Activation of cytosolic phospholipase A2 by basic fibroblast growth factor via a p42 mitogen-activated protein kinase-dependent phosphorylation pathway in endothelial cells

Transcriptional regulation of VEGFA expression in T-regulatory cells from breast cancer patients

The initiation of new blood vessel formation (neo-angiogenesis) is one of the primary requirements for the establishment of tumor. As the tumor grows beyond a certain size, a hypoxic-condition arises in the inner core of tumor, triggering the release of chemokines, which attract T-regulatory (Treg) cells in the tumor-site. The presence of FOXP3, a lineage-specific transcription factor, expressing Treg cells in various types of tumor implements immunosuppressive and tumor-promoting strategies. One such strategy is the invitation of endothelial cells for neo-vascularization in the tumor site. Here we report that as the disease progresses, Treg cells from breast cancer patients are capable of secreting high-amount of VEGFA. The VEGFA promoter lacks Treg-specific transcription factor FOXP3 binding site. FOXP3 in association with locus-specific transcription factor STAT3 binds to VEGFA promoter to induce its transcription in Treg cells obtained from breast cancer patients. Treg cell-secreted VEGFA induces neo-angiogenesis from endothelial cells under in-vitro conditions. Targeting Tregs in mice with breast tumor reduces tumor growth as well as the level of neo-angiogenesis in the tumor tissue.

A review of the biological and clinical implications of RAS-MAPK pathway alterations in neuroblastoma

Neuroblastoma is the most common extra-cranial solid tumor in children, representing approximately 8% of all malignant childhood tumors and 15% of pediatric cancer-related deaths. Recent sequencing and transcriptomics studies have demonstrated the RAS-MAPK pathway’s contribution to the development and progression of neuroblastoma. This review compiles up-to-date evidence of this pathway’s involvement in neuroblastoma. We discuss the RAS-MAPK pathway’s general functioning, the clinical implications of its deregulation in neuroblastoma, and current promising therapeutics targeting proteins involved in signaling.

Tumor Development and Angiogenesis in Adult Brain Tumor: Glioblastoma

Angiogenesis is the growth of new capillaries from the preexisting blood vessels. Glioblastoma (GBM) tumors are highly vascularized tumors, and glioma growth depends on the formation of new blood vessels. Angiogenesis is a complex process involving proliferation, migration, and differentiation of vascular endothelial cells (ECs) under the stimulation of specific signals. It is controlled by the balance between its promoting and inhibiting factors. Various angiogenic factors and genes have been identified that stimulate glioma angiogenesis. Therefore, attention has been directed to anti-angiogenesis therapy in which glioma proliferation is inhibited by inhibiting the formation of new tumor vessels using angiogenesis inhibitory factors and drugs. Here, in this review, we highlight and summarize the various molecular mediators that regulate GBM angiogenesis with focus on recent clinical research on the potential of exploiting angiogenic pathways as a strategy in the treatment of GBM patients.

CYP-derived eicosanoids: Implications for rheumatoid arthritis

Today the role of cytochrome P450 metabolites in inflammatory rheumatic disease, such as rheumatoid arthritis (RA) is still poorly understood. In this review we survey the current knowledge on cytochrome P450 metabolites in rheumatoid arthritis. The balance between CYP epoxygenase- and CYP ω- hydroxylase is correlated to the regulation of NF-κB. In RA patients synovial fluid there are higher levels of IL-6, which suppresses activities of CYP enzymes, such as CYP3A, CYP2C19, CYP2C9, and CYP1A2. EETs have anti-inflammatory effects, probably attributed to the PPARγ activation. EETs inhibit bone resorption and osteoclastogenesis, and can be considered as an innovative therapeutic strategy for rheumatoid arthritis. In reference to the CYP ɷ-hydroxylase pathway, 20-HETE is a pro-inflammatory mediator. While there is scarce information on the role of 20-HETE inhibitors and its antagonists in rheumatoid arthritis, the elevation of EETs levels by sEH inhibitors is a promising therapeutic strategy for rheumatoid arthritis patients. In addition, hybrid compounds, such as sEH inhibitors/FLAP inhibitors, or sEHI combined with NSAIDs/COXIBs are also important therapeutic target. However, studies investigating the effects of inflammation and rheumatic disease on CYP-mediated eicosanoid metabolism are necessary. Obtaining a better understanding of the complex role of CYP-derived eicosanoids in inflammatory rheumatic disease, such as rheumatoid arthritis will provide valuable insight for basic and clinical researchers investigation.

Conflicting Roles of 20-HETE in Hypertension and Stroke

Hypertension is the most common modifiable risk factor for stroke, and understanding the underlying mechanisms of hypertension and hypertension-related stroke is crucial. 20-hydroxy-5, 8, 11, 14-eicosatetraenoic acid (20-HETE), which plays an important role in vasoconstriction, autoregulation, endothelial dysfunction, angiogenesis, inflammation, and blood-brain barrier integrity, has been linked to hypertension and stroke. 20-HETE can promote hypertension by potentiating the vascular response to vasoconstrictors; it also can reduce blood pressure by inhibition of sodium transport in the kidney. The production of 20-HETE is elevated after the onset of both ischemic and hemorrhagic strokes; on the other hand, subjects with genetic variants in CYP4F2 and CYP4A11 that reduce 20-HETE production are more susceptible to stroke. This review summarizes recent genetic variants in CYP4F2, and CYP4A11 influencing 20-HETE production and discusses the role of 20-HETE in hypertension and the susceptibility to the onset, progression, and prognosis of ischemic and hemorrhagic strokes.

Andrographolide binds to ATP-binding pocket of VEGFR2 to impede VEGFA-mediated tumor-angiogenesis

Vasculogenesis and angiogenesis are process of formation of blood vessels. Blood vessels are evolved to distribute nutrients and oxygen to distant organs. These vessels are crucial for growth and repair of wounded tissue. During tumor condition there occurs imbalance in the growth of blood vessels which leads to neo-angiogenesis. Neo-angiogenesis is major perpetrator behind the establishment of tumor. Tumor cells secrete pro-angiogenic factor VEGFA which binds to VEGFR2 present over surface of endothelial cells and triggers formation of new blood vessels. To inhibit tumor-angiogenesis, a physiologically-safe small molecule inhibitor was screened which can potentially interact with kinase domain of VEGFR2 and inhibit its activity. Molecular-docking module and biochemical analysis identified andrographolide as one of the best docking molecules that binds to ATP-binding pocket of VEGFR2 and inhibits its kinase activity. Thus, for a more radical approach towards safe VEGFR2 inhibitor, andrographolide was repurposed to inhibit tumor-angiogenesis and reduce tumor burden.

Arachidonic Acid Metabolite as a Novel Therapeutic Target in Breast Cancer Metastasis

Metastatic breast cancer (BC) (also referred to as stage IV) spreads beyond the breast to the bones, lungs, liver, or brain and is a major contributor to the deaths of cancer patients. Interestingly, metastasis is a result of stroma-coordinated hallmarks such as invasion and migration of the tumor cells from the primary niche, regrowth of the invading tumor cells in the distant organs, proliferation, vascularization, and immune suppression. Targeted therapies, when used as monotherapies or combination therapies, have shown limited success in decreasing the established metastatic growth and improving survival. Thus, novel therapeutic targets are warranted to improve the metastasis outcomes. We have been actively investigating the cytochrome P450 4 (CYP4) family of enzymes that can biosynthesize 20-hydroxyeicosatetraenoic acid (20-HETE), an important signaling eicosanoid involved in the regulation of vascular tone and angiogenesis. We have shown that 20-HETE can activate several intracellular protein kinases, pro-inflammatory mediators, and chemokines in cancer. This review article is focused on understanding the role of the arachidonic acid metabolic pathway in BC metastasis with an emphasis on 20-HETE as a novel therapeutic target to decrease BC metastasis. We have discussed all the significant investigational mechanisms and put forward studies showing how 20-HETE can promote angiogenesis and metastasis, and how its inhibition could affect the metastatic niches. Potential adjuvant therapies targeting the tumor microenvironment showing anti-tumor properties against BC and its lung metastasis are discussed at the end. This review will highlight the importance of exploring tumor-inherent and stromal-inherent metabolic pathways in the development of novel therapeutics for treating BC metastasis.

Molecular mechanisms and cell signaling of 20-hydroxyeicosatetraenoic acid in vascular pathophysiology

Cytochrome P450s enzymes catalyze the metabolism of arachidonic acid to epoxyeicosatrienoic acids (EETs), dihydroxyeicosatetraenoic acid and hydroxyeicosatetraeonic acid (HETEs). 20-HETE is a vasoconstrictor that depolarizes vascular smooth muscle cells by blocking K+ channels. EETs serve as endothelial derived hyperpolarizing factors. Inhibition of the formation of 20-HETE impairs the myogenic response and autoregulation of renal and cerebral blood flow. Changes in the formation of EETs and 20-HETE have been reported in hypertension and drugs that target these pathways alter blood pressure in animal models. Sequence variants in CYP4A11 and CYP4F2 that produce 20-HETE, UDP-glucuronosyl transferase involved in the biotransformation of 20-HETE and soluble epoxide hydrolase that inactivates EETs are associated with hypertension in human studies. 20-HETE contributes to the regulation of vascular hypertrophy, restenosis, angiogenesis and inflammation. It also promotes endothelial dysfunction and contributes to cerebral vasospasm and ischemia-reperfusion injury in the brain, kidney and heart. This review will focus on the role of 20-HETE in vascular dysfunction, inflammation, ischemic and hemorrhagic stroke and cardiac and renal ischemia reperfusion injury.

The multiple roles of EG-VEGF/PROK1 in normal and pathological placental angiogenesis

Placentation is associated with several steps of vascular adaptations throughout pregnancy. These vascular changes occur both on the maternal and fetal sides, consisting of maternal uterine spiral arteries remodeling and placental vasculogenesis and angiogenesis, respectively. Placental angiogenesis is a pivotal process for efficient fetomaternal exchanges and placental development. This process is finely controlled throughout pregnancy, and it involves ubiquitous and pregnancy-specific angiogenic factors. In the last decade, endocrine gland derived vascular endothelial growth factor (EG-VEGF), also called prokineticin 1 (PROK1), has emerged as specific placental angiogenic factor that controls many aspects of normal and pathological placental angiogenesis such as recurrent pregnancy loss (RPL), gestational trophoblastic diseases (GTD), fetal growth restriction (FGR), and preeclampsia (PE). This review recapitulates EG-VEGF mediated-angiogenesis within the placenta and at the fetomaternal interface and proposes that its deregulation might contribute to the pathogenesis of several placental diseases including FGR and PE. More importantly this paper argues for EG-VEGF clinical relevance as a potential biomarker of the onset of pregnancy pathologies and discusses its potential usefulness for future therapeutic directions.

Niemann-pick type C2 deficiency in human fibroblasts confers robust and selective activation of prostaglandin E2 biosynthesis

Activated fibroblasts, also known as myofibroblasts, are mediators of several major human pathologies including proliferative fibrotic disorders, invasive tumor growth, rheumatoid arthritis, and atherosclerosis. We previously identified Niemann-Pick type C2 (NPC2) protein as a negative regulator of fibroblast activation (Csepeggi, C., Jiang, M., Kojima, F., Crofford, L. J., and Frolov, A. (2011) J. Biol. Chem. 286, 2078-2087). Here we report that NPC2-deficiency leads to a dramatic up-regulation of the arachidonic acid (AA) metabolic pathway in human fibroblasts. The major enzymes in this pathway, cPLA2 type IVA, COX-2, and mPGES-1, were dramatically up-regulated at both the transcriptional and translational levels. The specific phenotypic changes resulted in a >10-fold increase in the production and secretion of a key modulator of inflammation and immunity, prostaglandin E2. More importantly, AA metabolome profiling by liquid chromatography/tandem mass-spectrometry revealed the very specific nature of prostaglandin E2 up-regulation as the other analyzed AA metabolites derived from the COX-2, cytochrome P450, 5/15-lipoxygenase, and non-enzymatic oxidative pathways were mostly down-regulated. Blocking activity of cPLA2 efficiently suppressed expression of inflammatory cytokines, IL-1β and IL-6, thereby identifying cPLA2 as an important regulator of the inflammatory program in NPC2-null cells. Altogether, these studies highlight NPC2 as a specific regulator of AA metabolism and inflammation that suggests potential for NPC2 protein or its related signaling in the treatment of inflammatory diseases characterized by the presence of activated fibroblasts.

Arachidonic acid stimulates DNA synthesis in brown preadipocytes through the activation of protein kinase C and MAPK

Arachidonic acid (AA) is a polyunsaturated fatty acid that stimulates the proliferation of many cellular types. We studied the mitogenic potential of AA in rat brown preadipocytes in culture and the signaling pathways involved. AA is a potent mitogen which induces 4-fold DNA synthesis in brown preadipocytes. The AA mitogenic effect increases by NE addition. AA also increases the mitogenic action of different growth factor combinations. Other unsaturated and saturated fatty acids do not stimulate DNA synthesis to the same extent as AA. We analyzed the role of PKC and MEK/MAPK signaling pathways. PKC inhibition by bisindolilmaleimide I (BIS) abolishes AA and phorbol ester stimulation of DNA synthesis and reduces the mitogenic activity of different growth factors in brown preadipocytes. Brown preadipocytes in culture express PKC α, δ, ε and ζ isoforms. Pretreatment with high doses of the phorbol ester PDBu, induces downregulation of PKCs ε and δ and reproduces the effect of BIS indicating that AA-dependent induction of DNA synthesis requires PKC activity. AA also activates MEK/MAPK pathway and the inhibition of MEK activity inhibits AA stimulation of DNA synthesis and brown adipocyte proliferation. Inhibition of PKC δ by rottlerin abolishes AA-dependent stimulation of DNA synthesis and MAPK activation, whereas PKC ε inhibition does not produce any effect. In conclusion, our results identify AA as a potent mitogen for brown adipocytes and demonstrate the involvement of the PDBu-sensitive PKC δ isoform and MEK/MAPK pathway in AA-induced proliferation of brown adipocytes. Increased proliferative activity might increase the thermogenic capacity of brown fat.

EET signaling in cancer

Inflammation and angiogenesis in the tumor microenvironment are increasingly implicated in tumorigenesis. Endogenously produced lipid autacoids, locally acting small-molecule mediators, play a central role in inflammation and tissue homeostasis. These lipid mediators, collectively referred to as eicosanoids, have recently been implicated in cancer. Although eicosanoids, including prostaglandins and leukotrienes, are best known as products of arachidonic acid metabolism by cyclooxygenases and lipoxygenases, arachidonic acid is also a substrate for another enzymatic pathway, the cytochrome P450 (CYP) system. This eicosanoid pathway consists of two main branches: ω-hydroxylases which converts arachidonic acid to hydroxyeicosatetraenoic acids (HETEs) and epoxygenases which converts it to four regioisomeric epoxyeicosatrienoic acids (EETs; 5,6-EET, 8,9-EET, 11,12-EET, and 14,15-EET). EETs regulate inflammation and vascular tone. The bioactive EETs are produced predominantly in the endothelium and are mainly metabolized by soluble epoxide hydrolase to less active dihydroxyeicosatrienoic acids. EET signaling was originally studied in conjunction with inflammatory and cardiovascular disease. Arachidonic acid and its metabolites have recently stimulated great interest in cancer biology. To date, most research on eicosanoids in cancer has focused on the COX and LOX pathways. In contrast, the role of cytochrome P450-derived eicosanoids, such as EETs and HETEs, in cancer has received little attention. While CYP epoxygenases are expressed in human cancers and promote human cancer metastasis, the role of EETs (the direct products of CYP epoxygenases) in cancer remains poorly characterized. In this review, the emerging role of EET signaling in angiogenesis, inflammation, and cancer is discussed.

Signaling regulation of fetoplacental angiogenesis

During normal pregnancy, dramatically increased placental blood flow is critical for fetal growth and survival as well as neonatal birth weights and survivability. This increased blood flow results from angiogenesis, vasodilatation, and vascular remodeling. Locally produced growth factors including fibroblast growth factor 2 (FGF2) and vascular endothelial growth factor A (VEGFA) are key regulators of placental endothelial functions including cell proliferation, migration, and vasodilatation. However, the precise signaling mechanisms underlying such regulation in fetoplacental endothelium are less well defined, specifically with regard to the interactions amongst protein kinases (PKs), protein phosphatase, and nitric oxide (NO). Recently, we and other researchers have obtained solid evidence showing that different signaling mechanisms participate in FGF2- and VEGFA-regulated fetoplacental endothelial cell proliferation and migration as well as NO production. This review will briefly summarize currently available data on signaling mediating fetoplacental angiogenesis with a specific emphasis on PKs, ERK1/2, AKT1, and p38 MAPK and protein phosphatases, PPP2 and PPP3.

Cytochrome P450-derived eicosanoids: the neglected pathway in cancer

Endogenously produced lipid autacoids are locally acting small molecule mediators that play a central role in the regulation of inflammation and tissue homeostasis. A well-studied group of autacoids are the products of arachidonic acid metabolism, among which the prostaglandins and leukotrienes are the best known. They are generated by two pathways controlled by the enzyme systems cyclooxygenase and lipoxygenase, respectively. However, arachidonic acid is also substrate for a third enzymatic pathway, the cytochrome P450 (CYP) system. This third eicosanoid pathway consists of two main branches: ω-hydroxylases convert arachidonic acid to hydroxyeicosatetraenoic acids (HETEs) and epoxygenases convert it to epoxyeicosatrienoic acids (EETs). This third CYP pathway was originally studied in conjunction with inflammatory and cardiovascular disease. Arachidonic acid and its metabolites have recently stimulated great interest in cancer biology; but, unlike prostaglandins and leukotrienes the link between cytochome P450 metabolites and cancer has received little attention. In this review, the emerging role in cancer of cytochrome P450 metabolites, notably 20-HETE and EETs, are discussed.

Molecular mediators of angiogenesis

Angiogenesis, or the formation of new blood vessels from the preexisting vasculature, is a key component in numerous physiologic and pathologic responses and has broad impact in many medical and surgical specialties. In this review, we discuss the key cellular steps that lead to the neovascularization of tissues and highlight the main molecular mechanisms and mediators in this process. We include discussions on proteolytic enzymes, cell-matrix interactions, and pertinent cell signaling pathways and end with a survey of the mechanisms that lead to the stabilization and maturation of neovasculatures.

Inhibition of arachidonic acid metabolism and its implication on cell proliferation and tumour-angiogenesis

Arachidonic acid (AA) and its metabolites have recently generated a heightened interest due to growing evidence of their significant role in cancer biology. Thus, inhibitors of the AA cascade, first and foremost COX inhibitors, which have originally been of interest in the treatment of inflammatory conditions and certain types of cardiovascular disease, are now attracting attention as an arsenal against cancer. An increasing number of investigations support their role in cancer chemoprevention, although the precise molecular mechanisms that link levels of AA, and its metabolites, with cancer progression have still to be elucidated. This article provides an overview of the AA cascade and focuses on the roles of its inhibitors and their implication in cancer treatment. In particular, emphasis is placed on the inhibition of cell proliferation and neo-angiogenesis through inhibition of the enzymes COX-2, 5-LOX and CYP450. Downstream effects of inhibition of AA metabolites are analysed and the molecular mechanisms of action of a selected number of inhibitors of catalytic pathways reviewed. Lastly, the benefits of dietary omega-3 fatty acids and their mechanisms of action leading to reduced cancer risk and impeded cancer cell growth are mentioned. Finally, a proposal is put forward, suggesting a novel and integrated approach in viewing the molecular mechanisms and complex interactions responsible for the involvement of AA metabolites in carcinogenesis and the protective effects of omega-3 fatty acids in inflammation and tumour prevention.

Roles of extracellular signal-regulated kinase 1/2 on the suppression of myostatin gene expression induced by basic fibroblast growth factor

Basic fibroblast growth factor (bFGF, FGF-2) has an inhibitory effect on the expression of the myostatin gene in murine C2C12 myoblasts, as shown in our recent investigation. To further verify the regulatory effects of bFGF on the myostatin gene and to better understand its mechanism in skeletal muscle, and to promote clinical applications of bFGF to treat skeletal muscle diseases correlated to muscular dystrophy or AIDS and so on, recombinant human bFGF (rh-bFGF) was added into media and stimulated murine C2C12 myoblasts to investigate the dose-dependent effect of bFGF on suppression of myostatin gene expression and the role of extracellular signal-regulated kinase 1/2 (ERK1/2) in the regulatory mechanism. Simultaneously, complete coding sequence of ovine?8 kDa-bFGF gene was inserted into eukaryotic vector pCMV-neo (originated from pEGFP-N1 vector, from which the EGFP gene has been removed), the recombinant plasmid pCMV-neo-bFGF was harvested and injected into the mouse skeletal muscle of posterior limb. Expression levels of bFGF, myostatin, and ERK1/2 genes in murine C2C12 myoblasts and the skeletal muscle were analyzed by real-time reverse transcription-polymerase chain reaction and Western blotting analysis, respectively. The results showed that bFGF impaired the expression of myostatin gene in a dose-dependent manner in C2C12 cells, with increasing concentration of rh-bFGF, myostatin mRNA declined gradually. In addition, results in skeletal muscle indicated that bFGF also suppressed the expression of the myostatin gene in vivo. Furthermore, we found ERK1/2 participated in the regulatory mechanism of bFGF on the expression of the myostatin gene.

A bactericidal homodimeric phospholipases A2 from Bungarus fasciatus venom

Group IIA secretory phospholipases A(2) (sPLA(2)-II) is generally known to display potent gram-positive bactericidal activity, while group IA sPLA(2) (sPLA(2)-I) reportedly is not. In this work, a novel sPLA(2)-I named BFPA was identified from Bungarus fasciatus venom, and its antimicrobial activity was studied as well. The amino acid sequence of the venomous protein precursor was 145-amino acid in length, and contained a predicted 27-amino acid signal peptide and a 118-amino acid mature protein. Unlike the well-known sPLA(2)-Is, which have 14 half-cysteines forming 7 intramolecular disulfide bridges, BFPA possesses 15 half-cysteines. The additional cysteine might contribute to the formation of an intermolecular disulfide bridge of the homodimeric protein. In the biological activities assays, BFPA displayed the activities of anticoagulation and bactericidal against Escherichia coli and Staphylococcus aureus. This study is the first report about gram-positive bactericidal activity of sPLA(2)-I.

Endothelial cell anergy is mediated by bFGF through the sustained activation of p38-MAPK and NF-kappaB inhibition

Tumors escape from immune surveillance by, among other mechanisms, the down- regulation of endothelial adhesion molecules, such as ICAM-1, and by unresponsiveness to inflammatory signals, a process mediated by angiogenic factors that is called endothelial cell anergy. Here we present the cell biological regulation of these processes. The angiogenic basic fibroblast growth factor (bFGF/FGF-2) was found to inhibit tumor necrosis factor-alpha (TNF-alpha)- induced elevation of ICAM-1, at transcriptional level. Furthermore, we found that bFGF inhibits the TNF-mediated activation of NF-kappaB by blocking phosphorylation and degradation of IkappaBalpha. We also found that bFGF induces hyperphosphorylation of p38 MAPK on endothelial cells, whereas inhibition of such kinase abrogates the effect of bFGF on the TNF-mediated activation of NF-kappaB. Thus, we suggest that bFGF acts as an inhibitor of leukocyte adhesion in tumor vessels by decreasing the ICAM-1 expression through the sustained activation of p38-MAPK and via inhibition of NF-kappaB.

Emerging mechanisms for growth and protection of the vasculature by cytochrome P450-derived products of arachidonic acid and other eicosanoids

Arachidonic acid (AA) is an essential fatty acid that is metabolized by cyclooxygenase (COX), lipoxygenase (LOX) or cytochrome P450 (CYP) enzymes to generate eicosanoids which in turn mediate a number of biological activities including regulation of angiogenesis. While much information on the effects of COX and LOX products is known, the physiological relevance of the CYP-derived products of AA are less well understood. CYP enzymes are highly expressed in the liver and kidney, but have also been detected at lower levels in the brain, heart and vasculature. A number of these enzymes, including members of the CYP 4 family, predominantly catalyze conversion of AA to 20-hydroxyeicosatetraenoic acid (20-HETE) while the CYP epoxygenases generate mainly epoxyeicosatrienoic acids (EETs). This review will focus on the emerging roles of inhibitors of eicosanoid production with emphasis on the CYP pathways, in the regulation of angiogenesis and tumor growth. We also discuss current observations describing the protective effects of EETs for survival of the endothelium.

Group VIA Calcium-independent Phospholipase A2 Mediates Endothelial Cell S Phase Progression

Arachidonic acid and its metabolites have been previously implicated in the regulation of endothelial cell proliferation. Arachidonic acid may be liberated from cellular phospholipids by the action of group VIA calcium-independent phospholipase A2 (iPLA2-VIA). Consequently, we tested the hypothesis that iPLA2-VIA activity is linked to the regulation of endothelial cell proliferation. Inhibition of iPLA2 activity by bromoenol lactone (BEL) was sufficient to entirely block endothelial cell growth. BEL dose-dependently inhibited endothelial cell DNA synthesis in a manner that was reversed upon the exogenous addition of arachidonic acid. DNA synthesis was inhibited by the S-isomer and not by the R-isomer of BEL, demonstrating that endothelial cell proliferation is mediated specifically by iPLA2-VIA. iPLA2-VIA activity was critical to the progression of endothelial cells through S phase and is required for the expression of the cyclin A/cdk2 complex. Thus, inhibition of iPLA2-VIA blocks S phase progression and results in exit from the cell cycle. Inhibition of iPLA2-VIA-mediated endothelial cell proliferation is sufficient to block angiogenic tubule formation in co-culture assays. Consequently, iPLA2-VIA is a novel regulator of endothelial cell S phase progression, cell cycle residence, and angiogenesis.

Hypoxia Enhances Lysophosphatidic Acid Responsiveness in Ovarian Cancer Cells and Lysophosphatidic Acid Induces Ovarian Tumor MetastasisIn vivo

Lysophosphatidic acid (LPA) is elevated in ascites of ovarian cancer patients and stimulates growth and other activities of ovarian cancer cells in vitro. Tissue hypoxia is a critical factor for tumor aggressiveness and metastasis in cancers. We tested whether the ascites of ovarian cancer is hypoxic and whether hypoxia influences the effects of LPA on ovarian cancer cells. We found that ovarian ascitic fluids were hypoxic in vivo. Enhanced cellular responsiveness to LPA, including migration and/or invasion of ovarian cancer cells, was observed under hypoxic conditions. This enhancement could be completely blocked by geldanamycin or a small interfering RNA targeting hypoxia-inducible factor 1 alpha (HIF1 alpha). LPA-induced cell migration required cytosolic phospholipase A(2) (cPLA(2)) and LPA stimulates cPLA(2) phosphorylation in a HIF1 alpha-dependent manner under hypoxia conditions. Furthermore, we show for the first time that exogenous LPA enhances tumor metastasis in an orthotopic ovarian cancer model and HIF alpha expression in tumors. 17-Dimethylaminoethylamino-17-demethoxygeldanamycin (an inhibitor of the heat shock protein 90) effectively blocked LPA-induced tumor metastasis in vivo. Together, our data indicate that hypoxic conditions are likely to be pathologically important for ovarian cancer development. HIF1 alpha plays a critical role in enhancing and/or sensitizing the role of LPA on cell migration and invasion under hypoxic conditions, where cPLA(2) is required for LPA-induced cell migration.

Targeting the signaling pathway of acylation stimulating protein

Acylation stimulating protein (ASP; C3adesArg) stimulates triglyceride synthesis (TGS) and glucose transport in preadipocytes/adipocytes through C5L2, a G-protein-coupled receptor. Here, ASP signaling is compared with insulin in 3T3-L1 cells. ASP stimulation is not Galpha(s) or Galpha(i) mediated (pertussis and cholera toxin insensitive), suggesting G(alphaq) as a candidate. Phospholipase C (PLC) is required, because the Ca(2+) chelator 1,2-bis(o-aminophenoxy) ethane-N,N,N',N'-tetraacetic acid tetra(acetoxymethyl) ester and the PLC inhibitor U73122 decreased ASP stimulation of TGS by 93.1% (P < 0.0.001) and 86.1% (P < 0.004), respectively. Wortmannin and LY294002 blocked ASP effect by 69% (P < 0.001) and 116.1% (P < 0.003), respectively, supporting phosphatidylinositol 3-kinase (PI3K) involvement. ASP induced rapid, transient Akt phosphorylation (maximal, 5 min; basal, 45 min), which was blocked by Akt inhibition, resembling treatment by insulin. Downstream of PI3K, mamalian target of rapaycin (mTOR) is required for insulin but not ASP action. By contrast, both ASP and insulin activate the mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK(1/2)) pathway, with rapid, pronounced increases in ERK(1/2) phosphorylation, effects partially blocked by PD98059 (64.7% and 65.9% inhibition, respectively; P < 0.001). Time-dependent (maximal, 30 min) transient calcium-dependent phospholipase A(2) (cPLA(2))(-Ser505) phosphorylation (by MAPK/ERK(1/2)) was demonstrated by Western blot analysis. ASP signaling involves sequential activation of PI3K and PLC, with downstream activation of protein kinase C, Akt, MAPK/ERK(1/2), and cPLA(2), all of which leads to an effective and prolonged stimulation of TGS.

Oxidized phospholipids as triggers of inflammation in atherosclerosis

Chronic inflammatory diseases including atherosclerosis are major causes of morbidity and mortality worldwide. However, the factors, which trigger processes that determine the outcome of an inflammatory response, are still poorly understood. Accumulating evidence suggests that certain lipid oxidation products, such as oxidized phospholipids (OxPL), may represent endogenously formed factors that are capable of triggering vascular inflammation. This review will address important questions regarding mechanisms involved in acute and chronic inflammation, and discuss the role of OxPL as key players in triggering the inflammatory response in atherosclerosis. Better understanding of how OxPL contribute to vascular inflammation should lead to new strategies in the treatment of chronic inflammatory disorders.

Specific monocyte adhesion to endothelial cells induced by oxidized phospholipids involves activation of cPLA2 and lipoxygenase

Oxidized phospholipids stimulate endothelial cells to bind monocytes, but not neutrophils, an initiating event in atherogenesis. Here, we investigate intracellular signaling events induced by oxidized phospholipids in human umbilical vein endothelial cells (HUVECs) that lead to specific monocyte adhesion. In a static adhesion assay, oxidized 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphorylcholine and one of its components, 1-palmitoyl-2-oxovaleroyl-sn-glycero-3-phosphorylcholine, stimulated HUVECs to bind U937 cells and human peripheral blood monocytes but not HL-60 cells or blood neutrophils. Monocyte adhesion was dependent on protein kinases A and C, extracellular signal-regulated kinase 1/2, p38 mitogen activated protein kinases (MAPKs), and cytosolic phospholipase A(2) (cPLA(2)). Inhibition of 12-lipoxygenase (12-LOX), but not cyclooxygenases, blocked monocyte adhesion, and addition of 12-hydroxyeicosatetraenoic acid (12-HETE) mimicked the effects of oxidized phospholipids. Peroxisome proliferator-activated receptor alpha (PPARalpha) was excluded as a possible target for 12-HETE, because monocyte adhesion was still induced in endothelial cells from PPARalpha null mice. Together, our results suggest that oxidized phospholipids stimulate HUVECs to specifically bind monocytes involving MAPK pathways, which lead to the activation of cPLA(2) and 12-LOX. Further analysis of signaling pathways induced by oxidized phospholipids that lead to specific monocyte adhesion should ultimately lead to the development of novel therapeutic approaches against chronic inflammatory diseases.

Cellular and molecular analyses of vascular tube and lumen formation in zebrafish

Tube and lumen formation are essential steps in forming a functional vasculature. Despite their significance, our understanding of these processes remains limited, especially at the cellular and molecular levels. In this study, we analyze mechanisms of angioblast coalescence in the zebrafish embryonic midline and subsequent vascular tube formation. To facilitate these studies, we generated a transgenic line where EGFP expression is controlled by the zebrafish flk1 promoter. We find that angioblasts migrate as individual cells to form a vascular cord at the midline. This transient structure is stabilized by endothelial cell-cell junctions, and subsequently undergoes lumen formation to form a fully patent vessel. Downregulating the VEGF signaling pathway, while affecting the number of angioblasts, does not appear to affect their migratory behavior. Our studies also indicate that the endoderm, a tissue previously implicated in vascular development, provides a substratum for endothelial cell migration and is involved in regulating the timing of this process, but that it is not essential for the direction of migration. In addition, the endothelial cells in endodermless embryos form properly lumenized vessels, contrary to what has been previously reported in Xenopus and avian embryos. These studies provide the tools and a cellular framework for the investigation of mutations affecting vasculogenesis in zebrafish.

Heat-enhanced production of chitosanase from Streptomyces griseus in the presence of liposome

The effects of heat stress and liposome treatment on the growth of Streptomyces griseus cells and chitosanase production were investigated on the basis of using the designed strategy of a stress-mediated bioprocess. The effective conditions for increasing the interaction between chitosanase and the 1-palmitoyl-2-oleoyl-3-phosphocholine (POPC) liposome under heat stress condition were determined on the basis of the results of circular dichroism (CD) and dielectric dispersion analysis (DDA). Under these effective conditions, S. griseus cells were cultivated for the effective production of chitosanase. The results obtained from both CD spectra and DDA showed that heat stress enhances the interaction of the POPC liposomes and chitosanase. The strongest interaction between them could be obtained in the specific temperature range of 40-45 degrees C. The enhancement of the target chitosanase production was conducted under heat stress at 41 degrees C in the presence and absence of the POPC liposomes. The growth rates of S. griseus cells in the cases of heat (41 degrees C) and heat (41 degrees C)/POPC treatments were respectively 1.2 and 1.4 times higher than that obtained under the control condition. In the heat (41 degrees C) and heat (41 degrees C)/POPC treatments, chitosanase activity increased to 1.8 and 2 times, respectively, higher than that obtained under the control condition. Heat stress and the addition of the POPC liposomes could therefore be utilized to induce the potential functions of bacterial cells for the enhancement of the final target production.

Regulation of noncapacitative calcium entry by arachidonic acid and nitric oxide in endothelial cells

Several peptides, including vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF), activate the release of arachidonic acid (AA) and nitric oxide (NO) in endothelial cells (ECs). Both messengers are involved in EC proliferation and vascular permeability and control calcium homeostasis in different ways. Interestingly, it has been recently suggested that NO acts as a downstream mediator of AA-induced calcium entry in smooth muscle cells and isolated mouse parotid cells. In this paper, we have investigated the complex relationships that link intracellular calcium, AA, and NO in cultured endothelial cells. Using different experimental approaches, mainly simultaneous Ca2+ and NO fluorimetric confocal imaging, we provide evidence for a complex pathway leading to noncapacitative calcium entry (NCCE) in bovine aortic endothelial cells (BAECs). In particular, AA is able to induce NCCE through two different pathways: one dependent on eNOS recruitment and NO release, the other NO-independent. Finally, we show that NO increase is involved in the control of BAEC proliferation.

Role of phospholipase C and diacylglyceride lipase pathway in arachidonic acid release and acetylcholine-induced vascular relaxation in rabbit aorta

ACh stimulates arachidonic acid (AA) release from membrane phospholipids of vascular endothelial cells (ECs). In rabbit aorta, AA is metabolized through the 15-lipoxygenase pathway to form vasodilatory eicosanoids 15-hydroxy-11,12-epoxyeicosatrienoic acid (HEETA) and 11,12,15-trihydroxyeicosatrienoic acid (THETA). AA is released from phosphatidylcholine (PC) and phosphatidylethanolamine (PE) by phospholipase A2 (PLA2), or from phosphatidylinositol (PI) by phospholipase C (PLC) pathway. The diacylglycerol (DAG) lipase can convert DAG into 2-arachidonoylglycerol from which free AA can be released by monoacylglycerol (MAG) lipase or fatty acid amidohydrolase (FAAH). We used specific inhibitors to determine the involvement of the PLC pathway in ACh-induced AA release. In rabbit aortic rings precontracted by phenylephrine, ACh induced relaxation in the presence of indomethacin and N(omega)-nitro-L-arginine (L-NNA). These relaxations were blocked by the PLC inhibitor U-73122, DAG lipase inhibitor RHC-80267, and MAG lipase/FAAH inhibitor URB-532. Cultured rabbit aortic ECs were labeled with [14C]AA and stimulated with methacholine (10(-5) M). Free [14C]AA was released by methacholine. Methacholine decreased the [14C]AA content of PI, DAG, and MAG fractions but not PC or PE fractions. Methacholine-induced release of [14C]AA was blocked by U-73122, RHC-80267, and URB-532 but not by U-73343, an inactive analog of U-73122. The data suggested that ACh activates PLC, DAG lipase, and MAG lipase pathway to release AA from membrane lipids. This pathway is important in regulating vasodilatory eicosanoid synthesis and vascular relaxation in rabbit aorta.

Cytosolic phospholipase A2-alpha mediates endothelial cell proliferation and is inactivated by association with the Golgi apparatus

Arachidonic acid and its metabolites are implicated in regulating endothelial cell proliferation. Cytosolic phospholipase A2-alpha (cPLA2alpha) is responsible for receptor-mediated arachidonic acid evolution. We tested the hypothesis that cPLA2alpha activity is linked to endothelial cell proliferation. The specific cPLA2alpha inhibitor, pyrrolidine-1, inhibited umbilical vein endothelial cell (HUVEC) proliferation in a dose-dependent manner. Exogenous arachidonic acid addition reversed this inhibitory effect. Inhibition of sPLA2 did not affect HUVEC proliferation. The levels of cPLA2alpha did not differ between subconfluent and confluent cultures of cells. However, using fluorescence microscopy we observed a novel, confluence-dependent redistribution of cPLA2alpha to the distal Golgi apparatus in HUVECs. Association of cPLA2alpha with the Golgi was linked to the proliferative status of HUVECs. When associated with the Golgi apparatus, cPLA2alpha activity was seen to be 87% inhibited. Relocation of cPLA2alpha to the cytoplasm and nucleus, and cPLA2alpha enzyme activity were required for cell cycle entry upon mechanical wounding of confluent monolayers. Thus, cPLA2alpha activity and function in controlling endothelial cell proliferation is regulated by reversible association with the Golgi apparatus.

Curcumin Selectively Induces Apoptosis in Deregulated Cyclin D1-expressed Cells at G2 Phase of Cell Cycle in a p53-dependent Manner

Curcumin (diferuloylmethane) is known to induce apoptosis in tumor cells. In asynchronous cultures, with time-lapse video-micrography in combination with quantitative fluorescence microscopy, we have demonstrated that curcumin induces apoptosis at G(2) phase of cell cycle in deregulated cyclin D1-expressed mammary epithelial carcinoma cells, leaving its normal counterpart unaffected. In our search toward delineating the molecular mechanisms behind such differential activities of curcumin, we found that it selectively increases p53 expression at G(2) phase of carcinoma cells and releases cytochrome c from mitochondria, which is an essential requirement for apoptosis. Further experiments using p53-null as well as dominant-negative and wild-type p53-transfected cells have established that curcumin induces apoptosis in carcinoma cells via a p53-dependent pathway. On the other hand, curcumin reversibly inhibits normal mammary epithelial cell cycle progression by down-regulating cyclin D1 expression and blocking its association with Cdk4/Cdk6 as well as by inhibiting phosphorylation and inactivation of retinoblastoma protein. In addition, curcumin significantly up-regulates cell cycle inhibitory protein (p21Waf-1) in normal cells and arrests them in G(0) phase of cell cycle. Therefore, these cells escape from curcumin-induced apoptosis at G(2) phase. Interestingly, these processes remain unaffected by curcumin in carcinoma cells where cyclin D1 expression is high. Similarly, in ectopically overexpressed system, curcumin cannot down-regulate cyclin D1 and thus block cell cycle progression. Hence, these cells progress into G(2) phase and undergo apoptosis. These observations together suggest that curcumin may have a possible therapeutic potential in breast cancer patients.

Inhibitors of cytochrome P450 4A suppress angiogenic responses

Cytochrome P450 enzymes of the 4A family (CYP4A) convert arachidonic acid to 20-hydroxyeicosatetraenoic acid (20-HETE) in blood vessels of several vascular beds. The present study examined the effects of inhibiting the formation of 20-HETE with N-hydroxy-N'-(4-butyl-2-methylphenol) formamidine (HET0016) on the mitogenic response of vascular endothelial growth factor (VEGF) in human umbilical vein endothelial cells (HUVECs) in vitro, and on growth factor-induced angiogenesis in the cornea of rats in vivo. HET0016 (10 micromol/L and 20 microg, respectively) abolished the mitogenic response to VEGF in HUVECs and the angiogenic response to VEGF, basic fibroblast growth factor, and epidermal growth factor in vivo by 80 to 90% (P < 0.001). Dibromododecenyl methylsulfonimide (DDMS), a structurally and mechanistically different inhibitor of 20-HETE synthesis, also abolished angiogenic responses when tested with VEGF. Additionally, administration of the stable 20-HETE agonist, 20-hydroxyeicosa-6(Z) 15(Z)-dienoic acid (WIT003) induced mitogenesis in HUVECs and angiogenesis in the rat cornea in vivo. We studied the ability of HET0016 to alter the angiogenic response in the rat cornea to human glioblastoma cancer cells (U251). When administered locally into the cornea, HET0016 (20 microg) reduced the angiogenic response to U251 cancer cells by 70%. These results suggest that a product of CYP4A product, possibly 20-HETE, plays a critical role in the regulation of angiogenesis and may provide a useful target for reduction of pathological angiogenesis.

Vascular endothelial growth factor (VEGF)-A165-induced prostacyclin synthesis requires the activation of VEGF receptor-1 and -2 heterodimer

We previously reported that vascular endothelial growth factor (VEGF)-A(165) inflammatory effect is mediated by acute platelet-activating factor synthesis from endothelial cells upon the activation of VEGF receptor-2 (VEGFR-2) and its coreceptor, neuropilin-1 (NRP-1). In addition, VEGF-A(165) promotes the release of other endothelial mediators including nitric oxide and prostacyclin (PGI(2)). However, it is unknown whether VEGF-A(165) is mediating PGI(2) synthesis through VEGF receptor-1 (VEGFR-1) and/or VEGF receptor-2 (VEGFR-2) activation and whether the coreceptor NRP-1 potentiates VEGF-A(165) activity. In this study, PGI(2) synthesis in bovine aortic endothelial cells (BAEC) was assessed by quantifying its stable metabolite (6-keto prostaglandin F(1alpha), 6-keto PGF(1alpha)) by enzyme-linked immunosorbent assay. Treatment of BAEC with VEGF analogs, VEGF-A(165) (VEGFR-1, VEGFR-2 and NRP-1 agonist) and VEGF-A(121) (VEGFR-1 and VEGFR-2 agonist) (up to 10(-9) m), increased PGI(2) synthesis by 70- and 40-fold within 15 min. Treatment with VEGFR-1 (placental growth factor and VEGF-B) or VEGFR-2 (VEGF-C) agonist did not increase PGI(2) synthesis. The combination of VEGFR-1 and VEGFR-2 agonists did not increase PGI(2) release. Pretreatment with a VEGFR-2 inhibitor abrogated PGI(2) release mediated by VEGF-A(165) and VEGF-A(121), and pretreatment of BAEC with antisense oligomers targeting VEGFR-1 or VEGFR-2 mRNA reduced PGI(2) synthesis mediated by VEGF-A(165) and VEGF-A(121) up to 79%. In summary, our data demonstrate that the activation of VEGFR-1 and VEGFR-2 heterodimer (VEGFR-1/R-2) is essential for PGI(2) synthesis mediated by VEGF-A(165) and VEGF-A(121), which cannot be reproduced by the parallel activation of VEGFR-1 and VEGFR-2 homodimers with corresponding agonists. In addition, the binding of VEGF-A(165) to NRP-1 potentiates its capacity to promote PGI(2) synthesis.

The transcriptional response to Raf activation is almost completely dependent on Mitogen-activated Protein Kinase Kinase activity and shows a major autocrine component

The Raf protein kinases are major effectors of Ras GTPases and key components of the transcriptional response to serum factors, acting at least in part through the extracellular signal-regulated kinase/mitogen-activated protein kinase pathway. It has recently been suggested that Raf also may trigger other as yet uncharacterized signaling pathways. Here, we have used cDNA microarrays to dissect changes in gene expression induced by activation of inducible c-Raf-1 constructs in human mammary epithelial and ovarian epithelial cells. The majority of Raf-induced transcriptional responses are shown to be blocked by pharmacological inhibition of the Raf substrate mitogen-activated protein kinase kinase, indicating that potential mitogen-activated protein kinase kinase-independent Raf signaling pathways have no significant influence on gene expression. In addition, we used epidermal growth factor receptor inhibitory drugs to address the contribution of autocrine signaling by Raf-induced EGF family proteins to the Raf transcriptional response. At least one-half of the transcription induced by Raf activation requires epidermal growth factor (EGF) receptor function The EGF receptor-independent component of the Raf transcriptional response is entirely up-regulation of gene expression, whereas the EGF receptor-dependent component is an equal mixture of up- and down-regulation. The use of transcriptional profiling in this way allows detailed analysis of the architecture of signaling pathways to be undertaken.

Stimulation-dependent recruitment of cytosolic phospholipase A2-alpha to EA.hy.926 endothelial cell membranes leads to calcium-independent association

Cytosolic phospholipase A2-alpha (cPLA2-alpha) is a calcium-activated enzyme involved in agonist-induced arachidonic acid release. In endothelial cells, free arachidonic acid is predominantly converted into prostacyclin, a potent vasodilator and inhibitor of platelet activation. As the rate-limiting step in prostacyclin production is the generation of free arachidonic acid by cPLA2-alpha, this enzyme has become an attractive pharmacological target and the focus of many studies. Following stimulation with calcium-mobilizing agonists, cPLA2-alpha translocates to intracellular phospholipid membranes via its C2 domain. In this study, the calcium-induced association of cPLA2-alpha with EA.hy.926 endothelial cell membranes was investigated. Subcellular fractionation and immunofluorescence studies showed that following stimulation with histamine, thrombin or the calcium ionophore A23187, cPLA2-alpha relocated to intracellular membranes. Treatment of A23187-stimulated cells with EGTA or BAPTA-AM demonstrated that a substantial pool of cPLA2-alpha remained associated with membrane fractions in a calcium-independent manner. Furthermore, immunofluorescence microscopy studies revealed that cells stimulated for periods of greater than 10 min showed a high proportion of calcium-independent membrane-associated cPLA2-alpha. Calcium-independent membrane association of cPLA2-alpha was not due to hydrophobic or cytoskeletal interactions. Finally, the recombinant C2 domain of cPLA2-alpha exhibited calcium-independent membrane binding to membranes isolated from A23187-stimulated cells but not those isolated from nonstimulated cells. These findings suggest that novel mechanisms involving accessory proteins at the target membrane play a role in the regulation of cPLA2-alpha. Such regulatory associations could enable the cell to discriminate between the varying levels of cytosolic calcium induced by different stimuli.

Calcium and Its Role in the Nuclear Translocation and Activation of Cytosolic Phospholipase A2in Cells Rendered Sensitive to TNF-Induced Apoptosis by Cycloheximide

In these experiments, we investigated the role of calcium as a second messenger in the apoptotic activation of cytosolic phospholipase A(2) (cPLA(2)). As our model, we used a murine fibroblast cell line (C3HA) that was induced to undergo apoptosis by a combination of TNF and cycloheximide. Using fura 2 Ca(2+) imaging, we found strong evidence for an intracellular calcium response after 1 h of treatment, which correlated with the onset of phosphatidylserine externalization, but preceded effector procaspase processing by several hours. The response was strongest in the perinuclear region, where mean levels rose 83% (144 +/- 14 nM in untreated cells vs 264 +/- 39 nM in treated), while cells displaying morphological evidence of apoptosis had the highest levels of calcium (250-1000 nM). Verapamil blocked this response, indicating an extracellular source for the calcium. Fluorescence microscopy revealed a pattern of nuclear translocation of cPLA(2) during apoptosis, which was also blocked by verapamil, indicating an important role for calcium in this process. In addition, we found that verapamil prevented the release of [(3)H]arachidonic acid from C3HA cells induced to undergo apoptosis by the chemotherapeutic agents vinblastine, melphalan, and cis-platinum. Together, these data suggest that calcium is important for cPLA(2) activation by diverse apoptotic stimuli.

Cyclic stretch-induced cPLA2 mediates ERK 1/2 signaling in rabbit proximal tubule cells

BACKGROUND

Recent evidence from this laboratory have demonstrated a critical role of phospholipase A2 (PLA2) and arachidonic acid in angiotensin II type 2 (AT2) receptor-mediated kinase activation in renal epithelium independent of phosphoinositide- specific phospholipase C (PLC) and without the necessity of eicosanoid biosynthesis. In the present study, we investigated whether cyclic stress phosphorylates and activates the mitogen-activated protein kinase (MAPK) pathway and whether PLA2 activation mediates mechanotransduction in renal epithelial cells. The rational for studying kidney epithelial cells relates to their similarity to podocytes, which undergo mechanical stretch related to changes in intraglomerular pressure.

METHODS

To produce strain or stretch, primary cultures of rabbit proximal tubular cell cells are grown in tissue culture wells having a collagen-coated Silastic deformable membrane bottoms and applying vacuum to the well to generate alternating cycles of stretch and relaxation (30 cycles/min).

RESULTS

We found that cyclic stretching of rabbit proximal tubular cells caused a time- and intensity-dependent activation of extracellular signal-regulated kinases 1 and 2 (ERK 1/2) in proximal tubular cells as detected by its phosphorylation. In addition, mechanical stretch induced PLA2 activation and a subsequent rapid release of arachidonic acid. Inhibition of PLA2 by mepacrine and methyl arachidonyl fluorophosphonate ketone (AACOCF3) attenuated both arachidonic acid release and ERK 1/2 activation by cyclic stretch, supporting the importance of PLA2 as a mediator of mechanotransduction in renal proximal tubular cells. A requirement for extracellular Ca2+ and stretch-activated Ca2+ channels was also documented. Complete inhibition of ERK 1/2 by PD98059, a MAPK kinase (MEK) inhibitor, did not suppress stretch- induced PLA2 activation and arachidonic acid release, suggesting the later events were upstream of ERK 1/2. Cyclic stretch also caused rapid phosphorylation of the EGF receptor kinase and c-Src. Furthermore, arachidonic acid itself induced time- and dose-dependent phosphorylation of c-Src. In addition, the c-Src inhibitor PP2 and selective EGF receptor kinase inhibitor AG1478 attenuated both ERK 1/2 and EGF receptor phosphorylation by cyclic stretch.

CONCLUSION

PLA2 dependence for ERK 1/2 activation in response to cyclic stretch in proximal tubular epithelial cells was established in this report. In addition, these findings indicate cyclic stretch increased the tyrosine phosphorylation of the EGF receptor and c-Src and that c-Src acts upstream of the EGF receptor to mediate its phosphorylation, whereby both are critical for stretch- induced ERK 1/2 activation in rabbit proximal tubular cells. These observations documents for the first time a mechanism of mechanical stretch-induced kinase activation mediated by stretch activated Ca2+ channels and PLA2-dependent release of arachidonic acid.

Control of endothelial cell proliferation by calcium influx and arachidonic acid metabolism: A pharmacological approach

In physiological conditions, endothelial cell proliferation is strictly controlled by several growth factors, among which bFGF and VEGF are the most effective. Both bind to specific tyrosine kinase receptors and trigger intracellular signal cascades. In particular, bFGF stimulates the release of arachidonic acid (AA) and its metabolites in many types of endothelial cells in culture. In bovine aortic endothelial cells, it has been suggested that AA is released by the recruitment of cytosolic phospholipase A2 (cPLA2). AA metabolites are involved in the control of both endothelial cell motility (mostly via the cyclooxygenase pathway) and proliferation (via the lipoxygenase (LOX) cascade). On the other hand, evidence has been provided for a proliferative role of AA-induced calcium influx. By using a pharmacological approach, we have tried to elucidate the contribution to bovine aortic endothelial proliferation of the different pathways leading to production of AA and its metabolites. Two main informations were obtained by our experiments: first, AA release is not entirely due to cPLA2 involvement, but also to DAG lipase recruitment; second, cyclooxygenase derivatives play a role in the control of cell proliferation, and not only of motility. Moreover, by combining proliferation assays and single cell calcium measurements, we show that the blocking effect of carboxyamido-triazole (CAI), an inhibitor of tumor growth and angiogenesis acting on calcium influx-dependent pathways, including AA metabolism, is at least in part due to a direct effect on AA-induced calcium influx.

Mechanisms involved in the stimulation of prostacyclin synthesis by human lymphocytes in human umbilical vein endothelial cells

1 Endothelial cells play an important role in the modulation of vascular tone because of their ability to produce vasoactive substances such as prostacyclin (PGI(2)). Cell-cell contact between human umbilical vein endothelial cells (HUVEC) and peripheral blood lymphocytes has been shown to stimulate endothelial PGI(2) synthesis by increasing free arachidonic acid availability through endothelial cytosolic phospholipase A2 (cPLA(2)) activation. In this study, we sought to determine whether phospholipase C (PLC) and D (PLD) activation also contributes, besides cPLA(2), to the lymphocyte-induced PGI(2) synthesis in HUVEC, and to delineate further the potential mechanisms of cPLA(2) activation triggered by the interaction of HUVEC with lymphocytes. 2 Pretreatment of endothelial cells with the PI-PLC inhibitor U-73122 before the coincubation with lymphocytes markedly inhibited the PGI(2) output whereas the diacylglycerol (DAG) lipase inhibitor RHC 80267 and ethanol had no effect. These results suggest that PLC may be involved through inositol trisphosphate generation and calcium mobilization, and that neither DAG nor phosphatidic acid (PtdOH) was used as sources of arachidonic acid. 3 The stimulated PGI(2) synthesis was protein kinase C (PKC)-independent but strongly inhibited by the mitogen-activated protein kinase kinase (MEK) inhibitors PD98059 and U-0126 and by the Src kinase inhibitor PP1. 4 Immunoblot experiments showed an increased phosphorylation of the extracellular signal-regulated kinases 1/2 (ERK1/2) upon lymphocyte addition till 4 h coincubation. Phosphorylation was markedly inhibited by U-0126 and PP1 addition. 5 Collectively, these results suggest that the signaling cascade triggered by lymphocytes in endothelial cells involves an Src kinase/ERK1/2 pathway leading to endothelial cPLA(2) activation.

Inhibition of the MEK/ERK pathway has no effect on agonist-induced aggregation of human platelets

The activation of human platelets by a variety of agonists is accompanied by the phosphorylation of the extracellular signal-regulated kinase (ERK) isoforms of mitogen-activated protein (MAP) kinases. However, the role(s) of, and the substrate(s) for, these enzymes in platelet function remain unclear. Studies on ERKs in platelets have relied on pharmacological tools, including an inhibitor of ERK activation, U0126 [1,4-diamino-2,3-dicyano-1,4-bis(2-aminophenylthio)butadiene]. In the present study, the effects of U0126 and its "inactive" analogue, U0125 [1,4-diamino-2,3-dicyano-1,4-bis(phenylthio)butadiene], on human platelet aggregation and MAP kinase activity were examined. Several agonists with a variety of signaling pathways were studied including thrombin, a thromboxane analogue, arachidonic acid, collagen, calcium ionophores, and the phorbol ester phorbol myristate acetate (PMA). U0126, at concentrations consistent with inhibition of the isolated enzyme, inhibited ERK phosphorylation, and therefore MEK activation, in response to each agonist. Under such conditions, U0126 did not affect the phosphorylation of a second MAP kinase, p38(MAPK); however, platelet aggregation was also unaffected. Higher concentrations of U0126, and of U0125, inhibited platelet aggregation in response to collagen and PMA with no effect on that induced by the other agonists. These results dissociate ERK activation from platelet aggregation, suggesting an alternative role for ERKs in platelet function. In addition, the effects of higher concentrations of U0126 are likely due to an action on protein kinase C, likely unrelated to ERK inhibition, suggesting that the inhibitor concentration is crucial to the interpretation of such studies.

Possible mechanisms underlying pregnancy-induced changes in uterine artery endothelial function

The last 10 years has seen a dramatic increase in our understanding of the mechanisms underlying the pregnancy-specific adaptation in cardiovascular function in general and the dramatic changes that occur in uterine artery endothelium in particular to support the growing fetus. The importance of these changes is clear from a number of studies linking restriction of uterine blood flow (UBF) and/or endothelial dysfunction and clinical conditions such as intrauterine growth retardation (IUGR) and/or preeclampsia in both humans and animal models; these topics are covered only briefly here. The recent developments that prompts this review are twofold. The first is advances in an understanding of the cell signaling processes that regulate endothelial nitric oxide synthase (eNOS) in particular (Govers R and Rabelink TJ. Am J Physiol Renal Physiol 280: F193-F206, 2001). The second is the emerging picture that uterine artery (UA) endothelial cell production of nitric oxide (NO) as well as prostacyclin (PGI2) may be as much a consequence of cellular reprogramming at the level of cell signaling as due to tonic stimuli inducing changes in the level of expression of eNOS or the enzymes of the PGI2 biosynthetic pathway (cPLA2, COX-1, PGIS). In reviewing just how we came to this conclusion and outlining the implications of such a finding, we draw mostly on data from ovine or human studies, with reference to other species only where directly relevant.

Role of cyclooxygenase 2, p38 and p42/44 MAPK in the secretion of prostacyclin induced by epidermal growth factor, endothelin-1 and angiotensin II in rat ventricular cardiomyocytes

We studied the respective roles of cyclooxygenases (COX) isoforms as well as the p38 and p42/44 MAP kinase cascades in angiotensin II (AngII)-, endothelin-1 (ET-1)- and epidermal growth factor (EGF)-induced prostacyclin (PGI(2)) secretion in neonatal rat ventricular cardiomyocytes. Exposure of these cells for 1 h to 100 nM AngII, ET-1 or EGF resulted in an increase in prostacyclin formation which was abolished by the COX-2 specific inhibitor NS-398 (1 microM), while the COX-1 inhibitor valeryl salicylate (5 microM) had no effect. Agonist-induced prostacyclin secretion was also abolished in the presence of cycloheximide (10 microg/ml), indicating that newly synthesized proteins are necessary for this response. In this context, the COX-2 protein amount was significantly increased following 1 h incubation of cardiomyocytes, with AngII, ET-1 and EGF. These results indicate that in cardiomyocytes AngII, ET-1 and EGF induce both the synthesis and the activity of COX-2. Investigating the role of MAPK in the stimulation of prostacyclin induced by these three agonists, we found that both the p42/44 MAPK inhibitor PD 98059 (50 microM) and the p38 MAPK blocker SB 203580 (5 microM) prevented agonist-induced PGI(2) secretion without affecting COX-2 activity or synthesis. Our results show that p42/44 and p38 MAPK activation is at the basis of AngII-, ET-1- and EGF-induced prostacyclin secretion in cardiomyocytes. They further suggest that these MAPK act on a target(s) located upstream of COX-2.

Nuclear localisation of cytosolic phospholipase A2-alpha in the EA.hy.926 human endothelial cell line is proliferation dependent and modulated by phosphorylation

Cytosolic phospholipase A(2)-alpha (cPLA(2)-alpha) is a calcium-sensitive enzyme involved in receptor-mediated eicosanoid production. In resting cells, cPLA(2)-alpha is present in the cytosol and nucleus and translocates to membranes via its calcium-dependent lipid-binding (CaLB) domain following stimulation. cPLA(2)-alpha is also regulated by phosphorylation on several residues, which results in enhanced arachidonic acid release. Little is known about the factors controlling the nuclear localisation of cPLA(2)-alpha. Here the nuclear localisation of cPLA(2)-alpha in the EA.hy.926 human endothelial cell line was investigated. Nuclear localisation was dependent on proliferation, with subconfluent cells containing higher levels of nuclear cPLA(2)-alpha than contact-inhibited confluent or serum-starved cells. The broad-range protein kinase inhibitor staurosporine caused a decrease in the nuclear level of cPLA(2)-alpha, whereas the protein phosphatase inhibitor okadaic acid increased the level of nuclear cPLA(2)-alpha. Using inhibitors for specific mitogen-activated protein (MAP) kinases, both p42/44(MAPK) and p38(MAPK) were shown to be important in modulating nuclear localisation. Finally, inhibition of nuclear import and export using Agaricus bisporus lectin and leptomycin B, respectively, demonstrated that cPLA(2)-alpha contains functional nuclear localisation and export signals. Thus we have identified a novel mode of regulation of cPLA(2)-alpha. This, together with the increasing body of evidence supporting the role of nuclear lipid second messengers in gene expression and proliferation, may have important implications for controlling the growth of endothelial cells in angiogenesis and tumour progression.

Epidermal growth factor induces p11 gene and protein expression and down-regulates calcium ionophore-induced arachidonic acid release in human epithelial cells

p11, a member of the S-100 family of proteins, is the cellular ligand of annexin II and also interacts with the C-terminal region of cytosolic phospholipase A(2) (cPLA(2)), inhibiting cPLA(2) activity and arachidonic acid (AA) release. It has been reported that epidermal growth factor (EGF) induces cPLA(2) activation or cPLA(2) expression and subsequent AA release. It was of interest to study the effect of EGF on p11 production and on AA release in human epithelial cells (HeLa). EGF (20 ng/ml) treatment of HeLa cells increased the cellular p11 protein and the steady-state levels of p11 mRNA in a time- and dose-dependent manner but did not affect cPLA(2) protein expression over a 4-48-h incubation time. Transient transfection experiments of a reporter gene construct containing 1498 bp of the 5'-flanking region of p11 promoter demonstrated that EGF induced p11 gene expression at the transcriptional level. EGF caused a rapid phosphorylation of p44/42 and p38 kinases with a maximum level at 10 min. AG 1478 (EGF receptor tyrosine kinase inhibitor), PD 98059 (ERK1/2 inhibitor), and SB 203580 (p38 inhibitor) significantly inhibited EGF-induced p11 expression. EGF-induced AA release was significantly suppressed by AG 1478, PD 98059, SB 203580, and methyl arachidonyl fluorophosphate (a specific cPLA(2) inhibitor). Methyl arachidonyl fluorophosphate (50 microm) also significantly inhibited EGF-induced p11 expression, demonstrating that the activation of cPLA(2) may have a role in the EGF-induced p11 expression. Immunoprecipitation experiments showed that EGF induced increased p11 binding to cPLA(2) in a time- and dose-dependent manner. EGF treatment for 30 min increased -induced AA release, whereas EGF treatment for 24 h inhibited -induced AA release. These results suggest that EGF treatment increased p11 bound to cPLA(2) may lead to the late suppression of AA release induced by EGF.