Institute of Molecular Biology, Medical University Innsbruck, Innrain 80, A-6020, Innsbruck, Austria.
Institute of Clinical Biochemistry, Medical University Innsbruck, Innrain 80, A-6020, Innsbruck, Austria.
Biol Chem. 2020 Aug 27;401(9):1081-1092. doi: 10.1515/hsz-2020-0132.
Lipocalins, small extracellular hydrophobic molecule carriers, can be internalized by a variety of different cells. However, to date receptors have only been identified for human lipocalins. Here, we specifically investigated uptake mechanisms for lipocalins ß-lactoglobulin and Fel d 4 in HeLa and Chinese hamster ovary (CHO) cells. We provide evidence that cell surface heparan sulphate proteoglycan is essential for internalization of these lipocalins. In HeLa cells, lipocalin uptake was inhibited by competition with soluble heparin, enzymatic digestion of cellular heparan sulphate by heparinase and inhibition of its biosynthesis by sodium chlorate. Biochemical studies by heparin affinity chromatography and colocalization studies further supported a role of heparan sulphate proteoglycan in lipocalin uptake. Finally, lipocalin uptake was blocked in CHO mutant cells defective in glycosaminoglycan biosynthesis whereas in wild-type cells it was clearly detectable. Thus, cell surface heparan sulphate proteoglycan represents a novel component absolutely participating in the cellular uptake of some lipocalins.
脂联素是一种小的细胞外疏水分子载体，可以被多种不同的细胞内化。然而，到目前为止，只有人类脂联素的受体被鉴定出来。在这里，我们专门研究了 HeLa 和中国仓鼠卵巢（CHO）细胞中β-乳球蛋白和 Fel d 4 脂联素的摄取机制。我们提供的证据表明，细胞表面硫酸乙酰肝素蛋白聚糖对于这些脂联素的内化是必不可少的。在 HeLa 细胞中，脂联素的摄取被竞争结合的肝素、肝素酶对细胞硫酸乙酰肝素的酶解以及用氯酸钠抑制其生物合成所抑制。通过肝素亲和层析的生化研究和共定位研究进一步支持了硫酸乙酰肝素蛋白聚糖在脂联素摄取中的作用。最后，在糖胺聚糖生物合成缺陷的 CHO 突变细胞中，脂联素的摄取被阻断，而在野生型细胞中，脂联素的摄取明显可检测到。因此，细胞表面硫酸乙酰肝素蛋白聚糖是参与某些脂联素细胞内摄取的新型成分。
