Alterations in cell protein phosphorylation in human neutrophils exposed to influenza A virus. A possible mechanism for depressed cellular end-stage functions

When polymorphonuclear leukocytes (PMN) are exposed to most harvests of influenza A virus (depressing virus, DV) for 20 min, chemotactic, secretory, and oxidative functions are depressed upon subsequent exposure to soluble or particulate stimuli. Other harvests of influenza A virus (non-DV) do not alter these activities. The DV-induced changes in multiple functions suggest the virus may interfere with steps involved in PMN activation. Because some of these steps may be regulated by protein phosphorylation, we examined the effect of non-DV and DV on cellular protein phosphorylation. PMN loaded with 32P-labeled inorganic orthophosphate were exposed to non-DV, DV, or buffer for 30 min; cells were then treated with buffer, FMLP (10(-6) M), or PMA (100 ng/ml) for 30 s. Samples were sonicated and centrifuged; cytosolic and particulate fractions were analyzed by SDS-PAGE and autoradiography. Exposure of PMN to either non-DV or DV caused phosphorylation of several cell proteins. However, when DV-treated PMN were then stimulated with FMLP or PMA, further phosphorylation was inhibited compared to non-DV- or buffer-treated cells. This suggests that DV-induced depression of PMN end-stage functions may be due to changes in cell protein phosphorylation. DV could interfere with phosphorylation of PMN proteins by altering protein kinase activity. We therefore examined the influence of non-DV and DV on some parameters that could affect kinase function. PMN intracellular [Ca2+] was monitored by using the fluorescent Ca2+ indicator, Indo 1, and cAMP levels were measured by RIA. PMN treated with DV alone or DV plus FMLP had higher intracellular [CA2+] than PMN similarly treated with non-DV or buffer. Exposure of PMN to non-DV, DV, or buffer caused minimal changes in cAMP levels, and similar increases occurred in cAMP levels upon FMLP stimulation. To determine whether DV interferes with transmembrane signaling, the effect of influenza virus on PMN transmembrane potential was studied by using a fluorescent cyanine dye. Transmembrane potential changes were greater in PMN exposed to DV than to non-DV or buffer; however, subsequent stimulation with FMLP caused equivalent changes in transmembrane potential. Our data show that protein phosphorylation in PMN is induced by DV and non-DV infection; upon subsequent stimulation with FMLP or PMA, there is inhibited cellular phosphorylation only in PMN previously exposed to DV.(ABSTRACT TRUNCATED AT 400 WORDS)     

Lipopolysaccharide-induced stimulation of CD11b/CD18 expression on neutrophils. Evidence of specific receptor-based response and inhibition by lipid A-based antagonists.

Gram-negative bacterial septicemia is a common clinical syndrome resulting, in part, from the activation of phagocytic leukocytes by LPS. By using flow cytometry, we have characterized LPS-induced expression of the beta 2 integrin CD11b/CD18. After exposure to Salmonella minnesota R595 LPS, expression of neutrophil CD11b/CD18 is rapidly upregulated, beginning within 5 min and achieving a peak fluorescence (typically two- to threefold over base line) by 30 min. The increase in CD11b/CD18 expression was similar in kinetics and magnitude to that produced by FMLP, PMA, and human rTNF-alpha. Concentrations of LPS necessary to stimulate a response were as low as 1 ng/ml of R595 LPS; a maximal response was observed between 30 and 100 ng/ml. The upregulation of CD11b/CD18 due to LPS was not interrupted by protein synthesis inhibitors. A group of glucosamine disaccharide lipid A-like molecules: Rhodobacter sphaeroides lipid A, lipid IVA, KDO2IVA, and deacylated LPS were able to block the stimulatory effect of LPS. This inhibition was specific for the actions of LPS as stimulation of polymorphonuclear leukocytes (PMN) by FMLP, human rTNF alpha, PMA, and rewarming were not altered by the disaccharide inhibitors. PMN which were exposed to the specific disaccharide LPS antagonists and then washed, were refractory to stimulation by LPS. The monosaccharide lipid A precursor lipid X also blocked stimulation of neutrophils by LPS, although with a 100-fold reduction in potency. Unlike the disaccharide inhibitors, PMN exposed to lipid X were still responsive to LPS stimulation after washing. The PMN response to LPS was less sensitive in the absence of serum, although upregulation of CD11b/CD18 could still be seen using higher concentrations of LPS. Monoclonal antibody directed against CD14 (clone 3C10), also specifically inhibited LPS induced PMN CD11b/CD18 expression both in the presence and absence of serum. These findings support the hypothesis that LPS stimulates neutrophils by interacting with specific cellular receptors.     

Bacterial lipopolysaccharide stimulates phospholipid synthesis and phosphatidylcholine breakdown in cultured human leukemia monocytic THP-1 cells.

1. De novo synthesis of phospholipid and its catabolism in human leukemia monocytic THP-1 cells were investigated. 2. Radiolabelled precursors: [methyl-3H]chloride, [1,2-14C]ethanolamine and myo-[2-3H]inositol were readily incorporated into CHCl3-MEOH extractable lipid fraction as a function of time. 3. The radiolabels derived from choline, ethanolamine and inositol were preferentially incorporated into PC, PE and PI fraction, respectively. The data indicate that de novo PL synthesis takes place, and the CDP-choline pathway is operative as a major pathway for PC synthesized in THP-1 cells. 4. Bacterial endotoxin dose-dependently stimulated the incorporation of radiolabelled precursors. Approximately 50% stimulation in PC and PE synthesis was obtained in 20 hr, while the incorporation of [3H]inositol was rapidly stimulated by 170% within 4 hr, and the stimulation declined drastically thereafter. 5. LPS did not alter the radiolabel distribution into PL in any of the three cases. 6. In pulse-chase studies, the cells prelabelled with radioactive PL were exposed to LPS (1 micrograms/ml). The breakdown of PC was enhanced about 30% within the first 2 hr followed by a stimulated PC synthesis observed in the next 4 hr. In contrast, LPS did not induce the hydrolysis of PE and PI. 7. The data indicate that LPS produces a broad spectrum of stimulatory effects on PL synthesis and selectively stimulates the hydrolysis of PC via phospholipase C/D reaction in THP-1 cells.     

Cerebral Phospholipid Content and Na+, K+-ATPase Activity During Ischemia and Postischemic Reperfusion in the Mongolian Gerbil

Using bilateral carotid artery occlusion in adult gerbils we examined the effects of ischemia and ischemia/reperfusion on cerebral phospholipid content and Na+,K+-ATPase (EC 3.6.1.3) activity. In contrast to the large changes in phospholipid content and membrane-bound enzyme activity that have been observed in liver and heart tissues, we observed relatively small changes in the cerebral content of total phospholipid, phosphatidylcholine (PC), phosphatidylserine (PS), and phosphatidylethanolamine (PE) following ischemic intervals of up to 240 min. Following 15 min of ischemia the cerebral content of sphingomyelin (SM) was decreased to less than 50% of control values but returned to near-normal levels with longer ischemic periods. Significant decreases in the cerebral content of phosphatidylinositol (PI) and phosphatidic acid (PA) were observed following shorter intervals of ischemia (15-45 min). Na+,K+-ATPase activity of cerebral homogenates prepared from the brains of gerbils subjected to 30-240 min of ischemia was decreased but significantly different from control activity only after 30 min of ischemia (-29%, p less than or equal to 0.05). With the exception of PS, reperfusion for 60 min following 60 min of ischemia resulted in marked increases in cerebral phospholipid content with PC, SM, PI, and PA levels exceeding and PE levels equal to preischemic values. Longer periods of reperfusion (180 min) resulted in decreases in cerebral phospholipid content toward (PC, SM, PI, and PA) or below (PE) preischemic levels. In contrast, the cerebral content of PS significantly decreased during reperfusion (-51% at 60 min, p less than or equal to 0.05) and remained below preischemic values even after 180 min of reperfusion.(ABSTRACT TRUNCATED AT 250 WORDS)     

Regulation of phosphatidic acid phosphohydrolase activity during stimulation of human polymorphonuclear leukocytes.

Phosphatidic acid phosphohydrolase (PPH) activity was determined in human polymorphonuclear leukocytes (PMNs) by measuring the hydrolysis of [32P]phosphatidic acid (PA) added to cell sonicates. Enzyme activity was localized primarily to a soluble fraction. Soluble and particulate activities required magnesium and were inhibited by calcium, N-ethylmaleimide, sphingosine, and propranolol. The activity in unstimulated PMNs was 0.64 +/- 0.11 nmol of PA hydrolyzed.mg protein-1.min-1 in particulate and 4.20 +/- 0.42 in soluble fractions. Stimulation of PMNs with 1 microM f-Met-Leu-Phe (FMLP) for 10 min caused a slight decrease in soluble activity and a small increase in the activity of particulate fractions. Preincubation with 10 microM cytochalasin B for 5 min before FMLP stimulation markedly enhanced both of these changes. The effect of FMLP plus cytochalasin B was rapid (less than 10 s), whereas the calcium ionophore A23187 (1 microM) and phorbol myristate acetate (100 ng/ml) caused slower and smaller changes in enzyme activity. These results indicate that after chemoattractant stimulation; PPH activity decreases in the soluble fraction and increases in the particulate fraction suggesting that PPH may participate in signal transduction in the PMN.     

Differential activation of membrane phospholipid turnover by compound 48/80 and ionophore A23187 in rat mast cells

Membrane phospholipid turnover was investigated during histamine release from rat mast cells. Addition of calcium ionophore A23187 (0.5 microgram/ml) to mast cells prelabeled with [3H]glycerol induced the rapid and progressive increase in phosphatidic acid (PA) and 1,2-diacylglycerol (DG), which was concomitant with the small rise in phosphatidylinositol (PI). Loss of the level in triacylglycerol (TG) was very marked. Polyamine compound 48/80 (5 micrograms/ml) was shown to cause rises in PA, 1,2-DG, and PI without any significant changes in TG. Both stimuli increased incorporation of exogenous [3H]glycerol into phospholipids, indicating the involvement of de novo synthesis in phospholipid metabolism. Studies with [3H]arachidonic acid-labeled mast cells showed an enhanced liberation of radioactive arachidonate and metabolites upon histamine release. There were associated decreases of radioactivity in phosphatidylcholine (PC) and TG when exposed to A23187, while phosphatidylethanolamine (PE) was degraded as a result of 48/80 activation. The transient increases of [3H]arachidonoyl-1,2-DG and PA were caused by 48/80, while A23187 showed a gradual rise in the radioactivity in these two lipid fractions. These findings reflect activation of phospholipase C. When mast cells were activated by low concentrations of A23187 (0.1 microgram/ml) and 48/80 (0.5 microgram/ml), different behaviors of PI metabolism were observed. An early degradation of PI and a subsequent formation of 1,2-DG and PA suggest that the lower concentrations of these agents stimulate the PI cycle initiated by PI breakdown rather than de novo synthesis. These results demonstrate that marked and selective changes in membrane phospholipid metabolism occur during histamine release from mast cells, and that these reactions seem to be controlled by the coordination of degradation and biosynthesis, depending on the type and the concentration of stimulants. A23187 stimulates arachidonate release perhaps via the cleavages of PC and TG, whereas 48/80 liberates arachidonate from PE.     

Modulation of platelet-activating factor (PAF) synthesis and release from human polymorphonuclear leukocytes (PMN): role of extracellular albumin

Human neutrophilic polymorphonuclear leukocytes (PMN) stimulated with N'-formyl-methionyl-leucyl-phenylalanine (FMLP) in the presence of cytochalasin B but in the absence of human serum albumin (HSA) synthesized only small amounts of platelet-activating factor (PAF) that attained maximum levels within 60-120 s after stimulation; in addition, no release of PAF occurred. However, in the presence of 2.5 mg HSA/ml, there was a threefold increase in PAF synthesis, 30-40% of which was released within 5 min after FMLP stimulation. In the presence of 50 mg HSA/ml there was at least a fourfold increase in PAF synthesis and release, with maximal synthesis occurring 10-20 min after stimulation. Thus, the presence of HSA during PMN stimulation not only induced an albumin dose-dependent increase in PAF release but significantly augmented the synthesis of PAF. In contrast to PAF synthesis and release, the presence or absence of HSA had no effect upon lysosomal enzyme secretion from FMLP-stimulated PMN, which was maximal within 30-60s after stimulation. These results demonstrate that HSA plays an essential role in vitro in the synthesis and release of PAF from human PMN, and support the hypothesis that there is a cyclic PAF synthesis-release coupling mechanism in the stimulated human PMN.     

Lack of effect of pertussis toxin on TNF-alpha-induced formation of reactive oxygen intermediates by human neutrophils

When human PMN were plated on fetal calf serum-coated polystyrene surfaces, addition of TNF-alpha, FMLP or PMA elicited adhesion and H2O2 formation. These effects of TNF-alpha and FMLP, but not of PMA, were impaired by removal of extracellular Ca2+. In addition, H2O2 formation induced by FMLP but not by TNF-alpha or PMA was inhibited by prior treatment with pertussis toxin (250-500 ng/ml). Thus, although the sequelae of TNF-alpha-receptor interaction on human PMN remain to be characterized in detail, they do not involve a pertussis toxin-sensitive GTP-binding protein.     

Human neutrophil laminin receptors: activation-dependent receptor expression

Activated human polymorphonuclear leukocytes (PMN) isolated from peripheral blood specifically bind 125I-laminin after stimulation with phorbol 12-myristate 13-acetate (PMA) or f-Met-Leu-Phe (FMLP) at 37 degrees C. Changes in laminin receptor expression are stimulus dose dependent at both chemotactic (10(-10) M to 10(-6) M) concentrations of FMLP, and secretory (greater than 5 ng/ml) levels of PMA. In the presence of cytochalasin B (5 micrograms/ml), 10(-7) M FMLP activation stimulates specific laminin binding, with an apparent Kd = 3.9 X 10(-9) M and 6.47 X 10(5) binding sites/cell, reaching equilibrium within 10 min at 4 degrees C. This observed activation-dependent change in laminin receptor expression is not due to interference by endogenous laminin, because no fluorescein-visualized anti-laminin antibody bound to cells without added glycoprotein, regardless of the level of activation. Levels of neutrophil lysozyme release, which show a PMA dose dependence similar to that of receptor binding activity, suggest that granule-plasma membrane fusion may be significant during increases in receptor expression. A lack of receptor stimulation by PMA from a granule-deficient patient or in granule-depleted cytoplasts from normal donors additionally supports this hypothesis. Electroblot transfer and autoradiography of subcellular fractions from unstimulated PMN reveals the presence of a 68,000 dalton laminin-binding component in the secondary/tertiary granule (beta) fraction, which may represent an intracellular laminin receptor pool.     

Phospholipid metabolism in human neutrophils activated by N-formyl-methionyl-leucyl-phenylalanine. Degranulation is not required for release of arachidonic acid: studies with neutrophils and neutrophil-derived cytoplasts.

Neutrophils respond to chemoattractants by aggregating, degranulating, remodelling of phospholipids and releasing arachidonic acid. To determine whether ligand-induced remodelling of phospholipids depends on redistribution of intracellular organelles (degranulation), we compared phospholipid remodelling of human neutrophils with that of neutrophil-derived cytoplasts. Cytoplasts, organelle-depleted vesicles of cytosol surrounded by plasmalemma, cannot degranulate. Without a stimulus, [3H]arachidonate was incorporated preferentially into phosphatidylinositol (PI) and phosphatidylcholine (PC). Exposure of cytoplasts and neutrophils prelabelled with [3H]arachidonate or [14C]glycerol to fMet-Leu-Phe (10(-7) M) induced rapid changes in distribution of label and mass of individual phospholipids: [3H]arachidonate in phosphatidic acid (PA) increased 500% (120 s), [14C]glycerol incorporation and mass of PA approached 200% of unstimulated values, and [3H]arachidonate in PI decreased continuously; these data are compatible with activity of a PI/PA cycle. However, the mass of PI in both preparations and [14C]glycerol label in intact neutrophils increased initially (5 s), suggesting net synthesis and mobilization of more than one pool of PI. Heterogeneity of PC pools was also observed: [3H]arachidonate was lost from PC immediately upon addition of stimulus, whereas mass and [14C]glycerol values increased. Thus, net phospholipid synthesis, redistribution of arachidonate and activation of the PI/PA cycle are immediate responses of the neutrophil to receptor occupancy by chemoattractants. Furthermore, the similarity in response to fMet-Leu-Phe of neutrophils and granule-free cytoplasts indicates that these processes are independent of degranulation.     

Chemiluminescence properties of human,canine and rat polymorphonuclear cells

Human as well as canine and rat polymorphonuclear cells (PMN) were separated from whole blood by centrifugation. Two-step discontinuous Percoll gradients with distinct different densities were used. The chemiluminescence properties of the isolated PMN and of phagocytes in small quantities of whole blood were compared in luminol-enhanced assays after stimulation with various agents: non-opsonized zymosan (3.5 g/I), phorbol myristate acetate (PMA, 2.8 × 10^?6 mol/I), calcium ionophore A 23187 (10^?5 mol/l) and N-formylmethionyl-leucyl-phenylalanine (FMLP, 3.5 × 10^?6 mol/l). The isolated cells of the three species responded to all of the various stimuli. Species-related sensitivity could be ordered: human > canine > rat. Response to the various agents in the human cells can be ranked: PMA ? A 23187 > zymosan > FMLP; for the dog: A 23187 > PMA > zymosan > FMLP; and for the rat: zymosan ? PMA > FMLP ? A 23187. Time course and peak maximum response were different upon stimulation in the absence and presence of autologous plasma. Distinct soluble stimuli resulted in maximum responses below the baseline in the whole blood assays with canine (FMLP) and rat (FMLP, A 23187) phagocytes.     

Modulation of bovine milk galactosyltransferase activity by lipids

The effect of lipids singly and in combination on the ability of galactosyltransferase to transfer galactose to N-acetyl-D-glucosamine-forming lactosamine and to glucose forming lactose has been studied. Lecithins, as egg phosphatidylcholine (PC), or saturated as dimyristoylphosphatidylcholine and dipalmitoylphosphatidylcholine stimulated the activity of the enzyme to form lactosamine to different extents. Egg PC produced the greatest stimulation of all the lecithins tested. Egg phosphatidic acid (PA) inhibited the activity of the enzyme at very low concentrations of lipid. In mixed vesicles of gel phase or liquid crystalline phase lecithins and egg PA, the acidic lipid was able to overcome the stimulation produced by the lecithins. The dominant effect of the head group was demonstrated by the effects of gel phase dimyristoylphosphatidic acid (DMPA). In mixtures with PC, DMPA also was able to inhibit the enzyme for lactosamine synthesis but higher concentrations of the gel phase DMPA were required for inhibition compared to the liquid crystalline PA. Although the head group appeared to dominate the inhibition, the nature of the acyl chains of the lipid played a secondary role at least. Other acid lipids, phosphatidylserine (PS) and phosphatidylinositol (PI) were much less effective than PA. PS alone inhibited the activity of the enzyme. However, in mixed lipids (PS and egg PC), PS was unable to reverse the stimulation produced by PC while PC was able to reverse the inhibition produced by PS. PI alone had no effect on the enzyme activity. In mixtures with egg PC, the stimulating effect of PC was dominant. In the lactose synthetase reaction, the effect of lipids was similar to that of the lactosamine synthetase, i.e. PC stimulated and PA inhibited activity and in mixtures of PC and PA, the inhibitory effect of PA was dominant.     

Chemotactic peptide-induced changes in neutrophil actin conformation

The effect of the chemotatic peptide, N- formylmethionylleucylphenylalanine (FMLP), on actin conformation in human neutrophils (PMN) was studied by flow cytometry using fluorescent 7-nitrobenz-2-oxa-1,3-diazole (NBD)-phallacidin to quantitate cellular F-actin content. Uptake of NBD-phallacidin by fixed PMN was saturable and inhibited by fluid phase F-actin but not G-actin. Stimulation of PMN by greater than 1 nM FMLP resulted in a dose-dependent and reversible increase in F-actin in 70-95% of PMN by 30 s. The induced increase in F-actin was blocked by 30 microM cytochalasin B or by a t- BOC peptide that competitively inhibits FMLP binding. Under fluorescence microscopy, NBD-phallacidin stained, unstimulated PMN had faint homogeneous cytoplasmic fluorescence while cells exposed to FMLP for 30 s prior to NBD-phallacidin staining had accentuated subcortical fluorescence. In the continued presence of an initial stimulatory dose of FMLP, PMN could respond with increased F-actin content to the addition of an increased concentration of FMLP. Thus, FMLP binding to PMN induces a rapid transient conversion of unpolymerized actin to subcortical F-actin and repetitive stimulation of F-actin formation can be induced by increasing chemoattractant concentration. The directed movement of PMN in response to chemoattractant gradients may require similar rapid reversible changes in actin conformation.     

Phospholipid and phospholipase changes by jasmonic acid during stolon to tuber transition of potato

Potato tuber formation starts with the stolon swelling and is regulated by jasmonates. The cascade of events leading to tuber formation is not completely understood. The aim of this study was to evaluate phospholipid composition and phospholipase activities during four stages of stolon-to-tuber transition of Solanum tuberosum L., cv. Spunta, and involvement of phosphatidic acid (PA) in stolon cell expansion during early stages. Effects of jasmonic acid (JA) treatment on phospholipid content and activation of phospholipase D (PLD) (EC 3.1.4.4) and phosphatidylinositol-4,5-bisphosphate-specific phospholipase C (PIP₂-PLC) (EC 3.1.4.3) were studied in the early stages (first stage, hooked apex stolon; second stage, initial swelling stolon) of tuberization. All the phospholipid species identified, phosphatidylinositol (PI), phosphatidylserine (PS), phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylglycerol (PG), PA, and cardiolipin (CL), decreased as tuber formation progressed. PLD and PLC were activated in control tissues at an early stage. JA treatment caused a decrease of PC and PS in first stage stolons, accumulation of PA in second stage stolons, and modification of PLD and PLC activities. PA increased stolon cell area in the first and second stages. These findings indicate that phospholipid catabolism is activated from the early stages of tuber formation, and that JA treatment modifies the pattern of phospholipid (PC, PS, and PA) composition and phospholipase (PLD and PLC) activity. These phospholipids therefore may play a role in activation of an intracellular mechanism that switches the developmental fate of stolon meristem cells, causing differentiation into a tuber.     

Enhancement of phorbol ester-induced protein kinase activity in human neutrophils by platelet-activating factor

We have shown that platelet-activating factor (PAF), a weak primary stimulus for neutrophil superoxide generation, synergistically enhances neutrophil oxidative responses to the tumor promoter phorbol myristate acetate (PMA). Since PMA is known to cause cytosol-to-membrane shift of calcium-activated, phospholipid-dependent protein kinase (protein kinase c, PKC) in human neutrophils, we investigated the role of PAF in modifying PMA-induced PKC activation/translocation. Protein kinase activity was measured as the incorporation of 32P from gamma-32P-ATP into histone H1 induced by enzyme in cytosolic and particulate fractions from sonicated human neutrophils. PAF did not alter the sharp decrease in cytosolic PKC activity induced by PMA. However, in the presence of PAF and PMA, total particulate protein kinase activity increased markedly over that detected in the presence of PMA alone (144 +/- 9 pmoles 32P/10(7)PMN/minute in cells treated with 20 ng/ml PMA compared to 267 +/- 24 pmoles 32P in cells exposed to PMA and 10(-6)M PAF). The increase in total particulate protein kinase activity was synergistic for the two stimuli, required the presence of cytochalasin B during stimulation, and occurred at PAF concentrations of 10(-7) M and above. Both PKC and calcium-, phospholipid-independent protein kinase activities in whole particulate fractions were augmented by PAF as were both activities in detergent-extractable particulate subfractions. PAF did not directly activate PKC obtained from control or PMA-treated neutrophils. However, the PKC-enhancing effect of PAF was inhibited in the absence of calcium during cellular stimulation. PAF also increased particulate protein kinase activity in cells simultaneously exposed to FMLP but the effect was additive for these stimuli. These results suggest that PAF enhances PMA-induced particulate PKC activity by a calcium-dependent mechanism. The enhancing effect of PAF may be directly involved in the mechanism whereby the phospholipid "primes" neutrophils for augmented oxidative responses to PMA.     

The turnover of phospholipid fatty acyl chains is activated by the insecticide Dieldrin in Bufo arenarum oocytes

Dieldrin is a widespread environmental contaminant hazardous to many wildlife species. Some evidence obtained with Bufo arenarum oocytes indicates that Dieldrin decreases the fertilization rate in amphibian oocytes, but little is known about mechanisms by which the pesticide affects fertilization. Therefore, we investigated the effect of Dieldrin on oocyte phospholipid metabolism. Freshly obtained oocytes, prelabeled with 2 3H-glycerol or 9-10 3H palmitate, were exposed to 4 mg/L Dieldrin for 2 hours. Dieldrin reduced the amount of 2 3H-glycerol incorporation in all phosphoglycerides classes: PI, PA, PS, and SPH were affected in 80% of the cases and PC and PE were only reduced in 39% of the cases. The incorporation in neutral lipids was not affected. On the contrary, 9,10 3H-palmitate incorporation increased in PC, PI, and PA, but TAG and FFA decreased. The more efficient incorporation of 3H-palmitate compared with 3H-glycerol in Dieldrin-treated oocytes suggests the operation of an alternative route other than de novo synthesis for phospholipids. The retailoring of phosphoglycerides via a deacylation-acylation pathway was demonstrated. These changes in phospholipid metabolism could be associated with the activation of certain enzymes produced by the pesticide.     

CDw17: a neutrophil glycolipid antigen regulated by activation

The plasma membrane and intracellular granules of human polymorphonuclear neutrophils (PMN) contain large amounts of the glycolipid, lactosylceramide (LacCer; Gal beta 1----4Glc beta 1----1Cer). Despite its abundance, novel subcellular distribution, and lineage-restricted expression, nothing of PMN LacCer function is known. We examined the relationship between LacCer and PMN activation by assessing binding of anti-LacCer mAb (T5A7; anti-CDw17) to PMN during and after cell stimulation. CDw17 expression markedly decreased after treatment with PMA, dioctanoylglycerol, calcium ionophore, FMLP (with or without cytochalasin B or added Ca2+), TNF-alpha, or lymphotoxin. Depending on the stimulus, CDw17 declined to levels ranging from 70% (TNF, lymphotoxin) to less than 5% (phorbol ester, dioctanoylglycerol) of levels detected on untreated PMN. Loss of CDw17 from PMA-treated PMN followed dose- and temperature-dependent kinetics, with loss being detected after PMA treatment for 1 min. Membrane internalization explained PMA-induced loss of CDw17, as cell-associated 125I-anti-CDw17 became inaccessible to fluorescent anti-Ig after PMA treatment. CDw17 on PMN cytoplasts or retinoic acid-induced HL-60 cells was only slightly affected by stimulation, suggesting that down-regulation of the epitope is associated with granule exocytosis rather than superoxide production. Results with PMN from a patient with chronic granulomatous disease confirmed that normal superoxide production is not required for CDw17 loss induced by PMA or FMLP treatment. The data collectively demonstrate that reduced levels of cell-surface CDw17 are associated with granule exocytosis after PMN activation.     

Effect of light and protein phosphorylation on photoreceptor rod outer segment acyltransferase activity

Rod outer segments (ROS) exhibit high acyltransferase (AT) activity, the preferred substrate of which being lysophosphatidylcholine. To study factors possibly regulating ROS AT activity purified ROS membranes were assayed under conditions under which protein kinase C (PKC), cAMP-dependent protein kinase (PKA), and phosphatases were stimulated or inhibited. PKC activation produced a significant increase in the acylation of phosphatidylethanolamine (PE) and phosphatidylinositol (PI) with oleate, it inhibited phosphatidylcholine (PC) acylation, and phosphatidylserine (PS) and phosphatidic acid (PA) acylation remained unchanged. ROS PKA activation resulted in increased oleate incorporation into PS and PI while the acylation of PC, PE, and PA remained unchanged. Inhibition of ROS PKC or PKA produced, as a general trait, inverse effects with respect to those observed under kinase-stimulatory conditions. ROS phosphatase 2A was inhibited by using okadaic acid, and the changes observed in AT activity are described. These findings suggest that changes in ROS protein phosphorylation produce specific changes in AT activity depending on the phospholipid substrate. The effect of light on AT activity in ROS membranes was also studied and it is reported that acylation in these membranes remains unchanged independent of the illumination condition used.     

Stool Phospholipid Signature is Altered by Diet and Tumors

Intake of saturated fat is a risk factor for ulcerative colitis (UC) and colon cancer. Changes in the microbiota have been implicated in the development of UC and colon cancer. The host and the microbiota generate metabolites that may contribute to or reflect disease pathogenesis. We used lipid class specific quantitative mass spectrometry to assess the phospholipid (PL) profile (phosphatidylcholine [PC], phosphatidylethanolamine [PE], phosphatidylinositol [PI], phosphatidylserine [PS]) of stool from mice fed a high fat (HFD) or control diet with or without induction of colitis-associated tumors using azoxymethane and dextran sodium sulfate. The microbiota was assessed using qPCR for several bacterial groups. Colitis-associated tumors were associated with reduced bulk PI and PE levels in control diet fed mice compared to untreated mice. Significant decreases in the relative quantities of several PC species were found in colitis-associated tumor bearing mice fed either diet. Statistical analysis of the PL profile revealed distinct clustering by treatment group. Partial least squares regression analysis found that the relative quantities of the PS class profile best predicted bacterial abundance of Clostridium leptum and Prevotella groups. Abundance of selected PL species correlated with bacterial group quantities. Thus, we have described that a HFD and colitis-associated tumors are associated with changes in phospholipids and may reflect host-microbial interactions and disease states.     

Composition and metabolism of phospholipids of human leukocytes

Human mononuclear (MN) and polymorphonuclear (PMN) leukocytes were analyzed for their phospholipid, triglyceride, cholesterol and fatty acid content. The phospholipid/cholesterol ratio was 1.24 for both cels. MN cells contain more phosphatidylcholine (PC), but less phosphatidylserine (PS), phosphatidylethanolamine (PE) and sphingomyelin (SPH) than PMN cells when expressed as percent of total phospholipid. When expressed on the basis of lipid content per cell, MN cells contain less PS, PE and SPH but more triglyceride than PMN cells. PMN cells incorporate palmitic, stearic, linoleic and linolenic acids into their phospholipids, triglycerides or cholesterol esters. The incorporation into triglycerides was highest for all fatty acids. Of the phospholipids, the incorporation was highest into PC. Labeled fatty acids also were found in proteins which had been delipidized by exhaustive extraction with organic solvents. These represent tightly or covalently bound fatty acids. The incorporation of [³H]palmitic acid into this protein fraction is stimulated by insulin.