Comparison of alkylacylglycerol vs. diacylglycerol as activators of mitogen-activated protein kinase and cytosolic phospholipase A2 in human neutrophil priming.
In human neutrophils, the choline-containing phosphoglycerides contain almost equal amounts of alkylacyl- and diacyl-linked subclasses. In contrast to phosphatidylinositol hydrolysis which yields diacylglycerol, hydrolysis of choline-containing phosphoglycerides by phospholipase D coupled with phosphohydrolase yields both alkylacyl- and diacylglycerol. While diacylglycerol activates protein kinase C, alkylacylglycerol does not, and its role is unclear. Yet previous studies have shown that exogenous alkylacyl- and diacylglycerols can prime for the release of radiolabeled arachidonic acid (AA) in intact neutrophils stimulated by formyl-methionyl-leucyl-phenylalanine. We have now examined the effects of both diacylglycerol (1-oleoyl-2-acetylglycerol; OAG) and alkylacylglycerol (1-O-hexadecyl-2-acetylglycerol; EAG) on the activation of mitogen-activated protein (MAP) kinase and the 85-kDa cytosolic phospholipase A2 (cPLA2) in human neutrophils. We observed that while OAG could effectively activate p42 and p44 MAP kinases along with cPLA2 in a time- and concentration-dependent manner, EAG could not. A novel p40 MAP kinase isoform is also present and activated in response to OAG treatment; the behavior of this MAP kinase isoform is discussed. The activation of cPLA2 and MAP kinase by 20 microM OAG could be inhibited by pretreatment with 1 microM GF-109203X, a selective inhibitor of protein kinase C. Although only OAG activated cPLA2, both OAG and EAG primed for the release of AA mass as determined by gas chromatography/mass spectrometry. The priming of AA release by OAG may be explained by the phosphorylation of cPLA2 through the activation of protein kinase C linked to MAP kinase. However, priming by EAG appears to involve a separate mechanism that is dependent on a different PLA2. Our results support a role for phospholipase D-derived products modulating the activation of cPLA2, further supporting the idea of cross-talk among various phospholipases.
Nixon
A B
AB
Department of Biochemistry, Bowman Gray School of Medicine, Winston-Salem, N.C. 27157-1016, USA.
Seeds
M C
MC
Bass
D A
DA
Smitherman
P K
PK
O'Flaherty
J T
JT
Daniel
L W
LW
Wykle
R L
RL
D016718:Arachidonic Acid / Q000032:analysis; D003600:Cytosol / Q000201:enzymology; D004075:Diglycerides / Q000494:pharmacology*; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D020929:Mitogen-Activated Protein Kinase Kinases; D009504:Neutrophils / Q000187:drug effects* / Q000201:enzymology; D010741:Phospholipases A / Q000378:metabolism*; D054467:Phospholipases A2; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*
D004075:Diglycerides; D016718:Arachidonic Acid; C038237:1-oleoyl-2-acetylglycerol; C042096:1-O-hexadecanoyl-2-acetylglycerol; D011494:Protein Kinases; D020929:Mitogen-Activated Protein Kinase Kinases; D010741:Phospholipases A; D054467:Phospholipases A2