S1P3 receptors mediate the potent constriction of cerebral arteries by sphingosine-1-phosphate

We characterized the effect of Sphingosine-1-phosphate (S1P) on vascular tone. S1P selectively constricted isolated cerebral, but not peripheral arteries, despite ubiquitous expression of S1P(1), S1P(2), S1P(3) and S1P(5) receptor mRNA. Clostridium B and C3 toxins and the rho-kinase inhibitor Y27632 (trans-N-(4-pyridyl)-4-(l-aminoethyl)-cyclohexane carboxamide) reduced this vasoconstriction to S1P, indicating that the response was mediated through Rho. Pertussis toxin displayed only weak inhibition, suggesting minor involvement of G(i/o) protein. The S1P effect was specifically reduced by adenovirus bearing a s1p(3) but not s1p(2), antisense construct. Furthermore, suramin, which selectively blocks S1P(3) receptors, inhibited the vasoconstrictor effect of S1P, indicating that S1P(3) receptors account for at least part of S1P-mediated vasoconstriction in cerebral arteries. In vivo, intracarotid injection of S1P decreased cerebral blood flow, an effect prevented by suramin treatment. Because S1P constricts cerebral blood vessels and is released from platelets during clotting, the S1P/S1P(3) system constitutes a novel potential target for cerebrovascular disease therapy.     

Stimulation of intracellular sphingosine-1-phosphate production by G-protein-coupled sphingosine-1-phosphate receptors

Recently, a family of G-protein-coupled receptors named endothelial differentiation gene (Edg) receptor family has been identified, which are specifically activated by the two serum lipids, sphingosine-1-phosphate and lysophosphatidic acid. Sphingosine-1-phosphate can also act intracellularly to release Ca2+ from intracellular stores. Since in several cell types, G-protein-coupled lysophosphatidic acid or sphingosine-1-phosphate receptors mobilize Ca2+ in the absence of a measurable phospholipase C stimulation, it was analysed here whether intracellular sphingosine-1-phosphate production was the signalling mechanism used by extracellular sphingosine-1-phosphate for mobilization of stored Ca2+. Sphingosine-1-phosphate and the low affinity sphingosine-1-phosphate receptor agonist, sphingosylphosphorylcholine, induced a rapid, transient and nearly complete pertussis toxin-sensitive Ca2+ mobilization in human embryonic kidney (HEK-293) cells. The G-protein-coupled sphingosine-1-phosphate receptors, Edg-1, Edg-3 and Edg-5, were found to be endogenously expressed in these cells. Most interestingly, sphingosine-1-phosphate and sphingosylphosphorylcholine did not induce a measurable production of inositol-1,4,5-trisphosphate or accumulation of inositol phosphates. Instead, sphingosine-1-phosphate and sphingosylphosphorylcholine induced a rapid and transient increase in production of intracellular sphingosine-1-phosphate with a maximum of about 1.4-fold at 30 s. Stimulation of sphingosine-1-phosphate formation by sphingosine-1-phosphate and sphingosylphosphorylcholine was fully blocked by pertussis toxin, indicating that extracellular sphingosine-1-phosphate via endogenously expressed G(i)-coupled receptors induces a stimulation of intracellular sphingosine-1-phosphate production. As sphingosine-1-phosphate- and sphingosylphosphorylcholine-induced increases in intracellular Ca2+ were blunted by sphingosine kinase inhibitors, this sphingosine-1-phosphate production appears to mediate Ca2+ signalling by extracellular sphingosine-1-phosphate and sphingosylphosphorylcholine in HEK-293 cells.     

Targeting sphingosine-1-phosphate receptors in cancer

Sphingosine 1-phosphate (S1P) is a bioactive lipid with diverse biological functions, including cell proliferation, differentiation, angiogenesis, chemotaxis, and migration. Many of the activities of S1P are mediated through five closely related G-protein-coupled receptors of the sphingosine-1-phosphate receptor family (S1PR) which play a crucial role in sphingolipid metabolism. Each of these receptors appears to be tissue specific and to have demonstrated roles in the regulation of cell proliferation and survival in various cancer types. Further analysis of the function that S1PRs serve in hematological malignancies offers a great potential for the discovery of novel and selective therapeutic agents targeting these receptors. This review focuses on the characterization of S1PRs and their roles in cancer development in various signaling pathways mediated through specific G coupled protein. In particular, pharmacological agents targeting these S1PRs will be discussed and their potential will be examined.     

Different response patterns of several ligands at the sphingosine-1-phosphate receptor subtype 3 (S1P3)

Background and purpose:

Recently, some ligands targeting the sphingosine-1-phosphate receptor subtype 3 (S1P₃) have become available. The characterization of these compounds was mainly based on one functional read-out system, although S1P₃ receptors are known to activate different signal transduction pathways. Therefore, this study pharmacologically characterizes these compounds using different assays.

Experimental approach:

Using CHO-FlpIn cells expressing the human S1P₃ receptor the potencies and maximal effects of S1P, FTY720-P, VPC23019, VPC23153 and VPC24191 were determined in three different assays [inhibition of cAMP accumulation, elevation of intracellular calcium concentrations ([Ca²⁺]_i) and S1P₃ receptor internalization].

Key results:

All compounds tested inhibited forskolin-induced cAMP accumulation, increased [Ca²⁺]_i and induced S1P₃ receptor internalization but with different potencies and maximal effects. S1P was the most potent compound in all assays followed by FTY720-P. The VPC compounds were generally less potent than S1P and FTY720-P. Regarding the maximal effects, all compounds except VPC23153, behaved as full agonists in the cAMP accumulation assay. In the calcium assay, FTY720-P, VPC23019 and VPC24191 displayed partial and VPC23153 weak partial agonist activity, relative to S1P. Interestingly, treatment with the G_i inactivator Pertussis toxin, did not affect S1P-induced [Ca²⁺]_i elevations but inhibited those in response to the other compounds, by about 50%.

Conclusions and implications:

This study demonstrated differential response patterns at the S1P₃ receptor for a range of ligands. These differences could indicate the presence of functional selectivity at this receptor as FTY720-P and the VPC compounds seemed to signal predominantly via G_i– whereas S1P activated G_i and G_q-coupled pathways.     

The role of sphingosine-1-phosphate and its receptors in asthma

Sphingosine-1-phosphate (S1P) is a bioactive sphingolipid metabolite that plays important roles in allergic responses, including asthma and anaphylaxis, the incidence of which is rising worldwide especially in industrialized urban populations. In this review, we will discuss how S1P is formed and released, and how it acts at many cellular levels, including mast cells, the airway epithelium, airway smooth muscle and many immune cells. Since the actions of S1P on all of these cells could exacerbate allergic responses, the proteins that synthesize, release and respond to S1P offer plausible targets for a new generation of antiinflammatory therapeutics.     

BML-241 fails to display selective antagonism at the sphingosine-1-phosphate receptor, S1P(3)

BACKGROUND AND PURPOSE: The thiazolidine carboxylic acid, BML-241, has been proposed as a lead compound in development of selective antagonists at the sphingosine-1-phosphate receptor (S1P3), based on its inhibition of the rise in intracellular calcium concentrations ([Ca2+]i) in HeLa cells overexpressing S1P receptors. We have studied the antagonistic properties of BML-241 for the S1P(3) receptor in more detail. EXPERIMENTAL APPROACH: Chinese hamster ovary (CHO) cells stably transfected with the S1P3, S1P2 or alpha(1A)-adrenoceptors were used to investigate the effect of BML-241 on increases in [Ca2+]i mediated via different receptors. CHO-K1 cells were used to study ATP-induced [Ca2+]i elevations. Effects on S1P3 -mediated inhibition of forskolin-induced cAMP accumulation and on binding to alpha(1A)-adrenoceptors were also investigated. In addition, the effect of BML-241 on contractions of rat mesenteric artery induced by phenylephrine was studied in an organ bath. KEY RESULTS: High concentrations of BML-241 (10 microM) inhibited the rise in [Ca2+]i induced by S1P3 and S1P2 receptor stimulation; lower concentrations were ineffective. This high concentration of BML-241 also inhibited [Ca2+]i increases via P2 (nucleotide) receptor or alpha(1A)-adrenoceptor stimulation. Moreover, BML-241 (10 microM) inhibited alpha(1)-adrenoceptor-mediated contraction of rat mesenteric artery but did not displace [3H]-prazosin from alpha(1A)-adrenoceptors in concentrations up to 100 microM. BML-241 (10 microM) did not affect the S1P3 -mediated decrease of forskolin-induced cAMP accumulation. CONCLUSIONS AND IMPLICATIONS: We conclude that BML-241 is a low potency, non-selective inhibitor of increases in [Ca2+]i, rather than a specific antagonist at the S1P3 receptor.     

1-磷酸鞘氨醇及受体对自身免疫性疾病血管新生的影响

1-磷酸鞘氨醇(sphingosine-1-phosphate,S1P)是细胞膜鞘磷脂代谢过程产生的一类信号分子,在免疫系统中,与细胞膜表面的G蛋白偶联受体S1P受体(S1P receptors,S1PRs)结合,通过相关炎症信号通路,影响新生血管的形成。该文简述S1P及其受体通过细胞内信号转导对类风湿关节炎、多发性硬化症、结肠炎、系统性红斑狼疮等自身免疫性疾病微血管生成的影响,提出了S1P及其受体可能是治疗自身免疫性疾病血管炎症新的靶点。     

Role of sphingosine-1-phosphate (S1P) and the S1P2 receptor in allergen-induced, mast cell-dependent contraction of rat lung parenchymal strips

Lung parenchymal strips isolated from ovalbumin-sensitized rats manifest a mast cell-dependent, biphasic contraction when challenged with allergen. The first phase is mediated by the release of preformed 5-HT while the second phase is dependent on de novo synthesis of leukotrienes. Sphingosine 1-phosphate (S1P) is a sphingolipid metabolite which is readily generated in mast cells and has been demonstrated to be an important regulator of allergen-induced mast cell activation. We have used the parenchymal strip to explore the role of sphingosine 1-phosphate and the S1P₂ receptor in the two components of the acute response to allergen. Lung parenchymal strips were prepared from Brown Norway rats actively sensitized to ovalbumin. The strips were set up in organ baths and contractile responses measured isometrically. The inhibitors of sphingosine kinase, D-erythro-NN-dimethylsphingosine (dimethylsphingosine) and 4-[4-(4-chloro-phenyl)-thiazol-2-ylamino]-phenol (SKI-II) inhibited concentration-dependently both phases of the contractile response induced by 0.1 µg ml^?1 ovalbumin. The effects were seen at concentrations similar to those which inhibit the purified enzyme and were selective in that neither the contractile response to adenosine nor that to 5-hydroxytryptamine was affected. JTE-013 (a selective S1P₂ receptor antagonist) also blocked the response to ovalbumin (0.1 µg ml^?1). However, the concentrations of JTE-013 required (µM) were substantially higher than its affinity for the S1P₂ receptors (nM). However, when tested against a lower concentration of ovalbumin (0.03 µg ml^?1), JTE-013 inhibited the response with nM potency. These data demonstrate the importance of S1P and the S1P₂ receptor as regulators of allergen-induced activation of mast cells in their natural environment in the rat lung.     

Discovery of potent 3,5-diphenyl-1,2,4-oxadiazole sphingosine-1-phosphate-1 (S1P1) receptor agonists with exceptional selectivity against S1P2 and S1P3

A class of 3,5-diphenyl-1,2,4-oxadiazole based compounds have been identified as potent sphingosine-1-phosphate-1 (S1P1) receptor agonists with minimal affinity for the S1P2 and S1P3 receptor subtypes. Analogue 26 (S1P1 IC50 = 0.6 nM) has an excellent pharmacokinetics profile in the rat and dog and is efficacious in a rat skin transplant model, indicating that S1P3 receptor agonism is not a component of immunosuppressive efficacy.     

The role of sphingosine-1-phosphate and ceramide-1-phosphate in calcium homeostasis

During the last several years, sphingolipids have been identified as a source of important signaling molecules. Particularly, the understanding of the distinct biological roles of ceramide, sphingosine-1-phosphate (S1P), ceramide-1-phosphate (C1P) and lyso-sphingomyelin in the regulation of cell growth, death, senescence, adhesion, migration, inflammation, angiogenesis and intracellular trafficking has rapidly expanded. Additional studies have elucidated the biological roles of sphingolipids in maintaining a homeostatic environment in cells, as well as in regulating numerous cellular responses to environmental stimuli. This review focuses on the role of S1P and C1P in maintaining Ca2+ homeostasis. By studying changes in the metabolism of S1P and C1P in pathological conditions, it is hoped that altered sphingolipid-metabolizing enzymes and their metabolites can be used as therapeutic targets.     

Targeting sphingosine-1-phosphate in hematologic malignancies

Sphingosine-1-phosphate (S1P) is a pleiotropic bioactive lipid mediator that regulates several processes important for hematologic cancer progression. S1P is generated by two sphingosine kinases, SphK1 and SphK2, and is exported outside the cell, where it activates specific cell surface S1P G-protein coupled receptors in autocrine/paracrine manner, coined "inside-out signaling". In this review, we highlight the importance of SphK1 and inside-out signaling by S1P in hematologic malignancy. We also summarize the results of studies targeting the SphK1/S1P/S1P receptor axis and the effects of the S1P receptor modulator, FTY720, in hematologic malignancy.     

Establishment of the method for the measurement of sphingosine-1-phosphate in biological samples and its application for S1P research]

Sphingosine 1-phosphate (S1P), one of the sphingolipid metabolites, has been shown to participate in a variety of cellular responses including proliferation, differentiation, adhesion, motility, and apoptosis. These cellular responses elicited by S1P were first thought to be mediated through an intracellular target(s), but extracellular mechanisms through G-protein-coupled S1P receptors have also been suggested. In addition to the studies examining the functions of the lipid on the cells and tissues, the measurement of the lipid concentration is also important for understanding the physiological and pathophysiological roles of the lipid. We have recently developed a novel quantitative method for measurement of S1P, which was based on the competition of S1P in the samples with the labeled S1P on the S1P receptor Edg-1. Here, we compared our method with previously published ones in several points including specificity and simplicity. We further presented our recent results obtained by using this novel quantitative method and finally mentioned the prospects of the S1P measurement in lipid research, especially in relation to several disorders.     

Heterologous desensitization of the sphingosine-1-phosphate receptors by purinoceptor activation in renal mesangial cells

1 Sphingosine-1-phosphate (S1P) is considered a potent mitogen for mesangial cells and activates the classical mitogen-activated protein kinase (MAPK) cascade via S1P receptors. In this study, we show that S1P signalling is rapidly desensitized upon S1P receptor activation. A complete loss of S1P sensitivity occurs after 10 min of S1P pretreatment and remains for at least 8 h. A similar desensitization is also seen with the S1P mimetic FTY720-phosphate, but not with the nonphosphorylated FTY720, nor with sphingosine or ceramide. 2 Prestimulating the cells with extracellular ATP or UTP, which bind to and activate P2Y receptors on mesangial cells, a similar rapid desensitization of the S1P receptor occurs, suggesting a heterologous desensitization of S1P receptors by P2Y receptor activation. Furthermore, adenosine binding to P1 receptors triggers a similar desensitization. In contrast, two other growth factors, PDGF-BB and TGFbeta2, have no significant effect on S1P-induced MAPK activation. 3 S1P also triggers increased inositol trisphosphate (IP3) formation, which is completely abolished by S1P pretreatment but only partially by ATP pretreatment, suggesting that IP3 formation and MAPK activation stimulated by S1P involve different receptor subtypes. 4 Increasing intracellular cAMP levels by forskolin pretreatment has a similar effect on desensitization as adenosine. Moreover, a selective A3 adenosine receptor agonist, which couples to phospholipase C and increases IP3 formation, exerted a similar effect. 5 Pretreatment of cells with various protein kinase C (PKC) inhibitors prior to ATP prestimulation and subsequent S1P stimulation leads to a differential reversal of the ATP effect. Whereas the broad-spectrum protein kinase inhibitor staurosporine potently reverses the effect, the PKC-alpha inhibitor CGP41251, the PKC-delta inhibitor rottlerin and calphostin C show only a partial reversal at maximal concentrations. 6 Suramin, which is reported as a selective S1P3 receptor antagonist compared to the other S1P receptor subtypes, has no effect on the S1P-induced MAPK activation, thus excluding the involvement of S1P3 in this response. 7 In summary, these data document a rapid homologous and also heterologous desensitization of S1P signalling in mesangial cells, which is mechanistically triggered by PKC activation and eventually another staurosporine-sensitive protein kinase, as well as by increased cAMP formation.     

The coordination of prostaglandin E2 production by sphingosine-1-phosphate and ceramide-1-phosphate

The ability of pro-inflammatory cytokines such as interleukin-1beta (IL-1beta) to induce the major inflammatory mediator prostaglandin (PG) E(2) depends on the activation of two rate-limiting enzymes, phospholipase A(2) (PLA(2)) and cyclooxygenase 2 (COX-2). PLA(2) acts to generate arachidonic acid, which serves as the precursor substrate for COX-2 in the metabolic pathway leading to PGE(2) production. However, less is known about the mechanisms that coordinate the regulation of these two enzymes. We have provided prior evidence that sphingosine kinase 1 and its bioactive lipid product sphingosine-1-phosphate (S1P) mediate the effects of cytokines on COX-2 induction, whereas ceramide kinase and its distinct product, ceramide-1-phosphate (C1P), are required for the activation and translocation of cPLA(2) (FASEB J 17:1411-1421. 2003; J Biol Chem 278:38206-38213, 2003; J Biol Chem 279:11320-11326, 2004). Herein, we show that these two pathways are independent but coordinated, resulting in synergistic induction of PGE(2). Moreover, the combination of both S1P and C1P recapitulates the temporal and spatial activation of cPLA(2) and with COX-2 seen IL-1beta. Taken together, the results provide, for the first time, a mechanism that assures the coordinate expression and activation in time and space of COX-2 and cPLA(2), assuring maximal production of PGE(2).     

鞘氨醇-1-磷酸受体1在疼痛中的作用研究

鞘氨醇-1-磷酸受体1(sphingosine-1-phosphate receptor1,S1PR1)属于G蛋白偶联受体,其能调节多种下游信号分子和细胞功能。研究发现S1PR1在疼痛中发挥重要作用,但激活S1PR1产生致痛作用还是镇痛作用尚存在争议。该文讨论了S1P/S1PR1信号在疼痛研究中的最新观点与进展,以增进对其生物学功能及病理作用的了解。     

1-磷酸鞘氨醇(S1P)在心室重塑过程中对梗死区血流恢复及血管新生的作用研究

目的观察不同时间周期大鼠心肌梗死模型心肌组织中1-磷酸鞘氨醇(S1P)受体在梗死区的基因表达情况,探讨其在心肌梗死后心室重塑过程中对梗死区血流恢复及血管新生的作用。方法采用结扎左冠状动脉前降支(LAD)的方法,造成大鼠左室大面积心梗,建立大鼠心肌梗死模型,分别于术后6、12、24 h观察心肌梗死后心室重塑过程中血流的变化情况。然后处死大鼠,取其心肌组织,提取组织中的RNA,采用实时定量荧光技术(PCR)测定心肌组织中S1P受体mRNA在梗死区的表达情况。结果术后6 h,大鼠心肌血流量和心肌微血管壁通透性随时间节点的增加均明显降低;术后12 h,这种趋势趋缓。术后6 h,S1P1受体mRNA的表达水平呈明显下降趋势;与对照组相比,结扎梗死大鼠梗死区的S1P2受体mRNA在术后各时间节点表达水平均明显下降。术后6 h,结扎梗死大鼠梗死区的S1P3受体mRNA表达显著增强,但术后12 h出现较为明显的表达抑制现象。结论大鼠心肌梗死后的心肌血流恢复和新生血管早期可能与S1P1受体mRNA下调有关,随后与S1P2受体mRNA、S1P3受体mRNA逐渐上调有关。     

Cardiovascular effects of sphingosine-1-phosphate and other sphingomyelin metabolites

Upon various stimuli, cells metabolize sphingomyelin from the cellular plasma membrane to form sphingosylphosphorylcholine (SPC) or ceramide. The latter can be further metabolized to sphingosine and then sphingosine-1-phosphate (S1P). Apart from local formation, S1P and SPC are major constituents of blood plasma. All four sphingomyelin metabolites (SMM) can act upon intracellular targets, and at least S1P and probably also SPC can additionally act upon G-protein-coupled receptors. While the molecular identity of the SPC receptors remains unclear, several subtypes of S1P receptors have been cloned and their distribution in cardiovascular tissues is described. In the heart SMM can alter intracellular Ca(2+) release, particularly via the ryanodine receptor, and conductance of various ion channels in the plasma membrane, particularly I(K(Ach)). While the various SMM differ somewhat in their effects, the above alterations of ion homeostasis result in reduced cardiac function in most cases, and ceramide and/or sphingosine may be the mediators of the negative inotropic effects of tumour necrosis factor. In the vasculature, SMM mainly act as acute vasoconstrictors in most vessels, but ceramide can be a vasodilator. SMM-induced vasoconstriction involves mobilization of Ca(2+) from intracellular stores, influx of extracellular Ca(2+) via L-type channels and activation of a rho-kinase. Extended exposure to SMM, particularly S1P, promotes several stages of the angiogenic process like endothelial cell activation, migration, proliferation, tube formation and vascular maturation. We propose that SMM are an important class of endogenous modulators of cardiovascular function.     

Sphingosine 1-phosphate (S1P) induces shape change in rat C6 glioma cells through the S1P2 receptor: development of an agonist for S1P receptors

Treatment with isoprenaline led to a change in the cell morphology of rat C6 glioma cells. This morphological change was reverted by the addition of sphingosine 1-phosphate (S1P). Using this morphological change as a response marker we determined that DS-SG-44 ((2S,3R)-2-amino-3-hydroxy-4-(4-octylphenyl)butyl phosphoric acid) was an agonist of S1P receptors. The DS-SG-44-induced morphological reversion was not observed with such structurally related molecules as DS-SG-45 ((2S,3R)-2-amino-3-hydroxy-4-(3-octylphenyl)butyl phosphoric acid) and DS-SG-12 ((2S,3R)-2-amino-4-(4-octylphenyl)butane-1,3-diol). The S1P- and DS-SG-44-induced shape changes were neither reproduced with the S1P1/S1P3 receptor agonist VPC24191 nor inhibited by the S1P1/S1P3 receptor antagonist, VPC23019. Transfection with small interfering RNA (siRNA) for the S1P2 receptor greatly inhibited the DS-SG-44-induced shape change, and in part an S1P-induced response. In the presence of VPC23019, siRNA transfection for the S1P2 receptor almost completely blocked the S1P- and DS-SG-44-induced shape changes. Our results suggested that DS-SG-44, a newly-synthesized S1P analogue, acted as an S1P receptor agonist and that the S1P-induced shape change in rat C6 glioma cells was mediated mainly through the S1P2 receptor, and cooperatively through the S1P1/S1P3 receptors.