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Signal transduction pathway of human fibroblast growth factor receptor 3. Identification of a novel 66-kDa
1Department of Medicine, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114, USA.
Abstract:
Stimulation of fibroblast growth factor receptor 3 (FGFR3) results in a variety of functional effects, including regulation of epithelial cell growth and differentiation. In order to characterize the signaling pathway through which FGFR3 regulates cell growth, L6 cells lacking any endogenous FGFR were stably transfected with the two different human isoforms, FGFR3 IIIb and FGFR3 IIIc, that result from alternative splicing of exon III of the FGFR3 gene encoding the ligand binding domain. Expression of FGFR3 IIIc in stably transfected L6 cells conferred growth responses to several members of the FGF family including FGF-1, -2, -4, and -6, while FGFR3 IIIb-expressing cells responded only to FGF-1. Activation of FGFR3 upon ligand binding resulted in activation of mitogen-activated protein kinase pathway. FGFR3 utilizes two different pools of adapter protein GRB2 to link to Ras. Activated FGFR3 predominantly interacts with GRB2.Sos in complex with a previously identified 90-kDa protein and designated protein 80K-H. In addition, 80K-H.GRB2. Sos complex was found to contain a novel 66-kDa protein. Tyrosine phophorylation of the 66-kDa protein was dependent on ligand activation of FGFR3, suggesting that the 66-kDa protein may play an important role in FGFR3-specific signaling. In addition to this unique pathway, FGFR3 also links to GRB2.Sos complex via the adapter protein Shc. Furthermore, activated FGFR3 was not able to induce dissociation of GRB2.Sos complex following Sos phosphorylation. In summary, FGFR3 signaling pathway utilizes two GRB2-containing complexes; Shc.GRB2.Sos and 80K-H.pp66.GRB2.Sos; these two complexes may alternatively link FGFG3 to mitogen-activated protein kinase. Finally, activated FGFR3 was also found to result in phosphorylation of phospholipase C-gamma but reduced phosphorylation of c-Src.
Insights
Fibroblast growth factor receptor 3 (FGFR3) signaling activates the MAPK pathway through two distinct GRB2-containing complexes, influencing cell growth and differentiation. This research elucidates novel FGFR3 signaling mechanisms.
Area of Science:
- Cellular Biology
- Molecular Biology
- Signal Transduction
Background:
- Fibroblast growth factor receptor 3 (FGFR3) plays a crucial role in regulating epithelial cell growth and differentiation.
- Alternative splicing of FGFR3 exon III generates distinct isoforms (IIIb and IIIc) with different ligand-binding properties.
Purpose of the Study:
- To characterize the specific signaling pathways by which FGFR3 isoforms regulate cell growth.
- To identify the molecular adaptors and protein complexes involved in FGFR3 signal transduction.
Main Methods:
- Stable transfection of L6 cells with FGFR3 IIIb and FGFR3 IIIc isoforms.
- Analysis of cellular responses to various FGF ligands.
- Investigation of protein-protein interactions and tyrosine phosphorylation using biochemical assays.
Main Results:
- FGFR3 IIIc-expressing cells responded to FGF-1, -2, -4, and -6, while FGFR3 IIIb cells responded only to FGF-1.
- FGFR3 activation led to mitogen-activated protein kinase (MAPK) pathway activation.
- FGFR3 signaling involves two distinct GRB2-containing complexes: Shc.GRB2.Sos and 80K-H.pp66.GRB2.Sos.
- A novel 66-kDa protein, tyrosine phosphorylated upon FGFR3 activation, was identified within the 80K-H.GRB2.Sos complex.
Conclusions:
- FGFR3 signaling utilizes two parallel pathways, mediated by Shc.GRB2.Sos and 80K-H.pp66.GRB2.Sos complexes, to activate the MAPK pathway.
- The novel 66-kDa protein is a potential key player in FGFR3-specific signaling.
- FGFR3 activation also influences phospholipase C-gamma and c-Src phosphorylation, indicating broader signaling roles.