Secretory vesicle budding from the trans-Golgi network is mediated by phosphatidic acid levels

Phospholipid metabolism plays a central role in regulating vesicular traffic in the secretory pathway. In mammalian cells, activation of a Golgi-associated phospholipase D activity by ADP-ribosylation factor results in hydrolysis of phosphatidylcholine to phosphatidic acid (PA). This reaction has been proposed to stimulate nascent secretory vesicle budding from the trans-Golgi network. It is unclear whether PA itself or diacylglycerol (DAG), a metabolite implicated in yeast secretory vesicle formation, regulates budding. To distinguish between these possibilities we have used a permeabilized cell system supplemented with phospholipid-modifying enzymes that generate either DAG or PA. The data demonstrate that in mammalian cells accumulation of PA rather than DAG is a key step in regulating budding of secretory vesicles from the trans-Golgi network.