Cytosolic Phospholipase A2 Is Required for Macrophage Arachidonic Acid Release by Agonists That Do and Do Not Mobilize Calcium

Abstract

The 85-kDa cytosolic phospholipase A 2 (cPLA 2 ) mediates agonist-induced arachidonic acid release and eicosanoid production. Calcium and phosphorylation on Ser-505 by mitogen-activated protein kinases (MAPKs) regulate cPLA 2 . Arachidonic acid release and eicosanoid production induced by stimuli that do (A23187, zymosan) or do not (phorbol myristate acetate (PMA), okadaic acid) mobilize calcium were quantitatively suppressed in cPLA 2 -deficient mouse peritoneal macrophages. The contribution of MAPKs to cPLA 2 -mediated arachidonic acid release was investigated. Both extracellular signal-regulated kinases (ERKs) and p38 contributed to cPLA 2 phosphorylation on Ser-505. However, although ERK inhibition did not affect A23187-induced arachidonic acid release, it suppressed zymosan-, PMA-, and okadaic acid-induced arachidonic acid release under conditions where phosphorylation of cPLA 2 on Ser-505 was unaffected. This indicates an additional regulatory mechanism for the ERK pathway. A role for transcriptional regulation is suggested by data showing that cycloheximide and actinomycin D inhibited arachidonic acid release induced by zymosan, PMA and, okadaic acid but not by A23187. Our results show that MAPK pathways contribute to arachidonic acid release in macrophages through alternative mechanisms in addition to their ability to phosphorylate cPLA 2 on Ser-505 and suggest a role for new protein synthesis.

Polychlorinated biphenyls induce arachidonic acid release in human platelets in a tamoxifen sensitive manner via activation of group IVA cytosolic phospholipase A2-α

“…The catalytic domain can affect membrane association of the enzyme by modulating the rate of association and also the residence time at membranes [18]. Furthermore, there is now convincing evidence that calcium-independent pathways for cytosol-to-membrane translocation of cPLA 2 -α exists [19][20][21][22][23][24], thus, suggesting alternative mechanisms for membrane association. One such mechanism could involve calcium-independent association of cPLA 2 -α to anionic phospholipids [21,24,25].…”

Lipid Profiling Reveals Glycerophospholipid Remodeling in Zymosan-Stimulated Macrophages

“…On the basis of radiolabel studies, RPMs were reported to mobilize up to 50% of their 20:4 in response to the phagocytosis of zymosan, a yeast cell wall preparation that activates multiple receptors, including dectin-1 and toll-like receptor-2 (7). More than 90% of the radioactivity that appeared in the culture medium of zymosan-stimulated cells had been converted to eicosanoids, with the major metabolites identified as PGE 2 and PGI 2 (identified as its stable hydrolysis product, 6-ketoPGF 1R ), and minor quantities of hydroxyeicosatetraenoic acids. Leukotriene C 4 was identified later (5,(8)(9)(10)(11)(12).…”

Altered Endothelin-1 Signaling in Production of Thromboxane A2 in Kupffer Cells from Bile Duct Ligated Rats

“…The primary means by which AA is released from membranes is the agonist induced activation of the calcium dependent group IV  isoform of cPLA 2 , due to its high specificity and selectivity for glycerophospholipids containing AA at the sn-2 position. Although the agonist induced activation of cPLA 2  has been established as the rate limiting step of eicosanoid biosynthesis (17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27), the deacylation of diacylglycerol (DAG) via DAG lipase also produces AA for the synthesis of eicosianoids. In addition, DAG lipase has been suggested to mediate the release of AA in KCs (56,62).…”

“…The significance of cPLA 2 in eicosanoid production is further evident as cells and tissues from cPLA 2 -deficient mice fail to produce prostaglandins, leukotrienes, and thromboxanes (20,21). It is established that the primary function of cPLA 2  is to mediate agonist-induced release of AA for eicosanoid production (17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27). The regulation of cPLA 2 activity involves multiple components.…”

“…This domain is a Ca 2+ and phospholipid binding domain that promotes interaction of cPLA 2 with its target membrane. Although the phosphorylation of Ser505 by p38 mitogen activated protein kinase (p38 MAPK) and extracellular signal-regulated kinase 1/2 (ERK1/2) (29-31), Ser515 by Ca 2+ /Calmodulin protein kinase II (CaMKII) (32), and Ser727 by MAPK interacting kinase I (Mnk1) (33) have been implicated in the activation of cPLA 2 ; several studies have established that the phosphorylation of Ser505 is critical for maximal activation of cPLA 2 in most cell types in response to agonist stimulation in vivo and in vitro (26,(29)(30)(31)(34)(35)(36)(37).…”