Tumor necrosis factor-α induces adhesion molecule expression through the sphingosine kinase pathway

Abstract

The signaling pathways that couple tumor necrosis factor-␣ (TNF␣) receptors to functional, especially inf lammatory, responses have remained elusive. We report here that TNF␣ induces endothelial cell activation, as measured by the expression of adhesion protein E-selectin and vascular adhesion molecule-1, through the sphingosine kinase (SKase) signaling pathway. Treatment of human umbilical vein endothelial cells with TNF␣ resulted in a rapid SKase activation and sphingosine 1-phosphate (S1P) generation. S1P, but not ceramide or sphingosine, was a potent dosedependent stimulator of adhesion protein expression. S1P was able to mimic the effect of TNF␣ on endothelial cells leading to extracellular signal-regulated kinases and NF-B activation, whereas ceramide or sphingosine was not. Furthermore, N,N-dimethylsphingosine, an inhibitor of SKase, profoundly inhibited TNF␣-induced extracellular signal-regulated kinases and NF-B activation and adhesion protein expression. Thus we demonstrate that the SKase pathway through the generation of S1P is critically involved in mediating TNF␣-induced endothelial cell activation.Tumor necrosis factor-␣ (TNF␣) was originally described for its antitumor activity, but is now recognized to be one of the most pleiotropic cytokines in mediating systemic inflammatory and immune responses (1, 2). A major site for these TNF␣ actions is the vascular endothelium, where TNF␣ triggers endothelial cells to secrete various cytokines and induces or enhances the expression of adhesion molecules, such as vascular cell adhesion molecule-1 (VCAM-1), intercellular adhesion molecule-1 and E-selectin (3). The regulated expression of these adhesion molecules is essential for the recruitment of circulating blood cells to the endothelium during the inflammatory and immune responses (3-5).TNF␣ activity is exerted through binding two distinct membrane receptors, p55 (TNF␣-R1) and p75 (TNF␣-R2). Engagement of the TNF␣ receptors results in recruitment of two distinct classes of receptor-associated proteins, one the TRADD, FADD͞MORT1 and RIP family, and the other, the TRAF family (6-8). Both of these appear to couple TNF␣ receptors to downstream signaling cascades such as cysteine proteases and NF-B activation to regulate cell proliferation, differentiation, and programmed cell death (6). Recently, the lipid second messenger, ceramide, has also received attention in TNF␣ signaling (6, 9). TNF␣ stimulates the activation of sphingomyelinase, yielding ceramide that, in turn, can induce apoptosis and may play a role in apoptotic signaling in various cell types (6, 9). In addition, ceramide can be subsequently metabolized to sphingosine and sphingosine 1-phosphate (S1P), via ceramidase and sphingosine kinase (SKase) activation, respectively (10). These sphingomyelin metabolites were also proposed to play a variety of roles in regulation of cellular activities such as calcium mobilization, cell motility, and mitogenesis (9, 10). In this study, we demonstrate that TNF␣ promoted generation of ceramide that was...

Inhibition of Phosphatidylinositol 3-Kinase Sensitizes Vascular Endothelial Cells to Cytokine-initiated Cathepsin-dependent Apoptosis

“…A recent report has shown that selective lysosomal permeabilization by TNF in hepatocytes is paralleled by sphingosine-mediated lysosomal permeabilization (42). Inhibition of PI3K may sensitize EC to generate sphingosine either by the activation of sphingomyelinase (43) or by de novo biosynthesis (44).…”

Sphingosine 1-phosphate activates Weibel-Palade body exocytosis

“…Lysophospholipids increase endothelial cell surface expression of Eselectin and vascular cell adhesion molecule-1 in endothelial cells (13). Lysophospholipids also activate the transcription factor NF-B in endothelial cells, increasing the transcription of E-selectin, intracellular adhesion molecule-1, IL-8, and monocyte chemoattractant protein-1 (13)(14)(15)(16). These findings suggest that S1P may activate the endothelium, triggering endothelial expression of selectins and adhesion molecules, thus initiating vascular inflammation.…”

Sphingosine 1-phosphate stimulates proliferation and migration of human endothelial cells possibly through the lipid receptors, Edg-1 and Edg-3

“…Therefore, it is reasonable to speculate that the cellular function of vascular endothelial cells may be influenced by platelets through S1P. In endothelial cells, however, only a few studies have been reported on the S1P actions and, furthermore, the site of action of S1P has not yet been characterized [16,25,26].…”