A novel phosphatidic acid-selective phospholipase A1 that produces lysophosphatidic acid

International Union of Basic and Clinical Pharmacology. LXXVIII. Lysophospholipid receptor nomenclature

Lysophospholipids are cell membrane-derived lipids that include both glycerophospholipids such as lysophosphatidic acid (LPA) and sphingoid lipids such as sphingosine 1-phosphate (S1P). These and related molecules can function in vertebrates as extracellular signals by binding and activating G protein-coupled receptors. There are currently five LPA receptors, along with a proposed sixth (LPA₁-LPA₆), and five S1P receptors (S1P₁-S1P₅). A remarkably diverse biology and pathophysiology has emerged since the last review, driven by cloned receptors and targeted gene deletion ("knockout") studies in mice, which implicate receptor-mediated lysophospholipid signaling in most organ systems and multiple disease processes. The entry of various lysophospholipid receptor modulatory compounds into humans through clinical trials is ongoing and may lead to new medicines that are based on this signaling system. This review incorporates IUPHAR Nomenclature Committee guidelines in updating the nomenclature for lysophospholipid receptors ( http://www.iuphar-db.org/DATABASE/FamilyMenuForward?familyId=36).

Regulatory effect of lysophosphatidic acid on lymphocyte migration

Lysophosphatidic acid (LPA) is a lipid mediator that is known to exhibit chemotactic activity toward a variety of cancer cells. However, its effect on the immune system has not been studied extensively. Another lipid mediator, sphingosine-1-phosphate (S1P), has been shown to influence lymphocyte recirculation by regulating lymphocyte egress from lymphoid organs. In this study, we found that LPA inhibits spontaneous migration of mouse splenic lymphocytes through a chemorepulsive effect. We also demonstrated that LPA inhibits chemokine CCL21-induced lymphocyte migration. This inhibitory effect on CCL21-induced migration was observed for both T and B cells. The involvement of a receptor, LPA(1), LPA(2) or LPA(3), in the inhibition of the CCL21-induced migration was confirmed with a synthetic agonist, oleyl thiophosphate. Considering that the signaling by CCL21 through cognate receptor CCR7 contributes to lymphocyte homing and dendritic cell trafficking to lymph nodes, LPA may play a role as a key regulator of these processes. The inhibitory effect of LPA is in remarkable contrast to the effect of S1P receptor signaling, which is known to potentiate lymphocyte chemotaxis involving CCR7.

Aiming drug discovery at lysophosphatidic acid targets

Lysophosphatidic acid (LPA, 1-radyl-2-hydroxy-sn-glycero-3-phosphate) is the prototype member of a family of lipid mediators and second messengers. LPA and its naturally occurring analogues interact with G protein-coupled receptors on the cell surface and a nuclear hormone receptor within the cell. In addition, there are several enzymes that utilize LPA as a substrate or generate it as a product and are under its regulatory control. LPA is present in biological fluids, and attempts have been made to link changes in its concentration and molecular composition to specific disease conditions. Through their many targets, members of the LPA family regulate cell survival, apoptosis, motility, shape, differentiation, gene transcription, malignant transformation and more. The present review depicts arbitrary aspects of the physiological and pathophysiological actions of LPA and attempts to link them with select targets. Many of us are now convinced that therapies targeting LPA biosynthesis and signalling are feasible for the treatment of devastating human diseases such as cancer, fibrosis and degenerative conditions. However, successful targeting of the pathways associated with this pleiotropic lipid will depend on the future development of as yet undeveloped pharmacons.

Prevalent LIPH founder mutations lead to loss of P2Y5 activation ability of PA-PLA1alpha in autosomal recessive hypotrichosis

Autosomal recessive hypotrichosis (ARH) is characterized by sparse hair on the scalp without other abnormalities. Three genes, DSG4, LIPH, and LPAR6 (P2RY5), have been reported to underlie ARH. We performed a mutation search for the three candidate genes in five independent Japanese ARH families and identified two LIPH mutations: c.736T>A (p.Cys246Ser) in all five families, and c.742C>A (p.His248Asn) in four of the five families. Out of 200 unrelated control alleles, we detected c.736T>A in three alleles and c.742C>A in one allele. Haplotype analysis revealed each of the two mutant alleles is derived from a respective founder. These results suggest the LIPH mutations are prevalent founder mutations for ARH in the Japanese population. LIPH encodes PA-PLA(1)alpha (LIPH), a membrane-associated phosphatidic acid-preferring phospholipase A(1)alpha. Two residues, altered by these mutations, are conserved among PA-PLA(1)alpha of diverse species. Cys(246) forms intramolecular disulfide bonds on the lid domain, a crucial structure for substrate recognition, and His(248) is one amino acid of the catalytic triad. Both p.Cys246Ser- and p.His248Asn-PA-PLA(1)alpha mutants showed complete abolition of hydrolytic activity and had no P2Y5 activation ability. These results suggest defective activation of P2Y5 due to reduced 2-acyl lysophosphatidic acid production by the mutant PA-PLA(1)alpha is involved in the pathogenesis of ARH.

Autotaxin--an LPA producing enzyme with diverse functions

Autotaxin (ATX) is an ecto-enzyme responsible for lysophosphatidic acid (LPA) production in blood. ATX is present in various biological fluids such as cerebrospinal and seminal fluids and accounts for bulk LPA production in these fluids. ATX is a member of the nucleotide pyrophosphatase/phosphodiesterase (NPP) family and was originally isolated from conditioned medium of melanoma cells as an autocrine motility stimulating factor. LPA, a second-generation lipid mediator, binds to its cognate G protein-coupled receptors through which it exerts a number of biological functions including influencing cell motility and proliferation stimulating activity. Some of the biological roles of LPA can be mediated by ATX. However, there are other LPA-producing pathways independent of ATX. The accumulating evidences for physiological and pathological functions of ATX strongly support that ATX is an important therapeutic target. This review summarizes the historical aspects, structural basis, pathophysiological functions identified in mice studies and clinical relevance discovered by measuring the blood ATX level in human. The general features and functions of each NPP family member will be also briefly reviewed. The presence of the ATX gene in other model organisms and recently developed ATX inhibitors, both of which will be definitely useful for further functional analysis of ATX, will also be mentioned.

Biological roles of lysophosphatidic acid signaling through its production by autotaxin

Lysophosphatidic acid (LPA) exhibits a wide variety of biological functions as a bio-active lysophospholipid through G-protein-coupled receptors specific to LPA. Currently at least six LPA receptors are identified, named LPA(1) to LPA(6), while the existence of other LPA receptors has been suggested. From studies on knockout mice and hereditary diseases of these LPA receptors, it is now clear that LPA is involved in various biological processes including brain development and embryo implantation, as well as patho-physiological conditions including neuropathic pain and pulmonary and renal fibrosis. Unlike sphingosine 1-phosphate, a structurally similar bio-active lysophospholipid to LPA and produced intracellularly, LPA is produced by multiple extracellular degradative routes. A plasma enzyme called autotaxin (ATX) is responsible for the most of LPA production in our bodies. ATX converts lysophospholipids such as lysophosphatidylcholine to LPA by its lysophospholipase D activity. Recent studies on ATX have revealed new aspects of LPA. In this review, we highlight recent advances in our understanding of LPA functions and several aspects of ATX, including its activity, expression, structure, biochemical properties, the mechanism by which it stimulates cell motility and its pahto-physiological function through LPA production.

A novel enzyme immunoassay for the determination of phosphatidylserine-specific phospholipase A(1) in human serum samples

BACKGROUND

The bioactive lipid lysophosphatidylserine (LPS) is postulated to induce important biological responses and to be produced by phosphatidylserine-specific phospholipase A(1) (PS-PLA(1)). To evaluate the functional roles of LPS in vivo, a facile assay method for PS-PLA(1) has been awaited.

METHODS

Recombinant human PS-PLA(1) was produced using a baculovirus system, and anti-human PS-PLA(1) monoclonal antibodies were generated. Two clones were then selected for a 2-site immunoassay. The resulting PS-PLA(1) assay reagent was applied to a commercial automated immunoassay analyzer.

RESULTS

Satisfactory results were obtained for the within-run and between-run precision, interference, detection limit, and linearity of this PS-PLA(1) assay. The mean+/-SD of the serum PS-PLA(1) antigen concentration in the 191 healthy subjects was 33.8+/-16.6microg/l, and the central 95th percentile reference interval for the serum PS-PLA(1) antigen concentration was 13.8-74.1microg/l. The concentration was significantly (p<0.001) higher among men (13.8-80.6microg/l) than among women (12.1-68.8microg/l). We did not find a correlation between PS-PLA(1) and existing laboratory tests.

CONCLUSIONS

The present PS-PLA(1) assay method can be applied to clinical laboratory testing, and further studies are warranted to establish its clinical significance.

Autosomal-dominant woolly hair resulting from disruption of keratin 74 (KRT74), a potential determinant of human hair texture

Autosomal-dominant woolly hair (ADWH) is a rare disorder characterized by tightly curled hair. The molecular basis of ADWH has not previously been reported. In this study, we identified a Pakistani family with ADWH. The family showed linkage to chromosome 12q12-q14.1, containing the type II keratin gene cluster. We discovered a heterozygous mutation, p.Asn148Lys, within the helix initiation motif of the keratin 74 (KRT74) gene in all affected family members. KRT74 encodes the inner root sheath (IRS)-specific epithelial (soft) keratin 74. We demonstrate that the mutant K74 protein results in disruption of keratin intermediate filament formation in cultured cells, most likely in a dominant-negative manner. Furthermore, we sequenced the mouse Krt71-74 genes in the dominant Caracul-like 4 (Cal4) allele, which is characterized by a wavy-coat phenotype and maps to the same region of mouse chromosome 15 as the Caracul (Ca) and Reduced coat (Rco) alleles. We identified a heterozygous mutation, p.Glu440Lys, not in Krt74 but in the neighboring gene, Krt71. Krt71 was previously reported to harbor Ca and Rco mutations, as well as a coding SNP that is associated with curly-coated dogs. In this study, we define the ADWH phenotype resulting from a mutation in a hair-follicle-specific epithelial keratin in humans. Our findings not only further underscore the crucial roles of the IRS-specific epithelial keratin genes Krt71-74 in hair disorders but also open the possibility that these genes might function as genetic determinants of normal variation in hair texture across mammalian species.

Lipases and Related Molecules in Cancer

Lipases are enzymes that catalyze the hydrolysis of lipids. Based on protein structures and sequences, lipases can be classified into different protein families. The majority of conventional mammalian lipases are members of the protein super-families of serine esterases and alpha-beta hydrolases. Differential expression of lipases and related alpha-beta hydrolases in tumor cells has been observed. The physiological or patho-physiological functions of these tumor related enzymes are largely unknown. However, lipases are not only involved in energy metabolism but also in the metabolism of bioactive molecules, e.g. phosphatidic acid or arachidonic acid, suggesting that tumor-specifically expressed lipases might be interesting targets for the development of future treatment strategies. Moreover, independent of the patho-physiological function, tumor associated lipases can serve as targets for immunological treatment strategies. In addition, lipases with exclusive expression in single tumor entities can serve as potential diagnostic targets.

GPR35 is a novel lysophosphatidic acid receptor

GPR35 is a rhodopsin-like G protein-coupled receptor identified in 1998. It has been reported that kynurenic acid, a tryptophan metabolite, may act as an endogenous ligand for GPR35. However, the concentrations of kynurenic acid required to elicit the cellular responses are usually high, raising the possibility that another endogenous ligand may exist. In this study, we searched for another endogenous ligand for GPR35. Finally, we found that the magnitude of the Ca(2+) response induced by 2-acyl lysophosphatidic acid in the GPR35-expressing HEK293 cells was markedly greater than that in the vector-transfected control cells. Such a difference was not apparent in the case of 1-acyl lysophosphatidic acid. 2-Acyl lysophosphatidic acid also caused the sustained activation of RhoA and the phosphorylation of extracellular signal-regulated kinase, and triggered the internalization of the GPR35 molecule. These results strongly suggest that 2-acyl lysophosphatidic acid is an endogenous ligand for GPR35.

LPA receptors: subtypes and biological actions

Lysophosphatidic acid (LPA) is a small, ubiquitous phospholipid that acts as an extracellular signaling molecule by binding to and activating at least five known G protein-coupled receptors (GPCRs): LPA(1)-LPA(5). They are encoded by distinct genes named LPAR1-LPAR5 in humans and Lpar1-Lpar5 in mice. The biological roles of LPA are diverse and include developmental, physiological, and pathophysiological effects. This diversity is mediated by broad and overlapping expression patterns and multiple downstream signaling pathways activated by cognate LPA receptors. Studies using cloned receptors and genetic knockout mice have been instrumental in uncovering the significance of this signaling system, notably involving basic cellular processes as well as multiple organ systems such as the nervous system. This has further provided valuable proof-of-concept data to support LPA receptors and LPA metabolic enzymes as targets for the treatment of medically important diseases that include neuropsychiatric disorders, neuropathic pain, infertility, cardiovascular disease, inflammation, fibrosis, and cancer.

LPA(3), a unique G protein-coupled receptor for lysophosphatidic acid

Lysophosphatidic acid (LPA; 1- or 2-acyl-sn-glycerol-3-phosphate) is a phospholipid that is involved in numerous normal physiological and pathological processes such as brain development, blood vessel formation, embryo implantation, hair growth, neuropathic pain, lung fibrosis and colon cancer. Most of these functions are mediated by G protein-coupled receptors (GPCRs) specific to LPA. So far, six GPCRs for LPA have been identified: LPA(1)/Edg2, LPA(2)/Edg4, LPA(3)/Edg7, LPA(4)/GPR23/P2Y9, LPA(5)/GPR92 and LPA(6)/P2Y5. An intracellular target of LPA has also been proposed. Among the LPA receptors, LPA(3) is unique in that it is activated significantly by a specific form of LPA (2-acyl LPA with unsaturated fatty acids) and is expressed in a limited number of tissues such as the reproductive organs. Recent studies have shown that LPA(3)-mediated LPA signaling is essential for proper embryo implantation and have revealed an unexpected genetic linkage between LPA and prostaglandin signaling. Here we review recent advances in the study of LPA(3), especially studies using LPA(3)-deficient mice. In addition, we focus on the agonists and antagonists that are specific to each LPA receptor as important tools for the functional study of LPA signaling.

Lysophosphatidic acid (LPA) signaling in vertebrate reproduction

Lysophosphatidic acid (LPA) is a cell membrane phospholipid metabolite that can act as an extracellular signal. Its effects are mediated through at least five G protein-coupled receptors, LPA(1-5), and probably others as well. Studies in multiple species including LPAR-deficient mice and humans have identified or implicated important roles for receptor-mediated LPA signaling in multiple aspects of vertebrate reproduction. These include ovarian function, spermatogenesis, fertilization, early embryo development, embryo implantation, embryo spacing, decidualization, pregnancy maintenance and parturition. LPA signaling can also have pathological consequences, influencing aspects of endometriosis and ovarian cancer. Here we review recent progress in LPA signaling research relevant to female and male reproduction.

Measurement of endogenous lysophosphatidic acid by ESI-MS/MS in plasma samples requires pre-separation of lysophosphatidylcholine

The levels of lysophosphatidic acid (LPA) or lysophosphatidylcholine (LPC) in plasma have been shown to be markers for several human diseases, including cancers. Here we show that the presence of LPC or other lysophospholipids (LPLs) in lipids extracted from biological samples affects accurate measurement of endogenous LPA in biological samples. We report for the first time the artificial conversion of LPC and lysophosphatidylserine (LPS) to LPA at the ion source of electrospray ionization tandem mass spectrometry (ESI-MS/MS). To avoid the interference of LPC with the quantification of LPA, a method based on high-performance liquid chromatography (HPLC) separation of LPA from LPC has been developed.

In vitro analysis of LIPH mutations causing hypotrichosis simplex: evidence confirming the role of lipase H and lysophosphatidic acid in hair growth

Hypotrichosis simplex (HS) is a group of isolated alopecias that can be inherited as an autosomal-dominant or an autosomal-recessive trait. Hair loss usually begins in early childhood, and is diffuse and progressive. Mutations in LIPH, which encodes lipase member H, have recently been shown to cause an autosomal-recessive form of HS. Here we describe an Austrian HS patient who was found to be carrying compound heterozygous mutations in the LIPH gene: a 7-bp frameshift duplication (c.403_409dup; p.Gln137HisfsX1) and a recently reported 30-amino acid in-frame duplication (c.280_369dup; p.Gly94_Lys123dup). To examine the impact of LIPH mutations on lipid metabolism, we established an in vitro assay to measure the action of this phospholipase in a cell-based system. Both the 7-bp duplication frameshift mutation and all known in-frame mutations were observed to reduce the in vitro activity of the lipase in response to the addition of phosphatidic acid, the substrate of lipase H. The reduced production of lysophosphatidic acid (LPA) led to a reduced response of cells expressing the human G-protein-coupled receptor p2y5 (p2y5) receptor. Our study increases the spectrum of known LIPH mutations and provides biochemical evidence for the important role of lipase H and its product LPA in human hair growth.

Identification and characterization of a novel lysophosphatidic acid receptor, p2y5/LPA6

p2y5 is an orphan G protein-coupled receptor that is closely related to the fourth lysophosphatidic acid (LPA) receptor, LPA4. Here we report that p2y5 is a novel LPA receptor coupling to the G13-Rho signaling pathway. "LPA receptor-null" RH7777 and B103 cells exogenously expressing p2y5 showed [3H]LPA binding, LPA-induced [35S]guanosine 5'-3-O-(thio)triphosphate binding, Rho-dependent alternation of cellular morphology, and Gs/13 chimeric protein-mediated cAMP accumulation. LPA-induced contraction of human umbilical vein endothelial cells was suppressed by small interfering RNA knockdown of endogenously expressed p2y5. We also found that 2-acyl-LPA had higher activity to p2y5 than 1-acyl-LPA. A recent study has suggested that p2y5 is an LPA receptor essential for human hair growth. We confirmed that p2y5 is a functional LPA receptor and propose to designate this receptor LPA6.

The effect of inbreeding on the distribution of compound heterozygotes: a lesson from Lipase H mutations in autosomal recessive woolly hair/hypotrichosis

Autozygosity mapping in consanguineous families has proven to be a powerful method for identifying recessive disease genes. Using this technique with whole genome SNP data generated from low density mapping arrays, we previously identified two genes that underlie autosomal recessive woolly hair (ARWH/hypotrichosis; OMIM278150), specifically P2RY5 and Lipase H (LIPH). In the current study, we sought to identify a novel disease locus for ARWH/hypotrichosis by analyzing two large consanguineous families from Pakistan who had initially been excluded for mutations at either of these disease loci by haplotype analysis with microsatellite markers. A genome-wide analysis of 10 members from each of the two families failed to identify significant regions of autozygosity or linkage. Upon genotyping an additional 10 family members in one of the families, parametric linkage analysis identified a region on chromosome 3q27 with evidence for linkage (Z = 2.5). Surprisingly, this region contains the LIPH gene. Microsatellite markers located within the LIPH gene were used for haplotype analysis and demonstrated that not one, but two haplotypes were segregating with the phenotype in each of these families. DNA sequencing identified two distinct LIPH mutations (280_369dup90 and 659_660delTA). Each affected individual (n = 38) was either homozygous for one mutation (n = 7 and 16 respectively), or compound heterozygous (n = 15). A review of the literature identified several reports of compound heterozygotes in consanguineous families. Prompted by this finding, we derived the probability that a patient affected with a recessive disease is carrying two mutations at the disease locus. We suggest that the validity of the IBD assumption may be challenged in large consanguineous families.

Woolly antics between the sheaths

Hair is a potent cultural signal that when perceived as deficient can invite psychological trauma. Over the past few decades, researchers have successfully dissected several controls for hair follicle development and growth. However, we know relatively little about the genetic controls for hair fiber form and texture, despite wide variability in the expression of hair phenotypes among different, even very closely related, individuals. In this issue, Shimomura et al. present some intriguing insights into the potential role for lipase H in the control of hair form and texture.

Founder mutations in the lipase h gene in families with autosomal recessive woolly hair/hypotrichosis

Autosomal-recessive woolly hair (ARWH)/hypotrichosis is a hereditary hair disorder which is characterized by tightly curled hair and is associated with sparse hair. ARWH can be caused by mutations in the P2RY5 or lipase H (LIPH) gene. Disruption of either gene results in phenotypes with features of both wooly hair (WH) and hypotrichosis. In this study, we identified two Guyanese families with ARWH. Both families are of recent Indian descent. Mutation analysis resulted in the identification of mutations in the LIPH gene in both families. Affected individuals in the first family carry compound heterozygous mutations Ex7_8del and 1303_1309dupGAAAACG in the LIPH gene, while those in the second family have a homozygous mutation 659_660delTA in the LIPH gene. The mutations Ex7_8del and 659_660delTA were identified earlier in several Pakistani families with ARWH. Haplotype analysis using microsatellite markers close to the LIPH gene defined a founder haplotype shared in families from Pakistan and Guyana. Proteomic analysis of hair shaft samples from one of the families revealed no substantial changes among the proteins identified, indicating that the syndrome does not involve global alterations in protein expression. Our results further suggest a crucial role of LIPH gene in hair growth.

Mutations in the lipase H gene underlie autosomal recessive woolly hair/hypotrichosis

Woolly hair (WH) is characterized by the presence of fine and tightly curled hair. WH can appear as a symptom of some systemic diseases, or without associated findings (nonsyndromic WH). Nonsyndromic WH is known to be inherited as either an autosomal-dominant (OMIM 194300) or recessive (ARWH; OMIM 278150) trait. In this study, we identified 11 consanguineous families of Pakistani origin with ARWH, as well as associated features including sparse and hypopigmented hair shafts. We first checked for mutations in the P2RY5 gene, which encodes an orphan G-protein-coupled receptor that we recently identified as a cause of ARWH. However, none of the 11 families had mutations in the P2RY5 gene. To identify the disease locus, we performed linkage studies in one of these families using the Affymetrix 10K array, and identified a region of suggestive linkage on chromosome 3q27. This region contains the lipase H (LIPH) gene which has been recently shown to underlie an autosomal-recessive form of hypotrichosis. Mutation analysis resulted in the identification of a total of 5 pathogenic mutations in the LIPH of all 11 families analyzed. These results show that LIPH is a second causative gene for ARWH/hypotrichosis, giving rise to a phenotype clinically indistinguishable from P2RY5 mutations.

Autosomal recessive woolly hair with hypotrichosis caused by a novel homozygous mutation in the P2RY5 gene

During the last decade, several causative genes for hereditary hair diseases have been identified, which have disclosed the molecular mechanisms involved in hair follicle morphogenesis and cycling. We and others recently reported that mutations in the P2RY5 gene, encoding an orphan G protein-coupled receptor, underlie autosomal recessive woolly hair (WH)/hypotrichosis. Although these findings clearly reveal the involvement of P2RY5 mutations in hereditary hair diseases, the clinical manifestations of P2RY5 mutations have not completely been elucidated because of limited information to date. In this study, we ascertained a consanguineous family of Iranian origin with an affected girl showing sparse and hypopigmented scalp hair. She exhibited the WH phenotype with normal hair density at birth, but progressed with age to develop hypotrichosis. Direct sequencing analysis resulted in the identification of a novel homozygous mutation in the P2RY5 gene of the patient, which results in a non-conservative amino acid change, G146R, at the protein level. Our findings extend the mutation spectrum of P2RY5 mutations, and further support a crucial role of P2Y5 in hair growth in humans.

Lysophospholipid signaling in the function and pathology of the reproductive system

BACKGROUND

Lysophosphatidic acid (LPA) and sphingosine-1-phosphate (S1P) are two prominent signaling lysophospholipids (LPs) exerting their functions through a group of G protein-coupled receptors (GPCRs). This review covers current knowledge of the LP signaling in the function and pathology of the reproductive system.

METHODS

PubMed was searched up to May 2008 for papers on lysophospholipids/LPA/S1P/LPC/SPC in combination with each part of the reproductive system, such as testis/ovary/uterus.

RESULTS

LPA and SIP are found in significant amounts in serum and other biological fluids. To date, 10 LP receptors have been identified, including LPA(1-5) and S1P(1-5). In vitro and in vivo studies from the past three decades have demonstrated or suggested the physiological functions of LP signaling in reproduction, such as spermatogenesis, male sexual function, ovarian function, fertilization, early embryo development, embryo spacing, implantation, decidualization, pregnancy maintenance and parturition, as well as pathological roles in ovary, cervix, mammary gland and prostate cancers.

CONCLUSIONS

Receptor knock-out and other studies indicate tissue-specific and receptor-specific functions of LP signaling in reproduction. More comprehensive studies are required to define mechanisms of LP signaling and explore the potential use as a therapeutic target.

Dioleoyl phosphatidic acid induces morphological changes through an endogenous LPA receptor in C6 glioma cells

Previously, we suggested that dioleoyl phosphatidic acid (PA) and lysophosphatidic acid (LPA) increased [Ca(2+)](i) through endogenous LPA receptors coupled to pertussis toxin-sensitive G proteins in rat C6 glioma cells. In the present report, we investigated morphological changes and cytotoxicity induced by PA and LPA in C6 glioma cells. Isoproterenol treatment led to changes in the cell morphology of rat C6 glioma cells, which were reverted by the addition of PA and LPA. PA-and LPA-induced morphological reversions were inhibited by treatment with Ki16425, an LPA(1)/LPA(3) receptor antagonist. VPC32183, another LPA(1)/LPA(3) receptor antagonist with a different structure, only inhibited PA-induced morphological reversion but not LPA-induced reversion. However, the reversions were not inhibited by treatment with pertussis toxin, a specific inhibitor of G(i/o) proteins. In addition, cytotoxicity was only induced by LPA but not by PA in C6 glioma cells. Our results suggest that PA may act as a partial agonist at endogenous LPA receptors, which are sensitive to Ki16425 and coupled to PTX-insensitive G proteins, to evoke morphological changes in C6 glioma cells.

Age-dependent loss of sperm production in mice via impaired lysophosphatidic acid signaling

Approximately half of all infertility cases can be attributed to male reproductive dysfunction for which low sperm count is a major contributing factor. The current study identified receptor-mediated lysophosphatidic acid (LPA) signaling as a new molecular component influencing male fertility. LPA is a small signaling phospholipid, the effects of which are mediated through at least five G protein-coupled receptors, named LPA 1-5. LPA1/2/3, but not LPA4/5, show high expression in mouse testis. Mice deficient in LPA1/2/3 showed a testosterone-independent reduction of mating activity and sperm production, with an increased prevalence of azoospermia in aging animals. A significant increase of germ cell apoptosis also was observed in testes. Germ cell apoptosis led to a reduction in germ cell proliferation. These data demonstrate a novel in vivo function for LPA signaling as a germ cell survival factor during spermatogenesis.

A novel deletion mutation in LIPH gene causes autosomal recessive hypotrichosis (LAH2)

Autosomal recessive hypotrichosis is a rare hereditary disorder characterized by sparse hair on scalp and rest of the body of affected subjects. Recently, three clinically similar autosomal recessive forms of hypotrichosis [localized autosomal recessive hypotrichosis (LAH)1], LAH2 and LAH3 have been mapped on chromosomes 18q12.1, 3q27.3, and 13q14.11-q21.32, respectively. For these three loci, two genes DSG4 for LAH1 and LIPH for LAH2 have been identified. To date, only five mutations in DSG4 and two in LIPH genes have been reported. In this study, we have ascertained two large unrelated consanguineous Pakistani families with autosomal recessive form of hypotrichosis. Affected individuals showed homozygosity to the microsatellite markers tightly linked to LIPH gene on chromosome 3q27. Sequence analysis of the gene in the affected subjects from both the families revealed a novel deletion mutation in exon 5 (c.659-660delTA) causing frameshift and downstream premature termination codon. All the three mutations identified in the LIPH gene, including the one in this study, are deletion mutations.

Heterologous expression, and biochemical and cellular characterization of CaPLA1 encoding a hot pepper phospholipase A1 homolog

Phospholipid signaling has been recently implicated in diverse cellular processes in higher plants. We identified a cDNA encoding the phospholipase A1 homolog (CaPLA1) from 5-day-old early roots of hot pepper. The deduced amino acid sequence showed that the lipase-specific catalytic triad is well conserved in CaPLA1. In vitro lipase assays and site-directed mutagenesis revealed that CaPLA1 possesses PLA1 activity, which catalyzes the hydrolysis of phospholipids at the sn-1 position. CaPLA1 was selectively expressed in young roots, at days 4-5 after germination, and rapidly declined thereafter, suggesting that the expression of CaPLA1 is subject to control by a development-specific mechanism in roots. Because transgenic work was extremely difficult in hot peppers, in this study we overexpressed CaPLA1 in Arabidopsis so as to provide cellular information on the function of this gene. CaPLA1 overexpressors had significantly longer roots, leaves and petioles, and grew more rapidly than the wild-type plants, leading to an early bolting phenotype with prolonged inflorescence. Microscopic analysis showed that the vegetative tissues of 35S:CaPLA1 plants contained an increased number of small-sized cells, which resulted in highly populated cell layers. In addition, mRNAs for cell cycle-controlled proteins and fatty acid catabolizing enzymes were coordinately upregulated in CaPLA1-overexpressing plants. These results suggest that CaPLA1 is functionally relevant in heterologous Arabidopsis cells, and hence might participate in a subset of positive control mechanisms of cell and tissue growth in transgenic lines. We discuss possible biochemical and cellular functions of CaPLA1 in relation to the phospholipid signaling pathway in hot pepper and transgenic Arabidopsis plants.

Disruption of P2RY5, an orphan G protein-coupled receptor, underlies autosomal recessive woolly hair

The genetic determinants of hair texture in humans are largely unknown. Several human syndromes exist in which woolly hair comprises a part of the phenotype; however, simple autosomal recessive inheritance of isolated woolly hair has only rarely been reported. To identify a gene involved in controlling hair texture, we performed genetic linkage analysis in six families of Pakistani origin with autosomal recessive woolly hair (ARWH; OMIM 278150). All six families showed linkage to chromosome 13q14.2-14.3 (Z = 17.97). In all cases, we discovered pathogenic mutations in P2RY5, which encodes a G protein-coupled receptor and is a nested gene residing within intron 17 of the retinoblastoma 1 (RB1) gene. P2RY5 is expressed in both Henle's and Huxley's layers of the inner root sheath of the hair follicle. Our findings indicate that disruption of P2RY5 underlies ARWH and, more broadly, uncover a new gene involved in determining hair texture in humans.

Dioleoyl phosphatidic acid increases intracellular Ca2+ through endogenous LPA receptors in C6 glioma and L2071 fibroblasts

Phosphatidic acid (PA) increased intracellular Ca(2+) concentration ([Ca(2+)](i)) in C6 rat glioma and L2071 mouse fibroblast cells. Dioleoyl PA (PA, 18:1) was the most efficacious, followed by dipalmitoyl PA (16:0 PA) and dimyristoyl PA (14:0 PA). Lysophosphatidic acid (LPA) also increased the [Ca(2+)](i) in the both cells. PA desensitized LPA-induced Ca(2+) response completely in C6 cells, but partly in L2071 cells. Treatment of pertussis toxin (PTX), a specific inhibitor of G(i/o)-type G proteins, completely ameliorated LPA- and PA-induced Ca(2+) response in C6 cells. However, in L2071 cells, PTX inhibited PA-induced Ca(2+) increase by 80% and LPA-induced one by 20%. Ki16425, a specific inhibitor of LPA(1)/LPA(3) receptors, completely inhibited both LPA- and PA-induced Ca(2+) responses in C6 cells. On the other hand, in L2071 cells, Ki16425 completely inhibited PA-induced Ca(2+) response, but partly LPA-induced one. VPC32183, another specific inhibitor of LPA(1)/LPA(3) receptors, completely inhibited LPA- and PA-induced Ca(2+) responses in both C6 and L2071 cells. Therefore, PA and LPA appear to increase [Ca(2+)](i) through Ki16425/VPC32183-sensitive LPA receptor coupled to PTX-sensitive G proteins in C6 cells. In L2071 cells, however, LPA increases [Ca(2+)](i) through Ki16425-insensitive LPA receptor coupled to PTX-insensitive G proteins and Ki16425-sensitive LPA receptor coupled to PTX-sensitive G protein, whereas PA utilized only the latter pathway. Our results suggest that PA acts as a partial agonist on endogenous LPA receptors, which are sensitive to Ki16425 and coupled to PTX-sensitive G protein, but not on LPA receptors, which are not sensitive to Ki16425 and coupled to PTX-insensitive G protein.

P2X7 receptor-mediated phosphatidic acid production delays ATP-induced pore opening and cytolysis of RAW 264.7 macrophages

In macrophages, extracellular ATP (ATPe) stimulation of P2X7 receptors (P2X7R) results in cation channel opening, non-specific pore formation, secretion of cytokines, killing of intracellular bacteria and cytolysis. Signaling pathways controlling these diverse responses are currently under investigation. Among these pathways, phospholipase D (PLD) has been implicated in P2X7R-activated macrophages killing of intracellular pathogenic bacteria. Here we present evidence that early P2X7R-mediated PLD activation reduces pore opening and delays cytolysis of RAW 267.4 macrophages induced by ATPe. Use of inhibitors of PA metabolic enzymes suggests that PA, and not one of its metabolites, is the bioactive lipid. This is strengthened by the observation that addition of exogenous PA also reduces pore formation and cytolysis of RAW 264.7 macrophages. However, the beneficial effects of PA are only transient, due to its conversion into diacylglycerol through PA phosphatase-1 activity during prolonged P2X7R stimulation. Revealing that the PLD/PA pathway mediates survival of macrophages provides a potent strategy to inhibit P2X7R-mediated cytolysis by controlling PA metabolism. This will be important in the case of P2X7R-induced killing of intracellular bacteria which is lately associated with macrophage death, limiting the potency of ATPe to eliminate pathogenic bacteria.

A mutation in the lipase H (LIPH) gene underlie autosomal recessive hypotrichosis

Hereditary hypotrichosis is a rare autosomal recessive disorder characterized by sparse hair on scalp and rest of the body of affected individuals. Two forms of such hypotrichosis LAH and AH have been mapped on chromosome 18q12.1 and 3q27, respectively. Mutations in desmogelin 4 (DSG4) gene have been reported to underlie LAH. Recently, a deletion mutation in Lipase H (LIPH) gene, located at AH locus, has been identified in two ethnic groups of Russian population. In the present study, a four generation Pakistani family with AH phenotype has been mapped to chromosome 3q27. Sequence analysis of candidate gene LIPH revealed a novel five base pair deletion mutation (c.346-350delATATA) in exon 2 of the gene leading to frameshift and downstream premature termination codon. The mutation reported in the family, presented here, is the second mutation identified in LIPH gene. The identification of a genetic defect in LIPH suggests that this enzyme regulates hair growth.

Structure and function of extracellular phospholipase A1 belonging to the pancreatic lipase gene family

Phospholipase A1 (PLA1) is an enzyme that hydrolyzes phospholipids and produces 2-acyl-lysophospholipids and fatty acids and is conserved in a wide range of organisms. Mammals have several enzymes that exhibit PLA1 activity in vitro. The extracellular PLA1s include phosphatidylserine (PS)-specific PLA1 (PS-PLA1), membrane-associated phosphatidic acid (PA)-selective PLA1s (mPA-PLA1alpha and mPA-PLA1beta), hepatic lipase (HL), endothelial lipase (EL) and pancreatic lipase-related protein 2 (PLRP2), all of which belong to the pancreatic lipase gene family. The former three PLA1s differ from other members in their substrate specificities, structural features and gene organizations, and form a subfamily in the pancreatic lipase gene family. PS-PLA1, mPA-PLA1alpha and mPA-PLA1beta exhibit only PLA1 activity, while HL, EL and PLRP2 show triacylglycerol-hydrolyzing activity in addition to PLA1 activity. The tertiary structures of lipases have two surface loops, the lid and the beta9 loop. The lid and the beta9 loop cover the active site in its closed conformation. An alignment of amino acid sequences of the pancreatic lipase gene family members revealed two molecular characteristics of PLA1s in the two surface loops. First, lipase members exhibiting PLA1 activity (PS-PLA1, mPA-PLA1alpha and mPA-PLA1beta, EL, guinea pig PLRP2 and PLA1 from hornet venom (DolmI)) have short lids. Second, PS-PLA1, mPA-PLA1alpha, mPA-PLA1beta and DolmI, which exhibit only PLA(1) activity, have short beta9 loops. Thus, the two surface loops appear to be involved in the ligand recognition. PS-PLA1 and mPA-PLA1s specifically hydrolyze PS and PA, respectively, producing their corresponding lysophospholipids. Lysophosphatidylserine and lysophosphatidic acid have been defined as lipid mediators with multiple biological functions. Thus, these PLA1s have a role in the production of these lysophospholipid mediators.

A novel phospholipase from Trypanosoma brucei

Phospholipase A(1) activities have been detected in most cells where they have been sought and yet their characterization lags far behind that of the phospholipases A(2), C and D. The study presented here details the first cloning and characterization of a cytosolic PLA(1) that exhibits preference for phosphatidylcholine (GPCho) substrates. Trypanosoma brucei phospholipase A(1) (TbPLA(1)) is unique from previously identified eukaryotic PLA(1) because it is evolutionarily related to bacterial secreted PLA(1). A T. brucei ancestor most likely acquired the PLA(1) from a horizontal gene transfer of a PLA(1) from Sodalis glossinidius, a bacterial endosymbiont of tsetse flies. Nano-electrospray ionization tandem mass spectrometry analysis of TbPLA(1) mutants established that the enzyme functions in vivo to synthesize lysoGPCho metabolites containing long-chain mostly polyunsaturated and highly unsaturated fatty acids. Analysis of purified mutated recombinant forms of TbPLA(1) revealed that this enzyme is a serine hydrolase whose catalytic mechanism involves a triad consisting of the amino acid residues Ser-131, His-234 and Asp-183. The TbPLA(1) homozygous null mutants generated here constitute the only PLA(1) double knockouts from any organism.

Human Hair Growth Deficiency Is Linked to a Genetic Defect in the Phospholipase Gene LIPH

The molecular mechanisms controlling human hair growth and scalp hair loss are poorly understood. By screening about 350,000 individuals in two populations from the Volga-Ural region of Russia, we identified a gene mutation in families who show an inherited form of hair loss and a hair growth defect. Affected individuals were homozygous for a deletion in the LIPH gene on chromosome 3q27, caused by short interspersed nuclear element-retrotransposon-mediated recombination. The LIPH gene is expressed in hair follicles and encodes a phospholipase called lipase H (alternatively known as membrane-associated phosphatidic acid-selective phospholipase A1alpha), an enzyme that regulates the production of bioactive lipids. These results suggest that lipase H participates in hair growth and development.

Transcriptional regulation of lysophosphatidic acid-induced interleukin-8 expression and secretion by p38 MAPK and JNK in human bronchial epithelial cells

HBEpCs (human bronchial epithelial cells) contribute to airway inflammation by secreting a variety of cytokines and chemokines in response to allergens, pathogens, viruses and environmental toxins and pollutants. The potent neutrophil chemoattractant, IL-8 (interleukin-8), is a major cytokine secreted by HBEpCs. We have recently demonstrated that LPA (lysophosphatidic acid) stimulated IL-8 production in HBEpCs via protein kinase C delta dependent signal transduction. However, mechanisms of IL-8 expression and secretion are complex and involve multiple protein kinases and transcriptional factors. The present study was undertaken to investigate MAPK (mitogen-activated protein kinase) signalling in the transcriptional regulation of IL-8 expression and secretion in HBEpCs. Exposure of HBEpCs to LPA (1 microM) enhanced expression and secretion of IL-8 by 5-8-fold and stimulated threonine/tyrosine phosphorylation of ERK (extracellular-signal-regulated kinase), p38 MAPK and JNK (c-Jun N-terminal kinase). The LPA-induced secretion of IL-8 was blocked by the p38 MAPK inhibitor SB203580, by p38 MAPK siRNA (small interfering RNA), and by the JNK inhibitor JNK(i) II, but not by the MEK (MAPK/ERK kinase) inhibitor, PD98059. LPA enhanced the transcriptional activity of the IL-8 gene; that effect relied on activation of the transcriptional factors NF-kappaB (nuclear factor kappaB) and AP-1 (activator protein-1). Furthermore, SB203580 attenuated LPA-dependent phosphorylation of IkappaB (inhibitory kappaB), NF-kappaB and phospho-p38 translocation to the nucleus, NF-kappaB transcription and IL-8 promoter-mediated luciferase reporter activity, without affecting the JNK pathway and AP-1 transcription. Similarly, JNK(i) II only blocked LPA-mediated phosphorylation of JNK and c-Jun, AP-1 transcription and IL-8 promoter-mediated luciferase reporter activity, without blocking p38 MAPK-dependent NF-kappaB transcription. Additionally, siRNA for LPA(1-3) receptors partially blocked LPA-induced IL-8 production and activation of MAPKs. The LPA1 and LPA3 receptors, as compared with LPA2, were most efficient in transducing LPA-mediated IL-8 production. These results show an independent role for p38 MAPK and JNK in LPA-induced IL-8 expression and secretion via NF-kappaB and AP-1 transcription respectively in HBEpCs.

Transcriptional regulation of lysophosphatidic acid-induced interleukin-8 expression and secretion by p38 MAPK and JNK in human bronchial epithelial cells

HBEpCs (human bronchial epithelial cells) contribute to airway inflammation by secreting a variety of cytokines and chemokines in response to allergens, pathogens, viruses and environmental toxins and pollutants. The potent neutrophil chemoattractant, IL-8 (interleukin-8), is a major cytokine secreted by HBEpCs. We have recently demonstrated that LPA (lysophosphatidic acid) stimulated IL-8 production in HBEpCs via protein kinase C delta dependent signal transduction. However, mechanisms of IL-8 expression and secretion are complex and involve multiple protein kinases and transcriptional factors. The present study was undertaken to investigate MAPK (mitogen-activated protein kinase) signalling in the transcriptional regulation of IL-8 expression and secretion in HBEpCs. Exposure of HBEpCs to LPA (1 microM) enhanced expression and secretion of IL-8 by 5-8-fold and stimulated threonine/tyrosine phosphorylation of ERK (extracellular-signal-regulated kinase), p38 MAPK and JNK (c-Jun N-terminal kinase). The LPA-induced secretion of IL-8 was blocked by the p38 MAPK inhibitor SB203580, by p38 MAPK siRNA (small interfering RNA), and by the JNK inhibitor JNK(i) II, but not by the MEK (MAPK/ERK kinase) inhibitor, PD98059. LPA enhanced the transcriptional activity of the IL-8 gene; that effect relied on activation of the transcriptional factors NF-kappaB (nuclear factor kappaB) and AP-1 (activator protein-1). Furthermore, SB203580 attenuated LPA-dependent phosphorylation of IkappaB (inhibitory kappaB), NF-kappaB and phospho-p38 translocation to the nucleus, NF-kappaB transcription and IL-8 promoter-mediated luciferase reporter activity, without affecting the JNK pathway and AP-1 transcription. Similarly, JNK(i) II only blocked LPA-mediated phosphorylation of JNK and c-Jun, AP-1 transcription and IL-8 promoter-mediated luciferase reporter activity, without blocking p38 MAPK-dependent NF-kappaB transcription. Additionally, siRNA for LPA(1-3) receptors partially blocked LPA-induced IL-8 production and activation of MAPKs. The LPA1 and LPA3 receptors, as compared with LPA2, were most efficient in transducing LPA-mediated IL-8 production. These results show an independent role for p38 MAPK and JNK in LPA-induced IL-8 expression and secretion via NF-kappaB and AP-1 transcription respectively in HBEpCs.

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.

Structural basis of endothelial lipase tropism for HDL

Lipoprotein lipase (LPL) and endothelial lipase (EL), the most closely related enzymes among the members of the triglyceride lipase gene family with regard to primary sequence, have distinct lipolytic properties (triglyceride lipase vs. phospholipase) as well as different preferences for specific types of lipoproteins [triglyceride-rich lipoproteins vs. high density lipoprotein (HDL)] Lipid substrate specificity is believed to be conferred by the lid region located in the amino-terminal domain of the enzymes, whereas surprisingly little work has been done to identify the region mediating lipoprotein substrate specificity. To determine the domain responsible for lipoprotein preference within each enzyme, we generated the domain chimeric enzyme LPL-EL. The heterologous carboxy-terminal (C terminal) domain did not change lipid substrate preference (triglyceride vs. phospholipase) as determined by using artificial substrates. The EL C-terminal domain, however, enabled LPL-EL to bridge HDL particles like wild-type EL, whereas LPL only mediated binding of very low density lipoprotein. Unlike wild-type LPL, LPL-EL had substantial ability to hydrolyze HDL lipids similar to that of wild-type EL. Overexpression of LPL-EL in wild-type mice resulted in significantly reduced levels of HDL cholesterol and phospholipids by 93 and 85%, respectively, similar to the extent seen in EL-expressing mice, whereas no reduction of these parameters was observed in LPL-expressing mice. We conclude that the C-terminal domain of EL is crucial for the ability of EL to bind and to hydrolyze HDL and converts LPL to an enzyme fully capable of hydrolyzing HDL, highlighting the importance of the C-terminal lipase domain in lipoprotein substrate preference.

Contribution of phospholipase D in endothelin-1-mediated extracellular signal-regulated kinase activation and proliferation in rat uterine leiomyoma cells

Endothelin (ET)-1 is a mitogenic factor in numerous cell types, including rat myometrial cells. In the present study, we investigated the potential role of ET-1 in the proliferation of tumoral uterine smooth muscle cells (ELT-3 cells). We found that ET-1 exerted a more potent mitogenic effect in ELT-3 cells than in normal myometrial cells, as indicated by the increase in [3H]thymidine incorporation, cell number, and bromodeoxyuridine incorporation. The ET-1 was more efficient than platelet-derived growth factor and epidermal growth factor to stimulate proliferation. The ET-1-mediated cell proliferation was inhibited in the presence of U0126, a specific inhibitor of (mitogen-activated protein kinase ERK kinase), indicating that extracellular signal-regulated kinase (ERK) activation is involved. Additionally, ET-1 induced the activation of phospholipase (PL) D, leading to the synthesis of phosphatidic acid (PA). The ET-1-induced activation of PLD was twofold higher in ELT-3 cells compared to that in normal cells. The two cell types expressed mRNA for PLD1a and PLD2, whereas PLD1b was expressed only in ELT-3 cells. The exposure of cells to butan-1-ol reduced ET-1-mediated production of PA by PLD and partially inhibited ERK activation and DNA synthesis. Addition of exogenous PLD or PA in the medium reproduced the effect of ET-1 on ERK activation and cell proliferation. Collectively, these data indicate that ET-1 is a potent mitogenic factor in ELT-3 cells via a signaling pathway involving a PLD-dependent activation of ERK. This highlights the potential role of ET-1 in the development of uterine leiomyoma, and it reinforces the role of PLD in tumor growth.

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.