Sphingosine kinase mediates vascular endothelial growth factor-induced activation of ras and mitogen-activated protein kinases.
Vascular endothelial growth factor (VEGF) signaling is critical to the processes of angiogenesis and tumor growth. Here, evidence is presented for VEGF stimulation of sphingosine kinase (SPK) that affects not only endothelial cell signaling but also tumor cells expressing VEGF receptors. VEGF or phorbol 12-myristate 13-acetate treatment of the T24 bladder tumor cell line resulted in a time- and dose-dependent stimulation of SPK activity. In T24 cells, VEGF treatment reduced cellular sphingosine levels while raising that of sphingosine-1-phosphate. VEGF stimulation of T24 cells caused a slow and sustained accumulation of Ras-GTP and phosphorylated extracellular signal-regulated kinase (phospho-ERK) compared with that after EGF treatment. Small interfering RNA (siRNA) that targets SPK1, but not SPK2, blocks VEGF-induced accumulation of Ras-GTP and phospho-ERK in T24 cells. In contrast to EGF stimulation, VEGF stimulation of ERK1/2 phosphorylation was unaffected by dominant-negative Ras-N17. Raf kinase inhibition blocked both VEGF- and EGF-stimulated accumulation of phospho-ERK1/2. Inhibition of SPK by pharmacological inhibitors, a dominant-negative SPK mutant, or siRNA that targets SPK blocked VEGF, but not EGF, induction of phospho-ERK1/2. We conclude that VEGF induces DNA synthesis in a pathway which sequentially involves protein kinase C (PKC), SPK, Ras, Raf, and ERK1/2. These data highlight a novel mechanism by which SPK mediates signaling from PKC to Ras in a manner independent of Ras-guanine nucleotide exchange factor.
Shu
Xiaodong
X
Department of Biochemistry and Molecular Biology, Norris Comprehensive Cancer Center, Keck School of Medicine at the University of Southern California, Los Angeles, California 90089, USA.
Wu
Weicheng
W
Mosteller
Raymond D
RD
Broek
Daniel
D
D002277:Carcinoma; D016228:Endothelial Growth Factors / Q000378:metabolism*; D004730:Endothelium, Vascular / Q000166:cytology / Q000378:metabolism; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000378:metabolism; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins / Q000378:metabolism*; D008222:Lymphokines / Q000378:metabolism*; D020935:MAP Kinase Signaling System / Q000502:physiology; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000235:genetics / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000378:metabolism; D014407:Tumor Cells, Cultured; D001749:Urinary Bladder Neoplasms; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors; D020703:ras GTPase-Activating Proteins / Q000378:metabolism*; D020663:ras Guanine Nucleotide Exchange Factors / Q000378:metabolism; D000099157:Sphingosine Kinase
D016228:Endothelial Growth Factors; D004791:Enzyme Inhibitors; D036341:Intercellular Signaling Peptides and Proteins; D008222:Lymphokines; D020928:Mitogen-Activated Protein Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor); D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors; D020703:ras GTPase-Activating Proteins; D020663:ras Guanine Nucleotide Exchange Factors; D000099157:Sphingosine Kinase