Inagaki N, Thoenen H, Lindholm D
Department of Neurochemistry, Max Planck Institute for Psychiatry, Martinsried, Germany.
Eur J Neurosci. 1995 Jun 1;7(6):1125-33. doi: 10.1111/j.1460-9568.1995.tb01102.x.
The proto-oncogene product gp140prototrk (TrkA) is the receptor tyrosine kinase that mediates nerve growth factor-induced neuronal survival and differentiation. In receptor tyrosine kinases, specific intracellular tyrosine residues become phosphorylated after ligand binding and the phosphorylated tyrosines induce the cascade of signal transduction. Here we have identified intracellular tyrosine residues of TrkA involved in nerve growth factor-induced neurite outgrowth of PC12 cells, using site-directed mutagenesis and a PC12 cell line expressing very low levels of endogenous TrkA (PC12nnr5 cells). We analysed eight conserved intracellular tyrosine residues of TrkA while the three putative autophosphorylation sites conferring tyrosine kinase activity were left intact. Five tyrosine residues, Y499, Y643, Y704, Y760 and Y794, in rat TrkA were involved in nerve growth factor-induced neurite outgrowth. None of these tyrosines mediated the full activity of wild-type TrkA, and a pair of these tyrosines, Y760 and Y794, promoted neurite outgrowth in an additive manner. These data indicate that no single tyrosine is sufficient to induce complete neurite outgrowth but the five tyrosine residues Y499, Y643, Y704, Y760 and Y794 cooperate to exhibit the full activity of wild-type TrkA.
原癌基因产物gp140prototrk（TrkA）是一种受体酪氨酸激酶，可介导神经生长因子诱导的神经元存活和分化。在受体酪氨酸激酶中，特定的细胞内酪氨酸残基在配体结合后会发生磷酸化，而磷酸化的酪氨酸会引发信号转导级联反应。在此，我们利用定点诱变技术以及一种内源性TrkA表达水平极低的PC12细胞系（PC12nnr5细胞），确定了参与神经生长因子诱导PC12细胞轴突生长的TrkA细胞内酪氨酸残基。我们分析了TrkA的八个保守细胞内酪氨酸残基，同时使三个赋予酪氨酸激酶活性的假定自磷酸化位点保持完整。大鼠TrkA中的五个酪氨酸残基Y499、Y643、Y704、Y760和Y794参与了神经生长因子诱导的轴突生长。这些酪氨酸中没有一个介导野生型TrkA的全部活性，其中一对酪氨酸Y
