Milieu-induced, selective aggregation of regulated secretory proteins in the trans-Golgi network

Having established that xyloside-induced GAG chains can serve as a bulk flow marker in PC12 cells, we investigated whether they would be excluded from granin aggregates in the TGN . Saponin permeabilization of [35 S]sulfate-labeled TGN vesicles prepared from xyloside-treated PC12 cells showed that in both nonaggregative as well as aggregative milieu, only a small percentage of the [35 S]sulfate-labeled GAG chains was recovered in the pellet (Fig. 4 D) . This behavior of the GAG chains was in striking contrast to that of SgII which, in line with the results obtained with nonxyloside-treated PC12 cells (Fig . 2 A; Table I ), was largely retained in the permeabilized TGN vesicles in the aggregative milieu (Fig . 4 D) . We conclude from these results that the granin aggregates recovered in aggregative milieu largely excluded bulk flow markers .