title: Activation of sphingosine kinase by tumor necrosis factor-alpha inhibits apoptosis in human endothelial cells.
abstract: Human umbilical vein endothelial cells (HUVEC), like most normal cells, are resistant to tumor necrosis factor-alpha (TNF)-induced apoptosis in spite of TNF activating sphingomyelinase and generating ceramide, a known inducer of apoptosis. Here we report that TNF activates another key enzyme, sphingosine kinase (SphK), in the sphingomyelin metabolic pathway resulting in production of sphingosine-1-phosphate (S1P) and that S1P is a potent antagonist of TNF-mediated apoptosis. The TNF-induced SphK activation is independent of sphingomyelinase and ceramidase activities, suggesting that TNF affects this enzyme directly other than through a mass effect on sphingomyelin degradation. In contrast to normal HUVEC, in a spontaneously transformed endothelial cell line (C11) TNF stimulation failed to activate SphK and induced apoptosis as characterized by morphological and biochemical criteria. Addition of exogenous S1P or increasing endogenous S1P by phorbol ester markedly protected C11 cell line from TNF-induced apoptosis. Conversely, N, N-dimethylsphingosine, an inhibitor of SphK, profoundly sensitized normal HUVEC to killing by TNF. Thus, we demonstrate that the activation of SphK by TNF is an important signaling for protection from the apoptotic effect of TNF in endothelial cells.
authors.affiliation: Division of Human Immunology, The Hanson Centre for Cancer Research, Adelaide, South Australia 5000, Australia.
authors.forename: P
authors.initials: P
authors.lastname: Xia
authors.forename: L
authors.initials: L
authors.lastname: Wang
authors.forename: J R
authors.initials: JR
authors.lastname: Gamble
authors.forename: M A
authors.initials: MA
authors.lastname: Vadas
mesh_terms: D000581:Amidohydrolases / Q000378:metabolism; D017209:Apoptosis / Q000187:drug effects*; D002461:Cell Line, Transformed; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D055572:Ceramidases; D002518:Ceramides / Q000096:biosynthesis; D053938:DNA Fragmentation / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D020287:In Situ Nick-End Labeling; D008246:Lysophospholipids; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013108:Sphingomyelin Phosphodiesterase / Q000378:metabolism; D013110:Sphingosine / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*; D000099157:Sphingosine Kinase
chemical_list: D000581:Amidohydrolases; D055572:Ceramidases; D002518:Ceramides; D004791:Enzyme Inhibitors; D008246:Lysophospholipids; D017853:Phosphotransferases (Alcohol Group Acceptor); D013108:Sphingomyelin Phosphodiesterase; D013110:Sphingosine; D014409:Tumor Necrosis Factor-alpha; D000099157:Sphingosine Kinase; C060506:sphingosine 1-phosphate; C061800:N,N-dimethylsphingosine