calcimycin and phosphatidylethanol

Phospholipases generate important secondary messengers in several cellular processes, including cell death. Tumor necrosis factor (TNF) can induce two distinct modes of cell death, viz. necrosis and apoptosis. Here we demonstrate that phospholipase D (PLD) and cytosolic phospholipase A2 (cPLA2) are differentially activated during TNF-induced necrosis or apoptosis. Moreover, a comparative study using TNF and anti-Fas antibodies as cell death stimuli showed that PLD and cPLA2 are specifically activated by TNF. These results indicate that both the mode of cell death and the type of death stimulus determine the potential role of phospholipases as generators of secondary messengers.

Topics: Animals; Antibodies; Apoptosis; Arachidonic Acid; Calcimycin; Cell Cycle; Enzyme Activation; fas Receptor; Glycerophospholipids; Humans; Mice; Necrosis; Phospholipase D; Phospholipases; Phospholipases A; Phospholipases A2; Phosphorylation; Ploidies; Tetradecanoylphorbol Acetate; Tumor Cells, Cultured; Tumor Necrosis Factor-alpha

Madin-Darby canine kidney (MDCK) cells stimulated with 12-O-tetradecanoylphorbol-13-acetate (TPA) in the presence of ethanol synthesize phosphatidylethanol (PEt) instead of phosphatidic acid (PA) and diglyceride (DG). We have used ethanol to block the production of phospholipase D (PLD)-derived PA and DG (from PA hydrolysis) to study their role in signal transduction. In MDCK cells, TPA-stimulated prostaglandin E2 (PGE2) synthesis was inhibited by ethanol at concentrations which inhibit PA and DG formation. In addition, TPA elicited a prolonged increase in PGE2 synthesis that is dependent upon continuous activation of PLD. The TPA-stimulated translocation of protein kinase Calpha (PKCalpha) from cytosol to membrane was unaffected by ethanol. This suggests that PLD-derived products act downstream of PKC in TPA-stimulated prostaglandin synthesis. The calcium ionophore, A23187, did not activate PLD, and PGE2 synthesis in response to A23187 was unaffected by ethanol. TPA increased prostaglandin endoperoxide H synthase (PGHS) activity and increased the amount of immunodetectable prostaglandin endoperoxide H synthase 2 (PGHS-2). A23187 did not induce PGHS-2 and A23187-stimulated PGE2 synthesis appears to be due to the constitutively expressed PGHS-1. Blocking the formation of PLD-derived products, PA and DG, inhibited the induction of PGHS-2 by TPA. These results indicate that prolonged PGE2 synthesis in response to TPA is due to the continuous induction of PGHS-2, which is dependent upon PLD activation. In contrast, induction of PGHS-2 by epidermal growth factor was not affected by ethanol. Epidermal growth factor did not induce PKCalpha translocation nor activate PLD. Taken together, these data suggest that PLD-derived PA or DG act as second messengers in the induction of PGHS-2 by PKC-dependent pathways. The demonstration that inhibition of TPA-induced PA formation inhibits Raf-1 translocation in MDCK cells (Ghosh, S., Strum, J. C., Sciorra, V. A., Daniel, L. W. , and Bell, R. M. (1996) J. Biol. Chem. 271, 8472-8480) suggests that PA is the active PLD metabolite in TPA-stimulated signaling.

Topics: Animals; Calcimycin; Cell Line; Diglycerides; Dinoprostone; Dogs; Enzyme Activation; Enzyme Induction; Ethanol; Glycerophospholipids; Kidney; Kinetics; Phosphatidic Acids; Phospholipase D; Prostaglandin-Endoperoxide Synthases; Prostaglandins; Protein Kinase C; Tetradecanoylphorbol Acetate

The gastrointestinal hormone cholecystokinin and the muscarinic agonist carbamylcholine are involved in pancreatic enzyme secretion through phospholipase C activation and production of the second messengers inositol trisphosphate and diacylglycerol. However, cholecystokinin induces growth of the pancreas whereas carbamylcholine does not. This study investigated the possibility of a specific cellular signalling transduction system through which cholecystokinin may induce pancreatic growth. Rat pancreatic acini were preincubated with 3H choline or 3H myristic acid to label phosphatidylcholine. They were then stimulated by caerulein, phorbol myristate acetate, and carbamylcholine; choline and phosphocholine release as well as phosphatidic acid and phosphatidylethanol production were measured to establish phospholipase D (PLD) activation. Caerulein, phorbolester and carbamylcholine increased phosphocholine release. Choline release was induced early by caerulein and later by phorbolester but not by carbachol. PLD was activated by caerulein and phorbolester but not by carbamylcholine. Increased intracellular calcium by A23187 had no effect on PLD activation but its chelation by BAPTA prevented caerulein-induced PLD activation. In conclusion, PLD seems to be selectively activated by caerulein and phorbol ester by two different mechanisms which are insensitive to carbamylcholine. It is suggested that the PLD pathway might be the cellular signalling system leading to pancreatic growth.

Topics: Alkaloids; Animals; Calcimycin; Carbachol; Ceruletide; Cholecystokinin; Choline; Egtazic Acid; Enzyme Activation; Glycerophospholipids; In Vitro Techniques; Male; Pancreas; Phosphatidic Acids; Phospholipase D; Phosphorylcholine; Protein Kinase C; Rats; Rats, Sprague-Dawley; Signal Transduction; Staurosporine; Terpenes; Tetradecanoylphorbol Acetate; Type C Phospholipases

Activation of phospholipase D (PLD) by receptor-coupled stimuli (vasopressin, ATP), phorbol esters, and Ca2+ ionophores was studied in isolated rat hepatocytes, double labeled with [3H]arachidonate and [14C]stearate. Phosphatidylethanol (Peth) was formed when cells were stimulated in the presence of ethanol. The effect of combinations of agonists was not additive, indicating that the same PLD isozyme(s) were activated. With all agonists, the 3H- and 14C-specific radioactivity in Peth was higher than in any of the main phospholipid classes. The 3H/14C ratios of Peth and phosphatidylcholine (PC) were identical and differed from other phospholipid classes, indicating that the predominant PLD substrate was a PC pool labeled preferentially with radioactive fatty acids. Ethanol (50-300 mM) decreased the initial rate of phosphatidic acid (PA) formation, but did not affect total PLD activity. Agonist-induced changes in steady state accumulation of PA or 1,2-diacylglycerol were also unaffected. A slow degradation of Peth (apparent t1/2 > 60 min) occurred after ethanol removal from cells prestimulated with vasopressin. The rate of degradation was unaffected by agonists that stimulate PLD. Thus, Peth formation is a suitable cumulative indicator for PLD activation in intact hepatocytes. Peth accumulation declined over a period of 5-20 min, depending on the agonist. The decline was not due to increased Peth degradation, or limitations in substrate supply to PLD, or enzyme inhibition by accumulated Peth. Instead, a homologous desensitization of PLD occurs with all agonists. This desensitization may involve the action of selective protein kinase C isozymes.

Topics: Adenosine Triphosphate; Animals; Arachidonic Acid; Calcimycin; Diglycerides; Enzyme Activation; Ethanol; Glycerophospholipids; Liver; Male; Phosphatidic Acids; Phospholipase D; Rats; Rats, Sprague-Dawley; Stearic Acids; Tetradecanoylphorbol Acetate; Time Factors; Vasopressins

We have investigated whether phospholipase D (PLD) is involved in events leading to acrosomal exocytosis. Ram spermatozoa pre-labelled with [3H]alkyl-lysophosphatidylcholine and stimulated with the ionophore A23187 (1 microM) and Ca2+ (3 mM) in the presence of ethanol, showed a slow time-dependent increase in [3H]phosphatidic acid and [3H]phosphatidylethanol (PEt), the latter being clear evidence of PLD activity. Unlabelled cells similarly treated underwent acrosomal exocytosis. However, [3H]PEt formation was inhibited by high Ca2+ concentrations, although such conditions result in maximal acrosomal exocytosis. Treatment with A23187/Ca2+ led to a fast generation of [3H]alkyl-diglyceride and an increase in 1,2-diacylglycerol mass, which preceded [3H]PEt formation. The rises in [3H]alkyl-diglyceride and 1,2-diacylglycerol mass took place regardless of the presence or absence of ethanol. Inclusion of propranolol, a phosphatidic acid phosphohydrolase inhibitor, did not affect the early rise of labelled or unlabelled 1,2-diglycerides either. Stimulation of spermatozoa with A23187/Ca2+ in the presence of either ethanol or propranolol did not affect the occurrence of acrosomal exocytosis. Taken together, these results indicate that although Ca2+ entry triggers a late activation of PLD, this enzyme is not involved in the early generation of diglycerides. Moreover, they suggest that PLD does not make a substantial contribution in events leading to exocytosis of the sperm acrosome. Therefore, generation of diglycerides may take place primarily via phospholipase C.

Topics: Acrosome; Analysis of Variance; Animals; Calcimycin; Calcium; Diglycerides; Ethanol; Exocytosis; Glycerophospholipids; In Vitro Techniques; Lipid Metabolism; Male; Phosphatidic Acids; Phospholipase D; Sheep; Spermatozoa

It is now believed that PLD may contribute to the sustained generation of diacylglycerol (DAG) within activated cells. DAG can be formed from phosphatidylcholine by the sequential actions of PLD and phosphatidic acid phosphohydrolase. Phorbal myristate acetate (PMA, 1 microM), A23187 (10 microM) or platelet-activating factor (PAF, 100 nM) caused significant enhancement of intracellular 14C-phosphatidic acid levels 2-5 min after the addition of stimulus, in cultures of peritoneal macrophages pre-labelled with 14C-palmitate. Bacterial lipopolysaccharide (LPS) (5 micrograms/ml) or zymosan (375 micrograms/ml) also stimulated the production of 14C-phosphatidic acid, but over a longer time course (15-60 min). In the presence of 1% ethanol each stimulus caused significant production of 4C-phosphatidylethanol at the expense of 14C-phosphatidic acid, thus confirming a contribution of PLD in these reactions. This is the first report of PLD activity in this cell type.

Topics: Animals; Calcimycin; Cells, Cultured; Chromatography, Thin Layer; Glycerophospholipids; Lipopolysaccharides; Macrophages, Peritoneal; Mice; Phosphatidic Acids; Phospholipase D; Platelet Activating Factor; Tetradecanoylphorbol Acetate; Zymosan

Activation of human neutrophils by receptor-mediated agonists, the Ca2+ ionophore A23187, or the protein kinase C activator phorbol myristate acetate all stimulated phospholipase D activity. This was demonstrated by the increased formation of phosphatidic acid, and in the presence of ethanol, phosphatidylethanol (PEt) accumulation. EGTA completely inhibited A23187-induced PEt formation, but only one-half of the fMLP-induced PEt accumulation. Staurosporin, an inhibitor of protein kinase C, strongly inhibited PMA-induced PEt formation, but actually stimulated the formation of PEt in response to fMLP by several-fold. Thus, increased cytosolic Ca2+ and activated protein kinase C can each lead to activation of phospholipase D, but neither is required for receptor-mediated activation of phospholipase D activity. Wortmannin is an irreversible inhibitor of the oxidative burst, but does not inhibit NADPH oxidase or known components of signal transduction. Wortmannin inhibited activation of phospholipase D in response to fMPL. It did not directly inhibit phospholipase D, as the response to A23187 was unaffected. Wortmannin did not inhibit other fMPL-stimulated events, such as aggregation or adherence. We conclude that inhibition by wortmannin defines a third pathway to activation of phospholipase D. Further, its effect on phospholipase D correlates with its effect on the respiratory burst.

Topics: Androstadienes; Calcimycin; Calcium; Cell Adhesion; Cell Aggregation; Egtazic Acid; Enzyme Activation; Glycerophospholipids; Humans; N-Formylmethionine Leucyl-Phenylalanine; Neutrophils; Phosphatidic Acids; Phospholipase D; Phospholipases; Protein Kinase C; Tetradecanoylphorbol Acetate; Wortmannin

Normodense human eosinophils have been labeled in 1-0-alkyl-phosphatidylcholine (alkyl-PC) with 32P by incubating isolated cells with alkyl-[32P]lysoPC. Stimulation of these 32P-labeled cells with C5a, A23187 or PMA in the presence of 0.5% ethanol resulted in time- and dose-dependent formation of alkyl-[32P]phosphatidic acid (alkyl-[32P]PA) and alkyl-[32P]phosphatidylethanol (alkyl-[32P]PEt). Because cellular ATP does not contain 32P, alkyl-[32P]PA must have been formed by the hydrolytic action of phospholipase D (PLD) and not by the combined actions of phospholipase C and DG kinase. Regardless of the stimulating agent, alkyl-[32P]PEt formation paralleled that of alkyl-[32P]PA, suggesting that alkyl-PEt was the result of a PLD-catalyzed transphosphatidylation reaction between alkyl-PC and ethanol. These data provide the first definitive proof of receptor- and nonreceptor-mediated activation of PLD in normodense eosinophils derived from human blood.

Topics: Calcimycin; Complement C5a; Dose-Response Relationship, Drug; Enzyme Activation; Eosinophils; Ethanol; Glycerophospholipids; Humans; Kinetics; Lymphocyte Activation; Phosphatidic Acids; Phospholipase D; Phospholipases; Tetradecanoylphorbol Acetate

Human erythroleukaemia (HEL) cells were exposed to thrombin and other platelet-activating stimuli, and changes in radiolabelled phospholipid metabolism were measured. Thrombin caused a transient fall in PtdInsP and PtdInsP2 levels, accompanied by a rise in diacylglycerol and phosphatidic acid, indicative of a classical phospholipase C/diacylglycerol kinase pathway. However, the rise in phosphatidic acid preceded that of diacylglycerol, which is inconsistent with phospholipase C/diacylglycerol kinase being the sole source of phosphatidic acid. In the presence of ethanol, thrombin and other agonists (platelet-activating factor, adrenaline and ADP, as well as fetal-calf serum) stimulated the appearance of phosphatidylethanol, an indicator of phospholipase D activity. The Ca2+ ionophore A23187 and the protein kinase C activator phorbol myristate acetate (PMA) also elicited phosphatidylethanol formation, although A23187 was at least 5-fold more effective than PMA. Phosphatidylethanol production stimulated by agonists or A23187 was Ca2(+)-dependent, whereas that with PMA was not. These result suggest that phosphatidic acid is generated in agonist-stimulated HEL cells by two routes: phospholipase C/diacylglycerol kinase and phospholipase D. Activation of the HEL-cell phospholipase D in response to agonists may be mediated by a rise in intracellular Ca2+.

Topics: Adenosine Diphosphate; Calcimycin; Calcium; Cell Line; Enzyme Activation; Epinephrine; Glycerophospholipids; Humans; Kinetics; Leukemia, Erythroblastic, Acute; Myristic Acid; Myristic Acids; Phosphatidic Acids; Phosphatidylinositols; Phospholipase D; Phospholipases; Platelet Activating Factor; Tetradecanoylphorbol Acetate; Thrombin; Tumor Cells, Cultured