1. Naturally occurring tyrosine kinase inserts block high affinity binding of phospholipase C gamma and Shc to TrkC and neurotrophin-3 signaling.
- Author
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Guiton M, Gunn-Moore FJ, Glass DJ, Geis DR, Yancopoulos GD, and Tavaré JM
- Subjects
- 3T3 Cells, Amino Acid Sequence, Animals, Base Sequence, Binding Sites, Cell Division drug effects, DNA Primers, Enzyme Activation drug effects, Fibroblasts cytology, Fibroblasts drug effects, Fibroblasts metabolism, Isoenzymes metabolism, Kinetics, Mice, Molecular Sequence Data, Mutagenesis, Insertional, Neurotrophin 3, Phosphorylation, Receptor, Ciliary Neurotrophic Factor, Receptor, trkC, Receptors, Nerve Growth Factor isolation & purification, Recombinant Proteins metabolism, Substrate Specificity, Transfection, Calcium-Calmodulin-Dependent Protein Kinases metabolism, Nerve Growth Factors pharmacology, Protein-Tyrosine Kinases metabolism, Receptor Protein-Tyrosine Kinases metabolism, Receptors, Nerve Growth Factor metabolism, Signal Transduction, Type C Phospholipases metabolism
- Abstract
Neurotrophin-3 binds to the receptor tyrosine kinase, TrkC. Several naturally occurring splice variants of TrkC exist including those with 14- and 39-amino acid inserts within the tyrosine kinase homology region. When expressed in fibroblasts, full-length TrkC, but not the kinase insert variants, mediated neurotrophin-3-stimulated cell proliferation. We investigated the molecular basis of this signaling defect. The kinase inserts blocked the ability of TrkC to mediate neurotrophin-3 stimulated c-myc and c-fos transcription and activation of the AP-1 transcriptional complex. In cells expressing full-length TrkC, neurotrophin-3 promoted a sustained activation of mitogen-activated protein kinase; TrkC containing kinase inserts only mediated transient activation of mitogen-activated protein kinase. The kinase inserts specifically blocked neurotrophin-3-stimulated autophosphorylation of the phospholipase C gamma binding site on TrkC (tyrosine 789) resulting in a severe reduction in phospholipase C gamma association with TrkC and its tyrosine phosphorylation. Neurotrophin-3-stimulated phosphorylation of the Shc binding site (tyrosine 485) on TrkC, and tyrosine phosphorylation of Shc itself, was unaffected by the kinase inserts; however, the kinase inserts blocked high affinity Shc association with TrkC. It is proposed that the lack of high affinity binding of Shc and/or phospholipase C gamma to the TrkC kinase insert variants may be responsible for the inability of these variants to bring about a full biological response in fibroblasts.
- Published
- 1995
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