Suppression of cytoskeletal rearrangement in activated human neutrophils by botulinum C2 toxin. Impact on cellular signal transduction.

Abstract

Botulinum C2 toxin, a binary toxin which selectively ADP-ribosylates nonmuscle G-actin, was used to evaluate the role of cytoskeletal rearrangement in ligand-evoked signal transduction and secretory processes in human neutrophils (polymorphonuclear leukocyte). Preincubation with the combined toxin components reduced the basal F-actin content and nearly completely suppressed the actin assembly initiated by the peptide and lipid chemoattractants formyl-methionyl-leucyl-phenylalanine, platelet activating factor, and leukotriene B4. Superoxide production and elastase secretion were increased markedly under these conditions. Concomitantly, ligand-elicited phosphoinositide hydrolysis was augmented with particular increase in inositol monophosphate. This was paralleled by a severalfold amplification of diacylglycerol formation and sustained elevation of cytosolic calcium. The toxin-effected amplification of postreceptor events and secretory responses was most pronounced in response to formyl-methionyl-leucyl-phenylalanine greater than platelet activating factor greater than leukotriene B4. All metabolic and secretory effects in C2 toxin-pretreated cells were sensitive to pertussis toxin inhibition. In conjunction with the recent finding of unchanged formyl-methionyl-leucyl-phenylalanine receptor binding and dissociation dynamics under influence of C2 (Norgauer, J., Just, I., Aktories, K., and Sklar, L. A. (1989) J. Cell Biol. 109, 1133-1140), the present investigation suggests amplification of postreceptor events as a major mechanism underlying C2 toxin-related increase in polymorphonuclear leukocyte secretory responses. Cytoskeletal rearrangement, putatively linked to phosphoinositide turnover and calcium transients, thus appears to be operative in temporal and/or spatial limitation of chemoattractant-evoked cellular signal transduction.