Syndecan-1 mediates internalization of apoE-VLDL through a low density lipoprotein receptor-related protein (LRP)-independent, non-clathrin-mediated pathway.
Syndecan-1 mediates internalization of apoE-VLDL through a low density lipoprotein receptor-related protein (LRP)-independent, non-clathrin-mediated pathway.
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DOI：
10.1186/1476-511x-5-23
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发表时间：
2006-08-31
影响因子：
4.5
通讯作者：
Orlando RA
中科院分区：
文献类型：
--
作者：
Wilsie LC;Gonzales AM;Orlando RA
富含三酰甘油的极低密度脂蛋白(VLDL)颗粒是循环中脂肪酸的主要载体，因此是周围组织的丰富能量来源。受体介导的这些颗粒的摄取依赖于先前与载脂蛋白E(apoE-VLDL)的结合，在某些细胞类型中是由细胞表面硫酸乙酰肝素蛋白多糖(HSPG)引起的，在另一些细胞类型中是由低密度脂蛋白受体相关蛋白(LRP)引起的。尽管LRP在载脂蛋白E-VLDL摄取中的作用已被很好地研究，但介导载脂蛋白E-VLDL摄取的HSPG家族成员的身份尚未确定。我们研究了跨膜细胞表面HSPG Syndecan-1(Syn-1)是否能够介导apoE-VLDL的内化，并探讨了Syn-1与LRP对apoE-VLDL摄取的关系。在这项研究中，我们使用了一个人成纤维细胞系(GM00701)，它表达大量的LRP，但没有低密度脂蛋白受体活性，以消除其对apoE-VLDL摄取的贡献。尽管这些细胞中的LRP被大量的α-2巨球蛋白结合和内化所证实是完全活跃的，但缺乏对载脂蛋白E-极低密度脂蛋白的摄取。人Syn-1基因的表达恢复了这些细胞对apoE-VLDL的结合和摄取。与LRP配体结合拮抗剂对这种摄取的竞争作用很小或没有影响，而与肝素共同孵育则取消apoE-VLDL内化。去除Syn-1表达K+的细胞，阻断网状蛋白介导的内吞作用，并不抑制Syn-1内化apoE-VLDL。相比之下，用制霉菌素抑制脂筏功能的细胞处理，阻止了Syn-1摄取apoE-VLDL。这些数据表明，Syn-1能够在LRP很少或没有贡献的情况下介导人成纤维细胞对apoE-VLDL的摄取，并且Syn-1采取的内吞途径是不依赖于笼蛋白的，依赖于脂筏功能。这些数据与之前证明Syn-1与脂筏结构域相关的研究是一致的。
Triacylglyerol-rich very low density lipoprotein (VLDL) particles are the primary carriers of fatty acids in the circulation and as such serve as a rich energy source for peripheral tissues. Receptor-mediated uptake of these particles is dependent upon prior association with apolipoprotein E (apoE-VLDL) and is brought about by cell surface heparan sulfate proteoglycans (HSPG) in some cell types and by the low density lipoprotein receptor-related protein (LRP) in others. Although LRP's role in apoE-VLDL uptake has been well studied, the identity of the HSPG family member that mediates apoE-VLDL uptake has not been established. We investigated if syndecan-1 (Syn-1), a transmembrane cell surface HSPG, is able to mediate the internalization of apoE-VLDL and examined the relationship between Syn-1 and LRP toward apoE-VLDL uptake. For this study, we used a human fibroblast cell line (GM00701) that expresses large amounts of LRP, but possesses no LDL receptor activity to eliminate its contributions toward apoE-VLDL uptake. Although LRP in these cells is fully active as established by substantial α2macroglobulin binding and internalization, uptake of apoE-VLDL is absent. Expression of human Syn-1 cDNA restored apoE-VLDL binding and uptake by these cells. Competition for this uptake with an LRP ligand-binding antagonist had little or no effect, whereas co-incubation with heparin abolished apoE-VLDL internalization. Depleting Syn-1 expressing cells of K+, to block clathrin-mediated endocytosis, showed no inhibition of Syn-1 internalization of apoE-VLDL. By contrast, treatment of cells with nystatin to inhibit lipid raft function, prevented the uptake of apoE-VLDL by Syn-1. These data demonstrate that Syn-1 is able to mediate apoE-VLDL uptake in human fibroblasts with little or no contribution from LRP and that the endocytic path taken by Syn-1 is clathrin-independent and relies upon lipid raft function. These data are consistent with previous studies demonstrating Syn-1 association with lipid raft domains.