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Functional Characterization of RING-Type E3 Ubiquitin Ligases In Vitro and In Planta
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Functional Characterization of RING-Type E3 Ubiquitin Ligases In Vitro and In Planta

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WW domain HECT E3s target Cbl RING finger E3s for proteasomal degradation

Alessandra Magnifico1, Seth Ettenberg, Cuihong Yang

  • 1Regulation of Protein Function Laboratory, Center for Cancer Research, NCI-Frederick, Frederick, MD 21702, USA.

The Journal of Biological Chemistry
|August 9, 2003
PubMed

Insights

WW domain HECT E3 ubiquitin ligases, Nedd4 and Itch, degrade Cbl proteins, impacting tyrosine kinase regulation. This reveals a new regulatory pathway for Cbl substrates, including growth factor receptors and Src kinases.

Area of Science:

  • Molecular and Cellular Biology
  • Biochemistry
  • Signal Transduction

Background:

  • Cbl proteins are RING finger E3 ubiquitin ligases crucial for down-regulating tyrosine kinases.
  • The precise regulation of Cbl protein activity and stability is essential for cellular signaling pathways.

Purpose of the Study:

  • To investigate the role of WW domain HECT E3 ubiquitin ligases in the regulation of Cbl proteins.
  • To determine if Nedd4 and Itch can target Cbl proteins for degradation and elucidate the mechanism.

Main Methods:

  • Co-immunoprecipitation assays to detect protein interactions.
  • Western blotting to assess protein levels and ubiquitylation status.
  • Cell-based assays using epidermal growth factor receptor (EGFR) and Src kinase signaling models.

Main Results:

  • Nedd4 and Itch directly bind to Cbl proteins and mediate their proteasomal degradation.
  • This degradation is dependent on the HECT E3 ligase activity of Nedd4/Itch, not on Cbl's own E3 activity.
  • Nedd4 antagonizes Cbl-b-mediated down-regulation and ubiquitylation of EGFR and reverses Cbl-mediated degradation of active Src kinase.

Conclusions:

  • WW domain HECT E3s (Nedd4, Itch) act as negative regulators of Cbl proteins, targeting them for degradation.
  • This finding introduces a novel regulatory mechanism where HECT E3s ubiquitylate RING finger E3s, impacting signaling pathways involving tyrosine kinases.
  • This adds a new layer of control to Cbl substrate regulation, affecting receptor tyrosine kinases and non-receptor tyrosine kinases like Src.

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