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Activation of FGF receptors by mutations in the transmembrane domain
Y Li1, K Mangasarian, A Mansukhani
1Department of Microbiology and Kaplan Cancer Center, New York University School of Medicine, New York, NY 10016, USA.
Abstract:
Signaling through FGF receptors, which constitute a family of membrane-spanning tyrosine kinases, can stimulate cell proliferation, induce or inhibit cell differentiation and plays an important role in development. Recently, mutations in FGF receptors have been shown to be associated with a number of genetically dominant human skeletal disorders. A remarkably conserved mutation (Gly 380-->Arg) in the transmembrane region of FGFR-3 has been shown to be responsible for achondroplasia (ACH) but it was not clear whether such mutations result in loss of receptor function or constitutive activation. We have therefore made mutations in the transmembrane regions of murine FGFR-2 and FGFR-3 and studied their effect on receptor activity. We show here that the ACH mutation in FGFR-3 as well as two similar mutations in FGFR-2 result in constitutive activation of these receptors. This is manifested in their ability to become autophosphorylated in the absence of ligand in L6 cells, transforming activity on NIH3T3 fibroblasts, and the ability to inhibit myogenic differentiation in the absence of growth factor. Thus the transmembrane region of FGFR-2 and FGFR-3 plays a regulatory role in receptor function and the ACH mutation produces a dominant oversignaling receptor which is no longer regulated by FGF binding. These findings also support the newly identified role of FGF signaling as a negative regulator of bone growth.
Insights
Mutations in fibroblast growth factor receptors (FGFRs) cause skeletal disorders. The achondroplasia mutation in FGFR-3 leads to constitutive receptor activation, disrupting normal bone growth regulation.
Area of Science:
- Molecular Biology
- Genetics
- Cell Signaling
Background:
- Fibroblast growth factor receptors (FGFRs) are membrane-spanning tyrosine kinases crucial for cell proliferation, differentiation, and development.
- Mutations in FGFRs are linked to dominant human skeletal disorders.
- The specific mutation (Gly 380-->Arg) in FGFR-3 causing achondroplasia (ACH) was investigated for its functional consequence: loss of function or constitutive activation.
Purpose of the Study:
- To investigate the effect of mutations in the transmembrane regions of murine FGFR-2 and FGFR-3 on receptor activity.
- To determine if the achondroplasia mutation in FGFR-3 and similar mutations in FGFR-2 lead to constitutive receptor activation.
Main Methods:
- Site-directed mutagenesis was performed on the transmembrane regions of murine FGFR-2 and FGFR-3.
- Receptor activity was assessed by measuring autophosphorylation in L6 cells without ligand.
- Transforming activity was evaluated in NIH3T3 fibroblasts.
- Inhibition of myogenic differentiation in the absence of growth factor was assessed.
Main Results:
- The achondroplasia mutation in FGFR-3 and two analogous mutations in FGFR-2 resulted in constitutive receptor activation.
- Activated receptors showed ligand-independent autophosphorylation, transforming activity in NIH3T3 cells, and inhibition of myogenic differentiation.
- The transmembrane regions of FGFR-2 and FGFR-3 play a regulatory role in receptor function.
Conclusions:
- The achondroplasia mutation in FGFR-3 creates a constitutively active, dominant oversignaling receptor independent of FGF binding.
- These findings support a role for FGF signaling as a negative regulator of bone growth.
- Dysregulation of FGFR signaling through transmembrane mutations contributes to skeletal disorders.