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Association of the Src family tyrosine kinase Fyn with TrkB
1Novartis Pharma K.K., Research Department, Takarazuka Research Institute, Japan.
Abstract:
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.
Insights
Fyn tyrosine kinase interacts with TrkB, a receptor for brain-derived neurotrophic factor (BDNF). This interaction suggests Fyn
Area of Science:
- Neuroscience
- Molecular Biology
- Cell Signaling
Background:
- Fyn tyrosine kinase, a Src family member, is found in neurons and glia.
- Neurotrophins, like BDNF, signal through Trk receptors.
- The role of Fyn in Trk-dependent neurotrophin signaling is not well understood.
Purpose of the Study:
- To investigate the involvement of Fyn tyrosine kinase in Trk-dependent neurotrophin signal transduction pathways.
- To elucidate the molecular interaction between Fyn and the TrkB receptor.
Main Methods:
- In vitro binding assays using Fyn-Src homology domain 2 (SH2) and intracellular domain of TrkB (ICD-TrkB).
- Analysis of Fyn-TrkB association in primary rat cortical neurons stimulated with BDNF.
- Coprecipitation assays to detect endogenous Fyn and TrkB interaction.
Main Results:
- Fyn-SH2 domains bind to autophosphorylated ICD-TrkB with high affinity, comparable to PLCgamma-SH2 domains.
- Src-SH2 domains show significantly lower affinity for pICD-TrkB, indicating specificity.
- Fyn associates with TrkB in primary neurons, with BDNF stimulation increasing this interaction threefold.
Conclusions:
- Fyn tyrosine kinase is involved in TrkB-mediated neurotrophin signaling pathways.
- The interaction between Fyn and TrkB is specific and enhanced by neurotrophin stimulation.
- Fyn may play a crucial role in downstream signaling events initiated by TrkB activation.