G12/13 and Gq mediate S1P2-induced inhibition of Rac and migration in vascular smooth muscle in a manner dependent on Rho but not Rho kinase

Signaling controversy and future therapeutical perspectives of targeting sphingolipid network in cancer immune editing and resistance to tumor necrosis factor-α immunotherapy

Anticancer immune surveillance and immunotherapies trigger activation of cytotoxic cytokine signaling, including tumor necrosis factor-α (TNF-α) and TNF-related apoptosis-inducing ligand (TRAIL) pathways. The pro-inflammatory cytokine TNF-α may be secreted by stromal cells, tumor-associated macrophages, and by cancer cells, indicating a prominent role in the tumor microenvironment (TME). However, tumors manage to adapt, escape immune surveillance, and ultimately develop resistance to the cytotoxic effects of TNF-α. The mechanisms by which cancer cells evade host immunity is a central topic of current cancer research. Resistance to TNF-α is mediated by diverse molecular mechanisms, such as mutation or downregulation of TNF/TRAIL receptors, as well as activation of anti-apoptotic enzymes and transcription factors. TNF-α signaling is also mediated by sphingosine kinases (SphK1 and SphK2), which are responsible for synthesis of the growth-stimulating phospholipid, sphingosine-1-phosphate (S1P). Multiple studies have demonstrated the crucial role of S1P and its transmembrane receptors (S1PR) in both the regulation of inflammatory responses and progression of cancer. Considering that the SphK/S1P/S1PR axis mediates cancer resistance, this sphingolipid signaling pathway is of mechanistic significance when considering immunotherapy-resistant malignancies. However, the exact mechanism by which sphingolipids contribute to the evasion of immune surveillance and abrogation of TNF-α-induced apoptosis remains largely unclear. This study reviews mechanisms of TNF-α-resistance in cancer cells, with emphasis on the pro-survival and immunomodulatory effects of sphingolipids. Inhibition of SphK/S1P-linked pro-survival branch may facilitate reactivation of the pro-apoptotic TNF superfamily effects, although the role of SphK/S1P inhibitors in the regulation of the TME and lymphocyte trafficking should be thoroughly assessed in future studies.

Sympathetic Nervous System and Atherosclerosis

Atherosclerosis is characterized by the narrowing of the arterial lumen due to subendothelial lipid accumulation, with hypercholesterolemia being a major risk factor. Despite the recent advances in effective lipid-lowering therapies, atherosclerosis remains the leading cause of mortality globally, highlighting the need for additional therapeutic strategies. Accumulating evidence suggests that the sympathetic nervous system plays an important role in atherosclerosis. In this article, we reviewed the sympathetic innervation in the vasculature, norepinephrine synthesis and metabolism, sympathetic activity measurement, and common signaling pathways of sympathetic activation. The focus of this paper was to review the effectiveness of pharmacological antagonists or agonists of adrenoceptors (α1, α2, β1, β2, and β3) and renal denervation on atherosclerosis. All five types of adrenoceptors are present in arterial blood vessels. α1 blockers inhibit atherosclerosis but increase the risk of heart failure while α2 agonism may protect against atherosclerosis and newer generations of β blockers and β3 agonists are promising therapies against atherosclerosis; however, new randomized controlled trials are warranted to investigate the effectiveness of these therapies in atherosclerosis inhibition and cardiovascular risk reduction in the future. The role of renal denervation in atherosclerosis inhibition in humans is yet to be established.

The relationship between sphingosine-1-phosphate receptor 2 and epidermal growth factor in migration and invasion of oral squamous cell carcinoma

Sphingosine-1-phosphate (S1P) is a lipid mediator and its binding to the S1P receptor 2 (S1PR2) is reported to regulate cytoskeletal organization. Epidermal growth factor (EGF) has been shown to induce migration and invasion in tumour cells. Since binding of S1P to S1PR2 and EGF to the EGF receptors exhibit some overlapping functionality, this study aimed to determine whether S1PR2 was involved in EGF-induced migration and invasion of oral squamous cell carcinoma (OSCC) lines and to identify any potential crosstalk between the two pathways. Migration was investigated using the scratch wound assay while invasion was studied using the transwell invasion and multicellular tumour spheroid (MCTS) assays. Activity of Rac1, a RhoGTPase, was measured using G-LISA (small GTPase activation assays) while S1P production was indirectly measured via the expression of sphingosine kinase (Sphk). S1PR2 inhibition with 10 µM JTE013 reduced EGF-induced migration, invasion and Rac1 activity, however, stimulation of S1PR2 with 10 µM CYM5478 did not enhance the effect of EGF on migration, invasion or Rac1 activity. The data demonstrated a crosstalk between EGF/EGFR and S1P/S1PR2 pathways at the metabolic level. S1PR2 was not involved in EGF production, but EGF promoted S1P production through the upregulation of Sphk1. In conclusion, OSCC lines could not migrate and invade without S1PR2 regulation, even with EGF stimulation. EGF also activated S1PR2 by stimulating S1P production via Sphk1. The potential for S1PR2 to control cellular motility may lead to promising treatments for OSCC patients and potentially prevent or reduce metastasis.

Sphingosine 1-phosphate receptor 2 promotes erythrocyte clearance by vascular smooth muscle cells in intraplaque hemorrhage through MFG-E8 production

Intraplaque hemorrhage (IPH) accelerates atherosclerosis progression. To scavenge excessive red blood cells (RBCs), vascular smooth muscle cells (VSMCs) with great plasticity may function as phagocytes. Here, we investigated the erythrophagocytosis function of VSMCs and possible regulations involved. Based on transcriptional microarray analysis, Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis showed that genes up-regulated in human carotid atheroma with IPH were enriched in functions of phagocytic activities, while those down-regulated were enriched in VSMCs contraction function. Transcriptional expression of Milk fat globule-epidermal growth factor 8 (MFG-E8) was also down-regulated in atheroma with IPH. In high-fat diet-fed apolipoprotein E-deficient mice, erythrocytes were present in cells expressing VSMC markers αSMA in the brachiocephalic artery, suggesting VSMCs play a role in erythrophagocytosis. Using immunofluorescence and flow cytometry, we also found that eryptotic RBCs were bound to and internalized by VSMCs in a phosphatidylserine/MFG-E8/integrin α_Vβ₃ dependent manner in vitro. Inhibiting S1PR2 signaling with specific inhibitor JTE-013 or siRNA decreased Mfge8 expression and impaired the erythrophagocytosis of VSMCs in vitro. Partial ligation was performed in the left common carotid artery (LCA) followed by intra-intimal injection of isolated erythrocytes to observe their clearance in vivo. Interfering S1PR2 expression in VSMCs with Adeno-associated virus 9 inhibited MFG-E8 expression inside LCA plaques receiving RBCs injection and attenuated erythrocytes clearance. Erythrophagocytosis by VSMCs increased vascular endothelial growth factor-a secretion and promoted angiogenesis. The present study revealed that VSMCs act as phagocytes for RBC clearance through S1PR2 activation induced MFG-E8 release.

Sphingosine 1-phosphate receptor, a new therapeutic direction in different diseases

Sphingosine 1-phosphate receptor (S1PR), as a kind of G protein-coupled receptor, has five subtypes, including S1PR1, S1PR2, S1PR3, S1PR4, and S1PR5. Sphingosine 1-phosphate receptor (S1P) and S1PR regulate the trafficking of neutrophils and some cells, which has great effects on immune systems, lung tissue, and liver tissue. Presently, many related reports have proved that S1PR has a strong effect on the migration of lymphocytes, tumor cells, neutrophils, and many other cells via the regulation of signals, pathways, and enzymes. In this way, S1PR can regulate the relative response of the organism. Thus, S1PR has become a possible target for the treatment of autoimmune diseases, pulmonary disease, liver disease, and cancer. In this review, we mainly focus on the research of the S1PR for the new therapeutic directions of different diseases and is expected to assist support in the clinic and drug use.

Sphingosine-1-phosphate and Sphingosine-1-phosphate receptors in the cardiovascular system: pharmacology and clinical implications

Sphingosine-1-phosphate (S1P) is a lipid that binds and activates five distinct receptor subtypes, S1P₁, S1P₂, S1P₃, S1P₄, S1P₅, widely expressed in different cells, tissues and organs. In the cardiovascular system these receptors have been extensively studied, but no drug acting on them has been approved so far for treating cardiovascular diseases. In contrast, a number of S1P receptor agonists are approved as immunomodulators, mainly for multiple sclerosis, because of their action on lymphocyte trafficking. This chapter summarizes the available information on S1P receptors in the cardiovascular system and discusses their potential for treating cardiovascular conditions and/or their role on the clinical pharmacology of drugs so far approved for non-cardiovascular conditions. Basic research has recently produced data useful to understand the molecular pharmacology of S1P and S1P receptors, regarding biased agonism, S1P storage, release and vehiculation and chaperoning by lipoproteins, paracrine actions, intracellular non-receptorial S1P actions. On the other hand, the approval of fingolimod and newer generation S1P receptor ligands as immunomodulators, provides information on a number of clinical observations on the impact of these drugs on cardiovascular system which need to be integrated with preclinical data. S1P receptors are potential targets for prevention and treatment of major cardiovascular conditions, including hypertension, myocardial infarction, heart failure and stroke.

Sphingosine 1-phosphate and its receptors in ischemia

Sphingosine 1-phosphate (S1P), a metabolite of sphingolipids, is mainly derived from red blood cells (RBCs), platelets and endothelial cells (ECs). It plays important roles in regulating cell survival, vascular integrity and inflammatory responses through its receptors. S1P receptors (S1PRs), including 5 subtypes (S1PR1-5), are G protein-coupled receptors and have been proved to mediate various and complex roles of S1P in atherosclerosis, myocardial infarction (MI) and ischemic stroke by regulating endothelial function and inflammatory response as well as immune cell behavior. This review emphasizes the functions of S1PRs in atherosclerosis and ischemic diseases such as MI and ischemic stroke, enabling mechanistic studies and new S1PRs targeted therapies in atherosclerosis and ischemia in the future.

iPSC-derived progenitor stromal cells provide new insights into aberrant musculoskeletal development and resistance to cancer in down syndrome

Down syndrome (DS) is a congenital disorder caused by trisomy 21 (T21). It is associated with cognitive impairment, muscle hypotonia, heart defects, and other clinical anomalies. At the same time, individuals with Down syndrome have lower prevalence of solid tumor formation. To gain new insights into aberrant DS development during early stages of mesoderm formation and its possible connection to lower solid tumor prevalence, we developed the first model of two types of DS iPSC-derived stromal cells. Utilizing bioinformatic and functional analyses, we identified over 100 genes with coordinated expression among mesodermal and endothelial cell types. The most significantly down-regulated processes in DS mesodermal progenitors were associated with decreased stromal progenitor performance related to connective tissue organization as well as muscle development and functionality. The differentially expressed genes included cytoskeleton-related genes (actin and myosin), ECM genes (Collagens, Galectin-1, Fibronectin, Heparan Sulfate, LOX, FAK1), cell cycle genes (USP16, S1P complexes), and DNA damage repair genes. For DS endothelial cells, our analysis revealed most down-regulated genes associated with cellular response to external stimuli, cell migration, and immune response (inflammation-based). Together with functional assays, these results suggest an impairment in mesodermal development capacity during early stages, which likely translates into connective tissue impairment in DS patients. We further determined that, despite differences in functional processes and characteristics, a significant number of differentially regulated genes involved in tumorigenesis were expressed in a highly coordinated manner across endothelial and mesodermal cells. These findings strongly suggest that microRNAs (miR-24-4, miR-21), cytoskeleton remodeling, response to stimuli, and inflammation can impact resistance to tumorigenesis in DS patients. Furthermore, we also show that endothelial cell functionality is impaired, and when combined with angiogenic inhibition, it can provide another mechanism for decreased solid tumor development. We propose that the same processes, which specify the basis of connective tissue impairment observed in DS patients, potentially impart a resistance to cancer by hindering tumor progression and metastasis. We further establish that cancer-related genes on Chromosome 21 are up-regulated, while genome-wide cancer-related genes are down-regulated. These results suggest that trisomy 21 induces a modified regulation and compensation of many biochemical pathways across the genome. Such downstream interactions may contribute toward promoting tumor resistant mechanisms.

The ceramide-S1P pathway as a druggable target to alleviate peripheral neuropathic pain

Introduction: Neuropathic pain disorders are diverse, and the currently available therapies are ineffective in the majority of cases. Therefore, there is a major need for gaining novel mechanistic insights and developing new treatment strategies for neuropathic pain. Areas covered: We performed an in-depth literature search on the molecular mechanisms and systemic importance of the ceramide-to-S1P rheostat regulating neuron function and neuroimmune interactions in the development of neuropathic pain. Expert opinion: The S1P receptor modulator FTY720 (fingolimod, Gilenya®), LPA receptor antagonists and several mechanistically related compounds in clinical development raise great expectations for treating neuropathic pain disorders. Research on S1P receptors, S1P receptor modulators or SPHK inhibitors with distinct selectivity, pharmacokinetics and safety must provide more mechanistic insight into whether they may qualify as useful treatment options for neuropathic pain disorders. The functional relevance of genetic variations within the ceramide-to-S1P rheostat should be explored for an enhanced understanding of neuropathic pain pathogenesis. The ceramide-to-S1P rheostat is emerging as a critically important regulator hub of neuroimmune interactions along the pain pathway, and improved mechanistic insight is required to develop more precise and effective drug treatment options for patients suffering from neuropathic pain disorders.

Roles of sphingosine-1-phosphate signaling in cancer

The potent pleiotropic lipid mediator sphingosine-1-phosphate (S1P) participates in numerous cellular processes, including angiogenesis and cell survival, proliferation, and migration. It is formed by one of two sphingosine kinases (SphKs), SphK1 and SphK2. These enzymes largely exert their various biological and pathophysiological actions through one of five G protein-coupled receptors (S1PR1–5), with receptor activation setting in motion various signaling cascades. Considerable evidence has been accumulated on S1P signaling and its pathogenic roles in diseases, as well as on novel modulators of S1P signaling, such as SphK inhibitors and S1P agonists and antagonists. S1P and ceramide, composed of sphingosine and a fatty acid, are reciprocal cell fate regulators, and S1P signaling plays essential roles in several diseases, including inflammation, cancer, and autoimmune disorders. Thus, targeting of S1P signaling may be one way to block the pathogenesis and may be a therapeutic target in these conditions. Increasingly strong evidence indicates a role for the S1P signaling pathway in the progression of cancer and its effects. In the present review, we discuss recent progress in our understanding of S1P and its related proteins in cancer progression. Also described is the therapeutic potential of S1P receptors and their downstream signaling cascades as targets for cancer treatment.

Design, synthesis, and in vitro bioactivity evaluation of fluorine-containing analogues for sphingosine-1-phosphate 2 receptor

Twenty eight new aryloxybenzene analogues were synthesized and their in vitro binding potencies toward S1PR2 were determined using a [³²P]S1P competitive binding assay. Out of these new analogues, three compounds, 28c (IC₅₀ = 29.9 ± 3.9 nM), 28e (IC₅₀ = 14.6 ± 1.5 nM), and 28g (IC₅₀ = 38.5 ± 6.3 nM) exhibited high binding potency toward S1PR2 and high selectivity over the other four receptor subtypes (S1PR1, 3, 4, and 5; IC₅₀ > 1000 nM). Each of the three potent compounds 28c, 28e, and 28g contains a fluorine atom that will allow to develop F-18 labeled PET radiotracers for imaging S1PR2.

Vitamin D effects on sphingosine 1-phosphate signaling and metabolism in monocytes from type 2 diabetes patients and controls

Elevated sphingosine 1-phopshate (S1P) concentration was observed in type 2 diabetes mellitus (T2D). On the other side, 1α,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃) can influence the formation of sphingosine 1-phopshate (S1P) and the expression of S1P receptors, which are known to be involved in T2D. In order to evaluate mechanisms for the antiinflammatory potential of 1,25(OH)₂D₃, we investigated whether 1,25(OH)₂D₃ alters S1P signaling and metabolism in human CD14⁺ monocytes. Primary monocytes isolated from healthy controls (HC) and T2D patients were treated for 24 h with 10 nM 1,25(OH)₂D₃ in the absence or presence of 500 IU/ml interleukin-(IL)-1β. Thereafter, sphingosine kinase (SPHK)1, SPHK2 and S1P receptor 1-5 (S1P_1-5) mRNA expression levels were measured by TaqMan^™ analyses. Sphingolipid levels in cell supernatant were determined by high-performance liquid chromatography/tandem mass spectrometry (LC-MS/MS). 1,25(OH)₂D₃ treatment downregulated S1P₁ and S1P₂ mRNA expression compared to untreated monocytes of HC and T2D patients. In contrast, SPHK1, S1P₃ and S1P₄ mRNA expression levels were upregulated by 1,25(OH)₂D₃ treatment compared to the respective controls. Furthermore, reduced S1P₂ and increased S1P₃ and S1P₄ mRNA expression levels upon treatment with 1,25(OH)₂D₃ occurred in the presence of IL-1β. Additionally, S1P levels in cell supernatants were decreased in monocytes from HC and T2D patients by 1,25(OH)₂D₃ with or without IL-1β costimulation. The levels of sphingosine in cell supernatants were not influenced by 1,25(OH)₂D_3. Overall, our results demonstrate for the first time that 1,25(OH)₂D₃ treatment can influence S1P receptor and SPHK expression and S1P levels in primary monocytes of both HC and subjects with T2D. These findings justify further investigations into the sphingolipid metabolism and potential benefits of vitamin D treatment in diabetes.

Bioactive lysolipids in cancer and angiogenesis

While normal angiogenesis is critical for development and tissue growth, pathological angiogenesis is important for the growth and spread of cancers by supplying nutrients and oxygen as well as providing a conduit for distant metastasis. The interaction among extracellular matrix molecules, tumor cells, endothelial cells, fibroblasts, and immune cells is critical in pathological angiogenesis, in which various angiogenic growth factors, chemokines, and lipid mediators produced from these cells as well as hypoxic microenvironment promote angiogenesis by regulating expression and/or activity of various related genes. Sphingosine 1-phosphate and lysophosphatidic acid, bioactive lipid mediators which act via specific G protein-coupled receptors, play critical roles in angiogenesis. In addition, other lipid mediators including prostaglandin E₂, lipoxin, and resolvins are produced in a stimulus-dependent manner and have pro- or anti-angiogenic effects, presumably through their specific GPCRs. Dysregulated lipid mediator signaling pathways are observed in the contxt of some tumors. This review will focus on LPA and S1P, two bioactive lipid mediators in their regulation of angiogenesis and cell migration that are critical for tumor growth and spread.

Novel Adipokine, FAM19A5, Inhibits Neointima Formation After Injury Through Sphingosine-1-Phosphate Receptor 2

Background:

Obesity plays crucial roles in the development of cardiovascular diseases. However, the mechanisms that link obesity and cardiovascular diseases remain elusive. Compelling evidence indicates that adipokines play an important role in obesity-related cardiovascular diseases. Here, we found a new adipokine-named family with sequence similarity 19, member A5 (FAM19A5), a protein with unknown function that was predicted to be distantly related to the CC-chemokine family. We aimed to test whether adipose-derived FAM19A5 regulates vascular pathology on injury.

Methods:

DNA cloning, protein expression, purification, and N-terminal sequencing were applied to characterize FAM19A5. Adenovirus infection and siRNA transfection were performed to regulate FAM19A5 expression. Balloon and wire injury were performed in vivo on the rat carotid arteries and mouse femoral arteries, respectively. Bioinformatics analysis, radioactive ligand-receptor binding assays, receptor internalization, and calcium mobilization assays were used to identify the functional receptor for FAM19A5.

Results:

We first characterized FAM19A5 as a secreted protein, and the first 43 N-terminal amino acids were the signal peptides. Both FAM19A5 mRNA and protein were abundantly expressed in the adipose tissue but were downregulated in obese mice. Overexpression of FAM19A5 markedly inhibited vascular smooth muscle cell proliferation and migration and neointima formation in the carotid arteries of balloon-injured rats. Accordingly, FAM19A5 silencing in adipocytes significantly promoted vascular smooth muscle cell activation. Adipose-specific FAM19A5 transgenic mice showed greater attenuation of neointima formation compared with wild-type littermates fed with or without Western-style diet. We further revealed that sphingosine-1-phosphate receptor 2 was the functional receptor for FAM19A5, with a dissociation constant ( K d ) of 0.634 nmol/L. Inhibition of sphingosine-1-phosphate receptor 2 or its downstream G12/13-RhoA signaling circumvented the suppressive effects of FAM19A5 on vascular smooth muscle cell proliferation and migration.

Conclusions:

We revealed that a novel adipokine, FAM19A5, was capable of inhibiting postinjury neointima formation via sphingosine-1-phosphate receptor 2-G12/13-RhoA signaling. Downregulation of FAM19A5 during obesity may trigger cardiometabolic diseases.

Sphingosine 1-phosphate attenuates MMP2 and MMP9 in human anaplastic thyroid cancer C643 cells: Importance of S1P2

In anaplastic thyroid cancer C643 cells, sphingosine 1-phosphate (S1P) attenuates migration by activating the S1P2 receptor and the Rho-ROCK pathway. In the present study, we show that stimulating C643 cells with S1P decreases the expression, secretion and activity of matrix metalloproteinase-2 (MMP2), and to a lesser extent MMP9. Using receptor-specific antagonists, and S1P2 siRNA, we showed that the inhibition of expression of MMP2 is mediated through S1P2. Furthermore, S1P inhibited calpain activity, and inhibiting calpain pharmacologically, inhibited the effect of S1P on MMP2 expression and activity, and on MMP9 activity. S1P treatment increased Rho activity, and by incubating cells with the Rho inhibitor C3 transferase or the ROCK inhibitor Y27632, the S1P-induced inhibition of invasion and MMP2 expression and activity was abolished. We conclude that S1P attenuates the invasion of C643 cells by activating S1P2 and the Rho-ROCK pathway, by decreasing calpain activity, and by decreasing the expression, secretion and activity of MMP2 and, to a lesser extent, MMP9. Our results thus unveil a novel function for the S1P2 receptor in attenuating thyroid cancer cell invasion.

Sphingosine-1-phosphate receptors and innate immunity

Sphingosine-1-phosphate (S1P) is a signalling lipid that regulates many cellular processes in mammals. One well-studied role of S1P signalling is to modulate T-cell trafficking, which has a major impact on adaptive immunity. Compounds that target S1P signalling pathways are of interest for immune system modulation. Recent studies suggest that S1P signalling regulates many more cell types and processes than previously appreciated. This review will summarise current understanding of S1P signalling, focusing on recent novel findings in the roles of S1P receptors in innate immunity.

Human Naive and Memory T Cells Display Opposite Migratory Responses to Sphingosine-1 Phosphate

The role of sphingosine-1 phosphate (S1P) in leukocyte trafficking has been well deciphered in mice but remains largely unaddressed in humans. In this study, we assessed the ex vivo response to S1P of primary human T cell subsets. We found that tonsil but not blood leukocytes were responsive to S1P gradients, suggesting that T cell responsiveness is regulated during their recirculation in vivo. Tonsil naive T cells were readily chemoattracted by S1P in an FTY720-sensitive, S1PR1-dependent manner. Surprisingly, S1P had the opposite effect on effector memory T cells, resident memory T cells, and recently activated T cells, inhibiting their spontaneous or chemokine-induced migration. This inhibition was also more pronounced for CD4 T cells than for CD8 T cell subsets, and was dependent on S1PR2, as shown using the S1PR2 antagonist JTE-013. S1PR1 was progressively downregulated during T cell differentiation whereas S1PR2 expression remained stable. Our results suggest that the ratio between S1PR1 and S1PR2 governs the migratory behavior of T cell subsets. They also challenge previous models of the role of S1P in lymphocyte recirculation and suggest that S1P promotes retention of memory T cell subsets in secondary lymphoid organs, via S1PR2.

The endothelium in hypoxic pulmonary vasoconstriction

Hypoxic pulmonary vasoconstriction (HPV) in combination with hypercapnic pulmonary vasoconstriction redistributes pulmonary blood flow from poorly aerated to better ventilated lung regions by an active process of local vasoconstriction. Impairment of HPV results in ventilation-perfusion mismatch and is commonly associated with various lung diseases including pneumonia, sepsis, or cystic fibrosis. Although several regulatory pathways have been identified, considerable knowledge gaps persist, and a unifying concept of the signaling pathways that underlie HPV and their impairment in lung diseases has not yet emerged. In the past, conceptual models of HPV have focused on pulmonary arterial smooth muscle cells (PASMC) acting as sensor and effector of hypoxia in the pulmonary vasculature. In contrast, the endothelium was considered a modulating bystander in this scenario. For an ideal design, however, the oxygen sensor in HPV should be located in the region of gas exchange, i.e., in the alveolar capillary network. This concept requires the retrograde propagation of the hypoxic signal along the endothelial layer of the vascular wall and subsequent contraction of PASMC in upstream arterioles that is elicited via temporospatially tightly controlled endothelial-smooth muscle cell crosstalk. The present review summarizes recent work that provides proof-of-principle for the existence and functional relevance of such signaling pathway in HPV that involves important roles for connexin 40, epoxyeicosatrienoic acids, sphingolipids, and cystic fibrosis transmembrane conductance regulator. Of translational relevance, implication of these molecules provides for novel mechanistic explanations for impaired ventilation/perfusion matching in patients with pneumonia, sepsis, cystic fibrosis, and presumably various other lung diseases.

Gα12 regulates osteoclastogenesis by modulating NFATc1 expression

The G12 family of G protein alpha subunits has been shown to participate in the regulation of various physiological processes. However, the role of Gα12 in bone physiology has not been well described. Here, by micro‐CT analysis, we discovered that Gα12‐knockout mice have an osteopetrotic phenotype. Histological examination showed lower osteoclast number in femoral tissue of Gα12‐knockout mice compared to wild‐type mice. Additionally, in vitro osteoclastic differentiation of precursor cells with receptor activator of nuclear factor‐κB ligand (RANKL) showed that Gα12 deficiency decreased the number of osteoclast generated and the bone resorption activity. The induction of nuclear factor of activated T‐cell c1 (NFATc1), the key transcription factor of osteoclastogenesis, and the activation of RhoA by RANKL was also significantly suppressed by Gα12 deficiency. We further found that the RANKL induction of NFATc1 was not dependent on RhoA signalling, while osteoclast precursor migration and bone resorption required RhoA in the Gα12‐mediated regulation of osteoclasts. Therefore, Gα12 plays a role in differentiation through NFATc1 and in cell migration and resorption activity through RhoA during osteoclastogenesis.

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.

Sphingosine-1-Phosphate Receptor-2 Antagonists: Therapeutic Potential and Potential Risks

The sphingosine-1-phosphate (S1P) signaling system with its specific G-protein-coupled S1P receptors, the enzymes of S1P metabolism and the S1P transporters, offers a multitude of promising targets for drug development. Until today, drug development in this area has nearly exclusively focused on (functional) antagonists at the S1P₁ receptor, which cause a unique phenotype of immunomodulation. Accordingly, the first-in class S1P₁ receptor modulator, fingolimod, has been approved for the treatment of relapsing-remitting multiple sclerosis, and novel S1P₁ receptor (functional) antagonists are being developed for autoimmune and inflammatory diseases such as psoriasis, inflammatory bowel disease, lupus erythematodes, or polymyositis. Besides the S1P₁ receptor, also S1P₂ and S1P₃ are widely expressed and regulate many diverse functions throughout the body. The S1P₂ receptor, in particular, often exerts cellular functions which are opposed to the functions of the S1P₁ receptor. As a consequence, antagonists at the S1P₂ receptor have the potential to be useful in a contrasting context and different areas of indication compared to S1P₁ antagonists. The present review will focus on the therapeutic potential of S1P₂ receptor antagonists and discuss their opportunities as well as their potential risks. Open questions and areas which require further investigations will be emphasized in particular.

Sphingosine 1-Phosphate-Induced ICAM-1 Expression via NADPH Oxidase/ROS-Dependent NF-κB Cascade on Human Pulmonary Alveolar Epithelial Cells

The intercellular adhesion molecule-1 (ICAM-1) expression is frequently correlated with the lung inflammation. In lung injury, sphingosine-1-phosphate (S1P, bioactive sphingolipid metabolite), participate gene regulation of adhesion molecule in inflammation progression and aggravate tissue damage. To investigate the transduction mechanisms of the S1P in pulmonary epithelium, we demonstrated that exposure of HPAEpiCs (human pulmonary alveolar epithelial cells) to S1P significantly induces ICAM-1 expression leading to increase monocyte adhesion on the surface of HPAEpiCs. These phenomena were effectively attenuated by pretreatments with series of inhibitors such as Rottlerin (PKCδ), PF431396 (PYK2), diphenyleneiodonium chloride (DPI), apocynin (NADPH oxidase), Edaravone (ROS), and Bay11-7082 (NF-κB). Consistently, knockdown with siRNA transfection of PKCδ, PYK2, p47^phox, and p65 exhibited the same results. Pretreatment with both Gq-coupled receptor antagonist (GPA2A) and Gi/o-coupled receptor antagonist (GPA2) also blocked the upregulation of ICAM-1 protein and mRNA induced by S1P. We observed that S1P induced PYK2 activation via a Gq-coupled receptor/PKCδ-dependent pathway. In addition, S1P induced NADPH oxidase activation and intracellular ROS generation, which were also reduced by Rottlerin or PF431396. We demonstrated that S1P induced NF-κB p65 phosphorylation and nuclear translocation in HPAEpiCs. Activated NF-κB was blocked by Rottlerin, PF431396, APO, DPI, or Edaravone. Besides, the results of monocyte adhesion assay indicated that S1P-induced ICAM-1 expression on HPAEpiCs can enhance the monocyte attachments. In the S1P-treated mice, we found that the levels of ICAM-1 protein and mRNA in the lung fractions, the pulmonary hematoma and leukocyte count in bronchoalveolar lavage fluid were enhanced through a PKCδ/PYK2/NADPH oxidase/ROS/NF-κB signaling pathway. We concluded that S1P-accelerated lung damage is due to the ICAM-1 induction associated with leukocyte recruitment.

Disorders of Vascular Permeability

The endothelial barrier maintains vascular and tissue homeostasis and modulates many physiological processes, such as angiogenesis. Vascular barrier integrity can be disrupted by a variety of soluble permeability factors, and changes in barrier function can exacerbate tissue damage during disease progression. Understanding endothelial barrier function is critical for vascular homeostasis. Many of the signaling pathways promoting vascular permeability can also be triggered during disease, resulting in prolonged or uncontrolled vascular leak. It is believed that recovery of the normal vasculature requires diminishing this hyperpermeable state. Although the molecular mechanisms governing vascular leak have been studied over the last few decades, recent advances have identified new therapeutic targets that have begun to show preclinical and clinical promise. These approaches have been successfully applied to an increasing number of disease conditions. New perspectives regarding how vascular leak impacts the progression of various diseases are highlighted in this review.

Agonistic antibodies reveal the function of GPR56 in human glioma U87-MG cells

GPR56 is a member of the adhesion G protein-coupled receptor (GPCR) and is highly expressed in parts of tumor cells. The involvement of GPR56 in tumorigenesis has been reported. We generated agonistic monoclonal antibodies against human GPR56 and analyzed the action and signaling pathway of GPR56. The antibodies inhibited cell migration through the Gq and Rho pathway in human glioma U87-MG cells. Co-immunoprecipitation analysis indicated that the interaction between the GPR56 extracellular domain and transmembrane domain was potentiated by agonistic antibodies. These results demonstrated that functional antibodies are invaluable tools for GPCR research and should open a new avenue for therapeutic treatment of tumors.

Type 2 Iodothyronine Deiodinase Activity Is Required for Rapid Stimulation of PI3K by Thyroxine in Human Umbilical Vein Endothelial Cells

Thyroid hormones (THs) exert a number of physiological effects on the cardiovascular system. Some of the nongenomic actions of T3 are achieved by cross coupling the TH receptor (TR) with the phosphatidylinositol 3-kinase (PI3K)/protein kinase Akt (Akt) pathway. We observed that both T3 and T4 rapidly stimulated Akt phosphorylation and Ras-related C3 botulinum toxin substrate 1 (Rac1) activation, which resulted in cell migration, in a PI3K-dependent manner in human umbilical vein endothelial cells (HUVECs). We identified the expression of type 2 iodothyronine deiodinase (D2), which converts T4 to T3, and TRα1 in HUVECs. D2 activity was significantly stimulated by (Bu)2cAMP in HUVECs. The blockade of D2 activity through transfection of small interfering RNA (siRNA) specific to D2 as well as by addition of iopanoic acid, a potent D2 inhibitor, abolished Akt phosphorylation, Rac activation, and cell migration induced by T4 but not by T3. The inhibition of TRα1 expression by the transfection of siRNA for TRα1 canceled Akt phosphorylation, Rac activation, and cell migration induced by T3 and T4. These findings suggest that conversion of T4 to T3 by D2 is required for TRα1/PI3K-mediated nongenomic actions of T4 in HUVECs, including stimulation of Akt phosphorylation and Rac activation, which result in cell migration.

Heterotrimeric G-protein alpha-12 (Gα12) subunit promotes oral cancer metastasis

Oral squamous cell carcinoma (OSCC) has a propensity to spread to the cervical lymph nodes (LN). The presence of cervical LN metastases severely impacts patient survival, whereby the two-year survival for oral cancer patients with involved LN is ~30% compared to over 80% in patients with non-involved LN. Elucidation of key molecular mechanisms underlying OSCC metastasis may afford an opportunity to target specific genes, to prevent the spread of OSCC and to improve patient survival. In this study, we demonstrated that expression of the heterotrimeric G-protein alpha-12 (Gα12) is highly up-regulated in primary tumors and LN of OSCC patients, as assessed by quantitative polymerase chain reaction (qPCR) and immunohistochemistry (IHC). We also found that exogenous expression of the constitutively activated-form of Gα12 promoted cell migration and invasion in OSCC cell lines. Correspondingly, inhibition of Gα12 expression by shRNA consistently inhibited OSCC cell migration and invasion in vitro. Further, the inhibition of G12 signaling by regulator of G-protein signaling (RGS) inhibited Gα12-mediated RhoA activation, which in turn resulted in reduced LN metastases in a tongue-orthotopic xenograft mouse model of oral cancer. This study provides a rationale for future development and evaluation of drug candidates targeting Gα12-related pathways for metastasis prevention.

The sphingosine kinase 1/sphingosine-1-phosphate pathway in pulmonary arterial hypertension

RATIONALE

Sphingosine kinases (SphKs) 1 and 2 regulate the synthesis of the bioactive sphingolipid sphingosine-1-phosphate (S1P), an important lipid mediator that promotes cell proliferation, migration, and angiogenesis.

OBJECTIVES

We aimed to examine whether SphKs and their product, S1P, play a role in the development of pulmonary arterial hypertension (PAH).

METHODS

SphK1(-/-), SphK2(-/-), and S1P lyase heterozygous (Sgpl1(+/-)) mice, a pharmacologic SphK inhibitor (SKI2), and a S1P receptor 2 (S1PR2) antagonist (JTE013) were used in rodent models of hypoxia-mediated pulmonary hypertension (HPH). S1P levels in lung tissues from patients with PAH and pulmonary arteries (PAs) from rodent models of HPH were measured.

MEASUREMENTS AND MAIN RESULTS

mRNA and protein levels of SphK1, but not SphK2, were significantly increased in the lungs and isolated PA smooth muscle cells (PASMCs) from patients with PAH, and in lungs of experimental rodent models of HPH. S1P levels were increased in lungs of patients with PAH and PAs from rodent models of HPH. Unlike SphK2(-/-) mice, SphK1(-/-) mice were protected against HPH, whereas Sgpl1(+/-) mice were more susceptible to HPH. Pharmacologic SphK1 and S1PR2 inhibition prevented the development of HPH in rodent models of HPH. Overexpression of SphK1 and stimulation with S1P potentially via ligation of S1PR2 promoted PASMC proliferation in vitro, whereas SphK1 deficiency inhibited PASMC proliferation.

CONCLUSIONS

The SphK1/S1P axis is a novel pathway in PAH that promotes PASMC proliferation, a major contributor to pulmonary vascular remodeling. Our results suggest that this pathway is a potential therapeutic target in PAH.

Role of small GTPase protein Rac1 in cardiovascular diseases: development of new selective pharmacological inhibitors

A pathway-based genome-wide association analysis has recently identified Rac1 as one of the biologically important gene in coronary heart diseases. The role of the small GTPase Rac1 in cardiac hypertrophy and atherosclerosis has also been documented in clinical studies with the HMG-CoA reductase inhibitors and in in vitro and in vivo settings using transgenic and knockout mice. Thus, Rac1 has emerged as a new pharmacological target for the treatment of cardiovascular diseases. The activation state of Rac1 depends on the release of guanosine diphosphate and the binding of guanosine triphosphate. This cycling is regulated by the guanine nucleotide exchange factors, as activators, and by the GTPase-activating proteins. Three categories of selective Rac1 inhibitors have been developed affecting different steps of this pathway: antagonists of Rac1-guanine nucleotide exchange factor interaction, allosteric inhibitors of nucleotide binding to Rac1, and antagonists of Rac1-mediated NADPH oxidase activity. These chemical compounds have shown to selectively inhibit Rac1 activation in cultured cell lines without affecting the homologous proteins RhoA and Cdc42. Moreover, pioneer studies have been conducted with Rac1 inhibitors in in vivo experimental models of cardiovascular diseases with encouraging results. The present review summarizes the current knowledge of the role of Rac1 in cardiovascular diseases and the pharmacological approaches that have been developed to selectively inhibit its function.

Sphingosylphosphorylcholine induces α-smooth muscle actin expression in human lung fibroblasts and fibroblast-mediated gel contraction via S1P2 receptor and Rho/Rho-kinase pathway

Chronic airway diseases like COPD and asthma are usually accompanied with airway fibrosis. Myofibroblasts, which are characterized by expression of smooth muscle actin (α-SMA), play an important role in a variety of developmental and pathological processes, including fibrosis and wound healing. Sphingosylphosphorylcholine (SPC), a sphingolipid metabolite, has been implicated in many physiological and pathological conditions. The current study tested the hypothesis that SPC may modulate tissue remodeling by affecting the expression of α-SMA in human fetal lung fibroblast (HFL-1) and fibroblast mediated gel contraction. The results show that SPC stimulates α-SMA expression in HFL-1 and augments HFL-1 mediated collagen gel contraction in a time- and concentration-dependent manner. The α-SMA protein expression and fibroblast gel contraction induced by SPC was not blocked by TGF-β1 neutralizing antibody. However, it was significantly blocked by S1P2 receptor antagonist JTE-013, the Rho-specific inhibitor C3 exoenzyme, and a Rho-kinase inhibitor Y-27632. These findings suggest that SPC stimulates α-SMA protein expression and HFL-1 mediated collagen gel contraction via S1P2 receptor and Rho/Rho kinase pathway, and by which mechanism, SPC may be involved in lung tissue remodeling.

The sphingolipid receptor S1PR2 is a receptor for Nogo-a repressing synaptic plasticity

This study identifies a GPCR, S1PR2, as a receptor for the Nogo-A-Δ20 domain of the membrane protein Nogo-A, which inhibits neuronal growth and synaptic plasticity.

Nogo-A is a membrane protein of the central nervous system (CNS) restricting neurite growth and synaptic plasticity via two extracellular domains: Nogo-66 and Nogo-A-Δ20. Receptors transducing Nogo-A-Δ20 signaling remained elusive so far. Here we identify the G protein-coupled receptor (GPCR) sphingosine 1-phosphate receptor 2 (S1PR2) as a Nogo-A-Δ20-specific receptor. Nogo-A-Δ20 binds S1PR2 on sites distinct from the pocket of the sphingolipid sphingosine 1-phosphate (S1P) and signals via the G protein G₁₃, the Rho GEF LARG, and RhoA. Deleting or blocking S1PR2 counteracts Nogo-A-Δ20- and myelin-mediated inhibition of neurite outgrowth and cell spreading. Blockade of S1PR2 strongly enhances long-term potentiation (LTP) in the hippocampus of wild-type but not Nogo-A^−/− mice, indicating a repressor function of the Nogo-A/S1PR2 axis in synaptic plasticity. A similar increase in LTP was also observed in the motor cortex after S1PR2 blockade. We propose a novel signaling model in which a GPCR functions as a receptor for two structurally unrelated ligands, a membrane protein and a sphingolipid. Elucidating Nogo-A/S1PR2 signaling platforms will provide new insights into regulation of synaptic plasticity.

Recent studies have demonstrated an important role of Nogo-A signaling in the repression of structural and synaptic plasticity in mature neuronal networks of the central nervous system. These insights extended our understanding of Nogo-A's inhibitory function far beyond its well-studied role as axonal-growth inhibitor. Repression is mediated via two different Nogo-A extracellular domains: Nogo-66 and Nogo-A-Δ20. Here, we identify the G-protein coupled receptor S1PR2 as a high-affinity receptor for Nogo-A-Δ20 and demonstrate that S1PR2 binds this domain with sites different from the recently proposed S1P binding pocket. Interfering with S1PR2 activity, either pharmacologically or genetically, prevented Nogo-A-Δ20-mediated inhibitory effects. Similar results were obtained when we blocked G₁₃, LARG, and RhoA, components of the downstream signaling pathway. These findings revealed a strong increase in hippocampal and cortical synaptic plasticity when acutely interfering with Nogo-A/S1PR2 signaling, similar to previous results obtained by blocking Nogo-A. We thus provide a novel biological concept of multi-ligand GPCR signaling in which this sphingolipid-activated GPCR is also bound and activated by the high molecular weight membrane protein Nogo-A.

The orphan adhesion G protein-coupled receptor GPR97 regulates migration of lymphatic endothelial cells via the small GTPases RhoA and Cdc42

The important role of the lymphatic vascular system in pathological conditions such as inflammation and cancer has been increasingly recognized, but its potential as a pharmacological target is poorly exploited. Our study aimed at the identification and molecular characterization of lymphatic-specific G protein-coupled receptors (GPCRs) to assess new targets for pharmacological manipulation of the lymphatic vascular system. We used a TaqMan quantitative RT-PCR-based low density array to determine the GPCR expression profiles of ex vivo isolated intestinal mouse lymphatic (LECs) and blood vascular endothelial cells (BECs). GPR97, an orphan adhesion GPCR of unknown function, was the most highly and specifically expressed GPCR in mouse lymphatic endothelium. Using siRNA silencing, we found that GPR97-deficient primary human LECs displayed increased adhesion and collective cell migration, whereas single cell migration was decreased as compared with nontargeting siRNA-transfected control LECs. Loss of GPR97 shifted the ratio of active Cdc42 and RhoA and initiated cytoskeletal rearrangements, including F-actin redistribution, paxillin and PAK4 phosphorylation, and β1-integrin activation. Our data suggest a possible role of GPR97 in lymphatic remodeling and furthermore provide the first insights into the biological functions of GPR97.

The role of sphingosine 1-phosphate receptors in the treatment of demyelinating diseases

Sphingosine 1-phosphate receptors (S1PRs) are a family of G-protein coupled receptors composed of subtypes S1PR1–5 and activated by the endogenous ligand sphingosine 1-phosphate. S1PRs are modulated by the recently approved oral therapy for relapsing–remitting multiple sclerosis, called fingolimod (FTY720). The phosphorylated version of FTY720 (pFTY720) is a pan-S1PR agonist, with the exception of S1PR2. This drug promotes the internalization of S1PR1s in T cells and is said to act as a ‘functional antagonist’ making lymphocytes ‘blind’ to sphingosine 1-phosphate gradients and limiting cell egress from lymph nodes. This immunomodulatory effect of pFTY720 is proposed to be the prime mechanism by which this compound is efficacious in the treatment of multiple sclerosis. Importantly, however, S1PRs are also expressed in many other cell types, for example, cells of the cardiovascular system and the CNS. Studies have shown that pFTY720 enters the CNS and that modulation of S1PRs can alter the cellular physiology of neurons, astrocytes, microglia and oligodendrocytes. These works are suggestive of a potential role for S1PRs expressed in brain cells as targets for pFTY720. This article reviews the role of S1PRs in oligodendrocytes. The authors start by first debating whether pFTY720-mediated internalization of S1PRs causes ‘functional antagonism’ and/or ‘pathway-specific continued signaling’. The authors then describe the signaling pathways that are modulated by S1PRs expressed in oligodendrocytes and also outline the role of S1PRs in oligodendrocyte differentiation, process extension, survival and migration. Finally, the authors discuss the in vitro studies that suggest pFTY720 promotes myelination state versus the in vivo studies that suggest pFTY720 may not alter myelination. The authors conclude by suggesting that S1PRs in the CNS may be of potential use as drug targets not only for multiple sclerosis, but possibly for a number of other demyelinating disorders.

Sphingosine-1-phosphate receptor 2

Sphingosine-1-phosphate (S1P) is a potent bioactive sphingolipid involved in cell proliferation, angiogenesis, inflammation and malignant transformation among other functions. S1P acts either directly on intracellular targets or activates G protein-coupled receptors, specifically five S1P receptors (S1PRs). The identified S1PRs differ in cellular and tissue distribution, and each is coupled to specific G proteins, which mediate unique functions. Here, we describe functional characteristics of all five receptors, emphasizing S1PR2, which is critical in the immune, nervous, metabolic, cardiovascular, musculoskeletal, and renal systems. This review also describes the role of this receptor in tumor growth and metastasis and suggests potential therapeutic avenues that exploit S1PR2.

A sphingosine 1-phosphate receptor 2 selective allosteric agonist

Molecular probe tool compounds for the Sphingosine 1-phosphate receptor 2 (S1PR2) are important for investigating the multiple biological processes in which the S1PR2 receptor has been implicated. Amongst these are NF-κB-mediated tumor cell survival and fibroblast chemotaxis to fibronectin. Here we report our efforts to identify selective chemical probes for S1PR2 and their characterization. We employed high throughput screening to identify two compounds which activate the S1PR2 receptor. SAR optimization led to compounds with high nanomolar potency. These compounds, XAX-162 and CYM-5520, are highly selective and do not activate other S1P receptors. Binding of CYM-5520 is not competitive with the antagonist JTE-013. Mutation of receptor residues responsible for binding to the zwitterionic headgroup of sphingosine 1-phosphate (S1P) abolishes S1P activation of the receptor, but not activation by CYM-5520. Competitive binding experiments with radiolabeled S1P demonstrate that CYM-5520 is an allosteric agonist and does not displace the native ligand. Computational modeling suggests that CYM-5520 binds lower in the orthosteric binding pocket, and that co-binding with S1P is energetically well tolerated. In summary, we have identified an allosteric S1PR2 selective agonist compound.

Ovarian cancer G protein coupled receptor 1 suppresses cell migration of MCF7 breast cancer cells via a Gα12/13-Rho-Rac1 pathway

BACKGROUND

Ovarian cancer G protein coupled receptor 1 (OGR1) mediates inhibitory effects on cell migration in human prostate and ovarian cancer cells. However, the mechanisms and signaling pathways that mediate these inhibitory effects are essentially unknown.

METHODS

MCF7 cell line was chosen as a model system to study the mechanisms by which OGR1 regulates cell migration, since it expresses very low levels of endogenous OGR1. Cell migratory activities were assessed using both wound healing and transwell migration assays. The signaling pathways involved were studied using pharmacological inhibitors and genetic forms of the relevant genes, as well as small G protein pull-down activity assays. The expression levels of various signaling molecules were analyzed by Western blot and quantitative PCR analysis.

RESULTS

Over-expression of OGR1 in MCF7 cells substantially enhanced activation of Rho and inhibition of Rac1, resulting in inhibition of cell migration. In addition, expression of the Gα12/13 specific regulator of G protein signaling (RGS) domain of p115RhoGEF, but not treatment with pertussis toxin (PTX, a Gαi specific inhibitor), could abrogate OGR1-dependent Rho activation, Rac1 inactivation, and inhibition of migration in MCF7 cells. The bioactive lipids tested had no effect on OGR1 function in cell migration.

CONCLUSION

Our data suggest, for the first time, that OGR1 inhibits cell migration through a Gα12/13 -Rho-Rac1 signaling pathway in MCF7 cells. This pathway was not significantly affected by bioactive lipids and all the assays were conducted at constant pH, suggesting a constitutive activity of OGR1. This is the first clear delineation of an OGR1-mediated cell signaling pathway involved in migration.

Sphingosine 1-phosphate and human ether-a'-go-go-related gene potassium channels modulate migration in human anaplastic thyroid cancer cells

Anaplastic thyroid cancer (ATC) is the most aggressive form of human thyroid cancer, lacking any effective treatment. Sphingosine 1-phosphate (S1P) receptors and human ether-a'-go-go-related gene (HERG (KCNH2)) potassium channels are important modulators of cell migration. In this study, we have shown that the S1P(1-3) receptors are expressed in C643 and THJ-16T human ATC cell lines, both at mRNA and protein level. S1P inhibited migration of these cells and of follicular FTC-133 thyroid cancer cells. Using the S1P(1,3) inhibitor VPC-23019, the S1P(2) inhibitor JTE-013, and the S1P(2) receptor siRNA, we showed that the effect was mediated through S1P(2). Treatment of the cells with the Rho inhibitor C3 transferase abolished the effect of S1P on migration. S1P attenuated Rac activity, and inhibiting Rac decreased migration. Sphingosine kinase inhibitor enhanced basal migration of cells, and addition of exogenous S1P inhibited migration. C643 cells expressed a nonconducting HERG protein, and S1P decreased HERG protein expression. The HERG blocker E-4031 decreased migration. Interestingly, downregulating HERG protein with siRNA decreased the basal migration. In experiments using HEK cells overexpressing HERG, we showed that S1P decreased channel protein expression and current and that S1P attenuated migration of the cells. We conclude that S1P attenuates migration of C643 ATC cells by activating S1P(2) and the Rho pathway. The attenuated migration is also, in part, dependent on a S1P-induced decrease of HERG protein.

Sphingolipids and atherosclerosis

The atherosclerotic lesion contains a high amount of sphingolipids, a large group of structurally diverse lipids that regulate distinct biological functions beyond their role as structural membrane components. Assessment of their role in atherogenesis has been enabled after genes that regulate their metabolism had been identified and facilitated by the more wide availability of mass spectrometry. Here we discuss recent mechanistic insights obtained in animal and epidemiological studies that have greatly enhanced our understanding of mechanisms how sphingolipids affect the atherosclerotic process.

p63RhoGEF: a new switch for G(q)-mediated activation of smooth muscle

In normal and diseased vascular smooth muscle (SM), the RhoA pathway, which is activated by multiple agonists through G protein-coupled receptors (GPCRs), plays a central role in regulating basal tone and peripheral resistance. Multiple RhoA GTP exchange factors (GEFs) are expressed in SM, raising the possibility that specific agonists coupled to specific GPCRs may couple to distinct RhoGEFs and provide novel therapeutic targets. This review focuses on the function and mechanisms of activation of p63RhoGEF (Arhgef 25; GEFT) recently identified in SM and its possible role in selective targeting of RhoA-mediated regulation of basal blood pressure through agonists that couple through G(αq/11).

Fingolimod inhibits PDGF-B-induced migration of vascular smooth muscle cell by down-regulating the S1PR1/S1PR3 pathway

Platelet Derived Growth Factor (PDGF) and sphingosine-1-phosphate (S1P) pathways play a key role in mural cell recruitment during tumor growth and angiogenesis. Fingolimod, a S1P analogue, has been shown to exert antitumor and antiangiogenic properties. However, molecular targets and modes of action of fingolimod remain unclear. In this study, we confirmed the antagonizing action of S1P and PDGF-B on rat vascular smooth muscle cell (VSMCs) growth and migration. We then compared siRNA and/or fingolimod (100 nM) treatments on PDGFR-β, S1PR1 S1PR2 and S1PR3 expression. Fingolimod induced a 50% reduction in S1PR3 protein expression which was cumulative with that obtained with anti-S1PR3 siRNA. We found that siRNA-induced inhibition of both PDGFR-β and S1PR3 was the most effective means to block VSMC migration induced by PDGF-B. Finally, we observed that fingolimod treatment associated with anti-S1PR1 siRNA principally inhibited VSMC growth while in combination with anti-S1PR3 siRNA it strongly inhibited VSMC migration. These results suggest that for rat VSMCs, the PDGFR-S1PR1 pathway is predominantly dedicated to cell growth while PDGFR-S1PR3 stimulates cell migration. As an S1P analogue, fingolimod is considered a potent activator of S1PR1 and S1PR3. However, its action on the PDGFR-S1PR platform appears to be dependent on S1PR1 and S1PR3 specific downregulation. Considering that the S1P pathway has already been shown to exert various crosstalks with tyrosine kinase pathways, it seems of great interest to evaluate fingolimod potential in combination with the numerous tyrosine kinase inhibitors used in oncology.

Adhesion G protein-coupled receptors: signaling, pharmacology, and mechanisms of activation

The adhesion G protein-coupled receptors (GPCRs) are a distinct family of more than 30 receptors in vertebrate genomes. These receptors have been shown to play pivotal roles in a diverse range of biological functions and are characterized by extremely large N termini featuring various adhesion domains capable of mediating cell-cell and cell-matrix interactions. The adhesion GPCR N termini also contain GPCR proteolytic site motifs that undergo autocatalytic cleavage during receptor processing to create mature GPCRs existing as noncovalently attached complexes between the N terminus and transmembrane regions. There is mounting evidence that adhesion GPCRs can couple to G proteins to activate a variety of different downstream signaling pathways. Furthermore, recent studies have demonstrated that adhesion GPCR N termini can bind to multiple ligands, which may differentially activate receptor signaling and/or mediate cell adhesion. In addition, studies on several distinct adhesion GPCRs have revealed that truncations of the N termini result in constitutively active receptors, suggesting a model of receptor activation in which removal of the N terminus may be a key event in stimulating receptor signaling. Because mutations to certain adhesion GPCRs cause human disease and because many members of this receptor family exhibit highly discrete distribution patterns in different tissues, the adhesion GPCRs represent a class of potentially important drug targets that have not yet been exploited. For this reason, understanding the mechanisms of activation for these receptors and elucidating their downstream signaling pathways can provide insights with the potential to lead to novel therapeutic agents.

Effect of cyclic hydrodynamic pressure-induced proliferation of human bladder smooth muscle through Ras-related C3 botulinum toxin substrate 1, mitogen-activated protein kinase kinase 1/2 and extracellular regulated protein kinases 1/2

OBJECTIVES

To examine the role of Ras-related C3 botulinum toxin substrate 1, mitogen-activated protein kinase kinase 1/2 and extracellular regulated protein kinases 1/2 in the cyclic hydrodynamic pressure-induced proliferation of human bladder smooth muscle cells.

METHODS

Human bladder smooth muscle cells were exposed to cyclic hydrodynamic pressures in vitro with defined parameters (static, 100 cmH(2) O, 200 cmH(2) O and 300 cmH(2) O pressure) for 24 h. The proliferation of cells was assessed by flow cytometry. Ras-related C3 botulinum toxin substrate 1, mitogen-activated protein kinase kinase 1/2 and extracellular regulated protein kinases 1/2 messenger ribonucleic acid, and protein expression was analyzed by real-time polymerase chain reaction and Western blot. Specificity of the Rac1 was determined with real-time polymerase chain reaction and Western blot technique with small interfering ribonucleic acid transfection and Rac1 inhibitor (NSC23766).

RESULTS

The proliferation of human bladder smooth muscle cells was increased. Ras-related C3 botulinum toxin substrate 1, mitogen-activated protein kinase kinase 1/2 and extracellular regulated protein kinases 1/2 were activated by 200 and 300 cmH(2) O cyclic hydrodynamic pressure compared with static and 100 cmH(2) O pressure. The "knockdown" of activation of Rac1 using target small interfering ribonucleic acid transfection and Rac1 inhibitor (NSC23766) decreased proliferation of human bladder smooth muscle cells, and downregulated mitogen-activated protein kinase kinase 1/2, extracellular regulated protein kinases 1/2.

CONCLUSION

The Rac1 pathway is activated in mechanotransduction and regulation of human bladder smooth muscle cell proliferation in response to cyclic hydrodynamic pressure.

S1PR2 links germinal center confinement and growth regulation

Germinal centers (GCs) are sites of rapid B-cell proliferation and somatic mutation. These ovoid structures develop within the center of follicles and grow to a stereotypic size. The cell migration and interaction dynamics underlying GC B-cell selection events are currently under intense scrutiny. In recent study, we identified a role for a migration inhibitory receptor, S1PR2, in promoting GC B-cell confinement to GCs. S1PR2 also dampens Akt activation and deficiency in S1PR2 or components of its signaling pathway result in a loss of growth control in chronically stimulated mucosal GCs. Herein, we detail present understanding of S1PR2 and S1P biology as it pertains to GC B cells and place this information in the context of a current model of GC function.

Fingolimod potentiates the effects of sunitinib malate in a rat breast cancer model

Most of the antiangiogenic strategies used in oncology principally target endothelial cells through the vascular endothelial growth factor (VEGF) pathway. Multiple kinase inhibitors can secondarily reduce mural cell stabilization of the vessels by blocking platelet-derived growth factor receptor (PDGFR) activity. However, sphingosine-1-phosphate (S1P), which is also implicated in mural cell recruitment, has yet to be targeted in clinical practice. We therefore investigated the potential of a simultaneous blockade of the PDGF and S1P pathways on the chemotactic responses of vascular smooth muscle cells (VSMCs) and the resulting effects of this blockade on breast tumor growth. Due to crosstalk between the S1P and PDGF pathways, we used AG1296 and/or VPC-23019 to inhibit PDGFR-β and S1PR1/S1PR3 receptors, respectively. We showed that S1PR1 and S1PR3 are the principal receptors that mediate the S1P chemotactic signal on rat VSMCs and that they act synergistically with PDGFR-β during PDGF-B signaling. We also showed that simultaneous blockade of the PDGFR-β and S1PR1/S1PR3 signals had a synergistic effect, decreasing VSMC migration velocity toward endothelial cell and breast carcinoma cell-secreted cytokines by 65-90%. This blockade also strongly decreased the ability of VSMCs to form a three-dimensional cell network. Similar results were obtained with the combination of sunitinib malate (a VEGFR/PDGFR kinase inhibitor) and fingolimod (an S1P analog). Sunitinib malate is a clinically approved cancer treatment, whereas fingolimod is currently indicated only for treatment of multiple sclerosis. Orally administered, the combination of these drugs greatly decreased rat breast tumor growth in a syngeneic cancer model (Walker 256). This bi-therapy did not exert cumulative toxicity and histological analysis of the tumors revealed normalization of the tumor vasculature. The simultaneous blockade of these signaling pathways with sunitinib malate and fingolimod may provide an effective means of reducing tumor angiogenesis, and may improve the delivery of other chemotherapies.

Pharmacological relevance and potential of sphingosine 1-phosphate in the vascular system

Sphingosine-1-phosphate (S1P) was identified as a crucial molecule for regulating immune responses, inflammatory processes as well as influencing the cardiovascular system. S1P mediates differentiation, proliferation and migration during vascular development and homoeostasis. S1P is a naturally occurring lipid metabolite and is present in human blood in nanomolar concentrations. S1P is not only involved in physiological but also in pathophysiological processes. Therefore, this complex signalling system is potentially interesting for pharmacological intervention. Modulation of the system might influence inflammatory, angiogenic or vasoregulatory processes. S1P activates G-protein coupled receptors, namely S1P(1-5) , whereas only S1P(1-3) is present in vascular cells. S1P can also act as an intracellular signalling molecule. This review highlights the pharmacological potential of S1P signalling in the vascular system by giving an overview of S1P-mediated processes in endothelial cells (ECs) and vascular smooth muscle cells (VSMCs). After a short summary of S1P metabolism and signalling pathways, the role of S1P in EC and VSMC proliferation and migration, the cause of relaxation and constriction of arterial blood vessels, the protective functions on endothelial apoptosis, as well as the regulatory function in leukocyte adhesion and inflammatory responses are summarized. This is followed by a detailed description of currently known pharmacological agonists and antagonists as new tools for mediating S1P signalling in the vasculature. The variety of effects influenced by S1P provides plenty of therapeutic targets currently under investigation for potential pharmacological intervention.