in the regulation of multiple cellular functions, including growth, survival, adhesion, and chemotaxis (2,10,12,30,31). Gas 6 signaling is transduced via ligation with three known receptor tyrosine kinases (RTK), Axl (also UFO and Ark) (33), Rse (also Sky, Brt, Tyro-3) (19), and Mer (29).…”

“…Gas 6 also prevents growth arrest-induced death and promotes chemotaxis in vascular smooth muscle cells (10,31). Gas 6 is expressed in vascular endothelial cells (24,37) and inhibits granulocyte adhesion to activated endothelial cells in vitro (2). In human umbilical vein endothelial cells (HUVEC), Gas 6 promotes cellular viability in the absence of growth factors (34).…”

In brain, Axl recruits Grb2 and the p85 regulatory subunit of PI3 kinase; in vitro mutagenesis defines the requisite binding sites for downstream Akt activation

“…Also, the Axl receptor is expressed in Schwann cells, and endothelial cells (Li et al. 1996; Avanzi et al. 1998).…”