Nuclear receptor co-activator 4 interacts with RUVBL1/2 to maintain genome integrity through double-strand break repair

DNA double-strand breaks (DSBs) are among the most cytotoxic forms of chromosomal lesions and are primarily repaired through homologous recombination (HR) or non-homologous end joining (NHEJ). The precise repair of DSBs via HR necessitates 5'-3' end resection to generate 3'-single-stranded DNA (ssDNA) overhangs, which function as templates for repair synthesis. However, the proteins involved in HR, particularly those acting in the critical early stages preceding DNA end resection, and their regulatory mechanisms in response to ionizing radiation (IR), remain incompletely characterized. In this study, we identify the nuclear receptor co-activator NCOA4 as a novel DNA damage responsive protein. We demonstrate that this protein is recruited to sites of DNA damage and is enriched during the S/G2 phase of the cell cycle. Immunofluorescence and reporter gene assays demonstrate that depletion of NCOA4 reduces the IR-induced foci formation of RAD51 and RPA2 and impairs HR efficiency. Mechanistically, NCOA4 interacts with the AAA+ ATPases RUVBL1/2, and depletion of RUVBL1/2 has been shown to reduce the recruitment of NCOA4 at DNA damage sites. The knockdown of RUVBL1 or RUVBL2 phenocopies NCOA4 deficiency, and simultaneous knockdown of RUVBL1/2 and NCOA4 does not further reduce the RPA2 RIF, confirming that the entire NCOA4-RUVBL1/2 complex acts together to promote HR. Furthermore, depletion of NCOA4 has been shown to sensitize cancer cells to radiotherapy in tumor-bearing nude mouse models. Consequently, the present findings indicate that the NCOA4–RUVBL1/2 axis is capable of recognizing DNA double-strand breaks and promoting the homologous recombination repair pathway, thereby contributing to the maintenance of genomic integrity. This process may potentially play a role in modulating radioresistance in malignant tumors and expanding the landscape of therapeutic targets.