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Nerve growth factor induced stimulation of Ras requires Trk interaction with Shc but does not involve
B Hallberg1, M Ashcroft, D M Loeb
1Department of Cell and Molecular Biology, Umeå University, Sweden.
Abstract:
The TrkA receptor protein tyrosine kinase is involved in signalling PC12 cell differentiation and cessation of cell division in response to nerve growth factor (NGF). To assess the importance of adaptor proteins and Ras in NGF control of phosphoinositide 3-OH kinase (PI 3-kinase), specific receptor mutations in Trk have been employed. We show that phosphorylation of tyrosine 490, but not 785, of Trk is essential for activation of both Ras and PI 3-kinase in vivo, correlating with tyrosine phosphorylation of Shc and binding of Shc to the adaptor Grb2 and the Ras exchange factor Sos. A mutant receptor that lacks Y490 and Y785, but contains an introduced YxxM motif which binds the regulatory domain of PI 3-kinase, is unable to activate Ras despite causing increased PI 3-kinase activity. This indicates clearly that activation of PI 3-kinase by itself is not sufficient to cause activation of Ras, arguing against a model in which PI 3-kinase acts upstream of Ras. The Shc site of Trk is thus crucial for the activation of Ras and PI 3-kinase.
Insights
Nerve growth factor (NGF) signals through TrkA receptor tyrosine kinase. Phosphorylation at TrkA
Area of Science:
- Molecular Biology
- Cell Signaling
- Biochemistry
Background:
- The TrkA receptor protein tyrosine kinase mediates nerve growth factor (NGF) signaling.
- NGF signaling pathways control crucial cellular processes like differentiation and cell division.
- Adaptor proteins and Ras are key components in NGF-mediated signaling.
Purpose of the Study:
- To investigate the role of specific TrkA receptor mutations in NGF signaling.
- To determine the importance of adaptor proteins and Ras in NGF control of phosphoinositide 3-OH kinase (PI 3-kinase) activation.
- To elucidate the relationship between Ras and PI 3-kinase activation in response to NGF.
Main Methods:
- Utilized specific receptor mutations in TrkA to analyze signaling pathways.
- Assessed the phosphorylation status of TrkA tyrosines (Y490 and Y785).
- Investigated the activation of Ras and PI 3-kinase in vivo.
- Examined tyrosine phosphorylation of Shc and its binding to Grb2 and Sos.
Main Results:
- Phosphorylation of TrkA at tyrosine 490 (but not 785) is essential for Ras and PI 3-kinase activation.
- TrkA Y490 phosphorylation correlates with Shc tyrosine phosphorylation and Shc binding to Grb2 and Sos.
- A mutant TrkA receptor lacking Y490/Y785 but with an introduced PI 3-kinase binding motif activated PI 3-kinase but not Ras.
Conclusions:
- TrkA tyrosine 490 phosphorylation is critical for the activation of both Ras and PI 3-kinase.
- PI 3-kinase activation alone is insufficient to activate Ras, challenging models where PI 3-kinase acts upstream of Ras.
- The Shc binding site on TrkA is crucial for the activation of Ras and PI 3-kinase signaling.