Dvorin E, Gorder N L, Benson D M, Gotto A M
J Biol Chem. 1986 Nov 25;261(33):15714-8.
To identify the role of a specific apoprotein other than apoE which might be responsible for the receptor-mediated uptake of high density lipoprotein (HDL) by rat hepatocytes, 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC) was combined with rat apoE, apoA-I, or apoA-IV to form apoprotein-phospholipid complexes and the complexes were tested for their binding and uptake by primary rat hepatocytes. Apoprotein-POPC complexes were labeled with the specific fluorescent probe, 1,1-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine to monitor their uptake by cultured rat hepatocytes at 37 degrees C using digital fluorescence imaging microscopy or were labeled with 125I to study their binding to hepatocytes at 4 degrees C. POPC, either alone or with apoA-I, was not internalized by rat hepatocytes while complexes containing apoE or apoA-IV were taken up by the cells. Specific binding at 4 degrees C was demonstrated for apoE-free HDL, apoA-IV X POPC, and apoE X POPC but not for apoA-I X POPC. The binding of apoE-free HDL was inhibited by apoA-IV X POPC, apoE-free HDL, and apoA-IV + apoA-I X POPC but not by apoA-I X POPC. Binding of apoA-IV X POPC was inhibited by apoE-free HDL, apoA-IV X POPC, and apoA-IV + apoA-I X POPC, but not by apoE X POPC or apoE-enriched HDL. These data indicate that apoA-IV is a ligand responsible for the rat HDL binding to primary rat hepatocytes and that apoA-IV binds to a receptor site distinct from apoE-dependent receptors such as the apoB,E or chylomicron-remnant receptor.
为了确定除载脂蛋白E（apoE）之外的特定载脂蛋白在大鼠肝细胞通过受体介导摄取高密度脂蛋白（HDL）过程中可能发挥的作用，将1-棕榈酰-2-油酰磷脂酰胆碱（POPC）与大鼠apoE、apoA-I或apoA-IV结合，形成载脂蛋白-磷脂复合物，并检测这些复合物与原代大鼠肝细胞的结合及摄取情况。载脂蛋白-POPC复合物用特异性荧光探针1,1-二辛基-3,3,3',3'-四甲基吲哚碳菁进行标记，以利用数字荧光成像显微镜监测其在37℃时被培养的大鼠肝细胞摄取的情况，或者用125I进行标记，以研究其在4℃时与肝细胞的结合情况。单独的POPC或与apoA-I一起时，不会被大鼠肝细胞内化，而含有apoE或apoA-IV的复合物则会被细胞摄取。在4℃时，无apoE的HDL、apoA-IV×POPC和apoE×POPC表现出特异性结合，而apoA-I×POPC则没有。无apoE的HDL的结合受到apoA-IV×POPC、无apoE的HDL和apoA-IV+apoA-I×POPC的抑制，但不受apoA-I×POPC的抑制。apoA-IV×POPC的结合受到无apoE的HDL、apoA-IV×POPC和apoA-IV+apoA-I×POPC的抑制，但不受apoE×POPC或富含apoE的HDL的抑制。这些数据表明，apoA-IV是负责大鼠HDL与原代大鼠肝细胞结合的配体，并且apoA-IV与不同于apoE依赖性受体（如apoB、E或乳糜微粒残粒受体）的受体位点结合。
