Roles of sphingosine 1-phosphate on tumorigenesis

Sphingosine-1-phosphate related signalling pathways manipulating virus replication

Viruses can create a unique cellular environment that facilitates replication and transmission. Sphingosine kinases (SphKs) produce sphingosine-1-phosphate (S1P), a bioactive sphingolipid molecule that performs both physiological and pathological effects primarily by activating a subgroup of the endothelial differentiation gene family of G-protein coupled cell surface receptors known as S1P receptors (S1PR1-5). A growing body of evidence indicates that the SphK/S1P axis is crucial for regulating cellular activities in virus infections like respiratory viruses, enteroviruses, hepatitis viruses, herpes viruses, and arboviruses replicate. Depending on the type of virus, pro- or anti-viral activities of the SphK/S1P axis sometimes rely on the host immune system and sometimes directly through intracellular signalling pathways or cell proliferation. Recent research has shown novel roles of S1P and SphK in viral replication. Sphingosine kinase isoforms (SphK1 and SphK2) levels can be manipulated by several viruses to promote the effects that are expected. Regulation of cellular signalling pathways plays a significant role in the mechanism. The purpose of this review is to provide insight of the characters played by the SphK/S1P axis throughout diverse viral infection processes. We then assess potential therapeutic methods that are based on S1P signalling and metabolism during viral infections.

Activation of yes-associated protein mediates sphingosine-1-phosphate-induced proliferation and migration of pulmonary artery smooth muscle cells and its potential mechanisms

The aims of the present study were to examine the molecular mechanisms underlying sphingosine-1-phosphate (S1P)-induced rat pulmonary artery smooth muscle cells (PASMCs) proliferation/migration and to determine the effect of yes-associated protein (YAP) activation on S1P-induced PASMCs proliferation/migration and its potential mechanisms. S1P induced YAP dephosphorylation and nuclear translocation, upregulated microRNA-130a/b (miR-130a/b) expression, reduced bone morphogenetic protein receptor 2 (BMPR2), and inhibitor of DNA binding 1(Id1) expression, and promoted PASMCs proliferation and migration. Pretreatment of cells with Rho-associated protein kinase (ROCK) inhibitor Y27632 suppressed S1P-induced YAP activation, miR-130a/b upregulation, BMPR2/Id1 downregulation, and PASMCs proliferation/migration. Knockdown of YAP using small interfering RNA also suppressed S1P-induced alterations of miR-130a/b, BMPR2, Id1, and PASMCs behavior. In addition, luciferase reporter assay indicated that miR-130a/b directly regulated BMPR2 expression in PASMCs. Inhibition of miR-130a/b functions by anti-miRNA oligonucleotides attenuated S1P-induced BMPR2/Id1 downregulation and the proliferation and migration of PASMCs. Taken together, our study indicates that S1P induces activation of YAP through ROCK signaling and subsequently increases miR-130a/b expression, which, in turn, downregulates BMPR2 and Id1 leading to PASMCs proliferation and migration.

Prognostic Significance of Cytoplasmic SPNS2 Expression in Patients with Oral Squamous Cell Carcinoma

Background and Objectives: Oral squamous cell carcinoma (OSCC) is a malignant disease with a particularly high incidence in Taiwan. Our objective in this study was to elucidate the involvement of sphingolipid transporter 2 (SPNS2) expression and SPNS2 protein expression in the clinicopathological indexes and the clinical outcomes of OSCC patients. Materials and Methods: Immunohistochemistry analysis was performed for SPNS2 protein expression in samples from 264 cases of OSCC. Correlations of SPNS2 expression with clinicopathological variables and patient survival were analyzed. Results: Our results revealed that the cytoplasmic protein expression of SPNS2 in OSCC tissue specimens was lower than in normal tissue specimens. Negative cytoplasmic protein expression of SPNS2 was significantly correlated with T status and stage. Kaplan-Meier survival curve analysis revealed that negative cytoplasmic SPNS2 expression was predictive of poorer overall survival of OSCC patients in stage III/IV. We also determined that low SPNS2 expression was an independent prognostic factor related to overall survival among OSCC patients in stage III/IV from univariate Cox proportional hazard models. Multivariate Cox proportional hazard models revealed that cytoplasmic SPNS2 expression, T status, lymph node metastasis, and histological grade were independent prognostic factors for survival. Conclusions: Overall, this study determined that SPNS2 protein may be a useful prognostic marker for OSCC patients and potential therapeutic target for OSCC treatment.

Spinster homolog 2 in cancers, its functions and mechanisms

Spinster homolog 2 (SPNS2) is a multi-transmembrane transporter, widely located in the cell membrane and organelle membranes. It transports sphingosine-1-phosphate (S1P) into the extracellular space and the circulatory system, thus alters the concentration and the distribution of S1P, sphingosine-1-phosphate receptor (S1PRs) and S1P related enzymes, meaning that it exerts its functions via S1P signaling pathways. Studies also show that ectopic SPNS2 mediates parts of the physiological process of the cells. As of now, SPNS2 has been reported to participate in physiological processes such as angiogenesis, embryonic development, immune response and metabolisms. It is also associated with the transformation from inflammation to cancer as well as the proliferation and metastasis of cancer cells. In this review, we summarize the functions and the mechanisms of SPNS2 in the pathogenesis of cancer to provide new insights for the diagnosis and the treatments of cancer.

Discovery of Harmaline as a Potent Inhibitor of Sphingosine Kinase-1: A Chemopreventive Role in Lung Cancer

The sphingosine kinase-1/sphingosine-1-phosphate pathway is linked with the cancer progression and survival of the chemotherapy-challenged cells. Sphingosine kinase-1 (SphK1) has emerged as an attractive drug target, but their inhibitors from natural sources are limited. In this study, we have chosen harmaline, one of the β-carboline alkaloids, and report its mechanism of binding to SphK1 and subsequent inhibition. Molecular docking combined with fluorescence binding studies revealed that harmaline binds to the substrate-binding pocket of SphK1 with an appreciable binding affinity and significantly inhibits the kinase activity of SphK1 with an IC50 value in the micromolar range. The cytotoxic effect of harmaline on non-small-cell lung cancer cells by MTT assay was found to be higher for H1299 compared to A549. Harmaline induces apoptosis in non-small-cell lung carcinoma cells (H1299 and A549), possibly via the intrinsic pathway. Our findings suggest that harmaline could be implicated as a scaffold for designing potent anticancer molecules with SphK1 inhibitory potential.

Lipid Mediators Regulate Pulmonary Fibrosis: Potential Mechanisms and Signaling Pathways

Idiopathic pulmonary fibrosis (IPF) is a progressive lung disease of unknown etiology characterized by distorted distal lung architecture, inflammation, and fibrosis. The molecular mechanisms involved in the pathophysiology of IPF are incompletely defined. Several lung cell types including alveolar epithelial cells, fibroblasts, monocyte-derived macrophages, and endothelial cells have been implicated in the development and progression of fibrosis. Regardless of the cell types involved, changes in gene expression, disrupted glycolysis, and mitochondrial oxidation, dysregulated protein folding, and altered phospholipid and sphingolipid metabolism result in activation of myofibroblast, deposition of extracellular matrix proteins, remodeling of lung architecture and fibrosis. Lipid mediators derived from phospholipids, sphingolipids, and polyunsaturated fatty acids play an important role in the pathogenesis of pulmonary fibrosis and have been described to exhibit pro- and anti-fibrotic effects in IPF and in preclinical animal models of lung fibrosis. This review describes the current understanding of the role and signaling pathways of prostanoids, lysophospholipids, and sphingolipids and their metabolizing enzymes in the development of lung fibrosis. Further, several of the lipid mediators and enzymes involved in their metabolism are therapeutic targets for drug development to treat IPF.

S1PR1 as a Novel Promising Therapeutic Target in Cancer Therapy

Sphingosine-1-phosphate (S1P) can regulate several physiological and pathological processes. S1P signaling via its cell surface receptor S1PR1 has been shown to enhance tumorigenesis and stimulate growth, expansion, angiogenesis, metastasis, and survival of cancer cells. S1PR1-mediated tumorigenesis is supported and amplified by activation of downstream effectors including STAT3, interleukin-6, and NF-κB networks. S1PR1 signaling can also trigger various other signaling pathways involved in carcinogenesis including activation of PI3K/AKT, MAPK/ERK1/2, Rac, and PKC/Ca, as well as suppression of cyclic adenosine monophosphate (cAMP). It also induces immunological tolerance in the tumor microenvironment, while the immunosuppressive function of S1PR1 can also lead to the generation of pre-metastatic niches. Some tumor cells upregulate S1PR1 signaling pathways, which leads to drug resistant cancer cells, mainly through activation of STAT3. This signaling pathway is also implicated in some inflammatory conditions leading to the instigation of inflammation-driven cancers. Furthermore, it can also increase survival via induction of anti-apoptotic pathways, for instance, in breast cancer cells. Therefore, S1PR1 and its signaling pathways can be considered as potential anti-tumor therapeutic targets, alone or in combination therapies. Given the oncogenic nature of S1PR1 and its distribution in a variety of cancer cell types along with its targeting advantages over other molecules of this family, S1PR1 should be considered a favorable target in therapeutic approaches to cancer. This review describes the role of S1PR1 in cancer development and progression, specifically addressing breast cancer, glioma, and hematopoietic malignancies. We also discuss the potential use of S1P signaling modulators as therapeutic targets in cancer therapy.

Validated LC-MS/MS method of Sphingosine 1-phosphate quantification in human serum for evaluation of response to radiotherapy in lung cancer

Background

Sphingosine 1‐phosphate (S1P), a bioactive lipid, has been shown to mediate cancer processes. Therefore, accurate qualitative and quantitative determination is essential. The current assay method is still cumbersome to be of practical use worldwide and the aim of this study was therefore to develop a fast, accurate, precise and efficient LC‐MS/MS method for targeted analyses of S1P in serum samples.

Methods

Liquid chromatography‐tandem mass spectrometry (LC‐MS/MS) is an established method used for monitoring and analyzing S1P levels in serum. We determined the level of serum S1P in 256 patients with lung cancer and 36 healthy donors, and used Spearman';s rank correlation analysis to evaluate the difference in serum S1P levels between radiotherapy and nonradiotherapy patients.

Results

Standard curves were linear over ranges of 25–600 ng/mL for S1P with correlation coefficient (r²) greater than 0.9996. The lower limit of quantifications (LLOQs) was 25 ng/mL. The intra‐ and interbatch precisions and accuracy was less than 10% for S1P. The recoveries of the method were found to be 80%–98%. Serum S1P levels in healthy donors were different from those in patients (P < 0.001). Of 256 lung cancer patients, 124 (48.4%) received radiotherapy and were identified to have concomitant low serum S1P levels (222.13 ± 48.63), whereas 132 (51.6%) who had not received radiotherapy were identified to have high levels (315.16 ± 51.06). The serum S1P levels were therefore associated with radiotherapy (Spearman's Rho = −0.653, P < 0.001).

Conclusions

Our results indicated that this new LC‐MS/MS method is rapid, sensitive, specific and reliable for the quantification of S1P levels in serum samples. The level of S1P in serum samples of patients with lung cancer who received radiotherapy was significantly lower than that in patients who did not receive radiotherapy.

Key points

An improved method was established to quantify S1P levels in human serum by LC‐MS/MS, which enabled the change in serum S1P levels in lung cancer patients to be monitored, in combination with radiotherapy, and their clinical significance to be analyzed.

S1P Signaling in the Tumor Microenvironment

Sphingosine-1-phosphate (S1P), together with other phosphosphingolipids, has been found to regulate complex cellular function in the tumor microenvironment (TME) where it acts as a signaling molecule that participates in cell-cell communication. S1P, through intracellular and extracellular signaling, was found to promote tumor growth, angiogenesis, chemoresistance, and metastasis; it also regulates anticancer immune response, modulates inflammation, and promotes angiogenesis. Interestingly, cancer cells are capable of releasing S1P and thus modifying the behavior of the TME components in a way that contributes to tumor growth and progression. Therefore, S1P is considered an important therapeutic target, and several anticancer therapies targeting S1P signaling are being developed and tested in clinics.

Sphingosine 1-Phosphate Receptors and Metabolic Enzymes as Druggable Targets for Brain Diseases

The central nervous system is characterized by a high content of sphingolipids and by a high diversity in terms of different structures. Stage- and cell-specific sphingolipid metabolism and expression are crucial for brain development and maintenance toward adult age. On the other hand, deep dysregulation of sphingolipid metabolism, leading to altered sphingolipid pattern, is associated with the majority of neurological and neurodegenerative diseases, even those totally lacking a common etiological background. Thus, sphingolipid metabolism has always been regarded as a promising pharmacological target for the treatment of brain disorders. However, any therapeutic hypothesis applied to complex amphipathic sphingolipids, components of cellular membranes, has so far failed probably because of the high regional complexity and specificity of the different biological roles of these structures. Simpler sphingosine-based lipids, including ceramide and sphingosine 1-phosphate, are important regulators of brain homeostasis, and, thanks to the relative simplicity of their metabolic network, they seem a feasible druggable target for the treatment of brain diseases. The enzymes involved in the control of the levels of bioactive sphingoids, as well as the receptors engaged by these molecules, have increasingly allured pharmacologists and clinicians, and eventually fingolimod, a functional antagonist of sphingosine 1-phosphate receptors with immunomodulatory properties, was approved for the therapy of relapsing-remitting multiple sclerosis. Considering the importance of neuroinflammation in many other brain diseases, we would expect an extension of the use of such analogs for the treatment of other ailments in the future. Nevertheless, many aspects other than neuroinflammation are regulated by bioactive sphingoids in healthy brain and dysregulated in brain disease. In this review, we are addressing the multifaceted possibility to address the metabolism and biology of bioactive sphingosine 1-phosphate as novel targets for the development of therapeutic paradigms and the discovery of new drugs.

Sphingolipids in neurodegeneration (with focus on ceramide and S1P)

For many decades, research on sphingolipids associated with neurodegenerative disease focused on alterations in glycosphingolipids, particularly glycosylceramides (cerebrosides), sulfatides, and gangliosides. This seemed quite natural since many of these glycolipids are constituents of myelin and accumulated in lipid storage diseases (sphingolipidoses) resulting from enzyme deficiencies in glycolipid metabolism. With the advent of recognizing ceramide and its derivative, sphingosine-1-phosphate (S1P), as key players in lipid cell signaling and regulation of cell death and survival, research focus shifted toward these two sphingolipids. Ceramide and S1P are invoked in a plethora of cell biological processes participating in neurodegeneration such as ER stress, autophagy, dysregulation of protein and lipid transport, exosome secretion and neurotoxic protein spreading, neuroinflammation, and mitochondrial dysfunction. Hence, it is timely to discuss various functions of ceramide and S1P in neurodegenerative disease and to define sphingolipid metabolism and cell signaling pathways as potential targets for therapy.

Evaluation of chemotherapeutic and cancer-protective properties of sphingosine and C2-ceramide in a human breast stem cell derived carcinogenesis model

The overall goal of the present study was to evaluate the chemotherapeutic and cancer-protective properties of D-erythro-sphingosine (sphingosine) and C₂-ceramide using a human breast epithelial cell (HBEC) culture system, which represents multiple-stages of breast carcinogenesis. The HBEC model includes Type I HBECs (normal stem), Type II HBECs (normal differentiated) and transformed cells (immortal/non-tumorigenic cells and tumorigenic cells, which are transformed from the same parental normal stem cells). The results of the present study indicate that sphingosine preferentially inhibits proliferation and causes death of normal stem cells (Type I), tumorigenic cells, and MCF7 breast cancer cells, but not normal differentiated cells (Type II). In contrast to the selective anti-proliferative effects of sphingosine, C₂-ceramide inhibits proliferation of normal differentiated cells as well as normal stem cells, tumorigenic cells, and MCF7 cancer cells with similar potency. Both sphingosine and C₂-ceramide induce apoptosis in tumorigenic cells. Among the sphingosine stereoisomers (D-erythro, D-threo, L-erythro, and L-threo) and sphinganine that were tested, L-erythro-sphingosine most potently inhibits proliferation of tumorigenic cells. The inhibition of breast tumorigenic/cancer cell proliferation by sphingosine was accompanied by inhibition of telomerase activity. Sphingosine at non-cytotoxic concentrations, but not C₂-ceramide, induces differentiation of normal stem cells (Type I), thereby reducing the number of stem cells that are more susceptible to neoplastic transformation. To the best of our knowledge, the present study demonstrates one of the first results that sphingosine can be a potential chemotherapeutic and cancer-protective agent, whereas C₂-ceramide is not an ideal chemotherapeutic and cancer-protective agent due to its anti-proliferative effects on Type II HBECs and its inability to induce the differentiation of Type I to Type II HBECs.

Sphingosine-1-phosphate induced epithelial-mesenchymal transition of hepatocellular carcinoma via an MMP-7/ syndecan-1/TGF-β autocrine loop

Sphingosine-1-phosphate (S1P) induces epithelial–mesenchymal transition (EMT) in hepatocellular carcinoma (HCC). However, its underlying mechanism remains largely unknown. In the present study, we investigated the correlation between S1P and syndecan-1 in HCC, the molecular mechanism involved, as well as their roles in EMT of HCC. Results revealed a high serum S1P level presents in patients with HCC, which positively correlated with the serum syndecan-1 level. A significant inverse correlation existed between S1P₁ and syndecan-1 in HCC tissues. S1P elicits activation of the PI3K/AKT signaling pathways via S1P₁, which triggers HPSE, leading to increases in expression and activity of MMP-7 and leading to shedding and suppression of syndecan-1. The loss of syndecan-1 causes an increase in TGF-β1 production. The limited chronic increase in TGF-β1 can convert HCC cells into a mesenchymal phenotype via establishing an MMP-7/Syndecan-1/TGF-β autocrine loop. Finally, TGF-β1 and syndecan-1 are essential for S1P-induced epithelial to mesenchymal transition. Taken together, our study demonstrates that S1P induces advanced tumor phenotypes of HCC via establishing an MMP-7/syndecan-1/TGF-β1 autocrine loop, and implicates targetable S1P₁-PI3K/AKT-HPSE-MMP-7 signaling axe in HCC metastasis.

SPHK1 (sphingosine kinase 1) induces epithelial-mesenchymal transition by promoting the autophagy-linked lysosomal degradation of CDH1/E-cadherin in hepatoma cells

SPHK1 (sphingosine kinase 1), a regulator of sphingolipid metabolites, plays a causal role in the development of hepatocellular carcinoma (HCC) through augmenting HCC invasion and metastasis. However, the mechanism by which SPHK1 signaling promotes invasion and metastasis in HCC remains to be clarified. Here, we reported that SPHK1 induced the epithelial-mesenchymal transition (EMT) by accelerating CDH1/E-cadherin lysosomal degradation and facilitating the invasion and metastasis of HepG2 cells. Initially, we found that SPHK1 promoted cell migration and invasion and induced the EMT process through decreasing the expression of CDH1, which is an epithelial marker. Furthermore, SPHK1 accelerated the lysosomal degradation of CDH1 to induce EMT, which depended on TRAF2 (TNF receptor associated factor 2)-mediated macroautophagy/autophagy activation. In addition, the inhibition of autophagy recovered CDH1 expression and reduced cell migration and invasion through delaying the degradation of CDH1 in SPHK1-overexpressing cells. Moreover, the overexpression of SPHK1 produced intracellular sphingosine-1-phosphate (S1P). In response to S1P stimulation, TRAF2 bound to BECN1/Beclin 1 and catalyzed the lysine 63-linked ubiquitination of BECN1 for triggering autophagy. The deletion of the RING domain of TRAF2 inhibited autophagy and the interaction of BECN1 and TRAF2. Our findings define a novel mechanism responsible for the regulation of the EMT via SPHK1-TRAF2-BECN1-CDH1 signal cascades in HCC cells. Our work indicates that the blockage of SPHK1 activity to attenuate autophagy may be a promising strategy for the prevention and treatment of HCC.

Imipramine blocks acute silicosis in a mouse model

BACKGROUND

Inhalation of crystalline silica is associated with pulmonary inflammation and silicosis. Although silicosis remains a prevalent health problem throughout the world, effective treatment choices are limited. Imipramine (IMP) is a FDA approved tricyclic antidepressant drug with lysosomotropic characteristics. The aim of this study was to evaluate the potential for IMP to reduce silicosis and block phagolysosome membrane permeabilization.

METHODS

C57BL/6 alveolar macrophages (AM) exposed to crystalline silica ± IMP in vitro were assessed for IL-1β release, cytotoxicity, particle uptake, lysosomal stability, and acid sphingomyelinase activity. Short term (24 h) in vivo studies in mice instilled with silica (± IMP) evaluated inflammation and cytokine release, in addition to cytokine release from ex vivo cultured AM. Long term (six to ten weeks) in vivo studies in mice instilled with silica (± IMP) evaluated histopathology, lung damage, and hydroxyproline content as an indicator of collagen accumulation.

RESULTS

IMP significantly attenuated silica-induced cytotoxicity and release of mature IL-1β from AM in vitro. IMP treatment in vivo reduced silica-induced inflammation in a short-term model. Furthermore, IMP was effective in blocking silica-induced lung damage and collagen deposition in a long-term model. The mechanism by which IMP reduces inflammation was explored by assessing cellular processes such as particle uptake and acid sphingomyelinase activity.

CONCLUSIONS

Taken together, IMP was anti-inflammatory against silica exposure in vitro and in vivo. The results were consistent with IMP blocking silica-induced phagolysosomal lysis, thereby preventing cell death and IL-1β release. Thus, IMP could be therapeutic for silica-induced inflammation and subsequent disease progression as well as other diseases involving phagolysosomal lysis.

Sphingosine-1-phosphate suppresses chondrosarcoma metastasis by upregulation of tissue inhibitor of metalloproteinase 3 through suppressing miR-101 expression

Chondrosarcoma is the second most common primary malignancy form of bone cancer, exhibiting resistance to chemotherapy and radiation therapy as well as developing high metastasis ability in late‐stage tumors. Thus, understanding the metastatic processes of chondrosarcoma is considered a strategy for the treatment of this disease. Sphingosine 1‐phosphate (S1P), a bioactive sphingolipid, is produced intracellularly by sphingosine kinase (SphK) and is regarded as a second signaling molecule that regulates inflammation, proliferation, angiogenesis, and metastasis. However, the effect of S1P on chondrosarcoma remains uncertain. As demonstrated by the transwell, immunoblotting, and real‐time PCR analyses, we found that S1P inhibited cell migration and MMP‐2 expression through the upregulation of the tissue inhibitor of metalloproteinase‐3 (TIMP‐3) expression in human chondrosarcoma cells. Additionally, we also showed that microRNA (miRNA)‐101, which targets the 3′ untranslated region (3′UTR) of TIMP‐3, decreased significantly following S1P treatment. After transfection with miR‐101 mimics, the S1P‐regulated cell migration and TIMP‐3 expression were both reversed. Furthermore, we also showed that the S1P‐inhibited cell migration is mediated through the c‐Src/MEK/ERK signaling axis. Meanwhile, the in vivo study indicated that overexpression of SphK1 decreases chondrosarcoma metastasis to the lungs. Our results illustrate the clinical significance between SphK1, TIMP‐3, and miR‐101 in human chondrosarcoma patients. Taken together, our results suggest that S1P and miR‐101 may prove to be potential therapeutic targets for future chondrosarcoma treatment.

High-Resolution Expression Profiling of Peripheral Blood CD8+ Cells in Patients with Multiple Sclerosis Displays Fingolimod-Induced Immune Cell Redistribution

Fingolimod, a sphingosine-1-phosphate (S1P) receptor modulator, is an oral drug approved for the treatment of active relapsing-remitting multiple sclerosis (RRMS). It selectively inhibits the egress of lymphocytes from lymph nodes. We studied the changes in the transcriptome of peripheral blood CD8⁺ cells to unravel the effects at the molecular level during fingolimod therapy. We separated CD8⁺ cells from the blood of RRMS patients before the first dose of fingolimod as well as 24 h and 3 months after the start of therapy. Changes in the expression of coding and non-coding genes were measured with high-density Affymetrix Human Transcriptome Array (HTA) 2.0 microarrays. Differentially expressed genes in response to therapy were identified by t test and fold change and analyzed for their functions and molecular interactions. No gene was expressed at significantly higher or lower levels 24 h after the first administration of fingolimod compared to baseline. However, after 3 months of therapy, 861 transcripts were found to be differentially expressed, including interleukin and chemokine receptors. Some of the genes are associated to the S1P pathway, such as the receptor S1P5 and the kinase MAPK1, which were significantly increased in expression. The fingolimod-induced transcriptome changes reflect a shift in the proportions of CD8⁺ T cell subsets, with CCR7^- effector memory T cells being relatively increased in frequency in the blood of fingolimod-treated patients. In consequence, CCR7 mRNA levels were reduced by >80 % and genes involved in T cell activation and lymphocyte cytotoxicity were increased in expression. Gene regulatory programs caused by downstream S1P signaling had only minor effects.

Potential signaling pathway involved in sphingosine-1-phosphate-induced epithelial-mesenchymal transition in cancer

The developmental process of epithelial-mesenchymal transition (EMT) occurs when epithelial cells acquire invasive mesenchymal cell characteristics, and the activation of this process has been indicated to be involved in tumor progression. EMT could be induced by growth factors, cytokines and matrix metalloproteinases (MMPs). sphingosine-1-phosphate (S1P) is a biologically-active lipid that plays an important role in cancer metastasis. S1P also contributes to the activation of EMT. However, the mechanism underlying S1P-induced EMT is unclear. Increased evidence has demonstrated that the cell surface glycocalyx is closed associated with S1P and plays an important role in tumor progression, suggesting that S1P-induced EMT could be Snail-MMP signaling-dependent. Thus, we hypothesize that an S1P-glycocalyx-Snail-MMP signaling axis mediates S1P-induced EMT. This is an essential step towards improved understanding of the underlying mechanism involved in S1P-regulted EMT, and the development of novel diagnostic and anticancer therapeutic strategies.

SphK1 inhibitor SKI II inhibits the proliferation of human hepatoma HepG2 cells via the Wnt5A/β-catenin signaling pathway

AIM

Sphingosine 1-phosphate (S1P) promotes cell growth, proliferation and survival. Sphingosine kinase 1 (SphK1), which converts sphingosine to S1P, is a key promoter in cancer. We previously found that the SphK1 inhibitor II (SKI II), suppresses the cell growth and induces apoptosis in human hepatoma HepG2 cells. However, the precise regulatory mechanism and signaling pathway on SKI II inhibiting tumor growth remains unknown.

MAIN METHODS

The expressions of β-catenin and related molecules of Wnt/β-catenin signal were detected by western blot in HepG2 cells. And the mRNA expression of β-catenin was detected by RT-PCR. The Wnt5A gene was silenced by siRNA. The colony formation was determined by staining with crystal violet. And the cell growth was examined by SRB assay and BrdU assay.

KEY FINDINGS

We found that SKI II decreased the expression of β-catenin and the downstream molecules of β-catenin signal pathway and promotes the β-catenin degradation. In addition, SKI II induced the expression of Wnt5A, and then triggered β-catenin degradation. Furthermore, silencing Wnt5A decreased the anti-tumor effects of SKI II through recovering the expressions of β-catenin and downstream molecules of β-catenin signal pathway.

SIGNIFICANCE

SKI II-induced downregulation of HepG2 cell proliferation was associated with Wnt signaling pathway through Wnt5A-mediated β-catenin degradation. Our study revealed that a novel signal pathway was involved in SKI II-inhibited cell proliferation in human hepatoma cells.

Role of sphingosine 1-phosphate in human pancreatic cancer cells proliferation and migration

Deregulation of production or degradation of sphingosine 1-phosphate (S1P), a bioactive lipid, involves in tumor progression, metastasis and chemoresistance. Since the tumor progression effects of S1P and its mechanism in human pancreatic cancer is not fully understood, we investigated the role of S1P in Capan-1 and Panc-1 cells proliferation and migration. The effects of S1P on proliferation, invasion and migration were studied using MTT and transwell assay, respectively. The concentrations of MMP2 and MMP9 were detected by ELISA assay. Role of S1P on the expressions of tyrosine kinase and cell proliferation related proteins were assessed by western blot. Our results showed that cell proliferation and migration were mediated by low concentration of S1P treatment in both cell lines. In addition, we also investigated another survival mechanism of S1P in cell survival and tumor progression, Src signaling pathway. These results indicated that roles of S1P in tumor progression were S1P receptor-dependent through interaction with Src signaling pathway. In conclude, our data demonstrated the importance of this molecule as a target to design novel anticancer drugs in future through S1P receptors and Src signaling pathway.

Inhibition of SphK1 reduces radiation-induced migration and enhances sensitivity to cetuximab treatment by affecting the EGFR / SphK1 crosstalk

SphK1 is known to play a role in tumor progression, resistance to radiochemotherapy, and migration patterns. As the overall survival rates of squamous cell carcinoma of the head and neck (HNSCC) remain poor due to limitations in surgery and irradiation and chemotherapy resistance, SphK1 is an important enzyme to investigate. The purpose of this study was to elucidate the impact of SphK1 on irradiation efficacy of HNSCC in-vitro with emphasis on EGFR signaling. By immunhistochemical staining we found a positive correlation between EGFR and SphK1 expression in patient specimens. In colony formation assays irradiation sensitive cell lines showed a poor response to cetuximab, an EGFR inhibitor, and SKI-II, a SphK1 inhibitor, and vice versa. In irradiation sensitive cells an enhanced reduction of cell migration and survival was found upon simultaneous targeting of EGFR and SphK1. In the present study, we elucidated a linkage between the two signaling pathways with regard to the efficacy of cetuximab treatment and the impact on the migration behavior of tumor cells. We investigated the biological impact of inhibiting these pathways and examined the biochemical implications after different treatments. An understanding of the processes involved could help to improve the treatment of patients with HNSCC.

Sphingosine 1-phosphate interacts with Survivin pathway to enhance tumorigenesis in cancer cells

OBJECTIVES

Degradation of sphingosine 1-phosphate (S1P), as a bioactive lipid, or deregulation of its production involves in tumor progression, metastasis and chemoresistance. Since the tumor progression effects of S1P and its mechanism in chronic lymphoblastic leukemia and non-small cell lung cancer is not fully understood, we investigated the role and one of the mechanisms of S1P in tumor progression of SKW3 and H1299 cells.

MATERIALS AND METHODS

The effects of S1P on proliferation, invasion and migration was studied using MTT assay, soft-agar colony forming assay and trans-well migration assay, respectively. In order to find out the mechanisms of S1P action, the role of S1P on expression of Survivin gene was assessed by real-time RT-PCR.

RESULTS

Our results demonstrated that although invasion was shown only in H1299 cells, low concentration of S1P, especially at 1 μM, mediated proliferation and migration in both cell lines. In addition, these effects of S1P in tumor progression are S1P receptor-dependent, and Survivin plays a key role in S1P tumorigenesis.

CONCLUSION

Our results confirmed the involvement of S1P and its receptors in tumor progression of SKW3 and H1299. We also investigated another mechanism of S1P involved in cell survival, tumor progression, and Survivin signaling. In conclusion, data demonstrated the importance of this molecule as a target for designing new anticancer drugs such as anti-S1P monoclonal antibody for inhibiting major downstream signaling, which plays significant role in tumorigenesis.

Sphingosine-1-phosphate receptor 1 (S1PR1) expression in non-muscle invasive urothelial carcinoma: Association with poor clinical outcome and potential therapeutic target

AIM

Sphingosine-1-phosphate receptor 1 (S1PR1) promotes tumour cell survival, invasion, anti-apoptosis, metastasis and radio/chemo-resistance in various cancers. However, the expression pattern and prognostic implications of S1PR1 in urothelial carcinoma remain unclear and thus were addressed here.

METHODS

Tissue microarrays composed of 395 initially diagnosed and transurethral resected urothelial carcinomas of the urinary bladder were immunostained for S1PR1 and phosphor-signal transducer and activator of transcription 3 (pSTAT3). S1PR1 expression was analysed according to clinicopathological features, expression of several anti-apoptosis/proliferation-related markers and patient's survival.

RESULTS

S1PR1 positivity was observed in 45.3% of urothelial carcinomas. Among patients with non-muscle invasive urothelial carcinoma (NMIC), S1PR1 positivity was associated with higher grade (P<0.001), higher subepithelial invasive component (P=0.006), lower papillary component (P=0.002), presence of metastasis (P=0.042) and high cancer-specific death (P<0.001). S1PR1 expression was correlated with pSTAT3 (P<0.001), survivin (P=0.008) and Ki-67 (P<0.001) expression. S1PR1 positivity predicted a shorter cancer-specific survival (CSS) in NMICs (P<0.001) and stage T1/high grade (T1HG) tumours (P=0.002). The Cox multivariate model was composed of S1PR1, survivin, lymphovascular invasion and age, and C-index was 0.781. S1PR1 positivity was correlated with shorter CSS in p53-positive T1HG carcinoma (P=0.003) in contrast to p53-negative T1HG carcinoma (P=0.205). In p53-overexpressing NMIC, S1PR1 was the only variable of the survival model and the C-index was 0.719.

CONCLUSIONS

S1PR1 expression was associated with unfavourable clinicopathological features and the expression of several anti-apoptosis/proliferation-related markers in urothelial carcinoma. S1PR1 serves as an independent predictor of cancer-specific death in NMIC. The model including S1PR1 showed highly accurate prediction for CSS in NMIC patients regardless of the modality of adjuvant therapy.

Critical role of Spns2, a sphingosine-1-phosphate transporter, in lung cancer cell survival and migration

The sphingosine-1-phosphate (S1P) transporter Spns2 regulates myocardial precursor migration in zebrafish and lymphocyte trafficking in mice. However, its function in cancer has not been investigated. We show here that ectopic Spns2 expression induced apoptosis and its knockdown enhanced cell migration in non-small cell lung cancer (NSCLC) cells. Metabolically, Spns2 expression increased the extracellular S1P level while its knockdown the intracellular. Pharmacological inhibition of S1P synthesis abolished the augmented cell migration mediated by Spns2 knockdown, indicating that intracellular S1P plays a key role in this process. Cell signaling studies indicated that Spns2 expression impaired GSK-3β and Stat3 mediated pro-survival pathways. Conversely, these pathways were activated by Spns2 knockdown, which explains the increased cell migration since they are also crucial for migration. Alterations of Spns2 were found to affect several enzymes involved in S1P metabolism, including sphingosine kinases, S1P phosphatases, and S1P lyase 1. Genetically, Spns2 mRNA level was found to be reduced in advanced lung cancer (LC) patients as quantified by using a small scale qPCR array. These data show for the first time that Spns2 plays key roles in regulating the cellular functions in NSCLC cells, and that its down-regulation is a potential risk factor for LC.

Role of lysosomes in silica-induced inflammasome activation and inflammation in absence of MARCO

MARCO is the predominant scavenger receptor for recognition and binding of silica particles by alveolar macrophages (AM). Previously, it was shown that mice null for MARCO have a greater inflammatory response to silica, but the mechanism was not described. The aim of this study was to determine the relationship between MARCO and NLRP3 inflammasome activity. Silica increased NLRP3 inflammasome activation and release of the proinflammatory cytokine, IL-1β, to a greater extent in MARCO^−/− AM compared to wild type (WT) AM. Furthermore, in MARCO^−/− AM there was greater cathepsin B release from phagolysosomes, Caspase-1 activation, and acid sphingomyelinase activity compared to WT AM, supporting the critical role played by lysosomal membrane permeabilization (LMP) in triggering silica-induced inflammation. The difference in sensitivity to LMP appears to be in cholesterol recycling since increasing cholesterol in AM by treatment with U18666A decreased silica-induced NLRP3 inflammasome activation, and cells lacking MARCO were less able to sequester cholesterol following silica treatment. Taken together, these results demonstrate that MARCO contributes to normal cholesterol uptake in macrophages; therefore, in the absence of MARCO, macrophages are more susceptible to a greater inflammatory response by particulates known to cause NLRP3 inflammasome activation and the effect is due to increased LMP.

Roles of sphingosine-1-phosphate in reproduction

Sphingosine-1-phosphate (S1P) plays crucial roles in the regulation of cell growth, proliferation, differentiation, cell survival, migration, and angiogenesis. In the reproductive system, S1P protects mammalian germ cells from irradiation or chemotherapy-induced cell death in vivo and in vitro. Moreover, S1P could improve the survival rate of thawed ovary and transplanted ovary. Furthermore, S1P could improve the developmental potential of oocyte and preimplantation embryo. In conclusion, S1P plays important roles in reproduction.

Inflammatory and microenvironmental factors involved in breast cancer progression

The primary reason for the high mortality rate of breast cancer is metastasis, which can result in a poor survival rate. The tumor environment is important for promotion and invasion of cancer cells. Recent studies have shown that inflammation is associated with breast cancer. Therefore, it is important to investigate the role of the inflammatory and microenvironment in breast cancer progression and metastasis. The present review summarizes some of the markers for inflammation and breast cancer invasion, which may aid in the design of an appropriate therapy for metastatic breast cancer. The following four inflammatory markers are discussed in this review: (1) Tumor associated macrophages (TAMs); (2) Matrix metalloproteinases (MMPs); (3) Sphingosine 1-phosphate (S1P); (4) C-reactive protein (CRP). TAMs are commonly found in breast cancer patients, and high infiltration is positively correlated with poor prognosis and low survival rate. MMPs are well-known for their roles in the degradation of ECM components when cancer cells invade and migrate. MMPs are also associated with inflammation through recruitment of a variety of stromal cells such as fibroblasts and leukocytes. S1P is an inflammatory lipid and is involved in various cellular processes such as proliferation, survival, and migration. Recent studies indicate that S1P participates in breast cancer invasion in various ways. CRP is used clinically to indicate the outcome of cancer patients as well as acute inflammatory status. This review summarizes the current understanding on the role of S1P in CRP expression which promotes the breast epithelial cell invasion, suggesting a specific mechanism linking inflammation and breast cancer. The present review might be useful for understanding the relationship between inflammation and breast cancer for the development of pharmacological interventions that may control the primary molecules involved in the breast cancer microenvironment.

Sphingolipid content in the human uterus and pair-matched uterine leiomyomas remains constant

In the present work we sought to investigate the content of sphingolipids (sphingosine, sphinganine, sphingosine-1-phosphate and ceramide) in human fibroids and pair-matched healthy uterus tissue. We demonstrated that, in uterine leiomyomas, the contents of sphingosine, sphinganine, sphingosine-1-phosphate and ceramide remains quite constant. However, a trend towards elevation of ceramide and simultaneous reduction of sphingosine-1 phosphate levels was also noticed. Additionally, in uterine leiomyomas we found relevant activation of both PTEN and MAPK(ERK1/2) signaling pathways with only a minor change in AKT activity and relatively absent HIF-1α/AMPK activation. In conclusion, rather modest changes in sphingolipids are correlated with the activation of PTEN and MAPK(ERK1/2) signaling proteins in human uterine leiomyomas.

Extracellular and intracellular sphingosine-1-phosphate in cancer

Sphingosine-1-phosphate (S1P) was first described as a signaling molecule over 20 years ago. Since then, great strides have been made to reveal its vital roles in vastly different cellular and disease processes. Initially, S1P was considered nothing more than the terminal point of sphingolipid metabolism; however, over the past two decades, a large number of reports have helped unveil its full potential as an important regulatory, bioactive sphingolipid metabolite. S1P has a plethora of physiological functions, due in part to its many sites of actions and its different pools, which are both intra- and extracellular. S1P plays pivotal roles in many physiological processes, including the regulation of cell growth, migration, autophagy, angiogenesis, and survival, and thus, not surprisingly, S1P has been linked to cancer. In this review, we will summarize the vast body of knowledge, highlighting the connection between S1P and cancer. We will also suggest new avenues for future research.