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Sphingosine Kinase: Assay and Product Analysis

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The phosphorylation of long chain sphingoid bases on the primary alcohol group occurs in cells by the action of sphingosine kinase (1 3 ). Sphingosine kinase is present in the cytosolic fraction of most cells (4 7 ) and in the membrane fraction of certain tissues and organisms (8 ,9 ). The reaction product, sphingosine-1-phosphate (SPP), was considered for more than 20 yr to be merely an intermediate in the catabolism of long-chain sphingoid bases to palmitaldehyde and phosphoethanolamine (3 ,10 ). Studies in our lab stimulated new interest in the potential roles of SPP as a second messenger. Initially, we found that exogenous SPP initiated cell division of quiescent Swiss 3T3 fibroblasts (11 ) and induced inositol trisphosphate-independent release of calcium from intracellular stores (11 ,12 ). SPP also has been shown to affect several signal transduction pathways including phospholipase D activation (13 ), stimulation of the Raf/MEK/ERK signaling pathway (14 ,15 ), and inhibition of ceramide-induced activation of stress-activated protein kinase (SAPK/JNK) that leads to apoptotic responses (15 ). Additional effects of SPP include stimulation of tyrosine phosphorylation of focal adhesion kinase (FAK) and the cytoskeleton-associated protein paxillin (16 ). These tyrosine phosphorylations are mediated through the activation of the small G protein rho, which also mediates stress fiber formation induced by SPP (16 ).
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