ENDOPLASMIC RETICULUM-TO-CYTOSOL TRANSPORT OF FREE POLYMANNOSE OLIGOSACCHARIDES IN PERMEABILIZED HEPG2 CELLS

Free polymannose oligosaccharides have recently been localized to both the vesicular and cytosolic compartments of HepG2 cells, Here we inve stigated the possibility that free oligosaccharides originating in the lumen of the endoplasmic reticulum (ER) are transported directly into the cytosol. Incubation of permeabilized cells in the absence of ATP at 37 degrees C led to the intravesicular accumulation of free Man(9)G lcNAc(2) which was generated from dolichol-linked oligosaccharide in t he ER, This oligosaccharide remained stable within the permeabilized c ells unless ATP was added to the incubations at which time the Man(9)G lcNAc(2) was partially converted to Man(8)GlcNAc(2), and both these co mponents were released from an intravesicular compartment into the cyt osolic compartment of permeabilized cells. In contrast, when permeabil ized cells, primed with either free triglucosyloligosaccharide or a gl ycotripeptide, were incubated with ATP both these structures remained associated with the intravesicular compartment. As the conditions in w hich free oligosaccharides were transported out of the intravesicular compartment into the cytosolic compartment did not permit vesicular tr ansport of glycoproteins from the ER to the Golgi apparatus our data d emonstrate the presence of a transport process for the delivery of fre e polymannose oligosaccharides from the ER to the cytosol.