Glycosylation of apolipoproteins by cultured rat hepatocytes. Effect of tunicamycin on lipoprotein secretion.
Cultured rat hepatocytes were used to measure hepatic synthesis of rat plasma glycoproteins. [3H]Glucosamine was progressively incorporated into the protein of hepatocyte culture media very-low-density lipoprotein, low-density lipoprotein, high-density lipoprotein and the p greater than 1.21 g/ml fraction after 3.5 and 6.5 h incubation. Apolipoproteins B, E and C, as well as transferrin, were identified as glycoproteins. The association of radioactivity with apolipoprotein C of hepatocyte very-low-density and high-density lipoproteins suggests that apolipoprotein C-III-3, the only C apoglycoprotein in the rat, is synthesized de novo by the hepatocytes. Treatment of hepatocytes with tunicamycin, a specific inhibitor of protein glycosylation, resulted in a substantial decrease in [3H]glucosamine incorporation into hepatocyte very-low-density, low-density and high-density lipoproteins and p greater than 1.21 g/ml protein, but had little or no effect on secretion. In the rat, hepatic secretion of lipoproteins and transferrin does not appear to be dependent on prior protein glycosylation.
D000818:Animals; D001053:Apolipoproteins / Q000378:metabolism*; D002478:Cells, Cultured; D005944:Glucosamine / Q000031:analogs & derivatives* / Q000378:metabolism; D006023:Glycoproteins / Q000096:biosynthesis; D008074:Lipoproteins / Q000378:metabolism*; D008099:Liver / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D014415:Tunicamycin / Q000494:pharmacology*
D001053:Apolipoproteins; D006023:Glycoproteins; D008074:Lipoproteins; D014415:Tunicamycin; D005944:Glucosamine