Regulation of CD11b/CD18 expression in human neutrophils by phospholipase A2.
Recent evidence suggests that phospholipase A2 (PLA2)-derived lipid mediators may regulate a number of neutrophil responses including degranulation and adhesion. In view of the potential role of PLA2 in stimulus-secretion coupling, we examined the relationship between PLA2 activation and the surface expression of CD11b/CD18 (MAC-1) in human polymorphonuclear leukocytes (hPMNL), including the functional consequences of PLA2 inactivation on MAC-1-dependent adhesion. The selective inhibition of PLA2 by the marine natural products manoalide (MLD) and scalaradial (SLD) blocks [3H]arachidonic acid (AA) release in calcium ionophore A23187-stimulated neutrophils, and also inhibits secretion of specific and azurophilic granule constituents. Additional studies demonstrate that MLD, SLD, and other less potent PLA2 inhibitors such as 4-bromophenacylbromide and nordihydroguiaretic acid inhibit the surface expression of MAC-1 (IC50: MLD, 0.33 microM; SLD, 0.23 microM; 4-bromophenacylbromide, 2.8 microM; NDGA, 3.5 microM) at concentrations similar to those at which they inhibit [3H]AA release. Inhibitors of cyclooxygenase, 5-lipoxygenase, protein kinase C, or calcium channel antagonists have no effect on MAC-1 expression. PLA2 inactivation also prevents MAC-1 up-regulation in hPMNL stimulated with FMLP, IL-8, TNF-alpha, PMA, or platelet activating factor. In FMLP-stimulated hPMNL, under conditions in which no secondary granule constituents are secreted, MAC-1 and alkaline phosphatase up-regulation from intracellular granules is inhibited by MLD and SLD. Functional assays also demonstrate that MLD and SLD block MAC-1-dependent adhesion of activated neutrophils to keyhole limpet hemocyanin at concentrations that block the surface expression of MAC-1. [3H]AA release and MAC-1 expression in MLD and SLD-treated hPMNL could be recovered in the presence of 1 mM hydroxylamine in a time-dependent fashion, consistent with reported data that MLD and SLD inactivate PLA2 through Schiff base formation. In summary, these data emphasize the role of PLA2 as a key regulator of MAC-1 expression in models of neutrophil adhesion.
Jacobson
P B
PB
Department of Immunopathology, Parke-Davis Pharmaceutical Research/Division, Warner Lambert Company, Ann Arbor, MI 48105.
Schrier
D J
DJ
D016718:Arachidonic Acid / Q000378:metabolism; D002448:Cell Adhesion / Q000187:drug effects; D015550:Cell Degranulation; D004789:Enzyme Activation; D006718:Homosteroids; D006801:Humans; D016177:Macrophage-1 Antigen / Q000032:analysis*; D009504:Neutrophils / Q000187:drug effects / Q000276:immunology* / Q000502:physiology; D010741:Phospholipases A / Q000037:antagonists & inhibitors / Q000378:metabolism*; D054467:Phospholipases A2; D054830:Sesterterpenes; D013729:Terpenes / Q000494:pharmacology
D006718:Homosteroids; D016177:Macrophage-1 Antigen; D054830:Sesterterpenes; D013729:Terpenes; D016718:Arachidonic Acid; C071197:scalaradial; C045673:manoalide; D010741:Phospholipases A; D054467:Phospholipases A2