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

摘要: Regulated secretory proteins are thought to be sorted in the trans-Golgi network (TGN) via selective aggregation. The factors responsible for this aggregation unknown. We show here that two widespread regulated proteins, chromogranin B and secretogranin II (granins), remain an aggregated state when TGN vesicles from neuroendocrine cells (PC12) permeabilized at pH 6.4 1-10 mM calcium, conditions believed exist compartment. Permeabilization of immature granules under these allowed recovery electron dense cores. granin aggregates largely excluded glycosaminoglycan chains which served as constitutively secreted bulk flow markers. low pH, high calcium milieu was sufficient induce RER. In pituitary GH4C1 cells, proportion granins conserved higher upon hormonal treatment known increase granule formation. Our data suggest a decrease trigger TGN, segregating them constitutive proteins.