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Expression of a dominant negative FGF receptor inhibits axonal growth and FGF receptor phosphorylation stimulated by
J L Saffell1, E J Williams, I J Mason
1Department of Experimental Pathology, United Medical and Dental Schools, Guy's Hospital, London, United Kingdom.
Abstract:
The cell adhesion molecules (CAMs) NCAM, N-cadherin, and L1 are homophilic binding molecules that stimulate axonal growth. We have postulated that the above CAMs can stimulate this response by activating the fibroblast growth factor receptor (FGFR) in neurons. In the present study, we demonstrate that activation of NCAM and L1 can lead to phosphorylation of the FGFR. Both this and the neurite outgrowth response stimulated by all three of the above CAMs are lost when a kinase-deleted, dominant negative form of FGFR1 is expressed in PC12 cells. In addition, we have generated transgenic mice that express the dominant negative FGFR under control of the neuron-specific enolase (NSE) promoter. We show that cerebellar neurons isolated from these mice have also lost their ability to respond to NCAM, N-cadherin, and L1. A peptide inhibitor of phospholipase C gamma (PLCgamma) that inhibits neurite outgrowth stimulated by FGF also inhibited neurite outgrowth stimulated by the CAMs. Thus, we conclude that activation of the FGFR is both necessary and sufficient to account for the ability of the above CAMs to stimulate axonal growth, and that PLCgamma is a key downstream effector of this response.
Insights
Cell adhesion molecules (CAMs) activate fibroblast growth factor receptors (FGFRs) to promote axonal growth. This study confirms FGFR activation is essential for CAM-induced neurite outgrowth, involving phospholipase C gamma (PLCγ).
Area of Science:
- Neuroscience
- Cell Biology
- Molecular Biology
Background:
- Cell adhesion molecules (CAMs) like NCAM, N-cadherin, and L1 are known to stimulate axonal growth.
- A proposed mechanism involves the activation of fibroblast growth factor receptors (FGFRs) in neurons by these CAMs.
Purpose of the Study:
- To investigate whether CAMs stimulate axonal growth by activating FGFRs.
- To determine if FGFR activation is necessary and sufficient for CAM-mediated neurite outgrowth.
Main Methods:
- Expression of a dominant-negative FGFR1 in PC12 cells to block FGFR signaling.
- Generation of transgenic mice expressing dominant-negative FGFR under the neuron-specific enolase (NSE) promoter.
- Analysis of neurite outgrowth in response to CAMs in isolated cerebellar neurons from transgenic mice.
- Inhibition of phospholipase C gamma (PLCγ) to assess its role in the signaling pathway.
Main Results:
- Activation of NCAM and L1 leads to FGFR phosphorylation.
- Dominant-negative FGFR expression abolished both FGFR phosphorylation and CAM-stimulated neurite outgrowth.
- Cerebellar neurons from transgenic mice showed impaired responses to NCAM, N-cadherin, and L1.
- Inhibition of PLCγ blocked CAM-stimulated neurite outgrowth, similar to FGF inhibition.
Conclusions:
- Fibroblast growth factor receptor (FGFR) activation is both necessary and sufficient for cell adhesion molecule (CAM)-induced axonal growth.
- Phospholipase C gamma (PLCγ) acts as a crucial downstream effector in the CAM-FGFR signaling pathway for neurite outgrowth.