Brefeldin A-induced ADP-ribosylation in the structure and function of the Golgi complex

Brefeldin A (BFA) is a fungal metabolite that exerts generally inhibitory actions on membrane transport and induces the disappearance of the Golgi complex. Previously we have shown that BFA stimulates the ADP-ribosylation of two cytosolic proteins of 38 and 50 KD. The BFA-binding components mediating the BFA-sensitive ADP-ribosylation (BAR) and the effect of BFA on ARF binding to Golgi membranes have similar specificities and affinities for BFA and its analogues, suggesting that BAR may have a role in the cellular effects of BFA. To investigate this we used the approach to impair BAR activity by the use of BAR inhibitors. A series of BAR inhibitors was developed and their effects were studied in RBL cells treated with BFA. In addition to the common ADP-ribosylation inhibitors (nicotinamide and aminobenzamide), compounds belonging to the cumarin (novobiocin, cumermycin, dicumarol) class were active BAR inhibitors. All BAR inhibitors were able to prevent the BFA-induced redistribution of a Golgi marker (Helix pomatia lectin) into the endoplasmic reticulum, as assessed in immunofluorescence experiments. At the ultrastructural level, BAR inhibitors prevented the tubular-vesicular transformation of the Golgi complex caused by BFA. The potencies of these compounds in preventing the BFA effects on the Golgi complex were similar to those at which they inhibited BAR. Altogether these data support the hypothesis that BAR mediates at least some of the effects of BFA on the Golgi structure and function.