Tumova S, Hatch B A, Law D J, Bame K J
Division of Molecular Biology and Biochemistry, School of Biological Sciences, University of Missouri-Kansas City, Kansas City, MO 64110, USA.
Biochem J. 1999 Feb 1;337 ( Pt 3)(Pt 3):471-81.
Heparan sulphate proteoglycans on cell surfaces have been shown to mediate the degradation or recycling of several ligands. Since the interaction with ligand may affect proteoglycan catabolism once the complex is internalized, this could alter the cellular pool of heparan sulphate chains, with possible consequences for heparan sulphate-mediated cellular processes. We have recently demonstrated that the specific binding of basic fibroblast growth factor (bFGF) to heparan sulphate chains prevents the glycosaminoglycan from being degraded by partially purified heparanases from Chinese hamster ovary (CHO) cells [Tumova and Bame (1997) J. Biol. Chem. 272, 9078-9085]. The present study examines the effect of bFGF on heparan sulphate catabolism in intact cells. The distribution and size of the heparan sulphate degradation products in CHO cells was analysed in the presence and absence of bFGF using pulse-chase protocols. Although heparan sulphate molecules and bFGF are internalized through the same pathway, even relatively high concentrations of the growth factor do not have any inhibitory effects on glycosaminoglycan degradation. However, the interaction with the growth factor alters the distribution of heparan sulphate-degradation products, presumably by preventing secretion of the short heparanase-derived species. Our findings show that most of the free and bFGF-bound heparan sulphate chains are destined for lysosomes, which would be consistent with a recent hypothesis that the primary role of proteoglycan-mediated internalization of the growth factor is to remove bFGF from its site of action at the cell surface. However, in the presence of bFGF, a fraction of intracellular, heparanase-degraded heparan sulphate chains is delivered to the nucleus, suggesting that the glycosaminoglycan accompanies the growth factor to the organelle. It may be important for bFGF activity that the growth factor is protected from proteolytic degradation by its interaction with heparan sulphate. This work demonstrates that the internalization of a ligand along with the proteoglycan can affect the sorting of heparan sulphate-degradation products in endosomes, and the ultimate destination of the short glycosaminoglycan. It also provides evidence that formation of heparan sulphate-ligand complexes may regulate the recycling and degradation of both ligands and heparan sulphate chains and, consequently, affect their biological activities.
细胞表面的硫酸乙酰肝素蛋白聚糖已被证明可介导多种配体的降解或再循环。由于一旦复合物内化，与配体的相互作用可能会影响蛋白聚糖的分解代谢，这可能会改变硫酸乙酰肝素链的细胞池，对硫酸乙酰肝素介导的细胞过程产生可能的影响。我们最近证明，碱性成纤维细胞生长因子（bFGF）与硫酸乙酰肝素链的特异性结合可防止糖胺聚糖被来自中国仓鼠卵巢（CHO）细胞的部分纯化的乙酰肝素酶降解[Tumova和Bame（1997年）《生物化学杂志》272卷，9078 - 9085页]。本研究考察了bFGF对完整细胞中硫酸乙酰肝素分解代谢的影响。使用脉冲追踪实验方案，在有和没有bFGF的情况下分析了CHO细胞中硫酸乙酰肝素降解产物的分布和大小。尽管硫酸乙酰肝素分子和bFGF通过相同途径内化，但即使是相对高浓度的生长因子对糖胺聚糖降解也没有任何抑制作用。然而，与生长因子的相互作用改变了硫酸乙酰肝素降解产物的分布，推测是通过阻止短的源自乙酰肝素酶的片段的分泌。我们的研究结果表明，大多数游离的和与bFGF结合的硫酸乙酰肝素链都注定要进入溶酶体，这与最近的一个假设一致，即蛋白聚糖介导的生长因子内化的主要作用是将bFGF从其在细胞表面的作用位点移除。然而，在有bFGF存在的情况下，一部分细胞内、经乙酰肝素酶降解的硫酸乙酰肝素链被输送到细胞核，这表明糖胺聚糖伴随着生长因子进入该细胞器。生长因子通过与硫酸乙酰肝素相互作用而免受蛋白水解降解，这对bFGF的活性可能很重要。这项工作表明，配体与蛋白聚糖一起内化会影响内体中硫酸乙酰肝素降解产物的分选以及短糖胺聚糖的最终去向。它还提供了证据表明硫酸乙酰肝素 - 配体复合物的形成可能调节配体和硫酸乙酰肝素链的再循环和降解，从而影响它们的生物学活性。
