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Regulation of phospholipase D in HL-60 granulocytes. Activation by phorbol esters, diglyceride, and calcium ionophore via protein kinase- independent mechanisms.

It has recently been demonstrated that the chemotactic peptide N-formyl-Met-Leu-Phe activates phospholipase D (PLD) in dimethyl sulfoxide-differentiated HL-60 granulocytes to produce phosphatidic acid (PA) and, in the presence of ethanol, phosphatidylethanol (PEt) (Pai, J.-K., Siegel, M. I., Egan, R. W., and Billah, M. M. (1988) J. Biol. Chem. 263, 12472-12477). We now report that biologically active phorbol esters, a cell-permeable diacylglycerol, 1-oleoyl-2-acetylglycerol (OAG), and calcium ionophore A23187 are also potent inducers of PLD in these HL-60 granulocytes. HL-60 granulocytes have been selectively labeled in 1-O-alkyl-2-acyl-sn-glycero-3-phosphocholine (alkyl-PC) with 32P by incubating the cells with alkyl-[32P]lyso-phosphatidylcholine (PC). When these labeled cells are treated with phorbol 12-myristate 13-acetate (PMA), phorbol 12,13-dibutyrate, OAG, or A23187, alkyl-[32P]PA is formed. Because cellular ATP has not been labeled with 32P, the formation of alkyl-[32P]PA conclusively demonstrates PLD activation by these agents. In the presence of 0.5% ethanol, phorbol esters, OAG, and A23187 also induce formation of alkyl-[32P]PEt, demonstrating that the activated PLD catalyzes transphosphatidylation between the phosphatidyl moiety of the alkyl-[32P]PC and ethanol. Formation of alkyl-[32P]PA and alkyl-[32P]PEt in response to these various agents occurs in a time- and dose-dependent manner and exhibits differential Ca2+ requirements. Based on experiments with both [3H]alkyl-PC and alkyl-[32P]PC, it is concluded that alkyl-PA and alkyl-PEt formed in response to PMA, OAG, or A23187 are derived exclusively from PLD action on alkyl-PC. Furthermore, subthreshold concentrations of PMA (0.5-2.0 nM) or OAG (1.0-25 microM) combined with subthreshold levels of A23187 (15-60 nM) induce the formation of alkyl-[32P]PA and alkyl-[32P]PEt, suggesting that receptor-mediated activation of PLD might involve cooperative interactions between Ca2+ and diglyceride. Although PLD is activated by agents that also activate protein kinase C, the protein kinase C inhibitor, K252a, inhibits PMA-induced protein phosphorylation but causes only partial inhibition of PLD activation. We conclude that phorbol esters, OAG, and A23187 activate PLD in HL-60 granulocytes via protein kinase-independent as well as protein kinase-dependent mechanisms.

Calcimycin↗

Fecal diglycerides as selective endogenous mitogens for premalignant and malignant human colonic epithelial cells.

Diglycerides (DGs) have been found in fecal extracts at concentrations which induce mitogenesis of adenoma and some carcinoma cells but not normal cells in primary culture. DGs containing stearic, oleic, palmitic, and myristic acid side chains were found in fecal extracts from each of eight subjects. Synthetic 1,2-DGs, containing the fatty acids found in endogenous fecal DGs, induced mitogenesis in cultures of premalignant cells from each of 13 adenomas, covering all histological classes, and in cultures from two of four carcinomas. The potent adenoma mitogen, dimyristin, had no mitogenic activity on cultures of normal colonic epithelial cells from seven different subjects. These results suggest DGs may act as endogenous mitogens in the development of human colon cancer. The extent of adenoma mitogenesis was correlated with the chain length of the saturated R-groups: 16 greater than 14 greater than 12 greater than 10 greater than 8 much greater than 18. DGs with oleic acid residues, C18:1, were among the most active, while substitution of even one fatty acid residue with a stearic acid residue, C18:0, reduced or eliminated mitogenic activity. Dimyristin also induced enhanced levels of urokinase secretion from carcinoma cells, in parallel to the phorbol ester tumor promoter, 12-O-tetradecanoylphorbol-13-acetate. These results imply that DGs found in the colon induce a selective growth of benign colonic tumors and some carcinomas, and may enhance the invasive capacity of carcinomas, while leaving normal cells unaffected.

Adenoma↗

Selective priming of rate and duration of the respiratory burst of neutrophils by 1,2-diacyl and 1-O-alkyl-2-acyl diglycerides. Possible relation to effects on protein kinase C.

Both 1,2-diacyl- and 1-O-alkyl-2-acyl-sn-glycerols are released during stimulation of human polymorphonuclear leukocytes (PMNL). 1,2-Diacylglycerols have received intense interest as intracellular "second messengers" due to their ability to activate protein kinase C (Ca2+ phospholipid-dependent enzyme). However, little is known about bioactivities of the alkylacylglycerols. This study compared the ability of 1,2-diacyl- and 1-O-alkyl-2-acylglycerols to modulate the respiratory burst of stimulated PMNL, a response which depends on the activation of an NADPH oxidase to generate bactericidal species of reduced oxygen. Direct stimulation by N-formyl-Met-Leu-Phe caused an abrupt release of H2O2 which ceased within 2.5 min. Preincubation with diacylglycerols (1-oleoyl-2-acetylglycerol,5-30 microM, and 1,2-dioctanoylglycerol,2-5 microM) caused a decrease in lag time, 3-fold increase in initial rate of H2O2 release, and marked prolongation of the response to N-formyl-Met-Leu-Phe (features characteristic of a priming effect). Preincubation with alkylacylglycerols (1-O-delta 9-octadecenyl-2-acetylglycerol, 5-30 microM, and 1-O-octyl-2-octanoylglycerol, 20-50 microM) primed initiation (shortened lag time and increased velocity) but, in contrast to diacylglycerols, did not alter duration of H2O2 release. While low concentrations of diacylglycerols (5-30 microM) primed PMNL, higher concentrations (greater than or equal to 70 microM) stimulated the cells directly. In contrast, higher (70-100 microM) concentrations of alkylacylglycerols did not prime the responses but, in fact, inhibited priming (especially of duration) induced by diacylglycerol. The high concentrations of alkylacylglycerol also inhibited direct stimulation induced by high concentrations of diacylglycerol. Direct stimulation by high concentrations of diacylglycerol probably involves activation of protein kinase C, whereas alkylacylglycerol was found to inhibit activation of protein kinase C by diacylglycerol in vitro. Thus, diacylglycerols are complete priming agonists, altering both rate and duration of the response. In contrast, alkylacylglycerols may have biphasic, concentration-related effects in modulation of functions of PMNL. At low concentrations, they may facilitate initiation of functional events; however, as their concentration increases, they may serve to terminate responses. The distinct priming effects of these diglycerides also reveal that priming can involve at least two distinct events: 1) initiation and 2) prolongation.(ABSTRACT TRUNCATED AT 400 WORDS)

Cytosol↗

Synthesis of all-cis-1,3-diacylcyclopentane-1,2,3-triol-2-phosphate via acyl group migration in a cyclic diglyceride analog.

The acid-catalyzed isomerization of the diglyceride analog (1,2,3/0)-1,2-dipalmitoylcyclopentane-1,2,3-triol has been used to generate syn-syn-1,3-diacyl-cyclopentane-1,2,3-triol, a required intermediate in the synthesis of a symmetrical all-cis-1,2,3/0-2P cyclopentanoid phosphatidic acid analog. The all-cis cyclo-phosphatidic acid analog has therefore been obtained in the free acid form and as the diphenyl ester, dimethyl ester, and dipotassium salt derivatives. The compounds have been characterized by microanalysis and spectroscopic methods. The 1,2,3/0-2P analog is now available for comparative studies with the corresponding all-trans cyclophosphatidic acid (1,3/2-2P).

Cyclopentanes↗

Gravimetric determination of ethoxylated mono- and diglycerides in bread.

A gravimetric method is described for the quantitative determination of ethoxylated mono-and diglycerides (EMGs) in bread at levels as low 0.42% (dry sample). The air-dried pulverized samples are Soxhlet-extracted 22 h with an azeotropic mixture of n-propanol-water. The contents are evaporated to dryness, and then treated with 5% HCl in methanol to trans-esterify the fatty acids present which are then removed by petroleum ether extraction. The EMGs are subsequently precipitated from aqueous solution with phosphomolybdic acid in the presence of barium ions. The precipitate is weighed and compared with known amounts of standard carried through the same procedure.

Bread↗

Platelet-activating factor stimulates phosphatidic acid formation in cultured rat mesangial cells: roles of phospholipase D, diglyceride kinase, and de novo phospholipid synthesis.

Platelet-activating factor (PAF) stimulates phospholipase C (PLC)-induced hydrolysis of phosphatidylinositol-4,5-bisphosphate (PtdIns-4,5-P2). Yet, PAF-stimulated diglycerides (DG) are still elevated at time points where inositol polyphosphates have returned to basal levels. Thus, other signal transduction pathways that hydrolyze phosphatidylcholine (PtdCho) or phosphatidylethanolamine (PtdEth) and form DG and phosphatidic acids (PA) through either PLC or phospholipase D (PLD) may also mediate PAF-stimulated cellular responses. Initially the effects of PAF upon 32P-PA generation in mesangial cells (MC) were assessed. PA formation may be indicative of several metabolic pathways including PLD and DG kinase activities as well as de novo phospholipid synthesis. PAF (10(-7) M) increased 32P-PA formation as early as 5 seconds and this elevation persisted up to 15 minutes. When MC were pretreated with the DG kinase inhibitor-R59022, PAF-induced 32P-PA formation was diminished at early but not late time points, demonstrating that the initial component of PA formation may be due, in part, to PLC activation and subsequent phosphorylation of DG. The reciprocal reaction, PA phosphohydrolase, which dephosphorylates PA to from DG was not stimulated by PAF, suggesting that the sustained elevation of DG induced by PAF is primarily a reflection of PLC. 3H-glycerol pulse-labeling experiments suggest that PAF also stimulates de novo phospholipid synthesis which also contributes to PA formation. Conclusive proof for PLD in the generation of PA was obtained by assessing the formation of 3H-phosphatidyl-ethanol (PEt) from 3H-alkyl-lyso-glycero phosphocholine (GPC) and exogenous ethanol. PAF stimulated alkyl-PEt generation in the presence but not the absence of 0.5% ethanol. Also, PAF induced a concomitant elevation of alkyl-PA at 15 minutes and this elevation of alkyl-PA was reduced when the cells were exposed to exogenous ethanol, reflecting the formation of PEt. Corroborating evidence suggests that PAF stimulates 3H-choline and 3H-ethanolamine release, suggesting that PtdCho and PtdEth are substrates for PLD. Thus, these data demonstrate that MC respond to PAF with elevated PLD and DG kinase activities as well as with an increased rate of de novo lipid synthesis which increases PA, a potential intracellular signal.

Animals↗

Diglyceride kinase from Escherichia coli. Modulation of enzyme activity by glycosphingolipids.

Diglyceride kinase was purified from membranes of Escherichia coli K-12 using organic solvents. The enzyme apoprotein depended on lipids, such as cardiolipin (diphosphatidylglycerol), phosphatidylcholine or 1-monooleoylglycerol, for activity with 1,2-dipalmitoylglycerol. Mixed brain cerebrosides and gangliosides as well as defined ganglioside fractions and synthetic lactocerebroside were devoid of lipid cofactor activity. However, all these glycosphingolipids were strong inhibitors of activation by phosphatidylcholine. When cardiolipin was used as lipid activator with the detergent, Triton X-100, as solubilizing agent, the addition of mixed or purified gangliosides first (at about 0.4 mM) resulted in additional activation, but higher ganglioside concentrations were strongly inhibitory. Both effects were absolutely dependent on the presence of lipid-bound sialic acid and were not given by cerebrosides, by free sialic acid or by sialyl-lactose. The stimulating and inhibitory effects of glycosphingolipids could also be demonstrated when 1-monooleoylglycerol was used as substrate, lipid activator and solubilizing agent at the same time. The modulation of kinase activity by glycosphingolipids is discussed at the level of lipid/protein interactions.

Cardiolipins↗

Absence of diglyceride kinase activity in the photoreceptor cells of Drosophila mutants.

Diglyceride kinase (DG) activity was found to be almost absent in the photoreceptor cells of Drosophila vision mutants, norpA (no receptor potential A). Other enzymes related to the phosphatidic acid (PA) metabolism, such as monoacyl-glycerophosphate acyltransferase and PA phosphatase, were normal in the mutant. The deficiency in PA content in the retinular cells of norpA, demonstrated by 32P incorporation in vivo is, therefore, due to abnormal reduction in DG kinase activity. The DG kinase was found to be localized in the retinular cell by assaying its activity in the mutants rdgA (receptor cells degenerated) and sine oculis (compound eyes absent).

Animals↗

Cloning of the Pseudomonas aeruginosa gene encoding CDP-diglyceride synthetase.

The CDP-diglyceride synthetase (CDS)-encoding gene (cds) from Pseudomonas aeruginosa PAO1 was cloned and sequenced. The gene possessed an open reading frame of 813 bp capable of encoding a putative polypeptide of 271 amino acids (aa) (28 699 Da). The deduced aa sequence of CDS revealed a 67% similarity (45% identity) to Escherichia coli CDS.

Amino Acid Sequence↗

High-performance liquid chromatographic analysis of 3'-azido-3'-deoxythymidine monophosphate diglyceride, an anti-HIV glycerophospholipid.

A reversed-phase chromatographic method is described for the analysis of an experimental anti-AIDS drug 3'-azido-3'-deoxythymidine monophosphate diglyceride (AZT-MP-DG) [J.M. Steim et al., Biochem. Biophys. Res. Commun. 171, 458-464 (1990)] [1], a phosphatidic acid derivative of AZT. Analytical conditions were based upon conventional separations of glycerophospholipid species. Where AZT-MP-DG was monitored by UV absorption, there were two wavelength maxima. The response was linear in the concentration range used in this study. The peak was characterized by absorbance ratios with a rapid scanning UV detector.

Acquired Immunodeficiency Syndrome↗

Effect of the diglyceride lipase inhibitor, RG80267, on epithelial chloride secretion induced by various agents.

We previously reported that a diglyceride lipase inhibitor, RG80267, inhibits chloride secretion stimulated by adenosine agonists, stimuli whose effects appear unrelated to cAMP, cGMP or cytosolic calcium. Here, the effect of RG80267 on Cl- secretory responses to agents which do utilize these messengers was examined. RG80267 inhibited responses to vasoactive intestinal polypeptide, forskolin (cAMP-dependent) and E. coli heat stable enterotoxin (cGMP-dependent), but not to prostaglandin E1 or cholera toxin (cAMP-dependent). RG80267 enhanced responses to histamine (calcium-dependent). The inhibitory effect of RG80267 was not due to inhibition of cAMP accumulation. Arachidonic acid release may participate in chloride secretion. Vasoactive intestinal polypeptide, but not prostaglandin E1, released radiolabel from cells preloaded with [3H]arachidonic acid. There may thus be differences between mechanisms of various cyclic nucleotide-dependent chloride secretory responses. Arachidonic acid release may modulate the extent of secretion elicited by some secretagogues.

Alprostadil↗

Bacterial glycolipids. Glycosyl diglycerides in gram-positive bacteria.

1. The lipids of ten Gram-positive bacteria have been isolated and the presence in each of a glycosyl diglyceride was established. 2. The glycolipid fractions were isolated and deacylated to give water-soluble glycosides which were purified by paper chromatography. Partial structures for the glycosides have been deduced from chemical and enzymic studies. 3. Nine of the glycosides were disaccharides glycosidically linked to the 1-position of glycerol: the remaining glycoside contained a trisaccharide similarly linked to glycerol.

Bacillus subtilis↗

In-vitro evaluation of filaricidal activity of GABA and 1,3-dipalmitoyl-2-(4-aminobutyryl)glycerol HCl: a diglyceride prodrug.

A diglyceride ester of gamma-aminobutyric acid (GABA) has been synthesized and its filaricidal activity compared with GABA, and progabide in-vitro, on infective larvae and microfilariae of Molinema dessetae, a rodent filaria. GABA induced paralysis in infective larvae but was inactive on microfilariae. There were interactions between the culture medium and GABA. The ester drug at 0.1 mmol L-1 (1,3-dipalmitoyl-2-(4-aminobutyryl)glycerol HCl) was as active as progabide on infective larvae and hundredfold more potent than GABA. Its microfilaricidal activity at 1 mmol L-1 was lower than that progabide at 0.1 mmol L-1 but a delayed effect was observed. The data confirm filariae sensitivity to GABA derivatives.

Animals↗

Studies on the formation by rat brain preparations of CDP-diglyceride from CTP and phosphatidic acids of varying fatty acid compositions.

The enzyme, CTP:phosphatidate cytidylyltransferase (EC2.7.7.41) which catalyses formation of CDP-diglyceride from CTP and phosphatidic acid has been studied in rat brain preparations and other tissues. Improvement, as judged by the higher tissue activities obtained, in the assay method for this enzyme was achieved through use of phosphatidic acids sonicated in buffer-detergent solution saturated with ether and containing bovine serum albumin and use of short incubation times which essentially provided a measure of initial rates. The enzyme of rat brain microsomes yielded with 1,2-dioleolphosphatidic acid as substrate a pH optimum of 6.8 with maleate buffer and optimal concentrations of 60mM for MG2+, 6MM for CTP and 250 mug per 0.8 ml for phosphatidic acid. Enzyme activity was mainly located in the 90,000 X g fraction (microsomal) with small but significant activity in the 12,000 X g fraction. Comparison of activities (nanomoles CTP incorporated per milligram protein per minute) amongst tissues showed the following order: brain, 1.87; liver, 1.32; lung, 1.19; small intestine, 1.00; kidney, 0.69; heart, 0.41; diaphragm, 0.07; skeletal muscle, 0.02. Examination of the effect of varying the fatty acid composition in the phosphatidic acids added exogenously gave the following order (activities in parentheses); 1-stearoyl-2-oleoyl- (5.58), 1-oleoyl-2-stearoyl- (5.37), 1,2-dioleoyl- (4.49) 1-palmitoyl-2-oleoyl-(3.85), 1-stearoyl-2-arachidonoyl-(3.31), 1-arachidonoyl-2-stearoyl-(3.16), 1,2-diarachidonoyl-(0.72), 1,2-dicaproyl-(0.67), 1,2-dipalmitoyl-(0.67) and 1,2-distearoyl-(0.18). The single bis- and lysophosphatidic acids tested were inactive as substrates. Apart from a possible preference for one or more unsaturated fatty acids the transferase enzyme showed no selectivity in respect to the fatty acid distribution of phosphatidic acids.

Animals↗

Incorporation of an (125)I-labeled hexa-iodinated diglyceride analog into low-density lipoprotein and high specific uptake by cells of cervical carcinoma cell lines.

The feasibility of using low-density lipoprotein (LDL) to deliver cytotoxic drugs to tumor cells has been explored since the 1980s, when cells of a number of cancer cell lines were found to have higher LDL receptor activity than normal cells. Such differential uptake between tumor and normal cells may provide a unique opportunity to use LDL as a tumor-specific carrier of radiopharmaceuticals for the clinical management of cancer. In this study, an (125)I-labeled hexa-iodinated diglyceride analog, 1, 3-dihydroxypropan-2-one 1,3-diiopanoate (DPIP), was synthesized and incorporated into LDL using a fusion technique. It was found that approximately 500 [(125)I] DPIP molecules were incorporated into each LDL particle. Cells of three human cervical tumor cell lines, HeLa, SiHa and C-33A, were used to examine the cellular uptake of the [(125)I]DPIP-LDL conjugate. It was shown that the [(125)I]DPIP-LDL conjugate was specifically bound to and taken up by cervical tumor cells through an LDL receptor-mediated endocytosis pathway. The results suggest that LDL may be a selective carrier for delivering hydrophobic radiopharmaceuticals to cancer cells and particularly for the diagnosis of cervical tumors.

Binding Sites↗

Purification and properties of the membrane-bound CDP-diglyceride synthetase from Escherichia coli.

The enzyme CDP-diglyceride synthetase (CTP: phosphatidate cytidylyltransferase; EC 2.7.7.41) has been purified to 90% homogeneity from Escherichia coli cells that overproduce the enzyme 50-fold through the use of recombinant DNA technology. The purification required the use of different detergents at each step, illustrating the refractory hydrophobic nature of this protein. Apparent physical effects of EDTA on the enzyme were also utilized in the purification. The enzyme has an apparent minimum subunit mass of 27,000 daltons, as estimated by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. The amino acid composition of the protein was determined, and it correlates well with the theoretical protein product of the cds gene, the sequence of which is reported in the accompanying paper (Icho, T., Sparrow, C. P., and Raetz, C. R. H. (1985) J. Biol. Chem. 260, 12078-12083). The pure enzyme displays surface dilution kinetics when assayed in the presence of Triton X-100. As previously suggested on the basis of studies using partially purified preparations, the enzyme mechanism is sequential, and computer-calculated kinetic constants are reported herein. The substrate specificity of the enzyme is also investigated. This is the first time this enzyme has been purified to homogeneity from any source, despite the fact that it is essential for phospholipid biosynthesis in all organisms.

Amino Acids↗

Diglyceride kinase in human platelets.

Human platelets contain diglyceride kinase, an enzyme that catalyzes the phosphorylation of diacylglycerol by adenosine 5'-triphosphate to yield phosphatidic acid. The majority of the platelet enzyme is particulate-bound, and membrane fractions of platelet homogenates have a higher specific activity than granule fractions. Both deoxycholate and magnesium are necessary for optimal enzyme activity. The K(m) of the enzyme for adenosine 5'-triphosphate is 1.3 mm, and the apparent K(m) for diacylglycerol is 0.4 mm. The pH optimum is 6.6-6.8 in imidazole-HCl or maleate-NaOH buffer. The enzyme activity of platelets from normal subjects was similar to the activity from patients with renal and hepatic failure.

Adenosine Triphosphate↗

Triglyceride, diglyceride, monoglyceride, and cholesterol ester hydrolases in chicken adipose tissue activated by adenosine 3':5'-Monophosphate-dependent protein kinase. Chromatographic resolution and immunochemical differentiation from lipoprotein lipase.

Hormone-sensitive lipase and cholesterol ester hydrolase of chicken adipose tissue were markedly activated by adenosine 3':5'-monophosphate (cAMP)-dependent protein kinase (on the average, 235 to 275%; occasionally as much as 1000%). Diglyceride and monoglyceride hydrolases were also activated, but to a lesser extent (60 to 87%). The activation of all four hydrolases was inhibited by protein kinase inhibitor and reversed by the addition of exogenous protein kinase. Following activation by cAMP-dependent protein kinase, all four hydrolases were deactivated in a Mg2+-dependent reaction and then reactivated to or near initial levels on incubation with cAMP and Mg2+-ATP. The reversible deactivation is assumed to reflect activity of one or more protein phosphatases. The maximum activation obtainable for the four hydrolases decreased when the tissue had been previously exposed to glucagon, indicating that the glucagon-induced activation was probably similar to or identical with the activation demonstrated in cell-free preparations. The pH optima for the four hydrolase activities were similar (7.13 to 7.38). Although the absolute activities and relative degrees of kinase activation differed according to the particular emulsified substrates used, the results do not rule out the possibility that all four hydrolase activities are referable to a single hormone-sensitive hydrolase. Hormone-sensitive acyl hydrolases were separated from lipoprotein lipase by heparin-Sepharose affinity chromatography. Lipoprotein lipase was active against triolein, diolein, and monoolein, but not cholesterol oleate. Incubation of lipoprotein lipase with exogenous protein kinase, cAMP, and Mg2+ATP had no effect on any of the three hydrolase activities. Lipoprotein lipase was further purified to homogeneity and used to prepare antiserum in rabbits. The immunoglobin G fraction from these antisera completely inhibited lipoprotein lipase eluted from heparin-Sepharose columns. However, the hormone-sensitive hydrolase activities (not retained on heparin-Sepharose affinity chromatography) were not inhibited by anti-lipoprotein lipase immunoglobin G, and anti-lopoprotein lipase immunoglobin G did not affect the activation process in crude fractions. Thus, hormone-sensitive lipase and lipoprotein lipase, functionally distinct enzymes, have been physically resolved and immunochemically distinguished. Apparently lipoprotein lipase activity is not regulated, at least directly, by cAMP-dependent protein kinase.

Adenosine Triphosphate↗