Brissette L, Charest M C, Falstrault L, Lafond J, Rhainds D, Tremblay C, Truong T Q
Département des Sciences biologiques, Université du Québec à Montréal, Canada.
Biochem Cell Biol. 1999;77(2):157-63.
Selective uptake of cholesteryl esters (CE) from lipoproteins by cells has been extensively studied with high density lipoproteins (HDL). It is only recently that such a mechanism has been attributed to intermediate and low density lipoproteins (IDL and LDL). Here, we compare the association of proteins and CE from very low density lipoproteins (VLDL), IDL, LDL and HDL3 to HepG2 cells. These lipoproteins were either labelled in proteins with 125I or in CE with 3H-cholesteryl oleate. We show that, at any lipoprotein concentration, protein association to the cells is significantly smaller for IDL, LDL, and HDL3 than CE association, but not for VLDL. At a concentration of 20 microg lipoprotein/mL, these associations reveal CE-selective uptake in the order of 2-, 4-, and 11-fold for IDL, LDL, and HDL3, respectively. These studies reveal that LDL and HDL3 are good selective donors of CE to HepG2 cells, while IDL is a poor donor and VLDL is not a donor. A significant inverse correlation (r2 = 0.973) was found between the total lipid/protein ratios of the four classes of lipoproteins and the extent of CE-selective uptake by HepG2 cells. The fate of 3H-CE of the two best CE donors (LDL and HDL3) was followed in HepG2 cells after 3 h of incubation. Cells were shown to hydrolyze approximately 25% of the 3H-CE of both lipoproteins. However, when the cells were treated with 100 microM of chloroquine, a lysosomotropic agent, 85 and 40% of 3H-CE hydrolysis was lost for LDL and HDL3, respectively. The fate of LDL and HDL3-CE in HepG2 cells deficient in LDL-receptor was found to be the same, indicating that the portion of CE hydrolysis sensitive to chloroquine is not significantly linked to LDL-receptor activity. Thus, in HepG2 cells, the magnitude of CE-selective uptake is inversely correlated with the total lipid/protein ratios of the lipoproteins and CE-selective uptake from the two best CE donors (LDL and HDL3) appears to follow different pathways.
细胞从脂蛋白中选择性摄取胆固醇酯（CE）的过程已在高密度脂蛋白（HDL）方面进行了广泛研究。直到最近，这种机制才被归因于中密度脂蛋白和低密度脂蛋白（IDL和LDL）。在此，我们比较了极低密度脂蛋白（VLDL）、IDL、LDL和HDL3中的蛋白质和CE与HepG2细胞的结合情况。这些脂蛋白要么用125I标记蛋白质，要么用3H - 胆固醇油酸酯标记CE。我们发现，在任何脂蛋白浓度下，IDL、LDL和HDL3与细胞的蛋白质结合显著小于CE结合，但VLDL并非如此。在脂蛋白浓度为20微克/毫升时，这些结合显示IDL、LDL和HDL3的CE选择性摄取分别为2倍、4倍和11倍。这些研究表明，LDL和HDL3是HepG2细胞良好的CE选择性供体，而IDL是较差的供体，VLDL则不是供体。在四类脂蛋白的总脂质/蛋白质比率与HepG2细胞的CE选择性摄取程度之间发现了显著的负相关（r2 = 0.973）。在孵育3小时后，追踪了两种最佳CE供体（LDL和HDL3）的3H - CE在HepG2细胞中的去向。结果显示，细胞水解了两种脂蛋白中约25%的3H - CE。然而，当细胞用100微摩尔的溶酶体促渗剂氯喹处理时，LDL和HDL3的3H - CE水解分别损失了85%和40%。在缺乏LDL受体的HepG2细胞中，发现LDL和HDL3 - CE的去向相同，这表明对氯喹敏感的CE水解部分与LDL受体活性没有显著关联。因此，在HepG2细胞中，CE选择性摄取的程度与脂蛋白的总脂质/蛋白质比率呈负相关，并且来自两种最佳CE供体（LDL和HDL3）的CE选择性摄取似乎遵循不同的途径。
