Mascarelli F, Courtois Y
INSERM U 118, Association Claude-Bernard, Paris, France.
Bull Cancer. 1993 Sep;80(9):786-98.
Interactions between the two classes of fibroblast growth factor receptors 1) the high affinity receptors (HAR) a membrane glycoprotein containing an intrinsic tyrosine kinase activity, 2) low affinity receptors (LAR) cell surface proteoglycans containing heparan sulfate side chains (HSPG), and aFGF (MW: 15.5 kDa) were studied in bovine lens epithelial (BEL) cells. By Scatchard analysis of the aFGF binding to the BEL cell surface, we show that heparin at 10 micrograms/ml abolishes completely aFGF binding to LAR and reduces by half the number of aFGF HAR. By using cross-linking experiments, aFGF-HAR complexes are present in two forms (150 kDa and 135 kDa). Addition of heparin at 10 micrograms/ml abolishes the formation of the 150 kDa complex and does not affect the 135 kDa complex. Furthermore, binding of aFGF to LAR induces the spontaneous formation of a 31 kDa aFGF dimer. The dimerization process of aFGF on LAR is abolished by addition of heparin. During aFGF internalization at 37 degrees C, we have shown that aFGF-dimer is internalized, accumulated and degraded in the cell as is the 15.5 kDa native form. Heparin at 10 micrograms/ml suppresses specifically aFGF dimer internalization and reduces by half the total amount of internalized aFGF native form. Moreover, after aFGF binding and internalization, the affinity of HAR for aFGF increases concomitantly with its downregulation. Heparin does not seem to affect this phenomenon. All these results strongly suggest that an heteroreceptor dimer-aFGF complex (150 kDa) is formed by one molecule of HAR associated to one molecule of LAR through their respective interaction with a very stable homodimer of aFGF. Such a three component receptor complex induced by FGF dimerization may be a general process of FGF receptor activation which could explain the diversity of the biological response to FGF of different cell type expressing different HAR and LAR or HSPG.
在牛晶状体上皮（BEL）细胞中研究了两类成纤维细胞生长因子受体之间的相互作用：1）高亲和力受体（HAR），一种含有内在酪氨酸激酶活性的膜糖蛋白；2）低亲和力受体（LAR），含有硫酸乙酰肝素侧链（HSPG）的细胞表面蛋白聚糖，以及酸性成纤维细胞生长因子（aFGF，分子量：15.5 kDa）。通过对aFGF与BEL细胞表面结合的Scatchard分析，我们发现10微克/毫升的肝素完全消除了aFGF与LAR的结合，并使aFGF与HAR的结合数量减少一半。通过交联实验，aFGF - HAR复合物以两种形式存在（150 kDa和135 kDa）。添加10微克/毫升的肝素会消除150 kDa复合物的形成，而不影响135 kDa复合物。此外，aFGF与LAR的结合会诱导31 kDa的aFGF二聚体的自发形成。添加肝素会消除aFGF在LAR上的二聚化过程。在37℃下aFGF内化过程中，我们发现aFGF二聚体与15.5 kDa的天然形式一样被内化、积累并在细胞内降解。10微克/毫升的肝素特异性抑制aFGF二聚体的内化，并使内化的aFGF天然形式的总量减少一半。此外，在aFGF结合和内化后，HAR对aFGF的亲和力随着其下调而相应增加。肝素似乎不影响这一现象。所有这些结果强烈表明，一种异源受体二聚体 - aFGF复合物（150 kDa）是由一个HAR分子与一个LAR分子通过它们各自与一个非常稳定的aFGF同二聚体的相互作用而形成的。这种由FGF二聚化诱导的三组分受体复合物可能是FGF受体激活的一个普遍过程，这可以解释表达不同HAR、LAR或HSPG的不同细胞类型对FGF的生物学反应的多样性。
