Activation of group IV cytosolic phospholipase A2 in human eosinophils by phosphoinositide 3-kinase through a mitogen-activated protein kinase-independent pathway.
Activation of group IV cytosolic phospholipase A(2) (gIV-PLA(2)) is the essential first step in the synthesis of inflammatory eicosanoids and in integrin-mediated adhesion of leukocytes. Prior investigations have demonstrated that phosphorylation of gIV-PLA(2) results from activation of at least two isoforms of mitogen-activated protein kinase (MAPK). We investigated the potential role of phosphoinositide 3-kinase (PI3K) in the activation of gIV-PLA(2) and the hydrolysis of membrane phosphatidylcholine in fMLP-stimulated human blood eosinophils. Transduction into eosinophils of Deltap85, a dominant negative form of class IA PI3K adaptor subunit, fused to an HIV-TAT protein transduction domain (TAT-Deltap85) concentration dependently inhibited fMLP-stimulated phosphorylation of protein kinase B, a downstream target of PI3K. FMLP caused increased arachidonic acid (AA) release and secretion of leukotriene C(4) (LTC(4)). TAT-Deltap85 and LY294002, a PI3K inhibitor, blocked the phosphorylation of gIV-PLA(2) at Ser(505) caused by fMLP, thus inhibiting gIV-PLA(2) hydrolysis and production of AA and LTC(4) in eosinophils. FMLP also caused extracellular signal-related kinases 1 and 2 and p38 MAPK phosphorylation in eosinophils; however, neither phosphorylation of extracellular signal-related kinases 1 and 2 nor p38 was inhibited by TAT-Deltap85 or LY294002. Inhibition of 1) p70 S6 kinase by rapamycin, 2) protein kinase B by Akt inhibitor, or 3) protein kinase C by Ro-31-8220, the potential downstream targets of PI3K for activation of gIV-PLA(2), had no effect on AA release or LTC(4) secretion caused by fMLP. We find that PI3K is required for gIV-PLA(2) activation and hydrolytic production of AA in activated eosinophils. Our data suggest that this essential PI3K independently activates gIV-PLA(2) through a pathway that does not involve MAPK.
Myou
Shigeharu
S
Section of Pulmonary and Critical Care Medicine, Department of Medicine, University of Chicago, Chicago, IL 60637, USA.
Leff
Alan R
AR
Myo
Saori
S
Boetticher
Evan
E
Meliton
Angelo Y
AY
Lambertino
Anissa T
AT
Liu
Jie
J
Xu
Chang
C
Munoz
Nilda M
NM
Zhu
Xiangdong
X
D016718:Arachidonic Acid / Q000378:metabolism; D002454:Cell Differentiation / Q000235:genetics / Q000502:physiology; D004789:Enzyme Activation / Q000235:genetics; D004804:Eosinophils / Q000201:enzymology* / Q000378:metabolism / Q000502:physiology; D015696:Gene Products, tat / Q000235:genetics / Q000378:metabolism; D054513:Group IV Phospholipases A2; D006801:Humans; D007527:Isoenzymes / Q000096:biosynthesis; D017997:Leukotriene C4 / Q000096:biosynthesis; D020935:MAP Kinase Signaling System / Q000235:genetics; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000502:physiology*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010741:Phospholipases A / Q000378:metabolism*; D054467:Phospholipases A2; D010766:Phosphorylation; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000502:physiology; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D012694:Serine / Q000378:metabolism; D014161:Transduction, Genetic; D014316:Tritium
D016718:Arachidonic Acid; D015696:Gene Products, tat; D054513:Group IV Phospholipases A2; D007527:Isoenzymes; D017997:Leukotriene C4; D009240:N-Formylmethionine Leucyl-Phenylalanine; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010741:Phospholipases A; D054467:Phospholipases A2; D011493:Protein Kinase C; D011993:Recombinant Fusion Proteins; D012694:Serine; D014316:Tritium; C516389:PLA2G4A protein, human