Rat basophilic leukemia cell lines defective in phospholipid methyltransferase enzymes, Ca2+ influx, and histamine release: reconstitution by hybridization

Inhibitory Effects of Phenylpropanoid Derivatives from Oenanthe javanica on Antigen-Stimulated Degranulation in RBL-2H3 Cells

Two diacyldaucic acids (1 and 2), an α,β-unsaturated γ-lactone-type lignan (3) and its derivatives (4-6), and 12 known compounds were isolated from a traditional East Asian vegetable, Oenanthe javanica. The absolute configuration of 1 was validated by obtaining (+)-osbeckic acid through acid hydrolysis. The absolute configurations of 3-5 were determined by comparing their experimental and computed ECD data. The conclusion was supported by applying the phenylglycine methyl ester method to 3. Compound 6 was obtained as an interconverting mixture of isomers in a 3:1 trans- cis ratio. Several water-soluble components (1, 3, and 6) showed concentration-dependent inhibitory effects on antigen-stimulated degranulation in RBL-2H3 cells without producing any direct cytotoxicity against RBL-2H3 or HeLa cells.

Development of mast cells and importance of their tryptase and chymase serine proteases in inflammation and wound healing

Mast cells (MCs) are active participants in blood coagulation and innate and acquired immunity. This review focuses on the development of mouse and human MCs, as well as the involvement of their granule serine proteases in inflammation and the connective tissue remodeling that occurs during the different phases of the healing process of wounded skin and other organs. The accumulated data suggest that MCs, their tryptases, and their chymases play important roles in tissue repair. While MCs initially promote healing, they can be detrimental if they are chronically stimulated or if too many MCs become activated at the same time. The possibility that MCs and their granule serine proteases contribute to the formation of keloid and hypertrophic scars makes them potential targets for therapeutic intervention in the repair of damaged skin.

Purification and properties of phosphatidyl-N-monomethylethanolamine N-methyltransferase, the enzyme catalyzing the second and the third steps in the phosphatidylethanolamine N-methyltransferase system, from mouse liver microsomes

The phosphatidylethanolamine (PE) N-methyltransferase (MT) system is known to convert PE to phosphatidylcholine by three successive N-methylations. Phosphatidyl-N-monomethylethanolamine (PME) MT was purified 1,400-fold from mouse liver microsomes and separated from the PE-MT activity for the first time. This enzyme catalyzes N-methylations of PME and phosphatidyl-N,N-dimethylethanolamine, the intermediates of PE-MT system, but not PE, the initial substrate of the PE-MT system. In addition, a preparation with a different affinity to S-adenosyl-L-homocysteine catalyzing all the three methylations was obtained. These results suggest that at least two enzymes are involved in the PE-MT system.

Role of cyclic AMP during histamine release. Histamine release is not directly related to increase in cyclic AMP levels in rat mast cells activated by concanavalin A, anti-IgE, antigen, prostaglandin D2 and isoproterenol

Activation of mast cells by bridging of IgE-receptors or concanavalin A (Con A) results in a rapid initial rise and fall in cyclic AMP (cAMP) levels followed by a second rise in cAMP levels and histamine release (Sullivan, T. et al. (1976) J. Immunol. 117, 713-716; Lewis, R.A. et al. (1979) J. Immunol. 123, 1663-1668; Ishizaka, T. et al. (1981) Proc. Natl. Acad. Sci. U.S.A. 78, 6812-6816). trans-4-Guanidinomethylcyclohexanecarboxylic acid 4-tert-butylphenyl ester (GMCHA-OPhBut), a strong trypsin inhibitor and an anti-allergic agent (Muramatu, M. et al. (1982) Hoppe-Seyler's Z. Physiol. Chem. 363, 203-211; Takei, M. et al. Agents Actions, in press), strongly and dose-dependently inhibited the initial and second rises in cAMP levels, and release of histamine from rat mast cells by Con A, anti-IgE and antigen. Addition of GMCHA-OPhBut after the initial rise in cAMP inhibited the second rise in cAMP and histamine release. These results suggested a possible participation of a trypsin-like proteinase, probably pH 7 tryptase present in rat mast cells, in the activation of adenylate cyclase by the above secretagogues, and the initial rise in cAMP was not directly related to the latter events. The second rise in cAMP is induced by prostaglandin D2 (PGD2), a metabolic product of arachidonic acid. PGD2 elevated the cAMP levels in mast cells whereas no histamine was secreted. GMCHA-OPhBut did not inhibit the increase in cAMP by PGD2. Therefore, the strong inhibitory effect of GMCHA-OPhBut on the second rise in cAMP might depend on the inhibition of an earlier process than the activation of adenylate cyclase by PGD2.(ABSTRACT TRUNCATED AT 250 WORDS)

Modulation of phospholipid methylation in rabbit leukocytes by indomethacin

Methylation of membrane phospholipids has been implicated as an early biochemical signal for the chemotactic migration of phagocytic cells into inflammatory sites. In this study, the ability of indomethacin to modulate phospholipid methylation as one of its mechanisms of antiinflammatory action was investigated. Nontoxic doses of indomethacin (10(-4) M and 10(-5) M) were found to retard the methylation of phosphatidylmonomethylethanolamine (PMME) to phosphatidyldimethylethanolamine (PDME) and phosphatidylcholine (PC) in rabbit leukocytes, suggesting inhibition of methyltransferase II activity. Indomethacin was, however, without effect on the uptake of L-[methyl 3H]methionine by rabbit leukocytes. It is suggested that the inhibition of membrane phospholipid methylation could result in the suppression of inflammatory responses such as prostaglandin and leukotriene synthesis, generation of reactive oxygen radicals, and chemotaxis.

Developmental changes in the activity of phosphatidylethanolamine N-methyltransferases in rat brain

The activity of phosphatidylethanolamine N-methyltransferase (PeMT), an enzymic system that catalyses the synthesis of phosphatidylcholine (PtdCho) via sequential methylation of phosphatidylethanolamine (PtdEtn) using S-adenosylmethionine (AdoMet) as a methyl donor, was examined in brain homogenates from rats of various ages. The data thus obtained were consistent with the existence of two distinct enzyme activities within this enzyme system, i.e. one catalysing the methylation of PtdEtn [to form phosphatidyl-N-monomethylethanolamine (PtdMeEtn)], and the other catalysing the methylations of PtdMeEtn and phosphatidyl-NN-dimethylethanolamine (PtdMe2Etn) (to form PtdMe2Etn and PtdCho, respectively). PeMT (PtdEtn-methylating) activity per g of brain was 4-fold higher in neonatal than in adult brains. The enzyme activity in adult brains exhibited Michaelis-Menten kinetics for AdoMet, and its affinity for AdoMet was high (apparent Km 1.6 microM). In neonatal brain the relationships between AdoMet concentrations and PtdMeEtn formation were more complex: a sigmoidal component (with a Hill coefficient of 2.7), requiring 90 microM-AdoMet for half-saturation predominated over the high-affinity component (similar to that of the adult brain). PeMT (PtdMe2Etn-methylating) activity per g of brain increased 2-fold between the 5th and the 20th postnatal days and remained constant thereafter; it was higher than that of PeMT (PtdEtn-methylating) activity at all ages studied, and its affinity for AdoMet was low (apparent Km 99 microM). No sexual dimorphism in brain PeMT activity was observed at any age. We conclude that PeMT (PtdEtn-methylating) catalyses the rate-limiting step in PtdCho synthesis in rat brain, and that PtdCho formation via this pathway may be greatest during the neonatal period.

Isolation, characterization, and regulation of the prolactin receptor

The prolactin, or lactogenic hormone, receptor has been purified (approximately 80%) from lactating mouse liver and human term placenta by the nondenaturing zwitterionic detergent 3-[(3-cholamidopropyl)-dimethylammonio]-1-propane sulfonate and a prolactin affinity column. The isolated "core-binding unit" has a molecular weight of 37,000 +/- 2,000 daltons. It retains the specificity for lactogenic hormones and binds prolactin with an affinity (Ka = 2 to 6 X 10(9) M-1) similar to that of the receptor as it occurs in its membranous environment (Ka = 3 to 5 X 10(9) M-1). Whether this "core-binding unit" exists on the cell surface in a cryptic or active form is influenced greatly by its association with other membrane proteins and the concentration of phosphatidylcholine within its local membranous environment.

An enhanced incorporation of fatty acid into phosphatidyl choline that parallels histamine discharge in mast cells

Purified rat peritoneal and pleural mast cells preincubated briefly with radioactively labeled fatty acid were treated with A23187, which bypasses primary receptors in stimulating exocytosis. An enhanced incorporation of fatty acid into phosphatidyl choline (PC) that occurred in parallel with histamine release at 24-25 degrees C was observed and was initially proportional to the total amount of histamine discharged. Enhanced PC labeling and histamine secretion were also proportional at temperatures ranging from 17-37 degrees C. Both radioactive linoleic and palmitic acids were incorporated selectively at the beta-position of the glycerol backbone of PC. PC labeling by [3H]choline was not detectably different in control and stimulated cells, and phosphatidic acid did not exhibit selectively enhanced beta-acylation. Thus, the stimulated labeling in A23187-treated cells may occur secondary to the action of a phospholipase A2 that favors PC as a substrate. Other peritoneal cell types exhibit a very similar A23187-stimulated selective labeling of PC. Therefore, autoradiography has been used to provide a direct demonstration that in purified preparations, mast cells are the principal cell type engaged in A23187-elicited incorporation of fatty acid into PC. The efficacy of this approach has relied on special procedures devised to obtain significantly different autoradiographic grain densities between control and stimulated preparations that can be attributed to differences in the level of [3H]palmitate-labeled PC. Preliminary tests using compound 48/80 as a secretory stimulus for mast cells have identified a similar selectively enhanced PC labeling. In either case, however, consideration of possible relationships between PC metabolism and the secretory process are premature since they have not been tested directly.

Calcium signals and phospholipid methylation in eukaryotic cells

Rat basophil leukaemic (2H3) cells, mast cells and mouse thymocytes respond to stimulation by specific ligands with an increase in the free cytosolic Ca2+ concentration. The time courses of these Ca signals and the biological responses have been compared with changes in phospholipid metabolism. Increased phosphoinositide metabolism coincides with the Ca signals and the responses in each cell system, whereas any increase in phospholipid methylation during the response is less than one molecule per receptor and at least 5-50-fold less than the increases reported previously. Furthermore, no significant changes were detected in the concentration of S-adenosylmethionine, the methyl-group donor in the synthesis of methylated phospholipids. The hypothesis that phospholipid methylation is obligatory for receptor-mediated Ca signals is not supported by these data and requires critical re-evaluation.

Cellular calcium metabolism: activation and antagonism

The role of Ca2+ as a mediator of many cellular responses, including stimulus-secretion and excitation-contraction coupling, is reviewed. Pathways of Ca2+ mobilization are discussed in terms of both intracellular and plasmalemmal processes. The extent to which specific antagonists exist, active at these several sites, is noted, with particular emphasis on the clinically available Ca2+ channel antagonists, including verapamil, nifedipine, and diltiazem.

Basophil variants with impaired cromoglycate binding do not respond to an immunological degranulation stimulus

Cromoglycate, which inhibits IgE-mediated degranulation of mast cells and a basophilic rat tumour cell line (RBL-2H3) (ref.3), is a drug widely used in the treatment of allergic asthma. We have demonstrated the presence of specific binding sites for that drug on the membranes of basophils and mast cells and more recently, we have succeeded in isolating the cromoglycate-binding protein from the membranes of RBL-2H3 cells. These findings together with the chelation by cromoglycate of alkaline-earth ions in low polarity medium, suggest that the binding site of the drug may either be part, or closely related to the calcium gate. To further investigate this, we have selected variants of the RBL-2H3 cell line that are defective in cromoglycate binding but bind IgE normally. In these variants, which have similar histamine content to the parental cells, IgE-mediated challenge did not lead to Ca2+ influx, degranulation and histamine release. In contrast, these cells were able to release histamine on exposure to the Ca2+ ionophore A23187, indicating that the degranulation mechanism distal to the Ca2+ gating step is unaffected. Taken together, these findings suggest that cromoglycate-binding protein has a role in the transmembrane calcium influx which induces degranulation.

IgE-mediated chemotaxis of rat basophilic leukemia cells towards specific antigen

We evaluated chemotactic properties of four sublines of rat basophilic leukemia cells using blindwell Boyden chamber assays. After sensitization with a mouse monoclonal IgE directed against dinitrophenyl (DNP), cells from sublines 2H3-C and 926a underwent chemotaxis toward DNP-bovine serum albumin (BSA) and sublines RBL-1 and 4A did not. Chemotactic responses required specific IgE and were determined by the IgE antigen specificity used for sensitization. The threshold for chemotaxis was on the order of 10(-10) M DNP-BSA. Release of incorporated [3H]-serotonin did not always parallel chemotactic responses, which suggests that chemotaxis and secretion may be two unlinked processes that occur during basophil activation. Our results predict a possible in vivo mechanism whereby specific chemotactic responses of basophils and other FcR epsilon-bearing cells are mediated via specific IgE bound to membrane FcR epsilon.

Bradykinin stimulates phospholipid methylation, calcium influx, prostaglandin formation, and cAMP accumulation in human fibroblasts

The biochemical events that lead to bradykinin stimulation of cAMP accumulation in human fibroblasts were examined. Treatment of human fibroblasts with bradykinin increases phospholipid methylation, Ca2+ influx, arachidonic acid release, prostaglandin formation, and cAMP content. The dose-response curves of bradykinin for the increase in the above changes were similar. In human fibroblasts, exogenous arachidonic acid was mainly incorporated into phosphatidylcholine, followed by phosphatidylserine, phosphatidylethanolamine, and phosphatidylinositol. Bradykinin caused a release of arachidonic acid from methylated phospholipids (phosphatidylcholine) and phosphatidylinositol. 3-Deazaadenosine, a methyltransferase inhibitor, almost completely inhibited bradykinin-stimulated phospholipid methylation and Ca2+ influx and partially reduced arachidonic acid release and prostaglandin formation but had no effect on cAMP formation. Mepacrine, a phospholipase inhibitor, blocked bradykinin-induced arachidonic acid release, prostaglandin release, and cAMP accumulation. Indomethacin, a cyclooxygenase inhibitor, blocked the effect of bradykinin on cAMP accumulation. Prostaglandins E1 and E2, but not F2 alpha, increased accumulation of cAMP. These observations indicate that bradykinin generates cAMP via arachidonic acid release and subsequent formation of prostaglandins. Our findings suggest that arachidonic acid can arise from either phosphatidylcholine synthesized by the methylation pathway or phosphatidylinositol.

Absence of a direct role of phospholipid methylation in stimulus-secretion coupling and control of adenylate cyclase in guinea-pig and rat parotid gland

The present study was undertaken to investigate a possible involvement of phospholipid methyltransferases in the coupling of receptor-mediated stimulation to secretion. Phospholipid methyltransferases were assayed in isolated parotid acini in the presence of carbamoylcholine or isoprenaline. Carbamoylcholine reduced the incorporation of methyl groups into phospholipids, whereas isoprenaline showed no effect. Amylase secretion stimulated either by carbamoylcholine or by isoprenaline could not be affected by inhibitors of methyltransferases (3-deaza-adenosine alone or plus homocysteine thiolactone) under conditions where phospholipid methylation was strongly inhibited. The activity of adenylate cyclase in isolated parotid microsomal membranes was not inhibited or stimulated by S-adenosyl-homocysteine or -methionine respectively. These results indicate that phospholipid methylation does not play an essential role in stimulus-secretion coupling in the parotid gland.