Effect of pertussis toxin and neomycin on G-protein-regulated polyphosphoinositide phosphodiesterase. A comparison between HL60 membranes and permeabilized HL60 cells.

The promyelocytic HL60 cell can be differentiated with dimethyl sulphoxide or dibutyryl cyclic AMP leading to the appearance of fMetLeuPhe receptors on the cell surface. G-protein-stimulated polyphosphoinositide phosphodiesterase (PPI-pde) activity was assessed in membranes prepared from both differentiated and non-differentiated HL60 cells. Both the extent of the response and the rank order of potency of the GTP analogues to stimulate PPI-pde activation (guanosine 5'-[gamma-thio]triphosphate (GTP[S]) greater than guanosine 5'-[beta gamma-imido]triphosphate (p[NH]ppG) greater than guanosine 5'-[beta gamma-methylene]triphosphate (p[CH2]ppG) remains unchanged after differentiation with dimethyl sulphoxide. In comparison, differentiation by dibutyryl cyclic AMP leads to diminution of PPI-pde activity when stimulated by GTP[S] or fluoride, but not by millimolar concentrations of Ca2+. GTP[S]-stimulated PPI-pde in membranes is sensitive to the presence of Ca2+ (pCa 8-5). Pertussis-toxin pretreatment of intact HL60 cells leads to inhibition of both the secretory response and the formation of inositol phosphates when stimulated by fMetLeuPhe. In contrast, pertussis-toxin pretreatment has no effect on either GTP[S]- or fluoride-stimulated PPI-pde. Neomycin in a concentration-dependent manner inhibits both GTP[S] plus Ca2+ (pCa 5)-stimulated secretion and PPI-pde activation in streptolysin-O-permeabilized cells. The extent of PPI-pde activation in membranes compared with streptolysin-O-permeabilized cells reveals that the membrane preparation does not possess all the components that make up the inositide signalling system.