Involvement of a botulinum toxin-sensitive 22-kDa G protein in stimulated exocytosis of human neutrophils.

Abstract

Studies of human peripheral blood neutrophils (PMNs) demonstrated that botulinum neurotoxin D (BT-D) ADP-ribosylates a 22-kDa PMN G protein (G22k) and inhibits the exocytosis of both specific and azurophilic granules stimulated by FMLP. Furthermore, this inhibition of PMN exocytosis by BT-D was found to be correlated with the degree of irreversible ADP-ribosylation of G22k by BT-D and to require modification of at least 85% of PMN G22k before significant inhibition of secretion is observed. Although both pertussis toxin and BT-D inhibited exocytosis in FMLP-stimulated PMNs, the inhibitory effects of the two toxins were found to be additive. Pertussis toxin and BT-D also inhibited Ca2+/GTP/GTP gamma S-induced secretion in digitonin-permeabilized PMNs, but there were distinct differences between the inhibitory effects of the two toxins. In contrast to BT-D, the exotoxin botulinum C3 was found to ADP-ribosylate primarily a 24- to 25-kDa PMN protein, and it was not found to inhibit Ca(2+)- and GTP-induced secretion in permeabilized PMNs. Ultrastructural studies of BT-D-treated PMNs showed an accumulation of distinct membrane-bound organelles in the periphery of the cells after FMLP stimulation, suggestive of a toxin-induced block in organelle-plasma membrane fusion. Taken together, these findings indicate that BT-D-sensitive G22k has a functional role in stimulated exocytosis of PMNs.