Phorbol ester inhibits polyphosphoinositide phosphodiesterase activity stimulated by either Ca2+, fluoride or GTP analogue in HL60 membranes and in permeabilized HL60 cells.

The effect of PMA (phorbol 12-myristate, 13-acetate) on PPI-pde (polyphosphoinositide phosphodiesterase) activity in the promyelocytic cell-line HL60 was examined. HL60 cells were pretreated with PMA in a time- and concentration-dependent manner and PPI-pde activity was monitored both in streptolysin O-permeabilized cells and in membranes. PPI-pde activity was stimulated by either GTP gamma S (guanosine 5'-[gamma-thio]triphosphate), fluoride or Ca2+. Both the Ca2(+)-stimulated and the G protein-mediated PPI-pde activity in permeabilized HL60 cells is maximally inhibited (70-90%) after 60 min pretreatment of intact cells with 10nM PMA. PPI-pde activity can also be observed in membranes prepared from HL60 cells although this activity represents only 10% of the total activity seen in permeabilized cells. In membranes, where PPI-pde activity can also be stimulated by either via the G-protein or directly by Ca2+, PMA pretreatment was also inhibitory regardless of the mode of activation. We suggest that both the membrane-bound PPI-pde activity and that present in the permeabilized cells are targets for protein phosphorylation by protein kinase C leading to inhibition of the catalytic function.