Akt shows variable sensitivity to an Hsp90 inhibitor depending on cell context

Area of Science:

• Oncology
• Molecular Biology
• Biochemistry

Background:

• Heat shock protein 90 (Hsp90) inhibitors are investigated for cancer therapy due to their role in degrading oncogenic proteins.
• Cancer cells exhibit greater sensitivity to Hsp90 inhibitors than normal cells.

Purpose of the Study:

• To investigate the effect of the oncogenic tyrosine fusion kinase NPM-ALK on cellular sensitivity to the Hsp90 inhibitor geldanamycin.
• To elucidate the molecular mechanisms by which NPM-ALK influences protein stability and apoptosis in the presence of Hsp90 inhibition.

Main Methods:

• Analysis of Ba/F3 immortalized cell line sensitivity to geldanamycin.
• Expression of NPM-ALK oncogenic tyrosine fusion kinase via retroviral vector.
• Assessment of Akt and Cdk4 protein degradation, apoptosis levels, and Akt-Cdc37 chaperone binding.

Main Results:

• NPM-ALK expression rendered Akt and Cdk4 more resistant to geldanamycin-induced degradation.
• A slight reduction in apoptosis was observed in cells expressing NPM-ALK.
• Akt degradation was slower upon translation inhibition compared to geldanamycin treatment in NPM-ALK expressing cells, indicating NPM-ALK protects mature Akt.
• Akt failed to bind to the Cdc37 chaperone in the presence of NPM-ALK, correlating with increased Akt stability.

Conclusions:

• The oncogenic tyrosine fusion kinase NPM-ALK confers resistance to Hsp90 inhibition by stabilizing key client proteins like Akt and Cdk4.
• This stabilization appears to be mediated by impaired interaction between Akt and the Cdc37 chaperone.
• These findings have implications for the efficacy of Hsp90 inhibitors in cancers driven by NPM-ALK.