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Expression of two different forms of fibroblast growth factor receptor 1 in different mouse tissues and cell lines
1Walter and Eliza Hall Institute of Medical Research, Royal Melbourne Hospital, Victoria, Australia.
Abstract:
The fibroblast growth factor receptors (FGFRs) form a multigene family of at least four members, all having extracellular regions consisting of either two or three immunoglobin-like (Ig-like) domains. By RNase protection analysis we have analyzed the expression of FGFR-1 mRNA in various tissues and cell lines and demonstrated that all of the cell lines studied expressed at least two different forms of the FGFR-1 at similar levels. Although muscle and heart express forms having either two [FGFR-1 short (FGFR-1S)] or three [FGFR-1 long (FGFR-1L)] Ig-like domains, the developing brain and adult brain express only mRNA encoding the longer form. The two forms of the receptor were characterized further by stably introducing expression vectors expressing them into Rat-2 fibroblasts and FDC-P1 myeloid cells. Treatment of the transfected Rat-2 cells with acidic FGF (aFGF) or basic FGF (bFGF) resulted in focus formation. The transformed phenotype was observed even without addition of ligand after growth in culture for greater than 2 months. Cross-linking of 125I-labeled bFGF (125I-bFGF) to Rat-2 cells expressing either FGFR-1L or FGFR-1S yielded two similar complexes of 150 and 110 kDa. Although Rat-2 cells expressing FGFR-1L yielded similar complexes with 125I-labeled aFGF (125I-aFGF), only the 150-kDa complex was formed with cells expressing FGFR-1S. The 150-kDa complex was also observed when 125I-aFGF or 125I-bFGF was cross-linked to FDC-P1 cells expressing FGFR-1L. Significantly, these complexes were only observed when heparin was present in the cross-linking reaction. FDC-P1 cells expressing FGFR-1 bound aFGF and bFGF with high affinity but only in the presence of heparin. The factor dependence of these cells could be switched from interleukin 3 to FGF in the presence of heparin.
Insights
Fibroblast growth factor receptors (FGFRs) exist in short and long forms, with the long form prevalent in the brain. Heparin is crucial for FGFR-1 binding and cellular response to FGFs.
Area of Science:
- Molecular Biology
- Cell Biology
- Biochemistry
Background:
- Fibroblast growth factor receptors (FGFRs) are a multigene family with varying extracellular immunoglobulin-like (Ig-like) domains.
- FGFR-1 mRNA expression was analyzed in different tissues and cell lines.
Purpose of the Study:
- To analyze FGFR-1 mRNA expression in various tissues and cell lines.
- To characterize the functional differences between FGFR-1 short (FGFR-1S) and FGFR-1 long (FGFR-1L) forms.
- To investigate the role of heparin in FGFR-1 ligand binding and cellular signaling.
Main Methods:
- RNase protection analysis to study FGFR-1 mRNA expression.
- Stable transfection of Rat-2 fibroblasts and FDC-P1 myeloid cells with FGFR-1S and FGFR-1L expression vectors.
- Ligand cross-linking studies with radiolabeled FGFs (aFGF, bFGF) and heparin.
Main Results:
- All cell lines studied expressed at least two forms of FGFR-1.
- Developing and adult brain primarily express the longer form (FGFR-1L).
- Transfected cells expressing FGFR-1S or FGFR-1L showed transformed phenotypes upon FGF treatment.
- Heparin was essential for high-affinity binding of FGFs to FGFR-1 and for switching cell dependence from IL-3 to FGF.
Conclusions:
- FGFR-1 exists in at least two isoforms (FGFR-1S and FGFR-1L) with differential tissue expression.
- Heparin plays a critical role in mediating FGF signaling through FGFR-1.
- FGFR-1L is the predominant form in brain tissues.