Cross-talk between LPA1 and epidermal growth factor receptors mediates up-regulation of sphingosine kinase 1 to promote gastric cancer cell motility and invasion

Incorporating Novel Technologies in Precision Oncology for Colorectal Cancer: Advancing Personalized Medicine

Colorectal cancer (CRC) is one of the most heterogeneous and deadly diseases, with a global incidence of 1.5 million cases per year. Genomics has revolutionized the clinical management of CRC by enabling comprehensive molecular profiling of cancer. However, a deeper understanding of the molecular factors is needed to identify new prognostic and predictive markers that can assist in designing more effective therapeutic regimens for the improved management of CRC. Recent breakthroughs in single-cell analysis have identified new cell subtypes that play a critical role in tumor progression and could serve as potential therapeutic targets. Spatial analysis of the transcriptome and proteome holds the key to unlocking pathogenic cellular interactions, while liquid biopsy profiling of molecular variables from serum holds great potential for monitoring therapy resistance. Furthermore, gene expression signatures from various pathways have emerged as promising prognostic indicators in colorectal cancer and have the potential to enhance the development of equitable medicine. The advancement of these technologies for identifying new markers, particularly in the domain of predictive and personalized medicine, has the potential to improve the management of patients with CRC. Further investigations utilizing similar methods could uncover molecular subtypes specific to emerging therapies, potentially strengthening the development of personalized medicine for CRC patients.

KAI1/CD82 gene and autotaxin-lysophosphatidic acid axis in gastrointestinal cancers

The KAI1/CD82 gene inhibits the metastasis of most tumors and is remarkably correlated with tumor invasion and prognosis. Cell metabolism dysregulation is an important cause of tumor occurrence, development, and metastasis. As one of the important characteristics of tumors, cell metabolism dysregulation is attracting increasing research attention. Phospholipids are an indispensable substance in the metabolism in various tumor cells. Phospholipid metabolites have become important cell signaling molecules. The pathological role of lysophosphatidic acid (LPA) in tumors was identified in the early 1990s. Currently, LPA inhibitors have entered clinical trials but are not yet used in clinical treatment. Autotaxin (ATX) has lysophospholipase D (lysoPLD) activity and can regulate LPA levels in vivo. The LPA receptor family and ATX/lysoPLD are abnormally expressed in various gastrointestinal tumors. According to our recent pre-experimental results, KAI1/CD82 might inhibit the migration and metastasis of cancer cells by regulating the ATX-LPA axis. However, no relevant research has been reported. Clarifying the mechanism of ATX-LPA in the inhibition of cancer metastasis by KAI1/CD82 will provide an important theoretical basis for targeted cancer therapy. In this paper, the molecular compositions of the KAI1/CD82 gene and the ATX-LPA axis, their physiological functions in tumors, and their roles in gastrointestinal cancers and target therapy are reviewed.

Metabolomic Analysis Reveals that SPHK1 Promotes Oral Squamous Cell Carcinoma Progression through NF-κB Activation

BACKGROUND

Metabolic disorders are significant in the occurrence and development of malignant tumors. Changes of specific metabolites and metabolic pathways are molecular therapeutic targets. This study aims to determine the metabolic differences between oral squamous cell carcinoma (OSCC) tissues and paired adjacent noncancerous tissues (ANT) through liquid chromatography-mass spectrometry (LC-MS). SPHK1 is a key enzyme in sphingolipid metabolism. This study also investigates the potential role of SPHK1 in OSCC.

MATERIALS AND METHODS

This study used LC-MS to analyze metabolic differences between OSCC tissues and paired ANT. Principal component analysis (PCA) and partial least-squares discriminant analysis (PLS-DA) were applied to explain the significance of phospholipid metabolism pathways in the occurrence and development of OSCC. Through further experiments, we confirmed the oncogenic phenotypes of SPHK1 in vitro and in vivo, including proliferation, migration, and invasion.

RESULTS

The sphingolipid metabolic pathway was significantly activated in OSCC, and the key enzyme SPHK1 was significantly upregulated in oral cancer tissues, predicting poor OSCC prognosis. In this study, SPHK1 overexpression was associated with high-grade malignancy and poor OSCC prognosis. SPHK1 targeted NF-κB by facilitating p65 expression to regulate OSCC tumor progression and promote metastasis.

CONCLUSIONS

This study identified metabolic differences between OSCC and paired ANT, explored the carcinogenic role of overexpressed SPHK1, and revealed the association of SPHK1 with poor OSCC prognosis. SPHK1 targets NF-κB signaling by facilitating p65 expression to regulate tumor progression and promote tumor metastasis, providing potential therapeutic targets for diagnosing and treating oral tumors.

The central role of Sphingosine kinase 1 in the development of neuroendocrine prostate cancer (NEPC): A new targeted therapy of NEPC

Background

Neuroendocrine prostate cancer (NEPC) is often diagnosed as a sub‐type from the castration‐resistant prostate cancer (CRPC) recurred from the second generation of anti‐androgen treatment and is a rapidly progressive fatal disease. The molecular mechanisms underlying the trans‐differentiation from CRPC to NEPC are not fully characterized, which hampers the development of effective targeted therapy.

Methods

Bioinformatic analyses were conducted to determine the clinical correlation of sphingosine kinase 1 (SphK1) in CRPC progression. To investigate the transcriptional regulation SphK1 and neuroendocrine (NE) transcription factor genes, both chromosome immunoprecipitation and luciferase reporter gene assays were performed. To demonstrate the role of SphK1 in NEPC development, neurosphere assay was carried out along with several biomarkers determined by quantitative PCR and western blot. Furthermore, in vivo NEPC xenograft models and patient‐derived xenograft (PDX) model were employed to determine the effect of SphK1 inhibitors and target validation.

Results

Significant prevalence of SphK1 in NEPC development is observed from clinical datasets. SphK1 is transcriptionally repressed by androgen receptor‐RE1‐silencing transcription factor (REST) complex. Furthermore, sphingosine 1‐phosphate produced by SphK1 can modulate REST protein turnover via MAPK signaling pathway. Also, decreased REST protein levels enhance the expression of NE markers in CRPC, enabling the transition to NEPC. Finally, specific SphK1 inhibitors can effectively inhibit the growth of NEPC tumors and block the REST protein degradation in PDX.

Conclusions

SphK1 plays a central role in NEPC development, which offers a new target for this lethal cancer using clinically approved SphK1 inhibitors.

Differential Expression of the Sphingolipid Pathway Is Associated with Sensitivity to the PP2A Activator FTY720 in Colorectal Cancer Cell Lines

Protein phosphatase 2A (PP2A) is a ubiquitously expressed intracellular serine/threonine phosphatase. Deregulation of PP2A is a common event associated with adenocarcinomas of the colon and rectum. We have previously shown that breast cancer cell lines are sensitive to the PP2A activator FTY720, and that sensitivity is predicted by high Aurora kinase A (AURKA) mRNA expression. In this study, we hypothesized that high relative AURKA expression could predict sensitivity to FTY720-induced apoptosis in colorectal cancer (CRC). The CRC cell lines NCI H716, COLO320DM, DLD-1, SW480, and HT-29 show a high relative AURKA expression as compared to LS411N, T84, HCT116, SW48, and LOVO. Following viability assays, LS411N, T84, HCT116, and SW480 were shown to be sensitive to FTY720, whereas DLD-1 and HT-29 were non-sensitive. Hence, AURKA mRNA expression does not predict sensitivity to FTY720 in CRC cell lines. Differentially expressed genes (DEGs) were obtained by comparing the sensitive CRC cell lines (LS411N and HCT116) against the non-sensitive (HT-29 and DLD-1). We found that 253 genes were significantly altered in expression, and upregulation of CERS4, PPP2R2C, GNAZ, PRKCG, BCL2, MAPK12, and MAPK11 suggests the involvement of the sphingolipid signaling pathway, known to be activated by phosphorylated-FTY720. In conclusion, although AURKA expression did not predict sensitivity to FTY720, it is evident that specific CRC cell lines are sensitive to 5 µM FTY720, potentially because of the differential expression of genes involved in the sphingolipid pathway.

Lysophosphatidic Acid-Induced EGFR Transactivation Promotes Gastric Cancer Cell DNA Replication by Stabilizing Geminin in the S Phase

Geminin, an inhibitor of the DNA replication licensing factor, chromatin licensing and DNA replication factor (Cdt) 1, is essential for the maintenance of genomic integrity. As a multifunctional protein, geminin is also involved in tumor progression, but the molecular details are largely unknown. Here, we found that lysophosphatidic acid (LPA)–induced upregulation of geminin was specific to gastric cancer cells. LPA acted via LPA receptor (LPAR) 3 and matrix metalloproteinases (MMPs) signaling to transactivate epidermal growth factor receptor (EGFR) (Y1173) and thereby stabilize geminin expression level during the S phase. LPA also induced the expression of deubiquitinating protein (DUB) 3, which prevented geminin degradation. These results reveal a novel mechanism underlying gastric cancer progression that involves the regulation of geminin stability by LPA-induced EGFR transactivation and provide potential targets for the signaling pathway and tumor cell–specific inhibitors.

Lysophosphatidate Promotes Sphingosine 1-Phosphate Metabolism and Signaling: Implications for Breast Cancer and Doxorubicin Resistance

Lysophosphatidate (LPA) and sphingosine 1-phosphate (S1P) promote vasculogenesis, angiogenesis, and wound healing by activating a plethora of overlapping signaling pathways that stimulate mitogenesis, cell survival, and migration. As such, maladaptive signaling by LPA and S1P have major effects in increasing tumor progression and producing poor patient outcomes after chemotherapy and radiotherapy. Many signaling actions of S1P and LPA are not redundant; each are vital in normal physiology and their metabolisms differ. In the present work, we studied how LPA signaling impacts S1P metabolism and signaling in MDA-MB-231 and MCF-7 breast cancer cells. LPA increased sphingosine kinase-1 (SphK1) synthesis and rapidly activated cytosolic SphK1 through association with membranes. Blocking phospholipase D activity attenuated the LPA-induced activation of SphK1 and the synthesis of ABCC1 and ABCG2 transporters that secrete S1P from cells. This effect was magnified in doxorubicin-resistant MCF-7 cells. LPA also facilitated S1P signaling by increasing mRNA expression for S1P₁ receptors. Doxorubicin-resistant MCF-7 cells had increased S1P₂ and S1P₃ receptor expression and show increased LPA-induced SphK1 activation, increased expression of ABCC1, ABCG2 and greater S1P secretion. Thus, LPA itself and LPA-induced S1P signaling counteract doxorubicin-induced death of MCF-7 cells. We conclude from the present and previous studies that LPA promotes S1P metabolism and signaling to coordinately increase tumor growth and metastasis and decrease the effectiveness of chemotherapy and radiotherapy for breast cancer treatment.

Lysophosphatidic Acid Signaling in Cancer Cells: What Makes LPA So Special?

Lysophosphatidic acid (LPA) refers to a family of simple phospholipids that act as ligands for G protein-coupled receptors. While LPA exerts effects throughout the body in normal physiological circumstances, its pathological role in cancer is of great interest from a therapeutic viewpoint. The numerous LPA receptors (LPARs) are coupled to a variety of G proteins, and more than one LPAR is typically expressed on any given cell. While the individual receptors signal through conventional GPCR pathways, LPA is particularly efficacious in stimulating cancer cell proliferation and migration. This review addresses the mechanistic aspects underlying these pro-tumorigenic effects. We provide examples of LPA signaling responses in various types of cancers, with an emphasis on those where roles have been identified for specific LPARs. While providing an overview of LPAR signaling, these examples also reveal gaps in our knowledge regarding the mechanisms of LPA action at the receptor level. The current understanding of the LPAR structure and the roles of LPAR interactions with other receptors are discussed. Overall, LPARs provide insight into the potential molecular mechanisms that underlie the ability of individual GPCRs (or combinations of GPCRs) to elicit a unique spectrum of responses from their agonist ligands. Further knowledge of these mechanisms will inform drug discovery, since GPCRs are promising therapeutic targets for cancer.

Lysophosphatidic Acid Receptor Antagonists and Cancer: The Current Trends, Clinical Implications, and Trials

Lysophosphatidic acid (LPA) is a bioactive lipid mediator primarily derived from membrane phospholipids. LPA initiates cellular effects upon binding to a family of G protein-coupled receptors, termed LPA receptors (LPAR1 to LPAR6). LPA signaling drives cell migration and proliferation, cytokine production, thrombosis, fibrosis, angiogenesis, and lymphangiogenesis. Since the expression and function of LPA receptors are critical for cellular effects, selective antagonists may represent a potential treatment for a broad range of illnesses, such as cardiovascular diseases, idiopathic pulmonary fibrosis, voiding dysfunctions, and various types of cancers. More new LPA receptor antagonists have shown their therapeutic potentials, although most are still in the preclinical trial stage. This review provided integrative information and summarized preclinical findings and recent clinical trials of different LPA receptor antagonists in cancer progression and resistance. Targeting LPA receptors can have potential applications in clinical patients with various diseases, including cancer.

Sphingosine-1-phosphate receptor 3 signaling

Sphingosine-1-phosphate (S1P) is a bioactive lipid which regulates a series of physiological and pathological processes via binding to five S1P receptors (S1PR1-5). Although S1PR1-3 are widely expressed, the study of S1PRs, however, mainly addressed S1PR1 and S1PR2, and few studies focus on S1PR3-5. In recent years, a growing number of studies have shown that S1PR3 plays an important role in cell proliferation, differentiation, apoptosis, and migration, but its function is still controversial. This is the first comprehensive review paper about the role of S1PR3 signaling in cardiovascular function, tissue fibrosis, cancer, immune response, and neurological function. In addition, existing S1PR3 agonists and antagonists are listed at the end of the article, and we also put forward our opinion on the dispute of S1PR3 function.

Targeting sphingosine kinase 1 (SK1) enhances oncogene-induced senescence through ceramide synthase 2 (CerS2)-mediated generation of very-long-chain ceramides

Senescence is an antiproliferative mechanism that can suppress tumor development and can be induced by oncogenes such as genes of the Ras family. Although studies have implicated bioactive sphingolipids (SL) in senescence, the specific mechanisms remain unclear. Here, using MCF10A mammary epithelial cells, we demonstrate that oncogenic K-Ras (Kirsten rat sarcoma viral oncogene homolog) is sufficient to induce cell transformation as well as cell senescence-as revealed by increases in the percentage of cells in the G1 phase of the cell cycle, p21WAF1/Cip1/CDKN1A (p21) expression, and senescence-associated β-galactosidase activity (SA-β-gal). Furthermore, oncogenic K-Ras altered SL metabolism, with an increase of long-chain (LC) C18, C20 ceramides (Cer), and very-long-chain (VLC) C22:1, C24 Cer, and an increase of sphingosine kinase 1 (SK1) expression. Since Cer and sphingosine-1-phosphate have been shown to exert opposite effects on cellular senescence, we hypothesized that targeting SK1 could enhance oncogenic K-Ras-induced senescence. Indeed, SK1 downregulation or inhibition enhanced p21 expression and SA-β-gal in cells expressing oncogenic K-Ras and impeded cell growth. Moreover, SK1 knockdown further increased LC and VLC Cer species (C18, C20, C22:1, C24, C24:1, C26:1), especially the ones increased by oncogenic K-Ras. Fumonisin B1 (FB1), an inhibitor of ceramide synthases (CerS), reduced p21 expression induced by oncogenic K-Ras both with and without SK1 knockdown. Functionally, FB1 reversed the growth defect induced by oncogenic K-Ras, confirming the importance of Cer generation in the senescent phenotype. More specifically, downregulation of CerS2 by siRNA blocked the increase of VLC Cer (C24, C24:1, and C26:1) induced by SK1 knockdown and phenocopied the effects of FB1 on p21 expression. Taken together, these data show that targeting SK1 is a potential therapeutic strategy in cancer, enhancing oncogene-induced senescence through an increase of VLC Cer downstream of CerS2.

Spinster homolog 2 in cancers, its functions and mechanisms

Spinster homolog 2 (SPNS2) is a multi-transmembrane transporter, widely located in the cell membrane and organelle membranes. It transports sphingosine-1-phosphate (S1P) into the extracellular space and the circulatory system, thus alters the concentration and the distribution of S1P, sphingosine-1-phosphate receptor (S1PRs) and S1P related enzymes, meaning that it exerts its functions via S1P signaling pathways. Studies also show that ectopic SPNS2 mediates parts of the physiological process of the cells. As of now, SPNS2 has been reported to participate in physiological processes such as angiogenesis, embryonic development, immune response and metabolisms. It is also associated with the transformation from inflammation to cancer as well as the proliferation and metastasis of cancer cells. In this review, we summarize the functions and the mechanisms of SPNS2 in the pathogenesis of cancer to provide new insights for the diagnosis and the treatments of cancer.

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.

Sphingosine kinase and sphingosine-1-phosphate receptor signaling pathway in inflammatory gastrointestinal disease and cancers: A novel therapeutic target

Inflammatory gastrointestinal (GI) diseases and malignancies are associated with growing morbidity and cancer-related mortality worldwide. GI tumor and inflammatory cells contain activated sphingolipid-metabolizing enzymes, including sphingosine kinase 1 (SphK1) and SphK2, that generate sphingosine-1-phosphate (S1P), a highly bioactive compound. Many inflammatory responses, including lymphocyte trafficking, are directed by circulatory S1P, present in high concentrations in both the plasma and the lymph of cancer patients. High fat and sugar diet, disbalanced intestinal flora, and obesity have recently been linked to activation of inflammation and SphK/S1P/S1P receptor (S1PR) signaling in various GI pathologies, including cancer. SphK1 overexpression and activation facilitate and enhance the development and progression of esophageal, gastric, and colon cancers. SphK/S1P axis, a mediator of inflammation in the tumor microenvironment, has recently been defined as a target for the treatment of GI disease states, including inflammatory bowel disease and colitis. Several SphK1 inhibitors and S1PR antagonists have been developed as novel anti-inflammatory and anticancer agents. In this review, we analyze the mechanisms of SphK/S1P signaling in GI tissues and critically appraise recent studies on the role of SphK/S1P/S1PR in inflammatory GI disorders and cancers. The potential role of SphK/S1PR inhibitors in the prevention and treatment of inflammation-mediated GI diseases, including GI cancer, is also evaluated.

Sphingosine-1-Phosphate in the Tumor Microenvironment: A Signaling Hub Regulating Cancer Hallmarks

As a key hub of malignant properties, the cancer microenvironment plays a crucial role intimately connected to tumor properties. Accumulating evidence supports that the lysophospholipid sphingosine-1-phosphate acts as a key signal in the cancer extracellular milieu. In this review, we have a particular focus on glioblastoma, representative of a highly aggressive and deleterious neoplasm in humans. First, we highlight recent advances and emerging concepts for how tumor cells and different recruited normal cells contribute to the sphingosine-1-phosphate enrichment in the cancer microenvironment. Then, we describe and discuss how sphingosine-1-phosphate signaling contributes to favor cancer hallmarks including enhancement of proliferation, stemness, invasion, death resistance, angiogenesis, immune evasion and, possibly, aberrant metabolism. We also discuss the potential of how sphingosine-1-phosphate control mechanisms are coordinated across distinct cancer microenvironments. Further progress in understanding the role of S1P signaling in cancer will depend crucially on increasing knowledge of its participation in the tumor microenvironment.

Targeting Lysophosphatidic Acid in Cancer: The Issues in Moving from Bench to Bedside

Since the clear demonstration of lysophosphatidic acid (LPA)'s pathological roles in cancer in the mid-1990s, more than 1000 papers relating LPA to various types of cancer were published. Through these studies, LPA was established as a target for cancer. Although LPA-related inhibitors entered clinical trials for fibrosis, the concept of targeting LPA is yet to be moved to clinical cancer treatment. The major challenges that we are facing in moving LPA application from bench to bedside include the intrinsic and complicated metabolic, functional, and signaling properties of LPA, as well as technical issues, which are discussed in this review. Potential strategies and perspectives to improve the translational progress are suggested. Despite these challenges, we are optimistic that LPA blockage, particularly in combination with other agents, is on the horizon to be incorporated into clinical applications.

The component changes of lysophospholipid mediators in colorectal cancer

Although lysophospholipids are known to play an important role in the development and progression of several kinds of cancers, their role in human colorectal cancer is as yet unclear. In this study, we aim to investigate lysophospholipid levels in colorectal cancer tissues to identify lysophospholipids, the levels of which change specifically in colorectal cancers. We used liquid chromatography-tandem mass spectrometry to measure lysophospholipid levels in cancerous and normal tissues from 11 surgical specimens of sigmoid colon cancers, since recent advances in this field have improved detection sensitivities for lysophospholipids. Our results indicate that, in colon cancer tissues, levels of lysophosphatidylinositol and lysophosphatidylserine were significantly higher ( p = 0.025 and p = 0.01, respectively), whereas levels of lysophosphatidic acid were significantly lower ( p = 0.0019) than in normal tissues. Although levels of lysophosphatidylglycerol were higher in colon cancer tissues than in normal tissues, this difference was not found to be significant ( p = 0.11). Fatty acid analysis further showed that 18:0 lysophosphatidylinositol and 18:0 lysophosphatidylserine were the predominant species of lysophospholipids in colon cancer tissues. These components may be potentially involved in colorectal carcinogenesis.

Clinicopathological and biomolecular characteristics of stage IIB/IIC and stage IIIA colon cancer: Insight into the survival paradox

BACKGROUND

A survival paradox of stage IIB/IIC and IIIA colon cancer has been consistently observed throughout revisions of the TNM system. This study aimed to understand this paradox with clinicopathological and molecular differences.

METHODS

Clinicopathological characteristics of patients with pathologically confirmed stage IIB/IIC or IIIA colon cancer were retrospectively reviewed from a database. Publicly available molecular data were retrieved, and intrinsic subtypes were identified and subjected to gene sets enrichment analysis (GSEA).

RESULTS

Among the 159 patients included in the clinicopathological analysis, those at stage IIB/IIC had worse 3-year disease-free and overall survival than those at stage IIIA (59.3% vs 91.7%, P < 0.001 and 82.7% vs 98.5%, P < 0.001, respectively), even after adjusting for confounding factors. Data of 95 patients were retrieved from public databases, demonstrating a higher frequency of the microsatellite instable subtype in stage IIB/IIC. The consensus molecular subtype distribution pattern differed between the groups. The GSEA further suggested the protumor inflammatory reaction might be more prominent in stage IIB/IIC.

CONCLUSIONS

The survival paradox in colon cancer was confirmed and appears to be a multifactorial phenomenon not attributed to a single clinicopathologic factor. However, the greater molecular heterogeneity in stage IIB/IIC could contribute to the poor prognosis.

The sphingosine kinase-1/sphingosine-1-phosphate axis in cancer: Potential target for anticancer therapy

Sphingolipid metabolites, such as ceramide, sphingosine and sphingosine-1-phosphate (S1P), play many important roles in cellular activities. Ceramide and sphingosine inhibit cell proliferation and induce cell apoptosis while S1P has the opposite effect. Maintaining a metabolic balance of sphingolipids is essential for growth and development of cells. Sphingosine kinase (SPHK) is an important regulator for keeping this balance. It controls the level of S1P and plays important roles in proliferation, migration, and invasion of cancer cells and tumor angiogenesis. There are two isoenzymes of sphingosine kinase, SPHK1 and SPHK2. SPHK1 is ubiquitously expressed in most cancers where it promotes survival and proliferation, while SPHK2 is restricted to only certain tissues and its functions are not well characterized. SPHK1 is currently considered as a novel target for the treatment of cancers. Targeting SPHK1 would provide new strategies for cancer treatment and improve the prognosis of cancer patients. Here we review and summarize the current research findings on the SPHK1-S1P axis in cancer from many aspects including structure, expression, regulation, mechanism, and potential inhibitors.

The role of sphingosine-1-phosphate in inflammation and cancer progression

Many inflammatory mediators are involved in the process of carcinogenesis and cancer progression. In addition to cytokines and chemokines, lipid mediators have recently attracted attention as signaling molecules associated with inflammatory diseases. Sphingosine‐1‐phosphate (S1P) is a pleiotropic lipid mediator that regulates cell survival and migration, immune cell recruitment, angiogenesis and lymphangiogenesis. S1P also plays a significant role in inflammation and cancer. The gradation of S1P concentration in the blood, lymph and tissue regulates lymphocyte trafficking, an important component of inflammation. Furthermore, cancer cells produce elevated levels of S1P, contributing to the tumor microenvironment and linking cancer and inflammation. Future technological advances may reveal greater detail about the mechanisms of S1P regulation in the tumor microenvironment and the contribution of S1P to cancer progression. Considering the critical role of S1P in linking inflammation and cancer, it is possible that the S1P signaling pathway could be a novel therapeutic target for cancers with chronic inflammation.

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.

Lysophosphatidic acid regulates the motility of MCF10CA1a breast cancer cell sheets via two opposing signaling pathways

Aberrant cell migration leads to the dispersal of malignant cells. The ubiquitous lipid mediator lysophosphatidic acid (LPA) modulates cell migration and is implicated in tumor progression. Yet, the signaling cascades that regulate LPA's effect on cell motility remain unclear. Using time-lapse imaging and quantitative analyses, we studied the role of signaling cascades that act downstream of LPA on the motility of MCF10CA1a breast cancer cells. We found that LPA alters cell motility via two major signaling pathways. The Rho/ROCK signaling cascade is the predominant pathway that increases E-Cadherin containing cell-cell adhesions and cortical arrangement of actomyosin to promote slow, directional, spatially coherent and temporally consistent movement. In contrast, Gαi/o- and Gαq/11-dependent signaling cascades lessen directionality and support the independent movement of cells. The net effect of LPA on breast cancer cell migration therefore results from the integrated signaling activity of the Rho/ROCK and Gαi/o- and Gαq/11-dependent pathways, thus allowing for a dynamic migratory response to changes in the cellular or microenvironmental context.

Ceramide species are elevated in human breast cancer and are associated with less aggressiveness

Sphingolipids have emerged as key regulatory molecules in cancer cell survival and death. Although important roles of sphingolipids in breast cancer progression have been reported in experimental models, their roles in human patients are yet to be revealed. The aim of this study was to investigate the ceramide levels and its biosynthesis pathways in human breast cancer patients. Breast cancer, peri-tumor and normal breast tissue samples were collected from surgical specimens from a series of 44 patients with breast cancer. The amount of sphingolipid metabolites in the tissue were determined by mass spectrometry. The Cancer Genome Atlas was used to analyze gene expression related to the sphingolipid metabolism. Ceramide levels were higher in breast cancer tissue compared to both normal and peri-tumor breast tissue. Substrates and enzymes that generate ceramide were significantly increased in all three ceramide biosynthesis pathways in cancer. Further, higher levels of ceramide in breast cancer were associated with less aggressive cancer biology presented by Ki-67 index and nuclear grade of the cancer. Interestingly, patients with higher gene expressions of enzymes in the three major ceramide synthesis pathways showed significantly worse prognosis. This is the first study to reveal the clinical relevance of ceramide metabolism in breast cancer patients. We demonstrated that ceramide levels in breast cancer tissue were significantly higher than those in normal tissue, with activation of the three ceramide biosynthesis pathways. We also identified that ceramide levels have a significant association with aggressive phenotype and its enzymes have prognostic impact on breast cancer patients.

Lysophosphatidic acid (LPA) as a pro-fibrotic and pro-oncogenic factor: a pivotal target to improve the radiotherapy therapeutic index

Radiation-induced fibrosis is widely considered as a common but forsaken phenomenon that can lead to clinical sequela and possibly vital impairments. Lysophosphatidic acid is a bioactive lipid involved in fibrosis and probably in radiation-induced fibrosis as suggested in recent studies. Lysophosphatidic acid is also a well-described pro-oncogenic factor, involved in carcinogenesis processes (proliferation, survival, angiogenesis, invasion, migration). The present review highlights and summarizes the links between lysophosphatidic acid and radiation-induced fibrosis, lysophosphatidic acid and radioresistance, and proposes lysophosphatidic acid as a potential central actor of the radiotherapy therapeutic index. Besides, we hypothesize that following radiotherapy, the newly formed tumour micro-environment, with increased extracellular matrix and increased lysophosphatidic acid levels, is a favourable ground to metastasis development. Lysophosphatidic acid could therefore be an exciting therapeutic target, minimizing radio-toxicities and radio-resistance effects.

ABCC1-Exported Sphingosine-1-phosphate, Produced by Sphingosine Kinase 1, Shortens Survival of Mice and Patients with Breast Cancer

Sphingosine-1-phosphate (S1P), a bioactive sphingolipid mediator, has been implicated in regulation of many processes important for breast cancer progression. Previously, we observed that S1P is exported out of human breast cancer cells by ATP-binding cassette (ABC) transporter ABCC1, but not by ABCB1, both known multidrug resistance proteins that efflux chemotherapeutic agents. However, the pathologic consequences of these events to breast cancer progression and metastasis have not been elucidated. Here, it is demonstrated that high expression of ABCC1, but not ABCB1, is associated with poor prognosis in breast cancer patients. Overexpression of ABCC1, but not ABCB1, in human MCF7 and murine 4T1 breast cancer cells enhanced S1P secretion, proliferation, and migration of breast cancer cells. Implantation of breast cancer cells overexpressing ABCC1, but not ABCB1, into the mammary fat pad markedly enhanced tumor growth, angiogenesis, and lymphangiogenesis with a concomitant increase in lymph node and lung metastases as well as shorter survival of mice. Interestingly, S1P exported via ABCC1 from breast cancer cells upregulated transcription of sphingosine kinase 1 (SPHK1), thus promoting more S1P formation. Finally, patients with breast cancers that express both activated SPHK1 and ABCC1 have significantly shorter disease-free survival. These findings suggest that export of S1P via ABCC1 functions in a malicious feed-forward manner to amplify the S1P axis involved in breast cancer progression and metastasis, which has important implications for prognosis of breast cancer patients and for potential therapeutic targets.Implication: Multidrug resistant transporter ABCC1 and activation of SPHK1 in breast cancer worsen patient's survival by export of S1P to the tumor microenvironment to enhance key processes involved in cancer progression. Mol Cancer Res; 16(6); 1059-70. ©2018 AACR.

Cross-talk between sphingosine-1-phosphate and EGFR signaling pathways enhances human glioblastoma cell invasiveness

We show that glioblastoma multiform (GBM) cells overexpressing the constitutively active form of the epidermal growth factor receptor [epidermal growth factor receptor variant III (EGFRvIII) and U87MG human GBM cell line overexpressing EGFRvIII (EGFR+) cells] possess greater invasive properties and have higher levels of extracellular sphingosine-1-phosphate (S1P) and increased sphingosine kinase-1 (SK1) activity than the empty vector-expressing cells. Notably, the inhibition of SK1 or S1P receptors decreases the invasiveness of EGFR+ cells. Moreover, EGFR and MEK1 inhibitors reduce both SK1 activation and cell invasion, suggesting that the enhanced invasiveness observed in the EGFR+ cells depends on the increased S1P secretion, downstream of the EGFRvIII-ERK-SK1-S1P pathway. Altogether, the results of the present study indicate that, in GBM cells, EGFRvIII is connected with the S1P signaling pathway to enhance cell invasiveness and tumor progression.

The emerging role of FTY720 (Fingolimod) in cancer treatment

FTY720 (Fingolimod) is a clinically approved immunomodulating therapy for multiple sclerosis that sequesters T-cells to lymph nodes through functional antagonism of sphingosine-1-phosphate 1 receptor. FTY720 also demonstrates a proven efficacy in multiple in vitro and in vivo cancer models, suggesting a potential therapeutic role in cancer patients. A potential anticancer mechanism of FTY720 is through the inhibition of sphingosine kinase 1, a proto-oncogene with in vitro and clinical cancer association. In addition, FTY720's anticancer properties may be attributable to actions on several other molecular targets. This study focuses on reviewing the emerging evidence regarding the anticancer properties and molecular targets of FTY720. While the clinical transition of FTY720 is currently limited by its immune suppression effects, studies aiming at FTY720 delivery and release together with identifying its key synergetic combinations and relevant patient subsets may lead to its rapid introduction into the clinic.

The Role of Sphingosine-1-Phosphate and Ceramide-1-Phosphate in Inflammation and Cancer

Inflammation is part of our body's response to tissue injury and pathogens. It helps to recruit various immune cells to the site of inflammation and activates the production of mediators to mobilize systemic protective processes. However, chronic inflammation can increase the risk of diseases like cancer. Apart from cytokines and chemokines, lipid mediators, particularly sphingosine-1-phosphate (S1P) and ceramide-1-phosphate (C1P), contribute to inflammation and cancer. S1P is an important player in inflammation-associated colon cancer progression. On the other hand, C1P has been recognized to be involved in cancer cell growth, migration, survival, and inflammation. However, whether C1P is involved in inflammation-associated cancer is not yet established. In contrast, few studies have also suggested that S1P and C1P are involved in anti-inflammatory pathways regulated in certain cell types. Ceramide is the substrate for ceramide kinase (CERK) to yield C1P, and sphingosine is phosphorylated to S1P by sphingosine kinases (SphKs). Biological functions of sphingolipid metabolites have been studied extensively. Ceramide is associated with cell growth inhibition and enhancement of apoptosis while S1P and C1P are associated with enhancement of cell growth and survival. Altogether, S1P and C1P are important regulators of ceramide level and cell fate. This review focuses on S1P and C1P involvement in inflammation and cancer with emphasis on recent progress in the field.

Group III phospholipase A2 promotes colitis and colorectal cancer

Lipid mediators play pivotal roles in colorectal cancer and colitis, but only a limited member of the phospholipase A₂ (PLA₂) subtypes, which lie upstream of various lipid mediators, have been implicated in the positive or negative regulation of these diseases. Clinical and biochemical evidence suggests that secreted PLA₂ group III (sPLA₂-III) is associated with colorectal cancer, although its precise role remains obscure. Here we have found that sPLA₂-III-null (Pla2g3 ^-/-) mice are highly resistant to colon carcinogenesis. Furthermore, Pla2g3 ^-/- mice are less susceptible to dextran sulfate-induced colitis, implying that the amelioration of colonic inflammation by sPLA₂-III ablation may underlie the protective effect against colon cancer. Lipidomics analysis of the colon revealed significant reduction of pro-inflammatory/pro-tumorigenic lysophosholipids as well as unusual steady-state elevation of colon-protective fatty acids and their oxygenated metabolites in Pla2g3 ^-/- mice. Overall, our results establish a role of sPLA₂-III in the promotion of colorectal inflammation and cancer, expand our understanding of the divergent roles of multiple PLA₂ enzymes in the gastrointestinal tract, and point to sPLA₂-III as a novel druggable target for colorectal diseases.

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

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

Mechanisms of sphingosine 1-phosphate receptor signalling in cancer

S1P is a small bioactive lipid which exerts its effects following binding to a family of five G protein-coupled receptors, known as S1P_1-5. Following receptor activation, multiple signalling cascades are activated, allowing S1P to regulate a range of cellular processes, such as proliferation, apoptosis, migration and angiogenesis. There is strong evidence implicating the involvement of S1P receptors (S1PRs) in cancer progression and the oncogenic effects of S1P can result from alterations in the expression of one or more of the S1PRs and/or the enzymes that regulate the levels of S1P. However, cooperativity between the individual S1PRs, functional interactions with receptor tyrosine kinases and the sub-cellular localisation of the S1PRs within tumour cells also appear to play a role in mediating the effects of S1PR signalling during carcinogenesis. Here we review what is known regarding the role of individual S1PRs in cancer and discuss the recent evidence to suggest cross-talk between the S1PRs and other cellular signalling pathways in cancer. We will also discuss the therapeutic potential of targeting the S1PRs and their downstream signalling pathways for the treatment of cancer.

Immunohistochemical Detection of Sphingosine-1-Phosphate and Sphingosine Kinase-1 in Human Tissue Samples and Cell Lines

Sphingosine-1-phosphate (S1P) and the enzyme primarily responsible for its production, sphingosine kinase-1 (SphK-1), are dysregulated in multiple human diseases including cancer, multiple sclerosis (MS), diabetes, neurological diseases, fibrosis, and certain pathologies associated with impaired angiogenesis such as age-related macular degeneration (AMD). Antibody-based techniques to identify and localize S1P and SphK-1 within cells and tissue specimens represent a powerful tool, not only to understand biological role of these molecules but also to validate these unique in-class targets in multiple state diseases. Consequently, the potential applications of these molecules for therapy and diagnostic purposes are currently under investigation. Here, we describe a new improved technique, Agitated Low Temperature Epitope Retrieval (ALTER) for staining procedures, to identify expression of S1P and SphK-1 in human frozen tissue samples. The challenges encountered in the process of localization in tissue samples of lipid molecules such as S1P are discussed.

Sphingosine-1 Phosphate: A New Modulator of Immune Plasticity in the Tumor Microenvironment

In the last 15 years, increasing evidences demonstrate a strong link between sphingosine-1-phosphate (S1P) and both normal physiology and progression of different diseases, including cancer and inflammation. Indeed, numerous studies show that tissue levels of this sphingolipid metabolite are augmented in many cancers, affecting survival, proliferation, angiogenesis, and metastatic spread. Recent insights into the possible role of S1P as a therapeutic target has attracted enormous attention and opened new opportunities in this evolving field. In this review, we will focus on the role of S1P in cancer, with particular emphasis in new developments that highlight the many functions of this sphingolipid in the tumor microenvironment. We will discuss how S1P modulates phenotypic plasticity of macrophages and mast cells, tumor-induced immune evasion, differentiation and survival of immune cells in the tumor milieu, interaction between cancer and stromal cells, and hypoxic response.

Therapeutic potential of targeting sphingosine kinases and sphingosine 1-phosphate in hematological malignancies

Sphingolipids, such as ceramide, sphingosine and sphingosine 1-phosphate (S1P) are bioactive molecules that have important functions in a variety of cellular processes, which include proliferation, survival, differentiation and cellular responses to stress. Sphingolipids have a major impact on the determination of cell fate by contributing to either cell survival or death. Although ceramide and sphingosine are usually considered to induce cell death, S1P promotes survival of cells. Sphingosine kinases (SPHKs) are the enzymes that catalyze the conversion of sphingosine to S1P. There are two isoforms, SPHK1 and SPHK2, which are encoded by different genes. SPHK1 has recently been implicated in contributing to cell transformation, tumor angiogenesis and metastatic spread, as well as cancer cell multidrug-resistance. More recent findings suggest that SPHK2 also has a role in cancer progression. This review is an overview of our understanding of the role of SPHKs and S1P in hematopoietic malignancies and provides information on the current status of SPHK inhibitors with respect to their therapeutic potential in the treatment of hematological cancers.

G protein-coupled receptors as promising cancer targets

G protein-coupled receptors (GPCRs) regulate an array of fundamental biological processes, such as growth, metabolism and homeostasis. Specifically, GPCRs are involved in cancer initiation and progression. However, compared with the involvement of the epidermal growth factor receptor in cancer, that of GPCRs have been largely ignored. Recent findings have implicated many GPCRs in tumorigenesis, tumor progression, invasion and metastasis. Moreover, GPCRs contribute to the establishment and maintenance of a microenvironment which is permissive for tumor formation and growth, including effects upon surrounding blood vessels, signaling molecules and the extracellular matrix. Thus, GPCRs are considered to be among the most useful drug targets against many solid cancers. Development of selective ligands targeting GPCRs may provide novel and effective treatment strategies against cancer and some anticancer compounds are now in clinical trials. Here, we focus on tumor related GPCRs, such as G protein-coupled receptor 30, the lysophosphatidic acid receptor, angiotensin receptors 1 and 2, the sphingosine 1-phosphate receptors and gastrin releasing peptide receptor. We also summarize their tissue distributions, activation and roles in tumorigenesis and discuss the potential use of GPCR agonists and antagonists in cancer therapy.

Sphingosine kinase 1 is upregulated with lysophosphatidic acid receptor 2 in human colorectal cancer

AIM: To examine the expression of SphK1, an oncogenic kinase that produces sphingosine 1-phosphate (S1P), and its correlation with the expression of LPAR2, a major lysophosphatidic acid (LPA) receptor overexpressed in various cancers, in human colorectal cancer.

METHODS: Real-time reverse-transcription polymerase chain reaction was used to measure the mRNA expression of SphK1, LPAR2, and the three major S1P receptors in 27 colorectal cancer samples and corresponding normal tissue samples. We also examined the correlation between the expression of SphK1 and LPAR2.

RESULTS: Colorectal cancer tissue in 22 of 27 patients had higher levels of SphK1 mRNA than in normal tissue. In two-thirds of the samples, SphK1 mRNA expression was more than two-fold higher than in normal tissue. Consistent with previous reports, LPAR2 mRNA expression in 20 of 27 colorectal cancer tissue samples was higher compared to normal tissue samples. Expression profiles of all three major S1P receptors, S1PR1, S1PR2, and S1PR3, varied without any trend, with no significant difference in expression between cancer and normal tissues. A highly significant positive correlation was found between SphK1 and LPAR2 expression [Pearson’s correlation coefficient (r) = 0.784 and P < 0.01]. The mRNA levels of SphK1 and LPAR2 did not correlate with TNM stage.

CONCLUSION: Our findings suggest that S1P and LPA may play important roles in the development of colorectal cancer via the upregulation of SphK1 and LPAR2, both of which could serve as new therapeutic targets in the treatment of colorectal cancer.

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

Extracellular lysophosphatidate and sphingosine 1-phosphate (S1P) are important bioactive lipids, which signal through G-protein-coupled receptors to stimulate cell growth and survival. The lysophosphatidate and S1P signals are terminated partly by degradation through three broad-specificity lipid phosphate phosphatases (LPPs) on the cell surface. Significantly, the expression of LPP1 and LPP3 is decreased in many cancers, and this increases the impact of lysophosphatidate and S1P signaling. However, relatively little is known about the physiological or pharmacological regulation of the expression of the different LPPs. We now show that treating several malignant and nonmalignant cell lines with 1 μg/ml tetracycline, doxycycline, or minocycline significantly increased the extracellular degradation of lysophosphatidate. S1P degradation was also increased in cells that expressed high LPP3 activity. These results depended on an increase in the stabilities of the three LPPs and increased expression on the plasma membrane. We tested the physiological significance of these results and showed that treating rats with doxycycline accelerated the clearance of lysophosphatidate, but not S1P, from the circulation. However, administering 100 mg/kg/day doxycycline to mice decreased plasma concentrations of lysophosphatidate and S1P. This study demonstrates a completely new property of tetracyclines in increasing the plasma membrane expression of the LPPs.

LPA Induces Colon Cancer Cell Proliferation through a Cooperation between the ROCK and STAT-3 Pathways

Lysophosphatidic acid (LPA) plays a critical role in the proliferation and migration of colon cancer cells; however, the downstream signaling events underlying these processes remain poorly characterized. The aim of this study was to investigate the signaling pathways triggered by LPA to regulate the mechanisms involved in the progression of colorectal cancer (CRC). We have used three cell line models of CRC, and initially analyzed the expression profile of LPA receptors (LPAR). Then, we treated the cells with LPA and events related to their tumorigenic potential, such as migration, invasion, anchorage-independent growth, proliferation as well as apoptosis and cell cycle were evaluated. We used the Chip array technique to analyze the global gene expression profiling that occurs after LPA treatment, and we identified cell signaling pathways related to the cell cycle. The inhibition of these pathways verified the conclusions of the transcriptomic analysis. We found that the cell lines expressed LPAR1, -2 and -3 in a differential manner and that 10 μM LPA did not affect cell migration, invasion and anchorage-independent growth, but it did induce proliferation and cell cycle progression in HCT-116 cells. Although LPA in this concentration did not induce transcriptional activity of β-catenin, it promoted the activation of Rho and STAT-3. Moreover, ROCK and STAT-3 inhibitors prevented LPA-induced proliferation, but ROCK inhibition did not prevent STAT-3 activation. Finally, we observed that LPA regulates the expression of genes related to the cell cycle and that the combined inhibition of ROCK and STAT-3 prevented cell cycle progression and increased the LPA-induced expression of cyclins E1, A2 and B1 to a greater degree than either inhibitor alone. Overall, these results demonstrate that LPA increases the proliferative potential of colon adenocarcinoma HCT-116 cells through a mechanism involving cooperation between the Rho-ROCK and STAT3 pathways involved in cell cycle control.

Autotaxin and LPA1 and LPA5 receptors exert disparate functions in tumor cells versus the host tissue microenvironment in melanoma invasion and metastasis

Autotaxin (ENPP2/ATX) and lysophosphatidic acid (LPA) receptors represent two key players in regulating cancer progression. The present study sought to understand the mechanistic role of LPA G protein-coupled receptors (GPCR), not only in the tumor cells but also in stromal cells of the tumor microenvironment. B16F10 melanoma cells predominantly express LPA5 and LPA2 receptors but lack LPA1. LPA dose dependently inhibited invasion of cells across a Matrigel layer. RNAi-mediated knockdown of LPA5 relieved the inhibitory effect of LPA on invasion without affecting basal invasion. This suggests that LPA5 exerts an anti-invasive action in melanoma cells in response to LPA. In addition, both siRNA-mediated knockdown and pharmacologic inhibition of LPA2 reduced the basal rate invasion. Unexpectedly, when probing the role of this GPCR in host tissues, it was found that the incidence of melanoma-derived lung metastasis was greatly reduced in LPA5 knockout (KO) mice compared with wild-type (WT) mice. LPA1-KO but not LPA2-KO mice also showed diminished melanoma-derived lung metastasis, suggesting that host LPA1 and LPA5 receptors play critical roles in the seeding of metastasis. The decrease in tumor cell residence in the lungs of LPA1-KO and LPA5-KO animals was apparent 24 hours after injection. However, KO of LPA1, LPA2, or LPA5 did not affect the subcutaneous growth of melanoma tumors.

IMPLICATIONS

These findings suggest that tumor and stromal LPA receptors, in particular LPA1 and LPA5, play different roles in invasion and the seeding of metastasis.

FTY720 and cisplatin synergistically induce the death of cisplatin-resistant melanoma cells through the downregulation of the PI3K pathway and the decrease in epidermal growth factor receptor expression

Sphingosine kinase (SK), a key enzyme in sphingosine-1-phosphate (S1P) synthesis, is known to be overexpressed in various types of cancer cells. The effects of anticancer agents on SK1/S1P signaling have not yet been fully assessed in melanoma cells. In the present study, we investigated the effects of the combination of FTY720, an S1P receptor antagonist, and cisplatin, a DNA-damaging agent, on the induction of the death of human melanoma cells, as well as the molecular mechanisms involved. The viability of various human melanoma cell lines was examined following treatment with anticancer drugs. The cisplatin-resistant SK-Mel-28 and cisplatin-sensitive A375 cell lines were selected for this analysis. Protein expression and apoptotic rates were evaluated by western blot analysis following treatment with cisplatin and/or FTY720. Following treatment with a combination of FTY720 and cisplatin, cell viability significantly decreased and the expression of apoptosis-associated cleaved poly(ADP-ribose) polymerase (PARP) was significantly higher in comparison to treatment with cisplatin alone in the SK-Mel-28 cells. In addition, the combination of FTY720 and cisplatin reduced the protein expression of SK1 and the phosphorylation levels of phosphoinositide 3-kinase (PI3K), Akt and mTOR in the SK-Mel-28 cells; the expression of epidermal growth factor receptor (EGFR) was also markedly reduced. These findings suggest that FTY720 and cisplatin synergistically induce cell death through the downregulation of the PI3K/Akt/mTOR pathway and the decrease in EGFR expression in SK-Mel-28 cells. Thus, the combination of FTY720 and cisplatin may have therapeutic potential for chemotherapy-resistant melanoma, and the effects are likely exerted through the downregulation of S1P signaling.

Lysophospholipid receptor nomenclature review: IUPHAR Review 8

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

LPA receptor signaling: pharmacology, physiology, and pathophysiology

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

Lysophosphatidic acid stimulates activation of focal adhesion kinase and paxillin and promotes cell motility, via LPA1-3, in human pancreatic cancer

BACKGROUND

Pancreatic cancer is highly metastatic and with poor prognosis. In previous studies, lysophosphatidic acid (LPA) was shown to be a critical component of ascites which promoted the invasion and metastasis of pancreatic cancer. Two focal adhesion proteins, focal adhesion kinase (FAK) and paxillin, were crucially involved in cell migration, cytoskeleton reorganization, and the dynamics of focal adhesion.

OBJECTIVES

This study examined the involvement of LPA1-3 in LPA-induced activation of FAK and paxillin, and in cell motility, in pancreatic cancer PANC-1 cells.

METHODS

Reverse transcriptase polymerase chain reaction analysis was used to examine mRNA expression of LPA receptors in PANC-1. Cellular protein expression of FAK and paxillin was analyzed by western blotting. The subcellular location of FAK and paxillin was visualized by immunofluorescence. Cell migration was measured by use of a transwell migration chamber.

RESULTS

Three LPA receptors (LPA1, LPA2, and LPA3) were significantly expressed in PANC-1 cells. Treatment with LPA induced both time and dose-dependent tyrosine phosphorylation of FAK and paxillin. LPA also affected translocation of FAK and paxillin from cytoplasm to focal adhesions at the cell periphery and enhanced cell motility of PANC-1. Pretreatment with 3-(4-(4-((1-(2-chlorophenyl)ethoxy)carbonyl amino)-3-methyl-5-isoxazolyl)benzylsulfanyl)propanoic acid (Ki16425), an antagonist of LPA1 and LPA3, before LPA attenuated the LPA-induced tyrosine phosphorylation and redistribution of FAK and paxillin and abrogated LPA-induced cellular migration activity.

CONCLUSIONS

These results suggest LPA induces activation of FAK and paxillin via LPA1-3, which may contribute to the increased cell motility in human pancreatic cancer PANC-1 cells. Thus, an understanding of the regulation by LPA of cell motility in pancreatic cancer could identify novel targets for therapy.

Inflammatory lipid sphingosine-1-phosphate upregulates C-reactive protein via C/EBPβ and potentiates breast cancer progression

A crucial role of the inflammatory lipid sphingosine-1-phosphate (S1P) in breast cancer aggressiveness has been reported. Recent clinical studies have suggested that C-reactive protein (CRP) has a role in breast cancer development. However, limited information is available on the molecular basis for the expression of CRP and its functional significance in breast cell invasion. The present study aimed to elucidate the molecular link between S1P and CRP during the invasive process of breast epithelial cells. This is the first report showing that transcription of CRP was markedly activated by S1P in breast cells. Our data suggest that not only S1P treatment but also the endogenously produced S1P may upregulate CRP in breast carcinoma cells. Transcription factors CCAAT/enhancer-binding protein beta and c-fos were required for S1P-induced CRP expression. Coupling of S1P3 to heterotrimeric Gαq triggered the expression of CRP, utilizing signaling pathways involving reactive oxygen species (ROS), Ca(2+) and extracellular signal-related kinases (ERKs). S1P-induced CRP expression was crucial for the transcriptional activation of matrix metalloproteinase-9 through ERKs, ROS and c-fos, leading to breast cell invasion. Using a xenograft mice tumor model, we demonstrated that S1P induced CRP expression both in vitro and in vivo. Taken together, our findings have revealed a molecular basis for S1P-induced transcriptional activation of CRP and its functional significance in the acquisition of the invasive phenotype of human breast epithelial cells under inflammatory conditions. Our findings may provide useful information on the identification of useful therapeutic targets for inflammatory breast cancer.

Altered sphingolipid metabolism in patients with metastatic pancreatic cancer

Although numerous genetic mutations and amplifications have been identified in pancreatic cancer, much of the molecular pathogenesis of the disease remains undefined. While proteomic and transcriptomic analyses have been utilized to probe and characterize pancreatic tumors, lipidomic analyses have not been applied to identify perturbations in pancreatic cancer patient samples. Thus, we utilized a mass spectrometry-based lipidomic approach, focused towards the sphingolipid class of lipids, to quantify changes in human pancreatic cancer tumor and plasma specimens. Subgroup analysis revealed that patients with positive lymph node metastasis have a markedly higher level of ceramide species (C16:0 and C24:1) in their tumor specimens compared to pancreatic cancer patients without nodal disease or to patients with pancreatitis. Also of interest, ceramide metabolites, including phosphorylated (sphingosine- and sphinganine-1-phosphate) and glycosylated (cerebroside) species were elevated in the plasma, but not the pancreas, of pancreatic cancer patients with nodal disease. Analysis of plasma level of cytokine and growth factors revealed that IL-6, IL-8, CCL11 (eotaxin), EGF and IP10 (interferon inducible protein 10, CXCL10) were elevated in patients with positive lymph nodes metastasis, but that only IP10 and EGF directly correlated with several sphingolipid changes. Taken together, these data indicate that sphingolipid metabolism is altered in human pancreatic cancer and associated with advanced disease. Assessing plasma and/or tissue sphingolipids could potentially risk stratify patients in the clinical setting.

Therapeutic potential of targeting SK1 in human cancers

Sphingosine kinase 1 (SK1) is a lipid enzyme with oncogenic properties that converts the proapoptotic lipids ceramide and sphingosine into the antiapoptotic lipid sphingosine-1-phosphate and activates the signal transduction pathways that lead to cell proliferation, migration, the activation of the inflammatory response, and the impairment of apoptosis. There is compelling evidence that SK1 activation contributes to cancer progression leading to increased oncogenic transformation, tumor growth, resistance to therapies, tumor neovascularization, and metastatic spread. High levels of SK1 expression or activity have been associated with a poor prognosis in several human cancers. Recent studies using cancer cell and mouse models demonstrate a significant potential for SK1-targeting therapies to synergize with the effects of chemotherapy and radiotherapy; however, until recently the absence of clinically applicable SK1 inhibitors has limited the translation of these findings into patients. With the recent discovery of SK1 inhibiting properties of a clinically approved drug FTY720 (Fingolimod), SK1 has gained significant attention from both clinicians and the pharmaceutical industry and it is hoped that trials of newly developed SK1 inhibitors may follow soon. This review provides an overview of the SK1 signaling, its relevance to cancer progression, and the potential clinical significance of targeting SK1 for improved local or systemic control of human cancers.