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FGF receptors ubiquitylation: dependence on tyrosine kinase activity and role in downregulation

E Monsonego-Ornan1, R Adar, E Rom

  • 1Department of Molecular Cell Biology, Weizmann Institute of Science, Rehovot 76100, Israel.

FEBS Letters
|September 26, 2002
PubMed

Insights

Fibroblast growth factor receptor 3 (FGFR3) ubiquitylation depends on kinase activity but overactive mutants resist degradation. Phosphorylation is key for ubiquitylation, yet insufficient for downregulating internalization-resistant FGFR3 mutants.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Biochemistry

Background:

  • Receptor internalization and degradation are critical for regulating cell signaling.
  • Fibroblast growth factor receptor 3 (FGFR3) mutations cause developmental disorders like achondroplasia and thanatophoric dysplasia.
  • Understanding FGFR3 regulation is crucial for therapeutic development.

Purpose of the Study:

  • To compare the ubiquitylation and degradation of wild-type FGFR3 with its kinase-dead and overactive mutants.
  • To investigate the role of tyrosine kinase activity in FGFR3 ubiquitylation and downregulation.
  • To determine if phosphorylation is sufficient for the degradation of internalization-resistant FGFR3 mutants.

Main Methods:

  • Western blotting to assess protein levels and ubiquitylation.
  • Site-directed mutagenesis to create FGFR3 variants (K508A, G380R, K650E).
  • Treatment with fibroblast growth factor (FGF) ligand and c-Cbl overexpression.

Main Results:

  • FGFR3 ubiquitylation is directly proportional to its intrinsic tyrosine kinase activity.
  • Kinase inhibitors effectively block FGFR3 ubiquitylation.
  • Overactive FGFR3 mutants (G380R, K650E) exhibit excessive ubiquitylation but resist efficient degradation.
  • Ligand stimulation or c-Cbl overexpression does not rescue degradation of internalization-resistant FGFR3 mutants.

Conclusions:

  • Phosphorylation is essential for FGFR3 ubiquitylation.
  • Tyrosine kinase activity is necessary but not sufficient for FGFR3 degradation.
  • Internalization-resistant FGFR3 mutants evade degradation pathways despite ubiquitylation, highlighting a critical regulatory checkpoint.

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