sphingosine-kinase and lysophosphatidic-acid

Regulation of the motility of skeletal muscle precursor cells, such as satellite cells, is critically important for their proper recruitment at the site of tissue damage, and ultimately for its correct repair. Here we show that lysophosphatidic acid (LPA), which is well-recognized as a powerful bioactive agent, strongly stimulates cell migration of activated murine satellite cells. The biological effect exerted by LPA was found to be induced via activation of LPA1 and LPA3 , being abolished by cell treatment with the antagonist Ki16425, and severely impaired by siRNA-mediated down-regulation of the two receptor isoforms. In contrast, silencing of LPA2 potentiated the stimulation of cell motility by LPA, suggesting that it is negatively coupled to cell migration. Pharmacological inhibition of both sphingosine kinase (SK) isoforms using VPC96047, or the selective blocking of SK1 using VPC96091, abolished cell responsiveness to LPA; in agreement, gene silencing of SK1 or SK2 significantly reduced the biological effect of LPA. Moreover, the LPA-dependent stimulation of cell chemotaxis was found to be impaired by down-regulation of the sphingosine 1-phosphate (S1P) receptors S1P1 or S1P4 by specific siRNAs. In summary, the results obtained support the notion that the sphingosine kinase/sphingosine 1-phosphate (SK/S1P) axis is critically involved in the mechanism by which LPA elicits its pro-migratory action. This study provides compelling new information on the regulatory mechanisms of satellite cell motility, and reinforces the view that the SK/S1P signaling pathway plays a crucial role in the control of skeletal muscle precursor cell biology.

Topics: Animals; Cell Movement; Cells, Cultured; Lysophospholipids; Male; Mice; Mice, Inbred C57BL; Phosphotransferases (Alcohol Group Acceptor); Satellite Cells, Skeletal Muscle; Signal Transduction; Sphingosine

Lysophosphatidic acid (LPA) is an important phospholipid mediator in inflammation and immunity. Previously, we showed that autotaxin (ATX), the enzyme producing LPA from lysophosphatidylcholine (LPC), is induced by LPS in THP-1 cells via the activation of PKR, JNK and p38 MAPK. In this study, we find that ATX and LPA receptor 3 (LPA(3)) are coordinately up-regulated in LPS-stimulated THP-1 cells. PKR-mediated activation of JNK1 and p38 MAPK is required for both ATX and LPA(3) up-regulation. SPK1-mediated activation of the PI3K-AKT-β-catenin pathway is essential for ATX induction, while SPK1-mediated ERK activation is required for LPA(3) up-regulation. Either ATX or LPA(3) knockdown inhibited CCL8 induction by LPS, suggesting that ATX and LPA(3) are involved in CCL8 induction during the inflammatory process against bacterial infection.

Topics: beta Catenin; Cell Line; Chemokine CCL8; eIF-2 Kinase; Enzyme Activation; Extracellular Signal-Regulated MAP Kinases; Humans; Lipopolysaccharides; Lysophospholipids; Mitogen-Activated Protein Kinase 8; Monocytes; p38 Mitogen-Activated Protein Kinases; Phosphatidylinositol 3-Kinases; Phosphoric Diester Hydrolases; Phosphotransferases (Alcohol Group Acceptor); Receptors, Lysophosphatidic Acid; RNA, Small Interfering; Signal Transduction

In MKN1 gastric cancer cells, lysophosphatidic acid (LPA) upregulates expression of sphingosine kinase 1 (SphK1) and its downregulation or inhibition suppresses LPA mediated proliferation. Although LPA activates numerous signaling pathways downstream of its receptors, including extracellular-signal-regulated kinase 1/2, p38, JNK, and Akt, and the transactivation of the epidermal growth factor receptor, pharmacological and molecular approaches demonstrated that only activation of ERK1, in addition to the CCAAT/enhancer-binding protein β transcription factor, is involved in transcriptional upregulation of SphK1 by LPA. Our data implicate ERK1 as an important mediator of LPA signaling leading to upregulation of SphK1 and point to SphK1 and sphingosine-1-phosphate production as potential therapeutic targets in gastric cancer.

Topics: CCAAT-Enhancer-Binding Protein-beta; Cell Line, Tumor; Cell Proliferation; Gene Expression Regulation, Neoplastic; Humans; Lysophospholipids; Mitogen-Activated Protein Kinase 3; Phosphotransferases (Alcohol Group Acceptor); Protein Kinase Inhibitors; Stomach Neoplasms; Transcription, Genetic; Transcriptional Activation; Up-Regulation

Lysophosphatidic acid (LPA) and sphingosine-1-phosphate (S1P) are lysophospholipid mediators of diverse cellular processes important for cancer progression. S1P is produced by two sphingosine kinases, SphK1 and SphK2. Expression of SphK1 is elevated in many cancers. Here, we report that LPA markedly enhanced SphK1 mRNA and protein in gastric cancer MKN1 cells but had no effect on SphK2. LPA also up-regulated SphK1 expression in other human cancer cells that endogenously express the LPA(1) receptor, such as DLD1 colon cancer cells and MDA-MB-231 breast cancer cells, but not in HT29 colon cancer cells or MDA-MB-453 breast cancer cells, which do not express the LPA(1) receptor. An LPA(1) receptor antagonist or down-regulation of its expression prevented SphK1 and S1P(3) receptor up-regulation by LPA. LPA transactivated the epidermal growth factor receptor (EGFR) in these cells, and the EGFR inhibitor AG1478 attenuated the increased SphK1 and S1P(3) expression induced by LPA. Moreover, down-regulation of SphK1 attenuated LPA-stimulated migration and invasion of MNK1 cells yet had no effect on expression of neovascularizing factors, such as interleukin (IL)-8, IL-6, urokinase-type plasminogen activator (uPA), or uPA receptor induced by LPA. Finally, down-regulation of S1P(3), but not S1P(1), also reduced LPA-stimulated migration and invasion of MKN1 cells. Collectively, our results suggest that SphK1 is a convergence point of multiple cell surface receptors for three different ligands, LPA, EGF, and S1P, which have all been implicated in regulation of motility and invasiveness of cancer cells.

Topics: Blotting, Western; Breast Neoplasms; Cell Movement; Cell Proliferation; Chemotaxis; Colonic Neoplasms; ErbB Receptors; Humans; Interleukin-6; Interleukin-8; Lysophospholipids; Neoplasm Invasiveness; Phosphotransferases (Alcohol Group Acceptor); Receptors, Lysophosphatidic Acid; Receptors, Lysosphingolipid; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Sphingosine; Stomach Neoplasms; Transcriptional Activation; Tumor Cells, Cultured; Up-Regulation; Urokinase-Type Plasminogen Activator

Sphingosine 1-phosphate (Sph-1-P), a product of sphingomyelin metabolism, can act via a family of cognate G protein-coupled receptors or as an intracellular second messenger for agonists acting through their membrane receptors. In view of the general growth promoting and developmental effects of Sph-1-P on target cells, we hypothesized that it plays a role in adaptation of the uterus to pregnancy. We analyzed its potential role and that of the related lysophospholipid lysophosphatidic acid in the pregnant rat uterus by examining changes in mRNA levels of cognate receptors and enzymes involved in their turnover. Of these, only sphingosine kinase-1 (SphK1) was markedly changed ( approximately 30-fold increase), being localized in the glandular epithelium, vasculature, and the myometrium. Uterine SphK1 mRNA and protein levels paralleled those of serum progesterone, and treatment with progesterone or an antagonist elevated or reduced SphK1 mRNA expression, respectively. Progesterone also increased SphK1 mRNA steady-state levels in a rat myometrial/leiomyoma cell line (ELT3). Overexpressing human SphK1 in these cells resulted in increased levels of the cell cycle regulator cyclin D1 and increased myosin light-chain phosphorylation. Ectopic expression of SphK1 also resulted in increased proliferation rates, possibly in conjunction with increased cyclin D1 expression. These studies suggest that the uterine expression of SphK1 mediates processes involved in growth and differentiation of uterine tissues during pregnancy.

Topics: Animals; bcl-X Protein; Cell Line, Tumor; Cell Proliferation; Cyclin D1; Enzymes; Female; Genes, Dominant; Humans; Immunologic Techniques; Leiomyoma; Lysophospholipids; Mutation; Myometrium; Myosin Light Chains; Phosphorylation; Phosphotransferases (Alcohol Group Acceptor); Pregnancy; Pregnancy, Animal; Progesterone; Progestins; Rats; Rats, Sprague-Dawley; Receptors, Lysophospholipid; RNA, Messenger; Signal Transduction; Sphingosine; Uterus

Both acute and chronic hypoxia had no effect on S1P(1), S1P(3) or LPA(1) receptor transcript expression in human pulmonary smooth muscle cells. However, acute hypoxia increased sphingosine kinase SK1/2 and LPP1 mRNA transcript levels, while chronic hypoxia increased SK1 mRNA transcript alone. Acute hypoxia had no effect on S1P-, PDGF- or phorbol ester (PMA)-stimulated activation of ERK-1/2, but increased the ability of S1P to activate p38 MAPK. Chronic hypoxia increased the ability of S1P to stimulate the phosphorylation of ERK-1/2. Therefore, we have demonstrated for the first time that hypoxia can lead to marked changes in the expression of genes involved in S1P production and may modify post S1P receptor signal transduction pathways.

Topics: Cell Hypoxia; Cells, Cultured; Gene Expression Regulation; Humans; Lung; Lysophospholipids; MAP Kinase Signaling System; Myocytes, Smooth Muscle; Phosphatidate Phosphatase; Phosphotransferases (Alcohol Group Acceptor); Receptors, Lysophosphatidic Acid; Receptors, Lysosphingolipid; Sphingosine