Elevated levels of cAMP inhibit protein kinase C--independent mechanisms of endothelial platelet-derived growth factor-B chain and intercellular adhesion molecule-1 gene induction by lysophosphatidylcholine

Menthol Increases Bendiocarb Efficacy Through Activation of Octopamine Receptors and Protein Kinase A

Great effort is put into seeking a new and effective strategies to control insect pests. One of them is to combine natural products with chemical insecticides to increase their effectiveness. In the study presented, menthol which is an essential oil component was evaluated on its ability to increase the efficiency of bendiocarb, carbamate insecticide. A multi-approach study was conducted using biochemical method (to measure acetylcholinesterase enzyme activity), electrophysiological technique (microelectrode recordings in DUM neurons in situ), and confocal microscopy (for calcium imaging). In the electrophysiological experiments, menthol caused hyperpolarization, which was blocked by an octopamine receptor antagonist (phentolamine) and an inhibitor of protein kinase A (H-89). It also raised the intracellular calcium level. The effect of bendiocarb was potentiated by menthol and this phenomenon was abolished by phentolamine and H-89 but not by protein kinase C inhibitor (bisindolylmaleimide IX). The results indicate that menthol increases carbamate insecticide efficiency by acting on octopamine receptors and triggering protein kinase A phosphorylation pathway.

Luteolin suppresses inflammation through inhibiting cAMP-phosphodiesterases activity and expression of adhesion molecules in microvascular endothelial cells

Luteolin, an anti-inflammatory ingredient found in the Chinese herb Folium perillae, can inhibit not only the cyclic adenosine monophosphate (cAMP)-phosphodiesterases (PDEs) activity of neutrophils, but also the expression of lymphocyte function-associated antigen-1 in neutrophils, both of which result in a decrease in the adhesion between neutrophils and microvascular endothelial cells. However, the effect of luteolin on the cAMP-PDEs activity and expression of adhesion molecules in endothelial cells are not clear. In the present study, primary rat pulmonary microvascular endothelial cells and a lipopolysaccharide-induced rat acute pneumonia model were used to explore the role of luteolin on cAMP-PDEs activity, expression of adhesion molecules, and leukocyte infiltration. We demonstrate that rat pulmonary microvascular endothelial cells expressed high levels of cAMP-PDEs, specifically PDE4, and further luteolin exhibited dose-dependent inhibition on the activity of cAMP-PDEs or PDE4 in endothelial cells. Luteolin also had a significant inhibitory effect on the expression of vascular cell adhesion molecule (VCAM)-1, but not intracellular cell adhesion molecule (ICAM)-1 in microvascular endothelial cells. Further, we show that luteolin decreased the levels of soluble ICAM-1 (sICAM-1), but not soluble E-selectin in the serum of rats subjected to acute pneumonia. We also show that luteolin treatment decreased the wet/dry weight ratio of lung tissue and reduced the total number of serum leukocytes in a dose-dependent manner in a rat acute pneumonia model. In conclusion, these results demonstrate that luteolin suppresses inflammation, at least in part, through inhibiting both cAMP-PDEs or PDE4 activity and the expression of VCAM-1 (in vitro) and sICAM-1 (in vivo) in endothelial cells.

Lysophosphatidylcholine induces glial cell activation: role of rho kinase

Lysophosphatidylcholine (LPC), a major phospholipid component of atherogenic oxidized LDL, is implicated in atherosclerosis and, recently, in neurodegenerative diseases. We investigated the immunomodulatory functions of LPC in the central nervous system (CNS) using both an in vivo rat model, and in vitro culture systems of human primary astrocytes and a microglia cell line, HMO6. Compared with PBS injection, 20 nmol LPC-injection into the rat striatum increased astrocyte and microglial accumulation and elevated iNOS expression; concomitantly a time-dependent decrease in number of neurons was exhibited. In vitro studies on astrocytes and HMO6 cells showed that LPC increased the gene expression of proinflammatory factors IL-1beta, COX-2, and GM-CSF. LPC also induced chemotactic responses in HMO6 cells. Inhibition of rho kinase by fasudil, Y27632, or expressing a dominant negative form of rho kinase inhibited the LPC-induced IL-1beta mRNA expression in both astrocytes and HMO6. Moreover, intraperitoneal fasudil injection inhibited the LPC-induced microglial accumulation and iNOS expression and also was effective in protecting against neuronal loss. Silencing G2A, a specific receptor for LPC, inhibited proinflammatory gene expression and HMO6 migration. Overall, our results indicate that LPC induced considerable neuroinflammatory reactivity in glia mediated by rho kinase-dependent pathways with inhibition of these pathways conferring significant extents of neuroprotection.

Effect of pulmonary surfactant on TNF-α-activated endothelial cells and neutrophil adhesion in vitro

Pulmonary surfactant given to infants and adults with respiratory failure is metabolized and recycled to a large extent. A small proportion also enters the circulation in cases of increased permeability of the alveolar-capillary membrane. We therefore investigated whether exogenous surfactants such as a natural bovine (natSF) or a synthetic (synSF) preparation had an impact on inflammatory conditions involving the adhesion of neutrophils to endothelial cells. Human umbilical cord vein endothelial cells (HUVEC) were plated on coverslips until confluence, activated by tumor necrosis factor-alpha and incubated with or without surfactant in the media. Human neutrophils passed the HUVEC layer in a flow chamber and interactions were visualized using a video microscope. To test if surfactant affected the expression of cell adhesion molecules, RT-PCR analyses were performed for E-selectin, vascular cell adhesion molecule 1 (VCAM-1) and intercellular adhesion molecule 1 (ICAM-1). Using concentrations between 50 and 300 microg/ml of surfactant in the pre-incubation media the number of adherent neutrophils increased by 10-20% at the higher concentration of the natSF (*P < 0.05) whereas the synSF had no effect. Increased neutrophil adhesion was associated with a significant up-regulation of mRNA levels for E-selectin and VCAM-1; mRNA levels for ICAM-1, however, were not affected by the presence of surfactant. These observations indicate that natSF but not synSF might have pro-inflammatory effects when higher amounts of the exogenous dose reach the circulation. This might be explained by different fatty acid profiles, e.g. the presence of arachidonic acid in the natSF or higher concentrations of surfactant-associated protein-C in the synSF.

Different mechanisms of adhesion molecule expression in human dermal microvascular endothelial cells by xanthoma tissue-mediated and copper-mediated oxidized low density lipoproteins

BACKGROUND

Oxidation of low density lipoprotein (LDL) has been implicated in infiltration of foam cells derived from circulating monocytes. Monocyte adhesion to endothelial cells and migration into dermis are essential steps for infiltration of foam cells.

OBJECTIVE

We investigated the role of adhesion molecules contributing to the process of monocyte adhesion to human dermal microvascular endothelial cells (HDMEC). Special attention was paid to the signal transduction for adhesion molecule expression induced by two distinct types of oxidized LDL.

METHODS

HDMEC were incubated with xanthoma tissue-modified LDL (x-LDL), a model of extravasated LDL oxidized in xanthoma lesions, or Cu(2+)-treated LDL (Cu-LDL), a model of oxidized LDL. Adhesion of U937 cells, a human monocytic leukemia cell line, to HDMEC and expression of endothelial cell adhesion molecules on HDMEC were examined. Signal transduction pathways for the adhesion molecule expression were evaluated by employing specific inhibitors.

RESULTS

x-LDL induced adhesion of U937 cells to HDMEC through vascular cell adhesion molecule-1 (VCAM-1) and E-selectin by activating tyrosine kinase pathway. Cu-LDL up-regulated the adhesion through not only VCAM-1 and E-selectin but also intercellular cell adhesion molecule-1 (ICAM-1) by activating G(i) protein pathway.

CONCLUSION

Extravasated and oxidized LDL in xanthoma lesions contributes to foam cell recruitment by activating tyrosine kinase pathway and inducing adhesion of monocytes to HDMEC through VCAM-1 and E-selectin. Cu-LDL, on the other hand, activates G(i) protein pathway and induces the adhesion through ICAM-1, VCAM-1 and E-selectin.

Lysophosphatidylcholine alters vascular tone in rat aorta by suppressing endothelial [Ca(2+)](I) signaling

The detailed mechanism of how lysophosphatidylcholine (LPC) suppresses endothelium-dependent vasodilatation is unclear at present. We investigated the effects of LPC on endothelial intracellular calcium (EC [Ca(2+)](i)) signaling and vascular tone simultaneously using a new technique we developed. Fura-2-labeled rat aortic specimens were mounted in a tissue flow chamber and precontracted with phenylephrine (5 x 10(-8) M). Under either basal or agonist-stimulated conditions, the EC [Ca(2+)](i) level was calculated from fura 2 fluorescence ratio images, and the vascular tone was estimated by measuring the relative displacement of the fluorescence images. Although both acetylcholine (ACh)-induced EC [Ca(2+)](i) elevation and the concomitant vasorelaxation were partially suppressed in specimens pretreated with LPC (20 microM), the quantitative relationship between EC [Ca(2+)](i) elevation and the corresponding vasorelaxation was unaffected. A high concentration of LPC (40 microM) completely eliminated ACh-evoked [Ca(2+)](i) elevation and vasodilatation. It has been reported that exposing vascular tissue to a calcium-free buffer causes a reduction in the EC [Ca(2+)](i) level and the accompanying vasoconstriction. Pretreatment with 20 microM LPC reduced the basal EC [Ca(2+)](i) level and abolished the calcium-free solution-induced EC [Ca(2+)](i) reduction and vasoconstriction. We conclude that LPC impairs endothelium-dependent vasorelaxation mainly by reducing the basal EC [Ca(2+)](i) level and suppressing agonist-evoked EC [Ca(2+)](i) signaling.

Cyclic AMP inhibits stretch-induced overexpression of fibronectin in glomerular mesangial cells

Glomerular hypertension is proposed to play an important role in the progression of various glomerular diseases. Glomerular mesangial cells are considered to be exposed to the stretch stress due to glomerular hypertension and are found to produce the excess amount of extracellular matrix (ECM) proteins including fibronectin when exposed to the mechanical stretch. Herein, we provide the evidence that cAMP-generating agents inhibit the stretch-induced overexpression of fibronectin through the inhibition of the stretch-induced activation of mitogen-activated protein kinases (MAPKs) in protein kinase-A-dependent manner. We also found that the mechanical stretch enhanced the binding of nuclear extracts to activator protein-1 (AP-1)-like sequences in the promoter region of rat fibronectin gene and this enhancement was also prevented by the cAMP-generating agent. These results indicate that the agents, which activate cAMP/protein kinase-A axis, may work protectively against the injury from glomerular hypertension in mesangial cells.

Cyclic adenosine monophosphate regulates the expression of the intercellular adhesion molecule and the inducible nitric oxide synthase in brain endothelial cells

The authors studied whether cyclic AMP (cAMP), a widespread regulator of inflammation, modulates the cytokine-mediated expression of the intercellular adhesion molecule, intercellular adhesion molecule-1 (ICAM-1), and the inflammatory nitric oxide synthase 2 (NOS-2), in primary and immortalized brain endothelial cell cultures (GP8.3 cell line). When measured by enzyme-linked immunosorbent assay (ELISA), ICAM-1 was constitutively expressed and was up-regulated twofold by interleukin-1beta, with no effect of interferon-gamma. The NOS-2 activity, assessed by nitrite accumulation, was absent from untreated cultures but was induced by interleukin-1beta and interferon-gamma acting synergistically. Stimulation of cAMP-dependent pathways with forskolin or dibutyryl cAMP decreased ICAM-1 protein expression, whereas it increased NOS-2 protein expression. For both ICAM-1 and NOS-2, mRNA expression correlated with protein expression. Blockade of NOS activity with L-N-monomethylargiuine (L-NMMA) did not alter ICAM-1 expression, indicating that the nitric oxide released by NOS-2 did not cause the down-regulation of ICAM-1. Analysis of NFKB activation indicated that cAMP acted through a mechanism other than inhibition of nuclear translocation of NFKB. The authors conclude that cAMP modulates the expression of proinflammatory molecules in brain endothelium. This suggests that inflammatory processes at the blood-brain barrier in vivo may be regulated by perivascular neurotransmitters via cAMP.

Oxidized LDL and expression of monocyte adhesion molecules

Accumulation of substantial numbers of monocyte/macrophages, as well as activated T lymphocytes, in focal areas of arterial intima appears to be a hallmark of atherogenesis. Our report demonstrated that lysophosphatidylcholine (lyso-PC), a polar phospholipid component that is increased in atherogenic lipoproteins, such as oxidized LDL and remnants lipoproteins in diabetic and type III hyperlipidemic patients, can upregulate adhesion molecules for monocytes and T lymphocytes, and growth factors, such as heparin-binding epidermal growth factor-like growth factor and PDGF-A and B chains. Recently we identified the novel receptor for oxidized LDL, named Lox-1. Therefore in this paper we summarize the importance of the interaction between oxidized LDL and its receptor, LOX-1 in terms of early stage of atherogenesis.

Lysophosphatidylcholine phosphorylates CREB and activates the jun2TRE site of c-jun promoter in vascular endothelial cells

Lysophosphatidylcholine (lyso-PC), a polar phospholipid increased in atherogenic lipoproteins and atherosclerotic lesions, has been shown to induce transcription of a variety of endothelial genes relevant to atherogenesis. Lyso-PC has been shown to activate c-jun N-terminal kinase (JNK) and activator protein 1 (AP-1) and thereby stimulate transcription of the c-jun gene. Here we provide evidence that lyso-PC can phosphorylate cyclic AMP responsive element binding protein (CREB) and thereby activate the jun2 12-O-tetradecanoylphorbol 13-acetate response element (jun2TRE) site of the c-jun promoter, which appears to be the major molecular mechanism involved in lyso-PC-induced c-jun gene expression in cultured bovine aortic endothelial cells (BAEC). Transient transfection of BAEC with a 1.6-kbp c-jun promoter and luciferase reporter fusion gene resulted in a 12.9-fold increase in luciferase activity by lyso-PC treatment. Serial deletion mutation in c-jun promoter and luciferase reporter gene assay revealed that the 5' promoter region between nucleotide numbers -268 and -127, which contains a jun2TRE binding sequence, was most crucial for lyso-PC-induced transcription. The 5' promoter region between -76 and -27, which contains an AP-1 site, also affected lyso-PC-induced transcription of the c-jun gene. Point mutation in the jun2TRE site reduced lyso-PC-induced transcription of the c-jun promoter-luciferase fusion gene by a 70.3% decrease in c-jun promoter activity. Electrophoretic mobility shift assays showed increased binding of (32)P-labeled oligonucleotides with jun2TRE in nuclear extracts isolated from lyso-PC-treated BAEC, which was abolished or supershifted by anti-CREB antibody. Immunoblotting with anti-phosphorylated CREB antibody showed rapid phosphorylation of this protein after lyso-PC treatment. These results indicate that lyso-PC phosphorylates CREB, which was then bound to the jun2TRE site of the c-jun promoter and activated transcription. Activation of jun2TRE may play a key role in the transcriptional activation of c-jun as well as other endothelial genes depending upon these transcription factors.

Lysophosphatidylcholine activates mitogen-activated protein kinases by a tyrosine kinase-dependent pathway in bovine aortic endothelial cells

Lysophosphatidylcholine (lyso-PC) is a major component of an atherogenic lipoprotein. In this study, to investigate the involvement of mitogen-activated protein kinases in the signaling pathway by lyso-PC in endothelial cells, we measured the activity of extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) in bovine aortic endothelial cells. Lyso-PC activated ERK and JNK in a dose-dependent manner. However, the time courses of activation of these kinases were different. ERK and JNK activation by lyso-PC was inhibited by a tyrosine kinase inhibitor, herbimycin A, but not by a protein kinase C (PKC) specific inhibitor. We conclude, therefore, that lyso-PC-mediated ERK and JNK activation is caused by a tyrosine kinase-dependent mechanism, but not conventional types of PKC-dependent mechanisms.

A specific human lysophospholipase: cDNA cloning, tissue distribution and kinetic characterization

Lysophospholipases are critical enzymes that act on biological membranes to regulate the multifunctional lysophospholipids; increased levels of lysophospholipids are associated with a host of diseases. Herein we report the cDNA cloning of a human brain 25 kDa lysophospholipid-specific lysophospholipase (hLysoPLA). The enzyme (at both mRNA and protein levels) is widely distributed in tissues, but with quite different abundances. The hLysoPLA hydrolyzes lysophosphatidylcholine in both monomeric and micellar forms, and exhibits apparent cooperativity and surface dilution kinetics, but not interfacial activation. Detailed kinetic analysis indicates that the hLysoPLA binds first to the micellar surface and then to the substrate presented on the surface. The kinetic parameters associated with this surface dilution kinetic model are reported, and it is concluded that hLysoPLA has a single substrate binding site and a surface recognition site. The apparent cooperativity observed is likely due to the change of substrate presentation. In contrast to many non-specific lipolytic enzymes that exhibit lysophospholipase activity, hLysoPLA hydrolyzes only lysophospholipids and has no other significant enzymatic activity. Of special interest, hLysoPLA does not act on plasmenylcholine. Of the several inhibitors tested, only methyl arachidonyl fluorophosphonate (MAFP) potently and irreversibly inhibits the enzymatic activity. The inhibition by MAFP is consistent with the catalytic mechanism proposed for the enzyme - a serine hydrolase with a catalytic triad composed of Ser-119, Asp-174 and His-208.

Functional food science and the cardiovascular system

Cardiovascular disease has a multifactorial aetiology, as is illustrated by the existence of numerous risk indicators, many of which can be influenced by dietary means. It should be recalled, however, that only after a cause-and-effect relationship has been established between the disease and a given risk indicator (called a risk factor in that case), can modifying this factor be expected to affect disease morbidity and mortality. In this paper, effects of diet on cardiovascular risk are reviewed, with special emphasis on modification of the plasma lipoprotein profile and of hypertension. In addition, dietary influences on arterial thrombotic processes, immunological interactions, insulin resistance and hyperhomocysteinaemia are discussed. Dietary lipids are able to affect lipoprotein metabolism in a significant way, thereby modifying the risk of cardiovascular disease. However, more research is required concerning the possible interactions between the various dietary fatty acids, and between fatty acids and dietary cholesterol. In addition, more studies are needed with respect to the possible importance of the postprandial state. Although in the aetiology of hypertension the genetic component is definitely stronger than environmental factors, some benefit in terms of the development and coronary complications of atherosclerosis in hypertensive patients can be expected from fatty acids such as alpha-linolenic acid, eicosapentaenoic acid and docosahexaenoic acid. This particularly holds for those subjects where the hypertensive mechanism involves the formation of thromboxane A2 and/or alpha 1-adrenergic activities. However, large-scale trials are required to test this contention. Certain aspects of blood platelet function, blood coagulability, and fibrinolytic activity are associated with cardiovascular risk, but causality has been insufficiently proven. Nonetheless, well-designed intervention studies should be initiated to further evaluate such promising dietary components as the various n-3 and n-6 fatty acids and their combination, antioxidants, fibre, etc. for their effect on processes participating in arterial thrombus formation. Long-chain polyenes of the n-3 family and antioxidants can modify the activity of immunocompetent cells, but we are at an early stage of examining the role of immune function on the development of atherosclerotic plaques. Actually, there is little, if any, evidence that dietary modulation of immune system responses of cells participating in atherogenesis exerts beneficial effects. Although it seems feasible to modulate insulin sensitivity and subsequent cardiovascular risk factors by decreasing the total amount of dietary fat and increasing the proportion of polyunsaturated fatty acids, additional studies on the efficacy of specific fatty acids, dietary fibre, and low-energy diets, as well as on the mechanisms involved are required to understand the real function of these dietary components. Finally, dietary supplements containing folate and vitamins B6 and/or B12 should be tested for their potential to reduce cardiovascular risk by lowering the plasma level of homocysteine.

Lysophosphatidylcholine stimulates the release of arachidonic acid in human endothelial cells

Lysophosphatidylcholine (lyso-PC) is a product of phosphatidylcholine hydrolysis by phospholipase A2 (PLA2) and is present in cell membranes, oxidized lipoproteins, and atherosclerotic tissues. It has the ability to alter endothelial functions and is regarded as a causal agent in atherogenesis. In this study, the modulation of arachidonate release by lyso-PC in human umbilical vein endothelial cells was examined. Incubation of endothelial cells with lyso-PC resulted in an enhanced release of arachidonate in a time- and concentration-dependent manner. Maximum arachidonate release was observed at 10 min of incubation with 50 microM lyso-PC. Lyso-PC species containing palmitoyl (C16:0) or stearoyl (C18:0) groups elicited the enhancement of arachidonate release, while other lysolipids such as lysophosphatidylethanolamine, lysophosphatidylserine, lysophosphatidylinositol, or lysophosphatidate were relatively ineffective. Lyso-PC-induced arachidonate release was decreased by treatment of cells with PLA2 inhibitors such as para-bromophenacyl bromide and arachidonoyl trifluoromethyl ketone. Furthermore, arachidonate release was attenuated in cells grown in the presence of antisense oligodeoxynucleotides that specifically bind cytosolic PLA2 mRNA. Treatment of cells with lyso-PC resulted in a translocation of PLA2 activity from the cytosolic to the membrane fractions of cells. Lyso-PC induced a rapid influx of Ca2+ from the medium into the cells, with a simultaneous enhancement of protein kinase C (PKC) activity in the membrane fractions. The lyso-PC-induced arachidonate release was attenuated when cells were preincubated with specific inhibitors of PKC (staurosporine and Ro31-8220) or a specific inhibitor of mitogen-activated protein kinase/extracellular regulated kinase kinase (PD098059). Taken together, the results of this study show that lyso-PC caused the elevation of cellular Ca2+ and the activation of PKC, which stimulated cytosolic PLA2 in an indirect manner and resulted in an enhanced release of arachidonate.

Tyrosine phosphorylation of platelet endothelial cell adhesion molecule-1 induced by lysophosphatidylcholine in cultured endothelial cells

Lysophosphatidylcholine (lyso-PC), a biologically active phospholipid, appears to modulate various endothelial cell functions through tyrosine kinase-dependent signaling pathways. In cultured bovine aortic endothelial cells (BAEC), we have found that a 130 kDa protein (p130) was rapidly tyrosine phosphorylated within 2 min and sustained for, at least, 1 hr in response to 10 mumol/L of lyso-PC but not to phorbol myristate acetate (PMA). Prolonged preexposure to PMA did not affect lyso-PC-induced p130 tyrosine phosphorylation, suggesting that mechanisms independent of protein kinase C may be involved. Fractionation of the cell lysates revealed that p130 was detectable in the membrane fraction but not in the cytosolic fraction. Immunoprecipitation followed by immunoblotting of lyso-PC-treated BAEC identified p130 as bovine PECAM-1. Tyrosine phosphorylation of PECAM-1 appears to be one of the earliest events elicited by lyso-PC, and may play a role in lyso-PC-induced modulation of endothelial functions.

Expression of CD54 (intercellular adhesion molecule-1) and the beta 1 integrin CD29 is modulated by a cyclic AMP dependent pathway in activated primary rat microglial cell cultures

Microglial cell activation plays a central role in acute and chronic inflammatory processes associated with neurodegeneration. As macrophage activation is generally associated with the up-regulation of specific surface antigens, the expression of CD54, and CD29 were evaluated on CD11b positive neonatal rat microglial cell cultures by flow cytometry. These cells when exposed to lipopolysaccharide, LPS, and gamma interferon, IFN gamma, exhibited a 2-3 fold increase in CD54 expression, an increase in CD29 and no change in CD11b. Maximal increases in CD54 and CD29 staining on CD11b positive microglial cells were apparent 20-24 h after LPS and IFN gamma while nitrite production reflecting inducible nitric oxide synthase activity, continued to increase. The increases in CD29 and CD54 staining were inhibited in a dose dependent manner by agents which increased intracellular cAMP levels including 100 microM 8-bromoadenosine 3':5'-cyclic monophosphate but not 8-bromoadenosine monophosphate, the phosphodiesterase inhibitor isobutyl methylxanthine and by direct activation of adenylate cyclase with forskolin. Concomitant with the dose dependent decreases in CD29 and CD54 staining were increases in intracellular cAMP and reduced TNF secretion. These results suggest that regulation of CD29 and CD54 expression on activated microglial cells involves a cAMP dependent pathway.

Induction of endothelial platelet-derived growth factor-B-chain and intercellular adhesion molecule-1 by lysophosphatidylcholine

Lysophosphatidylcholine (lyso-PC) is a major phospholipid component of atherogenic lipoproteins. Lyso-PC has been shown to differentially upregulate the adhesion molecules, such as VCAM-1 and ICAM-1, as well as smooth muscle growth factors, such as PDGF-A, B chains and HB-EGF gene expression in various cultured endothelial cells. In this paper, we demonstrate increased expression of cell- and matrix-associated forms of PDGF-B protein elicited by lyso-PC and further characterized potential signal transduction mechanisms responsible for lyso-PC-induced human umbilical vein endothelial cell. Cycloheximide inhibited PDGF-B but not ICAM-1 mRNA induction by lyso-PC, suggesting the dependence on de novo protein synthesis for PDGF-B, but not ICAM-1. A protein kinase C (PKC) inhibitor did not block lyso-PC-induced increases in PDGF-B or ICAM-1 mRNA. The elevated level of cAMP blocked both PDGF-B and ICAM-1 upregulation by lyso-PC. However cAMP-elevating agents did not suppress ICAM-1 upregulation by PMA. Taken together, PDGF-B and ICAM-1 gene induction by lyso-PC may involve different signaling mechanisms; however, both appear to be independent of PMA-regulatable PKC activation but are suppressed by increased levels of intracellular cAMP.

Spontaneous transfer of monoacyl amphiphiles between lipid and protein surfaces

The kinetics of transfer of natural and fluorescent nonesterified fatty acids (NEFA) and lysolecithins (lysoPC) from phospholipid and protein surfaces were measured. The kinetics of transfer of 12-(1-pyrenyl)dodecanoic acid, from liquid crystalline and gel phase single unilamellar phospholipid vesicles, very low, low, and high density lipoproteins, human serum albumin, and rat liver fatty acid-binding protein, were first-order and characterized by similar rate constants. The halftimes (t1/2) of NEFA transfer from lipids and proteins were dependent on the acyl chain structure according to log t1/2 = -0.62n + 0.59m + 12.0, where n and m, respectively, are the numbers of carbon atoms and double bonds. The structure of the donor surface had a measurable but smaller effect on transfer rates. The kinetics of NEFA and lysoPC transfer are slow relative to the lipolytic processes that liberate them. Therefore, one would predict a transient accumulation of NEFA and lysoPC during lipolysis and an attendant modulation of many metabolic processes within living cells and within the plasma compartment of blood. These data will be useful in the refinement of current models of membrane and lipoprotein function and in the selection of fluorescent NEFA analogs for studying transport in living cells.

Activation of ICAM-1 promoter by lysophosphatidylcholine: possible involvement of protein tyrosine kinases

Lysophosphatidylcholine (lyso-PC) selectively upregulates the mRNA level of intercellular adhesion molecule-1 (ICAM-1) but not that of vascular cell adhesion molecule-1 (VCAM-1) in cultured human umbilical vein endothelial cells. Transfection studies show that lyso-PC activates the ICAM-1 promoter but not the VCAM-1 promoter. Gel mobility shift assays document an increase in NF-kappa B binding in cells treated with lyso-PC. The increases of ICAM-1 mRNA and NF-kappa B binding were inhibited by the protein tyrosine kinase inhibitors, genistein and lavendustin A, but not by inhibitors for cyclic AMP-dependent protein kinases or protein kinase C. Our results suggest that lyso-PC induces ICAM-1 expression most likely by activating NF-kappa B, and that the effect appears to be protein tyrosine kinase-dependent.