FGFR2 (Fibroblast Growth Factor Receptor 2) Notes - ISOFORMS Project

Key Isoform Biology

FGFR2 encodes a receptor tyrosine kinase with tissue-specific isoform switching that determines ligand specificity.

Critical Isoforms: IIIb vs IIIc

Isoform UniProt ID Exon Usage Ligand Specificity Tissue Expression
FGFR2IIIb P21802-1 Exon IIIb FGF1, FGF3, FGF7 (KGF), FGF10 EPITHELIAL
FGFR2IIIc P21802-3 Exon IIIc FGF1, FGF2, FGF4, FGF6, FGF9 MESENCHYMAL

The IIIb vs IIIc Switch

The Ig-like domain III is alternatively spliced:
- Exon IIIb encodes epithelial-specific splice variant
- Exon IIIc encodes mesenchymal-specific splice variant

This creates mutually exclusive ligand binding:
- FGF7 (KGF) binds ONLY to IIIb (epithelial)
- FGF2 binds preferentially to IIIc (mesenchymal)

Biological Significance: Epithelial-Mesenchymal Communication

The IIIb/IIIc isoform switching enables paracrine signaling:
- Mesenchyme produces FGF7/10 → signals to epithelium (IIIb)
- Epithelium produces FGF2/4 → signals to mesenchyme (IIIc)

This is critical for:
- Limb development
- Lung branching morphogenesis
- Prostate development
- Wound healing

Soluble/Secreted Isoforms

These may act as decoy receptors, similar to soluble FAS.

Cancer Relevance

Isoform switching in cancer:
- Epithelial-to-mesenchymal transition (EMT) includes IIIb→IIIc switch
- Some cancers inappropriately express IIIc in epithelial contexts
- Mis-splicing correlates with metastatic potential

GOA Annotation Status

Expected Annotation Issues

  1. "FGF receptor signaling pathway" - applies to both isoforms but with different ligands
  2. "fibroblast growth factor binding" - TRUE for both, but DIFFERENT FGFs
  3. Epithelial morphogenesis terms may be IIIb-specific
  4. Mesenchymal development terms may be IIIc-specific
  5. Any FGF7 (KGF) signaling annotations should be IIIb-specific
  6. Any FGF2 signaling annotations should be preferentially IIIc

Key References