Inhibition of hsp90 compromises the DNA damage response to radiation

Area of Science:

• Oncology
• Molecular Biology
• Radiotherapy Research

Background:

• Heat shock protein 90 (Hsp90) inhibitors are known to increase tumor cell sensitivity to radiation therapy.
• The precise mechanisms underlying Hsp90 inhibition's radiosensitizing effects, particularly concerning DNA damage response pathways, require further elucidation.

Purpose of the Study:

• To investigate the impact of the Hsp90 inhibitor 17-(dimethylaminoethylamino)-17-demethoxygeldanamycin (17DMAG) on the DNA damage response following radiation exposure in tumor cells.
• To elucidate the molecular mechanisms by which 17DMAG influences DNA repair, cell cycle checkpoint activation, and associated signaling pathways.

Main Methods:

• Utilized MiaPaCa tumor cells treated with 17DMAG and ionizing radiation.
• Assessed DNA double-strand break repair using gammaH2AX foci dispersal and neutral comet assays.
• Investigated the phosphorylation and interactions of key proteins including DNA-PKcs, ErbB1, ATM, and the MRE11/Rad50/NBS1 (MRN) complex via Western blotting and immunofluorescence.

Main Results:

• 17DMAG treatment inhibited the repair of radiation-induced DNA double-strand breaks.
• This inhibition correlated with reduced DNA-PK catalytic subunit (DNA-PKcs) phosphorylation and disrupted DNA-PKcs/ErbB1 interaction, suggesting impaired DNA-PK activation.
• 17DMAG abrogated G(2)/S cell cycle checkpoint activation and reduced radiation-induced ataxia-telangiectasia mutated (ATM) activation and foci formation.
• Hsp90 interaction with the MRN complex was observed, and 17DMAG reduced MRN complex foci formation and NBS1/ATM interaction, indicating compromised MRN complex function and ATM activation.

Conclusions:

• Hsp90 inhibition by 17DMAG compromises the DNA damage response to radiation by impairing both DNA repair and cell cycle checkpoint activation.
• The observed radiosensitization is linked to the disruption of DNA-PK and ATM signaling pathways, potentially mediated through interactions with ErbB1 and the MRN complex, respectively.
• These findings highlight Hsp90's critical role in DNA damage response mechanisms and suggest Hsp90 inhibitors as potential radiosensitizing agents in cancer therapy.