Comparison of alkylacylglycerol (EAG) and diacylglycerol (AAG) as activators of map kjnase(s) and cytosolic PLA2 in human neutrophil priming
In human neutrophils, the choline-containing phosphoglycerides act as precursors of both AAG and EAG via the action of phospholipase D. Previous studies have shown that both AAG and EAG can enhance the fMLP-stimulated release of arachidonic acid (AA) in intact neutrophils, yet AAG or EAG alone could not induce its release, a defining feature of priming. Further, AAG activates protein kinase C while EAG does not, and EAG may in fact inhibit its activity. We examined the effect of both AAG and EAG on the activation of MAP kinase(s) and cytpsolic phospholipase A2 (cPLA2). We observed that AAG effectively activated MAP kinase(s) (Western analysis) and cPLA2 (activity measurements and Western analysis) in a time- and dose-dependent manner whereas EAG did not. We also observed a previously undescribed, activatable MAP kinase isoform (p40) in human neutrophils that cross-reacts with ERK-1 antibodies but not with ERK-2 or the HOG1 (p38) related isoform. The activation of cPLA2 and MAP kinase(s) by 20 μM AAG could be abolished by pretreatment with 100 nM GF-109203X, a selective inhibitor of protein kinase C. Although only AAG activated cPLA2, both AAG and EAG primed for the release of AA as determined by GC/MS. In summary, AAG activated MAP kinase(s) and cPLA2, whereas EAG did not, yet both primed for the release of AA suggesting the existence of divergent priming mechanisms for the release of AA induced by the two diglycerides.
Nixon, AB; Seeds, MC; Smilherman, PK; Bass, PA; Wvkle, RL
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