Lysophospholipid mediators of immunity and neoplasia

The causal associations of circulating lipids with Barrett's Esophagus and Esophageal Cancer: a bi-directional, two sample mendelian randomization analysis

OBJECTIVE

The causal associations of circulating lipids with Barrett's Esophagus (BE) and Esophageal Cancer (EC) has been a topic of debate. This study sought to elucidate the causality between circulating lipids and the risk of BE and EC.

METHODS

We conducted two-sample Mendelian randomization (MR) analyses using single nucleotide polymorphisms (SNPs) of circulating lipids (n = 94,595 - 431,167 individuals), BE (218,792 individuals), and EC (190,190 individuals) obtained from the publicly available IEU OpenGWAS database. The robustness and reliability of the results were ensured by employing inverse-variance weighted (IVW), weighted median, MR-Egger, and MR-PRESSO methods. The presence of horizontal pleiotropy, heterogeneities, and stability of instrumental variables were assessed through MR-Egger intercept test, Cochran's Q test, and leave-one-out sensitivity analysis. Additionally, bidirectional MR and multivariable MR (MVMR) were performed to explore reverse causality and adjust for known confounders, respectively.

RESULTS

None of the testing methods revealed statistically significant horizontal pleiotropy, directional pleiotropy, or heterogeneity. Univariate MR analyses using IVW indicated a robust causal relationship between increased triglycerides and BE (odds ratio [OR] = 1.79, p-value = 0.009), while no significant association with EC was observed. Inverse MR analysis indicated no evidence of reverse causality in the aforementioned outcomes. In MVMR analyses, elevated triglycerides (TRG) were significantly and positively associated with BE risk (OR = 1.79, p-value = 0.041).

CONCLUSION

This MR study suggested that genetically increased triglycerides were closely related to an elevated risk of BE, potentially serving as a biomarker for the diagnosis of BE in the future.

Multi metabolomics-based analysis of application of Astragalus membranaceus in the treatment of hyperuricemia

Hyperuricemia (HUA) is a common metabolic disease that is an independent risk factor for comorbidities such as hypertension, chronic kidney disease, and coronary artery disease. The prevalence of HUA has increased over the last several decades with improved living standards and increased lifespans. Metabolites are considered the most direct reflection of individual physiological and pathological conditions, and represent attractive candidates to provide deep insights into disease phenotypes. Metabolomics, a technique used to profile metabolites in biofluids and tissues, is a powerful tool for identification of novel biomarkers, and can be used to provide valuable insights into the etiopathogenesis of metabolic diseases and to evaluate the efficacy of drugs. In this study, multi metabolomics-based analysis of the blood, urine, and feces of rats with HUA showed that HUA significantly altered metabolite profiles. Astragalus membranaceus (AM) and benbromomalone significantly mitigated these changes in blood and feces, but not in urine. Some crucial metabolic pathways including lipid metabolism, lipid signaling, hormones synthesis, unsaturated fatty acid (UFAs) absorption, and tryptophan metabolism, were seriously disrupted in HUA rats. In addition, AM administration exerted better treatment effects on HUA than benbromomalone. Furthermore, additional supplementation with UFAs and tryptophan may also induce therapeutic effects against HUA.

Bioactive potential of natural biomaterials: identification, retention and assessment of biological properties

Biomaterials have had an increasingly important role in recent decades, in biomedical device design and the development of tissue engineering solutions for cell delivery, drug delivery, device integration, tissue replacement, and more. There is an increasing trend in tissue engineering to use natural substrates, such as macromolecules native to plants and animals to improve the biocompatibility and biodegradability of delivered materials. At the same time, these materials have favourable mechanical properties and often considered to be biologically inert. More importantly, these macromolecules possess innate functions and properties due to their unique chemical composition and structure, which increase their bioactivity and therapeutic potential in a wide range of applications. While much focus has been on integrating these materials into these devices via a spectrum of cross-linking mechanisms, little attention is drawn to residual bioactivity that is often hampered during isolation, purification, and production processes. Herein, we discuss methods of initial material characterisation to determine innate bioactivity, means of material processing including cross-linking, decellularisation, and purification techniques and finally, a biological assessment of retained bioactivity of a final product. This review aims to address considerations for biomaterials design from natural polymers, through the optimisation and preservation of bioactive components that maximise the inherent bioactive potency of the substrate to promote tissue regeneration.

Bioactive Lipids in MSCs Biology: State of the Art and Role in Inflammation

Lipidomics is a lipid-targeted metabolomics approach that aims to the comprehensive analysis of lipids in biological systems in order to highlight the specific functions of lipid species in health and disease. Lipids play pivotal roles as they are major structural components of the cellular membranes and energy storage molecules but also, as most recently shown, they act as functional and regulatory components of intra- and intercellular signaling. Herein, emphasis is given to the recently highlighted roles of specific bioactive lipids species, as polyunsaturated fatty acids (PUFA)-derived mediators (generally known as eicosanoids), endocannabinoids (eCBs), and lysophospholipids (LPLs), and their involvement in the mesenchymal stem cells (MSCs)-related inflammatory scenario. Indeed, MSCs are a heterogenous population of multipotent cells that have attracted much attention for their potential in regulating inflammation, immunomodulatory capabilities, and reparative roles. The lipidomics of the inflammatory disease osteoarthritis (OA) and the influence of MSCs-derived lipids have also been addressed.

Regulation of tumor cell - Microenvironment interaction by the autotaxin-lysophosphatidic acid receptor axis

The lipid mediator lysophosphatidic acid (LPA) in biological fluids is primarily produced by cleavage of lysophospholipids by the lysophospholipase D enzyme Autotaxin (ATX). LPA has been identified and abundantly detected in the culture medium of various cancer cell types, tumor effusates, and ascites fluid of cancer patients. Our current understanding of the physiological role of LPA established its role in fundamental biological responses that include cell proliferation, metabolism, neuronal differentiation, angiogenesis, cell migration, hematopoiesis, inflammation, immunity, wound healing, regulation of cell excitability, and the promotion of cell survival by protecting against apoptotic death. These essential biological responses elicited by LPA are seemingly hijacked by cancer cells in many ways; transcriptional upregulation of ATX leading to increased LPA levels, enhanced expression of multiple LPA GPCR subtypes, and the downregulation of its metabolic breakdown. Recent studies have shown that overexpression of ATX and LPA GPCR can lead to malignant transformation, enhanced proliferation of cancer stem cells, increased invasion and metastasis, reprogramming of the tumor microenvironment and the metastatic niche, and development of resistance to chemo-, immuno-, and radiation-therapy of cancer. The fundamental role of LPA in cancer progression and the therapeutic inhibition of the ATX-LPA axis, although highly appealing, remains unexploited as drug development to these targets has not reached into the clinic yet. The purpose of this brief review is to highlight some unique signaling mechanisms engaged by the ATX-LPA axis and emphasize the therapeutic potential that lies in blocking the molecular targets of the LPA system.

Anaplasma phagocytophilum Manipulates Host Cell Apoptosis by Different Mechanisms to Establish Infection

Anaplasma phagocytophilum is an emerging zoonotic pathogen that causes human and animal granulocytic anaplasmosis and tick-borne fever of ruminants. This obligate intracellular bacterium evolved to use common strategies to establish infection in both vertebrate hosts and tick vectors. Herein, we discuss the different strategies used by the pathogen to modulate cell apoptosis and establish infection in host cells. In vertebrate neutrophils and human promyelocytic cells HL-60, both pro-apoptotic and anti-apoptotic factors have been reported. Tissue-specific differences in tick response to infection and differential regulation of apoptosis pathways have been observed in adult female midguts and salivary glands in response to infection with A. phagocytophilum. In tick midguts, pathogen inhibits apoptosis through the Janus kinase/signal transducers and activators of transcription (JAK/STAT) pathway, while in salivary glands, the intrinsic apoptosis pathways is inhibited but tick cells respond with the activation of the extrinsic apoptosis pathway. In Ixodes scapularis ISE6 cells, bacterial infection down-regulates mitochondrial porin and manipulates protein processing in the endoplasmic reticulum and cell glucose metabolism to inhibit apoptosis and facilitate infection, whereas in IRE/CTVM20 tick cells, inhibition of apoptosis appears to be regulated by lower caspase levels. These results suggest that A. phagocytophilum uses different mechanisms to inhibit apoptosis for infection of both vertebrate and invertebrate hosts.

Fibroblastic reticular cell-derived lysophosphatidic acid regulates confined intranodal T-cell motility

Lymph nodes (LNs) are highly confined environments with a cell-dense three-dimensional meshwork, in which lymphocyte migration is regulated by intracellular contractile proteins. However, the molecular cues directing intranodal cell migration remain poorly characterized. Here we demonstrate that lysophosphatidic acid (LPA) produced by LN fibroblastic reticular cells (FRCs) acts locally to LPA₂ to induce T-cell motility. In vivo, either specific ablation of LPA-producing ectoenzyme autotaxin in FRCs or LPA₂ deficiency in T cells markedly decreased intranodal T cell motility, and FRC-derived LPA critically affected the LPA₂-dependent T-cell motility. In vitro, LPA activated the small GTPase RhoA in T cells and limited T-cell adhesion to the underlying substrate via LPA₂. The LPA-LPA₂ axis also enhanced T-cell migration through narrow pores in a three-dimensional environment, in a ROCK-myosin II-dependent manner. These results strongly suggest that FRC-derived LPA serves as a cell-extrinsic factor that optimizes T-cell movement through the densely packed LN reticular network.

DOI:http://dx.doi.org/10.7554/eLife.10561.001

Small organs called lymph nodes are found throughout the body and help to filter out harmful particles and cells. Lymph nodes are packed with different types of immune cells, such as the T-cells that play a number of roles in detecting and destroying bacteria, viruses and other disease-causing microbes. Within the lymph node, T-cells crawl along a meshwork made up of cells called fibroblastic reticular cells. The T-cells appear to move in random patterns, but the signals that drive this movement remain ill-defined.

Now, Takeda et al. reveal that a lipid called lysophosphatidic acid (LPA), which is produced by the fibroblastic reticular cells, is responsible for regulating how T-cells move around inside the lymph nodes. T-cells are able to detect LPA via certain receptor proteins on their surface. Takeda et al. engineered mice that were either unable to produce a particular LPA receptor on their T-cells, or that produced less LPA than normal. The T-cells of these mice moved around less than T-cells in normal mice.

Further experiments revealed that LPA signaling also affects the signaling pathway that alters how well the T-cells stick to nearby surfaces. This suggests that LPA helps to optimize T-cell movement to allow the cells to navigate the small spaces found between the fibroblastic reticular cells. In the future, targeting the processes involved in LPA signaling could help to develop new treatments for disorders of the immune system.

DOI:http://dx.doi.org/10.7554/eLife.10561.002

Lysophospholipids and their G protein-coupled receptors in atherosclerosis

Lysophospholipids (LPLs) are bioactive lipid-derived signaling molecules generated by the enzymatic and chemical processes of regiospecific phospholipases on substrates such as membrane phospholipids (PLs) and sphingolipids (SLs). They play a major role as extracellular mediators by activating G-protein coupled receptors (GPCRs) and stimulating diverse cellular responses from their signaling pathways. LPLs are involved in various pathologies of the vasculature system including coronary heart disease and hypertension. Many studies suggest the importance of LPLs in their association with the development of atherosclerosis, a chronic and severe vascular disease. This paper focuses on the pathophysiological effects of different lysophospholipids on atherosclerosis, which may promote the pathogenesis of myocardial infarction and strokes. Their atherogenic biological activities take place in vascular endothelial cells, vascular smooth muscle cells, fibroblasts, monocytes and macrophages, dendritic cells, T-lymphocytes, platelets, etc.

Spinal cord compression injury in lysophosphatidic acid 1 receptor-null mice promotes maladaptive pronociceptive descending control

BACKGROUND

Although activation of the lysophosphatidic acid receptor 1 (LPA1) is known to mediate pronociceptive effects in peripheral pain models, the role of this receptor in the modulation of spinal nociception following spinal cord injury (SCI) is unknown.

AIM

In this study, LPA1 regulation of spinal excitability mediated by supraspinal descending antinociceptive control systems was assessed following SCI in both wild-type (WT) and maLPA1-null receptor mice.

METHODS

The effect of a T8 spinal compression in WT and maLPA1-null mice was assessed up to 1 month after SCI using histological, immunohistochemical and behavioural techniques analysis including electrophysiological recording of noxious toes-Tibialis Anterior (TA) stimulus-response reflex activity. The effect of a T3 paraspinal transcutaneous electrical conditioning stimulus on TA noxious reflex temporal summation was also assessed.

RESULTS

Histological analysis demonstrated greater dorsolateral funiculus damage after SCI in maLPA1-null mice, without a change in the stimulus-response function of the TA noxious reflex when compared to WT mice. While T3 conditioning stimulation in the WT group inhibited noxious TA reflex temporal summation after SCI, this stimulus strongly excited TA reflex temporal summation in maLPA1-null mice. The functional switch from descending inhibition to maladaptive facilitation of central excitability of spinal nociception demonstrated in maLPA1-null mice after SCI was unrelated to a general change in reflex activity.

CONCLUSIONS

These data suggest that the LPA1 receptor is necessary for inhibition of temporal summation of noxious reflex activity, partly mediated via long-tract descending modulatory systems acting at the spinal level.

Increased levels of sphingosine-1-phosphate in cerebrospinal fluid of patients diagnosed with tick-borne encephalitis

Background

Tick-borne encephalitis (TBE) is a serious acute central nervous system infection that can result in death or long-term neurological dysfunctions. We hypothesize that changes in sphingosine-1-phosphate (S1P) concentration occur during TBE development.

Methods

S1P and interleukin-6 (IL-6) concentrations in blood plasma and cerebrospinal fluid (CSF) were measured using HPLC and ELISA, respectively. The effects of S1P on cytoskeletal structure and IL-6 production were assessed using rat astrocyte primary cultures with and without addition of plasma gelsolin and the S1P receptor antagonist fingolimod phosphate (FTY720P).

Results

We report that acute inflammation due to TBE virus infection is associated with elevated levels of S1P and IL-6 in the CSF of infected patients. This elevated concentration is observed even at the earliest neurologic stage of disease, and may be controlled by glucocorticosteroid anti-inflammatory treatment, administered to patients unresponsive to antipyretic drugs and who suffer from a fever above 39°C. In vitro, treatment of confluent rat astrocyte monolayers with a high concentration of S1P (5 μM) results in cytoskeletal actin remodeling that can be prevented by the addition of recombinant plasma gelsolin, FTY720P, or their combination. Additionally, gelsolin and FTY720P significantly decreased S1P-induced release of IL-6.

Conclusions

TBE is associated with increased concentration of S1P and IL-6 in CSF, and this increase might promote development of inflammation. The consequences of increased extracellular S1P can be modulated by gelsolin and FTY720P. Therefore, blocking the inflammatory response at sites of infection by agents modulating S1P pathways might aid in developing new strategies for TBE treatment.

Progranulin stimulated by LPA promotes the migration of aggressive breast cancer cells

Activator and inhibitor roles for the 88-kDa-secreted glycoprotein progranulin (PGRN) have been demonstrated in ovarian cancer cells. Here, we investigated the effects of PGRN in breast cancer migration. Testing MCF7, MDA-MB-453, and MDA-MB-231 human breast cancer cells and the MCF10A breast epithelial cell line, we demonstrate that LPA-induced PGRN stimulation led to a significant increase in cell invasion of MDA-MB-453 and MDA-MB-231 cells only (p<0.05). Moreover, incubation with an anti-PGRN antibody, an inhibitor of the ERK pathway (PD98059) or both in combination inhibited the ability of MDA-MB-231 cells to invade. Furthermore, the expression of focal adhesion kinases promoted by LPA-induced PGRN was also inhibited by PD98059 alone or in combination with an anti-PGRN antibody (p<0.05). Taken together, these results suggest that the LPA activation of PGRN involving the ERK pathway is critical to promote MDA-MB-231 breast cancer cell invasion.

Lysophosphatidic acid stimulates cell migration, invasion, and colony formation as well as tumorigenesis/metastasis of mouse ovarian cancer in immunocompetent mice

We have already established human xenographic models for the effect of lysophosphatidic acid (LPA) on tumor metastasis in vivo. The purpose of this work is to establish a preclinical LPA effect model in immunocompetent mice. We first characterized the mouse epithelial ovarian cancer (EOC) cell line ID8 for its responsiveness to LPA in cell proliferation, migration, and invasion and compared these properties with those of human EOC. The signaling pathways related to cell migration were further investigated using pharmacologic and genetic approaches. The effects of LPA on the tumorigenesis of ID8 cells and mouse survival were then examined using two different mouse models (i.p. and orthotopic injections). LPA stimulated cell proliferation, migration, and invasion of mouse EOC ID8 cells in a manner closely resembling its activity in human EOC cells. The signaling pathways involved in LPA-induced cell migration in ID8 cells were also similar to those identified in human EOC cells. We have identified cyclooxygenase-1 and 15-lipoxygenase as two new signaling molecules involved in LPA-induced cell migration in both human and mouse EOC cells. In addition, LPA enhanced the tumorigenesis/metastasis of ID8 cell in vivo as assessed by increased tumor size, early onset of ascites formation, and reduced animal survival. We have established the first LPA-EOC preclinical model in immunocompetent mice. Because ID8 cells respond to LPA similar to human EOC cells, this model is very valuable in developing and testing therapeutic reagents targeting LPA in EOC.

The absence of LPA2 attenuates tumor formation in an experimental model of colitis-associated cancer

BACKGROUND & AIMS

Chronic inflammation is a risk factor for colon cancer (CC). Lysophosphatidic acid (LPA), a naturally produced phospholipid, mediates multiple effects that are vital to disease process, including inflammation and cancer. The expression of LPA receptor 2 (LPA2) is up-regulated in several types of cancer, including ovarian and colon cancer, but the importance of LPA and LPA2 in the development and progression of CC is unclear. In this study, we sought to determine whether LPA and LPA2 regulate the progression of CC in vivo.

METHODS

We examined the potential role of LPA in CC progression by administering LPA to mice heterozygous for the adenomatous polyposis coli (Apc) allele. We determined the loss of LPA2 function in tumorigenesis in the colon by treating mice with genetic deletion of LPA2 (LPA2-/-) with azoxymethane and dextran sulfate sodium.

RESULTS

We found that LPA increased tumor incidence in Apc(min/+) mice. LPA2-/- mice showed reduced mucosal damage and fewer tumors than wild-type (WT) mice. Reduced epithelial cell proliferation and decreases in beta-catenin, Krüppel-like factor 5, and cyclooxygenase-2 expression were observed in LPA2-/- mice. Unlike WT mice, induction of monocyte chemoattractant protein-1 and macrophage migration inhibitory factor was significantly attenuated in LPA2-/- mice with reduced infiltration by macrophages.

CONCLUSIONS

These results show that LPA is capable of promoting tumorigenesis in the colon. The absence of LPA2 attenuates several effects that contribute to cancer progression in vivo, and, hence, the current study identifies LPA2 as an important modulator of CC.

Lysophospholipid activation of G protein-coupled receptors

One of the major lipid biology discoveries in last decade was the broad range of physiological activities of lysophospholipids that have been attributed to the actions of lysophospholipid receptors. The most well characterized lysophospholipids are lysophosphatidic acid (LPA) and sphingosine 1-phosphate (S1P). Documented cellular effects of these lipid mediators include growth-factor-like effects on cells, such as proliferation, survival, migration, adhesion, and differentiation. The mechanisms for these actions are attributed to a growing family of 7-transmembrane, G protein-coupled receptors (GPCRs). Their pathophysiological actions include immune modulation, neuropathic pain modulation, platelet aggregation, wound healing, vasopressor activity, and angiogenesis. Here we provide a brief introduction to receptor-mediated lysophospholipid signaling and physiology, and then discuss potential therapeutic roles in human diseases.

LysoPtdOH enhances CXCL16 production stimulated by LPS from macrophages and regulates T cell migration

As a transmembrane chemokine, CXCL16 has been detected in various tissues and organs under normal and pathological conditions, it also plays an important role in macrophages/dendritic cells (DC) and T cell interactions and trafficking during inflammation and immune responses. LysoPtdOH, a bioactive lipid mediator has been indicated to regulate DC and epithelial functions during wound healing and inflammation responses. However, the direct link of CXCL16 expression with lysoPtdOH has not been established. Using monocyte-derived macrophages/DC (MoDC), we investigated the roles of lysoPtdOH in CXCL16 production and cell surface presentation. We found that macrophages/MoDC constitutively express and secrete CXCL16, lysoPtdOH significantly enhanced CXCL16 protein production stimulated with lipopolysaccharide (LPS) by more than twofold, which was reflected by increased mRNA transcription by 64-fold. Production of CXCL16 increased by lysoPtdOH and LPS from macrophages was inhibited around 70% by Pertussis toxin (G(i/o) specific inhibitor), exoC3 (Rho specific inhibitor), and pyrrolidine dithiocarbamate (the NF-kappaB-dependent pathway inhibitor) separately. LysoPtdOH treatment increased macrophages' chemotactic activity to activated T cells. The soluble form of CXCL16 produced by macrophages/MoDC was functionally chemoattractive to T cells.

Differential expression of inflammatory and immune response genes in sheep infected with Anaplasma phagocytophilum

Anaplasma phagocytophilum infects a wide variety of host species and causes the diseases tick-borne fever (TBF) in ruminants and granulocytic anaplasmosis in humans, horses and dogs. TBF in sheep has become one of the more prevalent tick-borne diseases in some regions of Europe. A. phagocytophilum infection modifies host gene expression and immune response. The objective of this research was to characterize differential gene expression in sheep experimentally and naturally infected with A. phagocytophilum by microarray hybridization and real-time RT-PCR. The results of these studies demonstrated in sheep the activation of inflammatory and innate immune pathways and the impairment of adaptive immunity during A. phagocytophilum infection. The characterization of the genes and their expression profiles in sheep in response to A. phagocytophilum infection advances our understanding of the molecular mechanisms of pathogen infection and the pathogenesis of TBF. Collectively, these results expand current information on the mammalian host response to A. phagocytophilum infection.

Lysophosphatidic acid modulates the activation of human monocyte-derived dendritic cells

Lysophosphatidic acid (LPA) is a biologically active lysophospholipid that can regulate immune activation. LPA can activate T cells and dendritic cells (DCs), but the effects of LPA on the ability of DCs to influence T cell polarization are not well understood. Human monocyte-derived DCs were differentiated in vitro in the presence of interleukin-4 (IL-4) and granulocyte-macrophage colonystimulating factor (GM-CSF), and matured with LPA and lipopolysaccharide (LPS) alone or in combination. DC activation was monitored by analyzing cell-surface expression of co-stimulatory receptors and cytokine production. The ability of DCs to influence T cell activation was determined using two models of DC:T cell co-culture. Maturation with LPS induced dose-dependent DC activation characterized by enhanced expression of co-stimulatory molecules (e.g., CD86) and production of cytokines including IL-6 and IL-10. Co-incubation with LPA attenuated the LPS-induced production of IL-6, without significantly affecting IL-10 secretion or the ability of DC to promote T cell proliferation. DCs matured in the presence of both LPA and LPS enhanced the production of interferon-gamma (IFN-gamma) when co-cultured with allogeneic T cells, compared with DC matured by LPS alone. Similar results were found using a model of allogeneic naïve T cell differentiation, where LPA- plus LPS-matured DC enhanced IFN-gamma as well as IL-4 secretion after restimulation. Lysophosphatidic acid fine-tunes the effects of LPS on human myeloid DC maturation, but does not exert a dominant effect on the ability of DC to influence Th cell polarization.

The lysophosphatidic acid (LPA) receptors their expression and significance in epithelial ovarian neoplasms

OBJECTIVE

To investigate the lysophosphatidic acid (LPA) receptors expression situation and their biological significance in human ovarian cancer cell lines and in human epithelial ovarian neoplasms.

METHODS

The reverse transcription-polymerase chain reaction (RT-PCR) and Western blotting were employed to measure the expression levels of LPA(1), LPA(2) and LPA(3) mRNA, LPA(2) and LPA(3) protein expression in cultured human ovarian cancer cell lines (3AO, SKOV3 and OVCAR3) and in human epithelial ovarian neoplasms. The immunocytochemical method was used to detect LPA(2) and LPA(3) protein expression in cultured human ovarian cancer cell lines.

RESULTS

RT-PCR revealed that all ovarian cancer cell lines expressed LPA(1), LPA(2) and LPA(3) mRNA. The positive rates (100%; 86.4%; 88.2%) of LPA(1) mRNA in normal ovarian tissue, benign tumor and ovarian cancer were no significant difference (p>0.05). The expression level of LPA(1) mRNA was significantly higher in normal ovarian tissue compared with that in benign tumor and in ovarian cancer tissue (p<0.01). LPA(1) expression level was no significant difference in both benign tumor and ovarian cancer tissue (p>0.05). LPA(2) mRNA-positive rates (92.6%) and expression level were significantly higher in ovarian cancer compared with that in benign tumor (31.8%) and in normal ovarian tissue (31.3%) (p<0.01); LPA(2) mRNA-positive rates and expression level were no significant difference in both benign tumor and normal ovarian tissue (p>0.05). LPA(3) mRNA-positive rates (92.6%) and expression level were significantly higher in ovarian cancer compared with that in benign tumor (31.8%) and in normal ovarian tissue (31.3%) (p<0.01), LPA(3) mRNA-positive rates and expression level were no significant difference in both benign tumor and normal ovarian tissue (p>0.05). LPA(1) mRNA expression level was significantly decreased compared with that of LPA(2) and LPA(3) in ovarian cancer (p<0.01); Western blotting clearly revealed that all ovarian cancer cell lines showed LPA(2) and LPA(3) protein. The positive rates and expression level of LPA(2) and LPA(3) protein were significantly increased in ovarian cancer (92.6%; 92.6%) compared with that in benign tumor (45.5%; 45.5%) and that in normal ovarian tissue (43.8%; 43.8%) (p<0.01); LPA(2) and LPA(3) protein-positive rates and expression level were no significant difference in both benign tumor and normal ovarian tissue (p>0.05). Correlation of clinicopathological parameters showed that LPA receptors mRNA and protein expression were associated with FIGO stage and histological grade, except pathologic types and age. The mRNA and protein expression of LPA(2) and LPA(3) in stages III and IV was significantly higher than that in stages I and II epithelial ovarian cancer (p<0.05). The mRNA and protein expression of pathologic grade G(3) was significantly higher compared with grade G(1) (p<0.05).

CONCLUSION

LPA(1), LPA(2) and LPA(3) mRNA and protein expressed widely in human epithelial ovarian neoplasms. LPA(2) and LPA(3) may be involved in the development and progression of human ovarian cancer. There was a significant correlation between LPA(2), LPA(3) and invasion and metastasis of epithelial ovarian cancer. LPA(2) and LPA(3) may be a prognostic indicator in patients with epithelial ovarian cancer.

LYSOPHOSPHATIDIC ACID REDUCES THE ORGAN INJURY CAUSED BY ENDOTOXEMIA-A ROLE FOR G-PROTEIN-COUPLED RECEPTORS AND PEROXISOME PROLIFERATOR-ACTIVATED RECEPTOR-γ

Exogenous lysophosphatidic acid (LPA) has been shown to beneficial in renal ischemia/reperfusion injury, wound healing and colitis. LPA acts via specific G-protein-coupled receptors and also peroxisome proliferator-activated receptor-gamma (PPAR-gamma). However, activation of PPAR-gamma is dependent on the presence of an unsaturated acyl chain. Here we investigate the effects of saturated LPA (18:0) and unsaturated LPA (18:1) on the organ injury associated with endotoxemia and the receptors mediating LPA activity. Male Wistar rats received either lipopolysaccharide (LPS, 6 mg/kg i.v.) or vehicle. The PPAR-gamma antagonist GW9662 (1 mg/kg i.v.), the LPA receptor antagonist Ki16425 (0.5 mg/kg i.v.) or vehicle was administered 30 min after LPS. LPA 18:0 or LPA 18:1 (1 mg/kg i.v.) or vehicle was administered 1 h after injection of LPS. Endotoxemia for 6 h resulted in an increase in serum levels of aspartate aminotransferase, alanine aminotransferase and creatine kinase. Therapeutic administration of LPA 18:0 or 18:1 reduced the organ injury caused by LPS. LPA 18:0 also attenuated the increase in plasma IL-1beta caused by LPS. Ki16425, but not GW9662, attenuated the beneficial effects of LPA 18:0, however, Ki16425 and GW9662 attenuated the beneficial effects of 18:1. In conclusion, LPA reduces the organ injury caused by endotoxemia in the rat. Thus, LPA may be useful in the treatment of shock of various aetiologies. The mechanism of action is related to acyl chain saturation, with LPA 18:0 acting via G-protein-coupled receptors and LPA 18:1 acting via G-protein-coupled receptors and PPAR-gamma.

Endogenous versus exogenous fatty acid availability affects lysosomal acidity and MHC class II expression

Although the immune system, inflammation, and cellular metabolism are linked to diseases associated with dyslipidemias, the mechanism(s) remain unclear. To determine whether there is a mechanistic link between lipid availability and inflammation/immune activation, we evaluated macrophage cell lines incubated under conditions of altered exogenous and endogenous lipid availability. Limiting exogenous lipids results in decreased lysosomal acidity and decreased lysosomal enzymatic activity. Both lysosomal parameters are restored with the addition of oleoyl-CoA, suggesting that fatty acids play a role in the regulation of lysosomal function. Cell surface expression of major histocompatibility complex (MHC)-encoded molecules is also decreased in the absence of exogenous lipids. Additionally, we observe decreased gamma-interferon stimulation of cell surface MHC class II. Using cerulenin to limit the endogenous synthesis of fatty acids results in decreased cell surface expression of MHC class II but does not appear to alter lysosomal acidity, suggesting that lysosomal acidity is dependent on exogenous, but not endogenous, fatty acid availability. Testing these conclusions in an in vivo mouse model, we observed statistically significant, diet-dependent differences in lysosomal acidity and MHC class II cell surface expression. Collectively, these data demonstrate a mechanistic link between lipid availability and early events in the immune response.

Mammalian G proteins and their cell type specific functions

Heterotrimeric G proteins are key players in transmembrane signaling by coupling a huge variety of receptors to channel proteins, enzymes, and other effector molecules. Multiple subforms of G proteins together with receptors, effectors, and various regulatory proteins represent the components of a highly versatile signal transduction system. G protein-mediated signaling is employed by virtually all cells in the mammalian organism and is centrally involved in diverse physiological functions such as perception of sensory information, modulation of synaptic transmission, hormone release and actions, regulation of cell contraction and migration, or cell growth and differentiation. In this review, some of the functions of heterotrimeric G proteins in defined cells and tissues are described.

Neutrophil sphingosine 1-phosphate and lysophosphatidic acid receptors in pneumonia

The phospholipids sphingosine 1-phosphate (S1P) and lysophosphatidic acid (LPA) act via transmembrane receptors S1P 1-5 and LPA 1-3, respectively. Both have been implicated in inflammatory responses. S1P and LPA receptor profiles on neutrophils of patients with pneumonia compared with healthy subjects were determined by PCR and Western blotting. Chemotaxis studies were performed to assess functional differences. S1P or LPA receptors were immunoprecipitated from neutrophils to assess receptor heterodimerization with CXCR1, an IL-8 receptor, by Western blotting. Receptors S1P 1, 4, and 5 and LPA 2 were expressed on neutrophils from both subject groups, but S1P 3 and LPA 1 receptor expression was mainly confined to neutrophils of patients with pneumonia. Chemotaxis of neutrophils from patients with pneumonia compared with control subjects was significantly increased in response to S1P and LPA. Pretreatment with S1P or LPA reduced IL-8-induced neutrophil chemotaxis and transcriptional expression of the CXCR1 receptor. Receptors S1P 3 and 4 and LPA 1 formed constitutive heterodimers with CXCR1. LPA treatment reduced the amount of LPA 1/CXCR1 heterodimer. Therefore, profiles of S1P and LPA receptors differ between neutrophils of patients with pneumonia and control subjects, with consequences for neutrophil function.

Lysophosphatidic acid enhances interleukin-13 gene expression and promoter activity in T cells

Lysophosphatidic acid (LPA) is a membrane-derived lysophospholipid with wide-ranging effects on multiple lung cells including airway epithelial and smooth muscle cells. LPA can augment migration and cytokine synthesis in lymphocytes, but its potential effects on Th2 cytokines have not been well studied. We examined the effects of physiological concentrations of LPA on IL-13 gene expression in human T cells. The Jurkat T cell line and human peripheral blood CD4+ T cells were incubated with LPA alone or with 1) pharmacological agonists of different signaling pathways, or 2) antibodies directed against the T cell receptor complex and costimulatory molecules. Luciferase-based reporter constructs driven by different lengths of the human IL-13 promoter were transfected by electroporation in Jurkat cells treated with and without LPA. The effects of LPA on IL-13 mRNA stability were examined using actinomycin D to halt ongoing transcription. Expression of mRNA encoding LPA2 and LPP-1 increased with T cell activation. LPA augmented IL-13 secretion under conditions of submaximal T cell activation. This was observed using pharmacological agonists activating intracellular calcium-, PKC-, and cAMP-dependent signaling pathways, as well as antibodies directed against CD3 and CD28. LPA only slightly prolonged IL-13 mRNA half-life in submaximally stimulated Jurkat cells. In contrast, LPA significantly enhanced transcriptional activation of the IL-13 promoter via regulatory elements contained within proximal 312 bp. The effects of LPA on IL-13 promoter activation appeared to be distinct from those mediated by GATA-3. LPA can augment IL-13 gene expression in T cells, especially under conditions of submaximal activation.

Type 4 sphingosine 1-phosphate G protein-coupled receptor (S1P4) transduces S1P effects on T cell proliferation and cytokine secretion without signaling migration

Sphingosine 1-phosphate (S1P) has diverse effects on T cells that are mediated by the predominant S1P1 and S1P4 G protein-coupled receptors (GPCRs). S1P4 is expressed principally by leukocytes, but little is known of its T cell effects in immunity. Two approaches were used to investigate S1P4 signals in T cells. First, S1P4 was introduced into D10G4.1 mouse Th2 cells and EL4.IL-2 mouse T cells lacking endogenous S1P GPCRs. Second, mouse splenic CD4 T cells were treated with FTY720 to suppress S1P1 and leave S1P4 GPCRs as the only functionally relevant S1P receptor. Unlike S1P1, S1P4 failed to transduce chemotactic responses of any of the S1P4-only T cells to S1P or the phyto-S1P ligand selective for S1P4, or to suppress their chemotactic responses to chemokines. The S1P-S1P4 axis significantly inhibited T cell proliferation in each of the S1P4-only T cells activated by anti-CD3 and anti-CD28 MoAbs. Secretion of IL-4 by S1P4-D10G4.1 cells, IL-2 by S1P4-EL4.IL-2, and IFN-gamma by FTY720-treated CD4 T cells were significantly inhibited by S1P. In contrast, S1P enhanced secretion of IL-10 by stimulated S1P4-D10G4.1 T cells. Thus, S1P4 mediates immunosuppressive effects of S1P by inhibiting proliferation and secretion of effector cytokines, while enhancing secretion of the suppressive cytokine IL-10.

Platelet-activating factor and human thyroid cancer

OBJECTIVE

Platelet-activating factor (PAF) is a pro-inflammatory and angiogenic lipid mediator involved in several types of cancer in humans. The levels of PAF, lyso-PAF (the PAF precursor), phospholipase A2 activity (PLA2, the enzymatic activity implicated in lyso-PAF formation) and acetylhydrolase activity (AHA, the PAF-degrading enzyme) were investigated in various diseased thyroid tissues.

SUBJECTS

Control and diseased tissue of patients with a hyperplastic goitre (n = 14), a benign adenoma (n = 12) and a papillary thyroid carcinoma (n = 15) were investigated.

RESULTS

PAF receptor transcripts were found in the human thyroid tissue. PAF, lyso-PAF, PLA2 and AHA were present in control thyroid tissues, their levels being significantly correlated with each other, suggesting tiny regulations of the PAF metabolic pathways inside the thyroid gland. PAF, lyso-PAF, PLA2 and AHA levels remained unchanged in diseased tissues of patients with a hyperplastic goitre, a benign adenoma and a papillary thyroid carcinoma. No difference was found between PAF, lyso-PAF, PLA2 and AHA levels with respect to the TNM tumour status and the histological sub-type of papillary thyroid carcinoma. No correlation was found between tissue PAF levels and those of vascular endothelial growth factor and basic fibroblast growth factor, two angiogenic growth factors involved in thyroid cancer and that mediate their effect through PAF release in breast and colorectal cancer.

CONCLUSION

PAF, PAF receptor transcripts and the enzymatic activities implicated in PAF production and degradation are present in the thyroid gland. While the physiological role of PAF is presently unknown in thyroid physiology, this study highlights no evidence for a potentially important role of PAF during human thyroid cancer, a result that markedly differs from breast and colorectal ones.

Lipid phosphate phosphatase-1 regulates lysophosphatidic acid-induced calcium release, NF-kappaB activation and interleukin-8 secretion in human bronchial epithelial cells

LPA (lysophosphatidic acid), a potent bioactive phospholipid, elicits diverse cellular responses through activation of the G-protein-coupled receptors LPA1-LPA4. LPA-mediated signalling is partially regulated by LPPs (lipid phosphate phosphatases; LPP-1, -2 and -3) that belong to the phosphatase superfamily. This study addresses the role of LPPs in regulating LPA-mediated cell signalling and IL-8 (interleukin-8) secretion in HBEpCs (human bronchial epithelial cells). Reverse transcription-PCR and Western blotting revealed the presence and expression of LPP-1-3 in HBEpCs. Exogenous [3H]oleoyl LPA was hydrolysed to [3H]-mono-oleoylglycerol. Infection of HBEpCs with an adenoviral construct of human LPP-1 for 48 h enhanced the dephosphorylation of exogenous LPA by 2-3-fold compared with vector controls. Furthermore, overexpression of LPP-1 partially attenuated LPA-induced increases in the intracellular Ca2+ concentration, phosphorylation of IkappaB (inhibitory kappaB) and translocation of NF-kappaB (nuclear factor-kappaB) to the nucleus, and almost completely prevented IL-8 secretion. Infection of cells with an adenoviral construct of the mouse LPP-1 (R217K) mutant partially attenuated LPA-induced IL-8 secretion without altering LPA-induced changes in intracellular Ca2+ concentration, phosphorylation of IkappaB, NF-kappaB activation or IL-8 gene expression. Our results identify LPP-1 as a key regulator of LPA signalling and IL-8 secretion in HBEpCs. Thus LPPs could represent potential targets in regulating leucocyte infiltration and airway inflammation.

Lysophospholipids in development: Miles apart and edging in

Sphingosine-1-phosphate (S1P) and lysophosphatidic acid (LPA) are endogenous bioactive lipids that participate in the regulation of mammalian cell proliferation, apoptosis, migration, and angiogenesis. These processes are each critical for successful embryogenesis, raising the possibility that lysophospholipid signaling may contribute to normal animal development. In fact, recent studies in developmental model systems have established that S1P and LPA are necessary for diverse developmental programs including those required for morphogenesis of vertebrate reproductive, cardiovascular and central and peripheral nervous systems (PNS), as well as the establishment of maternal-fetal circulation and the immune system. Genetic, morphological, and biochemical characterization of developmental model systems offer powerful approaches to elucidating the molecular mechanisms of lysophospholipid signaling and its contributions to animal development and postnatal physiology. In this review, the routes of S1P and LPA metabolism and our current understanding of lysophospholipid-mediated signal transduction in mammalian cells will be summarized. The evidence implicating lysophospholipid signaling in the development of specific vertebrate systems will then be reviewed, with an emphasis on signals mediated through G protein-coupled receptors of the Edg family. Lastly, recent insights derived from the study of simple metazoan models and implications regarding lysophospholipid signaling in organisms in which Edg receptors are not conserved will be explored.

G protein mediated signaling pathways in lysophospholipid induced cell proliferation and survival

Agonist activation of a subset of G protein coupled receptors (GPCRs) stimulates cell proliferation, mimicking the better known effects of tyrosine kinase growth factors. Cell survival or apoptosis is also regulated via pathways initiated by stimulation of these same GPCRs. This review focuses on aspects of signaling by the lysophospholipid mediators, lysophosphatidic acid (LPA), and sphingosine 1 phosphate (S1P), which make these agonists uniquely capable of modulating cell growth and survival. The general features of GPCR coupling to specific G proteins, downstream effectors and signaling cascades are first reviewed. GPCR coupling to G(i) and Ras/MAPK or to G(q) and phospholipase generated second messengers are insufficient to regulate cell proliferation while G(12/13)/Rho engagement provides additional complementary signals required for cell proliferation. Survival is best predicted by coupling to G(i) pathways that regulate PI3K and Akt, but other signals generated through different G protein pathways are also implicated. The unique ability of LPA and S1P to concomitantly stimulate G(i), G(q), and G(12/13) pathways, given the proper complement of expressed LPA or S1P receptors, allows these receptors to support cell survival and proliferation. In pathophysiological situations, e.g., vascular disease, cancer, brain injury, and inflammation, components of the signaling cascade downstream of lysophospholipid receptors, in particular those involving Ras or Rho, may be altered. In addition, up or downregulation of LPA or S1P receptor subtypes, altering their ratio, and increased availability of the lysophospholipid ligands at sites of injury or inflammation, likely contribute to disease and may be important targets for therapeutic intervention.

LPA2 receptor mediates mitogenic signals in human colon cancer cells

Lysophosphatidic acid (LPA) is a mediator of multiple cellular responses. LPA mediates its effects predominantly through the G protein-coupled receptors LPA1, LPA2, and LPA3. In the present work, we studied LPA2-mediated signaling using human colon cancer cell lines, which predominantly express LPA2. LPA2 activated Akt and Erk1/2 in response to LPA. LPA mediated Akt activation was inhibited by pertussis toxin (PTX), whereas Erk1/2 activation was completely inhibited by a blocker of phospholipase Cbeta, U-73122. LPA also induced interleukin-8 (IL-8) synthesis in the colon cancer cells by primarily activating LPA2 receptor. We also found that LPA2 interacts with Na+/H+ exchanger regulatory factor 2 (NHERF2). Activation of Akt and Erk1/2 was significantly attenuated by silencing of NHERF2 expression by RNA interference, suggesting a pivotal role of NHERF2 in LPA2-mediated signaling. We found that expression of LPA2 was elevated, whereas expression of LPA1 downregulated in several types of cancers, including ovarian and colon cancer. We conclude that LPA2 is the major LPA receptor in colon cancer cells and cellular signals by LPA2 are largely mediated through its ability to interact with NHERF2.

Differential effects of lysolipids on steroid synthesis in cells expressing endogenous LPA2 receptor

Incubation of ovarian luteal cells with the bioactive lipid mediator lysophosphatidic acid (LPA) for 180 min abolishes gonadotropin-induced steroid production with no attenuation of the cyclic AMP accumulation. Treatment with the lysolipid also diminishes [14C]steroid production in cells preloaded with either [14C]cholesterol or [14C]acetate. Neither the expression of steroidogenic acute regulatory (StAR) protein nor in vitro steroid synthesis is affected in isolated mitochondrial fractions. The LPA-induced attenuation of steroid production occurs only in the mid-cycle corpus luteum and is associated with a transient endogenous expression of mRNA for the lysophosphatidic acid A2 (LPA2) receptor (with no concomitant changes in the expression of LPA1 receptor). Expression of LPA2 is accompanied by LPA-induced sphingosine-1-phosphate (S1P) production. Because luteal cells, in the presence of the sphingosine kinase inhibitor dihydrosphingosine, can overcome the inhibitory effects of LPA on steroid synthesis, we suggest the possible requirement of intracellular S1P production. Interestingly, no LPA-induced inhibition of 8Br-cAMP-stimulated progesterone synthesis can be detected in Leydig tumor cell line MA10 cells expressing only LPA2 receptor. Surprisingly, however, exogenous S1P inhibits agonist-stimulated progesterone in both cell types by inhibiting cyclic AMP accumulation, suggesting different mechanisms of action.

Signaling mechanisms responsible for lysophosphatidic acid-induced urokinase plasminogen activator expression in ovarian cancer cells

Lysophosphatidic acid (LPA) enhances urokinase plasminogen activator (uPA) expression in ovarian cancer cells; however, the molecular mechanisms responsible for this event have not been investigated. In this study, we used the invasive ovarian cancer SK-OV-3 cell line to explore the signaling molecules and pathways essential for LPA-induced uPA up-regulation. With the aid of specific inhibitors and dominant negative forms of signaling molecules, we determined that the G(i)-associated pathway mediates this LPA-induced event. Moreover, constitutively active H-Ras and Raf-1-activating H-Ras mutant enhance uPA expression, whereas dominant negative H-Ras and Raf-1 block LPA-induced uPA up-regulation, suggesting that the Ras-Raf pathway works downstream of G(i) to mediate this LPA-induced process. Surprisingly, dominant negative MEK1 or Erk2 displays only marginal inhibitory effect on LPA-induced uPA up-regulation, suggesting that a signaling pathway distinct from Raf-MEK1/2-Erk is the prominent pathway responsible for this process. In this report, we demonstrate that LPA activates NF-kappaB in a Ras-Raf-dependent manner and that blocking NF-kappaB activation with either non-phosphorylable IkappaB or dominant negative IkappaB kinase abolished LPA-induced uPA up-regulation and uPA promoter activation. Furthermore, introducing mutations to knock out the NF-kappaB binding site of the uPA promoter results in over 80% reduction in LPA-induced uPA promoter activation, whereas this activity is largely intact with the promoter containing mutations in the AP1 binding sites. Thus these results suggest that the G(i)-Ras-Raf-NF-kappaB signaling cascade is responsible for LPA-induced uPA up-regulation in ovarian cancer cells.

Lysophosphatidic Acid Interacts with Transforming Growth Factor-β Signaling to Mediate Keratinocyte Growth Arrest and Chemotaxis

Lysophosphatidic acid (LPA, 1-acyl-glycerol-3-phosphate) plays an important role in diverse biological responses including cell proliferation, differentiation, survival, migration, and tumor cell invasion. The most prominent source of LPA is platelets from which it is released after thrombin activation and is assumed to be an essential function of this lysophospholipid in cutaneous wound closure. Therefore, we examined the role of LPA on biological responses of keratinocytes. Although LPA potently enhances keratinocyte migration, it strongly induces growth arrest of proliferating epidermal cells. Thus, LPA possesses analogous actions to transforming growth factor-beta (TGF-beta), which is also released from degranulating platelets at wounded sites. In contrast to LPA, the intracellular signaling events of TGF-beta have been clearly identified and indicate that Smad3 is involved in chemotaxis and cell growth arrest of keratinocytes induced by this cytokine. Here we show that LPA, although it does not alter TGF-beta release is capable to activate Smad3 and results in a heteromerization with Smad4 and binding of the complex to its specific DNA-promoter elements. LPA completely fails to induce chemotaxis in Smad3-deficient cells, whereas growth inhibition is at least in part reduced. These findings indicate an essential role of Smad3 in diverse biological properties of LPA-stimulated keratinocytes.

Lysophospholipid receptors: signaling and biology

Lysophospholipids (LPs), such as lysophosphatidic acid and sphingosine 1-phosphate, are membrane-derived bioactive lipid mediators. LPs can affect fundamental cellular functions, which include proliferation, differentiation, survival, migration, adhesion, invasion, and morphogenesis. These functions influence many biological processes that include neurogenesis, angiogenesis, wound healing, immunity, and carcinogenesis. In recent years, identification of multiple cognate G protein-coupled receptors has provided a mechanistic framework for understanding how LPs play such diverse roles. Generation of LP receptor-null animals has allowed rigorous examination of receptor-mediated physiological functions in vivo and has identified new functions for LP receptor signaling. Efforts to develop LP receptor subtype-specific agonists/antagonists are in progress and raise expectations for a growing collection of chemical tools and potential therapeutic compounds. The rapidly expanding literature on the LP receptors is herein reviewed.

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

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

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

Introduction

Lysophosphatidic acid (LPA) is a bioactive phospholipid with diverse effects on various cells. It interacts with at least three G-protein-coupled transmembrane receptors, namely LPA1, LPA2 and LPA3, whose expression in various tumours has not been fully characterized. In the present study we characterized the expression profile of LPA receptors in human breast cancer tissue and assessed the possible roles of each receptor.

Methods

The relative expression levels of each receptor's mRNA against β-actin mRNA was examined in surgically resected invasive ductal carcinomas and normal gland tissue using real-time RT-PCR. LPA2 expression was also examined immunohistochemically using a rat anti-LPA2 monoclonal antibody.

Results

In 25 cases normal and cancer tissue contained LPA1 mRNA at similar levels, whereas the expression level of LPA2 mRNA was significantly increased in cancer tissue as compared with its normal counterpart (3479.0 ± 426.6 versus 1287.3 ± 466.8; P < 0.05). LPA3 was weakly expressed in both cancer and normal gland tissue. In 48 (57%) out of 84 cases, enhanced expression of LPA2 protein was confirmed in carcinoma cells as compared with normal mammary epithelium by immunohistochemistry. Over-expression of LPA2 was detected in 17 (45%) out of 38 premenopausal women, as compared with 31 (67%) out of 46 postmenopausal women, and the difference was statistically significant (P < 0.05).

Conclusion

These findings suggest that upregulation of LPA2 may play a role in carcinogenesis, particularly in postmenopausal breast cancer.

Increased expression of CYR61, an extracellular matrix signaling protein, in human benign prostatic hyperplasia and its regulation by lysophosphatidic acid

Lysophosphatidic acid (LPA) is an endogenous lipid growth factor that is thought to play important roles in cell proliferation and antiapoptosis and therefore may have roles in the development and progression of benign prostatic hyperplasia (BPH). CYR61 (CCN1), on the other hand, is a growth factor-inducible immediate early gene that functions in cell proliferation, differentiation, and extracellular matrix synthesis. Here we show the close relationship between LPA-induced expression of CYR61 and prostate enlargement. CYR61 mRNA and protein were dramatically up-regulated by 18:1 LPA (oleoyl-LPA) within 1 and 2 h, respectively, in both stromal and epithelial prostatic cells. G protein-coupled receptors, i.e. Edg-2, Edg-4, and Edg-7, for LPA were also expressed in both stromal and epithelial prostatic cells. Furthermore, on DNA microarray analysis for normal and BPH patients, CYR61 was found to be related to the development and progression of BPH, regardless of symptoms. Although CYR61 mRNA was synthesized in hyperplastic epithelial cells, in many cases of BPH, CYR61 protein was detected in both the epithelial and stromal regions of BPH patient tissues. The functional contribution of CYR61 to prostatic cell growth was demonstrated by recombinant CYR61 protein and anti-CYR61 neutralizing antibodies, which inhibited CYR61-dependent cell spreading and significantly diminished cell proliferation, respectively. In conclusion, these data support the hypothesis that LPAs induce the expression of CYR61 by activating G proteincoupled receptors and that CYR61 acts as a secreted autocrine and/or paracrine mediator in stromal and epithelial hyperplasia, demonstrating the potential importance of this signaling mechanism in the disease.

Hyperlipidemia is a risk factor for lymphatic metastasis in superficial esophageal carcinoma

Although increased dietary fat or cholesterol has been reported to be a risk factor for the development of certain cancers, the effect of the serum lipid level on tumor metastasis has not been well documented. Fasting serum levels of total cholesterol (TC) and triglycerides (TG) were examined in 54 patients with superficial esophageal cancer (SEC) invading lamia musucularis or submucosal layer who underwent esophagectomy with classical lymphadenectomy. The association between lymph node metastasis and the preoperative serum lipid levels as well as the pathological findings was retrospectively analyzed. The levels of TC and TG were significantly higher in 18 node-positive than in 36 node-negative patients (TC: 205.4+/-38.9 vs. 174.5+/-26.8 mg/dl, P<0.01; TG: 152.0+/-68.5 vs. 88.7+/-28.6 mg/dl, P<0.001). Patients with hypercholesterolemia (TC >/= 220 mg/dl) and hypertriglyceridemia (TG >/= 150 mg/dl) showed extremely high rates of nodal metastasis (80 and 91%, respectively), that were significantly higher than those of patients with normal lipid levels (P<0.01 and P<0.001). When hyperlipidemia was defined as the presence of either hypertriglyceridemia or hypercholesterolemia, hyperlipidemia was an independent risk factor for nodal metastasis in SEC. Elevated serum lipid levels might bring favorable circumstances for the development of lymph node metastasis in the early stage of EC. Hyperlipidemia might prompt us to perform more studies to investigate possible metastasis.

Lysophospholipid G protein-coupled receptors

The many biological responses documented for lysophospholipids that include lysophosphatidic acid and sphingosine 1-phosphate can be mechanistically attributed to signaling through specific G protein-coupled receptors. At least nine receptors have now been identified, and the total number is likely to be larger. In this brief review, we note cogent features of lysophospholipid receptors, including the current nomenclature, signaling properties, development of agonists and antagonists, and physiological functions.

Induction of protein growth factor systems in the ovaries of transgenic mice overexpressing human type 2 lysophosphatidic acid G protein-coupled receptor (LPA2)

The lipid growth factor lysophosphatidic acid (LPA) is produced by ovarian cancer cells in quantities sufficient to attain concentrations of up to 10 microM. An autocrine circuit was demonstrated when ovarian cancer cells, but not normal ovarian surface epithelial cells, were proven to express LPA(2) (Edg-4) and LPA(3) (Edg-7) G protein-coupled receptors for LPA. Human LPA(2) now has been expressed transgenically in C57BL/6 mouse ovaries under direction of the alpha-inhibin large promoter. Human LPA(2) mRNA and protein were detected in all transgenic (TG) mouse ovaries at levels far higher than in other tissues and at least fivefold higher than in cultured lines of human ovarian cancer cells, with the expected sex cord-stromal distribution. Most LPA(2) TG ovaries produced significantly higher levels than non-TG ovaries of type A, but not type B, vascular endothelial growth factor (VEGF), isomers of VEGF-A, and urokinase-type plasminogen activator (uPA). Many LPA(2) TG ovaries had elevated expression of VEGF receptors 1 and 2, and a depressed level of type 2 PA inhibitor. Thus, the LPA-LPA(2) circuit regulates ovarian cells both directly and through increases in protein growth factor systems.

Discovery of new G protein-coupled receptors for lipid mediators

Successful sequencing of the human genome has opened a new era in the life sciences and has greatly accelerated biomedical research. Among various research endeavors benefiting from established genomic information, one of the most fruitful areas is the research on orphan G protein-coupled receptors (GPCRs). Many intercellular mediators, including peptides, lipids, and other small molecules, have found their GPCRs in the plasma membrane, e.g., relaxin and tyramine. In the past 14 months, more than one dozen papers have been published reporting the finding of intercellular lipid mediators acting on rhodopsin family GPCRs. This review focuses primarily on intercellular lipid mediators and their recently discovered GPCRs.

Phosphorylation and action of the immunomodulator FTY720 inhibits vascular endothelial cell growth factor-induced vascular permeability

FTY720, a potent immunosuppressive agent, is phosphorylated in vivo into FTY720-P, a high affinity agonist for sphingosine 1-phosphate (S1P) receptors. The effects of FTY720 on vascular cells, a major target of S1P action, have not been addressed. We now report the metabolic activation of FTY720 by sphingosine kinase-2 and potent activation of vascular endothelial cell functions in vitro and in vivo by phosphorylated FTY720 (FTY720-P). Incubation of endothelial cells with FTY720 resulted in phosphorylation by sphingosine kinase activity and formation of FTY720-P. Sphingosine kinase-2 effectively phosphorylated FTY720 in the human embryonic kidney 293T heterologous expression system. FTY720-P treatment of endothelial cells stimulated extracellular signal-activated kinase and Akt phosphorylation and adherens junction assembly and promoted cell survival. The effects of FTY720-P were inhibited by pertussis toxin, suggesting the requirement for Gi-coupled S1P receptors. Indeed, transmonolayer permeability induced by vascular endothelial cell growth factor was potently reversed by FTY720-P. Furthermore, oral FTY720 administration in mice potently blocked VEGF-induced vascular permeability in vivo. These findings suggest that FTY720 or its analogs may find utility in the therapeutic regulation of vascular permeability, an important process in angiogenesis, inflammation, and pathological conditions such as sepsis, hypoxia, and solid tumor growth.

Egress: a receptor-regulated step in lymphocyte trafficking

Blood lymphocyte numbers, which are maintained by recirculation through secondary lymphoid organs, are essential for the efficient development of immune responses. Recirculating populations of B and T lymphocytes are regulated by the sphingosine-1-phosphate (S1P) receptor-dependent control of lymphocyte egress. T-cell egress from thymus into blood, egress from lymph node and Peyer's patch into lymph, and B-cell egress into lymph are rapidly and completely inhibited by agonism of S1P receptors. Mesenteric lymph nodes show log-jamming of lymphocytes subjacent to sinus-lining endothelium. Agonism of S1P receptors produces rapid peripheral blood lymphopenia, which is maintained in the presence of receptor agonist. Effector CD4+ and CD8+ T cells, produced by clonal expansion in draining lymph node in response to antigen, are sequestered in lymph node and fail to reach the peripheral blood. The S1P receptor system may represent an early physiological link between the non-specific inflammatory response and the alteration of lymphocyte traffic through draining lymph nodes. Pharmacological subversion of the S1P receptor system, through systemic S1P agonist-induced inhibition of lymphocyte egress, suppresses antigenic responses to peripheral, but not to systemically, delivered antigen. This inhibition induces significant immunosuppression in models of transplantation and autoimmune tissue damage that may prove to be of clinical benefit.

Possible endocannabinoid control of colorectal cancer growth

BACKGROUND & AIMS

The endocannabinoids anandamide and 2-arachidonoylglycerol (2-AG) inhibit cancer cell proliferation by acting at cannabinoid receptors (CBRs). We studied (1). the levels of endocannabinoids, cannabinoid CB(1) and CB(2) receptors, and fatty acid amide hydrolase (FAAH, which catalyzes endocannabinoid hydrolysis) in colorectal carcinomas (CRC), adenomatous polyps, and neighboring healthy mucosa; and (2). the effects of endocannabinoids, and of inhibitors of their inactivation, on human CRC cell proliferation.

METHODS

Tissues were obtained from 21 patients by biopsy during colonoscopy. Endocannabinoids were measured by liquid chromatography-mass spectrometry (LC-MS). CB(1), CB(2), and FAAH expression were analyzed by RT-PCR and Western immunoblotting. CRC cell lines (CaCo-2 and DLD-1) were used to test antiproliferative effects.

RESULTS

All tissues and cells analyzed contain anandamide, 2-AG, CBRs, and FAAH. The levels of the endocannabinoids are 3- and 2-fold higher in adenomas and CRCs than normal mucosa. Anandamide, 2-AG, and the CBR agonist HU-210 potently inhibit CaCo-2 cell proliferation. This effect is blocked by the CB(1) antagonist SR141716A, but not by the CB(2) antagonist SR144528, and is mimicked by CB(1)-selective, but not CB(2)-selective, agonists. In DLD-1 cells, both CB(1) and CB(2) receptors mediate inhibition of proliferation. Inhibitors of endocannabinoid inactivation enhance CaCo-2 cell endocannabinoid levels and block cell proliferation, this effect being antagonized by SR141716A. CaCo-2 cell differentiation into noninvasive cells results in increased FAAH expression, lower endocannabinoid levels, and no responsiveness to cannabinoids.

CONCLUSIONS

Endocannabinoid levels are enhanced in transformed colon mucosa cells possibly to counteract proliferation via CBRs. Inhibitors of endocannabinoid inactivation may prove useful anticancer agents.

Arachidonic acid in mononuclear cells and its clinical significance in HCV cirrhotic patients

OBJECTIVES

An abnormal fatty acid pattern in patients with advanced liver cirrhosis (LC) has been reported in plasma phospholipids and some other tissues. To elucidate the significance of arachidonic acid deficiency on the clinical pathophysiology of LC and hepatocellular carcinoma (HCC), we analyzed the fatty acid compositions of mononuclear cell phospholipids, plasma alpha-tocopherol, and thiobarbituric acid-reactive substances and serum tumor necrosis factor-alpha (TNF-alpha) in cirrhotic patients infected with the hepatitis C virus with and without HCC.

METHODS

Twelve cirrhotic patients without HCC (LC patients) and 11 with HCC (HCC patients) were enrolled. Fatty acids were analyzed with gas chromatography. alpha-Tocopherol and TNF-alpha were analyzed by high-performance liquid chromatography and enzyme-linked immunosorbent assay, respectively. Statistical analysis was performed by using the unpaired t test with Welch's correction and Spearman's rank-correlation analysis.

RESULTS

Significantly low levels of linoleic, dihomo-gamma-linolenic, arachidonic, and eicosapentaenoic acids from mononuclear cell phospholipids were observed in LC and HCC patients compared with control subjects. Plasma alpha-tocopherol was lower and thiobarbituric acid-reactive substances were higher in HCC patients than in controls. Arachidonic acid molar percentage in mononuclear cell phospholipids correlated significantly with lymphocyte count (r = 0.460, P < 0.05) in the cirrhotic patients and with lymphocyte (r = 0.680, P < 0.01) and platelet (r = 0.763, P < 0.01) counts in all subjects.

CONCLUSIONS

These results suggested that arachidonic acid in mononuclear cells may have an important role in the pathophysiology of hepatitis C virus associated with cirrhosis and that nutritional management preventing arachidonic acid deficiency may have some beneficial effects on the progression of LC.

Secretory phospholipases A2 activate selective functions in human eosinophils

Secretory phospholipases A(2) (sPLA(2)s) are released in large amounts in the blood of patients with systemic inflammatory diseases and accumulate at sites of chronic inflammation, such as the airways of patients with bronchial asthma. Blood eosinophils or eosinophils recruited in inflammatory areas therefore can be exposed in vivo to high concentrations of sPLA(2). We have examined the effects of two structurally different sPLA(2)s (group IA and group IIA) on several functions of eosinophils isolated from normal donors and patients with hypereosinophilia. Both group IA and IIA sPLA(2) induced a concentration-dependent release of beta-glucuronidase, IL-6, and IL-8. Release of the two cytokines was associated with the accumulation of their specific mRNA. In addition, sPLA(2)s induced the surface expression of CD44 and CD69, two major activation markers of eosinophils. In contrast, none of the sPLA(2)s examined induced the production of IL-5, the de novo synthesis of leukotriene C(4) and platelet-activating factor, or the generation of superoxide anion from human eosinophils. Incubation of eosinophils with the major enzymatic products of the sPLA(2)s (arachidonic acid, lysophosphatidylcholine, or lysophosphatidic acid) did not reproduce any of the enzymes' effects. In addition, inactivation of sPLA(2) enzymatic activity by bromophenacyl bromide did not influence the release of beta-glucuronidase or of cytokines. Stimulation of eosinophils by sPLA(2)s was associated with activation of extracellular signal-regulated kinases 1/2. These results indicate that sPLA(2)s selectively activate certain proinflammatory and immunoregulatory functions of human eosinophils through mechanism(s) independent from enzymatic activity and from the generation of arachidonic acid.