Characterizing Sphingosine Kinases and Sphingosine 1-Phosphate Receptors in the Mammalian Eye and Retina.

Sphingosine 1-phosphate (S1P) signaling regulates numerous biological processes including neurogenesis, inflammation and neovascularization. However, little is known about the role of S1P signaling in the eye. In this study, we characterize two sphingosine kinases (SPHK1 and SPHK2), which phosphorylate sphingosine to S1P, and three S1P receptors (S1PR1, S1PR2 and S1PR3) in mouse and rat eyes. We evaluated sphingosine kinase and S1P receptor gene expression at the mRNA level in various rat tissues and rat retinas exposed to light-damage, whole mouse eyes, specific eye structures, and in developing retinas. Furthermore, we determined the localization of sphingosine kinases and S1P receptors in whole rat eyes by immunohistochemistry. Our results unveiled unique expression profiles for both sphingosine kinases and each receptor in ocular tissues. Furthermore, these kinases and S1P receptors are expressed in mammalian retinal cells and the expression of SPHK1, S1PR2 and S1PR3 increased immediately after light damage, which suggests a function in apoptosis and/or light stress responses in the eye. These findings have numerous implications for understanding the role of S1P signaling in the mechanisms of ocular diseases such as retinal inflammatory and degenerative diseases, neovascular eye diseases, glaucoma and corneal diseases.

S1PR1 predicts patient survival and promotes chemotherapy drug resistance in gastric cancer cells through STAT3 constitutive activation.

BACKGROUND: S1PR1-STAT3 inter-regulatory loop was initially suggested to be oncogenic in several cancer cells. However, the clinical relevance of this mechanism in tumor progression, disease prognosis and drug response was not established. METHODS: The correlations between S1PR1 transcription, overall survival and chemotherapy response of GC patients were tested using a large clinical database. The relevance of S1PR1 expression and STAT3 activation in both tumor tissues and cancer cell lines was also tested. The effect of S1PR1 high expression achieved by persistent STAT3 activation on tumor cell drug resistance was investigated in vitro and in vivo. FINDINGS: An enhanced S1PR1 expression was highly related with a reduced overall survival time and a worse response to chemotherapy drug and closer correlation to STAT3 in gastric cancer patients. The issue chip analysis showed that the expressions of S1PR1 and STAT3 activation were increased in higher graded gastric cancer (GC) tissues. Cellular studies supported the notion that the high S1PR1 expression was responsible for drug resistance in GC cells through a molecular pattern derived by constitutive activation of STAT3. The disruption of S1PR1-STAT3 signaling significantly re-sensitized drug resistance in GC cells in vitro and in vivo. INTERPRETATION: S1PR1-STAT3 signaling may participate drug resistance in GC, thus could serve as a drug target to increase the efficacy of GC treatment. FUND: This work was supported by the National Natural Science Foundation of China (No. 81570775, 81471095), the grant from the research projects in traditional Chinese medicine industry of China (No. 201507004-2).

Sphingolipid signaling modulates trans-endothelial cell permeability in dengue virus infected HMEC-1 cells.

Dengue has emerged as a major mosquito-borne disease in the tropics and subtropics. In severe dengue, enhanced microvascular endothelial permeability leads to plasma leakage. Direct dengue virus (DENV) infection in human microvascular endothelial cells (HMEC-1) can enhance trans-endothelial leakage. Using a microarray-based analysis, we identified modulation of key endothelial cell signaling pathways in DENV-infected HMEC-1 cells. One among them was the sphingolipid pathway that regulates vascular barrier function. Sphingosine-1-phosphate receptor 2 (S1PR2) and S1PR5 showed significant up-regulation in the microarray data. In DENV-infected cells, the kinetics of S1PR2 transcript expression and enhanced in vitro trans-endothelial permeability showed a correlation. We also observed an internalization and cytoplasmic translocation of VE-Cadherin, a component of adherens junctions (AJ), upon infection indicating AJ disassembly. Further, inhibition of S1PR2 signaling by a specific pharmacological inhibitor prevented translocation of VE-Cadherin, thus helping AJ maintenance, and abrogated DENV-induced trans-endothelial leakage. Our results show that sphingolipid signaling, especially that involving S1PR2, plays a critical role in vascular leakage in dengue.

Overexpression of sphingosine-1-phosphate receptors on reactive astrocytes drives neuropathology of multiple sclerosis rebound after fingolimod discontinuation.

We present the neuropathological description of an autoptic case of fatal rebound of disease activity after fingolimod discontinuation in a multiple sclerosis patient. MRI prior to the fatal outcome showed several large tumefactive demyelinating lesions. These lesions were characterized by prominent astrocytic gliosis, with a remarkable preponderance of large hypertrophic reactive astrocytes showing intense expression of sphingosine-1-phosphate receptor 1. Prominent astrocytic gliosis was also diffusely observed in the normal-appearing white matter. Dysregulated sphingosine-1-phosphate signaling on astrocytes following fingolimod withdrawal might represent a possible contributing mechanism to disease rebound and might account for the unusual radiological and neuropathological features observed in the present case.

Specific microRNA signatures responsible for immune disturbance related to hip fracture in aged rats.

BACKGROUND: Hip fracture is commonly associated with an overwhelming inflammatory response, which may lead to high rates of morbidity and mortality in the elderly. MicroRNAs (miRNAs) play important roles in the functions of immune system. However, the association between miRNA dysregulation and immune disturbance (IMD) related to elderly hip fracture is largely unknown. METHODS: In this study, microarray profiling was carried out to evaluate the differential expression patterns of miRNAs in plasma of the aged hip fracture rats with IMD, those without IMD, and normal aged rats, followed by validation using quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR). Genes and signaling pathways of the dysregulated miRNAs related to elderly hip fracture-induced IMD were investigated in silico using Gene Ontology and analysis of Kyoto Encyclopedia of Genes or Genomes. RESULTS: Dead or moribund rats with hip fracture exhibited significantly reduced TNF-α/IL-10 ratio compared with healthy controls and other hip fracture rats, which were therefore named as hip fracture rats with IMD. Seven serum miRNAs in hip fracture rats with IMD were significantly downregulated. qRT-PCR and in silico analysis revealed that miR-130a-3p likely participated in regulating the hip fracture-induced IMD. Furthermore, Western blot experiment demonstrated that in lung tissue, the reduction of miR-130a-3p was accompanied with the increase of the protein expression of interferon regulatory factor-1 (IRF1) and sphingosine-1-phosphate receptor 1 (SIPR1). CONCLUSIONS: miR-130a-3p desregulation may be associated with elderly hip fracture-induced IMD, which might act as a new potential biomarker for the diagnosis and prognosis of elderly hip fracture-induced IMD and a potential therapeutic target as well.

Reversing HIV latency via sphingosine-1-phosphate receptor 1 signaling.

OBJECTIVE: In this study, we looked for a new family of latency reversing agents. DESIGN: We searched for G-protein-coupled receptors (GPCR) coexpressed with the C-C chemokine receptor type 5 (CCR5) in primary CD4 T cells that activate infected cells and boost HIV production. METHODS: GPCR coexpression was unveiled by reverse transcriptase-PCR. We used fluorescence resonance energy transfer to analyze the dimerization with CCR5 of the expressed GPCR. Viral entry was measured by flow cytometry, reverse transcription by quantitative PCR, nuclear factor-kappa B translocation by immunofluorescence, long terminal repeat activation using a gene reporter assay and viral production by p24 quantification. RESULTS: Gαi-coupled sphingosine-1-phophate receptor 1 (S1P1) is highly coexpressed with CCR5 on primary CD4 T cells and dimerizes with it. The presence of S1P1 had major effects neither on viral entry nor on reverse transcription. Yet, S1P1 signaling induced NFκB activation, boosting the expression of the HIV LTR. Consequently, in culture medium containing sphingosine-1-phophate, the presence of S1P1 enhanced the replication of a CCR5-, but also of a CXCR4-using HIV-1 strain. The S1P1 ligand FTY720, a drug used in multiple sclerosis treatment, inhibited HIV-1 productive infection of monocyte-derived dendritic cells and of severe combined immunodeficiency mice engrafted with human peripheral blood mononuclear cells. Conversely, S1P1 agonists were able to force latently infected peripheral blood mononuclear cells and lymph node cells to produce virions in vitro. CONCLUSION: Altogether these data indicate that the presence of S1P1 facilitates HIV-1 replicative cycle by boosting viral genome transcription, S1P1 antagonists have anti-HIV effects and S1P1 agonists are HIV latency reversing agents.

Differential S1P Receptor Profiles on M1- and M2-Polarized Macrophages Affect Macrophage Cytokine Production and Migration.

Introduction. Macrophages are key players in complex biological processes. In response to environmental signals, macrophages undergo polarization towards a proinflammatory (M1) or anti-inflammatory (M2) phenotype. Sphingosine 1-phosphate (S1P) is a bioactive lysophospholipid that acts via 5 G-protein coupled receptors (S1P1-5) in order to influence a broad spectrum of biological processes. This study assesses S1P receptor expression on macrophages before and after M1 and M2 polarization and performs a comparative analysis of S1P signalling in the two activational states of macrophages. Methods. Bone marrow derived macrophages (BMDM) from C57 BL/6 mice were cultured under either M1- or M2-polarizing conditions. S1P-receptor expression was determined by quantitative RT-PCR. Influence of S1P on macrophage activation, migration, phagocytosis, and cytokine secretion was assessed in vitro. Results. All 5 S1P receptor subclasses were expressed in macrophages. Culture under both M1- and M2-polarizing conditions led to significant downregulation of S1P1. In contrast, M1-polarized macrophages significantly downregulated S1P4. The expression of the remaining three S1P receptors did not change. S1P increased expression of iNOS under M2-polarizing conditions. Furthermore, S1P induced chemotaxis in M1 macrophages and changed cytokine production in M2 macrophages. Phagocytosis was not affected by S1P-signalling. Discussion. The expression of different specific S1P receptor profiles may provide a possibility to selectively influence M1- or M2-polarized macrophages.

miR-127 enhances myogenic cell differentiation by targeting S1PR3.

MicroRNAs (miRNAs) have recently been implicated in muscle stem cell function. miR-127 is known to be predominantly expressed in skeletal muscle, but its roles in myogenic differentiation and muscle regeneration are unknown. Here, we show that miR-127 is upregulated during C2C12 and satellite cell (SC) differentiation and, by establishing C2C12 cells stably expressing miR-127, demonstrate that overexpression of miR-127 in C2C12 cells enhances myogenic cell differentiation. To investigate the function of miR-127 during muscle development and regeneration in vivo, we generated miR-127 transgenic mice. These mice exhibited remarkably accelerated muscle regeneration compared with wild-type mice by promoting SC differentiation. Mechanistically, we demonstrated that the gene encoding sphingosine-1-phosphate receptor 3 (S1PR3), a G-protein-coupled receptor for sphingosine-1-phosphate, is a target of miR-127 required for its function in promoting myogenic cell differentiation. Importantly, overexpression of miR-127 in muscular dystrophy model mdx mice considerably ameliorated the disease phenotype. Thus, our findings suggest that miR-127 may serve as a potential therapeutic target for the treatment of skeletal muscle disease in humans.

Effect of sphingosine kinase modulators on interleukin-1ß release, sphingosine 1-phosphate receptor 1 expression and experimental autoimmune encephalomyelitis.

BACKGROUND AND PURPOSE: The sphingosine analogue, FTY720 (GilenyaR ), alleviates clinical disease progression in multiple sclerosis. Here, we variously assessed the effects of an azide analogue of (S)-FTY720 vinylphosphonate (compound 5; a sphingosine kinase 1 activator), (R)-FTY720 methyl ether (ROMe, a sphingosine kinase 2 inhibitor) and RB-020 (a sphingosine kinase 1 inhibitor and sphingosine kinase 2 substrate) on IL-1ß formation, sphingosine 1-phosphate levels and expression of S1P1 receptors. We also assessed the effect of compound 5 and ROMe in an experimental autoimmune encephalomyelitis (EAE) model in mice. EXPERIMENTAL APPROACH: We measured IL-1ß formation by macrophages, sphingosine 1-phosphate levels and expression levels of S1P1 receptors in vitro and clinical score in mice with EAE and the extent of inflammatory cell infiltration into the spinal cord in vivo. KEY RESULTS: Treatment of differentiated U937 macrophages with compound 5, RB-020 or sphingosine (but not ROMe) enhanced IL-1ß release. These data suggest that these compounds might be pro-inflammatory in vitro. However, compound 5 or ROMe reduced disease progression and infiltration of inflammatory cells into the spinal cord in EAE, and ROMe induced a reduction in CD4+ and CD8+ T-cell levels in the blood (lymphopenia). Indeed, ROMe induced a marked decrease in expression of cell surface S1P1 receptors in vitro. CONCLUSION AND IMPLICATIONS: This is the first demonstration that an activator of sphingosine kinase 1 (compound 5) and an inhibitor of sphingosine kinase 2 (ROMe, which also reduces cell surface S1P1 receptor expression) have an anti-inflammatory action in EAE.

Inhibition of the SphK1/S1P signaling pathway by melatonin in mice with liver fibrosis and human hepatic stellate cells.

The sphingosine kinase 1/sphingosine 1-phosphate (SphK1/S1P) system is involved in different pathological processes, including fibrogenesis. Melatonin abrogates activation of hepatic stellate cells (HSCs) and attenuates different profibrogenic pathways in animal models of fibrosis, but it is unknown if protection associates with its inhibitory effect on the SphK1/S1P axis. Mice in treatment groups received carbon tetrachloride (CCl4 ) 5 µL g-1 body wt i.p. twice a week for 4 or 6 weeks. Melatonin was given at 5 or 10 mg kg-1  day-1 i.p, beginning 2 weeks after the start of CCl4 administration. At both 4 and 6 weeks following CCl4 treatment, liver mRNA levels, protein concentration and immunohistochemical labelling for SphK1 increased significantly. S1P production, and expression of S1P receptor (S1PR)1, S1PR3 and acid sphingomyelinase (ASMase) were significantly elevated. However, there was a decreased expression of S1PR2 and S1P lyase (S1PL). Melatonin attenuated liver fibrosis, as shown by a significant inhibition of the expression of α-smooth muscle actin (α-SMA), transforming growth factor (TGF)-ß and collagen (Col) Ι. Furthermore, melatonin inhibited S1P production, lowered expression of SphK1, S1PR1, SP1R3, and ASMase, and increased expression of S1PL. Melatonin induced a reversal of activated human HSCs cell line LX2, as evidenced by a reduction in α-SMA, TGF-ß, and Col I expression. Melatonin-treated cells also exhibited an inhibition of the SphK1/S1P axis. Antifibrogenic effect of SphK1 inhibition was confirmed by treatment of LX2 cells with PF543. Abrogation of the lipid signaling pathway by the indole reveals novel molecular pathways that may account for the protective effect of melatonin in liver fibrogenesis. © 2016 BioFactors, 43(2):272-282, 2017.

A MicroRNA302-367-Erk1/2-Klf2-S1pr1 Pathway Prevents Tumor Growth via Restricting Angiogenesis and Improving Vascular Stability.

RATIONALE: Angiogenic hypersprouting and leaky vessels are essential for tumor growth. MicroRNAs have unique therapeutic advantages by targeting multiple pathways of tumor-associated angiogenesis, but the function of individual miRNAs of miR302-367 cluster in angiogenesis and tumors has not yet been fully evaluated. OBJECTIVE: To investigate the functions of miR302-367 in developmental angiogenesis and tumor angiogenesis and explore the molecular mechanisms of microRNA for the treatment of pathological neovascularization-related diseases. METHODS AND RESULTS: Here, we show that miR302-367 elevation in endothelial cells reduces retinal sprouting angiogenesis and promotes vascular stability in vivo, ex vivo, and in vitro. Erk1/2 is identified as direct target of miR302-367, and downregulation of Erk1/2 on miR302-367 elevation in endothelial cells increases the expression of Klf2 and in turn S1pr1 and its downstream target VE-cadherin, suppressing angiogenesis and improving vascular stability. Conversely, both pharmacological blockade and genetic deletion of S1pr1 in endothelial cells reverse the antiangiogenic and vascular stabilizing effect of miR302-367 in mice. Tumor angiogenesis shares features of developmental angiogenesis, and endothelial specific elevation of miR302-367 reduces tumor growth by restricting sprout angiogenesis and decreasing vascular permeability via the same Erk1/2-Klf2-S1pr1 pathways. CONCLUSIONS: MiR302-367 regulation of an Erk1/2-Klf2-S1pr1 pathway in the endothelium advances our understanding of angiogenesis, meanwhile also provides opportunities for therapeutic intervention of tumor growth.

Sphingosine kinase-1, S1P transporter spinster homolog 2 and S1P2 mRNA expressions are increased in liver with advanced fibrosis in human.

The role of sphingosine 1-phosphate (S1P) in liver fibrosis or inflammation was not fully examined in human. Controversy exists which S1P receptors, S1P1 and S1P3 vs S1P2, would be importantly involved in its mechanism. To clarify these matters, 80 patients who received liver resection for hepatocellular carcinoma and 9 patients for metastatic liver tumor were enrolled. S1P metabolism was analyzed in background, non-tumorous liver tissue. mRNA levels of sphingosine kinase 1 (SK1) but not SK2 were increased in livers with fibrosis stages 3-4 compared to those with 0-2 and to normal liver. However, S1P was not increased in advanced fibrotic liver, where mRNA levels of S1P transporter spinster homolog 2 (SPNS2) but not S1P-degrading enzymes were enhanced. Furthermore, mRNA levels of S1P2 but not S1P1 or S1P3 were increased in advanced fibrotic liver. These increased mRNA levels of SK1, SPNS2 and S1P2 in fibrotic liver were correlated with α-smooth muscle actin mRNA levels in liver, and with serum ALT levels. In conclusion, S1P may be actively generated, transported to outside the cells, and bind to its specific receptor in human liver to play a role in fibrosis or inflammation. Altered S1P metabolism in fibrotic liver may be their therapeutic target.

FTY720 Attenuates Retinal Inflammation and Protects Blood-Retinal Barrier in Diabetic Rats.

PURPOSE: FTY720 has shown a protective effect in several diseases via inhibiting inflammation and decreasing vascular permeability. The purpose of this study was to assess the impact of FTY720 on inflammation and the blood-retinal barrier (BRB) in diabetic rats. METHODS: Male Wister rats were induced to develop diabetes by streptozotocin, and FTY720 was administered by oral gavage daily for 12 weeks. All experiments were performed at 12 weeks after model establishment. Gene expression was assessed by real-time PCR. Protein expression and/or distribution were assessed by Western blotting and/or immunohistochemistry. The BRB breakdown was determined by staining of retinal whole mounts and quantified using Evans blue. RESULTS: FTY720 induced lymphopenia in diabetic rats. Proinflammatory cytokines (TNF-α, IL-6, and IL-1ß) and adhesion molecules (inter-cellular cell adhesion molecule-1 and vascular cell adhesion molecule-1) were increased in retinas of diabetic rats. FTY720 significantly inhibited the up-regulation of these inflammatory factors. FTY720 also suppressed nuclear factor-κB activation seen in retinas of diabetic rats. Additionally, FTY720 prevented BRB breakdown and reduction of tight junction proteins (ZO-1, Occludin, and Claudin-5) in the retinas of diabetic rats. Down-regulation of S1P1 and S1P3 was also reversed by FTY720 in retinas of diabetic rats. CONCLUSIONS: FTY720 provides protection against diabetic retinopathy (DR), which may involve its anti-inflammatory and barrier-enhancing effects. The S1PR modulation may serve as a novel approach to treat patients with DR.

The hematopoietic oncoprotein FOXP1 promotes tumor cell survival in diffuse large B-cell lymphoma by repressing S1PR2 signaling.

Aberrant expression of the oncogenic transcription factor forkhead box protein 1 (FOXP1) is a common feature of diffuse large B-cell lymphoma (DLBCL). We have combined chromatin immunoprecipitation and gene expression profiling after FOXP1 depletion with functional screening to identify targets of FOXP1 contributing to tumor cell survival. We find that the sphingosine-1-phosphate receptor 2 (S1PR2) is repressed by FOXP1 in activated B-cell (ABC) and germinal center B-cell (GCB) DLBCL cell lines with aberrantly high FOXP1 levels; S1PR2 expression is further inversely correlated with FOXP1 expression in 3 patient cohorts. Ectopic expression of wild-type S1PR2, but not a point mutant incapable of activating downstream signaling pathways, induces apoptosis in DLBCL cells and restricts tumor growth in subcutaneous and orthotopic models of the disease. The proapoptotic effects of S1PR2 are phenocopied by ectopic expression of the small G protein Gα13 but are independent of AKT signaling. We further show that low S1PR2 expression is a strong negative prognosticator of patient survival, alone and especially in combination with high FOXP1 expression. The S1PR2 locus has previously been demonstrated to be recurrently mutated in GCB DLBCL; the transcriptional silencing of S1PR2 by FOXP1 represents an alternative mechanism leading to inactivation of this important hematopoietic tumor suppressor.

Sphingosine 1-phosphate signaling contributes to cardiac inflammation, dysfunction, and remodeling following myocardial infarction.

Sphingosine 1-phosphate (S1P) mediates multiple pathophysiological effects in the cardiovascular system. However, the role of S1P signaling in pathological cardiac remodeling following myocardial infarction (MI) remains controversial. In this study, we found that cardiac S1P greatly increased post-MI, accompanied with a significant upregulation of cardiac sphingosine kinase-1 (SphK1) and S1P receptor 1 (S1PR1) expression. In MI-operated mice, inhibition of S1P production by using PF543 (the SphK1 inhibitor) ameliorated cardiac remodeling and dysfunction. Conversely, interruption of S1P degradation by inhibiting S1P lyase augmented cardiac S1P accumulation and exacerbated cardiac remodeling and dysfunction. In the cardiomyocyte, S1P directly activated proinflammatory responses via a S1PR1-dependent manner. Furthermore, activation of SphK1/S1P/S1PR1 signaling attributed to ß1-adrenergic receptor stimulation-induced proinflammatory responses in the cardiomyocyte. Administration of FTY720, a functional S1PR1 antagonist, obviously blocked cardiac SphK1/S1P/S1PR1 signaling, ameliorated chronic cardiac inflammation, and then improved cardiac remodeling and dysfunction in vivo post-MI. In conclusion, our results demonstrate that cardiac SphK1/S1P/S1PR1 signaling plays an important role in the regulation of proinflammatory responses in the cardiomyocyte and targeting cardiac S1P signaling is a novel therapeutic strategy to improve post-MI cardiac remodeling and dysfunction.

miR-155 Deficiency Ameliorates Autoimmune Inflammation of Systemic Lupus Erythematosus by Targeting S1pr1 in Faslpr/lpr Mice.

MicroRNA-155 (miR-155) was previously found involved in the development of systemic lupus erythematosus (SLE) and other autoimmune diseases and the inflammatory response; however, the detailed mechanism of miR-155 in SLE is not fully understood. To explore the in vivo role of miR-155 in the pathogenesis of SLE, miR-155-deficient Fas(lpr/lpr) (miR-155(-/-)Fas(lpr/lpr)) mice were obtained by crossing miR-155(-/-) and Fas(lpr/lpr) mice. Clinical SLE features such as glomerulonephritis, autoantibody levels, and immune system cell populations were compared between miR-155(-/-)Fas(lpr/lpr) and Fas(lpr/lpr) mice. Microarray analysis, RT-PCR, Western blot, and luciferase reporter gene assay were used to identify the target gene of miR-155. miR-155(-/-)Fas(lpr/lpr) mice showed milder SLE clinical features than did Fas(lpr/lpr)mice. As compared with Fas(lpr/lpr) mice, miR-155(-/-)Fas(lpr/lpr) mice showed less deposition of total IgA, IgM, and IgG and less infiltration of inflammatory cells in the kidney. Moreover, the serum levels of IL-4 and IL-17a, secreted by Th2 and Th17 cells, were lower in miR-155(-/-)Fas(lpr/lpr) than Fas(lpr/lpr) mice; the CD4(+)/CD8(+) T cell ratio was restored in miR-155(-/-)Fas(lpr/lpr) mice as well. Sphingosine-1-phosphate receptor 1 (S1PR1) was found as a new target gene of miR-155 by in vitro and in vivo studies; its expression was decreased in SLE patients and Fas(lpr/lpr) mice. miR-155(-/-)Fas(lpr/lpr) mice are resistant to the development of SLE by the regulation of the target gene S1pr1. miR-155 might be a new target for therapeutic intervention in SLE.

Corticotrophin-releasing factor participates in S1PR3-dependent cPLA2 expression and cell motility in vascular smooth muscle cells.

This work is to investigate the role of CRF receptors in VSMC migration and the relevant mechanisms. We studied the role of CRF receptors in cell motility and found that S1P signaling pathway is involved in the regulation of cPLA2 induced by CRF. S1P is synthesized by Sphk1 and Sphk2 and binds to five GPCR designated S1P1-5. We observed that activation of CRFR1 resulted in increased cell migration, whereas activation of CRFR2 resulted in decreased cell migration. cPLA2 and iPLA2 were knocked down respectively to explore the corresponding effect on cell migration by means of shRNA interference. cPLA2 expression was increased by CRFR1 but decreased by CRFR2. On the contrary, iPLA2 expression was inhibited by CRFR1 but enhanced by CRFR2. The regulation of cPLA2 was in line with the regulation of Sphk1 and hence cell migration after the activation of CRFR1 or CRFR2. Consistently, S1P release was enhanced with CRFR1 activation. Both DMS (Sphk inhibitor) and CAY10444 (S1PR3 inhibitor) attenuated cPLA2 expression and thus decreased cell migration in response to CRF. In addition, CRF could not promote cell migration after S1PR3 silencing. Our results suggest the pro-migratory role of CRFR1-Sphk1-S1P-S1PR3-cPLA2 signaling pathway in VSMCs.

The Effect of Sphingosine 1-Phosphate/Sphingosine 1-Phosphate Receptor on Neutrophil Function and the Relevant Signaling Pathway.

BACKGROUND/AIMS: This study investigated the priming effect of sphingosine 1-phosphate (S1P) on formyl-Met-Leu-Phe-OH (fMLP)-activated neutrophils, by specific analysis of the neutrophil respiratory burst and the signaling pathway involved in S1P activity. METHODS: The neutrophil respiratory burst was indirectly detected by the cytochrome c reduction method and the dihydrorhodamine 123 staining method. The signal transduction pathways of neutrophil respiratory burst primed by S1P were detected by Western blotting. RESULTS: Our results showed that the S1P receptors (S1PRs) 1, 4 and 5 were the predominantly expressed neutrophil S1PRs at the cDNA level. After pretreatment with S1P, the fMLP-activated neutrophils released increased levels of superoxide anions. PI3K and Akt proteins were involved in the signaling pathway of the neutrophil respiratory burst primed by S1P. CONCLUSION: The results indicate that S1P is a new priming reagent for neutrophils and primes the respiratory burst of fMLP-activated neutrophils. S1P interacts with its receptors on neutrophils, resulting in NADPH oxidase activation by the PI3K-Akt cell signaling pathway and induction of the neutrophil respiratory burst.

The transcription factor KLF2 restrains CD4⁺ T follicular helper cell differentiation.

T follicular helper (Tfh) cells are essential for efficient B cell responses, yet the factors that regulate differentiation of this CD4(+) T cell subset are incompletely understood. Here we found that the KLF2 transcription factor serves to restrain Tfh cell generation. Induced KLF2 deficiency in activated CD4(+) T cells led to increased Tfh cell generation and B cell priming, whereas KLF2 overexpression prevented Tfh cell production. KLF2 promotes expression of the trafficking receptor S1PR1, and S1PR1 downregulation is essential for efficient Tfh cell production. However, KLF2 also induced expression of the transcription factor Blimp-1, which repressed transcription factor Bcl-6 and thereby impaired Tfh cell differentiation. Furthermore, KLF2 induced expression of the transcription factors T-bet and GATA3 and enhanced Th1 differentiation. Hence, our data indicate KLF2 is pivotal for coordinating CD4(+) T cell differentiation through two distinct and complementary mechanisms: via control of T cell localization and by regulation of lineage-defining transcription factors.

S1PR1 Tyr143 phosphorylation downregulates endothelial cell surface S1PR1 expression and responsiveness.

Activation of sphingosine-1-phosphate receptor 1 (S1PR1) plays a key role in repairing endothelial barrier function. We addressed the role of phosphorylation of the three intracellular tyrosine residues of S1PR1 in endothelial cells in regulating the receptor responsiveness and endothelial barrier function regulated by sphingosine 1-phosphate (S1P)-mediated activation of S1PR1. We demonstrated that phosphorylation of only Y143 site was required for S1PR1 internalization in response to S1P. Maximal S1PR1 internalization was seen in 20 min but S1PR1 returned to the cell surface within 1 h accompanied by Y143-dephosphorylation. Cell surface S1PR1 loss paralleled defective endothelial barrier enhancement induced by S1P. Expression of phospho-defective (Y143F) or phospho-mimicking (Y143D) mutants, respectively, failed to internalize or showed unusually high receptor internalization, consistent with the requirement of Y143 in regulating cell surface S1PR1 expression. Phosphorylation of the five S1PR1 C-terminal serine residues did not affect the role of Y143 phosphorylation in signaling S1PR1 internalization. Thus, rapid reduction of endothelial cell surface expression of S1PR1 subsequent to Y143 phosphorylation is a crucial mechanism of modulating S1PR1 signaling, and hence the endothelial barrier repair function of S1P.