Sphingosine kinase activation regulates hepatocyte growth factor induced migration of endothelial cells

Effects of sphingolipid metabolism disorders on endothelial cells

Many cardiovascular disorders, including atherosclerosis, hypertension, coronary heart disease, diabetes, etc., are characterized by endothelial cell dysfunction. Endothelial cell function is closely related to sphingolipid metabolism, and normal sphingolipid metabolism is critical for maintaining endothelial cell homeostasis. Sphingolipid metabolites or key enzymes in abnormal situation, including sphingosine, ceramide (Cer), sphingosine-1-phosphate (S1P), serine, sphingosine kinase (SPHK), ceramide kinase (Cerk), sphingosine-1-phosphate lyase (S1PL) etc., may have a protective or damaging effect on the function of endothelial cells. This review summarizes the effects of sphingolipid metabolites and key enzymes disordering in sphingolipid metabolism on endothelial cells, offering some insights into further research on the pathogenesis of cardiovascular diseases and corresponding therapeutic targets.

Role of Sphingolipids in Multiple Myeloma Progression, Drug Resistance, and Their Potential as Therapeutic Targets

Multiple myeloma (MM) is an incapacitating hematological malignancy characterized by accumulation of cancerous plasma cells in the bone marrow (BM) and production of an abnormal monoclonal protein (M-protein). The BM microenvironment has a key role in myeloma development by facilitating the growth of the aberrant plasma cells, which eventually interfere with the homeostasis of the bone cells, exacerbating osteolysis and inhibiting osteoblast differentiation. Recent recognition that metabolic reprograming has a major role in tumor growth and adaptation to specific changes in the microenvironmental niche have led to consideration of the role of sphingolipids and the enzymes that control their biosynthesis and degradation as critical mediators of cancer since these bioactive lipids have been directly linked to the control of cell growth, proliferation, and apoptosis, among other cellular functions. In this review, we present the recent progress of the research investigating the biological implications of sphingolipid metabolism alterations in the regulation of myeloma development and its progression from the pre-malignant stage and discuss the roles of sphingolipids in in MM migration and adhesion, survival and proliferation, as well as angiogenesis and invasion. We introduce the current knowledge regarding the role of sphingolipids as mediators of the immune response and drug-resistance in MM and tackle the new developments suggesting the manipulation of the sphingolipid network as a novel therapeutic direction for MM.

Barrier maintenance by S1P during inflammation and sepsis

Sphingosine 1-phosphate (S1P) is a multifaceted lipid signaling molecule that activates five specific G protein-coupled S1P receptors. Despite the fact that S1P is known as one of the strongest barrier-enhancing molecules for two decades, no medical application is available yet. The reason for this lack of translation into clinical practice may be the complex regulatory network of S1P signaling, metabolism and transportation.In this review, we will provide an overview about the physiology and the network of S1P signaling with the focus on endothelial barrier maintenance in inflammation. We briefly describe the physiological role of S1P and the underlying S1P signaling in barrier maintenance, outline differences of S1P signaling and metabolism in inflammatory diseases, discuss potential targets and compounds for medical intervention, and summarize our current knowledge regarding the role of S1P in the maintenance of specialized barriers like the blood-brain barrier and the placenta.

Sphingolipids Signaling in Lamellipodia Formation and Enhancement of Endothelial Barrier Function

Sphingolipids, first described in the brain in 1884, are important structural components of biological membranes of all eukaryotic cells. In recent years, several lines of evidence support the critical role of sphingolipids such as sphingosine, sphingosine-1-phosphate (S1P), and ceramide as anti- or pro-inflammatory bioactive lipid mediators in a variety of human pathologies including pulmonary and vascular disorders. Among the sphingolipids, S1P is a naturally occurring agonist that exhibits potent barrier enhancing property in the endothelium by signaling via G protein-coupled S1P1 receptor. S1P, S1P analogs, and other barrier enhancing agents such as HGF, oxidized phospholipids, and statins also utilize the S1P/S1P1 signaling pathway to generate membrane protrusions or lamellipodia, which have been implicated in resealing of endothelial gaps and maintenance of barrier integrity. A better understanding of sphingolipids mediated regulation of lamellipodia formation and barrier enhancement of the endothelium will be critical for the development of sphingolipid-based therapies to alleviate pulmonary disorders such as sepsis-, radiation-, and mechanical ventilation-induced acute lung injury.

The emerging role of FTY720 (Fingolimod) in cancer treatment

FTY720 (Fingolimod) is a clinically approved immunomodulating therapy for multiple sclerosis that sequesters T-cells to lymph nodes through functional antagonism of sphingosine-1-phosphate 1 receptor. FTY720 also demonstrates a proven efficacy in multiple in vitro and in vivo cancer models, suggesting a potential therapeutic role in cancer patients. A potential anticancer mechanism of FTY720 is through the inhibition of sphingosine kinase 1, a proto-oncogene with in vitro and clinical cancer association. In addition, FTY720's anticancer properties may be attributable to actions on several other molecular targets. This study focuses on reviewing the emerging evidence regarding the anticancer properties and molecular targets of FTY720. While the clinical transition of FTY720 is currently limited by its immune suppression effects, studies aiming at FTY720 delivery and release together with identifying its key synergetic combinations and relevant patient subsets may lead to its rapid introduction into the clinic.

Role of Sphingosine Kinase 1 and S1P Transporter Spns2 in HGF-mediated Lamellipodia Formation in Lung Endothelium

Hepatocyte growth factor (HGF) signaling via c-Met is known to promote endothelial cell motility and angiogenesis. We have previously reported that HGF stimulates lamellipodia formation and motility of human lung microvascular endothelial cells (HLMVECs) via PI3K/Akt signal transduction and reactive oxygen species generation. Here, we report a role for HGF-induced intracellular sphingosine-1-phosphate (S1P) generation catalyzed by sphingosine kinase 1 (SphK1), S1P transporter, spinster homolog 2 (Spns2), and S1P receptor, S1P₁, in lamellipodia formation and perhaps motility of HLMVECs. HGF stimulated SphK1 phosphorylation and enhanced intracellular S1P levels in HLMVECs, which was blocked by inhibition of SphK1. HGF enhanced co-localization of SphK1/p-SphK1 with actin/cortactin in lamellipodia and down-regulation or inhibition of SphK1 attenuated HGF-induced lamellipodia formation in HLMVECs. In addition, down-regulation of Spns2 also suppressed HGF-induced lamellipodia formation, suggesting a key role for inside-out S1P signaling. The HGF-mediated phosphorylation of SphK1 and its localization in lamellipodia was dependent on c-Met and ERK1/2 signaling, but not the PI3K/Akt pathway; however, blocking PI3K/Akt signaling attenuated HGF-mediated phosphorylation of Spns2. Down-regulation of S1P₁, but not S1P₂ or S1P₃, with specific siRNA attenuated HGF-induced lamellipodia formation. Further, HGF enhanced association of Spns2 with S1P₁ that was blocked by inhibiting SphK1 activity with PF-543. Moreover, HGF-induced migration of HLMVECs was attenuated by down-regulation of Spns2_. Taken together, these results suggest that HGF/c-Met-mediated lamellipodia formation, and perhaps motility is dependent on intracellular generation of S1P via activation and localization of SphK1 to cell periphery and Spns2-mediated extracellular transportation of S1P and its inside-out signaling via S1P₁.

Sphingosine kinase 1 improves cutaneous wound healing in diabetic rats

BACKGROUND

Diabetes is one of the most prevalent human metabolic diseases. Wound healing in diabetes is frequently impaired and treatment remains challenging. Sphingolipid metabolites play important roles in the regulation of glucose metabolism. SPK1 is the key enzyme in the sphingolipid metabolic pathway. S1P/SPK plays a pivotal role in the signalling pathways of diverse cellular processes including proliferation, differentiation, migration, apoptosis in diverse cell types.

METHODS

To investigate the role of sphingosine kinase 1 (SPK1) in skin injury, plasmids containing the SPK1 gene (pcDNA3-FLAG-SPK1) were applied to cutaneous wounds on a streptozotocin-induced diabetic rat model over a 21-day period. The wound area and rate of wound healing were determined. The histopathological features of the healed wounds were also observed, and SPK1 expression in the skin was detected by immunohistochemistry.

RESULTS

There was a significant decrease in wound area in diabetic rats treated with 125 and 60μg/wound pcDNA3-FLAG-SPK1 (P<0.001-0.01). The mean sizes of the wounds were 0.67±0.15cm(2), 0.83±0.18cm(2), and 1.09±0.23cm(2) in both treated and diabetic control group at the 7th day post-treatment respectively. In addition, wound healing in diabetic rats of test group was accelerated. At the 7th day, the mean rates of healing were 73.2±5.7% and 66±7.3% in test group of 125 and 60μg/wound respectively, and 55.4±9.9% in diabetic control group (P<0.001-0.01). Histology revealed that tissue sections from the treated diabetic rats contained more granulation tissue and capillaries than that of the control rats. There was high SPK1 expression in the skin of the treated diabetic rats.

CONCLUSIONS

SPK1 gene therapy may represent a novel approach to cutaneous wound healing.

Hepatopoietin Cn reduces ethanol-induced hepatoxicity via sphingosine kinase 1 and sphingosine 1-phosphate receptors

The hepatic growth factor hepatopoietin Cn (HPPCn) prevents liver injury induced by carbon tetrachloride in rats. Sphingosine 1-phosphate (S1P) is a bioactive sphingolipid produced by sphingosine kinase (SphK). S1P and S1P receptors (S1PRs) are involved in liver fibrogenesis and oxidative injury. This work sought to understand the mechanism by which SphK/S1P/S1PRs are involved in the protective effects of HPPCn on ethanol-induced liver injury and fibrosis. Transgenic mice with liver-specific overexpression of HPPCn (HPPCn(liver) (+/+)) were generated. Two ethanol feeding protocols were used to assess the protective effect of HPPCn on acute and chronic liver injury in mice. Specific inhibitors of S1PR1, S1PR2 and S1PR3 and siRNA were used to examine the roles of S1PRs in hepatic stellate cell (HSC) activation and hepatocyte apoptosis. Increased HPPCn expression in transgenic mice attenuated fibrosis induced by ethanol and carbon tetrachloride (CCl4). Treatment with recombinant human HPPCn prevented human hepatocyte apoptosis and HSC activation. JTE-013 or S1PR2-siRNA attenuated the effect of HPPCn on HSC activation induced by tumour necrosis factor-α (TNF-α). Consistent with the effect of N,N-dimethylsphingosine (DMS), suramin or S1PR3-siRNA treatment blocked HPPCn-induced Erk1/2 phosphorylation in human hepatocytes. This study demonstrated that HPPCn attenuated oxidative injury and fibrosis induced by ethanol feeding and that the SphK1/S1P/S1PRs signalling pathway contributes to the protective effect of HPPCn on hepatocyte apoptosis and HSC activation.

Therapeutic potential of targeting SK1 in human cancers

Sphingosine kinase 1 (SK1) is a lipid enzyme with oncogenic properties that converts the proapoptotic lipids ceramide and sphingosine into the antiapoptotic lipid sphingosine-1-phosphate and activates the signal transduction pathways that lead to cell proliferation, migration, the activation of the inflammatory response, and the impairment of apoptosis. There is compelling evidence that SK1 activation contributes to cancer progression leading to increased oncogenic transformation, tumor growth, resistance to therapies, tumor neovascularization, and metastatic spread. High levels of SK1 expression or activity have been associated with a poor prognosis in several human cancers. Recent studies using cancer cell and mouse models demonstrate a significant potential for SK1-targeting therapies to synergize with the effects of chemotherapy and radiotherapy; however, until recently the absence of clinically applicable SK1 inhibitors has limited the translation of these findings into patients. With the recent discovery of SK1 inhibiting properties of a clinically approved drug FTY720 (Fingolimod), SK1 has gained significant attention from both clinicians and the pharmaceutical industry and it is hoped that trials of newly developed SK1 inhibitors may follow soon. This review provides an overview of the SK1 signaling, its relevance to cancer progression, and the potential clinical significance of targeting SK1 for improved local or systemic control of human cancers.

Hepatocyte growth factor gene-modified mesenchymal stem cells reduce radiation-induced lung injury

Abstract Effective therapeutic strategies for radiation-induced lung injury (RILI) are lacking. Mesenchymal stem cells (MSCs), as gene therapy delivery vehicles, possess the ability to repair injured lung. In this study, we conducted MSC-based hepatocyte growth factor (HGF) gene therapy for RILI. Mice received single-dose radiation with 20 Gy of γ rays locally to the lung, and then were administered normal sodium, Ad-HGF-modified MSCs, or Ad-Null-modified MSCs. Ad-HGF-modified MSCs (MSCs-HGF) improved histopathological and biochemical markers of lung injury. MSCs-HGF could reduce secretion and expression of proinflammatory cytokines, including tumor necrosis factor-α, interferon-γ, interleukin (IL)-6, and intercellular adhesion molecule-1, and increase the expression of antiinflammatory cytokine IL-10. It could also decrease expression levels of profibrosis factors transforming growth factor-β, Col1a1 (collagen type 1, α1), and Col3a1, and inhibit fibrosis progress. MSCs-HGF could promote proliferation of lung epithelial cells and protect them from apoptosis, and improve the expression of endogenous HGF and its receptor c-Met significantly. We also found that sphingosine-1-phosphate receptor-1 expression was increased in injured lung. These results suggest MSC-based HGF gene therapy not only reduces inflammation but also inhibits lung fibrosis.

Neural differentiation of mesenchymal stem cells influences chemotactic responses to HGF

Recently, mesenchymal stem cells (MSCs) have been extensively used for cell-based therapies in neuronal degenerative disease. Although much effort has been devoted to the delineation of factors involved in the migration of MSCs, the relationship between the chemotactic responses and the differentiation status of these cells remains elusive. Here, we report that MSCs in varying neural differentiation states display different chemotactic responses to hepatocyte growth factor (HGF): first, the number of chemotaxing MSCs and the optimal concentrations of HGF that induced the peak migration varied greatly; second, time-lapse video analysis showed that MSCs in certain differentiation state migrated more efficiently toward HGF; third, the phosphorylation levels of Akt, ERK1/2, SAPK/JNK, and p38MAPK were closely related to the differentiation levels of MSCs subjected to HGF; and finally, although inhibition of ERK1/2 signaling significantly attenuated HGF-stimulated transfilter migration of both undifferentiated and differentiating MSCs, abolishment of PI3K/Akt, p38MAPK, or SAPK/JNK signaling only decreased the number of migrated cells in certain differentiation state(s). Blocking of PI3K/Akt or MAPK signaling impaired the migration efficiency and/or speed, the extent of which depends on the cell differentiation states. Meanwhile, F-actin rearrangement, which is essential for MSCs chemotaxis, was induced by HGF, and the time points of cytoskeletal reorganization were different among these cells. Collectively, these results demonstrate that neural differentiation of MSCs influences their chemotactic responses to HGF: MSCs in varying differentiation states possess different migratory capacities, thereby shedding light on optimization of the therapeutic potential of MSCs to be employed for neural regeneration after injury.

Critical role of S1PR1 and integrin β4 in HGF/c-Met-mediated increases in vascular integrity

Vascular endothelial cell (EC) barrier integrity is critical to vessel homeostasis whereas barrier dysfunction is a key feature of inflammatory disorders and tumor angiogenesis. We previously reported that hepatocyte growth factor (HGF)-mediated increases in EC barrier integrity are signaled through a dynamic complex present in lipid rafts involving its receptor, c-Met. We extended these observations to confirm that S1PR1 (sphingosine 1-phosphate receptor 1) and integrin β4 (ITGB4) are essential participants in HGF-induced EC barrier enhancement. Immunoprecipitation experiments demonstrated HGF-mediated recruitment of c-Met, ITGB4 and S1PR1 to caveolin-enriched lipid rafts in human lung EC with direct interactions of c-Met with both S1PR1 and ITGB4 accompanied by c-Met-dependent S1PR1 and ITGB4 transactivation. Reduced S1PR1 expression (siRNA) attenuated both ITGB4 and Rac1 activation as well as c-Met/ITGB4 interaction and resulted in decreased transendothelial electrical resistance. Furthermore, reduced ITGB4 expression attenuated HGF-induced c-Met activation, c-Met/S1PR1 interaction, and effected decreases in S1P- and HGF-induced EC barrier enhancement. Finally, the c-Met inhibitor, XL880, suppressed HGF-induced c-Met activation as well as S1PR1 and ITGB4 transactivation. These results support a critical role for S1PR1 and ITGB4 transactivation as rate-limiting events in the transduction of HGF signals via a dynamic c-Met complex resulting in enhanced EC barrier integrity.

Sphingosine-1-phosphate modulates expression of vascular endothelial growth factor in human articular chondrocytes: a possible new role in arthritis

AIM

Although sphingosine-1-phosphate (S1P) is suggested to have an important role in arthritis, its function in chondrocytes remains unknown. In contrast, vascular endothelial growth factor (VEGF) has been speculated to contribute to the pathogenesis of osteoarthritis (OA), most likely by regulating angiogenesis. We here investigated the in vitro effect of S1P on VEGF expression in human articular chondrocytes from OA patients.

METHODS

Human articular cartilage samples were obtained from patients with OA under informed consent. Chondrocytes were isolated by an enzymatic procedure, grown in monolayer culture, and then stimulated with S1P in the presence or absence of mitogen-activated protein kinase (MAPK) inhibitors or the Gi protein inhibitor pertussis toxin (PTX). VEGF expression and secretion in culture supernatants were analyzed using real-time polymerase chain reaction and enzyme-linked immunosorbent assay.

RESULTS

Although S1P did not enhance basal secretion of matrix metalloproteinase (MMP)-1 and MMP-13, it stimulated VEGF expression in human articular chondrocytes, both at the messenger RNA and protein levels. MAPK inhibitors SB203580 and PD98059 were not effective at suppressing VEGF induction; rather, blocking extracellular signal-regulated kinase (ERK) MAPK enhanced VEGF expression. The Gi protein inhibitor PTX partially attenuated S1P-induced VEGF secretion.

CONCLUSION

Our results suggest that S1P may contribute to the regulation of VEGF expression in human chondrocytes. S1P may therefore play a unique role in the pathophysiology of OA by regulating VEGF expression in chondrocytes.

Acetylation of sphingosine kinase 1 regulates cell growth and cell-cycle progression

Sphingosine kinase 1 (SPK1) is a key enzyme in the sphingolipid metabolic pathway. It forms an essential checkpoint to regulate the relative levels of bioactive sphingolipid metabolites, ceramide, sphingosine, and sphingosine 1-phosphate (S1P). Here, we present evidence that SPK1 is acetylated by the intrinsic acetyltransferase activity of p300/cAMP-response element-binding protein (CREB)-binding protein (CBP) at a conserved acetylation motif (the GK motif). This post-translational modification may be an important regulator of SPK1 protein, as acetylation by p300 or CBP increased its stability. Mutation of two lysine (K) residues in its GK motif to either arginine (R) or glutamine (Q) blocked SPK1 ubiquitination and prevented its degradation by the proteasome. The processes of acetylation and ubiquitination may compete for the same lysine residues and, therefore, form a switch for SPK1 protein regulation. Intriguingly, human embryonic kidney (HEK) 293 cells stably expressed the mutated form of SPK1, in which the K residue was mutated to Q (Q-SPK1), and this mutated form mimicked acetylated SPK1. These cells were larger in size and had a slower growth rate compared to cells that expressed wild-type SPK1 (W-SPK1) or the K/R-mutated SPK1 (R-SPK1). These data suggest that SPK1 acetylation plays a key role in cell growth, cell size, and cell-cycle control.

Therapeutic potential of targeting sphingosine kinase 1 in prostate cancer

Sphingosine kinase 1 (SK1) is a lipid enzyme with oncogenic properties that converts the proapoptotic lipid sphingosine into the antiapoptotic lipid sphingosine-1-phosphate, which activates the signal transduction pathways that lead to cell proliferation, migration, activation of the inflammatory response and impairment of apoptosis. Compelling evidence suggests that SK1 activation contributes to cancer progression leading to increased oncogenic transformation, tumor growth, resistance to therapies, tumor neovascularization and metastatic spread. High levels of SK1 expression or activity have been associated with poor prognosis in several cancers, including those of the prostate. Recent studies using prostate cancer cell and mouse models demonstrate a significant potential for SK1-targeting therapies to synergize with the effects of docetaxel chemotherapy and radiotherapy. However, until recently the absence of clinically applicable SK1 inhibitors has limited the translation of these findings into patients. With the recent discovery that clinically approved drug fingolimod has SK1-inhibiting properties, SK1 has gained significant attention from both clinicians and the pharmaceutical industry and it is hoped that trials of newly developed SK1 inhibitors might follow soon.

Sphingosine 1-phosphate signaling is involved in skeletal muscle regeneration

Sphingosine 1-phosphate (S1P) is a bioactive lipid known to control cell growth that was recently shown to act as a trophic factor for skeletal muscle, reducing the progress of denervation atrophy. The aim of this work was to investigate whether S1P is involved in skeletal muscle fiber recovery (regeneration) after myotoxic injury induced by bupivacaine. The postnatal ability of skeletal muscle to grow and regenerate is dependent on resident stem cells called satellite cells. Immunofluorescence analysis demonstrated that S1P-specific receptors S1P(1) and S1P(3) are expressed by quiescent satellite cells. Soleus muscles undergoing regeneration following injury induced by intramuscular injection of bupivacaine exhibited enhanced expression of S1P(1) receptor, while S1P(3) expression progressively decreased to adult levels. S1P(2) receptor was absent in quiescent cells but was transiently expressed in the early regenerating phases only. Administration of S1P (50 microM) at the moment of myotoxic injury caused a significant increase of the mean cross-sectional area of regenerating fibers in both rat and mouse. In separate experiments designed to test the trophic effects of S1P, neutralization of endogenous circulating S1P by intraperitoneal administration of anti-S1P antibody attenuated fiber growth. Use of selective modulators of S1P receptors indicated that S1P(1) receptor negatively and S1P(3) receptor positively modulate the early phases of regeneration, whereas S1P(2) receptor appears to be less important. The present results show that S1P signaling participates in the regenerative processes of skeletal muscle.

Sphingosine kinase as an oncogene: autocrine sphingosine 1-phosphate modulates ML-1 thyroid carcinoma cell migration by a mechanism dependent on protein kinase C-alpha and ERK1/2

Sphingosine 1-phosphate (S1P) induces migration of the human thyroid follicular carcinoma cell line ML-1 by activation of S1P(1) and S1P(3) receptors, G(i) proteins, and the phosphatidylinositol 3-kinase-Akt pathway. Because sphingosine kinase isoform 1 (SK) recently has been implicated as an oncogene in various cancer cell systems, we investigated the functions of SK in the migration, proliferation and adhesion of the ML-1 cell line. SK overexpressing ML-1 cells show an enhanced secretion of S1P, which can be attenuated, by inhibiting SK activity and a multidrug-resistant transport protein (ATP-binding cassette transporter). Furthermore, overexpression of SK enhances serum-induced migration of ML-1 cells, which can be attenuated by blocking ATP-binding cassette transporter and SK, suggesting that the migration is mediated by autocrine signaling through secretion of S1P. Inhibition of protein kinase C alpha, with both small interfering RNA (siRNA) and small molecular inhibitors attenuates migration in SK overexpressing cells. In addition, SK-overexpressing cells show an impaired adhesion, slower cell growth, and an up-regulation of ERK1/2 phosphorylation, as compared with cells expressing a dominant-negative SK. Taken together, we present evidence suggesting that SK enhances migration of ML-1 cells by an autocrine mechanism and that the S1P-evoked migration is dependent on protein kinase C alpha, ERK1/2, and SK.

Sphingosine kinase 1 is essential for proteinase-activated receptor-1 signalling in epithelial and endothelial cells

There is accumulating evidence that activation of sphingosine kinase 1 (SPHK1) is an important element in intracellular signalling cascades initiated by stimulation of multiple receptors, including certain growth factor, cytokine, and also G-protein coupled receptors. We here report that stimulation of the lung epithelial cell line A549 by thrombin leads to transient increase of SPHK1 activity and elevation of intracellular sphingosine-1-phosphate (S1P); abrogation of this stimulation by SPHK1-specific siRNA, pharmacological inhibition, or expression of a dominant-negative SPHK1 mutant blocks the response to thrombin, as measured by secretion of MCP-1, IL-6, IL-8, and PGE(2). Using selective stimulation of proteinase-activated receptors (PARs) a specific involvement of SPHK1 in the PAR-1 induced responses in A549 cell, including activation of NFkappaB, was evident, while PAR-2 and PAR-4 responses were independent of SPHK1. Moreover, PAR-1 or thrombin-induced cytokine production and adhesion factor expression of human umbilical vein endothelial cells was also seen to depend on SPHK1. Using dermal microvascular endothelial cells from SPHK1-deficient mice, we showed that absence of the enzyme abrogates MCP-1 production induced in these cells upon treatment with thrombin or PAR-1 activating peptide. We propose SPHK1 inhibition as a novel way to block PAR-1 mediated signalling, which could be useful in treatment of a number of diseases, in particular in atherosclerosis.

Sphingosine kinase is induced in mouse 3T3-L1 cells and promotes adipogenesis

Sphingosine 1-phosphate (S1P) is a lysophospholipid mediator that exerts numerous biological activities both as a receptor ligand and as an intracellular second messenger. In the present study, we explored roles of sphingosine kinase (SphK), an S1P-producing enzyme, in adipose tissue. We utilized mouse 3T3-L1 cells as an in vitro model of adipogenesis, using a mixture of insulin/dexamethasone/3-isobutyl-1-methylxanthine (IBMX) to induce differentiation. Real-time quantitative PCR (qRT-PCR) assays revealed that the expression levels of transcripts encoding both isoforms of SphK-1 and SphK-2 are up-regulated during adipogenesis (37.6- and 6.6-fold vs. basal, P < 0.05, respectively). Concomitantly, SphK-1/SphK-2 protein abundance and S1P contents of these cells increased at 3 days after hormonal stimulation. Loss-of-function approaches by pharmacological inhibition of SphK activity as well as by transfection with small interfering RNA (siRNA) against SphK-1 led to significant attenuation of lipid droplet accumulation and adipocyte marker gene expression. We detected marked elevation of SphK-1 mRNA in adipose tissue derived from 13-week-old ob/ob mice with obese phenotype than their lean littermates. These results suggest that increased expression of SphK, an S1P-producing enzyme, plays a significant role during adipogenesis, potentially providing a novel point of control in adipose tissue.

KAI1/CD82 suppresses hepatocyte growth factor-induced migration of hepatoma cells via upregulation of Sprouty2

We conducted a study concerning the suppressive mechanism of KAI1/CD82 on hepatoma cell metastasis. Hepatocyte growth factor (HGF) induces the migration of hepatoma cells through activation of cellular sphingosine kinase 1 (SphK1). Adenovirus-mediated gene transfer of KAI1 (Ad-KAI1) downregulates the SphK1 expression and suppresses the HGF-induced migration of SMMC-7721 human hepatocellcular carcinoma cells. Overexpression of KAI1/CD82 significantly elevates Sprouty2 at the protein level. Ablation of Sprouty2 with RNA interference can block the KAI1/CD82-induced suppression of hepatoma cell migration and downregulation of SphK1 expression. It is demonstrated that KAI1/CD82 suppresses HGF-induced migration of hepatoma cells via upregulation of Sprouty2.

"Inside-out" signaling of sphingosine-1-phosphate: therapeutic targets

Sphingosine 1-phosphate (S1P) is a bioactive sphingolipid metabolite involved in many critical cellular processes including proliferation, survival, and migration, as well as angiogenesis and allergic responses. S1P levels inside cells are tightly regulated by the balance between its synthesis by sphingosine kinases and degradation. S1P is interconvertible with ceramide, which is a critical mediator of apoptosis. It has been postulated that the ratio between S1P and ceramide determines cell fate. Activation of sphingosine kinase by a variety of agonists increases intracellular S1P, which in turn can function intracellularly as a second messenger or be secreted out of the cell and act extracellularly by binding to and signaling through S1P receptors in autocrine and/or paracrine manners. Recent studies suggest that this "inside-out" signaling by S1P may play a role in many human diseases, including cancer, atherosclerosis, inflammation, and autoimmune disorders such as multiple sclerosis. In this review we summarize metabolism of S1P, mechanisms of sphingosine kinase activation, and S1P receptors and their downstream signaling pathways and examine relationships to multiple disease processes. In particular, we describe recent preclinical and clinical trials of therapies targeting S1P signaling, including 2-amino-2-propane-1,3-diol hydrochloride (FTY720, fingolimod), S1P receptor agonists, sphingosine kinase inhibitors, and anti-S1P monoclonal antibody.

Treatment of chronical myocardial ischemia by adenovirus-mediated hepatocyte growth factor gene transfer in minipigs

Growth factor gene transfer-induced therapeutic angiogenesis has become a novel approach for the treatment of myocardial ischemia. In order to provide a basis for the clinical application of an adenovirus with hepatocyte growth factor gene (Ad-HGF) in the treatment of myocardial ischemia, we established a minipig model of chronically ischemic myocardium in which an Ameroid constrictor was placed around the left circumflex branch of the coronary artery (LCX). A total of 18 minipigs were randomly divided into 3 groups: a surgery control group, a model group and an Ad-HGF treatment group implanted with Ameroid constrictor. Ad-HGF or the control agent was injected directly into the ischemic myocardium, and an improvement in heart function and blood supply were evaluated. The results showed that myocardial perfusion remarkably improved in the Ad-HGF group compared with that in both the control and model groups. Four weeks after the treatment, the density of newly formed blood vessels was higher and the number of collateral blood vessels was greater in the Ad-HGF group than in the model group. The area of myocardial ischemia reduced evidently and the left ventricular ejection fraction improved significantly in the Ad-HGF group. These results suggest that HGF gene therapy may become a novel approach in the treatment of chronically ischemic myocardium.

Sphingosine kinase 1 gene transfer reduces postoperative peritoneal adhesion in an experimental model

BACKGROUND

Recovery of the surgically damaged mesothelial cell layer is a major process in reducing postoperative peritoneal adhesions. Sphingosine kinase (SPK) 1 is a signalling molecule involved in the regulation of proliferation and migration of various cell types. This study determined the effect of SPK-1 gene transfer on the recovery of damaged mesothelial cells and on peritoneal adhesion formation after surgery.

METHODS

Rat mesothelial cells were isolated and characterized by their expression of cytokeratin and vimentin. Their migration was determined by scratch wound motility assay. Cellular SPK-1 activity was measured by [gamma-32P]adenosine 5'-triphosphate incorporation. Wistar rats underwent laparotomy with subsequent caecum or uterine horn abrasion. Rats were randomized to either SPK-1 gene (Ad-SPK-1) transfer or control groups. The animals were killed 14 days after operation and peritoneal adhesions were graded.

RESULTS

Adenovirus-mediated SPK-1 gene transfer increased the cellular SPK-1 activity of mesothelial cells, leading to enhanced migration. Median adhesion scores were significantly lower in the Ad-SPK-1 group than in controls in both rat caecum (0.98 versus 2.60; P < 0.001) and rat uterine horn (0.28 versus 1.83; P < 0.001) models.

CONCLUSION

Adenovirus-mediated SPK-1 gene transfer promotes recovery of the surgically damaged mesothelial cell layer and prevents postoperative peritoneal adhesion formation.

Adenoviral gene transfer of sphingosine kinase 1 protects heart against ischemia/reperfusion-induced injury and attenuates its postischemic failure

Sphingosine kinase 1 (SPK1) has been identified as a central mediator of ischemia preconditioning and plays a protective role in ischemia/reperfusion (I/R)-induced cardiomyocyte death. In the present study, we investigated the protective effect of adenovirus-mediated SPK1 gene (Ad-SPK1) transfer on I/R-induced cardiac injury, and evaluated its therapeutic action on postinfarction heart failure. Cardiac SPK1 activity was increased about 5-fold by injection of Ad-SPK1, compared with injection of adenovirus carrying the green fluorescent protein gene (Ad-GFP). A more potent performance and a lower incidence of arrhythmia were observed in Ad-SPK1-injected hearts during the reperfusion period, compared with Ad-GFP-injected hearts. An enzymatic activity assay showed that creatine kinase release was also less in Ad-SPK1-injected hearts. To investigate the therapeutic action of the SPK1 gene on postischemic heart failure, the left anterior descending branch of the coronary artery in Wistar rats was ligated after direct intramyocardial injection of Ad-SPK1 or Ad-GFP as a control. Ad-SPK1 injection significantly preserved cardiac systolic and diastolic function, as evidenced by left ventricular (LV) systolic pressure, LV end-diastolic pressure, and peak velocity of contraction (dP/dt). The LV morphometric parameters of Ad-SPK1-treated animals were also preserved. In addition, SPK1 gene delivery significantly enhanced angiogenesis and reduced fibrosis. These results demonstrate that adenovirus-mediated SPK1 gene transfer could efficiently prevent I/R-induced myocardial injury and attenuate postischemic heart failure. Thus, SPK1 gene delivery would be a novel strategy for the treatment of coronary heart disease.

The tyrosine phosphatase HD-PTP: A novel player in endothelial migration

Endothelial migration, pivotal step of angiogenesis, is tightly tuned by tyrosine phosphorylation of different substrates, which results from the coordinated action of tyrosine kinases and phosphatases. Here we report that the tyrosine phosphatase HD-PTP has a role in modulating endothelial motility. Indeed, we found that endothelial cells downregulating HD-PTP after transfection with siRNA acquire a scattered and spindle-shaped phenotype and migrate more than controls. We also show that HD-PTP binds Focal Adhesion Kinase (FAK), a crucial regulator of cell migration. This interaction is strongly inhibited by treatment with basic Fibroblast Growth Factor, an angiogenic factor which stimulates endothelial cell migration. In cells downregulating HD-PTP, FAK is hyperphosphorylated on tyrosine residues and localizes in the focal adhesions, at the leading edge of the cell. We suggest that HD-PTP contributes to the regulation of endothelial motility by modulating the tyrosine phosphorylation of FAK.

Autocrine and paracrine roles of sphingosine-1-phosphate

Sphingosine-1-phosphate (S1P) is a bioactive sphingolipid metabolite that has been implicated in many biological processes, including cell migration, survival, proliferation, angiogenesis and immune and allergic responses. S1P levels inside cells are regulated tightly by the balance between its synthesis by sphingosine kinases and degradation by S1P lyases and S1P phosphatases. Activation of sphingosine kinase by any of a variety of agonists increases S1P levels, which in turn can function intracellularly as a second messenger or in an autocrine and/or paracrine fashion to activate and signal through S1P receptors present on the surface of the cell. This review summarizes recent findings on the roles of S1P as a mediator of the actions of cytokines, growth factors and hormones.

Sphingosine kinase-1 mediates BCR/ABL-induced upregulation of Mcl-1 in chronic myeloid leukemia cells

The signaling mechanisms responsible for BCR/ABL-induced regulation of Mcl-1 expression in chronic myelogenous leukemia (CML) cells remain unclear. In this study, we show that BCR/ABL could upregulate sphingosine kinase-1 (SPK1) expression via multiple signal pathways, including mitogen-activated protein kinase (MAPK), phosphoinositide 3-kinase (PI3K) and Janus kinase 2 (JAK2), leading to increase cellular SPK1 activity in CML cells. Retrovirus-mediated overexpression of bcr-abl gene in NIH-3T3, Ba/F3 and HL-60 cells results in upregulation and increased cellular activity of SPK1, whereas treatment of CML cells with specific inhibitors of the BCR/ABL, PI3K, MAPK and JAK2 pathways decreases BCR/ABL-induced SPK1 expression and cellular activity. BCR/ABL also induces upregulation of Mcl-1 expression in CML cells. Inhibition of SPK1 by adenovirus-mediated transfer of small interfering RNA or N,N-dimethylsphingosine reduced expression of Mcl-1 in CML cells. Our data indicated that BCR/ABL induces SPK1 expression and increases its cellular activity, leading to upregulation of Mcl-1 in CML cells. SPK1 silencing enhances the STI571-induced apoptosis of CML cell lines. It is suggested that SPK1 may be a potential therapeutic target in CML.

Hepatocyte growth factor attenuates eotaxin and PGD2-induced chemotaxis of human eosinophils

BACKGROUND

Hepatocyte growth factor (HGF) is known to influence a number of cell types, and regulate various biologic activities including cell migration, proliferation, and survival. In a recent study, we found that, in vivo, HGF suppresses allergic airway inflammation, i.e. the infiltration of inflammatory cells including eosinophils into the airway, and further, that HGF reduces Th2 cytokine levels; however, the directly physiologic role of HGF with eosinophils remains unclear. In this study, we investigate the potential of recombinant HGF to regulate the factor-induced chemotaxis of human eosinophils.

METHODS

Eosinophils were isolated from subjects with mild eosinophilia by modified CD16-negative selection. After culture with or without recombinant HGF, esoinophil chemotaxis was measured by Boyden chamber and KK chamber.

RESULTS

Treatment with HGF prevented eotaxin or prostaglandin D(2) (PGD(2))-induced chemotaxis of eosinophils. Moreover, we demonstrated that extracellular signal-regulated kinase (ERK) 1/2 and p38 mitogen-activated protein kinases as well as the enhancement of Ca(2+) influx, which are indispensable for eosinophil chemotaxis, were attenuated by HGF treatment.

CONCLUSION

Taken together, these data suggest that in allergic diseases, HGF not only mediates eosinophils through the inhibition of Th2 cytokines, but also regulates the function of eosinophils directly, provides further insight into the cellular and molecular pathogenesis of allergic reactions.

Renal mesangial cells: moving on sphingosine kinase-1

Sphingosine kinase-1 (SphK1) catalyses the phosphorylation of sphingosine to sphingosine-1-phosphate (S1P), which acts on at least five specific G-protein-coupled receptors and also intracellularly. SphK1 has been implicated in cell proliferation, cancer growth, chemoresistance, immune cell functions and cell migration. In this issue of the British Journal of Pharmacology, Klawitter et al. demonstrate that extracellular nucleotides stimulate the migration of renal mesangial cells. The nucleotides furthermore upregulated SphK1 expression and activity, and this enzyme was required for nucleotide-induced migration. Together with previous findings, these data raise exciting questions: by which mechanism does SphK1 regulate migration in mesangial cells, how is the interplay of purinoceptors and S1P receptors organized in these cells, and how would SphK1-deficient mice respond to kidney damage?

Shp-2 tyrosine phosphatase is required for hepatocyte growth factor-induced activation of sphingosine kinase and migration in embryonic fibroblasts

Shp-2, a ubiquitously expressed protein tyrosine phosphatase containing two Src homology 2 domains, plays an important role in integrating signaling from the cell surface receptors to intracellular signaling mechanisms. Previous studies have demonstrated that the Shp-2 is involved in hepatocyte growth factor (HGF)-induced cell scattering. Here we report that Shp-2 is required for the HGF-induced activation of sphingosine kinase-1 (SPK1), a highly conserved lipid kinase that plays an important role in cell migration. Loss-of-function mutation of Shp-2 did not affect the expression of SPK1, but resulted in its inactivation and the blockage of HGF-induced migration in embryonic fibroblasts. Reintroduction of functional wild type (WT) Shp-2 into the mutant cells partially restored SPK1 activation, and overexpression of SPK1 in these mutant cells enhanced HGF-induced cell migration. Inhibition of expression or activity of SPK1 in WT cells markedly decreased intracellular S1P levels and HGF-induced cell migration. Furthermore, we found that Shp-2 co-immunoprecipitated with SPK1 and c-Met in embryonic fibroblasts. These studies suggest that Shp-2 is an SPK1-interacting protein and that it plays an indispensable role in HGF-induced SPK1 activation.

Adenoviral-mediated gene expression of hepatocyte growth factor prevents postoperative peritoneal adhesion in a rat model

BACKGROUND

Mesothelial cell proliferation and migration play important roles in reducing formation of postoperative peritoneal adhesions. Hepatocyte growth factor (HGF) is a multifunctional cytokine that stimulates proliferation and migration of various cell types, including mesothelial cells.

METHODS

We investigated the effect of adenovirus-mediated HGF gene expression on the proliferation and migration of mesothelial cells and evaluated its preventive effects on postoperative formation of peritoneal adhesions. Rat mesothelial cells were isolated and characterized by expression of cytokeratin and vimentin.

RESULTS

Immunohistochemical staining showed that these cells expressed c-Met, the receptor for HGF. Adenoviral-mediated HGF gene transfer into mesothelial cells resulted in high expression of HGF and enhanced migration. To evaluate the preventive effects of adenoviral-mediated HGF gene transfer on the formation of postoperative peritoneal adhesion, we employed a rat model of cecum abrasion-induced adhesion formation in which 80% of the rats developed postoperative peritoneal adhesions. Local application of recombinant adenovirus carrying the HGF gene reduced adhesion formation in 16 of 20 control rats compared with 7 of 20 treated rats in this model.

CONCLUSIONS

These results suggest that adenoviral-mediated HGF gene transfer may be a novel strategy for preventing postoperative peritoneal adhesions.

Alphastatin downregulates vascular endothelial cells sphingosine kinase activity and suppresses tumor growth in nude mice bearing human gastric cancer xenografts

AIM: To investigate whether alphastatin could inhibit human gastric cancer growth and furthermore whether sphingosine kinase (SPK) activity is involved in this process.

METHODS: Using migration assay, MTT assay and Matrigel assay, the effect of alphastatin on vascular endothelial cells (ECs) was evaluated in vitro. SPK and endothelial differentiation gene (EDG)-1, -3, -5 mRNAs were detected by reverse transcription-polymerase chain reaction (RT-PCR). SPK activity assay was used to evaluate the effect of alphastatin on ECs. Matrigel plug assay in nude mice was used to investigate the effect of alphastatin on angiogenesis in vivo. Female nude mice were subcutaneously implanted with human gastric cancer cells (BGC823) for the tumor xenografts studies. Micro vessel density was analyzed in Factor VIII-stained tumor sections by the immunohistochemical SP method.

RESULTS: In vitro, alphastatin inhibited the migration and tube formation of ECs, but had no effect on proliferation of ECs. RT-PCR analysis demonstrated that ECs expressed SPK and EDG-1, -3, -5 mRNAs. In vivo, alphastatin sufficiently suppressed neovascularization of the tumor in the nude mice. Daily administration of alphastatin produced significant tumor growth suppression. Immunohistochemical studies of tumor tissues revealed decreased micro vessel density in alphastatin-treated animals as compared with controls.

CONCLUSION: Downregulating ECs SPK activity may be one of the mechanisms that alphastatin inhibits gastric cancer angiogenesis. Alphastatin might be a useful and relatively nontoxic adjuvant therapy in the treatment of gastric cancer.

Regulators of angiogenesis and strategies for their therapeutic manipulation

Angiogenesis provides a mechanism by which delivery of oxygen and nutrients is adapted to compliment changes in tissue mass or metabolic activity. However, maladaptive angiogenesis is integral to the process of several diseases common in Western countries, including tumor growth, vascular insufficiency, diabetic retinopathy and rheumatoid arthritis. Understanding the process of capillary growth, including the identification and functional analyses of key pro- and anti-angiogenic factors, provides knowledge that can be applied to improve/reverse these pathological states. Initially, angiogenesis research focused predominantly on vascular endothelial growth factor (VEGF) as a main player in the angiogenesis cascade. It is apparent now that participation of multiple angiogenic factors and signal pathways is critical to enable effective growth and maturation of nascent capillaries. The purpose of this review is to focus on recent progress in identifying angiogenesis signaling pathways that show promise as targets for successful induction or inhibition of capillary growth. The strategies applied to achieve these contradictory tasks are discussed within the framework of our existing fundamental knowledge of angiogenesis signaling cascades, with an emphasis on comparing the employment of distinctive tactics in modulation of these pathways. Innovative developments that are presented include: (1) inducing a pleiotropic response via activation or inhibition of angiogenic transcription factors; (2) modulation of nitric oxide tissue concentration; (3) manipulating the kallikrein-kinin system; (4) use of endothelial progenitor cells as a means to either directly contribute to capillary growth or to be used as a vehicle to deliver "suicide genes" to tumor tissue.

Role of sphingosine kinase 2 in cell migration toward epidermal growth factor

Sphingosine 1-phosphate (S1P), produced by two sphingosine kinase isoenzymes, denoted SphK1 and SphK2, is the ligand for a family of five specific G protein-coupled receptors that regulate cytoskeletal rearrangements and cell motility. Whereas many growth factors stimulate SphK1, much less is known of the regulation of SphK2. Here we report that epidermal growth factor (EGF) stimulated SphK2 in HEK 293 cells. This is the first example of an agonist-dependent regulation of SphK2. Chemotaxis of HEK 293 cells toward EGF was inhibited by N,N-dimethylsphingosine, a competitive inhibitor of both SphKs, implicating S1P generation in this process. Down-regulating expression of SphK1 in HEK 293 cells with a specific siRNA abrogated migration toward EGF, whereas decreasing SphK2 expression had no effect. EGF contributes to the invasiveness of human breast cancer cells, and EGF receptor expression is associated with poor prognosis. EGF also stimulated SphK2 in MDA-MB-453 breast cancer cells. Surprisingly, however, down-regulation of SphK2 in these cells completely eliminated migration toward EGF without affecting fibronectin-induced haptotaxis. Our results suggest that SphK2 plays an important role in migration of MDA-MB-453 cells toward EGF.