OVEREXPRESSION OF HUMAN LIPOPROTEIN-LIPASE ENHANCES UPTAKE OF LIPOPROTEINS CONTAINING APOLIPOPROTEIN B-100 IN TRANSFECTED CELLS

To investigate the role in lipoprotein metabolism of lipoprotein lipas e (LPL) secreted by tissues, we established two cell lines. Fusion pla smids containing either human LPL cDNA or antisense LPL cDNA under con trol of the cytomegalovirus promoter were transfected into Chinese ham ster ovary (CHO) cells, designated as CHO-LPL and CHO-anti-LPL, respec tively. CHO-LPL constitutively produced a high level of LPL, whereas C HO-anti-LPL produced a minimal level. When very-low-density lipoprotei n (VLDL) was incubated with CHO-LPL, VLDL triglycerides were hydrolyze d, intermediate-density lipoprotein (IDL) was produced, and apolipopro tein E contents increased. CHO-LPL took up and degraded I-125-VLDL at 37 degrees C four times more strongly than did CHO-anti-LPL. Whereas t he degradation of apolipoprotein E-deficient VLDL was only 12% that of normal VLDL in CHO-LPL, structural changes of the lipoprotein, includ ing apolipoprotein E expression on the lipoprotein surface, may be imp ortant for the cellular uptake of VLDL. Furthermore, we found that bin ding at 4 degrees C of VLDL and LDL to CHO-LPL was greater than to CHO -anti-LPL, and this binding difference was abolished by washing the ce lls with heparin. This suggests that cell surface LPL plays a role in the binding of lipoproteins to the cells. We conclude that both the co mposition of VLDL particles and their cellular binding are influenced by LPL secreted by cells, both of which may enhance the cellular uptak e of VLDL.