Identification of autotaxin as a neurite retraction-inducing factor of PC12 cells in cerebrospinal fluid and its possible sources

Abstract Cerebrospinal fluid (CSF) induced neurite retraction of differentiated PC12 cells; the action was observed in 15 min (a rapid response) and the activity further increased until 6 h (a long-acting response) during exposure of CSF to the cells. The CSF action was sensitive to monoglyceride lipase and diminished by homologous desensitization with lysophosphatidic acid (LPA) and by pretreatment with an LPA receptor antagonist Ki16425. Although fresh CSF contains LPA to some extent, the LPA content in the medium was increased during culture of PC12 cells with CSF. The rapid response was mimicked by exogenous LPA, and a long-acting response was duplicated by a recombinant autotaxin, lysophospholipase D (lyso-PLD). Although the lyso-PLD substrate lysophosphatidylcholine (LPC) was not detected in CSF, lyso-PLD activity and an approximately 120-kDa autotaxin protein were detected in CSF. On the other hand, LPC but not lyso-PLD activity was detected in the conditioned medium of a PC12 cell culture without CSF. Among neural cells examined, leptomeningeal cells expressed the highest lyso-PLD activity and autotaxin protein. These results suggest that leptomeningeal cells may work as one of the sources for autotaxin, which may play a critical role in LPA production and thereby regulate axonal and neurite morphological change.     

Selective degradation of tumor necrosis factor in sensitive cells, and production of membrane-active substance

The mode of action of tumor necrosis factor (TNF) was studied. On treatment of TNF-sensitive L929 cells with radioiodinated TNF, the TNF molecule was found to be internalized into the cells and extensively degraded. On treatment of TNF-insensitive embryonic fibroblast cells with TNF, less TNF was internalized and it was not degraded appreciably. The L929 cells excreted the degradation products of TNF into the culture medium, and this medium showed activity for degradation of liposomes composed of phosphatidylserine and phosphatidylcholine. The sensitive cells may contain some specific proteinase that cleaves TNF molecules.     

Biochemical and molecular characterization of a novel choline-specific glycerophosphodiester phosphodiesterase belonging to the nucleotide pyrophosphatase/phosphodiesterase family

Nucleotide pyrophosphatases/phosphodiesterases (NPPs) are ubiquitous membrane-associated or secreted ectoenzymes that release nucleoside 5'-monophosphate from a variety of nucleotides and nucleotide derivatives. The mammalian NPP family comprises seven members, but only three of these (NPP1-3) have been studied in some detail. Previously we showed that lysophospholipase D, which hydrolyzes lysophosphatidylcholine (LPC) to produce lysophosphatidic acid, is identical to NPP2. More recently an uncharacterized novel NPP member (NPP7) was shown to have alkaline sphingomyelinase activity. These findings raised the possibility that other members of the NPP family act on phospholipids. Here we show that the sixth member of the NPP family, NPP6, is a choline-specific glycerophosphodiester phosphodiesterase. The sequence of NPP6 encodes a transmembrane protein containing an NPP domain with significant homology to NPP4, NPP5, and NPP7/alkaline sphingomyelinase. When expressed in HeLa cells, NPP6 was detected in both the cells and the cell culture medium as judged by Western blotting and by enzymatic activity. Recombinant NPP6 efficiently hydrolyzed the classical substrate for phospholipase C, p-nitrophenyl phosphorylcholine, but not the classical nucleotide phosphodiesterase substrate, p-nitrophenyl thymidine 5'-monophosphate. In addition, NPP6 hydrolyzed LPC to form monoacylglycerol and phosphorylcholine but not lysophosphatidic acid, showing it has a lysophospholipase C activity. NPP6 showed a preference for LPC with short (12:0 and 14:0) or polyunsaturated (18:2 and 20:4) fatty acids. It also hydrolyzed glycerophosphorylcholine and sphingosylphosphorylcholine efficiently. In mice, NPP6 mRNA was predominantly detected in kidney with a lesser expression in brain and heart, and in human it was detected in kidney and brain. The present results suggest that NPP6 has a specific role through the hydrolysis of polyunsaturated LPC, glycerophosphorylcholine, or sphingosylphosphorylcholine in these organs.     

Extracellular and intracellular productions of lysophosphatidic acids and cyclic phosphatidic acids by lysophospholipase D from exogenously added lysophosphatidylcholines to cultured NRK52E cells

Lysophosphatidic acid (LPA) is a bioactive lysophospholipid that is a notable biomarker of kidney injury. However, it is not clear how LPA is produced in renal cells. In this study, we explored LPA generation and its enzymatic pathway in a rat kidney-derived cell, NRK52E cells. Culturing of NRK52E cells with acyl lysophosphatidylcholine (acyl LPC), or lyso-platelet activating factor (lysoPAF, alkyl LPC) was resulted in increased extracellular level of choline, co-product with LPA by lysophospholipase D (lysoPLD). Their activities were enhanced by addition of calcium ions to the cell culture medium, but failed to be inhibited by S32826, an autotaxin (ATX)-specific inhibitor. Liquid chromatography-tandem mass spectrometric analysis revealed the small, but significant extracellular production of acyl LPA/cyclic phosphatidic acid (cPA) and alkyl LPA/cPA. The mRNA expression of glycerophosphodiesterase (GDE) 7 with lysoPLD activity was elevated in confluent NRK52E cells cultured over 3 days. GDE7 plasmid-transfection of NRK52E cells augmented both extracellular and intracellular productions of LPAs (acyl and alkyl) as well as extracellular productions of cPAs (acyl and alkyl) from exogenous LPCs (acyl and alkyl). These results suggest that intact NRK52E cells are able to produce choline and LPA/cPA from exogenous LPCs through the enzymatic action of GDE7 that is located on the plasma membranes and intracellular membranes.     

The effect of n-3 PUFA on eNOS activity and expression in Ea hy 926 cells

The aim of this study was to evaluate the effects of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) on NO synthase (eNOS) activation in Ea hy 926 endothelial cells. EPA or DHA (0-80 microM), added to the culture medium during 24h, were dose-dependently incorporated into the cells. In control medium, eNOS activity (evaluated by the citrulline assay) and eNOS phosphorylation on Ser 1177 were correlated. They were increased by 10 microM histamine and prevented by 20 microM lysophosphatidylcholine (LPC). By contrast, EPA or DHA increased basal phosphorylation without affecting eNOS activity in non-stimulated cells, but dose-dependently decreased this activity in histamine-stimulated cells without modifying the phosphorylation level. Furthermore, EPA and DHA did not prevent the deleterious effects of LPC on histamine stimulation. In conclusion, incorporation of EPA and DHA could be deleterious for endothelial cells by deregulating the activation of eNOS and preventing NO liberation.     

Production of 1,2-didocosahexaenoyl phosphatidylcholine by bonito muscle lysophosphatidylcholine/transacylase

1,2-Didocosahexaenoyl phosphatidylcholine (PC), which has highly unsaturated fatty acid at both sn-1 and sn-2 positions of glycerol, is a characteristic molecular species of bonito muscle. To examine the involvement of a de novo route in its synthesis, the molecular species of phosphatidic acid (PA) were analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry using a 1,3-bis[bis(pyridin-2-ylmethyl)amino]propan-2-olato dizinc(II) complex, a novel phosphate-capture molecule. However, 1,2-didocosahexaenoyl species could not be detected. Next, 1,2-didocosahexaenoyl PC synthesis by the cytosolic lysophosphatidylcholine (LPC)/transacylase was examined using endogenous LPC from bonito muscle, in which the 2-docosahexaenoyl species is abundant. The LPC/transacylase synthesized 1,2-didocosahexaenoyl PC as the most abundant molecular species. For further characterization, the LPC/transacylase was purified to homogeneity from the 100,000 x g supernatant of bonito muscle. The isolated LPC/transacylase is a labile glycoprotein with molecular mass of 52 kDa including a 5-kDa sugar moiety. The LPC/transacylase showed a PC synthesis (transacylase activity) below and above the critical micelle concentration of substrate LPC, and fatty acid release (lysophospholipase activity) was always smaller than the transacylase activity, even with a monomeric substrate. These results suggest that the LPC/transacylase is responsible for the synthesis of 1,2-didocosahexaenoyl PC.     

Spider and bacterial sphingomyelinases D target cellular lysophosphatidic acid receptors by hydrolyzing lysophosphatidylcholine

Bites by Loxosceles spiders can produce severe clinical symptoms, including dermonecrosis, thrombosis, vascular leakage, hemolysis, and persistent inflammation. The causative factor is a sphingomyelinase D (SMaseD) that cleaves sphingomyelin into choline and ceramide 1-phosphate. A similar enzyme, showing comparable bioactivity, is secreted by certain pathogenic corynebacteria and acts as a potent virulence factor. However, the molecular basis for SMaseD toxicity is not well understood, which hampers effective therapy. Here we show that the spider and bacterial SMases D hydrolyze albumin-bound lysophosphatidylcholine (LPC), but not sphingosylphosphorylcholine, with K(m) values ( approximately 20-40 microm) well below the normal LPC levels in blood. Thus, toxic SMases D have intrinsic lysophospholipase D activity toward LPC. LPC hydrolysis yields the lipid mediator lysophosphatidic acid (LPA), a known inducer of platelet aggregation, endothelial hyperpermeability, and pro-inflammatory responses. Introduction of LPA(1) receptor cDNA into LPA receptor-negative cells renders non-susceptible cells susceptible to SmaseD, but only in LPC-containing media. Degradation of circulating LPC to LPA with consequent activation of LPA receptors may have a previously unappreciated role in the pathophysiology of secreted SMases D.     

The role of phospholipases from inflammatory macrophages in demyelination

Activated macrophages harvested from rat peritoneum were shown to contain phospholipase A₁, A₂ and lysophospholipase activities which were defined on a series of radiolabelled phospholipid substrates. During in vitro culture of these elicited macrophage populations, phospholipase enzymes were secreted into the culture medium. Radiolabelled myelin, prepared from young rats after intracerebral injection of¹⁴C acetate, was used as a substrate to analyze the susceptibility of central nervous system (CNS) myelin to attack by cell-associated and secreted macrophage enzymes. Homogenates of peritoneal macrophages degraded the myelin lipids at acid pH; phosphatidyl choline (PC) and ethanolamine phosphatide (EP) were both degraded with liberation of free fatty acid and small amounts of lysolipids. The ethanolamine lipids were most vulnerable; up to 20% of this fraction was degraded in six hours. Selected batches of macrophage culture supernatant similarly degraded the myelin EP at acid pH. These results suggest that phospholipase enzymes, released from activated macrophages in close proximity to the myelin sheath, may participate in primary demyelination in inflammatory CNS lesions.     

Analysis of lipolysis in adipocytes using a fluorescent fatty acid derivative

For facilitation of the experimental analysis of the mechanism and regulation of mobilization of fatty acids from adipose triacylglycerol (TAG) stores, which also represents important targets for pharmacological intervention with the pathogenesis of diabetes and obesity, we developed a convenient and reliable non-radioactive cell-based assay. Isolated rat adipocytes are incubated with the fluorescent fatty acid derivative, 12-((7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)dodecanoic acid (NBD-FA), in the presence of insulin. The resulting NBD-FA-labeled TAG is efficiently cleaved by hormone-sensitive lipase (HSL) in vitro. After removal of insulin and excess of free NBD-FA, lipolysis is initiated by addition of isoproterenol and/or adenosine deaminase. The amount of NBD-FA generated in total or released into the incubation medium in the presence of modulatory hormones or compounds is then monitored by thin layer chromatography and fluorescence imaging. Release of NBD-FA, glycerol and [3H]oleic acid from TAG follows similar kinetics and concentration dependence in response to various lipolytic and anti-lipolytic stimuli as well as inhibitors of HSL. Release of NBD-FA from adipocytes correlates well to translocation of HSL from the cytosol to TAG droplets. In addition, we found that a cell-free system consisting of NBD-FA-labeled TAG droplets with endogenous associated HSL closely reflects the lipolytic state of the adipocytes used for its preparation. In conclusion, release of NBD-FA from TAG in vivo and in vitro can be used as accurate index for (regulation of) lipolysis in primary and cultured adipocytes.     

Extracellular metabolism-dependent uptake of lysolipids through cultured monolayer of differentiated Caco-2 cells

Glycerophospholipids are known to be hydrolyzed in the intestinal lumen into free fatty acids and lysophospholipids that are then absorbed by the intestinal epithelial cells. A monolayer of enterocyte-differentiated Caco-2 cell is often used to assess the intestinal bioavailability of nutrients. In this study, we examined how differentiated Caco-2 cells process lysoglycerolipids such as lysophosphatidylcholine (LPC). Our findings were twofold. (1) Caco-2 cells secreted both a lysophospholipase A-like enzyme and a glycerophosphocholine-phosphodiesterase enzyme into the apical, but not basolateral, lumen, suggesting that food-derived LPC is converted to a free fatty acid, sn-glycerol-3-phosphate, and choline through two sequential enzymatic reactions in humans. The release of the latter enzyme was differentiation-dependent. (2) Fatty acid-releasing activities toward exogenous fluorescent LPC, lysophosphatidic acid and monoacylglycerol were shown to be higher on the apical membranes of Caco-2 cells than on the basolateral membranes. These results suggest that human intestinal epithelial cells metabolize lysoglycerolipids by two distinct mechanisms involving secreted or apical-selective expression of metabolic enzymes.     

Requirement of Osteopontin in the migration and protection against Taxol-induced apoptosis via the ATX-LPA axis in SGC7901 cells

Background  

Autotaxin (ATX) possesses lysophospholipase D (lyso PLD) activity, which converts lysophosphatidylcholine (LPC) into lysophosphatidic acid (LPA). The ATX-LPA signaling axis has been implicated in angiogenesis, chronic inflammation and tumor progression. Osteopontin (OPN) is an important chemokine involved in the survival, proliferation, migration, invasion and metastasis of gastric cancer cells. The focus of the present study was to investigate the relationship between the ATX-LPA axis and OPN.     

Purification and regiospecificity of multiple enzyme activities of phospholipase A(1) from bonito muscle

Phospholipase A(1) (PLA(1)), which catalyzes the hydrolysis of the sn-1 ester bond of diacyl phospholipids, was purified from 100,000 x g supernatant of bonito muscle to homogeneity by ammonium-sulfate precipitation and four consecutive column chromatographies (DEAE anion-exchange, ether-Toyopeal, hydroxylapatite and Toyopeal HW 50S columns). The final preparation showed a single band above the 67-kDa molecular marker on SDS-PAGE, and the molecular mass was determined to be 71.5 kDa by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry using bovine serum albumin as a standard for calibration. The N-terminal 8 amino residues were determined to be Ala-Pro-Ala-Glu-Lys-Val-Lys-Try. Regiospecificity of multiple enzyme activities of the PLA(1) was examined using positionally defined synthetic phosphatidylcholine (PC) and lysophosphatidylcholines (LPC). An acyl ester bond at the sn-1 position of PC was exclusively hydrolyzed by phospholipase activity, and 1-acyl LPC was cleaved to fatty acid and glycerophosphocholine by lysophospholipase (LPL) activity. However, the positional isomer, 2-acyl LPC was a poor substrate for LPL activity. PC/transacylation activity was also observed when excess 2-acyl LPC was supplied in the reaction mixture, and fatty acid at the sn-1 position of donor PC was transferred to the sn-1 position of acceptor LPC. These results demonstrate that the multiple enzyme activities of PLA(1), this is lysophospholipase, transacylase as well as phospholipase, have a strict regiospecificity at the sn-1 position of substrates.     

Autotaxin has lysophospholipase D activity leading to tumor cell growth and motility by lysophosphatidic acid production

Autotaxin (ATX) is a tumor cell motility-stimulating factor, originally isolated from melanoma cell supernatants. ATX had been proposed to mediate its effects through 5'-nucleotide pyrophosphatase and phosphodiesterase activities. However, the ATX substrate mediating the increase in cellular motility remains to be identified. Here, we demonstrated that lysophospholipase D (lysoPLD) purified from fetal bovine serum, which catalyzes the production of the bioactive phospholipid mediator, lysophosphatidic acid (LPA), from lysophosphatidylcholine (LPC), is identical to ATX. The Km value of ATX for LPC was 25-fold lower than that for the synthetic nucleoside substrate, p-nitrophenyl-tri-monophosphate. LPA mediates multiple biological functions including cytoskeletal reorganization, chemotaxis, and cell growth through activation of specific G protein-coupled receptors. Recombinant ATX, particularly in the presence of LPC, dramatically increased chemotaxis and proliferation of multiple different cell lines. Moreover, we demonstrate that several cancer cell lines release significant amounts of LPC, a substrate for ATX, into the culture medium. The demonstration that ATX and lysoPLD are identical suggests that autocrine or paracrine production of LPA contributes to tumor cell motility, survival, and proliferation. It also provides potential novel targets for therapy of pathophysiological states including cancer.     

Receptor-mediated internalization and degradation of urokinase is caused by its specific inhibitor PAI-1.

The receptor for urokinase plasminogen activator (uPA) has been previously shown not to internalize its ligand, but rather to focalize its activity at the cell surface, allowing a regulated cell surface plasmin dependent proteolysis. The receptor in fact binds the proenzyme pro-uPA and allows its very efficient conversion to the active two chains form. Receptor bound active uPA can also interact with its specific type 1 inhibiror (PAI-1) which is therefore able to inhibit the cell surface plasmin formation. In this paper we show that the uPA-PAI-1 complex bound to the uPA receptor is internalized and degraded. U937 cells were incubated at 4 degrees C with labeled uPA-PAI-1 (and other ligands), the temperature then raised to 37 degrees C and the fate of the ligand followed for 3 h thereafter. The uPA-PAI-1 complex was internalized into the cells (i.e. could not be dissociated by acid treatment) and thereafter degraded (i.e. appeared in the supernatant in a non TCA-precipitable form). Other ligands (free uPA, ATF and DFP-treated uPA) were not internalized nor degraded. The degradation of the uPA-PAI-1 complex is preceded by internalization and is inhibited by chloroquine, an inhibitor of lysosomal protein degradation. These data suggest the existence of a cellular cycle of uPA. After synthesis pro-uPA is secreted, bound to the receptor and activated to two chain uPA. On the surface, uPA can activate surface bound plasminogen to produce surface bound plasmin. In the presence of PAI-1 uPA activity is inhibited and plasmin production interrupted, while the uPA-PAI-1 complex is internalized and degraded.     

Regulation of lysophosphatidylcholine-metabolizing enzymes in isolated myocardial cells from rat heart

Enzymatic pathways involved in the metabolism of lysophosphatidylcholine were investigated in rat heart myocardial cells. Acyl CoA-dependent acyltransferase activity was localized in microsomes, and was much greater than lysophospholipase activity in either cytosolic or microsomal fractions. The cytosolic lysophospholipase was more sensitive to inhibition by palmitylcarnitine in comparison to free fatty acids. In contrast, free fatty acids (oleate and palmitate) produced a greater inhibition of the microsomal acyltransferase and lysophospholipase than did palmitylcarnitine. A reduction in the assay pH to 6.5 resulted in an increase in microsomal acyltransferase and cytosolic lysophospholipase activities, but brought about a marked reduction in the microsomal lysophospholipase activity. At pH 6.5, the percentage inhibition of the microsomal acyltransferase by palmitylcarnitine was reduced, whereas the inhibition by palmitic acid was enhanced. The inhibition of the microsomal lysophospholipase by both palmitylcarnitine and palmitic acid was reduced at pH 6.5. With respect to myocardial ischemia, the inhibition of microsomal acyltransferase by free fatty acids and the reduction in microsomal lysophospholipase activity due to acidosis may contribute to the elevation of cellular lysophosphoglycerides which are arrhythmogenic.     

Uptake and metabolism of fluorescent ceramide analogs by rat oligodendrocytes in culture.

We studied the metabolism of sphingolipids by oligodendrocytes derived from rat spinal cord by providing lipid vesicles with either N-lissamine-rhodaminyl-ceramide (LRh-Cer) or N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)-ceramide (NBD-Cer) to the cells cultured in a chemically-defined medium. With both probes the major fluorescent product turned out to be sphingomyelin (SM). Most of LRh-SM was not cell-associated but recovered from the culture medium, probably due to back-exchange to the lipid vesicles. The accumulation of LRh-SM, both in the cells and in the medium, was inhibited in the presence of monensin or brefeldin A, whereas the production of NBD-SM was much less affected by these Golgi perturbing drugs. With LRh-Cer as substrate, LRh-labelled fatty acid (FA), galactosyl- and sulfogalactosyl-ceramides (GalCer and SGalCer) were also formed. NBD-Cer, however, was metabolized to glucosylceramide (GlcCer) and GalCer but not to SGalCer or NBD-FA. These data demonstrate that chemical modifications of ceramide alter its metabolism in oligodendrocytes and that the metabolites of LRh-Cer reflect the glycolipid composition of myelin more closely than those of NBD-Cer.     

Purification and characterization of a lecithin-dependent haemolysin from Escherichia coli transformed by a Vibrio parahaemolyticus gene.

Lecithin-dependent haemolysin (LDH) of Vibrio parahaemolyticus was purified from Escherichia coli C600 transformed with a plasmid (pHL591) ligated with a 1.5 kb DNA fragment of V. parahaemolyticus. The final preparation comprised two LDH proteins with different molecular masses which were immunologically cross-reactive and had the same enzymic activity. The LDH was a phospholipase hydrolysing both fatty acid esters of phospholipid, i.e. it hydrolysed phosphatidylcholine (PC) to lysophosphatidylcholine (LPC) and then LPC to glycerophosphorylcholine (GPC). From this point of view, LDH should be classified as a phospholipase B. Phospholipase B, however, does not usually show haemolytic activity, because the intermediate (LPC), which is the actual haemolytic agent, is immediately hydrolysed to the final product (GPC). On the other hand, LPC formed by LDH action was comparatively stable, because the rates of the two reactions catalysed by LDH, PC to LPC and LPC to GPC, are almost the same. This is the reason that LDH shows haemolytic activity. Therefore, LDH of V. parahaemolyticus is an atypical phospholipase to be designated as phospholipase A2/lysophospholipase.     

Autotaxin的结构与功能

Autotaxin(ATX)是一个分泌型糖蛋白,具有磷酸二酯酶(PDE)活性,是胞外焦磷酸酶/磷酸二酯酶(ENPP)家族的一员.ATX还具有溶血磷脂酶D(lysoPLD)活性,能够以溶血磷脂酰胆碱(lysophosphatidylcholjne,LPC)为底物催化生成溶血磷脂酸(lysophosphatidic acid,LPA).ATX在很多肿瘤细胞中都有高表达,在肿瘤的发生、发展过程中有着重要作用,被认为是肿瘤治疗中一个可能的靶位.此外,ATX在神经系统、免疫系统中也发挥重要作用.目前已经建立了一系列快速检测ATX活性的方法,并在此基础上研发了相关疾病的诊断技术.基于ATX的多功能性,对其表达调控机理的研究和抑制剂的开发成为当前的研究热点.     

Subcellular localization and lysophospholipase/transacylation activities of human group IVC phospholipase A2 (cPLA2γ)

cPLA2γ was identified as an ortholog of cPLA2α, which is a key enzyme in eicosanoid production. cPLA2γ was reported to be located in endoplasmic reticulum (ER) and mitochondria and to have lysophospholipase activity beside phospholipase A2 (PLA2) activity. However, subcellular localization, mechanism of membrane binding, regulation and physiological function have not been fully established. In the present study, we examined the subcellular localization and enzymatic properties of cPLA2γ with C-terminal FLAG-tag. We found that cPLA2γ was located not only in ER but also mitochondria even in the absence of the prenylation. Purified recombinant cPLA2γ catalyzed an acyltransferase reaction from one molecule of lysophosphatidylcholine (LPC) to another, forming phosphatidylcholine (PC). LPC or lysophosphatidylethanolamine acted as acyl donor and acceptor, but lysophosphatidylserine, lysophosphatidylinositol and lysophosphatidic acid (LPA) did not. PC and phosphatidylethanolamine (PE) also acted as weak acyl donors. Reaction conditions changed the balance of lysophospholipase and transacylation activities, with addition of LPA/PA, pH > 8, and elevated temperature markedly increasing transacylation activity; this suggests that lysophospholipase/transacylation activities of cPLA2γ may be regulated by various factors. As lysophospholipids are known to accumulate in ischemia heart and to induce arryhthmia, the cPLA2γ that is abundant in heart may have a protective role through clearance of lysophospholipids by its transacylation activity.     

Autotaxin is overexpressed in glioblastoma multiforme and contributes to cell motility of glioblastoma by converting lysophosphatidylcholine to lysophosphatidic acid

Autotaxin (ATX) is a multifunctional phosphodiesterase originally isolated from melanoma cells as a potent cell motility-stimulating factor. ATX is identical to lysophospholipase D, which produces a bioactive phospholipid, lysophosphatidic acid (LPA), from lysophosphatidylcholine (LPC). Although enhanced expression of ATX in various tumor tissues has been repeatedly demonstrated, and thus, ATX is implicated in progression of tumor, the precise role of ATX expressed by tumor cells was unclear. In this study, we found that ATX is highly expressed in glioblastoma multiforme (GBM), the most malignant glioma due to its high infiltration into the normal brain parenchyma, but not in tissues from other brain tumors. In addition, LPA1, an LPA receptor responsible for LPA-driven cell motility, is predominantly expressed in GBM. One of the glioblastomas that showed the highest ATX expression (SNB-78), as well as ATX-stable transfectants, showed LPA1-dependent cell migration in response to LPA in both Boyden chamber and wound healing assays. Interestingly these ATX-expressing cells also showed chemotactic response to LPC. In addition, knockdown of the ATX level using small interfering RNA technique in SNB-78 cells suppressed their migratory response to LPC. These results suggest that the autocrine production of LPA by cancer cell-derived ATX and exogenously supplied LPC contribute to the invasiveness of cancer cells and that LPA1, ATX, and LPC-producing enzymes are potential targets for cancer therapy, including GBM.