The Role of Calcium and Phosphorylation of Cytosolic Phospholipase A2 in Regulating Arachidonic Acid Release in Macrophages

Arachidonic acid release is induced in macrophages with diverse agonists including calcium ionophores, phorbol myristate acetate (PMA), okadaic acid, and the phagocytic particle, zymosan, and correlates with activation of cytosolic phospholipase A2 (cPLA2). The role of calcium and phosphorylation of cPLA2 in regulating arachidonic acid release was investigated. Zymosan induced a rapid and transient increase in Ca2+i. This in itself is not sufficient to induce arachidonic acid release since ATP and platelet activating factor (PAF), agonists that induce transient calcium mobilization in macrophages, induced little arachidonic acid release. Unlike zymosan, which is a strong activator of mitogen-activated protein kinase (MAPK), ATP and PAF were weak MAPK activators and induced only a partial and transient increase in cPLA2 phosphorylation (gel shift). However, ATP or PAF together with colony stimulating factor-1 (CSF-1) synergistically stimulated arachidonic acid release. CSF-1 is a strong MAPK activator that induces a rapid and complete cPLA2 gel shift but not calcium mobilization or arachidonic acid release. Arachidonic acid release was more rapid in response to CSF-1 plus ATP or PAF than zymosan and correlated with the time course of the cPLA2gel shift. Although low concentrations of ionomycin induced a lower magnitude of calcium mobilization than ATP, the response was more sustained resulting in arachidonic acid release. A23187 and ionomycin induced weak MAPK activation, and a partial and transient cPLA2 gel shift. The MAPK kinase inhibitor, PD 98059 suppressed A23187-induced MAPK activation and cPLA2 gel shift but had little effect on arachidonic acid release. These results indicate that in macrophages a transient increase in Ca2+i and sustained phosphorylation of cPLA2 can act together to promote arachidonic acid release but neither alone is sufficient. A sustained increase in calcium is sufficient for inducing arachidonic acid release. However, PMA and okadaic acid induce arachidonic acid release without increasing Ca2+i, although resting levels of calcium are required, suggesting alternative mechanisms of regulation. Arachidonic acid release is induced in macrophages with diverse agonists including calcium ionophores, phorbol myristate acetate (PMA), okadaic acid, and the phagocytic particle, zymosan, and correlates with activation of cytosolic phospholipase A2 (cPLA2). The role of calcium and phosphorylation of cPLA2 in regulating arachidonic acid release was investigated. Zymosan induced a rapid and transient increase in Ca2+i. This in itself is not sufficient to induce arachidonic acid release since ATP and platelet activating factor (PAF), agonists that induce transient calcium mobilization in macrophages, induced little arachidonic acid release. Unlike zymosan, which is a strong activator of mitogen-activated protein kinase (MAPK), ATP and PAF were weak MAPK activators and induced only a partial and transient increase in cPLA2 phosphorylation (gel shift). However, ATP or PAF together with colony stimulating factor-1 (CSF-1) synergistically stimulated arachidonic acid release. CSF-1 is a strong MAPK activator that induces a rapid and complete cPLA2 gel shift but not calcium mobilization or arachidonic acid release. Arachidonic acid release was more rapid in response to CSF-1 plus ATP or PAF than zymosan and correlated with the time course of the cPLA2gel shift. Although low concentrations of ionomycin induced a lower magnitude of calcium mobilization than ATP, the response was more sustained resulting in arachidonic acid release. A23187 and ionomycin induced weak MAPK activation, and a partial and transient cPLA2 gel shift. The MAPK kinase inhibitor, PD 98059 suppressed A23187-induced MAPK activation and cPLA2 gel shift but had little effect on arachidonic acid release. These results indicate that in macrophages a transient increase in Ca2+i and sustained phosphorylation of cPLA2 can act together to promote arachidonic acid release but neither alone is sufficient. A sustained increase in calcium is sufficient for inducing arachidonic acid release. However, PMA and okadaic acid induce arachidonic acid release without increasing Ca2+i, although resting levels of calcium are required, suggesting alternative mechanisms of regulation. The production of the proinflammatory lipid mediators, the eicosanoids (i.e. prostaglandins and leukotrienes), is dependent on the availability of the precursor, free arachidonic acid. The release of arachidonic acid from the sn-2 position of membrane phospholipid is a highly regulated process that occurs in response to cell activation. Phospholipase A2(PLA2) 1The abbreviations used are: PLA2, phospholipase A2; cPLA2, cytosolic PLA2; MAPK, mitogen-activated protein kinase; MAPKK, MAPK kinase; PMA, phorbol myristate acetate; CSF-1, colony stimulating factor-1; DMEM, Dulbecco's modified Eagle's medium; PAF, platelet activating factor; Ca2+i, intracellular Ca2+. 1The abbreviations used are: PLA2, phospholipase A2; cPLA2, cytosolic PLA2; MAPK, mitogen-activated protein kinase; MAPKK, MAPK kinase; PMA, phorbol myristate acetate; CSF-1, colony stimulating factor-1; DMEM, Dulbecco's modified Eagle's medium; PAF, platelet activating factor; Ca2+i, intracellular Ca2+. enzymes, which cleave fatty acid from the sn-2 position of phospholipid, play a central role in controlling the release of arachidonic acid. The importance of the arachidonic acid-selective, 85-kDa cytosolic PLA2 (cPLA2) in mediating agonist-induced release of arachidonic acid is now well recognized (1Clark J.D. Schievella A.R. Nalefski E.A. Lin L.-L. J. Lipid Mediators Cell Signalling. 1995; 12: 83-117Crossref PubMed Scopus (422) Google Scholar,2Leslie C.C. J. Biol. Chem. 1997; 272: 16709-16712Abstract Full Text Full Text PDF PubMed Scopus (738) Google Scholar). cPLA2 is regulated post-translationally by both phosphorylation and calcium. Calcium plays a role by promoting binding of cPLA2 to membrane, which is mediated by a calcium-phospholipid-binding domain at the amino terminus of the enzyme (3Channon J.Y. Leslie C.C. J. Biol. Chem. 1990; 265: 5409-5413Abstract Full Text PDF PubMed Google Scholar, 4Clark J.D. Lin L.-L. Kriz R.W. Ramesha C.S. Sultzman L.A. Lin A.Y. Milona N. Knopf J.L. Cell. 1991; 65: 1043-1051Abstract Full Text PDF PubMed Scopus (1453) Google Scholar, 5Nalefski E.A. Sultzman L.A. Martin D.M. Kriz R.W. Towler P.S. Knopf J.L. Clark J.D. J. Biol. Chem. 1994; 269: 18239-18249Abstract Full Text PDF PubMed Google Scholar). Treatment of cells with calcium-mobilizing agonists has been shown to induce binding of cPLA2 to nuclear membrane and endoplasmic reticulum (6Schievella A.R. Regier M.K. Smith W.L. Lin L.-L. J. Biol. Chem. 1995; 270: 30749-30754Crossref PubMed Scopus (421) Google Scholar, 7Sierra-Honigmann M.R. Bradley J.R. Pober J.S. Lab. Invest. 1996; 74: 684-695PubMed Google Scholar, 8Glover S. Bayburt T. Jonas M. Chi E. Gelb M.H. J. Biol. Chem. 1995; 270: 15359-15367Crossref PubMed Scopus (314) Google Scholar). Stimulation of a variety of cell types with diverse agonists that induce arachidonic acid release also has been shown to promote serine phosphorylation of cPLA2 that is accompanied by an increase in cPLA2 activity and a decrease in electrophoretic mobility (gel shift) (1Clark J.D. Schievella A.R. Nalefski E.A. Lin L.-L. J. Lipid Mediators Cell Signalling. 1995; 12: 83-117Crossref PubMed Scopus (422) Google Scholar, 9Qiu Z.-H. de Carvalho M.S. Leslie C.C. J. Biol. Chem. 1993; 268: 24506-24513Abstract Full Text PDF PubMed Google Scholar, 10Lin L.-L. Lin A.Y. DeWitt D.L. J. Biol. Chem. 1992; 267: 23451-23454Abstract Full Text PDF PubMed Google Scholar). cPLA2 can be phosphorylated by protein kinase C, p42/p44 mitogen-activated protein kinases (MAPK), or protein kinase A in vitro but only phosphorylation by MAPK results in a significant increase in cPLA2 activity and induces a cPLA2gel shift (10Lin L.-L. Lin A.Y. DeWitt D.L. J. Biol. Chem. 1992; 267: 23451-23454Abstract Full Text PDF PubMed Google Scholar, 11Nemenoff R.A. Winitz S. Qian N.-X. Van Putten V. Johnson G.L. Heasley L.E. J. Biol. Chem. 1993; 268: 1960-1964Abstract Full Text PDF PubMed Google Scholar). MAPK phosphorylates cPLA2 at Ser-505 and phosphorylation of this site has been shown to be required for cPLA2-mediated arachidonic acid release in Chinese hamster ovary cells treated with a variety of agonists (12Lin L.-L. Wartmann M. Lin A.Y. Knopf J.L. Seth A. Davis R.J. Cell. 1993; 72: 269-278Abstract Full Text PDF PubMed Scopus (1643) Google Scholar). Current evidence indicates that cPLA2 phosphorylation at Ser-505 by MAPK in itself is not sufficient for arachidonic acid release (1Clark J.D. Schievella A.R. Nalefski E.A. Lin L.-L. J. Lipid Mediators Cell Signalling. 1995; 12: 83-117Crossref PubMed Scopus (422) Google Scholar). It has been shown in Chinese hamster ovary cells that phosphorylation of cPLA2 induced by PMA is not sufficient for inducing arachidonic acid release, but PMA acts synergistically with calcium ionophore (10Lin L.-L. Lin A.Y. DeWitt D.L. J. Biol. Chem. 1992; 267: 23451-23454Abstract Full Text PDF PubMed Google Scholar). In macrophages, CSF-1 induces cPLA2 phosphorylation but not arachidonic acid release although it can act synergistically with calcium mobilizing agonists (13Xu X.X. Rock C.O. Qiu Z.H. Leslie C.C. Jackowski S. J. Biol. Chem. 1994; 269: 31693-31700Abstract Full Text PDF PubMed Google Scholar). It has been suggested that an increase in intracellular calcium concentration Ca2+i, but not phosphorylation of cPLA2, is essential for arachidonic acid release in rat liver macrophages (14Ambs P. Baccarini M. Fitzke E. Dieter P. Biochem. J. 1995; 311: 189-195Crossref PubMed Scopus (58) Google Scholar). In platelets, thrombin-stimulated arachidonic acid release does not require phosphorylation of cPLA2 on Ser-505 (15Kramer R.M. J. Biol. Chem. 1996; Full Text Full Text PDF PubMed Scopus Google Scholar). Although indicate an role for an increase in Ca2+i in regulating arachidonic acid release, alternative mechanisms are by results that cPLA2-mediated arachidonic acid release induced by okadaic acid occurs without an increase in Ca2+i Carvalho E. Gelb M.H. J.R. Leslie C.C. J. Biol. Chem. 1996; Full Text Full Text PDF PubMed Scopus Google Scholar). In of macrophages were used a to the role of calcium and phosphorylation of cPLA2 in regulating arachidonic acid release. acid and acid were from were from and were from and the for were from Zymosan cell and were from Zymosan was Z.-H. de Carvalho M.S. Leslie C.C. J. Biol. Chem. 1993; 268: 24506-24513Abstract Full Text PDF PubMed Google Scholar). acid and PMA were from was from CSF-1 was a from The The MAPK kinase inhibitor, PD was by Davis PAF was from modified was from Dulbecco's modified Eagle's and were from were from concentrations were the from to cPLA2 was Carvalho M.S. Leslie C.C. Biochem. 1993; PubMed Scopus Google Scholar). MAPK to the and that were used for were from that and MAPK was from macrophages were and with acid Z.-H. de Carvalho M.S. Leslie C.C. J. Biol. Chem. 1993; 268: 24506-24513Abstract Full Text PDF PubMed Google Scholar). the cells were with and stimulated in of with agonists for the the macrophages were of calcium by in and for T. PubMed Scopus Google Scholar, E. P. J. Biol. Chem. 1990; 265: Full Text PDF PubMed Google Scholar). The cells were and treated with agonists in The was and at in a for and the cells were of The of in the cells and was by the macrophages were on with of A and on for the were for The was for in PubMed Scopus Google Scholar). of MAPK of were on and to the cPLA2 gel of were on and to a with for the membrane was at with at in and by with in for at The protein was the were on in at a of and for in a of in at The cells were with and to cells and in with and with the cells were for at in A and The were with and with and in A in the at used for Ca2+i were in a position in a of and The was with a to position the a The was in a and at with for the of was with an of Ca2+i was to the Ca2+i is the M. J. Biol. Chem. Full Text PDF PubMed Scopus Google the of was by cells with the was by of to the is the of the and is the of at at and The of from the which was by to the was to be were in a at a of and with the the cells were in of and with a with the calcium was of agonists was were were at and stimulated were on of and were by with of protein in for at or were from the by with of and of protein in for at The were with and with and were in of kinase ATP, factor protein kinase and of and at for were by and of of acid. A of the was which were with acid and with by cPLA2 was in the Carvalho E. Gelb M.H. J.R. Leslie C.C. J. Biol. Chem. 1996; Full Text Full Text PDF PubMed Scopus Google Scholar). cPLA2 from macrophages, cells were and Z.-H. de Carvalho M.S. Leslie C.C. J. Biol. Chem. 1993; 268: 24506-24513Abstract Full Text PDF PubMed Google Scholar). were used for were with essential and for in of essential and acid The cells were treated with or okadaic acid for cells were with in of A. cPLA2 was from cell a of for or a for cell Carvalho E. Gelb M.H. J.R. Leslie C.C. J. Biol. Chem. 1996; Full Text Full Text PDF PubMed Scopus Google Scholar). cPLA2 was on a by from the gel and from the gel acid Carvalho E. Gelb M.H. J.R. Leslie C.C. J. Biol. Chem. 1996; Full Text Full Text PDF PubMed Scopus Google Scholar). cPLA2 was protein to the acid acid were in of and was at a of by The were for at and by of and in a were in acid, and by was Carvalho E. Gelb M.H. J.R. Leslie C.C. J. Biol. Chem. 1996; Full Text Full Text PDF PubMed Scopus Google Scholar). Arachidonic acid release can be induced in macrophages by diverse agonists PMA, the calcium the inhibitor, okadaic acid, and the phagocytic This correlates with activation of cPLA2 which phosphorylated on serine resulting in an increase in were to the role of calcium in regulating arachidonic acid release. were with to the effect of agonists on in Ca2+i by This of cells in the The of the agonists that induce arachidonic acid release were with ATP, a calcium mobilizing in macrophages S. J. Biol. Chem. Full Text PDF PubMed Google Scholar, A. J. Biol. Chem. 1993; 268: Full Text PDF PubMed Google Scholar). Zymosan and ATP both induced a rapid increase in Ca2+i by the at The response of the was with by in to in Ca2+i in the to the but the response to A23187 was but in to zymosan and ATP, the increase in Ca2+i was more sustained and had not by okadaic acid PMA induced an increase in Ca2+i The of effect with PMA and okadaic acid was by cells not Although PMA and okadaic acid induced arachidonic acid release without increasing intracellular it was that resting levels of Ca2+i were the effect of the cells of calcium by including in the and the cells with on agonist-induced arachidonic acid release was calcium by the macrophages in suppressed arachidonic acid release in response to the the cells with in to calcium with suppressed arachidonic acid release in response to zymosan, and okadaic acid. The response to PMA was not in the cells the PMA and okadaic acid not induce an increase in Ca2+i, the of arachidonic acid release by suggested that this was the resting levels of and that this was required for arachidonic acid release. of the macrophages in was to decrease resting levels of Ca2+i by or by in cells not These results that although PMA and okadaic acid not induce an increase in Ca2+i, the resting of Ca2+i is for arachidonic acid release. were to the of calcium mobilization and in regulating arachidonic acid release. were used that induce strong MAPK activation to cPLA2 but with calcium or that promote calcium mobilization but little MAPK activation. A of the effect of ATP and PAF on the magnitude and time course of Ca2+i mobilization in macrophages is shown in ATP induced an increase in Ca2+i from to but to levels by PAF also induced a increase in Ca2+i to a lower magnitude than ATP but the response was more sustained In CSF-1 not promote an increase in Ca2+i both by and not The of agonists to and and promote an increase in cPLA2 phosphorylation was of was by that the of the CSF-1 and by which was a decrease in activity although activation of levels was by In ATP and PAF by and activation was transient to levels by with the of MAPK activation, CSF-1 induced a rapid and complete gel shift of cPLA2 that time with only a of cPLA2 to the by ATP and PAF by but the gel shift was not complete and was with a significant of the PLA2 to the by In zymosan induced a increase in with a complete gel shift by This is with a activation of MAPK by zymosan (13Xu X.X. Rock C.O. Qiu Z.H. Leslie C.C. Jackowski S. J. Biol. Chem. 1994; 269: 31693-31700Abstract Full Text PDF PubMed Google Scholar, Z.-H. Leslie C.C. J. Biol. Chem. 1994; 269: Full Text PDF PubMed Google Scholar). The effect of agonists on the time course of arachidonic acid release is shown in CSF-1 alone not arachidonic acid release and the response to ATP was PAF induced a release of arachidonic acid. However, CSF-1 together with ATP or PAF induced a release of arachidonic acid that In the response to zymosan was by at which arachidonic acid release to in the to These results that is a transient increase in calcium the time course of arachidonic acid release correlates with the time course of cPLA2 activation by course of MAPK activation and phosphorylation of were stimulated for the with ATP PAF CSF-1 or zymosan cell were for and MAPK or by time course of acid macrophages were to zymosan ATP PAF CSF-1 ATP plus CSF-1, or PAF plus The of the at was and a of the plus The results are of a and were in In to ATP and PAF, agonists that induce a sustained increase in Ca2+i the calcium A23187 and ionomycin promote of arachidonic acid release. does not is the for was used to the concentration of Ca2+i arachidonic acid release in the macrophages A of arachidonic acid in the with ionomycin from to that correlated with to induce an increase in Ca2+i more arachidonic acid was with ionomycin with ATP the magnitude of the calcium at concentrations was than with However, the increase in Ca2+i with ionomycin was more sustained than with ATP, which is with the of by the also induced a partial gel shift of cPLA2 This is with that A23187 induced an increase in cPLA2 activity in macrophages which was by although the magnitude of was than with arachidonic acid mobilizing agonists zymosan, and okadaic Z.-H. de Carvalho M.S. Leslie C.C. J. Biol. Chem. 1993; 268: 24506-24513Abstract Full Text PDF PubMed Google Scholar). the of A23187 to induce a cPLA2 gel shift at was and with the time course of arachidonic acid release A23187 induced a partial cPLA2 gel shift by that by the gel shift was not complete and it was Arachidonic acid release induced by A23187 was by and to in the to time course of A23187-induced arachidonic acid release and cPLA2 macrophages were to A23187 for the and the of the was and a of the plus the a of cPLA2 at of the macrophages with and without A23187 A is shown and the results were in Although a cPLA2 gel shift is of phosphorylation by MAPK, had that A23187 induced only a activation of MAPK Z.-H. Leslie C.C. J. Biol. Chem. 1994; 269: Full Text PDF PubMed Google Scholar). This was in a more and for and MAPK activity which the kinases and kinase activity in an in vitro an factor PMA, and okadaic acid induced a or increase in MAPK activity and a increase in MAPK activation. A23187 induced a low increase in MAPK activation but increase in MAPK The time course of p42/p44 activation was by an for MAPK with the results A23187 MAPK, and the response was weak with MAPK activation by In MAPK activation by A23187 was transient and to by The weak activation of MAPK by A23187 be by the inhibitor, PD 98059 and in with this PD 98059 the cPLA2 gel shift induced by A23187 However, arachidonic acid release induced by A23187 was only by PD 98059 at arachidonic acid release was These results that phosphorylation at Ser-505 is not for arachidonic acid release in cells is a sustained increase in of the inhibitor, on of A23187-induced cPLA2 gel shift and arachidonic acid release. macrophages were with concentrations of for and treated with A23187 for The of the was and a of the plus The results are of macrophages were with PD 98059 for and treated with A23187 for Cell were and by PD 98059 at the cPLA2 gel shift. A is shown and the results were in The results with PMA and okadaic acid that alternative mechanisms can arachidonic acid release in macrophages since agonists act without increasing Ca2+i. that cPLA2 is in cells cPLA2-mediated arachidonic acid release can be induced by okadaic acid and this occurs without an increase in Ca2+i Carvalho E. Gelb M.H. J.R. Leslie C.C. J. Biol. Chem. 1996; Full Text Full Text PDF PubMed Scopus Google Scholar). In the okadaic acid induces a increase in phosphorylation of cPLA2 on In the okadaic acid induced a decrease in electrophoretic mobility of cPLA2 than the shift to phosphorylation of Ser-505 with agonists PMA This that okadaic acid induces phosphorylation of on cPLA2 in were to okadaic acid induced phosphorylation of in were with stimulated with okadaic acid, and of the cPLA2 by were from macrophages cPLA2 from okadaic macrophages the of and an increase in of The from okadaic cells was to with from okadaic macrophages These results that is phosphorylated on cPLA2 in response to okadaic acid in the The of the is in cPLA2 from and this to be of of cPLA2 from cells and of cPLA2 from macrophages okadaic macrophages cells or from both cells and okadaic macrophages on the were by was in the with the on the and was in the The was the lower of the Arachidonic acid plays an role a and a of lipid mediators, levels in cells are The results of this that arachidonic acid release can be regulated in an by diverse mechanisms in has shown that agonist-induced arachidonic acid release is a process in cells J. E. 1992; PubMed Scopus Google Scholar, A. PubMed Scopus Google Scholar). that a variety of agonists that induce arachidonic acid release in macrophages cPLA2 by serine phosphorylation a Z.-H. de Carvalho M.S. Leslie C.C. J. Biol. Chem. 1993; 268: 24506-24513Abstract Full Text PDF PubMed Google Scholar, Z.-H. Leslie C.C. J. Biol. Chem. 1994; 269: Full Text PDF PubMed Google Scholar). In this agonists that act by diverse mechanisms were used to the of calcium and on Ser-505 in regulating arachidonic acid release in this cell of cPLA2 on Ser-505 was by the of agonists to induce a cPLA2 gel shift. Current evidence indicates that the gel shift is to phosphorylation on Ser-505 and that the of the gel shift can be used to the of phosphorylation at this MAPK site (10Lin L.-L. Lin A.Y. DeWitt D.L. J. Biol. Chem. 1992; 267: 23451-23454Abstract Full Text PDF PubMed Google Scholar). suggested that the okadaic gel shift of cPLA2 in cells be to phosphorylation of However, that in cells of cPLA2 the but not cPLA2 the a gel shift in response to okadaic acid. and agonists for macrophages, the results that neither a transient increase in Ca2+i, induced by ATP, phosphorylation of cPLA2 on Ser-505 induced by CSF-1, are sufficient for inducing arachidonic acid release. shown that CSF-1 phosphorylation and activity of cPLA2 in macrophages but is not on to induce arachidonic acid release (13Xu X.X. Rock C.O. Qiu Z.H. Leslie C.C. Jackowski S. J. Biol. Chem. 1994; 269: 31693-31700Abstract Full Text PDF PubMed Google Scholar). In the CSF-1 was not to induce an increase in Ca2+i but promote a phosphorylation of cPLA2 on The calcium-mobilizing agonists ATP and PAF were to be weak MAPK activators and induced only a partial and transient phosphorylation of cPLA2 on ATP induces a transient increase in Ca2+i and this together with weak to promote phosphorylation of cPLA2 were to induce arachidonic acid release. However, the transient increase in Ca2+i together with phosphorylation of cPLA2 on Ser-505 induced by CSF-1 act together to synergistically promote arachidonic acid release. Zymosan induces both a transient increase in calcium and phosphorylation of cPLA2 on Ser-505 and is a of arachidonic acid release. In the time course of arachidonic acid release correlated with the time course of cPLA2 phosphorylation on Ser-505 which was rapid for CSF-1 and for with ATP, PAF induced a low of arachidonic acid release. PAF to a of MAPK activation and cPLA2 phosphorylation ATP but it induced a more sustained increase in Ca2+i. In macrophages, PAF has been to induce a increase in Ca2+i, an to release from intracellular and a to of calcium A. PubMed Scopus Google Scholar). The results that the more sustained increase in calcium is to the of PAF to induce a low of arachidonic acid release. In arachidonic acid release has been to the of calcium 1993; PubMed Scopus Google Scholar, 1996; PubMed Scopus Google Scholar, J. Biochem. 1991; PubMed Scopus Google Scholar, T. S. T. J. Biochem. 1996; PubMed Scopus Google Scholar). results rat liver macrophages, it has been suggested that an increase in Ca2+i, but not is for arachidonic acid release (14Ambs P. Baccarini M. Fitzke E. Dieter P. Biochem. J. 1995; 311: 189-195Crossref PubMed Scopus (58) Google Scholar). However, results that cPLA2 phosphorylation on Ser-505 is required in macrophages is a transient increase in Ca2+i but that it is not essential is a sustained increase in Ca2+i from induced by the calcium It has been shown in cells that a of to nuclear membrane in response to calcium and it on the membrane than is only a transient increase in calcium occurs with S. Bayburt T. Jonas M. Chi E. Gelb M.H. J. Biol. Chem. 1995; 270: 15359-15367Crossref PubMed Scopus (314) Google Scholar). Although the calcium induce a transient cPLA2 gel the results that this phosphorylation little to arachidonic acid release since of MAPK activation and phosphorylation of cPLA2 on Ser-505 by the has effect on arachidonic acid release. However, results shown that CSF-1 can A23187-induced arachidonic acid release in the macrophages (13Xu X.X. Rock C.O. Qiu Z.H. Leslie C.C. Jackowski S. J. Biol. Chem. 1994; 269: 31693-31700Abstract Full Text PDF PubMed Google Scholar). This that the phosphorylation of Ser-505 be and more sustained occurs with CSF-1 to A23187-induced arachidonic acid release. These results that a sustained increase in intracellular calcium induced by A23187 be sufficient for arachidonic acid release. Although the that A23187 induces phosphorylation of a site that does not to a gel shift but to activation, this is since shown that A23187 induces only a increase in of cPLA2 in the macrophages Z.-H. de Carvalho M.S. Leslie C.C. J. Biol. Chem. 1993; 268: 24506-24513Abstract Full Text PDF PubMed Google Scholar). The results PMA and okadaic acid that arachidonic acid release can be induced in macrophages without an increase in Ca2+i. However, and intracellular calcium arachidonic acid release by suggesting that resting levels of calcium be of agonists induce phosphorylation of cPLA2 on Ser-505 but since this is not sufficient for inducing arachidonic acid release without an increase in Ca2+i, are The of PMA on to induce arachidonic acid release is to cell types macrophages and Z.-H. de Carvalho M.S. Leslie C.C. J. Biol. Chem. 1993; 268: 24506-24513Abstract Full Text PDF PubMed Google J. Clark J.D. P. J. Invest. 1994; PubMed Scopus Google Scholar). In cell types it is only with a calcium mobilizing (10Lin L.-L. Lin A.Y. DeWitt D.L. J. Biol. Chem. 1992; 267: 23451-23454Abstract Full Text PDF PubMed Google Scholar). The mechanisms in regulating arachidonic acid release in macrophages are In shown that okadaic acid induces phosphorylation of cPLA2 on a site it is in acid induces arachidonic acid release in the without an increase in Ca2+i Carvalho E. Gelb M.H. J.R. Leslie C.C. J. Biol. Chem. 1996; Full Text Full Text PDF PubMed Scopus Google Scholar). In the the gel shift of cPLA2 from okadaic cells that it is also phosphorylated on in to In of cPLA2 from okadaic macrophages by that it is phosphorylated on are to the of phosphorylation on