Mastoparan‐induced phosphatidylcholine hydrolysis by phospholipase D activation in human astrocytoma cells

The effect of mastoparan on phosphatidylcholine hydrolysis was examined in 1321N1 human astrocytoma cells. Mastoparan (3–30 μm) caused an accumulation of diacylglycerol (DG) and phosphatidic acid (PA) accompanied by choline release in a concentration‐ and time‐dependent manner. In the presence of 2% n‐butanol, mastoparan (3–100 μM) induced phosphatidylbutanol (PBut) accumulation in a concentration‐ and time‐dependent manner, suggesting that mastoparan activates phospholipase D (PLD). Propranolol (30–300 μM), a phosphatidate phosphohydrolase inhibitor, inhibited DG accumulation induced by mastoparan, supporting this idea. Depletion of extracellular free calcium ion did not alter the effect of mastoparan on PLD activity. A protein kinase C (PKC) inhibitor, calphostin C (1 μm), did not inhibit mastoparan‐induced PLD activation but the ability of mastoparan to stimulate phospholipase D activity was decreased in the PKC down regulated cells. PLD activity stimulated by mastoparan was not prevented by pretreatment of the cells with pertussis toxin (PT) or C3 ADP‐ribosyltransferase. Furthermore, guanine nucleotides did not affect PLD activity stimulation by mastoparan in membrane preparations. Mastoparan stimulated PLD in several cell lines such as RBL‐2H3, RBL‐1, HL‐60, P388, endothelial cells, as well as 1321N1 human astrocytoma cells. These results suggest that mastoparan induces phosphatidylcholine (PC) hydrolysis by activation of PLD, not by activation of phosphatidylcholine‐specific phospholipase C (PC‐PLC); mastoparan‐induced PLD activation is not mediated by G proteins. 1995 British Pharmacological Society