Molecular cloning and characterization of a novel human G-protein-coupled receptor, EDG7, for lysophosphatidic acid

The critical role and potential target of the autotaxin/lysophosphatidate axis in pancreatic cancer

Autotaxin, an ecto-lysophospholipase D encoded by the human ENNP2 gene, is expressed in multiple tissues, and participates in numerous critical physiologic and pathologic processes including inflammation, pain, obesity, embryo development, and cancer via the generation of the bioactive lipid lysophosphatidate. Overwhelming evidences indicate that the autotaxin/lysophosphatidate signaling axis serves key roles in the numerous processes central to tumorigenesis and progression, including proliferation, survival, migration, invasion, metastasis, cancer stem cell, tumor microenvironment, and treatment resistance by interacting with a series of at least six G-protein-coupled receptors (LPAR1-6). This review provides an overview of the autotaxin/lysophosphatidate axis and collates current knowledge regarding its specific role in pancreatic cancer. With a deeper understanding of the critical role of the autotaxin/lysophosphatidate axis in pancreatic cancer, targeting autotaxin or lysophosphatidate receptor may be a potential and promising strategy for cancer therapy.

Preparation of functional human lysophosphatidic acid receptor 2 using a P9∗ expression system and an amphipathic polymer and investigation of its in vitro binding preference to Gα proteins

Human lysophosphatidic acid receptor 2 (LPA₂), a member of the G-protein coupled receptor family, mediates lysophosphatidic acid (LPA)-dependent signaling by recruiting various G proteins. Particularly, it is directly implicated in the progression of colorectal and ovarian cancer through G protein signaling cascades. To investigate the biochemical binding properties of LPA₂ against various alpha subunits of G protein (G_α), a functional recombinant LPA₂ was overexpressed in E. coli membrane with a P9^∗ expression system, and the purified protein was stabilized with an amphipathic polymer that had been synthesized by coupling octylamine, glucosamine, and diethyl aminoproylamine at the carboxylic groups of poly-γ-glutamic acid. The purified LPA₂ stabilized with the amphipathic polymer showed selective binding activity to the various G_α proteins as well as agonist-dependent dissociation from G_αi3. Understanding the binding properties of LPA₂ against various G_α proteins advances the understanding of downstream signaling cascades of LPA₂. The functional LPA₂ prepared using a P9^∗ expression system and an amphipathic polymer could also facilitate the development of LPA₂-targeting drugs.

Evaluation of pancreatic cancer cell migration with multiple parameters in vitro by using an optical real-time cell mobility assay device

Background

Migration of cancer cell correlates with distant metastasis and local invasion, which are good targets for cancer treatment. An optically accessible device “TAXIScan” was developed, which provides considerably more information regarding the cellular dynamics and less quantity of samples than do the existing methods. Here, we report the establishment of a system to analyze the nature of pancreatic cancer cells using TAXIScan and we evaluated lysophosphatidic acid (LPA)-elicited pancreatic cell migration.

Methods

Pancreatic cancer cell lines, BxPC3, PANC-1, AsPC1, and MIAPaCa-2, were analyzed for adhesion as well as migration towards LPA by TAXIScan using parameters such as velocity and directionality or for the number of migrated cells by the Boyden chamber methods. To confirm that the migration was initiated by LPA, the expression of LPA receptors and activation of intracellular signal transductions were examined by quantitative reverse transcriptase polymerase reaction and western blotting.

Results

Scaffold coating was necessary for the adhesion of pancreatic cancer cells, and collagen I and Matrigel were found to be good scaffolds. BxPC3 and PANC-1 cells clearly migrated towards the concentration gradient formed by injecting 1 μL LPA, which was abrogated by pre-treatment with LPA inhibitor, Ki16425 (IC₅₀ for the directionality ≈ 1.86 μM). The LPA dependent migration was further confirmed by mRNA and protein expression of LPA receptors as well as phosphorylation of signaling molecules. LPA₁ mRNA was highest among the 6 receptors, and LPA₁, LPA₂ and LPA₃ proteins were detected in BxPC3 and PANC-1 cells. Phosphorylation of Akt (Thr308 and Ser473) and p42/44MAPK in BxPC3 and PANC-1 cells was observed after LPA stimulation, which was clearly inhibited by pre-treatment with a compound Ki16425.

Conclusions

We established a novel pancreatic cancer cell migration assay system using TAXIScan. This assay device provides multiple information on migrating cells simultaneously, such as their morphology, directionality, and velocity, with a small volume of sample and can be a powerful tool for analyzing the nature of cancer cells and for identifying new factors that affect cell functions.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-017-3218-4) contains supplementary material, which is available to authorized users.

Different origins of lysophospholipid mediators between coronary and peripheral arteries in acute coronary syndrome

Lysophosphatidic acids (LysoPAs) and lysophosphatidylserine (LysoPS) are emerging lipid mediators proposed to be involved in the pathogenesis of acute coronary syndrome (ACS). In this study, we attempted to elucidate how LysoPA and LysoPS become elevated in ACS using human blood samples collected simultaneously from culprit coronary arteries and peripheral arteries in ACS subjects. We found that: 1) the plasma LysoPA, LysoPS, and lysophosphatidylglycerol levels were not different, while the lysophosphatidylcholine (LysoPC), lysophosphatidylinositol, and lysophosphatidylethanolamine (LysoPE) levels were significantly lower in the culprit coronary arteries; 2) the serum autotaxin (ATX) level was lower and the serum phosphatidylserine-specific phospholipase A₁ (PS-PLA₁) level was higher in the culprit coronary arteries; 3) the LysoPE and ATX levels were significant explanatory factors for the mainly elevated species of LysoPA, except for 22:6 LysoPA, in the peripheral arteries, while the LysoPC and LysoPE levels, but not the ATX level, were explanatory factors in the culprit coronary arteries; and 4) 18:0 and 18:1 LysoPS were significantly correlated with PS-PLA₁ only in the culprit coronary arteries. In conclusion, the origins of LysoPA and LysoPS might differ between culprit coronary arteries and peripheral arteries, and substrates for ATX, such as LysoPC and LysoPE, might be important for the generation of LysoPA in ACS.

Expression and function of lysophosphatidic acid receptors (LPARs) 1 and 3 in human hepatic cancer progenitor cells

Hepatocellular carcinoma (HCC) is the most common primary cancer of the liver and is characterized by rapid tumor expansion and metastasis. Lysophosphatidic acid (LPA) signaling, via LPA receptors 1–6 (LPARs1–6), regulates diverse cell functions including motility, migration, and proliferation, yet the role of LPARs in hepatic tumor pathology is poorly understood. We sought to determine the expression and function of endothelial differentiation gene (EDG) LPARs (LPAR1–3) in human HCC and complimentary in vitro models. Human HCC were characterized by significantly elevated LPAR1/LPAR3 expression in the microenvironment between the tumor and non-tumor liver (NTL), a finding mirrored in human SKHep1 cells. Analysis of human tissue and human hepatic tumor cells in vitro revealed cells that express LPAR3 (HCC-NTL margin in vivo and SKHep1 in vitro) also express cancer stem cell markers in the absence of hepatocyte markers. Treatment of SKHep1 cells with exogenous LPA led to significantly increased cell motility but not proliferation. Using pharmacological agents and cells transfected to knock-down LPAR1 or LPAR3 demonstrated LPA-dependent cell migration occurs via an LPAR3-Gi-ERK-pathway independent of LPAR1. These data suggest cells that stain positive for both LPAR3 and cancer stem cell markers are distinct from the tumor mass per se, and may mediate tumor invasiveness/expansion via LPA-LPAR3 signaling.

LPA receptor 1 mediates LPA-induced ovarian cancer metastasis: an in vitro and in vivo study

Background

The facts that LPA is present at high concentration in ovarian cancer patients’ ascites and it may serve as a stimulator to cell migration, implicate the role of LPA in the ovarian cancer metastasis. Since LPA mediates various biological functions through its interaction with LPA receptors, we aim to investigate the correlation between the expression of LPA receptors and the metastasis of ovarian cancer.

Methods

To test whether the LPA responsiveness correlated with the metastatic capability of ovarian cancer cells, we performed LPA induced invasion assay and peritoneal metastatic colonization assay with a panel of established human ovarian cancer cell lines. The expression of LPAR1-3 in different ovarian cancer lines was examined by qRT-PCR. We also tested the effects of LPAR1 inhibition or overexpression on ovarian cancer cell's invasiveness. To confirm our laboratory results, we detected LPARs expression in specimens from 52 ovarian cancer patients by qRT-PCR and immunohistochemistry.

Results

Thirteen ovarian cancer cells were enrolled in the invasion assay. Ovarian cancer cell lines which responded well to LPA-induced invasion, also displayed good capability for metastatic colonization. On the contrary, cell lines with poor LPA responsiveness showed inferior metastatic potential in peritoneal colonization assay. High expression level of LPAR1 was detected in all of the metastatic ovarian cancer cell lines. T-test showed that LPAR1, not LPAR2 or LPAR3, expression was significantly higher in the metastatic cell lines than in the non-metastatic cell lines (P = 0.003). Furthermore, silencing LPAR1 alone could significantly reduce LPA-induced invasion (P < 0.001). Finally, we analyzed the correlation between the LPARs expression and clinicopathological features of the clinical cases. It indicated that LPAR1 expression rate increased significantly along with the more advanced stages (stage I: 16.67 %; II 50.00 %; III: 75.00 %; and IV: 100.00 %; P = 0.003). Besides that, LPAR1 expression was detected in all the 13 cases with abdominal metastasis more than 2 cm, 10 cases with retroperitoneal lymph node metastasis and 6 cases with hepatic metastasis. Moreover, the expression rate of LPAR2 significantly increased in ovarian cancer than in normal specimens (P = 0.039). LPAR3 expression showed the same trend as LPAR2, though the difference is not statistically significant (P = 0.275). Besides that LPAR2 and LPAR3 expression increased along with poorer differentiation (P = 0.002, P = 0.034, respectively).

Conclusions

Metastatic capability of ovarian cancer cells correlated well with their responsiveness to LPA for cell invasion. LPAR1 acts as the main mediator responsible for LPA-stimulated ovarian cancer cell invasion. LPAR2 and LPAR3 might play an role in carcinogenesis of ovarian cancer.

Lysophosphatidic Acid Synthesis and its Receptors' Expression in the Bovine Oviduct During the Oestrous Cycle

Lysophosphatidic acid (LPA) is a naturally occurring simple phospholipid which in the bovine reproductive system can be produced in the endometrium, corpus luteum, ovarian follicle and embryo. In this study, we examined the possibility that LPA receptors are expressed, and LPA synthesized, in the bovine oviduct. We found that the concentration of LPA was highest in infundibulum in the follicular phase of the oestrous cycle and was relatively high during the early-luteal phase in all examined parts of the oviduct. We also documented that LPA synthesis engages both available pathways for LPA production. The autotaxin (ATX) protein expression was significantly higher in the infundibulum compared to the isthmus during the follicular phase of the oestrous cycle. During the early-luteal phase of the oestrous cycle, ATX and phospholipase A2 (PLA2) protein expression was highest in ampulla, although the expression of LPARs was not as dynamic as LPA concentration in the oviduct tissue, and we presume that in the bovine oviduct, the most abundantly expressed receptor is LPAR2. In conclusion, our results indicate that the bovine oviduct is a site of LPA synthesis and a target for LPA action in the bovine reproductive tract. We documented that LPAR2 is the most abundantly expressed in the bovine oviduct. We hypothesize that in the bovine oviduct, LPA may be involved in the transport of gametes, fertilization and cellular signalling between the oviduct and cumulus-oocyte complex.

Lysophosphatidic Acid (LPA) Receptor 3-Mediated LPA Signal Transduction Pathways: A Possible Relationship with Early Development of Peri-Implantation Porcine Conceptus

Lysophosphatidic acid (LPA) is a phospholipid with a variety of fatty acyl groups that mediates diverse biological effects on various types of cells through specific G protein-coupled receptors. LPA appears to play a significant role in many reproductive processes, including luteolysis, implantation, and placentation. Our previous study in pigs demonstrated that LPA and the LPA receptor system are present at the maternal-conceptus interface and that LPA increases uterine endometrial expression of prostaglandin-endoperoxide synthase 2 (PTGS2) through LPA receptor 3 (LPAR3). However, the role of LPA in conceptuses during early pregnancy has not been determined. Therefore, this study examined the effects of LPA in cell proliferation, migration, and activation of the intracellular signaling pathway in porcine conceptuses by using an established porcine trophectoderm (pTr) cell line isolated from Day 12 conceptuses. All examined LPA species with various fatty acid lengths increased proliferation and migration of pTr cells as the dosage increased. Immunoblot analyses found that LPA activated intracellular signaling molecules, extracellular signal-regulated kinase 1/2 (ERK1/2), ribosomal protein S6 kinase 90 kDa (P90RSK), ribosomal protein S6 (RPS6), and P38 in pTr cells. Furthermore, LPA increased expression of PTGS2 and urokinase-type plasminogen activator (PLAU), and the LPA-induced increases in PTGS2 and PLAU expression were inhibited by LPAR3 siRNA. Collectively, these results showed that LPA promotes proliferation, migration, and differentiation of pTr cells by activating the ERK1/2-P90RSK-RPS6 and P38 pathways, indicating that the LPA-LPAR3 system may be involved in the development of trophoblast during early pregnancy in pigs.

G-Protein-Coupled Lysophosphatidic Acid Receptors and Their Regulation of AKT Signaling

A hallmark of G-protein-coupled receptors (GPCRs) is their ability to recognize and respond to chemically diverse ligands. Lysophospholipids constitute a relatively recent addition to these ligands and carry out their biological functions by activating G-proteins coupled to a large family of cell-surface receptors. This review aims to highlight salient features of cell signaling by one class of these receptors, known as lysophosphatidic acid (LPA) receptors, in the context of phosphatidylinositol 3-kinase (PI3K)-AKT pathway activation. LPA moieties efficiently activate AKT phosphorylation and activation in a multitude of cell types. The interplay between LPA, its receptors, the associated Gαi/o subunits, PI3K and AKT contributes to the regulation of cell survival, migration, proliferation and confers chemotherapy-resistance in certain cancers. However, detailed information on the regulation of PI3K-AKT signals induced by LPA receptors is missing from the literature. Here, some urgent issues for investigation are highlighted.

Studies on lysophosphatidic acid action during in vitro preimplantation embryo development

Assisted reproductive technologies, including in vitro embryo production (IVP), have been successfully used in animal reproduction to optimize breeding strategies for improved production and health in animal husbandry. Despite the progress in IVP techniques over the years, further improvements in in vitro embryo culture systems are required for the enhancement of oocyte and embryo developmental competence. One of the most important issues associated with IVP procedures is the optimization of the in vitro culture of oocytes and embryos. Studies in different species of animals and in humans have identified important roles for receptor-mediated lysophosphatidic acid (LPA) signaling in multiple aspects of human and animal reproductive tract function. The data on LPA signaling in the ovary and uterus suggest that LPA can directly contribute to embryo-maternal interactions via its influence on early embryo development beginning from the influence of the ovarian environment on the oocyte to the influence of the uterine environment on the preimplantation embryo. This review discusses the current status of LPA as a potential supplement in oocyte maturation, fertilization, and embryo culture media and current views on the potential involvement of the LPA signaling pathway in early embryo development.

Recent advances in targeting the autotaxin-lysophosphatidate-lipid phosphate phosphatase axis in vivo

Extracellular lysophosphatidate (LPA) is a potent bioactive lipid that signals through six G-protein-coupled receptors. This signaling is required for embryogenesis, tissue repair and remodeling processes. LPA is produced from circulating lysophosphatidylcholine by autotaxin (ATX), and is degraded outside cells by a family of three enzymes called the lipid phosphate phosphatases (LPPs). In many pathological conditions, particularly in cancers, LPA concentrations are increased due to high ATX expression and low LPP activity. In cancers, LPA signaling drives tumor growth, angiogenesis, metastasis, resistance to chemotherapy and decreased efficacy of radiotherapy. Hence, targeting the ATX-LPA-LPP axis is an attractive strategy for introducing novel adjuvant therapeutic options. In this review, we will summarize current progress in targeting the ATX-LPA-LPP axis with inhibitors of autotaxin activity, LPA receptor antagonists, LPA monoclonal antibodies, and increasing low LPP expression. Some of these agents are already in clinical trials and have applications beyond cancer, including chronic inflammatory diseases.

The autotaxin-lysophosphatidic acid pathway in pathogenesis of rheumatoid arthritis

Lysophosphatidic acid (LPA) is a phospholipid that is mainly produced by the hydrolysis of lysophosphatidylcholine (LPC) by lysophospholipase D, which is also called autotaxin (ATX). LPA interacts with specific G-protein coupled receptors and is involved in the regulation of cellular survival, proliferation, differentiation and motility. LPA also has roles in several pathological disorders, such as cancer and pulmonary, dermal and renal fibrosis. The involvement of the ATX-LPA pathway has recently been demonstrated in inflammatory responses and apoptosis of fibroblast-like synoviocytes (FLS) from patients with rheumatoid arthritis and during the development of experimental arthritis. This review summarises the current literature of the ATX-LPA pathway in rheumatoid arthritis.

The lysophosphatidic acid receptor LPA4 regulates hematopoiesis-supporting activity of bone marrow stromal cells

Lysophosphatidic acid (LPA) is a pleiotropic lipid mediator that acts through G protein-coupled receptors (LPA_1-6). Although several biological roles of LPA₄ are becoming apparent, its role in hematopoiesis has remained unknown. Here, we show a novel regulatory role for LPA₄ in hematopoiesis. Lpar4 mRNA was predominantly expressed in mouse bone marrow (BM) PDGFRα⁺ stromal cells, known as the components of the hematopoietic stem/progenitor cell (HSPC) niche. Compared with wild-type mice, LPA₄-deficient mice had reduced HSPC numbers in the BM and spleen and were hypersusceptible to myelosuppression, most likely due to impairments in HSPC recovery and stem cell factor production in the BM. Analysis of reciprocal BM chimeras (LPA₄-deficient BM into wild-type recipients and vice versa) indicated that stromal cells likely account for these phenotypes. Consistently, LPA₄-deficient BM stromal cells showed downregulated mRNA expression of stem cell factor and tenascin-c in vitro. Taken together, these results suggest a critical and novel role for the LPA/LPA₄ axis in regulating BM stromal cells.

Comparative analyses of lysophosphatidic acid receptor-mediated signaling

Lysophosphatidic acid (LPA) is a bioactive lipid mediator that activates G protein-coupled LPA receptors to exert fundamental cellular functions. Six LPA receptor genes have been identified in vertebrates and are classified into two subfamilies, the endothelial differentiation genes (edg) and the non-edg family. Studies using genetically engineered mice, frogs, and zebrafish have demonstrated that LPA receptor-mediated signaling has biological, developmental, and pathophysiological functions. Computational analyses have also identified several amino acids (aa) critical for LPA recognition by human LPA receptors. This review focuses on the evolutionary aspects of LPA receptor-mediated signaling by comparing the aa sequences of vertebrate LPA receptors and LPA-producing enzymes; it also summarizes the LPA receptor-dependent effects commonly observed in mouse, frog, and fish.

Anatomical location of LPA1 activation and LPA phospholipid precursors in rodent and human brain

Lysophosphatidic acid (LPA) is a signaling molecule that binds to six known G protein-coupled receptors: LPA1 -LPA6 . LPA evokes several responses in the CNS, including cortical development and folding, growth of the axonal cone and its retraction process. Those cell processes involve survival, migration, adhesion proliferation, differentiation, and myelination. The anatomical localization of LPA1 is incompletely understood, particularly with regard to LPA binding. Therefore, we have used functional [(35) S]GTPγS autoradiography to verify the anatomical distribution of LPA1 binding sites in adult rodent and human brain. The greatest activity was observed in myelinated areas of the white matter such as corpus callosum, internal capsule and cerebellum. MaLPA1 -null mice (a variant of LPA1 -null) lack [(35) S]GTPγS basal binding in white matter areas, where the LPA1 receptor is expressed at high levels, suggesting a relevant role of the activity of this receptor in the most myelinated brain areas. In addition, phospholipid precursors of LPA were localized by MALDI-IMS in both rodent and human brain slices identifying numerous species of phosphatides and phosphatidylcholines. Both phosphatides and phosphatidylcholines species represent potential LPA precursors. The anatomical distribution of these precursors in rodent and human brain may indicate a metabolic relationship between LPA and LPA1 receptors. Lysophosphatidic acid (LPA) is a signaling molecule that binds to six known G protein-coupled receptors (GPCR), LPA1 to LPA6 . LPA evokes several responses in the central nervous system (CNS), including cortical development and folding, growth of the axonal cone and its retraction process. We used functional [(35) S]GTPγS autoradiography to verify the anatomical distribution of LPA1 -binding sites in adult rodent and human brain. The distribution of LPA1 receptors in rat, mouse and human brains show the highest activity in white matter myelinated areas. The basal and LPA-evoked activities are abolished in MaLPA1 -null mice. The phospholipid precursors of LPA are localized by MALDI-IMS. The anatomical distribution of LPA precursors in rodent and human brain suggests a relationship with functional LPA1 receptors.

The status of the lysophosphatidic acid receptor type 1 (LPA1R)

The current status of the LPA₁receptor and its ligands in the drug development pipeline is reviewed.

Promising pharmacological directions in the world of lysophosphatidic Acid signaling

Lysophosphatidic acid (LPA) is a signaling lipid that binds to six known lysophosphatidic acid receptors (LPARs), named LPA₁-LPA₆. These receptors initiate signaling cascades relevant to development, maintenance, and healing processes throughout the body. The diversity and specificity of LPA signaling, especially in relation to cancer and autoimmune disorders, makes LPA receptor modulation an attractive target for drug development. Several LPAR-specific analogues and small molecules have been synthesized and are efficacious in attenuating pathology in disease models. To date, at least three compounds have passed phase I and phase II clinical trials for idiopathic pulmonary fibrosis and systemic sclerosis. This review focuses on the promising therapeutic directions emerging in LPA signaling toward ameliorating several diseases, including cancer, fibrosis, arthritis, hydrocephalus, and traumatic injury.

Expression and Function of LPA1 in Bladder Cancer

PURPOSE

LPA is one of several physiologically active lipid mediators that promote cell proliferation and invasion, and are present in serum, ascites and urine. LPA receptor is a G-protein coupled receptor that is considered a potential therapeutic target for some malignant cancers. We evaluated the expression of LPA receptors in bladder cancer and the effect of LPA in bladder cancer invasion.

MATERIALS AND METHODS

Using real-time polymerase chain reaction and immunohistochemical staining we determined LPA receptor expression in bladder cancer specimens from patients with bladder cancer, including 12 with Ta or T1 and 15 with T2-T4 disease. ROCK expression, myosin light chain phosphorylation and Matrigel™ invasion assays were done and morphological observations were made to assess LPA effects in T24 cells, which were derived from bladder cancer.

RESULTS

Notably LPA1 mRNA expression was significantly higher in muscle invasive bladder cancer specimens than in nonmuscle invasive specimens. Strong LPA1 expression was evident on cell membranes in muscle invasive specimens. T24 cell invasion was increased by LPA treatment and invasiveness was decreased by LPA1 siRNA or LPA1 inhibitor. LPA treatment increased ROCK1 expression and myosin light chain phosphorylation, and induced morphological changes, including lamellipodia formation and cell rounding.

CONCLUSIONS

Results indicate that LPA signaling via LPA1 activation promoted bladder cancer invasion. LPA1 might be useful to detect bladder cancer with highly invasive potential and become a new therapeutic target for invasive bladder cancer treatment.

Lysophosphatidic acid as a lipid mediator with multiple biological actions

Lysophosphatidic acid (LPA) is one of the simplest glycerophospholipids with one fatty acid chain and a phosphate group as a polar head. Although LPA had been viewed just as a metabolic intermediate in de novo lipid synthetic pathways, it has recently been paid much attention as a lipid mediator. LPA exerts many kinds of cellular processes, such as cell proliferation and smooth muscle contraction, through cognate G protein-coupled receptors. Because lipids are not coded by the genome directly, it is difficult to know their patho- and physiological roles. However, recent studies have identified several key factors mediating the biological roles of LPA, such as receptors and producing enzymes. In addition, studies of transgenic and gene knockout animals for these LPA-related genes, have revealed the biological significance of LPA. In this review we will summarize recent advances in the studies of LPA production and its roles in both physiological and pathological conditions.

Lysophospholipid receptors in drug discovery

Lysophospholipids (LPs), including lysophosphatidic acid (LPA), sphingosine 1-phospate (S1P), lysophosphatidylinositol (LPI), and lysophosphatidylserine (LysoPS), are bioactive lipids that transduce signals through their specific cell-surface G protein-coupled receptors, LPA1-6, S1P1-5, LPI1, and LysoPS1-3, respectively. These LPs and their receptors have been implicated in both physiological and pathophysiological processes such as autoimmune diseases, neurodegenerative diseases, fibrosis, pain, cancer, inflammation, metabolic syndrome, bone formation, fertility, organismal development, and other effects on most organ systems. Advances in the LP receptor field have enabled the development of novel small molecules targeting LP receptors for several diseases. Most notably, fingolimod (FTY720, Gilenya, Novartis), an S1P receptor modulator, became the first FDA-approved medicine as an orally bioavailable drug for treating relapsing forms of multiple sclerosis. This success is currently being followed by multiple, mechanistically related compounds targeting S1P receptor subtypes, which are in various stages of clinical development. In addition, an LPA1 antagonist, BMS-986020 (Bristol-Myers Squibb), is in Phase 2 clinical development for treating idiopathic pulmonary fibrosis, as a distinct compound, SAR100842 (Sanofi) for the treatment of systemic sclerosis and related fibrotic diseases. This review summarizes the current state of drug discovery in the LP receptor field.

Convergent regulation of neuronal differentiation and Erk and Akt kinases in human neural progenitor cells by lysophosphatidic acid, sphingosine 1-phosphate, and LIF: specific roles for the LPA1 receptor

The bioactive lysophospholipids lysophosphatidic acid (LPA) and sphingosine 1-phosphate (S1P) have diverse effects on the developing nervous system and neural progenitors, but the molecular basis for their pleiotropic effects is poorly understood. We previously defined LPA and S1P signaling in proliferating human neural progenitor (hNP) cells, and the current study investigates their role in neuronal differentiation of these cells. Differentiation in the presence of LPA or S1P significantly enhanced cell survival and decreased expression of neuronal markers. Further, the LPA receptor antagonist Ki16425 fully blocked the effects of LPA, and differentiation in the presence of Ki16425 dramatically enhanced neurite length. LPA and S1P robustly activated Erk, but surprisingly both strongly suppressed Akt activation. Ki16425 and pertussis toxin blocked LPA activation of Erk but not LPA inhibition of Akt, suggesting distinct receptor and G-protein subtypes mediate these effects. Finally, we explored cross talk between lysophospholipid signaling and the cytokine leukemia inhibitory factor (LIF). LPA/S1P effects on neuronal differentiation were amplified in the presence of LIF. Similarly, the ability of LPA/S1P to regulate Erk and Akt was impacted by the presence of LIF; LIF enhanced the inhibitory effect of LPA/S1P on Akt phosphorylation, while LIF blunted the activation of Erk by LPA/S1P. Taken together, our results suggest that LPA and S1P enhance survival and inhibit neuronal differentiation of hNP cells, and LPA1 is critical for the effect of LPA. The pleiotropic effects of LPA may reflect differences in receptor subtype expression or cross talk with LIF receptor signaling.

Separation and quantification of 2-acyl-1-lysophospholipids and 1-acyl-2-lysophospholipids in biological samples by LC-MS/MS

Lysophospholipids (LysoGPs) serve as lipid mediators and precursors for synthesis of diacyl phospholipids (GPs). LysoGPs detected in cells have various acyl chains attached at either the sn-1 or sn-2 position of the glycerol backbone. In general, acyl chains at the sn-2 position of 2-acyl-1-LysoGPs readily move to the sn-1 position, generating 1-acyl-2-lyso isomers by a nonenzymatic reaction called intra-molecular acyl migration, which has hampered the detection of 2-acyl-1-LysoGPs in biological samples. In this study, we developed a simple and versatile method to separate and quantify 2-acyl-1- and 1-acyl-2-LysoGPs. The main point of the method was to extract LysoGPs at pH 4 and 4°C, conditions that were found to completely eliminate the intra-molecular acyl migration. Under the present conditions, the relative amounts of 2-acyl-1-LysoGPs and 1-acyl-2-LysoGPs did not change at least for 1 week. Further, in LysoGPs extracted from cells and tissues under the present conditions, most of the saturated fatty acids (16:0 and 18:0) were found in the sn-1 position of LysoGPs, while most of the PUFAs (18:2, 20:4, 22:6) were found in the sn-2 position. Thus the method can be used to elucidate the in vivo role of 2-acyl-1-LysoGPs.

Lysophospholipid receptor nomenclature review: IUPHAR Review 8

Lysophospholipids encompass a diverse range of small, membrane-derived phospholipids that act as extracellular signals. The signalling properties are mediated by 7-transmembrane GPCRs, constituent members of which have continued to be identified after their initial discovery in the mid-1990s. Here we briefly review this class of receptors, with a particular emphasis on their protein and gene nomenclatures that reflect their cognate ligands. There are six lysophospholipid receptors that interact with lysophosphatidic acid (LPA): protein names LPA1 - LPA6 and italicized gene names LPAR1-LPAR6 (human) and Lpar1-Lpar6 (non-human). There are five sphingosine 1-phosphate (S1P) receptors: protein names S1P1 -S1P5 and italicized gene names S1PR1-S1PR5 (human) and S1pr1-S1pr5 (non-human). Recent additions to the lysophospholipid receptor family have resulted in the proposed names for a lysophosphatidyl inositol (LPI) receptor - protein name LPI1 and gene name LPIR1 (human) and Lpir1 (non-human) - and three lysophosphatidyl serine receptors - protein names LyPS1 , LyPS2 , LyPS3 and gene names LYPSR1-LYPSR3 (human) and Lypsr1-Lypsr3 (non-human) along with a variant form that does not appear to exist in humans that is provisionally named LyPS2L . This nomenclature incorporates previous recommendations from the International Union of Basic and Clinical Pharmacology, the Human Genome Organization, the Gene Nomenclature Committee, and the Mouse Genome Informatix.

Regulation of T cell motility in vitro and in vivo by LPA and LPA2

Lysophosphatidic acid (LPA) and the LPA-generating enzyme autotaxin (ATX) have been implicated in lymphocyte trafficking and the regulation of lymphocyte entry into lymph nodes. High local concentrations of LPA are thought to be present in lymph node high endothelial venules, suggesting a direct influence of LPA on cell migration. However, little is known about the mechanism of action of LPA, and more work is needed to define the expression and function of the six known G protein-coupled receptors (LPA 1-6) in T cells. We studied the effects of 18∶1 and 16∶0 LPA on naïve CD4+ T cell migration and show that LPA induces CD4+ T cell chemorepulsion in a Transwell system, and also improves the quality of non-directed migration on ICAM-1 and CCL21 coated plates. Using intravital two-photon microscopy, lpa2-/- CD4+ T cells display a striking defect in early migratory behavior at HEVs and in lymph nodes. However, later homeostatic recirculation and LPA-directed migration in vitro were unaffected by loss of lpa2. Taken together, these data highlight a previously unsuspected and non-redundant role for LPA2 in intranodal T cell motility, and suggest that specific functions of LPA may be manipulated by targeting T cell LPA receptors.

Application of in utero electroporation of G-protein coupled receptor (GPCR) genes, for subcellular localization of hardly identifiable GPCR in mouse cerebral cortex

Lysophosphatidic acid (LPA) is a lipid growth factor that exerts diverse biological effects through its cognate receptors (LPA1-LPA6). LPA1, which is predominantly expressed in the brain, plays a pivotal role in brain development. However, the role of LPA1 in neuronal migration has not yet been fully elucidated. Here, we delivered LPA1 to mouse cerebral cortex using in utero electroporation. We demonstrated that neuronal migration in the cerebral cortex was not affected by the overexpression of LPA1. Moreover, these results can be applied to the identification of the localization of LPA1. The subcellular localization of LPA1 was endogenously present in the perinuclear area, and overexpressed LPA1 was located in the plasma membrane. Furthermore, LPA1 in developing mouse cerebral cortex was mainly expressed in the ventricular zone and the cortical plate. In summary, the overexpression of LPA1 did not affect neuronal migration, and the protein expression of LPA1 was mainly located in the ventricular zone and cortical plate within the developing mouse cerebral cortex. These studies have provided information on the role of LPA1 in brain development and on the technical advantages of in utero electroporation.

Platelet receptors; an instrumental of platelet physiology

Platelets play an important role in hemostasis, inflammation, host defense, tumor growth and metastasis. Platelets receptors are instrumental in platelet-platelet aggregation and interaction of platelets with leukocytes, endothelial cells and coagulation factors. These receptors are also the targets for antiplatelet drugs. This review focuses on the role of platelet receptors in human physiology. Data were extracted from peer-reviewed journals using MEDLINE and EMBASE databases, and the following terms (platelets, platelet receptors, CD markers, integrins, tetraspanins, transmembrane receptors, prostaglandin receptors, immunoglobulin superfamily receptors) were used.

LPA receptor signaling: pharmacology, physiology, and pathophysiology

Lysophosphatidic acid (LPA) is a small ubiquitous lipid found in vertebrate and nonvertebrate organisms that mediates diverse biological actions and demonstrates medicinal relevance. LPA's functional roles are driven by extracellular signaling through at least six 7-transmembrane G protein-coupled receptors. These receptors are named LPA1-6 and signal through numerous effector pathways activated by heterotrimeric G proteins, including Gi/o, G12/13, Gq, and Gs LPA receptor-mediated effects have been described in numerous cell types and model systems, both in vitro and in vivo, through gain- and loss-of-function studies. These studies have revealed physiological and pathophysiological influences on virtually every organ system and developmental stage of an organism. These include the nervous, cardiovascular, reproductive, and pulmonary systems. Disturbances in normal LPA signaling may contribute to a range of diseases, including neurodevelopmental and neuropsychiatric disorders, pain, cardiovascular disease, bone disorders, fibrosis, cancer, infertility, and obesity. These studies underscore the potential of LPA receptor subtypes and related signaling mechanisms to provide novel therapeutic targets.

Lysophosphatidic acid (LPA) signaling in human and ruminant reproductive tract

Lysophosphatidic acid (LPA) through activating its G protein-coupled receptors (LPAR 1–6) exerts diverse cellular effects that in turn influence several physiological processes including reproductive function of the female. Studies in various species of animals and also in humans have identified important roles for the receptor-mediated LPA signaling in multiple aspects of human and animal reproductive tract function. These aspects range from ovarian and uterine function, estrous cycle regulation, early embryo development, embryo implantation, decidualization to pregnancy maintenance and parturition. LPA signaling can also have pathological consequences, influencing aspects of endometriosis and reproductive tissue associated tumors. The review describes recent progress in LPA signaling research relevant to human and ruminant reproduction, pointing at the cow as a relevant model to study LPA influence on the human reproductive performance.

The effect of lysophosphatidic acid during in vitro maturation of bovine oocytes: embryonic development and mRNA abundances of genes involved in apoptosis and oocyte competence

In the present study we examined whether LPA can be synthesized and act during in vitro maturation of bovine cumulus oocyte complexes (COCs). We found transcription of genes coding for enzymes of LPA synthesis pathway (ATX and PLA2) and of LPA receptors (LPAR 1–4) in bovine oocytes and cumulus cells, following in vitro maturation. COCs were matured in vitro in presence or absence of LPA (10⁻⁵ M) for 24 h. Supplementation of maturation medium with LPA increased mRNA abundance of FST and GDF9 in oocytes and decreased mRNA abundance of CTSs in cumulus cells. Additionally, oocytes stimulated with LPA had higher transcription levels of BCL2 and lower transcription levels of BAX resulting in the significantly lower BAX/BCL2 ratio. Blastocyst rates on day 7 were similar in the control and the LPA-stimulated COCs. Our study demonstrates for the first time that bovine COCs are a potential source and target of LPA action. We postulate that LPA exerts an autocrine and/or paracrine signaling, through several LPARs, between the oocyte and cumulus cells. LPA supplementation of maturation medium improves COC quality, and although this was not translated into an enhanced in vitro development until the blastocyst stage, improved oocyte competence may be relevant for subsequent in vivo survival.

Expression of lysophosphatidic acid receptors in the human lower esophageal sphincter

Lysophosphatidic acid (LPA) is a bioactive lipid that is involved in a variety of physiological and pathological processes occurring in the gastrointestinal tract. It acts via six distinct types of receptors, LPA1, LPA2, LPA3, LPA4, LPA5 and LPA6, which belong to the family of G protein-coupled receptors. The aim of the present study was to detect the expression of the LPA receptors in the human lower esophageal sphincter (LES). Quantitative polymerase chain reaction and western blotting were used to analyze the expression of LPA1-6 receptors in sling and clasp fibers from the human LES. The results showed that the protein and mRNA expression levels of various LPA receptors were significantly different. Specifically, the mRNA and protein expression levels of the LPA1 receptor were higher compared with those of the other receptors. The prevalence of the LPA1 receptor mRNA and protein indicates that the LPA1 receptor is likely to be involved in the regulation of human LES functions.

Development of lysophosphatidic acid pathway modulators as therapies for fibrosis

Lysophosphatidic acid (LPA) is a class of bioactive phospholipid that displays a wide range of cellular effects via LPA receptors, of which six have been identified (LPAR1–6). In serum and plasma, LPA production occurs mainly by the hydrolysis of lysophosphatidylcholine by the phospholipase D activity of autotaxin (ATX). The involvement of the LPA pathway in driving chronic wound-healing conditions, such as idiopathic pulmonary fibrosis, has suggested targets in this pathway could provide potential therapeutic approaches. Mice with LPAR1 knockout or tissue-specific ATX deletion have demonstrated reduced lung fibrosis following bleomycin challenge. Therefore, strategies aimed at antagonizing LPA receptors or inhibiting ATX have gained considerable attention. This Review will summarize the current status of identifying small-molecule modulators of the LPA pathway. The therapeutic utility of LPA modulators for the treatment of fibrotic diseases will soon be revealed as clinical trials are already in progress in this area.

GPR87 mediates lysophosphatidic acid-induced colony dispersal in A431 cells

We have previously reported that an orphan G protein-coupled receptor GPR87 was activated by lysophosphatidic acid (LPA) and that it induced an increase in the intracellular Ca(2+) levels in the CHO cells genetically engineered to express GPR87-Gα16 fusion protein. Because the Ca(2+) response was blocked by the LPA receptor antagonist Ki16425, GPR87 was suggested to be a putative LPA receptor. However, further studies are required to confirm whether GPR87 is an LPA receptor. A previous study showed that colonies of A431 cells treated with LPA showed rapid and synchronized dissociation. Because A431 cells have been shown to express GPR87, we used these cells to examine whether GPR87 acted as an LPA receptor. When A431 cells were treated with gpr87-specific siRNA, the expression of GPR87 was decreased and LPA-induced colony dispersal was significantly reduced. Treatment of the cells with lpa1 siRNA had an additive effect in decrease in the colony dispersal. Studies on the LPA-mediated signaling pathway in A431 cells indicated that transactivation of the epidermal growth factor receptor (EGFR) by LPA led to cell scattering. PD153035, an inhibitor of tyrosine-kinase of EGFR, and BB94, an inhibitor of metalloprotease which produces a ligand for EGFR, significantly prevented the LPA-induced scattering of A431 cells pretreated with lpa1 or gpr87-siRNA. These results strongly suggested that GPR87 acts as an LPA receptor and induces colony dispersal via the transactivation of EGFR in A431 cells.

The actions and metabolism of lysophosphatidylinositol, an endogenous agonist for GPR55

Lysophosphatidylinositol (LPI) is a subspecies of lysophospholipid and is assumed to be not only a degradation product of phosphatidylinositol (PI), but also a bioactive lysophospholipid mediator. However, not much attention has been directed toward LPI compared to lysophosphatidic acid (LPA), since the receptor for LPI has not been identified. During screening for an agonist for the orphan G protein coupled receptor GPR55, we identified LPI, 2-arachidonoyl LPI in particular, as an agonist for GPR55. Our efforts to identify an LPI receptor facilitated research on LPI as a lipid messenger. In addition, we also found that DDHD1, previously identified as phosphatidic acid-preferring phospholipase A1, was one of the synthesizing enzymes of 2-arachidonoyl LPI. Here, we summarized the background for discovering the LPI receptor, and the actions/metabolism of LPI. We also referred to the biosynthesis of PI, a 1-stearoyl-2-arachidonoyl species, since the molecule is the precursor of 2-arachidonoyl LPI. Furthermore, we discussed physiological and/or pathophysiological processes involving LPI and GPR55, including the relevance of LPI-GPR55 and cannabinoids, since GPR55 was previously postulated to be another cannabinoid receptor. Although there is no doubt that GPR55 is the LPI receptor, we should re-consider whether or not GPR55 is in fact another cannabinoid receptor.

The role of LPA and YAP signaling in long-term migration of human ovarian cancer cells

BACKGROUND

The Hippo-YAP signaling pathway is altered and implicated as oncogenic in many human cancers. However, extracellular signals that regulate the mammalian Hippo pathway have remained elusive until very recently when it was shown that the Hippo pathway is regulated by G-protein-coupled receptor (GPCR) ligands including lysophosphatidic acid (LPA) and sphingosine 1-phosphophate (S1P). LPA inhibits Lats kinase activity in HEK293 cells, but the potential involvement of a protein phosphatase was not investigated. The extracellular regulators of YAP dephosphorylation (dpYAP) and nuclear translocation in epithelial ovarian cancer (EOC) are essentially unknown.

RESULTS

We showed here that LPA dose- and time-dependently induced dpYAP in human EOC cell lines OVCA433, OVCAR5, CAOV3, and Monty-1, accompanied by increased YAP nuclear translocation. YAP was involved in LPA-induced migration and invasion of EOC cells and LPA3 was a major LPA receptor mediating the migratory effect. We demonstrated that G13, but not or to a lesser extent G12, Gi or Gq, was necessary for LPA-induced dpYAP and its nuclear translocation and that RhoA-ROCK, but not RhoB, RhoC, Rac1, cdc42, PI3K, ERK, or AKT, were required for the LPA-dpYAP effect. In contrast to results in HEK293 cells, LPA did not inhibit Mst and Lats kinase in OVCA433 EOC cells. Instead, protein phosphatase 1A (PP1A) acted down-stream of RhoA in LPA-induction of dpYAP. In addition, we identified that amphiregulin (AREG), a down-stream target of YAP which activated EGF receptors (EGFR), mediated an LPA-stimulated and EGFR-dependent long-term (16 hr) cell migration. This process was transcription- and translation-dependent and was distinct from a transcription- and YAP-independent short-term (4 hr) cell migration. EOC tissues had reduced pYAP levels compared to normal and benign ovarian tissues, implying the involvement of dpYAP in EOC pathogenesis, as well as its potential marker and/or target values.

CONCLUSIONS

A novel LPA-LPA3-G13-RhoA-ROCK-PP1A-dpYAP-AREG-EGFR signaling pathway was linked to LPA-induced migration of EOC cells. Reduced pYAP levels were demonstrated in human EOC tumors as compared to both normal ovarian tissues and benign gynecologic masses. Our findings support that YAP is a potential marker and target for developing novel therapeutic strategies against EOC.

Inhibition of lysophosphatidic acid increase by prestorage whole blood leukoreduction in autologous CPDA-1 whole blood

BACKGROUND

Lysophosphatidylcholine (LPC) has been implicated in the onset of transfusion-related acute lung injury (TRALI). In plasma, LPC is converted to lysophosphatidic acid (LPA) by autotaxin (ATX). The effect of leukoreduction in the accumulation of these bioactive lipids and ATX in human autologous blood has not been fully investigated.

STUDY DESIGN AND METHODS

The accumulation of choline-containing phospholipids (LPC, sphingomyelin [SM], and phosphatidylcholine [PC]), LPA, and ATX during the storage of autologous blood and the changes caused by leukoreduction were investigated. A total of 26 orthopedic patients were enrolled. Autologous blood was collected as whole blood and, after leukoreduction, preserved refrigerated until use. Prestorage leukoreduced (LR) and non-LR autologous blood samples were analyzed. The time-dependent changes and the effect of the filtration were compared.

RESULTS

A time-dependent and significant increase in the levels of LPA was observed in both non-LR and LR samples. The concentration of LPA was significantly reduced in LR compared to non-LR samples. The concentration of LPC was higher in LR compared to non-LR samples. The levels of PC, SM, and ATX were not affected by either the storage period or the leukoreduction.

CONCLUSIONS

Leukoreduction of autologous whole blood effectively reduced the accumulation of LPA. On the other hand, prestorage leukoreduction resulted in an increased concentration of LPC, without significantly affecting ATX. Further studies are necessary to confirm the role of LPA in the pathogenesis of adverse effects of blood transfusion, especially TRALI.

Lysophosphatidic acid produced by hen egg white lysophospholipase D induces vascular development on extraembryonic membranes

Lysophosphatidic acid (lysoPtdOH), a lysophospholipid mediator, exerts diverse physiological effects, including angiogenesis, through its specific G-protein-coupled receptors. Previously, we showed that unfertilized hen egg white contains polyunsaturated fatty acid-rich lysoPtdOH and lysophospholipase D (lysoPLD). Here, we examined whether lysoPtdOH was produced by lysoPLD in the presence and absence of a hen fertilized ovum and what the physiological role of lysoPtdOH in hen egg white is. Mass spectrometry showed that fertilized hen egg white contained about 8 μM lysoPtdOH before incubation with an ovum, mainly comprised of 18:1- (12.6 %), 18:2- (37.8 %) and 20:4-molecular species (41.5 %). In an early gestation period, the lysoPtdOH was increased up to 9.6 μM, concomitant with a decrease in the level of polyunsaturated lysophosphatidylcholine (lysoPtdCho). Moreover, lysoPtdOH-degrading activities were found in egg white and the vitelline membrane, showing that these enzymes control lysoPtdOH levels in egg white. In an egg yolk angiogenesis assay, two lysoPtdOH receptor antagonists, Ki16425 and N-palmitoyl serine phosphoric acid (NASP), inhibited blood vessel formation induced by exogenously added 18:1-lysoPtdOH and its precursor lysoPtdCho on the hen yolk sac. Ki16425 and NASP also inhibited blood vessel formation in the chorioallantoic membrane (CAM). Furthermore, the relatively higher levels of LPA₁, LPA₂, LPA₄ and LPA₆ mRNA were present in the yolk sac and CAM. These results suggest that lysoPtdOH produced from lysoPtdCho by the action of lysoPLD in hen egg white is involved in the formation of blood vessel networks through several lysoPtdOH receptors on various extraembryonic membranes, including the yolk sac membrane and CAM.

Migration of gastric cancer cells in response to lysophosphatidic acid is mediated by LPA receptor 2

Lysophosphatidic acid (LPA), a natural phospholipid, is able to modulate diverse cellular responses through LPA receptors (LPARs). Several studies have reported that LPAR2 gene expression is increased in a variety of cancer cells, suggesting that LPAR2 is involved in gastric cancer. The present study investigated the expression profiles of the LPAR and involvement of the receptor subtypes in the LPA-induced migration of gastric cancer cells using cell migration assays, RNA interference, quantitative real-time PCR and western blotting. LPAR2 was observed to be highly expressed in SGC-7901 cells, a human gastric cancer cell line, while LPAR1 and LPAR3 were not. Transient transfection with LPAR2 siRNA was observed to reduce LPAR2 mRNA in SGC-7901 cells and eliminate the LPA-induced cell migration. It was also observed that LPA-induced SGC-7901 cell migration was inhibited by the inhibitor for Gq/11 protein and p38. The results suggest that the LPAR2/Gq/11/p38 pathway regulates LPA-induced SGC-7901 cell migration. The present findings suggest that LPAR2 may be a potential target for the clinical treatment of gastric cancer.

Lipid phosphate phosphatase (LPP3) and vascular development

Lipid phosphate phosphatases (LPP) are integral membrane proteins with broad substrate specificity that dephosphorylate lipid substrates including phosphatidic acid, lysophosphatidic acid, ceramide 1-phosphate, sphingosine 1-phosphate, and diacylglycerol pyrophosphate. Although the three mammalian enzymes (LPP1-3) demonstrate overlapping catalytic activities and substrate preferences in vitro, the phenotypes of mice with targeted inactivation of the Ppap2 genes encoding the LPP enzymes reveal nonredundant functions. A specific role for LPP3 in vascular development has emerged from studies of mice lacking Ppap2b. A meta-analysis of multiple, large genome-wide association studies identified a single nucleotide polymorphism in PPAP2B as a novel predictor of coronary artery disease. In this review, we will discuss the evidence that links LPP3 to vascular development and disease and evaluate potential molecular mechanisms. This article is part of a Special Issue entitled Advances in Lysophospholipid Research.

Expression of lysophosphatidic acid receptors and local invasiveness and metastasis in Chinese pancreatic cancers

BACKGROUND AND OBJECTIVES

The present study evaluated the potential role of lysophosphatidic acid receptors (lpars) in processes leading to local invasiveness and metastasis in Chinese pancreatic carcinoma.

METHODS

Real-time reverse-transcriptase polymerase chain reaction and Western blot analysis were used to detect expression of lpars in tumour and adjacent non-tumour tissues from patients with surgically resected pancreatic carcinoma. Surgical specimens from 50 patients were examined for relative expression of each receptor's messenger rna (mrna) and protein. Findings were analyzed for correlations with tumour size, pathologic classification, clinical stage, and infiltration of capsule and lymphonodi.

RESULTS

Increased levels of mrna of lpars (lpar1 ≈ lpar3 < lpar2) were found in the pancreatic cancer tissues examined. Low levels of transcripts for lpar1, lpar2, and lpar3 receptors were detectable in adjacent non-tumour tissues. The difference in lpar1 protein expression between tumour and adjacent non-tumour tissues does not seem significant, but the signals of lpar2 expression in pancreatic cancer tumour tissues were significantly amplified compared with those in adjacent non-tumour tissues. Tumour and adjacent non-tumour tissues both weakly expressed lpar3 protein with no statistical difference. However, expression of lpar1, lpar2, and lpar3 showed an obvious correlation with infiltration of capsule cells, surrounding lymphonodi, and specific histopathologic features.

CONCLUSIONS

Lysophosphatidic acid receptor is a promising indicator for pancreatic cancer, and our findings suggested that lpar2 might be a potential target for clinical treatment of pancreatic cancer.

Current progress in non-Edg family LPA receptor research

Lysophosphatidic acid (LPA) is the simplest phospholipid yet possesses myriad biological functions. Until 2003, the functions of LPA were thought to be elicited exclusively by three subtypes of the endothelial differentiation gene (Edg) family of G protein-coupled receptors - LPA(1), LPA(2), and LPA(3). However, several biological functions of LPA could not be assigned to any of these receptors indicating the existence of one or more additional LPA receptor(s). More recently, the discovery of a second cluster of LPA receptors which includes LPA(4), LPA(5), and LPA(6) has paved the way for new avenues of LPA research. Analyses of these non-Edg family LPA receptors have begun to fill in gaps to understand biological functions of LPA such as platelet aggregation and vascular development that could not be ascribed to classical Edg family LPA receptors and are also unveiling new biological functions. Here we review recent progress in the non-Edg family LPA receptor research, with special emphasis on the pharmacology, signaling, and physiological roles of this family of receptors. This article is part of a Special Issue entitled Advances in Lysophospholipid Research.