Association of the Src family tyrosine kinase Fyn with TrkB.
Fyn tyrosine kinase, a member of the Src family, was recently reported to be present in neurons and glia cells. We investigated whether Fyn is involved in the Trk-dependent signal transduction pathways of neurotrophin. The Fyn-Src homology domain 2 (SH2) was observed to associate in vitro with the intracellular domain of TrkB (ICD-TrkB). This association was dependent on the autophosphorylation of ICD-TrkB. The Fyn-SH2 domains bound to phosphorylated ICD-TrkB (pICD-TrkB) with an affinity similar to the binding of phospholipase Cgamma (PLCgamma)-SH2 domains to its autophosphorylation site in TrkB. The Src-SH2 domains showed substantially lower affinity with pICD-TrkB, suggesting that the association between Fyn-SH2 and pICD-TrkB is not due to nonspecific interactions of SH2 domains with phosphorylated tyrosine residues. This is further supported by the observation that Fyn-SH2 was able to trap phosphorylated TrkB in cell lysate prepared from primary rat cortical neurons stimulated with brain-derived neurotrophic factor (BDNF). In contrast, endogenous Fyn was coprecipitated with TrkB from cortical neurons without BDNF stimulation. This basal association showed a threefold increase on BDNF stimulation, probably due to the SH2/phosphotyrosine interaction that was observed in the cell-free system. All these data suggest the involvement of Fyn in the neurotrophin signal transduction pathways downstream of TrkB.
Iwasaki
Y
Y
Novartis Pharma K.K., Research Department, Takarazuka Research Institute, Japan.
Gay
B
B
Wada
K
K
Koizumi
S
S
D000818:Animals; D016367:Baculoviridae; D019208:Brain-Derived Neurotrophic Factor / Q000494:pharmacology; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology; D007313:Insecta; D017774:Long-Term Potentiation / Q000502:physiology; D009474:Neurons / Q000737:chemistry / Q000187:drug effects / Q000201:enzymology*; D018696:Neuroprotective Agents / Q000378:metabolism*; D010766:Phosphorylation; D011485:Protein Binding / Q000502:physiology; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051076:Proto-Oncogene Proteins c-fyn; D051381:Rats; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism*; D020801:Receptor, Ciliary Neurotrophic Factor; D017475:Receptors, Nerve Growth Factor / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D018909:src Homology Domains / Q000502:physiology*
D019208:Brain-Derived Neurotrophic Factor; D018696:Neuroprotective Agents; D011518:Proto-Oncogene Proteins; D020801:Receptor, Ciliary Neurotrophic Factor; D017475:Receptors, Nerve Growth Factor; D020794:Receptor Protein-Tyrosine Kinases; C494961:Fyn protein, rat; D051076:Proto-Oncogene Proteins c-fyn