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Junken Aoki

Publications and source records attributed to Junken Aoki.

At least 37 records · Page 2Linked to original sources
PubMed2005

Group VIB Ca2+-independent phospholipase A2gamma promotes cellular membrane hydrolysis and prostaglandin production in a manner distinct from other intracellular phospholipases A2.

Although group VIA Ca2+-independent phospholipase A2beta (iPLA2beta) has been implicated in various cellular events, the functions of other iPLA2 isozymes remain largely elusive. In this study, we examined the cellular functions of group VIB iPLA2gamma. Lentiviral transfection of iPLA2gamma into HEK293 cells resulted in marked increases in spontaneous, stimulus-coupled, and cell death-associated release of arachidonic acid (AA), which was converted to prostaglandin E2 with preferred cyclooxygenase (COX)-1 coupling. Conversely, treatment of HEK293 cells with iPLA2gamma small interfering RNA significantly reduced AA release, indicating the participation of endogenous iPLA2gamma. iPLA2gamma protein appeared in multiple sizes according to cell types, and a 63-kDa form was localized mainly in peroxisomes. Electrospray ionization mass spectrometry of cellular phospholipids revealed that iPLA2gamma and other intracellular PLA2 enzymes acted on different phospholipid subclasses. Transfection of iPLA2gamma into HCA-7 cells also led to increased AA release and prostaglandin E2 synthesis via both COX-1 and COX-2, with a concomitant increase in cell growth. Immunohistochemistry of human colorectal cancer tissues showed elevated expression of iPLA2gamma in adenocarcinoma cells. These results collectively suggest distinct roles for iPLA2beta and iPLA2gamma in cellular homeostasis and signaling, a functional link between peroxisomal AA release and eicosanoid generation, and a potential contribution of iPLA2gamma to tumorigenesis.

Adenocarcinoma↗
PubMed2004

Dual mode regulation of migration by lysophosphatidic acid in human gastric cancer cells.

Lysophosphatidic acid (LPA), which interacts with at least three G protein-coupled receptors (GPCRs), LPA1/Edg-2, LPA2/Edg-4, and LPA3/Edg-7, is a lipid mediator with diverse effects on various cells. Here, we investigated the expression profiles of LPA receptors and patterns of LPA-induced migration in gastric cancer cells. Northern blot analysis revealed that various gastric cancer cells expressed variable levels of LPA1, LPA2, and LPA3 without a consistent pattern. Using a Boyden chamber assay, LPA markedly increased cell migration of LPA1-expressing cells, the effects of which were almost totally abrogated by Ki16425, an LPA antagonist against LPA1 and LPA3. In contrast, LPA by itself did not significantly induce migration in MKN28 and MKN74 cells, which exclusively expressed LPA2. However, when hepatocyte growth factor (HGF) was placed with LPA in the lower chamber, LPA induced migration of these cells in a dose-dependent manner. Immunoprecipitation analysis revealed that LPA induced transient tyrosine phosphorylation of c-Met in LPA2-expressing cells, which suggests that the transactivation of c-Met by LPA causes a cooperative migratory response with HGF to these cells. Our results indicate that LPA regulates the migration of gastric cancer cells in a receptor-specific manner and suggest that the expression pattern of LPA receptors may affect the metastatic behavior of gastric cancer.

Chemotaxis↗
PubMed2004

Alkyl lysophosphatidic acid and fluoromethylene phosphonate analogs as metabolically-stabilized agonists for LPA receptors.

We describe an efficient method for the synthesis of alkyl lysophosphatidic acid (LPA) analogs as well as alkyl LPA mono- and difluoromethylene phosphonate analogs. Each alkyl LPA analog was evaluated for subtype-specific LPA receptor agonist activity using a cell migration assay for LPA(1) activation in cancer cells and an intracellular calcium mobilization assay for LPA(2) and LPA(3) activation. Alkyl LPAs induced pronounced cell migration activity with equivalent or higher potency than sn-1-oleoyl LPA, while the alkyl LPA fluoromethylene phosphonates proved to be less potent agonists in this assay. However, each alkyl LPA analog activated Ca(2+) release by activation of LPA(2) and LPA(3) receptors. Interestingly, the absolute configuration of the sn-2 hydroxyl group of the alkyl LPA analogs was not recognized by any of the three LPA receptors. The use of alkyl LPA analogs further expands the scope of structure-activity studies, which will better define LPA-LPA receptor interactions.

Animals↗
PubMed2004

Over-expression of lysophosphatidic acid receptor-2 in human invasive ductal carcinoma.

INTRODUCTION: Lysophosphatidic acid (LPA) is a bioactive phospholipid with diverse effects on various cells. It interacts with at least three G-protein-coupled transmembrane receptors, namely LPA1, LPA2 and LPA3, whose expression in various tumours has not been fully characterized. In the present study we characterized the expression profile of LPA receptors in human breast cancer tissue and assessed the possible roles of each receptor. METHODS: The relative expression levels of each receptor's mRNA against beta-actin mRNA was examined in surgically resected invasive ductal carcinomas and normal gland tissue using real-time RT-PCR. LPA2 expression was also examined immunohistochemically using a rat anti-LPA2 monoclonal antibody. RESULTS: In 25 cases normal and cancer tissue contained LPA1 mRNA at similar levels, whereas the expression level of LPA2 mRNA was significantly increased in cancer tissue as compared with its normal counterpart (3479.0 +/- 426.6 versus 1287.3 +/- 466.8; P < 0.05). LPA3 was weakly expressed in both cancer and normal gland tissue. In 48 (57%) out of 84 cases, enhanced expression of LPA2 protein was confirmed in carcinoma cells as compared with normal mammary epithelium by immunohistochemistry. Over-expression of LPA2 was detected in 17 (45%) out of 38 premenopausal women, as compared with 31 (67%) out of 46 postmenopausal women, and the difference was statistically significant (P < 0.05). CONCLUSION: These findings suggest that upregulation of LPA2 may play a role in carcinogenesis, particularly in postmenopausal breast cancer.

Antibodies, Monoclonal↗
PubMed2004

Type II platelet-activating factor-acetylhydrolase is essential for epithelial morphogenesis in Caenorhabditis elegans.

Type II platelet-activating factor-acetylhydrolase [PAF-AH (II)] is an N-myristoylated enzyme that contains a lipase/esterase catalytic motif and selectively hydrolyzes the sn-2 acetyl ester of PAF and other short-chain acyl groups attached to phosphoglycerides. However, the physiological role of this enzyme remains to be elucidated. PAF-AH (II) is conserved in a variety of species ranging from a simple multicellular organism, Caenorhabditis elegans, to mammals. C. elegans possesses two homologous PAF-AH (II) genes, named paf-1 and paf-2. In this study, we generated these two loss-of-function mutants to elucidate the in vivo PAF-AH (II) function. Surprisingly, mutants of paf-2, a major isoform of C. elegans PAF-AH (II)s, exhibits gross defects in epithelial sheet formation, resulting in unsuccessful subsequent morphogenesis with complete penetrance. Moreover, paf-2 RNA interference worms show a variable abnormal morphology, including ectopic protrusions and a lumpy shape at the late embryonic and early larval stages due to epithelial organization defects. Consistent with these phenotypes, PAF-AH (II) is predominantly expressed in epithelial cells of C. elegans. This study demonstrates that PAF-AH (II) is essential for epithelial morphogenesis.

1-Alkyl-2-acetylglycerophosphocholine Esterase↗
PubMed2004

Prostatic acid phosphatase degrades lysophosphatidic acid in seminal plasma.

Lysophosphatidic acid (LPA) is a lipid mediator with multiple biological activities and is detected in various biological fluids, including human seminal plasma. Due to its cell proliferation stimulatory and anti-apoptotic activities, LPA has been implicated in the progression of some cancers such as ovarian cancer and prostate cancer. Here, we show that prostatic acid phosphatase, which is a non-specific phosphatase and which has been implicated in the progression of prostate cancer, inactivates LPA in human seminal plasma. Human seminal plasma contains both an LPA-synthetic enzyme, lysoPLD, which converts lysophospholipids to LPA and is responsible for LPA production in serum, and its major substrate, lysophosphatidylcholine. In serum, LPA accumulated during incubation at 37 degrees C. However, in seminal plasma, LPA did not accumulate. This discrepancy is explained by the presence of a strong LPA-degrading activity. Incubation of LPA with seminal plasma resulted in the disappearance of LPA and an accompanying accumulation of monoglyceride showing that LPA is degraded by phosphatase activity present in the seminal plasma. When seminal plasma was incubated in the presence of a phosphatase inhibitor, sodium orthovanadate, LPA accumulated, indicating that LPA is produced and degraded in the fluid. Biochemical characterization of the LPA-phosphatase activity identified two phosphatase activities in human seminal plasma. By Western blotting analysis in combination with several column chromatographies, the major activity was revealed to be identical to prostatic acid phosphatase. The present study demonstrates active LPA metabolism in seminal plasma and indicates the possible role of LPA signaling in male sexual organs including prostate cancer.

Acid Phosphatase↗
PubMed2004

Expression of NUDEL in manchette and its implication in spermatogenesis.

Nuclear distribution gene E-like product (NUDEL) is a mammal homologue of fungal NUDE and is involved in neuronal migration during brain development. High levels of NUDEL were expressed in murine testis as well as brain. During spermatogenesis, NUDEL was not detected until postnatal day 12 (P12), rising to significant levels at P27. NUDEL was localized predominantly along microtubules of the manchette in elongated spermatids. In maturing spermatids, NUDEL was observed only in the centrosomes, while mature testicular spermatozoa did not show any NUDEL expression. These results suggest that NUDEL plays an important role in germ cell formation, including nucleoplasmic transport and nucleus shaping by manchette microtubules.

1-Alkyl-2-acetylglycerophosphocholine Esterase↗
PubMed2004

Lysophosphatidic acid and autotaxin stimulate cell motility of neoplastic and non-neoplastic cells through LPA1.

Autotaxin (ATX) is a tumor cell motility-stimulating factor originally isolated from melanoma cell supernatant that has been implicated in regulation of invasive and metastatic properties of cancer cells. Recently, we showed that ATX is identical to lysophospholipase D, which converts lysophosphatidylcholine to a potent bioactive phospholipid mediator, lysophosphatidic acid (LPA), raising the possibility that autocrine or paracrine production of LPA by ATX contributes to tumor cell motility. Here we demonstrate that LPA and ATX mediate cell motility-stimulating activity through the LPA receptor, LPA(1). In fibroblasts isolated from lpa(1)(-/-) mice, but not from wild-type or lpa(2)(-/-), cell motility stimulated with LPA and ATX was completely absent. In the lpa(1)(-/-) cells, LPA-stimulated lamellipodia formation was markedly diminished with a concomitant decrease in Rac1 activation. LPA stimulated the motility of multiple human cancer cell lines expressing LPA(1), and the motility was attenuated by an LPA(1)-selective antagonist, Ki16425. The present study suggests that ATX and LPA(1) represent potential targets for cancer therapy.

Animals↗
PubMed2004

Mechanisms of lysophosphatidic acid production.

Lysophosphatidic acid is one of the most attractive phospholipid mediator with multiple biological functions and is implicated in various human diseases. In the past ten years much has been learned about the physiological roles of LPA through series of studies on LPA actions and its receptors. However, the molecular mechanisms of LPA have been poorly understood. LPA is produced in various conditions both in cells and in biological fluids, where multiple synthetic reactions occur. At least two pathways are postulated. In serum and plasma, LPA is mainly converted from lysophospholipids. By contrast, in platelets and some cancer cells, LPA is converted from phosphatidic acid. In each pathway, at least two phospholipase activities are required: phospholipase A1 (PLA1)/PLA2 plus lysophospholipase D (lysoPLD) activities are involved in the first pathway and phospholipase D (PLD) plus PLA1/PLA2 activities are involved in the second pathway. Now multiple phospholipases are identified that account for PLA1, PLA2, PLD, and lysoPLD activities. In the absence of specific inhibitors and genetically modified animals and individuals, the contribution of each phospholipase to LPA production can not be easily determined. However, apparently certain extracellular phospholipases such as secretory PLA2 (sPLA2-IIA), membrane-associated PA-selective PLA1 (mPA-PLA1), lecithin-cholesterol acyltransferase (LCAT), and lysoPLD are involved in LPA production.

Cell Movement↗
PubMed2004

Aberrant expression of lysophosphatidic acid (LPA) receptors in human colorectal cancer.

Lysophosphatidic acid (LPA) is a simple bioactive phospholipid with diverse effects on various cells, that interacts with three G protein-coupled transmembrane receptors, LPA1, LPA2, and LPA3. The expression pattern and functions of these LPA receptors in various tumors have not been fully examined, except in ovarian cancer. To evaluate the LPA receptor expression profile in human colorectal cancer and in normal mucosa, we used real-time reverse transcription-polymerase chain reaction (RT-PCR) and measured the expression levels of LPA1, LPA2, and LPA3 messenger RNA (mRNA) in 26 colorectal cancers and 16 corresponding normal tissue samples. Normal epithelium expressed both LPA1 and LPA2 mRNA at similar levels. In comparison, colorectal cancers expressed LPA1 mRNA at a significantly lower level (0.3-fold; P<0.05), and LPA2 mRNA at a significantly higher level (three-fold; P<0.05), as compared with normal tissues. Thus, the ratio of LPA2/LPA1 increased markedly during malignant transformation (18-fold increase). LPA3 mRNA was expressed at only a low level in both normal and cancer tissues. We also assessed LPA2 expression immunohistochemically using a rat anti-LPA2 monoclonal antibody, and confirmed high expression of LPA2 in colorectal cancer at the protein level. As for LPA1, we examined Western blot analysis for 16 matched normal and cancer tissues. It revealed a significant decrease in the expression of LPA1 protein in cancer tissues compared to normal mucosa in nine of 16 cases, and in the remaining seven cases the expression levels was much the same. These results suggested that alteration of LPA receptor expression might be an important event in the development of colorectal cancer, and therefore, LPA and its receptors could be a chemopreventive target against colorectal cancer.

Adenocarcinoma↗
PubMed2003

Enantioselective responses to a phosphorothioate analogue of lysophosphatidic acid with LPA3 receptor-selective agonist activity.

The metabolically stabilized LPA analogue, 1-oleoyl-2-O-methyl-rac-glycerophosphothioate (OMPT), is a potent agonist for the LPA(3) G-protein-coupled receptor. A new enantiospecific synthesis of both (2R)-OMPT and (2S)-OMPT is described. Calcium release assays in both LPA(3)-transfected insect Sf9 and rat hepatoma Rh7777 cells showed that (2S)-OMPT was 5- to 20-fold more active than (2R)-OMPT. Similar results were found for calcium release, MAPK and Akt activation, and IL-6 release in human OVCAR3 ovarian cancer cells.

Animals↗
PubMed2003

Synthesis of migration-resistant hydroxyethoxy analogues of lysophosphatidic acid.

[reaction: see text] The susceptibility of lysophosphatidic acid (LPA) to intramolecular acyl migration impedes the determination of specific receptor activation by the sn-1 and sn-2 LPA regioisomers. An efficient enantioselective synthesis of hydroxyethoxy (HE)-substituted analogues of sn-1-acyl and 2-acyl LPA derivatives that possess palmitoyl and oleoyl chains is described. While the palmitoyl derivatives fail to activate calcium release in cells transfected with LPA(2) or LPA(3) G-protein-coupled receptors, the LPA(3) receptor is activated by both 1-HE and 2-HE oleoyl LPA analogues with a potency 10-fold lower than that of the parent oleoyl LPA.

Acylation↗
PubMed2003

Vascular remodeling induced by naturally occurring unsaturated lysophosphatidic acid in vivo.

BACKGROUND: We previously identified unsaturated (16:1, 18:1, and 18:2) but not saturated (12:0, 14:0, 16:0, and 18:0) lysophosphatidic acids (LPAs) as potent factors for vascular smooth muscle cell (VSMC) dedifferentiation. Unsaturated LPAs strongly induce VSMC dedifferentiation via the coordinated activation of the extracellular signal-regulated kinase (ERK) and p38 mitogen-activated protein kinase (p38MAPK), resulting in the proliferation and migration of dedifferentiated VSMCs. Here, we investigated the effects of 18:1 and 18:0 LPAs (as representative unsaturated and saturated LPAs, respectively) on the vasculature in vivo. METHODS AND RESULTS: Rat common carotid arteries (CCAs) were treated transiently with 18:1 or 18:0 LPA and then examined by histological and biochemical analyses. The 18:1 but not 18:0 LPA potently induced vascular remodeling that was composed primarily of neointima. The incorporation of [3H]18:1 LPA into the CCAs revealed that a sufficient amount of unmetabolized [3H]18:1 LPA to induce VSMC dedifferentiation was present in the vascular wall. The 18:1 LPA-induced neointimal formation in vivo was also dependent on the coordinated activation of ERK and p38MAPK. Unlike balloon-injured CCAs, the 18:1 LPA-treated CCAs showed a histological similarity to human atherosclerotic arteries. CONCLUSIONS: This is the first report demonstrating a role for a naturally occurring unsaturated LPA in inducing vascular remodeling in vivo and provides a novel animal model for neointimal formation.

Animals↗
PubMed2003

Biochemical and molecular characterization of two phosphatidic acid-selective phospholipase A1s, mPA-PLA1alpha and mPA-PLA1beta.

We have identified a novel phospholipase A1, named mPA-PLA1beta, which is specifically expressed in human testis and characterized it biochemically together with previously identified mPA-PLA1alpha. The sequence of mPAPLA1beta encodes a 460-amino acid protein containing a lipase domain with significant homology to the previously identified phosphatidic acid (PA)-selective PLA1, mPA-PLA1alpha. mPA-PLA1beta contains a short lid and deleted beta9 loop, which are characteristics of PLA1 molecules in the lipase family, and is a member of a subfamily in the lipase family that includes mPA-PLA1alpha and phosphatidylserine-specific PLA1. Both mPA-PLA1beta and mPA-PLA1alpha recombinant proteins exhibited PA-specific PLA1 activity and were vanadate-sensitive. When mPAPLA1beta-expressing cells were treated with bacterial phospholipase D, the cells produced lysophosphatidic acid (LPA). In both mPA-PLA1alpha and beta-expressing cells, most of the PA generated by the phospholipase D (PLD) treatment was converted to LPA, whereas in control cells it was converted to diacylglycerol. When expressed in HeLa cells most mPA-PLA1alpha protein was recovered from the cell supernatant. By contrast, mPA-PLA1beta was recovered almost exclusively from cells. Consistent with this observation, we found that mPA-PLA1beta has higher affinity to heparin than mPA-PLA1alpha. We also found that the membrane-associated mPA-PLA1s were insoluble in solubilization by 1% Triton X-100 and were detected in Triton X-100-insoluble buoyant fractions of sucrose gradients. The present study raises the possibility that production of LPA by mPA-PLA1alpha and -beta occurs on detergent-resistant membrane domains of the cells where they compete with lipid phosphate phosphatase for PA.

Amino Acid Sequence↗
PubMed2003

Autotaxin hydrolyzes sphingosylphosphorylcholine to produce the regulator of migration, sphingosine-1-phosphate.

Autotaxin (ATX) is an exoenzyme that potently induces tumor cell motility, and enhances experimental metastasis and angiogenesis. ATX was shown recently to be identical to serum lysophospholipase D activity, producing lysophosphatidic acid (LPA) from lyso-glycerophospholipids. LPA, itself a strong chemoattractant for tumor cells, may mediate the actions of ATX. We now extend the substrate specificity to sphingosylphosphorylcholine (SPC), which ATX hydrolyzes to sphingosine-1-phosphate (S1P). Under migration assay conditions, this novel reaction for the production of S1P has a substrate (SPC) K(m) = 0.23 +/- 0.07 mM. In our responder cell lines (NIH3T3 clone7 and A2058), S1P exerts maximal biological effects at concentrations of 10-100 nM and is mimicked in its biological effects by ATX plus SPC. These effects include inhibition of ATX- and LPA-stimulated motility, and elevation of activated Rho. In NIH3T3 clone7 cells stimulated with platelet-derived growth factor and treated with 10-25 nM S1P, motility is not inhibited and activation of Rho is unaffected, indicating that S1P possesses specificity in its effects. The exoenzyme ATX can potentially regulate diverse processes such as motility and angiogenesis via the S1P family of receptors. Because ATX hydrolyzes nucleotides, lyso-glycerophospholipids, and phosphosphingolipids into bioactive products, it possesses the ability, depending on the availability of substrates, to act as positive or negative regulator of receptor-mediated activity in the cellular microenvironment.

3T3 Cells↗
PubMed2003

LIS1 missense mutations: variable phenotypes result from unpredictable alterations in biochemical and cellular properties.

Mutations in one allele of the human LIS1 gene cause a severe brain malformation, lissencephaly. Although most LIS1 mutations involve deletions, several point mutations with a single amino acid alteration were described. Patients carrying these mutations reveal variable phenotypic manifestations. We have analyzed the functional importance of these point mutations by examining protein stability, folding, intracellular localization, and protein-protein interactions. Our data suggest that the mutated proteins were affected at different levels, and no single assay could be used to predict the lissencephaly phenotype. Most interesting are those mutant proteins that retain partial folding and interactions. In the case of LIS1 mutated in F31S, the cellular phenotype may be modified by overexpression of specific interacting proteins. Overexpression of the PAF-AH alpha1 subunit dissolved aggregates induced by this mutant protein and increased its half-life. Overexpression of NudE or NudEL localized this mutant protein to spindle poles and kinetochores but had no effect on protein stability. Our results implicate that there are probably different biochemical and cellular mechanisms obstructed in each patient yielding the varied lissencephaly phenotypes.

1-Alkyl-2-acetylglycerophosphocholine Esterase↗
PubMed2003

The hydrolysis of lysophospholipids and nucleotides by autotaxin (NPP2) involves a single catalytic site.

Autotaxin (NPP2) is a tumor cell motility-stimulating factor that displays both a nucleotide pyrophosphatase/phosphodiesterase activity and a recently described lysophospholipase D activity. The hydrolysis of nucleotides is a metal-assisted reaction that occurs via a nucleotidylated threonine in the catalytic site. We show here that the catalytic site threonine and the metal-coordinating residues are also essential for the hydrolysis of lysophospholipids. In comparing the substrate specificity of NPP2 and the closely related NPP1 and NPP3, we found that only NPP2 displayed a lysophospholipase D activity, whereas NPP1 and NPP3 had a much higher nucleotide pyrophosphatase activity.

Animals↗