SphK1 Activity Research Articles

The role of ank in catabolic events of articular chondrocytes

s / Osteoarthritis and Cartilage 22 (2014) S57–S489 S133 210 THE ROLE OF ANK IN CATABOLIC EVENTS OF ARTICULAR CHONDROCYTES T. Kirsch y, T. Minashima y, K. Campbell y, S. Hadley z, Y. Zhang x. yNYU Sch. of Med., New York, NY; zBrigham Women’s Hosp., Harvard Med. Sch., Boston, MA, USA; xCtr. for Joint Surgery, Southwest Hosp., Third Military Med. Univ., Chong Qing, China Purpose: The progressive ankylosis protein (ANK) is a transmembrane protein that transports intracellular pyrophosphate (PPi) to the extracellular milieu. Lack of functional ANK in ank/ank mice or ank knockout mice leads to pathological mineralization of articular cartilage, ligaments, menisci and tendons resulting in arthritic changes because of the reduced amounts of extracellular PPi, a main mineralization inhibitor. We and others, however, have shown that ANK is expressed at low levels in healthy articular cartilage, and ANK expression levels drastically increase during osteoarthritis (OA) initiation and progression. These findings raise the possibility that ANK plays more complex and unknown functions in articular cartilage and OA pathology than only preventing basic calcium crystal formation. Therefore, the purpose of this study was to determine the role of ANK in catabolic events of articular chondrocytes. Methods: The interactions of ANK with Myb-binding protein 1a (MYBBP1a) and sphingosine kinase 1 (SPHK1)were identified using yeast two-hybrid screening and co-immunoprecipitation. To determine the role of these interactions in catabolic events of articular chondrocytes, ank/ank and wild type (WT) mouse chondrocytes or femoral heads were treated with interleukin-1beta (IL-1b) in the absence or presence of the SPHK inhibitor, SKI-II. Catabolic marker mRNA levels were analyzed by real time PCR; proteoglycan loss using safranin O staining and MMP-13 immunostaining were determined in femoral head explants; NF-kB activity was determined by transfecting chondrocytes with a NF-kBspecific luciferase reporter and analyzing nuclear translocation of p65 by immunoblotting; MYBBP1a nuclear or cytoplasmic amounts were determined by immunohistochemistry and immunoblotting. Results: Yeast two-hybrid screening and co-immunoprecipitation experiments revealed that the N-terminal region of ANK interacts with SPHK1, whereas the C-terminal region interacts withMYBBP1a. MYBBP1a isa cytoplasmicprotein that canshuttle into thenucleuswhere it represses NF-kB transcriptional activity. Consequently, the loss of ANK/MYBBP1a interactions resulted in increased MYBBP1a nuclear amounts and decreasedNF-kB activity in IL-1b-treated ank/ank chondrocytes compared to IL-1b-treated WT cells. The loss of ANK/SPHK1 interaction resulted in decreased SPHK1 activity in IL-1b-treated ank/ank chondrocytes compared to IL-1b-treated WT cells. Activation of NF-kB-dependent transcriptional activity by IL-1b involves translocation of NF-kB family members, in particular p65 (RelA) and p50, from the cytoplasm to the nucleus. The increase of the nuclear p65 amount and the decrease of the cytoplasmic p65 amount in IL-1b-treated ank/ank chondrocytes were markedly reduced compared to IL-1b-treatedWTcells. The SPHK inhibitor, SKI-II reduced the amount of nuclear p65 and increased the amount of cytoplasmicp65 in IL-1b-treatedWTchondrocytes butnot in IL-1b-treated ank/ank chondrocytes. Transfection with ank expression vector reduced nuclearMYBBP1a amounts and fully restored SPHK andNF-kB activities in IL-1b-treated ank/ank chondrocytes, whereas transfection with P5L mutant ank that doesnot interactwith SPHK1or F376del ank thatdoes not interact with MYBBP1a increased SPHK activity or reduced nuclear MYBBP1a, respectively, and consequently either transfection with P5L or F376del ank only partially restored NF-kB activity. Finally, lack of ANK/ MYBBP1a and SPHK1 interactions in ank/ank chondrocytes resulted in decreased catabolic marker mRNA levels, proteoglycan loss, and MMP-13 immunostaining in IL-1b-treated articular chondrocytes or femoral heads. Conclusion: This study shows that ANK interacts via the N-terminal and C-terminal cytoplasmic regions with SPHK1 and MYBBP1a, respectively. The ANK/MYBBP1a interaction results in the inhibition of the nuclear translocation of MYBBP1a. Nuclear MYBBP1a acts as a corepressor of NF-kB transcriptional activity. The ANK/SPHK1 interaction is a major regulator of SPHK1 activity. Both interactions stimulate NF-kB activity and ultimately catabolic events in IL-1b-treated articular chondrocytes. Since IL-1b and NF-kB play major roles in OA pathogenesis, our findings suggest that increased ANK expression in OA cartilage may be a major contributor to cartilage destruction. Future experiments are needed to fully understand the mechanisms of the interactions between ANK, MYBBP1a and SPHK1 in OA pathology and develop strategies to interfere with these interactions as a potential novel therapy for the treatment of OA. 211 OSX-CRE DIRECTED ABLATION OF SITE-1 PROTEASE IN MICE RESULTS IN KYPHOSIS AND SCOLIOSIS D. Patra, E. DeLassus, L.J. Sandell.Washington Univ. Sch. of Med., St. Louis,

Reduced sphingosine kinase-1 and enhanced sphingosine 1-phosphate lyase expression demonstrate deregulated sphingosine 1-phosphate signaling in Alzheimer’s disease

BackgroundThe accumulation of beta amyloid (Aβ) peptides, a hallmark of Alzheimer’s disease (AD) is related to mechanisms leading to neurodegeneration. Among its pleiotropic cellular effects, Aβ accumulation has been associated with a deregulation of sphingolipid metabolism. Sphingosine 1-phosphate (S1P) derived from sphingosine is emerging as a critical lipid mediator regulating various biological activities including cell proliferation, survival, migration, inflammation, or angiogenesis. S1P tissue level is low and kept under control through equilibrium between its synthesis mostly governed by sphingosine kinase-1 (SphK1) and its degradation by sphingosine 1-phosphate lyase (SPL). We have previously reported that Aβ peptides were able to decrease the activity of SphK1 in cell culture models, an effect that could be blocked by the prosurvival IGF-1/IGF-1R signaling.ResultsHerein, we report for the first time the expression of both SphK1 and SPL by immunohistochemistry in frontal and entorhinal cortices from 56 human AD brains. Immunohistochemical analysis revealed a decreased expression of SphK1 and an increased expression of SPL both correlated to amyloid deposits in the entorhinal cortex. Otherwise, analysis of brain tissue extracts showed a decrease of SphK1 expression in AD brains whereas SPL expression was increased. The content of IGF-1R, an activator of SphK1, was found decreased in AD brains as well as S1P1, the major receptor for S1P.ConclusionsCollectively, these results highlight the importance of S1P in AD suggesting the existence of a global deregulation of S1P signaling in this disease from its synthesis by SphK1 and degradation by SPL to its signaling by the S1P1 receptor.

Loss of the neuroprotective factor Sphingosine 1-phosphate early in Alzheimer’s disease pathogenesis

BackgroundThe greatest genetic risk factor for late-onset Alzheimer's disease (AD) is the ϵ4 allele of Apolipoprotein E (ApoE). ApoE regulates secretion of the potent neuroprotective signaling lipid Sphingosine 1-phosphate (S1P). S1P is derived by phosphorylation of sphingosine, catalysed by sphingosine kinases 1 and 2 (SphK1 and 2), and SphK1 positively regulates glutamate secretion and synaptic strength in hippocampal neurons. S1P and its receptor family have been subject to intense pharmacological interest in recent years, following approval of the immunomodulatory drug Fingolimod, an S1P mimetic, for relapsing multiple sclerosis.ResultsWe quantified S1P levels in six brain regions that are differentially affected by AD pathology, in a cohort of 34 post-mortem brains, divided into four groups based on Braak neurofibrillary tangle staging. S1P declined with increasing Braak stage, and this was most pronounced in brain regions most heavily affected by AD pathology. The S1P/sphingosine ratio was 66% and 64% lower in Braak stage III/IV hippocampus (p = 0.010) and inferior temporal cortex (p = 0.014), respectively, compared to controls. In accordance with this change, both SphK1 and SphK2 activity declined with increasing Braak pathology in the hippocampus (p = 0.032 and 0.047, respectively). S1P/sphingosine ratio was 2.5-fold higher in hippocampus of ApoE2 carriers compared to ApoE4 carriers, and multivariate regression showed a significant association between APOE genotype and hippocampal S1P/sphingosine (p = 0.0495), suggesting a new link between APOE genotype and pre-disposition to AD.ConclusionsThis study demonstrates loss of S1P and sphingosine kinase activity early in AD pathogenesis, and prior to AD diagnosis. Our findings establish a rationale for further exploring S1P receptor pharmacology in the context of AD therapy.

Sphingosine Kinase 1 and Sphingosine-1-Phosphate in Oxidative Stress Evoked by 1-Methyl-4-Phenylpyridinium (MPP+) in Human Dopaminergic Neuronal Cells

Sphingosine kinases (Sphk1/2) are crucial enzymes in regulation of the biostat between sphingosine-1-phosphate (S1P) and ceramide and play an important role in the pathogenesis/pathomechanism of Alzheimer's disease (AD). These enzymes synthesise S1P, which regulates neurotransmission, synaptic function and neuron cell proliferation, by activating five G protein-coupled receptors (S1P1-5). However, S1P synthesised by Sphk2 could be involved in amyloid β (Aβ) release by stimulation of Aβ precursor protein degradation. The significance of this bioactive sphingolipid in the pathogenesis of Parkinson's disease (PD) is unknown. The aim of our study was to investigate the expression level of Sphk1 and its role in human dopaminergic neuronal cell (SH-SY5Y) viability under oxidative stress, evoked by 1-methyl-4-phenylpyridinium (MPP+). Moreover, the mechanism of S1P action on the death signalling pathway in these experimental conditions was evaluated. Our study indicated marked downregulation of Sphk1 expression in this cellular PD model. Inhibition of Sphk1 decreased SH-SY5Y cell viability and concomitantly enhanced the reactive oxygen species (ROS) level. It was found that exogenous S1P (1 μM) exerted the neuroprotective effect by activation of Sphk1 and S1P1 receptor gene expression. Moreover, S1P downregulated Bax and harakiri, death protein 5 (Hrk/DP5) expression and enhanced cell viability in MPP+-treated cells. The neuroprotective mechanism of S1P is mainly dependent on S1P1 receptor signalling, which was indicated by using specific agonists and antagonists of S1P1 receptor. The results show that S1P and S1P1 receptor agonists protected a significant population of neuronal cells against death.

The key role of sphingosine kinases in the molecular mechanism of neuronal cell survival and death in an experimental model of Parkinson's disease.

Sphingosine kinases (Sphk1/2 EC 2.7.1.91) are responsible for synthesis of sphingosine-1-phosphate (S1P) and for regulation of the bioactive sphingolipids homeostasis. Sphingosine-1-phosphate can act as a potent messenger in an autocrine/paracrine manner through five specific G protein-coupled receptors (GPCR) S1P1-5. This sphingolipid is involved in the mechanism of transcription, mitochondrial function, neuronal viability and degeneration. Until now the involvement of Sphk1/2 and sphingolipid alterations in Parkinson's disease (PD) remains unknown. Recent studies have indicated the role of sphingolipids in the regulation of alpha-synuclein (ASN) in the PD brain. Our latest data demonstrated significant inhibition of Sphk1 gene expression and activity in an in vitro PD model, induced by 1-methyl-4-phenylpyridinium (MPP+). The aim of this study was to investigate the role of Sphks inhibition in ASN secretion and in the molecular mechanism of neuronal death in the PD model. Our study was carried out using neuronal dopaminergic SH-SY5Y control cells, transfected with the human gene for ASN or with an empty vector. These cells were treated with MPP+ (1-3 mM), which represents an experimental PD model, or with the Sphks inhibitor (1-5 µM SKI II) for 3-24 h. Our data indicated that MPP+ (3 mM) induced significant alterations of Sphks and S1P lyase (SPL) gene expression. Reduced activity of Sphk1 and Sphk2 in the cytosolic fraction and in the crude nuclear fraction, respectively, was observed. Sphks inhibition evoked enhancement of ASN secretion, suppression of PI3K/Akt phosphorylation and activation of gene expression for the pro-apoptotic Bcl-2 proteins Bax and BH3-only protein Harakiri. Moreover, a lower level of cytochrome c in the mitochondrial fraction and caspase-dependent degradation of DNA-bound enzyme poly(ADP-ribose) polymerase (PARP-1) were observed. The caspase inhibitor (20 µM Z-VAD-FMK) significantly enhanced neuronal cell viability in MPP+ oxidative stress. However, exogenous S1P (1 µM) exerted a more efficient neuroprotective effect as compared to Z-VAD-FMK. In summary, these data indicated that Sphk1 inhibition plays an important role in caspase-dependent apoptotic neuronal death in an experimental PD model.

Sphingosine kinases modulate the secretion of amyloid β precursor protein from SH-SY5Y neuroblastoma cells: the role of α-synuclein.

Sphingosine kinases (SphK 1&2) are involved in the regulation of cell survival, differentiation and neurotransmitter secretion. Current data suggest potential links between sphingolipid signalling, α-synuclein (ASN) and Alzheimer's disease (AD). Our aim was to investigate the possible role of SphKs and ASN in the regulation of the production and secretion of the amyloid β precursor protein (APP). We have previously shown that ASN intensified the secretion and toxicity of amyloid β (Aβ) to the point where it caused cell death. Our current results show that APP, the precursor protein for Aβ, is also influenced by ASN. The stable overexpression of wtASN in SH-SY5Y cells caused a three-fold, significant increase of the cellular APP level. This suggests that the influence of ASN on Aβ metabolism may actually occur at the level of APP protein rather than only through the changes of its cleavage into Aβ. To elucidate the mechanisms of APP modulation the cells were exposed to S1P and an SphK inhibitor (SKI). 72 h S1P treatment at 5 µM caused a nearly 50% reduction of the cellular APP signal. S1P also caused a tendency towards higher APP secretion, though the results were insignificant. The inhibition of SphKs decreased medium APP levels in a dose-dependent manner, reaching significance at 5 µM SKI with a correspondingly elevated intracellular level. Thus, it is reasonable to expect that in fact the influence of SphK activity on APP might be pro-secretory. This would also be in agreement with numerous articles on SphK-dependent secretion in the literature. The chronic nature of AD further suggests that subtle alterations in APP metabolism could have the potential to drive important changes in brain condition.

AP-1 regulates sphingosine kinase 1 expression in a positive feedback manner in glomerular mesangial cells exposed to high glucose

Our previous studies have confirmed that the sphingosine kinase 1 (SphK1)–sphingosine 1-phosphate (S1P) signaling pathway in the kidney under diabetic conditions is closely correlated with the pathogenesis of diabetic nephropathy (DN). The activation of SphK1–S1P pathway by high glucose (HG) can increase the expression of fibronectin (FN), an important fibrotic component, in glomerular mesangial cells (GMCs) by promoting the DNA-binding activity of transcription factor AP-1. However, the mechanism responsible for the sustained activation of SphK1–S1P pathway remains unclear. Given the binding motifs for AP-1 within the first intron of the SphK1 gene, we speculated that the activated AP-1 in the kidney under HG condition possibly regulates SphK1 expression in a positive feedback manner, thereby promoting the sustained activation of SphK1–S1P pathway and mediating the pathological progression of DN. Here, we observed the effect of AP-1 on SphK1 expression in GMCs and explored the molecular mechanism involved in the sustained activation of SphK1–S1P pathway. We found two consensus binding motifs for AP-1 in the promoter sequences and non-coding region downstream of the transcriptional initiation of the rat SphK1 gene by chromatin immunoprecipitation assay. The treatment of GMCs with both HG and S1P significantly increased the protein expression of c-Jun and c-Fos, and obviously enhanced the phosphorylation of c-Jun at Ser63 and Ser73, and c-Fos at Ser32. Knockdown of c-Jun and c-Fos with siRNAs substantially inhibited the expression of SphK1 and FN, whereas overexpression of c-Jun and c-Fos significantly increased the expression of SphK1 and FN. Curcumin treatment greatly decreased the levels of c-Jun, c-Fos, SphK1, and FN in the kidney tissues of diabetic rats. SiRNAs targeting SphK1 and S1P2 receptor respectively inhibited the phosphorylation of c-Jun (ser63 and ser73) and c-Fos (ser32), as well as FN expression under both normal and HG conditions. Our data demonstrated that the activated SphK1–S1P signaling pathway in GMCs under diabetic conditions is closely associated with AP-1 to form a positive feedback loop. This positive feedback loop functions as an important molecular basis for the sustained activation of SphK1–S1P pathway and increased FN expression that lead to the initiation and progression of DN.

Increased plasma sphingosine-1-phosphate in obese individuals and its capacity to increase the expression of plasminogen activator inhibitor-1 in adipocytes

Concentrations of plasminogen activator inhibitor-1 (PAI-1) are increased in obese individuals. One source of PAI-1 is adipocytes. Hypoxia develops within adipose tissue as it expands, presumably contributing to increased levels of sphingosine-1-phosphate (S1P). S1P is a breakdown product of sphingosine, ubiquitous in cell membranes. We have shown previously that S1P increases the expression of PAI-1 in human liver-derived cell line. In the present study, we aimed to determine whether hypoxia induces S1P in adipocytes, thereby potentially contributing to an increase in PAI-1 and hence constraints on fibrinolysis associated with obesity. Mouse 3T3-L1 adipocytes were exposed to CoCl2 to simulate hypoxia. Assays were performed for PAI-1 mRNA (quantitative PCR) and S1P (high-performance liquid chromatography). The physiologic concentration of S1P increased PAI-1 mRNA expression. The S1P2 receptor antagonist attenuated the increase in PAI-1. Adipocytes expressed sphingosine kinase 1/2 (SPHK1/2) and S1P lyase, key enzymes involved in S1P production and degradation. Hypoxia increased SPHK activity and decreased S1P lyase mRNA. Hypoxia reduced cytosolic sphingosine and increased S1P release into conditioned medium. Inhibitors of ABCA1 and ABCC1 reduced the release of S1P into conditioned media. In obese patients with uncomplicated dyslipidemia and hypertension, plasma S1P was increased compared with that in nonobese and lean individuals. Hypoxia in adipose tissue of obesity can promote elaboration of S1P that binds to S1P2 receptors in an autocrine or a paracrine manner. S1P potentially contributes toward increased expression of PAI-1 and consequent constraints on fibrinolysis. S1P production and extracellular transport provide an attractive target for therapy to attenuate impaired fibrinolysis associated with obesity.

Role and Regulation Of Erythrocyte Sphingosine Kinase 1 Activity In Normal and Sickle Cell Disease

Sickle Cell Disease (SCD) is a devastating genetic disorder attacking red blood cells (RBCs) and affecting millions of humans worldwide. The Glu/Val mutation in the sixth amino acid of β-globin leads to the polymerization of deoxygenated sickle hemoglobin and subsequent sickling, which initiates the disease. Although SCD has been studied for more than a century, factors that contribute to sickling remain unclear. Our lab recently conducted non-biased metabolomic screening and identified that the levels of a small signaling lipid, sphingosine 1-phosphate (S1P), were dramatically increased in SCD transgenic (Tg) mice and patients. Although S1P is enriched and stored in erythrocytes, the role of S1P in normal and sickle erythrocytes remains unknown. Here we revealed that elevated S1P is a previously unrecognized allosteric modulator collaboratively working with 2, 3-bisiphosphoglycerate (2, 3-BPG) to facilitate oxygen release and thereby triggers sickling. Subsequently, we found that the enzymatic activity of sphingosine kinase 1 (Sphk1), which is the only enzyme producing S1P inside red blood cell (RBCs), is significantly elevated in SCD Tg mice and patients. Intriguingly, we found that hypoxia condition significantly increases Sphk1 activity and decreases hemoglobin oxygen (O2) binding affinity in WT mice but not in Sphk1–deficient mice. In a view of 1) our finding that SphK1 activity is induced by hypoxia; 2) our recent finding that excessive adenosine signaling through the A2B adenosine receptor (ADORA2B) promoting sickling by induction 2,3-BPG (Zhang, et al, Nature Medicine, 2011) and 3) the fact that adenosine is a signaling nucleoside that elicits many physiological effects via its receptors under hypoxic conditions, we hypothesized that adenosine functions via its receptors regulating Sphk1 activity and S1P production in erythrocytes. To test this hypothesis, we conducted both pharmacological and genetic studies. First, we found that adenosine directly induces SphK1 activities in cultured primary mouse and human normal erythrocytes. Next, we found that genetic deletion or inhibition of ADORA2B significantly reduces adenosine-induced SphK1 activities in cultured RBCs. Extending in vitro studies to in vivo experiments, we showed that excess circulating adenosine in adenosine deaminase (ADA, adenosine degrading enzyme)-deficient mice leads to significantly increased erythrocyte SphK1 activities. Similar to in vitro studies, we further found that specific deletion of ADORA2B in ado-/-(i.e ado-/-/adora2b-/- double deficient mice) abolishes excess adenosine-induced SphK1 activities in RBCs. Mechanistically, we further revealed that extralcellular signal regulated kinase (ERK) and protein kinase A (PKA) function downstream of ADORA2B underlying adenosine-induced erythrocyte Sphk1 activity. Overall, our studies demonstrate that 1) S1P is an allosteric modulator to induce O2 release and trigger sickling; 2) elevated adenosine functions via ADORA2B coupled with PKA and ERK signaling network responsible for elevated erythrocyte SphK1 activities and S1P production. Therefore, our findings reveal a previously unrecognized role of SphK1-S1P in erythrocyte physiology and novel mechanisms regulating its activities, add a new insight to the pathophysiology of SCD and open up new therapies for the disease. Disclosures:No relevant conflicts of interest to declare.

Targeting Sphingosine Kinase Induces Apoptosis and Regression Of Virus-Associated Lymphoma In Vivo

Background and Specific Aim Sphingosine kinase (SphK) is overexpressed by a variety of cancers, and its phosphorylation of sphingosine results in accumulation of sphingosine-1-phosphate (S1P) and activation of anti-apoptotic signal transduction. Existing data indicate a role for S1P in viral pathogenesis, but roles for SphK and S1P in virus-associated cancer progression have not been defined. The Kaposi’s sarcoma-associated herpesvirus (KSHV) is the causative agent of primary effusion lymphoma (PEL)—a rapidly progressive tumor arising in body cavities which incurs a median survival time of around 6 months with standard therapeutic approaches. ABC294640 is an orally bioavailable small molecule inhibitor of SphK under evaluation in early-phase clinical trials, although no pre-clinical or clinical data are available for this agent for hematologic or virus-associated malignancies. Therefore, we sought to determine whether ABC294640 displays inhibitory effects for HIV/KSHV+ patient-derived PEL cells in vitro and in vivo, as well as potential mechanisms through which SphK regulates KSHV pathogenesis. Methodology Complementary in vitro assays were undertaken using RNAi and ABC294640 for targeting SphK1 and SphK2 in HIV/KSHV+ patient-derived PEL cell lines (uninfected B cell tumor lines were used as controls). qRT-PCR and immunoblots were used to quantify KSHV gene expression and signal transduction, respectively; MTT assays and flow cytometry were used to assess metabolic activity and apoptosis; and mass spectrometry was used to quantify different bioactive sphingolipid intermediates associated with SphK activity. ABC294640 was used in a murine PEL xenograft model to assess the effects of SphK inhibition on KSHV+ lymphoma progression in vivo. Results and Conclusions We find that targeting SphK induces caspase cleavage and apoptosis for KSHV+ patient-derived PEL cells in the presence or absence of co-infection with the Epstein-Barr virus (EBV), whereas uninfected B cell tumor lines are less readily affected. Validating these results, we find that systemic administration of ABC294640 induces tumor regression in the PEL xenograft model. Complimentary ex vivo and in vitro analyses revealed that ABC294640 suppresses constitutive signal transduction associated with proliferation and survival of PEL cells, and increases intracellular accumulation of pro-apoptotic sphingolipid intermediates as well as KSHV lytic genes previously associated with cancer cell death. These results justify additional studies to identify mechanisms for SphK and S1P regulation of virus-associated PEL pathogenesis. Importantly, they also justify evaluation of ABC294640 in clinical trials as a single agent, or in combination with existing approaches, for the treatment of PEL and possibly other malignancies associated with oncogenic viruses. Disclosures: No relevant conflicts of interest to declare.

Sphingosine Kinases Are Not Required for Inflammatory Responses in Macrophages

Sphingosine kinases (Sphks), which catalyze the formation of sphingosine 1-phosphate (S1P) from sphingosine, have been implicated as essential intracellular messengers in inflammatory responses. Specifically, intracellular Sphk1-derived S1P was reported to be required for NFκB induction during inflammatory cytokine action. To examine the role of intracellular S1P in the inflammatory response of innate immune cells, we derived murine macrophages that lack both Sphk1 and Sphk2 (MΦ Sphk dKO). Compared with WT counterparts, MΦ Sphk dKO cells showed marked suppression of intracellular S1P levels whereas sphingosine and ceramide levels were strongly up-regulated. Cellular proliferation and apoptosis were similar in MΦ Sphk dKO cells compared with WT counterparts. Treatment of WT and MΦ Sphk dKO with inflammatory mediators TNFα or Escherichia coli LPS resulted in similar NFκB activation and cytokine expression. Furthermore, LPS-induced inflammatory responses, mortality, and thioglycolate-induced macrophage recruitment to the peritoneum were indistinguishable between MΦ Sphk dKO and littermate control mice. Interestingly, autophagic markers were constitutively induced in bone marrow-derived macrophages from Sphk dKO mice. Treatment with exogenous sphingosine further enhanced intracellular sphingolipid levels and autophagosomes. Inhibition of autophagy resulted in caspase-dependent cell death. Together, these data suggest that attenuation of Sphk activity, particularly Sphk2, leads to increased intracellular sphingolipids and autophagy in macrophages.

Morin reduces hepatic inflammation-associated lipid accumulation in high fructose-fed rats via inhibiting sphingosine kinase 1/sphingosine 1-phosphate signaling pathway

SphK1/S1P signaling pathway is involved in the development of hepatic inflammation and injury. But its role in high fructose-induced NAFLD has not yet been reported. The aim of this study was to elucidate the crucial role of SphK1/S1P signaling pathway in high fructose-induced hepatic inflammation and lipid accumulation in rats. Moreover, the hepatoprotective effects of morin, a flavonoid with anti-inflammatory and anti-hyperlipedimic activities, on these hepatic changes in rats were investigated. High fructose-fed rats were orally treated with morin (30 and 60mg/kg) and pioglitazone (4mg/kg) for 8 weeks, respectively. Fructose feeding induced hyperlipidemia, and activated SphK1/S1P signaling pathway characterized by the elevation of SphK1 activity, S1P production as well as SphK1, S1PR1 and S1PR3 protein levels, which in turn caused NF-κB signaling activation to produce IL-1β, IL-6 and TNF-α and inflammation in the liver of rats. Subsequently, hepatic insulin and leptin signaling impairment and lipid metabolic disorder were observed in this animal model, resulting in liver lipid accumulation. Morin restored high fructose-induced the activation of hepatic SphK1/S1P signaling pathway in rats. Subsequently, the reduced NF-κB signaling activation by morin decreased inflammatory cytokine production, recovered insulin and leptin signaling impairment to reduce lipid accumulation and injury in the rat liver. These effects of morin were confirmed in Buffalo rat liver (BRL3A) cell model stimulated with 5mM fructose. Thus, the inhibition of hepatic SphK1/S1P signaling pathway may be a novel mechanism by which morin exerts hepatoprotection in high fructose-fed rats, possibly involving liver inflammation inhibition and lipid accumulation recovery.

Targeting sphingosine kinase 1 (SphK1) and apoptosis by colon-specific delivery formula of resveratrol in treatment of experimental ulcerative colitis in rats

Ulcerative colitis (UC) is a chronic inflammatory bowel disorder (IBD) that has an elevated risk of developing into colon cancer. In trials to develop new therapeutic alternatives for UC, it is important to fulfill modifying effects on pathogenic targets and to reach the colon in a high concentration. Thus, the current work has investigated a colon-specific delivery formula of resveratrol in targeting sphingosine kinase 1 (SphK1) and apoptotic pathways to control pathogenesis and its progression to any expected neoplasm. This work was conducted on 40 Wister albino rats equally divided into 4 groups where group I served as the normal control group. The untreated oxazolone-induced colitis in group II exhibited significant increase in SphK1 activity as well as activity of both myeloperoxidase (MPO) and caspase-3 with concomitant mild DNA fragmentation in colonic tissue. Colonic SphK1 activity showed significant positive correlation with the disease activity index (DAI) and histopathological score in this group. Comparable with treatment by the native resveratrol formula, nRes (group III), treatment by the colon-specific delivery resveratrol formula, cRes (group IV) caused significant decrease in the activity of SphK1 and MPO with massive DNA fragmentation in colonic tissue and non significant change in caspase-3 activity. The lowest DAI and histopathological score have been recorded in the group treated by the colon-specific delivery resveratrol formula. In conclusion, the anti-inflammatory and apoptotic effects of resveratrol could be attributed to its inhibitory effect on sphingosine kinase 1 (SphK1) providing a useful therapeutic tool to break the link between inflammation and carcinogenesis risk in ulcerative colitis.

Reduced sphingosine kinase 1 activity in dengue virus type-2 infected cells can be mediated by the 3′ untranslated region of dengue virus type-2 RNA

Sphingosine kinase 1 (SphK1) is a lipid kinase with important roles including regulation of cell survival. We have previously shown reduced SphK1 activity in cells with an established dengue virus type-2 (DENV-2) infection. In this study, we examined the effect of alterations in SphK1 activity on DENV-2 replication and cell death and determined the mechanisms of the reduction in SphK1 activity. Chemical inhibition or overexpression of SphK1 after established DENV-2 infection had no effect on infectious DENV-2 production, although inhibition of SphK1 resulted in enhanced DENV-2-induced cell death. Reduced SphK1 activity was observed in multiple cell types, regardless of the ability of DENV-2 infection to be cytopathic, and was mediated by a post-translational mechanism. Unlike bovine viral diarrhea virus, where SphK1 activity is decreased by the NS3 protein, SphK1 activity was not affected by DENV-2 NS3 but, instead, was reduced by expression of the terminal 396 bases of the 3' UTR of DENV-2 RNA. We have previously shown that eukaryotic elongation factor 1A (eEF1A) is a direct activator of SphK1 and here DENV-2 RNA co-localized and co-precipitated with eEF1A from infected cells. We propose that the reduction in SphK1 activity late in DENV-2-infected cells is a consequence of DENV-2 out-competing SphK1 for eEF1A binding and hijacking cellular eEF1A for its own replication strategy, rather than a specific host or virus-induced change in SphK1 to modulate viral replication. Nonetheless, reduced SphK1 activity may have important consequences for survival or death of the infected cell.

Loss of sphingosine kinase 1 predisposes to the onset of diabetes via promoting pancreatic β‐cell death in diet‐induced obese mice

Lipotoxic stress-induced β-cell death (lipotoxicity) is recognized as a key contributor to the development of type 2 diabetes mellitus (T2DM). The current study reports a critical role of sphingosine kinase 1 (SphK1) in β-cell survival under lipotoxic conditions. In an attempt to investigate the role of SphK1 in lipotoxicity in vivo, we fed Sphk1(-/-) and wild-type (WT) mice with a high-fat diet (HFD) or normal chow diet. Remarkably, while HFD-fed WT mice developed glucose intolerance and compensatory hyperinsulinemia, all HFD-fed Sphk1(-/-) mice manifested evident diabetes, accompanied by a nearly 3-fold reduction in insulin levels compared with the WT mice. Pancreatic β-cell mass was increased by 140% in HFD-fed WT mice but decreased to 50% in HFD-fed Sphk1(-/-) mice, in comparison with the chow diet control groups, respectively. Accordingly, by blocking the enzyme activity, expression of a dominant negative form of SphK1 markedly promoted palmitate-induced cell death in MIN6 and INS-1 β-cell lines. Moreover, primary islets isolated from Sphk1(-/-) mice exhibited higher susceptibility to lipotoxicity than WT controls. Of note, sphingosine 1-phosphate (S1P) profoundly abrogated lipotoxicity in β cells or the cells lacking SphK1 activity and Sphk1(-/-) islets, highlighting a pivotal role of S1P in β-cell survival under lipotoxic conditions. These findings could suggest a new therapeutic strategy for preventing β-cell death and thus the onset of T2DM.

Sphingosine kinase 1 plays a role in the upregulation of CD44 expression through extracellular signal-regulated kinase signaling in human colon cancer cells

Our previous study has shown that the activity and expression of sphingosine kinase (SPHK) regulated the sensitivity of human colon cancer cells to the chemotherapeutic oxaliplatin (L-OHP). In addition, the cancer stem cell marker CD44 increases cell resistance to anticancer drugs. Here, we use colon cancer cell lines to examine the relationship between SPHK1 activity and CD44 expression.CD44 expression was measured by western blotting and quantitative PCR in two human colon cancer cell lines: L-OHP-resistant RKO and L-OHP-sensitive HCT116. The regulation of CD44 by SPHK1 was examined by either blocking or overexpressing SPHK1 and by using an L-OHP-resistant HCT116 clone (HCT116-R).The levels of SPHK1, CD44, phosphorylated-Akt, and phosphorylated-extracellular signal-regulated kinase (ERK) were much higher in the RKO cells than in the HCT116 cells. The treatment of RKO cells with the SPHK inhibitor or SPHK1 silencing by RNA interference suppressed CD44 protein expression. SPHK1 and CD44 levels were much higher in HCT116-R cells compared with the parental HCT116 cells. Transfection of HCT116 cells with SPHK1 cDNA enhanced the expression of both CD44 and phosphorylated-ERK. The increase in the CD44 protein level was abolished by the inhibition of ERK phosphorylation. Treatment of RKO cells with the sphingosine-1-phosphate (S1P)2 receptor antagonist suppressed ERK phosphorylation and the expression of CD44 mRNA and protein. Exogenous stimulation with S1P increased ERK phosphorylation and CD44 protein expression in HCT116 cells, but treatment with an MEK inhibitor and S1P2 receptor antagonist blocked this effect.These findings indicate that SPHK1 and its product, S1P, contribute toward the regulation of CD44 protein expression through the ERK signaling pathway through S1P2 in human colon cancer cells.

Sphingosine kinase 1 enhances the proliferation and invasion of human colon cancer LoVo cells through up-regulating FAK pathway and the expression of ICAM-1 and VCAM-1

To investigate the effects of sphingosine kinase 1 (SphK1) on the proliferation, migration and invasion of human colon cancer LoVo cells, and to explore the related mechanisms. Human colon cancer LoVo cells were divided into three groups: phorbol 12-myristate 13-acetate (PMA) was used to induce the activation of SphK1 in the PMA group, N,N-dimethylsphingosine (DMS) used to suppress the activity of SphK1 in DMS group, and the cells treated with equal amount of 0.9 % NaCl instead of drugs served as the control group. The activity of SphK1 was assayed by autoradiography, the cell proliferation was assessed by MTT assay, cell migration and invasion were examined by Boyden chamber assay, concentrations of sICAM-1 and sVCAM-1 were assayed by ELISA, and RT-PCR and Western blot were used to evaluate the mRNA and protein expression in the cells. The activity of SphK1 was efficiently induced by PMA and significantly suppressed by DMS. PMA induced cell proliferation in a time- and dose-dependent manner. On the contrast, DMS suppressed cell proliferation in a time- and dose-dependent manner. After treating with PMA, the number of migrating and invasing cells were increased to 143.36 ± 8.73 and 118.46 ± 6.25, significantly higher than those of the control group (75.48 ± 6.12 and 64.19 ± 5.36). After treating with DMS, the number of migrating and invasing cells were decreased to 38.57 ± 3.24 and 32.48 ± 4.27, significantly lower than those of the control group (P < 0.01). The relative expression levels of FAK, ICAM-1 and VCAM-1 mRNA in the PMA group were 0.82 ± 0.06, 0.74 ± 0.05 and 0.89 ± 0.09, and those in the DMS group were 0.23 ± 0.02, 0.26 ± 0.03 and 0.37 ± 0.04, with significant differences between the PMA, DMS and control groups (P < 0.01). Compared with the control group, the relative expression levels of FAK and p-FAK proteins in the PMA group (0.52 ± 0.06 and 0.51 ± 0.06) were significantly elevated, and those of the DMS group (0.20 ± 0.03 and 0.09 ± 0.02) were significantly decreased. In addition, the concentrations of sICAM-1 and sVCAM-1 were significantly elevated with the activation of SphK1. On the contrary, those of the DMS group were significantly reduced with the suppression of SphK1 (Both P < 0.01). SphK1 may enhance the proliferation, migration and invasion of colon cancer LoVo cells through activating FAK pathway and up-regulating the expression of ICAM-1 and VCAM-1.

Sphingosine‐1‐phosphate signaling in inflammation and cancer

The sphingolipid metabolite sphingosine‐1‐phosphate (S1P) and the kinases that produce it have emerged as critical regulators of numerous fundamental biological processes important for inflammation and cancer. Activation of sphingosine kinases (SphKs) by a variety of agonists increases intracellular S1P. S1P can be secreted out of cells and bind to and signal through five specific G protein‐coupled receptors, designated S1PR1–5. It is now well established that this “inside‐out” signaling by S1P is important for many human diseases. The roles of the S1PRs in cell and organismal physiology will be discussed in detail and particularly their roles in chronic intestinal inflammation and colitis‐associated cancer (CAC). Focus will be on activation of SphK1 and how the SphK1‐S1P‐S1PR1 axis is at the nexus between NF‐κB and Stat3 and connects chronic inflammation and CAC. The development of inhibitors of SphK1 and small molecules that target specific subtypes of S1P receptors will also be discussed. The effectiveness of the pro‐drug FTY720 (known as Fingolimod or Gilenya), approved for the treatment of multiple sclerosis, has become the gold standard for S1P‐centric drugs, and will be used to illustrate the therapeutic value of modulating SphK1 and S1P receptor functions which holds great therapeutic promise.Supported by NIH grants R37GM043880, R01CA61774, and U19 AI077435.

Role of sphingosine kinases and sphingosine 1-phosphate in mediating adipogenesis

Recent Background: Development of obesity involves promotion of preadipocyte differrentiation. This study investigated the role that sphingosine kinases (SPHK) and ceramide-derived sphingosine 1-phosphate (S1P) play in adipocyte terminal differentiation. Materials and Methods: The mouse 3T3-L1 cell line was used as a model for adipogenesis. Cells were harvested at specific time points after initation of differentiation, and SPHK activity was measured. 3T3-L1 cells were treated with S1P and expression of early adipogenesis transcription markers was measured by real time PCR. The expression of S1P-receptors (S1PRs) during differentiation was measured. Results: SPHK activity is induced when 3T3-L1 cells are treated with insulin, dexamethasone, and isobutylmethylxanthine to induce differentiation. SPHK1 is active in preadipocytes and early in the differentiation process. Both SPHK1 and SPHK2 isozymes contribute to activity in differentiated adipocytes. Inhibition of SPHK1 attenuates adipocyte differentiation; however, extracellular S1P does not rescue the effect of SPHK1 inhibition on adipogenesis. Although treatment of preadipocytes with S1P induced message expression of the early adipogenesis transcription factor CC AAT/ binding proteinalpha, continued treatment did not fully support the development of differentiated adipocytes. Sphingosine 1-phosphate receptors (S1PRs) are expressed in preadipocytes and message expression declines markedly during adipocyte differentiation. Conclusion: These results demonstrate that the contribution of SPHK and S1P to adipogenesis is mediated primarily through biphasic activation of SPHK1 and 2 with extracellular S1P and S1PRs playing little role during preadipocyte differentiation.

Sphingosine kinase 1 promotes tumor progression and confers malignancy phenotypes of colon cancer by regulating the focal adhesion kinase pathway and adhesion molecules

Studies suggest a tumor-promoting function of sphingosine kinase 1 (SphK1) in some types of human tumors, however, its effect on colon cancer is still unclear. The aims of this study were to investigate the roles of SphK1 in the progression and tumor cell phenotypic changes in colon cancer. Moreover, the focal adhesion kinase (FAK) pathway and the expression of intercellular adhesion molecule‑1 (ICAM‑1) and vascular cell adhesion molecule‑1 (VCAM‑1) were detected to explore the mechanisms of SphK1 action. In this study, the expression of SphK1, FAK and phospho-FAK (p-FAK) was analyzed in 66 surgical specimens of primary colon cancer and matched adjacent normal tissues by immunohistochemistry and western blotting. In addition, N,N-dimethylsphingosine (DMS), SphK1 DNA and shRNA transfection were used to regulate the expression and activity of SphK1 in the LOVO colon cancer cell line. Tumor cell phenotypic changes were analyzed by cell viability, invasion and apoptosis assays. Results showed that the expression of SphK1, FAK and p-FAK in colon cancer tissues were significantly stronger compared to those in matched normal tissues. There was a close correlation between the expression of SphK1 and FAK or p-FAK and the co-expression of SphK1, FAK and p-FAK significantly associated with histological grade, Dukes' stage, lymph node metastasis and distant metastasis. Overexpression of SphK1 after DNA transfection enhanced tumor cell viability and invasiveness, but suppressed cell apoptosis. In contrast, suppression of SphK1 by DMS and shRNA reduced tumor cell viability and invasiveness, but promoted cell apoptosis. The expression of FAK, p-FAK, ICAM-1 and VCAM-1 in LOVO cells were increased with the overexpression of SphK1 but decreased with the suppression of SphK1. These findings indicate that SphK1 regulates tumor cell proliferation, apoptosis and invasion, which ultimately contributes to tumor progression and malignancy phenotype in colon cancer. FAK pathway, ICAM-1 and VCAM-1 may play critical roles in this SphK1‑mediated effect.