A specific binding site for lipoproteins containing apolipoprotein A-I on human hepatoma cell line HepG2

Interactions of lipoproteins containing apolipoprotein (apo) A-I with or without apoA-II with human hepatoma cell line HepG2 were studied to investigate the ligand specificity for high density lipoprotein receptor on human hepatic cells and their metabolism. The two types of lipoproteins were isolated by immunoaffinity chromatography, in which apoE-containing lipoproteins were removed. Specific binding kinetics at 0 degrees C were observed for the apoA-I-containing lipoproteins with or without apoA-II (Kd = 18 or 20 micrograms protein/ml, Bmax = 110 or 120 ng/mg cell protein, respectively). The binding of these lipoproteins to HepG2 cells was competitively inhibited by excess unlabeled apoA-I-containing lipoproteins or apoA-I-phospholipid complexes, but not by apoA-II.phospholipid complexes. Interactions of these lipoproteins with HepG2 cells at 37 degrees C were further examined. These results suggested that HepG2 cells have a specific binding site for apoA-I-containing lipoproteins, and that apoA-I might be a crucial component in the binding of these lipoproteins to human hepatic cells.