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Association with HSP90 inhibits Cbl-mediated down-regulation of mutant epidermal growth factor receptors

Seungchan Yang1, Shimian Qu, Marianela Perez-Tores

  • 1Department of Medicine, Breast Cancer Research Program, Vanderbilt-Ingram Comprehensive Cancer Center, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-6307, USA.

Cancer Research
|July 20, 2006
PubMed

Insights

Activating mutations in epidermal growth factor receptor (EGFR) drive non-small cell lung cancer. HSP90 inhibition restores normal receptor function and down-regulation, suggesting a therapeutic target for EGFR-mutant NSCLC.

Area of Science:

  • Oncology
  • Molecular Biology
  • Cell Signaling

Background:

  • Activating mutations in epidermal growth factor receptor (EGFR) are common in non-small cell lung cancer (NSCLC).
  • These EGFR mutations often confer sensitivity to tyrosine kinase inhibitors, indicating receptor dependence in cancer cells.
  • The precise mechanisms by which these mutants promote cancer and their regulation are not fully understood.

Purpose of the Study:

  • To investigate the functional consequences of specific EGFR mutations (L861Q and L858R) in NSCLC.
  • To explore the role of heat shock protein 90 (HSP90) in the regulation and function of mutant EGFR.
  • To identify potential therapeutic strategies targeting HSP90 in EGFR-mutant NSCLC.

Main Methods:

  • Utilized 32D cell lines stably expressing wild-type EGFR or mutant EGFR variants (L861Q, L858R).
  • Assessed ligand-independent receptor phosphorylation and cell viability.
  • Investigated ligand-induced receptor down-regulation (LIRD) and protein-protein interactions (EGFR, Cbl, CIN85).
  • Examined the effect of HSP90 inhibition using geldanamycin on EGFR ubiquitination and LIRD.

Main Results:

  • Mutant EGFR (L861Q, L858R) exhibited ligand-independent phosphorylation and viability, unlike wild-type EGFR.
  • Ligand-induced receptor down-regulation (LIRD) was impaired in cells expressing mutant EGFR.
  • Mutant EGFR showed constitutive association with Cbl but failed to associate with CIN85 upon ligand addition.
  • HSP90 inhibition with geldanamycin restored Cbl function, leading to receptor ubiquitination and LIRD.
  • EGFR mutants appear to form defective endocytic complexes, and HSP90 protects activated mutants from LIRD.

Conclusions:

  • EGFR mutants in NSCLC exhibit aberrant signaling and impaired down-regulation.
  • HSP90 plays a critical role in maintaining the conformation and function of mutant EGFR.
  • Targeting HSP90 may represent a viable strategy to restore normal receptor regulation and treat EGFR-mutant NSCLC.

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