SSphingosine-1-phosphate (S1P), the bioactive product of sphingosine kinase (SK) activation is a survival factor for endothelial cells. The mechanism of SK mediated survival was investigated in endothelial cells with moderately raised intracellular SK activity. Overexpression of SK mediated survival primarily through the activation of the phosphatidyl inositol-3 kinase (PI-3K/Akt) pathway, and an associated upregulation of the anti-apoptotic protein Bcl-2 and downregulation of the proapoptotic protein Bim. In addition there was an upregulation and dephosphorylation of the junctional molecule, platelet endothelial cell adhesion molecule-1 (PECAM-1), which was obligatory for activation of the PI-3K/Akt pathway, for SK-induced cell survival and for the changes in the apoptosis related proteins. Thus raised intracellular SK activity induced a molecule involved in cell-cell interactions to augment cell survival through a PI-3K/Akt dependent pathway. This is distinct from the activation of both PI-3K/Akt and mitogen-activated protein kinase (MAPK) pathways seen with exogenously added S1P. Cells overexpressing SK showed enhanced survival under conditions of serum deprivation and absence of attachment to extracellular matrix, suggesting a role for SK in the regulation of vascular phenomena that occur under conditions of stress, such as angiogenesis and survival in unattached states as would be required for a circulating endothelial cell.