a novel phosphatidic acid-selective phospholipase a1 that ...as prostate, testis, ovary, pancreas,...

A Novel Phosphatidic Acid-selective Phospholipase A1 that Produces

Lysophosphatidic Acid

Hirofumi Sonoda 1, Junken Aoki 1 *, Tatsufumi Hiramatsu 1, Mayuko Ishida 2,

Koji Bandoh 1, Yuki Nagai 1, Ryo Taguchi 2, Keizo Inoue 1,3, and Hiroyuki Arai 1

1 Graduate School of Pharmaceutical Sciences, The University of Tokyo, 7-3-1 Hongo,

Bunkyo-ku, Tokyo 113-0033, Japan

2 Faculty of Pharmaceutical Sciences, Nagoya City University, 3-1 Tanabe-dori, Mizuho-ku,

Nagoya, Aichi 467-0027, Japan

3 Present address

Faculty of Pharmaceutical Sciences, Teikyo University, Sagamiko, Tsukui, Kanagawa 199-

0195, Japan

* To whom all correspondence should be addressed.

Tel.: +81-3-5841-4723;

Fax: +81-3-3818-3173;

e-mail: [email protected]

Running title Phosphatidic acid-selective Phospholipase A1

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Copyright 2002 by The American Society for Biochemistry and Molecular Biology, Inc.

JBC Papers in Press. Published on June 12, 2002 as Manuscript M201659200 by guest on February 19, 2020

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Summary

Lysophosphatidic acid (LPA) is a lipid mediator with diverse biological

properties, although its synthetic pathways have not been solved fully. We report here the

cloning and characterization of a novel phosphatidic acid (PA)-selective phospholipase A1

(PLA1) that produces 2-acyl-LPA. The PLA1 was identified in the Genbank™ data base as a

close homologue of phosphatidylserine (PS)-specific PLA1 (PS-PLA1). When expressed in

insect Sf9 cells this enzyme was recovered from the Triton X-100 insoluble fraction and did

not show any catalytic activity toward exogenously added phospholipid substrates.

However, culture medium obtained from Sf9 cells expressing the enzyme was found to

activate EDG7/LPA3, a cellular receptor for 2-acyl-LPA. The activation of EDG7 was further

enhanced when the cells were treated with phorbol ester or a bacterial phospholipase D,

suggesting involvement of phospholipase D in the process. In the latter condition, an

increased level of LPA, but not other lysophospholipids, was confirmed by mass

spectrometry analyses. Expression of the enzyme is observed in several human tissues such

as prostate, testis, ovary, pancreas, and especially platelets. These data show that the

enzyme is a membrane-associated PA-selective PLA1 (mPA-PLA1) and suggest that it has a

role in LPA production.

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Introduction

Lysophosphatidic acid (1- or 2-acyl-lysophosphatidic acid; LPA) is a lipid mediator

with multiple biological functions (1-3). These include induction of platelet aggregation,

smooth muscle contraction, and stimulation of cell proliferation. LPA also promotes specific

responses of the cytoskeleton such as generation of actin stress fibers in fibroblasts or

inhibition of neurite outgrowth in neuronal cells. LPA evokes its multiple effects through G-

protein-coupled receptors (GPCR) that are specific to LPA (see below), with consequent

activation of phospholipase C (PLC) and phospholipase D (PLD), Ca2+ mobilization,

inhibition of adenylyl cycles, activation of mitogen-activated protein (MAP) kinase and

transcription of serum-response-element (SRE) transcriptional reporter genes, such as c-fos .

Recent studies have identified a new family of receptor genes for LPA (reviewed in (4, 5)).

Members of this family include three GPCRs belonging to the EDG (endothelial

differentiation gene) family, EDG2/LPA1 (6), EDG4/LPA2 (7) and EDG7/LPA3 (8). These

proteins may explain various cellular responses to LPA (6-8).

In contrast to the signal transduction mediated by LPA receptors, the molecular

mechanisms for LPA production are poorly understood. LPA is produced both in biological

fluids such as serum (9), and in various cells such as platelets (10, 11), and ovarian cancer

cells (12, 13). In these latter studies, it was speculated that LPA is produced by

phospholipase A2 (PLA2) from phosphatidic acid (PA) that is generated as a result of PLD

activation (12, 13). Tokumura et al. demonstrated that LPA is also produced in plasma from

lysophosphatidylcholine (LPC) by the action of lysophospholipase D, which may account for

the accumulation of LPA in aged plasma (14).

LPA, with various fatty acid species, has been detected in several biological systems.

For example, human serum contains LPA with both saturated (16:0, 18:0) and unsaturated

(16:1, 18:1, 18:2, 20:4) fatty acids (15). A similar LPA species was detected in human

platelets (10). The activity of LPA has been shown to be modulated by the length, degree of

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unsaturation, and linkage to the glycerol backbone of the fatty acyl chain (16-21). Of

particular interest is the detection of 2-linoleoyl-LPA in ascites from ovarian cancer patients,

which may account for the increased ability of the ascites to activate the growth of ovarian

cancer cell lines (22). We recently identified a novel LPA receptor, EDG7/LPA3, which

shows a relatively high affinity for 2-acyl-LPA with unsaturated fatty acid (8, 23). It is

generally accepted that the sn-1 position of glycerophospholipids is occupied by saturated

fatty acids whereas the sn-2 position is occupied by unsaturated fatty acids. This suggests

that phospholipase A1 (PLA1) as well as PLA2 are involved in LPA production.

PLA1 enzymes hydrolyze the sn-1 fatty acids from phospholipids. Although PLA1

activities are detected in many tissues and cell lines, a limited number of PLA1s have been

purified and cloned. We have purified and cloned a cDNA for phosphatidylserine-specific

PLA1 (PS-PLA1), a member of the lipase family, from the culture medium of activated rat

platelets. PS-PLA1 specifically hydrolyzes PS (24) and produces 2-acyl-

lysophosphatidylserine (LPS), which is a lipid mediator for mast cells (25), T cells (26) and

neural cells (27). We recently showed that PS-PLA1 stimulates histamine release from rat

peritoneal mast cells by hydrolyzing PS exposed on the surface of some cell types such as

apoptotic cells and activated platelets (25). Accordingly we searched GenBank™ for

sequences similar to PS-PLA1 and found one PS-PLA1 homologue. Here we demonstrate

that the PS-PLA1 homologue is a membrane-associated PA-selective PLA1 (mPA-PLA1) that

can produce a bioactive lysophospholipid, 2-acyl-LPA, by hydrolyzing PA generated by

PLD.

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Experimental Procedures

Materials

Phospholipase D from Actinomadura (28) was kindly donated by Meito Sangyo

(Tokyo, Japan). 1-oleoyl-LPA (18:1) and [3H] 1-oleoyl-LPA (18:1) were purchased from

Avanti Polar Lipids Inc. (Alabaster, AL) and Amersham Pharmacia Biotech (Uppsala,

Sweden), respectively. 2-oleoyl-LPA (18:1) was prepared as described previously (23).

Other chemicals were purchased from Wako Pure Chemical Industries (Osaka, Japan).

Clone Identification

The EST clone 789124 (GenBank™ accession AA149791) was identified by

searching the GenBank™ EST database using the amino acid sequence of rat PS-PLA1. The

cDNA clone was purchased from American Type Culture Collection (ATCC). The

nucleotide sequence of the clone was determined by DNA sequencing using an ABI PRISM

377 DNA sequencer. We also amplified the cDNA of mPA-PLA1 (nPLA1) by reverse-

transcriptase polymerase chain reaction (RT-PCR) using human colon-derived total RNA

(see below). The nucleotide sequence data reported in this paper have been submitted to the

GenBank™ database under the accession number AY036912 for human mPA-PLA1

Expression of mPA-PLA1 in Sf9 Cells

The DNA fragment covering the coding region of mPA-PLA1 (EcoRI-HindIII

fragment) was subcloned into the EcoRI and HindIII sites of pFASTBAC1 expression vector

(Life Technologies, Gaithersburg, MD) to generate a donor plasmid. Recombinant viruses

were prepared using the BAC-TO-BAC Baculovirus Expression System (Life Technologies)

according to the manufacturer's protocol. The resulting recombinant baculovirus was used to

infect Sf9 cells. Sf9 insect cells were grown in serum-free EX-CELL 420 insect cell medium

(Nichirei, Tokyo, Japan) at 27 °C. For infection, Sf9 cells were mixed with recombinant or

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wild-type Autographa californica nuclear polyhedrosis virus (AcNPV) to produce a

multiplicity of infection of 10 and the infected cells were further cultured for 48 h or 72 h at

27 °C.

PLA1 assay

Sf9 cells were harvested 72 h after baculovirus infection. The cells (1x107 cells/ml)

were suspended in phosphate-buffered saline (137 mM NaCl, 2.7 mM KCl, 8.1 mM

Na2HPO4 12H2O, 1.5 mM KH2PO4) and homogenized using a Potter-Elvehjem

homogenizer. The supernatant obtained by centrifugation of the homogenate at 190 x g for

10 min was centrifuged at 100,000 x g for 60 min and the resulting pellet was used as the

"membrane fraction". Dioleoyl-PA, dioleoyl-PS, dioleoyl-phosphatidylethanolamine

(dioleoyl-PE), and dioleoyl-phosphatidylcholine (dioleoyl-PC), containing a 14C-labeled

fatty acid at sn-1 position were prepared as described previously (24). The PA, PS, PE or

PC (40 µM each) were incubated at 37 °C for 30 min with membrane fraction prepared from

mPA-PLA1-expressing cells (100 µg protein) in 100 mM Tris-HCl (pH 7.5) with 4 mM

CaCl2. The fatty acid liberated was extracted by the modified Dole's method, and

radioactivity was measured with a scintillation counter as described previously (24).

Evaluation of EDG7 Activation

Evaluation of EDG7 activation was done by Ca2+ assays using EDG7-expressing Sf9

cells (Sf9-EDG7 cells) as described (23). 48 h after EDG7-baculovirus infection, the cells

were loaded with 2 mM Fura-2 acetoxymethyl ester (Fura-2 AM; Molecular Probes Inc.,

Eugene, OR) for 45 minutes. Free Fura-2 AM was washed out, and the cells were

resuspended in MBS (10 mM NaCl, 60 mM KCl, 17 mM MgCl2, 10 mM CaCl2, 110 mM

sucrose, 4 mM glucose, 0.1 % fatty acid-free BSA; (Sigma), and 10 mM MES, (pH 6.2)) to

produce a concentration of 106 cells/ml. To examine the activity of LPA, the measurement of

the ratio of emission wavelength of 500 nm by excitation wavelengths at 340 and 380 nm

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was performed in quartz cuvettes (total volume 1000µl) using a CAF-110 spectrofluorometer

(Japan Spectroscopy, Inc., Tokyo, Japan), or in 96-wells (total volume 200µl) using an

ARGUS-50/CA image analysis system (Hamamatsu Photonics K.K., Hamamatsu, Japan).

Exogenous PLD Treatment

Sf9 cells were harvested 72 h after baculovirus infection and suspended in MBS. Then

PLD from Actinomadura was added exogenously to the suspension to a final concentration of

0.25 units/ml, and the mixture was incubated for 30 minutes at 27 °C. After removing the

cells by centrifugation, the supernatant was used as "conditioned medium".

Lipid Preparation

Phospholipids were extracted by the method of Bligh and Dyer in acidic condition

(lower the pH to 3.0 with 1 N HCl). Lipids in the aqueous phase were re-extracted and

pooled with the previous organic phase. The extracted lipids were dried, dissolved in

chloroform/methanol (1:1) and used for functional bioassays and mass spectrometry (MS)

analysis. The recovery of lipids was monitored by the addition of trace amounts of 1-[3H]-

oleoyl-LPA to the samples. Under the above conditions, recovery of 1-[3H]-oleoyl-LPA

was always > 95 %. For MS analysis the lipids were concentrated 20-fold.

MS Analysis

MS analysis was performed essentially as described previously (29). Lipid extracts

from cells and conditioned media were analyzed by a Quattro II tandem quadrupole mass

spectrometer (Micromass, Manchester, UK) equipped with an electrospray ion-source (ESI-

MS). Two-microliter aliquots of samples (0.1-50 pmol/µl) dissolved in chloroform/methanol

(2:1) were introduced by means of a flow injector into the ESI chamber, at a flow rate of 2

µl/min. The eluting solvent was acetonitrile/methanol/water (2:3:1) containing 0.1 %

ammonium formate (pH 6.4). The mass spectrometer was operated in the positive and

negative ion scan modes. The nitrogen drying gas flow rate was 12 L/min and its

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temperature was 80 °C. Essentially, the capillary voltage was set at 3.7 kV and the cone

voltage was set at 30 V, both in the positive and negative ion scan modes. For MS/MS

experiments, 3-4 x 10-4 Torr of argon was used as the collision gas, and a collision energy of

30-40 V was used for obtaining fragment ions for precursor ions. In this system, we

obtained linearity up to 500 µM of LPA and 10 µM was the lower limit of detectable LPA

concentration.

Antibodies

A peptide consisting of the C-terminal 18 amino acids of mPA-PLA1 (434-

(C)MENVETVFQPILCPELQL-451) was conjugated with keyhole limpet hemocyanin. The

conjugate was injected into the hind foot pads of WKY/Izm rats using Freund's complete

adjuvant. The enlarged medial iliac lymph nodes from the rats were used for cell fusion with

mouse myeloma cells, PAI. The antibody-secreting hybridoma cells were selected by

screening with ELISA, immunofluorescence and Western blotting.

Western Blotting

Protein samples were separated by SDS-PAGE and transferred to nitrocellulose

membranes using the Bio-Rad protein transfer system. The membranes were blocked with

Tris-buffered saline containing 5 % (w:v) skimmed milk and 0.05 % (v:v) Tween 20,

incubated with anti-mPA-PLA1 monoclonal antibody (culture supernatant prepared from

clone 11H3), and then treated with anti-rat IgG-horseradish peroxidase. Proteins bound to

the antibodies were visualized with an enhanced chemiluminescence kit (ECL, Amersham

Pharmacia Biotech).

Immunofluorescent Staining

Sf9 cells infected with baculoviruses grown on cover glasses were fixed with ice-cold

methanol, and blocked with 10 % goat serum. After incubation with anti-mPA-PLA1

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monoclonal antibody (clone 11H3), followed by incubation with goat anti-rat IgG conjugated

with Alexa Fluor 488 (Molecular Probes Inc.), the bound antibody was detected with a

fluorescence microscope (Axiophot 2, Zeiss, Germany) and a confocal laser scanning

microscope (Fluoview, Olympus, Tokyo, Japan).

Northern Blotting

Human Multiple Tissue Northern Blots were purchased from CLONTECH (Palo

Alto, CA). The membrane was hybridized with a random-primed 32P-labeled EcoRI-XhoI

2.5 kb DNA probe at 65 °C for 4 h in Rapid Hybridization Buffer (Amersham Pharmacia

Biotech). The blot was rinsed in 2 x SSC at room temperature for 5 minutes, washed twice

in 0.5 x SSC–0.1 % SDS at 65 °C for 20 minutes, and used to expose Kodak X-Omat AR

film (Eastman Kodak company, New Haven, CT). The blots were re-hybridized with

glyceraldehyde-3-phosphate dehydrogenase (G3PDH) cDNA probe (CLONTECH) as an

internal standard.

RT-PCR

Human platelets were collected from healthy volunteers using standard protocol

as described previously (24). Total RNA was prepared using Isogen (Wako, Osaka, Japan).

Reverse transcription polymerase chain reaction (RT-PCR) was performed using Superscript

reverse transcriptase (Invitrogen), Ex-Taq polymerase (Takara, Kyoto, Japan). The

sequences of the two oligonucleotides used in RT-PCR were

TGCGAAGTAAATCATTCTTGTGAA (nucleotide position 39-62 and

TGTGACATCCATAGGACGCTACTG nucleotide position 1589-1566). Nucleotide

sequence of the PCR products were determined by direct sequencing.

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Results

Identification of a Novel PLA1 (nPLA1)

Our initial efforts to identify new phospholipases homologous to PS-PLA1 failed

using low stringency cross-hybridization techniques with PS-PLA1 sequences. A precise

search of the human Expressed Sequence Tags (EST) database was successful, and one PS-

PLA1-related gene fragment was identified (GenBank™ accession number AA149791).

DNA sequence analysis of the clone revealed that the sequence was highly homologous with

the entire open reading frames (ORFs) of rat and human PS-PLA1. This cDNA clone

contained a 1353-bp ORF, starting with the initiation codon (ATG) at nucleotide 91,

numbered as 1, and ending with a stop codon (TAA) at position 1444-1446 (Fig. 1A). This

ORF was flanked by 5' and 3' untranslated sequences of 90 bp and 1,001 bp, respectively,

and encoded 451 amino acids with a predicted molecular weight of 50,859 Da. Four

possible N-linked glycosylation sites and a hydrophobic sequence composed of 18 amino

acid residues at the N-terminus, were detected in the deduced amino acid sequence. This

hydrophobic sequence is probably a short signal sequence. By RT-PCR we detected a

cDNA that was identical to the DNA sequences in several human tissues (data not shown),

indicating the EST clone is not an artificial clone. The deduced amino acid sequence had

34.0 % identity with that of human PS-PLA1 (Fig. 1B), and the first half of the molecule,

which corresponds to the N-terminal catalytic domain of PS-PLA1 had an identity of about

40 %. Three of the amino acid residues in the ORF, Ser154, Asp178, and His248, are

completely conserved in the lipase family and are thought to make up a catalytic triad.

Like PS-PLA1, the molecule has a short lid composed of 12 amino acid residues

and a part of the β9 loop that is found in other lipases is deleted (Fig. 1B). Interestingly, the

same molecular features are also observed in all the hornet PLA1s that have been reported so

far (30-32). The lids and the β9 loops in lipases are implicated in the substrate recognition.

The phylogenetic tree in Fig. 1C and a BLAST search (data not shown) showed that the

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protein is the closest homologue of PS-PLA1 not only in the lipase family but also in the

database. Thus we tentatively designated this as a novel PLA1 (nPLA1).

nPLA1 Is a Membrane-associated Protein

In order to detect enzyme activity of the recombinant protein, we first tried to express

the protein in Sf9 insect cells by a baculovirus system and detected it as a protein band with

an apparent molecular weight of 55 kDa on a Western blotting using a monoclonal antibody

raised against the C-terminal 18 amino acids (see Materials and methods) (Fig. 2A). Unlike

PS-PLA1, which was mostly secreted into the culture medium when expressed in Sf9 cells

(24), the recombinant protein was detected only in the cell fraction (Fig. 2A). After high

speed centrifugation of the cell homogenate, the recombinant protein was detected

exclusively in the pellet (data not shown). In addition, it was found that the protein was

resistant to solubilization by Triton X-100 (Fig. 2A). Immunofluorescence images using the

anti-nPLA1 antibody and a confocal laser microscope are shown in Fig. 2B. This analysis

confirmed that the protein is localized exclusively to the plasma membrane.

Conditioned Medium from nPLA1-expressing Sf9 Cells Activates EDG7

We hypothesized that the newly identified protein would exhibit PLA1 and/or lipase

activity based on the similarity of its sequence to sequences of proteins in the lipase family.

We first determined whether the enzyme has PLA1 activity by an in vitro conventional assay

using various phospholipids as substrate and the membrane fraction from Sf9 cells

expressing nPLA1 (Sf9-nPLA1 cells) as an enzyme source. However, the protein in the

membrane fraction did not show any PLA activity toward exogenously added phospholipids

(data not shown).

Previously, we used Sf9 cells to characterize a novel LPA receptor that we isolated,

EDG7, which is a member of LPA receptor family. Cells expressing EDG7 (Sf9-EDG7

cells) were found to be strongly stimulated by exogenously added LPA (8). When we

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accidentally mixed the cultures of Sf9-nPLA1 and Sf9-EDG7 cells, we detected a small but

significant [Ca2+]i increase in Sf9-EDG7 cells (data not shown). This preliminary data

suggested that Sf9 cells expressing the newly identified protein may produce LPA, which

then stimulates EDG7. Accordingly we decided to analyze this phenomenon in more detail.

When we incubated Sf9-nPLA1 cells with medium containing 0.1 % BSA, we found that the

conditioned medium did induce a transient Ca2+ response in Sf9-EDG7 cells (Fig. 3A). The

response was not induced at all by a conditioned medium prepared from Sf9 cells infected

with wild-type baculovirus (Sf9-WT cells) (Fig. 3A). It was also shown that the conditioned

medium from the Sf9-nPLA1 cells desensitized the Ca2+ response induced by 100 nM LPA

(Fig. 3A) and that it did not induce any Ca2+ response in Fura-2-loaded Sf9-WT cells (data

not shown), confirming that the Ca2+ response is mediated by EDG7.

We next determined whether catalytic activity of nPLA1 is required for the induction

of a Ca2+ response. To do this we prepared a baculovirus to express mutant PLA1, in which

the putative active serine residue (Ser154) which is conserved among members of the

lipase/PLA1 family (Fig. 1B) was replaced with an alanine residue. Sf9 cells infected with

the mutant baculovirus (Sf9-mutPLA1 cells) expressed mutPLA1 protein at almost the same

level as Sf9-nPLA1 cells (Fig. 2A). However, the conditioned medium from Sf9-mutPLA1

cells did not induce any Ca2+ response in Sf9-EDG7 cells (Fig. 3B). This result indicates

that Ser154 is actually the active serine residue and that catalytic activity of nPLA1 is required

for the activation of EDG7. These results, taken together, indicate that LPA is continuously

produced and released from Sf9-nPLA1 cells.

Synthetic Pathway(s) for LPA in Sf9-nPLA1 Cells

From the data shown above, two pathways for LPA production were postulated in

which nPLA1 is involved. In the first pathway, nPLA1 hydrolyzes phospholipids which

results in an accumulation of lysophospholipids and a consequent degradation of the

lysophospholipids to LPA by the action of phospholipase D (PLD). In the second pathway,

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nPLA1 hydrolyzes PA and produces LPA. To test the first pathway, we determined whether

lysophospholipids are accumulated in Sf9-nPLA1 cells. For this we extracted phospholipids

from both Sf9-nPLA1 and Sf9-WT cells and performed lipid analysis by electrospray

ionization mass spectrometry (ESI-MS). As shown in Fig. 4, several compounds were

detected in the lipid fractions from both cell types. These included LPC (m/z 538 (16:1-LPC

ion paired with HCOOH) and 566 (18:1-LPC ion paired with HCOOH) in negative ion scan

mode), lysophosphatidylethanolamine (LPE) (m/z 450 (16:1-LPE) and 478 (18:1-LPE) in

negative ion scan mode), lysophosphatidylinositol (LPI) (m/z 569 (16:1-LPI), 597 (18:1-

LPI), 599 (18:0-LPI) in negative ion scan mode), and LPS (m/z 494 (16:1-LPS) and 522

(18:1-LPS), not shown). However, we did not observe any significant differences in the

expression profiles of lysophospholipids between Sf9-nPLA1 and Sf9-WT cells. We also

examined the lysophospholipid profiles in the conditioned media and did not observe any

difference in the expression of LPC, LPE, LPS and LPI (data not shown). Although a

significant difference in the activation of EDG7 was observed in the conditioned media

prepared from Sf9-nPLA1 and Sf9-WT cells (Fig. 3), signals corresponding to LPA were

not detected either in the conditioned medium or in the cells under the present conditions,

possibly due to a low sensitivity of the ESI-MS compared with the bioassay. Indeed, the

lower limit of LPA detection was only 10 µM for ESI-MS, whereas the bioassay could detect

1-oleoyl-LPA concentrations as low as 100 nM and 2-oleoyl-LPA concentrations as low as

10 nM.

To confirm the second pathway, we next examined whether activation of endogenous

PLD (Fig. 5) or exogenously added PLD (Fig. 6) affected the ability of the conditioned

medium from the Sf9-nPLA1 cells to activate EDG7. First we used the ability of phorbol 12-

myristate 13-acetate (PMA) to activate PLD via protein kinase C and that of short-chain

alcohol to inhibit PLD activity. As shown in Fig. 5, treatment of the cells with 100 nM PMA

for 30 minutes significantly enhanced the Ca2+ response in Sf9-EDG7 cells initiated by the

addition of conditioned medium from Sf9-nPLA1 cells. The enhancement was not induced

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by addition of conditioned medium from Sf9-WT cells treated with PMA (Fig. 5). We

further examined the effect of 1-butanol or 2-butanol on PMA-enhanced Ca2+ response.

Incubation of Sf9-nPLA1 cells with 100 nM PMA in the presence of 1-butanol at 0.5 %, a

concentration that completely inhibits PLD activity, completely blocked the Ca2+ response

enhanced by PMA treatment (Fig. 5), whereas 2-butanol, a positional isomer of 1-butanol

that does not have the ability to block PLD, at 0.5 % did not show such an effect (Fig. 5).

PMA, 1-butanol, or 2-butanol alone did not affect the Ca2+ responses (data not shown).

As shown in Fig. 6, the treatment of Sf9-nPLA1 cells with exogenously added PLD

significantly enhanced the ability of the conditioned medium to activate EDG7. The ability

of the conditioned medium from Sf9-nPLA1 cells to activate EDG7 was increased at least

100 times by the PLD treatment (Fig. 6). The conditioned media from Sf9-WT and Sf9-

mutPLA1 cells induced a small Ca2+ response in Sf9-EDG7 cells after the PLD treatment,

but they were at least 10 times less potent than the conditioned medium from Sf9-nPLA1

cells (Fig. 6), showing that a small amount of LPA is produced after the PLD treatment in

the absence of nPLA1. Addition of PLD alone to Sf9-EDG7 cells did not induce any

detectable Ca2+ response (data not shown). These two lines of evidences indicate that

nPLA1 produces 2-acyl-LPA by hydrolyzing PA generated on membranes by either

endogenously-expressed or exogenously-added PLD.

nPLA1 Is PA-selective PLA1

To further elucidate the substrate specificity of nPLA1, we next performed lipid

analysis of the conditioned medium prepared from Sf9-nPLA1 cells after the PLD treatment

using ESI-MS. As shown in Fig. 7, two major ion peaks (m/z 407 and 435) were detected

by ESI-MS (negative ion scan mode) in the lipid fraction extracted from the conditioned

medium from Sf9-nPLA1 cells after PLD treatment. These peaks are estimated from their

molecular weights to be 16:1-LPA and 18:1-LPA, respectively (29). They were only

weakly detected in the lipid fractions from Sf9-WT and Sf9-mutPLA1 cells even after the

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PLD treatment (Fig. 7). In the positive ion scan mode, four minor peaks m/z 409, 426, 437

and 454, were detected which were not detected in the lipid fractions from Sf9-WT and Sf9-

mutPLA1 cells (Fig. 7). 16:1-LPA and 18:1-LPA had m/z values of 407 and 435,

respectively, in the negative ion scan mode, 409 and 437, respectively, in the positive ion

scan mode, and 426 and 454, respectively, complexed with ammonium ion observed only in

the positive ion scan mode. The identities of the peaks were further confirmed by MS/MS

analysis of the daughter ions. The detected major fragment peaks from the precursor ion,

m/z 435, were m/z 78.7, 152.7, and 280.9. They correspond to PO3, cyclic

glycerophosphate, and oleic acid (18:1), respectively (data not shown). A similar result was

obtained from peak m/z 407 (data not shown). Thus we concluded that LPA with 16:1 and

18:1 were produced in Sf9-nPLA1 cells after the PLD treatment. Other than LPA, we

detected four ion peaks in the negative ion scan mode with m/z values 389 (16:1-cyclic PA

(cPA)), 417 (18:1-cPA), 450 (16:1-LPE) and 478 (18:1-LPE), and four ion peaks in the

positive ion scan mode with m/z values 452 (16:1-LPE), 480 (18:1-LPE), 494 (16:1-LPC)

and 522 (18:1-LPC), which were equally expressed among Sf9-nPLA1, Sf9-WT, and Sf9-

mutPLA1 cells. Other MS data (not shown) indicated that the major molecular species of

acyl chains at the sn-2 position of PC were specifically 16:1 and 18:1 fatty acids, while

those at the sn-1 position were 16:0, 16:1, 18:0 and 18:1 in Sf9 cells. This indicated that

16:1- and 18:1-LPA were generated as a result of the PLA1 reaction. All these results

support the hypothesis that the enzyme specifically acts on PA, and not on other

phospholipids, and hydrolyzes fatty acids at the sn-1 position, producing 2-acyl-LPA. Thus

we refer to the enzyme as membrane-associated PA-PLA1 (mPA-PLA1).

Expression of mPA-PLA1

We finally examined the tissue distribution of mPA-PLA1 by Northern blotting using

the full-length cDNA as a probe. The Northern blotting indicated that most of the human

tissues examined had a transcript of 3.3 kb and that some had transcripts of 4.4, 2.2 and 1.5

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kb. mPA-PLA1 is most abundantly expressed in prostate, testis, ovary, colon, pancreas,

kidney, and lung, and is expressed at lower levels in spleen, brain, and heart (Fig. 8A).

Interestingly, the expression pattern is similar, but not completely identical, to that of EDG7,

which is highly expressed in prostate, pancreas, ovary, testis, lung and heart (8). We also

examined mPA-PLA1 expression in human platelets since the cells have been well

characterized as LPA producing cells (10, 11). As shown in Fig. 8B, expression of mPA-

PLA1 in human platelets was confirmed by both mRNA and protein levels. A high level of

protein expression was observed in the cells, and was almost the same level observed in Sf9

overexpressing mPA-PLA1 (Fig. 8B).

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Discussion

The metabolic pathways for LPA synthesis are currently poorly understood and at

least three pathways have been postulated. In the first pathway, LPA is converted from PA

by PLA1 or PLA2, which has been observed to occur in erythrocytes and ovarian cancer cells

(12, 13, 33). In the second pathway, which may occur in platelets, diacylglycerol (DAG)

produced by PLC, could be deacylated by DAG lipase, with the resulting monoacylglycerol

(MAG) being further phosphorylated into LPA (34, 35). The third pathway involves

lysophospholipase D acting on LPC in plasma and may explain the large accumulation of

LPA in aged plasma (14). A similar reaction may occur on the cell surface, in which LPC

was converted to LPA by bacterial PLD (36). Enzymes involved in these process of LPA

synthesis have not been characterized fully. However, several PLA2 isoforms identified and

characterized biochemically have been implicated in LPA production. For example, studies

using inhibitors of PLA2 isoforms have suggested that sPLA2-IB, Ca2+ independent PLA2

(iPLA2), and cytosolic PLA2 (cPLA2) are partially involved in the LPA production of ovarian

cancer cells (12, 13). It was also proposed that sPLA2-IIA is able to produce LPA by

hydrolyzing PA exposed on the cell surface after phospholipid scrambling (37) or by

hydrolyzing PA on membrane microvesicles shed from erythrocytes (33).

The present investigation led to several interesting observations, allowing us to

propose a role of a novel PLA1 molecule, mPA-PLA1 in LPA production. What we showed

in this study are: (i) a low level of LPA that could activate EDG7 was continuously produced

and released into the medium in Sf9-mPA-PLA1 cells, (ii) the production of LPA in Sf9-

mPA-PLA1 cells was significantly increased after PLD administration (Fig. 7), and (iii) the

expression of mPA-PLA1 did not promote accumulation of any lysophospholipids including

LPC, LPE, LPI, and LPS in the cells (Fig. 4). (iv) We also observed that cPA was equally

detected in the media from Sf9-mPA-PLA1, Sf9-WT, and Sf9-mutPLA1 cells only after the

PLD treatment (Fig. 7). The bacterial PLD (from Actinomadura) used in this study converts

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lysophospholipids (LPC, LPE, LPS, and LPI) to cPA but not to LPA (T. Kobayashi,

Ochanomizu University, personal communication). All these results clearly indicate that

mPA-PLA1 produces LPA by hydrolyzing PA. We could not detect PLA1 activity of mPA-

PLA1 toward exogenously added PA liposome using a conventional assay for PLA1 or A2.

It can be speculated that the availability of exogenous substrate to the enzyme is limited, as

mPA-PLA1 is tightly associated with membrane phospholipids. mPA-PLA1 may hydrolyze

such phospholipids, which surround the enzyme on the plasma membrane, after the

phospholipids are converted to PA.

PA is a very minor component of phospholipids in mammalian cells and also in

Sf9 cells (38). This is consistent with the result that the LPA level was very low under

normal conditions (Fig. 5, and 6). It is thus reasonable to assume that the rate-limiting step

for LPA production in this pathway is generation of PA. PA could be generated by PLD or

sequentially by PLC and DAG kinase. We observed that exogenously added PLD strongly

promoted the production of LPA (Fig. 6 and 7) and that PMA-stimulated production of LPA

was suppressed by a PLD inhibitor, 1-butanol (Fig. 5). Thus, it is likely that PLD is

involved in the production of LPA mediated by mPA-PLA1. In mammalian cells, the

molecular identities of the two isozymes of PLD, PLD1 and PLD2, have been elucidated.

Among these two isozymes, PLD1 is activated by PMA both in vivo and in vitro through an

activation of protein kinase Cα (39). Although information about PLD isozyme(s) in Sf9

insect cells is limited (40), the observation that PMA stimulated LPA formation in Sf9-mPA-

PLA1 cells (Fig. 5) suggests an involvement of a PLD1-like molecule in the insect cells.

Consistent with this, it is reported by Shen et al. that LPA is produced and secreted from

ovarian cancer cells after they were treated with PMA (12).

LPA produced by mPA-PLA1 in Sf9 cells was rich in oleic acid (18:1) and

palmitoleic acid (16:1) (Fig. 7). Marheineke et al. reported that the major fatty acids in the

phospholipids from Sf9 cells were oleic acid, palmitoleic acid, and stearic acid (18:0), with a

small amount of palmitic acid (16:0) (38). This explains why LPA with linoleic acid (18:2)

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and arachidonic acid (20:4), which are the major fatty acids at the sn-2 position of

phospholipids of mammalian cells, was not detected. We observed that mPA-PLA1 is

abundantly expressed in human platelets that have been characterized well as LPA producing

cells (10, 11). In activated platelet, LPA with both saturated (16:0, 18:0) and unsaturated

(16:1, 18:1, 18:2, 20:4) has been detected. This suggests that both PLA1 and PLA2

isozymes are involved in the LPA production in the cells.

Although it is possible that EDG7 is activated by an entity other than LPA, this

seems unlikely for two reasons. First, the amount of LPA in the conditioned medium of Sf9-

mPA-PLA1 cells treated with PLD in approximately 5 µM based on the MS analysis (Fig. 7)

and 4 µM based on the dose response of EDG7 activation (Fig. 3C). Second, the amount of

LPA in the conditioned medium of untreated Sf9-mPA-PLA1 cells based on the bioassay is

approximately 400 nM, a concentration that can not be detected by MS analysis under the

present condition. These observation support the idea that LPA is the component that

activated EDG7.

What molecular structures determine the enzymatic activity of PLA1? Guinea pig

pancreatic lipase-related protein 2 (GPLRP2), which is 63 % identical to that of human

pancreatic lipase (HPL), differs from classical pancreatic lipases in that it displays both lipase

and PLA1 activity (41, 42). Based on the 3D structures of GPLRP2 and HPL, as well as a

modeling of hornet PLA1, two domain structures, the lid domain and the β9 loop, have been

suggested to play an essential role in substrate selectivity towards triacylglycerides and

phospholipids (43). The lid domain in lipases, which overlies the active site (44), has been

suggested to be involved in substrate recognition (45). One striking feature of molecules

belonging to the lipase family which show PLA1 activity is existence of "short" or "mini"

lids. In most of lipases the lids are composed of 22 or 23 amino acids. By contrast,

GPLRP2, hornet PLA1, PS-PLA1 and mPA-PLA1 have short lids composed of 5, 7, 12 and

12 amino acids, respectively (Fig. 1B). The other domain structure that is capable of

determining the substrate specificity of PLA1/lipase is the β9 loop, which is also located in

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the vicinity of the active site of lipases. The loop is present in HPL and GPLRP2 (showing

lipase activity), whereas it is absent in hornet PLA1, PS-PLA1 and mPA-PLA1. Thus,

simultaneous deletions of the β9 loop and the lid domain may determine the molecular

characteristics of PLA1 in the lipase family. These molecular features may allow us to

identify other PLA1 isozymes in the future.

mPA-PLA1 and PS-PLA1 form a subfamily within the lipase family (Fig. 1C). PS-

PLA1 produces LPS from PS (24, 46), a potential lysophospholipid mediator with an activity

to stimulate mast cell degranulation (47, 48) and neurite outgrowth (27). Recently we

showed that PS-PLA1 also functions as a synthetic enzyme of LPS (25). It is thus

reasonable to assume, from both structural and functional points of view, that these two

PLA1s have specialized common function(s) to produce lysophospholipid mediators.

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Acknowledgment

We thank Drs. Takashi Izumi (Gunma University) and Takao Shimizu (University of

Tokyo) for help in measurement of [Ca2+]i. This work was supported in part by research

grants from the Ministry of Education, Culture, Sports, Science and Technology , and by the

Human Frontier Special Program. Sonoda H. is a Research Fellow of the Japan Society for

the Promotion of Science.

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Abbreviations

The abbreviations used in this study are: PA, phosphatidic acid; PLA1,

phospholipase A1; mPA-PLA1, membrane-associated PA-selective PLA1; PS,

phosphatidylserine; PS-PLA1, PS-specific PLA1; PLA2, phospholipase A2; sPLA2-IIA, type

IIA secretory PLA2; PLD, phospholipase D; PC, phosphatidylcholine; PE,

phosphatidylethanolamine; LPA, lysophosphatidic acid; LPS, lysophosphatidylserine; LPC,

lysophosphatidylcholine; LPE, lysophosphatidylethanolamine; LPI,

lysophosphatidylinositol; EDG, endothelial differentiation gene; PCR, polymerase chain

reaction; EST, Expressed Sequence Tags; BSA, bovine serum albumin; ORF, open reading

frame; G3PDH, glyceraldehyde-3-phosphate dehydrogenase; SDS, sodium dodecyl sulfate;

SSC, standard saline citrate; [Ca2+]i, concentration of intracellular calcium ion; ESI-MS,

electrospray ionization mass spectrometry.

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Footnotes

The nucleotide sequence data reported in this paper have been submitted to the

GenBank database under the accession number AY036912 for human mPA-PLA1

Figure legends

Figure 1. Nucleotide and amino acid sequences of a newly identified human PLA1

(nPLA1)

(A) cDNA and amino acid sequence of human nPLA1. The first and second lines

indicate the nucleotide and the deduced amino acid sequences, respectively. Nucleotide and

amino acid positions are shown at the both sides. The consensus sequences for N-linked

glycosylation sites are boxed. Active serine, aspartic acid and histidine which make up the

catalytic triad of lipase are in bold and underlined. The putative signal sequence is

underlined. A short lid domain is doubly underlined. (B) Comparison of amino acid

sequences of nPLA1, human PS-PLA1, human pancreatic lipase (PL), human lipoprotein

lipase (LPL), and human hepatic lipase (HL). Amino acid residues conserved among all five

(phospho)lipases are indicated in bold. Ser, Asp, and His residues that are in italics and

underlined are the amino acid residues that form catalytic triads in the lipases. The lid

domains and β9 loops are indicated by shadowed boxes. (C) Phylogenetic relationship of

the lipase family and nPLA1. A phylogenetic tree was generated from ClustalW alignment

data using the GENETYX-MAC v10.1.6 (Software Development Co. Ltd., Tokyo, Japan).

This analysis found that nPLA1 and PS-PLA1 form a subfamily in the lipase family.

PLRP1, Pancreatic lipase-related protein 1; PLRP2, Pancreatic lipase-related protein 2.

Figure 2. Expression and cellular distribution of nPLA1 protein in Sf9 cells

(A) Sf9 cells were infected with nPLA1 (lanes a-d), wild-type (lanes e-h) or mutant

nPLA1 (lanes i-l) baculoviruses. 72 h after infection, the cells and culture supernatants were

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recovered. For each cell, culture supernatants (lanes a, e, and i), cells (lanes b, f, and j), Triton

X-100-soluble fraction of cells (lanes c, g, and k), and Triton X-100-insoluble fraction of cells

(lanes d, h, and l), (each derived from 5 x 105 cells), were prepared and were subjected to

Western blotting using anti-nPLA1 monoclonal antibody. (B) Sf9 cells infected with nPLA1

baculovirus were fixed with ice-cold methanol and incubated with anti-nPLA1 monoclonal

antibody. The bound antibody was detected by incubating the cells with goat anti-rat IgG

conjugated with Alexa Fluor 488. The phase contrast (a) and the fluorescence images (b) was

detected with a fluorescence microscope, and the confocal fluorescence image (c) was detected

with a confocal laser scanning microscope. nPLA1 protein is localized to the plasma membrane.

Scale bar, 20 µm (a, b) and 4 µm (c).

Figure 3. Conditioned medium prepared from nPLA1-expressing cells activates EDG7

(A) Sf9 cells infected with nPLA1 (Sf9-nPLA1 cells) or wild-type baculovirus (Sf9-

WT cells) were incubated with medium containing 0.1 % BSA (fatty acid free) for 30

minutes at 27 °C. Then the production of LPA was examined by subjecting the conditioned

media (40-fold dilution) to Fura-2-loaded EDG7-expressing Sf9 cells (Sf9-EDG7 cells). The

changes in [Ca2+]i were analyzed in CAF-110 as described in Experimental Procedures and

were expressed as the ratio of absorbance at 340 nm/380 nm. (B) Conditioned medium from

Sf9 cells infected with mutant nPLA1 (Sf9-mutPLA1 cells) was prepared as in (A), and it

was subjected to Fura-2-loaded Sf9-EDG7 cells (40-fold dilution). The conditioned medium

from Sf9-mutPLA1 did not induce any Ca2+ response in Sf9-EDG7 cells. (C) The activities

to induce increases in [Ca2+]i in Sf9-EDG7 cells were determined for each concentration of

1-oleoyl-LPA (open circle) or 2-oleoyl-LPA (closed circle).

Figure 4. Detection of lysophospholipids in Sf9-nPLA1 and Sf9-WT cells by MS

analysis

Phospholipids were recovered from both Sf9-nPLA1 and Sf9-WT cells, and were

subjected to lipid analysis using ESI-MS. The ESI-MS spectra of each lysophospholipid

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(LPC, LPE, and LPI) from both cells in the negative ion scan mode are shown. The

identities of each ion are 538 (16:1-LPC ion paired with HCOOH) and 566 (18:1-LPC ion

paired with HCOOH), 450 (16:1-LPE) and 478 (18:1-LPE) and 569 (16:1-LPI), 597 (18:1-

LPI) and 599 (18:0-LPI). The values representing 100 % of the Y-axis for LPC, LPE and

LPI are 1.7 x 105, 1.9 x 105 and 1.28 x 105 eV, respectively.

Figure 5. Possible involvement of intrinsic PLD in nPLA1-mediated EDG7 activation

Sf9-nPLA1 cells were treated with media containing PMA (100 nM), PMA + 1-

butanol (0.5 %), or PMA + 2-butanol (0.5 %), in the presence of 0.1 % BSA for 30 minutes

at 27 °C. Then the production of LPA was examined by subjecting the conditioned media to

Fura-2-loaded Sf9-EDG7 cells. The changes in [Ca2+]i were analyzed in CAF-110 as

described in Experimental Procedures and were expressed as the ratio of absorbance at 340

nm/380 nm. Values are the means ± S.E. of three independent experiments.

Figure 6. Exogenously added PLD enhanced the EDG7 activating potency of

conditioned medium from nPLA1-expressing cells

Sf9-nPLA1, Sf9-WT, and Sf9-mutPLA1 cells were incubated with medium

containing 0.1 % BSA (fatty acid free) for 30 minutes at 27 °C in the presence or absence of

0.25 units/ml of PLD from Actinomadura. Various concentrations of the conditioned media

were then subjected to Fura-2-loaded Sf9-EDG7 cells to evaluate LPA production. Changes

in [Ca2+]i were analyzed by an ARGUS-50 system as described in Experimental Procedures,

and were expressed as the ratio of absorbance at 340 nm/380 nm. Values are the means ±

S.E. of three independent experiments.

Figure 7. Detection of LPA in the conditioned medium from Sf9-nPLA1 cells after PLD

treatment by MS analysis

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The ESI-MS spectra of phospholipids from the conditioned media from Sf9-nPLA1,

Sf9-WT, and Sf9-mutPLA1 cells after they were treated with PLD from Actinomadura.

Results from both negative and positive ion scan mode are shown. The values representing

100 % of the Y-axis of negative and positive ion scan modes are 7.7 x 104 and 8.0 x 104 eV,

respectively. The major ions and their identities are 389 (16:1-cPA), 407 (16:1-LPA), 417

(18:1-cPA), 435 (18:1-LPA), 450 (16:1-LPE) and 478 (18:1-LPE) in negative ion scan

mode, and 409 (16:1-LPA), 426 (16:1-LPA ion paired with NH3), 437 (18:1-LPA), 454

(18:1-LPA ion paired with NH3), 494 (16:1-LPC) and 522 (18:1-LPC) in positive ion scan

mode.

Figure 8. Expression of mPA-PLA1 (nPLA1) in human tissues (A) and platelets (B)

(A) Two µg of polyA+ RNA from various human tissues (Human Multiple Tissue

Northern Blot, CLONTECH) were hybridized with probes specific for human mPA-PLA1

(upper panel) and G3PDH (lower panel). The origin of each RNA is shown at the top. The

molecular weight standard is shown at the left. (B) Expression of mPA-PLA1 in human

platelets was examined by both reverse transcription-polymerase chain reaction (RT-PCR)

and western blotting. The cDNA obtained from ATCC (see Materials and methods) was

used for positive control of PCR. Western blot analysis was performed as in Figure 2 using

the membrane fraction from human platelets and anti-mPA-PLA1 monoclonal antibody.

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1 TCCACGAGAAAATCCCACAGTGGAAACTCTTAAGCCTCTGCGAAGTAAATCATTCTTGTGAATGTGACACACGATCTCTCCAGTTTCCAT 90 91 ATGTTGAGATTCTACTTATTCATCAGTTTGTTGTGCTTGTCAAGATCAGACGCAGAAGAAACATGTCCTTCATTCACCAGGCTGAGCTTT 180 1 M L R F Y L F I S L L C L S R S D A E E T C P S F T R L S F 30

181 CACAGTGCAGTGGTTGGTACGGGACTAAATGTGAGGCTGATGCTCTACACAAGGAAAAACCTGACCTGCGCACAAACCATCAACTCCTCA 270 31 H S A V V G T G L N V R L M L Y T R K N L T C A Q T I N S S 60

271 GCTTTTGGGAACTTGAATGTGACCAAGAAAACCACCTTCATTGTCCATGGATTCAGGCCAACAGGCTCCCCTCCTGTTTGGATGGATGAC 360 61 A F G N L N V T K K T T F I V H G F R P T G S P P V W M D D 90

361 TTAGTAAAGGGTTTGCTCTCTGTTGAAGACATGAACGTAGTTGTTGTTGATTGGAATCGAGGAGCTACAACTTTAATATATACCCATGCC 450 91 L V K G L L S V E D M N V V V V D W N R G A T T L I Y T H A 120

451 TCTAGTAAGACCAGAAAAGTAGCCATGGTCTTGAAGGAATTTATTGACCAGATGTTGGCAGAAGGAGCTTCTCTTGATGACATTTACATG 540 121 S S K T R K V A M V L K E F I D Q M L A E G A S L D D I Y M 150

541 ATCGGAGTAAGTCTAGGAGCCCACATATCTGGGTTTGTTGGAGAGATGTACGATGGATGGCTGGGGAGAATTACAGGCCTCGACCCTGCA 630 151 I G V S L G A H I S G F V G E M Y D G W L G R I T G L D P A 180

631 GGCCCTTTATTCAACGGGAAACCTCACCAAGACAGATTAGATCCCAGTGATGCGCAGTTTGTTGATGTCATCCATTCCGACACTGATGCA 720 181 G P L F N G K P H Q D R L D P S D A Q F V D V I H S D T D A 210

721 CTGGGCTACAAGGAGCCATTAGGAAACATAGACTTCTACCCAAATGGAGGATTGGATCAACCTGGCTGCCCCAAAACAATATTGGGAGGA 810 211 L G Y K E P L G N I D F Y P N G G L D Q P G C P K T I L G G 240

811 TTTCAGTATTTTAAATGTGACCACCAGAGGTCTGTATACCTGTACCTGTCTTCCCTGAGAGAGAGCTGCACCATCACTGCGTATCCCTGT 900 241 F Q Y F K C D H Q R S V Y L Y L S S L R E S C T I T A Y P C 270

901 GACTCCTACCAGGATTATAGGAATGGCAAGTGTGTCAGCTGCGGCACGTCACAAAAAGAGTCCTGTCCCCTTCTGGGCTATTATGCTGAT 990 271 D S Y Q D Y R N G K C V S C G T S Q K E S C P L L G Y Y A D 300

991 AATTGGAAAGACCATCTAAGGGGGAAAGATCCTCCAATGACGAAGGCATTCTTTGACACAGCTGAGGAGAGCCCATTCTGCATGTATCAT 1080 301 N W K D H L R G K D P P M T K A F F D T A E E S P F C M Y H 330

1081 TACTTTGTGGATATTATAACATGGAACAAGAATGTAAGAAGAGGGGACATTACCATCAAATTGAGAGACAAAGCTGGAAACACCACAGAA 1170 331 Y F V D I I T W N K N V R R G D I T I K L R D K A G N T T E 360

1171 TCCAAAATCAATCATGAACCCACCACATTTCAGAAATATCACCAAGTGAGTCTACTTGCAAGATTTAATCAAGATCTGGATAAAGTGGCT 1260 361 S K I N H E P T T F Q K Y H Q V S L L A R F N Q D L D K V A 390

1261 GCAATTTCCTTGATGTTCTCTACAGGATCTCTAATAGGCCCAAGGTACAAGCTCAGGATTCTCCGAATGAAGTTAAGGTCCCTTGCCCAT 1350 391 A I S L M F S T G S L I G P R Y K L R I L R M K L R S L A H 420

1351 CCGGAGAGGCCTCAGCTGTGTCGGTATGATCTTGTCCTGATGGAAAACGTTGAAACAGTCTTCCAACCTATTCTTTGCCCAGAGTTGCAG 1440 421 P E R P Q L C R Y D L V L M E N V E T V F Q P I L C P E L Q 450

1441 TTGTAACTGTTGCCAGGACACATGGCCATAAATAATAGAAAGAAAGCTACAACCACAGGCTGTTTGAAAGCTTCACCTCACCTTTCTGCA 1530 451 L * (451)

1531 AAGCAGAAAAAGTATGAAAAAACCAAGGCTTTTTTCAGTAGCGTCCTATGGATGTCACATTGTACATCAAACAACCTTGTGATTATAAAA 16201621 CGATCCTGGGAAGGAGCCCCTAACTAGGGCAAGTCAGAAATAGCCAGGCTCGCAGCAGCGCAGCGCTGTGTCTGCTGTGTCCTGGGGCCT 17101711 CCCTTGTTCCGACCTGTCAATTCTGCTGCCTGTCACGCGGGTGGTTCTGCCCATCGCGGCTGCGGGTCAAGCATCTTCAAGGGAAGGACG 18001801 GACTGGAGGCCTCACCGTGGACTCAACTCTGCATTCTCCGTGCCACATTCCTCCAGTTCCCACACGTAGAAGGGAACGAAACTGACGTCT 18901891 ACCTCATGGGGCTGCTGTGTGGGTTTGGGAGGCAAAAATCTATGAAGGGTTTTTTGAAATCCCATAGGTGCCACATCTATGAGATGTTTG 19801981 ATAAATGTGAATATGCTTTTACATTTGGGCTTATCTAATTTGCAATAAGAGAGCCTCTCTCTATCAACACCAGCTTCTCTCTCGGGCTGT 20702071 TTGCTCAGGGAAGGCAAGAAAGCCACGTGCTGGCCCTCTGCCTTCTCTAAAGTGCTGTTGGAGCATGGAGGAGCTGGAGGAGATGGGGAT 21602161 GGACTGACAGCTAAGAGGGCGGCTGCTGGGACTAGATAGTGGATGAAGAAAGAAGGACGAGGAAGCCGTGGGGCAGCCTCTTCACATGGG 22502251 GACAGGGGATGGAGCATGAGGCAGGGGAAGGAAAAGCAGAGCTTATTTTTCACCTAAGGTGGAGAAGGATCACTTTACAGGCAACGCTCA 23402341 TTTTAAGCAACCCTTAAGAAATGTTTATGTTTCTTTATTACCAATGTAATCTATGATTATTGAAGGAAATTTAGAAAATGCGTAGATACA 24302431 AAAAAAAAAAAAAAAAA 2447

Sonoda et al. Fig. 1A

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nPLA1 1:MLRFY---LFI-SL----LCLSRSDA-EETCP-S-FTRLSFHSAV-VGTGLNVRLMLYTRKNLTCAQTI--NSSAF-G-NLNVTKKTTFI 74PS-PLA1 1:---MPPGPWESCFWVGGLILWLSVGSSGDAPPTPQPKCADFQSANLFEGTDLKVQFLLFVPSNPSCGQLVEGSSDLQNSGFNATLGTKLI 87PL 1:MLPLWTLSLLLGAVAGKEVCYERLGCFSDDSPWSGITERPLHILPWSPKDVNTRFLLYTNENPNNFQEVAADSSSISGSNFKTNRKTRFI 90LPL 1:---MESKAL-L-V-L-TLAVWLQSLTASRGGVAAA-DQRRDFIDIESKF-ALRTP--E-DTAEDTCHLIPGVAESVATCHFNHSSKTFMV 78HL 1:---MDTSPLCFSILL-VLCIFIQSSALGQSLKPEPFGRRAQAVETNKTLHEMKTRFLLFGETNQGCQIRINHPDTLQECGFNSSLPLVMI 86 nPLA1 75:VHGFRPTGSPPVWMDDLVKGL--LSVEDMNVVVVDWNRGATTLIYTHASSKTRKVAMVLKEFIDQMLAE-GASLDDIYMIGVSLGAHISG 161PS-PLA1 88:IHGFRVLGTKPSWIDTFIRTL--LRATNANVIAVDW-IYGSTGVYFSAVKNVIKL-SLEISLFLNKLLVLGVSESSIHIIGVSLGAHVGG 173PL 91:IHGFIDKGEEN-WLANVCKNL--FKVESVNCICVDW-KGGSRTGYTQASQNIRIVGAEVAYFVEFLQSAFGYSPSNVHVIGHSLGAHAAG 176LPL 79:IHGWTVTGMYESWVPKLVAALYKREPDS-NVIVVDW-LSRAQEHYPVSAGYTKLVGQDVARFINWMEEEFNYPLDNVHLLGYSLGAHAAG 166HL 87:IHGWSVDGVLENWIWQMVAALKSQPAQPVNVGLVDW-ITLAHDHYTIAVRNTRLVGKEVAALLRWLEESVQLSRSHVHLIGYSLGAHVSG 175 nPLA1 162:FVG--EMYDGWLGRITGLDPAGPLFNGKPHQDRLDPSDAQFVDVIHSDTD------ALGYKEPLGNIDFYPNGGLDQPGCPKTIL----- 238PS-PLA1 174:MVG--QLFGGQLGQITGLDPAGPEYTRASVEERLDAGDALFVEAIHTDTD------NLGIRIPVGHVDYFVNGGQDQPGCP-TFF----- 249PL 177:EAG--RRTNGTIGRITGLDPAEPCFQGTPELVRLDPSDAKFVDVIHTDGAPIVPNLGFGMSQVVGHLDFFPNGGVEMPGCKKNILSQIVD 264LPL 167:IAG-SL-TNKKVNRITGLDPAGPNFEYAEAPSRLSPDDADFVDVLHT-FTRGSPGRSIGIQKPVGHVDIYPNGGTFQPGCNIGEAIRVIA 253HL 176:FAGSSIGGTHKIGRITGLDAAGPLFEGSAPSNRLSPDDASFVDAIHT-FTREHMGLSVGIKQPIGHYDFYPNGGSFQPGCHFLELYRHIA 264 nPLA1 239:-GG-----FQYFKCDHQRSVYLYLSS-LRESCTITAYPCDSYQDYRNGKCVSCGTSQKESCPLLGYYADNWKDHLRGKDPPMTKAFFDTA 321PS-PLA1 250:YAG-----YSYLICDHMRAVHLYISAL-ENSCPLMAFPCASYKAFLAGRCLDCFNPFLLSCPRIGL-VEQGGVKIEPLPKEVKVYLLTTS 332PL 265:IDGIWEGTRDFAACNHLRSYKYYTDS-IVNPDGFAGFPCASYNVFTANKCFPC-PS--GGCPQMGHYADRYPG--KTNDVG-QKFYLDTG 347LPL 254:ERG-LGDVDQLVKCSHERSIHLFIDSLLNEENPSKAYRCSSKEAFEKGLCLSC---RKNRCNNLG-YEINKVRAKRSSKMYLKTRSQMPY 338HL 265:QHG-FNAITQTIKCSHERSVHLFIDSLLHAGTQSMAYPCGDMNSFSQGLCLSC---KKGRCNTLG-YHVRQEPRSKSKRLFLVTRAQSPF 349

nPLA1 322:EESPFCMYHYFVDIITWNKNVRRGDITIKLRDKAGNTTESKINHEPTTFQKY-HQVSLLARF-NQDLDKV-AAISLM--FS--TGSLIGP 404PS-PLA1 333:SAPYCMHHSLVEFHLKELRNKDTNIEVTFLSSNITSSSKITIPKQQRYGKGIIAHATPQCQI-NQVKFKFQSSNRVWK-KDRTTIIGKFC 420PL 348:DASNFARWRYKVSVTLSGKKV-TGHILVSLFGNKGNSKQYEI-FK-GTL-K--PDSTHSNEF-DSDVD-V-GDLQMVK-FIW-YNNVINP 426LPL 339:KVFHYQVKIHFSGTESETHTNQAFEISLYGTVAESENIPFTL-PEVSTNKTYSFLIYTEVDIGELLMLKLKWKSDSYF-S-W-S-D---- 419HL 350:KVYHYQLKIQFI-NQTETPIQTTFTMSLLGTKEKMQKIPITLGKGIASNKTYSFLITLDVDIGELIMIKFKWENSAVWANVWDTVQTIIP 438 nPLA1 405:RYKL-R---ILRMK-LRSLAHPERP-QLCRYDLVLMENVETVFQPIL-C-PELQL 451PS-PLA1 421:TALLPVNDREKMVCLPEPVNLQASVTVSCDLKIACV 456PL 427:TLP--R---VGASK-IIVETNVGKQFNFCSPE-TVREEVLLTLTP---C 465LPL 420:WWSSP---GFAIQKIRVKAGETQKKVIFCSREKVSHLQKGKAPAVFVKCHDKS-LNKKSG 475HL 439:WSTGPRHSGLVLKTIRVKAGETQQRMTFCSENTDDLLLRPTQEKIFVKCEIKSKTSKRKIR 499

β9 loop lid

lid

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Sonoda et al. Fig. 1C

PS-PLA1

nPLA1

endothelial lipase

lipoprotein lipase

hepatic lipase

pancreatic lipase

PLRP2

PLRP1

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Sonoda et al. Fig. 8B

RT-PCR

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Western blotting

human platelet 1 human platelet 2


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Nagai, Ryo Taguchi, Keizo Inoue and Hiroyuki AraiHirofumi Sonoda, Junken Aoki, Tatsufumi Hiramatsu, Mayuko Ishida, Koji Bandoh, Yuki

acidA novel phosphatidic acid-selective phospholipase A1 that produces lysophosphatidic

published online June 12, 2002J. Biol. Chem.

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a novel phosphatidic acid-selective phospholipase a1 that ...as prostate, testis, ovary, pancreas,...

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