ATM is the primary kinase responsible for phosphorylation of Hsp90α after ionizing radiation

Area of Science:

• Molecular Biology
• Cellular Biology
• Oncology

Background:

• Heat shock protein 90 (Hsp90) stabilizes numerous oncogenic signal transduction molecules.
• A specific Hsp90 isoform, Hsp90α, is phosphorylated at N-terminal threonine residues (T5/7) and participates in DNA damage response and apoptosis.
• The kinase responsible for Hsp90α phosphorylation post-ionizing radiation (IR) and its role in DNA repair remain unidentified.

Purpose of the Study:

• To identify the kinase that phosphorylates Hsp90α following IR.
• To elucidate the role of Hsp90α phosphorylation in the DNA damage response and repair.
• To explore the therapeutic potential of targeting Hsp90α phosphorylation for radiosensitizing cancer treatments.

Main Methods:

• Utilized ionizing radiation (IR) to induce DNA damage.
• Employed siRNA-mediated knockdown of Hsp90α.
• Analyzed Hsp90α and H2AX phosphorylation kinetics in wild-type and Hsp90α-null mouse embryonic fibroblasts (MEFs).

Main Results:

• Identified ATM as the kinase phosphorylating Hsp90α at T5/7 residues immediately after IR.
• Observed that Hsp90α T5/7 phosphorylation kinetics correlate with H2AX S139 phosphorylation (γH2AX) kinetics.
• Demonstrated that only nuclear Hsp90α undergoes ATM-mediated phosphorylation post-IR.
• Showed that Hsp90α knockdown sensitizes various cancer cells and fibroblasts to IR.
• Found reduced γH2AX levels in Hsp90α-null MEF cells, indicating Hsp90α's importance in γH2AX formation.

Conclusions:

• Hsp90α is a key component of ATM-mediated signal transduction following IR.
• Hsp90α phosphorylation by ATM is essential for efficient DNA damage response, specifically γH2AX formation.
• Targeting Hsp90α T5/7 phosphorylation presents a promising strategy for developing novel radiosensitizing therapies against cancer.