Key points are not available for this paper at this time.
Aggregation of IgE cell surface receptors on MMC-34 cells, a murine mast cell line, induces the synthesis and secretion of prostaglandin D2 (PGD2). Synthesis and secretion of PGD2 in activated MMC-34 cells occurs in two stages, an early phase that is complete within 30 min after activation and a late phase that reaches a maximum about 6 h after activation. The early and late phases of PGD2 generation are mediated by prostaglandin synthase 1 (PGS1) and prostaglandin synthase 2 (PGS2), respectively. Arachidonic acid, the substrate for both PGS1 and PGS2, is released from membrane phospholipids by the activation of phospholipases. We now demonstrate that in activated mast cells (i) secretory phospholipase A2 (PLA2) mediates the release of arachidonic acid for early, PGS1-dependent synthesis of PGD2; (ii) secretory PLA2 does not play a role in the late, PGS2-dependent synthesis of PGD2; (iii) cytoplasmic PLA2 mediates the release of arachidonic acid for late, PGS2-dependent synthesis of PGD2; and (iv) a cytoplasmic PLA2-dependent step precedes secretory PLA2 activation and is necessary for optimal PGD2 production by the secretory PLA2/PGS1-dependent early pathway. Aggregation of IgE cell surface receptors on MMC-34 cells, a murine mast cell line, induces the synthesis and secretion of prostaglandin D2 (PGD2). Synthesis and secretion of PGD2 in activated MMC-34 cells occurs in two stages, an early phase that is complete within 30 min after activation and a late phase that reaches a maximum about 6 h after activation. The early and late phases of PGD2 generation are mediated by prostaglandin synthase 1 (PGS1) and prostaglandin synthase 2 (PGS2), respectively. Arachidonic acid, the substrate for both PGS1 and PGS2, is released from membrane phospholipids by the activation of phospholipases. We now demonstrate that in activated mast cells (i) secretory phospholipase A2 (PLA2) mediates the release of arachidonic acid for early, PGS1-dependent synthesis of PGD2; (ii) secretory PLA2 does not play a role in the late, PGS2-dependent synthesis of PGD2; (iii) cytoplasmic PLA2 mediates the release of arachidonic acid for late, PGS2-dependent synthesis of PGD2; and (iv) a cytoplasmic PLA2-dependent step precedes secretory PLA2 activation and is necessary for optimal PGD2 production by the secretory PLA2/PGS1-dependent early pathway. INTRODUCTIONMast cells, an important cell type in allergic diseases, are widely distributed throughout vascularized tissue and epithelia. Activation of mast cells by aggregation of high affinity IgE receptors causes degranulation, releasing stored mediators of inflammation such as histamine and serotonin. Mast cell activation also induces the synthesis and release of leukotrienes and prostaglandin D2 (PGD2). Ligand stimulation in most cells elicits a relatively slow production of prostaglandins, peaking only after 4-6 h (1Herschman H.R. Cancer Metastasis Rev. 1994; 13: 241-256Crossref PubMed Scopus (315) Google Scholar, 2Herschman H.R. Biochim. Biophys. Acta. 1996; 1299: 125-140Crossref PubMed Scopus (1160) Google Scholar). In contrast, PGD2 synthesis in activated mast cells occurs in two stages, a rapid, early phase and a late, delayed phase (3Kawata R. Reddy S.T. Wolner B. Herschman H.R. J. Immunol. 1995; 155: 818-825PubMed Google Scholar, 4Murakami M. Bingham III, C.O. Matsumoto R. Austen K.F. Arm J.P. J. Immunol. 1995; 155: 4445-4453PubMed Google Scholar).Prostaglandin production is regulated by both phospholipases A2 (PLA2) 1The abbreviations used are: PLA2phospholipase A2sPLA2secretory phospholipase A2cPLA2cytoplasmic phospholipase A2iPLA2cytosolic, calcium-independent PLA2PGS1, prostaglandin synthase 1PGS2, prostaglandin synthase 2ATPCarachidonylthiophosphatidylcholineMAFPmethyl arachidonylfluorophosphonate. and prostaglandin synthases (PGS). PLA2 enzymes release arachidonic acid from membrane phospholipids. Free arachidonate is converted to prostaglandin H2 (PGH2), a common precursor for all prostanoids, by prostaglandin synthases. Several PLA2 enzymes have been implicated in arachidonate release following ligand stimulation of various cell types (5Clark J.D. Schievella A.R. Nalefski E.A. Lin L.L. J. Lipid Mediat. Cell Signal. 1995; 12: 83-118Crossref PubMed Scopus (425) Google Scholar, 6Murakami M. Kudo I. Inoue K. J. Lipid Mediat. Cell Signal. 1995; 12: 119-130Crossref PubMed Scopus (64) Google Scholar). Many cells also express two distinct prostaglandin synthases: PGS1, a primarily constitutively expressed form, and PGS2, an inducible PGS expressed following appropriate ligand stimulation in different cell types (1Herschman H.R. Cancer Metastasis Rev. 1994; 13: 241-256Crossref PubMed Scopus (315) Google Scholar, 2Herschman H.R. Biochim. Biophys. Acta. 1996; 1299: 125-140Crossref PubMed Scopus (1160) Google Scholar). Experiments using antisense oligonucleotide inhibition (7Reddy S.T. Herschman H.R. J. Biol. Chem. 1994; 269: 15473-15480Abstract Full Text PDF PubMed Google Scholar) and NS-398, a PGS2-specific inhibitor (1Herschman H.R. Cancer Metastasis Rev. 1994; 13: 241-256Crossref PubMed Scopus (315) Google Scholar, 8Herschman H.R. Xie W. Reddy S.T. BioEssays. 1995; 17: 1031-1037Crossref PubMed Scopus (81) Google Scholar), demonstrated that ligand-induced prostaglandin production in fibroblasts and macrophages requires induced PGS2 expression, despite the presence of active PGS1 enzyme. In contrast, the rapid, early phase of PGD2 synthesis in activated mast cells is mediated by pre-existing PGS1 (3Kawata R. Reddy S.T. Wolner B. Herschman H.R. J. Immunol. 1995; 155: 818-825PubMed Google Scholar, 4Murakami M. Bingham III, C.O. Matsumoto R. Austen K.F. Arm J.P. J. Immunol. 1995; 155: 4445-4453PubMed Google Scholar). The second, delayed phase of PGD2 synthesis in activated mast cells is similar to prostaglandin production in growth factor-induced fibroblasts and endotoxin-induced macrophages, requiring activation-induced PGS2 expression (3Kawata R. Reddy S.T. Wolner B. Herschman H.R. J. Immunol. 1995; 155: 818-825PubMed Google Scholar, 4Murakami M. Bingham III, C.O. Matsumoto R. Austen K.F. Arm J.P. J. Immunol. 1995; 155: 4445-4453PubMed Google Scholar).Following activation, mast cells secrete a low molecular weight PLA2, sPLA2 (9Fonteh A.N. Bass D.A. Marshall L.A. Seeds M. Samet J.M. Chilton F.H. J. Immunol. 1994; 152: 5438-5446PubMed Google Scholar). Fonteh et al. (9Fonteh A.N. Bass D.A. Marshall L.A. Seeds M. Samet J.M. Chilton F.H. J. Immunol. 1994; 152: 5438-5446PubMed Google Scholar) suggest that the sPLA2 released following activation plays a role in eicosanoid biosynthesis by activated mast cells. Activation of mast cells also induces the activation, translocation, and expression of cytoplasmic cPLA2 (10Nakatani Y. Murakami M. Kudo I. Inoue K. J. Immunol. 1994; 153: 796-803PubMed Google Scholar, 11Hirasawa N. Santini F. Beaven M.A. J. Immunol. 1995; 154: 5391-5402PubMed Google Scholar, 12Currie S. Roberts E.F. Spaethe S.M. Roehm N.W. Kramer R.M. Biochem. J. 1994; 304: 923-928Crossref PubMed Scopus (21) Google Scholar, 13Glover S. Bayburt T. Jonas M. Chi E. Gelb M.H. J. Biol. Chem. 1995; 270: 15359-15367Abstract Full Text Full Text PDF PubMed Scopus (314) Google Scholar). In this report we investigate the roles of sPLA2 and cPLA2 in early, PGS1-dependent PGD2 synthesis and late, PGS2-dependent PGD2 synthesis following mast cell activation by aggregation of high affinity IgE receptors.DISCUSSIONAggregation of mast cell IgE receptors results in two phases of PGD2 production, an early burst completed within 10-30 min and a second phase peaking after 5-6 h (3Kawata R. Reddy S.T. Wolner B. Herschman H.R. J. Immunol. 1995; 155: 818-825PubMed Google Scholar, 4Murakami M. Bingham III, C.O. Matsumoto R. Austen K.F. Arm J.P. J. Immunol. 1995; 155: 4445-4453PubMed Google Scholar). Pharmacologic studies demonstrated that the early PGD2 burst is due solely to activity of pre-existing PGS1 enzyme, while delayed PGD2 production in activated mast cells requires induced PGS2 synthesis (3Kawata R. Reddy S.T. Wolner B. Herschman H.R. J. Immunol. 1995; 155: 818-825PubMed Google Scholar, 4Murakami M. Bingham III, C.O. Matsumoto R. Austen K.F. Arm J.P. J. Immunol. 1995; 155: 4445-4453PubMed Google Scholar). Arachidonic acid, released from membrane phospholipids by PLA2, is a substrate for both PGS enzymes. Mast cells contain at least two distinct arachidonic acid precursor pools, whose arachidonate products remain segregated after release from cellular phospholipids (9Fonteh A.N. Bass D.A. Marshall L.A. Seeds M. Samet J.M. Chilton F.H. J. Immunol. 1994; 152: 5438-5446PubMed Google Scholar, 22Fonteh A.N. Chilton F.H. J. Immunol. 1993; 150: 563-570PubMed Google Scholar, 23Chilton F.H. Fonteh A.N. Surette M.E. Triggiani M. Winkler J.D. Biochim. Biophys. Acta. 1996; 1299: 1-15Crossref PubMed Scopus (209) Google Scholar). Moreover, mast cells have at least three distinct PLA2 isoforms (6Murakami M. Kudo I. Inoue K. J. Lipid Mediat. Cell Signal. 1995; 12: 119-130Crossref PubMed Scopus (64) Google Scholar, 24Murakami M. Kudo I. Umeda M. Matsuzawa A. Takeda M. Komada M. Fujimori Y. Takahashi K. Inoue K. J. Biochem. (Tokyo). 1992; 111: 175-181Crossref PubMed Scopus (71) Google Scholar). The temporal separation of PGD2 production by PGS1 and PGS2 in activated mast cells suggested that distinct phospholipid arachidonate pools and distinct phospholipases might provide arachidonate to the two prostaglandin synthase enzymes.The Late Phase of PGD2 Production in Activated Mast CellsThe inability of either antibody to sPLA2 or SB203347, the sPLA2 inhibitor, to reduce PGS2-dependent PGD2 production demonstrates that sPLA2 plays no role in the late phase of PGD2 synthesis. MAFP was initially described as a cytoplasmic type IV cPLA2 inhibitor, with no effect on type II sPLA2 (19Huang Z. Liu S. Street I. Laliberte F. Abdullah K. Desmarais S. Wang Z. Kennedy B. Payette P. Riendeau D. Weech P. Gresser M. Mediat. Inflamm. 1994; 3: 307-308Google Scholar). The late, PGS2-dependent phase of PGD2 production in activated mast cells is completely blocked by MAFP, suggesting that cPLA2 is required to provide arachidonate for this second component of PGD2 production. MAFP, however, also inhibits a cytosolic, calcium-independent PLA2 (iPLA2) (21Lio Y.C. Reynolds L.J. Balsinde H. Dennis E.A. Biochim. Biophys. Acta. 1996; 1302: 55-60Crossref PubMed Scopus (15) Google Scholar). When assayed previously, iPLA2 could not be detected in bone marrow-derived murine mast cells (25Currie S. Roberts E.F. Spaethe S.M. Roehm N.W. Kramer R.M. Biochem. J. 1994; 304: 923-928Crossref PubMed Scopus (21) Google Scholar). In our experiments, we found only a small fraction of MAFP-inhibitable phospholipase A2 activity present in extracts of activated mast cells to be calcium-independent (Fig. 10). In addition, specific iPLA2 inhibition in stimulated P388D1 macrophages enhances, rather than inhibits, arachidonate release (20Balsinde J. Dennis E.A. J. Biol. Chem. 1996; 271: 6758-6765Abstract Full Text Full Text PDF PubMed Scopus (341) Google Scholar). MAFP inhibition of late, PGS2-dependent PGD2 production in activated mast cells is, therefore, likely to be due to type IV cPLA2 inactivation. cPLA2 and PGS2 appear to be metabolically coupled in activated mast cells for the delayed phase of PGD2 synthesis. However, conclusive proof of this hypothesis will require the specific suppression of cPLA2 synthesis by antisense cPLA2, development of pharmacologic agents that more specifically inhibit cPLA2, or mast cells derived from animals in which the cPLA2 gene has been disrupted.The Early Phase of PGD2 Production in Activated Mast CellsPrevious experiments suggested that sPLA2 plays a role in PGD2 production following mast cell activation (9Fonteh A.N. Bass D.A. Marshall L.A. Seeds M. Samet J.M. Chilton F.H. J. Immunol. 1994; 152: 5438-5446PubMed Google Scholar). The ability, demonstrated here, of both a monoclonal antibody to sPLA2 (9Fonteh A.N. Bass D.A. Marshall L.A. Seeds M. Samet J.M. Chilton F.H. J. Immunol. 1994; 152: 5438-5446PubMed Google Scholar) and a specific sPLA2 inhibitor, SB203347 (15Marshall L.A. Hall R.H. Winkler J.D. Badger A. Bolognese B. Roshak A. Louis-Flamberg P. Sung C.-M. Chabot-Fletcher M. Adams J.L. Mayer R.J. J. Pharmacol. Exp. Ther. 1995; 274: 1254-1262PubMed Google Scholar), to completely block early, PGS1-dependent PGD2 production following mast cell activation supports this conclusion and demonstrates that sPLA2 and PGS1 are metabolically coupled. sPLA2 activity is required for the early phase of PGD2 production in activated mast cells. The low molecular weight, secreted PLA2 from mast cells has not been molecularly characterized. Three related murine genes encoding low molecular weight, secreted PLA2 enzymes of related structure are known, each with a cell type-specific distribution pattern (26Chen J. Engle S.J. Seilhamer J.J. Tischfield J.A. J. Biol. Chem. 1994; 269: 23018-23024Abstract Full Text PDF PubMed Google Scholar, 27Tischfield J.A. Xia Y.-R. Shih D.M. Klisak I. Chen J. Engle S.J. Siakotos A.N. Winstead M.V. Seilhamer J.J. Allamand V. Gyapay G. Lusis A.J. Genomics. 1996; 32: 328-333Crossref PubMed Scopus (91) Google Scholar). It will be of great interest to identify the PLA2 isoform(s) secreted by activated mast cells, since this enzyme(s) may represent an important target in mast cell eicosanoid production.Balsinde and Dennis (20Balsinde J. Dennis E.A. J. Biol. Chem. 1996; 271: 6758-6765Abstract Full Text Full Text PDF PubMed Scopus (341) Google Scholar) have demonstrated, in activated P388D1 macrophages, that “a functionally active cPLA2 appears to be necessary for sPLA2 to act.” Their results prompted us to examine the effects of preincubation of mast cells with MAFP on the early, sPLA2/PGS1-dependent phase of PGD2 synthesis in activated mast cells. An MAFP-sensitive step is required for one-half to two-thirds of the early phase of PGD2 production following the activation of mast cells by aggregation of their IgE receptors (Fig. 9). Since we have verified the inability of MAFP to block the enzymatic activity of either recombinant sPLA2 (Fig. 6) or the sPLA2 activity present in mast cell supernatants (Fig. 10), we conclude that the MAFP-sensitive step in early PGD2 production in response to aggregation of mast cell IgE receptors is likely to be mediated by cPLA2. Like the data of Balsinde and Dennis (20Balsinde J. Dennis E.A. J. Biol. Chem. 1996; 271: 6758-6765Abstract Full Text Full Text PDF PubMed Scopus (341) Google Scholar), our results suggest that a cPLA2-mediated function is required prior to the action of sPLA2. It should be emphasized that, although there exists a cPLA2-dependent event required for the early phase of PGD2 synthesis in activated mast cells, cPLA2 does not release arachidonic acid that is then available for PGD2 production by PGS1. Inhibition of sPLA2 by either SB203347 or mAbF10, which do not inhibit cPLA2, prevents all PGD2 production in the early phase of mast cell activation (Figs. 1, 2, 3).Spatial Separation of PGD2 Production in Mast CellsIn most cells, PGS1 is associated with the endoplasmic reticulum (1Herschman H.R. Cancer Metastasis Rev. 1994; 13: 241-256Crossref PubMed Scopus (315) Google Scholar, 2Herschman H.R. Biochim. Biophys. Acta. 1996; 1299: 125-140Crossref PubMed Scopus (1160) Google Scholar). In contrast, biochemical and ultrastructural analysis suggested that mast cell granules contain phospholipids (28Chock S.P. Schmauder-Chock E.A. J. Biol. Chem. 1989; 264: 2862-2868Abstract Full Text PDF PubMed Google Scholar), sPLA2 (29Chock S.P. Schmauder-Chock E.A. Cordella-Miele E. Miele L. Mukherjee A.B. Biochem. J. 1994; 300: 619-622Crossref PubMed Scopus (43) Google Scholar), and PGS1 (30Schmauder-Chock E.A. Chock S.P. J. Histochem. Cytochem. 1989; 37: 1319-1328Crossref PubMed Scopus (19) Google Scholar). Degranulation and exposure of granule contents to high extracellular calcium following aggregation of IgE receptors may activate sPLA2, leading to production of arachidonic acid substrate for PGS1 and the synthesis of the early PGD2 burst. Additional investigation of sPLA2 and PGS1 localization in resting and activated mast cells will be of great interest, now that two temporal phases of mast cell PGD2 production have been demonstrated.PGS2 is detected in both the endoplasmic reticulum and the nuclear envelope of mitogen-stimulated fibroblasts (31Morita I. Schindler M. Regier M.K. Otto J.C. Hori T. DeWitt D. Smith W.L. J. Biol. Chem. 1995; 270: 10902-10908Abstract Full Text Full Text PDF PubMed Scopus (510) Google Scholar). Subcellular PGS2 localization has not been reported in mast cells. Following mast cell activation, cPLA2 moves from the cytoplasm to the nuclear envelope (13Glover S. Bayburt T. Jonas M. Chi E. Gelb M.H. J. Biol. Chem. 1995; 270: 15359-15367Abstract Full Text Full Text PDF PubMed Scopus (314) Google Scholar). Ligand treatment also stimulates translocation of cPLA2 to the nuclear fraction in Chinese hamster ovary cells (32Schievella A.R. Regier M.K. Smith W.L. Lin L.-L. J. Biol. Chem. 1995; 270: 30749-30754Abstract Full Text Full Text PDF PubMed Scopus (421) Google Scholar) and in macrophages (33Peters-Golden M. McNish R.W. Biochem. Biophys. Res. Commun. 1993; 196: 147-153Crossref PubMed Scopus (176) Google Scholar). Assuming PGS2 is also localized predominantly at the nuclear envelope in mast cells after activation-induced synthesis, the data are consistent with the following model. Activated mast cells translocate cPLA2 to the nuclear envelope, where this enzyme releases arachidonate from phospholipids. Newly synthesized PGS2, also present in the nuclear envelope, utilizes this arachidonate to catalyze the late phase of PGD2 production. Mast cell PGS1 may not be able to use the arachidonate produced by cPLA2 for several reasons. It seems most likely that physical sequestration of PGS1 in mast cells may make cPLA2-dependent arachidonate, produced at the nuclear envelope, inaccessible to PGS1. Alternatively, PGS1 may be inactivated by a suicide reaction (34Rome L.H. Lands W.E. Proc. Natl. Acad. Sci. U. S. A. 1975; 72: 4863-4865Crossref PubMed Scopus (261) Google Scholar) during the early PGD2 synthesis phase, prior to adequate activation-induced cPLA2 translocation.Identification of the PLA2 and PGS isoforms that mediate the two phases of PGD2 production in activated mast cells may permit development of additional pharmacologic agents that can discriminate between these two PGD2 production pathways. In addition to mediating PGS1-dependent PGD2 production by mast cells following activation, sPLA2 released by activated mast cells can also initiate trans-cellular prostaglandin production by mobilizing arachidonate in a distal cell as substrate for PGS1 in that cell (16Reddy S.T. Herschman H.R. J. Biol. Chem. 1996; 271: 186-191Abstract Full Text Full Text PDF PubMed Scopus (109) Google Scholar). Specific inhibition of mast cell sPLA2 may, therefore, be an important pharmacologic target for several modes of prostaglandin production in chronic and acute inflammatory responses. INTRODUCTIONMast cells, an important cell type in allergic diseases, are widely distributed throughout vascularized tissue and epithelia. Activation of mast cells by aggregation of high affinity IgE receptors causes degranulation, releasing stored mediators of inflammation such as histamine and serotonin. Mast cell activation also induces the synthesis and release of leukotrienes and prostaglandin D2 (PGD2). Ligand stimulation in most cells elicits a relatively slow production of prostaglandins, peaking only after 4-6 h (1Herschman H.R. Cancer Metastasis Rev. 1994; 13: 241-256Crossref PubMed Scopus (315) Google Scholar, 2Herschman H.R. Biochim. Biophys. Acta. 1996; 1299: 125-140Crossref PubMed Scopus (1160) Google Scholar). In contrast, PGD2 synthesis in activated mast cells occurs in two stages, a rapid, early phase and a late, delayed phase (3Kawata R. Reddy S.T. Wolner B. Herschman H.R. J. Immunol. 1995; 155: 818-825PubMed Google Scholar, 4Murakami M. Bingham III, C.O. Matsumoto R. Austen K.F. Arm J.P. J. Immunol. 1995; 155: 4445-4453PubMed Google Scholar).Prostaglandin production is regulated by both phospholipases A2 (PLA2) 1The abbreviations used are: PLA2phospholipase A2sPLA2secretory phospholipase A2cPLA2cytoplasmic phospholipase A2iPLA2cytosolic, calcium-independent PLA2PGS1, prostaglandin synthase 1PGS2, prostaglandin synthase 2ATPCarachidonylthiophosphatidylcholineMAFPmethyl arachidonylfluorophosphonate. and prostaglandin synthases (PGS). PLA2 enzymes release arachidonic acid from membrane phospholipids. Free arachidonate is converted to prostaglandin H2 (PGH2), a common precursor for all prostanoids, by prostaglandin synthases. Several PLA2 enzymes have been implicated in arachidonate release following ligand stimulation of various cell types (5Clark J.D. Schievella A.R. Nalefski E.A. Lin L.L. J. Lipid Mediat. Cell Signal. 1995; 12: 83-118Crossref PubMed Scopus (425) Google Scholar, 6Murakami M. Kudo I. Inoue K. J. Lipid Mediat. Cell Signal. 1995; 12: 119-130Crossref PubMed Scopus (64) Google Scholar). Many cells also express two distinct prostaglandin synthases: PGS1, a primarily constitutively expressed form, and PGS2, an inducible PGS expressed following appropriate ligand stimulation in different cell types (1Herschman H.R. Cancer Metastasis Rev. 1994; 13: 241-256Crossref PubMed Scopus (315) Google Scholar, 2Herschman H.R. Biochim. Biophys. Acta. 1996; 1299: 125-140Crossref PubMed Scopus (1160) Google Scholar). Experiments using antisense oligonucleotide inhibition (7Reddy S.T. Herschman H.R. J. Biol. Chem. 1994; 269: 15473-15480Abstract Full Text PDF PubMed Google Scholar) and NS-398, a PGS2-specific inhibitor (1Herschman H.R. Cancer Metastasis Rev. 1994; 13: 241-256Crossref PubMed Scopus (315) Google Scholar, 8Herschman H.R. Xie W. Reddy S.T. BioEssays. 1995; 17: 1031-1037Crossref PubMed Scopus (81) Google Scholar), demonstrated that ligand-induced prostaglandin production in fibroblasts and macrophages requires induced PGS2 expression, despite the presence of active PGS1 enzyme. In contrast, the rapid, early phase of PGD2 synthesis in activated mast cells is mediated by pre-existing PGS1 (3Kawata R. Reddy S.T. Wolner B. Herschman H.R. J. Immunol. 1995; 155: 818-825PubMed Google Scholar, 4Murakami M. Bingham III, C.O. Matsumoto R. Austen K.F. Arm J.P. J. Immunol. 1995; 155: 4445-4453PubMed Google Scholar). The second, delayed phase of PGD2 synthesis in activated mast cells is similar to prostaglandin production in growth factor-induced fibroblasts and endotoxin-induced macrophages, requiring activation-induced PGS2 expression (3Kawata R. Reddy S.T. Wolner B. Herschman H.R. J. Immunol. 1995; 155: 818-825PubMed Google Scholar, 4Murakami M. Bingham III, C.O. Matsumoto R. Austen K.F. Arm J.P. J. Immunol. 1995; 155: 4445-4453PubMed Google Scholar).Following activation, mast cells secrete a low molecular weight PLA2, sPLA2 (9Fonteh A.N. Bass D.A. Marshall L.A. Seeds M. Samet J.M. Chilton F.H. J. Immunol. 1994; 152: 5438-5446PubMed Google Scholar). Fonteh et al. (9Fonteh A.N. Bass D.A. Marshall L.A. Seeds M. Samet J.M. Chilton F.H. J. Immunol. 1994; 152: 5438-5446PubMed Google Scholar) suggest that the sPLA2 released following activation plays a role in eicosanoid biosynthesis by activated mast cells. Activation of mast cells also induces the activation, translocation, and expression of cytoplasmic cPLA2 (10Nakatani Y. Murakami M. Kudo I. Inoue K. J. Immunol. 1994; 153: 796-803PubMed Google Scholar, 11Hirasawa N. Santini F. Beaven M.A. J. Immunol. 1995; 154: 5391-5402PubMed Google Scholar, 12Currie S. Roberts E.F. Spaethe S.M. Roehm N.W. Kramer R.M. Biochem. J. 1994; 304: 923-928Crossref PubMed Scopus (21) Google Scholar, 13Glover S. Bayburt T. Jonas M. Chi E. Gelb M.H. J. Biol. Chem. 1995; 270: 15359-15367Abstract Full Text Full Text PDF PubMed Scopus (314) Google Scholar). In this report we investigate the roles of sPLA2 and cPLA2 in early, PGS1-dependent PGD2 synthesis and late, PGS2-dependent PGD2 synthesis following mast cell activation by aggregation of high affinity IgE receptors.
Reddy et al. (Sat,) studied this question.