Canossa M, Rovelli G
Department of Neurobiology, Stanford University School of Medicine, Stanford, California 94305-5401, USA.
J Biol Chem. 1996 Mar 8;271(10):5812-8. doi: 10.1074/jbc.271.10.5812.
The potential for the activation of one Trk receptor by ligand binding to another Trk receptor was explored by determining if transphosphorylation on tyrosine residues can occur between receptors. For most of these experiments, functional chimeric receptors were used that contained the extracellular domain of the human type 2 tumor necrosis factor receptor and the transmembrane and cytoplasmic domains of rat TrkA, TrkB, or TrkC and that, when activated by the tumor necrosis factor, mediated the nerve growth factor-like biological activities in PC12 cells. Cotransfection experiments in COS-7 cells and fibroblasts showed that despite the presence of different extracellular regions, intermolecular transphosphorylation of homologous cytoplasmic domains occurred between TrkA or TrkB and their cognate chimeras. Heterologous transphosphorylation between TrkB and TrkC kinase domains was also observed when one partner was a chimeric receptor; however, TrkA did not transphosphorylate the TrkB or TrkC kinase domains of chimeric receptors or act as a transphosphorylation substrate for these two receptors. The failure of TrkA to take part in transphosphorylation reactions with TrkB and TrkC was confirmed using the natural receptors. Trk receptor transphosphorylation occurs in the two non-neuronal cell types, but TrkA is excluded from these reactions.
通过确定受体之间是否能发生酪氨酸残基的转磷酸化，来探究配体与另一种Trk受体结合从而激活一种Trk受体的可能性。在大多数这些实验中，使用了功能性嵌合受体，其包含人2型肿瘤坏死因子受体的胞外结构域以及大鼠TrkA、TrkB或TrkC的跨膜和胞质结构域，并且当被肿瘤坏死因子激活时，能在PC12细胞中介导类神经生长因子的生物学活性。在COS-7细胞和成纤维细胞中的共转染实验表明，尽管存在不同的胞外区域，但TrkA或TrkB与其同源嵌合体之间仍发生了同源胞质结构域的分子间转磷酸化。当其中一个伙伴是嵌合受体时，也观察到了TrkB和TrkC激酶结构域之间的异源转磷酸化；然而，TrkA不会使嵌合受体的TrkB或TrkC激酶结构域发生磷酸化，也不会作为这两种受体的转磷酸化底物。使用天然受体证实了TrkA未能参与与TrkB和TrkC的转磷酸化反应。Trk受体转磷酸化发生在两种非神经元细胞类型中，但TrkA被排除在这些反应之外。
