Sphingosine 1-phosphate (S1P) induces expression of E-selectin and adhesion of monocytes via intracellular signalling pathways in vascular endothelial cells

Abstract

Sphingosine 1-phosphate (S1P) – a constitutive component of human plasma – is implicated as a signalling molecule in the regulation of cell adhesion molecules (CAM) in vascular endothelial cells (EC), but the degree of the S1P-induced expression of CAM and the involvement of the S1P 1 receptor are still ambiguous. Here, we report that S1P, when added to vascular EC in the absence of other stimuli, induced a strictly proportional and concentration-dependent expression of E-selectin mRNA, of E-selectin protein and of the number of adhering THP-1 monocytes to EC. Experiments with exogenous [ 3H]S1P showed a multi-exponential influx kinetic of intracellular uptake of [ 3H]S1P up to a steady state level over 2 h. This process could be inhibited or enhanced by various synthetic modulators targeting both, S1P 1 receptor-dependent (Akt, ERK1/2) as well as independent DMS-sensitive pathways. The S1P 1 receptor signalling was shown to drive the sphingosine kinase – the rate limiting enzyme for the formation of S1P – to a higher or lower activity. Furthermore, S1P as an intracellular messenger induced the phosphorylation and nuclear translocation of the p65 subunit of NF-kappaB and in turn the expression of E-selectin and monocyte adhesion. Taken together, these results suggest that the physiologically controlled variation in intracellular S1P concentrations may represent a novel not yet known mechanism of fine-tuning the expression of proinflammatory and atherogenic E-selectin cell adhesion molecule by vascular endothelial cells.