Olwin B B, Rapraeger A
Department of Biochemistry, School of Medicine, University of Wisconsin, Madison 53706.
J Cell Biol. 1992 Aug;118(3):631-9. doi: 10.1083/jcb.118.3.631.
We have proposed a model in which fibroblast growth factor (FGF) signalling requires the interaction of FGF with at least two FGF receptors, a heparan sulfate proteoglycan (HSPG) and a tyrosine kinase. Since FGF may be a key mediator of skeletal muscle differentiation, we examined the synthesis of glycosaminoglycans in MM14 skeletal muscle myoblasts and their participation in FGF signalling. Proliferating and differentiated MM14 cells exhibit similar levels of HSPG, while differentiated cells exhibit reduced levels of chondroitin sulfate proteoglycans and heparan sulfate chains. HSPGs, including syndecan, present in proliferating cells bind bFGF, while the majority of chondroitin sulfate and heparan sulfate chains do not. Treatment of skeletal muscle cells with chlorate, a reversible inhibitor of glycosaminoglycan sulfation, was used to examine the requirement of sulfated proteoglycans for FGF signalling. Chlorate treatment reduced glycosaminoglycan sulfation by 90% and binding of FGF to high affinity sites by 80%. Chlorate treatment of MM14 myoblasts abrogated the biological activity of acidic, basic, and Kaposi's sarcoma FGFs resulting in terminal differentiation. Chlorate inhibition of FGF signalling was reversed by the simultaneous addition of sodium sulfate or heparin. Further support for a direct role of heparan sulfate proteoglycans in fibroblast growth factor signal transduction was demonstrated by the ability of heparitinase to inhibit basic FGF binding and biological activity. These results suggest that activation of FGF receptors by acidic, basic or Kaposi's sarcoma FGF requires simultaneous binding to a HSPG and the tyrosine kinase receptor. Skeletal muscle differentiation in vivo may be dependent on FGFs, FGF tyrosine kinase receptors, and HSPGs. The regulation of these molecules may then be expected to have important implications for skeletal muscle development and regeneration.
我们提出了一个模型，其中成纤维细胞生长因子（FGF）信号传导需要FGF与至少两种FGF受体、一种硫酸乙酰肝素蛋白聚糖（HSPG）和一种酪氨酸激酶相互作用。由于FGF可能是骨骼肌分化的关键介质，我们研究了MM14骨骼肌成肌细胞中糖胺聚糖的合成及其在FGF信号传导中的作用。增殖和分化的MM14细胞表现出相似水平的HSPG，而分化细胞中硫酸软骨素蛋白聚糖和硫酸乙酰肝素链的水平降低。增殖细胞中存在的包括syndecan在内的HSPG与bFGF结合，而大多数硫酸软骨素和硫酸乙酰肝素链则不结合。用氯酸盐（一种糖胺聚糖硫酸化的可逆抑制剂）处理骨骼肌细胞，以研究硫酸化蛋白聚糖对FGF信号传导的需求。氯酸盐处理使糖胺聚糖硫酸化降低了90%，FGF与高亲和力位点的结合降低了80%。氯酸盐处理MM14成肌细胞消除了酸性、碱性和卡波西肉瘤FGF的生物活性，导致终末分化。同时添加硫酸钠或肝素可逆转氯酸盐对FGF信号传导的抑制作用。乙酰肝素酶抑制碱性FGF结合和生物活性的能力进一步证明了硫酸乙酰肝素蛋白聚糖在成纤维细胞生长因子信号转导中的直接作用。这些结果表明，酸性、碱性或卡波西肉瘤FGF对FGF受体的激活需要同时与HSPG和酪氨酸激酶受体结合。体内骨骼肌分化可能依赖于FGF、FGF酪氨酸激酶受体和HSPG。那么可以预期，这些分子的调节对骨骼肌的发育和再生具有重要意义。
