Showing papers on "Sphingosine-1-phosphate published in 1996"

Sphingolipid metabolism and cell growth regulation.

Abstract: Sphingolipids have been implicated in the regulation of cell growth, differentiation, and programmed cell death. The current paradigm for their action is that complex sphingolipids such as gangliosides interact with growth factor receptors, the extracellular matrix, and neighboring cells, whereas the backbones--sphingosine and other long-chain or "sphingoid" bases, ceramides, and sphingosine 1-phosphate--activate or inhibit protein kinases and phosphatases, ion transporters, and other regulatory machinery. Tumor necrosis factor-alpha, interleukin 1beta, and nerve growth factor, for example, induce sphingomyelin hydrolysis to ceramide. Other agonists, such as platelet-derived growth factor, trigger further hydrolysis of ceramide to sphingosine and activate sphingosine kinase to form sphingosine 1-phosphate. These metabolites either stimulate or inhibit growth and may be cytotoxic (in some cases via induction of apoptosis), depending on which products are formed (or added exogenously), the cellular levels (...

Sphingosine-1-phosphate rapidly induces Rho-dependent neurite retraction: action through a specific cell surface receptor

Abstract: Sphingosine-1-phosphate (S1P) is a bioactive lysosphingolipid implicated in mitogenesis and cytoskeletal remodelling, but its mechanism of action is poorly understood. We report here that in N1E-115 neuronal cells, S1P mimics the G protein-coupled receptor agonist lysophosphatidic acid (LPA) in rapidly inducing neurite retraction and soma rounding, a process driven by Rho-dependent contraction of the actin cytoskeleton. S1P is approximately 100-fold more potent than LPA in evoking these shape changes, with an EC50 as low as 1.5 nM. Microinjection of S1P has no effect, neither has addition of sphingosine or ceramide. As with LPA, S1P action is inhibited by suramin and subject to homologous desensitization; however, the responses to S1P and LPA do not show cross-desensitization. We conclude that S1P activates its own high affinity receptor to trigger Rho-regutated cytoskeletal events. Thus, S1P and LPA may belong to an emerging family of bioactive lysophospholipids that act through distinct G protein-coupled receptors to mediate similar actions.

N,n-dimethylsphingosine inhibition of sphingosine kinase and sphingosine 1-phosphate activity in human platelets

Abstract: Potential sphingosine (Sph) metabolites include phosphorylated, N-acylated, and N-methylated derivatives. Phosphorylated Sph, i.e., sphingosine 1-phosphate (Sph-1-P), may act as an autocrine stimulator of blood platelets, as it is abundantly stored in platelets and released extracellularly and its exogenous addition induces platelet activation. In this study, we evaluated Sph-1-P formation and its effects in human platelets in the presence of other Sph metabolites. On addition of [3H]Sph to intact platelets, the label was rapidly converted to Sph-1-P. This conversion into [3H]Sph-1-P was inhibited by N,N-dimethylsphingosine (DMS) in a dose-dependent manner, but not by other structurally related Sph derivatives, including ceramide. The inhibition of Sph-1-P formation by DMS was reproduced using a cell-free system (Sph kinase obtained from platelet cytosolic fractions) and much stronger than that by dl-threo-dihydrosphingosine, which had been considered to be the strongest inhibitor of Sph kinase. Administr...

A novel membrane receptor with high affinity for lysosphingomyelin and sphingosine 1-phosphate in atrial myocytes

Abstract: Activation of IK(ACh) is the major effect of the vagal neutrotransmitter acetylcholine in the heart. We report that both lysosphingomyelin (D-erythro-sphingosyl-phosphorylcholine; SPC) and sphingosine 1-phosphate (SPP) activate IK(ACh) in guinea pig atrial myocytes through the same receptor with an EC50 of 1.5 and 1.2 nM, respectively. Pertussis toxin abolished the activation of IK(ACh) by either lipid. The putative receptor showed an exquisite stereoselectivity for the naturally occurring D-erythro-(2S,3R)-SPC stereoisomer, the structure of which was confirmed by mass spectroscopy and NMR. These lipids caused complete homologous and heterologous desensitization with each other but not with ACh, indicating that both act on the same receptor. This receptor displays a distinct structure-activity relationship: it requires an unsubstituted amino group because N-acetyl-SPC, lysophosphatidic acid and lysophosphatidylcholine were inactive. Because SPP and SPC are naturally occurring products of membrane lipid metabolism, it appears that these compounds might be important extracellular mediators acting on a family of bona fide G protein-coupled receptors. Expression of these receptors in the heart raises the possibility that sphingolipids may be a part of the physiological and/or pathophysiological regulation of the heart. Based on their ligand selectivity we propose a classification of the sphingolipid receptors.

Effect of acidic phospholipids on sphingosine kinase.

Abstract: Sphingosine-1-phosphate (SPP) is a unique sphingolipid metabolite involved in cell growth regulation and signal transduction. SPP is formed from sphingosine in cells by the action of sphingosine kinase, an enzyme whose activity can be stimulated by growth factors. Little is known of the mechanisms by which sphingosine kinase is regulated. We found that acidic phospholipids, particularly phosphatidylserine, induced a dose-dependent increase in sphingosine kinase activity due to an increase in the apparent Vmax of the enzyme. Other acidic phospholipids, such as phosphatidylinositol, phosphatidic acid, phosphatidylinositol bisphosphate, and cardiolipin stimulated sphingosine kinase activity to a lesser extent than phosphatidylserine, whereas neutral phospholipids had no effect. Diacylglycerol, a structurally similar molecule which differs from phosphatidic acid in the absence of the phosphate group, failed to induce any changes in sphingosine kinase activity. Our results suggest that the presence of negative charges on the lipid molecules is important for the potentiation of sphingosine kinase activity, but the effect does not directly correlate with the number of negative charges. These results also support the notion that the polar group confers specificity in the stimulation of sphingosine kinase by acidic glycerophospholipids. The presence of a fatty acid chain in position 2 of the glycerol backbone was not critical since lysophosphatidylserine also stimulated sphingosine kinase, although it was somewhat less potent. Dioleoylphosphatidylserine was the most potent species, including a fourfold stimulation, whereas distearoyl phosphatidylserine was completely inactive. Thus, the degree of saturation of the fatty acid chain of the phospholipids may also play a role in the activation of sphingosine kinase. © 1996 Wiley-Liss, Inc.

Structural requirements of sphingosylphosphocholine and sphingosine-1-phosphate for stimulation of activator protein-1 activity.

Abstract: The sphingolipids sphingosine-1-phosphate (SPP) and sphingosylphosphocholine (SPC) stimulate mitogenesis in Swiss 3T3 fibroblasts and stimulate DNA binding activity of activator protein-1 (AP-1). We show that SPP and SPC were more potent agents than nonphosphorylated sphingosines and N-acyl-sphingolipids (ceramides) with respect to DNA synthesis, AP-1 DNA binding activity, and AP-1 trans-activation, illustrating the importance of the terminal phosphate group. The free 2-amino group and the 4E double bond of SPC and SPP were found to be important for these activities. Although the combination of decreasing the sphingoid backbone chain length of SPC by two carbons and hydrogenating the 4E bond only slightly reduced its effects, in contrast, the same modifications in SPP significantly decreased its mitogenic and AP-1 trans-activation effects. Furthermore, substitution of the 3-hydroxyl group in SPP with hydrogen decreased its ability to stimulate DNA synthesis and to stimulate AP-1 transcriptional activity. Thus, critical sphingolipid structural components for AP-1 activation and mitogenic stimulation include the free 2-amino group, the free 3-hydroxyl group, the 4,5-trans double bond, and terminal phosphorylation. These observations may be relevant for clinical uses of these compounds in applications such as wound healing and inhibition of metastasis.

Sphingosine-1-Phosphate - A New Lipid Signaling Molecule

Abstract: Sphingolipid metabolites have been suggested to play an important role in cellular signaling. Branching pathways of sphingolipid metabolism may regulate either apoptosis or mitogenic effects depending on the cell type and the nature of the stimulus. Ceramide produced by sphingomyelinase activation has been shown to induce apoptosis and cell growth arrest, whereas further metabolites of ceramide, sphingosine and sphingosine-1-phosphate (SPP), induce mitogenesis in many cell types and have been implicated as second messengers in cellular proliferation induced by PDGF and serum. Mitogens such as PDGF and serum, but not EGF, increase levels of sphingosine and SPP and also activate cytosolic sphingosine kinase activity. Dihydrosphingosine, an inhibitor of sphingosine kinase, reduces DNA synthesis induced by PDGF and serum but not by EGF. Thus elevation of sphingosine and SPP levels and activation of sphingosine kinase may have important biological roles in signal transduction pathways activated by specific growth factors. SPP mobilizes calcium from internal stores in an inositol trisphosphate-independent manner, increases phosphatidic acid levels by activation of PLD, and also activates extracellular signal regulated kinases (ERK), which are all prominent events in the control of cellular proliferation. SPP-induced activation of the transcription factor AP-1, one of the transcription factors activated by the ERK pathway, is the first link between the effects of sphingolipids metabolites on cellular proliferation and gene expression. Recently, we found that SPP prevents the appearance of the hallmarks of apoptosis, such as intranucleosomal DNA fragmentation and morphological changes, that result from elevations of ceramide. Our results suggest that the balance between intracellular levels of ceramide and SPP determines the fate of the cell.