Pertussis toxin produces differential inhibitory effects on basal, P2-purinergic, and chemotactic peptide-stimulated inositol phospholipid breakdown in HL-60 cells and HL-60 cell membranes.

Abstract

P2-purinergic receptor agonists (UTP) and formylated peptide receptor agonists (FMLP) were found to be equally efficacious in eliciting rapid 6-7-fold increases in inositol polyphosphate accumulation in differentiated HL-60 granulocytes. The activation of this response by either agonist was substantially but incompletely inhibited in cells treated with pertussis toxin. Thus, in cells containing only 1-10% of the control level of non-ADP-ribosylated Gi-2/3, UTP induced rapid 2-fold increases in inositol polyphosphate accumulation whereas smaller 50% increases were observed in FMLP-stimulated cells. Washed membranes prepared from control and toxin-treated HL-60 cells were used to characterize this toxin-insensitive activation of phospholipase C further. The agonist-independent stimulation of phospholipase C by either millimolar Ca2+ or the nonhydrolyzable GTP analog guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S) was only modestly attenuated by toxin treatment. There was a 70-80% decrease in the rate and extent of phospholipase C activity stimulated by GTP per se in the absence of receptor agonists. The rate and extent of FMLP-induced potentiation of GTP-dependent phospholipase C activity were also inhibited by greater than 80% in toxin-treated membranes. Conversely, the potency and efficacy characterizing UTP-induced potentiation of GTP-dependent phospholipase C activity were only modestly attenuated (less than 20% inhibition). The results indicate that P2-purinergic receptors (and perhaps other Ca2(+)-mobilizing receptors) activate both pertussis toxin-sensitive and toxin-insensitive pathways for phospholipase C regulation in phagocytic leukocytes.