INVOLVEMENT OF A BOTULINUM TOXIN-SENSITIVE 22-KDA G-PROTEIN IN STIMULATED EXOCYTOSIS OF HUMAN NEUTROPHILS

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 gr anules stimulated by FMLP. Furthermore, this inhibition of PMN exocyto sis by, BT-D was found to be correlated with the degree of irreversibl e ADP-ribosylation of G22k by BT-D and to require modification of at l east 85% of PMN G22k before significant inhibition of secretion is obs erved. Although both pertussis toxin and BT-D inhibited exocytosis in FMLP-stimulated PMNs, the inhibitory effects of the two toxins were fo und to be additive. Pertussis toxin and BT-D also inhibited Ca2+/GTP/G TPgammaS-induced secretion in digitonin-permeabilized PMNs, but there were distinct differences between the inhibitory effects of the two to xins. 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 Ca2+- and GTP-induced secretion in permeabilized PMNs. Ult rastructural studies of BT-D-treated PMNs showed an accumulation of di stinct membrane-bound organelles in the periphery of the cells after F MLP stimulation, suggestive of a toxin-induced block in organelle-plas ma membrane fusion. Taken together, these findings indicate that BT-D- sensitive G22k has a functional role in stimulated exocytosis of PMNs.