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 membranes, causes the rapid disassembly of the Golgi complex and potently stimulates the ADP-ribosylation of two cytosolic proteins of 38 and 50 kDa. These proteins have been identified as the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and a novel guanine nucleotide binding protein (BARS-50), respectively. The role of ADP-ribosylation in mediating the effects of BFA on the structure and function of the Golgi complex was analyzed by several approaches including the use of selective pharmacological blockers of the reaction and the use of ADP-ribosylated cytosol and/or enriched preparations of the BFA-induced ADP-ribosylation substrates, GAPDH and BARS-50. A series of blockers of the BFA-dependent ADP-ribosylation reaction identified in our laboratory inhibited the effects of BFA on Golgi morphology and, with similar potency, the ADP-ribosylation of BARS-50 and GAPDH. In permeabilized RBL cells, the BFA-dependent disassembly of the Golgi complex required NAD+ and cytosol. Cytosol that had been previously ADP-ribosylated (namely, it contained ADP-ribosylated GAPDH and BARS-50), was instead sufficient 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 control of the structure and function of the Golgi complex.