Role of carbohydrate in glycoprotein secretion by human hepatoma cells

We have previously shown that export of nine proteins by human hepatoma cells falls into three discrete kinetic classes with intracellular retention half-times of approximately 35 min, 77 min and 115 min. To determine if carbohydrate on secretory glycoproteins determines the secretory class we have measured the kinetics of export of the nine proteins after tunicamycin-treatment of cultures. We found no apparent correlation between the kinetic class of a secretory protein and sensitivity of secretion to tunicamycin-treatment. For example, three glycoproteins are exported with rapid kinetics and secretion of only one, alpha 1-protease inhibitor, is inhibited by tunicamycin treatment. In addition, three glycoproteins are secreted with intermediate kinetics and tunicamycin-treatment inhibits the secretion of two of these proteins, alpha 2-macroglobulin and ceruloplasmin but not the third, plasminogen.