Tetracyclines increase lipid phosphate phosphatase expression on plasma membranes and turnover of plasma lysophosphatidate

Pancreatic CAF-Derived Autotaxin Drives Autocrine CTGF Expression to Modulate Protumorigenic Signaling

Autotaxin (ATX), encoded by ENPP2, is a clinical target in pancreatic ductal adenocarcinoma (PDAC). ATX catalyzes the production of lysophosphatidic acid (LPA), an important regulator within the tumor microenvironment (TME), yet the protumorigenic action of the ATX/LPA axis in PDAC remains unclear. In this study, by interrogating patient samples and cell line datasets, we show that the PDAC TME, rather than cancer cells, is responsible for the majority of ENPP2 expression and highlight a key role for cancer-associated fibroblast (CAF)-derived ATX in autocrine and paracrine protumorigenic signaling. Using the clinical-stage ATX inhibitor, IOA-289, we identified connective tissue growth factor (CTGF), also known as CCN2, as a downstream mediator of ATX signaling in the PDAC CAF-derived cell line, 0082T. Genetic ablation or pharmacologic inhibition of ATX in 0082T CAFs reduced CTGF secretion via modulation of LPA/LPA receptor signaling. Despite the loss of ATX function, extracellular levels of LPA were paradoxically increased, indicating a role for ATX beyond its enzymatic activity and suggesting a role for its LPA chaperone function in the LPA/LPA receptor signaling in CAFs. As CAFs are the main source for CTGF in the PDAC TME, these findings suggest a role for ATX in promoting a protumorigenic microenvironment via modulation of CAF secretion not only via its LPA-producing activity but also via its LPA chaperone function, providing a potential mechanism for the antitumor effects of ATX inhibition.

Autotaxin and Lysophosphatidate Signaling: Prime Targets for Mitigating Therapy Resistance in Breast Cancer

Overcoming and preventing cancer therapy resistance is the most pressing challenge in modern breast cancer management. Consequently, most modern breast cancer research is aimed at understanding and blocking these therapy resistance mechanisms. One increasingly promising therapeutic target is the autotaxin (ATX)-lysophosphatidate (LPA)-lipid phosphate phosphatase (LPP) axis. Extracellular LPA, produced from albumin-bound lysophosphatidylcholine by ATX and degraded by the ecto-activity of the LPPs, is a potent cell-signaling mediator of tumor growth, invasion, angiogenesis, immune evasion, and resistance to cancer treatment modalities. LPA signaling in the post-natal organism has central roles in physiological wound healing, but these mechanisms are subverted to fuel pathogenesis in diseases that arise from chronic inflammatory processes, including cancer. Over the last 10 years, our understanding of the role of LPA signaling in the breast tumor microenvironment has begun to mature. Tumor-promoting inflammation in breast cancer leads to increased ATX production within the tumor microenvironment. This results in increased local concentrations of LPA that are maintained in part by decreased overall cancer cell LPP expression that would otherwise more rapidly break it down. LPA signaling through six G-protein-coupled LPA receptors expressed by cancer cells can then activate virtually every known tumorigenic pathway. Consequently, to target therapy resistance and tumor growth mediated by LPA signaling, multiple inhibitors against the LPA signaling axis are entering clinical trials. In this review, we summarize recent developments in LPA breast cancer biology, and illustrate how these novel therapeutics against the LPA signaling pathway may be excellent adjuncts to extend the efficacy of evolving breast cancer treatments.

Decreased Lipid Phosphate Phosphatase 1/3 and Increased Lipid Phosphate Phosphatase 2 Expression in the Human Breast Cancer Tumor Microenvironment Promotes Tumor Progression and Immune System Evasion

The LPP family is comprised of three enzymes that dephosphorylate bioactive lipid phosphates both intracellularly and extracellularly. Pre-clinical breast cancer models have demonstrated that decreased LPP1/3 with increased LPP2 expression correlates to tumorigenesis. This though has not been well verified in human specimens. In this study, we correlate LPP expression data to clinical outcomes in over 5000 breast cancers from three independent cohorts (TCGA, METABRIC, and GSE96058), investigate biological function using gene set enrichment analysis (GSEA) and the xCell cell-type enrichment analysis, and confirm sources of LPP production in the tumor microenvironment (TME) using single-cell RNA-sequencing (scRNAseq) data. Decreased LPP1/3 and increased LPP2 expression correlated to increased tumor grade, proliferation, and tumor mutational burden (all p < 0.001), as well as worse overall survival (hazard ratios 1.3-1.5). Further, cytolytic activity was decreased, consistent with immune system invasion. GSEA data demonstrated multiple increased inflammatory signaling, survival, stemness, and cell signaling pathways with this phenotype across all three cohorts. scRNAseq and the xCell algorithm demonstrated that most tumor LPP1/3 was expressed by endothelial cells and tumor-associated fibroblasts and LPP2 by cancer cells (all p < 0.01). Restoring the balance in LPP expression levels, particularly through LPP2 inhibition, could represent novel adjuvant therapeutic options in breast cancer treatment.

Lipid phosphate phosphatase 3 in smooth muscle cells regulates angiotensin II-induced abdominal aortic aneurysm formation

Genetic variants that regulate lipid phosphate phosphatase 3 (LPP3) expression are risk factors for the development of atherosclerotic cardiovascular disease. LPP3 is dynamically upregulated in the context of vascular inflammation with particularly heightened expression in smooth muscle cells (SMC), however, the impact of LPP3 on vascular pathology is not fully understood. We investigated the role of LPP3 and lysophospholipid signaling in a well-defined model of pathologic aortic injury and observed Angiotensin II (Ang II) increases expression of PLPP3 in SMCs through nuclear factor kappa B (NF-κB) signaling Plpp3 global reduction (Plpp3+/-) or SMC-specific deletion (SM22-Δ) protects hyperlipidemic mice from AngII-mediated aneurysm formation. LPP3 expression regulates SMC differentiation state and lowering LPP3 levels promotes a fibroblast-like phenotype. Decreased inactivation of bioactive lysophosphatidic acid (LPA) in settings of LPP3 deficiency may underlie these phenotypes because deletion of LPA receptor 4 in mice promotes early aortic dilation and rupture in response to AngII. LPP3 expression and LPA signaling influence SMC and vessel wall responses that are important for aortic dissection and aneurysm formation. These findings could have important implications for therapeutics targeting LPA metabolism and signaling in ongoing clinical trials.

Inhibition of autotaxin by bile salts and bile salt-like molecules increases its expression by feedback regulation

BACKGROUND

Autotaxin is an enzyme that converts lysophospholipid into lysophosphatidic acid (LPA), a highly potent signaling molecule through a range of LPA receptors. It is therefore important to investigate which factors play a role in regulating ATX expression. Since we have reported that ATX levels increase dramatically in patients with various forms of cholestasis, we embarked on a study to reveal factors that influence the enzyme activity ATX as well as its expression level in vitro and in vivo.

METHODS

Bile from cholestatic patients was fractionated by HPLC and analyzed for modulation of ATX activity. ATX expression was measured in fibroblasts upon stimulation or inhibition of LPA signaling.

RESULTS

Surprisingly, ATX activity was stimulated by most forms of its product LPA, but it was inhibited by bile salts and bile salt-like molecules, particularly by 3-OH sulfated bile salts and sulfated progesterone metabolites that are known to accumulate during chronic cholestasis and cholestasis of pregnancy, respectively. Activation of fibroblasts by LPA decreased ATX expression by 72%. Conversely, inhibition of LPA signaling increased ATX expression 3-fold, indicating strong feedback regulation by LPA signaling. In fibroblasts, we could verify that inhibition of ATX activity by bile salts induces its expression. Furthermore, induction of cholestasis in mice causes increased plasma ATX activity.

CONCLUSIONS

Multiple biliary compounds that accumulate in the systemic circulation during cholestasis inhibit ATX activity and thereby increase ATX expression through feedback regulation. This mechanism may contribute to increased serum ATX activity in patients with cholestasis.

Lysophosphatidic Acid: Promoter of Cancer Progression and of Tumor Microenvironment Development. A Promising Target for Anticancer Therapies?

Increased expression of the enzyme autotaxin (ATX) and the consequently increased levels of its product, lysophosphatidic acid (LPA), have been reported in several primary tumors. The role of LPA as a direct modulator of tumor cell functions—motility, invasion and migration capabilities as well as resistance to apoptotic death—has been recognized by numerous studies over the last two decades. Notably, evidence has recently been accumulating that shows that LPA also contributes to the development of the tumor microenvironment (TME). Indeed, LPA plays a crucial role in inducing angiogenesis and lymphangiogenesis, triggering cellular glycolytic shift and stimulating intratumoral fibrosis. In addition, LPA helps tumoral cells to escape immune surveillance. Treatments that counter the TME components, in order to deprive cancer cells of their crucial support, have been emerging among the promising new anticancer therapies. This review aims to summarize the latest knowledge on how LPA influences both tumor cell functions and the TME by regulating the activity of its different elements, highlighting why and how LPA is worth considering as a molecular target for new anticancer therapies.

Physiological and pathological functions of sphingolipids in pregnancy

Signaling by the bioactive sphingolipid, sphingosine 1-phosphate (S1P), and its precursors are emerging areas in pregnancy research. S1P and ceramide levels increase towards end of gestation, suggesting a physiological role in parturition. However, high levels of circulating S1P and ceramide are correlated with pregnancy disorders such as preeclampsia, gestational diabetes mellitus and intrauterine growth restriction. Expression of placental and decidual enzymes that metabolize S1P and S1P receptors are also dysregulated during pregnancy complications. In this review, we provide an in-depth examination of the signaling mechanism of S1P and ceramide in various reproductive tissues during gestation. These factors determine implantation and early pregnancy success by modulating corpus luteum function from progesterone production to luteolysis through to apoptosis. We also highlight the role of S1P through receptor signaling in inducing decidualization and angiogenesis in the decidua, as well as regulating extravillous trophoblast migration to anchor the placenta into the uterine wall. Recent advances on the role of the S1P:ceramide rheostat in controlling the fate of villous trophoblasts and the role of S1P as a negative regulator of trophoblast syncytialization to a multinucleated placental barrier are discussed. This review also explores the role of S1P in anti-inflammatory and pro-inflammatory signaling, its role as a vasoconstrictor, and the effects of S1P metabolizing enzymes and receptors in pregnancy.

Lipid Phosphate Phosphatases and Cancer

Lipid phosphate phosphatases (LPPs) are a group of three enzymes (LPP1–3) that belong to a phospholipid phosphatase (PLPP) family. The LPPs dephosphorylate a wide spectrum of bioactive lipid phosphates, among which lysophosphatidate (LPA) and sphingosine 1-phosphate (S1P) are two important extracellular signaling molecules. The LPPs are integral membrane proteins, which are localized on plasma membranes and intracellular membranes, including the endoplasmic reticulum and Golgi network. LPPs regulate signaling transduction in cancer cells and demonstrate different effects in cancer progression through the breakdown of extracellular LPA and S1P and other intracellular substrates. This review is intended to summarize an up-to-date understanding about the functions of LPPs in cancers.

Role of Adipose Tissue-Derived Autotaxin, Lysophosphatidate Signaling, and Inflammation in the Progression and Treatment of Breast Cancer

Autotaxin (ATX) is a secreted enzyme that produces lysophosphatidate (LPA), which signals through six G-protein coupled receptors, promoting tumor growth, metastasis, and survival from chemotherapy and radiotherapy. Many cancer cells produce ATX, but breast cancer cells express little ATX. In breast tumors, ATX is produced by tumor-associated stroma. Breast tumors are also surrounded by adipose tissue, which is a major bodily source of ATX. In mice, a high-fat diet increases adipocyte ATX production. ATX production in obesity is also increased because of low-level inflammation in the expanded adipose tissue. This increased ATX secretion and consequent LPA signaling is associated with decreased adiponectin production, which results in adverse metabolic profiles and glucose homeostasis. Increased ATX production by inflamed adipose tissue may explain the obesity-breast cancer association. Breast tumors produce inflammatory mediators that stimulate ATX transcription in tumor-adjacent adipose tissue. This drives a feedforward inflammatory cycle since increased LPA signaling increases production of more inflammatory mediators and cyclooxygenase-2. Inhibiting ATX activity, which has implications in breast cancer adjuvant treatments, attenuates this cycle. Targeting ATX activity and LPA signaling may potentially increase chemotherapy and radiotherapy efficacy, and decrease radiation-induced fibrosis morbidity independently of breast cancer type because most ATX is not derived from breast cancer cells.

GPR50 Promotes Hepatocellular Carcinoma Progression via the Notch Signaling Pathway through Direct Interaction with ADAM17

Hepatocellular carcinoma (HCC) is a leading cause of cancer-related death worldwide, and it is thus critical to identify novel molecular biomarkers of HCC prognosis and elucidate the molecular mechanisms underlying HCC progression. Here, we show that G-protein-coupled receptor 50 (GPR50) in HCC is overexpressed and that GPR50 knockdown may downregulate cancer cell progression through attenuation of the Notch signaling pathway. GPR50 knockdown was found to reduce HCC progression by inactivating Notch signaling in a ligand-independent manner through a disintegrin and metalloproteinase metallopeptidase domain 17 (ADAM17), a proteolytic enzyme that cleaves the Notch receptor, which was corroborated by GPR50 overexpression in hepatocytes. GPR50 silencing also downregulated transcription and translation of ADAM17 through the AKT/specificity protein-1 (SP1) signaling axis. Notably, GPR50 was found to directly interact with ADAM17. Overall, we demonstrate a novel GPR50-mediated regulation of the ADAM17-Notch signaling pathway, which can provide insights into HCC progression and prognosis and development of Notch-based HCC treatment strategies.

Signalling by lysophosphatidate and its health implications

Extracellular lysophosphatidate (LPA) signalling is regulated by the balance of LPA formation by autotaxin (ATX) versus LPA degradation by lipid phosphate phosphatases (LPP) and by the relative expressions of six G-protein-coupled LPA receptors. These receptors increase cell proliferation, migration, survival and angiogenesis. Acute inflammation produced by tissue damage stimulates ATX production and LPA signalling as a component of wound healing. If inflammation does not resolve, LPA signalling becomes maladaptive in conditions including arthritis, neurologic pain, obesity and cancers. Furthermore, LPA signalling through LPA1 receptors promotes fibrosis in skin, liver, kidneys and lungs. LPA also promotes the spread of tumours to other organs (metastasis) and the pro-survival properties of LPA explain why LPA counteracts the effects of chemotherapeutic agents and radiotherapy. ATX is secreted in response to radiation-induced DNA damage during cancer treatments and this together with increased LPA1 receptor expression leads to radiation-induced fibrosis. The anti-inflammatory agent, dexamethasone, decreases levels of inflammatory cytokines/chemokines. This is linked to a coordinated decrease in the production of ATX and LPA1/2 receptors and increased LPA degradation through LPP1. These effects explain why dexamethasone attenuates radiation-induced fibrosis. Increased LPA signalling is also associated with cardiovascular disease including atherosclerosis and deranged LPA signalling is associated with pregnancy complications including preeclampsia and intrahepatic cholestasis of pregnancy. LPA contributes to chronic inflammation because it stimulates the secretion of inflammatory cytokines/chemokines, which increase further ATX production and LPA signalling. Attenuating maladaptive LPA signalling provides a novel means of treating inflammatory diseases that underlie so many important medical conditions.

Role of the autotaxin-lysophosphatidate axis in the development of resistance to cancer therapy

Autotaxin (ATX) is a secreted enzyme that hydrolyzes lysophosphatidylcholine to produce lysophosphatidate (LPA), which signals through six G-protein coupled receptors (GPCRs). Signaling through LPA is terminated by its degradation by a family of three lipid phosphate phosphatases (LPPs). LPP1 also attenuates signaling downstream of the activation of LPA receptors and some other GPCRs. The ATX-LPA axis mediates a plethora of activities such as cell proliferation, survival, migration, angiogenesis and inflammation, which perform an important role in facilitating wound healing. This wound healing response is hijacked by cancers where there is decreased expression of LPP1 and LPP3 and increased expression of ATX. This maladaptive regulation of LPA signaling also causes chronic inflammation, which has been recognized as one of the hallmarks in cancer. The increased LPA signaling promotes cell survival and migration and attenuates apoptosis, which stimulates tumor growth and metastasis. The wound healing functions of increased LPA signaling also protect cancer cells from effects of chemotherapy and radiotherapy. In this review, we will summarize knowledge of the ATX-LPA axis and its role in the development of resistance to chemotherapy and radiotherapy. We will also offer insights for developing strategies of targeting ATX-LPA axis as a novel part of cancer treatment. This article is part of a Special Issue entitled Lysophospholipids and their receptors: New data and new insights into their function edited by Susan Smyth, Viswanathan Natarajan and Colleen McMullen.

Mechanism of sphingosine 1-phosphate clearance from blood

The interplay of sphingosine 1-phosphate (S1P) synthetic and degradative enzymes as well as S1P exporters creates concentration gradients that are a fundamental to S1P biology. Extracellular S1P levels, such as in blood and lymph, are high relative to cellular S1P. The blood-tissue S1P gradient maintains endothelial integrity while local S1P gradients influence immune cell positioning. Indeed, the importance of S1P gradients was recognized initially when the mechanism of action of an S1P receptor agonist used as a medicine for multiple sclerosis was revealed to be inhibition of T-lymphocytes' recognition of the high S1P in efferent lymph. Furthermore, the increase in erythrocyte S1P in response to hypoxia influences oxygen delivery during high altitude acclimatization. However, understanding of how S1P gradients are maintained is incomplete. For example, S1P is synthesized but is only slowly metabolized by blood yet circulating S1P turns over quickly by an unknown mechanism. Prompted by the counterintuitive observation that blood S1P increases markedly in response to inhibition S1P synthesis (by sphingosine kinase 2 (SphK2)), we studied mice wherein several tissues were made deficient in either SphK2 or S1P degrading enzymes. Our data reveal a mechanism whereby S1P is de-phosphorylated at the hepatocyte surface and the resulting sphingosine is sequestered by SphK phosphorylation and in turn degraded by intracellular S1P lyase. Thus, we identify the liver as the primary site of blood S1P clearance and provide an explanation for the role of SphK2 in this process. Our discovery suggests a general mechanism whereby S1P gradients are shaped.

Hypoxia Downregulates LPP3 and Promotes the Spatial Segregation of ATX and LPP1 During Cancer Cell Invasion

Hypoxia is a common characteristic of advanced solid tumors and a potent driver of tumor invasion and metastasis. Recent evidence suggests the involvement of autotaxin (ATX) and lysophosphatidic acid receptors (LPARs) in cancer cell invasion promoted by the hypoxic tumor microenvironment; however, the transcriptional and/or spatiotemporal control of this process remain unexplored. Herein, we investigated whether hypoxia promotes cell invasion by affecting the main enzymes involved in its production (ATX) and degradation (lipid phosphate phosphatases, LPP1 and LPP3). We report that hypoxia not only modulates the expression levels of lysophosphatidic acid (LPA) regulatory enzymes but also induces their significant spatial segregation in a variety of cancers. While LPP3 expression was downregulated by hypoxia, ATX and LPP1 were asymmetrically redistributed to the leading edge and to the trailing edge, respectively. This was associated with the opposing roles of ATX and LPPs in cell invasion. The regulated expression and compartmentalization of these enzymes of opposing function can provide an effective way to control the generation of an LPA gradient that drives cellular invasion and migration in the hypoxic zones of tumors.

Increasing the low lipid phosphate phosphatase 1 activity in breast cancer cells decreases transcription by AP-1 and expressions of matrix metalloproteinases and cyclin D1/D3

Metastasis is the leading cause of mortality in breast cancer patients and lysophosphatidate (LPA) signaling promotes this process. LPA signaling is attenuated by lipid phosphate phosphatase-1 (LPP1) whose activity is decreased in cancers. Consequently, increasing LPP1 levels suppresses breast tumor growth and metastasis. This study shows that increasing LPP1 in breast cancer cells decreases transcription through cFos and cJun. This decreases production of cyclin D1/D3 and matrix metalloproteinases (MMPs), which provides new insights into the role of LPP1 in controlling tumor growth and metastasis. Methods: Invasiveness was determined by a Matrigel invasion assay. MMP expression was measured by qPCR, multiplex LASER bead technology and gelatin zymography. Levels of cJUN, cFOS, FRA1, cyclin D1, and cyclin D3 were determined by qPCR and western blotting. Collagen was determined by Picro-Sirius Red staining. Results: Increasing LPP1 expression inhibited invasion of MDA-MB-231 breast cancer cells through Matrigel. This was accompanied by decreases in expression of MMP-1, -3, -7, -9, -10, -12 and -13, which are transcriptionally regulated by the AP-1 complex. Increasing LPP1 attenuated the induction of mRNA of MMP-1, -3, cFOS, and cJUN by EGF or TNFα, but increased FRA1. LPP1 expression also decreased the induction of protein levels for cFOS and cJUN in nuclei and cytoplasmic fractions by EGF and TNFα. Protein levels of cyclin D1 and D3 were also decreased by LPP1. Although FRA1 in total cell lysates or cytoplasm was increased by LPP1, nuclear FRA1 was not affected. LPP1-induced decreases in MMPs in mouse tumors created with MDA-MB-231 cells were accompanied by increased collagen in the tumors and fewer lung metastases. Knockdown of LPP1 in MDA-MB-231 cells increased the protein levels of MMP-1 and -3. Human breast tumors also have lower levels of LPP1 and higher levels of cJUN, cFOS, MMP-1, -7, -8, -9, -12, -13, cyclin D1, and cyclin D3 relative to normal breast tissue. Conclusion: This study demonstrated that the low LPP1 expression in breast cancer cells is associated with high levels of cyclin D1/D3 and MMPs as a result of increased transcription by cFOS and cJUN. Increasing LPP1 expression provides a novel approach for decreasing transcription through AP-1, which could provide a strategy for decreasing tumor growth and metastasis.

Interrelations of Sphingolipid and Lysophosphatidate Signaling with Immune System in Ovarian Cancer

The sphingolipid and lysophosphatidate regulatory networks impact diverse mechanisms attributed to cancer cells and the tumor immune microenvironment. Deciphering the complexity demands implementation of a holistic approach combined with higher-resolution techniques. We implemented a multi-modular integrative approach consolidating the latest accomplishments in gene expression profiling, prognostic/predictive modeling, next generation digital pathology, and systems biology for epithelial ovarian cancer. We assessed patient-specific transcriptional profiles using the sphingolipid/lysophosphatidate/immune-associated signature. This revealed novel sphingolipid/lysophosphatidate-immune gene-gene associations and distinguished tumor subtypes with immune high/low context. These were characterized by robust differences in sphingolipid-/lysophosphatidate-related checkpoints and the drug response. The analysis also nominates novel survival models for stratification of patients with CD68, LPAR3, SMPD1, PPAP2B, and SMPD2 emerging as the most prognostically important genes. Alignment of proprietary data with curated transcriptomic data from public databases across a variety of malignancies (over 600 categories; over 21,000 arrays) showed specificity for ovarian carcinoma. Our systems approach identified novel sphingolipid-lysophosphatidate-immune checkpoints and networks underlying tumor immune heterogeneity and disease outcomes. This holds great promise for delivering novel stratifying and targeting strategies.

Targeting the autotaxin - Lysophosphatidic acid receptor axis in cardiovascular diseases

Lysophosphatidic acid (LPA) is a well-characterized bioactive lipid mediator, which is involved in development, physiology, and pathological processes of the cardiovascular system. LPA can be produced both inside cells and in biological fluids. The majority of extracellularLPAis produced locally by the secreted lysophospholipase D, autotaxin (ATX), through its binding to various β integrins or heparin sulfate on cell surface and hydrolyzing various lysophospholipids. LPA initiates cellular signalling pathways upon binding to and activation of its G protein-coupled receptors (LPA1-6). LPA has potent effects on various blood cells and vascular cells involved in the development of cardiovascular diseases such as atherosclerosis and aortic valve sclerosis. LPA signalling drives cell migration and proliferation, cytokine production, thrombosis, fibrosis, as well as angiogenesis. For instance, LPA promotes activation and aggregation of platelets through LPA5, increases expression of adhesion molecules in endothelial cells, and enhances expression of tissue factor in vascular smooth muscle cells. Furthermore, LPA induces differentiation of monocytes into macrophages and stimulates oxidized low-density lipoproteins (oxLDLs) uptake by macrophages to form foam cells during formation of atherosclerotic lesions through LPA1-3. This review summarizes recent findings of the roles played by ATX, LPA and LPA receptors (LPARs) in atherosclerosis and calcific aortic valve disease. Targeting the ATX-LPAR axis may have potential applications for treatment of patients suffering from various cardiovascular diseases.

Coming of Age for Autotaxin and Lysophosphatidate Signaling: Clinical Applications for Preventing, Detecting and Targeting Tumor-Promoting Inflammation

A quarter-century after the discovery of autotaxin in cell culture, the autotaxin-lysophosphatidate (LPA)-lipid phosphate phosphatase axis is now a promising clinical target for treating chronic inflammatory conditions, mitigating fibrosis progression, and improving the efficacy of existing cancer chemotherapies and radiotherapy. Nearly half of the literature on this axis has been published during the last five years. In cancer biology, LPA signaling is increasingly being recognized as a central mediator of the progression of chronic inflammation in the establishment of a tumor microenvironment which promotes cancer growth, immune evasion, metastasis, and treatment resistance. In this review, we will summarize recent advances made in understanding LPA signaling with respect to chronic inflammation and cancer. We will also provide perspectives on the applications of inhibitors of LPA signaling in preventing cancer initiation, as adjuncts extending the efficacy of current cancer treatments by blocking inflammation caused by either the cancer or the cancer therapy itself, and by disruption of the tumor microenvironment. Overall, LPA, a simple molecule that mediates a plethora of biological effects, can be targeted at its levels of production by autotaxin, LPA receptors or through LPA degradation by lipid phosphate phosphatases. Drugs for these applications will soon be entering clinical practice.

S1P Lyase Regulation of Thymic Egress and Oncogenic Inflammatory Signaling

Sphingosine-1-phosphate (S1P) is a potent lipid signaling molecule that regulates pleiotropic biological functions including cell migration, survival, angiogenesis, immune cell trafficking, inflammation, and carcinogenesis. It acts as a ligand for a family of cell surface receptors. S1P concentrations are high in blood and lymph but low in tissues, especially the thymus and lymphoid organs. S1P chemotactic gradients are essential for lymphocyte egress and other aspects of physiological cell trafficking. S1P is irreversibly degraded by S1P lyase (SPL). SPL regulates lymphocyte trafficking, inflammation and other physiological and pathological processes. For example, SPL located in thymic dendritic cells acts as a metabolic gatekeeper that controls the normal egress of mature T lymphocytes from the thymus into the circulation, whereas SPL deficiency in gut epithelial cells promotes colitis and colitis-associated carcinogenesis (CAC). Recently, we identified a complex syndrome comprised of nephrosis, adrenal insufficiency, and immunological defects caused by inherited mutations in human SGPL1, the gene encoding SPL. In the present article, we review current evidence supporting the role of SPL in thymic egress, inflammation, and cancer. Lastly, we summarize recent progress in understanding other SPL functions, its role in inherited disease, and SPL targeting for therapeutic purposes.

Hepatocyte autotaxin expression promotes liver fibrosis and cancer

Autotaxin (ATX) is a secreted lysophospholipase D that catalyzes the production of lysophosphatidic acid (LPA), a pleiotropic growth-factor-like lysophospholipid. Increased ATX expression has been detected in various chronic inflammatory disorders and different types of cancer; however, little is known about its role and mode of action in liver fibrosis and cancer. Here, increased ATX expression was detected in chronic liver disease (CLD) patients of different etiologies, associated with shorter overall survival. In mice, different hepatotoxic stimuli linked with the development of different forms of CLDs were shown to stimulate hepatocyte ATX expression, leading to increased LPA levels, activation of hepatic stellate cells (HSCs), and amplification of profibrotic signals. Hepatocyte-specific, conditional genetic deletion and/or transgenic overexpression of ATX established a liver profibrotic role for ATX/LPA, whereas pharmacological ATX inhibition studies suggested ATX as a possible therapeutic target in CLDs. In addition, hepatocyte ATX ablation and the consequent deregulation of lipid homeostasis was also shown to attenuate hepatocellular carcinoma (HCC) development, thus implicating ATX/LPA in the causative link of cirrhosis and HCC.

CONCLUSION

ATX is a novel player in the pathogenesis of liver fibrosis and cancer and a promising therapeutic target. (Hepatology 2017;65:1369-1383).

Doxycycline attenuates breast cancer related inflammation by decreasing plasma lysophosphatidate concentrations and inhibiting NF-κB activation

Background

We previously discovered that tetracyclines increase the expression of lipid phosphate phosphatases at the surface of cells. These enzymes degrade circulating lysophosphatidate and therefore doxycycline increases the turnover of plasma lysophosphatidate and decreases its concentration. Extracellular lysophosphatidate signals through six G protein-coupled receptors and it is a potent promoter of tumor growth, metastasis and chemo-resistance. These effects depend partly on the stimulation of inflammation that lysophosphatidate produces.

Methods

In this work, we used a syngeneic orthotopic mouse model of breast cancer to determine the impact of doxycycline on circulating lysophosphatidate concentrations and tumor growth. Cytokine/chemokine concentrations in tumor tissue and plasma were measured by multiplexing laser bead technology. Leukocyte infiltration in tumors was analyzed by immunohistochemistry. The expression of IL-6 in breast cancer cell lines was determined by RT-PCR. Cell growth was measured in Matrigel™ 3D culture. The effects of doxycycline on NF-κB-dependent signaling were analyzed by Western blotting.

Results

Doxycycline decreased plasma lysophosphatidate concentrations, delayed tumor growth and decreased the concentrations of several cytokines/chemokines (IL-1β, IL-6, IL-9, CCL2, CCL11, CXCL1, CXCL2, CXCL9, G-CSF, LIF, VEGF) in the tumor. These results were compatible with the effects of doxycycline in decreasing the numbers of F4/80⁺ macrophages and CD31⁺ blood vessel endothelial cells in the tumor. Doxycycline also decreased the lysophosphatidate-induced growth of breast cancer cells in three-dimensional culture. Lysophosphatidate-induced Ki-67 expression was inhibited by doxycycline. NF-κB activity in HEK293 cells transiently expressing a NF-κB-luciferase reporter vectors was also inhibited by doxycycline. Treatment of breast cancer cells with doxycycline also decreased the translocation of NF-κB to the nucleus and the mRNA levels for IL-6 in the presence or absence of lysophosphatidate.

Conclusion

These results contribute a new dimension for understanding the anti-inflammatory effects of tetracyclines, which make them potential candidates for adjuvant therapy of cancers and other inflammatory diseases.

Electronic supplementary material

The online version of this article (doi:10.1186/s12943-017-0607-x) contains supplementary material, which is available to authorized users.

Altered Expression of Sphingosine-1-Phosphate Metabolizing Enzymes in Oral Cancer Correlate With Clinicopathological Attributes

We have determined the gene expression of sphingosine-1-phosphate (S1P) metabolizing enzymes (SphK1, SphK2, SGPL1, SGPP1, SGPP2, PPAP2A, PPAP2B, and PPAP2C) by quantitative real-time polymerase chain reaction in tumor tissues and adjacent normal tissues of 50 oral squamous cell carcinoma (OSCC) patients. Expression of SphK1 and SGPP1 genes was up-regulated significantly in 70% and 75% OSCC tumors respectively. Importantly, expression of SphK2 and PPAP2B was down-regulated in the tumor tissues of 70% OSCC patients. Expression of SphK2 and PPAP2B negatively correlated with tumor-node-metastasis (TNM) staging and tumor volume respectively. Furthermore, LPP1 is an independent predictor of TNM staging and lymph node ratio.