Abstract
1. Chemotaxis of human neutrophils is mediated by numerous agents [e.g. N-formyl-methionyl-leucyl-phenylalanine (FMLP) and platelet activating factor (PAF)] whose receptors are coupled to phospholipase C. However, the subsequent transduction pathway mediating cell movement remains obscure. We now propose involvement of mono(ADP-ribosyl)transferase activity in receptor-dependent chemotaxis. 2. Human neutrophils were isolated from whole blood and measurements were made of FMLP or PAF-dependent actin polymerization and chemotaxis. The activity of cell surface Arg-specific mono(ADP-ribosyl)transferase was also measured. Each of these activities was inhibited by vitamin K3 and similar IC50 values obtained (4.67 +/- 1.46 microM, 2.0 +/- 0.1 microM and 4.7 +/- 0.1 microM respectively). 3. There were similar close correlations between inhibition of (a) enzyme activity and (b) actin polymerization or chemotaxis by other known inhibitors of mono(ADP-ribosyl)transferase, namely vitamin K1, novobiocin, nicotinamide and the efficient pseudosubstrate, diethylamino(benzylidineamino)guanidine (DEA-BAG). 4. Intracellular Ca2+ was measured by laser scanning confocal microscopy with two fluorescent dyes (Fluo-3 and Fura-Red). Exposure of human neutrophils to FMLP or PAF was followed by transient increases in intracellular Ca2+ concentration, but the inhibitors of mono(ADP-ribosyl)transferase listed above had no effect on the magnitude of the response. 5. A panel of selective inhibitors of protein kinase C, tyrosine kinase, protein kinases A and G or phosphatases 1 and 2A showed no consistent inhibition of FMLP-dependent polymerization of actin. 6. We conclude that eukaryotic Arg-specific mono(ADP-ribosyl)transferase activity may be implicated in the transduction pathway mediating chemotaxis of human neutrophils, with involvement in the assembly of actin-containing cytoskeletal microfilaments.