Sphingosine-1-phosphate mobilizes intracellular calcium and activates transcription factor NF-kappa B in U937 cells

Effect of phospholipid transfer protein on plasma sphingosine-1-phosphate

Plasma phospholipid transfer protein (PLTP) is a risk factor for cardiovascular diseases. Sphingosine-1-phosphate (S1P), carried by high-density lipoprotein (HDL), is a potent lipid mediator and is also associated with cardiovascular diseases. We found that germline Pltp gene knockout (KO) mice have decreased circulating S1P without influencing apoM, a major S1P carrier on HDL. We then hypothesized that, like apoM, PLTP is another S1P carrier. We established inducible Pltp-KO, Apom-KO, and Pltp/Apom double KO mice and measured plasma lipoprotein and S1P levels under different diets. We found that PLTP deficiency, and the double deficiency have a similar effect on HDL reduction. Importantly, we found that all mice have about 50% reduction in plasma S1P levels, compared to WT mice, and PLTP deficiency significantly reduces apoM levels (about 40%), while apoM deficiency has no effect on PLTP activity, indicating that PLTP depletion reduces S1P through HDL reduction. To further evaluate this HDL reduction-mediated effect, we overexpressed PLTP which also caused a reduction of HDL. We found that the overexpression reduces S1P and apoM as well as apoA-I, a major apolipoprotein on HDL. Furthermore, we found that albumin (another reported S1P carrier) deficiency in mice has no effect on plasma S1P. We also found that the influence of PLTP on HDL may not require its direct binding to the particle. In conclusion, PLTP is not a direct S1P carrier. PLTP depletion or overexpression in adulthood dramatically reduces plasma S1P through HDL reduction. ApoM, but not albumin, deficiency reduces plasma S1P levels.

Cardiomyocyte-Targeting Peptide to Deliver Amiodarone

BACKGROUND

Amiodarone is underutilized due to significant off-target toxicities. We hypothesized that targeted delivery to the heart would lead to the lowering of the dose by utilizing a cardiomyocyte-targeting peptide (CTP), a cell-penetrating peptide identified by our prior phage display work.

METHODS

CTP was synthesized thiolated at the N-terminus, conjugated to amiodarone via Schiff base chemistry, HPLC purified, and confirmed with MALDI/TOF. The stability of the conjugate was assessed using serial HPLCs. Guinea pigs (GP) were injected intraperitoneally daily with vehicle (7 days), amiodarone (7 days; 80 mg/kg), CTP-amiodarone (5 days; 26.3 mg/kg), or CTP (5 days; 17.8 mg/kg), after which the GPs were euthanized, and the hearts were excised and perfused on a Langendorff apparatus with Tyrode's solution and blebbistatin (5 µM) to minimize the contractions. Voltage (RH237) and Ca2+-indicator dye (Rhod-2/AM) were injected, and fluorescence from the epicardium split and was captured by two cameras at 570-595 nm for the cytosolic Ca2+ and 610-750 nm wavelengths for the voltage. Subsequently, the hearts were paced at 250 ms with programmed stimulation to measure the changes in the conduction velocities (CV), action potential duration (APD), and Ca2+ transient durations at 90% recovery (CaTD90). mRNA was extracted from all hearts, and RNA sequencing was performed with results compared to the control hearts.

RESULTS

The CTP-amiodarone remained stable for up to 21 days at 37 °C. At ~1/15th of the dose of amiodarone, the CTP-amiodarone decreased the CV in hearts significantly compared to the control GPs (0.92 ± 0.05 vs. 1.00 ± 0.03 ms, p = 0.0007), equivalent to amiodarone alone (0.87 ± 0.08 ms, p = 0.0003). Amiodarone increased the APD (192 ± 5 ms vs. 175 ± 8 ms for vehicle, p = 0.0025), while CTP-amiodarone decreased it significantly (157 ± 16 ms, p = 0.0136), similar to CTP alone (155 ± 13 ms, p = 0.0039). Both amiodarone and CTP-amiodarone significantly decreased the calcium transients compared to the controls. CTP-amiodarone and CTP decreased the CaTD90 to an extent greater than amiodarone alone (p < 0.001). RNA-seq showed that CTP alone increased the expression of DHPR and SERCA2a, while it decreased the expression of the proinflammatory genes, NF-kappa B, TNF-α, IL-1β, and IL-6.

CONCLUSIONS

Our data suggest that CTP can deliver amiodarone to cardiomyocytes at ~1/15th the total molar dose of the amiodarone needed to produce a comparable slowing of CVs. The ability of CTP to decrease the AP durations and CaTD90 may be related to its increase in the expression of Ca-handling genes, which merits further study.

Cardiomyocyte Targeting Peptide to Deliver Amiodarone

Background

Amiodarone is underutilized due to significant off-target toxicities. We hypothesized that targeted delivery to the heart would lead to lowering of dose by utilizing a cardiomyocyte targeting peptide (CTP), a cell penetrating peptide identified by our prior phage display work.

Methods

CTP was synthesized thiolated at the N-terminus, conjugated to amiodarone via Schiff base chemistry, HPLC purified and confirmed with MALDI/TOF. Stability of the conjugate was assessed using serial HPLCs. Guinea pigs (GP) were injected intraperitoneally daily with vehicle (7 days), amiodarone (7 days; 80mg/Kg), CTP-amiodarone (5 days;26.3mg/Kg), or CTP (5 days; 17.8mg/Kg), after which GPs were euthanized, hearts excised, perfused on a Langendorff apparatus with Tyrode's solution and blebbistatin (5μM) to minimize contractions. Voltage (RH237) and Ca 2+ -indicator dye (Rhod-2/AM) were injected, fluorescence from the epicardium split and focused on two cameras capturing at 570-595nm for cytosolic Ca 2+ and 610-750nm wavelengths for voltage. Subsequently, hearts were paced at 250ms with programmed stimulation to measure changes in conduction velocities (CV), action potential duration (APD) and Ca 2+ transient durations at 90% recovery (CaTD 90 ). mRNA was extracted from all hearts and RNA sequencing performed with results compared to control hearts.

Results

CTP-amiodarone remained stable for up to 21 days at 37°C. At ∼1/15 th of the dose of amiodarone, CTP-amiodarone decreased CV in hearts significantly compared to control GPs (0.92±0.05 vs. 1.00±0.03m/s, p=0.0007), equivalent to amiodarone alone (0.87±0.08ms, p=0.0003). Amiodarone increased APD (192±5ms vs. 175±8ms for vehicle, p=0.0025), while CTP-amiodarone decreased it significantly (157±16ms, p=0.0136) similar to CTP alone (155±13ms, p=0.0039). Both amiodarone and CTP-amiodarone significantly decreased calcium transients compared to controls. CTP-amiodarone and CTP decreased CaTD 90 to an extent greater than amiodarone alone (p<0.001). RNA-seq showed that CTP alone increased the expression of DHPR and SERCA2a, while decreasing expression of proinflammatory genes NF-kappa B, TNF-α, IL-1β, and IL-6.

Conclusions

Our data suggests that CTP can deliver amiodarone to cardiomyocytes at ∼1/15 th the total molar dose of amiodarone needed to produce comparable slowing of CVs. The ability of CTP to decrease AP durations and CaTD 90 may be related to its increase in expression of Ca-handling genes, and merits further study.

Sphingosine 1-phosphate modulation and immune cell trafficking in inflammatory bowel disease

Immune cell trafficking is a critical element of the intestinal immune response, both in homeostasis and in pathological conditions associated with inflammatory bowel disease (IBD). This process involves adhesion molecules, chemoattractants and receptors expressed on immune cell surfaces, blood vessels and stromal intestinal tissue as well as signalling pathways, including those modulated by sphingosine 1-phosphate (S1P). The complex biological processes of leukocyte recruitment, activation, adhesion and migration have been targeted by various monoclonal antibodies (vedolizumab, etrolizumab, ontamalimab). Promising preclinical and clinical data with several oral S1P modulators suggest that inhibition of lymphocyte egress from the lymph nodes to the bloodstream might be a safe and efficacious alternative mechanism for reducing inflammation in immune-mediated disorders, including Crohn's disease and ulcerative colitis. Although various questions remain, including the potential positioning of S1P modulators in treatment algorithms and their long-term safety, this novel class of compounds holds great promise. This Review summarizes the critical mediators and mechanisms involved in immune cell trafficking in IBD and the available evidence for efficacy, safety and pharmacokinetics of S1P receptor modulators in IBD and other immune-mediated disorders. Further, it discusses potential future approaches to incorporate S1P modulators into the treatment of IBD.

ROS-Influenced Regulatory Cross-Talk With Wnt Signaling Pathway During Perinatal Development

Over a century ago, it was found that a rapid burst of oxygen is needed and produced by the sea urchin oocyte to activate fertilization and block polyspermy. Since then, scientific research has taken strides to establish that Reactive Oxygen Species (ROS), besides being toxic effectors of cellular damage and death, also act as molecular messengers in important developmental signaling cascades, thereby modulating them. Wnt signaling pathway is one such developmental pathway, which has significant effects on growth, proliferation, and differentiation of cells at the earliest embryonic stages of an organism, apart from being significant role-players in the instances of cellular transformation and cancer when this tightly-regulated system encounters aberrations. In this review, we discuss more about the Wnt and ROS signaling pathways, how they function, what roles they play overall in animals, and mostly about how these two major signaling systems cross paths and interplay in mediating major cellular signals and executing the predestined changes during the perinatal condition, in a systematic manner.

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.

Sphingolipids as mediators of inflammation and novel therapeutic target in inflammatory bowel disease

Morbidity of inflammatory gastrointestinal (GI) diseases continues to grow resulting in worsen quality of life and increased burden on public medical systems. Complex and heterogenous illnesses, inflammatory bowel diseases (IBDs) encompass several inflammation -associated pathologies including Crohn's disease and ulcerative colitis. IBD is often initiated by a complex interplay between host genetic and environmental factors, lifestyle and diet, and intestinal bacterial components. IBD inflammatory signature was linked to the pro-inflammatory cytokine tumor necrosis factor-α (TNF-α) signaling pathway that is currently targeted by IBD therapies. Sphingolipid signaling was identified as one of the key mediators and regulators of pro-inflammatory conditions, and, specifically, TNF-α related signaling. All GI tissues and circulating immune/blood cells contain activated sphingolipid-metabolizing enzymes, including sphingosine kinases (SphK1 and SphK2) that generate sphingosine-1-phosphate (S1P), a bioactive lipid and ligand for five G-protein coupled membrane S1P receptors (S1PRs). Numerous normal and pathogenic inflammatory responses are mediated by SphK/S1P/S1PRs signaling axis including lymphocyte trafficking and activation of cytokine signaling machinery. SphK1/S1P/S1PRs axis has recently been defined as a target for the treatment of GI diseases including IBD/colitis. Several SphK1 inhibitors and S1PRs antagonists have been developed as novel anti-inflammatory agents. In this review, we discuss the mechanisms of SphK/S1P signaling in inflammation-linked GI disorders. The potential role of SphK/S1PRs inhibitors in the prevention and treatment of IBD/colitis is critically evaluated.

Impact of Phospholipid Transfer Protein in Lipid Metabolism and Cardiovascular Diseases

PLTP plays an important role in lipoprotein metabolism and cardiovascular disease development in humans; however, the mechanisms are still not completely understood. In mouse models, PLTP deficiency reduces cardiovascular disease, while its overexpression induces it. Therefore, we used mouse models to investigate the involved mechanisms. In this chapter, the recent main progresses in the field of PLTP research are summarized, and our focus is on the relationship between PLTP and lipoprotein metabolism, as well as PLTP and cardiovascular diseases.

Acid ceramidase promotes drug resistance in acute myeloid leukemia through NF-κB-dependent P-glycoprotein upregulation

Acute myeloid leukemia (AML) is the most common acute leukemia in adults. More than half of older AML patients fail to respond to cytotoxic chemotherapy, and most responders relapse with drug-resistant disease. Failure to achieve complete remission can be partly attributed to the drug resistance advantage of AML blasts that frequently express P-glycoprotein (P-gp), an ATP-binding cassette transporter. Our previous work showed that elevated acid ceramidase (AC) levels in AML contribute to blast survival. Here, we investigated P-gp expression levels in AML relative to AC. Using parental HL-60 cells and drug-resistant derivatives as our model, we found that P-gp expression and efflux activity were highly upregulated in resistant derivatives. AC overexpression in HL-60 conferred resistance to the AML chemotherapeutic drugs, cytarabine, mitoxantrone, and daunorubicin, and was linked to P-gp upregulation. Furthermore, targeting AC through pharmacologic or genetic approaches decreased P-gp levels and increased sensitivity to chemotherapeutic drugs. Mechanistically, AC overexpression increased NF-κB activation whereas NF-kB inhibitors reduced P-gp levels, indicating that the NF-kappaB pathway contributes to AC-mediated modulation of P-gp expression. Hence, our data support an important role for AC in drug resistance as well as survival and suggest that sphingolipid targeting approaches may also impact drug resistance in AML.

The role of sphingosine 1 phosphate in coronary artery disease and ischemia reperfusion injury

Coronary artery disease (CAD) is a common cause of morbidity and mortality worldwide. Atherosclerotic plaques, as a hallmark of CAD, cause chronic narrowing of coronary arteries over time and could also result in acute myocardial infarction (AMI). The standard treatments for ameliorating AMI are reperfusion strategies, which paradoxically result in ischemic reperfusion (I/R) injury. Sphingosine 1 phosphate (S1P), as a potent lysophospholipid, plays an important role in various organs, including immune and cardiovascular systems. In addition, high-density lipoprotein, as a negative predictor of atherosclerosis and CAD, is a major carrier of S1P in blood circulation. S1P mediates its effects through binding to specific G protein-coupled receptors, and its signaling contributes to a variety of responses, including cardiac inflammation, dysfunction, and I/R injury protection. In this review, we will focus on the role of S1P in CAD and I/R injury as a potential therapeutic target.

Regulatory role of sphingosine kinase and sphingosine-1-phosphate receptor signaling in progenitor/stem cells

Balanced sphingolipid signaling is important for the maintenance of homeostasis. Sphingolipids were demonstrated to function as structural components, second messengers, and regulators of cell growth and survival in normal and disease-affected tissues. Particularly, sphingosine kinase 1 (SphK1) and its product sphingosine-1-phosphate (S1P) operate as mediators and facilitators of proliferation-linked signaling. Unlimited proliferation (self-renewal) within the regulated environment is a hallmark of progenitor/stem cells that was recently associated with the S1P signaling network in vasculature, nervous, muscular, and immune systems. S1P was shown to regulate progenitor-related characteristics in normal and cancer stem cells (CSCs) via G-protein coupled receptors S1Pn (n = 1 to 5). The SphK/S1P axis is crucially involved in the regulation of embryonic development of vasculature and the nervous system, hematopoietic stem cell migration, regeneration of skeletal muscle, and development of multiple sclerosis. The ratio of the S1P receptor expression, localization, and specific S1P receptor-activated downstream effectors influenced the rate of self-renewal and should be further explored as regeneration-related targets. Considering malignant transformation, it is essential to control the level of self-renewal capacity. Proliferation of the progenitor cell should be synchronized with differentiation to provide healthy lifelong function of blood, immune systems, and replacement of damaged or dead cells. The differentiation-related role of SphK/S1P remains poorly assessed. A few pioneering investigations explored pharmacological tools that target sphingolipid signaling and can potentially confine and direct self-renewal towards normal differentiation. Further investigation is required to test the role of the SphK/S1P axis in regulation of self-renewal and differentiation.

Sphingosine 1-Phosphate and Atherosclerosis

Sphingosine 1-phosphate (S1P) is a potent lipid mediator that works on five kinds of S1P receptors located on the cell membrane. In the circulation, S1P is distributed to HDL, followed by albumin. Since S1P and HDL share several bioactivities, S1P is believed to be responsible for the pleiotropic effects of HDL. Plasma S1P levels are reportedly lower in subjects with coronary artery disease, suggesting that S1P might be deeply involved in the pathogenesis of atherosclerosis. In basic experiments, however, S1P appears to possess both pro-atherosclerotic and anti-atherosclerotic properties; for example, S1P possesses anti-apoptosis, anti-inflammation, and vaso-relaxation properties and maintains the barrier function of endothelial cells, while S1P also promotes the egress and activation of lymphocytes and exhibits pro-thrombotic properties. Recently, the mechanism for the biased distribution of S1P on HDL has been elucidated; apolipoprotein M (apoM) carries S1P on HDL. ApoM is also a modulator of S1P, and the metabolism of apoM-containing lipoproteins largely affects the plasma S1P level. Moreover, apoM modulates the biological properties of S1P. S1P bound to albumin exerts both beneficial and harmful effects in the pathogenesis of atherosclerosis, while S1P bound to apoM strengthens anti-atherosclerotic properties and might weaken the pro-atherosclerotic properties of S1P. Although the detailed mechanisms remain to be elucidated, apoM and S1P might be novel targets for the alleviation of atherosclerotic diseases in the future.

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.

Sphingosine-1-Phosphate and Its Receptors: A Mutual Link between Blood Coagulation and Inflammation

Sphingosine-1-phosphate (S1P) is a versatile lipid signaling molecule and key regulator in vascular inflammation. S1P is secreted by platelets, monocytes, and vascular endothelial and smooth muscle cells. It binds specifically to a family of G-protein-coupled receptors, S1P receptors 1 to 5, resulting in downstream signaling and numerous cellular effects. S1P modulates cell proliferation and migration, and mediates proinflammatory responses and apoptosis. In the vascular barrier, S1P regulates permeability and endothelial reactions and recruitment of monocytes and may modulate atherosclerosis. Only recently has S1P emerged as a critical mediator which directly links the coagulation factor system to vascular inflammation. The multifunctional proteases thrombin and FXa regulate local S1P availability and interact with S1P signaling at multiple levels in various vascular cell types. Differential expression patterns and intracellular signaling pathways of each receptor enable S1P to exert its widespread functions. Although a vast amount of information is available about the functions of S1P and its receptors in the regulation of physiological and pathophysiological conditions, S1P-mediated mechanisms in the vasculature remain to be elucidated. This review summarizes recent findings regarding the role of S1P and its receptors in vascular wall and blood cells, which link the coagulation system to inflammatory responses in the vasculature.

Sphingosine-1-phosphate induces thrombin receptor PAR-4 expression to enhance cell migration and COX-2 formation in human monocytes

Thrombin is not only a central factor in blood coagulation but also stimulates inflammatory processes, including monocyte responses, via activation of PARs. The signaling lipid S1P is a major determinant of monocyte function. Here, we established an interaction between S1P and human monocyte responses to thrombin. S1P induced PAR-1 and PAR-4 mRNA and total protein expression in human monocytes and U937 cells in a concentration (0.1-10 μM)- and time (1-24 h)-dependent manner, respectively. However, only PAR-4 cell-surface expression was increased significantly by S1P, whereas PAR-1 remained unaffected. This response was associated with activation of the Akt, Erk, and p38 pathway and induction of COX-2 but not COX-1. PAR-4-mediated induction of COX-2 was prevented by the PI3K inhibitor LY (10 μM). Preincubation of human monocytes with S1P (1 μM; 16 h) resulted in an enhanced chemotaxis toward thrombin or to selective AP for PAR-4 but not PAR-1. Furthermore, down-regulation of PAR-4 transcription with siRNA attenuated the chemotactic response to thrombin and AP4. In conclusion, S1P enhances monocyte responses to thrombin via up-regulation of PAR-4 expression, which promotes cell migration and COX-2 abundance. This mechanism may facilitate monocyte recruitment to sites of vessel injury and inflammation.

Oncogenic properties of sphingosine kinases in haematological malignancies

The sphingosine kinases (SphKs) have relatively recently been implicated in contributing to malignant cellular processes with particular interest in the oncogenic properties of SPHK1. Whilst SPHK1 has received considerable attention as a putative oncoprotein, SPHK2 has been much more difficult to study, with often conflicting data surrounding its role in cancer. Initial studies focused on non-haemopoietic malignancies, however a growing body of literature on the role of sphingolipid metabolism in haemopoietic malignancies is now emerging. This review provides an overview of the current state of knowledge of the SphKs and the bioactive lipid sphingosine 1-phosphate (S1P), the product of the reaction they catalyse. It then reviews the current literature regarding the roles of S1P and the SphKs in haemopoietic malignancies and discusses the compounds currently available that modulate sphingolipid metabolism and their potential and shortcomings as therapeutic agents for the treatment of haematological malignancies.

Targeting sphingosine-1-phosphate in hematologic malignancies

Sphingosine-1-phosphate (S1P) is a pleiotropic bioactive lipid mediator that regulates several processes important for hematologic cancer progression. S1P is generated by two sphingosine kinases, SphK1 and SphK2, and is exported outside the cell, where it activates specific cell surface S1P G-protein coupled receptors in autocrine/paracrine manner, coined "inside-out signaling". In this review, we highlight the importance of SphK1 and inside-out signaling by S1P in hematologic malignancy. We also summarize the results of studies targeting the SphK1/S1P/S1P receptor axis and the effects of the S1P receptor modulator, FTY720, in hematologic malignancy.

Dissecting the role of the S1P/S1PR axis in health and disease

Sphingosine-1-phosphate (S1P) is a pleiotropic sphingophospholipid generated from the phosphorylation of sphingosine by sphingosine kinases (SPHKs). S1P has been experimentally demonstrated to modulate an array of cellular processes such as cell proliferation, cell survival, cell invasion, vascular maturation, and angiogenesis by binding with any of the five known G-protein-coupled sphingosine 1 phosphate receptors (S1P1-5) on the cell surface in an autocrine as well as a paracrine manner. Recent studies have shown that the S1P receptors (S1PRs) and SPHKs are the key targets for modulating the pathophysiological consequences of various debilitating diseases, such as cancer, sepsis, rheumatoid arthritis, ulcerative colitis, and other related illnesses. In this article, we recapitulate these novel discoveries relative to the S1P/S1PR axis, necessary for the proper maintenance of health, as well as the induction of tumorigenic, angiogenic, and inflammatory stimuli that are vital for the development of various diseases, and the novel therapeutic tools to modulate these responses in oral biology and medicine.

Mitochondria control functional CaV1.2 expression in smooth muscle cells of cerebral arteries

RATIONALE

Physiological functions of mitochondria in contractile arterial myocytes are poorly understood. Mitochondria can uptake calcium (Ca(2+)), but intracellular Ca(2+) signals that regulate mitochondrial Ca(2+) concentration ([Ca(2+)](mito)) and physiological functions of changes in [Ca(2+)](mito) in arterial myocytes are unclear.

OBJECTIVE

To identify Ca(2+) signals that regulate [Ca(2+)](mito), examine the significance of changes in [Ca(2+)](mito), and test the hypothesis that [Ca(2+)](mito) controls functional ion channel transcription in myocytes of resistance-size cerebral arteries.

METHODS AND RESULTS

Endothelin (ET)-1 activated Ca(2+) waves and elevated global Ca(2+) concentration ([Ca(2+)](i)) via inositol 1,4,5-trisphosphate receptor (IP(3)R) activation. IP(3)R-mediated sarcoplasmic reticulum (SR) Ca(2+) release increased [Ca(2+)](mito) and induced mitochondrial depolarization, which stimulated mitochondrial reactive oxygen species (mitoROS) generation that elevated cytosolic ROS. In contrast, a global [Ca(2+)](i) elevation did not alter [Ca(2+)](mito), mitochondrial potential, or mitoROS generation. ET-1 stimulated nuclear translocation of nuclear factor (NF)-kappaB p50 subunit and ET-1-induced IP(3)R-mediated mitoROS elevated NF-kappaB-dependent transcriptional activity. ET-1 elevated voltage-dependent Ca(2+) (Ca(V)1.2) channel expression, leading to an increase in both pressure (myogenic tone)- and depolarization-induced vasoconstriction. Baseline Ca(V)1.2 expression and the ET-1-induced elevation in Ca(V)1.2 expression were both reduced by IP(3)R inhibition, mitochondrial electron transport chain block, antioxidant treatment, and NF-kappaB subunit knockdown, leading to vasodilation.

CONCLUSIONS

IP(3)R-mediated SR Ca(2+) release elevates [Ca(2+)](mito), which induces mitoROS generation. MitoROS activate NF-kappaB, which stimulates Ca(V)1.2 channel transcription. Thus, mitochondria sense IP(3)R-mediated SR Ca(2+) release to control NF-kappaB-dependent Ca(V)1.2 channel expression in arterial myocytes, thereby modulating arterial contractility.

An autocrine sphingosine-1-phosphate signaling loop enhances NF-kappaB-activation and survival

BACKGROUND

Sphingosine-1-phosphate (S1P) is a bioactive lipid that regulates a multitude of cellular functions, including cell proliferation, survival, migration and angiogenesis. S1P mediates its effects either by signaling through G protein-coupled receptors (GPCRs) or through an intracellular mode of action. In this study, we have investigated the mechanism behind S1P-induced survival signalling.

RESULTS

We found that S1P protected cells from FasL-induced cell death in an NF-kappaB dependent manner. NF-kappaB was activated by extracellular S1P via S1P2 receptors and Gi protein signaling. Our study also demonstrates that extracellular S1P stimulates cells to rapidly produce and secrete additional S1P, which can further amplify the NF-kappaB activation.

CONCLUSIONS

We propose a self-amplifying loop of autocrine S1P with capacity to enhance cell survival. The mechanism provides increased understanding of the multifaceted roles of S1P in regulating cell fate during normal development and carcinogenesis.

Dual Role of Oxidized LDL on the NF-KappaB Signaling Pathway

Atherosclerosis is a slowly evolutive age-linked disease of large arteries, characterized by a local lipid deposition associated with a chronic inflammatory response, leading potentially to acute plaque rupture, thrombosis and ischemic heart disease. Atherogenesis is a complex sequence of events associating first expression of adhesion molecules, recruitment of mononuclear cells to the endothelium, local activation of leukocytes and inflammation, lipid accumulation and foam cell formation. Low density lipoproteins (LDLs) become atherogenic after undergoing oxidation by vascular cells, that transform them into highly bioreactive oxidized LDL (oxidized LDLs). Oxidized LDLs are involved in foam cell formation, and trigger proatherogenic events such as overexpression of adhesion molecules, chemoattractant agents growth factors and cytokines involved in the inflammatory process, cell proliferation and apoptosis. Moreover, this toxic effect of oxidized LDLs plays probably a role in plaque erosion/rupture and subsequent atherothrombosis. Several biological effects of oxidized LDLs are mediated through changes in the activity of transcription factors and subsequently in gene expression. Oxidized LDLs exert a biphasic effect on the redox-sensitive transcription factor NF-kappaB, which can be activated thereby up-regulating proinflammatory gene expression, such as adhesion molecules, tissue factor, scavenger receptor LOX-1. On the other hand, higher concentrations of oxidized LDLs may inhibit NF-kappaB activation triggered by inflammatory agents such as LPS, and may thereby exert an immunosuppressive effect. This review is an attempt to clarify the mechanism by which oxidized LDLs may up- or down-regulate NF-kappaB, the role of NF-kappaB activation (or inhibition), and the consequences of the oxidized LDLs-mediated NF-kappaB dysregulation and their potential involvement in atherosclerosis.

Protective effects of immunophilin ligands on testicular torsion/detorsion damage in rats

OBJECTIVES

The purpose was to investigate the role of immunophilin ligands in ischemia/reperfusion (I/R)-induced germ cell apoptosis in the rat.

MATERIALS AND METHODS

Sprague-Dawley rats were divided into five groups with ten animals in each. In animals undergoing torsion/detorsion, right testes were rotated 720 degrees for 1 h. A baseline group was for basal normal values. The sham-operated group served as a control group. The TD group underwent torsion/detorsion surgery alone; the cyclosporine-A group (TD-CsA) received intravenous cyclosporine injection (5 mg/kg) at the time of detorsion, and the FK-506 group (TD-FK) received intravenous FK-506 (3.5 mg/kg) at the time of detorsion. For measurement of lipid peroxidation and antioxidant enzyme activities, the right testes of five animals in each group were excised after 4-h reperfusion. Germ cell apoptosis indices were determined 24 h following detorsion in the right testes of the remaining five animals in each group.

RESULTS

Malondialdehyde (MDA) levels in the TD group were significantly higher compared to control and baseline groups. Moreover, testicular MDA values in TD-CsA and TD-FK groups were significantly lower than in TD. There were also significant decreases in catalase and superxide dismutase activities in the TD group compared to control and baseline groups. These values in TD-CsA and TD-FK groups were significantly higher than in TD. The mean germ cell apoptosis scores were significantly higher in TD animals compared to control and baseline groups; however, CsA and FK-506 treatment significantly reduced the apoptosis compared with the TD group.

CONCLUSION

We have shown that administration of immunophilin ligands in testicular torsion decreases ischemia/reperfusion (I/R) cellular damage. The results of biochemical studies suggest that reduction of oxidative stress along with attenuated neutrophil accumulation by immunophilin ligands may have a major role in their cytoprotective effects.

Sphingosine 1-phosphate induces EGFR expression via Akt/NF-kappaB and ERK/AP-1 pathways in rat vascular smooth muscle cells

Sphingosine 1-phosphate (S1P) has been shown to regulate expression of several genes in vascular smooth muscle cells (VSMCs) and contributes to arteriosclerosis. However, the mechanisms regulating epidermal growth factor receptor (EGFR) expression by S1P in aortic VSMCs remain unclear. Western blotting and RT-PCR analyses showed that S1P induced EGFR mRNA and protein expression in a time- and concentration-dependent manner, which was attenuated by inhibitors of MEK1/2 (U0126) and phosphatidylinositide 3-kinase (PI3K; wortmannin), and transfection with dominant negative mutants of ERK and Akt, respectively. These results suggested that S1P-induced EGFR expression was mediated through p42/p44 MAPK and PI3K/Akt pathways in VSMCs. In accordance with these findings, S1P stimulated phosphorylation of p42/p44 MAPK and Akt which was attenuated by U0126 and wortmannin, respectively. Furthermore, S1P-induced EGFR upregulation was blocked by a selective NF-kappaB inhibitor helenalin. Immunofluorescent staining and reporter gene assay revealed that S1P-induced activation of NF-kappaB was blocked by wortmannin, but not by U0126, suggesting that activation of NF-kappaB was mediated through PI3K/Akt. Moreover, S1P-induced EGFR expression was inhibited by an AP-1 inhibitor curcumin and tanshinone IIA. S1P-stimulated AP-1 subunits (c-Jun and c-Fos mRNA) expression was attenuated by U0126 and wortmannin, suggesting that MEK and PI3K/ERK cascade linking to AP-1 was involved in EGFR expression. Upregulation of EGFR by S1P may exert a phenotype modulation of VSMCs. This hypothesis was supported by pretreatment with AG1478 or transfection with shRNA of EGFR that attenuated EGF-stimulated proliferation of VSMCs pretreated with S1P, determined by XTT assay. These results demonstrated that in VSMCs, activation of Akt/NF-kappaB and ERK/AP-1 pathways independently regulated S1P-induced EGFR expression in VSMCs. Understanding the mechanisms involved in S1P-induced EGFR expression on VSMCs may provide potential therapeutic targets in the treatment of arteriosclerosis.

Phospholipase D1 plays a key role in TNF-alpha signaling

The primary characteristic features of any inflammatory or infectious lesions are immune cell infiltration, cellular proliferation, and the generation of proinflammatory mediators. TNF-alpha is a potent proinflammatory and immuno-regulatory cytokine. Decades of research have been focused on the physiological/pathophysiological events triggered by TNF-alpha. However, the signaling network initiated by TNF-alpha in human leukocytes is still poorly understood. In this study, we report that TNF-alpha activates phospholipase D1 (PLD1), in a dose-dependent manner, and PLD1 is required for the activation of sphingosine kinase and cytosolic calcium signals. PLD1 is also required for NFkappaB and ERK1/2 activation in human monocytic cells. Using antisense oligonucleotides to reduce specifically the expression of PLD isozymes showed PLD1, but not PLD2, to be coupled to TNF-alpha signaling and that PLD1 is required to mediate receptor activation of sphingosine kinase and calcium transients. In addition, the coupling of TNF-alpha to activation of the phosphorylation of ERK1/2 and the activation of NFkappaB were inhibited by pretreating cells with antisense to PLD1, but not to PLD2; thus, demonstrating a specific requirement for PLD1. Furthermore, use of antisense oligonucleotides to reduce expression of PLD1 or PLD2 demonstrated that PLD1 is required for TNF-alpha-induced production of several important cytokines, such as IL-1beta, IL-5, IL-6, and IL-13, in human monocytes. These studies demonstrate the critical role of PLD1 in the intracellular signaling cascades initiated by TNF-alpha and its functional role for coordinating the signals to inflammatory responses.

Text mining of full-text journal articles combined with gene expression analysis reveals a relationship between sphingosine-1-phosphate and invasiveness of a glioblastoma cell line

Background

Sphingosine 1-phosphate (S1P), a lysophospholipid, is involved in various cellular processes such as migration, proliferation, and survival. To date, the impact of S1P on human glioblastoma is not fully understood. Particularly, the concerted role played by matrix metalloproteinases (MMP) and S1P in aggressive tumor behavior and angiogenesis remains to be elucidated.

Results

To gain new insights in the effect of S1P on angiogenesis and invasion of this type of malignant tumor, we used microarrays to investigate the gene expression in glioblastoma as a response to S1P administration in vitro. We compared the expression profiles for the same cell lines under the influence of epidermal growth factor (EGF), an important growth factor. We found a set of 72 genes that are significantly differentially expressed as a unique response to S1P. Based on the result of mining full-text articles from 20 scientific journals in the field of cancer research published over a period of five years, we inferred gene-gene interaction networks for these 72 differentially expressed genes. Among the generated networks, we identified a particularly interesting one. It describes a cascading event, triggered by S1P, leading to the transactivation of MMP-9 via neuregulin-1 (NRG-1), vascular endothelial growth factor (VEGF), and the urokinase-type plasminogen activator (uPA). This interaction network has the potential to shed new light on our understanding of the role played by MMP-9 in invasive glioblastomas.

Conclusion

Automated extraction of information from biological literature promises to play an increasingly important role in biological knowledge discovery. This is particularly true for high-throughput approaches, such as microarrays, and for combining and integrating data from different sources. Text mining may hold the key to unraveling previously unknown relationships between biological entities and could develop into an indispensable instrument in the process of formulating novel and potentially promising hypotheses.

Effects of feeding Fusarium verticillioides (formerly Fusarium moniliforme) culture material containing known levels of fumonisin B1 in Japanese quail (Coturnix coturnix japonica)

One hundred fifty 1-d-old quail chicks (Coturnix coturnix japonica) were divided into 2 groups. The 2 groups were designated as controls (CX) and fumonisin-fed birds (FX) with each containing 50 and 100 chicks, respectively. The birds in group CX were maintained on quail mash alone, whereas the birds in group FX were maintained on diets supplemented with 300 ppm of fumonisin B1 from Fusarium verticillioides (formerly Fusarium moniliforme) culture material from 1 d. Quail chicks in both groups were examined daily for clinical signs and mortality. Five randomly selected quail from each group were individually weighed on 0, 7, 14, 21, and 28 d post-feeding (DPF). After weighing, blood was collected from these birds at 7, 14, 21, and 28 DPF for hematological studies and at 14, 21, and 28 DPF for biochemical studies. Fumonisin B1-fed birds (FX) had ruffled feathers, reduced feed and water intake, poor body growth, and greenish mucus diarrhea with 59% mortality. Nearly 30% of the fumonisin B1-fed birds showed nervous signs during the 4-wk experimental period. From 7 DPF onward, BW in group FX were significantly lower than those in group CX. Fumonisin feeding significantly increased hemoglobin, packed cell volume, total erythrocyte count, and total leukocyte count. There was also a significant increase in aspartate transaminase and alanine transaminase in the fumonisin-fed group. Fumonisins significantly increased concentrations of total serum protein and albumin on 14 and 21 DPF, serum calcium and cholesterol levels from 14 DPF onward, and creatinine from 21 DPF onward. This study revealed that the addition of F. verticillioides culture material supplying a level of 300 ppm of FB1/kg of diet is highly toxic to quail chicks, resulting in heavy mortality, decreased growth rate, and significant alterations in hemato-biochemical parameters.

Novel role of sphingosine kinase 1 as a mediator of neurotrophin-3 action in oligodendrocyte progenitors

We had found previously that neurotrophin-3 (NT-3) is a potent stimulator of cAMP-response element binding protein (CREB) phosphorylation in cultured oligodendrocyte progenitors. Here, we show that CREB phosphorylation in these cells is also highly stimulated by sphingosine-1-phosphate (S1P), a sphingolipid metabolite that is known to be a potent mediator of numerous biological processes. Moreover, CREB phosphorylation in response to NT-3 involves sphingosine kinase 1 (SphK1), the enzyme that synthesizes S1P. Immunocytochemistry and confocal microscopy indicated that NT-3 induces translocation of SphK1 from the cytoplasm to the plasma membrane of oligodendrocytes, a process accompanied by increased SphK1 activity in the membrane fraction where its substrate sphingosine resides. To examine the involvement of SphK1 in NT-3 function, SphK1 expression was down-regulated by treatment with SphK1 sequence-specific small interfering RNA. Remarkably, the capacity of NT-3 to protect oligodendrocyte progenitors from apoptotic cell death induced by growth factor deprivation was abolished by down-regulating the expression of SphK1, as assessed by terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) assay. Altogether, these results suggest that SphK1 plays a crucial role in the stimulation of oligodendrocyte progenitor survival by NT-3, and demonstrate a functional link between NT-3 and S1P signaling, adding to the complexity of mechanisms that modulate neurotrophin function and oligodendrocyte development.

Sphingosine-1-phosphate induces COX-2 expression via PI3K/Akt and p42/p44 MAPK pathways in rat vascular smooth muscle cells

Sphingosine 1-phosphate (S1P) has been shown to regulate smooth muscle cell proliferation, migration, and vascular maturation. S1P increases the expression of several proteins including COX-2 in vascular smooth muscle cells (VSMCs) and contributes to arteriosclerosis. However, the mechanisms regulating COX-2 expression by S1P in VSMCs remain unclear. Western blotting and RT-PCR analyses showed that S1P induced the expression of COX-2 mRNA and protein in a time- and concentration-dependent manner, which was attenuated by inhibitors of MEK1/2 (U0126) and PI3K (wortmannin), and transfection with dominant negative mutants of p42/p44 mitogen-activated protein kinases (ERK2) or Akt. These results suggested that both p42/p44 MAPK and PI3K/Akt pathways participated in COX-2 expression induced by S1P in VSMCs. In accordance with these findings, S1P stimulated phosphorylation of p42/p44 MAPK and Akt, which was attenuated by U0126, LY294002, or wortmannin, respectively. Furthermore, this up-regulation of COX-2 mRNA and protein was blocked by a selective NF-kappaB inhibitor helenalin. Consistently, S1P-stimulated translocation of NF-kappaB into the nucleus was revealed by immnofluorescence staining. Moreover, S1P-stimulated activation of NF-kappaB promoter activity was blocked by phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 and helenalin, but not by U0126, suggesting that involvement of PI3K/Akt in the activation of NF-kappaB. COX-2 promoter assay showed that S1P induced COX-2 promoter activity mediated through p42/p44 MAPK, PI3K/Akt, and NF-kappaB. These results suggested that in VSMCs, activation of p42/p44 MAPK, Akt and NF-kappaB pathways was essential for S1P-induced COX-2 gene expression. Understanding the mechanisms involved in S1P-induced COX-2 expression on VSMCs may provide potential therapeutic targets in the treatment of arteriosclerosis.

Individual and Combined Effects of Fusarium moniliforme Culture Material, Containing Known Levels of Fumonisin B1, and Salmonella Gallinarum Infection on Liver of Japanese Quail

Three hundred day-old Japanese quail (Coturnix coturnix japonica) were divided into two groups with 150 quail in each group. One group was maintained on quail mash alone, while Fusarium moniliforme culture material was added to quail mash in the second group from day 5 of age and was supplied at a rate of 150 ppm fumonisin B1 (FB1)/kg mash. At day 21, each group was further subdivided into two groups, yielding four groups with 75 birds apiece, which served as the control (group CX), the Salmonella Gallinarum alone group (group CS), the FB1 alone group (group FX), and the group fed FB1 and infected with Salmonella Gallinarum (group FS). An oral challenge with Salmonella Gallinarum organisms (2 x 10(4) colony-forming units/ml) was given to groups CS and FS at 21 days of age. Three quail each were necropsied on day 21 (0 day interval) from groups CX and FX only. At subsequent intervals (i.e., 1, 2, 3, 5, 7, 10, 14, and 21 days postinfection [DPI]), three quail were euthanatized from all four groups (CX, CS, FX, and FS). The gross and microscopic lesions were recorded in both mortality and euthanatized birds at the above intervals. The ultrastructural studies were done at 5 DPI. Mild to moderate hepatomegaly and pale discoloration of liver were observed in group FX, while congestion, hemorrhages, necrosis, and mild to severe hepatomegaly were the predominant gross lesions in both infected groups (CS and FS). The gross lesions in quail inoculated with Salmonella Gallinarum alone (group CS) generally developed slowly, appeared more widely scattered, and involved comparatively less surface area in contrast to the rapidly progressive and frequently confluent lesions in the combination group (FS), especially in the first 5 days of infection. Mild to marked hepatocellular swelling, multifocal hepatic necrosis, and hepatocellular and bile duct hyperplasia were the characteristic microscopic changes in the FX group. Microscopic lesions in quail of group CS comprised congestion, vacuolar changes, and focal necrosis in early stages, followed by granulomatous lesions at later intervals. Similar but more severe lesions were observed in the combination group (FS). Based on transmission electron microscopy, the maximum effect of FB1 toxicity was observed on mitochondria and endoplasmic reticulum. In general, the mitochondriae showed diverse form and structure, some of which appeared to lose their intact outer membrane, and the mitochondrial cristae were disoriented. The deformity in the cisternae structure of rough endoplasmic reticulum, with their rearrangement into round or tubular forms either bearing granular surface or leading to accumulation of smooth endoplasmic reticulum, was evident only in groups FX and FS. We conclude that the continuous presence of fumonisins in the diets of young quail might increase their susceptibility to or the severity of Salmonella Gallinarum infection.

Down-regulation of brain nuclear factor-kappa B pathway in the cyclooxygenase-2 knockout mouse

Cyclooxygenase (COX) is the rate-limiting enzyme in the synthesis of prostaglandins (PGs) from arachidonic acid. Evidence suggests that neuronal COX-2 gene expression is mainly regulated by the transcription factor nuclear factor kappa-B (NF-kappaB). The present study was undertaken to determine whether there is a shared regulation of NF-kappaB or of nuclear factor of activated T-cells cytoplasmic (NFATc) with COX-2 and whether these transcription factors known to regulate COX-2 expression are altered in brain from COX-2 knockout (COX-2-/-) mice compared to wild type. We found a decrease in NF-kappaB DNA-protein binding activity, which was accompanied by a reduction of the phosphorylation state of both I-kappaBalpha and p65 proteins in the COX-2-/- mice. The mRNA and protein levels of p65 were also reduced in COX-2-/- mice, whereas total cytoplasmic I-kappaB protein level was not significantly changed. Taken together, these changes may be responsible for the observed decrease in NF-kappaB DNA binding activity. NF-kappaB DNA binding activity was selectively affected in the COX-2-/- mice compared to the wild type as there was no significant change in NFATc DNA binding activity. Overall, our data indicate that constitutive brain NF-kappaB activity is decreased in COX-2 deficient mice and suggest a reciprocal coupling between NF-kappaB and COX-2.

Sphingosine-1-phosphate: an emerging therapeutic target

Sphingosine-1-phosphate (SPP) is a polar sphingolipid metabolite that has received increasing attention as both an extracellular mediator and an intracellular second messenger. SPP is the ligand of a family of specific cell surface G-protein coupled receptors (GPCR), known as the endothelial differentiation gene-1 (EDG-1) family. These receptors, which include EDG-1, -3, -5, -6 and -8, regulate diverse processes including cell migration, angiogenesis, vascular maturation, heart development, neurite retraction and soma rounding. In addition, abundant evidence indicates that SPP also acts as an intracellular lipid messenger, regulating calcium mobilisation, cell growth and survival. The relative intracellular level of SPP and ceramide, another sphingolipid metabolite associated with cell death and cell growth arrest, is an important factor in determining cell fate. Changes in SPP and ceramide have been implicated in a number of pathological conditions in which apoptosis plays an important role, including cancer and neurodegenerative disorders, as well as in atherosclerosis and allergic responses. This review will examine the biosynthesis, metabolism and potential functions of SPP in diverse diseases in order to illuminate targets for the pharmaceutical and therapeutic manipulation of SPP levels.

Basal and induced sphingosine kinase 1 activity in A549 carcinoma cells: function in cell survival and IL-1beta and TNF-alpha induced production of inflammatory mediators

Sphingosine-1-phosphate, a lipid mediator produced by sphingosine kinases, regulates diverse cellular processes, ranging from cell growth and survival to effector functions, such as proinflammatory mediator synthesis. Using human A549 epithelial lung carcinoma cells as a model system, we observed transient upregulation of sphingosine kinase type 1 (SPHK1) enzyme activity upon stimulation with both TNF-alpha or IL-1beta. This transient activation of SPHK1 was found to be required for cytokine-induced COX-2 transcription and PGE2 production, since not only specific siRNA (abolishing both basal and induced SPHK1 enzyme activity), but also a dominant-negative SPHK1 mutant (suppressing induced SPHK1 activity only) both reduced COX-2 and PGE2. Furthermore, TNF-alpha- or IL-1beta-induced transcription of selected cytokines, chemokines, and adhesion molecules (IL-6, RANTES, MCP-1, and VCAM-1) was found to require SPHK1 activation. Suppression of SPHK1 activation led to reduction of cytokine-induced IkappaBalpha phosphorylation and consequently diminished NFkappaB activity due to reduced nuclear translocation of RelA (p65), explaining the dependence of inflammatory mediator production on SPHK1 activation. Inhibition of basal SPHK1 activity by N,N-dimethylsphingosine or by downregulation of its expression using siRNA induced spontaneous apoptosis in A549 cells, an effect that can be explained through interference with constitutive NFkappaB activity in this cell type. In contrast, expression of the dominant-negative mutant did not induce apoptosis. Taken together, these findings demonstrate a role of SPHK1 activation in proinflammatory signalling and of SPHK1 basal activity in survival of A549 lung carcinoma cells.

From calcium to NF-kappa B signaling pathways in neurons

NF-kappa B plays crucial roles in the nervous system, including potential roles in long-term responses to synaptic plasticity, pro- or antiapoptotic effects during developmental cell death, and neurodegenerative disorders. We report here the characterization of signaling pathways leading to the constitutive activation of NF-kappa B in primary cultures of neonatal cerebellar granule neurons, consecutive to calcium entry into the cytosol. We found that opening of calcium channels at the plasma membrane and at intracellular stores is indispensable for the basal NF-kappa B activity. We demonstrated further that three cellular sensors of the cytosolic Ca(2+) levels, calmodulin, protein kinases C (PKCs), and the p21(ras)/phosphatidylinositol 3-kinase (PI3K)/Akt pathway are simultaneously involved in the steps linking the Ca(2+) second messenger to NF-kappa B activity. Calmodulin triggers the activity of calcineurin, a phosphatase which plays a role in the basal NF-kappa B activity, while stimulation of both the calmodulin kinase II and Akt kinase pathways results in the up-regulation of the transcriptional potential of the p65 subunit of NF-kappa B. Finally, using pharmacological and molecular approaches, we analyze interactions between these three pathways at different levels and demonstrate a connection between PKCs and PI3K. All three components converge towards NF-kappa B, at the level of both nuclear translocation and transcriptional activity. These results stand in contrast to the situation in nonneuronal cells, which either do not respond to Ca(2+) or do not simultaneously activate all three cascades. By using a global approach in studying signaling pathways in neurons, these results provide further evidence to validate the concept of networks of transducing cascades, specific to cells and to physiological situations.

Sphingosine kinase, sphingosine-1-phosphate, and apoptosis

The sphingolipid metabolites ceramide (Cer), sphingosine (Sph), and sphingosine-1-phosphate (S1P) play an important role in the regulation of cell proliferation, survival, and cell death. Cer and Sph usually inhibit proliferation and promote apoptosis, while the further metabolite S1P stimulates growth and suppresses apoptosis. Because these metabolites are interconvertible, it has been proposed that it is not the absolute amounts of these metabolites but rather their relative levels that determines cell fate. The relevance of this "sphingolipid rheostat" and its role in regulating cell fate has been borne out by work in many labs using many different cell types and experimental manipulations. A central finding of these studies is that Sph kinase (SphK), the enzyme that phosphorylates Sph to form S1P, is a critical regulator of the sphingolipid rheostat, as it not only produces the pro-growth, anti-apoptotic messenger S1P, but also decreases levels of pro-apoptotic Cer and Sph. Given the role of the sphingolipid rheostat in regulating growth and apoptosis, it is not surprising that sphingolipid metabolism is often found to be disregulated in cancer, a disease characterized by enhanced cell growth, diminished cell death, or both. Anticancer therapeutics targeting SphK are potentially clinically relevant. Indeed, inhibition of SphK has been shown to suppress gastric tumor growth [Cancer Res. 51 (1991) 1613] and conversely, overexpression of SphK increases tumorigenicity [Curr. Biol. 10 (2000) 1527]. Moreover, S1P has also been shown to regulate angiogenesis, or new blood vessel formation [Cell 99 (1999) 301], which is critical for tumor progression. Furthermore, there is intriguing new evidence that S1P can act in an autocrine and/or paracrine fashion [Science 291 (2001) 1800] to regulate blood vessel formation [J. Clin. Invest. 106 (2000) 951]. Thus, SphK may not only protect tumors from apoptosis, it may also increase their vascularization, further enhancing growth. The cytoprotective effects of SphK/S1P may also be important for clinical benefit, as S1P has been shown to protect oocytes from radiation-induced cell death in vivo [Nat. Med. 6 (2000) 1109]. Here we review the growing literature on the regulation of SphK and the role of SphK and its product, S1P, in apoptosis.

Sphingosine kinase interacts with TRAF2 and dissects tumor necrosis factor-alpha signaling

Tumor necrosis factor-alpha (TNF) receptor-associated factor 2 (TRAF2) is one of the major mediators of TNF receptor superfamily transducing TNF signaling to various functional targets, including activation of NF-kappa B, JNK, and antiapoptosis. We investigated how TRAF2 mediates differentially the distinct downstream signals. We now report a novel mechanism of TRAF2-mediated signal transduction revealed by an association of TRAF2 with sphingosine kinase (SphK), a lipid kinase that is responsible for the production of sphingosine 1-phosphate. We identified a TRAF2-binding motif of SphK that mediated the interaction between TRAF2 and SphK resulting in the activation of the enzyme, which in turn is required for TRAF2-mediated activation of NF-kappa B but not JNK. In addition, by using a kinase inactive dominant-negative SphK and a mutant SphK that lacks TRAF2-binding motif we show that the interaction of TRAF2 with SphK and subsequent activation of SphK are critical for prevention of apoptosis during TNF stimulation. These findings show a role for SphK in the signal transduction by TRAF2 specifically leading to activation of NF-kappa B and antiapoptosis.

Effective cytotoxicity against human leukemias and chemotherapy-resistant leukemia cell lines by N-N-dimethylsphingosine

We evaluated the cytotoxicity of dimethylsphingosine (DMS) against four human leukemia cell lines: two acute (HL60 and a multi-drug resistance MDR-positive derivative HL60-dox) and two blast crisis chronic myelogenous leukemias (JFP1, from a treatment refractory patient and K562), and against blasts isolated from 11 leukemia patients. Cell line viability decreased proportionally to DMS concentration and treatment time (P<0.001). HL60-dox and JFP1 were the most sensitive, indicating DMS efficacy against human leukemia MDR. Importantly, leukemia samples showed a similar sensitivity to DMS as that of the cell lines, firstly demonstrating PKC-independent sphingolipid activity against fresh human tumor specimens. DMS-based chemotherapy may improve leukemia treatment.

Sphingosine 1-phosphate activates nuclear factor-kappa B through Edg receptors. Activation through Edg-3 and Edg-5, but not Edg-1, in human embryonic kidney 293 cells

Sphingosine 1-phosphate (S1P) exerts a variety of actions as a second messenger or as an agonist that binds to one or more members of the Edg family of G protein-coupled receptors. By using human embryonic kidney 293 cells, we show that S1P activates nuclear factor-kappa B (NF-kappa B) in a receptor-dependent fashion. Edg-3 and Edg-5, which are coupled to G(i), G(q), and G(13), affect activation of NF-kappa B, whereas Edg-1, which is coupled to G(i) alone, does not. We find that the activation of NF-kappa B requires protein kinase C and Ca(2+), probably downstream of G(q), but that the activation of Rho alone by S1P, whether through G(q) or G(13), does not translate into the activation of NF-kappa B. G beta gamma has little effect of its own but potentiates the activation of NF-kappa B achieved through other G proteins. We conclude that the activation of NF-kappa B by S1P is a receptor-mediated process that relies primarily on the activation of a phospholipase C by G(q) and secondarily on effector regulation through other G proteins.

Abeta(1-42) and aluminum induce stress in the endoplasmic reticulum in rabbit hippocampus, involving nuclear translocation of gadd 153 and NF-kappaB

Apoptosis may represent a prominent form of neuronal death in chronic neurodegenerative disorders, such as Alzheimer's disease. Although apoptosis under mitochondrial control has received considerable attention, mechanisms used within the endoplasmic reticulum (ER) and nucleus in mediating apoptotic signals are not well understood. A growing body of evidence is emerging from different studies which suggests an active role for the ER in regulating apoptosis. Disturbances of ER function have been shown to trigger two different apoptotic pathways; one involves cross-talk with mitochondria and is regulated by the antiapoptotic Bcl-2, and the second is characterized by the activation of caspase-12. Also, stress in the ER has been suggested to result in the activation of a number of proteins, such as gadd 153 and NF-kappa, and in the downregulation of the antiapoptotic protein, Bcl-2. In the present study, the intracisternal injection in aged rabbits of either the neurotoxin aluminum maltolate or of Abeta(1-42), has been found to induce nuclear translocation of gadd 153 and the inducible transcription factor, NF-kappaB. Translocation of these two proteins is accompanied by decreased levels of Bcl-2 in both the ER and the nucleus. Aluminum maltolate, but not Abeta, induces caspase-12 activation which is a mediator of ER-specific apoptosis; this is the first report of the in vivo activation of caspase-12. These findings indicate that the ER may play a role in regulating apoptosis in vivo, and could be of significance in the pathology of neurodegeneration and related disorders.

Endoplasmic reticulum D-myo-inositol 1,4,5-trisphosphate-sensitive stores regulate nuclear factor-kappaB binding activity in a calcium-independent manner

The transcription factor nuclear factor-kappaB (NF-kappaB) plays critical roles in neuronal survival and plasticity and in activation of immune responses. The activation of NF-kappaB has been closely associated with changes in intracellular calcium levels, but the relationship between the two remains unclear. Here we report that inhibition of endoplasmic reticulum (ER) d-myo-inositol 1,4,5-trisphosphate (IP(3))-gated calcium release caused decreased basal NF-kappaB DNA-binding activity in cultured rat cortical neurons. Activation of NF-kappaB in response to tumor necrosis factor-alpha and glutamate was completely abolished when IP(3) receptors were blocked, and NF-kappaB activation in response to depletion of ER calcium by thapsigargin treatment was also decreased by IP(3) receptor blockade. We further investigated the relationship between IP(3) receptor activation and NF-kappaB activity using a cell-free system. Microsomes enriched in the ER were isolated from adult rat cerebral cortex, resuspended, and treated with agents that induce or inhibit ER calcium release. They were then recentrifuged, and the supernatant was added to cytoplasmic extract isolated from the same source tissue. We found that microsomes released an NF-kappaB-stimulating signal in response to activation of IP(3) receptors or inhibition of the ER Ca(2+)-ATPase, but not in response to ryanodine. Studies of intact cells and cell-free preparations indicated that the signal released from the ER was not calcium and was heat- and trypsin-sensitive. Our data suggest that activation of IP(3) receptors is required for a major component of both constitutive and inducible NF-kappaB binding activity in neurons and that decreasing ER intraluminal calcium levels triggers release of a diffusible NF-kappaB-activating signal from the ER.

Sphingosine 1-phosphate signalling via the endothelial differentiation gene family of G-protein-coupled receptors

Sphingosine 1-phosphate (S1P) is stored in and released from platelets in response to cell activation. However, recent studies show that it is also released from a number of cell types, where it can function as a paracrine/autocrine signal to regulate cell proliferation, differentiation, survival, and motility. This review discusses the role of S1P in cellular regulation, both at the molecular level and in terms of health and disease. The main biochemical routes for S1P synthesis (sphingosine kinase) and degradation (S1P lyase and S1P phosphatase) are described. The major focus is on the ability of S1P to bind to a novel family of G-protein-coupled receptors (endothelial differentiation gene [EDG]-1, -3, -5, -6, and -8) to elicit signal transduction (via G(q)-, G(i)-, G(12)-, G(13)-, and Rho-dependent routes). Effector pathways regulated by S1P are divergent, such as extracellular signal-regulated kinase, p38 mitogen-activated protein kinase, phospholipases C and D, adenylyl cyclase, and focal adhesion kinase, and occur in multiple cell types, such as immune cells, neurones, smooth muscle, etc. This provides a molecular basis for the ability of S1P to act as a pleiotropic bioactive lipid with an important role in cellular regulation. We also give an account of the expanding role for S1P in health and disease; in particular, with regard to its role in atherosclerosis, angiogenesis, cancer, and inflammation. Finally, we describe future directions for S1P research and novel approaches whereby S1P signalling can be manipulated for therapeutic intervention in disease.

Sphingosine 1-phosphate signalling in mammalian cells

Sphingosine 1-phosphate is formed in cells in response to diverse stimuli, including growth factors, cytokines, G-protein-coupled receptor agonists, antigen, etc. Its production is catalysed by sphingosine kinase, while degradation is either via cleavage to produce palmitaldehyde and phosphoethanolamine or by dephosphorylation. In this review we discuss the most recent advances in our understanding of the role of the enzymes involved in metabolism of this lysolipid. Sphingosine 1-phosphate can also bind to members of the endothelial differentiation gene (EDG) G-protein-coupled receptor family [namely EDG1, EDG3, EDG5 (also known as H218 or AGR16), EDG6 and EDG8] to elicit biological responses. These receptors are coupled differentially via G(i), G(q), G(12/13) and Rho to multiple effector systems, including adenylate cyclase, phospholipases C and D, extracellular-signal-regulated kinase, c-Jun N-terminal kinase, p38 mitogen-activated protein kinase and non-receptor tyrosine kinases. These signalling pathways are linked to transcription factor activation, cytoskeletal proteins, adhesion molecule expression, caspase activities, etc. Therefore sphingosine 1-phosphate can affect diverse biological responses, including mitogenesis, differentiation, migration and apoptosis, via receptor-dependent mechanisms. Additionally, sphingosine 1-phosphate has been proposed to play an intracellular role, for example in Ca(2+) mobilization, activation of non-receptor tyrosine kinases, inhibition of caspases, etc. We review the evidence for both intracellular and extracellular actions, and extensively discuss future approaches that will ultimately resolve the question of dual action. Certainly, sphingosine 1-phosphate will prove to be unique if it elicits both extra- and intra-cellular actions. Finally, we review the evidence that implicates sphingosine 1-phosphate in pathophysiological disease states, such as cancer, angiogenesis and inflammation. Thus there is a need for the development of new therapeutic compounds, such as receptor antagonists. However, identification of the most suitable targets for drug intervention requires a full understanding of the signalling and action profile of this lysosphingolipid. This article describes where the research field is in relation to achieving this aim.

Glycosphingolipid-induced relocation of Lyn and Syk into detergent-resistant membranes results in mast cell activation

Sphingosine, sphingosine-1-phosphate, and the more complex sphingolipid ceramide exert strong immunomodulatory effects on a variety of leukocytes. However, little is known regarding such a potential of glycosphingolipids, a class of sugar derivatives of sphingosine. Here we demonstrate that galactosylsphingosine, one of the smallest representatives of this group, accumulates in the detergent-resistant membranes resulting in the relocation of the tyrosine kinases Lyn and Syk into this compartment. The result of this is an enhanced tyrosine phosphorylation and kinase activity leading to priming and activation of mast cells by conveying a weak yet significant activation of the mitogen-activated protein kinase pathway(s). In comparison to IgE/Ag triggering, galactosylsphingosine stimulates the mitogen-activated protein kinase pathway more rapidly and favors c-Jun NH2-terminal kinase 1 activation over extracellular signal-regulatory kinase 1 and 2. At the transcription factor level, this "ultratransient signaling event" results in an activation of JunD as the predominant AP-1 component. In this respect, the effects of galactosylsphingosine are clearly distinct from the signaling elicited by other sphingolipids without the sugar moiety, such as sphingosine-1-phosphate.

Diverse effects of sphingosine on calcium mobilization and influx in differentiated HL-60 cells

Sphingosine induces a biphasic increase in cytosolic-free Ca(2+)([Ca(2+)](i)) with an initial peak followed by a sustained increase in HL-60 cells differentiated into neutrophil-like cells. The initial peak is not affected by the presence of ethylene glycol bis (beta-aminoethyl ether) N, N, N', N-tetraacetic acid (EGTA) in the buffer and appears to be dependent on conversion of sphingosine to sphingosine -1-phosphate (S1P) by sphingosine kinase, since it is blocked by the presence of N, N-dimethylsphingosine (DMS), which, like sphingosine, causes a sustained increase itself. The sustained increase that is elicited by sphingosine or DMS is abolished by the presence of EGTA in the buffer. The sustained sphingosine-induced Ca(2+)influx does not appear due to Ca(2+)influx through store-operated Ca(2+)(SOC) channels, since the influx is not inhibited by SKF 96365, nor is it augmented by loperamide. In addition, sphingosine and DMS attenuate the Ca(2+)influx through SOC channels that occurs after depletion of intracellular stores by ATP or thapsigargin. Both the initial peak and the sustained increase in [Ca(2+)](i)elicited by sphingosine can be blocked by phorbol 12-myristate 13-acetate (PMA)-elicited activation of protein kinase C. Thus, in HL-60 cells sphingosine causes a mobilization of Ca(2+)from intracellular Ca(2+)stores, which requires conversion to S1P, while both sphingosine and DMS elicit a Ca(2+)influx through an undefined Ca(2+)channel and cause a blockade of SOC channels.

Edg-6 as a putative sphingosine 1-phosphate receptor coupling to Ca(2+) signaling pathway

The endothelial differentiation gene-6 (Edg-6) was recently identified as an orphan G-protein-coupled receptor. Its predicted amino acid sequence is very close to Edg family of receptor proteins whose ligand is supposed to be lysophosphatidic acid (LPA) or lysosphingolipid such as sphingosine 1-phosphate (S1P) and sphingosylphosphorylcholine (SPC). Transfection of the Edg-6 into Chinese hamster ovary (CHO) cells and K562 cells resulted in the appearance of high-affinity [(3)H]S1P binding activity. Among lipids employed, S1P and, even though less potent, SPC, displaced the [(3)H]S1P binding, but LPA was inactive. In Edg-6-transfected CHO cells, an increase in cytosolic Ca(2+) concentration in response to S1P or SPC was clearly enhanced without change in the LPA-induced action as compared with the vector-transfected cells. The enhancement of the Ca(2+) response was associated with a significant accumulation of inositol phosphate, reflecting activation of phospholipase C. Similar enhancement of Ca(2+) response to S1P or SPC was also observed in Edg-6-expressing K562 cells. These lipid-induced actions in CHO cells and K562 cells expressing Edg-6 were markedly suppressed by pertussis toxin treatment. We conclude that Edg-6 is one of S1P or lysosphingolipid receptors that couple to phospholipase C-Ca(2+) system through pertussis toxin-sensitive G-proteins.

Apoptosis in Ca2 + reperfusion injury of cultured astrocytes: roles of reactive oxygen species and NF-kappaB activation

We previously reported that incubation of cultured astrocytes in Ca2 + -containing medium after exposure to Ca2 + -free medium caused Ca2 + influx followed by delayed cell death. Here, we studied the mechanisms underlying the Ca2 + -mediated injury of cultured astrocytes. Our results show that Ca2 + reperfusion injury of astrocytes appears to be mediated by apoptosis, as demonstrated by DNA fragmentation and prevention of death by caspase-3 inhibitors. Paradoxical Ca2 + challenge stimulated rapidly reactive oxygen species (ROS) production. Ca2 + reperfusion injury of astrocytes was influenced by several reagents which modified ROS production. When astrocytes were exposed to hydrogen peroxide (H2O2) for 30 min and then incubated without H2O2 for 1-5 days, cell toxicity including apoptosis was observed. Ca2 + reperfusion injury induced by Ca2 + depletion or H2O2 exposure was blocked by the iron chelator 1, 10-phenanthroline, the NF-kappaB inhibitor pyrrolidinedithiocarbamate and the calcineurin inhibitor FK506. Incubation in normal medium after H2O2 exposure rapidly increased the level of nuclear NF-kappaB p65 subunit, and the effect was blocked by 1,10-phenanthroline, pyrrolidinedithiocarbamate and FK506. These findings indicate that Ca2 + reperfusion-induced apoptosis is mediated at least partly by ROS production and ROS cause NF-kappaB activation in cultured astrocytes.