Brefeldin A-regulated retrograde transport into the endoplasmic reticulum of internalised wheat germ agglutinin.

The effects of the fungal metabolite brefeldin A (BFA) on the endocytic routes of internalised wheat germ agglutinin (WGA) were studied in human HepG2 hepatoma cells, drawing particular attention to the application times in relation to the membrane dynamics occurring at the trans Golgi face during endocytosis. As shown in previous studies, transport of internalised WGA into the Golgi apparatus can be classified in three stages being characterised by predominance of vesicular endosomes (stage I), formation of an extended endocytic trans Golgi network (stage II) and uptake of WGA into the stacked Golgi cisternae (stage III). BFA treatment of the cells led to rapid tubular-reticular transformations of the Golgi stacks. Retrograde transport and further destinations of internalised WGA depended on the time of BFA application. When BFA was administered during stages I or II, WGA was localised within the BFA-induced tubules and networks, but never was found within the endoplasmic reticulum. By contrast, BFA treatment during stage III led to a redistribution of internalised WGA into cisternae of the endoplasmic reticulum. These results show that BFA administered according to a precise time schedule can be used as a regulatory agent that allows to control retrograde traffic of internalised molecules into the endoplasmic reticulum.