Sorting and budding of constitutive secretory vesicles in hepatocytes and hepatoma cells.

We have isolated a population of post-TGN secretory vesicles from hepatocytes. These vesicles of 100-150 nm diameter carry heparan sulfate proteoglycans. Secretory proteins (albumin, apo-lipoprotein E, fibrinogen) are sorted into different post-TGN secretory vesicles. A member of the ARF family of small GTP-binding proteins is associated with these vesicles. A unique peripheral membrane protein of these vesicles (VAPP14) was shown to exist also on the TGN. Brefeldin A leads to a dissociation of VAPP14 from the TGN. Antibodies against VAPP14 inhibit budding of proteoglycan containing vesicles from the TGN in a cell-free system. Inhibition occurred also in the presence of GTP-gamma-S. The same type of vesicles exists in H35 Reuber hepatoma cells.