p97/VCP inhibition causes excessive MRE11-dependent DNA end resection promoting cell killing after ionizing radiation

The ATPase p97 is a central component of the ubiquitin-proteasome degradation system. p97 uses its ATPase activity and co-factors to extract ubiquitinated substrates from different cellular locations, including DNA lesions, thereby regulating DNA repair pathway choice. Here, we find that p97 physically and functionally interacts with the MRE11-RAD50-NBS1 (MRN) complex on chromatin and that inactivation of p97 blocks the disassembly of the MRN complex from the sites of DNA damage upon ionizing radiation (IR). The inhibition of p97 function results in excessive 5′-DNA end resection mediated by MRE11 that leads to defective DNA repair and radiosensitivity. In addition, p97 inhibition by the specific small-molecule inhibitor CB-5083 increases tumor cell killing following IR both in vitro and in vivo. Mechanistically, this is mediated via increased MRE11 nuclease accumulation. This suggests that p97 inhibitors might be exploited to improve outcomes for radiotherapy patients. [Display omitted] •p97 interacts with MRE11 and regulates its retention on chromatin after IR•p97 inactivation causes excessive MRE11-mediated DNA end resection•p97-mediated MRE11 chromatin retention causes HR defects but efficient SSA•CB-5083 radiosensitizes cells and suppresses tumor growth in vivo after IR Kilgas et al. show that p97/VCP interacts with the MRN complex. Inactivating p97 blocks MRN disassembly from chromatin, causing MRE11 chromatin retention and excessive 5′-DNA end resection, along with HR defects and RAD52-mediated SSA. This change in DSB repair pathway choice radiosensitizes cells, which is rescued by inactivation of MRE11.