Arachidonic acid release in BW755C-pretreated rat peritoneal mast cells stimulated with A23187, concanavalin A and compound

PGE2-mediated upregulation of iNOS in murine breast cancer cells through the activation of EP4 receptors

We report here that endogenous prostaglandin E(2) (PGE(2)) resulting from cyclooxygenase (COX)-2 expression in a highly metastatic murine breast cancer cell line C3L5 upregulates IFN-gamma + LPS-induced nitric oxide (NO) synthase (iNOS) expression and NO production. This action of PGE(2) is mediated through the EP(4) receptor in a cAMP-dependent manner. Both nonselective and selective COX-2 inhibitors suppressed IFN-gamma + LPS-induced NO production, which was largely restored by exogenous PGE(2) or EP(4) receptor agonist PGE(1) alcohol. EP(4) antagonist AH-23848B inhibited NO production with a concomitant downregulation of iNOS mRNA in IFN-gamma + LPS-stimulated cells. cAMP dependence of NO production by cells under inducible conditions was demonstrated by the use of known modulators of intracellular cAMP. Since both COX-2 and iNOS are implicated in breast cancer progression, our findings of EP(4) receptor-mediated upregulation of iNOS in COX-2-expressing breast cancer cells suggest that blocking COX-2 and/or EP(4) may provide a simple therapeutic modality in this tumor model.

The role of leukotriene C4 in biphasic release of histamine from mouse mastocytoma cell line (P-815)

1. A biphasic change of compound 48/80-induced histamine release was observed in mastocytoma cell line (P-815). 2. The first and second phase of compound 48/80-induced histamine release were elicited via a different pathway. 3. The second phase of compound 48/80-induced histamine release was provoked with leukotriene (LT) C4. 4. The results suggest that this biphasic release may be one of the important regulatory mechanisms for the production of histamine.

Enhancement of phospholipase A2 activation by phosphatidic acid endogenously formed through phospholipase D action in rat peritoneal mast cell

Contribution of phosphatidic acid (PA) generated by activated phospholipase (PL) D to PLA2 activation was studied in rat peritoneal mast cells. Exogenous didecanoyl PA induced arachidonate liberation in the permeabilized cells which was inhibited by p-bromophenacyl bromide. Upon exposure of the cells to ethanol in a high enough concentration to prevent PA formation, A23187-induced arachidonate liberation was suppressed by 50% and the rest was completely inhibited by p-bromophenacyl bromide. In contrast, propranolol, which enhanced PA accumulation, significantly increased the arachidonate liberation. These results suggest that A23187-induced PLA2 activation may be potentiated, at least in part, by PA generated through PLD action.

Arachidonic acid metabolism during antigen and ionophore activation of the mouse bone marrow derived mast cell

This study has examined the metabolism of arachidonic acid in the mouse bone marrow-derived mast cell (BMMC) during immunologic and nonimmunologic activation. The predominant pools of endogenous arachidonate in the mast cells were found in ethanolamine (46%), choline (39%) and inositol (14%) containing glycerolipids. Initial studies established conditions where equilibrium labelling of these major phospholipids in the BMMC could be reached. Upon challenge, arachidonate was lost from all major phospholipid classes (phosphatidylethanolamine greater than phosphatidylcholine greater than phosphatidylinositol). There was a small but significant increase in the amount of label associated with phosphatidic acid during cell activation. Arachidonate was distributed among 1-acyl, 1-alkyl and 1-alk-1-enyl-linked subclasses of PC and PE. The rank order of loss of labelled arachidonate from the major PE and PC subclasses during antigen and ionophore activation was 1-alk-enyl-2-arachidonoyl-GPE greater than 1-acyl-2-arachidonoyl-GPC greater than 1-acyl-2-arachidonoyl-GPE greater than 1-alkyl-2-arachidonoyl-GPC. Labelled products released into the supernatant fluids and free arachidonic acid within the cell accounted for the bulk of arachidonate lost from phospholipids. Labelled products in the supernatant fluids were composed of LTB4, LTC4, PGD2 and free arachidonic acid. BMMC phospholipids were also labelled for 24 hr with [3H]choline, [3H]myoinositol or [14H]ethanolamine and labelled 2-lyso phospholipids were measured after cell activation. Radioactivity in lysophospholipids from PC, PE and PI increased significantly between 30 s and 2 min after antigen activation and then declined. Taken together, these studies suggest that arachidonate is mobilized predominantly from PE and in particular 1-alk-1-enyl-2-arachidonoyl-GPE by the direct removal of arachidonate from the sn-2 position of the molecule. Most of this arachidonate is then released from cells as eicosanoids or free fatty acid.

Stimulation of arachidonic acid release by guanine nucleotide in saponin-permeabilized neutrophils: evidence for involvement of GTP-binding protein in phospholipase A2 activation

Addition of a guanine nucleotide analog, guanosine 5'-O-(thiotriphosphate) (GTP gamma S)(1-100 microM) induced release of [3H]arachidonic acid from [3H]arachidonate-prelabeled rabbit neutrophils permeabilized with saponin. The chemotactic peptide N-formyl-methionyl-leucyl-phenylalanine (fMLP)-induced arachidonate release was enhanced by GTP gamma S, Ca2+, or their combination. Ca2+ alone (up to 100 microM) did not effectively stimulate lipid turnover. However, the combination of fMLP plus GTP gamma S elicited greater than additional effects in the presence of resting level of free Ca2+. The addition of 100 microM of GTP gamma S reduced the Ca2+ requirement for arachidonic acid liberation induced by fMLP. Pretreatment of neutrophils with pertussis toxin resulted in the abolition of arachidonate release and diacylglycerol formation. Neomycin (1 mM) caused no significant reduction of arachidonate release. In contrast, about 40% of GTP gamma S-induced arachidonate release was inhibited by a diacylglycerol lipase inhibitor, RHC 80267 (30 microM). These observations indicate that liberation of arachidonic acid is mediated by phospholipase A2 and also by phospholipase C/diacylglycerol lipase pathways. Fluoride, which bypasses the receptor and directly activates G proteins, induced arachidonic acid release and diacylglycerol formation. The fluoride-induced arachidonate release also appeared to be mediated by these two pathways. The loss of [3H]arachidonate was seen in phosphatidylinositol, phosphatidylcholine, and phosphatidylethanolamine. These data indicate that a G protein is involved between the binding of fMLP to its receptor and activation of phospholipase A2, and also that the arachidonic acid release is mediated by both phospholipase A2 and phospholipase C/diacylglycerol lipase.

Guanosine 5'-(gamma-thio)triphosphate stimulates arachidonic acid liberation in permeabilized rat peritoneal mast cells

The exocytotic histamine secretion from ATP-permeabilized and Mg-resealed rat peritoneal mast cells is markedly enhanced by the addition of guanosine 5'-(gamma-thio)triphosphate (GTP gamma S) at a concentration of 100 uM. GTP gamma S also caused a great enhancement of arachidonic acid liberation from these cells. The level of released arachidonic acid in permeabilized cells enhanced by GTP gamma S in the absence of Ca2+ was nearly equal to the level of permeabilized cells incubated in the presence of Ca2+ but without GTP gamma S, suggesting the Ca2+ sparing effect of GTP gamma S. From the time sequential changes in the [3H]arachidonate radioactivities in various phospholipids, it is conceivable that nucleotide-dependent arachidonic acid release was mediated via phospholipase A2 pathway. The entrapment of a diacylglycerol (DG) lipase inhibitor, RHC 80267, caused suppression of both Ca2+- and guanine nucleotide-dependent arachidonic acid liberation in mast cells, indicating contribution of DG lipase pathway for arachidonic acid generation.