Phospholipase D in homogenates from HL-60 granulocytes: implications of calcium and G protein control

Occupancy of chemotactic peptide receptors leads to rapid initiation of phospholipase D (PLD) activity in intact dimethylsulfoxide-differentiated HL-60 granulocytes (Pai, J.-K, Siegel, M.I., Egan, R.W., and Billah, M.M. (1988) J. Biol. Chem. 263, 12472). To gain further insight into the activation mechanisms, PLD has been studied in cell lysates from HL-60 granulocytes, using 1-0-alkyl-2-oleoyl-[32P]phosphatidylcholine (alkyl-[32P]PC), 1-0-[3H]alkyl-2-oleoyl-phosphatidylcholine [( 3H]alkyl-PC) and [14C]arachidonyl-phospholipids as substrates. In the presence of Ca2+ and GTP gamma S, post-nuclear homogenates degrade alkyl-[32P]PC to produce 1-0-alkyl-[32P]phosphatidic acid (alkyl-[32P]-PA), and in the presence of ethanol, also 1-0-alkyl-[32P]phosphatidylethanol (alkyl-[32P]PEt). By comparing the 3H/32P ratios of PA and PEt to that of PC, it is concluded that PA and PEt are formed exclusively by a PLD that catalyzes both hydrolysis and transphosphatidylation between PC and ethanol. Furthermore, PC containing either ester- or ether-linkage at the sn-1 position is degraded in preference to phosphatidylethanolamine and phosphatidylinositol by PLD in HL-60 cell homogenates. It is concluded that HL-60 granulocytes contain a PC-specific PLD that requires both Ca2+ and GTP for activation.