ANTIBODIES AGAINST HIGH-DENSITY-LIPOPROTEIN BINDING-PROTEINS ENHANCE HIGH-DENSITY-LIPOPROTEIN UPTAKE BUT DO NOT AFFECT CHOLESTEROL EFFLUX FROM RAT HEPATOMA-CELLS

High-density lipoprotein plays a key role in the reverse cholesterol t ransport pathway as well as in the delivery of cholesterol to the live r and steroidogenic tissues. Metabolism of high-density lipoprotein is determined by one of its apolipoproteins, apolipoprotein A-I; however , the identity and function of cellular protein which binds high-densi ty lipoprotein remains unclear. The effect of antibodies against rat h igh-density lipoprotein binding proteins, HB1 and HB2, on high-density lipoprotein metabolism in a rat hepatoma cell line were studied. Cell s were preincubated with the antibodies and I-125-labeled high-density lipoprotein binding and uptake as well as cholesterol biosynthesis an d cholesterol efflux to human plasma or isolated high-density lipoprot ein were studied. Both antibodies reacted specifically with HB1 and HB 2 on the ligand and Western blots, but their binding was not blocked b y high-density lipoprotein. Both antibodies inhibited I-125-labeled hi gh-density lipoprotein binding to cells by 20-40%, but stimulated (125 )-labeled high-density lipoprotein uptake by up to 2.5-fold. The antib odies had no effect on cholesterol efflux or on cholesterol synthesis, It is concluded that high-density Lipoprotein binding proteins, HB1 a nd HB2, may be involved in high-density lipoprotein uptake in the live r rather than in mediating cholesterol efflux. (C) 1997 Elsevier Scien ce Ltd.