Endocytosis of receptor tyrosine kinases is driven by monoubiquitylation, not polyubiquitylation

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Growth factors bind receptor tyrosine kinases (RTKs), initiating signaling cascades.
• Receptor endocytosis typically terminates RTK signaling.
• The ubiquitin ligase c-Cbl mediates epidermal growth factor receptor (EGFR) endocytosis through ubiquitylation.

Purpose of the Study:

• To elucidate the specific type of ubiquitylation mediated by c-Cbl on EGFRs.
• To determine the role of different ubiquitylation types in RTK signaling termination.
• To investigate the mechanism by which c-Cbl regulates EGFR endocytosis and desensitization.

Main Methods:

• In vitro ubiquitylation assays using c-Cbl and EGFR.
• Generation and utilization of receptor and ubiquitin mutants.
• Cell-based assays to assess EGFR endocytosis and degradation.

Main Results:

• c-Cbl mediates monoubiquitylation, not polyubiquitylation, of EGFRs in isolation.
• A single ubiquitin modification is sufficient to induce EGFR endocytosis and degradation.
• c-Cbl attaches a founder monoubiquitin to the EGFR kinase domain, followed by additional monoubiquitins.

Conclusions:

• RTK desensitization is achieved through the conjugation of multiple monoubiquitins, a mechanism distinct from polyubiquitin-dependent proteasomal degradation.
• Monoubiquitylation by c-Cbl is the key event for EGFR endocytosis and signaling termination.
• This finding reveals a novel regulatory pathway for RTK signaling control.