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* Department of Developmental and Molecular Biology, Phospholipase D (PLD) is a phospholipid
hydrolyzing enzyme whose activation has been implicated in mediating signal transduction pathways, cell
growth, and membrane trafficking in mammalian cells. Several laboratories have demonstrated that small
GTP-binding proteins including ADP-ribosylation factor (ARF) can stimulate PLD activity in vitro and an
ARF-activated PLD activity has been found in Golgi
membranes. Since ARF-1 has also been shown to enhance release of nascent secretory vesicles from the
TGN of endocrine cells, we hypothesized that this reaction occurred via PLD activation. Using a permeabilized cell system derived from growth hormone and
prolactin-secreting pituitary GH3 cells, we demonstrate
that immunoaffinity-purified human PLD1 stimulated
nascent secretory vesicle budding from the TGN approximately twofold. In contrast, a similarly purified
but enzymatically inactive mutant form of PLD1, designated Lys898Arg, had no effect on vesicle budding
when added to the permeabilized cells. The release of
nascent secretory vesicles from the TGN was sensitive
to 1% 1-butanol, a concentration that inhibited PLD-catalyzed formation of phosphatidic acid. Furthermore, ARF-1 stimulated endogenous PLD activity in Golgi
membranes approximately threefold and this activation
correlated with its enhancement of vesicle budding.
Our results suggest that ARF regulation of PLD activity plays an important role in the release of nascent secretory vesicles from the TGN.
Department of Anatomy and Structural Biology, Albert Einstein
College of Medicine, Bronx, New York 10461; and § Department of Pharmacology, and Institute for Cell and Molecular Biology,
State University of New York, Stony Brook, New York 11794
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