Regulation of phospholipase d and its role in membrane traffic

Phospholipase D (PLD) converts phospholipids into phosphatidic acid (PA). A mammalian form of the enzyme which hydrolyzes phosphatidylcholine preferentially is regulated by two classes of monomeric G proteins, Arf and Rho, and by protein kinase C (PKC). All three classes of regulators require activation and their stimulatory effects on PLD are synergistic, in vitro. The action of PKC occurs through its regulatory domain rather than through phosphorylation by its kinase activity. Arf-sensitive PLD activity is higher in preparations enriched for Golgi membranes. This Arf-stimulated activity is inhibited by brefeldin A in membranes of cells sensitive to this toxin. In the presence of ethanol, PLD forms phosphatidylethanol rather than phosphatidic acid. Ethanol inhibited Arf-dependent formation of coated vesicfes in an in vitro system. Treatment of Golgi membranes with an exogenous PLD enzyme stimulated binding of coatomer to these membranes. A phosphatase activity that hydrolyzes PA is also enriched in Golgi preparations. These and other data indicate that mammalian PLD and production of PA is regulated in a complex fashion by a variety of signalling pathways and suggest that the action of PLD and phospholipid turnover is important in orocesses of intracellular orotein traffic.