SphK1 Activity Research Articles

Sphingosine kinase 1 overexpression is regulated by signaling through PI3K, AKT2, and mTOR in imatinib-resistant chronic myeloid leukemia cells

As a better understanding of the molecular basis of carcinogenesis has emerged, oncogene-specific cell-signaling pathways have been successfully targeted to treat human malignances. Despite impressive advances in oncogene-directed therapeutics, genetic instability in cancer cells often manifest acquired resistance. This is particularly noted in the use of tyrosine kinase inhibitors therapies and not more evident than for chronic myeloid leukemia. Therefore, it is of great importance to understand the molecular mechanisms affecting cancer cell sensitivity and resistance to tyrosine kinase inhibitors. In this study, we used continuous exposure to stepwise increasing concentrations of imatinib (0.6-1 μM) to select imatinib-resistant K562 cells. Expression of BCR-ABL increased both at RNA and protein levels in imatinib-resistant cell lines. Furthermore, expression levels of sphingosine kinase 1 (SphK1) were increased significantly in resistant cells, channeling sphingoid bases to the SphK1 pathway and activating sphingosine-1-phosphate-dependent tyrosine phosphorylation pathways that include the adaptor protein Crk. The partial inhibition of SphK1 activity by N,N-dimethylsphingosine or expression by small interfering RNA increased sensitivity to imatinib-induced apoptosis in resistant cells and returned BCR-ABL to baseline levels. To determine the resistance mechanism-induced SphK1 upregulation, we used pharmacological inhibitors of the phosphoinositide 3-kinase/AKT/mammalian target of rapamycin signaling pathway and observed robust downmodulation of SphK1 expression and activity when AKT2, but not AKT1 or AKT3, was suppressed. These results demonstrate that SphK1 is upregulated in imatinib-resistant K562 cells by a pathway contingent on a phosphoinositide 3-kinase/AKT2/mammalian target of rapamycin signaling pathway. We propose that SphK1 plays an important role in development of acquired resistance to imatinib in chronic myeloid leukemia cell lines.

Effect of sphingosine kinase 1 on the apoptosis, migration and invasion of colon cancer HT-29 cells and its molecular mechanisms

To investigate the effect of sphingosine kinase 1 (SphK1) on the proliferation, apoptosis, migration and invasion of colon cancer TH-29 cells and to explore its molecular mechanisms. Phorbol 12-myristate 13-acetate (PMA) was used to induce the activity of SphK1 and N, N-dimethylsphingosine (DMS) was used to suppress the activity of SphK1. Cell prolieration and apoptosis were detected by MTT assay and flow cytometry, respectively. The migration and invasion capabilities of the cells were assessed in Transwell chambers. The activity of SphK1 was assayed by autoradiography. Western blot was used to evaluate the protein expression of SphK1, p38, phosphorylated p38 (p-p38) and SAPK/JNK. PMA and DMS were able to induce and suppress the activity and protein expression of SphK1 in a time-dependent manner, respectively. PMA enhanced and DMS suppressed the cell viability in a time- and dose-dependent manner. Being treated with 100 nmol/L PMA or 50 µmol/L DMS for 0, 6, 12, 24 h, the cell apoptosis rates of PMA group were (9.35 ± 0.84)%, (7.61 ± 0.48)%, (5.53 ± 0.76)% and (0.56 ± 0.33)%, contrastly, that of DMS group were (9.18 ± 0.94)%, (12.06 ± 1.41)%, (19.80 ± 2.36)% and (31.85 ± 3.60)%, respectively. Compared with the control group, the cell migration and invasion capabilities of the PMA group were significantly enhanced, and that of the DMS group were significantly suppressed. The migration cell number of control, PMA and DMS groups were 68.75 ± 6.15, 109.33 ± 11.63 and 10.83 ± 2.48, the invasion cell number of control, PMA and DMS groups were 55.42 ± 4.50, 90.58 ± 7.06 and 9.58 ± 2.39, respectively. With the elevating activity and expression of SphK1, the protein expressions of p38, p-p38 and SAPK/JNK were strikingly suppressed. On the contrary, after treating with DMS the protein expressions of p38, p-p38 and SAPK/JNK were enhanced. SphK1 potently enhances the prolieration, migration and invasion of colon cancer HT-29 cells, meanwhile suppresses the cell apoptosis. The suppressing of the p38 and SAPK/JNK signalling pathways may be one of its molecular mechanisms.

Intracellular S1P Generation Is Essential for S1P-Induced Motility of Human Lung Endothelial Cells: Role of Sphingosine Kinase 1 and S1P Lyase

BackgroundEarlier we have shown that extracellular sphingosine-1-phosphate (S1P) induces migration of human pulmonary artery endothelial cells (HPAECs) through the activation of S1P1 receptor, PKCε, and PLD2-PKCζ-Rac1 signaling cascade. As endothelial cells generate intracellular S1P, here we have investigated the role of sphingosine kinases (SphKs) and S1P lyase (S1PL), that regulate intracellular S1P accumulation, in HPAEC motility.Methodology/Principal FindingsInhibition of SphK activity with a SphK inhibitor 2-(p-Hydroxyanilino)-4-(p-Chlorophenyl) Thiazole or down-regulation of Sphk1, but not SphK2, with siRNA decreased S1Pint, and attenuated S1Pext or serum-induced motility of HPAECs. On the contrary, inhibition of S1PL with 4-deoxypyridoxine or knockdown of S1PL with siRNA increased S1Pint and potentiated motility of HPAECs to S1Pext or serum. S1Pext mediates cell motility through activation of Rac1 and IQGAP1 signal transduction in HPAECs. Silencing of SphK1 by siRNA attenuated Rac1 and IQGAP1 translocation to the cell periphery; however, knockdown of S1PL with siRNA or 4-deoxypyridoxine augmented activated Rac1 and stimulated Rac1 and IQGAP1 translocation to cell periphery. The increased cell motility mediated by down-regulation was S1PL was pertussis toxin sensitive suggesting “inside-out” signaling of intracellularly generated S1P. Although S1P did not accumulate significantly in media under basal or S1PL knockdown conditions, addition of sodium vanadate increased S1P levels in the medium and inside the cells most likely by blocking phosphatases including lipid phosphate phosphatases (LPPs). Furthermore, addition of anti-S1P mAb to the incubation medium blocked S1Pext or 4-deoxypyridoxine-dependent endothelial cell motility.Conclusions/SignificanceThese results suggest S1Pext mediated endothelial cell motility is dependent on intracellular S1P production, which is regulated, in part, by SphK1 and S1PL.

Sphingosine kinases regulate NOX2 activity via p38 MAPK-dependent translocation of S100A8/A9

Neutrophils play a fundamental role in host defense by neutralizing pathogens through the generation of ROS by NOX2. In nonexcitable cells, Ca(2+) influx is essentially mediated via SOCE, a complex mechanism in which depletion of intracellular Ca(2+) stores from the ER results in Ca(2+) entry through Ca(2+) SOCs at the plasma membrane. In this regard, it is well established that extracellular Ca(2+) entry participates to NOX2 activation. S1P, produced by SphKs, has been involved in Ca(2+) homeostasis and thus, could intervene in NOX2 regulation. The aim of this study was to characterize the importance of SphKs in NOX2 activation and the signaling cascade involved in this mechanism. Treatment of neutrophil-like dHL-60 cells by DHS, a SphK inhibitor, and SphK siRNA inhibited fMLF-induced NOX2 activity. Sequential activation of cells by thapsigargin and the phorbol ester PMA revealed that SphK-regulated NOX2 activity relies on intracellular Ca(2+) store depletion. Confocal microscopy and immunoblot analysis showed that stimulation by thapsigargin and PMA mediated S100A8/A9 recruitment to the plasma membrane and p38 MAPK activation. S100A8/A9 translocation decreased when SphK activity was blocked. This result was confirmed in purified human neutrophils, which were physiologically stimulated by fMLF. In addition, p38 MAPK was found to be regulated by SphKs. These results define a pathway leading to NOX2 activation, in which p38 MAPK-mediated S100A8/A9 translocation is regulated by Ca(2+) store depletion-dependent SphK activation.

A rapid assay for assessment of sphingosine kinase inhibitors and substrates

Sphingosine kinases (SphKs) catalyze the transfer of phosphate from adenosine triphosphate (ATP) to sphingosine to generate sphingosine 1-phosphate (S1P), an important bioactive lipid molecule that mediates a diverse range of cell signaling processes. The conventional assay of SphK enzymatic activity uses [γ-32P]ATP and sphingosine as substrates, with the radiolabeled S1P product recovered by organic extraction, displayed by thin layer chromatography, and quantified by liquid scintillation counting. Although this assay is sensitive and accurate, it is slow and labor-intensive; thus, it precludes the simultaneous screening of more than a few inhibitor compounds. Here we describe a 96-well assay for SphKs that is rapid and reproducible. Our method, which takes advantage of the limited solubility of S1P, detects radioactive S1P adhering to the plate by scintillation proximity counting. Our procedure obviates extraction into organic solvents, postreaction transfers, and chromatography. Furthermore, our assay enables assessment of both inhibitors and substrates, and it can detect endogenous SphK activity in cell and tissue extracts. The SphK kinetic parameter, Km, and the Ki values of inhibitors determined with our assay and the conventional assay were indistinguishable. These results document that our assay is well-suited for the screening of chemical libraries of SphK inhibitors.

A Sphingosine Kinase Form 2 Knockout Sensitizes Mouse Myocardium to Ischemia/Reoxygenation Injury and Diminishes Responsiveness to Ischemic Preconditioning

Sphingosine kinase (SphK) exhibits two isoforms, SphK1 and SphK2. Both forms catalyze the synthesis of sphingosine 1-phosphate (S1P), a sphingolipid involved in ischemic preconditioning (IPC). Since the ratio of SphK1 : SphK2 changes dramatically with aging, it is important to assess the role of SphK2 in IR injury and IPC. Langendorff mouse hearts were subjected to IR (30 min equilibration, 50 min global ischemia, and 40 min reperfusion). IPC consisted of 2 min of ischemia and 2 min of reperfusion for two cycles. At baseline, there were no differences in left ventricular developed pressure (LVDP), ± dP/dtmax, and heart rate between SphK2 null (KO) and wild-type (WT) hearts. In KO hearts, SphK2 activity was undetectable, and SphK1 activity was unchanged compared to WT. Total SphK activity was reduced by 53%. SphK2 KO hearts subjected to IR exhibited significantly more cardiac damage (37 ± 1% infarct size) compared with WT (28 ± 1% infarct size); postischemic recovery of LVDP was lower in KO hearts. IPC exerted cardioprotection in WT hearts. The protective effect of IPC against IR was diminished in KO hearts which had much higher infarction sizes (35 ± 2%) compared to the IPC/IR group in control hearts (12 ± 1%). Western analysis revealed that KO hearts had substantial levels of phosphorylated p38 which could predispose the heart to IR injury. Thus, deletion of the SphK2 gene sensitizes the myocardium to IR injury and diminishes the protective effect of IPC.

Tumour necrosis factor alpha (TNF- ) stimulation of cells with established dengue virus type 2 infection induces cell death that is accompanied by a reduced ability of TNF- to activate nuclear factor B and reduced sphingosine kinase-1 activity

Tumor necrosis factor alpha (TNF-α) has an antiviral role in some infections but in dengue virus (DENV) infection it is linked to severe pathology. We have previously shown that TNF-α stimulation cannot activate nuclear factor κB (NF-κB) to the fullest extent in DENV-2-infected cells. Here, we investigate further responses of DENV-2-infected cells to TNF-α, focussing particularly on cell death and pro-survival signals. TNF-α stimulation of productively DENV-2-infected monocyte-derived macrophages or HEK-293 cells induced caspase-3-mediated cell death. While TNF-α induced comparable degradation of the inhibitor of NF-κB alpha (IκB-α) and NF-κB activation in mock-infected and DENV-2-infected cells early in infection, later in infection and coinciding with TNF-α-induced cell death, TNF-α-stimulated IκB-α degradation and NF-κB activation was reduced. This was associated with reduced levels of sphingosine kinase-1 (SphK1) activity in DENV-2-infected cells; SphK1 being a known mediator of TNF-α-stimulated survival signals. Transfection experiments demonstrated inhibition of TNF-α-stimulated NF-κB activation by expression of DENV-2 capsid (CA) but enhancement by DENV-2 NS5 protein. DENV-2 CA alone, however, did not induce TNF-α-stimulated cell death or inhibit SphK1 activity. Thus, productively DENV-2-infected cells have compromised TNF-α-stimulated survival pathways and show enhanced susceptibility to TNF-α-stimulated cell death, suggesting a role for TNF-α in the killing of healthy productively DENV-2-infected cells. Additionally, the altered ability of TNF-α to activate NF-κB as infection progresses is reflected by the opposing actions of DENV-2 CA and NS5 proteins on TNF-α-stimulated NF-κB activation and could have important consequences for NF-κB-driven release of inflammatory cytokines.

Abstract B68: EGCG and theaflavin are direct inhibitors of the oncogenic lipid kinase, sphingosine kinase 1

Abstract Epigallocatechin-3-gallate (EGCG) and theaflavin are polyphenols from green and black tea, respectively, that have been shown to have anti-cancer/anti-inflammatory effects through their antioxidant properties. Recent studies indicate that these tea polyphenols may also target the sphingosine kinase (SphK)/sphingosine-1-phosphate (S1P) signaling pathway. Therefore we examined whether these tea polyphenols can directly inhibit SphK1 catalytic activity. To accomplish this, we performed in vitro SphK activity assays to determine the kinetics properties of EGCG and theaflavin toward SphK1. These analyses indicate that EGCG, and its related tea polyphenols theaflavin, GCG and catechin all directly inhibit SphK1 catalytic activity. Further kinetic analysis indicates that EGCG is a non-competitive inhibitor of SphK1 (Ki = 450-500 nM). These data are the first demonstration of a direct inhibitory effect of tea polyphenols on SphK1 catalytic activity. Importantly, given the oncogenic role of SphK1, they suggest that SphK1 is a target of the anti-cancer/anti-inflammatory actions of the tea polyphenols such as EGCG and theaflavin. They further suggest that inhibiting SphK1 activity, using tea polyphenols, can be an effective chemopreventative strategy and that the structures of these polyphenols could serve as novel molecular scaffolds for the development of SphK inhibitors. Citation Information: Cancer Prev Res 2010;3(12 Suppl):B68.

FTY720 (Fingolimod) Sensitizes Prostate Cancer Cells to Radiotherapy by Inhibition of Sphingosine Kinase-1

Radiotherapy is widely used as a radical treatment for prostate cancer, but curative treatments are elusive for poorly differentiated tumors where survival is just 15% at 15 years. Dose escalation improves local response rates but is limited by tolerance in normal tissues. A sphingosine analogue, FTY720 (fingolimod), a drug currently in phase III studies for treatment of multiple sclerosis, has been found to be a potent apoptosis inducer in prostate cancer cells. Using in vitro and in vivo approaches, we analyzed the impact of FTY720 on sphingolipid metabolism in hormone-refractory metastatic prostate cancer cells and evaluated its potential as a radiosensitizer on cell lines and prostate tumor xenografts. In prostate cancer cell lines, FTY720 acted as a sphingosine kinase 1 (SphK1) inhibitor that induced prostate cancer cell apoptosis in a manner independent of sphingosine-1-phosphate receptors. In contrast, γ irradiation did not affect SphK1 activity in prostate cancer cells yet synergized with FTY720 to inhibit SphK1. In mice bearing orthotopic or s.c. prostate cancer tumors, we show that FTY720 dramatically increased radiotherapeutic sensitivity, reducing tumor growth and metastasis without toxic side effects. Our findings suggest that low, well-tolerated doses of FTY720 could offer significant improvement to the clinical treatment of prostate cancer.

Sphingosine kinase-1 activity and expression in human prostate cancer resection specimens

Purpose Sphingosine kinase-1 (SphK1) was shown in preclinical models and non-genitourinary cancers to be instrumental in cancer progression, adaptation to hypoxia and in tumour angiogenesis. No data were available in human prostate cancer. The present study was designed to assess SphK1 expression and activity in radical prostatectomy specimens and to research correlations with clinical features. Materials and methods Transverse section of fresh tissue was obtained from 30 consecutive patients undergoing laparoscopic prostatectomy. SphK1 enzymatic activities of tumour and normal counterpart were determined. Relationships with PSA, Gleason sum, pathological stage, resection margin status and treatment failure were researched. SphK1 pattern of expression was then assessed on tissue microarray. Results A significant 2-fold increase in SphK1 enzymatic activity(11.1 ± 8.4 versus 5.9 ± 3.2 ( P < 0.04)) was observed in cancer. The upper quartile of SphK1 activity was associated with higher PSA (16.7 versus 6.4 ng/ml, P = 0.04), higher tumor volumes (20.7 versus 9.8, P = 0.002), higher rates of positive margins (85.7% versus 28.6%, P = 0.01) and surgical failure (71.4% versus 9.5%, P = 0.003) than the lower three quartiles. Odds ratios (OR) for treatment failure showed a strong relationship with SphK1 activity (OR: 23.7, P = 0.001), positive resection margins (OR: 15.0, P = 0.007) and Gleason sum (⩾4 + 3, OR: 8.0, P = 0.003). Tissue microarrays showed discrete epithelial expression that varied with Gleason sum with significant relationship between SphK1 expression and higher Gleason sum. Conclusion In complement to preclinical literature, the demonstrated relationships between SphK1-increased activity in cancer and relevant clinical features confirm a central role for SphK1 in prostate cancer that herald promising avenues in risk-assessment and treatment.

The role of sphingosine kinase-1 in EGFRvIII-regulated growth and survival of glioblastoma cells

We have previously shown that high expression levels of the lipid kinase sphingosine kinase-1 (SphK1) correlate with poor survival of glioblastoma (GBM) patients. In this study we examined the regulation of SphK1 expression by epidermal growth factor receptor (EGFR) signaling in GBM cells. As the EGFR gene is often overexpressed and mutated in GBM, and EGFR has been shown to regulate SphK1 in some cell types, we examined the effect of EGF signaling and the constitutively active EGFRvIII mutant on SphK1 in GBM cells. Treatment of glioma cell lines with EGF led to increased expression and activity of SphK1. Expression of EGFRvIII in glioma cells also activated and induced SphK1. In addition, siRNA to SphK1 partially inhibited EGFRvIII-induced growth and survival of glioma cells as well as ERK MAP kinase activation. To further evaluate the connection between EGFR and SphK1 in GBM we examined primary neurosphere cells isolated from fresh human GBM tissue. The GBM-derived neurosphere cell line GBM9, which forms GBM-like tumors intracranially in nude mice, maintained expression of EGFRvIII in culture and had high levels of SphK1 activity. EGFR inhibitors modestly decreased SphK1 activity and proliferation of GBM9 cells. More extensive blockage of SphK1 activity by a SphK inhibitor, potently blocked cell proliferation and induced apoptotic cell death of GBM9 cells. Thus, SphK1 activity is necessary for survival of GBM-derived neurosphere cells, and EGFRvIII partially utilizes SphK1 to further enhance cell proliferation.

Determination of sphingosine kinase activity in biological samples by liquid chromatography–tandem mass spectrometry

Sphingosine kinase (SphK) is a key enzyme in modulating the levels of sphingosine 1-phosphate (S1P) as well as an important enzyme in numerous biological responses. Using C17-sphingosine as a substrate, we established a rapid, sensitive and highly efficient method for determination of SphK activity by analyzing the product C17-sphingosine 1-phosphate (C17-S1P) using liquid chromatography-tandem mass spectrometry. The standard curve for C17-S1P was linear over a wide range (10-1000 ng/mL) with correlation coefficient (r(2)) greater than 0.999. The lower limit of quantification for C17-S1P was 10 ng/mL. The K(m) values for C17-sphingosine and ATP were determined to be 28.17 and 188.5 microM, respectively. More importantly, the SphK activity dramatically increased in cultured HEK 293 cells expressing wild-type SphK1 as well as cells treated with tumor necrosis factor-alpha, a sphingosine kinase activator. In contrast, the SphK activity decreased in cultured HEK 293 cells treated with dimethylsphngosine, a sphingosine kinase inhibitor. In conclusion, this method was sensitive and rapid in the determination of SphK acitivity, providing striking utilities in exploring the sphingosine kinase signaling pathway and screening active compounds targeting SphK activity.

The involvement of sphingosine kinase 1 in LPS‐induced Toll‐like receptor 4‐mediated accumulation of HIF‐1α protein, activation of ASK1 and production of the pro‐inflammatory cytokine IL‐6

Toll-like receptors (TLRs) lie in the core of resistance to infectious diseases allowing host immune cells to specifically detect pathogens by recognising their specific molecular patterns. Cell membrane-associated TLR4 (recognises lipopolysaccharide (LPS) of Gram-negative bacteria) and endosomal TLR7/8 (recognise viral single-stranded RNA) are known to activate hypoxia inducible factor-1α (HIF-1α) protein (necessary for cellular adaptation to the inflammatory stress) via redox-dependent mechanism. TLR4 triggers the cross talk between HIF-1α and apoptosis signal-regulating kinase 1 (ASK1), whereas TLR7/8 activates HIF-1α in the ASK1-independent manner. Here, we report that in THP-1 and RAW264.7 macrophages, ligand-induced activation of the TLR4 but not TLR7/8 induces activation and transcriptional upregulation of sphingosine kinase 1 (SphK1) in extracellular signal-regulating kinase and phospholipase C-1γ/PI3 kinase-dependent manner. TLR4-mediated SphK1 activation was found to be critical for the redox-dependent activation of HIF-1α and ASK1, as well as for the prevention of LPS-induced activation of caspase 3 and the expression of pro-inflammatory cytokine interleukin-6.

Glucocorticoids protect renal mesangial cells from apoptosis by increasing cellular sphingosine-1-phosphate

Neutral ceramidase (NCDase) and sphingosine kinases (SphKs) are key enzymes regulating cellular sphingosine-1-phosphate (S1P) levels. In this study we found that stress factor-induced apoptosis of rat renal mesangial cells was significantly reduced by dexamethasone treatment. Concomitantly, dexamethasone increased cellular S1P levels, suggesting an activation of sphingolipid-metabolizing enzymes. The cell-protective effect of glucocorticoids was reversed by a SphK inhibitor, was completely absent in SphK1-deficient cells, and was associated with upregulated mRNA and protein expression of NCDase and SphK1. Additionally, in vivo experiments in mice showed that dexamethasone also upregulated SphK1 mRNA and activity, and NCDase protein expression in the kidney. Fragments (2285, 1724, and 1126 bp) of the rat NCDase promoter linked to a luciferase reporter were transfected into rat kidney fibroblasts and mesangial cells. There was enhanced NCDase promoter activity upon glucocorticoids treatment that was abolished by the glucocorticoid receptor antagonist RU-486. Single and double mutations of the two putative glucocorticoid response element sites within the promoter reduced the dexamethasone effect, suggesting that both glucocorticoid response elements are functionally active and required for induction. Our study shows that glucocorticoids exert a protective effect on stress-induced mesangial cell apoptosis in vitro and in vivo by upregulating NCDase and SphK1 expression and activity, resulting in enhanced levels of the protective lipid second messenger S1P.

A Novel Function of Sphingosine Kinase 1 Suppression of JNK Activity in Preventing Inflammation and Injury

The mechanism underlying the protective effect of sphingosine kinase 1 (SphK1) in inflammatory injury is not clear. We demonstrated using SphK1-null mice (SphK1(-/-)) the crucial role of SphK1 in suppressing lipopolysaccharide-induced neutrophil oxidant production and sequestration in lungs and mitigating lung inflammatory injury. This effect of SphK1 was independent of the production of sphingosine 1-phosphate, the product of SphK1 activity. The anti-inflammatory effect of SphK1 in the lipopolysaccharide model was mediated through SphK1 interaction with JNK. SphK1 stabilization of JNK in turn inhibited JNK binding to the JNK-interacting protein 3 (JIP3) and thus abrogated the activation of NADPH oxidase and oxidant generation and resultant NF-kappaB activation. Therefore, SphK1-mediated down-regulation of JNK activity serves to dampen inflammation and tissue injury.

Sphingosine kinase 1 and sphingosine-1-phosphate receptor 2 are vital to recovery from anaphylactic shock in mice

Sphingosine kinase 1 (SphK1) and SphK2 are ubiquitous enzymes that generate sphingosine-1-phosphate (S1P), a ligand for a family of G protein-coupled receptors (S1PR1-S1PR5) with important functions in the vascular and immune systems. Here we explore the role of these kinases and receptors in recovery from anaphylaxis in mice. We found that Sphk2-/- mice had a rapid recovery from anaphylaxis. In contrast, Sphk1-/- mice showed poor recovery from anaphylaxis and delayed histamine clearance. Injection of S1P into Sphk1-/- mice increased histamine clearance and promoted recovery from anaphylaxis. Adoptive cell transfer experiments demonstrated that SphK1 activity was required in both the hematopoietic and nonhematopoietic compartments for recovery from anaphylaxis. Mice lacking the S1P receptor S1PR2 also showed a delay in plasma histamine clearance and a poor recovery from anaphylaxis. However, S1P did not promote the recovery of S1pr2-/- mice from anaphylaxis, whereas S1pr2+/- mice showed partial recovery. Unlike Sphk2-/- mice, Sphk1-/- and S1pr2-/- mice had severe hypotension during anaphylaxis. Thus, SphK1-produced S1P regulates blood pressure, histamine clearance, and recovery from anaphylaxis in a manner that involves S1PR2. This suggests that specific S1PR2 agonists may serve to counteract the vasodilation associated with anaphylactic shock.

Abstract LB-35: A monoclonal sphingosine 1-phosphate antibody inhibits intratumoral hypoxia and sensitizes to docetaxel in prostate cancer animal model

Abstract The reduction in the normal level of tissue oxygen tension or hypoxia is a characteristic of solid tumors that triggers the activation of signaling pathways promoting neovascularization, metastasis, increased tumor growth, and resistance to treatments. The activation of the transcription factor hypoxia-inducible factor 1α (HIF-1α) has been identified as the master mechanism of adaptation to hypoxia. In a recent study (Ader et al, Cancer Res, 2008), we identified the sphingosine kinase 1/sphingosine 1-phosphate (SphK1/S1P) pathway, which elicits various cellular processes including cell proliferation, cell survival, or angiogenesis, as a new modulator of HIF-1α activity under hypoxic conditions Indeed, we have shown that SphK1 activity (which generates S1P) was rapidly stimulated under low oxygen conditions. The pharmacological inhibition and RNA silencing of SphK1 activity could prevent the accumulation of HIF-1α and its transcriptional activity in multiple cancer cell lineages - including prostate - suggesting a canonical pathway. We have suggested that inhibiting the SphK1/S1P signaling, that is up-regulated under low oxygen tension, might help normalizing the tumor microenvironment and increase tumor sensitivity to radiation and chemotherapy, in the broader concept of « normalization of tumor vessels » as tumor oxygenation is known to enhance response to chemotherapy and radiation (reviewed in Ader et al., Cancer Res, 2009). S1P is believed to exert most of its actions as a specific ligand for a family of five cognate G protein-coupled receptors to elicit paracrine or autocrine signaling cascades. We now provide evidence that inhibition of the S1P exogenous signaling, through pharmacological inhibition of its receptors or by taking advantage of a monoclonal antibody neutralizing S1P, blocks HIF-1α accumulation and its transcriptional activity in prostate cancer cells exposed to hypoxia. More importantly, in an orthotopic (o.t) xenograft model of prostate cancer, we show that a monoclonal antibody directed against S1P markedly reduces intratumoral hypoxia and modifies vessel architecture within 5 days of treatment. Finally, we demonstrate for the first time that a monoclonal antibody directed against S1P could sensitize to the antitumoral effects of docetaxel, the ‘gold standard’ treatment for hormone-refractory prostate cancer. Indeed, a 5-day anti-S1P antibody pretreatment markedly sensitizes to docetaxel in an o.t. PC-3/green fluorescent protein model established in nude mice. The combination anti-S1P antibody together with docetaxel was not only accompanied by a smaller primary tumor volume compared to docetaxel treatment but also markedly reduced the occurrence and number of metastases. In conclusion, these data establish the proof-of-concept that blocking the exogenous action of S1P, by reducing intratumoral hypoxia, can sensitize to docetaxel-based chemotherapy in prostate cancer animal model. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-35.

Abstract 838A: Characterization of sphingosine kinase isoenzyme selective inhibitors

Abstract Sphingosine kinases (SphKs) play key roles in cell proliferation, migration and inflammation by catalyzing the formation of sphingosine-1-phosphate (S1P). However, the two isoenzymes, SphK1 and SphK2, play only partially overlapping roles in tumor epithelial cells. Our genetic approach (siRNA) revealed that SphK2 knockdown cells had more effects on decreasing cell proliferation and migration than SphK1 knockdown. A novel non-radioactive HPLC method based on florescence was developed to measure the activities of SphK. It revealed the increased SphK1 activity induced by SphK2 knockdown could not rescue the cells from apoptosis. In order to confirm the results from the genetic approach, we developed pharmacological approaches that used SphK isoenzymes selective inhibitors to dissect the functions of SphK isoenzymes. After the structure optimization of the lead compounds identified by high throughput screening, two compounds were identified as SphK inhibitors: 3-(4-Chlorophenyl)adamantane-1-carboxylic acid (pyridin-4-ylmethyl)amide hydrochloride salt - termed ABC294640 and 3-(4-Chlorophenyl)adamantane-1-carboxylic acid [2-(3,4-dihydroxyphenyl)ethyl]amide - termed ABC294735. The inhibition specificities of these compounds were characterized. ABC294640 is a SphK2 selective inhibitor (IC50 60μM), while ABC294735 (IC50SphK1 6μM, IC50SphK2 10μM) and SKI-II (IC50SphK1 2μM, IC50SphK2 1μM) are dual inhibitors in the presence of 10μM sphingosine as substrate. Lineweaver-Burk plots using the data from recombinant SphK1/2 active enzymes and kinase assay kit revealed ABC294640, ABC294735 and SKI-II were SphK competitive inhibitors. A possibly SphK1-selective inhibitor has also been identified by high-throughput screening and is currently being characterized. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 838A.

107 INCREASED SPHINGOSINE KINASE-1 ACTIVITY AND EXPRESSION IN PROSTATE CANCER

You have accessJournal of UrologyProstate Cancer: Basic Research I1 Apr 2010107 INCREASED SPHINGOSINE KINASE-1 ACTIVITY AND EXPRESSION IN PROSTATE CANCER Bernard Malavaud, Dimitri Pchejetski, Catherine Mazerolles, Geisilène Silva Russano de Paiva, Cyril Clavet, Nicolas Doumerc, Stuart Pitson, Pascal Rischmann, and Olivier Cuvillier Bernard MalavaudBernard Malavaud Toulouse, France More articles by this author , Dimitri PchejetskiDimitri Pchejetski Toulouse, France More articles by this author , Catherine MazerollesCatherine Mazerolles Toulouse, France More articles by this author , Geisilène Silva Russano de PaivaGeisilène Silva Russano de Paiva Toulouse, France More articles by this author , Cyril ClavetCyril Clavet Toulouse, France More articles by this author , Nicolas DoumercNicolas Doumerc Toulouse, France More articles by this author , Stuart PitsonStuart Pitson Adélaïde, Australia More articles by this author , Pascal RischmannPascal Rischmann Toulouse, France More articles by this author , and Olivier CuvillierOlivier Cuvillier Toulouse, France More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2010.02.156AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES Sphingosine kinase-1 (SphK1) was shown in preclinical models and non-genitourinary cancers to be instrumental in cancer progression, adaptation to hypoxia and tumor angiogenesis. No data were available in human prostate cancer. The present study was designed to assess SphK1 expression and activity in radical prostatectomy specimens and to research correlations with relevant clinical features. METHODS A 3-mm thick slice was obtained at the veru montanum level from 30 consecutive patients undergoing laparoscopic prostatectomy. Relationship between SphK1 enzymatic activity and PSA, Gleason sum, pathological stage, resection margin status and treatment failure was researched by univariate and multivariate analysis. SphK1 pattern of expression was then assessed on tissue micro array. RESULTS A significant two-fold increase (11.1¡À8.4 vs. 5.9¡À3.2 (p<0.04)) was observed in cancer. The upper quartile of SphK1 activity was associated with higher PSA (16.7 vs. 6.4 ng/mL, p=0.04), higher tumor volumes (20.7 vs. 9.8, p=0.002), higher rates of positive margins (85.7 vs. 28.6%, p=0.01) and surgical failure (71.4 vs. 9.5%, p=0.003) than the lower three quartiles. Odds Ratios for treatment failure showed a strong relationship with SphK1 activity (OR:23.7, p=0.001), positive resection margins (OR:15.0, p=0.007) and Gleason Sum (¡Ý4+3, OR:8.0, p=0.003). In logistic regression, SphK1 activity (p=0.04) and Gleason Sum (p=0.09) were independent predictors of treatment failure. Tissue microarrays showed discrete epithelial expression that varied with Gleason sum with strong relationship between SphK1 expression and higher Gleason sum. CONCLUSIONS Relationships between SphK1 activity and relevant clinical features support a central role for SphK1 in prostate cancer that could herald promising avenues in cancer risk-assessment and treatment. © 2010 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 183Issue 4SApril 2010Page: e44 Advertisement Copyright & Permissions© 2010 by American Urological Association Education and Research, Inc.MetricsAuthor Information Bernard Malavaud Toulouse, France More articles by this author Dimitri Pchejetski Toulouse, France More articles by this author Catherine Mazerolles Toulouse, France More articles by this author Geisilène Silva Russano de Paiva Toulouse, France More articles by this author Cyril Clavet Toulouse, France More articles by this author Nicolas Doumerc Toulouse, France More articles by this author Stuart Pitson Adélaïde, Australia More articles by this author Pascal Rischmann Toulouse, France More articles by this author Olivier Cuvillier Toulouse, France More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

Sphingosine Kinase-1 Is Central to Androgen-Regulated Prostate Cancer Growth and Survival

BackgroundSphingosine kinase-1 (SphK1) is an oncogenic lipid kinase notably involved in response to anticancer therapies in prostate cancer. Androgens regulate prostate cancer cell proliferation, and androgen deprivation therapy is the standard of care in the management of patients with advanced disease. Here, we explored the role of SphK1 in the regulation of androgen-dependent prostate cancer cell growth and survival.Methodology/Principal FindingsShort-term androgen removal induced a rapid and transient SphK1 inhibition associated with a reduced cell growth in vitro and in vivo, an event that was not observed in the hormono-insensitive PC-3 cells. Supporting the critical role of SphK1 inhibition in the rapid effect of androgen depletion, its overexpression could impair the cell growth decrease. Similarly, the addition of dihydrotestosterone (DHT) to androgen-deprived LNCaP cells re-established cell proliferation, through an androgen receptor/PI3K/Akt dependent stimulation of SphK1, and inhibition of SphK1 could markedly impede the effects of DHT. Conversely, long-term removal of androgen support in LNCaP and C4-2B cells resulted in a progressive increase in SphK1 expression and activity throughout the progression to androgen-independence state, which was characterized by the acquisition of a neuroendocrine (NE)-like cell phenotype. Importantly, inhibition of the PI3K/Akt pathway—by negatively impacting SphK1 activity—could prevent NE differentiation in both cell models, an event that could be mimicked by SphK1 inhibitors. Fascinatingly, the reversability of the NE phenotype by exposure to normal medium was linked with a pronounced inhibition of SphK1 activity.Conclusions/SignificanceWe report the first evidence that androgen deprivation induces a differential effect on SphK1 activity in hormone-sensitive prostate cancer cell models. These results also suggest that SphK1 activation upon chronic androgen deprivation may serve as a compensatory mechanism allowing prostate cancer cells to survive in androgen-depleted environment, giving support to its inhibition as a potential therapeutic strategy to delay/prevent the transition to androgen-independent prostate cancer.