Reich-Slotky R, Bonneh-Barkay D, Shaoul E, Bluma B, Svahn C M, Ron D
Department of Biology, Technion, Israel Institute of Technology, Technion City, Haifa.
J Biol Chem. 1994 Dec 23;269(51):32279-85.
The fibroblast growth factors (FGFs) act through high affinity tyrosine kinase receptors and, in addition, interact with lower affinity receptors that represent cell- or matrix-associated heparan sulfate proteoglycans. These lower affinity receptors modulate the biological activities of FGFs, but the mechanism by which they exert these effects is rather controversial. We have previously shown (Ron, D., Bottaro, D. P., Finch, P. W., Morris, D., Rubin, J. S., and Aaronson, S. A. (1993) J. Biol. Chem. 268, 2984-2988) that heparin potentiates the mitogenic activity of acidic FGF (aFGF) but inhibits that of the keratinocyte growth factor (KGF) in cells that express the KGF receptor (KGFR). Both growth factors bind the KGFR with high affinity. To gain an insight into the mechanism by which heparin modulates the biological activity of aFGF and KGF, we studied the effect of heparin and cell-associated heparan sulfates on the binding of these two growth factors to the KGFR. To work in a well defined system, we expressed functional KGFR in L6E9 myoblasts that lack detectable high affinity binding sites for FGFs. Low concentrations of heparin inhibited the binding of KGF to the KGFR. By contrast, similar concentrations of heparin enhanced the binding of aFGF to this receptor. The effect of heparin was not unique to L6E9 cells expressing the KGFR; it was also observed in Balb/MK cells that naturally express KGFR. Treatment of cells with sodium chlorate, which blocks sulfation of proteoglycans, reduced the binding of aFGF to its low and high affinity binding sites by 95 and 80%, respectively. In contrast, the binding of KGF to its high affinity binding sites was enhanced about 2-fold. Similar results were obtained after degradation of cell-associated heparan sulfates by heparinase and heparitinase. Heparin restored the high affinity binding of aFGF to chlorate-treated cells and completely abolished the high affinity binding of KGF. Binding competition experiments suggest that aFGF and KGF bind to the same population of cell-associated heparan sulfates. In addition, KGF is apparently interacting with an as yet unidentified type of low affinity binding site that is not affected by chlorate or heparan sulfate-degrading enzymes. An important property of the FGF high affinity receptors is their ability to bind more than one ligand with high affinity. Based on the differential effect of cell-associated heparan sulfates on the binding of KGF and aFGF to the KGFR, we propose a regulatory role for cell-associated heparan sulfates as coordinators of the interaction of aFGF and KGF with the KGFR.(ABSTRACT TRUNCATED AT 400 WORDS)
成纤维细胞生长因子（FGFs）通过高亲和力酪氨酸激酶受体发挥作用，此外，还与代表细胞或基质相关硫酸乙酰肝素蛋白聚糖的低亲和力受体相互作用。这些低亲和力受体调节FGFs的生物学活性，但其发挥这些作用的机制颇具争议。我们之前已经表明（罗恩，D.，博塔罗，D.P.，芬奇，P.W.，莫里斯，D.，鲁宾，J.S.，和阿伦森，S.A.（1993年）《生物化学杂志》268卷，2984 - 2988页），在表达角质形成细胞生长因子受体（KGFR）的细胞中，肝素可增强酸性FGF（aFGF）的促有丝分裂活性，但会抑制角质形成细胞生长因子（KGF）的活性。两种生长因子都以高亲和力结合KGFR。为深入了解肝素调节aFGF和KGF生物学活性的机制，我们研究了肝素和细胞相关硫酸乙酰肝素对这两种生长因子与KGFR结合的影响。为在一个明确的系统中开展研究，我们在缺乏可检测到的FGFs高亲和力结合位点的L6E9成肌细胞中表达功能性KGFR。低浓度肝素可抑制KGF与KGFR的结合。相比之下，类似浓度的肝素可增强aFGF与该受体的结合。肝素的这种作用并非表达KGFR的L6E9细胞所特有；在天然表达KGFR的Balb/MK细胞中也观察到了这种现象。用氯酸钠处理细胞可阻断蛋白聚糖的硫酸化，分别使aFGF与其低亲和力和高亲和力结合位点的结合减少95%和80%。相比之下，KGF与其高亲和力结合位点的结合增强了约2倍。在用肝素酶和硫酸乙酰肝素酶降解细胞相关硫酸乙酰肝素后也获得了类似结果。肝素可恢复aFGF与经氯酸钠处理细胞的高亲和力结合，并完全消除KGF的高亲和力结合。结合竞争实验表明，aFGF和KGF与同一群细胞相关硫酸乙酰肝素结合。此外，KGF显然与一种尚未明确的低亲和力结合位点相互作用，该位点不受氯酸钠或硫酸乙酰肝素降解酶的影响。FGF高亲和力受体的一个重要特性是它们能够以高亲和力结合不止一种配体。基于细胞相关硫酸乙酰肝素对KGF和aFGF与KGFR结合的不同影响，我们提出细胞相关硫酸乙酰肝素作为aFGF和KGF与KGFR相互作用的协调者具有调节作用。（摘要截取自400字）
