Novel apoprotein A-I-containing lipoprotein produced by a human hepatoma-derived cell line HuH-7

Abstract

The apoprotein A-I (apo A-I)-containing lipoprotein (LP HuH.7apoA-I) was isolated from the concentrated conditioned medium of human hepatoma-derived cell line HuH-7 by immunoaffinity chromatography. Lp HuH-7apoA-I consists of two kinds of lipoproteins. One is a lipoprotein of large particle size (Lp L) with broad electrophoretic mobility on agarose gel ranging from the origin to the position of prebeta-lipoprotein. Lp L is protein-rich in composition (protein, 75.4% by weight) and is heterogeneous in size (34-17 nm in diameter) electron microscopically. However, the most intriguing properties of Lp L are its partial electrophoretic mobility towards the cathode on agar gel. The other lipoprotein is of small particle size (Lp s). It demonstrates prebeta-electrophoretic mobility on agarose gel. Lp s is also protein-rich in composition (protein, 95.4% by weight) and is heterogeneous in size (16.5–8.4 nm in diameter) electron microscopically. Lp L is obviously different from LP-X and LP-Y in property, although LP-X, LP-Y and a part of Lp L migrate towards the cathode on agar gel elecrrophoresis. Lp s is also different from human apo A-I-containing lipoprotein without apo A-II in property, although these two lipoproteins possess the same mobility on agarose gel elecrrophoresis. These results indicate that both Lp L and Lp s are novel lipoproteins which have not yet been reported. The major isoproteins of the apo A-I of Lp HuH-7apoA-I are aPo A-I isoprotein 2 (apo A-I 2), apo A-I isoprotein 4 (apo A-I 4) and apo A-I isoprotein 5 (apo A-I 5), and are different from those of apo A-I in human plasma and in the conditioned medium of hepatoma-derived cell line HepG2. This result suggests the presence of a proteinase which converts proapoprotein A-I (apo A-I 2) to apoprotein A-I (apo A-I 4) in the conditioned medium of HuH-7.