Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “PHOSPHATIDES”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 307 records · Page 17Linked to original sources
PubMed2001

Aging promotes a different phosphatidic acid utilization in cytosolic and microsomal fractions from brain and liver.

Among the morphological and biochemical changes taking place in the membranes of aged tissues, we reported in previous studies on alterations in phospholipid synthesis and phospholipid-specific fatty acid composition. Phosphatidic acid (PA) and diacylglycerol (DAG) are central intermediates in phosphoglyceride and neutral lipid biosynthetic pathways and have also recently been implicated in signal transduction. The present paper shows the effect of aging on phosphatidate phosphohydrolase (PAPase) activiy, which operates on phosphatidic acid to synthesize diacylglycerol. Two forms of mammalian PAPase can be indentified on the basis of subcellular localization and enzyme properties, one involved predominantly in lipid synthesis (PAP 1) and the other in signal transduction (PAP 2). Microsomal and cytosolic fractions of brain and liver from 3.5-month-old (adult) and 28.5-month-old (aged) rats were used. PAPase isoform activities were differentiated on the basis of N-ethylmaleimide (NEM) sensitivity and Mg(2+)-dependency. Our results demonstrate that aging caused PAP 2 to increase in brain microsomal fractions but did not affect PAP 1, whereas in brain cytosolic fractions, it caused a strong decrease in PAP 1 (57%). The distribution of enzymes between microsomes and cytosol changed in aged rats with respect to adult rats, showing a translocation of PAP 1 from cytosol to microsomes. In addition, an increase in the production of monoacylglycerol (MAG) was observed in microsomes from aged brain. PAP 2 activity in liver microsomal fractions from aged rats showed no changes with respect to adult rats whereas PAP 1 activity increased 228% in microsomal fractions and 76% in cytosolic fractions in this tissue. The distribution of PAP 1 activity between microsomal and cytosolic fractions in liver tissue was also affected in aged rats, indicating a translocation of this form of the enzyme from cytosolic to microsomal fractions. The production of monoacylglycerol in liver microsomes also increased, whereas there was a decrease in MAG formation from cytosolic fraction. The changes observed in the two PAPase forms in brain and liver of aged rats with respect to adult rats suggest that PA is differently utilized by the PAPase isoforms, probably generating aging-related DAGs different to those present in adults and required for specific cellular functions. The changes observed in liver PAP 1 from aged with respect to adult rats suggest that such changes could be related with modifications in lipid homeostasis induced by age-altered hormonal balance. However, PA-modified utilization during aging through PAP 2 activity could be related to alterations in neural signal transduction mechanisms.

Aging↗
PubMed2000

Cell surface activities of the human type 2b phosphatidic acid phosphatase.

Several isozymes of mammalian type 2, Mg(2+)-independent phosphatidic acid phosphatase (PAP-2) have recently been cloned, and they are predicted to have their catalytic sites exposed at the cell surface membranes. We investigated the mode of utilization of extracellular lipid substrates by the human PAP-2b expressed in HEK293 cells as a green fluorescent fusion protein. We first confirmed the plasma membrane localization of the expressed PAP-2b. PAP-2b actively hydrolyzed exogenously added lysophosphatidic acid and short-chain phosphatidic acid. In the case of dephosphorylation of lysophosphatidic acid, the reaction products, including inorganic phosphate and monoacylglycerol, were recovered exclusively in the extracellular medium. Interestingly, PAP-2b exhibited negligible activities toward long-chain phosphatidic acid either exogenously when added or generated within the membranes by treating the cells with bacterial phospholipase D. These findings indicate that PAP-2b acts at the outer leaflet of cell surface bilayers and can account for the ecto-PAP activities previously described for various types of cells.

Cell Line↗
PubMed1984

Triglyceride metabolism in human liver: studies on hepatic phosphatidic-acid phosphatase in obese and non-obese subjects.

According to current concepts, soluble phosphatidic-acid phosphatase, converting phosphatidic acid into a diglyceride, is a rate-limiting enzyme in the hepatic biosynthesis of triglycerides. The present paper is the first report on this enzyme in human liver. The enzyme activity was assayed in ammonium sulphate precipitates of cytosol obtained from human liver biopsies. The activity was stimulated by preincubation with alkaline phosphatase and inhibited by Mg-ATP, suggesting that phosphorylation-dephosphorylation may be of some importance for the expression of the activity of the enzyme. When assayed under optimal conditions, the activity obtained in liver biopsies from normal-weight gallstone patients averaged 12.8 +/- 2.0 nmol min-1 (mg protein)-1 (mean +/- SEM) (n = 17). The enzyme activity was slightly higher in liver biopsies from morbidly obese subjects 16.4 +/- 2.8 nmol min-1 (mg protein)-1 (n = 14). The difference between the two groups of subjects was probably in part sex-dependent and was not statistically significant. A similar small and insignificant difference between the two groups of subjects was found when the enzyme activity was assayed in the maximally stimulated state--i.e. after incubation with alkaline phosphate. These findings suggest that an increased capacity of the soluble phosphatidic-acid phosphatase is not of major importance for the increased triglyceride synthesis known to occur in obesity. Other factors (i.e. availability of substrate and cofactors) may be of greater importance.

Adult↗
PubMed1992

Oleate stimulation of diacylglycerol formation from phosphatidylcholine through effects on phospholipase D and phosphatidate phosphohydrolase.

Hydrolysis of exogenous phosphatidylcholine (PtdCho) to 1,2-diacylglycerol by rat liver plasma membranes was stimulated by oleate concentrations as low as 0.1 mM. In the presence of 75 mM ethanol, the fatty acid also enhanced phosphatidylethanol (PtdEtOH) formation from PtdCho. These effects were also observed with linoleate and arachidonate, but not with saturated fatty acids or detergents, and were minimal in microsomes or mitochondria. Release of [3H]choline from exogenous Ptd[3H]Cho was stimulated by oleate, whereas phosphoryl[3H]choline formation was inhibited. Oleate and other unsaturated, but not saturated, fatty acids also stimulated the conversion of exogenous [14C]phosphatidic acid to [14C]diacylglycerol. These data are consistent with stimulatory effects of these fatty acids on both phospholipase D and phosphatidate phosphohydrolase in liver plasma membranes. The stimulatory effect of guanosine 5'-O-[3-thio]triphosphate) (20 microM) on PtdEtOH and diacylglycerol formation from PtdCho was enhanced by low concentrations of oleate. Phospholipase A2 also stimulated PtdEtOH and diacylglycerol formation from exogenous PtdCho. It is proposed that unsaturated fatty acids may play a physiological role in the regulation of diacylglycerol production through activation of phospholipase D and phosphatidate phosphohydrolase.

Animals↗
PubMed1984

Studies on the effects of magnesium ion and propranolol on iris muscle phosphatidate phosphohydrolase.

The properties, subcellular distribution, and the effects of Mg2+ and propranolol on phosphatidate phosphohydrolase (EC 3.1.3.4) from rabbit iris smooth muscle have been investigated. The particulate and soluble (0-30% (NH4)2SO4 fraction) enzymes were assayed using aqueous phosphatidate dispersions and membrane-bound phosphatidate as substrates, respectively. When measured with aqueous substrate, activity was detected in both the particulate and soluble fractions, with the highest relative specific activity found in the microsomal fraction. Maximum dephosphorylation by the microsomal enzyme was about 1100 nmol of inorganic phosphate released/h per milligram protein and occurred at pH 7.0-7.5. In general Mg2+ inhibited the phosphohydrolase activity of the microsomal fraction and stimulated that of the soluble fraction, and the effects of the divalent cation on both of these activities were reversed by propranolol. The microsomal enzyme was slightly stimulated by deoxycholate and inhibited by the divalent cations Mg2+, Ca2+, and Mn2+ at concentrations greater than 0.25 mM. In contrast, the soluble enzyme was stimulated by Mg2+. Inhibition of the microsomal enzyme by Mg2+ (0.5 mM) was reversed by both EDTA, which also stimulated at higher concentrations (1 mM), and propranolol (0.1-0.2 mM). The inhibitory effect of Ca2+ on the enzyme was not reversed by propranolol. In the absence of Mg2+, the microsomal enzyme was inhibited by propranolol in a dose-dependent manner, and both in the absence and presence of the divalent cation the soluble enzyme was inhibited by the drug in a similar manner. These data suggest that the cationic moiety of propranolol may act by competing at the Mg2+-binding sites.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1996

Inhibition of the insulin receptor tyrosine kinase by phosphatidic acid.

The lipid second messenger, phosphatidic acid, inhibits the intrinsic tyrosine kinase activity of the insulin receptor in detergent-lipid mixed micelles or in reconstituted membranes. Enzymatic studies revealed that this lipid second messenger inhibits the catalytic activity of partially purified insulin receptor without affecting the affinity of the receptor for insulin. Selectivity in the protein-lipid interaction is suggested by the inability of several other acidic lipids to affect the kinase activity of the receptor and by the relative insensitivity of the inhibition to increasing ionic strength and, in some cases, micelle surface charge. Lysophosphatidic acid and phosphatidic acids with short acyl chains do not affect significantly the receptor's kinase activity, suggesting that hydrophobic interactions are involved in the inhibition. Thus, both a high affinity interaction of the insulin receptor with the phosphate headgroup and a stabilizing hydrophobic interaction with the acyl chains contribute to the inhibitory protein-lipid interaction. The selective sensitivity of the insulin receptor to phosphatidic acid suggests that the receptor-mediated generation of this lipid in the plasma membrane could negatively modulate insulin receptor function.

Adenosine Triphosphate↗
PubMedDate not supplied

Modulation of luminol chemiluminescence of fMet-Leu-Phe-stimulated neutrophils by affecting dephosphorylation and the metabolism of phosphatidic acid.

This paper is addressed to study how PKC-mediated effects and phosphatidic acid interact together in activation of NADPH-oxidase in formyl-methionyl-leucyl-phenylalanine (fMet-Leu-Phe) stimulated neutrophils as detected by luminol chemiluminescence. The early luminescence response in fMet-Leu-Phe-stimulated cells (up to 5 min after stimulation) depends mainly on reactive oxygen species generated extracellularly, whereas all later events are caused by oxidation of luminol inside the cells. The two protein phosphatase inhibitors, okadaic acid and calyculin A, dramatically increased the late luminescence of cells. This enhancement was totally inhibited by the phospholipase D modulator butanol, while the protein kinase C (PKC) inhibitor bisindolylmaleimide I was insensitive. The early luminescence response of the cells was slightly inhibited by both protein phosphatase inhibitors and depended on protein kinase C as well as on phospholipase D activities. Propranolol, an inhibitor of phosphatidate phosphohydrolase, enhanced all parts of luminescence response of fMet-Leu-Phe-stimulated neutrophils at concentrations up to 2.5 x 10(-5) mol/L. While the late luminescence response of propranolol-treated cells was not inhibited by the PKC inhibitor bisindolylmaleimide I, the first response depended on protein kinase C. The inhibitor of diacylglycerol kinase R59949 enhanced the luminescence signal only during the first 4 min in fMet-Leu-Phe-stimulated cells. Only diacylglycerols derived from phospholipase C, such as 1-stearoyl-2-arachidonoyl-sn-glycerol, were able to initiate an oxidative burst in cells. Saturated diacylglycerols (e.g. 1,2-dipalmitoyl-sn-glycerol or 1,2-distearoyl-sn-glycerol) did not yield any luminol chemiluminescence, although they were incorporated into the plasma membrane, as evidenced by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. Our results demonstrate that phosphatidic acid produced by phospholipase D is responsible for NADPH-oxidase activity in fMet-Leu-Phe-stimulated neutrophils over the entire measuring time, whereas PKC-mediated processes are only involved during the first 5 min.

Diglycerides↗
PubMed1995

Multifunctional phosphatidic acid signaling in mammary epithelial cells: stimulation of phosphoinositide hydrolysis and conversion to diglyceride.

We have shown previously that phosphatidic acid esterified to polyunsaturated fatty acids is mitogenic for primary cultures of mouse mammary epithelial cells embedded within collagen gels. We hypothesized that this mitogenic competence resulted from the ability of this phospholipid to activate multiple signal transduction pathways in mammary epithelium. A closer examination of this hypothesis was undertaken by examining the effect of exogenous phosphatidic acid on phosphoinositide (PI) hydrolysis and its intracellular metabolism to diglyceride, an activator of protein kinase C. For assays of phosphoinositide-specific phospholipase C activation, mammary epithelial cells from virgin Balb/c mice were isolated by collagenase dissociation of mammary glands and cultured on the surface of Type I collagen-coated culture dishes. Phosphatidic acid (PA) stimulated a sustained increase in inositol phosphates and caused inositol phospholipid depletion when added to cells in which inositol phospholipids were prelabeled with 3H-myoinositol. This effect was specific for PA among phospholipids tested. Neither lineoleic acid, that can be released from PA, nor prostaglandin E2 affected PI hydrolysis. When mammary epithelial cells were cultured inside collagen gels in the presence of exogenous PA or phosphatidylcholine (PC) radiolabeled with 3H-glycerol, PA was found to persist intracellularly and be dephosphorylated to diglyceride (an activator of protein kinase C) to a greater extent than PC, a nonmitogenic phospholipid. In contrast to PA, epidermal growth factor (EGF) only slightly stimulated PI hydrolysis, showing that these two different growth-promoting factors do not actively couple to the same signal transduction pathways in mammary epithelial cells. These results show that PA may activate multiple pathways in mammary epithelial cells either directly or via its metabolism to diglyceride.

Animals↗
PubMed1988

Effects of acetylcholine and other agents on 32P-prelabeled phosphoinositides and phosphatidate in crude synaptosomal preparations.

Experimental conditions are described which permit effects of various agents on polyphosphoinositides and phosphatidic acid (PA) to be evaluated simultaneously in crude nerve-ending preparations from rat brain. Acetylcholine (3-100 microM) or carbachol (30-1,000 microM) induced the hydrolysis of prelabeled polyphosphoinositides and, at the same time, stimulated the net label incorporated in phosphatidic acid. All muscarinic effects were blocked by atropine or pirenzepine. Non-muscarinic agonists (glutamate, adenosine, norepinephrine) stimulated polyphosphoinositide hydrolysis in this preparation, but of these only norepinephrine affected phosphatidic acid turnover. A potentiation of acetylcholine-induced phosphoinositide turnover by KCl was observed, as well as an apparent selective inhibition of PIP2 hydrolysis by LiCl. Acetylcholine-stimulated turnover of PA was not necessarily coupled to phosphoinositide hydrolysis.

Acetylcholine↗
PubMed1993

Calcium-independent activation of protein kinase C by the dianionic form of phosphatidic acid.

Phosphatidic acid in the form of small unilamellar vesicles has a dissociation constant of about 8.3 as determined by 31P nuclear magnetic resonance (NMR) spectroscopy. The activation of protein kinase C (PKC) by monovalent phosphatidic acid or phosphatidylserine occurs only in the presence of Ca2+. However, PKC activity on membranes of divalent anionic phosphatidic acid is independent of Ca2+ concentration.

Calcium↗
PubMed1998

Disruption of a gene encoding phosphatidic acid phosphatase causes abnormal phenotypes in cell growth and abnormal cytokinesis in Saccharomyces cerevisiae.

Phosphatidic acid phosphatase (PAP) is an enzyme involved in lipid metabolism. Diacylglycerol (DG) and phosphatidic acid (PA) are a substrate and a product of PAP, respectively, and function as second messengers in several signal transduction pathways in animals. To investigate the function of PAP in Saccharomyces cerevisiae, we analyzed changes in cellular phenotypes of a mutant that has a disrupted PAP gene. Two putative genes for PAP (ScPAP1 and ScPAP2) are in the S. cerevisiae genome. We generated a ScPAP1-null mutant and observed its cellular phenotypic changes. The ScPAP1-null mutant cells aggregated in liquid culture, and microscopical analyses showed that these mutant cells have an abnormal cell shape and abnormal cytokinesis during cell division. The ScPAP1 is possibly involved in cell growth and cytokinesis in S. cerevisiae. Yeast phosphatidic acid phosphatase is possibly involved in cell growth and cytokinesis.

Amino Acid Sequence↗
PubMed2000

Enhancement of the migration of metastatic human breast cancer cells by phosphatidic acid.

Phosphatidic acid (PA), lysophosphatidic acid (LPA), and sphingosine 1-phosphate (SPP) are naturally occurring phospholipids which induce a variety of effects as extracellular messengers. In this study, we compared the effects of these phospholipid signaling molecules on the migration of invasive and noninvasive breast cancer cell lines, an index of the metastatic potential of these cells. As previously demonstrated, invasive MDA-MB-231 breast cancer cells exhibited increased constitutive (nonstimulated) migration in comparison to poorly invasive MCF-7 cells. Phosphatidic acid employed at nanomolar concentrations markedly potentiated migration of the invasive cells but had no effect on migration of either the noninvasive MCF-7 cells or nonneoplastic human epithelial cells. Lysophosphatidic acid and sphingosine 1-phosphate inhibited both the directed (chemotactic) and random (chemokinetic) migration of MDA-MB-231 cells. Experiments were undertaken to characterize the signaling pathway involved in constitutive and PA-stimulated migration of MDA-MB-231 cells. The tyrosine kinase inhibitors staurosporine and genistein inhibited constitutive and PA-induced migration in a dose-dependent manner, consistent with a role for tyrosine phosphorylation in the migratory response. In addition, the phosphatidylinositol (PI) 3' kinase inhibitors wortmannin and LY294002 strongly inhibited both the constitutive and PA-stimulated migration of the invasive breast cancer cells, indicating that PI-3' kinase plays an important role in the metastatic migration of breast cancer cells. Finally, PA-induced migration of MDA-MB-231 was markedly attenuated by pretreatment of cells with Clostridium difficile Toxin B, pertussis toxin and suramin, implying a role for a Gi receptor-dependent process involving activation of the small GTP-binding protein Rho. Since an enhanced ability to migrate heightens the metastatic potential of cells within solid tumors, our results suggest that the metastatic capabilities of breast cancer cells may be enhanced by a receptor-driven cellular process initiated by phosphatidic acid or related lipid phosphate messengers.

Breast Neoplasms↗
PubMed1998

Impairment of the sarcolemmal phospholipase D-phosphatidate phosphohydrolase pathway in diabetic cardiomyopathy.

Experimental evidence suggests that the myocardial phospholipase D (PLD)-phosphatidate phosphohydrolase (PAP) signalling pathway may regulate Ca2+ movements and contractile performance of the heart. As abnormal Ca2+ homeostasis is associated with diabetic cardiomyopathy, we examined the functional status of the PLD/PAP pathway in sarcolemmal (SL) membranes isolated from insulin-dependent diabetic rat hearts at 8 weeks after a single i.v. injection of streptozotocin (65 mh/kg b.w.). Compared to age-matched controls, SL PLD hydrolytic (producing phosphatidic acid, PtdOH) and transphosphatidylation activities were significantly depressed in diabetic animals, while SL PAP was significantly augmented. The net effect of the altered enzyme activities in diabetic animals was a severely diminished (by 67% of controls) membrane level of PLD-derived PtdOH. Two weeks of insulin therapy to the 6 week diabetic animals normalized PLD, while PAP activity and PtdOH level were significantly modified, but had not completely reverted to control values. The observed changes were not due to hypothyroidism associated to the diabetic model as the induction of hypothyroidism in healthy non-diabetic animals did not affect SL PLD and PAP. The results suggest that the severe reduction of PLD-derived PtdOH and increased production of sn-1,2-diacylglycerol by phosphatidate phosphohydrolase may lead to an impairment of the bioprocesses mediated by these signalling lipids.

Animals↗
PubMed1984

Phosphatidic acid regulates the activity of the channel-forming ionophores alamethicin, melittin, and nystatin: a 1H-NMR study using phospholipid membranes.

The regulation of ion channels by phosphatidic acid (a proposed active metabolite in the phosphatidylinositol effect) was investigated using 1H-NMR spectroscopy and small unilamellar phospholipid vesicles. Transport across egg-yolk phosphatidylcholine (egg PC) and dipalmitoyl phosphatidylcholine (DPPC) vesicular membranes in the presence of the channel-forming ionophores alamethicin, melittin, and nystatin was monitored using the lanthanide probe ion Pr3+. In the absence of the ionophores, phosphatidic acid (PA) alone was found to have no ionophore properties, but in the presence of the ionophores the incorporation of 3 mol % phosphatidic acid in the bilayer markedly increased the rate of transport using melittin and nystatin, but decreased the rate using alamethicin, independent of the type of phosphatidylcholine used. The presence of PA in the bilayer also stimulated the production of lytic type channels, the extent of which were both ionophore- and lipid-dependent. These results are discussed in terms of possible molecular interactions between the PA, the individual ionophores, and type of lipid used.

Alamethicin↗
PubMed1983

Histamine release by phosphatidic acid from isolated mast cells of two types of genetically different rats.

Phosphatidic acid produced a similar dose-dependent release of histamine from isolated peritoneal mast cells of two types of rat, one of which did not release histamine when dextran was present in the incubation mixture. This release induced by phosphatidic acid resembled that evoked by a basic secretagogue like compound 48/80, being independent of exogenous calcium and unaffected by either phosphatidyl serine or its lyso derivative. The non-cytotoxic release of histamine induced by phosphatidic acid is therefore distinct from that by dextran and does not involve dextran receptors residing on the plasma membrane of mast cells of rats which show the dextran anaphylactoid reaction.

Animals↗
PubMed1981

The importance of the production of phosphatidic acid for the release of arachidonic acid in stimulated platelets.

Phosphatidic acid is formed by platelets as a result of the combined activities of phospholipase C and diacylglycerol kinase. The initial thrombin-activated phospholipase C-mediated reaction is quinacrine insensitive and is followed by quinacrine-sensitive phospholipase A2 activities. The phosphatidic acid released probably results in cellular calcium gating, which, among other actions, might release arachidonic acid by activating phospholipases A2. Indeed, we have detected a phosphatidic acid-specific phospholipase A2 in platelets, which might have an important role in the liberation of arachidonic acid.

Arachidonic Acid↗
PubMed1975

Phosphatidic acid metabolism, calcium ions and transmitter release from electrically stimulated synaptosomes.

Synaptosomes isolated from guinea pig brain cortex were stimulated electrically in a medium containing [32P]-orthophosphate. The electrical stimulation caused increased labelling of phosphatidic acid in a synaptic vesicle fraction prepared by osmotic shock of the incubated synaptosomes. Electrical stimulation also provokes transmitter release from the synaptosomes. Both increased phosphatidate labelling and transmitter release required calcium ions in the medium. The effects are discussed in relation to earlier work with acetylcholine and the possible involvement of membrane phosphatidic acid in transmitter release by exocytosis.

Animals↗
PubMed1980

Microsomal phosphatidic acid phosphohydrolase of rat mammary tissue: I. General properties.

The microsomal bound phosphatidic acid phosphohydrolase from lactating rat mammary tissue had a specific activity of six nmoles per mg protein per minute. The optimum pH was 7.0; magnesium at 1.3 mM was required for maximum activity, and at low substrate concentrations magnesium lowered the Km of the enzyme for phosphatidic acid. Diglycerides exerted little effect while diglyceride ether stimulated enzyme activity. Inorganic salts, i.e., potassium phosphate and potassium chloride, enhanced rates of phosphatidic acid hydrolysis under standard assay conditions.

Animals↗