The formation of ceramide-1-phosphate during neutrophil phagocytosis and its role in liposome fusion

Ceramide, a product of agonist-stimulated sphingomyelinase activation, is k nown to be generated during the phagocytosis of antibody-coated erythrocyte s by polymorphonuclear leukocytes. Agonist-stimulated formation of ceramide -1-phosphate is now shown to occur in (PO4)-P-32-labeled neutrophils. Ceram ide-1-phosphate is formed by a calcium-dependent ceramide kinase, found pre dominately in the neutrophil plasma membrane. The neutrophil kinase is spec ific for ceramide because, in contrast to the bacterial diglyceride kinase, ceramide is not phosphorylated under conditions specific for diglyceride p hosphorylation, Conversely, 1,2-diacylglycerol does not serve as substrate for the neutrophil ceramide kinase, Ceramide kinase activation occurs in a time-dependent fashion, reaching peak activity 10 min after formyl peptide stimulation and challenge with antibody coated erythrocytes. The lipid kina se activity is optimal at pH 6.8. Because the formation of the phagolysosom e is a critical event in phagocytosis, the effect of ceramide-1-phosphate i n promoting the fusion of liposomes was determined. Both the addition of in creasing concentrations of sphingomyelinase D and ceramide phosphate promot ed liposomal fusion, In summary, ceramide-1-phosphate is formed during phag ocytosis through activation of ceramide kinase. Ceramide-1-phosphate may pr omote phagolysosome formation.