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V600E B-Raf requires the Hsp90 chaperone for stability and is degraded in response to Hsp90 inhibitors

O M Grbovic1, A D Basso, A Sawai

  • 1Program in Molecular Pharmacology and Chemistry and Department of Medicine, Memorial Sloan-Kettering Cancer Center, New York, NY 10021, USA.

Proceedings of the National Academy of Sciences of the United States of America
|December 24, 2005
PubMed

Insights

Heat shock protein 90 (Hsp90) is crucial for the stability of mutated B-Raf in melanoma. Inhibiting Hsp90 degrades mutant B-Raf, offering a potential therapeutic strategy for melanoma treatment.

Area of Science:

  • Oncology
  • Molecular Biology
  • Biochemistry

Background:

  • The Raf family kinases, including B-Raf, are critical regulators of cell signaling.
  • B-Raf mutations are prevalent in melanoma and other cancers, driving tumor growth.
  • Heat shock protein 90 (Hsp90) is a molecular chaperone involved in protein folding and stability.

Purpose of the Study:

  • To investigate the role of Hsp90 in the stability and function of Raf kinases, particularly mutated B-Raf.
  • To evaluate the therapeutic potential of Hsp90 inhibition in melanoma models.

Main Methods:

  • Assessing the Hsp90 dependence of Raf-1, A-Raf, and B-Raf isoforms.
  • Analyzing the interaction of mutated B-Raf with the Hsp90-cdc37 complex.
  • Treating melanoma cells and tumors with the Hsp90 inhibitor 17-allylamino-17-demethoxygeldanamycin.
  • Measuring B-Raf degradation, mitogen-activated protein kinase (MAPK) activation, cell proliferation, apoptosis, and antitumor activity.

Main Results:

  • Raf-1 and A-Raf require Hsp90 for stability, while wild-type B-Raf does not.
  • Mutated, activated B-Raf binds to the Hsp90-cdc37 complex, which is essential for its stability and function.
  • Hsp90 inhibition leads to degradation of mutant B-Raf, suppressed MAPK signaling, reduced cell proliferation, and induced apoptosis.
  • Treatment with an Hsp90 inhibitor demonstrated significant antitumor activity in melanoma models.

Conclusions:

  • Activated, mutated B-Raf proteins are dependent on Hsp90 for proper folding and stability.
  • Hsp90 plays a critical role in the clonal evolution of melanomas dependent on B-Raf mutations.
  • Hsp90 inhibition is a promising therapeutic strategy for treating melanoma and other B-Raf-driven tumors.

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