Role of brefeldin A-dependent ADP-ribosylation in the control of intracellular membrane transport

The fungal toxin brefeldin A (BFA) dissociates coat proteins from Golgi mem branes, causes the rapid disassembly of the Golgi complex and potently stim ulates the ADP-ribosylation of two cytosolic proteins of 38 and 50 kDa. The se proteins have been identified as the glycolytic enzyme glyceraldehyde-3- phosphate dehydrogenase (GAPDH) and a novel guanine nucleotide binding prot ein (BARS-50), respectively. The role of ADP-ribosylation in mediating the effects of BFA on the structure and function of the Golgi complex was analy zed by several approaches including the use of selective pharmacological bl ockers of the reaction and the use of ADP-ribosylated cytosol and/or enrich ed preparations of the BFA-induced ADP-ribosylation substrates, GAPDH and B ARS-50. A series of blockers of the BFA-dependent ADP-ribosylation reaction identif ied in our laboratory inhibited the effects of BFA on Golgi morphology and, with similar potency, the ADP-ribosylation of BARS 50 and GAPDH. In permea bilized RBL cells, the BFA-dependent disassembly of the Golgi complex requi red NAD(+) and cytosol. Cytosol that had been previously ADP-ribosylated (n amely, it contained ADP-ribosylated GAPDH and BARS-50), was instead suffici ent to sustain the Golgi disassembly induced by BFA. Taken together, these results indicate that an ADP-ribosylation reaction is part of the mechanism of action of BFA and it might intervene in the contr ol of the structure and function of the Golgi complex.