A Role for VCP/p97 in the Processing of Drug-Stabilized TOP2-DNA Covalent Complexes

Area of Science:

• Molecular Biology
• Cellular Biology
• Cancer Research

Background:

• DNA topoisomerase II (TOP2) poisons create TOP2-DNA covalent complexes, trapping TOP2 on DNA double-strand breaks (DSBs).
• Proteasomal degradation of TOP2 is a key step in repairing these TOP2-induced DSBs.
• Valosin-containing protein (VCP/p97), a AAA ATPase, facilitates protein degradation by unfolding substrates and aiding their proteasomal processing.

Purpose of the Study:

• To investigate the role of VCP/p97 in the repair of TOP2-DNA covalent complexes.
• To determine if VCP/p97 is required for the proteasomal degradation of TOP2-DNA adducts.

Main Methods:

• Inhibition of VCP/p97 in cells treated with the TOP2 poison etoposide.
• Analysis of TOP2A and TOP2B covalent complex accumulation.
• Assessment of histone H2A.X phosphorylation as a marker for DSBs.

Main Results:

• VCP/p97 inhibition led to the accumulation of etoposide-induced TOP2A and TOP2B covalent complexes.
• This accumulation was epistatic with the proteasomal pathway, indicating VCP/p97's involvement in proteasomal degradation.
• Inhibition of VCP/p97 reduced etoposide-induced histone H2A.X phosphorylation, suggesting fewer DSBs.

Conclusions:

• VCP/p97 is required for the proteasomal degradation of TOP2-DNA covalent complexes.
• VCP/p97 acts as a mediator in repairing DNA double-strand breaks induced by TOP2 poisons.
• Targeting VCP/p97 could potentially enhance the efficacy of TOP2 poison chemotherapy.