Inhibition of phosphatidic acid synthesis alters the structure of the Golgi apparatus and inhibits secretion in endocrine cells

In mammalian cells, activation of a Golgi-associated phospholipase D by ADP ribosylation factor results in the hydrolysis of phosphatidylcholine to fo rm phosphatidic acid (PA), This reaction stimulates the release of nascent secretory vesicles from the trans-Golgi network of endocrine cells. To unde rstand the role of PA in mediating secretion, me have exploited the transph osphatidylation activity of phospholipase D. Rat anterior pituitary GH3 cel ls, which secrete growth hormone and prolactin, were treated with 1-butanol resulting in the synthesis of phosphatidylbutanol rather than PA. Under th ese conditions transport from the ER through the Golgi apparatus and secret ion of polypeptide hormones were inhibited quantitatively, Furthermore, the in vitro synthesis of phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P- 2) by Golgi membranes was inhibited quantitatively, Most significantly, in the presence of 1-butanol the architecture of the Golgi apparatus was disru pted, resulting in its disassembly and fragmentation. Removal of the alcoho l resulted in the rapid restoration of Golgi structure and secretion of gro wth hormone and prolactin. Our results suggest that PA stimulation of PtdIn s(4,5)P-2 synthesis is required for maintaining the structural integrity an d function of the Golgi apparatus.