SIGNAL-TRANSDUCTION PATHWAYS LEADING TO ARACHIDONIC-ACID RELEASE FROM NEUTROPHILIC HL-60 CELLS - THE INVOLVEMENT OF G-PROTEIN, PROTEIN-KINASE-C AND PHOSPHOLIPASE A(2)

Arachidonic acid release from undifferentiated and neutrophilic HL-60 cells was studied. In neutrophilic cells it was stimulated by N-formyl-Met-Leu-Phe and mastoparan by a mechanism involving G(i) protein and phospholipase C and was largely dependent on diacyglycerol lipase. Maximum release from both cell types was achieved with fluoride and required cellular energy. Inhibitor studies suggest that arachidonic acid release by fluoride stimulation leads to phospholipase A2 activation with signal transduction involving phospholipase C and protein kinase C. Only neutrophilic cells responded to phorbol ester if Ca2+-ionophore was simultaneously present but this effect was abolished by extended treatment with phorbol ester. Thus, protein kinase C plays a major role in highly stimulated neutrophilic cells. These cells are differently equipped with protein kinase C isoenzymes compared with undifferentia- ted cells. In contrast, both cell types contain similar levels of type II and cytosolic phospholipases A(2), the former being by far the more prevalent.